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Protozoology

by

R. P. HALL

New York University

New York

PRENTICE-HALL, INC.

1953

PRENTICE HALL ANIMAL SCIENCE SERIES
H. Burr Steinbach, Editor

Copyright, 1953, by

PRENTICE HALL, INC.

70 Fifth A\'enue, New York

All rights reserved. No part of this book mav be repro-
duced in any form, by mimeograph or any other means,
without permission in writing from the publishers.

L.C. Cat. Card No.: 52-14030

PRINTED IN THE UNITED STATES OF AMERICA

L. i tj .''. .*^- ■■'

ACKNOWLEDGMENTS

The writer is much indebted to several colleagues
for their patience in reading portions ot the manu-
script and tor their helpful suggestions, and also to
the many investigators whose contributions of re-
prints have greatly eased the task of reviewing the
literature.

R. P. Hall

Contents

CHAPTER PAGE

I. General Morphology of the Protozoa 1

II. Reproduction and Life-Cycles 54

III. The Classification of Protozoa 103

IV. The Mastigophora 116

V. The Sarcodina 201

VI. Sporozoa 269

VII. Ciliophora 332

VIII. Physiology 428

IX. Heredity in Protozoa 506

X. Host-Parasite Relationships 527

XI. Protozoa of the Digestive and Urogenital Tracts . 544

XII. The Blood Flagellates 574

XIII. Malaria 597

XIV. Immunity and Resistance 627

Index 654

67853

I

General Morphology
of the Protozoa

Variations in form of the body

Colonial organization

Non-colonial groupings

Cortex, secreted coverings and skeletons

Pseiidopodia

Flagella and associated structures
Flagella
Axostyles

Costa, cresta, pelta and aciculum
The parabasal apparatus
Multiple karyomastigonts and mastigonts

Cilia and their derivatives

Fibrillar systems

Neuromotor apparatus
Silver-line system
Neuroneme system
Infraciliary network
The infraciliature
Sensory bristles

Significance of fibrillar systems
Silver-line systems of flagellates

Myonemes and contractile stalks

Trichocysts and nematocysts

The cytostome and associated structmes

\'acuoles of Protozoa
Contractile vacuoles
Sensory vacuoles
Vacuoles in flotation

Chromatophores, pigments, pyrenoids,
photoreceptors
Chromatophores
Pyrenoids
Pigments
Photoreceptors

Cytoplasmic inclusioirs
Cytoplasmic food reserves
Chromidia
Mitochondria
\'acuome
Osmiophilic inclusions and organelles

Nuclei of Protozoa
Vesicular nuclei
Nuclear dimorphism
Dispersed nuclei

Literature cited

T.

HE Protozoa include a variety of microorganisms which, by
general agreement of protozoologists, are currently assigned to the phy-
lum. More specific characterization of the Protozoa is difficult and even
the name of the phylum, as applied to the groups it conventionally in-
cludes, is not entirely appropriate. Many flagellates — those usually listed
as Phytomastigoda, Phytomastigina, or Phytomastigophora — are com-
monly considered algae by botanists. Also, the Mycetozoida (Mycetozoa)

1

2 General Morphology of the Protozoa

of j^rotozoologists are nothing else than the slime-molds of botanists, and
the Sarcosporidia, usually considered Sporozoa, are believed by some
workers to be molds.

This situation, which suggests that protozoologists are unable to dis-
tinguish animals from plants, is somewhat disconcerting to those who
favor consistency in taxonomy. Consequently, various taxonomic reforms
have been suggested. The old term. Protista, recalls such an effort by
Haeckel, but the Protista were only a heterogeneous collection of micro-
organisms with the plant and animal labels obscured. A more positive
reform was proposed by Calkins (17) in his decision to eliminate the
chlorophyll-bearing flagellates from the Phylum Protozoa. On the face
of it, the proposal seemed to be an admission that zoologists had been
in error in laying claim to the "Phytomastigophora." However, some of
the more interesting colorless phytoflagellates were saved from a botanical
fate by arbitrary transfer to the "Zoomastigophora." The resulting mix-
tures could not be justified on the basis of sound taxonomic criteria;
hence, this innovation has not been generally accepted. The basic classifi-
cation of Copeland (33) recognizes a separate Kingdom Protoctista which
includes the Protozoa and various groups of algae and fungi. While this
suggestion sidesteps the problem of deciding which Protozoa are animals
and which are plants, it seems to imply that such Protozoa as the ciliates
are more closely related to the red algae and related organisms than they
are to the Kingdom Animalia.

At present, many protozoologists continue to list the phytoflagellates
and slime-molds as Protozoa, although they realize that botanists have no
objections to placing these groups in the plant kingdom. While the cur-
rent practice is a bit confusing taxonomically, there is the advantage that
botanists and protozoologists can legitimately maintain equal interest in
these groups which apparently represent mergers of the plant and animal
kingdoms.

From the morphological standpoint. Protozoa are often referred to as
unicellular animals, in contrast to the multicellular Metazoa. The small
size and simple structure of many Protozoa tend to justify this designa-
tion. On the other hand, some Protozoa are not so small and are measur-
able in millimeters, or even centimeters, instead of microns. Furthermore,
the uninucleate condition is far from universal. Many species possess more
than one nucleus, and the numbers range from two to many hundreds.
Examples are found in each of the major taxonomic groups. Structural
complexity often extends beyond a mere increase in number of nuclei.
Mycetozoan protoplasm, as noted in Physarum (167), is traversed by chan-
nels through which a liquid, containing many granules, flows back and
forth in a sort of primitive circulatory system. Multiplicity of flagellar
units is associated with multinuclearity in Mastigophora. The result may
be many nucleo-flagellar units (karyomastigonts), as in certain Calonym-

General Morphology of the Protozoa 3

phidae (Fig. 1. 10, D). In addition to normally multinucleate Protozoa,
many species are uninucleate in one phase of the life-cycle and multi-
nucleate in another.

Such structural diversity has led protozoologists into difficulties with
the Cell Theory. Dobell (45), who suggested that Protozoa are non-cel-
lular organisms, was one of the first to revolt against strict application of
the Cell Theory to this group. Such an interpretation has appealed to
some zoologists. A different concept, favored by Kofoid (138) for example,
is that some Protozoa are unicellular while others are multicellular.
Protozoan "multicellularity" is considered analogous to metazoan multi-
cellularity as seen in syncytial tissues. According to this view, the Protozoa
are the phylum in which multicellularity originated in animals.

The evolutionary transition from Protozoa to Metazoa involved dif-
ferentiation beyond the separation of reproductive and somatic cells.
Hyman (98) has stressed the characteristic establishment of an axis along
which morphological and physiological differentiation has occurred. Such
colonial types as Volvox, in spite of their specialized somatic and repro-
ductive "cells," are usually considered Protozoa. The distinction is mainly
one of degree, since Volvox has several attributes of an organism in the
metazoan sense. The colony moves as a unit, with apparently coordinated
flagellar activity, and exhibits some degree of polarity with functional
differentiation. The colony may produce daughter colonies asexually or it
may develop gametes. The zygote develops into a young colony in a man-
ner not unlike that in which a fertilized egg produces a young metazoan
individual. The Myxosporida, another exceptional group, show somatic
differentiation in that some cells produce spore-membranes while others
give rise to the polar capsules of the myxosporidian spore. In other words,
the separation of Protozoa from Metazoa in borderline cases may involve
somewhat arbitrary decisions influenced to some extent by factors of
taxonomic convenience.

VARIATIONS IN FORM OF
THE BODY

Protozoa range from approximately spherical forms to bizarre
shapes not readily explained on a functional basis. Symmetry is often
poorly defined. Most active swimmers show spiral torsion in some degree
and this tendency toward asymmetry is presumably correlated with the
usual spiral course in locomotion (62, 136). However, universal sym-
metry and radial symmetry may be noted in various floating and sessile
species, respectively, and bilateral symmetry is apparent in such genera
as Giardia and Octomitus. In Protozoa which are not spherical, form of
the body may be rather characteristic of a given species under particular
conditions. However, form is often relatively constant rather than abso-
lutely so, and within specific limits, may be modified by environmental

4 General Morphology o£ the Protozoa

conditions and activities of the organism. Even the nature and quantity
of the available food may influence form as well as size of the body. Such
a relationship is striking in Tetrahymena vorax (Fig. 1. 1) when strains
are fed on different diets (118). In addition to the usual variations, attrib-

Fig. 1. 1. Influence of diet on form and size in Tetrahymena vorax.
A. Organism from young broth culture (saprozoic nutrition). B. Speci-
men from older broth culture. C. A ciliate fed on Aerobacter cloacae.
D. A ciliate fed on killed Tetrahymena geleii. E. A large carnivore from
a culture fed living T. geleii. F. A carnivore after transfer to a culture
of living yeast. Ingested food, peristomial area, and contractile vacuole
are indicated diagrammatically but cilia are not shown. x450 (after
Kidder, Lilly, and Claff).

utable to environmental or inherent factors, dimorphic and polymorphic
life-cycles include two or more different morphological stages. Naegleria
gruberi (Chapter V), for example, exhibits both flagellate and amoeboid
stages. Although adaptive trends may be assumed, specific correlation of
form with habitat is impossible in many instances. Yet certain generaliza-

General Morphology of the Protozoa 5

tions are permissible for sessile, floating, swimming, and creeping types.
Floating types, free from the usual stresses of locomotor activity, often
approach a spherical form. Active swimmers are usually elongated, with
a major axis more or less parallel to the path of locomotion. Creeping

Fig. 1. 2. AC. Gonium sociale: side view (A); surface view (B); colony
with superficial continuous matrix (C); x900 (after Pascher). D, E. Gonium
sp., portions of colonies showing supposed protoplasmic connections impreg-
nated with silver; x760 (after Klein). F. Syncrypta volvox; x580 (after Stein).
G. Protoplasmic connections of somatic flagellates in Volvox; xl800 (after
Janet).

forms are frequently flattened and may show differentiated dorsal and
ventral surfaces. Sessile ciliates and flagellates are often more or less
conical, attached to the substratum directly or by a secreted stalk.

In individual Protozoa, form of the body may be maintained by a
thickened cortex (the differentiated outer zone of cytoplasm), by various

6 General Morphology of the Protozoa

secreted layers (pellicle, theca, lorica, test, and shell of particular groups),
and by internal structures such as radiolarian skeletons. The gross mor-
phology of protozoan aggregates and colonies depends upon the means
by which the individual organisms are bound together.

COLONIAL ORGANIZATION

The usual colony consists of similar organisms joined together in
some particular jDattern so that the form of the mature colony is char-
acteristic of the genus or species. As a rule, any member of the colony
may undergo fission or budding. In the Phytomonadida, this is true in
Gonium, Pandorina, and Platydorina but apparently not in Eudorina,
Pleodorina, and Volvox. However, flagellates isolated from colonies of

Fig. 1. 3. Arboroid colonies. A. Phalansterium digitatum, branching ma-
trix; x290 (after Lemmermann). B. Zoothamnium adamsi, portion of colony
showing stalk with continuous branching fibril; diagrammatic (after Stokes).
C. Hyalobryon ramosum, loricate type; x720 (after Awerinzew). D. Poterio-
dendron petiolatum; each lorica with stalk; x290 (after Lemmermann).
E. Cladomonas fruticulosa with continuous branching "lorica"; x290 (after
Lemmermann).

General Morphology of the Protozoa 7

Eudorina, Gonium, and Pandorina may undergo fission and produce
daughter colonies (11). The component flagellates of the Volvox colony
are differentiated into somatic and reproductive individuals and the
former are believed to lose their reproductive ability when the colony
reaches maturity.

Protozoan colonies are usually classified on the basis of their organiza-
tion. Spheroid and discoid colonies, containing a matrix secreted by the
associated organisms during development of the colony, are represented
by such ciliates as Ophrydium and various flagellates — Syncrypta, Go-
nium, Pandorina, Volvox, and others. In Gonium sociale, for example, the
matrix shows two components (Fig. 1. 2, C), a "cell wall" enclosing each
flagellate and a continuous outer gelatinous layer. In some specimens (Fig.
1. 2, A, B) the outer layer is lacking. Each flagellate in the Volvox colony
is enclosed in a thin cell wall and a thick outer sheath. Except in V.
aureus, the boundaries of the individual sheaths are readily distinguished.
The flagellates appear to be joined by protoplasmic strands in certain
species of Volvox (Fig. 1. 2, G) and apparently also in Eudorina, Gonium,
and Pandorina (11). Dried colonies of Gonium (Fig. 1. 2, D, E), after
silver impregnation, show "silver-line" connections between adjacent
flagellates (131).

In arboroid colonies (Fig. 1. 3), the individual organisms are arranged
in a branching pattern. Stalks are characteristic of many arboroid colonies.
In different species, each organism may have its own stem which is at-
tached to a common stalk, or each stalk of the framework may bear more
than one organism. Such stalks may be gelatinous or sometimes solid and
relatively firm, and in certain cases they are elastic tubes containing
contractile fibrils. In other arboroid types, colonial organization is main-
tained by attachment of one lorica to another (Fig. 1. 3, C, D), or by a
continuous tubular "lorica" in which the organisms are located at the
tips of the branches (Fig. 1. 3, E).

NON-COLONIAL GROUPINGS

Certain other aggregates are not colonies in the strict sense. So-
called catenoid colonies have been described in dinoflagellates (Fig. 1.
4, D) and certain astomatous ciliates (Fig. 1. 4, C). These chains arise in
repeated fission without prompt separation of daughter organisms and
are temporary groupings rather than true colonies. Palmella stages (Fig. 1.
4, A) of certain flagellates develop in much the same manner as spheroid
and discoid colonies. However, the palmella does not show a well defined
range in size, the number of organisms varies with size of the mass, and
the flagellates lack flagella. The term, gleocystis stage, is sometimes applied
to similar aggregates in which an individual gelatinous layer surrounds
each organism (Fig. 1. 4, B).

8 General Morphology of the Protozoa

Fig. 1. 4. A. Palmella stage, as seen in Haematococcus and related
Phytomonadida; diagrammatic (after Wollenweber). B. Gleocystis stage, as
found in various Chlamydomonadidae; diagrammatic (after Goroschan-
kin). C. Chain ("catenoid colony") of Haptophrya niichiganensis; x90
(after Bush). D. Chain formed in fission of Gonyaulax catenella; x580
(after Whedon and Kofoid).

CORTEX, SECRETED COVERINGS,
AND SKELETONS

No well developed cortex is apparent in simple flagellates or
typical amoebae. The superficial cytoplasmic layer of Amoeba proteus
is formed from, and gives rise to endoplasm continuously during amoe-
boid activity and thus lacks the relative permanence of the cortex in more
specialized Protozoa. However, some amoeboid organisms have a thin
pellicle similar to that of Amoeba verrucosa. In this species, the pellicle
maintains itself under mechanical stress in microdissection (96).

At the other extreme, the relatively thick cortex of a ciliate may con-
tain basal granules, fibrils, myonemes, mitochondria, and other inclu-
sions, and sometimes trichocysts. Although often flexible, the layer is at
least firm enough to maintain a typical body form in the swimming
ciliate. The pellicle covering the surface of ciliates seems to be a distinct

General Morphology of the Protozoa 9

layer, and Blepharisma undulans is said to shed its pellicle after treat-
ment with strychnine. The cilia are withdrawn and the body retracted,
leaving a space beneath the pellicle, and the ciliate later emerges through
the old cytostomal area or the region of the posterior contractile vacuole
(169).

Surface layers of flagellates range from a delicate periplast or pellicle,
similar to that of certain amoebae, to thick tests or shells. The flexible

Ir

Fig. 1. 5. A, B. Ventral and dorsal thecal plates in Gonyaulax acatenella;
x560 (after Whedon and Kofoid). C. Vaginicola longicoUis, optical section of
lorica; xl40 (after Penard). D. Stokesiella lepteca, stalked lorica; xl060 (after
Stokes). E. Test of Euglypha alveolata; x350 (after Leidy). F. Difflugia corona;
xl35 (after Leidy). G. Tintinnopsis nucula, optical section of lorica; diagram-
matic; x570 (after Campbell).

periplast of many Euglenida permits a characteristic euglenoid movement
("metaboly"), but tends to maintain a characteristic form in the swim-
ming flagellate. This periplast presumably is a secreted layer, since it
becomes separated from the underlying cytoplasm in plasmolysis (22).
Thickened pellicular layers, as seen in LepocincUs and Phacus, may be so
firm that the body shows little change in shape. Such membranes are
often decorated with ridges, papillae or other markings.

The theca of many Phytomonadida and Dinoflagellida is a secreted

10 General Morphology of the Protozoa

covering applied directly to the surface of the body and is comparable to
the thick cell wall found in higher plants. The flagella emerge through
pores in the theca. A theca may be somewhat flexible, allowing slight
changes in form, or it may be rigid. The firmness imparted by cellulose
or pectins is sometimes increased by impregnation with inorganic salts
to produce a hard covering, as in Phacotus, Trachelomonas, and some of
the dinoflagellates. The theca of many dinoflagellates is differentiated into
a number of plates (Fig. 1. 5, A, B), the pattern varying with the species.
Lorica, test, and shell are terms applied to coverings which often fit
less closely than the theca and hence are less comparable to the typical
cell wall of plants. A lorica (Fig. 1. 5, C, D) is usually a tubular or vase-
like structure with an opening through which the anterior part of the

^v

A

B

^r^'

Fig. 1. 6. Groups of myxopodia (A) and axopodia (B); diagrammatic.

body or its appendages can be extended. The base of the lorica, in sessile
species, may be attached directly to the substratum or may end in a
stalk. In colonial types (Fig. 1. 3, C, D), one lorica may be attached to
another directly or by means of a stalk. A lorica may be composed en-
tirely of secreted material or may be reinforced with diatom shells, sand
grains, or other foreign particles.

The tests (or shells) of many Sarcodina vary widely in form and com-
position. Some appear to be homogeneous. Others consist mainly of sep-
arate elements cemented together, as in Euglypha and Difflugia (Fig. 1.
5, E, F). The test of Euglypha is composed of plates, formed within the
body prior to fission; that of Difflugia is made of sand grains embedded
in a secreted cement. The comparable arenaceous tests of certain Foram-
iniferida (Chapter V) are built of sand grains, discarded tests, sponge

General Morphology o£ the Protozoa H

spicules, or other materials cemented together over a thin chitinous test.
The composition of other foramiferan tests varies from group to group.
That of the AUogromiidae is typically chitinous, while the majority of
the multichambered tests are calcareous. Siliceous tests also have been re-
ported in a few Foraminiferida. In many species at least, the foraminif-
eran test is not really external; instead, it is normally enclosed within a
thin layer of cytoplasm.

The simplest skeletons of Radiolarida are represented by scattered
siliceous spicules, while the more complicated types are structures unique
among the Protozoa (Chapter V). In the Acantharina long spines radiate
in definite patterns from the center of the body. To these elements is
often added a lattice-work shell, joining and supported by the spines.
Siliceous skeletons of other Radiolarida are quite varied in structure.
Spherical types may be composed of several concentric lattice-work shells,
and sometimes of spicules in addition. Bilateral types, conical forms, and
other departures from radial symmetry are fairly common.

PSEUDOPODIA

Pseudopodia are temporary organelles which can be retracted and
formed anew, depending upon activities of the organism. Four major
types may be distinguished — lobopodia, filopodia, myxopodia, and
axopodia.

Lobopodia, which have relatively dense outer layers and more fluid
inner zones, are relatively broad pseudopodia with rounded tips. Short
or slender lobopodia may be hyaline, but larger ones usually show a clear
ectoplasm enclosing a granular endoplasm. Lobopodia are characteristic
of amoebae, certain flagellates, and certain testate rhizopods (Fig. 1. 5, F).

Filopodia are slender hyaline pseudopodia which taper from base to
pointed tip and also tend to branch and anastomose. In addition, filo-
podia may fuse locally to produce thin webs of cytoplasm. The absence
of circulating granules helps to distinguish filopodial from myxopodial
nets.

Myxopodia (rhizopodia, or reticulopodia), characteristic of the Foram-
iniferida, are filamentous structures (Fig. 1. 6, A) which branch and
anastomose into complex networks often covering a wide area. Such nets
are efficient food-traps and are fairly effective locomotor organelles. In
addition, the digestive activities of myxopodia are usually marked in
Foraminiferida (Chapter V). The comparatively dense inner zone of the
myxopodium has been considered fibrillar in structure (198). The fluidity
of the outer layer is indicated by the active circulation of cytoplasmic
granules, as illustrated by Elphidium (Polystomella) crispum (103).

Axopodia (Fig. 1. 6, B) tend to radiate singly from the surface of more
or less spherical organisms (Heliozoida, Radiolarida). The axial filament
of a typical axopodium has been described as a fibrillar tube enclosing a

12 General Morphology of the Protozoa

homogeneous core (193, 195). In contrast to the axial filament, the outer
cytoplasm is a sol, as indicated by the movement of inclusions. Axial
filaments may converge in a central granule (Acanthocystis and related
genera) or they may end separately in the cytoplasm (Actinosphaerium).

FLAGELLA AND ASSOCIATED
STRUCTURES

Flagella

These organelles are found in Mastigophora and in flagellate stages
of Sarcodina and Sporozoa. A typical fiagellum is composed of a sheath,
which may be circular, elliptical, or flattened in cross-section, and an
inner axoneme. The latter, according to some workers, is the active por-
tion of the fiagellum while the sheath is merely protective. Others think
that the axoneme is only an elastic support for a contractile sheath. The
axoneme arises from a granule, the blepharoplast . and may or may not
extend beyond the sheath as a distal end-piece (Fig. 1. 7, F). A terminal
knob (Fig. 1. 7, H), instead of a filament, is evident in silver preparations
of Trypanosoma rhodesiense (127). The anterior flagella of Hexamitus
pulcher (130) also are unusual in that they arise from external rod-like
structures (Fig. 1. 7, E) of uncertain significance.

The finer structure of the fiagellum^ is incompletely known, although
investigations with the electron microscope (13, 56, 180, 199) have sup-
plemented earlier observations. The axoneme may be composed of one,
two (Astasia, Euglena), three {Peraneyna), or perhaps more fibrils, while
the sheath apparently contains a spirally coiled filament in certain species.

The sheath in some flagella shows lateral filaments (Fig. 1. 7, A, C),
the mastigonemes (43) or "Flimmer," the nature of which is uncertain.
Although observed in living Mallomonas acaroides in dark-field (217),
they may be artifacts (173) or may represent fibrils of the sheath which
are frayed out laterally under certain conditions (180). At any rate, such
filaments appear consistently in some species and not in others. In the
stichoneynatic fiagellum (43), a single row of filaments extends along one
side of the sheath (Fig. 1. 7, A), as in Astasia and Euglena (13). In the
pantojiematic type there are two or more rows of mastigonemes. Only a
terminal filament is present in the acronematic, or "lash" fiagellum (174),
while the pantacronematic type shows both a terminal filament and one
or more rows of mastigonemes. A simple type, found in Cryptomonadida
and Dinoflagellida (174), shows neither terminal filament nor masti-
gonemes. These characteristics of the fiagellum seem to be constant within
various groups and may furnish significant information in studies on
taxonomy and phylogeny (174, 217).

In the majority of flagellates, the flagellum extends forward from its

^ This subject has been reviewed in several papers (13, 174, 180, 217).

General Morphology o£ the Protozoa 13

origin, whereas a trailing flagellum (Fig. 1. 9, F) arises anteriorly but is
trailed posteriorly in swimming. A trailing flagellum may be of the con-
ventional type, or it may be ribbon-like as in Macrotrichomonas pulchra
(126). The undulating rnembrajie of Trichomonas and related genera
(Fig. 1. 7, G, I) contains a marginal flagellum which originates in an
anterior blepharoplast and extends posteriorly, sometimes beyond the end

niiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiir^ "^

c

Fig. 1. 7. A-D. Deflandre's types of flagella: stichonematic (A), acrone-
matic (B). }3aiUonematic (C), pantacioneniatic (D). E. Hexarnitus pulcher,
flagella with rod-like basal portions; protargol; x3460 (after Kirby and
Honigljerg). F. Acronematic flagella of Moiiocercomonoides piUeata; pro-
targol; \3960 (after Kirby and Honigberg). G. Ribbon-like flagellum of
undulating menil,rane in Trittichomoims imiris; protargol; x2810 (after
Kirby and Honigberg). H. Terminal knob on flagellum of Tiypaiwsoma
brucei; protargol; xI790 (after Kirbv). I. Undulating membrane in Penta-
trichomonas honiinis; x2660 (after Wenrich). J. Axial flagellum and ribbon-
like transverse flagellum of Gyrodinium dorsum x470 (after Kofoid and
Swezy). Key: a, axostyle; c, costa; /, flagellum in undulating membrane.

of the membrane. This marginal flagellum is sometimes ribbon-like, as in
Tritrichomonas muris (130). The undulating membrane of Trypanosoma
originates near the posterior end of the body and extends to the anterior
end (Fig. 1. 7, H).

The majority of species have only one or two flagella. More than four
are rare in free-living flagellates, although not in parasites. When several
flagella are present, they may differ in size, structure, and activity.
Pentatrichomonas hominis (Fig. 1. 7, I), for instance, has four relatively

14 General Morphology of the Protozoa

short anterior flagella, a longer fifth flagellum, and an undulating mem-
brane. A typical dinoflagellate (Fig. 1. 7, J) has a transverse flagellum,
lying in a spiral groove (the girdle), and an axial (or longitudinal) flagel-
lum extending posteriorly from a lateral or postero-lateral origin.

Axostyles

The axostyle (Fig. 1. 8) varies from a filament to a thick hyaline
rod, usually joined to a blepharoplast and extending posteriorly along
the major axis of the body. The axostyle may end in the body or may
project externally, sometimes tapering to a filament which may serve for
attachment to the host (124). The anterior end is often expanded into a

Fig. 1, 8. Axostyles. A. Capitulum and anterior portion of axostyle in
Hyperdevescovina insignita; xl800 (after Kirby). B. Slender axostyle in
Monocercomonoides pilleata; x3600 (after Kirby and Honigberg). C. Mul-
tiple axostyles of Snyderella tabogae; diagrammatic; x350 (after Kirby).
D. Tritrichomonas augusta, axostyle with inclusions; xl950 (after Kofoid
and Swezy). E. Axostyle with capitulum in BuUanympha silvestri; x750
(after Kirby). Key: a, axostyle; b, blepharoplast; c, capitulum; ct, cortex;
m, mastigont; n, nucleus; t, trailing flagellum; u, undulating membrane.

General Morphology of the Protozoa 15

capitulum (Fig. 1. 8, A, E). Many multinucleate species contain a num-
ber of axostyles, one for each mastigont, and the distal portions of the
axostyles form a bundle extending posteriorly as in Snyderella (Fig. 1.
8, C).

Staining reactions of the axostyle vary in different species. Iron-hema-
toxylin stains the axostyle of Monocercomonoides pilleata (Fig. 1. 8, B)
but not that of certain other flagellates. The organelle appears homo-
geneous in some species, shows a sheath and a core in others (Fig. 1. 8,
A), and sometimes contains stainable granules (Fig. 1. 8, D). The axo-
style of Trichomonas termopsidis (124) is stained brown in iodine solu-
tion.

Costa, cresta, pelta, and aciculum

The costa (Fig. 1. 7, G; 1. 8, D) arises from a blepharoplast and
extends along the base of the undulating membrane in various tricho-

Fig. 1. 9. AC. Pelta, different views, Hexamastix citelli; x6500 (after
Kirby and Honigberg). D. Aciculum of Cryptobia helicis; kinetoplast indi-
cated diagramraatically; x5330 (after Kozloff). E. Cresta, small type, Cadu-
ceia kofoidi; x3060 (after Kirby). F. Large cresta, Macrotrichornonas emer-
soni; shelf-like unguis attached; trailing flagelluni ribbon-like; xl425 (after
Kirby). Key: a, axostyle; ac, aciculum; cr, cresta; ct, cortex; k, kinetoplast;
71, nucleus; p, pelta; t, trailing flagellum; u, unguis.

16 General Morphology of the Protozoa

monad flagellates. The function of the costa is uncertain, although it may
add firmness to the cytoplasm underlying the undulating membrane.

The cresta (Fig. 1, 9, E, F), possibly a homologue of the costa, is
present in Macrotrichomonas and related genera. This organelle is a
somewhat triangular membrane, often visible in the living organism and
apparently capable of independent movement (125). The broad anterior
end is usually joined to a blepharoplast, while the rest of the cresta ex-
tends posteriorly with its outer margin near the periplast. The length, in
different species, ranges from about 1.5[x to almost that of the body. A
trailing flagellum, sometimes loosely adherent to the periplast anteriorly,
may parallel the cresta (Fig. 1. 9, F) and thus simulate the relationship
between the undulating membrane and the costa.

The pelta (Fig. 1. 9, A, C), demonstrable by the Bodian silver tech-
nique, is a crescentic membrane lying anterior to and separate irom the
blepharoplasts in certain flagellates. The pelta may be homologous with
a membranous extension of the axostylar capitulum in certain devesco-
vinid flagellates (128).

The acicuhim (Fig. 1. 9, D) of Cryptobia helicis, a needle-like structure
lying opposite the kinetoplast and extending approximately to the origin
of the anterior flagellum, is detectable in living material but is best
demonstrated by the Bodian silver technique (141).

The parabasal apparatus

In many parasitic and a few free-living flagellates a parabasal
apparatus, an organelle of unknown function, forms part of the mastigont
(Fig. 1. 10). The simplest type is a small compact body, often attached
by a rhizoplast to a blepharoplast. At the other extreme, the apparatus
may be a large branched structure or may be composed of separate
elements.

The index of refraction of the parabasal body is approximately that
of the cytoplasm and vital staining is rather slow (71); consequently,
the organelle is not readily seen in the living flagellate. The apparent
internal structure may vary with the species as well as with methods of
fixation and staining (47, 123).

The parabasal apparatus of free-living flagellates shows little variety
(Fig. 1. 10, H, L, N-P). One or two small parabasal bodies have been
described in several species; one or more long slender bodies, in certain
others. In the tetranucleate Polykrikos schwartzi (27), each band-like
parabasal body is attached to a ring encircling the intracytoplasmic por-
tion of an axial flagellum. The parabasal body of Codosiga elegans (196)
is of special interest because it closely resembles a structure (Fig. 1. 10,
M) described in choanocytes of calcareous sponges (218).

Among parasitic flagellates, the complexity of the parabasal apparatus
varies widely. The small kinetoplast of Trypanosoma hnicei (Fig. 1. 10,

Fig. 1. 10. Parabasal apparatus in different flagellates. A. Tetramitus bu-
fonis; x2200 (after Duboscq and Grasse). B. Pseudodevescovitia imiflagellata;
xllOO (after Kirby). C. Single mastigont of Snyderelln lahogae (see Fig.
1. 8, C): diagrammatic (after Kirby). D. Stephaiwnyinfyha nehimbitim. dia-
grammatic optical section showing karyomastigonts; x750 (after Kirby). E.
Karyomastigont of 5. nelumbium; xI870 approx. (after Kirby). F. Hyper-
devescovina torquata; xl050 (after Kirby). G. Macrotriclionionas ramosa;
xl360 (after Kirby). H. Bodo caudatus; x3600 (after HoUande). I. Leptomonas
ctenocephali; diagrammatic (after A. and M. Lwoff). }. Trypanosoma brucei,
kinetoplast seen on edge; protargol; diagrammatic (after Kirby). K. T. brucei,
surface view of kinetoplast (after Kirby). L. Codosiga elegans, a choanoflagel-
late; diagiammatic (after de Saedeleer). M. Choanocyte of a sponge, Clathrina
coriacea; diagrammatic (after Volkonsky). N. Chilomonas Paramecium; x2850
(after Hollande). O. Polytoma uvella; diagrammatic (after Volkonsky). P.
Cercobodo heimi; x3450 approx. (after Hollande). Key: a, axostyle; ab, apical
body; b, blepharoplast; co, collar; cr, cresta; f, parabasal filament; k, kineto-
plast; Aw, karyomastigont; n, nucleus; p, parabasal apparatus; pn, para-
nuclear body; r, periflagellar ring; rh, rhizoplast.

18 General Morphology o£ the Protozoa

J, K) is fairly typical of the Trypanosomidae, although the mastigont
of Leptomonas ctenocephali (151) is less simple. In addition to the kine-
toplast, a periflagellar ring in L. ctenocephali gives rise to a long para-
basal filament (Fig. I. 10, I). A simple elongated parabasal body is found
in certain uninucleate Trichomonadidae (Fig. 1. 10, A) and in each
complete mastigont of such multinucleate genera as Stephanonympha,
Calonympha, and Snyderella (Fig. I. 10, C-E). In certain flagellates a long
parabasal body is coiled around the axostyle (Fig. 1. 10, F), while the
apparatus of Macrotrichomoyias ramosa (126) is branched (Fig. 1. 10, G)
and that of Pseudodevescovina uniflagellata is compound (Fig. 1.10, B).
A complex apparatus, often including many separate elements, occurs
also in various Hypermastigida (47).

The special term, hinetoplast (127), has been applied to the parabasal
body of trypanosomes and related flagellates. This usage seems justified.
Kinetoplasts are Feulgen-positive (104, 152, 188, 192) and are demon-
strable by methods of fixation and staining which are unsatisfactory for
the trichomonad parabasal body. Finthermore, the kinetoplast divides
in fission whereas this is rarely the case in other types of parabasal
apparatus.

Multiple karyomastigonts and mastigonts

The kinetic elements of many multinucleate flagellates have in-
creased in number along with their nuclei. Each flagellar unit (mastigont)
is associated with a nucleus in Coronympha and Stephanonympha (Fig.
1. 10, D). Such flagellates thus contain a number of karyomastigonts, each
composed of a nucleus and associated blepharoplasts, flagella, parabasal
body, and axostyle. This appears to be the primitive condition in such
flagellates. Two sets of flagella are associated with each of the four
nuclei in Polykrikos sclnvartzi (25); the flagellar apparatus has doubled
independently of the nucleus without otherwise disrupting the basic
karyomastigont (Fig. 4. 20, G). Caloyiympha represents an intermediate
condition showing both karyomastigonts and mastigonts, the latter being
far more numerous. A degree of specialization rare in flagellates — inde-
pendence of nucleus and mastigont — is represented by Snyderella tabogae
(Fig. 1. 8, C), in which the several dozen nuclei are all dissociated from
the hundreds of mastigonts.

CILIA AND THEIR DERIVATIVES

Cilia are structurally similar to flagella but are shorter and more
restricted in movement and are generally present in greater numbers.
Prorodon teres, for example, is equipped with about 11,600 cilia (231). A
cilium, like the flagellum, apparently consists of a sheath and an axoneme
ending in a basal granule. A "sensory" component has been described as

General Morphology of the Protozoa 19

a thin argentophilic layer covering the axial filament and tapering distally
to a granular "end-organ" (132), Electron micrographs indicate that the
unfixed, dehydrated axoneme is composed of fibrils in Paramecium,
whereas a sheath is suggested merely by possible remnants of an envelop-
ing layer (102, 199).

In certain ciliates an accessory "ciliary corpuscle" (30) is attached to
the basal granvde; in some instances, the accessory body may be mito-
chondrial in nature (26). Two accessory granules have been reported in
certain ciliates (132). A slender fibril, the ciliary rootlet, extends inward
from the basal gianule in some ciliates, but is said to be absent in certain
primitive species (29). From many of the basal granules in Opalijia
obtrigonoidea (Fig. 1. 11, G), fibrils extend dorso-ventrally through the
cytoplasm to end in basal granules on the opposite side of the body (34).
Whether these fibrils are homologous with the ciliary rootlets of other
ciliates is uncertain.

Cilia lie in meridional or spiral rows in the less specialized ciliates.
Although such a pattern is usually rather constant within a species,
changes from spiral to meridional to spiral, and even a reversal of the
spirals, occur in certain species with complex life-cycles (150). Individual
cilia, in ciliates with sculptured pellicles, may emerge from grooves, from
the margins of such grooves, or from individual pits in different cases.

The simple cilium is the primitive locomotor structure in ciliates.
Many species possess compound organelles which have arisen by fusion of
cilia in longitudinal or transverse rows, or in tufts. Such organelles are
known as undulating membraries, memhranelles and cirri. An undulating
membrane, formed by the fusion of one or more longitudinal rows of
cilia, lies in the peristome (oral "groove") of various species. Rippling
movements of the membrane drive particles to the cytostome. This organ-
elle may not be permanent in quite the same sense that cilia are so
considered, since the membrane of Blepharisma undulans may break up,
spontaneously or after injury, into individual cilia. The cilia eventually
fcuse again into an undulating membrane (24). Memhranelles, which are
more or less triangular flaps formed by fusion of two or more transverse
rows of cilia, are found especially in the peiistomial area (Fig. 1. 15, H).
Each membranelle of Spirostomum ambiguum contains a double row of
cilia whose basal granules end in a plate parallel to the surface of the
body (Fig, 1, 11, E), A basal lamella, extending inward from the plate,
tapers to an end-thread which joins a basal fibril in the endoplasm (8),
Cirri, characteristic of the Hypotrichina, consist of tufts of cilia probably
embedded in a matrix (Fig. 1, 11, C, D). The number of cilia varies with
the size of the cirrus — in Oxytricha fallax, for example, three or more in
the small marginal cirri and 8-18 in the ventral, frontal, and anal cirri
(146).

20

General Morphology of the Protozoa

P^

T^^^T^ %t vo;

es-

©/ ^®y<s

..?:(?Ji.?/</..l!ly.Ai

Fig. 1. 11. A. Longitudinal fibril joining basal gianules in Entorhi-
pidiiim echini; longitudinal section of cortex; xl890 (after Lynch). B. Trans-
verse connecting fibrils in E. echini; cross-section of cortex; xl800 (after
Lynch). C. Frayed cirrus of Oxytricha fallax showing component cilia; x2025
(after Lund). D. cirrus of O. fallax; xl725 (after Lund). E. A membra-
nelle of Spiiostomum anihiguimj; diagrammatic (after Bishop). F. Basal
granules and connecting fibrils in Tillina canalifera; diagrammatic (after
Turner). G. Dorso-ventral fibrils joining basal granules in Opalina obtri-
gonoidea; longitudinal section; xllOO (after Cosgrove). Kev: b, basal fibril;
c, cilium; e, end-thread; es, endoplasmic spherule; j, longitudinal fibril; g,
basal granule; gi, primary basal gianule; gs, secondary basal granule; I,
basal lamella; m, membranelle; p, basal plate; t, transverse fibril; tr, tricho-
cyst.

FIBRILLAR SYSTEMS

The basal granules in each longitudinal row of cilia are joined by
a fibril. Transverse fibrils may also link the basal granules in some species
(Fig. 1. 11, A, B). Tillina canalifera (123) is unusual in that longitudinal
and transverse fibrils join secondary basal granules, which in turn are
connected by rhizoplasts to superficial primary basal granules from which
the cilia arise (Fig. 1. 11, F). In Opali?ia obtrigorioidea, oblique fibrils
join basal granules in different longitudinal rows but longitudinal fibrils
cannot be detected (34). This situation suggests possible modification of
the primitive symmetr)' during the evolution of opalinid ciliates.

The longitudinal fibrils in certain ciliates seem to be morphologically
independent (29). In other species, the fibrils are joined in complex

General Morphology o£ the Protozoa 21

fibrillar systems (64, 132, 211) referred to as neuromotor apparatus,
silver-line system, neuroneme system, and infraciliature by different
workers. These "systems" have been demonstrated by various techniques,
so that it is difficult to correlate each one with all the others. In general,
however, the neuromotor system seems to be both endoplasmic and
ectoplasmic while the other fibrillar systems occupy a superficial position.

Fig. 1. 12. Silver-line systems (after Klein). A. Prorodon teres; narrow-
mesh type with some orientation of filjrils. B. Primitive narrow-mesh type.
C. Striation-system in Cyclidiutn glaucoma. D. Double striation-system in
Cinetochilum marmritaccum.

Neuromotor apparatus

The neuromotor system of Euplotes (79, 209, 212, 238) includes a
relatively small number of fibrils (Fig. 1, 13, G). Those from the anal
cirri converge anteriorly in a "motorium," from which a membranelle
fibril passes anteriorly and to the left, and then posteriorly beneath the
peristomial membranelles. In addition, groups of fibrils extend from the
basal plates of the frontal and ventral cirri into the endoplasm. Although
the first and second frontal cirri are joined by such fibrils, no intercon-
nections have been demonstrated for the other cirri (79). A comparable
neuromotor apparatus has been described in other ciliates (211).

Silver-line system

The observations of Klein (132, 134) and others have revealed a
silver-line system, in many ciliates. The name of the system is derived from
Klein's technique, in which reduced silver is deposited on superficial
structures. The argentophilic "silver-lines" are assumed to be plastic
structures having the capacity to grow, split, undergo resorption, and
then reappear (132).

The primitive system is a narrow-mesh (0.75-1. 0|j.) network containing
the basal granules (Fig. 1. 12, B). The fibrils themselves extend through
the interstices of the ectoplasmic alveoli. Since a narrow-mesh network
has been reported in Dileptus, Oxytricha, Epalxis, Spirostomum, Stentor,

22 General Morphology o£ the Protozoa

Fig. 1. 13. A. Myonemes in anterior half of Stentor coeruleus; dia-
grammatic (after Dierks). B. Portion of a myoneme (S. coeruleus) showing
cross-striations; diagrammatic (after Dierks). C. A neuroneme in Para-
mecium; diagrammatic (after Gelei). D-E. Myonemes in Monocystis agilis,
longitudinal and transverse sections; diagrammatic (after Roskin and
Levinson). F. Sensory bristle of Euplotes patella; diagrammatic (after
Hammond). G. Neuromotor system of Euplotes (patella) eurystomum,
showing major fibrils and incisions made in microdissection; x680 (after
Taylor). Key: c, cilium; cf, anal-cirrus fibril; cm, circular myoneme; g,
basal granule; Ic, longitudinal canal containing myoneme; Im, longitudinal
myoneme; m, motorium; /«/, fibril to membranelles; n. neuroneme; p,
pellicle; r, rodlet of "rosette"; s, "sensory" fibril; t, trichocyst; tg, tricho-
cyst-granule; 1-5, approximate planes of incisions in Taylor's operations.

General Morphology of the Protozoa 23

and also in Podophrya (Suctorea), this primitive system obviously is not
limited to unspecialized ciliates.

Specialization of the silver-line system involves first an increase in
diameter of the mesh, so that a single mesh comes to enclose a group of
ectoplasmic alveoli. As the mesh widens, the silver-lines decrease in num-
ber and begin to parallel the rows of basal granules (Fig. 1. 12, A). In
meridional ciliation, the system may be reduced to ineridians bearing the
basal granules and sometimes joined by transverse commissures (Fig. 1.
12, C) — so-called striation-systems. Each meridian is sometimes double
(Fig. 1. 12, D). Or the silver-line may be a bundle of fibrils. In Colpidiitm
colpoda (132), each meridian is said to split just behind the cytostome
into primary and secondary meridians. The basal granules lie very close
together in the fused anterior meridians. Posteriorly, the basal granules
in the primary meridians are spaced at fairly short and rather regular
intervals; those in the secondary meridians, at longer and more irregular
intervals.

In addition to the basal granules of cilia, the silver-line system includes
trichocyst-granules and protrichocyst-granules, all three types being con-
sidered '"relator-granules" which relate the corresponding structures to
the silver-lines. The protrichocyst-granules also have been considered
tec tin-granules (12), which presumably are extruded through secretory
pores in the pellicle (65). The relator-granules, especially the basal gran-
ules, may persist after their organelles have disappeared in phylogeny,
and thus represent persistent traces of much more primitive conditions
(132).

Both the fibrils and the relator-granules are said to lie at the same
level in the ectoplasm (132). However, the network ("indirect system"
of Klein) apparently does not occupy the same plane as the basal gran-
ules and longitudinal fibrils in Paramecium caudatum, since the latter are
not in focus in photomicrographs which show the network clearly (67).
Lund (145) concluded that the peripheral "network" in P. multimicro-
nucleatum represents pellicular ridges upon which silver is deposited in
dried specimens. The correlation between pellicular markings and the
silver-line pattern also has been stressed by Jacobson (100). Therefore,
the exact nature of Klein's superficial network remains uncertain. The
silver-line meridians, which join the basal granules, appear to be sub-
pellicular.

Neuroneme system

This system (64, 67), demonstrable by the techniques of Gelei
and Horvath (68), joins the basal granules and possibly corresponds to
the meridians of Klein. In sectioned material, the neuronemes of Para-
mecium caudatum (Fig. 1. 13, C) appear as zigzag lines joining the basal
granules to the more superficial trichocyst-granules (64). The neuronemes
are not continuous with the superficial silver-line network of Klein.

24 General Morphology of the Protozoa

Infraciliary network

This system lies at the level of the basal granules or somewhat
deeper, between the alveolar and the inner ectoplasmic layers (62).
Neither the basal granules nor the trichocysts are directly connected with
this system, and no connection with the outer network has been observed.
The longitudinal fibrils of the infraciliary system generally follow the
pattern of the ciliary rows.

The infraciliature

The basal fibril, or kinetodesma, of Chatton's infraciliature is
considered to be separate from the ciliary meridian of Klein. The silver-
line fibril is said to lie on the left of the basal granules while the
kinetodesma lies on the right (26, 29, 214). However, such regularity in
position of the silver-line is not apparent in some of Klein's figures, and
in ciliates showing "circular fibrils" in the silver-lines, basal granules may
lie on the circular fibril or may be enclosed by it (133).

Sensory bristles

So-called sensory bristles, apparently associated with the fibrillar
systems of certain ciliates, are well developed on the dorsal surface of
Euplotes (79, 212). Each bristle arises from a granule at the base of a pit
which is surrounded by a "rosette" of rodlets (Fig. 1. 13, F). On the
ventral surface, two or three similar rosettes without bristles lie near
the base of each cirrus. Analogous structures, supposedly sensory in func-
tion, have been described in Didinium and certain other genera (63).

Significance of fibrillar systems

According to various workers, the fibrillar systems of ciliates are
contractile fibrils, supporting or skeletal structures, organizers in the onto-
genetic development of related organelles (134), coordinating systems,
and delicate circulatory systems for transporting such materials as nucleo-
proteins to the basal granules and trichocysts (86),

Except for whatever support these hypotheses may derive from mor-
phological relationships, the data bearing on functions of fibrillar systems
are meager. The results of microdissection suggest a coordinating func-
tion in Euplotes (209). The adoral membranelles in this hypotrich are
important in swimming, while the anal cirri play a major part in creep-
ing. Cutting the membranelle-fibril (Fig. 1. 13, G) destroyed coordination
of the membranelles so that swimming movements were abnormal. Sever-
ing the fibrils to the anal cirri affected both creeping and swimming,
while destruction of the motorium disturbed the coordination of the anal
cirri and membranelles. Incisions not severing the neuromotor fibrils
failed to modify swimming or creeping movements. Similar experiments

General Morphology of the Protozoa 25

(236) indicate that coordination of the ciliary beat in Paramecium is
dependent upon impulses transmitted longitudinally through the ecto-
plasm. These findings seem to eliminate Klein's superficial network as a
coordinating system in Paramecium and suggest, instead, such a function
for the longitudinal fibrils (superficial fibrils of the neuromotor appa-
ratus, neuronemes of Gelei, kinetodesmas of Chatton and possibly the
silver-meridians of Klein). More recently, it has been concluded that the
cortical localization of acetycholinesterase in Tetrahymena pyriformis
supports the hypothesis that conduction by the fibrillar system is similar
to conduction along nerve fibres (201a).

Silver-line system of flagellates

Among the dinoflagellates, Polykrikos schwartzi (28) and such
gymnodinioid types as Gyrodinium pavillardi and Gymnodinium splen-
dens show an argentophilic surface network, while impregnation merely
blackens the sutures of the thecal plates in peridinioid species (6). Im-
pregnation of Gonium, Eudorina, and Volvox (Fig. 1. 2, D, E) demon-
strates silver-lines in the individual flagellates (131), while the silver-lines
of various Euglenida (106, 131) apparently correspond to the pellicular
striations visible in living material. In addition, the flagella of Pyrso-
nymphidae (105), as well as the pellicular ridges and the margin of the
undulating membrane in Trypanosoma rotatoriuyn (106), are impreg-
nated with silver.

MYONEMES AND CONTRACTILE
STALKS

Myonemes are well developed in various large ciliates which are
capable of changing form rapidly. The band-like and cross-striated
myonemes of Stentor coeruleus (44) extend from the posterior end of the
body to the adoral zone, sometimes branching to follow the rows of cilia
(Fig. 1. 13, A, B). Posteriorly, the myonemes turn inward and anteriorly
as a bundle which finally branches into fibrils that disappear in the
endoplasm. Among the flagellates, swimming of the medusa-like Lepto-
discus and Craspedotella is attributed to myonemes which bring about
rhythmic contractions of the body (177). Pellicular ridges in such large
trypanosomes as Trypanosoma rotatorium have been considered myo-
nemes, but their contractile nature is uncertain. Some of the larger
gregarines apparently possess both circular and longitudinal myonemes
(Fig. 1. 13, D, E) enclosed in individual ectoplasmic canals (194). Many
Protozoa have no myonemes but the absence of such structures does not
eliminate contractility. This fundamental property is exhibited by many
species which seem to show no appropriate differentiations at the micro-
scopic level.

Well developed myonemes (stalk-muscles, or spasmonemes) are found

26 General Morphology of the Protozoa

also in the stalks of certain ciliates. The stalk-muscle of Zoothamnium
extends spirally within a sheath continuous with the protoplasm of the
body. Between the sheath and the surface of the stalk, there is a matrix
filled with elastic fibrils which arise from a differentiated area, the
scopula, in the aboral body wall (182). The stalk-muscle extends almost
to the base of the stalk, where it is attached by a fibrillar bundle to the
basal disc. The individual stalk-muscles of the Carchesium colony are
attached to the bases of their own stalks, so that each stalk-muscle
contracts independently.

TRICHOCYSTS AND NEMATOCYSTS

Trichocysts are cortical structures reported in certain ciliates and
flagellates. Trichocyst-bearing Holotrichida are represented by several
dozen genera. In addition, trichocysts have been reported in some Het-
erotrichina (e.g., Blepharisma) and in Strombidiiun among the Oli-

# ^

Fig. 1. 14. A. Nematocyst of Polykrikos; xl450 (after Kofoid and Swezy).
B. Fusiform and spherical trichocysts of Gonyostomum semen; diagram-
matic (after Chadefaud). C, D. Trichocysts of Dileptus anser before and
after discharge; x3080 (after Hayes). E. Developing and mature trichocysts
in Parayneciiim caudatum; diagrammatic; xl280 (after Jacobson). Key: c,
cortex; ch, chromatophore; /, fibril (A), fusiform trichocyst (B); 5, spherical
trichocyst; st, stylet; t, trichocyst; td, developing trichocyst.

gotrichina (200). Trichocysts may be widely scattered over the body
(Parameciiwi), limited to the peristomial area (Dileptus), or borne on
tentacles or papillae [Actinobolina, Legendrea). Development of tricho-
cysts from macronuclear granules has been reported. However, this
phenomenon has not been confirmed (100), although developing tricho-
cysts (Fig. 1. 14, E) appear in the cytoplasm of Frontonia leucas and
Paramecium caudatum. The outgrowth of trichocysts from "trichocysto-
somes," granules produced by division of basal granules, also has been
reported (150). So-called protrichocysts of various ciliates have been in-
terpreted also as deposits of tectin, used in formation of the cyst mem-
brane or the lorica (12, 200).

General Morphology of the Protozoa 27

The trichocysts of Dileptus gigns (215) show no internal organization
and form no detectable structures upon discharge. These trichocysts
(toxicysts), which change shape during contortions of the ciliate and be-
come almost spherical under pressure of a coverslip, are believed to
contain a fluid. Comparable trichocysts are found in the tips of retrac-
tile tentacles in Actinobolina (225), and the flask-shaped trichocysts of
Conchophthirhis mytili (116) also may be similar to those of D. gigos.

Trichocysts of certain other ciliates are discharged as recognizable
structures. Such is the case in Legendrea, Frontonia, Paramecium, Pror-
odon, and Dileptus anser. In electron micrographs (101, 102), discharged
trichocysts of Paramecium show a pointed tip resembling a golf tee, and
a transversely striated shaft. The trichocyst of Dileptus anser consists of
a thread-like extension into the cytoplasm and a bulbous portion which
tapers to a subpellicular granule (Fig. 1.14, C). Upon discharge (Fig. 1.
14, D), the positions of these components are reversed, the trichocyst-
granule adhering to the pellicle (81). Discharge apparently involves turn-
ing the trichocyst inside out.

Trichocysts have been interpreted as offensive and defensive weapons
and as organelles of attachment. Under artificial stimulation, trichocysts
of Entorhipidium pilatum are often expelled from the body but they
sometimes backfire into the endoplasm (148). Therefore, the behavior of
trichocysts under artificial conditions should be interpreted cautiously. A
protective function is often suggested but has not been adequately dem-
onstrated in Paraynecium. Another suggestion for Paramecium (197) is
that the trichocyst, which hardens after extrusion so that only the tip
remains sticky, serves in anchoring the ciliates. The stimulus to natural
discharge, in which only a portion of the trichocyst is discharged, is said
to be contact with solid objects. In contrast to the trichocysts of Para-
?7iecium, those of Dileptus gigas apparently are offensive and defensive
weapons. They paralyze some organisms, induce cytolysis of others, and
cause vigorous reactions in additional Protozoa (215). Paralysis of flagel-
lates and small ciliates is produced by trichocysts of Dileptus anser, and
even large rotifers react vigorously (81). Contact of rotifers with the
tentacles of Actinobolina vorax also may be followed by paralysis (225).

Trichocysts have been reported in various flagellates (77). Two types
have been described in Gonyostominn (Fig. 1. 14, B) — spindle-shaped
trichocysts and small spherical ones, both distributed in the cortex. The
former become long filaments when discharged; the latter give rise to
short delicate filaments (21). The "trichocysts" of Chilomonas, repre-
sented by refractile bodies lining the pharyngeal groove, are discharged
as long slender threads. Another type, possibly represented by small
cortical inclusions, gives rise to short thin filaments. Filamentous struc-
tures also have been interpreted as discharged trichocysts in species of
Polykrikos, Peridinium, Diplopsalis, and Ceratium (142).

28 General Morphology of the Protozoa

Certain subcuticular inclusions of Euglenida — the cortical globules of
Euglena archaeoplastidiata, which are expelled and stained brown in
iodine solution (22), and the rod-like bodies beneath the pellicular
striations of Peranema trichophorum (23) — also have been homologized
with trichocysts of ciliates. These inclusions are demonstrable by mito-
chondrial techniques in Peranema trichophorum (74). It has been sug-
gested (88) that such subcuticular bodies of Euglenida are merely
substances accumulated for the secretion of cyst membranes and similar
layers.

Among the dinoflagellates, Polykrikos and Neynatodiniu^n contain
nematocysts resembling those of coelenterates (27, 136). The similarity
is so close that some workers have considered such nematocysts (Fig. 1.
14, A) to be foreign bodies ingested by the flagellates. However, this in-
terpretation is not supported by the regtdar occurrence of nematocysts in
certain species and their absence in others feeding on the same plankton.
The nematocysts lie free in the cytoplasm and nothing is known about
their possible discharge under natural conditions.

THE CYTOSTOME AND ASSOCIATED
STRUCTURES

The ingestion of solid food by organisms with a well developed
cortex usually occurs through a cytostome, which often opens into a
cytopharynx. The area leading to or surrounding the cytostome often
forms a specialized peristome in ciliates. Although a typical cytostome
and cytopharynx ("gullet") are to be expected only in holozoic organisms
with a well difl:erentiated body wall, interestingly similar structures occur
in certain amoebae (Fig. 1. 15, C, E, F) — Amoeba vespertilio and Hart-
manella sp. (99), and also Dientajnoeba fragilis (230), and Entamoeba
muris (227). Aside from their greater permanence, the cytostome and
cytopharynx of various flagellates represent little advance beyond the
condition seen in these amoebae. In ciliates, however, the peristomial
area may be equipped with an undulating membrane, a row of mem-
branelles, or differentiated zones of cilia.

