AN INTRODUCTION TO THE STUDY
OF THE PROTOZOA

,
AN INTRODUCTION TO THE

STUDY OF THE PEOTOZOA

WITH SPECIAL REFERENCE TO
THE PARASITIC FORMS

E. A. MINCHIN, M.A., PH.D., F.E.S.

PROFESSOR OF PROTOZOOLOGY IN THE UNIVERSITY OF LONDON

ILLUSTRATED

LONDON
EDWARD AENOLD

1912

[All rights reserved]

PREFACE

THIS book, as its name implies, is intended to serve as an intro-
duction to the subject with which it deals, and not in any way as a

ERRATA

Page 188, line 29, "yyrenoids" should be " pyrenoids."
Page 202, line 3 from bottom, " hTe " should be "The.'
Page 351, lines 8 and 9 from bottom should be transposed.

it attempts to define the position of these organisms in Nature, and
to determine, as far as possible, in this way exactly what should be
included under the term " Protozoa," and what should be excluded
from the group. Secondly, its function is to guide the student
through the maze of technicalities necessarily surrounding the study
of objects unfamiliar in daily life, and requiring, consequently, a
vocabulary more extensive than that of common language ; and
with this aim in view, care has been taken to define or explain fully
all technical terms, since confusion of thought can be avoided only
by a clear understanding of their exact significance and proper
application. Thirdly, it aims at introducing the student to the
vast series of forms comprised in the Protozoa and their systematic
classification, based on their mutual affinities and inter-relationships,
so far as these can be inferred from their structural peculiarities and
their life-histories. And, incidentally, attention has been drawn
specially to those parts of the subject where the Protozoa throw

PREFACE

THIS book, as its name implies, is intended to serve as an intro-
duction to the subject with which it deals, and not in any way as a
complete treatise upon it. The science of " protozoology," as it is
now generally termed, covers a vast field, and deals with an immense
series of organisms infinitely varied in form, structure, and modes of
life. In recent years the recognition of the importance of the
Protozoa to mankind in various ways, and especially from the
medical point of view, has focussed attention upon them, and has
brought about a great increase of our knowledge concerning these
forms of life. To set forth adequately and in full detail all that is
now known about the Protozoa would be a task that could not be
attempted in a volume of this size, but would require a work many
times larger.

The aim of the present work is essentially didactic — that is to say,
it is intended to furnish a guide to those who, having at least some
general knowledge of biology, desire a closer acquaintance with the
special problems presented by the Protozoa. First and foremost,
it attempts to define the position of these organisms in Nature, and
to determine, as far as possible, in this way exactly what should be
included under the term " Protozoa," and what should be excluded
from the group. Secondly, its function is to guide the student
through the maze of technicalities necessarily surrounding the study
of objects unfamiliar in daily life, and requiring, consequently, a
vocabulary more extensive than that of common language ; and
with this aim in view, care has been taken to define or explain fully
all technical terms, since confusion of thought can be avoided only
by a clear understanding of their exact significance and proper
application. Thirdly, it aims at introducing the student to the
vast series of forms comprised in the Protozoa and their systematic
classification, based on their mutual affinities and inter-relationships,
so far as these can be inferred from their structural peculiarities and
their life-histories. And, incidentally, attention has been drawn
specially to those parts of the subject where the Protozoa throw

vi PREFACE

great light on some of the fundamental mysteries of living matter —
as, for example, sex — and a special chapter dealing with the
physiology of the Protozoa has been added.

In so wide a field it is almost necessary to exercise some favour-
itism in the choice of objects, and greater stress has been laid in
this work upon the parasitic forms, both on account of the many
interesting biological problems which they present, and also because
they come into closer relationship with the practical needs of human
life than the non-parasitic species. The author wishes, however,
to point out clearly that he is not a medical man, but one who
approaches the study of the parasitic Protozoa solely from the
standpoint of a naturalist who is more concerned, so to speak, with
the interests of the parasite than with those of the host. Conse-
quently, purely medical problems — such as, for example, the
symptoms and treatment of diseases caused by trypanosomes and
other Protozoa — are not dealt with hi this book, since the author
deems it no part of his task to attempt to instruct medical men
concerning matters with which they are better acquainted by their
training and experience than himself. The needs of medical men
have, however, been specially kept in view, and the author hopes
that the book will succeed in supplying them with useful informa-
tion, at least from a general zoological or biological standpoint.

In a science, such as protozoology, which is growing actively and
receiving continually new additions, and in which most of the data
are based upon an elaborate and delicate technique, there are
necessarily many controversial matters to be dealt with. In such
cases the points at issue have been reviewed critically, and the
author has, wherever possible, attempted to give a lead by indicating
more or less decisively what is, in his opinion, the most probable
solution of the problem under discussion. Such judgments, how-
ever, are not intended to be put forward in a dogmatic or polemical
spirit, since the author recognizes fully that any conclusion now
reached may be upset entirely by fresh evidence to the contrary.

The vast literature of the Protozoa would, if cited in full, easily
fill by itself a volume of the size of the present one. It has been
necessary, therefore, to restrict the limits of the bibliography as
much as possible, both by selecting carefully the memoirs to be
cited and by abbreviating their titles. The works selected for
reference comprise, first, comprehensive treatises which deal with
the subject, or with some part of it in a general way, and in which
full references to older works will be found ; secondly, classical
memoirs on particular subjects, also containing, as a rule, full
bibliographies ; and, thirdly, such memoirs of recent date as have

PREFACE vii

been deemed worthy of citation. In the many cases where the
same authors have published several works on a given subject, only
the last of them is cited — for example, the volume of researches
published recently by Mathis and Leger (473) covers the ground of
the earlier memoirs published by these authors, which are therefore
not cited ; similarly, the memoir upon amoebae by Nagler (95)
covers the earlier work of Hartmann and Nagler upon Amoeba
diploidea. Since it was quite impossible to make the bibliography
in any way exhaustive, the aim has been to make it, like the rest
of the book, introductory to the subject. It is hoped that any
reader who, desirous of pursuing further some special subject,
consults the references cited will find in them and in the further
works quoted in them the means of acquiring complete information
with regard to modern knowledge concerning all the points in
question. The following classes of memoirs are not cited, however,
in the bibliography, unless there was some special reason for doing
so : faunistic works, papers describing new species, and writings of
a polemical character.

New memoirs on Protozoa are being published continually, so
rapidly, and in so many different periodicals (some of them very
difficult to obtain), that the author fears he may himself have
overlooked many such, especially of those publications which have
appeared very recently, while the book was in course of preparation.
For such omissions, some of which have already come under his
notice, he can but apologize, and at the same time promise that
they shall be rectified in future editions, if the patronage of those
interested in the subject enables further editions of this book to be
published. The present edition does not, however, profess to deal
with works published later than 1911.

In order to further the object of making this book a guide to the
technicalities of the subject, the plan has been adopted of printing
in heavier black type in the index the numbers of those pages on
which the term cited is fully explained, or, in the case of taxonomic
names, is referred to its place in the systematic classification. In
this way the index can be used as a glossary by anyone wishing to
ascertain the significance of a technical term, or, though necessarily
to a more limited extent, the systematic position of a genus, family,
or order of the Protozoa. All that is necessary for this purpose is
to look up the word in the index, and then to turn to the page or
pages indicated by black type.

The author has, in a few cases, modified the technical terminology
in current use, or has made additions to it. The adjective in general
use relating to chromatin is " chromatic," with its various deriva-

viii PREFACE

tives (" achromatic," etc.) ; since, however, these adjectives have
a totally different meaning and use in optics, they have been altered
to chromatinic, etc., in so far as they relate to chromatin. New
terms used in this book are chromidiosome (p. 65, footnote), endosome
(p. 73), as an equivalent to the German Binnenkorper, and gregarinula
(p. 169).

In conclusion, it is the author's pleasant duty to return thanks to
those of his colleagues who have kindly rendered him assistance in
his task. He is especially indebted for much help and many
valuable suggestions and criticisms to Dr. H. M. Woodcock, whose
unrivalled knowledge of recent bibliography has been throughout of
the utmost assistance ; and to Dr. J. D. Thomson and Miss Muriel
Robertson for many helpful discussions upon matters of fact or
theory. Dr. A. G. Bagshawe, Professor J. B. Farmer, F.R.S., Mr.
W. F. Lanchester, Dr. C. J. Martin, F.R.S., and Dr. P. Chalmers
Mitchell, F.R.S., have kindly read through some of the chapters, and
have given valuable advice and criticism. In justice to these gentle-
men, however, it should be stated that they are in no way responsible
for any of the theoretical opinions put forward by the author. The
majority of the figures have been specially drawn from the original
sources, or from actual preparations by Mr. R. Brook-Greaves and
Miss Mabel Rhodes, to both of whom the author's best thanks
are due.

LISTER INSTITUTE OF PREVENTIVE
MEDICINE, CHELSEA, S.W.,
July 1, 1912.

CONTENTS

CHAPTER PAGES

I. INTRODUCTORY — THE DISTINCTIVE CHARACTERS OF THE PROTOZOA

AND OF THEIR PRINCIPAL SUBDIVISIONS - - 1 12

II. THE MODES OF LIFE OF THE PROTOZOA - - 13 — 28

The Four Types of Nutrition, 13-15 ; Problems of Parasitism,
15-28.

III. THE ORGANIZATION OF THE PROTOZOA — EXTERNAL FORM AND

SKELETAL STRUCTURES - - 29 — 39

IV. THE ORGANIZATION OF THE PROTOZOA (continued) — THE PROTO-

PLASMIC BODY - ... 40 — 44

V. THE ORGANIZATION OF THE PROTOZOA (continued) — DIFFERENTIATIONS

OF THE ECTOPLASM AND ENDOPLASM - 45 — 64

A. Ectoplasmic Organs — (1) Protective, 45 ; (2) Kinetic and
Locomotor, 46 ; (3) Excretory, 60 ; (4) Sensory, 61.

B. Endoplasmic Organs, 62.

VI. THE ORGANIZATION OF THE PROTOZOA (continued) — THE NUCLEAR
APPARATUS — CHROMATIN, NUCLEUS, CHROMIDIA, CENTRO-
SOMES, AND BLEPHAROPLASTS - - - 65 — 99

VII. THE REPRODUCTION OF THE PROTOZOA- - - - 100 — 124

Types of Fission, 100 ; Division of the Nucleus, 101 ; Division
of_the Cell-Body, 122.

VIII. SYNGAMY AND SEX IN THE PROTOZOA - - 125 — 161

Nature of the Sexual Process, 125 ; Occurrence of Sexual
Phenomena and their Importance in the Life of the Organism,
128 ; Maturation and Reduction, 142 ; Examples of Syngamy
and Reduction in Protozoa, 147 ; Theories of the Origin and
Significance of the Syngamic Process, 154.

x CONTENTS

CHAPTER PAGES

IX. POLYMORPHISM AND LIFE-CYCLES or THE PROTOZOA - - 162 — 185
A. Polymorphism, 162-176 ; B. Life-Cycles, 177-185.

X. THE GENERAL PHYSIOLOGY OF THE PROTOZOA - - 186 — 211

(1) Nutrition and Assimilation, 187; (2) Respiration, 195;
(3) Excretion and Secretion, 197 ; (4) Transmutation of
Energy, 199 ; (5) Reactions to Stimuli and Environments,
201 ; (6) Degeneration and Regeneration, 208.

XL SYSTEMATIC REVIEW OF THE PROTOZOA: THE SARCODINA - 212 — 256

A. Rhizopoda— I. Amcebaea, 218 ; II. Foraminifera, 231 ;
III. Xenophyophora, 237 ; IV. Mycetozoa, 239.

B. Actinopoda— V. Heliozoa, 244 ; VI. Radiolaria, 249.

XII. SYSTEMATIC REVIEW OF THE PROTOZOA : THE MASTIGOPHORA 257 — 279

I. Flagellata, 257 ; II. Dinoflagellata seu Peridiniales, 276 ;
III. Cystoflagellata seu Rhynchoflagellata, 278.

XIII. THE H^JMOFLAGELLATES AND ALLIED FORMS - - 280 — 322

I. Trypanosoma, 283 ; II. Trypanoplasma, 309 ; III. Crithidia,
312 ; IV. Leptomonas, 313 ; V. Leishmania, 316 ; VI. Prowa-
zekia, 319.

XIV. THE SPOROZOA : I. THE GREGARINES AND COCCIDIA - - 323 — 355

I. Gregarinoidea, 326 ; II. Coccidia, 341.

Comparison of the Life-Cycles of Gregarines and Coccidia, 354.

XV. THE SPOROZOA: II. THE H^BMOSPORIDIA - - - 356 — 397

(1) Hsemamoebae, 357; (2) Halteridia, 365; (3) Leucocytozoa,
369 ; (4) Haemogregarines, 371 ; (5) Piroplasms, 378 ; Affinities
of the Haemosporidia, 388 ; of the Telosporidia, 395.

XVI. THE SPOROZOA: III. THE NEOSPORIDIA - - - 398 — 429

I. Myxosporidia, 399 ; II. Actinomyxidia, 409 ; III. Micro-
sporidia, 411 ; IV. Sarcosporidia, 419 ; V. Haplosporidia, 423.
Incertce Sedis, 425.

XVII. The INFUSORIA - 430—461

I. Ciliata, 430; II. Acinetaria, 455.

CONTENTS xi

CHAPTER PAGES

XVIII. AFFINITIES AND CLASSIFICATION OF THE MAIN SUBDIVISIONS —

DOUBTFUL GROUPS - - 462 — 474

General Phylogeny of the Protozoa, 463.
Spirochaetes, 466 ; Chlamydozoa, 470.

BIBLIOGRAPHY - . 475 — 504
INDEX - .... 505—517

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AN INTRODUCTION TO THE STUDY
OF THE PROTOZOA

CHAPTER I

INTRODUCTORY — THE DISTINCTIVE CHARACTERS OF THE
PROTOZOA AND OF THEIR PRINCIPAL SUBDIVISIONS

THE Protozoa are a very large and important group of organisms,
for the most part of minute size, which exhibit a wide range of
variation in structural and developmental characters, correlated
with the utmost diversity in their modes of life. Nevertheless,
however greatly adaptation to the conditions of life may have
modified their form, structure, or physiological properties, a certain
type of organization is common to all members of the group. The
most salient feature of the Protozoa is their unicellular nature ;
that is to say, the individual in this subdivision of living beings is
an organism of primitive character, in which the whole body has
the morphological value of a single " cell," a mass of protoplasm
containing nuclear substance (chromatin) concentrated into one or
more nuclei. However complex the structure and functions of the
body, the organs that it possesses are parts of a cell (" organellae "),
and are never made up of distinct cells ; and at least one nucleus
is present, or only temporarily absent, as a constant integral part
of the organism. The unicellular nature of the Protozoa, though a
constant character, cannot, however, be used by itself to define
the group, since it is also a peculiarity of many other distinct types
of simple living things.

As an assemblage of organisms of primitive nature from which,
in all probability, the ordinary plants and animals have originated
in the remote past by divergent processes of evolution, the Protozoa
have always possessed very great interest from the purely scientific
and philosophical point of view. Of recent years, however, they
have also acquired great practical importance from the relations
that have been discovered to exist between Protozoa of parasitic
habit and many diseases of man and animals. Hence the study of
the Protozoa has received an immense impetus, and has been

1

2 THE PROTOZOA

cultivated zealously even by many who are not professed biologists,
with the result that our knowledge of these organisms has made
very great strides in the last two decades, and is advancing so
rapidly that it becomes increasingly difficult for any single person
to keep pace with the vast amount of new knowledge that is pub-
lished almost daily at the present time.

While the attention that is now focussed upon the Protozoa has
led to a most gratifying increase of scientific and medical knowledge
concerning particular forms, it tends frequently to a certain vague-
ness in the notions held with regard to the nature and extent of
the group as a whole. This is owing largely to the fact that many
are now attracted to the study of the Protozoa whose aims are
purely practical, and who investigate only a limited number of
species in minute detail, without having an adequate foundation
of general knowledge concerning other forms. Hence it is important
to attempt toirame a general definition of the Protozoa, or at least
to characterize these organisms in such a way as to enable a dis-
tinction to be drawn between them and other primitive forms of
life. This object may be attained logically in two ways — either by
considering the distinctive characters of the group, or by enu-
merating the types of organisms which constitute it ; in more
technical phraseology, by determining either the connotation or the
denotation of the term Protozoa. To attempt this task will be
the object of the present chapter.

The name Protozoa was first used in 1820* as an equivalent
of the German word Urthiere, meaning animals of a primitive or
archaic type. This fitting designation superseded rapidly the older
term Infusoria (Infusionsthierchen) , used to denote the swarms
of microscopic organisms which make their appearance in organic
infusions exposed to the air. The word Infusoria is now em-
ployed in a restricted sense, as the name of one of the principal
subdivisions of the Protozoa (pp. 12 and 430).

The first attempt at a scientific definition of the Protozoa was
given by von Siebold, who defined them, from a strictly zoological
standpoint, as unicellular animals. This definition, or a modifica-
tion of it, is still the one given, as a rule, in zoological textbooks ;
and from this time onwards the animal kingdom was subdivided
universally into the Protozoa and the Metazoa. The Protozoa,
as organisms in which the individual is a single cell, are regarded
as those which come first (TT/JWTOS) in the ascending scale of animal
life, or in the course of organic evolution ; the Metazoa, in which
the individual is an organism composed of many cells, come after
a) the simpler forms of life in rank and time.