The peristome of Paramecium multimicromicleatum (Fig. 1. 15, G)
is lined with cilia, while the pharynx is equipped with a dorsal zone of
long cilia and the penniculus, a band of closely set cilia extending spirally
from an antero-dorsal origin to the ventral pharyngeal wall. Activity of
these specialized cilia drives particles into a zone of paraoesophageal
fibrils which are continued from the wall of the cytopharynx into the
endoplasm as the postoesophageal fibrils. When enough particles are
trapped, a food vacuole develops as a bulge in the dorsal wall of the
gullet. After separation from the gullet, the vacuole is guided into the
endoplasm by the surrounding postoesophageal fibrils which exert a sort
of "peristaltic" effect (147). The peristomial area, or "oral groove," serves

General Morphology of the Protozoa 29

/o )

■^

/

u---

L.'^ A

//.■

; : /

'"*- D

: • 1

'■•.■■. w

Fig. 1. 15. A. Section across the peristome of Oxytriclia jallax; xl225
(after Lund). B. Section through the middle of the peristome in Euplotes
aediculatus; x445 (after Pierson). C. Gullet-like structure in Amoeba iuve-
nalis after ingestion of a flagellate; diagrammatic (after Ivanic). D. Pharyn-
geal-basket in Chilodonella labiata; diagrammatic (after MacDougall). E, F.
Gullet-like structures in Dientamoeba fragilis; xl930 (after Wenrich). G.
Gullet (peristomial area) in Paramecium midtimicronucleatiim; diagram-
matic; x670 (after Linid). H. Peristome of Stylonychia; diagrammatic; x720
(after Lund). Key: b, pharvngeal-ljasket; c, cirrus; d, dorsal cilia; f, postoe-
sophageal fibrils; g, basal granule of cilium; m, row of membranelles; p,
basal granules of penniculus; u, undulating membrane; v, food vacuole; vd,
developing food vacuole.

as a scoop which directs water toward the cytostome. The cytostome and
associated structures in Paramecium thus form an efficient mechanism for
concentrating small particles and delivering them to the food vacuole.
In Oxytricha (146) and Stylonychia (147) the left margin of the peri-
stome bears a row of adoral membranelles, while an undulating mem-
brane extends along much of the right peristomial wall (Fig. 1. 15, A,

30

General Morphology of the Protozoa

H). In addition, dorsal and lateral fibrils extend forward in the peri-
stomial cortex and, by their contractions, produce undulations of the
cortex near the cytostome. Both sets extend, as the postoesophageal fibrils,
past the base of the pharynx and deep into the cytoplasm, their move-
ments guiding each newly formed food vacuole, much as in Paramecium.
The small undulating membrane and the lack of cytostomal fibrils

ct-l

Fig. 1. 16. A. Contractile tube of Haptophiya michiganensis; xlOO (after
MacLennan). B. Contractile vacuole and pore in Eudiplodinium maggii;
x830 (after MacLennan). C. "Sensory" vacuole of Blepharoprosthium; dia-
grammatic (after Dogiel). D. Row of "statocysts" in Loxodes rostrum; body
cilia omitted; xl60 (after Penard). E. Single "statocyst" of L. striatus; dia-
grammatic (after Penard). F. Contractile vacuole and canals in Paramecium
miiltimicronucleatum; x720 (after King). G. Contractile vacuole and canals
in Tillina canalijera, diagrammatic (after Turner). Key: cp, pellicular cap;
ct, cortex; fe, endoplasmic fibril; ^v, fibrils at surface of vacuole; g, granules
in vacuole; s, "statocvst."

General Morphology o£ the Protozoa 31

suggest that Euplotes harpa, and perhaps other Euplotidae, cannot con-
centrate small food particles very efficiently (147), although the peri-
stomial area is partially enclosed ventrally by an extension of the right
peristomial wall (Fig. 1,15, B). In cultures, E. harpa thrives best on food
particles larger than bacteria (147).

In such ciliates as Chilodonella and Prorodon the pharynx is sur-
rounded by a conical or cylindrical "pharyngeal basket" (Fig. 1. 15, D)
which undergoes dilation during ingestion (179). The basket is com-
posed of rods which are probably protein in nature (153) and, in certain
species, may represent fused bundles of slender trichites (179). Conver-
gence and apparent fusion of the rods posteriorly may be noted, as in
Chilodofiella (153). There are circumpharyngeal trichites in Spathidium
(235) and Didiniwn (179) also, although a compact basket is lacking.
The paralysis of small ciliates after contact with the cytostomal region of
S. spathula (235) suggests that the trichites function much like tricho-
cysts of certain other ciliates.

The pharyngeal-rod apparatus ("Staborgan") of Perayieyna and similar
holozoic Euglenida (Chapter IV) includes two longitudinal rods extend-
ing posteriorly from the cytostome and a smaller curved element at the
rim of the cytostome (23). The conical "siphon" of Ryitosiphon (23) is
possibly a derivative of the rod-apparatus but its homologies are un-
certain.

VACUOLES OF PROTOZOA

Contractile vacuoles

Contractile vacuoles, characteristic of fresh-water species, are ab-
sent in most parasitic and marine Protozoa. The position, number, and
accessory structures of the contractile vacuoles vary in different Protozoa.
In such genera as Amoeba, the position of the vacuole changes with
movements of the organism. Differentiation of the cortical layer is gen-
erally accompanied by a relatively fixed position of the contractile
vacuole.

The origin of a new vacuole after discharge (systole) usually involves
the appearance of a few minute vacuoles in the area where the new con-
tractile vacuole will develop. These small vacuoles fuse into a single
larger one. Later increase in volume (diastole) of the contractile vacuole
involves various processes. In certain ciliates, the young vacuole is fed by
one or more canals (Fig. 1, 16, F, G). The newly formed vacuole in
Spirostomum ambiguutn (42), for example, fuses with a long canal which
in turn receives fluid by fusion with small vacuoles. The new vacuole in
Paramecium multimicronucleatiim (119) is fed in similar fashion by sev-
eral canals. Growth of the new vacuole in Amoeba (80), Euplotes (210),
and many other Protozoa depends, to some extent at least, upon fusion

32 General Morphology of the Protozoa

with smaller vacuoles. In fact, growth of the vacuole in spurts, instead
of a steady increase in volume, suggests that fluid enters the contractile
vacuole of Amoeba proteus almost entirely through the fusion with ac-
cessory vacuoles (161). In Eudiplodinhim, however, growth of the vacuole
in late diastole apparently is not dependent upon accessory vacuoles,
and the vacuolar membrane presumably is responsible for the segrega-
tion of fluid (161).

Systole usually involves discharge of the contents directly to the out-
side of the body, but there are exceptions. The vacuoles of Euglenida
empty into the reservoir ("gullet"); those of Epistylis and related ciliates
(55) empty into the pharynx, often termed the "vestibule" in view of its
several functions. The point of discharge is often a differentiated pore as
in Parnmeciutn (119) and the Ophryoscolecidae (154). Except during
systole, this pore is sealed by a membrane (Fig. 1. 16, B, F) apparently
derived from the wall of the preceding vacuole.

A long contractile tube (Fig. 1. 16, A), instead of a contractile vacuole,
extends throughout most of the body between the endoplasm and dorsal
ectoplasm in Haptophrya (160). This tube is an apparently permanent
structure which is divided in binary fission. Excretory canals extend to
dorsal pores, which vary in number with length of the ciliate. Systole
involves one or more waves of contraction, but the wall of the tube does
not collapse completely, and does not disappear. After systole, small
vacuoles appear in the wall of the tube and then fuse to form a continuous
lumen.

Sensory vacuoles

A supposedly sensory vacuole, located anteriorly under a pellicular
cap (Fig. 1. 16, C), occurs in parasitic ciliates belonging to the families
Biitschliidae and Paraisotrichidae (46). Fibrils on the wall of the vacuole
converge toward the pellicular cap, while the vacuolar cavity contains a
number of granules ("statoliths"). Superficially similar vacuoles (Fig. 1.
16, D, E), forming a row near the aboral surface of the body, have been
described in Loxodes. These vacuoles ("Miiller's vesicles") have been in-
terpreted both as statocysts (179) and as "excretion-vacuoles" (187).

Vacuoles in flotation

Cytoplasmic vacuoles may play an important part in flotation. In
Radiolarida (Chapter V), the foamy outer cytoplasm (calymma) is filled
with vacuoles which maintain the organisms at a particular depth in the
ocean. Under appropriate stimulation, collapse of the vacuoles and re-
traction of pseudopodia increase the specific gravity and the organisms
sink. When new vacuoles develop in the calymma, the organisms rise
again. An analogous phenomenon has been described in Arcella (10).
The appearance of gas bubbles in the peripheral cytoplasm, supposedly

General Morphology of the Protozoa 33

induced by reduction in oxygen tension of the medium, causes the organ-
ism to rise toward the surface. Perhaps the zone of vacuoles beneath the
theca of Ceratium (53) also functions in flotation.

CHROMATOPHORES, PIGMENTS, PYRENOIDS,
PHOTORECEPTORS

Chromatophores

Chromatophores, found in many phytoflagellates, vary in number,
size, color, and form in different groups. Some flagellates contain one
large cup-shaped chromatophore, or an H-type in which two large lobes
are joined by a connective (Fig. 1. 17, A, E, F, I). The chromatophores
in Peridininm umbunattim form an anastomosing network with lobes
extending into the endoplasm (Fig. 1. 17, J). Some of the Euglenidae
contain many small flattened chromatophores arranged in a peripheral
layer (Fig. 1. 17, G).

Pigment-free leucoplasts, homologous with chromatophores, have been
reported in Polytoma (219) and Polytomella (185). Since Pringsheim
(183) has pointed out that peripheral mitochondrial networks have
sometimes been interpreted as leucoplasts, the status of leucoplast-bearing
species requires further investigation.

Pyrenoids

These structures (Fig. 1. 17, B, C, J, L), which are usually asso-
ciated with chromatophores, vary from solid bodies to aggregates of
granules, around which starch or paramylum may accumulate. Each
pyrenoid in Euglena americana (Fig. 1. 17, L), for example, consists of
two plano-convex masses adherent to the chromatophore and covered by
paramylum (88). The extraplastidial "pyrenoids" of certain Crypto-
monadida are termed amphosomes by Hollande (88), who believes that
homologous structures are unknown in other flagellates. The amphosome
of Cryptomonas dangeardii (Fig. 1. 17, N) consists of two chromophilic
plates separated by chromophobic material, and is sometimes surrounded
by starch grains. The functional significance of the amphosome is un-
known.

Pyrenoids have been interpreted as reserves of protein, as structures
involved in the synthesis of polysaccharides, and even as intracellular
symbiotes. The second assumption is consistent with the frequent occur-
rence of starch or similar materials immediately surrounding the pyre-
noids. According to various reports, pyrenoids may be resorbed occasion-
ally, they may be reduced in number during formation of cysts and
zygotes, and they may arise by division or be formed de novo. Such appar-
ent variations in behavior are of little assistance in functional inter-
pretations.

34 General Morphology of the Protozoa

Fig. 1. 17. A, E, F, I. Chiomatophores in Chlamydomonas agloeformis,
C. umbouata, C. inversa and C. bicocca; diagrammatic (after Pascher).
B, C. Compound pyrenoids of Pyramidomonas montana, with and without
starch deposits; xl200 (after Geitler). D. Granular stigma of Eiiglena;
diagrammatic. G. Chromatophores in Euglena geniculata (?); xl500 (after
Hollande). H. Ocellus with granular pigment in Protopsis neapolitana;
x550 (after Kofoid and Swezy). J. Chromatophore "network" in Peri-
dinium umbonatuni; diagrammatic optical section (after Geitler). K. Pe-
ripheral chromatophores in Cnlacium vesiculosum; xl380 (after Johnson).
L. A chromatophore with pyrenoid and paramylum shell in Euglena
americana; diagrammatic (after Hollande). M. Ocellus with pigment-cup
in Erythropsis cornuta; x320 (after Kofoid and Swezy). N. Amphosorae
in Cryptomonas dangeardii; chromatophores omitted; x2700 (after Hol-
lande). Key: a, amphosome; cli, chromatophore; cp, pigment-cup; g, gran-
ular pigment; /, lens; n, nucleus; p, paramylum; py, pyrenoid; s, starch;
st, stigma.

General Morphology of the Protozoa 35

Pigments

The pigments of chromatophores vary in different groups of the
phytoflagellates, and may have some phylogenetic as well as taxonomic
significance. Chlorophyll of one variety or another presumably is always
present although the green color may be masked by other pigments to
produce shades of greenish-yellow, yellow, brown, and rarely blue. Blue
chromatophores have been reported (143) in Cyanomonas coeruleus,
Chroomonas setoniensis, Cyanomastix morgani, and Gymnodinium lim-
netician.

In addition to the pigments of chromatophores, various red, yellow,
violet, brown, blue, and green pigments are found in the cytoplasm of
certain Protozoa, many of them species without chromatophores. The
blue-green granules ("stentorin") of Stentor coeruleus, which contain
lipoproteins and resemble mitochondria, lie mainly in longitudinal ecto-
plasmic bands. These granules usually disappear after 24-48 hours of
starvation (223). The pink pigment of Blepharisma undulans, which is
also peripheral (169), is bleached after exposure to light, and is regen-
erated in darkness (69). This pigment is quite toxic to species of Para-
mecium, various other ciliates, and also to rotifers (70).

Chromatographic techniques (18, 204, 205, 206) have been used in the
identification of certain pigments. In Dinoflagellida, chlorophylls a and
c, ^-carotene ("yellow haematochrome"), and several xanthophylls (di-
noxanthin, diadinoxanthin, neodinoxanthin, peridinin) have been dis-
tinguished. Peridinin, which may be limited to dinoflagellates among the
Protozoa, is possible identical with sulcatoxanthin isolated from certain
sea anemones and probably derived from their symbiotic algae (82).
Chrysomonadida contain chlorophyll a (but apparently no chlorophyll
b), ^-carotene and the xanthophyll, lutein. Euglenida contain chloro-
phylls a and b, ^-carotene and also red haematochrome (euglenarhodon),
a xanthophyll closely related to the astacene of Crustacea. Phytomonadida
contain chlorophylls a and b and, in such species as Haematococcus plu-
vialis, a red haematochrome similar to that of Euglenida.

The functional significance of most protozoan pigments is unknown.
The absorption of energy in photosynthesis is, of course, dependent
mainly upon the chlorophylls, of which chlorophyll a is probably most
important. However, carotenoid pigments also may serve in absorbing
the predominantly blue-green light of low intensity received by marine
species in fairly deep water (50, 205). The red pigment of Euglejia rubra
may be protective in reflecting light from the red end of the spectrum.
This species thrives in shallow water reaching a temperature of 35-45°
in bright sunlight. Under such conditions the pigment forms a layer
just outside the chromatophores (107). In the laboratory, peripheral
migration of the pigment occurs at temperatures of 30-40° in either dark-

36

General Morphology of the Protozoa

/.'•%•■

\

(2--' B

A\

/ /"'N

p---f •(■•;'

\ 0. .; /

D

c

1

1

1
I

k// 1

1

-gv

m

ill

t
if

H '^-^.J^

Fig. 1. 18. A. Bacilliform paramylum bodies in Euglena acus; x750
(after Deflandre). B. Small paramylum bodies of Distigma proteiis; x3640
(after Hollande). C. Paramylum bodies (p) of Euglena spirogyra; x850
(after Dangeard). D. Polysaccharide reserves in Cliilomonas parameciinn:
x4500 (after Hollande). E. Chromatoid bodies and glycogen "vacuole" in
Entamoeba invadens; x2350 (after Geiman and Ratcliffe). F. Skeletal plates
and glycogen granules in cross-section of Polyplastron multivesiculatum;
diagrammatic; endoplasm omitted (after MacLennan). G. Cross-section of
right dorsal skeletal plate, P. multivesiculatum ; x4720 (after MacLennan).
H. Starch grains at smface of chromatophore in Cryptomonas ovata; x2250
(after Hollande). Key: c, chromatophore; ch, chromatoid body; g, glyco-
gen blocks; gg, glycogen granule; gv, glycogen "vacuole"; m, macro-
nucleus; n, nucleus; p, pharynx; 5, starch; sk, skeletal plate.

General Morphology of the Protozoa 37

ness or light and also after irradiation with infrared or visible light. With
the effects of temperature controlled, light from the blue end of the
spectrum is more effective than that of longer wave lengths (108). The
accumulation of a similar red pigment in Haematococcus pluvialis has
been attributed to the exhaustion of nitrogenous or other foods. Massive
production of this pigment occurs also in young cultures exposed to light
in a medium containing acetate; salts of butyric and certain other acids
show no such effect (152). In acetate-free medium, intensely red "haemato-
cyst" stages are commonly developed in bright sunlight but not in dim
light (52).

Photoreceptors

A stigma is characteristic of many chlorophyll-bearing flagellates,
and occurs also in certain colorless phytoflagellates. The stigma of Eu-
glenida is typically a flattened mass of reddish granules embedded in a
matrix (Fig. 1. 17, D), whereas a granular organization is not apparent
in typical phytomonad and chrysomonad flagellates. The stigma of Volvox
and related colonial types is said to contain a concave mass of pigment
and a hyaline lens (164). The stigma is usually located near the anterior
end of the flagellate, but lies near the middle of the body in some species.
The typical position in Euglenida (Fig. 1. 17, D) is near the wall of the
reservoir.

Certain dinoflagellates (Pouchetiidae) possess an ocellus composed of
a hyaline lens and a dark mass of pigment (melanosome) partially cover-
ing the lens. In certain species the melanosome can be extended over
the surface of the lens or contracted toward the base (Fig. 1.17, M). The
melanosome may be homogeneous except for a core of red pigment at
the base of the lens, or may be merely a loose aggregate of granules as in
Protopsis neapolitana (Fig. 1. 17, H).

CYTOPLASMIC INCLUSIONS

Cytoplasmic food reserves

Foods of various kinds are frequently stored in the cytoplasm of
Protozoa and, in any one species, the amount and type of reserves may
vary with environmental conditions. Starch is the major reserve in young
cultures of Polytoma iivella; lipids predominate after 15-30 days (220).
In P. iiveUa, and probably in Protozoa generally, less food is stored in
rapidly growing than in slowly growing cultures.

Polysaccharide reserves of phytoflagellates occur as granules or as larger
bodies sometimes of characteristic shape and size. Synthesis of these car-
bohydrates is not dependent upon chlorophyll and may be expected in
both colorless and pigmented species. The supposed presence of colorless
"chromatophores" (leucoplasts) in non-pigmented phytoflagellates has
been questioned (183). Paramylum (or "paramylon") of Euglenida occurs

38

General Morphology of the Protozoa

mainly as refractile endoplasmic bodies (Fig. 1. 18, A-C), but may be
found also at the surface of the pyrenoid (Fig. 1. 17, L) in chlorophyll-
bearing species. In addition, glycogen-like inclusions occur in Euglena
(22) and Peranema (23). The leucosin of Chrysomonadida (Chapter IV)
is stored as bodies (Fig. 4. 1, D-F) which are often relatively large. Starch
may be deposited as fine granules or larger bodies in Cryptomonadida,
Phytomonadida, and Dinoflagellida. Starch grains are deposited on the
inner surface of the chromatophore in Cryptomonas ovata (Fig. 1.18, H),
while the reserves of Chilomonns, which are composed of ^-amylose and
amylopectin (97), are scattered refractile bodies (Fig. 1.18, D). In Phyto-
monadida and Dinoflagellida, starch occurs both as scattered granules and
as deposits around pyrenoids.

Glycogen, or a similar material, is common in groups other than the
phytoflagellates. Little is known about the chemical nature of these in-
clusions. Such reserves are distributed as fine granules in Paramecium
(186), but may be concentrated posteriorly in Stentor (222, 240). In the
Ophryoscolecidae, the skeletal plates (Fig. 1. 18, F, G) contain much of
the glycogen (155), although cytoplasmic granules may occur also (154).
Glycogen or paraglycogen is generally deposited during heavy feeding
and consumed in starvation, as traced in Stentor (222, 223). Such reserves
also may be deposited before encystment — as in Dileptus (207), Ich-
thyophthirius (156), and certain Endamoebidae — and consumed before
excystment. The paraglycogen of Ichthyophthirius is formed as small
granules within a mitochondrial sphere which disappears after the para-
glycogen mass reaches a diameter of 5-6[jl (156). A similar development
has been observed in gregarines (109), whereas glycogen is deposited in
association with the parabasal body of Cryptobia helicis (48).

Lipids are probably stored by most, if not all. Protozoa, under certain
conditions. The accumulation of fat in Stentor has been attributed to
low oxygen tensions (240), and stored lipids are characteristic of old
rather than young cultures of Polytoma uvella (220). Lipids may be
distributed through the endoplasm or else concentrated in one region
as in Anoplophrya (51). In Stentor coernleus (223), these inclusions vary
from small granules to bodies as large as the macronuclear nodes. So-called
bodies of Maupas, believed to contain at least some lipids, occur in vari-
ous Cryptomonadida as two refractile ellipsoidal inclusions (88). In Ich-
thyophthirius, the fatty acids and glycerol which reach the cytoplasm are
first segregated into globules within which neutral fat is formed (156).
A similar process has been described in Opalina (114).

Protein reserves have been described as basophilic granules, metachro-
matic granules, chromatoid bodies, albuminoid reserves, and chromidia.
Such reserves occur as scattered granules through the endoplasm, they
may be stored in peripheral globules in Opalina (115), or they may be
deposited as fairly large masses. Chromatoid bodies (Fig. 1,18, E), repre-

General Morphology of the Protozoa 39

senting the third condition, are refractile inclusions present in young
cysts in certain Endamoebidae. Little is known about the origin of protein
reserves. However, protein granules are extruded from the macronucleus
of Ichthyophthirius multifiJiis after the ciliates invade a host and begin
to feed (156). Similar achromatic bodies in the macronucleus of Blepha-
risma midulans also have been interpreted as protein reserves (239). The
chromatoid bodies of Entmnoeba histolytica on the other hand, are
formed by the coalescence of clear vacuoles which appear in the cytoplasm
(90). Dietary factors may influence the synthesis of protein reserves. Stor-
age of protein granules in Polytoma uvella, for example, is extensive in
a medium containing butyrate, but is much less noticeable with acetate
(220).

Volutin granules, known in many Protozoa, presumably should be con-
sidered nitrogenous reserves (158). Although the term has been used
rather loosely, volutin may be considered metachromatic material which
is Feulgen-negative but is stainable by a modified technique which omits
preliminary hydrolysis (158, 188). The disappearance of volutin in try-
panosomes and haemogregarines after digestion with ribonuclease in-
dicates that the granules contain ribonucleic acid (5). Such granules are
resorbed in old cultures and during induced starvation of Polytoma uvella
(220); they accumulate during active feeding of Oxymonas dimorpha and
decrease in the motile phase (32), and are apparently a reserve food in
Pelomyxa caroUnensis (233).

Crystalline inclusions are found in various species. The crystals of
Amoeba proteus apparently contain amino acids, presumably derived
from digested food (165, 166), but the composition of such inclusions in
many other Protozoa remains to be determined. As traced in Paramecium
bursaria (232), crystals accumulate during holozoic feeding and then
disappear gradually as the supply of bacteria in the culture is exhausted
and the ciliates become increasingly dependent upon their symbiotic
algae.

Chromidia

Originally, chromidia were defined as granules derived from the
nucleus. Certain "generative" chromidia were considered extranuclear
chromatin granules with a potential ability to form aggregates and de-
velop into nuclei. In other cases, extrusion of chromidia from the nucleus
was believed to be a means of restoring a normal nucleo-cytoplasmic ratio.
In more recent literature, a variety of inclusions — probably including
mitochondria, volutin granules and protein granules ("albuminoid re-
serves") — have been referred to as chromidia. Since the older chromidial
theories are no longer accepted, and the identities of the more modern
"chromidia" are so varied, it seems advisable to drop the term as a
designation for cytoplasmic inclusions of Protozoa.

40 General Morphology of the Protozoa

Mitochondria

Mitochondria (or chondriosomes), which seem to be generally
present in Protozoa, were observed as early as 1910 in Chilomonas, Cryp-
tomonas, and Noctihica (54). Subsequently, mitochondria have been
described in many species (76, 77, 158). Mitochondria are to be expected
in Protozoa during the active phase of the life-cycle, but may be absent in
the cyst, as reported for Ichthyophthirhis multifiUis, in which the mito-
chondria disappear rapidly after encystment (156, 159). Reportedly mito-
chondria-free sporozoites of Monocystis (94) may be an analogous case.
In addition, mitochrondria have not been found in active stages of a
marine amoeba, FlabeUula mira (89).

Mitochondria may occur as granules, short rods, filaments, or fila-
mentous networks. The form is more or less characteristic of a species,
although some variation may be expected. Filamentous mitochondria
(Fig. 1. 19, A), apparently less common than other types, have been
described in Chlorogonium, Chlamydomonas, and Polytoma. Such fila-
ments are often anastomosed in a superficial network. Mitochondrial nets
also have been observed in green and colorless strains of Euglena gracilis
(95). Similar networks, which occasionally break up into short rods, occur
in Glenodiyiium sociaJe and other dinoflagellates (7). These inclusions
are usually stainable vitally with Janus green B, although the reaction
may be less intense than that of metazoan mitochondria. Good results
have also been reported with Janus red (91). Special fixatives, such as
the chromate-osmic mixtures, are advisable for good permanent prepara-
tions.

The cytoplasmic distribution of mitochondria varies with the species.
Random cytoplasmic distribution (Fig. 1. 19, B) is common, but aggrega-
tion around food vacuoles is sometimes noted (166). The mitochondria
of Chilomonas (Fig. 1. 19, D) and Cryptomonas, as well as those of Phy-
tomonadida and Euglenida, are believed by Hollande (88) to be entirely
peripheral. Certain endoplasmic inclusions of these flagellates, previously
interpreted as mitochondria after demonstration with mitochondrial tech-
niques (76, 77), are said to be cytoplasmic vacuoles. Peripheral mitochon-
dria of ciliates may be oriented in rows, as in Nyctotherus cordiformis
(93). Association of peripheral mitochondria with the basal granules has
been described in Colpidiiim colpoda and other ciliates (26), but this is
not the case in Tillina canalifera (213). Mitochondria of Bursaria truri-
catella are mostly peripheral during conjugation but are scattered through
the cytoplasm in other phases of the life-cycle (181).

Various functions have been assigned to the mitochondria. Morpho-
genetic interpretations include a mitochondrial origin of pyrenoids (20)
and the derivation of Golgi material, parabasal bodies, blepharoplasts,
and the stigma from mitochondria (1). Supposed physiological activities

General Morphology of the Protozoa 41

.r--n

B

D

/.O.a

a

(va:55w^

> ' '.-..•.%

H

/^\.

/:.\

E F G ~-^^

"-■. \-y/

t..^ y

Fig, 1. 19. A. Mitochondrial network in Polytuiiia uvellu; \2700 (after
HoUande). B. Mitochondria and one nucleus in Protoopalina hylarnm; dia-
grammatic (after Richardson and Horning). C. Granules stained with neu-
tral red in Chlamydomouas variabilis: \1170 (after Dangeard). D. Nfitochon-
dria in Chilomonas Paramecium; x270O (after HoUande). E. Neiitral-red
granules in Paramecium caudatum; x3I0 (after Dunihue). F. Neutral-
red granules in EugJena polymorpha; x635 (after Dangeard). G. Osmio-
philic inclusions in associated "gametocytes" of Gregarina cuneata; x635
(after Jo\et-Lavergne). H. Osniiophilic inclusions in P. caudatum; x245
(after Dunihue). I. Osniiophilic inclusions in Protoopalina hylarurn; dia-
grammatic (after Richardson and Horning). Key: c, chromatophore; ^v, food
vacuole; n, nucleus; v, developing food vacuole.

are even more varied: association with the deposition of lipids in grega-
rines (112); a causative role in amoeboid movement (19); mitochondrial
origin of digestive enzymes (92); transportation of waste products to con-
tractile vacuoles (165); transportation of enzymes to food vacuoles and
of digested materials away from the vacuoles (166); and association with
the deposition of paraglycogen (156). A belief that protozoan mitochon-
dria are involved in oxidations is in accord with the demonstration that
mitochondria contain most of the succinic dehydrogenase in liver cells
(87). Joyet-Lavergne (113) reported the capacity of mitochondria in gre-

42 General Morphology of the Protozoa

garines to oxidize leuco-derivatives of various dyes, and suggested that
such oxidations are effected partly with the aid of glutathione and vita-
min A, previously detected in mitochondria (35, 111). The localization
of cytochrome oxidase in mitochondria also has been determined for
Stentor coeruleus (224).

Vacuome

The term, vacuome, was introduced as a collective designation for
the vacuoles in plant cells (36). According to later views (72), the vacuome
is distinct from the mitochondria and shows several characteristic proper-
ties. It may be stained vitally with dilute solutions of neutral red and
certain other dyes which do not stain mitochondria. Furthermore, the
vacuome is not reliably demonstrated by mitochondrial techniques, al-
though often impregnated by Golgi methods.

Cytoplasmic inclusions of Protozoa were probably first referred to as
a vacuome by Dangeard (37), although neutral-red-stainable granules
had been described much earlier. The vacuome, in microorganisms gen-
erally, consists of small globules or granules rather than obvious vacuoles
(39). The reverse is true in higher plants. The vacuome of Protozoa in-
cludes small inclusions (Fig. 1. 19, C, E, F) which are distinguishable from
mitochondria in vital staining with mixtures of neutral red and Janus
green B. In certain species, it is evident that the elements of the vacuome
are normal inclusions of the living organism. The available data (76, 77,
158) suggest that a vacuome is generally present in Protozoa, although
apparently lacking in Conchophthirius mytili (116) and disappearing
during encystment of Ichthyophthirius multifiliis (156). Elements of the
vacuome are scattered through the endoplasm in many species. In certain
gregarines (110), however, the distribution varies in different stages of the
life-cycle. Adhesion of neutral-red granules to newly formed food vacuoles
(Fig. 1. 19, E) also occurs in certain ciliates.

The ability to segregate neutral red apparently is not limited to one
type of inclusions. Dangeard (38) stained not only the usual vacuome but
also the cortical "mucous granules" (sometimes called trichocysts) in cer-
tain Euglenida. Bush (16) also found two types of neutral-red granules in
Haptophrya michiganensis. Food vacuoles of Protozoa also are stainable
with neutral red but they are usually not considered a part of the vac-
uome, in view of their different origin and behavior.

Guilliermond (72) has pointed out that the vacuome of plants func-
tions in segregation and storage of metabolic products, and should be
considered a part of the deutoplasm, or paraplasm, rather than living
protoplasm. The vacuome may have comparable functions in Protozoa.
As shown by micro-incineration, the vacuome of Paramecium caudatum
segregates appreciable quantities of minerals (162), and the number of
neutral-red granules decreases in this species during starvation (49). The

General Morphology of the Protozoa 43

vacuome of Opalina is said to serve for the storage of proteins (114). In
addition, the vacuome contains volutin in Chilomonas Paramecium (59),
Peranema trichophorum (23), Polytoma uvella (219), and species of
Euglena (22, 178).

The neutral-red granules which collect on the food-vacuole in certain
ciliates (Fig. 1. 19, E) have been called digestive granules. Prowazek (184)
suggested that they enter the food-vacuoles of Paramecium aurelia and
participate in digestion. Similar conclusions have been reported for P.
caudatum (192), Vorticella (218), and Tetrahymena pyriformis (221).
Both Koehring (135) and Dunihue (49), while confirming aggregation
at the surface, have denied that the neutral-red granules penetrate the
food-vacuole in Paramecium. Such granules apparently get into food-
vacuoles of Ichthyophthirins without penetrating a membrane. The gran-
ules collect on a freshly formed food-vacuole, a new membrane is de-
veloped around the mass, and the original vacuolar membrane then
disappears (156). Although no such relationship has been detected in
certain other ciliates (75, 78), the behavior of these inclusions in Parame-
cium and Ichthyophthirins may justify their designation as digestive
granules.

Osmiophilic inclusions and organelles

A number of osmiophilic structures and inclusions have been in-
terpreted as protozoan Golgi material. The nature of such material is
undoubtedly varied, and complete agreement has not been reached in
regard to the identity of protozoan Golgi apparatus.- Even a single species
has sometimes been credited with two or more kinds of Golgi material.
This situation is not surprising because the Golgi techniques are not
absolutely specific. Furthermore, selection of the appropriate inclusions
is handicapped by the lack of a precise concept of protozoan "Golgi
material" and specific criteria for identifying such material.^

Protozoan Golgi material apparently was first described as osmiophilic
rings and crescents in Monocystis ascidiae (84). Comparable inclusions
(Fig. 1. 19, G-I) have been reported subsequently in many species of
Mastigophora, Sarcodina, Sporozoa, and Ciliatea. The distribution and
relative number of such "Golgi bodies" apparently vary within a species.
Golgi material may even disappear in the cyst and arise de novo after
excystment, as in Ichthyophthirins (157) and Protoopalina (189). Young

-This subject has been discussed in several reviews (76, 77, 83, 121, 158, 202, 208).

^This situation in protozoan cytology merely reflects the unstable position of "Golgi
material" in metazoan cytology. Some workers maintain that ". . . the Golgi apparatus
is a gross artifact" (176). According to another view, "a tissue lacking the full com-
plement of Golgi substance would be unable to function normally" (237). Likewise,
the statement that "efforts to demonstrate a Golgi apparatus in living, or fresh, somatic
cells have been unsuccessful" (175), may be contrasted with the conclusion that "the
Golgi apparatus can be seen in most, and perhaps all, living animal cells" (237).

44 General Morphology of the Protozoa

stages of Monocystis agilis contain comparatively few Golgi bodies; the
older stages show more numerous inclusions (85). Changes in cytoplasmic
distribution also occur at different stages in the life-cycles of gregarines
(109).

7 he parabasal apparatus of flagellates has been homologized with meta-
zoan Golgi material (48). The stigma of Euglena also has been considered
Golgi apparatus (71) on the basis of its supposed homology with the
parabasal body of certain other flagellates. Mangenot (163) has objected
that the stigma is more probably a modified plastid and that impregnation
has no significance beyond the fact that carotenoid pigments will reduce
osmium tetroxide. The endoplasmic spherules of Opalma also have been
considered ecjuivalent to the parabasal apparatus of flagellates and hence
to represent Golgi bodies (122). However, the endoplasmic spherules are
distinct from the Golgi material described in Protoopalina (189). Even
the recognition of authentic parabasal bodies as Golgi material has been
opposed on several grounds (123, 208).

Inclusions superficially resembling Golgi networks have been described.
A simple "net" was produced in Plasmodium praecox by the fusion of
osmiophilic globules (35). A more complicated net, supposedly arising
from the food vacuole, has been reported in Entamoeba gingivalis (19),
while the Golgi apparatus of Peranema trie hop horiitn (14) has been pic-
tured as fibrils resembling the silver-line systems of certain euglenoid
flagellates.

The membrane of the contractile vacuole, which is osmiophilic in
Chilomonas Paramecium and certain ciliates (51, 170, 171), also has been
considered Golgi apparatus. Gatenby and Singh (58) have extended this
concept to the wall of the reservoir (gullet) in Copromonns suhtilis
(Euglenida). If the wall of the contractile vacuole is to be homologized
with the Golgi apparatus, it probably should be osmiophilic in Protozoa
generally. Such is not the case, since the contractile vacuole of various
ciliates and flagellates is not osmiophilic (15, 75, 84, 168).

Another suggestion (35, 75, 110) is that neutral-red granules may be
recognized as Golgi material because elements of the vacuome are im-
pregnated by Golgi techniques in a number of species. Sound objections
to this generalization have arisen. Attempts to impregnate the neutral-
red granules of several species by the usual Golgi methods have failed
(16, 40, 124, 139, 154, 157, 213). Furthermore, the osmiophilic bodies of
certain gregarines move toward the centripetal pole in the ultracentrifuge,
whereas the neutral-red granules are not noticeably displaced (40). Also,
the neutral-red granules oi Paramecium (120) and Ichthyophthirius (159)
remain stratified with the food vacuoles, although other cytoplasmic in-
clusions are displaced. The significance of the results obtained with the
ultracentrifuge is uncertain. In the case of metazoan Golgi bodies, the

General Morphology of the Protozoa 45

centrifuge frequently separates chromophilic and chromophobic sub-
stances (190), sends the chromophilic elements to either the centrifugal
pole (191) or to the centripetal pole (3), sometimes stratifies the Golgi
bodies in different zones (237), and sometimes separates the "vacuome"
and the Golgi bodies (237).

NUCLEI OF PROTOZOA

Under the general term, nucleus, are included the micronucleus
and the macronucleus of ciliates and the vesicular nuclei of other Pro-

5"><

%.

.4.2: • Vi

Fig. 1. 20. Nuclei. A. Heteronema acus; x4290 (after Loefer). B. Mul-
tiple endosomes in H. acus; chromatin omitted; x3740 (after Loefer). C.
Haematococcus pluvialis; x3280 (after Elliott). D. lodamoeba biUschlii;
x4000 (after Wenrich). E. Chilomastix magna; x9360 (after Kirby and
Honigberg). F. Entamoeba histolytica; x3900 (after Wenrich). G. Zelleriella
elliptica; x2340 (after Chen). H. Pelomyxa carolinensis; x2070 (after
Kudo). Key: c, chromatin; e, endosome; g, peripheral "chromatin" gran-
ules; n, nucleolus.

tozoa. On the basis of nuclear equipment, two types of Protozoa may thus
be recognized. In one group, the nuclei in binucleate and multinucleate
species are of the same kind, so far as structure can be determined and

46 General Morphology of the Protozoa

functions inferred. In Ciliophora, with the apparent exception of the
Protociliatia,^ nuclei are differentiated into micronuclei and macronuclei
which differ in size, in structure, and in behavior during fission and
conjugation.

Vesicular nuclei

The vesicular nuclei of Mastigophora, Sarcodina, and Sporozoa
vary so much in structure that morphological classifications are neces-
sarily arbitrary. However, it is possible to recognize two general types —
those with an endosome and those without. In the endosome-type (Fig. 1.
20, A-D, F) the chromatin lies between the nuclear membrane and a more
or less central body, the endosome. The endosome apparently does not
contribute directly, at least in a morphological sense, to the formation of
chromosomes. A negative Feulgen reaction, indicating the absence of
desoxyribonucleic acid, has been reported for the endosome in Euglenida,
Phytomonadida and trypanosomes (104) and in Entamoeba coli, E. his-
tolytica, Endolimax nana, and lodamoeba hiltschlii (228). In encysted
Giardia Ia?nblia, however, the endosome is intensely Feulgen-positive
(144). The endosome of Entamoeba miiris also gives a positive reaction
(226). The nucleus in Entamoeba (Fig. 1. 20, F) contains a small endo-
some and relatively little chromatin; that of Endolimax and lodamoeba
(Fig. 1. 20, D), a large endosome and a small amount of chromatin. The
well defined peripheral granules, adherent to the nuclear membrane and
commonly considered chromatin granules, are Feulgen-negative in Enta-
moeba muris (226), E. coli, and E. histolytica (228). The discovery that the
chromosomes develop from a zone of minute Feulgen-positive "granvdes"
around the endosome of these amoebae emphasizes the need for critical
study of the smaller protozoan nuclei. The nucleus of Euglenida (Fig.
1. 20, A, B) contains abundant Feulgen-positive chromatin and a rather
large endosome which is sometimes fragmented. The endosome disap-
pears early in mitosis in the Endamoebidae and phytomonad flagellates,
but it persists and undergoes division in Euglenida and such dinoflagel-
lates as Oxyrrhis marina (73).

Nuclei without endosomes (Fig. 1. 20, E, G, H) may contain several
nucleoli which often disappear in mitosis, although they persist in Zelleri-
ella (31). The chromatin is usually distributed throughout the nucleus
and its appearance may suggest some sort of a nuclear framework or
"network." Such nuclei are characteristic of many Heliozoida, Radiola-
rida, Hypermastigida, Dinoflagellida, opalinid ciliates, and Sporozoa.

^Although Konsuloff (140) has maintained that the Feulgen-negative endoplasmic
spherules of Opalinidae are macronuclei, this interpretation has not been accepted.
Furthermore. Metcalf's "macrochromosomes," supposedly homologous with the macro-
nuclear chromatin of other ciliates, are merely Feulgen-negative nucleoli (31).

General Morphology of the Protozoa 47

Nuclear dimorphism

The Ciliophora are unique in that all species, except the sup-
posedly primitive opalinids, have both micronuclei and macronuclei —
unless Stephanopogon mesnili (149) is another valid exception. In S.
mesnili, all of the nuclei are similar in size and structure, and their
division closely resembles that of the micronucleus in typical ciliates.
Perhaps this case is analogous to that of Dileptiis (81, 216), discussed
below. In the typical ciliates, more than one micronucleus or macronu-
cleus may be characteristic of a species and the number of each type some-
times varies independently. Stentor coeriileus, for example, may show
10-42 micronuclei distributed irregularly along the 7-23 links of the macro-
nuclear chain (201). Both types of nuclei have a common origin from
the synkaryon formed in conjugation. The division-products of the syn-
karyon, presumably identical cytologically and genetically, undergo diver-
gent metamorphosis in conjugation. A developing micronucleus under-
goes reduction in size and often a decrease in staining capacity. The de-
veloping macronucleus increases in size, undergoes changes in internal
structure and may show extensive changes in form before reorganization
is completed. The nature of the changes involved in the development of
macronuclei is still unknown. On the basis of genetic data (203), it has
been suggested that the macronucleus is a compound nucleus composed
of many units, each with its own diploid set of genes. At each fission, the
macronucleus divides amitotically, contributing approximately half of
its units to each daughter ciliate. Subsequently, the normal number of
units is restored by mitotic processes within each reorganizing macronu-
cleus. This theory is interesting, but adequate morphological grounds for
such an interpretation are lacking. The ciliate micronucleus, in contrast
to the macronucleus, undergoes mitosis during reproduction of the or-
ganism.

Macronuclei vary considerably in form, size and number. The simplest
are spherical to ovoid bodies (Fig. 1. 21, C) containing many densely
staining granules perhaps embedded in an achromatic framework (159).
The macronucleus of Paramecium is stretched in the ultracentrifuge and
the contents are stratified in two zones, the chromatin granules appar-
ently being denser than the achromatic substance (120). The Feulgen
technicjue indicates that different types of granules are stainable with
hematoxylin. Uniformly small granules, scattered through the macro-
nucleus of certain ciliates, are Feulgen-positive; certain larger granules
give a negative reaction (57, 104, 156). The staining capacity of these
Feulgen-positive granules in Stentor coeruleiis is not affected by ribonu-
clease (223).

Macronuclei are not always compact. The macronucleus of Euplotes

48 General Morphology o£ the Protozoa

(Fig. 1, 21, B) and that of Vorticella wind through much of the endoplasm,
while that of Conchophthirius caryoclada (117) is irregularly lobate (Fig.
1. 21, A). The two slender macronuclei of Spathidiiim spathula (235) ex-
tend nearly the length of the ciliate and may sometimes be joined pos-
teriorly. In various species of Spirostomiim and Stentor (Fig. 1. 21, F)

Fig. 1. 21. Macronuclei. A. Conchophthir'nis caryoclada; diagrammatic;
x440 (after Kidder). B. Euplotes; diagrammatic; x460 (after Turner). C.
Ichthyophthirius multifiliis; x630 (after MacLennan). D, E. Nyctotherus
gyoeryanus, longitudinal and transverse sections; karyophore attached to
macronucleus; diagrammatic (after Grasse). F. Stentor type; diagrammatic.
Key: k, karyophore; m, macronucleus.

there is a chain of macronuclear nodes joined by filaments. In certain
ciliates, the macronucleus is suspended from the cortex by a fibrillar
"karyophore" (Fig. 1. 21, D, E).

The significance of nuclear dimorphism remains uncertain. It is usually
assumed that the macronucleus is involved in metabolic activities. In this
connection, the extensive resorption of the macronucleus during starva-
tion of Stentor coeruleiis (223) is of interest. The micronucleus is sup-

General Morphology of the Protozoa 49

posedly concerned mainly with reproduction and sexual phenomena and
therefore is primarily of genetic interest. The occurrence of apparently
amicronucleate strains in several species — Oxytricha hymenostoma (41),
Oxytricha fallax, Urostyla grandis (234), and Tillifia magna (4), among
others — suggests that the micronucleus is not actually essential to giowth
and fission. Observations on the regeneration of fragments (2) indicate
that the macronucleus is essential for complete regeneration of ciliates.
The importance of the micronucleus apparently varies with the species.
Some species fail to grow, or even to regenerate, without a micronucleus,
while macronucleate fragments containing no micronuclei have given rise
to amicronucleate races in other species — Stentor coeruleiis (201) and
Oxytricha fallax (9), for example.

Dispersed nuclei

So-called dispersed nuclei have been described in certain Protozoa,
although the older accounts have not been confirmed in more recent
investigations and such interpretations were undoubtedly based upon in-
adequate cytological techniques. However, the ciliate Dileptiis has been
cited for many years as an example in which chromatin granules, scat-
tered through the endoplasm, are the substitute for a nucleus. The con-
dition in Dileptus gigas has been analyzed by Visscher (216). During post-
conjugant reorganization the synkaryon divides into two nuclei, one of
which produces 32-64 micronuclei, and the other a comparable number
of macronuclei. The latter eventually divide further into the many scat-
tered inacronuclear derivatives characteristic of the normal ciliate. The
nuclear apparatus of Dileptus anser (81) may include as many as 200 small
macronuclei measuring 2-3[x and containing fine Feulgen-positive gran-
viles. A few of the macronuclei can usually be found in division at almost
any time, but they all seem to divide almost simultaneously just before
binary fission.

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General Morphology of the Protozoa 51

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52 General Morphology of the Protozoa

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II

Reproduction and Life-Cycles

Methods of reproduction
Binary fission
Budding and schizogony

Nuclear division

Eumitosis and paramitosis
The micronucleus of ciliates
The achromatic figure
The macronucleus

Life-cycles

General features
Cysts

Encystment
Excystment

Sexual phenomena

Varieties of sexual phenomena
Meiosis in relation to the life-cycle
Syngamy
Pedogamy
Autogamy
Conjugation

Factors inducing conjugation
Mating types in ciliates
Nuclear phenomena of uncertain sig-
nificance

The physiological life-cycle

Literature cited

I

,N iMANY Protozoa, reproduction occurs at frequent intervals,
with relatively short periods of growth intervening under favorable con-
ditions. In other cases, growth may extend over a period of several to
many days, so that reproduction occurs at comparatively long intervals.
Depending upon the species, reproduction may or may not be preceded
regularly by sexual phenomena. Of the species which do show sexual
activity, some normally undergo syngamy as a prelude to a reproductive
phase while others show sporadic sexual activity.

METHODS OF REPRODUCTION

The less complex Protozoa reproduce either by binary fission or
by simple budding. In either case, the nucleus undergoes mitosis; or
mitosis of the micronucleus and "amitosis" of the macronucleus occur in
Ciliophora. Cytoplasmic division is approximately equal in fission, un-
equal in budding.

Although reproduction in uninucleate species is comparable in some
respects to cell division in higher organisms, the structiual specialization
of many Protozoa introduces complications. The new organisms must be
equipped with various organelles, the nature of which varies with the

54

Reproduction and Life-Cycles 55

species. Parental organelles such as flagella are often inherited equally or
unequally by the daughter organisms which later produce enough new
structures to complete their equipment. Even the paraglycogen reserves of
Stentor coeruleus, normally stored posteriorly, are shifted to the middle

c e?" .:•■ '.•'"•I

W^.'

\:ji ■<<^^'\

•%#

Fig. 2. 1. A. Multinucleate stage (schizont) of Ovivora thalassemae;
superficial section; xlOOO (after Mackinnon and Ray). B. Schizogony in
O. thalassemae; xlOOO (after Mackinnon and Ray). C, D. Plasmotomy in
Pelomyxa carolinensis; division into two and three individuals; x40 (after
Kudo). E, F. Coronympha octonaria; xl650 (after Kirby); vegetative stage
showing nuclei and flagellar groups (E); nuclear groups at end of telo-
phase, just before plasmotomy (F),

56

Reproduction and Life-Cycles

of the body and then shared between the daughter organisms in transverse
fission (238). Blepharoplasts, basal granules, kinetoplasts, and sometimes
chromatophores and pyrenoids, are self-reproducing. Their duplication
during fission fills the needs of the daughter organisms. Other structures,
including the cirri of certain ciliates and the parabasal apparatus of cer-
tain flagellates, undergo resorption so that each daughter organism must
develop a set of its own — in the case of cirri, apparently by outgrowth
from inherited basal granules. The resorption of parental structures is
sometimes extensive. Reproduction may thus involve dedifferentiation of
the old body as well as the differentiation of new structures in the de-
veloping daughter organisms. The beginning of differentiation, in two
new centers of organization within the parental body, possibly supplies
the stimulus for subsequent dedifferentiation.

Reproduction of multinucleate Protozoa, or of multinucleate stages in
the life-cycle, may involve either budding or fission. In many Sporozoa a
young uninucleate stage grows, with repeated mitoses, into a multinu-
cleate Plasmodium (Fig. 2. 1, A) which then reproduces by schizogony.
Essentially, schizogony is multiple budding in which separation of uni-
nucleate buds from a residual mass of protoplasm is completed within a
short time (Fig. 2. 1, B). Certain multinucleate Protozoa normally divide
into several organisms, each of which receives some of the parental nuclei.
This process, not necessarily synchronized with nuclear division, is known
as plasmotomy. Both schizogony and plasmotomy have been described
in Coelosporidmrn (119), while plasmotomy is characteristic of Pelomyxa
(158). In the latter (Fig. 2. 1, C, D), plasmotomy produces 2-6 smaller
organisms, among which the parental nuclei are distributed at random.
Less variation is characteristic of Coronyinpha octonnria (151), in which
all eight nuclei usually undergo mitosis and the daughter nuclei separate
in groups of eight before plasmotomy occurs (Fig. 2. 1, E, F).

Binary fission

In Mastigophora, fission may occur in the active stage, within
a cyst, or in non-flagellated palmella stages (Fig. 2. 2, K). The plane
of fission is most frequently longitudinal and the division-furrow usually
appears first at the anterior end (Fig. 2. 2, I). Among the dinoflagellates,
however, fission is often oblique and may be almost transverse in late
stages (Fig. 2. 2, A-H). Spirotrichonympha bispira divides transversely,
although related species undergo longitudinal fission (61). Mitosis in
Trichomonadida is commonly followed by migration of the karyomasti-
gonts to opposite sides of the body and fission is then completed by cyto-
plasmic constriction (Fig. 2. 2, J).

Cytoplasmic structures^ may undergo division, resorption followed by
origin de novo, or partial resorption followed by growth and differentia-

^ The literature on several groups of flagellates has been reviewed by Kirby (152).

Reproduction and Life-Cycles 57

tion. Duplication of blepharoplasts, apparently by division, is character-
istic of fission in the flagellate stage. The behavior of blepharoplasts in
non-flagellated stages of Phytomastigophorea is mostly unknown, al-
though they persist as division-centers in Eudorina illinoisiensis (117).
The fate of other cytoplasmic structures in fission seems to be variable.

Fig. 2. 2. A-G. Fission and regeneration of missing portions of tfie body
and theca in Ceratium hiruncUnella; diagrammatic (after Entz). H. Late fis-
sion in Oxyrrhis mariym; nuclei and fiagella indicated diagrammatical!) :
xHOO (after Hall). I. Heteronema acus; division of body starting at anterior
end; endosomes shown, chromosomes omitted; xl395 (after Loefer). J. Late
fission in Tritrichomonas augusta; xl305 (after Kofoid and Swezy). K. Fission
in palmella stage of Haematococcus pluvialis; xl815 (after Elliott). L. Early
fission in a lophomonad flagellate; nucleus divided and new sets of organelles
developing; old organelles degenerating; diagrammatic; xl25 (after Kirby).

58 Reproduction and Life-Cycles

The stigma divides in Chlamydomonas nasuta (140), whereas the old
stigma passes to one daughter flagellate in Platydorma caudata (228).
Division of the chroma tophores has been reported in certain Euglenida
(115). Division of pyrenoids has been described in Eudorina illinoisiensis
(117); resorption of the old pyrenoid and differentiation of new ones occur
in Chlamydomonas nasuta (140).

Flagella probably do not split in fission and the few reports of such
a process are based upon inadequate evidence. Retention of the old
flagella has been described most frequently. In biflagellate and multi-
flagellate species, each daughter organism may receive one or more of the
original flagella and develop the necessary new ones, as in Heteronema
(163) and Trichonympha (152). However, flagellar resorption occurs in
Monas (210) and in Phytomonadida which divide within a parental theca.
The old flagella and associated structures also degenerate in Lophomonas
and related genera (Fig. 2. 2, L). The axostyle of trichomonad flagellates,
the pharyngeal-rod apparatus of Heteronema (163), the siphon of Ento-
siphon (115), and the cresta of devescovinid flagellates (152) undergo
resorption, whereas the costa of trichomonads apparently is retained by
one of the daughter flagellates. The kinetoplast of Trypanosomidae di-
vides but parabasal bodies of other flagellates usually do not. One of
the exceptions is Cliilomonas Paramecium in which each daughter re-
ceives part of the old parabasal apparatus (115). Parabasal bodies are
sometimes retained intact, as in Barbulanympha laurabuda (66); or partial
or complete resorption may occur. Although complete resorption of the
parabasal body sometimes occurs in Trichoynonas termopsldis and various
devescovinid flagellates, a portion often remains attached to its blepharo-
plast. In these cases, the parabasal of one daughter is regenerated from the
persisting fragment while that of the other is differentiated de novo (152).

The rigid theca of Ceratiiim (Fig. 2. 2, A-G) and related dinoflagellates
is divided in fission and the missing portions are regenerated. On the
other hand, such testate flagellates as Trachelomonas volvocina usually
undergo fission within the test, one daughter emerging to produce a new
test (99).

The simpler Sarcodina often show little of cytological interest aside
from division of the nucleus. However, the cytoplasmic changes in
Amoeba proteus (39, 162) indicate that the physical aspects of fission are
not particularly simple (Fig. 2. 3, A-C). The presence of a shell compli-
cates reproduction of many Sarcodina. In primitive genera {Cochlio-
podium, Pseudodiffliigia), the simple test is divided in fission. Euglypha
alveolata secretes reserve shell-plates and stores them (Fig. 2. 3, D) until
the next fission, when they are passed to one of the daughter organisms.
The other retains the old test. In typical Foraminiferida, schizogony has
replaced binary fission.

Fission in ciliates is typically transverse (Fig. 2. 4, H) and, in at least

Reproduction and Life-Cycles 59

yry:^^%

Fig. 2. 3. A-C. Surface changes during fission in Amoeba protcus; earlv
division (A); stage with nucleus in anaphase (B); shortly before constriction
of the body (C): diagrammatic fafter Chalkley and Daniel). D. Reserve shell-
plates stored in Euglypha; x8I0 (after Hall and Loefer). Key: /, ingested
food; 71, nucleus; s, reserve shell-plates.

certain species, there seems to be a definite division-plane which is not
displaced by amputations just before fission (256). However, the plane
of fission in Peritrichida passes from the oral to the aboral end and is
morphologically longitudinal (Fig. 2. 4, A-C). The plane of fission in
Opalinidae also is oblique or almost longitudinal. CyatJwdiniian piri-
jorme (Fig. 2. 4, D-F) is unusual, in that the plane of fission passes
through the originally longitudinal axis of the body but separates the
posterior ends of the daughter ciliates in late fission (164).

Reorganization in ciliates is often striking, and may involve macronu-
clei as well as cytoplasmic structures. The old cirri are resorbed in Urojiy-
chia (229), dedifferentiation of the peristomial area occurs in Bursaria
(212), and resorption of the peristomial membranelles in Fabrea (79).
In Chilodonella imcinatus (165), the old pharyngeal basket, cytostome,
and many body cilia are resorbed. On the other hand, Euplotes (107),

60

Reproduction and Life-Cycles

Colpidium, Glaucoma (49), and Stentor (238) retain the peristomial or-
ganelles. Division of the parental cytostome and peristome occurs in
CyclocJiaeta astropectinis (51) and possibly in other peritrichs.

The infraciliature shows genetic continuity through multiplication of
basal granules, as traced in Chilodonella (49), Foettingeriidae (48), Opa-
lina (42), and Ichthyophthirius (71), among others. In Tetrahymena and
similar ciliates (Fig. 2. 4, G, H), the development of a new mouth for the
posterior daughter involves the multiplication of basal granules at a
particular level in the stomatogenous row. These basal granules later give
rise to membranelles of the new peristomial area. The continuity of basal

Fig. 2. 4. A. Late fission in Opisthouecta heriueguyi, x410 (after Kofoid
and Rosenberg). B, C. Fission in Scyphidia ameiuri; ciliation not shown;
diagrammatic (after Thompson, Kirkegaard and Jahn). D-F. Fission in Cya-
thodiniuyn piriforme (after Lucas); two new sets of cilia move into the trans-
verse axis (D, E), and posterior ends of daughter organisms are separated in
fission (F); D, E, xl220; F, xll60. G, H. Fission in a hypothetical ciliate
similar to Tetrahymena; basal granules (indicated diagrammatically) multiply
in a particular region of the stomatogenous row (G) and liecome organized
into new adoral membranes (H).

Reproduction and Life-Cycles

61

granules is especially striking in Podophrya fixa, which shows the usual
ciliated larva and non-ciliated adult of the Suctorea. Basal granules per-
sist in the adult, and during reproduction, those in the cortex of the
bud multiply and form rows from which the cilia of the larva arise (50a).
All the cilia, and apparently their basal granules also, are resorbed in
Cyathodinium (164). New infraciliatures appear as endoplasmic units
which migrate to opposite surfaces of the body, where cilia then arise from
the new basal granules (Fig. 2. 4, D, E). This process resembles the
formation of new mastigonts in Lophomonas.

Budding and schizogony

In simple budding nuclear division is accompanied by unequal
division of the cytoplasm. Budding in ciliates is typically external, while
both internal and external budding occur in Suctorea. In internal bud-
ding of Tokophrya lemnarum (Fig. 2. 5), a slit-like cavity appears in the
endoplasm during division of the micronucleus, and is gradually extended
to cut out a spheroidal mass of cytoplasm following division of the macro-

Fig. 2. 5. Internal budding in Tokophrya lemnarum; tentacles not shown
(after Noble). A. Cytoplasmic cleft developing; macronucleus dividing and
micronuclear division completed; xl050. B. Completely separated bud en-
closed in pouch; ciliary bands developing; x660. C. Expulsion of bud from
brood pouch; x660. D. Ciliated larval stage; x715.

62 Reproduction and Life-Cycles

nucleus. After differentiation of cilia, the larva begins to rotate within
the brood pouch. Increasingly vigorous contractions of the parent finally
expel the larva (196). The development of sporoblasts in various Cnido-
sporidea (Chapter VI) also may be considered a form of internal budding.

In certain other Protozoa, budding may follow a series of nuclear di-
visions. Tritrichomonas aiigiista, although usually reproducing by fission,
sometimes develops into a somatella which undergoes budding (Fig. 2.
14, F, G). A similar process in Colacium vesiciilosum (Fig. 2. 14, A, B)
involves a multinucleate stage without flagella or reservoirs. These struc-
tures appear in each bud before it is separated from the parental somatella
(134).

Schizogony, involving the production of several to many buds more
or less simultaneously, is characteristic of certain Protozoa. This process
is especially efficient in many Sporozoa in which the plasmodium (Fig. 2.
1, A) often contains many nuclei before schizogony (Fig. 2. 1, B). A
schizont of Eimeria bovis, for example, may produce as many as 170,000
merozoites (108).

NUCLEAR DIVISION

Although mitosis has been reported in most species which have
been studied carefully, the small size of many nuclei has made it difficult
to interpret the structure of chromosomes in early mitosis and in the
interphase. The interphase chromatin of Cryptomonadida (115) and
ZellerieUa elUptica (Fig. 1. 19, G) has been described as fine granules dis-
persed on a network; that of Pelomyxa carolinensis (Fig. 2. 7, A), as
Feulgen-positive granules and short filaments. The Feulgen-positive inter-
phase chromatin of Euglenida, according to different reports (115), ranges
from periendosomal granules to a continuous spireme which in optical
section simulates separate gianules. Actually, it has been impossible to
find stages suggesting an achromatic network containing chromatin gran-
ules in some of the Euglenida and Dinoflagellida. Instead, beaded chromo-
somes seem to persist through vegetative stages. In general, however,
chromosomes of the later prophases seem to develop from some sort of a
"reticulum" and, in such favorable material as Pamphagus hyalinus (17),
the process has been traced in living material. In certain species of Enta-
moeba (Fig. 1. 20, F) and in Naegleria gruberi (207), the chromosomes
develop from a finely granular or reticular zone of Feulgen-positive mate-
rial around the endosome. The persisting "peripheral chromatin" gran-
ules, apparently adherent to the nuclear membrane in Entamoeba, may
give rise to chromosome-like bodies perhaps analogous to the nucleoli of
ZellerieUa (58). Interpretations are even more difficult in Endamoeba
blattae because the interphase nucleus is Feulgen-negative, although
Feulgen-positive chromosomes appear in mitosis (177).

The origin of chromosomes from an endosome or a karyosome, in

Reproduction and Life-Cycles

63

nuclei supposedly containing no interphase "chromatin granules," has
been reported in certain Protozoa. In some of these, such as Endolimax
nana, periendosomal material has been demonstrated in more recent in-
vestigations (240). Furthermore, Noble (200) reports a functional separa-
tion of endosomal granules and periendosomal chromatin in Entamoeba
gifigwalis, in spite of their intermingling during early prophases. How-
ever, the interphase precursors of the chromosomes have not yet been
identified with certainty in many Protozoa and much remains to be
learned about the earliest stages of mitosis in most species.

The observations of Cleveland (63) on Holoniastigotoides have shown
that the chromosomes persist as such throughout the mitotic cycle. The
diagrammatically clear behavior of the chromosomes in this genus sup-
j3lies a logical pattern for interpreting mitosis in smaller nuclei. Each
chromosome consists of a coiled chromoyiema embedded in a matrix. Only
the matrix is distinguished in heavily stained preparations, but both com-
ponents can be detected with phase-contrast microscopy and also by
ordinary microscopy in suitably stained preparations. The disappearance
of major coiling and the apparent lengthening of each chromonema, as
the chromosomal matrix disappears late in mitosis, result in long twisted
filaments. This stage, in small nuclei containing a nvnnber of chromo-
somes, would suggest the interphase "reticulum" described in various
species. If the uncoiled chromosomes are very slender, optical sections of
a small nucleus might suggest a granular organization of the chromatin.
Origin of chromosomes from such a "granular" or "reticular" interphase,
in the light of chromosomal behavior in Holomastigotoides, may involve
only a condensation of preexisting chromosomes. Each chromonema be-
comes more and more tightly coiled (in the "major coils" of Cleveland)
as a new matrix is developed. The result is the more or less compact
chromosome of the later prophases. According to Cleveland, duplication
of each chromonema occins before the development of the new matrix.

Eumitosis and paramitosis

Differences in chromosomal behavior and the structure of the
achromatic division-figure have formed the bases for various classifications
of protozoan mitoses. Among these systems, that of Belai- (20) has the
advantage of simplicity in recognizing two general types, eumitosis and
paramitosis.

Characteristic features of eumitosis are longitudinal splitting of the
chromosomes, the development of compact prophase chromosomes, and
the appearance of an equatorial belt of chromosomes within the spindle.
Many protozoan mitoses can be fitted into such a scheme.

Nuclear division in Dimorpha mutans (Fig. 2. 6) is representative.
Mitosis is initiated by division of the centrosome, and the subsequent
development of an amphiaster is accompanied by the formation of short

64 Reproduction and Life-Cycles

chromosomes from the interphase chromatin. The nucleus moves into
the spindle, the nuclear membrane is said to disappear, and the chromo-
somes form an equatorial plate. Additional examples are found in Actino-
phrys (18), Pelomyxa (Fig. 2. 7), and Zelleriella (58).

In paramitosis, condensation of the prophase chromosomes is less
marked and a typical equatorial plate is not developed. In Aggregata
eberthi (Fig. 2. 8, A-D), only one end of each chromosome extends into

Fig. 2. 6. Mitosis in Diniorpha mutans; euniitotic type; basal portions of
flagella and a few axopodia are indicated at the poles of the division-figure;
x3135 (after Belaf).

the equatorial zone of the spindle. Since the daughter chromosomes sep-
arate before they are shortened, later stages of mitosis suggest transverse
division of long chromosomes. Long chromosomes persist also in certain
Radiolarida (20), Dinoflagellida (29, 106), Euglenida (3, 115, 157), and in
Teratonympha (Fig. 2. 8, E, F).

The picture presented during separation of the daughter chromosomes
depends upon the position of the centromeres and the length of the
chromosomes. Terminal centromeres (Fig. 2. 10, H), which have been
demonstrated in Holojnastigotoides (63), probably occur in Aggregata

Reproduction and Life-Cycles

65

^'\ /'

/ « > *U'Vf.>i,i...f*--

D

•-^#»*# \

~ E

hi/in n^/H /

Fig. 2. 7. Mitosis in Pcloinyxa caroUnensis. A. Interphase; x2300. B.
Early prophase; x2300. C. Late prophase; x2645. D, E. Separation of daugh-
ter chromosomes; x2990. F. Chnnping of chromosomes in late anaphase;
x2990 (after Kudo).

and in Euglenida and Dinoflagellida. The appearance of Y-shaped daugh-
ter chromosomes during anaphases, as described in PleurotricJia lanceo-
lata (173), would suggest median instead of terminal centromeres.

Persistence of the nuclear membrane throughout mitosis is character-
istic of many Protozoa. However, a large portion of the old membrane is
discarded after division of the nucleus in Holomastigotoides (63) and
disappearance of the membrane in the prophase has been described in
Dimorpha mutatis (20).

The micronucleus of ciliates

The small size of the micronucleus increases the difficulty of inter-
preting chromosomal behavior. Longitudinal splitting of the chromo-
somes has been reported in some species and transverse division in others,
but decisions are difficult for the almost spherical chromosomes found in
certain ciliates. Longitudinal splitting has been described in Pleurotricha
(173), Stylonychia (119a), Concliophtliirius (144), and in pregamic di-
visions in Euplotes (234). In the last three cases, members of each pair
of daughter chromosomes slip past each other toward the poles of the
spindle (Fig. 2. 9).

66 Reproduction and Life-Cycles

if ^^^\

^. :«^'* i/^ A

/

Fig. 2. 8. AD. Mitosis in Aggregata eberthi; paramitotic type; x3790
(after Belaf). E, F. Long chromosomes in the dividing nucleus of Terato-
nynipha; x2400 (after Cleveland).

The achromatic figure

Both extranuclear and intranuclear achromatic figures have been
described in Protozoa. The extranuclear figure is sometimes represented
merely by the centrosomes and a paradesmose (156) which ranges from a
delicate fibril to a bundle of fibrils in different species (Fig. 2. 10, A-G).
The fibrillar paradesmose, as seen in Gigantomonas, differs mainly in

Reproduction and Life-Cycles 67

degree from the extranuclear spindle of Pseudotrichouymplia and similar
types (Fig. 2. 10, I, J). Comparable extranuclear spindles occur in certain
dinoflagellates (29, 195) and in Aggregata (20). Since the nuclear mem-
brane persists in such forms as Pseudotrichonympha, some of the astral
rays, during development of the spindle, make connections with the cen-
tromeres at the nuclear membrane. Each chromosome in HoJomastigo-
t aides (Fig. 2. 10, H), for example, ends in a terminal centromere which
remains anchored to the nuclear membrane. Duplication of the centro-
mere parallels that of the chromonema. In some of the Hypermastigida,
development of the spindle and its connections with the chromosomes has
been followed in living flagellates. Pulls exerted on the achromatic figure

D

Fig. 2. 9. Mitosis in the ciliatc, CoDchophthirius auodontae; x3995
(after Kidder). A. Longitudinal splitting of the chromosomes. B, C. Sepa-
ration of daughter chromosomes. D. Nuclear division nearly completed.

cause corresponding movements of the chromosomes; when the tension
is released, the fibrils and chromosomes snap back into place (59).

Intranuclear figures have been described in the micronuclei of ciliates,
in Actinophrys (IS), Monocystis (184), ^nd Euglyph a (120), among others
(Fig. 2. 11, E-L). In some of these cases, the spindle ends in centrosomes
which seem to be embedded in the nuclear membrane or else adherent to
it. An intranuclear spindle is typical of the dividing micronucleus (Fig.
2. 11, E, F), although little is known about division-centers in ciliates.
The spindle sometimes extends into achromatic masses ("polar caps")
which may or may not contain "centrioles." Only a granule has been
described at each pole in certain ciliates, and even the granules seem to
be missing in others.

68 Reproduction and Life-Cycles

Fig. 2. 10. A, B. Paradesmose in Tritrichomonas augusta; x2390 (after
Kofoid and Swezy). C-E. Paradesmose in Metadevescovina cuspidata; early
division (C), x2160; nuclens divided and other organelles duplicated (D),
xl800; later stage with very long paradesmose (E), xl440 (after Kirby). F, G.
Fibrillar paradesmose in Giga)itonw>ias herciilea; late anaphase (F), xl710:
nuclear division completed (G), x725 (after Kirby). H. Centromeres in Holo-
mastigotoides; portions of chromosomes indicated diagrammatically; xl260
(after Cleveland). I, J. Extranuclear spindle in Pseudotrichony?npha; chromo-
somes moving toward poles (I), x935; later stage (J), chromosomes not shown,
x735 (after Cleveland). Key: a, axostyle; c, cresta; ce, centromere; p, parades-
mose.

The significance of the persisting endosome in Euglenida and certain
dinoflagellates (Fig. 2. 11, A-D) is uncertain. Although this structure oc-
cupies an axial position and is divided in mitosis, there is no good evi-
dence that the endosome is analogous to an intranuclear spindle.

The macronucleus

The simpler macronuclei often divide by mere elongation and
constriction into approximately equal parts, although unequal division
occurs occasionally (71). Division of the compact macronucleus is not

Reproduction and Life-Cycles

69

always simple, however. A regular elimination of material (Fig. 2. 12)
from the macronucleus during division, or from the daughter nuclei
afterward, has been described in such genera as Ancistruma (142), Col-
poda (145), Tillina (14), Chilodonella (167), Colpidiinn, Glaucoma, and
Urocentnun (146). The significance of this process is unknown.

Ciliates with more than one macronucleus and those with long beaded
or band-like macronuclei may show more complicated nuclear changes.

Fig. 2. 11. A-D. Behavior of the endosome during mitosis in Heteronema
acus; A, B, D, x2890; C, x2270 (after Loefer). E. Intranuclear spindle, micro-
nucleus of Steutor coeruleus; x2365 (after Mulsow). F. Intranuclear spindle,
micronucleus of Stylonychia pustulata; xI730 (after IvaniC). G-I. Intra-
nuclear spindle in Oxymonas grandis; xl330 (after Cleveland). J-L. Intranu-
clear spindle in Pyrsonympha; early stage in development (J), x2920; later
stages (K, L), xl98r) (after Cleveland).

70

Reproduction and Life-Cycles

The C-shaped macronucleus of Euplotes (Fig. 2. 13, A-D) is shortened
and thickened, and undergoes changes in staining reactions which sug-
gest progressive internal changes. The two macronuclei of Stylonychia
pustiilata (227) fuse into a single body which then divides. The macro-
nuclear chains of Spirostornum, Stentor, and Blepharisma also undergo

Fig. 2. 12. Elimination of chromatin during macronuclear division in
Colpidium colpoda. A. Central chromatin mass evident just before divi-
sion. B-E. Stages in division. F. Separation of discarded mass from a daugh-
ter macronucleus. A-E, x510; F, x700 (after Kidder and Diller).

extensive condensation. In Spirostomiim ambiguum (22) and Stentor
coeriileiis (238) the macronuclear nodes gradually fuse into a compact
central body, which then undergoes moderate elongation and a final
constriction (Fig. 2. 13, E-I). In Blepharisma imdiilans, the anterior and
posterior macronuclear nodes fuse into two masses, while the middle
nodes gradually disappear. The anterior and posterior masses then fuse
into one body which elongates and undergoes division (238, 255).

Reproduction and Life-Cycles 71

LIFE-CYCLES

General features

The simple life-cycles of many species include only an active phase
and a cyst. With the cyst apparently eliminated, the "cycle" reaches the
limit of simplicity in such types as Entamoeba gingivalis and Pentatricho-
monas hom'mis. Other modifications of this basic pattern include: (a)
the development of two or more stages in the active phase; (b) the intro-
duction of sexual phenomena, which may appear in a sexual phase alter-
nating with an asexual phase in the cycle.

Two or more active stages occur in the life-cycles of many Protozoa. In
addition, immature and adult forms of a single organism may be quite

Fig. 2. 13. AD. Changes preceding division of ilie macronucleus in
Eiiplotes; stages in condensation (AC); elongation jnst before division (D);
x485 (after Tnrner). E-I. Division of the macroiniclens in Slentor coeruleus;
diagrammatic (after \Veisz).

72 Reproduction and Life-Cycles

Fig. 2. 14. A, B. Soniatella and reproduclion by budding in Colacium
vesiculosum (after Johnson); A, xl840; B, xl380. C-E. Metamorphosis of flag-
ellate into amoeboid stage in Tetramitus rostratus; x2080 (after Bunting).

F, G. Somatella and formation of bud in Tritrichomonas aiignsta; F, x2100;

G, xl200 (after Kofoid and Swezy). H-J. Gigmitomonas Jierculea, flagellate
stage (H), xlOOO; uninucleate amoeboid stage (I), x385; multinucleate amoe-
boid stage (J), xl35; diagrammatic (after Kirby). Key: c, chromatophore; cr,
crcsta; r, rhizostyle; t, trailing flagellum.

Reproduction and Life-Cycles 73

different in appearance and behavior. Examples include the ciliated larva
and non-ciliated adult of Suctorea and the stalkless telotroch and the
stalked adult of vorticellid ciliates. Dimorphism sometimes involves the
alternation of amoeboid and flagellate stages (Fig. 2. 14, C-E; H-J).
The flagellate stage may be temporary, as in Naegleria; or it may be the
dominant stage, as in Tetramitus and certain Chrysomonadida. The flag-
ellate, Gigantomonas herculea, shows amoeboid-flagellate dimorphism in
which reproduction is limited to the amoeboid phase. Reproductive stages
in Haematococciis and related genera also are typically non-flagellated.
The dominant phase in Colaciiim (134) is a non-flagellated form which
occasionally produces flagellate buds (Fig. 2. 14, A, B). Dimorphism also
may involve the alternation of a gamete-producing stage and one which
undergoes asexual reproduction, as in Foraminiferida. Life-cycles char-
acterized by more than two active stages are found in certain Trypano-
somidae, in many Sporozoa, and in some of the Ciliophora.

Protozoan life-cycles may be considered adaptive in that they represent
responses to changes in the environment, and perhaps favor, or insure
survival when such changes occur. Occurrence of a cycle as such probably
is dependent directly upon the environment. This seems evident in
parasitic species which must reach a susceptible host in order to complete
the cycle, or in many instances even to survive for more than a short time.
Within a suitable host, there is often reasonable security during comple-
tion of a life-cycle, but establishment in a host does not necessarily insure
independence of external conditions. For example, the development of
Plasmodium vivax in the mosquito may be retarded or prevented by un-
favorable temperatures. A modification of environmental conditions may
induce a marked change in the cycle, in parasitic as well as free-living
species. Maintenance of Plasmodium- gallinaceum in chick-tissvie cultures
has caused a normal stock to lose its ability to produce pigmented ery-
throcytic stages. Chicks inoculated from such cultures always died from
exoerythrocytic infections, always without showing normally pigmented
erythrocytic stages, and often without any erythrocytic parasites at all
(160). In some cases it has been possible to eliminate cyclic changes by
strict control of environmental conditions, as in the prevention of con-
jugation and encystment in ciliates by Woodruff, Beers, and others. Such
elimination of cyclic changes does not necessarily mean that the particular
life-cycles have no significance. Since a given cycle presumably adapts a
species to changing environments it may normally encounter, a perfectly
uniform environment may fail to evoke the cycle.

Cysts

Encysted stages, in which the organism is enclosed Avithin a cyst
membrane, are a common feature of protozoan life-cycles. On rhe basis

74 Reproduction and Life-Cycles

of apparent functions, protective and reproductive cysts have been dis-
tinguished.

Protective cysts may be developed directly from active stages, from
zygotes in Volvox and Gregarinida, or from sporoblasts (division-products
of the zygote) in Coccidia. Such cysts usually possess rather firm walls
(Fig. 2. 15, AD), the composition of which varies from group to group.

Fig. 2. 15. A. Cyst of Ceratium liiruncUnella; x385 (after Hall). B. Pro-
tective cyst of Didinium nasuhim; outer (ectocyst) and inner (mesocyst)
membranes evident; x310 (after Beers). C. Protective cyst of Bursaria
truncatella; xl35 (after Beers). D. Encysted zygote of Volvox globator;
diagrammatic (after Janet). E. Reproductive cyst in Gyrodinium sp.; x240
(after Kofoid and Swezy). F. Reproductive cyst in Colpoda citcuUus; x735
(after Kidder and Claff). Key: c, chromatophore; e, developing ectocyst;
71, nucleus in syncytial layer enclosing zygote; zn, nucleus of zygote.

The cyst membranes of many ciiiates are probably composed largely of
proteins (172), although the inner meinbrane (endocyst) may be carbo-
hydrate in nature (100). In Endamoebidae and Giardia, the properties
of the cyst wall resemble those of keratins (155). Siliceous cyst walls are
characteristic of Chrysomonadida, and walls composed largely of sand
grains are produced in Difflugia (203). Many of the thick-walled cysts
show spines, ridges, or other surface markings. A compound cyst wall
(Fig. 2. 16, C), composed of two or more membranes, is not uncominon.

Reproduction and Life-Cycles 75

In such cases one of the membranes — the ectocyst of Bursoria (16), the
mesocyst of Didiniimi (12), the outer membrane of Volvox (122) — is often
thicker and more rigid than the others. This heavy membrane may be
continuous like the others, or it may, as in Bursaria (Fig. 2. 17, A), con-
tain an "emergence-pore" closed by a thin membrane. The two-layered
cyst of Naegleria contains several analogous pores (207). Double or mul-
tiple resting cysts are sometimes produced in Colpodidae. The double cyst
of Tillina magna shows only one ectocyst, but each of the contained
ciliates has its own mesocyst and endocyst (11).

The protective qualities of cysts vary with the species. Dried cysts of
Colpoda ciiciilhis have remained viable for more than five years (69).
Cysts of Naegleria gruberi also withstand drying (207). Drying at room
temperature prolongs the life of protective cysts of Stylonethes sterkii but
kills those of Euplotes taylori (90). Cysts of Didinium nasutum do not
survive desiccation although they have remained viable for ten years in
sealed containers of hay infusion (10). Cysts of Endamoebidae also do
not survive drying. However, cysts of Entamoeba histolytica, kept moist
under refrigeration, have remained viable for 46 days (245). Woodruffia
metabolica produces two types of resting cysts, a stable one which resists
desiccation, and an unstable type which does not (136). Resistance of
protective cysts to unfavorable temperatures is sometimes striking. Thor-
oughly dried cysts of Colpoda have resisted exposure to dry heat at 100°
for three hours (23), and immersion in liquid air for 13.5 hours (230).

Reproductive cysts are those in which fission, budding, and sometimes
gametogenesis and syngamy occur m different species. However, repro-
ductive activities are not limited entirely to reproductive cysts, since
mitosis occurs in the protective cysts of Giardia and various Endamoe-
bidae. The wall of the reproductive cyst, although sometimes compound,
is usually thin and has relatively little protective value. Such cysts are
known in various dinoflagellates (Fig. 2. 15, E) and in certain free-living
and parasitic ciliates. Fission within a cyst is characteristic of Colpoda
ciicullus and related species (Fig. 2. 15, F). A similar cyst serves also for
attachment of Ichthyophthirius m,ultifiliis to the substratum (172). The
gametocyst of gregarines probably should be included in this type. Cysts
which are presumably of the reproductive type have been referred to as
"feeding cysts" in certain dinoflagellates, because they are formed after
the organisms ingest a large amount of food.

Encystment

Precystic changes in the organism usually precede secretion of a
cyst wall. Material for the membrane sometimes accumulates as globules
in the peripheral cytoplasm. Food vacuoles may be eliminated, as in
Endamoebidae, and cytoplasmic reserves such as starch or glycogen are
often stored in abundance. Since cysts usually approach a spherical form.

76 Reproduction and Life-Cycles

there is a corresponding change in shape o£ the body. In such genera as
Euplotes (90), softening of the pellicle must precede this change in form.
Partial or complete resorption of locomotor organelles is common. As
traced in Woodruffia metabolica, the cilia begin to shorten as the organ-
ism rounds up, and shortening is completed after 22-24 hours. The endo-
cyst is not secreted until after the cilia have disappeared (136). Encystment
apparently involves some loss of water, with a corresponding increase in
density of the protoplasm. The resistance to desiccation, noted in stable
cysts but not in unstable cysts of W. tnetabolica, is attributed to a lower
water content of the former (136).

The occurrence of encystment has been correlated with various envi-
ronmental changes. Encystment of Euplotes taylori seems to be related to
evaporation of the culture medium (90), while Bursaria truncatella en-
cysts when transferred singly or in groups to food-free spring water (16).
Encystment of Didinium nasutum is induced by crowding, either with or
without a food supply (15). Colpoda (duodennria) steinii encysts when
starved, and the percentage of cysts increases with the number of organ-
isms present. Encystment of this ciliate has been attributed to the inac-
tivation of essential enzyme systems by metabolic products (231). The
lack of materials for synthesis of such enzymes should produce the same
effect, and encystment of C. steinii in pure culture has followed elimina-
tion of thiamine, pyridoxine, nicotinamide, or pantothenic acid from the
standard medium, or the omission of foods known to contain several
B-vitamins (91). An abundance of food has been considered essential for
encystment of some species, but such a food supply would favor rapid
multiplication with subsequent crowding. Encystment of ciliates also has
been related to an unusually low or high pH of the medium (68), al-
though Didinium nasutum encysts most frequently within the range
favorable to growth (7).

The varied data on encystment obviously hinder selection of any one
factor as the key to this process. However, such a theory as that of Taylor
and Strickland (231) lends itself to possible correlation with several envi-
ronmental changes. The inactivation of a critical enzyme system might
result from accumulation of metabolic poisons — induction by waste prod-
ucts and by crowding. Inactivation might be accelerated by a deficiency
of materials for synthesizing such enzymes — induction by starvation and
crowding. Also, the inactivation of an enzyme system might occur more
rapidly at one pH than at another.

Excystment

Excystment often includes the regeneration of peripheral organ-
elles as well as a certain amount of internal reorganization. Rupture of
the cyst membranes may involve two different mechanisms. The more
important seems to be the absorption of water by the protoplasm early

Reproduction and Life-Cycles 77

in excystment. The resulting increase in volume forcibly ruptures rigid
membranes. In ciliates, the absorbed water may accumulate in a large
excystment-vacuole (Fig. 2. 16, A), apparently identical with the con-
tractile vacuole of Euplotes taylori (90) and Didinium nasutum (12), or
in a number of vacuoles as in Tillina magna (11). The second mechanism
involves the secretion of enzymes which digest the endocyst and perhaps
other flexible membranes. This enzymatic action, first described in Col-
poda ciicuUus (100), probably occurs also in Tillina and Didinium.
The first signs of excystment in Didinium nasutum (Fig. 2. 16) are the

Fig. 2. 16. Exc)stment in Didinmm nasutum; x275 (after Beers). A.
Appearance of excystment-vacuole. B. Ectocyst and mesocyst almost rup-
tured. C. Endocyst protruding from ruptured outer membranes. D. Organ-
ism after discharge of excystment-vacuole. E, F. Active ciliate in endocyst,
which increases in diameter. G. Escape of ciliate. Key: ec, ectocyst; en,
endocyst; in, mesocvst; v, excystment-vacuole.

beginning of cyclosis and the appearance of a small posterior vacuole.
When the vacuole grows to about half the volume of the body, a bulge
appears at the opposite pole of the cyst. A little later, the mesocyst and
ectocyst are ruptured and the organism slips out, still within the endo-
cyst. The ciliate soon becomes very active within the endocyst, which
gradually increases in diameter. The membrane becomes thinner and
thinner, and finally seems to dissolve in the medium. Excystment is com-
pleted within four hours. At emergence, the meridionally arranged cilia
extend from the anterior ciliary girdle about halfway to the posterior
end of the body. Later on, the posterior cilia of the longitudinal rows

78 Reproduction and Life-Cycles

develop into a posterior girdle, while the intermediate cilia disappear.
The primitive ciliary pattern of Holotrichida is thus recapitulated to
some extent during excystment of D. nasutiim (12).

Excystment of Biirsaria truncatella (Fig. 2. 17) is strikingly different.
Cyclosis begins early, and a hyaline area of cytoplasm just beneath the
emergence-pore becomes more apparent. After a time, the opercular mem-

Fig. 2. 17. Excystment in Bursaria truncatella; x200 (after Beers).
A. Appearance of a "hyaline cap" in the cytoplasm. B, C. Emergence of
the ciliate through the ruptured opercular membrane. D. Young excysted
ciliate. E. Older stage with developing peristomial membranelles. Key:
b, "bridge" joining endocyst and ectocyst; ec, ectocyst; en, endocyst; h,
hyaline cap; o, opercular membrane; p, emergence-pore.

brane bulges outward, and then breaks suddenly as a column of cytoplasm
erupts through the pore. The endoplasm streams into the protruded part
of the body and ciliary activity, which now increases, tends to move the
body through the pore in repeated thrusts. Emergence is completed,
posterior end first, and the immature organism swims away. During the
next hour the peristomial groove and membranelles are differentiated,
and the adult form is gradually assumed (16).

Reproduction and Life-Cycles 79

The physiological aspects of excystment are probably no less compli-
cated than the morphological changes. Excystment of Colpodo steinii
involves several stages. In an initial phase, the length of which is in-
fluenced by temperature but not by oxygen tension, essential organic
substances are absorbed from the medium. The activities of three later
periods, distinguishable by varying susceptibility of the cysts to X-rays,
are influenced by oxygen tension but not by organic components of the
medium (25). Weyer (241) suggested that excystment of Gastrostyla
steinii is induced solely by organic substances elaborated by bacteria in
the medium. Excystment of DicUniiim nasutum, in various media, de-
pends upon the presence of living bacteria. Previously bacterized culture
fluids are inactive after being heated or filtered to remove the bacteria
(13). Entamoeba histolytica will excyst in the absence of living bacteria,
but only at a low oxidation-reduction potential (216).

Barker and Taylor (5) apparently were the first to show that excyst-
ment can be induced specifically by adding certain animal or plant ex-
tracts to basal media. Some substance or group of substances was active
for Colpoda steinii in dilutions as high as 1: 100,000,000. In attempts to
isolate these factors, two concentrates from hay extract were found to be
active separately, and also to show complementary effects in combinations
(232). The activity of hay extracts was next related to salts of organic
acids (acetic, citric, fumaric, malic, and tartaric), the effectiveness of
which was quadrupled by a co-factor prepared from hay and replaceable
by certain sugars in dilute solutions (105). Tavo crystalline substances,
prepared from corn leaves, proved active at concentrations of 2.0-4.0 x
10-^ gm/ml in the presence of suitable co-factors. The co-factors, pre-
pared from corn extract and essentially inactive themselves, could be
replaced in part by a sugar solution and certain combinations of thiamine,
nicotinic acid, nicotinamide, adenylic acid, citrate, and malate (206). A
later report (226) indicates that potassium ions, not replaceable by so-
dium ions, are essential to excystment of C. steinii. Several vitamins pro-
duced no significant effect, although certain carbon sources (citrate,
glutamate, malate, and propionate) and adenosine triphosphate showed
some activity.

Requirements for excystment are less complex in certain other ciliates.
Distilled water induces excystment of TilUna magna (11) and Colpoda
cucullus (147), and dilution of the original medium is effective for
Euplotes taylori (89).

SEXUAL PHENOMENA

Varieties of sexual phenomena

Although sexual processes are not necessarily a prerequisite to
reproduction as they so commonly are in Metazoa, and although many

80

Reproduction and Life-Cycles

Protozoa undergo such activity at irregular intervals, the life-cycles of
certain species cannot be completed without syngamy. For example, the
mosquito phase of the life-cycle in Plasmodium must be initiated by
gametogenesis and syngamy. The same thing is true for the formation of
spores (protective cysts) in Eimeria and related genera.

Various kinds of sexual phenomena have been described in Protozoa.
Syngamy, in which two gametes fuse completely to form a zygote, may
involve gametes which are similar in appearance (isogamy), or are of two
types (anisogamy). Pedogamy appears to be an unusual type of syngamy
in which the two gametes are not more than one or two cell-generations
removed from a single gametocyte. Autogamy involves the formation of
two gametic nuclei, and their subsequent fusion to form a synkaryon
(zygotic nucleus) within a single organism. Parthenogejiesis, or the de-
velopment of a gamete without syngamy, has been reported but its status
in Protozoa is uncertain. Typical conjugation involves the exchange of
haploid pronuclei (gametic nuclei) between two paired organisms, the
formation of a synkaryon in each, and then nuclear reorganization.

Meiosis in relation to the life-cycle

A reduction of the chromosomes to the haploid number may occur
in gametogenesis {gametic meiosis), in an early division of the zygote

TABLE 2. 1. TYPES OF MEIOSIS IN PROTOZOA

Gametic

Zygotic

Mastigophora

Notila proteus (65a)
Paradinium poucheti (40)

Sarcodina

Actinophrys sol (18)

Foraminiferida (185, 186, 187, 188)

Gregarinida

Monocystis spp. (36, 184, 190)
Urospora lagidis (189)

Haemosporidia

Plasmodium falciparum, P. vivax,
probably gametic (168)

Cnidosporidia

Ceratomyxa blennius (198)
Guyenotia sphaerulosa (194)
Myxidium gasterostei (199)
M. incurvatum (193)
Myxobolus guyenoti (192)
Sphaeromyxa sabrazesi (193)
Triactinomyxon ignotum, T. legeri (169)
Tetractinomyxon intermedium (118)
^schokkella rovignensis (92)

Mastigophora

Euconympha imla (65b)
Glenodinium bibiniensijorme (74)
Oxymonas doroaxostylus (64)
Phytomonadida (202, 213, 213a, 257)
Saccinobaculus ambloaxostylus (65)
Trichonympha (62)

Gregarinida

Actinocephalus parvus (237)
Apolocystis elongata (204)
Diplocystis schneideri (121)
Gregarina blattarum (225)
Stylocephalus longicollis (103)
^gosoma globosum (197)

Coccidia

Adelea ovata (102)
Adelina cryptoceri (254)
A. deronis (112)
Aggregata eberihi ild, 11)
Karyolysus zuluetei (209)
Klossia helicina (191)
Ovivora thalassemae (170)

Reproduction and Life-Cycles 81

(zygotic meiosis), or in one of the pregamic divisions in conjugation
(conjugant meiosis). The type of meiosis varies in different Protozoa
(Table 2. 1). Available data indicate that the Heliozoida, Foraminiferida,
Cnidosporidia, and Ciliophora are diploid throughout most of the life-
cycle. Among the Mycetozoida, some of the Plasmodiophorina are said
to be predominantly haploid. Nuclear fusion, supposedly occurring at
the end of the vegetative phase, may be followed immediately by meiosis
(116, 236). In such cases, meiosis might be considered zygotic, although
the uninucleate haploid products promptly encyst, becoming "spores."
Some of the Eumycetozoina are believed to undergo syngamy just before
development of the plasmodium begins, and presumably are diploid
throughout the vegetative phase. In such cases, meiosis apparently pre-
cedes the formation of "spores," which give rise to the gametes after ex-
cystment. The Coccidia and a number of the Gregarinida are haploid
organisms, although a few of the gregarines seem to be diploid. Among the
flagellates, gametic meiosis has been reported in two species, and zygotic
meiosis in a number of others.

Syngamy

In addition to many established cases of syngamy (Table 2. 1) in
Protozoa, a nimiber of descriptions need confirmation. The lack of critical
evidence does not in itself justify dismissal of such reports. Syngamy in
Zoomastigophorea was described occasionally in the older literature but
most protozoologists remained unconvinced. The investigations of Cleve-
land (62, 64, 65, 65a, 65b) have supplied cytological evidence that was
previously lacking. Certain descriptions of syngamy in trypanosomes (86,
87) do not approach the cytological standards set by Cleveland. However,
the trypanosomes are not particularly favorable material for studying
chromosomal behavior and the accumulation of adequate evidence will
be correspondingly difficult.

The status of sexual phenomena in Phytomastigophorea other than
the Phytomonadida remains uncertain. A fairly recent description (21)
of syngamy in Euglena has not been confirmed, and the often cited case
of "Copromonas subtilis" (75) is questionable. In "C. subtilis" the so-
called reduction-divisions involved the extrusion of small granules ("polar
bodies") from the nucleus, whereas meiosis, as demonstrated in many
Protozoa, is a genuine nuclear division. Other reports of syngamy in
Euglenida also offer inadequate evidence. Among the Dinoflagellida,
syngamy has been reported in Ceratium hirundinella (85), Coccodinium
mesnili (41) and Noctiluca milaris (104). Syngamy and formation of
zygotes have been described in Glenodinium lubiniensijorme , a hetero-
thallic species which apparently undergoes zygotic meiosis (74). These
accounts receive additional support from a brief account of meiosis in
Paradinium poucheti (40).

82 Reproduction and Life-Cycles

Among the Sarcodina, descriptions of syngamy have been published for
several Testacida (20-)) and Amoebida. Careful studies of chromosomal
behavior have not been reported. Some supposed instances of syngamy in
Amoebida have appeared in peculiar life-cycles which seem to be elim-
inated by the use of pure-line cultures (135) and the occurrence of sexual
phenomena in this order is still unproven.

Although isogamy has been reported in some Sarcodina, gregarines and
Phytomonadida, certain of these examples involve gametes which are
similar in size and form but are distinguishable by vital staining or other
means. Miihl (183) noted that members of each pair, in syzygy of certain
gregarines, show different staining reactions with neutral red. These ob-
servations have since been confirmed and extended (138). Such differences
in staining reactions have been related to differences in oxidation-reduc-
tion potentials of the two gametocytes, which may differ also in the
quantity and distribution of cytoplasmic inclusions (138, 139).

Physiological differentiation of similar gametes also has been reported
in Chlamydomonadidae. Species of Chlamydomonas may be homothallic
(synoecious) or heterothallic (heteroecious). In homothallic species a
single culture will develop gametes of both "sexes." Every motile flag-
ellate in such a culture is a potential gamete capable of uniting with a
flagellate of the opposite sex in the same culture. As observed in the
laboratory, syngamy occurs in heterothallic species only when two cultures
containing gametes of opposite sexes are mixed imder favorable condi-
tions. Moewus (180, 181, 182) has attributed such differentiation to
specific substances produced by CJilamydomonas.- The original assump-
tions were based upon certain effects produced by fluids from cultures.
(1) A motility factor in culture fluid stimulates rapid formation of flag-
ella upon addition to a culture containing palmella stages. (2) Termones
determine the sex of the gametes derived from palmella stages in hetero-
thallic races. Gynotermones cause production of female gametes; andro-
termones, the production of male gametes. (3) Gamones, concerned mainly
with mutual attraction of the gametes, modify sexually inactive flagel-
lates so that they can undergo syngamy. Androgamones from male cul-
tures cause agglutination of female gametes under favorable conditions;
gynogamones from female cultures have a comparable effect on male
gametes.

Spectroscopic analysis of active substances, concentrated from large
volumes of culture filtrates, indicated that they were carotenoid deriva-
tives. In subsequent tests, the effects of culture filtrates were more or less
duplicated by certain derivatives of protocrocin. Accordingly, it was as-
sumed that protocrocin, synthesized by the flagellates, is broken down in
the presence of light in a series of reactions, each controlled by a par-
ticular gene. The products include picrocrocin, which in turn yields

^ The work of Moewus and his colleagues has been reviewed by Sonneborn (220, 221).

Reproduction and Life-Cycles

83

safranal and glucose, and crocin, which is decomposed into gentiobiose
and cis- and i)77?f5-dimethylcrocetin esters. Crocin (or a related glycoside
of crocetin) seems to be the motility factor, active for C. eugaynetos in
dilutions as high as 4 x 10-^^. The action of gynotermones was duplicated

i-?r:

Fig. 2. 18. A-E. Forniatioii of luicrogamctes in Ovivora tlialasscmae; A, B,
\1000: C-E, x2690 (after Mackinnon and Ray). F. Female gametocyte of O.
thalassemae; x900 (after Mackinnon and Ray). G. Microgamete of I'olvox
aureus; xl900 (after Janet). H. Macrogamete of Volvox globator shortly after
entrance of the microgamete (/??); diagrammatic (after Janet).

by picrocrocin; that of androtermones, by safranal. The gamones were
believed to be mixtures of the cis- and /rfl?75-crocetin esters and the in-
tensity of "maleness" or "femaleness" exhibited by gametes was attributed
to the cis-/trans- ratio in a given mixture.

The behavior of certain American stocks of Chlatnydojnonas differs to

84 Reproduction and Life-Cycles

some extent from that reported by Moewus. Strains of C. reinhardi, C.
minutissima, and C. intermedia, for example, become motile and develop
sexual activity in darkness as well as in light (214, 215). However, light
seems to be required for clumping and pairing of C. moewusi (161).

Prior to the work of Moewus, Schreiber (213) had described -|- and —
strains in Goniurn and Pandorina, mixtures of different clones producing
zygotes in some combinations but not in others. Tests with lines started
from division-products of zygotes indicated that differentiation occurred
in the first or second postzygotic fission.

Aside from such biochemical differentiation of similar gametes, the
development of minor structural differences apparently preceded the
evolution of marked gametic dimorphism. Among the gregarines, for
example, primitive anisogamy may involve differences in size of the nuclei,
differences in shape, and slight differences in size of the gametes. This
trend culminated in the development of small microgametes, resembling
spermatozoa in their low cytoplasmic content, and relatively large macro-
gametes containing appreciable amounts of stored food. Such extreme
differentiation is characteristic of certain Sporozoa (Coccidia, Haemo-
sporidia) and Volvox (Fig. 2. 18).

Pedogamy

In this process, attributed to Actinophrys and Actinosphaerium, a
single organism encysts and then divides into two or more "gametocytes."
After meiosis occurs, the resulting gametes undergo syngamy. In repeat-
ing earlier observations on Actinophrys sol, Belaf (18) described a reduc-
tional division in each gametocyte, followed by degeneration of one of
the two haploid nuclei. Fusion of the uninucleate gametes was then fol-
lowed by encystment of the zygote. The occurrence of syngamy in Helio-
zoida seems unquestionable but the validity of "pedogamy" may be less
certain. It has been suggested that, as in certain Foraminiferida (185),
two associated "gametocytes" secrete a common cyst membrane. However,
such an interpretation is not supported by Belaf's data.

Autogamy

The older literature (109) contains numerous descriptions of au-
togamy. In a typical account, the nucleus of an encysted amoeba divides
and each daughter nucleus undergoes meiosis. The haploid nuclei then
fuse in pairs. Or, fusion may be preceded by degeneration of all except
two haploid nuclei, so that only one synkaryon is produced. Believing
that such cases are open to more plausible explanations, protozoologists
generally had considered autogamy a highly dubious process.

The cjuestion was reopened by Diller's (70) report of autogamy in
Paramecium aurelia. Autogamy, followed by meiosis of the synkaryon,
was reported shortly afterward in Phacus pyrnm (157), although this

Reproduction and Life-Cycles 85

account has not been confirmed. Diller's observations on P. aurelia have
been followed by descriptions of autogamy in P. bursaria (5o) and P.
trichium (72). Cases of autogamy in which ciliates form a conjugant pair
but fail to exchange pronuclei have been referred to as cytogamy in P.
caudatum (243). In addition, certain genetic data (Chapter IX) agree with
the cytological evidence for autogamy in Paramecium. Up to a certain
point, nuclear behavior in autogamy parallels that in conjugation. Mat-
uration divisions are normal and pronuclei are formed. Instead of recip-
rocal transfer, however, fusion of two pronuclei occurs within the same
ciliate. It is uncertain whether autogamy is a normal process in its own
right or merely abortive conjugation. Chen (55) has found that, in con-
jugating trios of P. bursaria, a small area of cytoplasmic contact will
initiate autogamy in the odd member which is left out of the normal
pairing.

Conjugation

The onset of conjugation in mass cultures of certain ciliates is
indicated by a tendency for the organisms to adhere on contact, some-
times forming clumps containing many individuals. The nature of this
mating reaction is uncertain, although such a process suggests that the
ciliates develop sticky surfaces. This initial reaction in Paramecium
bursaria (126) seems to involve chance contact which leads to clumping.
In general, such a preliminary reaction seems to be independent of later
pairing and may be insignificant, or may not occur at all, in certain clones
of P. bursaria and in various other ciliates. The stalked conjugant of
Vorticella microstoma seems to exert some sort of attraction for motile
microconjugants passing within a distance of a millimeter (88).

Clumping in P. bursaria is followed, after a half hour or so, by gradual
breaking up of the aggregates. At the end of several hours, only pairs and
single ciliates remain as a rule. Groups of three or four persist occasion-
ally, but only two members of each group are properly paired for con-
jugation (55). Pairing seems to depend upon favorable conditions and
may be influenced by temperature and intensity of light.

The positions assumed by the paired conjugants (Fig. 2. 19) and the
extent of cytoplasmic fusion vary with the species. Contact commonly in-
volves the peristomial areas of the two conjugants. However, fusion at
the posterior ends occurs in Ancistrocoma myae (154), and fusion of oral
to aboral surface in Kidderia mytili (141). Among the Peritrichida, the
microconjugant becomes attached near the aboral end of the body in
Opisthonecta (211) and Vorticella, but near the oral end in Scyphidia
(233). In certain Apostomina, conjugants in lateral contact undergo re-
peated fission to produce chains and conjugation then proceeds between
corresponding members of the chains (47). The extent of fusion in con-
jugation apparently is influenced by the nature of the body wall. In

86 Reproduction and Life-Cycles

ciliates with a firm cuticle, fusion, or sometimes merely adhesion, may
involve a limited area of the body such as the left margin of the peristome
in Euplotes (234).

As a rule, the micronucleus undergoes three pregamic divisions (Fig.

Fig. 2. 19. Pairing in conjugation. A. Nyctotlienis cordiformis; x430
(after Wichterman). B. Pleurotricha lanceolata; x275 (after Manvvell). C.
Ancistroconm niyae, fusion of posterior ends; x2395 (after Kofoid and
Bush). D. Cycloposthium bipalmatuin, adoral organelles omitted; diagram-
matic (after Dogiel). E. Scyphidia ameirui; diagrammatic (after Thompson,
Kirkegaard and Jahn). F. Vorticella microstoma; x700 (after Finley). G.
Euplotes (patella) eurystomiis: x346 (after Turner).

41, A-D). More commonly the second, but sometimes the first (101) of
these, is reductional. However, exceptions to the usual pattern have been
noted. The third pregamic division is sometimes omitted in Paramechim
trichium (72), and micronuclei may even be exchanged just after the first
division (73). When several or many micronuclei are present, the num-

Reproduction and Life-Cycles

87

ber participating in the pregamic divisions varies with the species. Only
one of the many micronuclei undergoes the first division in Dileptus
gigas (235), but two or more may do so in other species. Comparable dif-
ferences in nuclear behavior have also been reported for the second and
third divisions. Furthermore, variation may occur within a single species.
For instance, 2-5 (and possibly 1-5) products of the second pregamic di-
vision may complete the third division in Paramecium aurelia (70). In

Fig. 2. 20. A. First pregamic division, early anaphase, Kidderia mytili;
xl875 (after Kidder). B. Late anaphase, second pregamic (reductional) divi-
sion, K. mytili; x2100 (after Kidder). C-G. Chilodonella uiiciimtiis: nuclei
just before the third pregamic division (C); late third division (D); fusion
of pronuclei (E); first division of the synkaryon (F, G); diagrammatic (after
MacDougall).

any case, the nuclei which do not undergo a particular division in the
series soon degenerate.

In typical conjugation the third pregamic division produces two or
more pronuclei. One of these, a migratory pronucleus, passes into the
opposite conjugant and fuses with a stationary pronucleus to form a
synkaryon (Fig. 2. 20, E). The actual exchange of pronuclei, which has
been questioned occasionally, is supported by recent cytological and
genetic data and has been observed in living specimens of Paramecium
bursaria (244).

Fusion of the pronuclei is followed by a reorganization in which the

88

Reproduction and Life-Cycles

synkaryon divides one or more times. Some or all of the resulting nuclei
may differentiate into macronuclei and micronuclei. Only one nuclear
division precedes differentiation in Nyctotherus cordifortnis (242), several
species of Chilodonella (167), and a few other ciliates (143). Differentia-
tion occurs after the second division in Paramecium aurelia (70), Eiiplotes
eurystomus (234), and about twenty other species (143). Differentiation
follows the third division in Bwsaria truncateUa (205), O pisthonecta
henneguyi (211), Parachaenia myae (154), Vorticella microstoma (88),
Paramecium bursaria (57), P. trichium (72), P. caiidatum, and a number
of other species (143). Differentiation after a fourth postzygotic division
has been reported in Kidderia mytili (143) and Parameciuvi multimicro-
nucleatum (159). Behavior of the nuclei in ciliates showing two or more
postzygotic divisions differs from species to species. All of the nuclei may

Fig. 2. 21. Development of a new macronucleus following conjugation in
Nyctotherus cordiformis; A-D, xllSO; E, x765 (after Wichterman).

remain functional, or some of them may degenerate. Variations may occur
also in individual species, as in P. caiidatum (71) and P. trichium (72).

Development of the micronucleus usually involves a decrease in size,
whereas a differentiating macronucleus grows and often undergoes ex-
tensive changes in form as well as internal organization. The young
macronucleus of Nyctotherus cordiformis (Fig. 2. 21) soon becomes finely
granular and stains more intensely. Later, the granules give rise to threads
during growth of the nucleus and then, as differentiation nears comple-
tion, the threads are replaced by the granules characteristic of the mature
macronucleus. The early stages of differentiation are similar in Euplotes
eurystomus. After the threads are replaced by granules the developing
macronucleus elongates, extends posteriorly, and makes contact with a
remnant of the old macronucleus. Fusion results in a complete macro-
nucleus (234).

Depending upon the species, postconjugant fissions may or may not be

Reproduction and Life-Cycles

89

necessary to restore the normal nuclear situation. Therefore, the final
result of typical conjugation is the formation of 2-8 reorganized ciliates
from a pair of exconjugants. In Metopus sigmoides (201), the pronucleus
of one conjugant (the "donor") is accompanied by a large amount of
cytoplasm during migration. After separation of the conjugants, the donor
eventually dies. Conjugation in Opisthonecta (211), Urceolaria (67), and
Vorticella (88) also produces only one functional exconjugant. One con-
jugant is a microconjugant, produced by budding, and the other is a
macroconjugant. In Vorticella ynicrostoma (Fig. 2. 22), a microconjugant

Fig. 2. 22. Conjugation in Vorticella microstoma. A. Formation of micro-
conjugant by budding. B. Fusion of microconjugant and macroconjugant;
micronucleus of former in the first pregamic division; second pregamic divi-
sions of the microconjugant have produced four nuclei. D. Two spindle-
shaped pronuclei are distinguishable. E. Synkar)'on and remnants of de-
generating macronuclei. F. One micronucleus in division; seven developing
macronuclei. xl050 (after Finley).

90 Reproduction and Life-Cycles

becomes attached near the aboral end of a macroconjiigant. Fusion then
occurs and the endoplasm of the microconjugant giadually flows into the
macroconjugant, leaving the pellicle behind. Pregamic divisions and for-
mation of a synkaryon then occur much as in other ciliates.

Conjugation is often considered an orderly process which, once started,
goes through a fixed series of nuclear activities. This is not always the
case and variations are striking in several species. Furthermore, conjuga-
tion between particular strains of a species may be abnormal. For instance,
in conjugation of certain Russian strains (variety IV) with several Amer-
ican strains of P. biirsaria, the first pregamic division is usually not com-
pleted and all conjugants die before or after separation. The lethal effect
is produced after cytoplasmic fusion, but before the exchange of pro-
nuclei (57, 132). Mixtures of certain abnormal strains of P. hursaria
with normal strains undergo typical pairing, but separation occurs after
a few hours. The micronucleus enlarges slightly but does not start the
first pregamic division (56). Polyploidy seems to have arisen frequently in
P. hursaria, probably through the fusion of more than two pronuclei in
conjugation (52). Chromosomal variations also are produced by matings
between diploid and polypoid strains, as well as between micronucleate
and amicronucleate races. In the latter case, each exconjugant contains a
single haploid nucleus which undergoes three divisions and probably
produces a new nuclear apparatus (53).

Nuclear behavior varies also in Parameciinn trichium (72, 73). Micro-
nuclei are sometimes transferred just after the second or even the first
pregamic division. Occasionally only one of the migratory pronuclei ac-
tually migrates, so that conjugants sometimes contain one and three pro-
nuclei. There also may be no exchange of pronuclei, with resulting
autogamy in each conjugant. After the second pregamic division, three
haploid nuclei sometimes degenerate and the fourth, without dividing
again, migrates into the other conjugant. Each exconjugant thus contains
a haploid nucleus which undergoes postzygotic divisions. Heteroploidy
occurs frequently in P. trichium and has been noted also in P. aiirelia and
P. caudatum (71). The exchange of macronuclear fragments has been ob-
served in P. trichium (72) — but not in other species of Paramecium — and
also in several species of Chilodonella (166, 167).

Factors inducing conjugation

The possible causes of conjugation have been discussed for many
years. Diverse ancestry was one of the prerequisites suggested by Maupas
(176) and the more recent discovery of mating types has proven that
apparently hereditary differentiation of potential conjugants does exist
in certain species. However, conjugation has been observed within single
clones, and also among the descendants of a single exconjugant after only
a few fissions. Some of these matings between closely related conjugants

Reproduction and Life-Cycles 91

— as reported in Paramecium (4, 30, 94, 123), Spatliidiiwi (253), Urolep-
tus (34), and Euplotes (149) — have not yet been correlated with the basic
concepts of mating types. Autogamy might bring about differentiation
within clones of Paramechim, but such an explanation is of uncertain
validity for other ciliates in which autogamy is unknown.

Sexual maturity as a requirement for conjugation also was suggested
by Maupas, who believed that strains of ciliates are immature when first
established in cultures and must complete a certain number of genera-
tions before they can conjugate. In contrast to this view, conjugation has
occurred at intervals of only a few days in Paramecium aurelia (217) and
P. caudatum (4). Jennings (130) has suggested that the duration of "im-
maturity" in P. bursaria varies inversely with the food supply.

Starvation is the third factor which Maupas considered essential. More
recently, conjugation of Paramecium multimicronucleatum (93), Spathi-
dium spathula (253) and Uroleptus mobilis (34), among others, has been
found to follow exhaustion of the food supply. On the other hand, con-
jugation has occurred in P. aurelia (123) just as a rich food supply was
beginning to decline, and also in P. caudatum (4), shortly before the pop-
ulations reached the maximum. The nature of the significant changes
which accompany or precede starvation is not yet known. However, the
physiological condition of individual ciliates seems to be an important
factor, since Boell and Woodruff (24) observed successful conjugation of
P. calkinsi only between ciliates with subnormal respiratory rates. A mat-
ing reaction between a normal ciliate and one with a low respiratory rate
sometimes occurred but conjugation was never completed. Ciliates with
high respiratory rates failed to show any mating reactions.

Various environmental factors also have been correlated with conjuga-
tion. Darkness apparently favors and light suppresses conjugation in P.
aurelia (219), although light shows no comparable effect on P. caudatum
(97) or Euplotes patella (148). Temperature also influences conjugation,
and different optima have been noted for different varieties of P. aurelia
(223). In one variety the frequency of conjugation has ranged from zero
at 24.5° to 68 per cent at 17.6° (219). Conjugation in ConchopJtthirius
lamellidens, parasitic on the gills of a fresh-water mussel, has been ob-
served most frequently on the day following the new moon (208). Dilu-
tion of the medium with weak solutions of aluminum and iron chlorides
is said to have induced conjugation of Paramecium caudatum (258), but
Ball (4) obtained negative results with several clones of P. aurelia and
P. caudatum. One clone of P. caudatum did respond to such treatment
but distilled water was just as effective as the salt solutions. Conjugation
of Glaucoma scintillans has been stimulated by decreasing the salt con-
tent of the medium or increasing the concentration of glucose (43), and
also by adding pyruvic acid to the medium (45).

The bacterial flora of cultures also may influence the incidence of con-

92 Reproduction and Life-Cycles

jugation. Chatton and Chatton (44) found that Glaucoma scintillans
conjugated when fed on Escherichia coli, Proteus vulgaris, Shigella dysen-
teriae, or Staphylococcus aureus, but not on Pseiidomonas aeruginosa, P.
fluorescens or any one of several other bacterial species. Conjugation of
P. caudatum was observed in cultures containing only a gram-negative
bacillus, but not in other cultures containing at least three kinds of bac-
teria (46). Accordingly, it was suggested that so-called conjugating and
non-conjugating races of ciliates may be determined by the bacterial flora.
This conclusion was not supported by Sonneborn and Cohen (222) who
induced conjugation invariably in a Johns Hopkins strain and never in
Woodruff's strain of P. aurelia when both strains were maintained on the
same bacterial types.

Mating types in ciliates^

Following the observations of Sonneborn (218, 219) on Para-
mecium aurelia, P. calkinsi, and P. trichium and those of Jennings (124,
125) on P. bursaria, mating types have been demonstrated also in P.
caudatum (95, 96, 97, 98, 98a), P. midtimicronucleatum (94, 95), and
Euplotes patella (148,149).

The situation in P. bursaria may be illustrated as follows. Two strains,
A and B, have been established in pure lines. Conjugation does not occur
among ciliates of strain A or among those of strain B, although mixtures
of the two do show conjugation. Therefore strains A and B seem to be-
long to different sexes. A third strain, C, tested in the same way with
strain A, behaves like strain B, and consequently might be expected to
have the same sex. However, conjugation occurs also in mixtures with
strains B and C. A fourth strain, D, is found to conjugate with any of the
other three. At this point, conjugation in P. bursaria begins to strain
basic concepts of bisexuality in animals, and confusion in terminology
has been avoided by the substitution of "mating type" for "sex." Further
investigation has demonstrated additional groups of mating types. A
second group, or variety, contains eight mating types (E, F, G, H, J, K,
L, M) which will not conjugate with the four types (A-D) in variety I.
Mating types N, O, P, and O have been assigned to a third variety, since
they will not conjugate with types belonging to varieties I and II. Variety
IV contains types R and S, which do not mate with members of varieties
I, II or III. Variety V is represented by mating type T, composed of
strains obtained from Russia, and will not mate with members of the
other varieties (132). A more recently recognized variety VI, including
strains from Czechoslovakia, England and Ireland, contains mating types
U, V, W and X (55).

In Paramecium aurelia seven varieties have been recognized (224).
Six of these contain two mating types, and one type has been assigned to

^This subject has been reviewed by Kimball (150).

Reproduction and Life-Cycles 93

variety 7. Normal conjugation occurs between the two mating types of
each variety, but not between strains belonging to different varieties.
Thirteen varieties, each with two mating types, have been identified in
P. caudatum (98a).

At first, it was believed that conjugation never occurred between mem-
bers of different varieties in P. aurelia and P. hursaria, but exceptions
have been reported more recently. Type R of variety IV occasionally
conjugates with four types of variety II in P. hursaria, althovigh the par-
ticipants die during or shortly after conjugation (]?)2). Similar cases have
been observed in P. aurelia (224). Mating type I will conjugate occasion-
ally with type X, and mating type II with types V, IX, and XIII. Mating
reactions in these intervarietal crosses of P. aurelia are always less intense
than those within the same variety — only 1-40 per cent as many conjugant
pairs in different combinations. In P. caudatum (98) intervarietal matings
have occurred between variety 10 (type XX) and varieties 8 (type XV)

TABLE 2. 2. INDUCTION OF CONJUGATION IN EUPLOTES
PATELLA BY FLUIDS FROM CULTURES

Mating types

of treated ciliates

Culture
fluids

I

II

III

IV

V

VI

I

—

4-

4-

4-

4-

4-

II

+

+

4-

4-

4-

+

III

4-

—

—

4-

—

4-

IV

-

-

4-

—

4-

■ 4-

V

4-

4-

4-

4-

—

+

VI

—

4-

4-

4-

—

—

and 9 (type XVII), and also betAveen variety 2 (type IV) and variety 8
(type XV).