* For the detailed history of the growth of scientific knowledge of the Protozoa,
see Biitschli (2), pp. i-xviii.

DISTINCTIVE CHARACTERS OF THE PROTOZOA 3

Siebold's generalization was a great step in advance, introducing
clear and orderly ideas into the place of the chaotic notions pre-
viously held, and setting definite limits to the group Protozoa by
excluding from it various types of organisms, such as Sponges,
Rotifers, etc., which had hitherto been classed as Protozoa, but
which were now referred definitely to the Metazoa. Nevertheless
Siebold's definition presents many difficulties, especially when con-
sidered from a wider standpoint than that of the zoologist. This
will be apparent if the two words of the definition given above,
" unicellular animals," be considered critically.

1. " Unicellular." — Accepting the standpoint of the cell -theory, it
has already been noted that many other organisms besides Protozoa
must be regarded as single cells. Moreover, it is found that many
organisms which must be classed as Protozoa appear constantly in
a multicellular condition ; such are the well-known genus Volvox
and its allies, besides examples of other orders. In all cases of this
kind, however, the constituent cells are morphologically equivalent,
and are to be regarded as complete individuals more or less inde-
pendent, showing as a rule no differentiation, or, if any, only into
reproductive and vegetative individuals ; and the multicellular
organism as a whole is to be regarded as a colony of unicellular
individuals primitively similar but secondarily differentiated, it may
be, in relation to special functions. Such multicellular Protozoa
present, in fact, a perfect analogy with the colonial forms seen in
many groups of animals higher in the scale, especially the Ccelentera,
where also the members of a colony, primitively equivalent and
similar amongst themselves, may become differentiated secondarily
for the performance of distinct functions by a process of division
of labour among different individuals. It is not possible to con-
found the multicellular Protozoa with the Metazoa, in which the
organism is not only composed of many cells, but exhibits also
cell-differentiation based on mutual physiological dependence of
the cells on one another, leading to the formation of distinct tissues ;
that is to say, aggregations or combinations of numerous cells, all
specialized for the performance of a particular function, such as
contraction, secretion, and so forth.

The essential feature of the Protozoa, as contrasted with the
higher animals or plants, is to be sought in the independence and
physiological completeness of the cell -individual. The Metazoa
are tissue-animals, in which the primitive individuality of the cell
is subordinated to, or has a restraint imposed upon it by, the
corporate individuality of the cell -aggregate. In the Protozoa the
cells are complete individuals, morphologically and physiologically
of equal value. If, however, as few will doubt, the Metazoa have
been evolved from simple unicellular ancestors, similar to the

4 THE PROTOZOA

Protozoa, then there must have existed an unbroken series of
transitions between these two types of living beings. Hence, as
in all attempts to classify living beings, sharp verbal distinctions
between Protozoa and Metazoa are rendered possible only through
the extinction of intermediate forms, or by ignoring such forms if
known to exist. It is expedient rather to recognize distinct types
of organization characteristic of the Protozoa and the Metazoa
respectively, and to compare and contrast them, than to attempt
to limit these groups by precise definitions.

2. " Animals." — This part of the definition raises more difficulties
than their cellular nature. In the higher forms of life the distinc-
tion between animals and plants is an obvious and natural one ; it
is by no means so in the lower organisms. In the ranks of the
simplest living creatures, those of animal nature are not marked
off by any sharply defined structural or other features from those of
vegetable nature, and cannot be separated from them in any scheme
of classification which claims to be founded upon, or to express, the
true natural affinities and relationships of the objects dealt with.
As will be explained more fully in the next and subsequent chapters ,
the distinction between animal and vegetable is, at its first appear-
ance, nothing but a difference in the mode in which the organisms
obtain their living. Forms that are obviously closely allied in all
their characters may differ in this respect, and in some cases even
one and the same species may nourish itself at one time as a plant,
at another as an animal, according to circumstances. In short, the
difference between plant and animal is primarily a distinction based
upon habits and modes of life, and, like all such distinctions, does
not furnish characters that can be utilized for systematic classifica-
tion until the mode of life has continued so long, and the habit has
become so engrained, as to leave an impress upon the entire
structural characteristics of the organism.

The Protozoa cannot therefore be defined strictly and con-
sistently as organisms of animal nature, for, though the vast majority
of them certainly exhibit animal characteristics, it is impossible to
exclude from the group many which live temporarily or permanently
after the manner distinctive of the vegetable kingdom, and which
are plants, to all intents and purposes, leading on in an unbroken
series to the simplest algae.

For this reason it has been proposed to unite all the simplest and
most primitive forms of life in one " kingdom " under the title
Protista (Protistenreich, Haeckel), irrespective of their habit of life
and metabolism, whether animal or vegetable. The kingdom
Protista is then to be considered as equivalent in systematic value
to the animal and vegetable kingdoms, which in their turn are
restricted in their application to true animals and plants as ordinarily

DISTINCTIVE CHARACTERS OF THE PROTOZOA

understood. The term Protista thus unites under a single
systematic category the vast assemblage of simple and primitive
living beings from which the animal and vegetable kingdoms have
taken origin, and have developed, by a continuous process of
natural evolution, in different directions in adaptation to divergent
modes of life.

The conception of a Protistan kingdom separate from the animal and
vegetable kingdoms is open to the objection that it contains organisms
which are- indubitably of animal or vegetable
nature respectively. The relations of the
Protista to other living things may be repre-
sented graphically by the accompanying dia-
gram (Fig. 1), where the circle represents the
Protista, the two triangles the animal and
vegetable kingdoms respectively. It is seen
that the separation of the Protista as a
systematic unity cuts across the ascending
series of evolution ; to express it figuratively,
it is a transverse cleavage of the phylogenetic
" tree." A truly natural classification of living
things, however, is one which expresses their
genetic affinities and follows their pedigrees
and lines of descent ; it should represent a
vertical cleavage of the ancestral tree. Judged
by this standard, the kingdom of the Protista
can only be regarded as a convenient makeshift

or compromise, rather than as a solution of a FIG. 1. — Graphic representa-
difficult problem — that, namely, of giving a
natural classification of the most primitive
forms of life.

tion of the relation of the
animal and vegetable king-
doms to the kingdom of the
Protista (Protistenreich).
The Protozoa are represented
by the portion of the triangle
representing the animal
kingdom which lies within
the circle representing the
Protista.

Whether the kingdom Protista be
accepted or not as a natural and valid
division of living beings, it is imperative
to subdivide it further, not only on
account of its vast extent and unwieldy
size, but also because it comprises organisms very diverse in nature,
requiring for their study the application of methods of technique
and investigation often entirely different in kind. Hence in actual
practice the Protista are partitioned among at least three different
classes of scientific workers — zoologists, botanists, and bacteri-
ologists— each studying them by special methods and to some extent
from different points of view.

It is necessary, therefore, to consider from a general standpoint
the principal types of organization comprised in the kingdom
Protista, and we can recognize at the outset two chief grades of
structure, bearing in mind always that transitional forms between
them must exist, or at least must have existed.

In the first grade, which is represented by the Bacteria and allied
groups of organisms, a type of organization is found which is
probably the more primitive, though by many regarded as the

6

THE PROTOZOA

result of degeneration and specialization. These organisms do not
conform, to the type of structure of the cell, as this word is usually
understood, since they do not exhibit, speaking generally, a division
of the living body substance into a nucleus distinct from the
cytoplasm ;* but the chromatin is distributed through the proto-
plasmic body in the condition of scattered lumps or granules
(" chromidia "), and in many cases it constitutes, apparently, the
whole or a very large proportion of the substance of the body.

FIG. 2. — Amoeba proteus. A, An individual in active movement ; the arrows
indicate the direction of the currents in the protoplasm ; at r is seen a pseudo-
podium which is nearly completely retracted and has assumed a mulberry-
like appearance ; c.v., contractile vacuole ; /., fsecal matter extruded at the
end of the body posterior in movement ; the nucleus is obscured by the
opacity of the protoplasm. B, An individual in the act of capturing its prey
(P1), an Infusorian (Urocentrum) ; two pseudopodia have flowed round it,
as shown by the arrows, and met at the point c, enclosing the prey ; another
Infusorian (P2) is seen in a food vacuole in the body ; N., nucleus ; other
letters as in A. After Leidy (226), magnified 200 diameters.

Further, the body in organisms of the bacterial type is of definite
form, limited in many cases by a rigid envelope or cuticle, and
special organs of locomotion are either absent or present in the
form of so-called " flagella," structures perhaps different in nature
from the flagella of truly cellular organisms. But the most remark-
able and significant feature of organisms of the bacterial type is
seen in the many different modes of metabolism and assimilation

* The significance of the terms " nucleus," " cytoplasm," " chromidia," etc.,
w ill be explained more fully in subsequent chapters.

DISTINCTIVE CHARACTERS OF THE PROTOZOA 7

seen to occur amongst them. Although their metabolism is in
general distinctly of a vegetative or saprophytic type, it often
exhibits peculiarities not found in any true plant.*

In the second grade of the Protista, the organism possesses the
characteristics of a true cell, in that the body shows a differentia-
tion of the living substance into two quite distinct parts — the
cytoplasm, or general body -protoplasm, in which is lodged at least
one nucleus, a body representing a concentration and organiza-
tion of the chromatin-substance. In some cases the nuclear sub-
stance or chro matin may be in the scattered, chromidial condition

FIG. 3. — Actinosphcerium eichhornii. ect., Ectoplasm; end., endoplasm ; c.v.1, a
contractile vacuole at its full size ; c.v.2, a contractile vacuole which has just
burst ;f.v., f.v., food vacuoles ; D., a large diatom engulfed in the protoplasm ;
ps., pseupopodia ; N., one of the numerous nuclei. After Leidy (226), magni-
fied 250 diameters.

during certain phases of the life-history, but such a condition is
comparatively rare and probably always temporary. The body-
protoplasm may be limited by a firm envelope, or may, on the other
hand, be naked, in which case the body-form may be quite in-
definite. Organs of locomotion, when present, are of various kinds ;
and these organs may serve also for the capture and ingestion of
food. And, finally, the metabolism is always one of the four types

* For a summary and review of different modes of metabolism among bacterial
organisms, see article " Fermentation " in Thorpe's " Dictionary of Applied
Chemistry " (Longmans).

THE PROTOZOA

described in more detail in the next chapter — namely, animal-like
(holozoic), plant-like (holophytic), fungus-like (saprophytic), or at
the expense of some other living organism (parasitic).

The cellular organisms that constitute the
second or higher grade of the Protista are
commonly partitioned between botanists and
zoologists as Protophyta (unicellular alga? and
oes^M?$?°l fungi) and Protozoa respectively. It has been
pointed out already, however, that this

!0'jf

e.r-

-N

m

I

FIG. 4. — Euglena syi-
rogyra. ces., (Esopha-
gus; st., stigma; c.r.,
reservoir of the con-
tractile vacuole; P,P,
paramylum - bodies ;
N., nucleus. After
Stein.

FIG. 5. — Trichomonas eberthi, from the intestine of the
common fowl, fll., Anterior flagella, three in number ;
p.fl., posterior flagellum, forming the edge of the
undulating membrane ; chr.L, " chromatinic line,"
forming the base of the undulating membrane ; chr.b.,
" chromatinic blocks " ; II., blepharoplast from which
all four flagella arise ; m., mouth-opening ; N., nucleus
ax., axostyle. After Martin and Robertson.

DISTINCTIVE CHARACTERS OF THE PROTOZOA 9

method of subdividing them is purely arbitrary and artificial ; it
leads to the result that many forms are claimed by both sides, and
are always to be found described in both botanical and zoological
treatises. It is nevertheless convenient for
many reasons to retain the group Protozoa, even
though we are obliged to include in it some
forms which are plants in every sense of the
word. The systematist who desires to give a
rigidly logical definition of the Protozoa is,
then, confronted with a dilemma : either to
exclude from it forms with plant-like metab-
olism which naturally belong to it, or, by tills
admitting such forms, to impair the universal
applicability of the definition given. Such //££®y|£
difficulties arise in every attempt to apply
rigid verbal definitions to natural groups of
living things-; they are the direct outcome of
the fact that all organisms have undergone and
are undergoing a process of evolution, whereby
they adapt themselves to new conditions of
life and acquire new characters, as a result of
which any two forms now distinct are or
have been, connected by intermediate forms. /;f ^^^\\ ^.np

N

B

FIG. 6. — Trypanosoma remaki of the pike. A , Slender
form (" var. parva "). B, Stout form (" var.
magna "). After Minchin, x 2,000.

FIG. 7. — Gregarina
pctymorpha, parasite
of the digestive tract
of the mealworm ;
" syzygy " of two
individuals attached
to one another. In
each individual, N.,
nucleus; pr., proto-
merite, or anterior
segment of the body;
d., deutomerite, or
posterior segment.
After Schneider.

10

THE PROTOZOA

The attempt, therefore, made in the following paragraph to give
a diagnosis of the Protozoa must not be regarded as a definition
of the group in the rigidly logical sense, but merely as the construc-
tion of a general type, the characters of which are liable to a
certain amount of variation in special cases — a compromise between
the claims of logic and the versatility of Nature.

The Protozoa, then, are Protista
in which the organization is of the
cellular type, with nucleus distinct
from the cytoplasm. They are uni-
cellular, in the sense that the cell
constitutes an entire individual,

Oes~-^$mWMm which may exist singly and in-

dependently or in the form of cell-
colonies ; but in the latter case the

N liiSllflHi- cells are not subordinated to the

individuality of the entire cell-
—fe. aggregate by the formation of

FIG. 8. — Stentor roese/n, fully expanded.
ces., (Esophagus ; N, band-like macro-
nucleus ; c.v., contractile vacuole, con-
nected with a long feeding- canal (/.c.)
stretching down the body ; H, gelat-
inous house into which the animal
can retract itself completely ;/., fibres
attaching the extremity to the stalk
to the house. After Stein.

CM-

an.

FIG. 9. — Nyctotherus cordijormis ,
parasite of the rectum of the frog.
N, Macronucleus ; n, micronucleus ;
gr., mass of granules in front of the
macronucleus ; ces., oesophagus; c.v.,
contractile vacuole ; an., anus
(cytopyge). After Stein.

tissues. The body protoplasm is naked or clothed with a firm
envelope, which is usually not of the nature of cellulose. Proto-
plasmic organs are usually present for purposes of locomotion and
for the capture and ingestion of food. Chlorophyll is usually
absent as a cell -constituent, and the metabolism is usually of the
animal type. To these characters it may be added, though not
as special peculiarities of Protozoa, that reproduction takes place

DISTINCTIVE CHARACTERS OF THE PROTOZOA 11

always by some form of fission— that is to say, division of the body
into smaller parts ; that the phenomena known as " syngamy " and
" sex " occur, perhaps universally, throughout the group ; and that
it is very characteristic of
Protozoa, as compared with
other Protista, to exhibit in
their life-history a develop-
mental cycle, more or less
complicated, in the course of
which the organism may appear
under very different forms at
different stages in its develop-
ment.

The Protozoa, as thus under-
stood, are commonly divided
into four main subdivisions,
termed "classes." Other
methods of classifying the
Protozoa have been suggested,
which will be considered later ;
for the present the old-
established subdivisions are
sufficient for our purpose.

CLASS I., SARCODINA.*—
Protozoa in which the proto-
plasmic body is naked or non-
corticate — that is to say,
without a limiting envelope
in the form of a cuticle,
membrane, or stiff cortical
layer ; consequently the body
tends to be either more or less
spherical in floating forms, or
to have an irregular, con-
tinually changing shape in
creeping forms. Organs serving
for locomotion and capture of
food are furnished by tem-
porary extensions of the living
protoplasm, termed pseudo-
podia. •' A skeleton or shell
may be present. Examples

* The name is derived from sarcode, the term coined by Dujardin to denote
the living substance, subsequently named by von Mohl protoplasm, the term now
universally employed.

FIG. 10. — Acineta grandis. si., Stalk ; th.,
theca ; s., suctorial tentacles. After
Saville Kent.

12 THE PROTOZOA

are Amoeba (Fig. 2), Difflucjia (Fig. 16), Actinosphwrium
(Fig. 3), etc.

CLASS II., MASTIGOPHORA.* — Protozoa in which the organs of
locomotion and food-capture in the adult are flagella, slender fila-
ments which are capable of performing active whip-like, lashing
movements. The body -protoplasm may be naked or corticate.
Examples are Euglena (Fig. 4), Trichomonas (Fig. 5), Trypanosoma
(Fig. 6), etc.

CLASS III., SPOROZOA. — Protozoa occurring always as parasites
of other organisms, and without definite organs for locomotion or
ingestion of food in the adult condition. The reproduction takes
place, typically, by formation of resistant seed -like bodies, termed
spores, containing one or more minute germs, termed sporozoites.
Examples are Gregarina (Fig. 7), Coccidium (Fig. 152), the malarial
parasites (Fig. 156), etc.

CLASS IV., INFUSORIA. — Protozoa in which the organs of loco-
motion and food-capture are cilia, small vibratile filaments dis-
tinguished from flagella by their smaller size, by differences in
their mode of movement, and by being present usually, in primitive
forms at least, in great numbers like a fine fur over the whole or
a part of the surface of the body. The cilia may be present through-
out life (subclass Cilia ta), or only in the early stages of the life-
history (subclass Acinetaria). The body -protoplasm is always cor-
ticate. Examples are Stentor (Fig. 8), Nyctotherus (Fig. 9), Acineta
(Fig. 10), etc.