The situation in Euplotes patella (148, 149) resembles that in P. hur-
saria. Six mating types have been recognized in one variety, and there
may be additional varieties. The mating reactions of E. patella are espe-
cially interesting because specific mating-type substances are released into
the culture medium. Fluid from cultures of one mating type will induce
conjugation among the ciliates of a single mating type in certain cases
(Table 2. 2). The nature of this effect is uncertain. Kimball apparently
favors the view that conjugation is induced in animals which are all of
the same mating type, rather than that the mating type is changed in
some of the treated ciliates and not in others. A particular mating-type
substance induces conjugation only in a type which does not produce that
substance, and these effects have been correlated with the inheritance of
mating types in E. patella (Chapter IX).

Certain analogous effects of culture fluid have been observed in Para-

94 Reproduction and Life-Cycles

meciiim bursaria (54). Fluid from cultures of several Russian strains (type
T) induces conjugation within individual mating types of varieties II,
III, IV and VI, although the effect is usually limited to a small percentage
of the ciliates in a culture.

The recognition of mating types in certain ciliates has shown that con-
jugating pairs, in these species at least, are composed of physiologically
different organisms. However, the relation of mating types to the concept
of bisexuality in animals remains uncertain in Paramecium bursaria and
Euplotes patella. On the other hand, P. aurelia and P. caiiclatum might
possibly be interpreted as species composed of "bisexual" varieties which
interbreed with difficulty or not at all.

Nuclear phenomena of uncertain significance

Endomixis (250) was originally described in Paramecium aurelia
as a complete nuclear reorganization occurring in individual ciliates
(251). Macronuclear disintegration and two micronuclear divisions occur
without the usual third pregamic division of conjugation. Only two of
these eight micronuclear derivatives persist, so that the first fission leaves
each ciliate with one functional nucleus. Two nuclear divisions occur.
Two of the products then differentiate into macronuclei, while the others
divide to form four micronuclei. A second fission completes the reorgan-
ization.

The significance of endomixis in the life-cycle is still unknown. Wood-
ruff believed that meiosis does not occur — although the second pregamic
division is reductional in conjugation of P. aurelia — and he suggested
that endomixis might be analogous to diploid parthenogenesis. The dis-
covery of autogamy in P. aurelia (70) and the accumulation of genetic
data have thrown doubt upon the occurrence of endomixis in P. aurelia.

Hemixis involves unusual behavior of the macronucleus only. The
process has been observed in Paramecium aurelia, P. caudatum, and P.
multimicronucleatum. (70). In one type of hemixis there is a precocious
division of the macronucleus and the normal nuclear situation is restored
in the next fission. In another type, the macronucleus extrudes one or
more densely staining masses and then behaves normally in subsequent
fissions. A third type of hemixis combines the elimination of chromatic
material with precocious division of the macronucleus.

THE PHYSIOLOGICAL LIFE-CYCLE

The description of conjugation by O. F, Miiller in 1786 stimulated
much interest in the sexual activities of Protozoa. For many years, it was
believed that the "ovary" (macronucleus) of ciliates gave rise to "ova"
(products of macronuclear disintegration), while the "testis" (micro-
nucleus) produced "spermatozoa" (chromosomes). In conjugation, two
hermaphroditic ciliates were supposed to exchange spermatozoa. In cer-

Reproduction and Life-Cycles 95

tain cases, small organisms (probably parasites) within the conjugants
were interpreted as "embryos" developing within viviparous parents.
These interpretations were overthrown by Biitschlii (26, 27) and Engel-
mann (80), who showed that the supposed ovary and testis are nuclei
and suggested that products of the micronuclei might be exchanged in
conjugation. The fusion of pronuclei in conjugation was reported a few
years later (133).

Once conjugation was found to involve nuclear reorganization, and
occasionally the reorganization of locomotor structures, the process was
interpreted as a sort of rejuvenation. Engelmann (80) suggested that it
was unnecessary to suspect any other effect. Biitschli (27) supported a
physiological interpretation — ciliates become senescent during continued
fission and as a result reproduce less and less frequently until conjuga-
tion rejuvenates them and restores the normal reproductive rate.

This question was first considered experimentally by Maupas, whose
isolation-culture technique (175, 176) involved tracing single ciliates from
one generation to the next in order to detect possible senescence. Since
all his strains died eventually, Maupas suggested that ciliates, like higher
animals, pass through a cycle of youth, maturity, and old age, ending in
death. The characteristic feature of maturity was assumed to be an ability
to conjugate normally. Conjugation was believed to rejuvenate ciliates
only during the phase of maturity, and therefore was a prophylactic
rather than a therapeutic measure.

Biitschli (28) maintained that conjugation increased fission-rate after
a gradual decline. Hertwig's (113) observations on split-pairs — conjugants
separated at the beginning of conjugation and used for starting parallel
clones — indicated that fission-rates were usually higher in non-conjugant
than in exconjugant lines. As a result, he concluded that conjugation
merely regulates metabolism so as to prevent physiological exhaustion.
Later investigations were designed to test the theories of Biitschli, Hert-
wig, and Maupas.

Joukowsky (137), after studying exconjugant and non-conjugant lines
of Paramecium caudatum and Pleurotricha lanceolata, concluded that the
degenerative changes described by Maupas were the result of unsatis-
factory conditions in cultures. There were no characteristic differences
between exconjugant and non-conjugant lines, neither type showed a
decreasing fission-rate, and there appeared to be no physiological cycle.

The next important papers were those of Calkins (30, 31, 38) who
started isolation-cultures of Paramecium, caudatum on February 1, 1901,
Four lines were started from each of two ciliates and transfers were made
daily or every other day. After a time, recurrent "depressions* developed.
The early depressions, believed to represent the senescence reported by
Maupas, were cured by measures other than conjugation. The depression
of May, 1901, apparently was cured by jolting during a train ride to

96 Reproduction and Life-Cycles

Woods Hole; that of August, 1901, by extract of raw beef; that of De-
cember, 1901, by beef extract; that of March, 1902, by a slight rise in
temperature; that of June, 1902, by brain extract. Since the lines were re-
juvenated by artificial means, the results were considered analogous to
artificial parthenogenesis (31).

In these early papers. Calkins suggested that ciliates have the "poten-
tial of endless existence" without conjugation. Later on, however, the
depressions became more severe. The "B" lines became extinct after 16
months, the "A" lines in December, 1902. Attempts to rejuvenate the
ciliates — treatments with beef extract, pancreas, brain, mutton broth,
lecithin, pineapple extract, apple juice, several acids and salts, dried
Paramecium, the electric current and nitroglycerin — were all unsuccessful.
As a result, Calkins (33) was convinced that the final depressions arose
from "germinal exhaustion" which could not be prevented by external
stimulation. Therefore, strains of P. caudatum must pass through a cycle
of youth, maturity, and old age unless vitality is renewed by conjugation.
A gradual decrease in fission-rate accompanied senescence and the re-
juvenation by conjugation was believed to include an increase in fission-
rate.

The observations of Enriques soon questioned the inevitability of
senescence. The first important demonstration (81) was that excessive
bacterial growth may lead to effects simulating senescence. Later results
(82, 83) included the maintenance of Glaucoma scintiUans without con-
jugation for almost 700 generations. The ciliates remained healthy so
long as fresh medium was supplied; the use of old medium induced
depressions. At this point, Enriques suggested that exhaustion of the in-
vestigators patience is a more important factor than senescence of the
ciliates in such investigations.

On May 1, 1907, Woodruff started the line of Paratnecium aurelia
which was to deal a more serious blow to the physiological life-cycle. In
May, 1908, the strain had passed 490 generations (246), and at the end
of four years (247), had survived for 2,121 generations without conjuga-
tion. By this time, the evidence indicated that P. aurelia might reproduce
indefinitely without conjugation, or else that the "cycle" must be longer
than that of any ciliate investigated previously.

The conclusion suggested by Woodruff's strain of P. aurelia did not
remain unchallenged. Calkins and Gregory (37) maintained that some
strains of Paramecium are conjugating races while others are non-con-
jugating, and it was argued that Woodruff's strain was a non-conjugating
race which should not be compared with the conjugating strain of
Calkins. Woodruff (248) met this objection by reporting conjugation in
mass-cultures started from his strain at the end of 4,102 generations. The
completion of 25 years without conjugation was reported in 1932 (249).

Evidence against the physiological cycle gradually accumulated from

Reproduction and Life-Cycles 97

other sources. Glaucoma scintillans showed no senescence after 2,700
generations (84). Lines of Paramecium caudatum lived for ten years
without conjugation or decrease in vitality (178, 179). The colonial flagel-
late, Eudorina elegans, was maintained for eight years without syngamy
or indications of senescence (110, 111). Actinophrys sol passed more than
1,200 generations without syngamy (19). Spathidium spathula, previously
credited with a cycle, survived for a thousand generations without con-
jugation or endomixis (252). Didinium nasutum was maintained by Beers
without conjugation or a decrease in vitality so long as the food supply
was adequate (8). However, depressions were readily induced by an
inadequate diet (9).

In contrast to various other ciliates, Uroleptus mobilis failed to follow
the prevailing pattern. Instead, a physiological cycle was reported, with
the strains living an average of 350 generations (34, 35). Attempts to
prolong the cycle by varying the environmental conditions were unsuc-
cessful (2), and this species remains one in which the cycle has not been
eliminated. More recently, Jennings (127, 131) concluded that his experi-
ence with Paramecium bursaria also supports the concept of a physiologi-
cal cycle, although some clones were maintained for eight years before
their health began to decline.

In spite of the fact that strains of various ciliates could be grown in
the laboratory for long periods without conjugation — and perhaps they
could be maintained indefinitely — one question remained unanswered.
Does conjugation really have any stimulatory or rejuvenating effect on
ciliates?

The early investigations had produced little information. A few ob-
servations by Hertwig (114) on Dileptus gigas and some inconclusive data
cited by Calkins (33) represented the available evidence. Some years later,
the first convincing experiments were reported by Calkins (34). Several
strains of Uroleptus mobilis, which were entering depressions, showed a
higher fission-rate and greater longevity after conjugation than the non-
conjugant parental stocks. Comparable effects of conjugation were re-
ported subsequently in Spathidium spathula (253) and Paramecium
bursaria (131).

At present it seems clear that conjugation, whether or not it is essential,
can produce a physiological stimulation in at least certain strains. How-
ever, it is equally evident that conjugation is no universal remedy for
senescent ciliates. In fact, the odds are slightly against survival after con-
jugation in Paramecium bursaria. Records kept for 20,478 exconjugants
show that under conditions in which all non-conjugant lines remained
vigorous, 29.7 per cent of the conjugating ciliates died before the first
post-conjugant fission, and only 47.3 per cent survived for more than four
fissions (127). Conjugation between inbred lines is even more dangerous,
and mortality often reaches 90-100 per cent in such cases in P. bursaria

98 Reproduction and Life-Cycles

(129). Conjugation between old stocks which are not closely related also
may be almost 100 per cent lethal, although unrelated young stocks may
show little or no mortality after conjugation (148).

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Ill

The Classification of Protozoa

Taxonomy prior to 1900 Prospective sources of taxonomic data

Taxonomic systems of the twentieth cen- The identification of Protozoa
^"■^y Literature cited

X

HE CLASSIFICATION of Protozoa scrvcs various useful purposes
in addition to furnishing a system for filing species in appropriate cata-
logs. A sound taxonomy favors progress in comparative morphology and
physiology since it facilitates correlation of the information bearing on
related organisms. The projection of experimental and observational data
on a taxonomic background also is helpful in planning investigations to
extend or limit the application of preliminary findings. In fact, without
some knowledge of taxonomic relationships, the choice of material for
certain types of research would be analogous to "wildcat" drilling for oil.
Although a certain amount of "wildcatting" is always needed, the orderly
development of a field often depends extensively upon systematically
directed efforts. As more is learned about the interrelationships of Pro-
tozoa, the benefits derived from the field of taxonomy will become increas-
ingly important.

A major aim of taxonomy^ is the assignment of organisms to species
and larger groups on the basis of degree of kinship. If the available data
are extensive enough and have been interpreted correctly, such a tax-
onomic system not only indicates degrees of relationship among existing
species, but also furnishes sound clues to phylogenetic relationships. Un-
fortunately, this taxonomic ideal has not yet been realized for the Phylum
Protozoa as a whole.

The limitations of current systems are numerous. In the first place,
the boundaries of the phylum are subject to debate, particularly in the
case of phytoflagellates. In studying the Phytomastigophorea and their

^ General problems of zoological classification and conventional taxonomic procedures
have been reviewed in a compact monograph by Caiman (6).

103

104 The Classification of Protozoa

relatives, the taxonomist encounters organisms which range from typical
flagellates (of which many are apochlorotic and some are holozoic) to
filamentous algae with temporary flagellate stages. In assigning algal
flagellates to the Phylum Protozoa and leaving their close relatives with
the botanists, protozoologists obviously have made arbitrary decisions
which are more indicative of taxonomic convenience than of biological
relationships. The dual taxonomic role of the slime-molds as Sarcodina
and Fungi indicates another point at which the boundaries of the Phylum
Protozoa are obscure. Comparable uncertainty exists at the lower levels
of protozoan taxonomy, and there are instances in which orders appar-
ently overlap to such a degree that the exact positions of certain genera
are still uncertain. In modern taxonomic practice, it is no novelty for a
particular genus or family to be moved from one subphylum, class, or
order to another. Old orders have sometimes disappeared completely, in
suppressions or amalgamations, and new orders have been carved out of
older groups. The continued erection of new genera and species is paral-
leled to some extent by the suppression of old names. In other words, a
certain amount of taxonomic confusion extends throughout much of the
Phylum Protozoa. This confusion does not indicate chaos. Instead, it is
the result of continued activity in a field still seriously handicapped by
the lack of adequate information.

TAXONOMY PRIOR TO 1900

Although current classifications leave much room for improvement,
there has been tren;iendous progress since Gesner described one of the
Foraminiferida as a mollusc in 1565. Protozoa apparently were first sep-
arated from other animalcules in 1752, when John Hill placed some of
them in his group of Gymnia (animalcules without external organs). In
1786, O. F. Miiller (17) erected the Infusoria (including about 150 species
of Protozoa) as a subdivision of the worms, and divided the group into
species with, and those without, visible locomotor organelles.

Ehrenberg's (10) more extensive monograph included descriptions of
about 350 species from original observations, but an important part of
his taxonomic system was based upon a liberal interpretation of the
Infusoria as complete organisms. On the basis of feeding experiments with
pigments, Ehrenberg concluded that a digestive system is characteristic
of ciliates. "Polygastric" types were believed to have a mouth, oesophagus,
many stomachs, a spiral intestine, an anus, and possibly a pancreas. The
Infusoria were separated into Anentera (without a digestive tract) and
Enter odela (with a digestive tract). The Anentera were subdivided into
Gymnia (no visible appendages), including about 30 genera of flagellates;
Pseudopoda (with pseudopodia), including Amoeba, Arcella, and certain
Suctorea; and Epitricha (with cilia), including a few ciliates and several
dinoflagellates. Additional ciliates were placed in the Enterodela which

The Classification of Protozoa 105

were subdivided, on the basis of number and position of openings to the
supposed digestive tract, into Anopisthia (with one terminal opening),
Enantiatreta (with an opening at each end of the body), Allotreta (with
a lateral opening), and Catotreta (with a ventral opening).

Ehrenberg's basic misinterpretation of protozoan morphology was soon
corrected by Dujardin (9) who reached the conclusion that Infusoria are
simple organisms composed of a fundamental living substance, sarcode.
Repetition of Ehrenberg's feeding experiments indicated that the sup-
posedly fixed stomachs of ciliates are merely food vacuoles. Dujardin
divided the Infusoria into Asymmetrica and Symmetrica. The former
included species without visible locomotor organelles (bacteria), those
with pseudopodia (mostly Sarcodina, in the modern sense), those with
flagella, and those with cilia (about 50 genera of ciliates). The Sym.metrica
included the ciliate genus Coleps.

In 1845, von Siebold (20) redefined the "Protozoa," in which Goldfuss
(11) had included certain coelenterates with the "Infusoria," and char-
acterized them as unicellular animals. Although such a characterization
is inadequate by modern standards, von Siebold's definition served a
useful purpose in stressing morphological differences between Protozoa
and higher animals. The Protozoa now included the Class Infusoria — the
Astoma, without a mouth {Opalina and the flagellates), and the Stoma-
toda, with a mouth (about 30 genera of ciliates) — and the Class Rhizo-
poda with (pseudopodia).

Further investigation brought more recruits to the Protozoa. In 1845,
von Kolliker concluded that gregarines are Protozoa instead of trema-
todes, and this interpretation was supported by Stein in 1848. Increased
interest in these organisms finally led to Leuckart's erection of the
Sporozoa in 1879. Preliminary observations of Meyen, and the extensive
work of Huxley on Thalassicolla led J. Muller, in 1858, to establish the
Radiolaria as a subdivision of the Rhizopoda. The group Ciliata was set
up by Perty in 1852; the Flagellata, by Cohn in 1853; and extensive in-
vestigations on both groups were reported by Claparede and Lachmann
in 1858-1861. By the time Stein's (21) monograph was completed, the
Flagellata were divided into 15 families, some of which are now con-
sidered orders; the Ciliata, into the orders Holotricha, Heterotricha,
Hypotricha, and Peritricha. Stein's classification of ciliates on the basis
of distribution of cilia has been carried on, with modifications, into later
systems.

Contemporary contributions included Haeckel's separation of the Heli-
ozoa from the Radiolaria, erection of the Mastigophora by Diesing,
the Sporozoa by Leuckart, the Myxosporidia and the Dinoflagellata by
Biitschli, and the Sarcosporidia by Balbiani. As a result, the classification
of Protozoa began to resemble more modern systems.

Kent's monograph (14) covered the following groups:

106 The Classification of Protozoa

Class 1. Rhizopoda

Order 6. Choano-Flagellata

Order 1. Amoebina

Order 7. Spongida

Order 2. Gregarinida

Order 8. Flagellata-F.ustomata

Order 3. Arcellinida

Order 9. Cilio-Flagellata

Order 4. Foraminifera

Class 3. Ciliata

Order 5. Labyrinthulida

Order 1. Holotricha

Order 6. Radiolaria

Order 2. Heterotricha

Class 2. Flagellata

Order 3. Hypotricha

Order 1. Mycetozoa

Order 4. Peritricha

Order 2. Trypanosomata

Class 4. Tentaculifera

Order 3. Rhizo-Flagellata

Order 1. Actinaria

Order 4. Radio-Flagellata

Order 2. Suctoria

Order 5. Flagellata-Pantostomata

Kent's system differed from more recent ones in several respects— assign-
ment of the Mycetozoa and the Spongida (sponges) to the Flagellata;
inclusion of the gregarines in the Rhizopoda; recognition of a Class Ten-
taculifera to include the Suctoria and Actinaria.

Biitschli (2) recognized the Class Sporozoa, although some of the mod-
ern Coccidia were grouped with gregarines. The Microsporidia were listed
as an appendix to the Sporozoa, with exact relationships to be determined.
Among the Mastigophora, the Euglenoidina included several of the
modern Chloromonadida, while such types as Bodo (now in the Proto-
mastigida) and Ejitosiphon (one of the Euglenida) were assigned to the
Heteromastigoda. Butschli's Isomastigoda included the Chrysomonadida,
Cryptomonadida and Phytomonadida of current systems, as well as cer-
tain Polymastigida and the dinoflagellate Oxyrrhis. The Trichonym-
phidae (now in the Hypermastigida) were listed as an appendix to the
ciliates.

Class 1. Sarkodina
Subclass 1. Rhizopoda
Order 1. Rhizopoda
Suborder 1. Amoebaea
Suborder 2. Testacea
Suborder 3. Perforata
Subclass 2. Heliozoa
Subclass 3. Radiolaria
Class 2. Sporozoa

Subclass 1. Gregarinida
Order 1. Monocystidea
Order 2. Polycystidea
Subclass 2. Myxosporidia
Subclass 3. Sarcosporidia
Class 3. Mastigophora
Order 1. Flagellata
Suborder 1. Monadina
Suborder 2. Euglenoidina

TAXONOMIC SYSTEMS OF THE
TWENTIETH CENTURY

Suborder 3. Heteromastigoda
Suborder 4. Isomastigoda
Order 2. Choanoflagellata
Order 3. Dinoflagellata
Suborder 1. Adinida
Suborder 2. Dinifera
Order 4. Cystoflagellata
Class 4. Infusoria
Subclass 1. Ciliata

Order 1. Gymnostomata
Order 2. Trichostomata
Suborder 1. Aspirotricha
Suborder 2. Spirotricha
Section 1. Heterotricha
Section 2. Oligotricha
Section 3. Hypotricha
Section 4. Peritricha
Subclass 2. Suctoria

The system proposed by Calkins (3) showed several changes. The
Suborder Perforata (Foraminifera) became the Order Reticulariida. The

The Classification of Protozoa 107

silicoflagellates, now considered a subdivision of the Chrysomonadida,
appeared as a separate order. The Order Phytoflagellida included groups
now separated as the Orders Phytomonadida and Chloromonadida. The
gregarines, coccidians, and haemosporidians were assigned to separate
orders in the Telosporidia.

Class 1. Sarcodina

Subclass 1. Rhizopoda
Order 1. Amoebida
Suborder 1. Gymnamoebina
Suborder 2. Thecanioebina
Order 2. Reticular! ida
Suborder 1. Nuda
Suborder 2. Imperforina
Suborder 3. Perforina
Suborder 4. Tinoporinae
Subclass 2. Heliozoa

Order 1. Aphrothoracida
Order 2. Chlamydophorida
Order 3. Chalarathoracida
Order 4. Desmothoracida
Subclass 3. Radiolaria
(20 orders)
Class 2. Mastigophora
Subclass 1. Flagellida
Order 1. Monadida
Order 2. Choanoflagellida
Order 3. Heteromastigida
Order 4. Polymastigida
Order 5. Euglenida
Order 6. Phytoflagellida
Suborder 1. Chloromonadina
Suborder 2. Chronionadina

Suborder 3. Chlamydomonadina
Suborder 4. Volvocina
Order 7. Silicoflagellida
Subclass 2. Dinoflagellida
Order 1. Adinida
Order 2. Dinoferida
Order 3. Polydinida
Subclass 3. Cystoflagellidia
Class 3. Sporozoa

Subclass 1. Telosporidia
Order 1. Grcgarinida
Order 2. Coccidia
Order 3. Hacmosporidiida
Subclass 2. Neosporidia
Order 1. Myxosporidiida
Order 2. Sarcosporidiida
Class 4. Infusoria
Subclass 1. Ciliata

Order 1. Holotrichida

Suborder 1. Gymuostomina
Suborder 2. Trichostomlna
Order 2. Heterotrichida
Suborder 1. Poly trichina
Suborder 2. Oligotrichina
Order 3. Hypotrichida
Order 4. Peritrichida
Subclass 2. Suctoria

The system of Dofiein (7) differed in several respects from that of
Calkins. The phylum was divided into two subphyla, Plasmodroma and
Ciliophora. The "Infusoria" disappeared, the Ciliata and Suctoria being
advanced to classes of Ciliophora. In addition, the Foraminifera and
Mycetozoa were recognized as orders of the Rhizopoda, and the Tricho-
nymphidae were listed as an appendix to the Mastigophora.

Subphylum 1. Plasmodroma
Class 1. Rhizopoda
Order 1. Amoebina
Order 2. Heliozoa
Order 3. Radiolaria
Order 4. Foraminifera
Order 5. Mycetozoa
Class 2. Mastigophora
Subclass 1. Flagellata
Order 1. Protomonadina
Order 2. Polymastigina
Order 3. Euglenoidina
Order 4. Chromomonadina

Order 5,
Subclass 2.

Order 1.

Order 2.

Subclass 3.

Class 3. Spor

Subclass I.

Order 1

Order 2
Subclass 2.

Order 1.

Order 2.
Subphylum 2.

, Phytomonadina

Dinoflagellata

Adinida

Dinifera

Cystoflagellata
ozoa

Telosporidia
. Coccidiomorpha
. Gregarinida
, Neosporidia

Cnidosporidia

Sarcosporidia
Ciliophora

108 The Classification of Protozoa

Class 1. Ciliata

Order 1. Holotricha
Order 2. Heterotricha
Order 3. Oligotricha

Order 4. Hypotricha
Order 5. Peritricha
Class 2. Suctoria

Hartmann (12) recognized five orders of Neosporidia among the Spo-
rozoa. To the Subclass Flagellata, was added the Order Binucleata to in-
clude some of the Trypanosomidae and Haemosporidia as supposedly
binucleate organisms. Since the binucleate nature of these organisms has
never been established (21), the Order Binucleata has not been accepted
by later workers.

Subphylum 1. Plasmodroma
Class 1. Rhizopoda

Order 1. Amoebina

Order 2. Mycetozoa

Order 3. Foraminifera

Order 4. Heliozoa

Order 5. Radiolaria
Class 2. Mastigophora

Subclass I. Flagellata
Order 1. Protomonadina
Order 2. Polymastigina
Order 3. Binucleata
Order 4. Euglenoidea
Order 5. Chromomonadina
Order 6. Phytomonadina

Subclass 2. Dinoflagellata
Order 1. Adinida
Order 2. Dinifera

Subclass 3. Cystoflagellata

Class 3. Telosporidia
Order 1. Coccidia
Order 2. Gregarinida

Class 4. Neosporidia
Order 1. Myxosporidia
Order 2. Microsporidia
Order 3. Sarcosporidia
Order 4. Actinomyxidia
Order 5. Haplosporidia
Subphylum 2. Ciliophora

Class 1. Ciliata

Order 1. Holotricha
Order 2. Heterotricha
Order 3. Oligotricha
Order 4. Hypotricha
Order 5. Peritricha

Class 2. Suctoria

In the system of Minchin (16) the subphyla Plasmodroma and Cilio-
phora were dropped and the Class Infusoria restored. The Heliozoa and
Radiolaria were recognized as subdivisions of the Actinopoda. In the
Ciliata, erection of the Sections Aspirigera and Spirigera stressed dif-
ferences in adoral ciliation.

Class 1. Mastigophora
Subclass 1. Flagellata
Order 1. Pantastomatina
Order 2. Protomonadina
Order 3. Polymastigina
Order 4. Euglenoidina
Order 5. Chromomonadina
Suborder 1. Chrysomonadina
Suborder 2. Cryptomonadina
Order 6. Phytomonadina
Subclass 2. Dinoflagellata
Order 1. Adinidia
Order 2. Dinifera
Subclass 3. Cystoflagellata
Class 2. Sarcodina

Subclass 1. Rhizopoda
Order 1. Amoebaea

Suborder 1. Reticulosa
Suborder 2. Lobosa
Order 2. Foraminifera
Order 3. Xenophyophora
Order 4. Mycetozoa
Subclass 2. Actinopoda
Order 1. Heliozoa
Order 2. Radiolaria
Class 3. Sporozoa

Subclass 1. Telosporidia
Order 1. Gregarinoidea
Suborder 1. Eugregarinae
Suborder 2. Schizogregarinae
Order 2. Coccidia
Order 3. Haemosporidia
Subclass 2. Neosporidia
Division 1. Cnidosporidia

The Classification of Protozoa 109

Order 1. Myxosporidia
Order 2. Actinomyxidia
Order 3. Microsporidia
Order 4. Sarcosporidia

Division 2. Haplosporidia
Order 1. Haplosporidia
Class 4. Infusoria
Subclass 1. Ciliata

Section 1. Aspirigera
Order I. Holotricha

Suborder 1. Astomata
Suborder 2. Gymnostomata
Suborder 3. Hymenostomata
Section 2. Spirigera

Order 1. Heterotricha
Suborder 1. Polytricha
Suborder 2. Oligotricha

Order 2. Hypotricha

Order 3. Peritricha
Subclass 2. Acinetaria (Suctoria)

In 1926 two new systems, proposed by Calkins (4) and Wenyon (23),
reflected several diff^erences of opinion in treatment of the Sarcodina,
Mastigophora, and Sporozoa. Wenyon's separation of the Cnidosporidia
from other Sporozoa as a group of equal rank apparently represents a
more realistic appraisal than that reflected in most classifications. In both
systems, the Chrysomonadida and Cryptomonadida appeared as separate
orders, and the Chloromonadida also in that of Calkins. ^Venyon's trans-
fer of the Cystoflagellata to the Zoomastigina is not generally favored. In
the Ciliata, Wenyon followed Minchin in stressing differences in ciliature
of the Holotrichida and the other orders. Wenyon retained the subphyla
Plasmodroma and Ciliophora, whereas Calkins advanced the Mastigo-
phora, Sarcodina, Sporozoa, and Infusoria to subphyla.

The system of Calkins (4):

Subphylum 1. Mastigophora

Class 1. Phytomastigoda
Order 1. Chrysomonadida
Order 2. Cryptomonadida
Order 3. Dinoflagellida
Order 4. Phyloinonadida
Order 5. Euglcnida
Order 6. Chloromonadida

Class 2. Zoomastigoda
Order 1. Pantastomatida
Order 2. Protomastigida
Order 3. Polymastigida
Order 4. Hypermastigida
Subphylum 2. Sarcodina

Class 1. Actinopoda
Subclass 1. Heliozoa
Subclass 2. Radiolaria

Class 2. Rhizopoda
Subclass 1. Proteomyxa
Subclass 2. Mycetozoa

The system of Wenyon (23):

Subclass 3. Foraminifera
Subclass 4. Amoebaea
Subphvium 3. Infusoria
Class 1. Ciliata

Order 1. Holotrichida
Order 2. Hcttrotrichida
Order 3. Oligotrichida
Order 4. Hypotrichida
Order 5. Peritrichida
Class 2. Suctoria
Subphylum 4. Sporozoa
Class 1. Telosporidia
Subclass 1. Gregarinida
Subclass 2. Coccidiomorpha
Order 1. Coccidia
Order 2. Haemosporidia
Class 2. Neosporidia

Subclass 1. Cnidosporidia
Subclass 2. Sarcosporidia

Subphylum 1. Plasmodroma

Class 1. Rhizopoda

Order I. Amoebida

Order 2. Heliozoa

Order 3. Radiolaria

Order 4. Foraminifera
Order 5. Mycetozoa
Class 2. Mastigophora

Subclass 1. Phytomastigina
Order 1. Chrysomonadina

no The Classification of Protozoa

Order 2. Chryptomonadina
Order 3. Dinoflagellata
Order 4. Euglenoidida
Order 5. Phytomonadida

Subclass 2. Zoomastigina
Order 1. Protomonadida
Order 2. Hypermastigida
Order 3. Cystoflagellata
Order 4. Diplomonadida
Order 5. Polymonadida
Class 3. Cnidosporidia

Order 1. Myxosporidiida

Order 2. Microsporidia
Class 4. Sporozoa

Subclass 1. Coccidiomorpha
Order 1. Coccidiida
Order 2. Adeleida

Subclass 2. Gregarinina
Order 1. Schizogregarinida
Order 2. Eugregarinida
Subphylum 2. Ciliophora
Group 1. Protociliata

Class 1. Opalinata
Group 2. Euciliata
Class 1. Ciliata

Subclass 1. Aspirigera

Order 1. Holotrichida
Subclass 2. Spirigera

Order 1. Heterotrichida
Order 2. Oligotrichida
Order 3. Hypotrichida
Order 4. Peritrichida
Class 2. Suctoria

In the later system of Doflein and Reichenow (8) the Heterochlorida
were added to the orders of Mastigophora, although the Phytomastigoda
(Phytomastigina) and Zoomastigoda (Zoomastigina) were not recognized
as subclasses. Addition of the Testacea increased the orders of Rhizopoda
to six. Several new groups of ciliates were recognized and the Order Spiro-
tricha was rescued, with modifications, from Biitschli's (2) system.

Subphylum 1. Plasmodroma
Class 1. Mastigophora

Order 1. Chrysomonadina
Order 2. Heterochloridina
Order 3. Cryptomonadina
Order 4. Dinoflagellata
Order 5. Euglenoidina
Order 6. Chloromonadina
Order 7. Phytomonadina
Order 8. Polymastigina
Order 9. Rhizomastigina
Class 2. Rhizopoda
Order 1. Amoebina
Order 2. Testacea
Order 3. Foraminifera
Order 4. Heliozoa
Order 5. Radiolaria
Order 6. Mycetozoa
Class 3. Sporozoa

Subclass 1. Telosporidia
Order 1. Gregarinae

Order 2. Coccidia
Order 3. Haemosporidia
Subclass 2. Cnidosporidia
Order 1. Myxosporidia
Order 2. Microsporidia
Subclass 3. Sarcosporidia
Subclass 4. Haplosporidia
Subphylum 2. Ciliophora
Class 1. Ciliata

Subclass 1. Protociliata
Subclass 2. Euciliata
Order 1. Holotricha
Order 2. Spirotricha

Suborder I. Heterotricha
Suborder 2. Oligotricha
Suborder 3. Entodiniomorpha
Suborder 4. Ctenostomata
Suborder 5. Hypotricha
Order 3. Peritricha
Order 4. Chonotricha
Class 2. Suctoria

The system of Kudo (15) suggested progressive changes in treatment
of the Sporozoa.

Subphylum 1. Plasmodroma
Class 1. Mastigophora

Subclass 1. Phytomastigina
Order 1. Chrysomonadida

Order 2. Cryptomonadida
Order 3. Dinoflagellida
Order 4. Phytomonadida
Order 5. Euglenoidida

The Classification of Protozoa HI

Order 6. Chloromonadida

Subclass 2. Zoomastigina
Order 1. Pantastomatida
Order 2. Protomonadida
Order 3. Polymastigida
Order 4. Hypermastigida
Class 2. Sarcodina

Subclass 1. Rhizopoda
Order 1. Proteomyxa
Order 2. Mycetozoa
Order 3. Foraminifera
Order 4. Amoebaea
Order 5. Testacea

Subclass 2. Actinopoda
Order I. Heliozoa
Order 2. Radiolaria
Class 3. Sporozoa

Subclass 1. Telosporidia
Order 1. Coccidia
Order 2. Haemosporidia

Order 3. Giegarinida
Subclass 2. Cnidosporidia
Order 1. Myxosporidia
Order 2. Actinomyxidia
Order 3. Microsporidia
Order 4. Helicosporidia
Subclass 3. Acnidosporidia
Order 1. Sarcosporidia
Order 2. Haplosporidia
Subphylum 2. Ciliophora
Class 1. Ciliata

Subclass 1. Protociliata
Subclass 2. Euciliata
Order 1. Holotrichida
Order 2. Heterotrichida
Order 3. Oligotrichida
Order 4. Hypotrichida
Order 5. Peritrichida
Class 2. Suctoria

In a later classification Calkins (5) omitted the Phytomastigophora, as
a group, from the Mastigophora, However, the Peranemidae, a family of
Euglenida, was transferred to the Protomonadida to contain Peranema
and several related genera. Other Peranemidae (such as Heteronema,
Anisonema, Dinema, and Entosiphon) were placed in the family Bodoni-
dae of the Protomonadida. The Mastigophora were divided into two
classes, Protomastigota (the Order Protomonadida) and Metamastigota.
The opalinid ciliates were reduced from a separate subclass (Protociliata)
to a family in the Astomida.

Subphylum 1. Mastigophora
Class 1. Protomastigota

Older 1. Protomonadida
Class 2. Metamastigota
Order 1. Hypermastigida
Order 2. Polymastigida

Suborder 1. Monokaryomastigina
Suborder 2. Diplokaryomastigina
Suborder 3. Polykaryomastigina
Subphylum 2. Sarcodina
Class 1. Actinopoda
Subclass 1. Heliozoa
Subclass 2. Radiolaria
Class 2. Rhizopoda

Subclass 1. Proteomyxa
Subclass 2. Mycetozoa
Subclass 3. Foraminifera
Subclass 4. Amoebaea
Order 1. Amoebida
Order 2. Testacea
Subphylum 3. Infusoria
Class 1. Ciliata

Subclass 1. Holotricha
Order 1. Astomida
Order g. Gymnostoniida

Subclass 2. Spirotricha
Order 1. Heterotrichida
Order 2. Oligotrichida
Order 3. Ctenostomida
Order 4. Hypotrichida
Subclass 3. Peritricha
Subclass 4. Chonotricha
Class 2. Suctoria
Subphylum 4. Sporozoa
Class 1. Telosporidia
Subclass 1. Gregarinina
Order 1. Eugregarinida
Order 2. Schizogregarinida
Subclass 2. Coccidiomorpha
Order 1. Coccidiida
Suborder 1. Eimeriina
Suborder 2. Haemosporidiina
Suborder 3. Babesiina
Order 2. Adeleida
Class 2. Cnidosporidia
Order 1. Myxosporidia
Order 2. Actinomyxidia
Order 3. Microsporidia
Class 3. Acnidosporidia

112 The Classification of Protozoa

In 1936 a list of subdivisions of the Protozoa, as generally favored
by a number of American protozoologists, was prepared for the American
Association for the Advancement of Science (18). This list of names, with
their authors, illustrates the multiple origins of current systems.

Phylum Protozoa Goldfuss 1820 em. von Siebold 1845
Subphylum 1. Plasmodroma Dofiein 1901
Class 1. Mastigophoia Diesing 18(55.

Subclass 1. Phytomastigophora Calkins 1909
Order 1. Chrysomonadida Stein 1878
Order 2. Heterochlorida Pascher 1912
Order 3. Cryptomonadida Stein 1878
Order 4. Dinoflagellida Butschli 1885
Order 5. Euglenida Blochmann 1895
Order 6. Chloromonadida Klebs 1892
Order 7. Phytomonadida Blochmann 1895
Subclass 2. Zoomastigophora Calkins 1909
Order 1. Pantastomatida Minchin 1912
Order 2. Protomastigida Klebs 1893
Order 3. Polymastigida Klebs 1893
Order 4. Hypermastigida Grassi 1911
Class 2. Sarcodina Hertwig and Lesser 1874 em. Biitschli 1880
Subclass 1. Rhizopoda von Siebold 1845

Order 1. Amoebida ClaparMe and Lachmann 1858
Order 2. Proteomyxa Lankester 1885
Order 3. Testacea Schultze 1854
Order 4. Foraminifera d'Orbigny 1826
Order 5. Mycetozoa de Bary 1859
Subclass 2. Actinopoda Calkins 1909
Order 1. Heliozoa Haeckel 1866
Order 2. Radiolaria Haeckel 1866
Class 3. Sporozoa Leuckart 1879

Subclass 1. Telosporidia Schaudinn 1900
Order 1. Gregarinida Lankester 1866
Order 2. Coccidiomorpha Doflein 1901
Suborder 1. Coccidia Leuckart 1879
Suborder 2. Haemosporidia Danilewsky 1886
Subclass 2. Cnidosporidia Dofiein 1901
Order 1. Myxosporidia Biitschli 1881
Order 2. Actinomyxidia Stole 1899
Order 3. Microsporidia Balbiani 1883
Subclass 3. Sarcosporidia Balbiani 1882
Order 1. Sarcosporidia Balbiani 1882
Order 2. Globidia Badudieri 1932
Subclass 4. Haplosporidia Caullery and Mesnil 1899
Subphylum 2. Ciliophora Doflein 1901
Class 1. Ciliata Perty 1852

Subclass 1. Protociliata Metcalf 1918

Order 1. Opalinata Stein 1867
Subclass 2. Euciliata Metcalf 1918
Order 1. Holotrichida Stein 1859

Suborder 1. Gymnostomina Biitschli 1889
Suborder 2. Trichostomina Biitschli 1889
Suborder 3. Astomina Minchin 1912
Order 2. Spirotrichida Biitschli 1889
Suborder 1. Heterotrichina Stein 1859

The Classification of Protozoa 113

Suborder 2. Oligotrichina Biitschli 1887

Suborder 3. Tintinnoina Claparede and Lachmann 1858

Suborder 4. Entodinioinorphina Reichenow 1929

Suborder 5. Hypotrichina Stein 1859
Order 3. Peritrichida Stein 1859
Order 4. Chonotrichida ^^'alIengren 1896
Class 2. Suctoria ClaparMe and Lachmann 1858

Pearse's report (18), in which the preceding names were listed,
strongly advocated adoption of the following endings for names of tax-
onomic groups: phylum, -a; subphylum, -a; class, -ea; subclass, -ia; order,
-ida; suborder, -ina. The obvious advantages of such imiformity, both to
professional taxonomists and to students, far outweigh any potential re-
strictions on creative license in formulating new taxonomic names. This
system of uniform spelling has been adopted in one recent classification
(13), and will be adhered to in the following chapters on taxonomy of the
Protozoa.

The writer will follow the system outlined below; this is similar to the
classification adopted by Jahn and Jahn (13).

Subphylum 1. Mastigophora

Class 1. Phytomastigophorea
Order 1. Chrysomonadida
Order 2. Heterochlorida
Order 3. Cryptomonadida
Order 4. Dinoflagellida
Order 5. Phytomonadida
Order 6. Euglenida
Order 7. Chloromonadida

Class 2. Zoomastigophorea
Order 1. Rhizomastigida
Order 2. Protomastigida
Order 3. Polymastigida
Order 4. Trichoraonadida
Order 5. Hypermastigida
Subphylum 2. Sarcodina

Class 1. Actinopodea
Order 1. Helioflagellida
Order 2. Heliozoida
Order 3. Radiolarida

Class 2. Rhizopodea
Order 1. Proteomyxida
Order 2. Mycetozoida
Order 3. Amoebida
Order 4. Testacida
Order 5. Foraminiferida
Subphylum 3. Sporozoa

Class 1. Telosporidea
Subclass I. Gregarinidia
Order 1. Eugregarinida
Order 2. Schizogregarinida
Subclass 2. Coccidia

Subclass 3. Haemosporidia
Class 2. Cnidosporidea
Order 1. Myxosporida
Order 2. Actinomyxida
Order 3. Microsporida
Order 4. Helicosporida
Class 3. Acnidosporidea
Subclass 1. Sarcosporidia
Subclass 2. Haplosporidia
Subphylum 4. Ciliophora
Class 1. Ciliatea

Subclass 1. Protociliatia

Order 1. Opalinida
Subclass 2. Euciliatia
Order 1. Holotrichida
Suborder 1. Astomina
Suborder 2. Gymnostomina
Suborder 3. Trichostomina
Suborder 4. Hymenostomina
Suborder 5. Thigmotrichina
Suborder 6. Aposloniina
Order 2. Spirotrichida

Suborder 1. Heterotrichina
Suborder 2. Tintinnina
Suborder 3. Oligotrichina
Suborder 4. Eiitodiniomorphina
Suborder 5. Hypotrichina
Suborder 6. Ctenostomina
Order 3. Peritrichida
Order 4. Chonotrichida
Class 2. Suctorea

114 The Classification of Protozoa

PROSPECTIVE SOURCES OF
TAXONOMIC DATA

As will be noted in Chapters 4-7, there are still many taxonomic
areas in which inadequate information makes disagreements unavoidable.
Since it becomes increasingly evident that superficial characteristics form
an inadequate foundation for a natural classification of Protozoa, present
differences of opinion cannot be reconciled completely until more is
known about the morphology, biochemistry, physiology, and life-cycles
of many species. Therefore, future progress will depend largely upon the
contributions of specialists working in different fields. Such details as
the finer structure of flagella, the organization of ciliary patterns and
peristomial areas in ciliates, distribution of the various types of chloro-
phyll and other pigments in flagellates, the composition of stored foods,
the structure of endoplasmic organelles, the organization of nuclei, and
the basic details of mitosis should all contribute to the development of
a less imperfect taxonomic system. The bearing of biochemical data on
taxonomic questions may prove to be very important. The determination
of minimal food requirements and the analysis of synthetic potentialities,
which are possible for species established in chemically defined bacteria-
free media, may yield clues to relationships now obscured by morphologi-
cal specializations. Taxonomists may even become concerned with such
matters as comparative data on digestive enzymes. For instance, the ob-
servation that Amoeba proteus (Chaos diffluens) and Pelomyxa caroUnen-
sis (Chaos chaos) are similar in their content of peptidase and catheptic
proteinase and are both quite different from Pelomyxa palustris (1), is
especially interesting in view of the disputes concerning their generic
status. And finally, a more thorough analysis of life-cycles is probably
essential for the satisfactory classification of various genera and families
whose taxonomic status is uncertain at present.

THE IDENTIFICATION OF
PROTOZOA

In beginning a study of the Protozoa, the student is often interested
in identifying species as they are encountered in the laboratory. Un-
fortunately, such identifications are not always easy, and are occasionally
impossible with the more readily available library facilities. There is no
comprehensive determinative manual for the Protozoa as a whole. Nor
is there available a complete manual for any of the four major groups
of Protozoa. As a result, the identification of a particular species some-
times becomes a problem for the specialist with extensive knowledge of
a certain taxonomic group. In some cases, as pointed out by Pringsheim
(19), the establishment of pure-line cultures from single organisms may
be a desirable, or even an essential step.

However, the existence of such difficulties does not mean that the
student should consider the task of identification a hopeless one. Many

The Classification of Protozoa 115

of the better known species are described recognizably in general taxa-
nomic works that are widely accessible. In addition, there are increasing
numbers of monographs dealing with single genera or families. It is only
in the areas not adequately covered by general monographs and not yet
touched by special surveys, that the protozoologist encounters major diffi-
culties. In such cases, identification of a species may involve a laborious
search through isolated and sometimes numerous papers dealing with
members of the genus in question.

For those who are beginning to cultivate an acquaintance with the
Protozoa, an illustrated key written by Jahn and Jahn (13) will prove
to be very helpful. The authors have explained the use of taxonomic keys
and have included instructive discussions of the criteria to be considered
in identifying members of the major groups. This key also will be useful
to the advanced student who has not specialized in taxonomy of the
Protozoa. For species not listed by Jahn and Jahn, more extensive taxo-
nomic works must be consulted. A number of these special monographs
are listed in Chapters IV-VII.

LITERATURE CITED

1. Andresen, N. and H. Holter 1949. Science 110: 114.

2. Biitschli, O. 1880-1889. "Protozoa" in Bronn's Klassen und Ordnungen des Thier-

reiclis (Leipzig).

3. Calkins, G. N. 1901. The Protozoa (New York: Columbia Press).

4. 1926. The Biology of the Protozoa (Philadelphia: Lea & Febiger).

5. 1933. The Biology of the Protozoa, 2d ed. (Philadelphia: Lea & Febiger).

6. Caiman, W. T. 1949. The Classification of Animals: an Introduction to Zoological

Taxonomy (New York: J. Wiley & Sons).

7. Doflein, F. 1902. Arch. f. Protistenk. 2: 169.

8. and E. Reichenow 1927-1929. Lehrbuch der Protozoenkunde (Jena: G.

Fischer).

9. Dujardin, F. 1841. Histoire naturelle des zoophytes (Paris).

10. Ehrenberg, C. G. 1838. Die Infusionsthierchen als volkommene Organismen

(Leipzig).

11. Goldfuss, G. A. 1820. Handbuch der Zoologie (Niirnberg).

12. Hartmann. M. 1907. Arch. f. Protistenk. 10: 139.

13. Jahn, T. L. and F. F. Jahn 1949. How to Knoiv the Protozoa (Dubuque: W. C.

Brown Co.).

14. Kent, W. S. 1880-1882. A Manual of the Infusoria; including a description of all

known flagellate, ciliate and tentaculiferous Protozoa, British and foreign, and
an account of the organization and affinities of the sponges (London).

15. Kudo, R. R. 1931. Handbook of Protozoology (Springfield: Thomas).

16. Minchin, E. A. 1912. An Introduction to the Study of the Protozoa (London:

Arnold).

17. Miiller, O. F. 1786. Animalcula infusoria fiuviatilia et marina (Havniae et Leipzig).

18. Pearse, A. S. 1936. Zoological Names. A List of Phyla, Classes and Orders (Durham:

Duke University Press).

19. Pringsheim, E. G. 1949. Pure Cultures of Algae. Their Preparation and Maintenance

(Cambridge).

20. Siebold, C. T. E. and H. Stannius v. 1845. Lehrbuch der vergleichende Anatomic,

H. 1.

21. Stein, S. N. F. v. 1859-1883. Der Organismus der Infusionsthiere (Leipzig).

22. Swezy, O. 1916. Univ. Calif. Publ. Zool. 16: 185.

23. Wenyon, C. M, 1926. Protozoology (London: Balli^re, Tindall & Cox),

IV

The Mastigophora

Class 1. Phytomastigophorea
Order 1. Chrysomonadida

Suborder 1. Euchrysomonadina
Family I. Chromulinidae
Family 2. Syncryptidae
Family 3. Ochromonadidae
Family 4. Prymnesiidae
Suborder 2. Silicoflagellina
Suborder 3. Coccolithina
Suborder 4. Rhizochrysodina
Family 1. Rhizochrysidae
Family 2. Myxochrysidae
Suborder 5. Chrysocapsina
Family 1. Chrysocapsidae
Family 2. Celloniellidae
Family 3. Hydruridae
Family 4. Nageliellidae
Order 2. Heterochlorida

Suborder 1. Euheterochlorina
Suborder 2. Rhizochloridina
Suborder 3. Heterocapsina
Order 3. Cryptomonadida
Family 1. Cryptochrysidae
Family 2. Cryptomonadidae
Family 3. Nephroselmidae
Order 4. Dinoflagellida
Suborder 1. Prorocentrina
Suborder 2. Gymnodinina
Family 1. Protonoctilucidae
Family 2. Gymnodiniidae
Family 3. Polykrikidae
Family 4. Noctilucidae
Suborder 3. Peridinina
Family 1. Glenodiniidae
Family 2. Gonyaulacidae
Family 3. Peridiniidae
Family 4. Ceratiidae
Family 5. Dinophysidae
Family G. Heterodiniidae
Suborder 4. Dinocapsina
Suborder 5. Dinococcina
Family 1. Phytodiniidae
Family 2. Blastodiniidae
Family 3. Ellobiopsidae
Order 5. Phytomouadida
Family 1. Polyblepharidae

Family 2. Chlamydomonadidae
Family 3. Haematococcidae
Family 4. Phacotidae
Family 5. Spondylomoridae
Family 6. \'olvocidae

Order 6. Euglenida

Suboider 1. Euglenoidina
Suborder 2. Peranemoidina
Suborder 3. Petalomonadoidina

Order 7. Chloromonadida

Class 2. Zoomastigophorea
Order 1. Rhizomastigida
Order 2. Proiomastigida
Family 1. Codosigidae
Family 2. Phalansteriidae
Family 3. Trypanosomidae
Family 4. Cryptobiidae
Family 5. Amphimonadidae
Family 6. Bodonidae
Order 3. Polymastigida
Family 1. Trimastigidae
Family 2. Tetramitidae
Family 3. Streblomastigidae
Family 4. Retortomonadidae
Family 5. Callimastigidae
Family 6. Polymastigidae
Family 7. Pyrsonymphidae
Family 8. Hexamitidae
Order 4. Trichomonadida

Family 1. Monocercomonadidae
Family 2. Dcvescovinidae
Family 3. Calonymphidae
Family 4. Trichomonadidae
Order 5. Hypermastigida
Suborder 1. Lophomonadina
Family 1. Lophomonadidae
Family 2. Joeniidae
Family 3. Kofoidiidae
Suborder 2. Trichonymphina
Family I. Hoplonymphidae
Family 2. Staurojoeninidae
Family 3. Holomastigotidae
Family 4. Trichonymphidae
Family 5. Teratonymphidae

Literature cited

116

The Mastigophora 117

T„

HE Mastigophora possess flagella at some stage of the life-
cycle, although many develop pseudopodia and show amoeboid activity.
The group may be divided into two classes, Phytomastigophorea and
Zoomastigophorea.

CLASS 1. PHYTOMASTIGOPHOREA

The phytoflagellates range from typical plants to forms whose
affinities with animals are more apparent, and some genera have even
occupied positions in both the Phytomastigophorea and the Zoomasti-
gophorea in different systematic treatises. The majority possess chroma-
tophores which contain chlorophyll, although the green color may be
masked to some extent by other pigments. The rest of the phytoflagellates
are colorless. Some differ from their pigmented homologues mainly in the
lack of chromatophores, and in certain instances, both colorless and pig-
mented species belong to the same genus. At the other extreme, certain
predominantly holozoic species have developed new organelles which
assist in feeding.

Life-cycles may involve dimorphism, sometimes with alternation of
amoeboid and flagellate stages, or flagellate and palmella stages. Sexual
phenomena are well known in Phytomonadida and have been reported
occasionally in certain other orders (Chapter II).

The Phytomastigophorea^ may be divided into the following orders:

(1) Chrysumonadida: usually one or two flagella, sometimes three; typ-
ically with one or two, biu sometimes more chromatophores ranging from
golden-yellow to greenish-yellow or brown; a few genera lack chromato-
phores: no cytopharynx or "reservoir" is present; the cyst wall is typically
siliceous and contains a pore; encystment is endogenous; stored reserves
include leucosin and lipids, but no starch; many species are naked, some
secrete a lorica or test, others are enclosed in a membrane to which silice-
ous scales or calcareous elements (coccoliths) are added; the majority are
solitary, but some genera develop arboroid or spheroid colonies.

(2) Heterochlorida: typically naked, with two unequal flagella; one
to a dozen or more chromatophores, pale yellow-green, or sometimes pale
yellow; no cytopharynx; reserves include leucosin and lipids, but no
starch; the cyst wall, which may contain two layers, lacks a pore; encyst-
ment is endogenous, as in Chrysomonadida.

(3) Cryptomonadido: biflagellate; pellicle usually restricts changes in

^ From the botanical standpoint, the Class Phytomastigophorea is a somewhat artifi-
cial arrangement of certain algal groups. As considered in the present chapter, the
Chrysomonadida represent part of the algal Class Chrysophyceae, the Phytomonadida
correspond to the Order Volvocales of the Class Chlorophyceae, and the Dinoflagellida
to the Class Dinophyceae. A modern discussion of the phytoflagellates as algae has been
published by Smith (260).

118 The Mastigophora

form of the body, which often shows dorso- ventral differentiation; some
genera have an open ventral "pharyngeal" groove; in others the groove is
closed, posteriorly or throughout its length, to form a pouch; refractile
granules ("trichocysts") usually lie just beneath the wall of the groove
or pouch; there may be a single bilobed chromatophore or two or more
chromatophores which are usually brown, less commonly red, blue, blue-
green, or green; starch and lipids are stored.

(4) Dinoflagellida: biflagellate forms, typically with two grooves, a
transverse girdle and a longitudinal sulcus in the body wall or theca; one
of the flagella typically lies in the girdle; chromatophores, when present,
are usually golden-brown to dark-brown, sometimes green or bluish-green;
starch and lipids are stored.

(5) Phytomonadida: except in one family, there is a distinct membrane
of cellulose or pectins, or a test impregnated with calcium or iron salts;
usually two or four, sometimes eight flagella; there is often a single cup-
shaped chromatophore; one or more pyrenoids are usually present; chloro-
phyll typically is not masked by other pigments; starch and lipids are
stored; red haematochrome accumulates in some species.

(6) Euglenida: relatively large forms, usually with one or two flagella
arising from an anterior reservoir ("gullet"); pellicle may be flexible or
relatively rigid; green chromatophores, usually numerous and equipped
with pyrenoids; reserves include paramylum and lipids; some species
accumulate red haematochrome.

(7) Chloromonodida: typically biflagellate, one flagellum trailing; the
body is often flattened dorso-ventrally, with a shallow groove on the
ventral surface; presence of a cytopharynx, reported for some species, has
been denied (232); chromatophores, when present, are typically numerous
and grass-green (or "meadow-green"); no stigma is reported; lipids are
stored.

Order 1. Chrysomonadida

This group, represented by fossils from Upper Cretaceous to recent
deposits, is widely distributed in salt, brackish and fresh water. Although
chromatophores occur in the majority, colorless holozoic species are com-
mon and there is a marked trend toward holozoic nutrition in many pig-
mented types. Formation of pseudopodia is fairly common. Some species
possess delicate pseudopodia which superficially resemble the myxopodia
of Foraminiferida and capture food in comparable fashion. Others form
lobopodia. Non-flagellated amoeboid and palmella stages are not unusual
and have become the dominant phase in some life-cycles. Most species
measure less than 50[j, and the majority probably less than half as much,
although some fossils exceed 100[x. One, two, or three flagella may be
present; if two, they may be equal or unequal in length. Mastigonemes

The Mastigophora H9

(pantonematic pattern) have been reported on the flagellum, or on one of
two flagella (200).

In the simpler species a thin periplast permits moderate amoeboid
activity. Cortical specialization has followed several trends: (1) the de-
position of a secreted layer just outside the periplast; (2) development
of a lorica (Fig. 4. 2, A, F) or a test (Fig. 4. 2, C, D); (3) development of

Fig. 4. 1. A. Ochromoyias granularis Doflein, showing nucleus and
stored lipids; chromatophore omitted; x2100 (after D.). B. Chromulina
annulata Conrad; ribbon-like chromatophore, mass of leucosin; x3000
(after C). C. Ochromonas reptans Conrad; two chromatophores, leucosin
granules; x2250 (after C). D. O. granularis, typical chromatophore, mod-
erate leucosin; x2025 (after Doflein). E. O. granularis, chromatophore dis-
placed by large mass of leucosin; xl875 (after Doflein). F. Chromulina
commutata Pascher, narrow chromatophore, leucosin granules; xl400
(after P.). G. Unusually large chromatophore in Ochromonas sp.; schematic
(after Pascher). H, I. Chrysapsis fenestrata Pascher, posterior and lateral
views of net-like chromatophore; x2100 (after P.). J. Ochromonas pinguis,
large chromatophore, peripheral zone of lipoid globules; x2500 (after
Conrad).

120 The Mastigophora

a siliceous skeleton (Fig. 4. 9). The simplest type of secreted covering is
represented by the layer of "mucus" in Monas (Fig. 4. 3, E, F). Secreted
membranes may be thin, or they may be quite thick as in some of the
Coccolithina (Fig. 4. 2, K). Siliceous scales (Fig. 4. 2, G) or calcareous
coccoliths (Fig. 4, 10) are added to the membrane in various genera. In

Fig. 4. 2. A. Dmobryon utriculus Stein, single loricate flagellate; x700
(after Pascher). B. Hyalobryon voigtii Lemmermann, a single flagellate
(colony shown in Fig. 1. 2, C); xlSOO (after Pascher). C. Cfnysococcus umbo-
natus with test; xl845 (after Conrad). D. Pseudokephyrion mmutissimum
Conrad, test only; x3000 (after C). E. Dinobryon stokesii Lemmermann,
single lorlca; x960 (after Pascher). F. Single lorica of Hyalobiyon lauterbornii
Lemmermann; x810 (after Pascher). G. Mallomonas dentata Conrad, chroma-
tophore, covering of siliceous scales (some bearing spines); x2500 (after C).
H. Stokesiella lepteca (Stokes) Lemmermann; xl045 (after S.). L Kephyrion
spirale (Lackey) Conrad, test only; x4500 (after C). J. Derepyxis amphora
Stokes; x880 (after S.). K. Syracosphaera mediterranea Lohmann, shell mem-
brane after dissolution of coccoliths in acid; single chromatophore; basal por-
tions of the two equal flagella; x2100 (after L.).

The Mastigophora 121

some cases the inorganic elements apparently are adherent to the "shell-
membrane"; in others, they are embedded in the membrane (46, 186).

Chromatophores (Fig. 4. 1, B-J) range from the network of Chrysapsis
fenestrata to a broad plate or a narrow ribbon. In addition to the usual
colors — golden-yellow to greenish-brown or brown — blue chromatophores
have been reported (173). Pigments include chlorophyll a, lutein (a
xanthophyll) and ^-carotene. Supposed pyrenoids have been noted in
some species but not in many others. A stigma may or may not be present
in chlorophyll-bearing forms. Species within a genus, such as Chromulina,

Fig. 4. 3. A-D. Ochromonas granulans (after Doflein). A. Specimen with
three food vacuoles, chromatophore, leucosin; xl650. B. Temporarilv at-
tached form just after ingestion of food; x2100. C. An amoeboid form just
after ingesting a bacillus; x2025. D. Nucleo-flagellar connections; x2100. E, F.
Monas vestita, during and after ingestion of food; note stigma and outer layer
of "mucus" with radiating strands; xl800 approx. (after Reynolds). G. Oiko-
monas termo (Ehrbg.) Kent, ingestion of a bacterium just completed; xl600
(after Lemmermann).

122 The Mastigophora

apparently may differ in this respect. Some colorless species (Fig. 4. 3, E)
also have a stigma. Scattered granules, similar in color to the stigma, have
been reported in Dinobryon, Mallomonas, and other genera (247).

Solid food is ingested by certain pigmented species as well as colorless
types (Fig. 4. 3), and ingestion often involves formation of a food-cup
in a particular region. Refractile granules of leucosin (Fig. 4. 1, B-F) and

Fig. 4. 4, Apochlorotic colonial types. A, B. Cladonema pauperum
Pascher; portion of colony and a single flagellate; schematic (after P.). C, D.
Codoiwdendrnn ocellatum Pascher; portion of the Diuobryon-\i\^e colony,
and a single flagellate showing stigma and ingested food; schematic (after
P.). E, F. Monadodendrnn distans Pascher; portion of a colony and a single
flagellate; schematic ('after P.).

globules of oil or fat (Fig. 4. 1, A) are stored. Leucosin is sometimes con-
sidered a polysaccharide but its chemical nature has not been determined.
Colonial organization is fairly common. Arboroid types include Hyalo-
bryon (Fig. 1. 2), Dinobryon, Codonodendron (Fig. 4. 4, C) and certain
other loricate genera and also such naked forms as M onadodendron (Fig.
4. 4, E) and Cladonema (Fig. 4. 4, A). Spheroid colonies are developed in
Synura (Fig. 4. 5, C), Cyclonexis (Fig. 4. 5, A, B), Syncrypta (Fig. 1. 2, F)
and ChrysosphaereJla (Fig. 4. 5, D), among others.

The Mastigophora 128

Life-cycles often include palmella or amoeboid stages. Species such as
Ochromnnas granularis (66) may become amoeboid (Fig. 4. 3, C) without
losing the fiagella. Amoeboid and flagellate phases occur in Chrysamoeba
radians (66) and Myxochrysis paradoxa (203); in the latter (Fig. 4. 6,
A-C), the amoeboid stage develops into a large plasmodium. A palmella is
dominant in life-cycles of the Chrysocapsina; an amoeboid phase, in the
Rhizochrysodina.

Endogenous formation of a siliceous cyst wall is characteristic (247). As

Fig. 4. 5. A, B. CycJonexis annularis Stokes, lateral and surface views; x720
(after S.). C. Synura uvella Ehrbg.; x310 (after Stein). D. Chrysosphaerella
longispina Laiiterborn; x540 (after L.).

encystment begins in Uroglena sonaica (Fig. 4. 7, H-J) the fiagella are
resorbed and the organism, packed with fat globules, becomes approxi-
mately spherical. Within the cytoplasm, a thin membrane is laid down.
This membrane gradually increases in thickness, a pore is differentiated,
and surface decorations are added. The development of a plug finally
closes the pore, separating the endocystic from the subsequently discarded
ectocystic protoplasm (50). The plug may or may not be siliceous in dif-
ferent species. In either case, the ping is either dislodged or dissolved in
excystment. Encystment in Ochromo7ias granularis (66) resembles that in
Uroglena. In certain other types, such as Chromulina (67), part or all

124 The Mastigophora

of the external cytoplasm is drawn into the cyst before the pore is plugged.
Binucleate cysts, described in Dinobryon divergens (Fig. 4. 7, D-F), appar-
ently are the result of nuclear division just before encystment (92). The
mature cyst (Fig. 4. 7) is approximately spherical, but the external appear-

Fig. 4.6. A-C. Myxochrysis pnradoxa; flagellate phase (B) and stages in
development of the plasniodiuni; xI6()0 (after Pascher). D-F. Kremastochrysis
pendens Pascher; non-flagellated forms suspended from the umbrella-like
float, and a flagellate stage; schematic (after P.) G. Formation of slender
pseudopodia in Dinobryon sertularia; diagrammatic (after Pascher). H. Gleo-
cystis-stage in D. sertularia; diagrainmatic (after Pascher).

ance varies with the presence or absence of surface decorations and a
collar around the pore.

Following suggestions of Pascher (214), five suborders may be recog-
nized: Euchrysomonadina, with a dominant flagellate stage; Silicoflagel-
lina, with a siliceous skeleton; Coccolithina, with a peripheral zone of
coccoliths; Rhizochrysodina, with a dominant amoeboid or plasmodial
stage; Chrysocapsina, with a dominant palmella.

The Mastigophora 125

Fig. 4. 7. A. Cyst of Cladonema pauper urn; diagrammatic (after
Pascher). B. Cvst of Ochromouas reptans; x2250 (after Conrad). C. Cyst of
Cellionella palensis; diagrammatic (after Pascher). D-F. Dinohryon diver-
gens; completion of nuclear division (D) is sometimes followed li\ encvst-
ment (E) to produce a binucleate cyst (F); xl2I0 (after Geitler). G. Cvst of
Ochromonas ludibunda: xl500 (after Conrad). H-J. Stages in development
of the cyst wall in Uragleiia snniara; diagrammatic (after Conrad).

Suborder 1. Euchrysomonadina. On the basis of flagellar equipm-nt
four families have been erected: Chromulinidae, with one flagelltun.
Syncryptidae, with two equal flagella; Ochromonadidae, with one long
and one short fiagellum; and Prymnesiidae, with three flagella.

Family 1. Chromulinidae. This group includes solitary and colonial
types. The type genus, Chromulina Cienkowski (67), contains small
naked flagellates with one band-like chromatophore or two smaller ones
(Fig. 4. 1, B, F). Amoeboid changes in form are observed in some species.

Solitary types without a lorica or test are assigned to Chromulina and several addi-
tional genera: Amphichrysis Korshikoff (165); Chrysapsis Pascher (202; Fig. 4. 1, H, I);

126 The Mastigophora

Clirysogleyia Wislouch (207); and the colorless Oikomonas Kent (181; Fig. 4. 3, G).
Cyrtophora Pascher and Pedinella AV^ysotzki contain stalked sessile forms (202). In
Epicysiis Pascher (211), there is an epiphytic non-flagellated phase and a Chromulina-
like stage. In Pyrainidochrysis Pascher, the firm membrane is decorated with three
longitudinal flanges, while that of Mihroglena Ehrenberg contains numerous granules
(202). These granules may be analogous to the cortical inclusions of Ochromonas
pingitis (Fig. 4. 1, J), or possibly represent primitive coccoliths.

Solitary loricate forms include: Bicoeca Clark, without chromatophores (181); Chryso-
coccocystis Conrad (47); LepochromuUna Scherffel (202); Histiona Voigt, colorless forms
with a stalked lorica (225); and Palatinella Lauterborn, with several slender pseudopodia
("tentacles") sunounding the flagellum (202).

A test (or "shell") is present in the following: Chrysococcus Klebs (174; Fig. 4. 2,
C), swimming types with a spheroid to ovoid test; Kepfiyrion Pascher (Fig. 4. 2, I),
tests with a recognizable neck (51).

Siliceous plates cover much or all of the body in Mallomouas Perty and Chryso-
sphaercUa Lauterborn. Mallomonas (Fig. 4. 2, G) includes about sixty species (45, 48),
differing in shape and arrangement of the scales, and in the presence or absence of
spines. Chrysosphaerella (Fig. 4. 5, D) includes .spheroid colonial forms. "Pseudomallo-
monas Chodat" apparently falls within the limits of the genus Mallomonas (48).

Loricate colonial types without chlorophyll are included in Codonodendron Pascher
(Fig. 4. 4, C, D) and Stephauocodon Pascher (224). In the latter, the simple four- or
eight-rayed colonies are formed by the adherence of loricae near their basal ends. Also,
Poteriodendron Stein may belong in this group (93).

Family 2. Syncryptidae. Two flagella of equal length are characteristic.
Syncrypta Ehrenberg (Fig. 1. 2, F) includes spherical colonies with the
flagellates embedded in a granular matrix (202). In Chlorodesmiis Phil-
lips (202), pairs of flagellates, adherent basally, are aligned in simple
band-like colonies. The cortex is decorated with spines, perhaps similar
to the siliceous scales of Synura. Derepyxis Stokes (Fig. 4. 2, J) includes
solitary loricate types (202, 207).

Family 3. Ochromonadidae. This group, like the Chromulinidae, in-
cludes both solitary and colonial forms. Ochromonas Wysotzki (Fig. 4. 1,
A, C, D-F) contains flagellates with a flexible periplast permitting changes
in shape and sometimes the formation of a temporary protoplasmic
"stalk" (Fig. 4. 3, B). A detailed cytological description is available for
Ochromonas graniilaris Doflein (66). The colorless homologue of Ochro-
monas, the genus Monas Miiller (including Sterromonas Kent and
Physomonas Kent) contains at least 13 species (243), some of which have
a stigma. The periplast of Monas vestita (Stokes) Reynolds is enclosed
in a mucous envelope from which radiate slender mucotis threads (Fig.
4. 3, E, F).

Additional solitary non-loricate types are assigned to the following genera: Ochry-
ostylon Pascher, usually sessile with, or sometimes without, a delicate stalk (222);
StomatocJione Pascher, colorless, usually sessile with a short protoplasmic stalk (222);
Kremastochrysis Pascher (Fig. 4. 6, D-F), with an Ochromoiias-Mke flagellate stage and
a dominant non-flagellated form attached to a float which suspends the organism from
the surface of the water (223).

Solitary loricate types are included in several genera. The lorica of the sessile
Epipyxis Ehrenberg resembles that in the colonial Dinobryon (Fig. 4. 2, A). A stalked
Dmobryon-type lorica is characteristic of Stylnpyxis Bolochonzew (202) and the color-

The Mastigophora 127

less Stokesiella (210; Fig. 4. 2, H). A cup-shaped to spheroid lorica bears a slender
stalk in Arthrochrysis Pascher (222) and the colorless Arthropyxis (222). The stalked
lorica of Poteriochromonas Scherffel (202) is funnel-shaped; that of Stenocodon Pascher
(222) is compressed laterally, with an oval mouth. The stalkless lorica of Pseudo-
kephyrion Pascher (Fig. 4. 2, D) — including "Kcphyriopsis Pascher and Ruttner" — is
cup-shaped.

Arboroid colonies of loricate flagellates arc included in Dinobryon Ehrenberg (1,
202; Fig. 4. 2, A) and its colorless homologue, Hyalobryon Lauterborn (202; Fig. 4. 2,
B). In the apochlorotic Codonobotrys Pascher (222). a cluster of individually stalked
loricate flagellates is attached to a heavy common stalk. Stylobrynn Fromentel (181),
another colorless type, probably belongs to the Ochromonadidae.

Non-loricate arboroid colonies are assigned to several genera. In Anthophysis Bory
and Ceplialothamnion Stein, both colorless genera, the flagellates are attached in
clusters at the ends of branching stalks (181). In the colorless Cladonema Kent em.
Pascher (Fig. 4. 4, A), MonadodendroJi Pascher (Fig. 4. 4, E, F), and Dendromonas
Stein (181), as well as in the pigmented Chrysodendron Pascher (207) which often
forms small colonies, the flagellates are attached singly to branches of the stalk.

More or less spherical colonies are characteristic of several genera. In Uroglena
Ehrenberg, including Uroglenopsis (181), the flagellates are embedded in a gelatinous
matrix (50). No matrix is evident in Cyclonexis Stokes (Fig. 4. 5, A, B), Skadovskiella
KorshikofE (163. 165), Synochromonas Korshikoff (165), or Synura Ehrenberg (165;
Fig. 4. 5, C).

Fig. 4. 8. Prymnesiidae. A. Prymnesium parvum Carter;
x2360 (after C). B, C. Platychrysis pigra Geitler, flagellate and
amoeboid stages; xl850 (after Carter). D. ChrysochromiiUna
parva Lackey; x3200 approx. (after L.).

Family •/. Prymnesiidae. These flagellates have three flagella and a
rather plastic body. Prymyiesiiwi Massart (Fig. 4. 8, A) has a short in-
active median flagellum and two long ones, and usually two yellow-green
to brown chromatophores. Platychrysis Geitler (Fig. 4. 8, B, C) shows both
amoeboid and flagellate stages. The flagella of the latter resemble those of
Prymnesium, but are coiled and apparently inactive in the amoeboid
stage (31). In Chrysochromulina Lackey (174; Fig. 4. 8, D) the median
flagellum is longer than the other two, which are usually trailed in
swimming.

128 The Mastigophora

An interesting occurrence of Prymnesium pai-viim has been reported
in brackish fish-ponds in Palestine. Populations of the flagellates reached
500,000/ml. or more, changing the color of the water to a yellowish-
brown and resulting in death of many fish (241).

Suborder 2. Silicoflagellina. These widely distributed marine flagellates
occur also as fossils from Upper Cretaceous to recent deposits. Their
taxonomic position was in doubt until Borgert (124) discovered the
flagellum and assigned them to a new group, the Silicoflagellata. Their

Fig. 4. 9. Silicoflagellina. A-H. Skeletons of various species (after De-
flandre). A. Dictyocha crux, x560. B. D. octonaria, x560. C. D. triacantha
Ehrbg. from Tertiary, x345. D. D. navinda Ehrbg. from Tertiary, x345.
E. Vallacerta hortoni Hanna from Upper Cretaceous, x540. F. Dictyocha
speculum Ehrbg. from Tertiary, x630. G. D. polyactis Ehrbg. from Ter-
tiary, x630. H. D. fibula Ehrbg., x560. I. D. speculum, showing nucleus,
chromatophores, and internal skeleton; xl320 (after Deflandre).

The Mastigophora 129

characteristic siliceous skeleton varies in complexity in difierent species
and has been interpreted as an external structure and as an internal
one (Fig. 4. 9, I) by different workers (63). A single flagellum, numerous
greenish-brown chromatophores, and stored granules of leucosin appear
to be typical.

Generic boundaries have been disputed to some extent. However,

^J^

Fig. 4. 10. Coccolithina. A. Discosphaera tubifer (Murray and Black-
man) Lohmann: schematic optical section showing rhabdoliths and two
chromatophores; x2800 (after L.). B. Single rhabdolith from Rhabdo-
sphaera claviger M. and B.; schematic (after Murray and Blackman). C.
Rhabdosphaera stylifer Lohmann, showing nucleus and two chromato-
phores; x2100 (after L.). D. Surface view of placolith from Coccolithus
wallichi; x2700 (after Lohmann). E. Optical section of coccolith from Coc-
colithus pelagica; schematic (after Murrav and Blackman). F. Coccolithus
ivallichi showing arrangement of coccoliths; xl800 (after Lohmann). G.
Hymenomonas roseola Stein; xT'jO (after Pascher). H. Longitudinal section
of rhabdolith from Discosphaera tubifer; schematic (after Lohmann). L
Syracosphaera pulchra. anterior coccoliths with spines; xl900 (after Loh-
mann).

130 The Mastigophora

Lyramula Hanna and Vallacerta Hanna (Fig. 4. 9, E) seem to be limited
to fossils from the Upper Cretaceous (101), while Dictyocha Ehrenberg
(Fig. 4. 9, AD, F-I) includes both living and fossil types. According to
Deflandre (63), three generic names — Cannophilus, Distephanus, and
Mesocena — have been applied to forms which fall within the genus
Dictyocha.

Suborder 3. Coccolithina. These flagellates occur mostly in salt and
brackish water; only a few are known from fresh water (46). Collections
in the Mediterranean (186) have yielded specimens from depths of 400
meters, but the flagellates are most abundant in the zone above 100
meters. Two flagella of equal length have been observed most frequently.
However, a few supposedly uniflagellate types have been reported; also
flagella have not yet been seen in some described species. Either two or
four chromatophores may be present (179). Little is known about the
life-cycles. Schiller (250) has noted in two species of Calyptrosphaera
stages which suggest fission within the theca, and he has pointed out
the need for study of the Coccolithina in cultures.

The diagnostic feature of the group is the possession of calcareous
coccoUths which may be deposited at the surface of, or embedded within,
a secreted membrane (Fig. 4. 2, K). Several types of coccoliths (186, 250)
are known. Solid platelets (discoliths), with or without spines, are found
in Syracosphaera (Fig. 4. 10, I), Pontosphaera, and related genera. Per-
forated coccoliths {tremaliths) are of various kinds. Elongated trema-
liths containing a long canal are known as rhabdoUths (Fig. 4. 10, A, B),
while simple perforated plates or double discs joined by a short canal
are called placoliths (Fig. 4. 10, D). Structme of the coccoliths has been
used as a basis for differentiating several families (127).

Representative genera include Acantltoica Lohinann (46, 250), Calyptrosphaera Loh-
mann (250), Coccolithus Schwarz (Fig. 4. 10, F), Deutschlandia Lohmann (250), Dis-
cosphaera Haeckel (250; Fig. 4. 10, A), Halopappus Lohmann (250), Hymenomonas
Stein (127, 174; Fig. 4. 10, G), Pontosphaera Lohmann (186, 260), Rhabciosphaera
Haeckel (250; Fig. 4. 10, C), Syracosphaera Lohmann (31, 186, 250), and Umbilicosphaera
Lohmann (186).

It is uncertain whether Hymenomonas actually belongs in this group. A pitted "shell"
has been reported in H. roseola Stein (174), although discrete coccoliths have been
described in H. dariubiensis (127).

Suborder 4. Rhizochrysodina. The amoeboid phase is dominant. In
the Rhizochrysidae, the amoeboid stages are solitary or else form loose
aggregates with pseudopodial attachments. Genera which develop true
Plasmodia are placed in the Myxochrysidae.

Family 1. Rhizochrysidae. Net-like aggregates of naked organisms (221)
are produced in Rhizochrysis Pascher (Fig. 4. 11, E) Chrysarachnion
Pascher (Fig. 4. 11, G), and the apochlorotic Lenkapsis Pascher. Similar
aggregates of thecate organisms (221) are formed in Heliapsis Pascher

The Mastigophora 131

7\ \ >v /

\:'-;\ \r:^>/ /,:^'Nvi V,^;?

B

^^^^i

^'T-

,^^*

w ..•>'^""

'•;

'^

^ w

A ''

Fig. 4. 11. Rhizochrysodina. A. Heliapsis mutabilis Pascher, x550 approx.
(after P.). B. Cl>r\'sidiastntm catenatutti Lauterborn, x810 (after Pascher).
C. Heliochrysis erodians Pascher, xl380 approx. (after P.). D. H. sphagnicola
Pascher, parasitic stage; x610 approx. (after P.). E. Rhizorhrysis planktonica,
xl400 (after Pascher). F. Hetcrolag\uion oedogonii Pascher, x3300 (after P.).
G. Chrysarachnion insidians Pascher; diagrammatic (after P.). H. Lagynion
subovatiim Prescott and Croasdale; x665 (after P. &: C).

(Fig. 4. 11, A). Chrysidiastrum Lauterborn (Fig. 4. 11, B) shows a strong
tendency to produce chains instead of definite nets.

The family also contains a number of solitary types. Chrysamoeba Klebs inchidcs
naked amoeboid forms with a Chromulina-like flagellate stage, as in C. radians (66).
Thecate species are assigned to several genera. Hcterolagynion Pascher (Fig. 4. 11, F)
includes epiphytic forms, the lorica of which lacks a neck like that in Lagynion (201,
211; Fig. 4. 11, H). Eleuthcropyxis Scherffel (248), Plagiorhiza Vascher, Platytheca
Stein, Kybotion Pascher, and the colorless Leuknpyxis Pascher resemble Lagynion and
Hetcrolagynion in that pseudopodia emerge through a single opening in the lorica

132 The Mastigophora

(221). In Diporidion Pascher and Porostylon Pascher, there are two pores in the lorica,
which bears a stalk in the latter genus (220). In Heliochrysis Pascher (Fig. 4. II, C,
D), intracellular parasites of Sphagnum, as well as in the similar Heliaktis Pascher,
Chrysocriniis Pascher, and Stephanoporos Pascher. the spheroid to ovoid theca contains
a number of pores through which slender pseudopodia extend (220).

Family 2. Myxochrysidae. In the life-cycle of Myxochrysis Pascher
(203), a Chromuli)ia-\ike flagellate becomes an amoeboid stage which

Fig. 4. 12. Chrysocapsina. A-E. Celloniella pale?isis (after Pascher). A.
Branching palmella in flowing water, xlO. B. Bladder-like stage attached to
stones in dripping water. C. Tip of branch of palmella, highly magnified. D.
Amoeboid stage. E. Flagellate stage (C-E, diagrammatic). F. NagelieUa natam
Scherffel, x4o6 approx. (after S.).

develops into a plasmodium (Fig. 4. 6, A-C). The mature plasmodium
secretes a thick brownish membrane, within which many uninucleate
naked stages or cysts are produced. Cysts hatch into the flagellate or
amoeboid forms.

Suborder 5. Chrysocapsina. The dominant stage is a palmella which
may grow to a fairly large size in some genera.

Family 1. Chrysocapsidae. The organisms are distributed throughout
the matrix which is not highly differentiated, and fission may occur in
any region of the palmella. The matrix of Chrysocapsa Pascher (202) is

The Mastigophora 133

spheroid; that of Phaeoplaca Chodat (90), discoid; and the matrix of
Phaeosphaera West and West (202) is cylindrical and sometimes
branched.

Family 2. Celloniellidae. Fission does not occur throughout the pal-
mella. Instead, growth of the palmella depends upon fission in particular
groups of cells which produce new points of growth. In the sessile
Celloniella Pascher (Fig. 4. 12, A-E), the form of the palmella varies
with rate of flow of the water in which the mass is suspended (209).

Family 3. Hydruridae. Hy drums Agardh (152, 202) resembles Celloni-
ella, but the palmella is profusely branched and sometimes reaches a
length of 25-30 cm. Furthermore, fission apparently is limited to the
apical flagellates in each branch.

Family 4. NagelieUidae. Species of Nageliella Correns (202, 248),
usually epiphytic on algae, develop a somewhat discoid palmella from
the free surface of which extends a bundle of gelatinous filaments. In
N. natans (Fig. 4. 12, F) each filament contains an axial fibril which arises
from the apical end of each flagellate (248).

Order 2. Heterochlorida

These flagellates have a flexible periplast, typically two unequal
flagella, and one or more pale yellow-green or pale yellow chromato-
phores. The occurrence of pyrenoids is doubtful. Leucosin and lipids
are stored.

Endogenous encystment (Fig. 4. 13, A-D) is known in Chloromeson
and Myxochloris (216). Unlike that in Chrysomonadida, the cyst wall
is composed of two unequal valves and lacks a pore. In addition to the
encystment of uninucleate stages, an entire plasmodium of Myxochloris
sphagnicola may become enclosed in a membrane apparently containing
pectins (213).

On the basis of life-histories, the Heterochlorida may be divided into
three suborders: Euheterochlorina, with a dominant flagellate stage;
Rhizochloridina, with a dominant non-flagellated or plasmodial stage;
Heterocapsina, with a dominant palmella.

Suborder 1. Euheterochlorina. Representative types (Fig. 4. 13) in-
clude Chloromeson Pascher (31, 212, 216), Nephrochloris Geitler and
Gemisi (31), and Olithodiscus Carter (31).

Suborder 2. Rhizochloridina. Myxochloris Pascher (Fig. 4. 14, D-G),
Rhizochloris Pascher (Fig. 4. 14, A-C) and the loricate Stipitococcus
West and West (Fig. 4. 14, H) are included. The dominant stage in
Rhizochloris arachnoides is a small amoeba with slender pseudopodia
and a number of chromatophores. An amoeboid plasmodium also has
been observed. The flagellate stage apparently has only one flagellum.
The vegetative stage of Myxochloris sphagnicola (213) is a plasmodium

134 The Mastigophora

Fig. 4. 13. Euheterochlorina. AD. Chloromeson agile Pascher; successive
sta^^es in encystment; schematic (after P.). E, F. Nephrochloris salina Carter,
different aspects; E, x2430; F, x2250 (after C). G. Chloromeson parva Carter;
stigma, one chromatophore; x2360 (after C). H-J. Olithodiscus liiteus
Carter; dorsal, ventral and ventro-lateral views; xl340 (after Carter). K.
Cyst of O. hi tens; xl275 (after C).

endoparasitic in Sphagnum. Encystment of the plasmodium is followed
by division into smaller plasmodia or into uninucleate flagellate or amoe-
boid stages.

Suborder 3. Heterocapsina. A palmella is the dominant stage (218)
in C hlorosaccus L.uther, Gleochloris Pascher, and Malleodendroyi Pascher.

Order 3. Cryptomonadida

These typically biflagellate forms are widely distributed in fresh
water and fairly common in salt and brackish waters. Some marine types
have been reported as parasites (symbiotes?) in Radiolarida. A rather
constant body form, often with dorso-ventral differentiation, is charac-
teristic. A ventral groove, or "pharynx," is commonly present. The
"pharynx" of Chilomonas, which may represent the primitive condition,
is an open groove extending almost to the middle of the body (Fig. 4.

The Mastigophora 135

,ro

Fig. 4, 14. A-C. Rhizochloris arachnoidcs Carter (after C). A. Flagellate
stage, x2180. B. Amoeboid stage, x2080. C. Amoeboid stage, xl540. D-G. Myxo-
chloris spliagnicola, diagrammatic (after Pascher): flagellate stage (D), Plas-
modium endoparasitic in Sphagiiiim (E), developing cyst (F) and mature cyst
(G). H. Stipitococcus capense Prescott and Croasdale, x665 (after P. & C.).

15, L). In Cryptomonas (Fig. 4. 15, I-K) the posterior part of the pharynx
is closed ventrally to form a pouch, leaving the anterior portion an open
furrow. The wall of the pharynx and the groove is lined with refractile
granules ("trichocysts"), usually visible in the living organism. These
inclusions disappear in old cysts of Cryptomonas (110). The pharynx of
the holozoic genus Cyathomonas is a pouch extending posteriorly and
ventrally from the anterior end of the body, and partly encircled an-
teriorly by an incomplete ring of trichocysts.

One, two, or more chromatophores have been reported. The single
chromatophore of Cryptomonas (Fig. 4. 15, 1) and similar types is bilobed,
a condition interpreted occasionally as two separate chromatophores.
The chromatophore is usually brown, less commonly green, blue-green,
or red. Storage of starch and lipids is characteristic. The colorless Chilo-
monas Paramecium synthesizes amylopectin and ^-amylose (117), and
pectins have been reported in the endocyst in Cryptomonas (110).

Three families have been recognized: Cryptochrysidae, Cryptomo-
nadidae, and Nephroselmidae.

Family 1. Cryptochrysidae. The pharyngeal groove, along which rows

136 The Mastigophora

Fig. 4. 15. Cryptochrysidae and Cryptomonadidae. A. Chroomonas vectinsis
Carter, xl845 (after C). B. Cyst of Cryptomonas ovata, xl770 approx. (after
Hollande). C. Rhodomonas bnltica Karsten, xl440 (after Carter). D. Crypto-
chrysis commutata Pascher, xl250 (after P.). E. Rhodomoyias lacustris Pascher
and Ruttner, x2400 (after Pascher). F, G. Cryptochrysis atlantica Lackey, ven-
tral and lateral views; xl450 approx. (after L.). H. Chroomonas baltica
(Biittner) Carter, xl560 (after C). I. Cryptomonas similis Hollande, showing
gidlet, contractile vacuole, chromatophore and nucleus; diagiammatic (after
H.). J, K. Cryptomonas ovata, diagrammatic cross-sections anterior to, and at
the level of the nucleus; note gullet, "trichocysts" and chromatophore (after
Hollande.) L. Chilomonas Paramecium, showing "pharyngeal" groove and
contractile vacuole; diagrammatic (after Hollande).

of refractile granules are usually visible, is not closed ventrally. The
flagella arise near the anterior end of the groove.

Chlorophyll-bearing types include: Chroomonas Hansgirg (31, 202; Fig. 4. 15, A, H),
with one or two bluish chromatophores; Cryptochrysis Pascher (175, 202; Fig. 4. 15, D,

The Mastigophora 13'

F, G); Cyanomonas Oltmanns (173, 202), with several blue-green chromatophores);
Rhodomonas Karsten (31, 202; Fig. 4. 15, C, E), with reddish-brown chromatophores.
Chromatophores are lacking in Chilomonas Ehrenberg (110; 202; Fig. 4. 15, L).

Family 2. Cryptomonadidae. In these flagellates, the pharyngeal groove
is closed ventrally, through part or all of its length, to form a pouch.
The genus Cryptomonas Ehrenberg (110, 202; Fig. 4. 15, I-K) includes
chlorophyll-bearing forms; Cyathomonas Fromentel (110, 202), color-

B

a:)

D

Fig. 4. 16. A. Protochrysis phaeophycearum Pascher, xl500
(after P.). B. Cross-section of same. C. Nephroselmis olivacea Stein,
xl300 (after S.). D. Cross-section of jV. oUxmcea.

less holozoic types in which the pharyngeal pouch is a functional gullet.
Family 3. Nephroselmidae. As compared with the other families, the
Nephroselmidae show a modification of the primitive cryptomonad or-
ganization. If the origin of the flagella is considered anterior, these
flagellates have become shortened along the anterior-posterior axis and
correspondingly elongated along the transverse axis. The result is a
more or less bean-shaped body, with the pharyngeal-groove and bases of
the flagella lying near the equatorial plane. The two genera, Nephro-
selmis Stein (202; Fig. 4. 16, C, D) and Protochrysis Pascher (202; Fig. 4.
16, A, B) differ in shape of the body in cross-section.

Order 4. Dinoflagellida

This order includes many living species and a variety of fossil
types (75). Most dinofiagellates are marine, forming an important part
of the plankton. Under conditions not yet fidly understood, the popu-
lations of certain dinofiagellates in localized areas may increase tre-
mendously, sometimes to densities above 5,000,000 per liter. The result
is discoloration of the water — "red water" or "red tide" — and lumi-
nescence at night, and occasionally the death of fish in large num-
bers (42).

138 The Mastigophora

The flagellate stages of many species fall within the range, 10-200[ji,.
However, certain parasitic types grow to diameters of 600-700[jl, while
Noctiluca scintillans sometimes measures 1.0-1.5 mm. A girdle and a
sulcus are characteristic of flagellate stages (Fig. 4. 17, A). The girdle
(or annulus) is a groove which usually encircles the body in a descending,
or sometimes in an ascending, left-hand spiral, although the two ends
may meet in the same plane. In extreme cases, the girdle may trace more
than one complete spiral, or it may be rudimentary as in Protonocfiliiai

Fig. 4. 17. A. Gymnodinlum dorsum Kofoid and Swezy; pusules opening
into flagellar pores; x940 (after K. & S.). B. Cochliodinium lebourae Kofoid
and Swezy, spirally twisted sulcus; x525 (after K. & S.). C. Amphidiniopsis
kofoidi Woloszynska, dorsal view showing intercalary bands; x630 (after
W.). D. Gymnodinium racemosus .Cofoid and Swezy, showing chromato-
phores; x475 (after K. & S.). E. Protonoctiluca (Protoditiifer) tentaculatum
(K. & S.), showing tentacle arising from sulcus; x700 approx. (after Kofoid
and Swezy). F. Cross-section of apical horn, Ceratium hirundinella; diagram-
matic (after Entz). G. Erythropsis extrudens Kofoid and Swezy, showing
prod and outline of ocellus; x450 (after K. & S.). Key: b, intercalary band;
e, epicone; //?, flagellar pore; g, girdle; /;, hypocone; //, longitudinal flagel-
lum; o, ocellus; p, pusule; pr, prod; 5, sulcus; t, transverse flagellum; te,
tentacle.

The Mastigophora 139

(Fig. 4. 17, E). The epicone and hypocone, the anterior and posterior
regions of the body, are marked off by the girdle. The sulcus (longi-
tudinal furrow) is usually a straight groove intersecting the girdle, al-
though it may undergo spiral torsion (Fig. 4. 17, B), or may be expanded
into a "ventral area." From the sulcus arise the tentacle of Protodinifer
(Fig. 4. 17, E) and the prod of Erythropsis (Fig. 4. 17, G). The two
flagella of typical species also emerge through one or two flagellar pores
in the sulcus (Fig. 4. 17, A). The transverse flagellum is often ribbon-
like (81, 159). Occasionally, as in Peridinium, species within a genus
may differ in this respect (81).

A theca, composed of a cellulose-like substance and sometimes im-
pregnated with calcium salts, is present in many dinoflagellates. The
typical theca is composed of plates, the margins of which may be sepa-
rated by intercalary bands (Fig. 4. 17, C) in some species and particularly
in older specimens. The theca covering the epicone is known as the
epitheca; the posterior portion, as the hypotheca. The two are joined
by the girdle hand, composed of one or more girdle plates. The theca
may, as in Ceratium hirundinella (Fig. 4. 17, F), contain pores through
which extend cytoplasmic papillae.

There are commonly two vacuoles, or pusules (Fig. 4. 17, A), usually
containing a pink fluid. A slender c^jial extends directly from each
pusule to a flagellar pore or else joins a common canal which opens
externally. Intake of fluid has been observed in pusules of Peridinium
steini (155), and it has been suggested that a pusule may function as a
pharynx for intake of liquids and possibly solid particles (159).

The nucleus usually contains one or more nucleoli and many long
chromosomes whose beaded structure may persist through mitosis.
Chromatophores, present in many species, are often golden-brown to
dark-brown, although sometimes yellow, orange, green, or bluish-green.
In addition, various cytoplasmic pigments — either diffuse or forming
granules or globules — occur in many species (159). The known pigments
include chlorophyll a, chlorophyll r, peridinin, /^-carotene, dinoxanthin,
diadinoxanthin, and neodinoxanthin (Chapter I). Stored reserves in-
clude starch and lipids. A simple stigma, composed of red granules,
occurs in various fresh-water species. At the other extreme, the Pou-
chetiidae possess a complex ocellus (Fig. 1. 17, H, M) composed of a
lens and a mass of pigment.

The group shows a strong trend toward holozoic feeding, as indicated
by inclusions which are obviously ingested food in many species and
apparently such in others. In the chlorophyll-free Cochliodinium rosa-
ceum (159), Oxyrrhis marina (Fig. 4. 18, C), Noctiluca milaris, and
others, holozoic nutrition is undoubtedly important. Ingested food also
appears in various chlorophyll-bearing species of Gymnodinium, Gyro-
dinium, and Amphidinium (159). Furthermore, such thecate types as

140 The Mastigophora

Ceratium (106) may capture and presumably digest microorganisms
outside the theca by means of pseudopodial nets (Fig. 4. 18, A, B). These
pseudopodia apparently arise from cytoplasmic papillae extending
through pores in the theca (Fig. 4. 17, F).

The life-cycle may be apparently simple, or may show dimorphism or
polymorphism (159). Sexual phenomena have been reported in several
species (Chapter II). Fission is typically oblique (Fig. 2. 2, A-H) and,
in armored species, involves regeneration of different portions of the
theca by the daughter organisms. In contrast, as represented by certain
species of Glenodinium, fission may occur within the theca and the

'-nv%'^

Fig 4. 18. A, B. Capture of microorganisms by pseudopodial networks
in Ceratium 'hirundinella; x425 (after Hofender). C. Oxyrrhis marina, four
food vacuoles, nucleus in outline; x885 (after Hall).

daughter organisms are liberated as naked forms which later secrete a
theca. In other cases, each daughter organism develops a new theca
before it emerges from the parental one. Incomplete separation after
fission may result in chains (Fig. 4. 19, I), which are characteristic of
certain species but not of others. Reproductive cysts, known in a number
of species, may be more or less spherical ("pyrocystis" type) or some-
times crescentic ("crescent-cysts"). In Gymnodinium lunula (159), cres-
cent-cysts are developed within a pyrocystis-stage. Fresh-water species
may produce a thick-walled protective cyst, as in Ceratium hirundinella
(Fig. 2. 15, A). A palmella stage in which fission occurs is known in
some species, and is the dominant phase in Gleodinium (Fig. 4. 24, C,
D). In Amyloodinium ocellatum (Fig. 4. 19, A-C) the dominant phase

The Mastigophora 141

is a large ovoid stage, attached by means of a hold-fast to the gill-fila-
ments of a marine fish. At maturity, the parasite drops off the host,
the hold-fast is retracted, and the corresponding gap in the cellulose-
membrane is closed. Fission then results in many gymnodinioid flagel-
lates which seek a new host (26, 199).

The Dinoflagellida may be divided into five suborders: Prorocentrina,
with a bivalve theca but no distinct girdle or sulcus; Gymnodinina,

Fig. 4. 19. A-C. Amyloodinium ocellatum, X475 (after Nigrelli); para-
sitic stage (A), palmella stage after several fissions (B), and flagellate stage
(C). D, E. Exuviella perforata Gran, valve view and ventral view; xl230
approx. (after Lebour). F, G. Oxyrrhis marina Dujardin, ventral and dorsal
views; x875 (after Hall). H. Oxyrrhis teiitaculifera Conrad, ventral view
showing long tentacle; xl890 (after C.). I. Gymnodinium catenatum, chain
formation; x350 (after Graham).

142 The Mastigophora

athecate types with a girdle and sulcus; Peridinina, with a theca com-
posed of separate plates; Dinocapsina, with a dominant palmella and
a gymnodinioid flagellate stage; Dinococcina, in which the life-cycle may
include a dominant "pyrocystis" or crescent-cyst stage, a floating or at-
tached palmella, and a gymnodinioid flagellate stage.

Fig. 4. 20. A. Gyrodinium melo Kofoid and Swezy, x475 (after K. & S.).
B. Gyrodinium submarinum Kofoid and Swezy, x425 (after K. & S.). C.
Torodinium teredo Kofoid and Swezy, x300 (after K. & S.). D. Gymnodi-
nium dissimile Kofoid and Swezy, x475 (after K. & S.). E. Amphidinium
dentatum Kofoid and Swezy, x575 (after K. & S.). F. Cochliodinium pul-
chellum Lebour, x720 (after K. & S.). G. Polykrikos scfnvartzi Biitschli,
x250 (after K. & S.). H. Pavillardia tentaculijera Kofoid and Swezy, x475
(after K. & S.). I. Noctiluca scintiUans, x60 approx. (after K. & S.). Key:
/, longitudinal flagellum; p. oral pouch; t, tentacle.

Suborder 1. Prorocentrina. This group includes Exuviella Cienkowski
(178, 249, 252), Porella Schiller (252) and Prorocentrum Ehrenberg
(249, 252). Exuviella perforata (Fig. 4. 19, D, E) is a small marine flagel-
late with a thick bivalved theca. Each somewhat flattened valve is ap-
proximately circular in outline and shows a central conical invagination.
The flagella, emerging anteriorly through pores in one valve, show a
differentiation into longitudinal and transverse types. The two chroma-
tophores are yellowish-brown to yellow.

The Mastigophora 143

Suborder 2. Gymnodinina. These are the unarmored dinoflagellates
(159) which, except for some of the Gymnodiniidae, are limited to salt
water.

Family 1. ProtoJioctilucidae. The girdle and sulcus are rudimentary
and the transverse flagellum is not appreciably flattened. A tentacle is
characteristic. There are no chromatophores and the organisms are holo-
zoic. The family includes Oxyrrhis Dujardin (Fig. 4. 19, F-H) and Proto-
noctiluca Fabre-Domergue (Protodinifer Kofoid and Swezy). In the latter
(Fig. 4. 17, E), the shallow girdle extends about one-fourth the circum-
ference of the body, and the tentacle, arising from the sulcus, is more
pronounced than in Oxyrrhis. Only one pusule is present. The longitu-
dinal flagellum is vestigial in Protonoctiliica but is well developed in
Oxyrrhis.

Family 2. Gymnodiniidae. Both girdle and sulcus are well developed
and the transverse flagellum is typically flattened. Neither a tentacle nor
an ocellus is present. Some species lack chromatophores and a number
are holozoic. The family, represented in both fresh and salt water, in-
cludes the following genera: Amphidinium Claparede and Lachmann,
Cochliodiniuni Schiitt, Gyinnodiniiim Stein em. Kofoid and Swezy, Gyro-
diniiim Kofoid and Swezy {Spirodinium Schiitt), Massartia Conrad (10,
31, 44), and Torodininm Kofoid and Swezy (159).

The genera may be distinguished largely on the basis of their girdles. The girdle
forms one complete turn in Amphidinium, Gymnndinium, Massartia, and Torodinium.
In Amphidinium (Fig. 4. 20, E) the girdle is anterior, so that the epicone is small. The
girdle of Gymnodinium (Figs. 4. 17, D, 4. 20, D) lies nearer the equator and the ends
are displaced less than one-fifth the body length. Massartia differs from Gymnodinium
in having a larger and broader epicone. The girdle of Torodinium (Fig. 4. 20, C) is
posterior and the epicone is several times as long as the hypocone. Posteriorly, the
sulcus forms a half-turn around the body before intersecting the girdle. In Gyrodinium
(Fig. 4. 20, A, B) the girdle makes 1.0 to less than 1.5 turns and the ends are dis-
placed not less than one-fifth the body length. The girdle of Cochliodiniuni (Fig. 4.
20, F) makes 1.5 or more turns around the body.

Family 3. Polykrikidae. The single genus, Polykrikos Biitschli (Fig. 4.
20, G), contains permanent linear somatellae composed of two, four, or
eight zooids as a rule, although chains of sixteen have been observed,
Nematocysts are present. All species are marine.

Family 4. Noctihicidae. The diagnostic feature is a mobile tentacle
which arises in the sulcal area and extends posteriorly. The known spe-
cies are marine. Two genera, Noctihica Suriray and Pavillardia Kofoid
and Swezy, are assigned to the family. Pavillardia (Fig. 4, 20, H) shows a
body and girdle of the Gymnodinium-type, but a longitudinal flagellum
is absent and a tentacle arises from the posterior end of the sulcus. In
Noctihica (Fig. 4. 20, I), the mature organism is a highly vacuolated
spheroidal stage ranging from 200 to 2,000[j, in diameter. A short longitu-
dinal flagelJum is present. The girdle is vestigial, and the posterior por-

144 The Mastigophora

tion of the sulcus is expanded into a deep pouch extending to the base
of the tentacle.

Suborder 3. Peridinina. A theca composed of separate plates is charac-
teristic. Such features as relative size of the epicone and hypocone, extent
and torsion of the girdle and sulcus, and the number and arrangement
of thecal plates are important in taxonomy. Three small families differ
from the rest with respect to development of the girdle. In the Sino-
diniidae, the girdle is an irregular belt, instead of a groove, and shows

Fig. 4. 21. A-D. Glenodinium cinctum Ehrbg., x580 approx. (after Eddy);
ventral, apical, dorsal, and antapical views. E. Hemidinium nasiitum Stein,
ventral view showing girdle, sulcus, and thecal plates; schematic (after Wolo-
szynska). F. Palmella stage of H. nasutum; schematic (after Baumeister). G-J.
Diplopsalis lenticulata Bergh; x700 (after Lebour); ventral, lateral, antapi-
cal, and apical views. K, L. Heterodinium scrippsi Kofoid, dorsal and ventral
views; plates numbered; x350 (after K.).

The Mastigophora 145

no marginal ridges (lists), whereas the Lissodiniidae and Podolampidae
have undergone apparently complete suppression of the girdle (197).

The thecal plates are usually differentiated into several circular series
(Fig. 4. 21, K, L), and those in each series are conventionally numbered in
order, beginning at the left of the sulcal plane or the mid-ventral suture
(155). The apical plates (numbered V, 2', 3' . . .) extend to the apical
pore, or sometimes to a closing plate if the pore is closed. Anterior inter-
calary plates (la, 2a, . . .) lie between the apical and precingular plates.
Precingular plates (1", 2", . . .) extend from the apical or intercalary
plates to the girdle. The girdle plates (1, 2, 3 . . .) line the girdle. Post-
cingular plates {V", 2' ", . . .) lie in the hypotheca between the girdle
and the antapical plates (or posterior intercalary plates, if present). Pos-
terior intercalary plates (Ip, 2p, . . .) lie between the postcingular and
antapical plates. The a7itapical plates {\"",2"", . . .) cover the posterior
end. According to Kofoid's (155) system, the plate formula for Diplopsalis
lenticulata (Fig. 4. 21, G-J) would be written as 3'la6"5'"r'" (omitting
the girdle).

Fainily 1. Glenodiniidae. These flagellates have a thin theca, with plates
which are not easily distinguished, and were at one time assigned to the
Gymnodinina. Most species are known from fresh water (74, 254). Gleno-
dinium (Ehrbg.) Stein (Fig. 4. 21, A-D) differs from Glenodiniopsis
VVoloszynska (Fig. 4. 22, M-O) in number of postcingular plates and in
a sulcus limited mostly or entirely to the hypocone. In Hemidinium Stein
(9, 11; Fig. 4. 21, E), the girdle extends only about a half turn. A palmella
stage (Fig. 4. 21, F), resembling that of Gleodinium, has been reported for
H. nasutum (11).

Family 2. Gonyaulacidae. The thecal plates are distinct and one antapi-
cal plate is characteristic. Several species are known from fresh water (74,
254), but most are marine. Species of Gonyaiilax have attracted attention
as the source of mussel poisoning on the Pacific Coast (Chapter X) and
as a component of "red tide."

The family includes Chalubinskia Woloszynska (Fig. 4. 22, E-H), Dinosphaera Kofoid
and Michener (157), Diplopsalis Bergh (178), Entzia Lebour (178), and Gonyaulax
Diesing em. Kofoid (156). Gonyaulax (Fig. 1. 5, A, B) has a plate formula of
l-6'0-3a6"66' "Ipl" ", while Dinosphaera (Fig. 4. 22, A-D) has 5 postcingulars and no
posterior intercalary. Diplopsalis (Fig. 4. 21, G-J) has the plate formula, 3'la6"5' "1" ";
Entzia, 4'l-2a7"5' "1" ", but otherwise similar to Diplopsalis. Chalubinskia (Fig. 4. 22,
E-H) has 3 postcingular and 1 antapical plates.

Family 3. Peridiniidae. The thecal plates are distinct as in the Gonyaul-
acidae, but there are two antapical plates. Many species occur in fresh
water (74, 254); others are marine.

The family includes Peridiniurn Ehrenberg (64; Fig. 4. 22, I-K), Amphidiniopsis
Woloszynska (Figs. 4. 17, C, 4. 22, L), Glenodiniopsis Woloszynska (Fig. 4. 22, M-O),

146 The Mastigophora

Fig. 4. 22. AD. DiuospJmera palustris, ventral, dorsal, apical, and anta-
pical views; x575 approx. (after Eddy). E-H. Chalubinskia tatrica Wolo-
szynska, ventral, left lateral, apical, and antapical views; x675 (after W.).
I-K. Peridiniufn kulczynskii Wolosz)nska, \entral, apical, and antapical
views; x835 (after W.). L. Amphidiniopsis kofoidi Woloszynska, ventral view;
x630 (after W.). M-O. Glenodiniopsis steinii W'olos/ynska, ventral view;
x850 (after W.). P, Q. Sphaerodinium limneticuui Woloszynska, x800 ap-
prox. (after W.). R. Staszicella dinobryonis Woloszynska, x720 (after W.).

Sphaerodinium Woloszynska (Fig. 4. 22, P, Q), and Staszicella AVoloszynska (Fig. 4. 22,
R). Tfie epitheca is distinctly smaller than the hypotheca in Amphidiniopsis and
Staszicella. The two genera are distinguished by the sulcus, which extends to the apex
in Amphidiniopsis, but only a short distance into the epitheca in Staszicella.

Family 4. Ceratiidae. The epitheca is prolonged into an apical horn,
the hypotheca into two or three posterior horns (Fig. 4. 23, A). The genus
Ceratium Schrank is represented by many marine and several fresh-water
species (74, 80). Species differ in number of posterior horns, in form and
length of the horns, and in the sculpturing and detailed pattern of the
thecal plates. Of the posterior horns, the accessory may be vestigial or

The Mastigophora 147

Fig. 4. 23. A. Ceratium hirundinella O. F. M., ventral view; diagram-
matic (after Entz). B-D. Dinophysis diegensis Kofoid, ventral, dorsal, and
right lateral views; B, C, x445; D, x505 (after K.). E, F. Dolichodinmm
lineatum (Kofoid and Michener) Kofoid and Adamson, dorsal and ventral
views; x700 (after K. & A.). Key: g, gullet; s, sulcal area.

lacking, as in some strains of C. furcoides (Levander) Langhans; in addi-
tion, the antapical and postequatorial horns may be reduced in length,
as in C. brachyceros Daday. The apical horn shows differences in length
and is curved instead of straight in C. cornutiim Schrank and C. ciir-
virostre Kaas.

Family 5. Dinophysidae. The elongated body is laterally compressed,
with a minute epitheca, and the girdle is bordered by prominent flanges
("collars"). The theca consists of right and left valves, joined in a median
suture. Known species are marine. Dinophysis Ehrenberg (252; Fig. 4. 23,
B-D), Phalacronia Schiller (252) and Oxyphysis Kofoid are included in
the family.

Family 6. Heterodiniidae. The precingular ledge (or list) is well de-
veloped but the postcingular ledge is reduced or absent. A ventral pore
lies between the apical pore and the single flagellar pore. The plate
formula is 3-4'0-la6"6 6-7' "3"". The family includes Heterodinium
Kofoid (Fig. 4. 21, K, L) and Dolichodinium Kofoid and Adamson (Fig.
4. 23, E, F).

Suborder 4. Dinocapsina. A dominant palmella and a gymnodinioid

148 The Mastigophora

flagellate stage are the diagnostic features. In the palmella, a pectic sheath
may enclose the usual cellulose membrane. The suborder includes only
the family Gleodiniidae. The type genus is Gleodinium Klebs (132, 270;
Fig. 4. 24, C, D). Structure and division of the nucleus in G. montanum,
as noted in material from cultures (242), conform to the dinoflagellate

Fig. 4. 24. A, B. Cystoclnnum iners Gcitler, crescent-cysts containing one
and two organisms, the latter showing gymnodinioid featmes; x500 approx.
(after Thompson). C, D. Gleodinium montanittn Klebs. showing fission in
palmella stage; x625 approx. (after Thompson). E. Hypnodinium spliae-
ricum Klebs; stigma (beneath sulcus), chromatophores, large reddish oil
globule; xl95 approx. (after Thompson). F, G. Dinopodiella phaseolus
Pascher, sessile and flagellate stages; xl250 approx. (after P.). H, I. Tetra-
dinium javanicum Klebs, stalked and unstalked forms; schematic (after
Thompson). J, K. Phytodinedria procubans Pascher, sessile and flagellate
stages; xl250 approx. (after P.). L. Stylodinium sphaera Pascher, x940 ap-
prox. (afler P.).

The Mastigophora 149

pattern. Urococcus Kiitzing, in which the pahnella shows a very thick and
stratified sheath, has been referred to the family (259).

Suborder 5. Dinococcina. The dominant phase is a "pyrocystis" or a
"crescent-cyst" stage and the flagellate stages are typically gymnodinioid.
The non-flagellated stage, which may be floating or sessile, has a cellulose
membrane and is enclosed in a sheath composed of pectin.

Family 1. Phytodiniidae. This group, as the most typical family, shows
the characteristics of the suborder. A number of American species have
been described by Thompson (270).

The family includes: Cystodinedria Pascher (226); Cystodinium Klebs (11, 91, 205,
208, 225; Fig. 4. 24, A, B); Dinastridium Pascher (205); D'mopodiella Pascher (226; Fig.
4. 24, F, G); Dissodinium Klebs (205); Hylmodinhun Klebs (205; Fig. 4. 24, E); Phyto-
dinedria Pascher (226; Fig. 4. 24, J, K); Phytodinium Klebs (205); Rnciborskia Wolo-
szynska (219); Stylodinium Klebs (11, 205, 226; Fig. 4. 24, L); and Tetradinium Klebs
(91, 205; Fig. 4. 24, H, I). According to Baumeister (11), the flagellate stage of
"Stylodinium tarnuni" has a theca composed of discrete plates.

Fig. 4. 25. A-C. Blastodinium spiuulosum Chatton; undivided parasitic
stage (A), x210; trophocyte and four small sporocytes (B), x2I0; flagellate
stage (C), X1840 (after C). D-F. Haplozoon dogieli, x325 (after Shumway);
young parasite (D), trophocyte and gonocvte (E), gonocytes and sporocytes
(F). G. Flagellate stage of Haplozoon clymenellae, xl520 (after Shumway).
FI-L. Coccodinium duboscqi Chatton and Biecheler, parasitic in Peridinium
sp.; growth and nuclear division preceding merogony (H-K); g>mnodinioid
stage (L); schematic (after C. & B.).

150 The Mastigophora

Family 2. Blastodiniidae. This group (36) includes intestinal parasites
of copepods and sessile polychaetes; ectoparasites of copepods, annelids,
and salpids; intracellular parasites of Siphonophora, tintinnioid ciliates,
Radiolarida, and eggs of copepods; and parasites of the body cavity in
copepods. Amyloodinium (Fig. 4. 19, A-C) parasitizes the gills of marine
fish (26, 199), and Oodinium limneticum (118) has been described from
the same location in fresh-water fish. Chromatophores are present in some
Blastodiniidae and absent in others.

In a representative life-cycle (Fig. 4. 25, D-F), the young parasite divides
into two cells, a "trophocyte" and a "gonocyte." The latter undergoes a
number of divisions to produce "sporocytes" which develop into gymno-
dinioid flagellates. In the meantime, the trophocyte may divide into a
second gonocyte and a trophocyte. The second gonocyte produces another
generation of sporocytes, and the procedure may be repeated several
times. This pattern is not followed in Amyloodinium, which apparently
does not produce differentiated trophocytes and gonocytes.

The family includes Amyloodinium Hovasse and Brown (115; Fig. 4. 19, A-C),
Apodinium Chatton (36), Atelodinium Chatton (36), Blastodinium Chatton (36; Fig. 4.
25, A-C), Chytriodinium Chatton (36), Duboscquella Chatton (36), Endodinium Hovasse
(111), Haplozoon Dogiel (258; Fig. 4. 25, D-G), Merodinium Chatton (37) from Radio-
larida, Oodinium Chatton (36, 112), Paradinium Chatton (37), Protoodinium Hovasse
(112), Syndi7iium Chatton (36), and Trypanoditiium Chatton (36). Coccodiuium Chat-
ton and Biecheler (Fig. 4. 25, H-L), parasitic in other dinoflagellates, possibly should
be referred to this family.