Bibliography. — For a list of general works on Protozoa, see p. 476.
* Derived from the Greek /*d(rri£, a whip, equivalent to the Latin flagellum.

CHAPTER II
THE MODES OF LIFE OF THE PROTOZOA

PROTOZOA, as simple protoplasmic organisms, can only exist in an
active state in a fluid medium. Hence the free-living, non-parasitic
forms are aquatic, either marine or fresh-water in habitat. A
certain number of species, however, are semi-terrestrial in their mode
of life, creeping on damp surfaces or living in a minimum of
moisture. Examples of such forms are the Amoebae, etc., found in
the soil, or Mycetozoa, which in the plasmodial phase (p. 239) creep
on tree-trunks, logs, and so forth. None of these forms, however,
can remain active in perfectly dry surroundings, but pass into a
resting state when desiccated.

It has been stated already that the methods by which Protozoa
gain their livelihood vary greatly in different cases. Considered
generally, these methods may be classified under four types :

I. The majority of Protozoa nourish themselves after the manner
of animals — that is to say, they are entirely dependent for food and
sustenance on other organisms which they capture, devour, and
digest. Such forms are said technically to be holozoic, a word sig-
nifying " completely animal-like "; they are unable to utilize simpler
chemical substances in order to build up the protein constituents
of the living body, but require proteins ready-made for their
sustenance.

II. A certain number of Protozoa — all, with rare exceptions,
belonging to the class Mastigophora — possess in their body-sub-
stance peculiar colour-bearing corpuscles, so-called chromatophores or
chromoplasts, containing chlorophyll or a pigment of allied nature,
by means of which they are able to decompose carbon dioxide in
the sunlight, liberating the oxygen and making use of the carbon
in order to build up the protein and other constituents of the living
body. Such organisms are entirely similar in their metabolism
to the ordinary green plants, and are hence termed holopliytic. or
" completely plant-like."

The holophytic condition, in which the chlorophyll-bodies form an integral
part of the structure of the body, and are to be regarded simply as proto-
plasmic organs, must be distinguished carefully from a state of things often

13

14 THE PROTOZOA

found in holozoic Protozoa of all classes — namely, the presence in the body
substance of symbiotic independent organisms of vegetable nature, as described
below.

III. A certain number of Protozoa that have no chlorophyll or
similar pigment in their bodies are, nevertheless, free from the
necessity of preying upon other organisms in order to obtain their
sustenance, since they are able to live upon organic substances in
solution, the products of the metabolism or decay of other living
organisms. Such forms are termed saprophytic (or saprozoic), since
their mode of life is similar to that of a saprophyte, such as a fungus.
It is not necessary that they should be supplied with ready-made
proteins in their food, since they are able to build up their protein
constituents from substances of simpler chemical nature. Many
examples of saprophytic forms are found amongst the free-living
Flagellata.

Lauterborn (17) has coined the useful term sapropelic (from the Greek
frr)\6s, mud) to denote a mode of life which must be regarded as a special
type of the saprophytic method, partly also of the holozoic — namely, the
mode of life of those fresh- water organisms that live in a mud or ooze composed
almost entirely of the decaying remains of dead plants and other debris of
a similar nature. A very characteristic fauna occurs under these conditions.

IV. Finally, many Protozoa of all classes live as parasites — that
is to say, at the expense of some other living being, which is termed
the host.

These four modes of life can be used only to a very limited extent
for classificatory purposes ; it is only possible to do so in those
cases where a particular habit of life, long' continued, has resulted
in definite structural characteristics, and more especially in the
loss of organs requisite for other modes of life — as, for example, in
the case of the subdivision Phytoflagellata, of the order Flagellata,
where the holophytic habit has become so ingrained that only
structural features proper to vegetable life are retained.

In other cases it is clear that a given habit of life in different
organisms does not necessarily indicate close affinity between them.
In the first place, we find closely allied forms living in different
ways. Examples of all the four methods of metabolism described
above are to be found in the single order Flagellata, and through-
out the Protozoa there are commonly to be found parasitic forms
closely allied to free-living forms. In the second place, different
types of metabolism may be found as transitory phases in the life
of one and the same individual or species. Thus the common
Euglena (Fig. 4), a flagellate possessing chromatophores and living
normally in a holophytic manner, is able to maintain itself as a
saprophyte if deprived of the sunlight necessary for a holophytic
mode of life (p. 188) Striking examples of variability in the
mode of nutrition are seen also in the section Chrysomoiiadina of

THE MODES OF LIFE OF THE PROTOZOA 15

the Flagellata, where a given species may be either holozoic or
holophytic,* according to circumstances.

The bionomics of Protozoa — that is to say, their relations to their
environment and to other organisms — constitute a very important
branch of knowledge, both practical and theoretical, especially in
the case of parasitic forms. Considering the subject from the point
of view of the four modes of life already described, it is clear, in
the first place, that the holophytic forms are entirely independent
of all other living organisms, and require for* their continued
existence only sunlight and a suitable environment, containing the
necessary inorganic substances, at a temperature which permits
the continuance of vital processes and activities.

Saprophytic organisms, however, in so far as they require for
their sustenance materials produced by living bodies, are dependent
directly or indirectly upon other organisms for their existence.
Purely holozoic forms, also, cannot exist without other forms of
life upon which, or upon the products of which, they can feed.
But neither holozoic nor saprophytic organisms are dependent,
as a rule, upon any other particular form of life, but only upon living
things generally ; though in some cases such forms may be specialized
in their nutrition to such an extent as to be unable to exist without
some particular food.

A parasitic form, on the other hand, is entirely dependent, as a
rule, for its existence on some particular organism or limited group
of organisms which constitute its host or hosts. It must, however,
be understood clearly that an organism living in or upon the body
of another organism is not necessarily a parasite by any means.
In the first place, a distinction must be drawn between parasitism
and symbiosis, by which is meant an association of two organisms
for mutual benefit, f Good examples of symbiosis are seen in
some of the Sarcodina, Radiolaria, and Foraminifera, the proto-
plasm of which contains constantly intrusive organisms, known as
zoochlorellce or zooxanthellce, according as they contain a green or a
yellow pigment. Zoochlorellae are green algae of the order Proto-
coccacece ; zooxanthellae are holophytic flagellates of the suborder
Cryptomonadina — e.g., Cryptomonas schaudinni, symbiotic in the
foraminifer Peneroplis (Winter, 28). These organisms penetrate

* For example, the species Chromulina ftavicans. See Biitschli (2), vol. ii., p. 865.

f The term " symbiosis " is often much misused, especially by medical writers,
by whom it is commonly applied to any association of two distinct organisms ;
for instance, " pure mixed cultures " of amoebae with some species of bacillus,
where the amoebae are simply feeding on the bacteria, are often spoken of as
'" symbiosis," although the advantage is clearly only on one side in such an asso-
ciation. It should be understood that the term " symbiosis " is a technical term
of long standing in biology, and is used not merely in its strict etymological sig-
nificance of " living together," but in the special and restricted sense of " living
together for the mutual benefit of the two organisms concerned."

16 THE PROTOZOA

into the body of their host, lose their flagella, and nourish them-
selves by means of their pigment, which has the nature and proper-
ties of plant-chlorophyll ; that is to say, it decomposes carbon dioxide
in the sunlight and liberates oxygen. The carbon dioxide is
obtained from the respiratory processes of the host, which in its
turn utilizes the oxygen produced by the symbionts (p. 197), and
thus each organism supplies the needs of the other. When the
host enters upon its reproductive processes and breaks up into a
vast number of swarm-spores, the symbionts develop flagella and
swim off, doubtless to seek for lodging elsewhere.

It is a matter of convenience to distinguish as epizoic those
organisms which live upon, or are attached to, and as entozoic
those which live within, the body or substance of the particular
form of life with which they are associated. Epizoic forms may
be entirely harmless to the creature upon which they occur ; they
may simply utilize its body as a coign of vantage where they readily
obtain their food, which may consist in some cases of nutritious
substances dropped or rejected by the animal that carries them ;
or they may obtain the benefits of shelter or transport, especially
when the epizoic form in question is itself of sedentary habit.
Every naturalist is acquainted with the sea-anemones that live
habitually upon hermit-crabs, probably to the advantage of both
animals — at all events, to the detriment of neither. There are
many similar cases among Protozoa. The appendages of Crustacea,
especially of the Cladocera and Copepoda, are often thickly beset
with sessile Vorticellids and Acinetaria, which obtain a convenient
lodging, but provide their own board. Other forms occur similarly
on the stems of hydroids, as, for example, Acineta papillifera on
Cordylophora lacustris. Amoebae are found creeping on the exterior
of Calcareous Sponges, nourishing themselves on diatoms and other
organisms. Similar instances could be multiplied indefinitely.

On the other hand, epizoic forms may be dangerous parasites,
nourishing themselves at the expense of the animal they infest,
and sometimes inflicting much damage upon it. It can be easily
understood that an epizoic form which at first lived harmlessly upon
some animal, drawing its supplies of food from the surrounding
medium, might acquire the habit ultimately of obtaining its nourish-
ment from the living substratum upon which it has planted itself.
Examples of epizoic parasites are the flagellate Costia necatrix
(p. 272) and the ciliate Ichthyophthirius multifiliis (p. 450), both of
which are epizoic parasites of fishes, attaching themselves to the
skin and destroying the epidermis ; as a result, the way is left open
for fungi and bacteria to penetrate the skin, and so produce ulcera-
tion and suppuration, which may be fatal.

All certain instances of Protozoa acting as external parasites are

THE MODES OF LIFE OF THE PROTOZOA 17

found amongst aquatic animals, and it can be readily understood
that a delicate protoplasmic organism could only pass from one
host to another in a fluid medium, or by the help of special mechan-
isms adapted to aerial transport or transmission by contact. It
should be mentioned, however, that some human contagious skin-
diseases are suspected to be due to the agency of parasites of the
nature of Protozoa.*

Like the epizoic forms, there are many entozoic Protozoa which
inhabit the bodies, and especially the intestines, of other animals,
but which are in no way to be regarded as parasites ; they feed
merely on various substances to be found there, such as waste
particles of food, excreted or faecal matter, or on other organisms,
such as bacteria, yeasts, and the like — in short, on substances which
from the point of view of the host are superfluous, or even harmful.
Many examples of such organisms could be cited ; a good one is the
common Ghlamydophrys stercorea, found in the faeces and digestive
tract of man and many animals. The common intestinal flagellates
belonging to the genus Trichomonas (Fig. 5) and other genera are,
similarly, not to be regarded as true parasites in any sense of the
word. The common Lophomonas blattarum (Fig. 45) from the
intestine of the cockroach feeds chiefly upon bacteria and yeasts.
Many of these intestinal Protozoa are perhaps useful, rather than
harmful, to their hosts.

On the other hand, the vast majority of organisms, Protozoa or
otherwise, that live in the interior of other living creatures are there
for no good or useful purpose ; their habitat is alone sufficient to
render them suspect. Two modes of parasitism may be distin-
guished from a general point of view. On the one hand, the para
site may merely intercept the food of the host and rob it of its
sustenance. On the other hand, the parasite may nourish itself
upon the living substance or vital fluids of its host.

Organisms which rob the host of its food may do so in one of two
ways. They may appropriate the raw food-material, which they
then ingest and devour after the strictly holozoic method of feeding ;
examples of this mode of life are possibly to be found in the extensive
infusorian fauna to be found in the stomachs of ruminants. Or
they may absorb the fluid products of the digestion of the host by
diffusion through the surface of the body of the parasite ; examples
of this mode of parasitism are to be seen, probably, in the case of
the Gregarines so common in the guts of insects. Parasites of the

* For example, the so-called Coccidioides immitis, a name given to bodies found
in certain South American skin diseases ; see Blanchard (633), p. 108. Molluscum
contagiosum has also been attributed to parasites referred by some to the Protozoa.
In both these instances, however, the exact nature of the parasitic bodies is far
from clear ; the parasite of molluscurn contagiosum should probably be referred
to the Chlarnydozoa (p. 470).

2

18 THE PROTOZOA

type that may be denoted as food-robbers are in general very
harmless to their hosts.

Those parasites, however, that nourish themselves on the sub-
stance of the host may produce the most dangerous effects on its
health and well-being. As in the case of the food-robbers, parasites
of this kind may absorb their food in one of two ways. They may
devour solid portions of the host's body in a holozoic manner ; an
example of this is seen in Entamoeba histolytica (Fig. 90), the parasite
of amoebic dysentery, which devours portions of the host's tissue,
such as epithelial cells, or blood-corpuscles. But more usually the
parasites absorb their nourishment in a fluid form through the
surface of their body, doubtless by the help of enzymes secreted by
them. Hence it is typical of true parasites to have lost all trace
of special organs for the capture, ingestion, or digestion, of solid
food.

Just as in the epizoic mode of life a harmless or even beneficial
commensalism may degenerate by insensible gradations into
dangerous parasitism, so the same is true of the entozoic habit.
An organism which begins by being a scavenger readily becomes a
food-robber. Lophomonas, for instance, may be seen to contain
starch-grains and other substances which probably belong to the
food of its host. A further but easy gradation leads to the entozoic
organism devouring portions of its host. A good example of this is
seen in two of the entozoic amoebae of the human intestine : the
common Entamceba coli (Fig. 89) appears to be chiefly a scavenger,
harmless to its host, and not deserving the reproach of parasitism ;
on the other hand, E. histolytica is a dangerous parasite. So also
an entozoic organism, which begins by merely absorbing the pro-
ducts of digestion, may end by absorbing the substance of its host.
It is highly probable that in many entozoic organisms the mode of
feeding may vary according to circumstances, and that an organism
which may be a harmless commensal under some conditions may
become a more or less dangerous parasite under others.

The entozoic Protozoa which are truly parasitic may inhabit a
variety of situations in the bodies of their hosts. In some cases the
host is another species of Protozoon, into the body of which the
intruder penetrates, living either in the cytoplasm or the nucleus.
Amoebae are very subject to the attacks of intranuclear parasites,
and the young stages of many Acinetans are parasitic upon other
Infusoria. When the host is one of the Metazoa, the invading
organism may be in like manner intracellular or intranuclear in
habitat ; or it may penetrate into the tissues, living amongst and
between the constituent cells ; or it may inhabit, finally, one of the
internal cavities of the body, such as the digestive tract, general
body-cavity, spaces containing blood or lymph, cavities of the renal

THE MODES OF LIFE OF THE PROTOZOA 19

or urinary organs, etc., either living free in the cavity it inhabits, or
attached to the lining epithelium.

As diverse as the modes of parasitism among Protozoa are the
effects they produce on their hosts. Some parasites produce no
perceptible disturbance in the well-being of their host ; even when
they destroy cells and portions of tissues, the damage may be slight,
and is quickly made good without appreciable permanent injury
being done. From this condition of more or less perfect harmless-
ness there is a continuous gradation in the ascending capacity for
harmfulness, culminating in species which bring about the death of
their hosts with greater or less rapidity. Hence parasitic Protozoa
are commonly distinguished as pathogenic or non-pathogenic ; but
since there is no precise limit to the degree of sickness or indis-
position which justifies the application of the term " pathogenic,"
it is perhaps more convenient to distinguish them as lethal or non-
lethal. It is not possible, however, to lay down hard-and-fast
distinctions in these matters, since a parasite which is not lethal
under some circumstances may become so under others ; for instance,
an animal living a free and natural life may be quite well able to
resist the attacks of parasites to which it succumbs in captivity.
Moreover, it must be borne in mind that such terms as " lethal " or
" pathogenic " can only be applied to a parasite in its relation to a
particular host, since, as will be shown below, a parasite which is
harmful to one host may be harmless to another.

It is far from clear in what way the pathogenic effects of parasitic
Protozoa are produced. If the action and reaction of host and
parasite were relations dependent simply on the number or relative
total bulk of parasites present in a given host, the problems of
parasitism would be comparatively simple ; but in many cases this
is obviously very far from being the case. The effect produced by
a given species of parasite upon a given species of host is a specific
reaction, which differs markedly when one of the two dramatis
personce is changed. It is not uncommon to find insects with their
digestive tract or body-cavity crammed with parasitic Gregarines
of relatively large size, but apparently none the worse for it. On
the other hand, large mammals may succumb to the effects of
minute parasites in relatively scanty numbers — in the sense, that
is, that the aggregate bulk of the parasites may be infinitesimal
compared to the bulk of the host. A better comparison is furnished
by considering closely-allied species of parasites and hosts respec-
tively. A rat may have its blood swarming with Trypanosoma
lewisi, without apparently being any the worse for it. On the other
hand, in a man dying of sleeping sickness, caused by T. gambiense,
or in a ruminant dying of nagaiia (tsetse-fly disease), caused by
T. brucii, the trypanosomes may be so scanty as to be exceedingly

20 THE PROTOZOA

difficult to detect.* These facts suggest strongly that the parasites
produce specific toxins ; but the " sarcocystine " produced by para-
sites of the genus Sarcocystis (Sarcosporidia)f is almost the only case
up to the present, in which a toxin has been isolated from a Pro-
tozoan parasite. Laveran and Pettit (19), however, claim tc have
obtained " trypanotoxins " from trypanosomes.