Family 3. Ellohiopsidae. These ectoparasites of Crustacea resemble the
Blastodiniidae in their parasitic stages, but the known free-living stages
show no obvious relationships to dinoflagellates. Therefore, the tax-
onomic position of the group is uncertain. Ellobiopsis Caullery (32) is
the type genus.

Order 5. Phytomonadida

These flagellates are mostly ovoid to spherical, but various spindle-
shaped, hemispherical, flattened, and spirally twisted types are known.
Medusochloris phi ale, one of the more unusual forms, is a medusa-like
flagellate which swims mainly by contractions of the body (204). Except
in the Polyblepharidae, the body is enclosed in a distinct membrane, com-
posed at least partly of cellulose. In the Phacotidae the membrane is im-
pregnated with calcium salts to form a "shell." One to eight, but usually
two or four flagella are present. The flagella of membrane-covered species
may emerge through one opening or through individual flagellar pores
(Fig. 4. 26, A-C). In the first case the flagella may or may not arise from a
cytoplasmic papilla. Contractile vacuoles vary in number and position,
but there are often two near the bases of the flagella. A single large green
chromatophore is typical, although two or more smaller ones occur in

The Mastigophora 151

some species. The usual single chromatophore is cup-shaped (Fig. 4. 26,
B). However, lobed, "H-shaped," and other variations are known (Fig. 4.
26, D-J). The nucleus lies in the inner zone of cytoplasm. One or more
pyrenoids, typically spherical or ellipsoidal, but sometimes U-shaped (Fig.
4. 26, K, L), are characteristic of green species. A single pyrenoid usually

Fig. 4. 26. AC. Flagellar insertions, schematic: A, Chlamydomonas na-
suta (after Kater); B. C. longirubra (after Pascher); C. C. ignova (after
KorshikofF). D-J. \'arious types of chromatophores; pyrenoids indicated as
clear areas; schematic: D. Chlamydomonas obversa (after Pascher); E. Chlo-
rogonium elongatiim (after Dangeard); F, G. Chlamydomonas ovata (after
Dangeard); H. C. basistellata (after Pascher); I. C. korschikoffia (after
Pascher); J. Gigaiitochloris permaxima (after Pascher). K, L. Unusual U-
shaped pyrenoid; optical cross-section and lateral view of flagellate; starch
granules surround the pyrenoid; diagrammatic (after Vlk).

lies in the posterior portion of the cup-shaped chromatophore; if several
pyrenoids are present, distribution is variable. A stigma, when present,
is a rounded or discoid structure, usually anterior in position but some-
times near the equator. Starch, stored both in the cytoplasm and around
the pyrenoid of chlorophyll-bearing species, occurs also in colorless types.
Lipids, although usually not abundant, are stored by many phytoinonads.
A reddish pigment (red haematochrome) also may be accumulated in the

152 The Mastigophora

cytoplasm. In the "haematocyst" of Haematococcus phivialis (76), the
pigment may completely mask the chromatophore.

The order may be divided into four families of solitary types and two
of colonial genera. Among the solitary types, a typical cellulose mem-
brane is lacking in the Polyblepharidae, present in the Chlamydomonadi-
dae, and is replaced by a calcified bivalve "shell" in the Phacotidae. In
the Haematococcidae cytoplasmic processes extend into the thick mem-
brane. Colonial genera with a well developed matrix are assigned to the
Volvocidae; those without a matrix, to the Spondylomoridae. The order
has been surveyed by Pascher (206).

Family 1. Polyblepharidae. These are typically solitary types with
somewhat flexible bodies. The genus Raciborskiella (Fig. 4. 27, C) is ex-
ceptional in that 4-8 flagellates may remain attached posteriorly to form
simple aggregates (colonies?). Flagellar numbers of 1, 3, 4, 5, 6, and 8
have been reported, but there are usually two or four. Binary fission
occurs in the flagellate stage, and the old flagella are usually inherited
by the daughter organisms.

Chlorophyll-bearing species are included in the following genera: BipecUnomonas
Carter (31), Diuialiella Teodoresco (227), Hetcromastix Korshikov (31), Korschikoffia
Pascher (206), Mesostiginn Laiiterborn (206; Fig. 4. 27, D), Pedinomoiias Korshikov
(206), Phyllocardium Korshikov (162), Pocillomonas Steinecke (206). Polyblepharides
Dangeard {2d&), Pyramimouas Schm^rda. (Pyramidomonas Stein) (23,31,89,217; Fig. 4.

27, J), Raciborskiella Wislouch (206; Fig. 4. 27, C), Spennatozopsis Korshikov (2^)6).
TrichJoris ScherfFel and Pascher (206; Fig. 4. 27, K), and Tetrachlnris Pascher and
Jahoda (227) with four flagella. Chromatophores are lacking in Furcilla Stokes (206)
and Polytomella Aragao (128, 206; Fig. 4. 27, F-I). Cytological descriptions are avail-
able for Pyramimonas (25, 89) and Polytomella (128).

Collodictyon Carter (244; Fig. 4. 27, A, B) is sometimes included in this family. How-
ever, the plastic body, the longitudinal groove, the development of pseudopodia, and
the lack of information on stored reserves cast doubt upon the validity of such an
assignment.

a

Family JC Chlamydomonadidae. There is a well-developed membrane,
within which fission results in two or more daughter organisms (Fig. 4.

28, A, B). In Chlamydomonas nasuta (129), the plane of the first fission
is perpendicular to the long axis of the body. Prior to fission, the or-
ganism either rotates within its membrane through an arc of 90°, or else
the chromatophore and nucleus change their positions accordingly (Fig.
4. 28, C, D). The plane of the second fission is perpendicular to that of
the first. In various species, adhesion of the membranes of adjacent or-
ganisms often produces large palmellar aggregates or sheets, especially
during growth on a solid medium.

The following genera contain chlorophyll-bearing species: Apiococcus Korshikov
(206), Brachiomonas Bohlin (206; Fig. 4. 28, F), Carteria Diesing (23, 206, 217; Fig. 4.
28, O), Characiochloris Pascher (206), Chlawydonwnas Ehrenberg (94, 206, 217; Fig.
4. 28, C, D, G). Chlorobrachis Korshikov (206.' 256), Chloroceras Schiller (207), Chloro-
goniuin Ehrenberg (206; Fig. 4. 26, E), Clilornphysema Pascher (206), Diplostauron

The Mastigophora 153

Fig. 4. 27. A. B. Collodictyon triciliatiim Carter, basal portions of flagella,
longitudinal groove, development of pseiidopodia; x500 (after Rhodes). C.
Raciborskiella uroglenoides Swirenko, cluster of four flagellates; xlOOO ap-
prox. (after S.). D. Mesostigma viride Lauterhorn: x2100 approx. (after
Pascher). E. Ped'niomonas minor Korshikoff, x3100 approx. (after K.). F-I.
Polytomella citri Kater; living specimen showing stored food and contractile
vacuoles (F): a variation in form, nucleus stained (G); young (H) and older
(I) cysts; x2250 (after K.). J. Pyramijnojias tetrarhynchus Schmarda; large
chromatophore indicated as transparent to show positions of pyrenoid, an-
terior nucleus and contractile ^acuoles; xl425 (after Geitler). K. Trichloris
paradoxa ScherfEel; xllOO approx. (after S.).

Korshikov (217), Fortiella Pascher (206). Gigautochloris Pascher (206; Fig. 4. 26, J),
Gleomonas Rlebs (206), Hypnomonas Korshikov (206). Lobomonas Dangeard (206; Fig.
4. 28, E), Malleochloris Pascher (206), Nautococcus Korshikov (161; Fig. 4. 28, I, J),
Phyllomonas Korshikov (206), Platychloris Pascher (206), Platymonas West (31; Fig. 4.
28, N), Scourfieldia West (206; Fig. 4. 28. K, L), Selenochloris Pascher (207, 217),
Sphaerellopsis Korshikov (206), Sphenochloris Pascher (206), Spirogonium Pascher (206),
and Stylosphaeridium Geitler (206).

Colorless types are included in the following genera: Chlamydoblepharis France
(206), Hyalogonium Pascher (206; Fig. 4. 28, M), Parapolytoma Jameson (121), Poly-
tnma Ehrenberg (206), Tetrablepharis Senn (206), and Tussetia Pascher (206).

154 The Mastigophora

Four flagella are present in Carteria, Chlorobrachis, Fortiella, Malleochloris, Platy-
monas, Spirogonium, and Tetrablepharis; one flagellum in Chloroceras and Seleno-
chloris: two flagella in other genera. In some cases, a knowledge of life-cycles is
essential for assignments to genera. In Nautococcus, for example, there is a typical
flagellate stage in addition to the floating stage without flagella (Fig. 4. 28, I, J); in
Stylosphaeridium, the corresponding non-flagellated stage is epiphytic on filamentous
algae. Cytological descriptions are available for Chlamydomonas (129), Chlorogonium
(102), Parapolytoma (121), and Polytoma (78, 110).

Fig. 4. 28. A, B. Fission in Chlamydomonas seriata Pascher (schematic,
after P.). C, D. Rotation of the chromatophore at the beginning of fission
in Chlamydomonas nasuta; schematic (after Kater). E. Lobomonas roslrata
Hazen; xl750 approx. (after H.). F. Brachiomonas ivestiana Pascher; .x690
approx. (after P.). G. Chlamydomonas umbonata Pascher, xl330 approx.
(after P.). H. Tussetia polytomoides Pascher, xl400 approx. (after P.). I, J.
Nautococcus mammilatus Korshikofl^; stage with umbrella-like float, xl250;
flagellate stage, x2500 (after K.). K, L. Scourfieldia complanata West, views
of l)road and narrow surfaces; xl725 approx. (after W.). M. Hyalogonium
klebsii Pascher, x500 approx. (after P.). N. Platymonas tetrathele West,
xl430 (after Carter). O. Carteria coccifera Pascher, x960 (after P.).

The Mastigophora 155

Family 3. Haematococcidae. The outer membrane is separated from
the periplast by a thick layer of "gelatinous material" into which extend
cytoplasmic processes. These features have been considered adequate
grounds for separating the family from the Chlamydomonadidae (260).
The Haematococcidae include Haematococcus Agardh (76; Fig. 4, 29,
H) and Stephanosphaera Cohn (256; Fig. 4. 29, F, G).

Family 4. Phacotidae. The rather rigid membrane is often impregnated

Fig. 4. 29. A, B. Dysinorphococcus variabilis Takeda, surface view and
median optical section; xl200 (after Bold). C-E. Pteromonas anguJosa Lem-
mermann, edge view, broad side, and outline in cross-section; xlOOO approx.
(after Pascher). F, G. Stephanosphaera pluvialis Cohn, colony and young stage;
diameter of colony reaches 50-60/x; diagrammatic (after Pascher). H. Haeyna-
tococcus pluvialis Flotow em. Wille, large flagellate stage; xl500 (after
Elliott).

with calcium or iron compounds and possibly contains little or no cellu-
lose. A bivalve membrane (or "shell"), which does not fit the enclosed
organism very closely, is present in at least some genera. Fission occurs
within the membrane.

The family includes the following genera: Cephalomonas Higinbotham (104), Coc-
comonas Stein (206), Dysinorphococcus (23; Fig. 4. 29, A, B), Pedinopera Pascher (206),
Phacotus Perty (206, 207), Pteromonas Seligo (174, 206; Fig. 4. 29, C-E), Thoracomonas
Skvortzow (206, 217), Wislouchiella (207).

Family 5. Spondylomoridae. The membranes of the individual flagel-
lates are thin and the colony is not held together by a matrix. The larger

156 The Mastigophora

colonies are composed of two or four circlets of flagellates so arranged
that one organism does not lie directly above another. Individual flagel-
lates have two or four flagella. Daughter colonies are produced by fission
of any member of a colony within its original membrane. In contrast to
the Volvocidae, a plakea stage is not formed in development.

The family includes the following genera: Pascheriella Korshikov (164; Fig. 4. 30, B),
Pyrobotrys Arnoldi (Chlamydobotrys Korshikov) (256; Fig. 4. 30, A), Spotidylotnorum
Ehrenberg (206. 207; Fig. 4. 30, D).

In Corone Fott (Fig. 4. 30, C), the widely separated flagellates are joined by tough
strands. Since this type of organization differs from that of typical Spondylomoridae,
perhaps a new family Coronidae should be recognized, as suggested by Fott (84).

Fig. 4. 30. A. Pyrobotrys (Chlamydobotrys) squarrosa (Korshikofl), xl050
(after K.). B. Pasclieriella tetras Korshikotf, xl575 (after K.). C. Corone bo-
hemica Fott; length of colony (without flagella), 35-50^; flagella (one pair
shown full length) measure 35-40^ (after F.). D. Spondylomorum quater-
narium Ehrbg. (after Stein); colonies reach lengths of 50-70yn.

Family 6. Volvocidae. This group differs from the Spondylomoridae in
two major features: colonial organization is maintained by a matrix, and
a plakea stage (Fig. 4. 32, C) appears in the development of a young
colony.

The Mastigophora 157

The following genera are included: Eudorina Ehrenberg (103, 206); Go7iium Miiller
(103, 206; Fig. 4. 31, D); Pandorina Bory (206; Fig. 4. 31, A); Platydorina Kofoid (154,
268; Fig. 4. 31, B, C); Pleodorina Shaw (206); Stephanoon Schewiakoff (206); Volvox
Linnaeus (259); Volvuima Playfair (95).

Life-histories show basic similarities throughout the group, btit certain
genera are less specialized than others. In Gotiiiim, Pandorina, and
Platydorina, daughter colonies may be produced by any member of the
parental colony. This is not the case in certain other genera. Reproduc-
tion is limited to flagellates of the posterior four rows in Eudorina, to

Fig. 4. 31. A. Patidorina morum (Miiller) Bory (after Smith); colonies
may reach 250^ in diameter. B, C. Platydorina caudata Kofoid; surface
view, x225; lateral view, x260 (after K.). D. Gonium pectorale Miiller; colo-
nies reach diameters of 60-70/^; diagrammatic.

those in the posterior half of the colony in Pleodorina, and to a few
flagellates ("gonidia") in the posterior half of the Volvox colony.

In development of a daughter colony, continued fission within the
original membrane produces a hollow spherical or hemispherical stage,
the plakea (Fig. 4. 32, C), in which the anterior ends of the flagellates
are directed centrally. Later development in Gonium pectorale (103) in-
volves a flattening of the plakea, and then further inversion, so that the
young colony becomes slightly convex on the anterior, or flagellated,
surface. In Platydorina (268) the plakea is a hollow sphere with a single
opening (phialopore). After the 32-cell stage is reached, inversion occurs
through the phialopore and the inverted daughter colony becomes a
hollow sphere (Fig. 4. 32, Q). Further development involves collapse of

158 The Mastigophora

the sphere, with intercalation of flagellates from opposite sides so that
flagella are present on both surfaces (Fig. 4. 32, R). As secretion of the
matrix begins, the young colony approaches the adult form at about
the time cUssolution of the parental matrix occurs.

Fig. 4. 32. A-G. Development of a daughter colony in Volvox aureus;
pyrenoids are indicated as black dots; diagrammatic (after Zimmermann).
A-C. Fission results in a plakea, in which the anterior ends of the flagellates
are directed centrally. D-G. The plakea undergoes inversion to produce the
young colony. H-K. Mature zygotes, x615 (after Smith): Volvox perglobator
(H), V. globator (I), V. aureus (J), V. weismanni (K), L-P. The mature
macrogamete (L) of Platydorina caudata emerges from the parent colony
(M, N); a microgamete (O) then penetrates the macrogamete (P); diagram-
matic (after Taft). Q. Platydorina caudata, optical section of young colony
after inversion and tlevelopment of flagella; diagrammatic (after Taft). R.
Young plate-like colony (lateral view) derived from the earlier spherical
stage (Q); diagrammatic (after Taft).

The Mastigophora 159

Development of the Volvox colony (170, 234, 287) also involves the
formation of a spherical plakea with a phialopore and the inversion
("extroversion") of the plakea through the phialopore to produce a
young colony (Fig. 4. 32, AG). This process of inversion in Volvox is of
some general interest in its similarity to a process which the "stomatoblas-
tida" undergoes in certain species of Grant ia and Sycon (73). In general,
the young colonies of Volvox escape separately after rupturing the sur-
rounding membranes, but those of V. aureus may emerge through a com-
mon pore in the wall of the colony.

The details of sexual reproduction vary somewhat in different genera
and species. The gametes are similar in Gonium, but anisogamy is obvi-
ous in Eudorina, Payidorina, Platydorina, Pleodorina, and Volvox. Some
species of Eudorina and Volvox are heterothallic and others are homo-
thallic, althotigh the homothallic species of Volvox are protandrous. Some
of the heterothallic species of Volvox show sexual dimorphism involving
dwarf male colonies and large female colonies (259). Pleodorina is usually
heterothallic, with occasional homothallic variants. Such variation is
known also in the typically heterothallic Volvox aureus. Pandorina,
Platydorina, and at least some species of Gonium (255) are heterothallic.

Sexual reproduction is preceded by differentiation of gametes. The de-
veloping macrogametes in Platydorina caudata (268) show no significant
increase in volume but they become denser in appearance and acquire a
yellowish tinge as they approach maturity. The flagella are retained and
the mature macrogamete emerges from the colony as an active flagellate
(Fig. 4. 32, L-N). The macrogametes escape from the female colony in
Pandorina also, whereas those of Eudorina, Pandorina, and Volvox
remain in place and are fertilized there. The development of micro-
gametes in Platydorina is similar to that of a daughter colony. Fission, at
the 32-cell stage, results in a curved plakea which soon undergoes inver-
sion and develops into a sphere. Flagella are developed and the spheroid
packets escape intact from the colonial matrix. Upon contact with macro-
gametes, the packet dissociates into its component gametes and fertiliza-
tion occurs (Fig. 4. 32, O, P).

Microgametes of Volvox develop from enlarged cells resembling the
"gonidia." Development of microgametes is precocious in Volvox sperma-
tosphaera, V. weismannia, and several other species in that packets of
gametes reach maturity while young male colonies are still within the
parental colony. In other heterothallic species, mature packets develop
only after the male colonies emerge from the parent and grow to about
the size of female and asexual colonies. Volvox spermatosphaera differs
from other species in that every flagellate in the male colony may develop
into a packet of gametes. The mature packet is discoid in Volvox aureus,
V. spermatosphaera, and V. weismannia, while spheroid packets are de-
veloped in V. globator, V. perglobator, and several others (259), The

160 The Mastigophora

spheroid packet results when fission produces 256 or more cells; the in-
verted plakea remains plate-like when the number is only 16-128.

The developing macrogamete of Volvox, early in the life of the young
colony, grows into a large spheroidal cell containing much stored food.
Microgametes enter female colonies, sometimes before the ova are fully
grown, and finally penetrate the ova as they approach or reach maturity.
After fertilization, the zygote encysts. The ectocyst may show characteristic
decorations (Fig. 4. 32, H-K). After disintegration of the female colony
the cyst sinks to the bottom, where it remains dormant until the follow-
ing spring. Under natural conditions, colonial forms may occur only
during two or three months of the year, so that the encysted zygote
is the predominant phase of the cycle (259). In laboratory cultures, how-
ever, repeated generations of asexual colonies have been obtained over a
period of a year or more (275).

Order 6. Euglenida

The Euglenidai are rather large flagellates, mostly with one or
two flagella. The body is generally elongated and often spindle-shaped,
with some degree of spiral torsion, but modifications occur in such genera
as PJiacus (Fig. 4. 34, I-L). The reservoir (Fig. 4. 33, A-D), or "gullet,"
from which the flagella arise, is a characteristic feature. Flagellates as-
signed to two genera, Chlorachne and Ottonia, apparently lack reservoirs,
but Schiller's (251) descriptions do not supply conclusive evidence that
these are Euglenida. One or two contractile vacuoles empty into the
reservoir, and each flagellum is inserted in the posterior or postero-dorsal
wall of this cavity. The pellicle permits euglenoid movement (metaboly)
in many species but it may be only slightly flexible, as in Euglena acus,
or rather rigid in such genera as Menoidium and Phacus. As reported for
Euglena viridis (228), this membrane gives negative tests for cellulose,
but is completely digested by trypsin and presumably contains proteins.
According to Chadefaud (34), the pellicle (Fig. 4. 33, E) consists of a thin
epicuticle and a deeper and thicker cuticle. Only the epicuticle extends
into the reservoir. The usually noticeable spiral striations seem to be
cuticular ridges (34); presumably the rows of papillae in Euglena
spirogyra are comparable decorations. The distribution of peripheral
inclusions, and sometimes that of the chromatophores, may follow the
spiral decorations of the pellicle. In addition to the pellicle, a lorica oc-
curs in Ascoglena and Klebsiella (Fig. 4. 33, K, L); a shell, or test, in
Trachelomonas (Fig. 4. 33, J).

Perhaps the majority of Euglenida are chlorophyll-bearing, although
there are many colorless species. The chromatophores range from one to
many and also vary in size and form (Fig. 4. 33, F-J) in different species.
The green color of chlorophyll is not masked by other pigments. How-

^ The literature on Euglenida has been reviewed by Jahn (119).

The Mastigophora 161

Fig. 4. 33. A-D. Flagella and reservoir: Euglena mutabilis (A), Euglena-
morpha, green form (B), Eutreptia (C), Distigma (D); diagrammatic (after
Hollande). E. Plasmolyzed specimen of Eugleua archaeoplastidiata, pellicle
separated from body, two pyrcnoids shown; schematic (after Chadefand).
F-I. Various types of chromatophores in Euglena: E. geniculata (F), E. ana-
baena (G), E. viridis (H), E. variabilis (I); schematic (after Pringsheim).
J. Trachelomonas volvocina Ehrbg., showing test, chromatophores, stigma,
nucleus (outline); x720 (after Deflandre). K, L. Klebsiella alligata, external
view of lorica and optical section through posterior end; xlOOO approx.
(after Pascher). M. Euglena gracilis, palmella; x455 (after Krichenbauer).
N. E. gracilis, somatella with six luiclei; chromatophores not shown; x675
(after Krichenbauer). O. Phacus caudata, four daughter flagellates being
produced from a somatella; x850 (after Krichenbauer).

162 The Mastigophora

ever, red haematochrome may accumulate in the cytoplasm in large
amounts, as in Euglena rubra (125). Pyrenoids are usually attached to
chromatophores or to non-pigmented "pyrenophores" (34). A typical
pyrenoid consists of two pyrenosomes, each covered with a paramylum
shell and applied to a surface of the chromatophore (Fig. 1. 17, L). The
inner pyrenosome may be reduced in size, and is lacking in some cases
(34). In such types as Euglena gracilis (Fig. 4. 34, A), there are many
chromatophores, each of which probably bears a pyrenoid. At the other
extreme, represented by Euglena archaeoplastidiata (Fig. 4. 33, E), there
is one chromatophore equipped with two pyrenoids (34). Bleaching of
the chromatophores in Euglena gracilis apparently is accompanied by
resorption of the pyrenoids, which reappear if the flagellates are returned
to the light and develop chlorophyll (240). A stigma, lying on the wall
of the reservoir near the paraflagellar body (Fig. 4. 33, A-C), is charac-
teristic of green species and also of certain colorless types (120, 237, 240).
The stigma may divide in fission (8), or may undergo dispersal and re-
aggregation of the piginent granules (96). Flagellar number and struc-
ture vary. The bifurcated flagellum of Phacus (Fig. 4. 34, H) and Euglena
has been interpreted as a biflagellate condition (Fig. 4. 33, A) in which
a rudimentary flagellum is often fused distally with a normal flagellum
(110). The bifurcation apparently is absent in Colacium (123) and
Rhabdomo7ias (99) but present in Menoidium (240). The situation in
Astasia has been disputed, some workers reporting a non-bifurcated and
others a bifurcated flagellum. More recent observations (240) indicate
that the flagellum, in at least certain species of Astasia, is much like that
of Euglena and that the rudimentary flagellum may or may not be in-
dependent of the normal flagellum. Such observations support the view
that a biflagellate condition is the primitive one and indicate the desir-
ability of reexamining those species in which a simple flagellum has been
reported. No "bifurcation" has been reported in biflagellate or triflagel-
late species. A paraflagellar body (photoreceptor, or flagellar swelling) is
characteristic of green species (Fig. 4. 33, A-C) but is absent in colorless
forms.

Stored reserves include lipids and paramylum; the latter is an iodine-
negative polysaccharide, insoluble in hot water and yielding glucose on
hydrolysis. Paramylum is deposited as refractile bodies which may show
concentric stratification in dilute solutions of KOH (62). Size and form
may be fairly constant for a species, while the number ranges from typi-
cally one (Phacus longicauda) or two {Euglena spirogyra) large bodies to
many small ones.

The life-cycle may include a flagellate stage, a palmella (Fig. 4. 33, M),
and a cyst. Fission may occur in both palmella and flagellate stages.
Palmella stages are unknown in many species and their distribution
within the order remains uncertain, although they may be absent in

The Mastigophora 163

colorless species (240). A palmella is dominant in the cycle of Eugleno-
capsa ochracea (263), and a sessile non-flagellated stage plays a compa-
rable role in Colacium vesicidosum (Fig. 4. 35, O, P). The sessile stage of
the latter is derived from a flagellate which becomes attached at its flag-
ellar end. The flagellum and reservoir disappear, a sheath and stalk are
secreted, and mitosis may produce as many as eight nuclei. A naked

Fig. 4. 34. A-D. Euglena: E. gracilis Klebs (A), xl200; E. sociabilis Dan-
geard (B), x450; E. pisciformis Klebs (C), xl650; E. tripteris (D), x475 (after
Johnson). E. Eutreptiella marina da Cunha. xl600 approx. (afte; da C). F.
Trachelomonas hystrix, test only; x600 (after Dangeard). G. Euglena oxyu-
ris Schmarda, x350 (after Johnson). H. Phacus p\rum, showing two large
lateral paramylum bodies, small discoid chromatophores, nucleus (in out-
line); xl750 (after Krichenbauer). I, J. Phacus quinquenwrginatus Jahn and
Shawhan, surface and anterior views; length, 35-52/^; schematic (after Allegre
and Jahn). K, L. Phacus torta Lemmermann, broad sinface and anterior
end; length, 80-100/^; schematic (after Allegre and Jahn).

164 The Mastigophora

multinucleate form also has been observed in cultures (123). Either mul-
tinucleate stage may produce flagellate buds. A comparable plasmodium
has been reported in Euglena gracilis (Fig. 4. 33, N) and Phacits caudata
(Fig. 4. 33, O) by Krichenbauer (167); also, in Astasia klehsii. In A.
klebsii no fission occurs in the plasmodial stage, which apparently origi-
nates as a result of increased osmotic pressure in old cultures. Even a
return to a normal medium does not induce fission (57).

Although the Euglenida are mostly fresh-water flagellates, a number
of genera are represented in salt-water and certain fresh-water species
have become adapted to sea water under laboratory conditions (82).
However, Euglena gracilis grows only in a salt concentration less than
that of 40 per cent sea water (185).

Although it is not difficult to recognize Euglenida, in view of their
characteristic features, subdivision of the group into taxonomically sound
suborders and families apparently remains a problem for the future. The
old three-family system — Euglenidae, Astasiidae, and Peranemidae — was
convenient up to a certain point. Green flagellates could be placed in the
Euglenidae, and holozoic types, often with a pharyngeal-rod apparatus.
could be assigned to the Peranemidae. The residue of colorless flagel-
lates could be dropped into the Astasiidae. Various observations have
disturbed this taxonomic tranquillity. The discovery of colorless stigma-
bearing flagellates (good species of Euglena except for the absence of
chromatophores), the recognition of Hyalocephalus as a colorless homo-
logue of Phacus, and recent observations on the loss of chlorophyll in
Euglena make the presence or absence of chromatophores a feature of
doubtful value in separating families. In fact, certain generally recog-
nized species of Astasia are possibly nothing more than colorless strains
of Euglena (239). Furthermore, Pringsheim and others have observed
that growth of Euglena gracilis in darkness, following treatment with
streptomycin, induces loss of the stigma after the chromatophores have
disappeared. This new creation is a genetically stable strain which would
be eliminated automatically from the old family Euglenidae. The old
family Peranemidae also is not homogeneous in that a pharyngeal-rod
apparatus is present in some genera and not in others, holozoic nutrition
has not been demonstrated in certain cases, and differences in flagellar
apparatus are well known.

Hollande (110) has divided the Euglenida into three groups which, in
conformity with the present system, would be recognized as suborders —
Euglenoidina, Peranemoidina, and Petalomonadoidina. These suborders
would be divided into appropriate families as adequate information be-
comes available. Although separation of the Peranemoidina and Petalo-
monadoidina may not be clear cut, if the siphon of Entosiphon (Fig. 4.
37, B) is only a modified rod-apparatus as seen in Peranema (Fig. 4. 36,

The Mastigophora 16!

Fig. 4. 35. A. Distiginopsis grassci HoUande, x2430 approx. (after H.). B.
Eutreptia viridis Perty, x240 (after Lenimennann). C. Astasia comma Pring-
sheim, x835 approx. (after P.). D. Menoidium cultellus Pringsheim, x500 ap-
prox. (after P.). E. Astasia dangeardii Lemmermann, x860 approx. (after
Pringsheim). F. Cryptoglena pigra Ehrl)g., xl300 (after Lemmermann). G.
Rhal)dnmouas incurva Presenilis, xl470 (after Hall). H. Astasia longa Pring-
sheim, x720 approx. (after P.). I. Astasia torta Pringsheim, x835 approx.
(after P.). J. Lepocinclis niarssoni Lemm., showing two lateral paramylum
bodies; xGOO (after L.). K, L. Pliacus pleurouectes (O. F. M.) Dujardin, dor-
sal surface and anterior end; chromatophores not shown; length, 40-lOOju:
schematic (after Allegre and Jahn). M. Menoidium obtusum Pringsheim, xr)00
approx. (after P.). N. Ascoglemi vaginicola Stein, with lorica; x412 (after
Lemmermann). O, P. Colacium vesiculosum Ehrbg., a budding multinucleate
sessile stage and a uninucleate stage; xl955 (after Johnson). Q. Distigma sen-
nii Pringsheim, x900 approx. (after P.).

166 The Mastigophora

C, D), Hollande's system seems to have certain advantages in the present
stage of taxonomic progress.

Suborder 1. Euglenoidina. These flagellates have one or more flagella,
may or may not contain chlorophyll, are not holozoic, may be metabolic,
or may have a rigid pellicle. The flagellar sheath is not swollen at the
base. On the basis of flagellar equipment, Hollande (110) recognized
the families Euglenamorphidae, Eutreptiidae, Distigmidae, Euglenidae,
and Menoidiidae, but the erection of definitive families may require more
information than is now available.

The following genera may be assigned to the suborder: Ascoglena Stein (202; Fig. 4.
33, N); Astasia Dujardin (236, 238, 239, 240; Fig. 4. 35, C, E, H, I); Colacium Ehren-
berg (123, 202; Fig. 4. 35, O, P); Cryptoglena Ehrenberg (202; Fig. 4. 35, F); Distigma
Ehrenberg (108, 172, 236; Fig. 4. 35, Q), without chroraatophores; Distig)nopsis Hol-
lande (110; Fig. 4. 35, A); Euglena Ehrenberg (124, 202; Fig. 4. 34, A-D. G); Euglena-
morpha Wenrich (277;, Fig. 4^ 33, B), from tadpoles; Eiitreptia Perty (202; Fig. 4. 35,
B); Eutreptiella da Cunha (Fig. 4. 34, E); Hyalocephalus Pringsheim (236), a colorless

Fig. 4. 36. A. Peranemopsis striata Lackey; one long anterior flagellum;
no second flagellum like that of Peranerna, and only one pharyngeal-rod;
length, 90-110^ (after L.). B. Urceolus cyclostomus (Stein) Mereschkowski,
showing vestibule, reservoir, pharyngeal-rod apparatus, nucleus, ingested
food; x933 (after Klebs). C. Peranerna trichophorum (Ehrbg.) Stein,
slightly contracted, ventral vieu' showing pharyngeal-rod apparatus and
trailing flagellum adherent to the body; in swimming, the anterior flagel-
lum (shown in part) is extended as in Peranemopsis (A); schematic (after
Chadefaud). D. Pharyngeal-rod apparatus of P. trichophorum, right lateral
aspect; schematic (after Chadefaud). E. Heteronema acus (Ehrbg.) Stein;
ingested Euglena in a food-vacuole not yet separated from the reservoir;
flagella shown leaving cytostome; x2240 (after Loefer).

The Mastigophora 167

"Phacus"; Khawkinea Jahn and McKibben (120), similar to Euglena except for the
absence of chromatophores; Klebsiella Pascher (215; Fig. 4. 33, K, L); Lepocinclis Perty
(49, 202; Fig. 4. 35, J); Menoidium Perty (236, 238; Fig. 4. 35, M); Phacus Dujardin
(3, 202, 230; Fig. 4. 34, H-L); Rhabdoinonas Fresenius (99, 238; Fig. 4. 35, G); Tra-
chelomonas Ehrenberg (60, 202; Figs. 4. 33, J, 4. 34, F). In addition, Euglenocapsa
Steinecke (263), in which a palmella stage is dominant, may be a valid genus.

Suborder 2. Peranemoidina. These are colorless, metabolic types with
two flagella, one of which is trailed. Each flagellum is said to be swollen

Fig. 4. 37. A. Marsupiogaster striata Schewiakoff, x835 (after S.). B. Etito-
siphon sulcatum (Duj.) Stein; length, 20-25/t; siphon, gullet, nucleus and
food vacuoles; schematic (after Lackey). C, D. Triangulomonas rigida
Lackey; 18x15;^; surface and lateral views (after L.). E. Sphenomonas teres;
length, 20-40/i; large retractile inclusion of uncertain nature, smaller para-
mylum bodies (after Hollande). F. Tropidoscyphus octocostalus Stein, show-
ing prominent ridges; x412 (after Lemmermann). G. Anisonema aci^ius Duj.,
showing one "pharyngeal-rod," nucleus, ingested food; x633 (after Lemmer-
mann). H. Notosolenus apocarnptus Stokes; length, S-lO^ii; short trailing
flagellum arises from convex ventral surfaces (after S.). I,J. Petalomonas
dorsalis Stokes, 38-45/n; entire flagellate and optical cross-section (after
Shawhan and Jahn).

168 The Mastigophora

at the base (110). Solid food is usually ingested. The characteristic
pharyngeal-rod apparatus, which lies dorsal to the reservoir, is composed
of two long rods and a shorter falcate rod which extends ventrally at its
anterior end (Fig. 4. 36, C, D).

The conclusion of Tannreuther (268a), that the rod apparatus in
Peranema is a "perforatorium" used for piercing the prey, has been con-
firmed by Chen (38). The identity of the cytostome and gullet in these
holozoic Euglenida has been disputed. Chen (38) and Pitelka (229),
among others, have been convinced that ingestion takes place through a
cytostome and gullet independent of the reservoir and its external open-
ing. Chadefaud (35), on the other hand, maintains that there is no
separate gullet in at least certain members of the group. Previous ob-
servations on the continuity of food vacuoles with the cavity of the reser-
voir (Fig. 4. 36, E) in Heteronema (184) and Peranema (100) support
the latter conclusion.

The following genera are included: Heteronema Stein (184, 202; Fig. 4. 36, E);
Peranema Dujardin (35, 202, 229; Fig. 4. 36, C, D), trailing flagellum adherent to the
pellicle; Peranemopsis Lackey (175; Fig. 4. 36, A); Urceolus Mereschkowsky (202; Fig.
4. 36, B). However, Pitelka (229) has considered Heteronema a synonym of Peranema.

Suborder 3. Petalomonadoidina. The body of these colorless flagellates
is typically compressed and not plastic. There may be one or two flagella
and each flagellum is swollen at the base (110). Some species are definitely
holozoic. A pharyngeal-apparatus, described for several genera, may or
may not be homologous with that of Peranema.

The suborder includes the following genera (110): Anisonema Dujardin (202; Fig. 4.
37, G); Dinema Perty (202); Entosiphon Stein (110, 171, 202; Fig. 4. 37, B); Marsupio-
gaster Schewiakoff (202; Fig. 4. 37, A); Notosolenus Stokes (202; Fig. 4. 37, H); Peta-
lomonas Stein (251; Fig. 4. 37, I, J); Scytomonas Stein (202); Sphenomonas Stein (110,
202); Triangiilomonas Lackey (175; Fig. 4. 37, C, D); Tropidoscyphus Stein (202; Fig.
4. 37, F).

Order 7. Chloromonadida

Little is known about these flagellates. The described species are fairly
large (30-100[jl) forms with somewhat plastic bodies which are usually
dorso-ventrally flattened, and may show a ventral groove arising near the
anterior end. The numerous bright green chromatophores are peripheral
and radially arranged in Chattonella (Fig. 4. 38, B) and Gonyostomum
(Fig. 4. 38, H). The pigments are said to include xanthophylls as well as
chlorophyll; the mixture turns blue-green in dilute acid (69). No stigma
has been reported. Oil droplets are usually stored. Glycogen also occurs
in Gonyostomum semeyi (114), but starch apparently is not formed. There
are typically two flagella, one of which is trailed.

A gullet (Fig. 4. 38, E, H, J) not unlike the reservoir of Euglenida

Fig. 4. 38. A, B. Chattonella subsalsa Biecheler; length, 30-50^; surface
view showing chromatophores, ventral groove, and basal portions of flagella;
optical section showing chromatophores, nucleus, and flagellar connections
(after B.). C. Merotrirhia capitatu Skuja, showing ventral groove, chromato-
phores, and "trichocysts"; x550 (after S.). D. Nuclear cap and flagellar con-
nections in Vacuolaria virescens; schematic (after Poisson and HoUande).
E. Vacuolaria viridis (Dangeard) Senn, longitudinal section of stained speci-
men showing nucleus, "gidlet," and chromatophores; diagrammatic (after
Fott). F. Vacuolaria virescens Cienkowski; length, 50-150^; stained specimen
showing chromatophores, contractile vacuole, nucleus and nuclear cap; sche-
matic (after Poisson and Hollande). G. Dividing nucleus of V. virescens;
diagrammatic (after Poisson and Hollande). H-J. Gonyostomum semen
Diesing, length 40-65;^. H. Diagrammatic optical section showing chromato-
phores, trichocysts, nucleus (in outline), and contractile vacuole lateral to
"reservoir" (after Chadefaud). I. Ventral view, showing groove and flagella.
J. Optical section showing outline of nucleus and reservoir; diagrammatic
(after Drouet and Cohen). K. Fission in palmella stage, Vacuolaria virescens;
schematic (after Poisson and Hollande).

170 The Mastigophora

has been described in some species. However, it has been suggested that
in Vacuolaria (Fig. 4. 38, F) at least, a large contractile vacuole has pre-
viously been misinterpreted as a gullet (232). The lack of such a gullet
would suggest that the Chloromonadida are not closely related to the
Euglenida. The dividing nucleus of Vacuolaria (Fig. 4. 38, G), strikingly
different from the euglenoid type, points to the same conclusion, as does
the insertion of the fiagella (Fig. 4. 38, B, F). The fiagella of Gonyosto-
rnum semen, on the other hand, apparently arise from the base of the
triangular cavity, or "gullet" (70). A peculiar "supranuclear cap" (Fig.
4. 38, D), lying just anterior to the nucleus, occurs in Vacuolaria (232).
Various globular, discoid, or spindle-shaped bodies, subpellicular in dis-
tribution (Fig. 4. 38, C, H), have been interpreted as mucous globules
(15, 232) and as trichocysts (33). Upon discharge, such inclusions give
rise to filaments in Gonyostomum (33). The cytoplasm of Gonyostomum
semen (114) and Chattonella subsala (15) is differentiated into two zones,
apparently separated by a delicate membrane ("central capsule"), per-
haps merely an interface. The outer zone contains the chromatophores,
vacuome, fat globules, and trichocysts. Fission occurs in flagellate stages
of Chattonella (16) and Gonyostommii (69, 114), and in palmella stages
of Vacuolaria (Fig. 4. 38, K). Cysts with a thick membrane have been re-
ported in Gonyostomiun (69).

The Chloromonadida are fresh water types whose ecological distribu-
tion may be somewhat restricted. Gofiyostotnum semen, for instance,
seems to be limited to the rather acid waters of marshes (114),

Tfie following genera have been referred to the order: Chattojiella Biecheler (15,
16; Fig. 4. 38, A, B), Coelomonas Stein (231), Gonyostomum Diesing (33, 69, 70, 114;
Fig. 4. 38, H-J), Merotrichia Mereschkowski (Fig. 4. 38, C), Rhaphidomonas Stein,
Rickertia Conrad (43), Thaumatomastix Lauterborn, Thaumatomonas de Saedeleer
(246), Trentonia Stokes (264), and Vacuolaria Cienkowski (83, 232). Three of these
generic names are said to be invalid, since Rhaphidomonas is a synonym of Gony-
ostomum, and both Coelomonas and Trentonia appear to be synonyms of Vacuolaria
(232). The relationships of Thaumatomastix, Thaumatomonas, and Rickertia to Chat-
tonella, Gonyostomum, and Vacuolaria need further investigation.

CLASS 2. ZOOMASTIGOPHOREA

These flagellates have no chromatophores and they store lipids
and glycogen but apparently no starch or paramylum. Some are sapro-
zoic but there are many holozoic species. The body is generally rather
plastic and no cellulose membrane or test is produced. Many are small
and simple in structure, while others are perhaps as complex as any of
the Protozoa. Zoomastigophorea occur as parasites in various groups of
invertebrates, in all classes of vertebrates, and also in certain plants. As
free-living flagellates, they are found in the soil and in both fresh and
salt water. The life cycle is simple in the majority, but polymorphic

The Mastigophora 171

cycles are known, as in the Trypanosmidae, and sexual phenomena have
been reported in a few instances, most recently by Cleveland (Chapter II).

Present classifications are tentative at best and are based, to an im-
portant extent unfortunately, upon somewhat artificial criteria rather
than upon detailed information which might suggest natural relation-
ships. The recent erection of the order Trichomonadida (147), the result
of a long series of intensive studies, has set a sound pattern for the pos-
sible establishment of additional coherent orders within certain areas of
the class. In the meantime, the remnants of the "Polymastigida" may
be retained, along with the other older orders, for taxonomic convenience.
Accordingly, the Zoomastigophorea may be subdivided as follows:

Order I. Rhizomastigida. This inadequately defined group of amoe-
boid flagellates has served occasionally as a repository for genera of un-
certain taxonomic position, and has also been treated as a family of the
Protomastigida.

Order 2. Protomastigida. These are solitary or colonial types with one
or two fiagella. The body is plastic but does not show the amoeboid
activity of the Rhizomastigida.

Order 3. Polymastigida. The remnants of the old Order Polymastigida
include mostly uninucleate and binucleate species, although there are a
few with a number of nuclei. There are usually 3-8 fiagella.

Order 4. Trichomonadida. These are uninucleate or multinucleate
(but not binucleate) flagellates with an axostyle, a parabasal body, and
a mastigont of 3-6 fiagella. One of the fiagella is typically a trailing fiag-
ellum which may or may not form part of an undulating membrane.

Order 5. Hypermastigida. These are uninucleate flagellates with many
fiagella. The known sjoecies are intestinal parasites of termites, wood
roaches and cockroaches.

Order 1. Rhizomastigida

This order may be limited to flagellates with 1-4 fiagella and
amoeboid bodies which often show considerable pseudopodial activity.
In at least some species, a cytoplasmic fibril ("rhizostyle") of uncertain
significance extends posteriorly from one of the blepharoplasts.

The following genera may be assigned to the order: Heliobodo Valkanov (276; Fig.
4. 39, I); Histomonas Tyzzer (20, 273, 274, 280; Fig. 4. 39, A-F); Mastigamoeba Schulze
(153); Mastigella Frenzel (88, 97, 153; Fig. 4. 39, L); Mastigina Frenzel (12, 13, 88; Fig.
4. 39, J, K); and Rhizomastix Alexeieff (191; Fig. 4. 39, G, H). Tricholimax Frenzel
apparently is a synonym of Mastigina Frenzel (97). Certain other genera, sometimes
included in the Rhizomastigina, probably do not belong here. Pteridomonas Penard
possibly should be referred to the Chrysomonadida, while Actinomonas Kent and
Dimorpha Gruber probably belong in the Helioflagellida (Chapter V). The relationships
of Multicilia Cienkowski (177) are uncertain on the basis of available data. Although
the body is amoeboid, the many fiagella (or axopodia?) and the 1-4 nuclei are not very
strong inducements for retaining this genus in the Rhizomastigida.

172 The Mastigophora

Fig. 4. 39. A-F. Uistomonas nieleagridis Tyzzer: A. Rounded stage showing
nucleo-flagellar connections, x2310 (after Bishop). B. Specimen with four flagella
and rhizostyle, xl866 (after Wenrich). C. Daughter nuclei joined by paradesmose,
x2310 (after Bishop). D. Uniflagellate form with rhizostyle, x2310 (after Bishop).
E. Ingestion of food by means of a "tube," xl866 (after Wenrich). F. Elongated
imiflagellate form, x2310 (after Bishop). G. Rhizomast/x gracilis Alexeieff, nu-
cleus and rhizostyle stained; x2000 (after Mackinnon). H. Cyst of R. gracilis,
two nuclei and two rhizostyles; x2000 (after Mackinnon). I. Heliohndo radians
Wilkanov; x2400 (after V.). J, K. Mastigina hylae (Frenzel) Goldschmidt (after
Becker); specimen showing nucleus, flagellum, rhizostyle extending posteriorly,
and cap-like "cape" fitting over nucleus anteriorly (J), x515; pattern of proto-
plasmic streaming (K), diagrammatic. L. Mastigella polyniastix Frenzel, x400
(after F.).

Species of Mastigatnoeba and Mastigella are similar with respect to the
single flagellum and the development ot slender pseudopodia. However,
the nucleus is approximately central and not connected with the flag-
ellum in Mastigella, while the nucleus in Mastigamoeha is anterior and

The Mastigophora 173

apparently joined to the blepharoplast. In Mastigina the nucleus is an-
terior as in Mastigamoeha and is joined to the blepharoplast, but slender
pseudopodia seem to be lacking. The nucleoflagellar relationships of
Mastigina liylae (Frenzel) Goldschmidt have been described by Becker
(12). In addition to the flagellum, two other structures are joined to the
blepharoplast (Fig. 4. 39, J). A rhizostyle extends posteriorly, and a cap-
shaped "cape" fits over the anterior surface of the nucleus. From the cape,
filaments extend to the anterior end of the body.

Rhizornastix gracilis Alexeieff, recovered from an axolotl and from
crane-fly grubs, shows a rhizostyle, extending almost to the posterior end
of the body (Fig. 4. 39, G), but there is no "cape" as in Mastigina hylae
and the nucleus is central (191). Nuclear division occurs within the cyst
(Fig. 4. 39, H), and a second rhizostyle develops by outgrowth from a
blepharoplast.

HeJiobodo (Fig. 4. 39, I) includes spheroid uninucleate organisms with
two flagella and many slender pseudopodia which apparently are not
axopodia. Whether this genus actually belongs in the Rhizomastigida is
uncertain.

Histomonas meleagridis Tyzzer (Fig. 4. 39, A-F) is associated with
"blackhead" (enterohepatitis) in turkeys and chickens. An interesting
featiue of blackhead in turkeys is that young birds are readily infected
by feeding them embryonated eggs of the cecal worm, Heterakis gallinae.
The flagellates apparently remain viable in such eggs for more than a
year when kept in a refrigerator (189). H. meleagridis is an amoeboid or
slug-like organism which may produce slender pseudopodia and is ca-
pable of changing shape rapidly (20). Some of these slender pseudopodia
may correspond to the tubular protrusions (Fig. 4. 39, E) noted by Wen-
rich (280) in stained preparations. The unusual variability in number of
flagella raises questions concerning the validity of Histomonas meleagridis
as a specific name for all the various strains described from birds. One
flagellum is typical in cultures from chickens (20), although binucleate
forms with two flagella, and tetranucleate forms with four, occur occa-
sionally. In material from ring-neck pheasants (280), flagellate stages
nearly always showed four flagella. Flagellar resorption occurs at an early
stage of nuclear division so that non-flagellated uninucleate and bi-
nucleate forms are common and tetranucleate stages without flagella are
sometimes seen (20). Whether the "rhizostyle" is a normal organelle, or
merely an occasionally observed remnant of the paradesmose is still un-
certain.

Order 2. Protomastigida

These are relatively small organisms with one or two flagella. The
body is typically plastic, but not markedly amoeboid. Nutrition is sapro-
zoic in some types and holozoic in many others. The order includes

174 The Mastigophora

Fig. 4. 40. A. Salpingoeca brunnea Stokes, with theca; x660 (after France).

B. Codonocladium iimbellatum (Tatein) Stein, x325 (after Lemmermann).

C. Desmarella moniliformis Kent, typical linear "colony"; x477 (after Lem-
mermann). D. Lagenoeca globulosa France, free-swimming loricate type; x530
(after Lemmermann). E. Diplosigopsis entzii France, sessile loricate type; x600
(after F.). F. Spliaeroeca volvox Lauterborn, x350 (after Lemmermann). G.
Protospongia hacckelii Kent, x442 (after Lemmermann). H. Codonosigopsis
socialis (France) Lemmermann, with double collar; x500 (after F.). L Diplo-
siga socialis Frenzel, with double collar; xl350 (after F.). J. Monosiga angus-
tata Kent, x2000 (after K.). K. Codosiga botn'tis Ehrbg.; length of body
(excluding collar), 7-16/n; body enclosed in a mucous envelope (outline em-
phasized); schematic (after Lapage).

free-living species and parasites of invertebrates, vertebrates, and certain
plants. The life-cycle is often simple, but is dimorphic to polymorphic in
Trypanosomidae. Interrelationships of the different families are not en-
tirely clear and the limits of the order have been disputed to some extent.
For example, Trimastix Kent and Tricercomonas Wenyon and O'Connor
have been classified both with Protomastigida and the Polymastigida.

The Mastigophora 175

Six families may be assigned to the order: Codosigidae, Phalansteriidae,
Trypanosomidae, Cryptobiidae, Amphimonadidae, and Bodonidae.

Family 1. Codosigidae. This group (30, 181) includes species with a
"collar" (Fig. 4. 40). As described in Codosiga (Fig. 4. 40, K), this collar
is a protoplasmic membrane which can be extended as a hollow cone
surroimding the basal portion of the flagellum (176). The collar can be
retracted completely. The body is enclosed in a thin "mucous envelope"
apparently continuous with the stalk. During feeding, the anterior end
of the body contracts away from the envelope and food particles, driven
by flagellar currents, drop into this space. As the body surges back against
the envelope, the food particles apparently are forced into the body. The
expanded collar evidently directs food into the space between the body
and the envelope. Many choanoflagellates resemble the choanocytes of
sponges to such a degree that Kent (130) included them with the sponges
in his order "Choano-flagellata." The similarity may involve not only
the collar but also a parabasal body, or apical body (Fig. 1. 10, L, M). A
single flagellum is characteristic. An interesting feature of the sessile
Codosiga botrytis is that flagellates which become detached swim stalk-
first (176). Both solitary and colonial forms are known. In addition, tem-
porary clusters of several flagellates, failing to separate after fission, may
remain attached to a stalk, as in Codosiga (176).

The family includes several genera of naked flagellates — Codoiiosigopsis Senn (Fig.
4. 40, H); Codosiga James-Clark (Fig. 4. 40, K); Desmarella Kent (174; Fig. 4. 40, C);
Diplosiga Frenzel (Fig. 4. 40, I); and Monosiga Kent (245; Fig. 4. 40. J). A lorica is
present in several others: Diplosigopsis France (Fig. 4. 40, E); Lagenoeca Kent (Fig.
4. 40, D); and Salpingoeca James-Clark (Fig. 4. 40, A). Spheroid colonies are developed
in Protospongia Kent (Fig. 4. 40, G) and Sphaeroeca Lauterborn (Fig. 4. 40, F).

Poteriodendron Stein and Histiona Voigt, sometimes grouped with the choanoflagel-
lates, probably are Chrysomonadida (93. 224). This is also the case for Bicoeca James-
Clark (222).

Family 2. Phalansteriidae. Little is known about Phalansterium Cien-
kowski (181; Fig. 1. 3, A), although the presence of a simple collar
closely fitting the flagellum suggests a relationship to the Codosigidae.
The genus includes both branching and spheroid or discoid colonies
with a granular matrix.

Family 3. Trypanosomidae. These parasites have a single flagellum
ending in a blepharoplast, near which lies a spheroid or discoid kineto-
plast (Fig. 1. 10, J, K). The flagellum may or may not form part of an
undulating membrane. Life-cycles are dimorphic or polymorphic. Four
different types (Fig. 4. 41) occur in the family — the leishmanial, lepto-
monad, crithidial, and trypanosomal forms. In invertebrate hosts, the
flagellates are often attached to the lining of the digestive tract or to
other surfaces, Such stages are sometimes referred to as haptomonads;

176 The Mastigophora

the unattached flagellates, as nectomonads. Attachment may involve loss
of the distal portion of the flagellum, although the axoneme persists
between the kinetoplast and the tip of the body (Fig. 4. 41, J).

On the basis of life-cycles, six genera have been recognized (285):
Crithidia, Herpetomonas, Leishmania, Leptomonas, Phytomonas, and
Trypanosoma. Only leptomonad and leishmanial forms are found in
Leptomonas, Leishmania, and Pliytomonas.

Fig. 4. 41. A, B. Leptomonas patellae Porter, leptomonad and leish-
manial forms; x3120 (after P.). C, D. Leishmania chamaelonis Wenyon,
leptomonad and leishmanial forms; from cloaca of Chamaeleon vulgaris;
x2750 (after Wenyon). E-G. Crithidia euryophthalmi McCulloch, from
Euryophthahnus coyivivus; leishmanial stage from hind-gut, crithidial stage
(with narrow undulating membrane) from crop, and crithidial haptomonad
from hind-gut; xl875 (after McC). H-K. Trypanosoma lewisi; form from
blood of the rat, small metacyclic trypanosome from hind-gut of flea, two
crithidial haptomonads from the hind-gut, and a stage in intracellular re-
production (stomach of flea); H-J, x2400; K, xl350 (after Wenyon). L. Tryp-
anosoma brucei, xl800 (after Wenyon). M-R. Herpetomonas muscarum,
leptomonad form, two crithidial stages, trypanosomal form, and two leish-
manial stages; xI600 approx. (after Wenyon).

The Mastigophora 177

Leptomonas Kent (Fig. 4. 41, A, B) includes parasites of invertebrates.
However, the type species — Leptomonas bhtschlii Kent from the gut of
a nematode {Trilobiis gracilis) — has not been studied in detail and it is
not yet certain that more recently erected species actually belong in Kent's
genus. According to current concepts of the genus, both haptomonad and
nectomonad leptomonads may occur in the digestive tract and leishmanial
stages are to be expected in the posterior intestine. The leishmanial
forms of L. ctenocephali, which become resistant to desiccation (284),
are voided in the feces and ingested by flea larvae. The infection persists
through development of the flea (68).

Phytomonas Donovan. Members of this genus occur in invertebrates
and plants. Phytomonas davidi (85) is found as leptomonad and leish-
manial forms in the latex of Euphorbia segetalis and in the digestive tract
of a bug, Stenocephalus agilis, which feeds on the plant. After a period
of multiplication in the insect, leptomonad stages appear in the salivary
glands. These are presumably the forms infective for plants. In addition,
transfer of leishmanial stages from insect to insect has been reported.

Leishmania Ross (Fig. 4. 41, C, D). The life-cycle involves a vertebrate
and an invertebrate host. In mammals, the leishmanial form is predom-
inant, or else the only stage found, and occurs primarily in lymphoid-
macrophage cells, and occasionally in mononuclear and polynuclear
leucocytes of the peripheral blood. Leishmanial stages ingested by the
invertebrate hosts (species of Phlebotomus) develop into leptomonad
forms which multiply in the digestive tract. Infective stages are eventu-
ally inoculated into a vertebrate. Leishmania donovani, L. tropica, and
L. brasiliensis, which are parasitic in man, are discussed in Chapter XII.
Leishmania chamaeleonis, in contrast to the typical species of mammals,
occurs both as leptomonad and leishmanial forms in the cloaca of a
chameleon (285).

Crithidia Leger (Fig. 4. 41, E-G). Crithidial, leptomonad, and leish-
manial forms occur in the invertebrate hosts. However, the leptomonad
forms may be mere transitory stages in fission or in development of
crithidial and leishmanial forms. The type species, C. fasciculata, was
described from the intestine of Anopheles maculipennis (180). Leish-
manial stages, produced in the hind-gut, apparently are eliminated and
then ingested by new hosts. The occurrence of infections with C. lepto-
coridis in nymphs of the box-elder bug (188) indicates that insects may
become infected before the adult stage is reached.

Herpetomonas Kent (Fig. 4. 41, M-R) is limited to invertebrates, but
the life-cycle includes trypanosomal forms as well as the other types.
Detailed studies of the type species, H. muscarum (Leidy) Kent — some-
times known as H. muscae-domesticae (Stein) Kent — have shoAvn that
trypanosomal stages occur in flies (283) and in cultures (68). Leishmanial

178 The Mastigophora

stages may arise either from leptomonad or trypanosomal forms in the
natural host, and the crithidial stage typically lacks an undulating mem-
brane.

Trypanosoma Gruby (Fig. 4. 41, H-L). The life-cycle usually involves
both vertebrates and invertebrates (arthropods, leeches). The trypano-
somal stage occurs in the blood of vertebrates, while leptomonad and
crithidial forms are rare, if they are found at all. Intracellular leishmanial
stages may occur, as in T. cruzi. All four stages may occur in the inverte-
brate host. Haptomonads may be expected in insects infected with T.
lewisi (hind-gut of fleas), T. vivax (proboscis of Glossina morsitans), or
T. gamhiense ("salivary glands" of Glossina palpalis), for example. The
stage infective for vertebrates — the metacyclic trypanosome — is typically
an active trypanosomal form often derived from crithidial haptomonads.

Methods of transfer from invertebrate to vertebrate vary with the
species of Trypanosoma. In one group, which includes T. cruzi of man,
T. lewisi of rats, and T. melophagiu7n of sheep, metacyclic forms are
voided from the hind-gut of the vector, and infection of the vertebrate
follows contamination of wounds or mucous membranes. The metacyclic
stages of T. gamhiense, T. rhodesiense, T. evansi, and similar species de-
velop anteriorly in the vector and are transferred to the vertebrate host
by inoculation. A third type, represented by T. equiperdum, is trans-
ferred in vertebrates by coital contact and the vector has dropped out of
the cycle.

Vertebrate hosts of trypanosomes include fishes. Amphibia, aquatic and
terrestrial reptiles, birds, and various groups of mammals. Most species
of Trypanosoma, if not all, are probably non-pathogenic in their natural
hosts, or at least produce no serious damage. In man and domesticated
ungulates, however, several species cause diseases of considerable medical
and economic importance. This is particularly true in the tsetse fly areas
of Africa, where sleeping sickness of man (Chapter XII) and trypanosomi-
asis in cattle, sheep, horses, and goats have been important hindrances
to economic and social progress.

Family 4. Cryptobiidae. These are biflagellate parasites with a kineto-
plast somewhat larger than that of the Trypanosomidae. One of the
flagella extends anteriorly. The other, which is usually adherent to the
body and may or may not form part of an undulating membrane, extends
posteriorly as a free trailing portion.

The genera Cryptobia Leidy (Fig. 4. 42, A) and Trypanoplasma La-
veran and Mesnil are usually included, although some workers believe
that Trypanoplasma is a synonym of Cryptobia. However, this question
needs further study, since an undulating membrane has been described
in various species of Trypanoplasma but is absent in Cryptobia helicis
(166). Furthermore, the aciculum of C. helicis may be lacking in T^ypano-

The Mastigophora 179

\ '

Fig. 4. 42, A. Cryptobia helicis Leidy, sliowing "parabasal body" (at left),
trailing flagellum, aciculum, (at right) and nucleus; x2970 (after Kozloff).
B. Amphiinoiias globosa Kent, x480 (after Lenimermann). C. Amphiynonas
cyclopum (Kent) Blochmann, xl500 (after K.). D. Diploniita socialis Kent,
with lorica; xlOOO (after Lenimermann). E. Bodo caudatus HoUande, x2250
(after H.). F, G. Streptomonas cordata (Perty) Klebs; different views show-
ing keel; xl334 (after Lemniermann). H. Pleuromonas jaculans Perty, x767
(after Lemniermann). L Spongomonas iivella Stein; gelatinous matrix con-
tains many granules; x347 (after Lemmerniann). J. Proteromonas lacerti
(Grassi), showing "parabasal body" and a ring which encircles the flagellar
axoneme and parabasal rhizoplast; x2550 approx. (after Grasse). K. Colpo-
nema loxodes Stein; trailing flagelhnn extends along prominent ventral
groove; endoplasm is "granular"; xl200 (after Klebs). L. Pseudobodo m'mima
Hollande; compact "parabasal body" anterior to the nucleus; x3600 (after
H.). M. Dinomonas tuberculata Kent; xl7I0 (after K.). N. Phyllomitus amy-
lophagus Klebs; ventral view showing pharyngeal groove and elongated
"parabasal body"; x3375 (after Hollande).

180 The Mastigophora

plasma. Species of Cryptobia occur in the seminal vesicles and digestive
tract of molluscs and certain other invertebrates, and in the digestive
tract of marine fish. Species of Trypanoplasma occur in the blood of
marine and fresh-water fishes.

Family 5. Amphimonadidae. These are naked or loricate types with
two equal flagella (181). Naked types may be either free-swimming or
sessile. Colonial forms are assigned to several genera. The group as a
whole is much in need of investigation.

Solitary types include Amphimonas Dujardin (245; Fig. 4. 42, B, D), Diplomita Kent
(Fig. 4. 42, D), Spiromonas Perty (181), and Streptomonas Klebs (Fig. 4. 42, F, G).
Colonial types are assigned to Cladotnonas Stein (Fig. 1. 3, F), Rhipidodendron Stein
(181) and Spongomonas Stein (Fig. 4. 42, I).

Family 6. Bodonidae. These are solitary naked flagellates reported from
fresh and salt water, and from the digestive tract of certain reptiles and
Amphibia. One of the two flagella is usually trailed in swimming. A para-
basal apparatus is known in several genera. The Feulgen-positive para-
basal body of Bodo divides in fission (110) and is thus similar to the
kinetoplast of Trypanosomidae.

The following genera are included: Bodo (Ehrbg.) Stein {Proiuazekia Hartmann and
Chagas) (110; Fig. 4. 42, E); Cercobodo Krassiltschick (109, 110; Fig. 1. 10, P); Cerco-
monas Dujardin (113, 282); Colponema Stein (151; Fig. 4. 42, K); Dinomonas Kent
(130; Fig. 4. 42, M); Phyllomitus Stein (110; Fig. 4. 42, N); Pleuromonas Perty (181;
Fig. 4. 42, H); Proteromonas Kunstler {Prowazekella Alexeieff) (98; Fig. 4. 42, J), from
the intestine of lizards and salamanders; Pseudobodo Hollande (110; Fig. 4. 42, L).

Order 3. Polymastigida

Erection of the Order Trichomonadida by Kirby (147) has re-
moved from the old Order Polymastigida several families of closely
related uninucleate and multinucleate flagellates. As retained here, the
Polymastigida include families which are excluded from the Trichomo-
nadida but form an otherwise heterogeneous group. This arrangement
will serve a practical purpose until accumulated data permit a more
satisfactory classification. In this restricted sense, the Polymastigida
usually have 3-8 flagella and one, two, or occasionally a number {Micro-
rhopalodina) of nuclei. A parabasal apparatus is known in the Hexa-
mitidae but its homology with that of the Trichomonadida is not yet
certain. Seven families are retained in the order: Trimastigidae, Tetra-
mitidae, Streblomastigidae, Retortomonadidae, Callimastigidae, Poly-
mastigidae, and Pyrsonymphidae.

Family 1. Trimastigidae. There are three flagella, one anterior and
two trailing (181). Almost nothing is known about the cytology of the
group. One genus has been reported from salt water and two others
from fresh water. The family includes Dallingeria Kent and Trimastix

The Mastigophora 181

Fig. 4. 43. A. Retortomunas gryllotalpae (Grassi) Stiles, ventral view
showing peristomial fibril, two flagella, nucleus (in outline); x2000 (after
Wenrich). B. Chilonwstix intestiiialis Kuczynski, ventral view showing peri-
stomial fibril, four flagella, food vacuole, nucleus (in outline): x2000 (after
Wenrich). C. Macrumastix lapsa Stokes, x2250 (after Lemmermann). D, E.
Costia necatrix (Henneguy) Leclerq; ventral view showing groove and bases
of flagella; lateral view; x3750 (after Tavolga and Nigrelli). F. Coprnmastix
prowazeki Aragao, showing groove (at left), nucleus and rhi/ostyle; xI444
(after A.). G. Retortomonas gryllotalpae, lateral view (after Wenrich). H.
Relortomonas agilis Mackinnon, x2880 (after Ludwig). I, J. Chilomastix
magna Becker, showing nucleus, peristomial fibril, and intracytoplasmic
band but not the cytostomal flagellum (I), x2160; protargol technique, show-
ing peristomial fibril and flagella (J), x2850 (after Kirby and Honigberg).
K. Tetrarnitus rostratus Perty, showing groove, rhizostyle, nucleus; x2250
(after Hollande). L. Tetrarnitus salinus (Entz) Kirby, showing groove, ante-
rior nucleus, and food vacuole developing at base of gullet; x2320 (after K.).
M. Streblomastix strix Kofoid and Swezy, showing flagella and long slender
nucleus; xHOO (after K. & S.).

182 The Mastigophora

Kent, both with a long anterior flagellum, and Macromastix Stokes (Fig.
4. 43, C) with a short anterior flagelkim. A lateral membrane (or keel?),
which is not an undulating membrane, extends the length of the body
in Trimastix. The flagellar equipment of Macromastix resembles that of
the chrysomonad genus Prymneshim Massart (Fig. 4. 8, A). Similarly,
Chrysochromiilina (Fig. 4. 8, D) is similar to DaUingeria and Trimastix.
Perhaps the Trimastigidae should be investigated for possible affinities
with the Chrysomonadida.

Family 2. Tetramitidae. There are four unequal or equal flagella, one
or two of which may be trailed. No parabasal body or axostyle has been
reported, although a rhizostyle is present in Tetramitus (Fig. 4. 43, K)
and Copromastix (Fig. 4. 43, F). A dimorphic cycle involving flagellate
and amoeboid stages is known in Tetramitus (29, 110).

The following genera have been included in the family: Costia Leclerq
(7, 59, 269; Fig. 4. 43, D, E), from the skin of fish; Tetramitus Perty (29,
110, 153, 245; Figs. 4. 43, K, L, 2. 14, C-E), in which the life-cycle includes
amoeboid and flagellate stages; and Tricercomonas Wenyon and O'Con-
nor (22, 65, 285; Fig. 11. 2, A-E), from the intestine of man. Enteromonas
Fonseca may be an additional valid genus, although Dobell (65) has con-
cluded that Tricercomo7ias is merely a synonym of Enteroynonas. How-
ever, da Cunha and Muniz (53), as well as Fonseca, have described
Entero?nonas intestinalis with one long and two short flagella, and in
contrast to Tricercomonas, without any trace of a fourth flagellum or
caudal extension. The status of Copromastix Aragao is uncertain. C.
prowazeki Aragao (Fig. 4. 43, F) is so similar to Tetramitus rostratus (29,
110) that the two flagellates probably should be referred to the same
genus.

Family 3. Streblomastigidae. These parasites of termites {Termopsis),
have an unusually slender body with a few spirally wound ridges and an
anterior group of four flagella (131, 158). The flagella arise from the
anterior tip of the body which can be extended as a slender holdfast
organ. The only known genus is Streblomastix Kofoid and Swezy (Fig.
4. 43, M).

Family 4. Retortomonadidae. This family (278) includes Retortomonas
Grassi {Embadomonas Mackinnon) (Fig. 4. 43, A, G, H) and Chilomastix
Alexeieff (Fig. 4. 43, B, I, J). Both Retortomonas (18, 150, 187, 278) and
Chilomastix (149, 198, 278) possess a cytostomal groove, in the margin of
which a cytoplasmic fibril extends across the anterior end and posteriorly
along each side. A true parabasal body is lacking. The significance of a
differentiated intracytoplasmic "band/' sometimes apparent just beneath
the right limb of the peristomial fibril (149), is uncertain. In both genera,
a single trailing flagellum emerges from the cytosomal groove. Retorto-
monas is distinguished from Chilomastix by the presence of one instead
of three anterior flagella. The cytostomal flagellum in Chilomastix has
been interpreted as part of an undulating membrane by Nie (198) and

The Mastigophora 183

Fig. 4. 44, A, B. Monocercomonoides pilleata Kirby and Honigberg; pro-
targol technique (A), showing pelta, "costa," axostyle, trailing flagellum,
bases of anterior flagella; specimen showing flagellar connections, nucleus,
and axostyle (B); x2880 (after K. & H.). C. Callimastix equi Hsiung, show-
ing heavy tuft of flagella; xll66 (after H.). D. Dinenympha ftmbriata Kirby;
nucleus, heavy axostyle, four adherent flagella which become free posteri-
orly, and bacteria attached to the body; xIOOO (after K.). E. Pyrsonympha
minor Powell; nucleus, axostyle (split posteriorly); the adherent flagella
arise from the apical "centroblepharoplast" and extend posteriorly as eight
spiral cords; x900 (after P.). F. Oxymonas dimorpha Connell, non-flagel-
lated attached form with extended rostellum; axostyle and subpellicular
supporting fibrils extend posteriorly from rostellum; nucelus and ingested
wood chips indicated; x425 (after C). G. O. dimorpha, motile form, rostel-
lum not extended; xI750 (after C). H. Polymastix phyUophagae Travis and
Becker; nucleus, axostyle, adherent bacilli; x2400 (after T. & B.). I. Micro-
rhopalodina {Proboscidiella) multinucleata (Kofoid and Swezy), showing
rostellum (which may be extended to several times body length), multiple
karyomastigonts (each with a heavy axostyle); bacteria are usually attached
to the body; xllSO (after K. & S.). J. Saccinobacubis doroaxostylus Cleve-
land; broad axostyle, nucleus, flagella; x600 (after C),

184 The Mastigophora

several earlier workers. Such a relationship remains doubtful in certain
species of Chilomastix (149).

Both Retortomonas and Chilomastix are represented by species in in-
sects and vertebrates. Chilomastix mesnili and Retortomonas intestinalis
of man are discussed in Chapter XI.

Family 5. Callimastigidae. This family includes Callimastix Weissen-
berg (Fig. 4. 44, C), represented by species from the stomachs of cattle,
goats and sheep, from the cecum and colon of horses, and from the body
cavity of Cyclops. The most striking feature is a compact antero-lateral
group of flagella which beats as a unit.

Family 6. Polymastigidae. Four flagella arise as two pairs from the
anterior end of the body. There is an axostyle but apparently no para-
basal body. A pelta is present in Moriocercomonoides pilleata (149), and
a possibly homologous structure ("parabasal body") occurs in Polymastix
phyllophagae (272). The family includes Polymastix Biitschli (98; Fig.
4. 44, H) from insects and Monocercomonoides Travis (149, 271; Fig. 4.
44, A, B) from rodents and insects.

Family 7. Pyrsonymphidae. These are uninucleate or multinucleate
flagellates. Each karyomastigont usually contains four, but sometimes
eight or twelve flagella, and one axostyle. An intranuclear spindle ap-
pears in mitosis (39). Some members of the family (e.g., Kirbyella,
Oxymonas) are attached, by means of an extensible rostellum, to the gut
wall of termites.

The family (139) includes several uninucleate genera — Dinenympha Leidy (133, 160;
Fig. 4. 44, D), Pyrsonympha Leidy (160, 233; Fig. 4. 44, E), Saccinobaculus Cleveland
(39; Fig. 4. 44, J) from the wood roach, Metasaccinohacuhis de Freitas (87), and
Oxymonas Janicki {Opisthomitus Duboscq and Grasse) (41, 52; Fig. 4. 44, F, G) — and
the multinucleate Microrhopalodina Grassi and Foa (Proboscidiella Kofoid and Swezy)
(159a; Fig. 4. 44, I) and Kirbyella Zeliff (286).

Oxymonas, Microrhopalodina, and Kirbyella seem to be restricted to the termite
genus Kalotermes; Saccinobaculus, to the wood roach; the rest of the group, to
Reticulotermes.

Family 8. Hexamitidae. These are binucleate organisms with six or
eight flagella and, in at least certain genera, parabasal bodies and axo-
styles. Bilateral symmetry is typical of the family. The group includes
free-living and parasitic types. Species of Giardia are widely distributed
intestinal parasites of vertebrates. Giardia lamhlia of man is discussed in
Chapter XI. Hexamita meleagridis (105, 194) is associated with a catarrhal
enteritis in young turkeys. Other species of Hexamita have been reported
from monkeys (279), Amphibia (267), fishes (58), leeches (17), reptiles
and rodents, and also as free-living flagellates. The genus Trepomonas
also contains both free-living and parasitic species.

The family includes the following genera: Giardia Kunstler (Fig. 4. 45, H), Gyro-
nionas Seligo (245; Fig. 4. 45, E, F), Hexamita Dujardin (Octomitus Prowazek) (Fig. 4.

The Mastigophora 185

Fig. 4. 45. Hexamitidae. A. Urophagus rostratus (Stein) Klebs, xl200
(after K.). B. Hexamita pitheci (da Cunha and Muniz) Wenrich, from Ma-
cacus rhesus: paired nuclei, axostyies and flagella; x3465 (after W.). C. Hexa-
mita gigas Bishop, from a leech (Haemopsis sangiiisugae); elongated nuclei,
two axostyies, food vacuoles; x2640 (after B.). D. Trigonomonas compressa
Klebs, x833 (after K.). E, F. Gyromonas ambulans Seligo, narrow and broad
surfaces; x945 (after S.). G. Trepomonas agilis Dujardin; two comma-shaped
nuclei, paired flagella, ingested bacteria; x2500 (after Bishop). H. Giardia
muris (Grassi), showing axostyle, paired nuclei, parabasal bodies, and flag-
ella; concave ventral area indicated in outline; x2550, schematic (after
Kofoid and Christiansen).

45, B, C), Trepomonas Dujardin (19; Fig. 4. 45, G), Trigonomonas Klebs (153; Fig. 4.
45, D), and Urophagus Klebs (Fig. 4. 45, A). It is possible that Urophagus should be
considered a synonym of Hexamita.

Order 4. Trichomonadida

These flagellates have an axostyle, a parabasal body (not a kineto-
plast), and a mastigont of 3-6 flagella (147). One flagellum is a trailing
flagellum which may or may not form part of an undulating membrane.
Each mastigont is typically associated with one nucleus, although a
partial or complete dissociation has occurred in certain multinucleate
species. A paradesmose appears in mitosis. Members of the order, as now
known, are uninucleate or multinucleate, not binucleate.

186 The Mastigophora

Fig. 4. 46. A. Devescovina vestita Kirby, showing adherent baciUi, trail-
ing flagellum, projecting axostyle, basal portions of anterior flagella; xll65
(after K.). B. Hexamastix termopsidis Kirby; nucleus, axostyle, jDarabasal
body, ingested bacteria; x2100 (after K.). C, D. Tricercomitus termopsidis
Kirby; rounded form showing nucleus and axostyle (C), xl650; slender form
(D) from recently molted nymph, xl600 (after K.). E. Pseudotrichomonas
keiliui Bishop, with short undulating membrane; x2970 (after B.). F. Deves-
covina arta Kirby; ribbon-like trailing flagelhmi, small cresta, parabasal
body curled aroimd axostyle; xI190 (after K.). G. Parajoenia grassii Janicki;
stout axostyle with anterior expansion, branched parabasal body, pennant-
like costa, four flagella, adherent spirochetes; subcuticular inclusions shown
posteriorly; x875 (after Kirby). H. Monocercomonas verreus Honigberg,
with projecting axostyle; x3420 (after H.). I. Monocercomonas phyllophagae
(Travis and Becker); heavy axostyle, long trailing flagellum; x2700 (after
T. & B.).

The Mastigophora 187

Family 1. Monocercomonadidae. There is either a free or an adherent
trailing flagelhini but no cresta and no undulating membrane with its
underlying costa. The group includes parasites of the digestive tract in
termites, certain other insects, and all classes of vertebrates. However, the
distribution of particular genera ranges from that of Tricercomitus, in
termites only, to that of Monocercoconas, reported from various groups
of vertebrates and insects, including termites.

The family contains the following genera: Hexamastix AlexeiefF (136; Fig. 4. 46,
B). Monocercomonas Grassi (Eiitrirlininastix Kofoid and Swezy, Trichomastix Bloch-
mann) (137; Fig. 4. 46, H, I), Protrichnmonas Alexeieff (2), Pseudotrichomonas Bishop
(21; Fig. 4. 46. E), Tetratrichomastix Mackinnon (190), and Tricercomitus Kirby (136;
Fig. 4.^46, C, D).

Family 2. Devescovinidae. A group of three anterior flagella is char-
acteristic and there is also a trailing flagellum which becomes a rather
broad ribbon in some species. The trailing flagellum is often adherent to
the body through part of its length but there is no undulating membrane.
Bacteria are commonly attached to the surface of the body. The charac-
teristic cresta varies from a small narrow structure to a wide band ex-
tending almost the length of the body. The parabasal body ranges from
a short rod to a long structure coiled around the axostyle. The axostyle
may curve forward along one side of the nucleus. More commonly, the an-
terior part of the axostyle is flattened into a capitulum. The Devesco-
dinidae are known from termites, almost entirely from the Kalotermitidae.
The occurrence of encystment is doubtful and flagellates probably are
transferred by proctodeal feeding.

The following genera are included: BuUanympha Kirby (148; Fig. 1. 8, E), Caduceia
Franca (142; Fig. 4. 47, B), Devescoviua Foa (141; Fig. 4. 46, A, F), Foaina Janicki (143;
Fig. 4. 47, C), Gigantomonas Dogicl (146; Fig. 2. 14, H-J), Hyperdevescovina Kirby
(148; Fig. 4. 47, E). Macrotriclwinonas Grassi (142; Fig. 4. 47, D), Metadevescovina
Light (145; Fig. 4. 47, A), Parajoenia Janicki (143; Fig. 4. 46, G), and Pseudodevescovina
Sutherland (145; Fig. 4. 47, F). Gigantomojjas differs from the others in that the cycle
includes an amoeboid stage, sometimes multinucleate, in which elements of the mas-
tigont may be much reduced.

Family 3. Calonymphidae. These are multinucleate flagellates with
eight (Coronympha) to hundreds of mastigonts (Snyderella), each usu-
ally containing four flagella. One of the four is typically a trailing flag-
ellum. The cresta is well developed in some species but is small or else
lacking in others. The axostyles range from fairly heavy separate struc-
tures to slender filaments which form a compact axial bundle. Coronym-
pha, Metacoronympha, and Stephanonympha contain karyomastigonts
exclusively. In Calonympha there are both karyomastigonts and masti-
gonts, while the mastigonts and nuclei are completely dissociated in
Snyderella. The Calonym25hidae have been reported mostly from the

188 The Mastigophora

Fig, 4. 47. A. Metadevescovina modica Kirby, x750 (after K.). B. Cadu-
ceia bugnioni Kirby; adherent spirochetes indicated, bacilli not shown; axo-
style expanded anteriorh; long parabasal body coiled around axostyle; x700
(after K.). C. Foaina taeniola Kirby, xl310 (after K.). D. Marrotrichomonas
lighti (Connell) Kirby; large cresta (stippled), long coiled parabasal body:
x700 (after K.). E. Hy perdenescovina mitrata Kirby, x750 (after K.). F.
Pseudodevescovina iiniflagellnta Sutherland; axostyle expanded anteriorly,
complex parabasal apparatus; x750 (after Kirby).

termite genus Kalotermes; Snyderella seems to be limited to a single
species of that genus.

The family includes Calonympha Tok (122), Coronympha Kirby (135a, 140; Fig. 4.
48, F), Metacoronympha Kirby (140), Snyderella Kirby (135a; Figs. 1. 8, C; 1, 10, C),
and Stephanonympha Janicki (134; Fig. 1. 10, D, E),

Family 4, Trichomonadidae. These are uninucleate types with an un-
dulating membrane and an underlying costa. In addition, a pelta occuzs

The Mastigophora 189

Fig. 4. 48. A. Trichomonas limacis Dujardin, showing pclta, beaded
and bifurcated parabasal body, axostyle, and nucleus; x2415 (after Koz-
loff). B. Tritrichomouas augusta Alexeieff; axostyle, nucleus, parabasal
body, heavy costa; xl680 approx. (after Samuels). C. Tritrichomouas foetus,
parabasal body not shown; x2795 (after Wenrich and Emmerson). D. Tri-
chomonas gallinae (Rivolta) Stabler, x3400 (after S.). E. Pseudotrypano-
soma gigantea Grassi; heavy costa, long parabasal body parallel to axostyle,
long undulating membrane; x575 (after Kirby). F. Coronympha clevelajidi
Kirby, showing anterior circle of karyomastigonts, axostyles extending pos-
teriorly; xl400 (after K.).

in some species. The group is widely distributed in vertebrates and cer-
tain invertebrates. Several parasites of man are discussed in Chapter XI.
TricJwmonas gallinae is a pathogen in the anterior digestive tract of
pigeons (261, 262); Tritrichonionas foetus is a parasite of the genital
tract in cattle (196, 281); Trichomonas gallinarum occurs in the ceca of
chickens and turkeys and the liver of turkeys. Like Histomonas rnele-

190 The Mastigophora

agridis, T. gaUinarum is associated with "blackhead" in poultry (4, 5).

The family includes the following genera: Pentatrichomonas Mesnil (Fig. 11. 3, AC);
Pentatrichomonoides Kirby (137); Pseudotrypanosoma Grassi (137; Fig. 4. 48, E);
Trichomonas Donne (Fig. 4. 48, A, D), for which Morgan (195) has published a host-
parasite catalog; and Tritrichomonas Kofoid (Fig. 4. 48, B, C).

Order 5. Hypermastigida

These are uninucleate organisms with many flagella. Multiple axo-
styles and parabasal bodies also are characteristic. All known species are
intestinal parasites of termites, wood roaches or cockroaches. Feeding
methods may be saprozoic or holozoic, and some species ingest wood chips
swallowed by the host (77). Two suborders, Lophomonadina and Tricho-
nymphina, have been recognized.

Suborder 1. Lophomonadina. In this group, the flagella and associated
structures are arranged in one anterior group which is resorbed in fission.
The suborder includes three families which differ in arrangement of the
flagella.

Family 1. Lophomonadidae. The blepharoplasts form an anterior ring
so that the flagella, if numerous (Fig. 4. 49, C), form a distinct tuft. The
axostyle, at least in Lophomonas and Torquenympha (Fig. 4. 49, B), is
a bundle of fibrils enclosing the nucleus anteriorly. The fibrillar bundle
may be split posteriorly into several fibrils in Torquenympha (27). Mem-
bers of the group are known from the digestive tract of cockroaches
[Lophomonas), the wood roach (Prolophomonas), and certain termites
(Torquenympha).

The family includes Prolophomonas Cleveland (39), Lophomonas Stein (168, 169),
and Torquenympha Brown (27). The flagella number 24 or less in Prolophomonas
(Fig. 4. 49, A) and Torquenympha, but are more numerous in Lophomonas.

Family 2. Joeniidae. Although limited to an anterior area, the blepharo-
plasts are arranged in longitudinal rows instead of a compact ring. As a
result, there may be an anterior tuft of flagella, as in Joenia and Joenopsis,
while the rest of the flagella are trailed. The flagellar rows may extend
past the middle of the body in Joenopsis (55), but are shorter in Micro-
joenia (27, 55; Fig. 4. 49, D). A paired parabasal apparatus is quite
simple in Microjoenia. In Joenopsis and Joenia, however, there are two
filaments to which are attached numerous rod-like parabasal bodies (55).

The following genera have been reported from termites: Joenia Grassi, Joenopsis
Cutler, Joenina Grassi (98a), Mesojoenia Grassi and Foa, and Microjoenia Grassi.

Family 3. Kofoidiidae. The flagella are arranged in a spiral series of
permanent bundles. The nucleus lies within a "suspensorium" from
which filaments radiate into the cytoplasm. These filaments may be

The Mastigophora 191

0^''

^S^' > \ " "^1^ i;//i 'ijf'

^1 M K .^ ri#

/;/ V

WM

Fig. 4. 49. A. Prolopliomouas tocopola Cleveland, showing axostyles,
nucleus, food vacuoles; xl200 (after C). B. Torqitetiyinpha octoplus
Brown, showing parabasal bodies and fibrillar axostyle which surrounds
the nucleus anteriorly; xl645 (after B.). C. Lophomonas striata Biitschli,
showing axostvlar filaments which form a "calyx" enclosing the nucleus;
adherent bacteria (Fusiformis lophomonadis Grassc) indicated on body;
xl475 approx. (after Kudo). D. Microjoenia ratcliffei Brown, showing two
parabasal bodies, axost^le, nucleus, and anterior rows of blepharoplasts;
x2380 (after B.). E. Koifoidia loriculata Light, showing bundles (loriculae)
of flagella; xl75. F. A', loriculata, anterior end of body showing nucleus
suspended in membranous "suspensorium," bases of several loriculae, and
body fibrils extending into cytoplasm; x750 (after L.).

analogous to the axostylar bundle in Torque?iympha and Lophomonas.
The general organization, although more complex, is similar to that in
Lophomonas. The type genus is Kofoidia Light (183; Fig. 4. 49, E, F),
reported from one species of Kalotermes.

Suborder 2. Trichonymphina. The retention of flagella and associated
structures in fission is characteristic. Organization is basically bilateral,
and there are either two or four sets of organelles which are separated
equally in fission. Encystment is known for species of Macrospironympha
and Trichonympha in the wood roach (39), but not for the Trichonym-
phina of termites.

192 The Mastigophora

Fig. 4. 50. A. Staurojoenina assimilis Kirby. showing four flagellar groups,
rhizoplast bands extending anteriorly from the nucleus, and the major body
filaments extending posteriorly; cuticular striations indicated at lateral mar-
gins; X330 (after K.). B. Optical section, anterior end of S. assimilis, showing
four flagellar groups; X330 (after Kirby). C. Barbitlanympha ufalula Cleve-
land; two anterior flagellar gioups. nucleus surrounded by parabasal bodies;
axostylar filaments extend posteriorly; x20o (after C). D. Uiinyinpha talca
Cleveland; two flagellar groups, nucleus suspended by nuclear sleeve; axo-
stylar filaments extending posteriorly; X3r,o (after C). E, F. Hoplonympha
natator Light; surface view showing two flagellar tufts and spiral pellicular
grooves (E); optical section showing nucleus suspended by rhizoplast bands
(enclosed in granular column); a delicate endoplasmic thread (primitive
axostyle?) extends posteriorly; X855 (after L.).

Family 1. Hoplonymphidne. The flagella arise in tAvo anterior groups.
One group passes to each daughter organism in fission. Hoplonympha is
represented in termites; three other genera, in the wood roach (Crypto-
cercus).

The Mastigophora 193

^S'

[v

■'■/■iv.:' :i'-

i''\'iV''

Fie. 4. 51. A. Holomastigotoides hemigymnum Grassi; nucleus, axostyle
(expanded anteriorly), flagellar bands (flagella indicated only at sides of
body); x320 approx. (after Mackinnon). B. Spirotrichonympha elegans
(Mackinnon); rostellar tube, nucleus, axostUe (expanded anteriorly), flag-
ellar bands (only the marginal flagella are shown); xl820 (after M.). C.
Spirnnympha porteri Koidzumi; axostvle, nucleus, flagellar l)ands with at-
tached parabasal bodies; marginal flagella indicated; adherent spirochetes
posterior to the flagellar bands have sometimes been mistaken for flagella;
xl600 approx. (after Brown).

The family includes Barbulanymplta Cleveland (39; Fig. 4. 50, C), Hoplonympha
Light (182; Fig. 4. 50, E, F), RhyncJwnympha Cleveland (39), and Urinympha
Cleveland (39; Fig. 4. 50, D).

Family 2. Staurojueuinidae. The flagella are arranged in four anterior
groups. A number of slender fibrillar axostyles are attached to each
flagellar group, and in Idionympha four groups of slender parabasal
"cords" are associated with the flagellar groups.

The family includes Staurojoenina Grassi (133a; Fig. 4. 50, A, B) from
termites and Idionympha Cleveland (39) from the wood roach.

Family 3. Holomastigotidae. The flagella arise from bands of basal
granides which extend spirally around the body. Two, four, or more
bands have been reported in different species. Apparent variations within
a species possibly involve duplication in fission.

The family includes Holomastigotes Grassi (72, 160), Holomastigotoides Grassi and
Foa (14, 160, 192; Fig. 4. 51, A), Leptospironympha Cleveland (39), Macrospironympha
Cleveland (39), Spironympha Koidzumi (28; Fig. 4. 51, C), Spirotrichonymphella
Grassi, Spirotrichonympha Grassi (54, 72, 160, 193; Fig. 4. 51, B) and Spirotrichosoma
.Sutherland (266). Leptospironympha and Macrospironympha have been reported from
the wood roach; the other genera, from termites.

194 The Mastigophora

i;Vr->v'-',AOi.

^Mi.

■■:^y

B

IP^P-

Fig. 4. 52. A. Teratonympha sp. from Reticulotermes speratus; anterior
end of body showing rostral tube, rostra! flagella, nuclear "sleeve" extending
from nucleus into rostral tube, and supporting fibrils surround nuclear
sleeve and nucleus; the fibrils end posteriorly in the first flagellar band;
x840 (after Cleveland). B. Surface view of Teratonympha showing circular
flagellar bands; flagella indicated diagrammatically; x280 (after Cleveland).
C. Eucomonympha inula Cleveland, showing rostrum with anterior cap
(operculum), nucleus, and fibrillar axostyles extending posteriorly; x350
(after C). D. Triclwnympha corbula Kirby, showing three flagellar zones
and the parabasal bodies surrounding the nucleus; x475 (after K.).

Family 4. Trichonymphidae. Except for the tip of the rostrum, the sur-
face of the body is flagellated in certain genera {Deltotrichonyynpha ,
Eucomonympha, Mixotricha, Pseudotrichonympha). In others, a small or
a large posterior portion is bare. The flagella are arranged in longitu-
dinal rows, and may form two or three transverse zones diffiering in

The Mastigophora 195

length of the flagella. The parabasal apparatus consists of a number of
parabasal cords, usually encircling the nucleus and attached by filaments
to the parabasal lamella at the base of the rostrum (71, 144). Differences
in form, size, and number of the cords are useful taxonomic features. In
the rostrum, the conical anterior end of the body (Fig. 4. 52, C, D), the
blepharoplasts and the parabasal lamella, internal to them, form a rostral
"tube." This tube is sometimes widened posteriorly into a cone, as in
Eucomonympha (Fig. 4. 52, C).

The family contains Deltotrichonympha Sutherland (72, 266), Eucomonympha Cleve-
land (39; Fig. 4. 52, C), Mixotricha Sutherland (266), Pseudotrichonympha Grassi
(39, 160), and Trichonympha Leidy (39, 138. 144; Fig. 4. 52, D). Trichonympha is
represented in termites (three families) and in the wood roach (39). Eucomonympha
has been reported from the wood roach; the other genera, from single families of
termites.

Family 5. Teratonymphldoe. This family was erected for Teratonytnplm
Koidzumi (Cyclonympha Dogiel) from termites. The rostrum is similar
to that of Trichonymphidae, but the post-rostral flagella arise from cir-
cular bands underlying grooves which give the body a segmented appear-
ance (40, 160; Fig. 4. 52, A, B).

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196 The Mastigophora

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The Mastigophora 197

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136. 1930. Univ. Calif. Publ. Zool. 33: 393.

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198 The Mastigophora

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146. 1946. Uriiv. Calif. Publ. Zool. 53: 163.

147. 1947. /. Parasit. 33: 214.

148. 1949. Univ. Calif. Publ. Zool. 45: 319.

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150. and 1950. Univ. Calif. Publ. Zool. 55: 35.

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162. 1927. Arch. f. Protistenk. 58: 441.

163. 1927. Arch. f. Protisteiik. 58: 450.

164. 1928. Arch. f. Protistenk. 61: 223.

165. 1929. Arch. f. Protistenk. 67: 253.

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193. 1927. Quart. J. Micr. Sci. 71: 47.

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The Mastigophora 199

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208. 1928. Arch. f. Protistenk. 63: 241.

209. 1929. Arch. f. Protistenk. 68: 637.

210. 1929. Atin. Protistol. 2: 157.

211. 1930. Beih. Bot. Centralhl. 47: 271.

212. 1930. Arch. f. Protistenk. 69: 401.

213. 1930. Arch. f. Protistenk. 72: 311.

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215. 1931. Arch. f. Protistenk. 73: 315.

216. 1932. Beih. Bot. Centralbl. 49: 293.

217. 1932. Arch. f. Protistenk. 76: 1.

218. 1932. Arch. f. Protistenk. 77: 305.

219. 1932. Beih. Bot. Centralbl. 49: 549.

220. 1940. Arch. f. Protistenk. 93: 331.

221. 1940. Arch. f. Protistenk. 94: 295.

222. 1942. Arch. f. Protistenk. 96: 75.

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250. 1925. Arch. f. Protistenk. 51: 1.

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200 The Mastigophora

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V
The Sarcodina

Class 1. Actinopodea
Order 1. Helioflagellida
Order 2. Heliozoida

Suborder 1. Actinophrydina
Suborder 2. Acanthocystidina
Suborder 3. Desniothoracina
Order 3. Radiolarida
Life-cycles
Taxonomy

Suborder 1. Actipylina
Suborder 2. Peripylina
Suborder 3. Monopylina
Suborder 4. Tripylina

Class 2. Rhizopodea

Order 1. Proteomyxida
Family I. Labyrinthulidae
Family 2. Pseudosporidae
Family 3. Vampyrellidae

Order 2. Mycetozoida
Suborder 1. Acrasina
Suborder 2. Plasmodiophorina
Suborder 3. Eumycetozoina

Order 3. Araoebida

Family 1. Dimastigamoebidae

Family 2. Amoebidae

Family 3. Endamoebidae
Order 4. Testacida

Pseudopodia

Contents of the test

Life-histories

Ecological relationships

Taxonomy

Family 1. Arcellidae
Family 2. Difflugiidae
Family 3. Euglyphidae
Order 5. Foraminiferida

Pseudopodia and their activities

Tests

The endoplasm

Life-cycles

Reproduction of the agamont
Gametogenesis and syngamy
Duration of the life-cycle

Taxonomy

Family Allogromiidae
Literature cited

T

.HE Sarcodina are mostly floating or creeping organisms, al-
though a number are sessile. The thin periplast permits the formation
of pseudopodia and the amoeboid movement of naked species. Locomo-
tion may or may not involve the formation of definite pseudopodia.
Certain amoebae, for instance, move by a protoplasmic flow which in-
volves the body as a whole and does not depend upon pseudopodia. Some
Sarcodina also develop flagella at certain stages in the life-cycle. Flagel-
late stages occur as gametes in various Foraminiferida; in certain other
Sarcodina, a similar status of the flagellate stage is suspected but not
proven. In addition, there are cases in which the flagellate stage seems
to be merely a second active phase in a dimorphic life-cycle. The ability

201

202 The Sarcodina

to develop a test is widely distributed. Such structures are found in
Testacida and Foraminiferida and in the majority of Heliozoida. The
lattice-work skeletons of many Radiolarida are analogous developments.

The Sarcodina as a group are widely distributed in fresh and salt
water and in the soil. However, the Radiolarida have remained marine
and the Foraminiferida which have invaded fresh water are primitive
types sometimes considered Testacida. A number of the Sarcodina are
parasitic. Various sessile forms may be epiphytic or epizooic, but endo-
parasitism is limited to the more primitive species or to possibly degen-
erate representatives of certain groups.

On the basis of pseudopodial equipment, the Sarcodina are often di-
vided into two classes, Actinopodea and Rhizopodea. By definition, the
Actinopodea possess axopodia. The Rhizopodea may have any other kind
of pseudopodia but do not develop axopodia.

CLASS 1. ACTINOPODEA

These are mostly floating or sessile organisms, although flagellate
stages are known in a few genera. Accessory lobopodia are developed oc-
casionally, at least in certain species. The class may be divided into three
orders: (1) Helioflagellida, with one or more flagella as either a perma-
nent feature or a characteristic of the dominant phase in a dimorphic
cycle; (2) Heliozoida, in which a flagellate stage apparently is rare and
the inner cytoplasm is not separated from the outer zones by a central
capsule; (3) Radiolarida, in which a central capsule is characteristic and
skeletal structures are more highly developed than in Heliozoida.

Order 1. Helioflagellida

The relationships of this group are uncertain, and members of the
order have been classified as Rhizomastigida (Mastigophora) and Pro-
teomyxida, as well as Helioflagellida. The presence of axopodia, and also
a "central granule" in certain genera, suggests closer affinities with the
Heliozoida than with the Rhizomastigida or Proteomyxida. The Helio-
flagellida are of interest as possible sources of data bearing on phylogeny
of the Actinopodea.

The following genera may be assigned to the order: Acinetactis Stokes (141, 143;
Fig. 5. 1, A); Actinomonas Kent (45; Fig. 5. 1, K); Ciliophrys Gruber (45; Fig. 5. 1, D,
E); Dimorpha Gruber (Fig. 5. 1, I-J); Dimorphella Valkanov (143; Fig. 5. 1, B, C);
and Tetradimorpha Hsiung (61; Fig. 5. 1, F-H). A "central granule," from which the
axoncmes of the axopodia radiate, has been demonstrated in Dimorpha, Dimorphella.
and Tetradimorpha. This central granule behaves as a centrosome during mitosis in
Dimorphella elegans (Fig. 5. 1, C). With the possible exception of Tetradimorpha, the
pseudopodia show the granules characteristic of axopodia; streaming of the granules
has been described in Acinetactis and Dimorphella. More or less complete retraction
of the pseudopodia occurs in swimming stages of Acinetactis, Ciliophrys, Dimorpha,
and Tetradimorpha. Both marine and fresh-water species of Ciliophrys have been
described; the other genera have been reported from fresh water.

The Sarcodina 203

/m\

.-''' -' / '• < 'i '•

i-*;v^*i

Fig. 5. 1. Helioflagellida. A. Acinetactis arnaudoffi Valkanov; two fiagella.
granular axopodia; x800 (after V.). B, C. Dimorphella elegans Valkanov; fiag-
ella and axopodia arising from a central gianule (B); stage in division (C);
x2400 (after V.). D, E. Ciliophrys marina Caullery;" axopodia retracted in
flagellate stage (D); granular axopodia extended (E); x960 (after Griessmann)'.'
F-H Tetradimorpha radiata Hsiung; axopodia extended, nucleus central, x325
(F); typical swimming stage, x480 (G); stained preparation showing nucleus,
blepharoplast, axonemes of retracted axopodia (H), x490 (after H.). I-J. Di-
morpha mutans Gruber; axopodia and flagella arising from a central granule
(I); axopodia retracted (J); xl060 approx. (after Blochmann). K. Actitiomonas
mirabiUs Kent, one flagellum, axopodia extended; xl360 (after Griessmann).

Order 2. Heliozoida

The Heliozoida possess radially arranged axopodia which rarely
anastomose, and typically contain globules or granules. A flow of granules
along the axopodia is characteristic. The finer structure of the pseudo-

204 The Sarcodina

podia has been discussed by Roskin (126). The inner and peripheral zones
of cytoplasm are not separated by a central capsule. Most Heliozoida are
approximately spherical floating types, and except for a few species of
Acanthocystis, Camptonema, and certain other genera, occur in fresh
water. The recognition of typical Heliozoida is easy enough. However,
it is difficult to detect axonemes in the delicate pseudopodia of certain

/ 7/ / I \ \ '•

B

Fig. 5. 2. Basic morphological types in Heliozoida; diagrammatic. A. Acan
thocystis-type: test composed of separate plates, spines sometimes present
nucleus not central; axopodia radiate from a central granule. B. Clathrulina
type, as in Desmothoracina: perforated test not composed of separate scales;
stalk often present. C. Acti7iophrys-type: no test; nucleus approximately cen
tral in uninucleate forms. D. Nuclear division in Acanthocystis aculeata, show
ing supposed central granules at the poles of the spindle; xlOlO (after Belar)

forms and there are some species in which axonemes have not yet been
reported.

With respect to the peripheral cytoplasm and its derivatives, Heliozoida
may be divided into naked types and those which secrete some sort of a
test. The test may contain discrete scales or spines (Fig. 5. 2, A), or it
may be a continuous capsule containing many pores (Fig. 5. 2, B). In
such naked types as Actinophrys (Fig. 5. 2, C), the outer cytoplasm con-
tains many vacuoles, one or more of which may be contractile. The vac-
uolated layer encloses a thick granular zone of cytoplasm within which,
in uninucleate species, a large nucleus is more or less centrally located.

The Sarcodina 205

Around the nucleus, there is a hyaline layer in which the axonemes end.
In the Acanthocystis-type (Fig. 5. 2, A), the vacuolated zone is lacking
and the body is covered with a test composed of skeletal elements em-
bedded in a capsule. Some such covering is found in the majority of
Heliozoa. Beneath the relatively thin ectoplasm there is a thick granular
zone containing one or more contractile vacuoles, food vacuoles, and
other inclusions. Within the granular layer, a zone of clear cytoplasm
contains the "central granule" and a nucleus. The central granule, in
which the axonemes converge, resembles a centrosome in its behavior
dining mitosis (Fig. 5. 2, D). However, Stern (139), on the basis of multi-
nucleate and other abnormal stages seen in cultures, has argued that the
central granule does not really function as a centrosome.

Fig. 5. 3. A-D. Ingestion of a fiagellate by Acanthocystis aculeata, succes-
sive stages; xl215 (after Stern). E. Formation of a food vacuole outside the
test in Hedriocystis pellucida; xl050 (after Hoogenraad). F. A large lobo-
podium, in addition to axopodia, in Raphidocystis infestans; x8I5 (after
VVctzcl). G. Cytostome-like structure, with food vacuole at the base of the
"gullet," in Actinosphaerium eichorni; x34 (after Okada). H. A ciliate (Para-
mecium) attacked by a group of Raphidocystis infestans; xl28 (after Wetzel).
I. A ciliate completely surrounded by such a group; stained preparation; x238
(after Wetzel).

206 The Sarcodina

Feeding is predominantly holozoic, and food includes other Protozoa,
algae, and occasionally rotifers or other small invertebrates. After cap-
ture of such organisms, axial filaments may disappear in the immediate
region and a layer of cytoplasm surrounds the prey (Fig. 5. 3, E). Occa-
sionally, captured microorganisms pass immediately into the deeper cy-
toplasm where digestion is completed (Fig. 5. 3, A-D). In addition to
axopodia, lobopodia are sometimes formed (158) and the ingestion of
food by means of gullet-like "food cups" also may occur (Fig. 5. 3, G).
A protozoan version of the hunting pack has been described in Raphi-
docystis infestans (158). A ciliate, for example, may be attacked by a
number of these Heliozoida, which adhere to the prey and may fuse to
form a continuous layer of protoplasm enclosing the captured food (Fig.
5. 3, H, I). A simple life-cycle — including an active stage and a cyst — has
been reported in a number of Heliozoida. Cysts with a siliceous ectocyst
have been described in certain species (108). An alternation of genera-
tions, in one of which flagellate gametes are produced, has been reported
in Wagnerella borealis (163), although this account has not been con-
firmed. The formation of a flagellate daughter organism (Fig. 5. 7, D,
L), which leaves the parental test, has been described in Monomastigo-
cystis (129) and Hedriocystis (54).

The work of Belar and his predecessors has established the occurrence
of pedogamy in certain Heliozoida, or at least the occurrence of syngamy
following a gametic meiosis (Chapter II). The zygote so produced nor-
mally undergoes encystment.

Subdivision of the Heliozoida has been based largely upon the presence
or absence of skeletal elements and their structure. On such a basis, the
group may be divided into three suborders: (1) Actinophrydina, the
naked types; (2) Acanthocystidina, with a gelatinous capsule in which
separate skeletal elements are usually embedded; and (3) Desmothora-
cina, with a continuous test containing a number of pores.

Suborder 1. Actinophrydina. There is no capsule or test enclosing the
outer zone of vacuolated cytoplasm. Since there is no central granule, the
axopodia may end near the nuclear membrane (Fig. 5. 4, E) in uninu-
cleate species, or near a nucleus or inner margin of the vacuolated layer
in inultinucleate types. Just beneath the vacuolated zone of Actinosphae-
rium eichorni, there is a finely granular layer (Fig. 5. 4, B) which may
serve as a support for the bases of the axopodia (83, 108). Inside the
granular layer lies the finely vacuolated endoplasm. The boundary be-
tween endoplasm and ectoplasm is not so sharply defined in the smaller
Actinophrydina.

The suborder includes the following genera: Actinophrys Ehrenberg (5, 6, 83. 108;
Fig. 5. 4, C-F), uninucleate fresh-water types; Actinosphaerium Stein (83, 108; Fig. 5.
4, A, B), multinucleate fresh-water types; Cawptonema Schaudinn (133), multinucleate
marine forms. Actinosphaerium eichornii, which often measures more than 300^^ and

The Sarcodina 207

rM.

T--.;»-: ■ y.V.*^-:---

B

^J'-^'^'^-^x

I F

Fig. 5. 4. Actinophrydina: A. Actinosphaerium eichorni Ehrenberg (diam-
eter may reach or exceed SOOfi); axopodia, peripheral zone of vacuoles; in-
gested food (after Penard). B. Portion of peripheral cytoplasm, A. eichorni,
showing an axoneme ending in a granular layer just beneath the vacuolated
zone; diagrammatic (after Penard). C, D. Actinophrys pontica Valkanov;
stained specimen (C), xl200; fused aggregate of three organisms (D), x800
(after V.). E, F. Actinophrys sol Ehrenberg; stamed section of small specimen
showing axonemes extending to nucleus, x975; living specimen from culture,
x325 (after Belar).

may exceed 1000/^ in diameter, is the largest of the Actinophrydina. Other species fall
within the range, 25-150/1.

Suborder 2. Acanthocystidina. There is typically a secreted capsule,
sometimes "gelatinous" (Fig. 5. 5, A, G), in which skeletal elements are
embedded. The ectoplasm is not extensively vacuolated. In some genera at
least, the axonemes are known to end in a central granule. Data are
lacking in other cases, In Astrodiscuhis (Fig. 5. 5, A), the capsule is thick

208 The Sarcodina

but contains no skeletal elements. In other genera, the capsule varies in
thickness and may be reduced to a thin membrane which binds the
skeletal structures together. With the apparent exception of Heterophrys,
the skeletal elements are siliceous. Aside from a few species such as
Lithocolla glohosa (108), in which foreign particles are cemented to a
thin capsule, the skeletal scales and spicules are products of the organism.

^ ! /

--t'

k
9

i

rh

I

■^■:^<H' ...

^^^

^ s -*/•■; © - A * . lib ^>j3

f D

H

.^

Fig. 5. 5. Acanthocystidina: A. Astrodisculus radians Greet, "gelatinous"
covering without scales; x575 approx. (after Penard). B. Pinaciophora fliivia-
tills Greef (diameter, 45-50fi), test composed of scales (after Penard). C.
AcantJiocystis rubella Penard (diameter, 23-27/i); portion of body showing
tangential scales; radially arranged spines are enclosed within the axopodia
(after P.). D. Cienkowskya mereschkowskyi (diameter about 60(a), a sessile
form; scales embedded in gelatinous mantle; distal portions of axopodia not
shown (after Villeneuve). E-G. Raphidocystis infestans Wetzel; cyst being
released from ruptured test (E) and freed cyst (F), x570; dividing form,
skeletal elements dissolved with HFl to show gelatinous envelope (G), x820
(after W.). H. Raphidiophrys pallida Schulze, x2.50 (after Penard).

The Sarcodina 209

The differentiation of genera is based to an important extent upon
thickness of the capsule and the form and arrangement of the skeletal
elements (Fig. 5. 6, A-H).

The following genera arc included in the suborder: Acarithoryslis Carter (83, 108
154; Fig. 5. 5, C); Actinolophus Schulze (149; Fig. 5. 6, I); AstrocUsculus Greef (108
Fig. 5. 5, A); Cienkowskya Schaudinn (149; Fig. 5. 5, D); Elaeorhanis Greef (108)
Heterophrys Archer (108; Fig. 5. 6, J); Lithocolla Schulze (108); Oxnerella Dobell (34)

B

K

t 1

1

?

'1

T

El

i

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?

H

^1 G

Q

E F

^\{ml :/'/

Xv

. . ^\\^^\.

^/' I

/

Fig. 5. 6. Acanthocystidina: A-H. Skeletal elements: A. Raphidocystis
ambigua; B. Acanthocystis mimetica, spine and scales; C. A. aculeata, spine
and scales; D. Raphidiophrys elegans, surface and edge views of scales; E.
Raphidocystis glutinosa; F. Raphidiophrys intermedia, surface and edge
views of scales; G. Spine of Heterophrys myriopoda; H. Raphidocystis
leniani; schematic (after Penard). I. Actinolophus pedunculatus Schulze
(body, 35 x 30;n), sessile on Bryozoa; radially arranged bodies within test
believed to be ingested food (after Villeneuve). J. Heterophrys myriopoda
Archer, x330 (after Penard). K. Pompholyxophrys punicea Archer, x400
approx. (after Penard).

210 The Sarcodina

Pinaciocystis Roskin (128); Pinaciophora Greef (108; Fig. 5. 5, B); Pompholyxophrys
Archer (108; Fig. 5. 6, K); Raphidiophrys Archer (108, 158; Fig. 5. 5, H); Raphidocystis
Penard (108, 158; Figs. 5. 3, F, H, I, 5. 5, E-G); and Wagnerella Mereschkowski (163).
The status of Myriophrys Penard (108) is uncertain. The secreted envelope with
adherent scales, the slender granular pseudopodia, and the large eccentric nucleus
would seem to qualify the genus for the Acanthocystidina. A coat of undulating "cilia
or flagella" complicates matters. Perhaps these "flagella" should be investigated as
possible bacteria adherent to the body. The genus Chondropus Greef (108) must re-
main unassigned until more is known about the organisms.

^k.-

C£ i^-Q

/- ,.c^

■•-• :•■.■:■■ J

g G

If

H

iL

Fig. 5. 7. Desmothoracina: A-F. Monomastigocystis brachypoiis De Saede-
leer (width, 9-15//): specimen with short stalk (A); optical cross-section (B);
in fission (C, D) one daughter organism develops into a flagellate (E); cyst
(F) with double membrane (after De S.). G-L. Hedriocystis pellucida:
young specimen without test (G), schematic (after Valkanov); mature form
(H), x700; fission (I, J), x315; one daughter organism becomes a biflagellate
stage which leaves the test (K, L), x525 (after Hoogenraad). M. Clathrulina
ehgans Cienkowski; diameter of test, 60-90;i (after Penard).

The Sarcodina 211

Suborder 3. Desmothoracina. In this group, there is a non-siliceous
(108) one-piece test (Fig. 5. 2, B) containing pores through which pseu-
dopodia are extended. Certain genera contain sessile types with stalks.
The stalk in Hedriocystis (Fig. 5. 7, G, H) is said to be merely an exten-
sion of the body resembling a slender pseudopodium (144). In Clathru-
lina (Fig. 5. 8, E-H), the young organism first develops a protoplasmic
stalk by outgrowth from the body. An outer covering is then secreted

B i

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.^....:::fj||^M|^::.::::.....

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' C

'"%^'

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a-

Hill

Fig. 5. 8. Desmothoracina: A. Hedriocystis reticulata Penard, x500 ap-
prox. (after P.). B. Choanocystis lepidula Penard, x730 approx. (after P.).
C. Clathrella foreli Penard; diameter of test, 40-55/i (after P.). D. Elastcr
greefi Grimm, x700 (after Penard). E-H. Clathrulina e/ega?J5 ^ienkowski: '
cytoplasm grows down over the original stalk (F) and produces a hollow
stalk (G), which becomes continuous with the test in older forms (H);
schematic (after Valkanov).

212 The Sarcodina

and the protoplasmic core disappears, leaving a tubular mature stalk
attached only to the test (144).

Although little is known about the life-cycles, fission within the test,
the development of a flagellate stage from one of the daughter organisms,
and encystment have been described (Fig. 5. 7) in Monomastigocystis
(129) and Hedriocystis (54).

The taxonomic relationships of the Desmothoracina are still debatable.
Superficially, they show striking resemblances to typical Heliozoida. Al-
though the granular pseudopodia seem to be axopodia, they are some-
times so slender that the presence of axonemes is uncertain. The nucleus
is central in some species and eccentric in others, but no central granule
has been demonstrated. In view of the apparent absence of axonemes
and a central granule, Valkanov (148) suggested transfer of the Desmo-
thoracina to the Foraminiferida as another monothalamous group.

The following genera have been assigned to the suborder: Choaiiocystis Penard (108;
Fig. 5. 8, B); ClathruUna Cienkowski (83, 108, 144; Fig. 5. 7, M); Blaster Grimm (108;
Fig. 5. 8, D); Hedriocystis Hertwig and Lesser (54, 108, 144; Fig. 5. 7, G-L); Monomasti-
gocystis de Saedeleer (129; Fig. 5. 7, A-F).

Order 3. Radiolarida

These marine organisms, with a geological history dating at least
from Lower Silurian and probably from Cambrian time, are apparently
the oldest known group of animals. Their most striking feature is their
skeleton, which has undergone specialization to a remarkable degree. The
general organization of the body and the possession of axopodia relate
them to the Heliozoida, but the central capsule, separating inner and
outer zones of protoplasm, is a differential feature.

The central capsule is nearly always a distinct layer, usually single
but sometimes double (Fig. 5. 13, A), and can be detected without diffi-
culty except in a few Actipylina (Acantharina). The capsule may be
spherical, ovoid, or sometimes lobate or branched (Fig. 5. 11, C), and is
composed of organic material designated variously as chitin, pseudochitin,
or tectin. The capsule may be resorbed more or less completely in fission
of the simpler species, it may increase in diameter with growth of the
organism, and it may be somewhat changeable in form even in the mature
organism. Perforations, either distributed uniformly or concentrated in
one or more groups, permit cytoplasmic continuity and also serve as
taxonomic features.