Considering the facts of parasitism generally, as a problem of
natural history, two guiding principles must be borne in mind
clearly : the first is that any organism, parasitic or otherwise, tends
to be adapted in the best possible manner to the circumstances of
its natural environment ; the second is that, so long as a parasite is
entirely dependent on its host for its existence, it is to its utmost
disadvantage to bring about the death of its host. When, therefore,
a given parasite is constantly lethal to a particular host or hosts,
one of two explanations must bs sought for : either the case is one
of a disharmony — that is to say, of imperfectly-adjusted relations
between the host and parasite ; or the parasite must obtain from
the death of the host advantages in the matter of the continuance
of the species sufficient to compensate for the temporary loss
through destruction of individuals.

The conditions to which a parasite requires to be adapted are
different in many ways from those that influence the life of a free-
living organism. When once a parasite has obtained a footing in
its proper host, the problem of food-supply is solved for it, since
it finds itself lodged in the midst of abundant nutriment so long as
its host lives. On the other hand, if the species is to be main-
tained, it is essential that the parasite should be able to infect new
hosts, a difficult undertaking, and one in which the chances are
all against the parasite in most cases. To insure dissemination of
the species a large number of offspring must be produced, and
special mechanisms and adaptations may be necessary to insure
their reaching their destination. Hence, the more parasites become
specialized and adapted to their peculiar mode of life, the more the
organs and functions of nutrition tend to become simplified, and
the greater the tendency to elaboration and extreme fertility of the
reproductive function.

Considered generally, a parasitic Protozoon reproduces itself
within a given host with one of two results : in the first place, with
that of overrunning the host and establishing itself there ; in the
second place, with that of producing forms destined to infect new
hosts. Forms produced in the first manner may be termed the
" multiplicative phases " ; their function is to produce a stock of
the parasite. From the stock are given off what may be termed

* Compare Laveran and Mesnil (391), pp. 146-150.

f Laveran and Mesuil (18) ; Teichmann (25) ; Teichinann and Braun (26).

THE MODES OF LIFE OF THE PROTOZOA 21

the " propagative phases," which as a rule do not multiply further
in the host in which they are produced, but await their chance of
being transferred to a new host ; and if such a chance be not given
to them, they die off and are replaced by fresh propagative forms
from the stock (see further below, Chapter IX., p. 166).

So long as the nutritive or multiplicative function is the most
important one in the life of a parasite, and until it has matured its
propagative phases, the death of the host is the greatest disaster
that can befall it. The ideal host, from the point of view of a para-
site, is one that is " tolerant " to it — that is to say, one that can
support the presence of the parasite and keep it supplied with the
nutriment it requires, without suffering in health or vigour to any
marked extent. When once, however, the parasite has made the
necessary provision for propagating the species, the life or death
of the host may become a matter of indifference to the parasite,
or may even in some cases be necessary for the dissemination of the
offspring. This will be apparent from a consideration of the methods
by which parasitic Protozoa infect new hosts.

The passage of a parasite from one host to another includes two
manoeuvres : the passing out from the first host, and the passing
into the second. Primitively it may be supposed that this migra-
tion was effected simply by the unaided efforts of the parasite itself —
that is to say, that the active motile parasite would force its way
out of one host, move freely in the surrounding medium, and sooner
or later attack and penetrate a fresh host. This primitive method
of transference doubtless occurs in many cases, especially amongst
epizoic forms (e.g., IchthyophtJiirius, p. 450). In the case of entozoic
parasites its occurrence is less common, but it is found in a certain
number of cases. The young stages of many Acinetaria, parasitic
in Ciliata, probably seek out their hosts and penetrate into them ;
after a period of juvenile parasitism they leave the host's body and
become free-living, non-parasitic organisms. Active migration of
this kind, however, is very rare amongst entozoic parasites. In the
first place, the conditions of life within a living body, in the midst of
organic fluids, are so different from those in the open water, whether
salt or fresh, that it is hardly to be expected that a delicate unicellular
organism adapted to the one mode of life could stand the sudden
change to the other. In the second place, it is clear that active
migration of parasitic Protozoa could only be effected when the host
is an aquatic animal, and not when it leads a terrestrial life. The
only instances of active migration known with certainty to occur
in the case of Protozoa parasitic on terrestrial animals are those
in which the parasite can penetrate a mucous membrane, and is
thus able to pass from one host to another when two such surfaces
are in contact. In this way the trypanosome of dourine in horses

22 THE PROTOZOA

(T. equiperdum) passes from one host to another during coitus, and
the transmission of the parasite of syphilis is another instance.

Speaking generally, and excluding for the moment those cases
in which the transmission is brought about by means of an inter-
mediary host, the propagative phases of the parasitic Protozoa
take the form of inactive, resting stages in which the body of the
parasite is protected against adverse external conditions by tough
protective membranes. In the form of resistant cysts or spores,
the parasites in a dormant state offer a passive and inert resistance
to the elements ; they are disseminated like seeds, and they ger-
minate when they reach a suitable environment, but not till then.

Many, perhaps the majority of parasitic Protozoa, occupy posi-
tions in the body of the host whence the propagative phases can pass
without difficulty to the exterior. This is the case when the para-
site is lodged in organs which have ducts or passages leading directly
or indirectly to the exterior — such as, for instance, the digestive
tract and its dependencies, or the urinary organs and ducts. In all
such cases the propagative stages of the parasite pass harmlessly
to the exterior. The host may in this manner get rid entirely of its
parasites, without, however, necessarily acquiring immunity to
fresh infections ; or, on the other hand, the parasite may keep up its
numbers in the host by continual multiplication to produce a stock
from which are sent forth incessant relays of the propagative phases
destined to infect new hosts. In the majority of parasitic Pro-
tozoa the relations to the host are of this type, and the parasites are
neither lethal nor pathogenic tc any great extent.

On the other hand, there are many instances in which parasitic
Protozoa occupy a position in the body of the host whence escape
by anatomical channels is not possible. This is the case when the
parasite inhabits some closed space in the body, such as the ccelome
or general body-cavity, or the blood-system ; or when it attacks
deeply-situated cells or tissues of the body. In some cases wrhere
natural means of exit from the body occur, they may be unsuitable
for the dissemination of the parasite, as in the case of those forms
parasitic in the genital organs of one sex of the host. In cases of
this kind there are at least six known methods whereby parasitic
Protozoa are disseminated and transferred to fresh hosts.

1. The resistant stages of the parasite may be set free by the
death and decay of its host. This appears to be the manner in
which some of the tissue-infecting parasites of the order Myxo-
sporidia, especially the family Myxobolidce, are disseminated ; they
are for the most part parasites of fishes, and are often very deadly
in their effects.

2. The parasite may cause tumours and ulcers, which suppurate,
and so set free the cysts or spores of the parasite. This, again, is

THE MODES OF LIFE OF THE PROTOZOA 23

an effect often produced by tissue-parasites, such as the Myxobolidce,
or by species of Microsporidia. In such cases also the parasite is
pathogenic to its host, and frequently lethal.

3. The parasite remains in the host until the latter is eaten by
some animal which preys upon it. The propagative phases of tha
parasite are able, however, to resist digestion by the animal that
has devoured their former host, and pass unaltered through its
intestine, to be finally cast out with the dejecta. This is almost
certainly the method by which the common Monocystis of the earth-
worm infects its host. The parasite produces resistant spores in
the worm ; the worm is eaten by a bird, mole, frog, or some other
animal, through the digestive tract of which the spores pass un-
altered ; they are scattered abroad with the faeces, and may then
be swallowed by another earthworm, in which they germinate and
produce an infection.

4. As in the last case, the host, together with its .parasites, is
devoured by some animal, in which, however, the parasite is not
merely carried passively, but again becomes actively parasitic.
Hence in this case there is an alternation of hosts, one of the two
hosts becoming infected by devouring the other. This mode of
infection, which is well known to occur commonly among parasitic
worms, such as Cestodes, is probably also frequent among Pro-
tozoa ; but at present only two cases of it are known with certainty.
One is that of the species of the genus Aggregata (vide infra, p. 353),
parasites of crabs and cephalopods, such as the cuttle-fish and the
octopus. In the cephalopod the parasite forms resistant spores
which pass out with the faeces, and may then be devoured by crabs.
In the crab the spores germinate and give rise to a second form of
the parasite, which lives and multiplies in its new host. If, as fre-
quently happens, the crab is eaten by a cephalopod, the parasite
completes its life-cycle by becoming once more a parasite of the
cephalopod. Another case is that of Hcemogregarina muris in the
rat- mite (p. 376, infra).

5. The Protozoa parasitic in the blood of vertebrates are dis-
seminated by blood-sucking invertebrates, such as leeches, ticks,
or insects, which take up the parasites by sucking the blood of an
infected animal. Later on the parasite may be inoculated into a
second vertebrate host by the invertebrate when it sucks blood at
a later feed. In some cases the transference of the blood-parasite
may be effected in a purely direct and mechanical manner by the
invertebrate, but in most cases the invertebrate plays the part of a
true host, in which the parasite multiplies and goes through a cycle
of development. Hence in such cases also there is an alternation
of hosts and a complicated life-cycle, of which the life-history of
the malarial parasite is a good example (vide infra, p. 359). It

24 THE PROTOZOA

need only be noted here that in such cases resistant spores or cysts
become unnecessary and superfluous for the propagation of the
parasite, and tend to disappear from its developmental cycle.

6. In some cases the parasite may penetrate the ovary of its host,
pass into the ova, and thus infect the embryo and the next genera-
tion. Transmission of this kind is known in a certain number of
cases ; it is never the sole method of transmission, but is always
supplementary to other methods. For instance, in " pebrine " of
silkworms, caused by Nosema bombycis, the spores of the parasite
are liberated in the ordinary way from the caterpillar either with the
faeces or by its death, and are then eaten accidentally on the leaves
by other silkworms ; but a certain number of the parasites pene-
trate into the ovary and form spores, which pass through the pupal
and imaginal stages of the host into the next generation of silk-
worms, which are born infected. In this way the parasite is able
to tide over the winter season, when the ordinary method of infec-
tion would be impossible. The blood-parasites of the genus
Piroplasma (p. 384, infra) afford another example of germinative
infection in the ticks which transmit them.

To turn now to the methods by which parasitic Protozoa pene-
trate into new hosts ; there are four known methods, which, after
what has been said, can be summarized very briefly. The com-
monest is the method of casual or contaminative infection, where
the host infects itself accidentally by taking up the propagative
phases of the parasite from its surroundings — most usually by way
of the mouth, with the food, but it may be by way of the respira-
tory organs. Other modes of infection are the contagious, as in
dourine, already mentioned ; the inoculative, as in malaria and
other diseases caused by blood-parasites ; and the so-called " heredi-
tary " or " germinative " method, as in Nosema bombycis and other
cases.

From the foregoing summary of the methods by which parasitic
Protozoa are propagated from one host to another, it is clear that
there are very few cases in which it is of direct advantage to the
parasite to cause the death of its host. Even where it is necessary,
for the propagation of the parasite, that the host should be destroyed
by some other animal, as in the case of the Monocystis of the earth-
worm, the interests of the parasite are not furthered, and may,
indeed, be damaged, if it cause disease or death to the host. In
the case of blood-parasites, transmitted by the inoculative method,
it may be necessary for the propagation of the parasite that the
required phases should be sufficiently abundant in the blood of the
vertebrate host to insure the invertebrate host becoming infected
when it sucks the blood ; then large numbers of the parasite may be
detrimental to the well-being of the host to a greater or less extent,

THE MODES OF LIFE OF THE PROTOZOA 25

and one interest of the parasite may, so to speak, clash with another.
But in all cases alike it is perfectly clear that the death of the host
before the parasite has matured its propagative phases leads simply
to the extirpation of the parasite, and is a suicidal policy on its
part, a glaring disharmony in Nature. This conclusion is borne out
by a general survey of the facts of parasitism in the Protozoa, since
the vast majority of these parasites are quite harmless to their
hosts, and lethal parasites, greatly in the minority when compared
with harmless forms, must be considered as exceptional and aberrant
types of parasites, from a general point of view.

The parasitic Protozoa of lethal properties present a problem
which can be best attacked by considering and comparing two
cases of closely allied parasites, the one harmless, the other lethal,
to their hosts. Very instructive cases of this kind are furnished
by trypanosomes (vide infra, p. 285). The common parasite of the
rat, Trypanosoma lewisi, is perfectly harmless as a rule to its host,
and the infection runs a very definite course. When the parasite is
introduced into the blood of a healthy and susceptible rat, it enters
at once upon a period of rapid multiplication, which lasts about
twelve days. At the end of that time the parasite swarms in the
rat's blood, without perceptibly affecting its general health. After
about twelve or thirteen days the multiplication of the parasite
ceases entirely ; the swarming period lasts generally about a month,
and after that the parasites begin steadily to diminish and dis-
appear, until after a variable length of time, usually three to five
months, the blood is quite free from them, and the rat, cured from
the attack, is now quite immune to the parasite, and cannot be
infected by it a second time.

The behaviour and effects of a pathogenic trypanosome, such as
T. brucii, when introduced into a rat's blood, contrast sharply
with that just described. Not only do the trypanosomes begin
to multiply at once, but they never cease to do so while the host
remains alive. By the fifth or sixth day there are practically more
trypanosomes in the blood than blood-corpuscles, and the death
of the host soon follows when this stage has been reached.

Trypanosoma lewisi is a type of a well-marked group of try-
panosomes, which may be conveniently denoted the lewisi-group
(Fig. 11). Such are T. cuniculi of the rabbit ; T. duttoni of the
mouse ; T. rabinowitschi of the hamster ; T. blanchardi of the dor-
mouse ; T. microti of Microtus arvalis ; and T. elyomis of the lerot
(Eliomys quercinus). All these species of trypanosomes are ex-
ceedingly similar in their appearance and structure ; each species,
however, appears to be perfectly specific to its particular species
of host. The trypanosome of the rat, for instance, will not flourish
in any other host, not even in a mouse, under normal circumstances.

26

THE PROTOZOA

Roudsky suggests that all this group of trypanosomes constitutes
in reality a single species ; in any case, it is reasonable to regard
them as forms recently evolved from a common ancestor, incipient
species which have not advanced beyond the stage of physiological
differentiation.

In like manner, T. brucii is a type of a group of trypanosomes
which may be termed the 6mcw'-group (Fig. 12) ; other members
of it are T. gambiense, the parasite of human sleeping sickness ;
T. evansi, causing surra in horses ; T. equiperdum, of dourine in
horses ; and several other species. These forms also are exceedingly
similar in appearance and structure, though easily distinguishable
from members of the lewisi -group. They are all of them very
lethal, as a rule, to their hosts ; and they differ further from the try-

FIG. 11. — Trypanosomes of the lewisi-gronp. A, T. lewisi (rat) ; B, T. duttoni
(mouse) ; C, T. cuniculi (rabbit) ; D, T. microti (Microtus arvalis) ; E, T.
elyomis (Eliomys quercinus) ; A and C, from preparations ; B, after Thiroux ;
D, after Laveran and Pettit; E, after Franca. All figures magnified 2,000
diameters.

panosomes of the lewisi-group in the fact that a given member of
the brucii-grouip is not specific to a particular host, but can flourish
and exert its lethal powers in a great variety of vertebrate hosts —
a fact which, coupled with their very similar morphology, renders
the exact determination of the species of this group very difficult,
and often a matter of controversy. All these facts point to the
brucii-group being also descended from a common ancestral form ;
they may be regarded as incipient species in which the process of
evolution has not yet the degree of physiological specialization
reached in the lewisi-group. This view receives support from the
fact that a new race or species of the brucii-groiip has been made
known this year (1911) — namely, T. rhodesiense, a trypanosome
pathogenic to human beings which appears to have come into
existence as a species very recently.

THE MODES OF LIFE OF THE PROTOZOA

27

A further point of great interest in this connection is that
T '. brucii in Africa appears, from the observations of Bruce, to
"occur as a natural parasite of wild game, and to be as harmless to
these its natural hosts as T. lewisi is to rats. The physiological
difference between these two species is that T. lewisi is perfectly
specific to its natural host, whereas T. brucii is capable of flourish-
ing in others, with most deadly effects. Hence the pathogenic
properties of T. brucii would appear to be exerted on hosts to which

FIG. 12. — Trypanosomes of the frrucn-group. A, B, C, T. brucii of "nagana," three
forms — slender, intermediate, and stumpy ; D, E, F, T. gambiense of sleeping
sickness, the three corresponding forms ; G, H, T. evansi of " surra," two forms ;
I, T. vivax ; J, T. nanum. A to C, I, and J, after Bruce, Hamerton, Bateman,
and Mackie (411); G and H, after Bruce (404); D to F, from preparations.
All figures magnified 2,000 diameters.

it is a new parasite, and not on those to which, like T. lewisi, it
has established harmonic relations in the course of evolution.
The pathogenic properties of T. brucii, and doubtless of other
similar forms, may from this point of view be characterized as a
disharmony associated with the first steps in the origin of species.