The skeleton of the Actipylina may be composed largely of strontium
sulphate, usually with a radial arrangement of the skeletal elements. The
basic components are spines which extend radially from the center of the
body, passing through the central capsule (Fig. 5. 9, A). At the surface of
the body there may also be a lattice-work test, or shell, which is fused with
the radial spines (Fig. 5. 9, D). For the other groups of Radiolarida, silice-

The Sarcodina 213

ous skeletal elements are the rule. Rods and spines, if present, always
lie outside the capsule. In addition to rod-like elements, or in their
absence, one or more lattice-work layers may be deposited, peripheral
to, and concentric with, the central capsule. The lattice framework may
be spherical or non-spherical (bell-shaped, helmet-shaped, etc.), and in

/';'

ti^^^-

/'/ hwyr

^;

Fig. 5. 9. A. Acanthometra pellucida, showing central capsule, axial rods
and "myonemes" (myophrisks) joining the superficial cytoplasm and the
sheaths of the axial rods; x200 (after Moroff and Stiasny). B, C. Axial rods
and myophrisks in Actipylina; ectoplasmic layer expanded and myophrisks
contracted (B); ectoplasmic layer contracted and myonemes extended (C);
schematic (after Schewiakoff). D. Dorotaspis lieteropora Bernstein, showing
lattice-work shell and axial rods; schematic (after B.).

the latter case may approach bilateral symmetry. Complicated skeletons
already had been developed early in the known history of the Radiolarida
(Fig. 5. 11, A, B).

The intracapsular cytoplasm contains the nucleus or nuclei, stored re-
serves, pigment granules in some species, and the so-called "yellow cells"
in the Actipylina. The number of nuclei varies. The Actipylina are typ-

214 The Sarcodina

ically multinucleate, while the Monopylina and Tripylina are usually
uninucleate. The extracapsular cytoplasm is concerned primarily with
flotation, capture of food, and digestion. Several layers may be recog-
nizable (Fig. 5. 11, D): the sarcomntrix, a so-called digestive layer next to
the central capsule; the vacuolated calymma, which is a thick zone in some
species; a thin layer outside the calymma; and the zone of axopodia whose
axonemes often arise in the sarcoma trix. Food is captured much as in the
Heliozoida. Since the size of solitary species ranges from about 50[x to
several millimeters, the larger Radiolarida are able to feed on copepods
and other small Crustacea, as well as on algae and Protozoa which come
in contact with the pseudopodia.

The "yellow-cells" (zooxanthellae), present in many Radiolarida al-
though not in the Tripylina, are more numerous in species with a well-
developed calymma. They are typically intracapsular in the Actipylina,
extracapsular in other groups. In the living host, these parasites are com-
monly spherical to ovoid. After death of the host, they may develop into
palmella stages which give rise to flagellates. Certain of these flagellates
have been referred to the Dinoflagellida (22, 58). Their reputed status as
symbiotes remains somewhat uncertain.

Some of the Radiolarida, such as Collozoum and Sphaerozoum, are
colonial forms (16, 140) in which a number of central capsules are em-
bedded in an elongated or more or less spherical mass of extracapsular
cytoplasm. In certain species at least, each central capsule contains a
number of nuclei. Skeletal elements are often reduced to scattered spic-
ules, although lattice-work shells occur in some species.

Life-cycles. As a result of the difficulties in obtaining adequate material
for study, little is known about the life-cycles of Radiolarida. Various
accounts in the older literature suggest that the life-cycles may be fairly
complex, but more extensive observations are needed. Since some of the
shallow-water species will survive in the laboratory for reasonable periods,
perhaps the application of techniques which have already been so pro-
ductive for Foraminiferida would yield valuable information on Radio-
larida.

Although reproduction has been traced in relatively few species, fission
occurs in species with simple skeletal elements. The central capsule is
divided, and any skeletal elements are passed on to the two daughter
organisms. Fission also has been reported within the helmet-shaped skele-
ton of certain Tripylina. One daughter organism retains the old shell;
the other leaves and develops a new one. According to Brandt (14), cer-
tain Thallophysidae may undergo a complicated plasmotomy which fol-
lows dedifferentiation of the adult, and results in a number of small
organisms, each with several nuclei. Budding possibly occurs in a few
species (15), but the process needs further investigation.

Evidence for sexual phenomena in Radiolarida is still inconclusive, al-

The Sarcodina 215

though the literature contains repeated descriptions of flagellate stages
(flagellispores) — supposedly gametes. However, syngamy has not been ob-
served, and Chatton (23) concluded that some of these supposed flagellate
stages are probably parasites. This conclusion certainly seems justified for
"flagellispores" which are similar to dinoflagellates. However, some of
these flagellates (80) obviously are not dinoflagellates (Fig. 5. 10) and
they show a marked resemblance to flagellate gametes of Foraminiferida
(Fig. 5. 42).

Although the Radiolarida are not swimmers, at least some of them
apparently can rise or sink in response to changing environmental con-
ditions. A collapse of vacuoles in the calymma increases the specific grav-
ity of the organism and thus induces sinking; regeneration of the vacuoles
reverses this effect. Such a mechanism enables species living near the

Fig. 5. 10. "Flagellispores" (gametes?) of Radiolarida: A, B. Acantho-
metra pellucida, dividing gametocyte showing paradesmose (A) and biflag-
ellate gamete (B); x4000 (after Le Calvez). C. Xiphicantha alata, x4000
(after Le Calvez). D, E. Coelodendrum ramosissimum, living (D) and
stained (E); x2550 (after Le Calvez).

surface to sink when disturbed by rough wave action or when the tem-
perature becomes unfavorable.

The majority of species probably live within the upper 1,500 feet, al-
though a few forms have been dredged from depths of 2-3 miles. Within
this vertical range, the fauna varies to a considerable extent with depth.
The majority of the Peripylina are found within the upper 200 feet, while
the Actipylina are most abundant below 150-200 feet. The Tripylina are
to be found mainly within a range of 1,200 to 3,500 feet. The group as a
whole is widely distributed over the oceans, although specific distribution
varies considerably. Some species show essentially universal distribution
while others may be limited to tropical or to polar waters. The greatest
variety of species occurs within the equatorial zone. Radiolarian skeletons,
sinking to the bottom, make up deposits of radiolarian ooze, and many
fossil types are known.

216 The Sarcodina

Taxonomy.^ The Radiolarida are subdivided, on the basis of skeletal
structure and the distribution of pores in the capsule, into four suborders:
(1) Actipylina ("Acantharia"), with a skeleton composed basically of
radial spines which penetrate the central capsule to converge in the mid-
dle of the body; (2) Peripylina ("Spumellaria"), often with no skeleton
or one limited to disconnected extracapsular rods and less commonly with
a perforated shell; the spherical central capsule shows uniformly dis-
tributed pores; (3) Monopylina ("Nasselaria"), with a thick central cap-
sule in which the pores are limited to one zone, or "porous plate" (Fig.

•..■"•-•!-^^»_-'^ ■ '^ >' ' ' ■ '■-' ' ■'/.•••■'; .-•'' .•-

■■■■.::t — T' ir ' ^•— \ , ' -■[, ■ ^-^i .•"■;.■■■".'■

..."::-.>-^,'i:'-;-- :_ /■ : • ',- ■• ." - ■'• , ./;

•^\::^>'"*^\: : ';. ,-^- ■.;; ^.j '- -r,::"--*,^,_^.Zj;vz'.'.

%

•'A

••^;fe^^'%?

D

Fig. 5. 11. A. Ceiiosphaera tnacroponi Riist, from Ordovician (Lower
Silurian) deposits; x]20 approx. (after R.). B. Staurolonche micropora Riist
(Ordovician), xl20 approx. (after R.). C. Branched central capsule of Cyto-
r'ndus spinosus, x5 (after Schroder). D. ThalassicoUa nucleata, from living;
central capsule (surroimded by zone of small vacuoles), layer of hyaline
cytoplasm, calymma, and axopodia (after Huth).

5. 12, F); and (4) Tripylina ("Phaeodaria"), in which the central capsule
has one major and two accessory openings (Fig. 5. 13, A).

Suborder 1. Actipylina. The central capsule, sometimes irregular in
shape, is rather uniformly perforated, although arrangement of the pores
in rows or fields is often recognizable. The skeleton consists mainly of
rods which converge inside the central capsule (Fig. 5. 9, A-C) and usually
show an arrangement described by Miiller's "law." There are often twenty

^ More detailed information will be found in such special monographs as the follow-
ing: general: Haeckel, E. 1887. Challenger Rep., Zool. 18; Hertwig, R. 1879. Der
Organismus der Radiolarien (Jena); Actipylina: Popofsky, A. 1904. Ergebn. Plankton-
exped. 3, 1907. Nordisches Plankton 16; Schewiakoff, W. 1926. Fauna Flora G. Neapel
37; Peripyliyia: Schroder, O. 1914. Nord. Plankt. 17; Monopylina: Popofsky, A. 1913.
Ergebn. Deutsch. Siidpol.-exp. Bd. 14, Zool. 6; Tripylina: Borgert, A. 1903-1911. Ergebn.
Planktonexp. 3.

The Sarcodina 217

(sometimes multiples of twenty) rods which form a characteristic pattern.
An equatorial group emerges from the body in a plane essentially 90°
from either pole, and two other groups emerge in planes about 45° above
and below the equatorial plane. The basic skeleton is sometimes modified
by lateral outgrowths from the rods which form a perforated shell, com-
posed typically of twenty plates. Two such shells, concentric with the
central capsule, are present in certain species. The outer layer of extra-
capsular cytoplasm is joined to the skeletal rods, apparently by contrac-
tile fibrils ("myophrisks") which are said to bring about minor changes
in form and volume of the body (Fig. 5. 9, B, C) and thus to aid in
controlling flotation.

The suborder includes such genera as the following: Acantlwcliiasma Krohn, Acan-
thometm Midler (Acaiithoinetron Haeckel) (94; Fig. 5. 9, A), AcantJionia Haeckel,
Actmelius Haeckel, Amphilonche Haeckel, Diplocolpus Haeckel, Diploconus Haeckel,

Fig. 5. 12. A-C. Skeletal features of Monopylina: tripod and central cap-
sule (A); tripod and ring enclosing central capsule (B); helmet-like skeleton
(cephalis, capitulum) derived from the more primitive tripod and ring (C);
schematic (after Haeckel). D. Helmet-like skeleton of Eucyrlidium cranioidcs
Haeckel, xllO approx. (after H.). E. Skeleton of Dictyophimus gracilipes
Bailey, schematic (after Bernstein). F. Lithocircus annularis Hertwig, skel-
eton, central capsule with perforated plate, nucleus (in outline); schematic
(after H.).

218 The Sarcodina

Dorotaspis Haeckel (Fig. 5. 9, D), Hexaconus Haeckel, Litholopus Haeckel, Lithoptera
Miiller, Phractaspis Haeckel, Podactinelius Schroder, Sphaerocapsa Haeckel, and Tlioro-
capsis Haeckel.

Suborder 2. Peripylina. There is a fairly thick spherical central capsule
in which numerous pores are uniformly distributed. There is no skeleton
at all in some species. In others, a relatively simple skeleton consists of
scattered extracapsular spicules, a perforated shell, or both. The lattice-
work shells may be single, or in certain families, often multiple in a con-
centric series. In CoUosphaera, Collozoum, and Sphaerozoiim the central
capsules, instead of separating after fission, remain embedded in a com-
mon extracapsular mass to form colonies which may measure several
centimeters.

The following genera have been included in the Peripylina: Acanthosphaera Ehren-
berg, Arcliidiscus Haeckel, Cenolarcus Haeckel, CenospJiaera Ehrenberg (Fig. 5. 11, A),
Chitoanastrum Haeckel, CoUosphaera Miiller, Collozoum Haeckel (140), Cromyodrymus
Haeckel, Cytocladus Schroder, Druppula Haeckel, Euchitonia Haeckel, Lampoxanthiurn
Haeckel, Orosphaera Haeckel, Physeiuaticum Haeckel, Pipetla Haeckel, Sphaerozoum
Meyen, Staurocyclia Haeckel, Staurosphaera Haeckel, Thalassicolla Huxley (62; Fig. 5.
II, D), Thalassolampe Haeckel, Thallasophysa (14), Thalassothamnus Hacker.

Suborder 3. Monopylina. The thick-walled central capsule (Fig. 5. 12,
F), which may be radially or bilaterally symmetrical, shows a single porous
plate or, more often, a single field of small pores with thickened walls.
The pseudopodia usually arise opposite this field. The siliceous skeleton,
composed of solid elements, may show three distinct parts (tripod, capit-
ulum, and ring). The basic form of the tripod (Fig. 5. 12, A) suggests
the name applied to the structure. The ring, if present, is attached to
the tripod (Fig. 5. 12, B). Outgrowths from the ring and tripod may result
in a hemlet-shaped shell, the capitulum (Fig. 5. 12, C-E). Modification of
these three basic elements, by suppressions or by the addition of append-
ages and decorations, gives rise to a variety of skeletons.

The suborder includes the following genera: Cortiniscus Haeckel, Cystidium Hert-
wig, Dictyophimus Ehrenberg (Fig. 5. 12, E), Eucyrtidium Haeckel (Fig. 5. 12, D),
Lithocircus Miiller (Fig. 5. 12, F), Protympanium Haeckel, Stichoformis Haeckel,
Theopera Haeckel, Theophormis Haeckel, Triplagia Haeckel, Zygostephanus Haeckel.

Suborder 4. Tripylina. The central capsule has one major (the astro-
pyle) and two accessory openings (parapyles), the latter usually lying
opposite the first (Fig. 5. 13, A). The astropyle typically is covered with
a striated plate, in which the central openings are often drawn out into
tubes. A characteristic feature is an accumulation of greenish-brown mate-
rial (perhaps the reinnants of diatoms and other food) just outside the
astropyle. This colored material ("phaeodium") is responsible for the
name, "Phaeodaria," often applied to this suborder.

The siliceous skeletons show a wide range in complexity. The skeletons

The Sarcodina 219

Fig. 5. 13. A Central capsule of Trip)lina, showing inner and outer
layers, astropyle, two parapyles, and large nucleus; diagrammatic (after
Gamble). B. Bivalve shell and its appendages, galea with nasal process, or
rhizocanna; astropyle drawn out into a tube; diagrammatic (after
Gamble). C. Costanidiuin sol Hacker, portion of skeleton showing lattice-
work shell and radial elements; diameter of shell, 400-500^ (after H.). D.
Skeleton of Challengeron armatum Borgert, xl70 (after B.).

of Aulacantha and related genera consist of separate elements, hollow
radially arranged rods and sinaller tangentially distributed spicules. The
latter are often replaced by a lattice-work shell (Fig. 5. 13, C, D); or two
shells may be present, one just outside the central capsule. In some genera,
only the inner shell is developed. Several families show a bivalve inner
shell (Fig. 5. 13, B), and each valve sometimes bears a hollow apj^endage,
the galea.

The group includes the following genera: Aulacantha Haeckel (13), Aulosphaera
Haeckel, Cannosphaera Haeckel, Castanidium Haeckel (Fig. 5. 13, C), Challengeron
Haeckel (Fig. 5. 13, D), Circoporus Haeckel, Coelacantha Hertwig, Coeloden-
drum Haeckel, Coementella Borgert, Conchoceras Haeckel, Euphysetta Haeckel,
Medusetta Haeckel, Tuscarilla Haeckel, Tuscarora Murray.

CLASS 2. RHIZOPODEA

These Sarcodina may have lobopodia, filopodia, or myxopodia but
do not develop axopodia and do not show a foamy peripheral cytoplasm.
Tests, well developed in certain groups, may be composed mainly of
organic material, with or without added foreign particles, or largely of

220 The Sarcodina

inorganic materials such as calcium salts. Binuclearity and multinuclear-
ity are not uncommon.

The group is usually divided into five orders: (1) Proteomyxida, which
often develop slender filopodia, sometimes delicate ones which super-
ficially resemble axopodia; (2) Mycetozoida, plasmodial organisms, which
move primarily by protoplasmic flow, and certain other types which de-
velop a pseudoplasmodium; (3) Amoebida, naked forms which usually
show lobopodia; (4) Testacida, which have a simple test and may form
filopodia or lobopodia in different genera; (5) Foraminiferida, which have
either a simple or a multi-chambered test and typically develop myxo-
podia.

Order 1. Proteomyxida

This order is not clearly defined and the interrelationships of the
families usually assigned to it need investigation. The mature stage in
certain genera is a large plasmodium; in others, an amoeboid uninucleate
organism. Both flagellate and amoeboid stages occur in certain genera;
in other cases, a flagellate stage is unknown. Three families are often
included in this order: (1) Labyrinthulidae, uninucleate organisms which
grow in "nets" and may form an aggregate (pseudoplasmodium) before
encystment; (2) Pseudosporidae, uninucleate forms with amoeboid and
flagellate stages; (3) Vampyrellidae, in which the mature stage is a plas-
modium.

Family 1. Labyrinthulidae. These are little known Proteomyxida which
parasitize eel grass and various algae. The organisms usually form a
peculiar network (Fig. 5. 14, A, D), the organization of which has been
disputed in Lobyrinthula. According to one interpretation, the individual
organisms are joined by cytoplasmic processes; according to another view
(145), they are held together by a tubular membrane in L. zopfi (Fig. 5.
14, A, B). Neither interpretation is supported by the observations of
Young (162) on Labyrhitluila mocrocystis, in which the "connections"
are interpreted as filamentous "tracks" secreted by the individual organ-
isms. At the advancing end of a net the organisms first form a clump (Fig.
5. 14, D). Then, hyaline filaments, one from each individual, "dart" for-
ward to a length several times that of tlie organism. The filaments wave
about until they meet and fuse to form a track. The organisms, by a
method still undetermined, glide along such a track "like a drop of
glycerin rolling down a taut silk thread" (162). One organism may over-
take and pass another without either one leaving the track. Since the
organisms may leave the track independently, they apparently do not lie
within a tube. Growth of the net involves fission of the organisms.

The life-cycles need more investigation. A slowly moving pseudoplas-
modium, composed of a mass of organisms embedded in a thin matrix,
has been observed in Labyrinthula macrocystis (162). Encystment of 1-8

The Sarcodina 221

Fig, 5. 14. A-C. Labyrinthula zopfi Valkanov (individual organisms reach
8/i in length): portion of Hving network (A); two organisms stained (B);
encysted stage, from hving (C); schematic (after V.). D, E. Labyrinthula
macrocystis Cienkowski: vegetative network (D), x380 approx.; single organism,
stained, showing nucleus and vacuole (E), x2700 approx. (after Young).

organisms within one membrane has been described in Labyrinthula
zopfi (Fig. 5. 14, C), and in L. macrocystis, a membrane may be formed
around a pseudoplasmodium composed of 5-100 organisms (162).

The family includes Labyrinthula Cienkowski (145, 162), reported from eel grass and
certain marine algae (Cladophora, Chaetomorpha); and Labyrinthomyxa Duboscq (35),
reported from Laniinaria. Labyrinthula macrocystis has been found associated with a
fungal disease of eel grass (120, 162), and it is possible that the organisms, by attack-
ing the plant cells, contribute to the spread of infection.

Family 2. Pseudosporidae. These organisms invade filamentous algae
and Volvocidae. The parasitic stages are amoeboid. Either flagellate or
amoeboid "swarm-cells" may be produced, depending apparently upon
the species. The best known genus is Pseiidospora Cienkowski (127, 134,
135; Fig. 5. 15). Several other genera- — Protomonas Cienkowski, Apheli-
dium Scherffel, Amoeboaphelidiujn Scherffel, Aphelidiopsis Scherffel,
Pseudosporopsis Scherffel, Barbetia Dangeard — appear to be related to
Pseudospora and presumably belong to the same family (134).

A fairly complex life-cycle has been described for Pseudospora parasi-
tica (135). Growth of the young amoeboid stage into a mature form may
be followed by formation of a "zoocyst," or reproductive cyst (Fig. 5. 15,
A-D). According to Schussnig (135), gametes eventually are produced

222 The Sarcodina

Fig. 5. 15. A-J. Pseudospora parasitica Cienkowski: A, B. Young and older
amoeboid stages. C, D. Formation of "zoocyst." E, F. Production of uni-
nucleate amoebae and their escape from the cyst. G. An amoeboid "gamete."
H, Stage supposedly produced by fusion of two gametes. I. Nuclear fusion is
said to have occurred in the "zygote." J. A "sporocyst" has developed from
the encysted zygote; schematic (after Schussnig). K, L. Pseudospora rovig-
nensis Schussnig, amoeboid and flagellate stages; schematic (after S.). M-O.
Pseudospora volvocis Cienkowski, flagellate, amoeboid, and encysted stages;
xlHO approx. (after Roskin).

and syngamy occurs (Fig. 5. 15, G-I). The supposed zygote promptly en-
cysts. Within the "zoocyst," a second membrane ("sporocyst") is secreted to
produce a resting cyst (Fig. 5. 15, J). Flagellate "swarm-cells" and small
amoebae also have been reported in P. rovignensis (135), P. eudorini, and
P. volvocis (127).

The taxonomic position of the family is still uncertain and it has been

The Sarcodina 223

V'.

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Fig. 5. 16. A-D. Vampyrella lateritia Leidy, schematic (after Hoogen-
raad): specimens showing different forms of pseudopodia (AC); organism
ingesting contents of a Spirogyra cell. E-G. Vampyrella closterii I'oisson and
Mangenot (after P. and M.): E. Specimen attached to Closterhim and ingest-
ing contents of the alga; xl58. F. Cyst attached to empty cell wall of
Closterium; xl58. G. Section of cyst showing central mass of ingested food,
nuclei, mitochondria, and a peripheral zone of neutral-red-stainable vacu-
oles; x563. H, I. Arachnula impatiens Cienkowski (after Dobell): small speci-
men with a number of nuclei and several contractile vacuoles, x200; cyst
with several nuclei and ingested diatoms, x500.

suggested that Pseudospora may belong in the Dimastigamoebidae (Order
Amoebida) rather than in the Proteoinyxida (127).

Family 3. Vampyrellidae. The mature stage, in the type genus, is a
fairly large plasmodium. Reproduction involves plasmotomy, and multi-
nucleate cysts are formed by plasmodia. These general characteristics are

224 The Sarcodina

clearly represented in Arachnula Cienkowski (Fig. 5. 16, H, I), Leptomyxa
Goodey (Fig. 5. 17), and Vampyrella Cienkowski (Fig. 5. 16, A-G). Arach-
nula may be a synonym of Vampyrella (33). Chlamydomyxa Archer,
as represented by C. montana Lankester, closely resembles Leptomyxa
Goodey and it is not certain that the two should be placed in separate
genera. The mature stage of C. montata is a large plasmodium, the pseu-
dopodia are similar to those of Leptomyxa, and several endocysts are
produced within an ectocyst.

The life-cycles appear to be fairly simple. Excystment of a young plas-
modium is followed normally by growth and nuclear division. In addi-

Fig. 5. 17. A-G. Leptomyxa reticulata Goodey: A. Multinucleate plas-
modium, which may reach lengths of 2-3 mm.; x550. B. Ectocyst with six
endocysts; x880. C. Single endocyst; x880. D. Small plasmodium after emer-
gence from cyst. E. Plasmodium penetrating a root; x3I2. F. Plasmodium ex-
tending through several cells; x312. G. Stamed cyst with many nuclei; xl83.
A-D, after Singh; E-G, after MacLennan. H. Biornyxa merdaria Hollande,
x960 approx. (after H.). I. Biornyxa vagans Leidy, xl25 (after L.).

The Sarcodina 225

tion, fusion of several plasmodia into a single large one measuring as
much as I500[jl has been described in J'ampyrella closterii (112). Plas-
motomy within the cyst has been reported in Arachnula (33) and Vajn-
pyrella (112). The details of encystment may vary slightly. In a strain of
Leptomyxa reticulata recovered from hops (88), the cysts (Fig. 5. 17, G)
were large (425-900[j.) and contained only one endocyst. In other strains
(43, 138) several multinucleate endocysts have been found within an
ectocyst (Fig. 5. 17, B).

Leptomyxa reticulata occurs in the soil (138) and as a secondary in-
vader of diseased hops (88). Arachmila itnpatie7is has been described from
fresh and brackish water (33), while species of Vampyrella attack Spiro-
gyra (85) and Closteriinn (112) by digesting a portion of the cell wall
and sucking out the contents.

Both large plasmodial forms (Fig. 5. 17, I) and smaller uninucleate
organisms (52; Fig. 5. 17, H) have been assigned to Biomyxa Leidy but

Fig. 5. 18. A-G. Hyalodiscus rubicundus Hertwig and Lesser: oval forms
(35-70 X 20-50yn) seen from above (A) and from the side (B); invading cells
of Oedogoniutn (C, D); resting form with radiating pseudopodia (E); speci-
mens in locomotion, seen from above (F) and from the side (G); A-D, after
Hoogenraad; E-G, after Penard. H-K. Vampyrellidium vagana Zopf: various
amoeboid forms (H-J); resting cyst (K); schematic (after Ivanic).

226 The Sarcodina

the life-cycles are still unknown. Hyalodiscus Hertwig and Lesser (Fig.
5. 18, A-G) includes small organisms which may attack filamentous algae.
Although several morphological varieties occur, the production of a
large plasmodial stage has not been demonstrated for this genus. Schaeffer
(132) concluded that Hyalodiscus belongs in the Amoebidae. Vampy-
rellidmm Zopf (Fig. 5. 18, H-K) is similar to Hyalodiscus. The "axopodia"
of V. vagajis (63) resemble the ectoplasmic ridges of Thecamoeba (132).

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Fig. 5. 19. A. Actinocoma ramosa Penard (14-26/i); pseudopodia may
show small granules in movement (after P.). B-D. Nnclearia caulescens
Penard (16-20^); free stage (B); form temporarily attached by pseiido-
podiinn (C); specimen with a gelatinous sheath (D); after P. E. Gephyra-
jnoeba delicatula Goodey, specimen clinging to cyst from which it has just
emerged; x375 (after G.).

The Status of Gephyramoeba Goodey (Fig. 5. 19, E) is somewhat un-
certain. Although Gephyramoeba delicatula occasionally reaches lengths
of 250jjL, the organisms remain uninucleate and their cysts apparently
have a single membrane (43). Nuclearia Cienkowski (Fig. 5. 19, B-D)
includes uninucleate and multinucleate forms, either naked or with a
capsule through which the pseudopodia extend. Actinocoma Penard, as
represented by A. ramosa (Fig. 5. 19, A) is similar to noncapsulated uni-
nucleate forms of Nuclearia. These organisms apparently have little in
common with the plasmodia of Vampyrella and Leptomyxa.

The Sarcodina 227

Order 2. Mycetozoida

The mature stage of the Mycetozoida^ is either a large plasmodium
or a pseudoplasmodium. On the basis of differences in morphology and
life-history, three suborders may be recognized: (1) Acrasina ("Acra-
siales"), in which the structural unit is the uninucleate stage, although
pseudoplasmodia may be formed by aggregation of myxamoebae with-
out cytoplasmic fusion; (2) Plasrnodiophorina ("Plasmodiophorales"),
parasites which are plasmodia at maturity but do not produce sporangia;
(3) Eumycetozoina (Euplasmodida, "Myxogastres"), the typical free-

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PJL

Fig. 5. 20. A, B. Dirtyostcliinn inucoroides Brefeld (after Schuckmann):
active amoeboid stage with ingested bacteria, x440 (A); portion of pseudo-
plasmodium showing spindle-shaped organisms, x440. C-M. Dictyosteliiim
discoideuni Raper (after Bonner): C-I. Successive stages in development of
a pseudosporangium from a pseudoplasmodium; diagrammatic. J. Pseudo-
sporangium, almost mature, showing basal disc, stalk, and spores; schematic,
xl40 approx. K-M. Diagrams illustrating changes in position of "cells"
during development of a pseudosporangium (M) from a pseudoplasmodium
(K). KEY: b, basal disc "cells"'; s, spore "cells"; 1, 2, 3, stalk "cells" of three
different regions.

^ Detailed discussions of the Mycetozoida will be found in several monographs (46,
84, 86) and modern data have been reviewed by Martin (89).

228 The Sarcodina

living Mycetozoida in which the mature stage is a migiatory plasmodium;
more or less complex sporangia are produced in many genera.

Suborder 1. Acrasina. In this group, a small uninucleate "myxamoeba"
is released from the cyst ("spore"). Sexual phenomena have not been
demonstrated. These myxamoebae (Fig. 5. 20, A) lead an active life,
feeding typically on bacteria and undergoing fission. Under certain con-
ditions, which include a favorable humidity (Hi/) and perhaps partial
exhaustion of food (117), a pseudoplasmodium is developed by the ad-
hesion of myxamoebae to one another (Fig. 5. 20, B). In spite of its
organization, the pseudoplasmodium of Dictyostelium discoideiim moves
as a polarized vmit (116) and may grow by fission of the component
myxamoebae. The myxamoebae are said to cease feeding after formation
of the pseudoplasmodium in Dictyostelium (137) and the aggregate ap-
parently is a preliminary step toward sporulation.

Sporulation in some of the simpler Acrasina, such as Guttulina, in-
volves merely a heaping up of the m)T{amoebae into a compact mass and
then secretion of a cyst membrane (117). In such specialized types as
Dictyostelium discoideum (11), a pseudoplasmodium, under favorable
conditions, may first vmdergo a certain amount of migration. At sporula-
tion, the pseudoplasmodium gradually assumes an upright position and
becomes reorganized into a pseudosporangium (Fig. 5. 20, C-I). During
the late migratory phase, the posterior components of the pseudoplas-
modium are differentiated into intensely staining pre-spore cells; the
anterior units become stalk-cells; those at the base of the pseudoplasmo-
dium, basal-disc cells. Later on, the pre-spore cells are transformed into
spores. Morphogenesis also involves changes in position of the units. The
stalk-cells most anterior in the migratory stage are pushed up to and over
the top of the stalk-sheath and do^vn toward the basal disc during de-
velopment of the pseudosporangium. As a result, the relative positions
of various groups of cells are reversed (Fig. 5. 20, K-M). The pseudo-
sporangia are quite specialized also in Polysphojidylium. One interesting
feature of this commimal process is that sporulation follows a specific
pattern. Even after being crushed and mixed together, pseudoplasmodia
of two different species may reorganize and then produce their typical
spore-bearing structures (118).

The best known genus is Dictyostelium Brefeld, species of which have been investi-
gated in detail by several workers (II, 114, 116, 137). Certain species of Dictyostelium
have been maintained in cultures (12, 25, 115, 116, 137). Other genera (102) include
Acrasis Van Tieghem, Coenonia Van Tieghem, Guttulina Cienkowski, GuttuUnopsis
Olive, and Polyspliondylium Brefeld. The status of Sappi7jia Dangeard, sometimes
included in this group, is uncertain (117).

The Acrasina are free-living forms found commonly in soil and on decaying wood,
leaves, and straw, and all of them apparently feed on bacteria.

Suborder 2. Plasmodiophorina. These organisms invade cells in the
roots and underground stems of higher plants. Infections are often ac-

The Sarcodina 229

companied by the hypertrophy of tissues and formation of galls. A host
index has been published by Karling (70). The mature stage is a plas-
modium which may divide into small plasmodia or may give rise to
uninucleate cysts ("spores"). Although chitin has been reported, cellulose
apparently is not produced by the Plasmodiophorina.

Fig. 5. 21. A-I. Typical life-cycle of Plasmodiophorina, diagrammatic
(after Cook): A. Uninucleate cyst ("spore"). B. Excystment. C. Flagellate
stage. D. Amoeboid stage, after loss of flagellum. E. Amoeboid stage sup-
posedly formed by fusion of two flagellates. F. Binucleate amoeboid stage.
G. Plasmodium in host cell. H. Products of plasmotomy. I. Developing
spores. J-M. Sporomyxa tenebrionis Rietschel (from Tenebrio moUtor), xl890
(after R.): uninucleate stage (J); amoeboid form with four nuclei (K); de-
veloping "spores" in sporocyst (L); uninucleate spore (M).

In a typical life-cycle (Fig, 5. 21, A-I) excystment releases a myxoflag-
ellate in the soil. This flagellate ("swarm-cell") penetrates a cell in a
root-hair of the plant host and becomes a myxamoeba. Or, according to
some accounts (27), two myxoflagellates or two amoebae may fuse to
produce a diploid myxamoeba. At any rate, the myxamoeba develops
into a Plasmodium which, at maturity, mav undergo plasmotomy or
produce uninucleate cysts (Fig. 5. 21, H, I).

230 The Sarcodina

Relationships to the Eumycetozoina are not yet clear and further in-
vestigation of the life-cycle is needed. In certain species, meiosis is sup-
posed to precede formation of spores (28, 57, 155). For the group as a
whole, however, data on gametogenesis and syngamy are inadequate from
a cytological standpoint.

About a dozen genera have been erected, largely on the basis of the
arrangement of spores in the spore-masses and the shape of the masses.
However, Palm and Burk (105), in preparations of Sorosphaera from one
host species, found so much variation in the spore-masses that they
questioned the validity of the conventional generic criteria. On this basis,
they suggested that six generic names (Clathrosoriis Ferdinandsen and
Winge, Ligniera Maire and Tison, Mernbranosonis Ostenfeld and Peter-
sen, Ostenjeldiella Ferdinandsen, Sorodisciis Lagerheim and Winge,
Spongospora Brunchorst) might be considered synonyms of Sorosphaera
Schroeter. Furthermore, the authors suggested the advisability of placing
all described Plasmodiophorina in only two genera, Plasmodiophora
Woronin and Cystospora Elliott (37).

Cook (27), on the other hand, recognized the following genera: Plas-
modiophora Woronin (29, 91), Spongospora Brunchorst (77, 104), Lig-
niera Maire and Tison (26), Sorodisciis Lagerheim and \Vinge (157),
Sorosphaera Schroeter (10, 155) and Tetramyxa Goebel. These genera are
differentiated partly by the arrangement and form of the spores (27).
Spherical spores occur in groups of four without a common membrane
in Tetramyxa; ellipsoidal or pyriform spores are grouped in irregular
"spore-balls" within a common membrane in Sorosphaera; and in hollow
spore-balls without a common membrane in Spongospora. A flat "spore-
cake," composed of urn-shaped spores, is surrounded by a membrane in
Sorodiscus; and in Ligyiiera and Plasmodiophora the spores are neither
aggregated nor enclosed in a common inembrane. The taxonomic status
of Sporomyxa Leger (125; Fig. 5. 21, J-M), Peltomyxa Leger, Cystospora
Elliott, and Trematophlyctis Patouillard has been disputed. According to
Cook (27), these genera do not belong in the Plasmodiophorina.

Suborder 3. Eumycetozoina. The Eumycetozoina (Euplasmodia) in-
clude several hundred species of "slime-molds." The mature stage is a
migratory plasmodium which reaches a length of several inches to a foot
or more. Examined microscopically, the plasmodium in such types as
Physarum shows many channels of various sizes. Through the channels
flows a liquid containing many granules, the direction of flow being
reversed at intervals (92). As the plasmodium moves, vessels may be re-
sorbed in some areas and formed anew in others. The cytoplasm may be
hyaline, or with inclusions and pigments, may be white or various shades
of violet, blue, green, yellow, orange, red, and brown. Unfortiuiately,
these colors vary so much, under both natural and experimental condi-
tions, that they are not thoroughly reliable as taxonomic characteristics

The Sarcodina 231

(69). The diet may influence color of the plasmodium, since some species
become pink in association with Serratia marcescens (69). The pigment
of Physarum polycephalum is a pH-indicator, changing from yellow-
green at pH 8.2 to a deep red-orange at pH 1.0 (136). Certain species
with yellow pigment apparently require light for completion of the life-
cycle, while several non-pigmented species develop sporangia equally well
in light and in darkness (44).

The Plasmodium is holozoic, feeding largely on bacteria and other
microorganisms. A number of species have been grown in cultures with
a variety of microorganisms as food (19, 44, 60, 100). In addition, Fiiligo
septica, BadJiamia foliicola, and several others have been grown in pure
cultures on autoclaved yeast (25), but the specific food requirements of
these organisms are yet to be determined.

The Eumycetozoina occur on rotting leaves and logs, and the plasmo-
dium usually grows in or beneath such decaying materials. The plasmo-
dium penetrates decaying wood by extending slender processes through
the interstices and, under experimental conditions, may pass through
filters with pores measuring about 1.0[a (92). Shortly before sporulation,
the Plasmodium creeps to an exposed position, sometimes on trunks or
stems of nearby plants, where conditions will facilitate desiccation and
dispersal of spores. Subsequent behavior varies in different species. In
the simpler cases a plasmodium merely gives rise to a compact flattened
mass, or aetJiaUinn (Fig. 5. 23, A), or to an irregularly lobate body
(plasmodiocarp) which retains to some extent the outline of the plasmo-
dium (Fig. 5. 23, B). In either case, the entire mass becomes enclosed in
a membrane and may be considered a single large spore-case (sporocarp).
More often, the plasmodium produces individual sporangia (Fig. 5. 23,
C-I), stalked in many species but not in others.

The sporangia usually begin development as dense areas which become
segmented into knob-like masses. In many cases, the young sporangium
undergoes vertical growth, followed by differentiation of a stalk and a
spore case; in others, the sporangia remain sessile. The surface of the
sporangium typically becomes enclosed in a resistant wall (peridium),
which is commonly wrinkled at maturity. In stalked types, the peridium
is usually continuous with the covering of the stalk, and the stalk extends
to the substratum to end in a basal network, the hypothallus. Inside the
peridium, a capillitium (a network of threads or bands) is often devel-
oped, although lacking in Cribraria, Licea, and related genera. The first
indication of the capillitium in Physarum polycephalum (60) is the ap-
pearance of lacunae within the sporangium. These channels develop into
hollow threads whose junctions (nodes) become filled with calcium salts
as the sporangium approaches maturity. In other species, calcium may be
deposited throughout the capillitium, may be limited to the peridium or
its inner surface, or may not be deposited at all. The capillitial net, per-

232 The Sarcodina

haps by contractions induced by desiccation, probably helps to distribute
the spores after rupture of the peridium. During development of the
capillitium, nuclear division may continue in the sporangial protoplasm
for a time, but uninucleate pre-spores eventually are produced. These
become enclosed in membranes to form the characteristic spores.

In addition to sporulation, another method of producing resistant
stages is known in the Eumycetozoina. An entire plasmodium may be-

Fig. 5. 22. A-I. Physariim polycephalum, xl360 (after Howard): A. Spore.
B. Completion of mitosis; spore membrane ruptured. C. Completion of fission
at excystment. D. Amoeboid flagellate. E. Swimming flagellate. F. Flagellate
zygote shortly after fusion of gametes. G. Amoeboid zygote after loss of
flagella. H. Encysted zygote; gametic nuclei not yet fused. I. Zygote after first
nuclear division in formation of young plasmodium. J-L. Arcyria cinerea
(after Kranzlin): J-K. Stages in development of sporangiimi, x23. L. Portion
of cross-section through a sporangium, showing spores, peridituii, and part
of a capillitial thread ("elater"), x375.

come sclerotized (17) upon subjection to desiccation. The plasmodium
becomes partly dehydrated and is enclosed in a membrane, the sclerotiuni,
said to consist inainly of cellulose. Once sclerotized, the organism can re-
main viable for several months and then become active again in the
presence of adequate moisture and oxygen.

Development of the spores after liberation seems to be a complicated
process. Prior to germination, each spore in Ceratiomyxa (41) develops
four nuclei, so that a quadrinucleate amoeboid stage is released. The
amoeboid stage is said to produce eight uninucleate myxoflagellates, sup-

The Sarcodina 233

posedly gametes which fuse in pairs to produce amoeboid zygotes. In a
number of other Eumycetozoina (40), one or two amoeboid "swarm-cells"
are liberated and each amoeba then develops a flagellum. In Physarum
polycephalum, for instance, the spore nucleus divides once at the begin-
ning of germination and fission produces two amoeboid stages. One
amoeba emerges, develops a flagellum, and then swims away. The second
amoeba then repeats the process (59). Syngamy of the myxoflagellates
produces amoeboid zygotes (60). Except perhaps for slight differences in

C ,M

Fig. 5. 23. Sporangia in various Eumycetozoina (after MacBride): A. An
aethallium of Fuligo septica, xO.75. B. A plasmodiocarp of Hcmitrichia
serpula, x2.2. C. Sessile sporangia of Trichia inconspiciia, xll. D. Physarum
leiicopus, xll. E. Didymiiirn annulatum, xl3.5. F. Trichia decipiens, x6 ap-
prox. G. Didymiiim melanosperrnum, x7.5. H. Section showing capillitium
in sporangium of Physarella oblonga, x24. I. Badhamia magna, \.l.b.

vital staining, there is no evidence for two distinct types of "swarm-cells"
(69), and this question remains open for the suborder. Although meiosis
has been reported just before formation of the uninucleate "protospores"
in Ceratiomyxa (41), there is much uncertainty as to the exact stage in
which this process occurs in Eumycetozoina generally.

The following genera have been included in the suborder: Arcyria Wiggers (74),
Amaurochaete Rostafinski, Badhairiia Berkeley, Ceratiomyxa Schroter (41), Cribraria
Persoon, Didymium Schriider, Fuligo Haller, Licea Schrader, Lycogala Adanson (153),
Margarita Lister, Orcadella Wingate, Physarum Persoon (59, 60), Reticularia Bulliard,
Stemonitis Gleditsch (7), Trichia Haller, Tubulina Persoon.

Order 3. Amoebida

The Amoebida normally form lobopodia in locomotion, or else
move by a wave-like protoplasmic flow. Some species form slender acces-

234 The Sarcodina

sory pseudopodia which may have httle or no function in locomotion.
A hyahne ectoplasm and a granular endoplasm are usually distinguish-
able. A flagellate stage has been reported in several species usually
assigned to the order; in the rest, the cycle apparently is monomorphic.
Many species occur in the digestive tract of invertebrates and vertebrates;
others are free-living in fresh and salt water and in the soil.

The order is often divided into three families: Dimastigamoebidae,
in which the life-cycle includes both a flagellate and an amoeboid phase;
Amoebidae, free-living species without a flagellate stage; and Endamoe-
bidae, the endoparasitic amoebae.

Family 1. Dimastigamoebidae. The dimorphic cycle includes a domi-
nant amoeboid phase and a flagellate phase of relatively short duration.
Members of the family have been reported from fresh water and from
cultures inoculated with feces of certain insects and of various verte-
brates (including man).

Naegleria griiberi is the best known representative (113, 156, 161). The
small amoeboid stage (Fig. 5. 24, A, B, I) commonly forms one large
lobopodium. The nucleus contains a large Feulgen-negative endosome
which divides in mitosis. The flagellate stage (Fig. 5. 24, C, D, M), which
has two equal flagella, is a temporary one under the conditions reported;
ingestion of food has been described in only one instance (113). The
transformation from amoeba to flagellate is induced by diluting the cul-
ture medium with water (113, 161). Cysts (Fig. 5. 24, E-H) are usually
but not always uninucleate. The cyst membrane shows two well-defined
layers and also several opercula, through one of which the organism
emerges during excystment.

The generic composition of the family has been disputed. The type
genus, Dimastigamoeba Blochmann (9), is based on Dimastigamoeba
(Dimorpha) radiata (Klebs). The amoeboid phase (73) develops slender
radially arranged pseudopodia; the flagellate stage has two unequal flag-
ella, one of which is usually trailed. Dimastigamoeba simplex Moroff
(Fig. 5. 24, Q) is similar to D. radiata (93). The genus Naegleria Alexeieff
em. Calkins (2, 18) includes species with a flagellate stage showing two
equal flagella, and an amoeboid stage which moves by means of a blunt
lobopodium. There seems to be no sound reason for assuming that
Naegleria is a synonym of Dimastigamoeba. The status of Trimastiga-
7noeba Whitmore is uncertain, since stages with two, three, and four
approximately equal flagella were figured for T. philippinensis (159).
Such material might suggest a biflagellate organism in various stages of
flagellar duplication prior to fission. Hollande (53) has suggested that
Naegleria Alexeieff is a synonym of Vahlkampfia Chatton and Lalung-
Bonnaire (Fig. 5. 26, A-F). However, a flagellate stage was not reported
in V. punctata (24), and the structure of the dividing nucleus, although
similar to it, is not identical with that described for N. griiberi (113).

The Sarcodina 235

Fig. 5. 24. Dimastigamoebidae. AM. Naegleria gruberi: A. Unusually
elongated amoeba. B. Amoeba with four nuclei. C. Flagellate stage, from
living. D. Flagellate with three nuclei. E, F. Cysts with one and three nuclei.
G. Amoeba leaving cyst. H. Cyst showing several pores and unusual separa-
tion of inner and outer membranes. I-M. Stages in development of flagellate
(M) from amoeboid stage (I). A-G, xl600 (after Wilson); H, x2400 (after
Wenyon); I-M, xl215 (after Rafalko). N-P. Naegleria (Vahlkampfia) tachy-
podia (Glaser): rounded amoeba, two blepharoplasts on nuclear membrane
(N), x2010; amoeba, from living (O), xlI20; flagellate (P), x2010 (after
Pietschmann). Q. Dimastigamoeba simplex MorofE (20-40 X 10-12^), flagellate
stage showing long trailing fiagelluxn (after M.).

Until it is shown that the type species o£ Vahlkampfia has a flagellate
phase, there is no justification for placing this genus in the family
Dimastigamoebidae as now constituted. "Vahlkampfia" tachy podia Glaser
does show a flagellate stage (HI) closely resembling that of N. gruberi

236 The Sarcodina

^z^^ Xz^

yo^ ^

M

Fig. 5. 25. Various types of amoeboid activity in Amoebidae: A. Locomo-
tion without formation of distinct pseudopodia, cctoplasmic ridges distinct,
as in Tliecamoeba verrucosa. B. Formation of conical pseudopodia along
anterior margin and on free siuface during locomotion, as in Mayorella
bigemma. C. Formation of large pseudopodia which direct locomotion, as in
Amoeba proteus. D. Formation of a ninnber of large pseudopodia, including
several which direct locomotion, as in Amoeba dubia. E. Floating form with
slender and sometimes spiral pseudopodia, as in Astramoeba flagellipodia.
F. Slug-like forms moving by protoplasmic flow, as in Trichamoeba clava;
uroid (slender cytoplasmic projections at posterior end) present. G-L. Loco-
motion of "walking" type, as seen in thriving cultures of Chaos (Pelomyxa)
carolinensis. M-O. Acanthamoeba castcUanii (Douglas) \'olkonsky (12-30/i),
showing different forms of pseudopodia in one species. A-F, schematic (after
Schaeffer); G-L, schematic (after Wilber); M-O, after Volkonsky.

The Sarcodina 237

(Fig. 5. 24, N-P) and therefore should be transferred to the genus
Naegleria.

Family 2. Amoebidae. These are the free-living amoebae which lack a
flagellate phase. Although complex cycles involving polymorphism and
syngamy have been described, such interpretations apparently were based
on cultures contaminated with other species of Amoebidae, Mycetozoa,
and water-molds (67). At present, it appears that the life-cycle is limited
to the amoeboid stage and a cyst.

Classification of the Amoebidae is not yet on a satisfactory basis and
there remains a certain amount of disagreement concerning the genera
which should be recognized. Furthermore, the concept of a single family
for all the free-living amoebae is subject to the objection that habitat is
not necessarily an accurate gauge of zoological relationships. Conse-
quently, there is at least a reasonable basis for various suggestions that
the group should be split into less heterogeneous families. In a sense,
problems of taxonomy are complicated by the very simplicity of amoebae.
Lack of the more obvious fixed characteristics typical of many other
groups necessarily limits the taxonomist to consideration of range in size,
form of the body, type of pseudopodia, methods of locomotion, structure
of the nucleus, and the form and nature of cytoplasmic inclusions. Aside
from the nuclear picture, which should show reasonable constancy, these
characteristics vary within greater or lesser limits and presumably are
subject to significant environmental influences. The effective utilization
of such dynamic traits in taxonomy obviously demands extensive knowl-
edge of amoebae, particularly as living organisms. Consequently, there is
much need for the detailed study of many species which are not yet
thoroughly characterized. In some cases, adequate characterization may
depend upon pure-line cultures for determining the range in form and
behavior to be expected of jiarticular species. The systematic investiga-
tion of nuclear structure and division, on the order of some recent work
with Naegleria (113), also should yield information of taxonomic value.
For instance, a nucleus with a large endosome is characteristic of both
Vnhlkampfia (24) and Acanthamoeha (150), but the mitotic pictures are
strikingly different, the endosome being resorbed in the latter.

It has been pointed out very clearly (132) that amoebae differ char-
acteristically (Fig. 5. 25) with respect to types of pseudopodia, methods
of locomotion, form of the body and the nature of its changes in form,
presence or absence of a "uroid" (a gioup of thin cytoplasmic projections
at the posterior end), form of the nucleus, and even the types of cyto-
plasmic crystals in certain large fresh-water species. Some amoebae, for
example, form determinate pseudopodia which grow to a more or less
definite size and are then withdrawn, never becoming large enough to
include the entire amoeba and thus not directing locomotion. Others
develop indeterminate pseudopodia which are not restricted in size and

238 The Sarcodina

Fig. 5. 26. A-F. Vahlkampfia punctata (Dangeard) Chatton and Lalung-
Bonnaire: amoeba stained to show nucleus (A), xl710; stages in mitosis,
showing division of the endosome and other features (B-F), x3420 (after C.
& L-B.). G. Astramoeba Stella Schaeffer in active locomotion, x875 approx.
(after S.); compare with floating stage of A. flagellipodia (Fig. 5. 25, E). H.
Mayorella conipes Schaeffer, showing conical pseudopodia which do not
direct locomotion; xll55 approx. (after S.). I. Trichanweba pallida Schaef-
fer, a marine type showing typical uroid; xllOO approx. (after S.). J-M.
Amoeba proteus (Pallas) Leidy average length about 600 fi): amoeba in loco-
motion, showing typical pseudopodia and ectoplasmic ridges (J); broad (K)
and narrow (L, M) aspects of typical discoid nuclei (after Schaeffer). N-P.
Amoeba dubia Schaeffer (average length usually about 400^^): typical amoeba
(N), polar and lateral views (O, P) of the elongated nucleus (after S.).

The Sarcodina 239

may, as "main pseudopodia," become large enough to include the whole
organism and thus direct locomotion. And there are also certain amoebae
which develop no typical pseudopodia at all during locomotion. Such is
the case in Trichamoeba and Thecamoeba, in which locomotion is best
characterized as protoplasmic flow. The eventual correlation of such
characteristics with adequate cytological data should furnish a much
clearer picture of generic boundaries and relationships than is now
available for the free-living amoebae.

Some of the genera which have been proposed for various types of Amoebidae are
listed below; certain others have been characterized by Schaeffer (132).

Acanthamoeba \'olkonsky (50, 150; Fig. 5. 25, M-O); Amoeba Ehrenberg (Fig. 5. 26,

Fig. 5. 27. A. Flabelhda mira Schaeffer (marine), in locomotion; xl740
approx. (after S.). B. Dinamoeba mirabilis Leidy, characteristic spine-like
pseudopodia; some specimens show adherent rods, possibly bacteria; xl25
(after L.). C. Thecamoeba orbis Schaeffer, in locomotion, showing typical
ectoplasmic ridges; xl600 (after S.). D. Hartmanella kUtzkei Arndt, many
ingested bacteria, stained preparation; xl250 approx. (after A.). E. Pelo-
myxa ("gray type," P. palustris), longitudinal section of slug-like body
showing many nuclei, several food vacuoles, central axis, and tail-piece
("telspn") of hyaline cytoplasm; x53 approx. (after Okada).

240 The Sarcodina

J-P), represented by Amoeba proteus (Pallas) Leidy em. Schaeffer and A. dubia Schaeffer
(131); Astramoeba Vejdowsky (132; Figs. .5. 25, E, 5. 26, G), erected for A. radiosa
(Ehrenberg); Chaos Linnaeus, represented by Chaos (Pelomyxa) caroUnensis (71, 75,
76, 160; Fig. 5. 25, G-L), multinucleate types which sometimes measure 4-5 mm. in
length; Dinamoeba Leidy (83, 107, 132; Fig. 5. 27, B), erected for D. mirabilis; Flabel-
luhi Schaeffer (132; Fig. 5. 27, A); Hartmanella Alexeieff (150; Fig. 5. 27, D); MuyoreUa
Schaeffer (132; Figs. 5. 25, B, 5. 26, H); Pelomyxa Greef (Fig. 5. 27, E), represented
by P. palustris (83, 101, 107, 152), multinucleate types which move by protoplasmic
flow and may reach a length of more than 2 mm; Thecamoeba Fromentel (132; Fig. 5.
27, C), established for T. {Amoeba) verrucosa (Ehrenberg); Trichamoeba Fromentel
(132; Figs. 5. 25, F, 5. 26, I); Vahlkampfia Chatton and Lalung-Bonnaire (24; Fig. 5. 26,
A-F). It is possible that Hyalodiscus Hertwig and Lesser (Fig. 5. 18, A-G) also should be
included in this group.

Family 3. Endamoebidae. These are parasitic amoebae, found typically
in the digestive tract of invertebrates and vertebrates. The range of hosts

mm

^-^^C-/

B

^jsd0i^'

■f: ■ -' -^ J'j \ ' • " ■ ■' \

Fig. 5. 28. A-C. Entamoeba invadens Rodhain: amoeba in liver smear
from Coluber constrictor (A); binucleate cyst with many chromatoid bodies
(B); cyst with four nuclei (C); xl260 (after Geiman and Ratcliffe). D.
Endolimax terjnitis Kirby, xI600 (after K.). E. Endamoeba granosa Hender-
son, from termites; x500 (after H.). F, G. Endamoeba simulans Kirby, from
termites; amoeba with much ingested material (F); cyst with fom^ nuclei
(G); x530 (after K.). H. Hydramoeba hydroxena (Entz) Reynolds and
Looper, section through the outer surface of Hydra showing destruction of
the epithelium; x560 (after R. & L.).

The Sarcodina 241

may be wide even within a single genus, since different species of Endo-
limax have been reported from termites and from primates. Most Enda-
moebidae are probably endocommensals, or else approach such a status.
However, there are notable exceptions, such as Entamoeba histolytica of
man (Chapter XI), and E. invadens which may produce fatal infections
in various reptiles (39, 119). As in the case of the Amoebidae, the assign-
ment of genera to this family is based upon their sharing a common
habitat rather than upon a consideration of more valid taxonomic cri-
teria. It is not impossible that some of the Endamoebidae are more closely
related to certain free-living amoebae than they are to other members of
their own "ecological" family. The following genera have been included
in the Endamoebidae:

Endamoeba Leidy (Fig. 5. 28, E-G), erected for Biitschli's Amoeba blattae (90, 95),
contains parasites of cockroaches and termites (49).

Entamoeba Casagrandi and Barbagallo (Fig. 5. 28, A-C) includes species from the
major groups of vertebrates. Although the validity of this generic name, as distinct
from Endamoeba Leidy, has been disputed extensively, reasons for retaining Entatnoeba
as a generic name for E. coli and related amoebae are ably presented by Kirby (72).
This usage emphasizes the fact that E. blattae and E. coli cannot logically be placed
in the same genus. The three species parasitic in man are discussed in Clhapter XI.

EndoUmax Kuenen and Swellengrebel (Fig. 5. 28, D) is represented in termites and
cockroaches as well as various \ertebrates. E. nana of man is described in Chapter XI.

Dientamoeba Jepps and Dobell includes a parasite of the human colon, while
lodamoeba Dobell is represented in pigs and in man (Chapter XI).

Hydramoeba Reynolds and Looper (121, 122; Fig. 5. 28, H) includes a rather large
amoeba which attacks the epithelial layers of Hydra, often with fatal results.

Order 4. Testacida

These are typically creeping organisms which develop lobopodia
or filopodia and possess one-chambered tests. The primitive test is com-
posed of an apparently single secreted layer. The material is said to be
"pseudochitin" (1). The flexibility of the test in Pamphagus and Cochlio-
podimn, for instance, indicates there is no significant addition of inor-
ganic material. Mixtures of silica with the basic "chitinous" material are
found in relatively firm tests which maintain a characteristic shape, as in
Hyalospheiiia.

The test of most Testacida apparently contains two layers (Fig. 5. 29,
J). The inner layer is composed of "chitin," sometimes mixed with sili-
ceous material. The structure of the outer layer varies in different genera.
Although apparently bivalve in Clypeolina rnarginata (109), this layer
seems to be continuous in other Testacida. In Arcella (Fig. 5. 29, C-F),
more or less spherical elements are cemented together in a honeycomb
pattern. In Amphizonella (Fig. 5. 29, L), the test is sometimes covered
with a "gelatinous" layer. Difflugiidae ingest sand grains, and occasionally
diatom shells, which are used with little or no modification in construc-
tion of the test. Such particles are embedded in a "chitinous" cement.
The test of Centropyxis (Fig. 5. 29, K) apparently is constructed of a

242 The Sarcodina

"chitinoid-siliceous" material which is usually, although not always, en-
crusted with sand grains. In Lecquereusia (Fig. 5. 29, A), sand grains or
diatom shells are ingested and then modified in form before addition to
the test (107). In the Euglyphidae (Fig. 5. 29, G-I), foreign particles are
replaced by scales, which are formed and stored in the cytoplasm prior
to fission. These scales are insoluble in hot sulfuric acid in Nebela collaris
and seem to be completely siliceous (87). The Euglyphidae are thought
to produce such scales from absorbed minerals, rather than by the modi-
fication of ingested particles. In Euglypha (47), it is possible to observe
cytoplasmic inclusions showing similar optical properties and forming a
graded series from small globules to typical scales. Such a "series" implies
a gradual growth of the scale by addition of material from the cytoplasm.

The color of the test varies with the species and often to some extent
with the individual specimen. Various shades of yellow and brown are
the rule, and the color may become darker as the animal grows older.
The yellow-brown tests presumably contain iron, w^hile the occasionally
observed violet tints (Heleopera) are attributed to manganese.

Pseudopodia. The pseudopodia of Testacida are of two general types,
slender lobopodia (Fig. 5. 29, B, C) and typica