The problem of the origin of diseases caused by parasites is
essentially a problem of the same nature as the origin of species.
The first step in the formation of new species is a process of varia-
tion in an established species. Similarly, in the process of forma-

28 THE PROTOZOA

tion of new species of parasites, the first step would be the acquisi-
tion by the parasite of the power of living in hosts other than that
to which it is specific. How such a variation might arise in Nature
is impossible to conjecture in the present state of knowledge ; but
some experiments that have been carried out upon T. lewisi show
that conditions can modify the apparent fixity of its characters.
Roudsky (22, 23) found that after prolonged culture on artificial
media, and subsequent rapid passages through rats, it was possible
to infect mice with T. lewisi. Wendelstadt and Fellmer (27) have
shown that T. lewisi, if inoculated into cold-blooded vertebrates, can
persist there for a time, and then becomes virulent to rats.* In
both cases it is evident that the normal specific properties of the
parasite have been induced to vary by changes in the conditions of
life, with the result that they become similar to those characteristic
of the pathogenic trypanosomes.

If it be true that a parasite attacking a new host is at first patho-
genic to it, but tends in the course of evolution to establish more
harmonic relations with the host, the question arises as to how
such relations are brought about. There are two organisms con-
cerned, and the problem affects them both. In the case of the
host the adaptation to the effects of the parasite may be both
individual and racial, in the latter case to be perhaps largely ex-
plained by the elimination of individuals less fitted by their con-
stitution to resist the parasite. In the case of the parasite, also, the
problem may be considered from both points of view ; deadly strains
of the parasite contribute to their own destruction. Interesting
observations bearing on the individual adaptability of strains of
Schizotrypanum cruzi have been made by Chagas (425). This para-
site, when inoculated into guinea-pigs, was found to kill them in
about six days ; this is its initial virulence to this host. After
repeated passages through guinea-pigs, it was found that the viru-
lence diminished, until guinea-pigs inoculated with strains of attenu-
ated virulence lived as much as six weeks before they succumbed
to the effects of the parasite. If, when this result had been attained,
the parasite was given a single passage through a marmoset, it was
then found to have regained its primary virulence to guinea-pigs.

The study of the exact mechanism of the physiological relations
between parasites and their hosts is the task of the investigations
upon immunity and kindred problems which now engross so large
a share of the attention of scientific workers, but which cannot be
considered here in detail.

Bibliography. — For references, see p. 476.
* See also Sleeping Sickness Bulletin, No. 22, p. 412, and No. 24, p. 81,

CHAPTER III

THE ORGANIZATION OF THE PROTOZOA— EXTERNAL FORM
AND SKELETAL STRUCTURES

A UNICELLULAR organism of any kind is a more or less minute mass
or corpuscle of the living substance, protoplasm, containing
usually other substances, fluid, solid, or even in some rare instances
gaseous, in greater or less amount — substances which are either
the product of its own vital activity or have been taken up into
the body from without. As will be shown in more detail in the
next chapter, protoplasm is a substance or complex of substances
which, considered in the aggregate, exhibits the physical properties
of a viscid fluid. Some samples of protoplasm may be less, others
more fluid, but the essentially fluid nature of the whole mass of
protoplasm composing the cell -body is very obvious, as a rule, in
the case of Protozoa.

A drop of a fluid substance, when suspended in another fluid with
which it is not miscible, tends immediately, under the action of the
physical laws of surface-tension, to assume the geometrical form in
which the surface is least in proportion to the mass ; that is to say,
it tends to become a perfect sphere, except in so far as this tendency
may be altered or modified by the contact or pressure of other
bodies, or by the operation of other forces or conditions which
oppose the action of surface-tension.

The sphere may therefore be regarded as the primary form of
the living cell — the form, that is to say, which the organism tends
to assume under the influence of physical forces when not checked
or inhibited in their operation by other factors. A great many
Protozoa exhibit the spherical form in a striking manner, especially
those species which float more or less freely in the water, such as the
Heliozoa (Fig. 3) and Radiolaria (Fig. 13). But the majority of
Protozoa depart more or less widely from the primitive spherical
form, for reasons which must be considered in detail.

In the first place, departure from a spherical form may be merely
temporary, the result of vital activity producing altered conditions
of surface-tension. In order that a drop of fluid may assume a
spherical form as the result of surface-tension, its surface must be

29

30

THE PROTOZOA

homogeneous — that is to say, of similar nature in all parts ; if,
however, its surface be heterogeneous, and differs in different parts,
local inequalities of surface-tension may be the result, and then a
perfectly spherical form cannot be maintained so long as the surface
remains heterogeneous. Thus an organism, such as an amoeba, in
which the protoplasm is quite naked and exposed at the surface of
the body, tends always to have a spherical form in the resting state ;
but when it enters upon a phase of vital activity, it may assume
various forms which can be explained by supposing that the surface-
tension is altered at one or more regions of the surface as the result

EP

FIG. 13. — Thalassicclla (Thalassophysa) pelagica, Haeckel, an example of a species
of floating habit combined with radiate symmetry and spherical body-form.
CK, Central capsule ; EP, extracapsular protoplasm ; al, vacuoles in the
calymma (see p. 251) ; ps., pseudopodia. The small dots in the calymma
represent " yellow cells " (p. 252). After Lankester, magnified 25 diameters.

of local changes in chemical constitution, brought about by the
vital activity of the protoplasm (Rhumbler, 34, and p. 200 infra).
In consequence, the spherical form characteristic of the resting
state undergoes modification in various ways when the organism
becomes active. In floating forms the sphere throws out radiating
processes, so-called " pseudopodia," in all directions (Figs. 3, 13).
In creeping species the body assumes the indefinite and constantly
changing form, with pseudopodia extruded in every direction, which
is characteristic of the amoeba (Fig. 2), and hence commonly termed
" amoeboid." In all such cases, when the animal passes into a

THE ORGANIZATION OF THE PROTOZOA 31

resting, inactive condition, or when the vital activity is temporarily
inhibited by some shock or stimulus, such as an electric current
suddenly turned on, physical forces reassert their sway, and under
the influence of surface-tension the pseudopodia are retracted, and
the body rounds itself off and returns to the spherical form.

Apart, however, from temporary and variable departures from
the primary and fundamental spherical form, many unicellular
organisms exhibit a constant body-form which is often widely
different from the sphere, and which is characteristic of particular
species, or for the corresponding stages in the life-history of a
given species, and varies only within the narrowest limits, if at all.

The problem of form-production in Protozoa, like all other bio-
logical problems, may be considered from two points of view. In
the first place, there is the question why a particular species has
such and such a form. The answer to this question must be sought
in the habits and mode of life of the species and its relation to the
environment. In general it may be said that each species pos-
sesses, or tends to possess, the body-form best adapted to its par-
ticular mode of life, though it is not always easy to trace the
correlation of form and habit in special cases. A broad distinction
may be drawn, however, between species which move freely in
their environment and those which are fixed and sessile in habit.
In freely-moving species, again, a further distinction can be drawn
between those which float or swim in the medium, and those which
creep on a firm substratum. Free-swimming species tend to the
form of an ovoid, more or less elongated, with the longitudinal axis
lying in the direction of forward movement (Fig. 14). Creeping
forms tend to be more or less flattened, and spread, as it were, upon
the substratum, leading in extreme cases to the differentiation of a
ventral surface, in contact with the substratum, from a dorsal
surface on the opposite side. Sedentary forms tend to be more or
less vasiform, often with the point of attachment drawn out into a
stalk or peduncle of greater or less length. A frequent peculiarity
of the body-form in Protozoa, whether fixed or free, is the tendency
to a more or less pronounced spiral twist. Bilateral symmetry, on
the other hand, is a comparatively rare phenomenon in these
organisms ; examples are found among the Flagellata — e.g., Lamblia
intestinalis (Fig. 117).

The second question which arises is, Given a particular specific
form, how is the form developed and maintained, on physiological
or mechanical principles ? To this question the answer must be
sought in the structure of the individual, and more especially in
the formation and possession of special structural elements, more
or less rigid in nature, which determine the form and support the
soft body. Such structures may be external to the body, in the

32

THE PROTOZOA

form of cuticular productions or envelopes of various kinds, or
internal, in the form of an axis or framework. Both these types
of form-determining or skeletal elements, as they may be termed
broadly, may be present together in a given organism.

1. Cuticular and Exoskeletal Structures. — In the Sarcodina gener-
ally, and in a few examples of the Mastigophora and Sporozoa, the
body-protoplasm is quite naked at the surface, as already stated,
and not covered by any cuticle or firm covering. With these
exceptions, the bodies of Protozoa are clothed by a firm cortical

cv.

FIG. 14. — Prorodon teres. N, Macronucleus ; n, micronucleus ; o, mouth ; as.,
oesophagus surrounded by rod-apparatus (p. 433) ; f.v., food vacuoles ; c.v.,
contractile vacuole surrounded by feeding- vacuoles ; al., alveolar layer ;
st, meridional rows of cilia ; a., anal pore. After Schewiakoflf, magnified 600
diameters.

layer, which is produced either as a differentiation of, or secretion
by, the most superficial layer of the protoplasmic body, and which
receives various names in different cases.

The very first beginnings of a cortical layer are seen in some
species of amoebae, such as Amoeba verrucosa — species in which 'the
protoplasm, extremely viscid and slow-flowing, forms a delicate
investing pellicle at the surface. In these cases the pellicle is so
thin that it does not hinder the amoeboid movement appreciably
(Fig. 23). A further advance is seen in some of the Flagellata,

THE ORGANIZATION OF THE PROTOZOA

33

where a thin cuticle is present which permits changes in shape,
caused by the contractility of the enclosed protoplasmic body.
Such forms are not amoeboid, but exhibit rhythmical changes of
form produced by contractions of the superficial body-layer in a
manner somewhat recalling peristaltic movement, and are com-
monly said to be metabolic (Fig. 15) : and
since such movements are characteristic
of some species of the genus Euglena,
they are sometimes called euglenoid.

In most cases, however, in which a
cuticle or firm cortex is present, a definite
and characteristic body-form is main-
tained, subject only to such changes as
may result from curvatures of the body,
or temporary shortening of its axis in a
particular direction, brought about by
the contractility of the living body. An
envelope of this kind, which may vary in
consistence from a thin, flexible cuticle
to a rigid inflexible cuirass, or " lorica,"
inhibits completely the natural tendency
of the fluid protoplasmic body to round
itself off — a tendency, however, which
frequently reasserts itself during resting
phases of the organism, when the cortex
may be softened or absorbed. Hence it
is very common to find that the resting
phases of Protozoa revert to the primi-
tive spherical form, whatever the shape
characteristic of the organism in an
active state.

A close-fitting cortex or cuticle which
is essentially a part of the body itself
must be distinguished clearly from struc-
tures built up by the organism externally
to the body to afford shelter or support.
Such a structure is termed variously a
"shell," "test," or "house." The
formation of protective shells, into which
the body can be completely retracted,

and' from which it can emerge to a greater or less extent, is of
extremely common occurrence amongst the naked-bodied Sarcodina.
The forms of these shells, their structure and mode of formation,
exhibit an almost infinite variety, and can only be described here in
a quite general manner.

3

FIG. 15. — Astasid tenax, two
individuals showing the
changes of form due to
metabolic movement, oes.,
(Esophagus ; c.r., reservoir
of the contractile vacuole ;
N., nucleus. After Stein.

34 THE PROTOZOA

As regards material, the shells may be composed of elements
secreted by the organism (" autophya," Haeckel), as in Hyalosphenia
(Fig. 16, B), or of foreign particles taken up by the animal from its
surroundings ("xenophya "), as in Difflugia (Fig. 16, A). Skeletal
elements secreted by the organism may be of organic or inorganic
nature. In the former case they are probably chitinous in most
cases, or composed of a substance allied to chitin ; in the latter they
are either calcareous or siliceous. A good example of the formation
of a shell is seen in Euglypha (Fig. 59), where the chitinous plates
composing it are formed first of all in the interior of the proto-
plasmic body, and pass to the surface to build up the shell. When
the shell is built up of foreign particles, the material employed may
vary greatly, and consists generally of particles of sand, grit, etc.,

B

FIG. 16. — Examples of shells or houses formed by Protozoa. A, Difflugia spiralis,
which forms a house built up of foreign bodies ; B, Hyalosphenia cuneata, in
which the house is built up of plates secreted by the animal itself (compare
also Euglypha, Fig. 59). Both these species belong to the order Amcebsea ;
the pseudopodia (ps.) are seen streaming out of the mouth of the shell. After
Leidy ; A magnified 250, B 500 diameters.

taken up at hazard from the environment. Such shells are de-
scribed technically as " arenaceous." In the case of Difflugia,
Verworn (36) was able to cause it to build up its test of various
materials, such as particles of coloured glass or other substances,
when these were supplied to it exclusively. Many species of
Foraminifera, however, form their tests exclusively of particular
materials under natural conditions. Thus, in the genus Haliphy-
sema (Fig. 17) the test is formed of sponge-spicules ; in Technitella
thompsoni the calcareous plates of echinoderms are selected ; and
other instances could be cited in which the organism selects habitually
for its shell certain materials from a varied environment in which
the particular materials required may be far from common in
occurrence relatively to other particles apparently equally suitable
(see especially Heron- Allen and Earland). Verworn (36) found that

CHAPTER V

THE ORGANIZATION OF THE PROTOZOA (Continued)—
DIFFERENTIATIONS OF THE ECTOPLASM AND ENDOPLASM

A. Ectoplasmic Organs.

THE various structures and organs produced from the ectoplasm
are best classified by the functions they subserve, under the headings
of protective, kinetic and locornotor, excretory, and sensory
mechanisms.

1. The protective function of the ectoplasm is often seen in
organisms in which no cuticle or envelope is present. It has been
observed, for instance, that the species of Myxosporidia that
inhabit the gall-bladders or urinary bladders of their hosts resist
the effects of the medium in which they live so long as their ecto-
plasm is intact, but succumb if it be injured.

In most Protozoa other than those belonging to the class Sarco-
dina, however, a special protective envelope or cortex is present at
the surface of the body, and such forms are commonly said to be
corticate. A cuticle may be formed in various ways, distinguished
by the use of different terms. It may represent the entire ecto-
plasm, modified in its entirety to form an envelope, as in the peri-
plast of the Flagellata ; it may represent a transformation or modi-
fication of only the most superficial layer of the ectoplasm, as in
the pellicle of the Infusoria and of some amoabae — for instance,
Amoeba verrucosa, the epicyte of the gregarines, etc. ; or it may arise
as a secreted layer deposited at the surface of the ectoplasm, and not
derived from a modification of the substance of the ectoplasm itself,
in wliich case it is termed a " cell -membrane."

Whatever its mode of origin, the cuticle may be developed to a
very variable degree, from the thinnest possible membrane, some-
times very difficult to discover, to a thick and tough investment
which may be termed a " cuirass " or " lorica " (" Panzer "), when
it is formed by thickening of a pellicle ; or a " house " or " shell,"
when it is a greatly thickened cell- membrane standing off from the
body. In many cases the cuticle undergoes local thickenings to
form spikes or hooks, which may serve as organs of attachment,
as in the epimeritc of gregarines (Fig. 142).

45

46 THE PROTOZOA

In addition to the passive protection afforded by a cuticle, organs
of active defence may be present in the ectoplasm in the form of
bodies known as trichocysts, found commonly in many ciliate In-
fusoria (p. 447, Fig. 187) ; they are little oval or spindle-shaped
bodies which on suitable stimulation are converted explosively into
a stiff thread which is shot out from the surface of the body. (For
the nematocyst-like organs known as " polar capsules," in Myxo-
sporidia and allied organisms, see p. 399, infra.}

2. The ectoplasm is shown to be the seat of movement both by
the fact that motile organs arise from it and by the frequent
presence in it of special contractile mechanisms. The motile
organs which are found in the Protozoa are pseudopodia, flagella, cilia
with their various modifications, and undulating membranes ; any
of these structures may subserve the function of food capture in
addition to, or instead of, that of locomotion. These organs will
now be described in order, after which contractile mechanisms will
be dealt with.

(1) Pseudopodia are organs of temporary nature, extruded from
the protoplasm when required, and retracted when no longer needed.
They can be formed, probably, in all cases in which the body
protoplasm is naked, or limited only by a cuticle not of sufficient
thickness to inhibit the movements of the underlying protoplasm.
They arise simply as an eruption of the protoplasm at some point
at the surface of the body, forming an outgrowth or process which
varies greatly in different cases as regards size, length, width, com-
position, and activity.

Pseudopodia always arise in the first instance from the ectoplasm,
and may consist throughout of this layer alone, in which case they
are relatively stiffer and more rigid ; or a core of endoplasm may
flow into the pseudopodium when it has grown to a certain length,
in which case the pseudopodium is more fluid and flexible. The
formation of a pseudopodium is best studied in a common amceba,
such as Amoeba proteus (Fig. 2) or A. Umax (Fig. 20) ; it is then seen
to arise as a protrusion of the ectoplasm, forming a shallow promi-
nence at the surface of the body. The prominence continues to
grow out from the body, and is at first hyaline, transparent, and
free from granulations, since it consists of ectoplasm alone. In
some cases the pseudopodium may grow to a relatively very large
size, and still consist of clear ectoplasm alone, as in Entamoeba
histolytica (Fig. 90), a form rather exceptional in this respect ; more
usually, so soon as the budding pseudopodium has reached a certain
not very great size, a core of granular endoplasm flows into it and
forms the axial part of the pseudopodium. It is then easier to study
the formation of the pseudopodium, since the granules in the endo-
plasm permit the characteristic flowing movements and currents to

THE ORGANIZATION OF THE PROTOZOA

37

either case the spicules grow by accretion — that is to say, by deposi-
tion of fresh layers of inorganic substance upon that already laid
down — and if such accretion takes place at one end of a rod-shaped
spicule, it may have the result that the opposite extremity of the
spicule is pushed outwards by the continued growth, with the result
that the oldest portion of the spicule projects freely far beyond the
limits of the body.

As regards material, spicules are usually either calcareous or
siliceous — in the first case generally carbonate of lime, in the second

FIG. 18. — Acanthocystis chcetophora, a Heliozoon with a skeleton of slender radiating
siliceous spicules, each forked at the distal end. In the interior of the body
are seen numerous symbiotic algae (dark) and non-contractile vacuoles (clear) ;
one vacuole of larger size is seen, probably the contractile vacuole. sp., sp.,
Spicules ; ps., ps., pseudopodia. After Leidy, magnified 750 diameters.

case amorphous silica. In the family Acanthometridce among the
Radiolaria the spicules are formed of a substance which was thought
to be of organic nature, and was named " acanthin," but which
has been found to consist of strontium sulphate.

As regards their form and relation to the body, the spicules in
the simplest cases are rod-shaped or needle-like elements disposed
radially or tangentially. A simple type of spicular skeleton is seen
in Acanthocystis (Fig. 18), in which elongated siliceous rods, fre-

38

THE PROTOZOA

FIG. 19. — Clathrvlina degans, a Heliozoon with a lattice-like skeleton, attached by
a stalk. Two individuals are seen, the younger with its stalk attached to the
head of the older ; in the younger the lattice-work is still very delicate. Both
individuals are sending out numerous radiating pseudopodia, very delicate
and slender. After Leidy, magnified 750 diameters.

THE ORGANIZATION OF THE PROTOZOA 39

quently branched at their distal ends, are arranged like radii of the
spherical body, projecting freely for some distance from the surface.
In other cases the spicules may be disposed tangentially to the body,
as in the family Collides amongst the Radiolaria, and in other forms
belonging to this order. From a simple type of skeleton composed
of separate spicules, more complicated types of skeletons are de-
rived by fusion of the spicules to form a connected framework.
The commonest type of this is a fusion of tangentially-disposed
spicules to form a lattice- work ; an example of this is seen in
Clathrulina (Fig. 19), in which a lattice-like skeleton is formed at
the surface of the body, standing off from it like a shell. Skeletons
of this type are especially characteristic of the Radiolaria, a group
in which the architecture of the skeleton may reach a very high
degree of complication and exhibits endless variety. The lattice-
like framework, made up of tangentially-arranged spicules united
together, may be further strengthened by radially-disposed beams.
As the animal grows, it may outgrow the framework first laid down,
and another lattice-work is formed concentric with the first, and
connected with it by radial beams ; later on a third and a fourth
such framework is formed, as the organism continues to grow in
size. Skeletons formed in this way may be " homaxon " — that is to
say, built up on the axes of a sphere ; or " monaxon," with one
principal axis ; or may follow various plans of symmetry, or may be
asymmetrical (p. 250, infra).

Bibliography. — For references, see p. 477.

CHAPTER IV

THE ORGANIZATION OF THE PROTOZOA (Continued)—
THE PROTOPLASMIC BODY

THE substance composing the bodies of Protozoa was termed
originally sarcode by Dujardin ; but after it had been shown to be
identical in nature with the living substance of the cells of animals
and plants, the same term was employed universally for both, and
the word protoplasm, coined by von Mohl to designate the living
substance of plant-cells, supplanted the older term sarcode, which
has now quite dropped out of current use.

It would be impossible within the limits of the present work to
discuss in detail the various theories that have been put forward
with regard to the nature and constitution of protoplasm ; they
can only be summarized in brief outline here. Protoplasm, when
seen under the microscope with powers of moderate strength,
presents itself as a viscid, semi-fluid substance, sometimes clear and
hyaline in special regions, but always showing, throughout at least
the greater part of its substance, numerous granulations, which
vary greatly in size, from relatively coarse grains to those of the
minutest size visible with the power of the microscope used. The
most important of these granulations are the so-called "chromatin-
grains," which are discussed fully in Chapter VI. ; in this chapter
only non-chromatinic granules are dealt with. The coarser proto-
plasmic grains may be present in greater or less quantity, or may
be entirely absent ; they are to be regarded for the most part as
so-called metaplastic bodies — that is to say, as stages in, or by-
products of, the upward or downward metabolism of the organism.
On the other hand, the minute, ultimate granules, or " microsomes,"
are never absent, except over limited areas, in any sample of proto-
plasm. It is on the constant presence of granules that the so-called
granular theory of protoplasm, especially connected with the name
of Altmann, has been founded. On this view, each minute granule
is regarded as an elementary organism, or " biobjast," capable in
itself of all vital functions, and equivalent to a single free-living
bacterium, just as a single cell of a Metazoan body may be compared
with a single Protozoan organism. Protoplasm, on this view, js rer

40

THE ORGANIZATION OF THE PROTOZOA 41

garded as a colony of bioblasts, imbedded in a fluid matrix, com-
parable in a general way to a zoogloea-colony of bacteria.

A special and important class of metaplastic granules are the so-called
" deutoplasmic " bodies, consisting of reserve food- materials stored up in
the protoplasmic substance. Examples of such are the yolk-granules of ova,
the paraglycogen-grains of gregarines, the plastinoid bodies of coccidia,
starch-grains in holophytic forms, etc.

Amongst the granulations of the protoplasm, special mention must be
made of the bodies known generally as chondriosomes and mitochondria, but also
by a variety of other names (cytomicrosomes, bioblasts, spherules or sphero-
plasts, and, collectively, ergastoplasm). The chondriosomes are not to be
classed with the temporary, metaplastic inclusions, but are permanent ele-
ments of the cell- protoplasm. The chondriosomes of Protozoa have recently
been the subject of detailed study by Faure-Fremiet (38'5). In the living
condition they are small transparent bodies, feebly refractile, and of a pale
grey tint. In shape they are generally spherical, and vary from 0*5 /i to
1'5 n in diameter. In some cases the chondriosome appears homogeneous in
structure ; in others it presents the appearance of a vacuole with fluid con-
tents and a denser peripheral layer. In contact with water or with weak
alkalis they swell up immediately. When the nucleus (in Infusoria the
micronucleus) divides, the chondriosomes also divide simultaneously, and the
daughter- chondriosomes are sorted out between the two daughter- cells ;
they have, however, no direct relation with the nuclear apparatus. In the
process of division each chondriosome becomes first rod-like, then dumb-bell-
shaped, and is finally constricted directly into two halves.

A purely chemical definition of the chondriosomes, according to Faure-
Fremiet, cannot be given. They exhibit the reactions of a fatty acid, and
can be considered as combinations of fatty acids or of phosphates of albumin.
The physiological function of the chondriosomes is not clear, but Faure-
Fremiet considers that they " play an important part in the life and evolu-
tion of the sexual cell," in Protozoa or Metazoa, and are active in the elabora-
tion of deutoplasmic substances of fatty nature, into which they may be
transformed directly.

It has been shown, however, that the minute granules of proto-
plasm do not lie isolated from one another, suspended freely in a
matrix, but are seen in the microscopic image to be connected with
one another by fine lines or darker streaks, the whole forming a
delicate network, at the nodes of which the granules are lodged.
In some cases the granule itself is perhaps only an optical effect
produced by a node of the network. On these appearances has
been founded the so-called reticular theory of protoplasm, connected
especially with the names of Heitzmann, Schafer, and others. On
this view protoplasm has been regarded as composed of an exceed-
ingly fine reticulum, a network or feltwork ramifying in all planes,
bearing the granulations at its nodal points, and bathed throughout by
a fluid, more or less watery sap, or enchylema. The fibrillar theory of
Flemming may be regarded as a modification of the reticular theory.

Against the reticular theory of protoplasm, it may be urged that
it leads to physical difficulties, in view of the generally fluid nature
of protoplasm. For the reticulum must itself be either of a fluid
pr a £o}jd nature ; if fluid, it presents the condition of one fluid

42 THE PROTOZOA

suspended in the form of a network in another fluid with which it
does not mix — a condition which could not exist for more than an
instant of time, since the fluid reticulum must break up immediately
into minute droplets. If, on the other hand, the reticulum is of
rigid consistence, the protoplasm as a whole could not be fluid,
any more than a sponge soaked in water could behave as a fluid
mass in the aggregate. The difficulty can, however, be overcome
by supposing the apparent reticulum to be the optical expression,
not of a fine network of fibrils, but of delicate lamellae limiting
minute closed chambers, or alveoli. Then the fine line seen with the
microscope joining any two adjacent nodal points would be the
optical section of the wall or lamella separating two contiguous
alveoli, and protoplasm as a whole would possess a honeycombed
structure comparable to that of a fine foam or lather — the fluid
lamellae of the foam represented by the apparent reticulum of the
protoplasm, and the air-contents of the individual bubbles repre-
sented by the enchylema. Or, to express the state of things in a
different manner, protoplasm could be regarded as an emulsion of
very fine structure, composed of two fluids not miscible with one
another — namely, the more fluid enchylema, which is suspended
in the form of minute droplets in the more viscid substance forming
the alveolar framework. This is the so-called alveolar theory,
especially connected with the name of Butschli ; by this conception
of protoplasmic structure, not only are the necessary physical con-
ditions satisfied, but an explanation is given for many peculiarities
of protoplasmic bodies, such as the radiate arrangement of the
meshes of the reticulum commonly observed either at the surface of
the body or around solid or fluid bodies contained in the proto-
plasm, and so forth.

The various theories that have been mentioned all assume tacitly
that protoplasm is monomorphic — that is to say, that it possesses
one fundamental type of minute structure. Fischer, on the other
hand, seeks to unite all the different theories by supposing that
protoplasm is a polymorphic substance — that is to say, one that
may exhibit a diversity of structure at different times and under
different conditions, as the result of changes produced by its inherent
vital activity. Thus, he supposes that a given mass of protoplasm
may be at one time homogeneous, and at another time granular,
reticular, fibrillar, or alveolar, as the result of a process of " vital
precipitation," and that by reabsorption of the structural elements
it may return to a homogeneous condition. Faure-Fremiet (38 and
38'5) also regards protoplasm as a homogeneous fluid, which is pre-
cipitated by reagents, and which normally contains, in suspension,
a certain number of granulations, some temporary, others per-
manent in nature ; compare also Degen (154).

THE ORGANIZATION OF THE PROTOZOA 43

Those investigators of the Protozoa who have expressed an
opinion on the subject have been for the most part in favour of the
alveolar theory of protoplasm, since it was first propounded by its
author, Biitschli (see especially Rhumbler). Protozoa as a rule
are very favourable objects in which to study the foam-like structure
of the protoplasm (compare Schaudinn, 130, p. 188). But what-
ever view be held as to the ultimate structure of protoplasm, its
essentially fluid nature is very apparent in these organisms, and is
a point upon which it is very important to be clear. The fluid
condition of the living substance is manifested directly by the
streaming movements to be observed in it, and indirectly by a
number of phenomena, such as the tendency, already mentioned,
of the body to round itself off when at rest, and the tendency of all
vacuoles to assume a spherical form. A vacuole is a drop of fluid
suspended in the protoplasmic body, and may be regarded as
formed by the bursting and running together of many minute
alveoli, just as a large bubble in a foam may arise by the union of
many smaller ones ; or by the gradual enlargement of a single
alveolus by diffusion of fluid into it from neighbouring alveoli, until
it attains proportions relatively gigantic. Vacuoles assume uni-
formly spherical contours, except when they are deformed by
mutual pressure from crowding together or from other causes. In
some cases the protoplasm may be so full of coarse vacuoles that it
exhibits an obvious frothy structure, which must by no means be
confounded with the ultimate alveolar structure of the protoplasm,
a structure which is exceedingly delicate, only to be observed with
high powers of the microscope and with careful attention to all
details of microscopic technique. Examples of vacuolated bodies
are seen especially in Heliozoa — e.g., Actinosphcerium (Fig. 3).

The statement, however, that protoplasm generally is of fluid
nature admits of its exhibiting many degrees of fluidity, and some
samples of protoplasm are far more viscid than others. This is
true both of different species of organisms, of the same species at
different phases of its development, and of different parts of the
same organism. In some cases portions of the protoplasm may be
stiffened to a degree that perhaps oversteps the ill-defined boundary
between the liquid and solid states of matter. In a great many
Protozoa, perhaps the majority of them, the protoplasm of the
body is divisible, more or less distinctly, into two regions —
namely :

1. An external or cortical zone, termed ectoplasm or ectosarc ; in
appearance and consistence typically clear, hyaline, more refringent,
finely granular or without visible granulations, and of more viscid
nature ; in function protective, kinetic, excretory, and sensory.

2. An internal or medullary region, the endoplasm or endosarc ;

44 THE PROTOZOA

opaque, less refringent and coarsely granular ; the seat of trophic
and reproductive functions.

These two zones of the protoplasmic body are, in the more primi-
tive forms, differentiations of the protoplasm more or less tem-
porary and transient in nature. For instance, in an amoeba which
is in active movement, fluid endoplasm is constantly flowing along
the axes of the pseudopodia towards their tips, where it comes into
contact with the surrounding medium, the water or other fluid in
which the amoeba lives. Under the influence of the medium the
endoplasm is converted into ectoplasm, becomes of stiffer, less fluid
consistence, and loses its coarse granulations. At the same time,
at the hinder end of the amoeba, ectoplasm is continually passing
into the interior of the body, where it becomes liquefied and granular
in structure, and is converted into endoplasm (Rhumbler, 34).

In Protozoa, however, which do not exhibit amoeboid movement,
the ectoplasm and endoplasm may be two independent layers, well
defined and perfectly separate the one from the other. The ecto-
plasm is the seat of those functions which are connected with the
relation of the organism to the outer world, to the environment
in which it lives ; the endoplasm, on the other hand, is concerned
specially with the internal affairs, so to speak, of the protoplasmic
body. In the following two chapters the various organs of the
Protozoa will be considered under the headings of the layer from
which they are formed, and according to the functions they perform

Bibliography. — For references, see p. 477.

THE ORGANIZATION OF THE PROTOZOA

35

in the case of Difflugia the foreign particles used are taken up by the
pseudopodia during the process of being retracted ; the surface of
the pseudopodium then becomes wrinkled, and particles of debris
are caught in these wrinkles, and so drawn into the interior of the
protoplasmic body, in which they are stored up in the fundus of
the shell, like the plates in Euglypha, and are utilized in the growth
of the shell, or in repairing damages to it, or in building a new shell
when the animal reproduces itself by division.

FIG. 17. — Halipliysema, lumanowiczii, a foraminifer which builds up its house out
of sponge-spicules. A, part of the protoplasm stained to show the nuclei (n.) ;
B, a living specimen with expanded pseudopodia (p.). After Lankester (11).

The simplest architectural type of shell or test is a simple spherical or
oval capsule, usually with a large aperture at one pole through which the
protoplasm is able to creep out in order to capture food or perform the function
of locomotion (Fig. 16). The wall of the test may be imperforate, or may
have fine pores through which also the protoplasm can stream out. With
continued growth of the organism, the original shell may become too small
for its requirements. Then the organism may reproduce itself by fissior.

36 THE PROTOZOA

and the daughter- individual forms a new shell for itself. In many cases the
shell formed by the daughter is larger than that of the parent ; for instance,
in Centropyxis aculeata and other species, in which the young individuals
multiply by fission, and each time they do so, the new shell formed is larger
than the old one, until the full size of the adult individual is reached
(Schaudinn, 131), after which point the new shell formed after the process
of fission is of the same size in both the parent and the daughter- individual.
In such cases the shell is always a single chamber, and is described technically
as " monothalamous."

In other cases, however, the organism does not multiply by fission when
it has outgrown its first shell, but forms a new shell of larger size which is in
continuity with its first shell ; the protoplasmic body now occupies both the
chambers of the shell formed in this way. With further growth more chambers
are formed, giving rise to a complex " polythalamous " shell composed of
many chambers all occupied by the protoplasmic body (p. 232, infra). For a
detailed study of the developmental mechanics of shell-formation, see
Rhumbler (35).

2. Internal Skeletal Structures. — In many cases in which the proto-
plasmic body is naked at the surface, or bears only an extremely
thin cuticle, a definite body-form may be maintained by means of
internal supporting fibrils or other similar structures (Koltzoff,
30, 31). In some cases such structures may be of temporary nature.
A beautiful example of this is seen in the delicate organic axes
formed in the pseudopodia of Heliozoa (Fig. 22), in the form of
slender needle-like rods secreted by the protoplasm to stiffen the
pseudopodia, and absorbed again when the pseudopodia are re-
tracted. In other cases, supporting structures of organic nature
may be permanent constituents of the protoplasmic body ; such are
the axial rods, or " axostyles," found in many flagellates, such as
Trichomonas (Fig. 5, ax.), Lophomonas (Fig. 45), etc., slender flexible
rods of organic substance which form a supporting axis for the body.
Previous to division the axostyle is absorbed, and new axostyles
are formed in the daughter-individuals. The axostyles are stated
to arise from a centrodesinose (p. 103, infra) formed in the process
of division of the blepharoplast (Dobell, 236) or of the centriole of
the nucleus (Hartmann and Chagas, 62) ; the centrodesmose per-
sists after division is complete, and its two halves become the
axostyles of the two daughter-individuals. In Trichomonas eberthi,
however, Martin and Robertson (348) find that the axostyles arise
after division quite independently of the centrodesmoses or other
nuclear structures. In Octomitus (Fig. 116) two axostyles are present.

From supporting structures of organic nature, such as the
axostyles or the organic axes of the pseudopodia mentioned above,
it is not difficult to derive the more rigid and permanent elements
known as " spicules," in which the organic basis becomes indurated
by deposits of inorganic mineral substance. In some cases spicules
may perhaps consist entirely of mineral substance deposited
directly within the living substance without any organic basis. In

THE ORGANIZATION OF THE PROTOZOA 47

be followed. In the growing pseudopodium a strong current can
be observed flowing down the axis to the tip, and there spreading
out and breaking up into weaker currents which turn round and
flow backwards along the surface of the pseudopodium. In amoebae
with a very viscid surface layer the back-currents are very feeble,
ceasing a short way from the tip of the pseudopodium, and often
scarcely discernible, or even absent altogether ; in species with a
fluid ectoplasm, however, the back - currents are distinctly seen,
and may even pass back and bend round again to join the forward
axial current, as described by Rhumbler (34) in Amoeba blattce.

While the extrusion of the pseudopodium is an active process,
the retraction requires nothing but the action of purely physical
forces of surface-tension to explain it. The protoplasm then flows
back into the body of the animal, and may present some character-
istic appearances in doing so. If one surface is in contact with the
substratum on which the animal is creeping, the adhesion of the
pseudopodium often causes the tip to be drawn out into slender
processes like spikes or hairs. At the same time the surface of the

FIG. 20. — Diagram to show the protoplasmic currents in a Umax-
amoeba which is moving forward in the direction indicated by
the large arrow on the left. The smaller arrows indicate the
direction, and their length the intensity, of the currents in
different parts of the body. A forwardly-directed " fountain
current " starts from near the hinder end, and passes along
the axis of the body to the extremity anterior in movement ;
there it turns outwards and passes back along the sides of the
body, diminishing rapidly in intensity, and finally dying out in
the regions where the two dots are placed. After Rhumbler
(34).

pseudopodium may present a wrinkled appearance, as the viscid
ectoplasm shrinks in consequence of the rapid withdrawal of the
fluid endoplasm.

The pseudopodia of different species of organisms, or even of
the same species at different periods of the life-cycle, vary greatly
in form, appearance, and structural characters, and the more im-
portant variations require a special terminology. In the first
place, the pseudopodia may be broad and thick relatively to their
length, as in Amoeba proteus (Fig. 2) ; they are then termed " lobose "
(" lobopodia "), and usually have a core of endoplasm. A typical
lobose pseudopodium is, in fact, nothing more than an outgrowth
of the body-protoplasm as a whole. In the most extreme cases of
this t}^pe, the whole body flows forward in one direction, forming,
as it were, a single pseudopodium. Such a mode of progression is
characteristic of Amoeba Umax (Fig. 20) and other similar forms,
in which the body glides forward like a slug as the animal creeps
over substratum ; the end which is anterior in movement is rounded,

48 THE PROTOZOA

while the posterior end commonly becomes drawn out into processes
similar to those seen in a pseudop odium in process of retraction.
In other forms, such as A. proteus (Fig. 2), the pseudopodia are sent
out on all sides and balance each other, in which case there is very
little translation of the body as a whole, and the pseudopodia serve
chiefly for food-capture. If, however, the outflow of the pseudo-
podia is strongest on one side of the body, the organism moves in
that direction as a whole, and the larger, more strongly developed
pseudopodia counteract and overcome the pull exerted by those
that are weaker. It will be readily understood, therefore, that the
most rapid powers of progression are possessed by the slug-like
amcebse, in which a single pseudop odium drags the whole body along
without opposition from others.

Rhumbler (34) has drawn attention to the existence of two
modes of progression exerted by amoebae of the lobose type. In the
more fluid species which creep upon a substratum to which they
adhere more or less firmly, like Amoeba proteus, the animal pro-
gresses by a flowing movement, such as has been described ; this is
the commonest type of amoeboid locomotion. On the other hand,
in species of the type of A. verrucosa and A. terricola the very
slightly fluid body is limited by a thin pellicle, and does not adhere
to the substratum ; then progression is effected by " rolling "
movement. The animal throws out a number of pseudopodia on
one side, which cause it ultimately to overbalance and roll over to
that side ; by continued repetition of this procedure, a slow progres-
sion in a particular direction is effected. At other times, however,
A. verrucosa may flow along like other amcebse.

Contrasting with the lobose pseudopodia are the slender, thread-
like, so-called " filose " pseudopodia, formed entirely of ectoplasm.
Pseudopodia of this type can effect a slow creeping movement, but
are not very effective for locomotion, and serve for food-capture
principally, or even entirely, as in the radiate floating forms
(Heliozoa and Radiolaria) ; food is entangled by them and drawn
into the body. The filose pseudopodia may radiate from the
body in all directions, remaining separate from one another, or
they may anastomose to form networks, and are then termed
" reticulose." Pseudopodia of the reticulose type are specially
characteristic of the Foraminifera (Fig. 21). Radiate pseudopodia
which do not form anastomoses, on the other hand, characterize
the groups of the Heliozoa and Radiolaria, organisms of floating
habit. As noted above, pseudopodia of the radiate type are
generally supported by an axial rod, a secreted structure of firm,
elastic nature, and are hence known as axopodia. The actual rod
reaches some way into the endoplasm, often to the centre of the
body, as in Acanthocystis (Fig. 18), Wagner etta (Fig. 48), etc. ; it

THE ORGANIZATION OF THE PROTOZOA

49

—-*M

FIG. 21. — Gromia ovi-
formis, M. Schultze
(=G. ovoidea,
Rhumbler), living
specimen with out-
stretched pseudo-
podial network
(ps.), in which a
diatom (d.), Navi-
cula sp., is en-
tangled and will be
drawn into the
shell (sh.). Other
diatoms are seen
inside the shell, and
at its fundus
several nuclei are
! seen as clear spheri-
cal bodies in the
protoplasm. The
pseudopodial net-
work is drawn at
a magnification of
about 200 linear,
but for want of
space is repre-
sented extending
over about one-
third of the area
over which it com-
monly spreads. A
part of the pseu-
dopodial network
is reflected back
over the shell, and
streams out back-
wards from the
pole opposite to
the shell - mouth.
After M. Schultze.

50

THE PROTOZOA

is probably of endoplasmic origin, and is pushed out from it in a
centrifugal direction. As it grows out, the ectoplasm forms a
sheath over it, and extends usually some way beyond it. When
the pseudopodium is retracted, the axial rod is liquefied and
absorbed by the protoplasm.

Food-capture is effected by the pseudopodia in various ways (see
p. 189). In forms with lobose pseudopodia they flow round the body

to be ingested, enclosing it
on all sides, and finally
imprisoning the prey in
a closed chamber of the
living substance, together
with a drop of water which
forms the food - vacuole
(Fig. 2, P1, P2) in which
the prey is digested (p. 192,
infra). A very noticeable
feature of pseudopodia of
all kinds is their adhesive-
ness, due to the secretion
of a slimy substance at the
surface of the ectoplasm.
In Difflugia, if the pseudo-
podia be touched gently
with a glass rod, the slime
can be drawn out into
threads, like the mucus of
a snail (Rhumbler, 34).
The adhesive power of the
pseudopodia is of service
both in adhering to the
surface upon which they
creep and in the capture
of their food.

The slow -flowing
amoebae, such as A. verru-
cosa, do not as a rule flow
round the body to be in-
gested, but draw it into their interior, as if by suction. In this
manner A. verrucosa absorbs and devours filamentous algae (Fig. 23),
which are " imported " into the interior of the body and there coiled
up and digested. Rhumbler has shown that this process can be
imitated by drops of fluid ; for instance, a drop of chloroform in water
will draw in a thread of shellac and coil it up in its interior in a
manner similar to the ingestion of an algal filament by an amoeba.

end

FIG. 22. — Portion of an Actinosphcerium, magni-
fied about 660 linear. ecL, Ectoplasm with
larger vacuoles ; end., endoplasm with smaller
vacuoles ; N., nucleus ; ps., pseudopodia ;
ax., delicate axial rod in the pseudopodia.
After Leidy.

THE ORGANIZATION OF THE PROTOZOA

51

The pseudopodia of the filose type adhere firmly to organisms
suitable for food with which they come in contact, and it can be
observed that the prey is both held fast and killed by them, in-
dicating that the pseudopodia secrete some toxic substance in
addition to that of an adhesive nature. In the reticulose type,
diatoms and organisms of various kinds are entangled in the
pseudopodial network (Fig. 21), and are generally digested there
also.

In a few cases pseudopodia exhibit a peculiar form of movement
known as nutation. An example of this is seen in the remarkable
Heliozoon described by Schaudinn (43) under the name Camptonema
nulans (Fig. 47), which possesses slender axopodia in which the axial

FIG. 23. — Four stages in the ingestion of an Oscillarian filament (/.) by Amceba
verrucosa. In A the amoeba has crept along the filament ; in B one end of
the amoeba is bending up, and is about to fuse with the rest of the body,
producing a twist in the filament ; in G two have been produced ; in D a
considerable length of the filament has been drawn into the amoeba, and is
twisted up into a stout coil. A, B, and C, are drawn at intervals of quarter
of an hour, D several hours later. After Rhumbler (34).

filament does not extend the whole length of the pseudopodium.
The pseudopodia perform a slow rotating movement, and "describe
the mantle of a cone, sometimes acute, sometimes obtuse, remaining
stretched out straight for their entire length, and bending only at their
base." Similar movements are performed by the pseudopodia of
Trichosph cerium (p. 229) and Wagnerella (p. 246). In Camptonema
the pseudopodia also have the power of bending suddenly when
brought in contact with prey, which they capture like the tentacles of
a polyp. The bending takes place beyond the point at which the
axial filament ceases. Movements of this kind are transitional to
those seen in flagella.

(2) Flagella are vibratile thread-like extensions of the protoplasm,
capable of performing very complicated lashing movements in

52

THE PROTOZOA

every direction. A flagellum consists of an elastic axial core
enclosed in a contractile sheath or envelope (Fig. 24), from the
extremity of which the core protrudes freely in some cases, forming
a so-called " end-piece." The flagellum takes origin from a more
or less deeply-seated granule, the blepharoplast, or basal granule,
which will be described in dealing with the nuclear apparatus
(p. 82, infra). The elastic axis, arising from the blepharoplast,
can be regarded as a form -deter mining element of endoplasmic
origin, the sheath as an ectoplasmic motor substance. A flagellum
is usually cylindrical in form, with the axial
filament central in cross-section, but may be
band-like, with the axial filament at or near
one edge ; it is usually of even thickness
throughout its whole length, but when the
axial filament is exposed to form a terminal
end - piece the flagellum tapers to a fine
point.

Like pseudopodia, flagella serve primarily for
locomotion, and secondarily for food-capture,
which is effected by causing food-particles to
impinge on some point or aperture at the surface
of the body, where they are ingested. In their
relation to locomotion two types of flagella can
be distinguished, termed by Lankester pulsella
and tractella respectively. A pulsellum is
situated at the end of the body which is
posterior in movement — that is to say, it is a
flagellum which by its activity propels the body
forwards. Flagella of this type occur in OxyrrTiis
(p. 278) and in the Choanoflagellata (p. 271),
but are comparatively rare in the Protozoa. In
the majority of cases the flagella are tractella —
that is to say, their action is such as to drag the
body after them — hence they are situated at
the end which is anterior in progression. Con-
sidered generally, the movements performed by
tractella are of two types. In some cases the entire flagellum is
thrown into even, sinuous undulations, and the body of the
flagellate progresses with a smooth, gliding movement, which may
be extremely rapid, and is then well expressed by the French
phrase " mouvement en fleche "; this type of movement is well
seen in the trypanosomes and allied genera, such as Leptomonas,
etc. In most free-living flagellates, however, the flagellum is held
out stiff and straight for the proximal two-thirds or so of its
length, while the distal third performs peculiar whirling or pulsating

FIG. 24. — Structure
of the flagellum of
Euglena. ax., Axial
filament; c.p., con-
tractile protoplasm
enveloping the
axial filament ;e. p.,
end - piece of the
flagellum, consist-
ing of the axial fila-
ment exposed ; r,
root of the flagel-
lum passing into
the body (compare
Fig. 84). After
Biitschli (3).

THE ORGANIZATION OF THE PROTOZOA

53

-a/

cv.

movements,* which drag the body along in a succession of more or
less distinct jerks.

In many flagellated organisms, forwardly-directed flagella may
be combined with so-called "trailing flagella" (" Schlepp-geissel "),
which are directed backwards, running along the side of the body,
either quite free (Fig. 25) or united to the body
by an undulating membrane (Fig. 5). In such
cases the trailing flagellum is perhaps the chief
organ of propulsion, acting as a pulsellum, while
the forwardly-directed flagellum or flagella may
function more as tactile organs or feelers than
as locomotor organs. The flagellum may also
serve as an organ of temporary attachment in
some cases, especially in parasitic flagellates ;
it then often exhibits at its distal extremity a
distinct bead -like swelling or enlargement,
doubtless of adhesive nature. Such terminal
enlargements are sometimes seen, however, in
free -swimming forms.

There are many grounds for assuming the existence
of a gradual transition from flagella to pseudopodia,
and especially to the slender axopodia seen in
Heliozoa, etc. In organs of each kind the typo of
structure is essentially similar, an axis of firm elastic
nature, which is pushed out from the endoplasm, in
many cases from a basal granule of centrosomic nature
(p. 82), and is covered over by a sheath of contractile
fluid ectoplasm. The difference between them is one
of degree, the axopodia being relatively shorter in
proportion to their thickness, and consequently less
flexible, but the nutating and bending movements
seen in axopodia are essentially similar in type to
those manifested by flagella. The Heliozoa arc con-

nectod with the Flagellata by transitional forms which
indicate that their pseudopodia have arisen as
modifications of flagella (p. 248). Goldschmidt, who
discusses the whole question (41, pp. 116-122), de-
scribes in a Cercomonas-liko flagellate the shorten-
ing of the flagellum, and its transformation into
a pseudopodium which swings to and fro. A
flagellum may be considered as having arisen by
modification and specialization of an axopodium,
and as capable in many instances of reverting to
that type of organ. (Compare also p. 465, infra.)

(3) Cilia are slender, thread-like extensions of the ectoplasm which
differ from flagella mainly in three points : they are as a rule much
shorter relatively to the size of the body ; they are present
usually in much greater numbers, and in their most primitive

FIG. 25. — Anisonema
grande, ventral view,
showing the " hetero-
mastigote " arrange-
ment of the flagella.
a./., Anterior flagel-
lum ; p.f., posterior
trailing flagellum ;
S, oesophagus; c.v.,
contractile vacuolc
surrounded by a
number of feeding
vacuolcs ; N.,
nucleus ; an., anus
(cytopyge). After
Stein.

* For a detailed description and analysis of these movements, see Delage and
Herouard (6), pp. 305-312.

54 THE PROTOZOA

of arrangement form, as it were, a furry covering to the body ; and
their movements are different from those of flagella. A cilium
performs simple regular movements of alternate contraction and
relaxation, whereby it is first bent like a bow, with a slight spiral twist
(Schuberg, 44), and then becomes straightened out again ; from
this it may be inferred that the contractile substance is developed
mainly on one side of the elastic axis — on that side, namely, which
becomes concave during contraction — instead of ensheathing the
axis completely, as in most flagella. Then the bending of the
cilium would be the result of active contractility, acting against-*
the elasticity of the axis, which is operative in causing the
cilium to straighten out again when the contractile substance is
relaxed.

Cilia are usually implanted in rows on the surface of the body,
and their movements are co-ordinated in such a way that the con-
traction— or, as it may be better termed, the pulsation — of a given
cilium takes place slightly after the one in front of it, and before the
one behind it (Fig. 26). On the other hand, the neighbouring cilia
of adjacent rows pulsate in unison ; consequently, when a ciliated

//I

FIG. 26. — Diagram of ciliary movement, representing the successive phases of
contraction and expansion in a row of cilia. After Verworn.

surface is seen from above with sufficient magnification, the move-
ments of the cilia produce an optical effect similar to that seen in a
cornfield when the wind blowing across it gives rise to an appearance
of waves following each other in a continuous succession. When,
however, a row of cilia is seen in side-view, the successive beats of
the cilia may produce the illusion of a rotating wheel ; hence the
origin of such names as Rotifer, Trochophore, etc., applied to
Metazoan organisms bearing rings or girdles of stout cilia.

In spite of the apparent differences between cilia and flagella,
there is no difficulty in regarding cilia as derived ancestrally from
flagella by a process of modification and specialization in structure,
movement, number, arrangement, and co-ordination. Like pseudo-
podia and flagella, cilia may serve both for locomotion and food-
capture. In many cases the. cilia specialized for these two functions
may be sharply distinct ; the food-capturing cilia, found in connec-
tion with the mouth and the peristomial region, are commonly
much longer than the locomotor cilia, and show the tendency to
form fusions presently to be described. In sedentary forms loco
motor cilia may be absent in the ordinary state of the animal, and
only developed temporarily during motile phases. On the other

THE ORGANIZATION OF THE PROTOZOA 55

hand, in a purely parasitic form such as Opalina (p. 439), in which
a mouth is entirely absent, only locomotor cilia are present.

The chief modifications of cilia, apart from variations in size and
function, are the result of a tendency to adhere or fuse together ;
thus arise various types of organs, of which the most common are
the cirri, membrawllce, and undulating membranes. Cirri are organs
resembling bristles, formed by fusion of a tuft of cilia, just as the
hairs of an ordinary camel's -hair paint-brush adhere when moistened
so as to form a flexible pencil. In many cases the cirri have frayed-
*-out ends, in which the component cilia are distinct from one
another ; and reagents often cause a cirrus to break up into
separate cilia. Cirri have a locomotor function, and are especially
characteristic of the ciliate Infusoria which are of creeping habit
(order Hypotricha, p. 440, infra). The cirri occur on the ventral
surface of the body — that is to say, on the side of the body turned
towards the substratum on which the organism creeps, using the
cirri practically as legs.

Membranellae are flapping or swinging membranes formed by
fusion of two or more transverse rows of cilia implanted side by
side, and adhering to form a flat membrane, the free edge of which
often has a fringed or frayed border, representing the free ends of
the component cilia. Membranellse occur usually in the region of
the peristome in spiral rows, implanted one behind the other, and
each membranella performs simple movements of alternate flexion and
expansion, comparable to those of a single cilium. Both in structure,
origin, and movements, the membranellse must be distinguished
clearly from the undulating membranes presently to be described.

Undulating membranes are sheet-like extensions of the ectoplasm,
which perform rippling movements, comparable to those of a sail
placed edgewise to the wind ; or, better still, to the undulating
movements performed by the dorsal fin of a sea-horse (Hippocampus)
or a pipe-fish (Syngnathus) when swimming. The undulating mem-
branes of Ciliata consist simply of a single row of cilia fused together.
Such membranes are found commonly in the oesophagus of In-
fusoria ; in the vestibule of Vorticellids there are two membranes
of this kind. In some genera, such as Pleuronema (Fig. 27), they
represent the principal food-capturing organ, and reach a great
development. Pleuronema swims about by means of its cilia, and
comes to rest sooner or later in a characteristic attitude, with the
cilia projecting stiffly from the body ; the large undulating membrane
is then protruded from the mouth, and serves by its movements to
waft food-particles down the oesophagus.

Undulating membranes are also of common occurrence in the
Flagellata, where they are of a different type from those of Ciliata.
The undulating membrane in this class is always found in connec-

56

THE PROTOZOA

tion with a flagellum, and is to be regarded as a web of the ecto-
plasm (periplast) connecting the flagellum to the surface of the
body. Such a condition may arise either by attachment of a back-
wardly-directed trailing flagellum to the side of the body, as in
Trichomonas (Fig. 5) and Trypanoplasma (Fig. 36), or by the
shifting backwards of the point of origin of an anterior flagellum,
as is well seen in the transition from crithidial to trypanif orm phases
in the development of trypaiiosomes (Fig. 131). As a rule, only the
proximal portion of the flagellum is involved in the formation of

FIG. 27. — Pleuronema chrysalis. M, The undulating membrane ; o, mouth ;
N, macronucleus ; n, micro nucleus ; c.v., contractile vacuole ; f.v., food
vacuole ; a., anal pore. After Schewiakoff, magnified 660 diameters.

the undulating membrane, and the distal portion projects freely
beyond it ; but in some cases a distal free portion of the flagellum
may be quite absent, and then flagellum and undulating membrane
are co-extensive (Fig. 12, J). Undulating membranes in Flagellata
appear to be specially related to the endoparasitic mode of life, and
in free-living species they are found rarely, if ever ; they may be
regarded as an adaptation to life in a broth-like medium, such as the
intestinal contents, or the blood of a vertebrate, containing many
suspended particles or corpuscles. In such cases the membrane
may assist the organism to force its way between the solid bodies
suspended in the fluid medium. Undulating membranes may, how-

THE ORGANIZATION OF THE PROTOZOA 57

ever, serve for other functions than that of locomotion, in flagel-
lates as well as in ciliates. In large, stout forms of trypanosomes,
for example, the animal may remain perfectly still while its mem-
brane is rippling actively, and in that case the function of the mem-
brane is probably to cause currents in the fluid surrounding the
body, and to change and renew the liquid bathing the body-surface.
In such a case it has been noted that the undulating membrane
may from time to time reverse the direction of its movements, the
waves running for a time from the hinder end forwards, and then
for a time in the opposite direction (Minchin and Woodcock, 42,
p. 150). It is probable that the undulating membranes which pass
down the vestibule of Vorticellids can reverse their movements in a
similar manner, since this passage serves both for passage of food-
particles to the mouth and for the ejection of excreta from the anal
pore and the contractile vacuoles.

The only structures found in free-living Flagellata which can be
compared at all with undulating membranes are the peculiar
" collars " found in the Choanoflagellata (Fig. 110), and also in the
collar-cells of sponges. Each collar is an extension of the ecto-
plasm which grows up from the edge of a circular area round the
insertion of the flagellum, forming a membrane like a cuff or sleeve
surrounding the basal portion of the flagellum, but quite distinct
from the flagellum itself, and not formed in actual connection with
it like the undulating membrane of a trypanosome. The collar
differs further from a true undulating membrane in not being
energetically motile, but only slowly protrusible and retractile. It
has been stated, both for Choanoflagellates and for the collar-cells of
sponges, that the collar is formed by a spirally-folded membrane.
Their function appears to be that of assisting in food-capture by
a sessile, flagellated organism.

(4) Contractile mechanisms in Protozoa, when they are visible,
take the form of so-called myonemes, minute contractile fibrils run-
ning in various directions in the ectoplasm, like an excessively
minute system of muscle-fibres. Such elements are not found in
Sarcodina or in the non-corticate forms of the other classes ; in
naked forms with amoeboid movement the ectoplasm, as has been
pointed out above, is only a temporary differentiation of the proto-
plasmic body, which can arise by conversion of the endoplasm, and
which can be changed back again into endoplasm. Myonemes occur
commonly, however, in those Flagellata, Sporozoa, or Infusoria,
which owe a definite body-form to the presence of a firm cuticle or
cortex, representing a stable ectoplasm. The myonemes are often,
however, extremely fine, and sometimes escape detection in cases
in which we can infer their presence with certainty from the move-
ments or contractions of the organism or of its ectoplasm. As a

58

THE PROTOZOA

general rule they are visible more or less clearly in the larger, but
not in the more minute, species. Thus, in trypanosomes, myonemes
can be made out in large forms as delicate lines running parallel to
the undulating membrane (Fig. 28), but in small species of trypano-
somes it may be impossible to discover them, although the nature
of their movements may leave no doubt as to the existence of con-
tractile mechanisms in the ectoplasm. In other cases, both motile
species possessing myonemes and non-motile species lacking them
may occur within the limits of a single group, as in Gregarines,
where the motile species show a very distinct layer of myonemes

(Fig. 29) ; while the non-motile
forms have a much thinner ecto-
plasm, represented practically by
the cuticle alone, with no trace
of myonemes. In the non-motile
trophozoites of the Coccidia myo-

FIG. 28. — Trypanosoma pe cce, stout
form stained with iron-ha&matoxylin
to show myonemes. After Minchin,
X 2,000.

FIG. 29. — Gregarina munieri, showing
the layer of myonemes at the surface
of the body, slightly diagrammatic.
After Schneider.

nemes are similarly absent. In the ciliate Infusoria the myonemes
run parallel to, and beneath, the rows of cilia, and in species of
large size and great powers of contractility, such as Stentor, the
myonemes are lodged in canals and show a transverse stria tion
(Fig. 186, 7).

According to Schaudinn, these motile mechanisms, both flagella
and myonemes, are derived from the achromatic spindle of a
dividing nucleus. In the development of a trypanosome from a
non-flagellated condition, he describes the entire kinetic apparatus
as arising from a nuclear spindle consisting of two polar centro-
somes connected by a centrodesmose (p. 103, infra), and by mantle

THE ORGANIZATION OF THE PROTOZOA

59

fibres, but with chromosomes apparently rudimentary or absent.
Such a spindle is stated to persist and to grow greatly in length,
one pole of it finally projecting beyond the anterior end of the body.
The centrosome at the proximal pole of the spindle becomes the
blepharoplast or basal granule of the flagellum ; the centrodesmose
itself becomes the flagellum, or at least its axial elastic filament ;

N

FIG. 30. — Development of the locomotor apparatus of try pano somes. A — F, De-
velopment of Trypanosoma nocluce : A, the single nucleus of the "ookinete "
is dividing into two unequal halves ; in each half a centriole is seen, connected
with its twin by a centrodesmose ; B, the division of the nucleus complete ;
the two sister-nuclei still connected by a centrodesmose uniting the centrioles ;

C, the smaller nucleus (n.) is dividing unequally to furnish a third nucleus (^.g-) ',

D, E, the third nucleus is dividing to furnish a proximal (b.g.*-) and a distal
(b.g.2) centriole, while the fibrils of the achromatic spindle become the myo-
nemes (my. ) ; F, development of the trypanosome — N, trophonucleus ; n, kineto-
nucleus; 6.?.1, basal granule (true blepharoplast) of the flagellum. In 0 the
pigment (P) present in the earlier stages is being thrown off. After Schau-
dinn (132).

G, stage in the development of the merozoitc of Trypanosoma rotatorium
into the trypanosome-form ; N, trophonucleus, still connected by a cen-
trodesmose with n, the kinetonucleus, which has budded off b.g., the basal
granule of the flagellum. After Machado (469).

the distal centrosome is carried out on the tip of the flagellum ; and
the mantle fibres form the myonemes, stated in this case to be eight
in number, of the body, which are continued on into the contractile
sheath of the flagellum (Fig. 30). However fascinating the views
put forward by Schaudinn, with regard to these points, may be, it
must be stated that the greatest doubt attaches to the correctness

60 THE PROTOZOA

of the observations upon which they are founded, and that they
lack confirmation entirely.*

3. Organs apparently of excretory function are present in many
Protozoa as the so-called " contractile vacuoles," one or more droplets
of clear liquid which make their appearance in the ectoplasm, grow
to a certain size, and then burst, emptying their contents to the
exterior. When the contractile vacuole reaches its full size, it often
bulges inwards far beyond the limits of the ectoplasm, and hence
may appear to lie in the endoplasm ; but its first appearance is
always in the ectoplasm, to which it strictly belongs.

In non-corticate amoeboid forms the contractile vacuoles simply
empty themselves to the exterior, and the changing form of the
body does not permit of determining whether the position of the
vacuole is a constant one. It is common in amoebae for the vacuole
to be lodged in the region of the body which is hindmost in progres-
sion ; but this may be simply the mechanical consequence of the
streaming movements in the protoplasm, whereby the vacuole is
carried along to the hinder end of the body. In corticate forms,
on the other hand, the contractile vacuoles are constant both in
number and position, and void their contents through a definite
pore in the cuticle, directly or indirectly ; in many Flagellata and
Infusoria, for instance, the vacuoles do not discharge directly to
the exterior, but into the oesophagus or into a reservoir- vacuole
communicating with the oesophagus.

The growth of the contractile vacuole is caused by fluid draining
into it from the body-protoplasm. In amoebae and forms of simple
structure no channels supplying the contractile vacuole are visible,
and it must be supposed to be fed by a process of diffusion through
the protoplasm from all parts of the body. In the highly-organized
ciliate Infusoria, however, the deepest layer of the ectoplasm has a
loose, spongy texture, and forms a definite excretory layer full of
spaces containing fluid, which drains into one or more main canals

* It must be added further that, to judge from the figures left by Schaudinn
and published on Plate xxix. of his collected works (" Fritz Schaudinn's Arbei-
ten," Hamburg and Leipzig, 1911), the statements cited above appear to be
founded on preparations made by a method of technique which is recognized
generally as giving unsound cytological results — namely, the method of dried
films stained by the Romanowsky stain. Schaudinn's statements are nevertheless
cited above on account of the numerous theoretical discussions and speculations
in modern protozoological and cytological literature of which they have been the
foundation. For my part, I disbelieve entirely in the theory that the flagellum
represents a centrodesmose between two centrosomes ; I regard it as a simple
outgrowth from a blepharoplast of a nature essentially similar to the axopodium
of a Heliozoon. It is curious that no one has as yet extended Schaudinn's theory
to the axopodia, the axial filament of which should also represent a centrodesmose,
if that view is correct for the axial filament of the flagellum, a view that seems
to me quite unthinkable from a phylogenetic standpoint. Is it to be supposed
that the formation of each pseudopodium by a Heliozoon represents a rudimentary
mitosis ?

THE ORGANIZATION OF THE PROTOZOA

61

supplying the contractile vacuole or vacuoles. Thus, in Stentor
(Fig. 8) the single vacuole is fed by a canal running the length of
the Tbody, and in Paramecium (Fig. 185) the two vacuoles are each
surrounded by a number of canals forming a star-shaped figure.

As regards the function of the contractile vacuoles, it should be
noted in the first place that their contents are always fluid and
watery, and never contain solid particles of any kind. The fluid
which a contractile vacuole drains from the body is doubtless
replaced by water absorbed from the surrounding medium by
diffusion through the superficial layer of the protoplasm, or it
may be through the mouth in some cases. The contractile vacuole
is generally regarded as the organ of
nitrogenous excretion, comparable
functionally to the urinary organs of
the Metazoa, but it is highly probable
that the liquid discharged from it
contains also the carbon dioxide pro-
duced by the respiratory process.
Hence the contractile vacuole may
be regarded as both excretory and
respiratory in function (see also
p. 197, infra).

4. In the majority of Protozoa
there are no organs for which a defi-
nite sensory or nervous function can
be claimed, although these organ-
isms show by their reactions to the
environment or to stimuli that they
possess sensory and psychical func-
tions. In some cases, however,
certain organs can be asserted to
have a sensory function, exhibited
in sensitiveness either to impressions

of touch or light. Thus, in many Flagellates the flagella appear to
be tactile as well as locomotor in function, and in Ciliata tactile
cilia occur, especially in the creeping hypotrichous forms.

Sensitiveness to light is a marked feature of many Protozoa,
even of quite undifferentiated forms, such as amoebae. Rhumbler
(34) has shown that many amoebae cease feeding in a strong light,
and even disgorge food that they have taken in when suddenly
subjected to the intense illumination necessary for microscopic
study. This characteristic is, however, most marked in the holo-
phytic species, to which light is a necessity for their plant-like
metabolism. In the holophytic Flagellates a red pigment-spot, or
stigma, is found constantly, situated close to the anterior end of the

FIG. 31. — Pouchetia cornuta, one of
the Dinoflagellata, to show the
large stigma (st.), in front of
which is a lens (I.). After Schiitt
(386).

62 THE PROTOZOA

body (Fig. 4, st.). The belief that the stigma is the seat of light-
perception receives support from the fact that in some cases it is
found associated with lens-like structures, which evidently serve
to concentrate light upon it and act as dioptric elements, as in
Pouchetia (Fig. 31).

B. Endoplasmic Organs.

The bulk of the endoplasm in proportion to that of the whole
body varies greatly in different Protozoa. In Flagellata, for
example, the protoplasmic body must be considered as consisting
almost entirely of endoplasm, the ectoplasm furnishing only the
delicate periplast and myonemes. Similarly, in motionless para-
sitic forms, such as the Coccidia or the " coelomic " Gregarines
(p. 326, infra), the body within the cuticle is entirely endoplasm.
On the other hand, in Ciliata, in which the ectoplasm may give rise
to a number of different structures, the endoplasm is often a rela-
tively restricted region of the body. In these examples that have
been cited, the ectoplasm and endoplasm are probably stable
layers, and their relative proportions are consequently more or less
constant for a given phase of the life-history ; but in amoeboid forms,
as already pointed out, ectoplasm and endoplasm are interchange-
able, and the amount of each layer present in an organism varies
with the extent of its body-surface ; that is to say, the proportion of
ectoplasm to endoplasm is greatest when the amoaba is moving
actively and throwing out many pseudopodia, and least when it is
in a resting condition and has assumed the spherical form.

As stated above, the endoplasm is a fluid, granular substance,
which contains various enclosures connected with the nutritive
function, and also the nucleus or nuclei. Hence it may be re-
garded as the seat of trophic and reproductive functions. The
nuclear apparatus will be dealt with in a separate chapter, since it
belongs, strictly speaking, neither to the ectoplasm nor the endo-
plasm, though commonly lodged in the latter. In this chapter
only the structural elements connected with the function of food
ingestion and assimilation will be described.

The contents of the endoplasm vary greatly, according to the
mode of life of the organism. In saprophytic and most parasitic
forms no special organs are found in connection with the nutritive
function, the food being simply absorbed in a soluble condition
at the surface of the body, probably by the aid of enzymes secreted
by the organism, but not by any recognizable organs. In holozoic
and holophytic forms, however, special organs, differing widely in
each case, are present for the assimilation or elaboration of food.

1. In holozoic Protozoa the organs of assimilation take the form
offood-vaciioles, minute droplets of fluid in which the solid particles

THE ORGANIZATION OF THE PROTOZOA 63

ingested as food are suspended and gradually digested. In some
cases, however, and especially when the prey is relatively large,
no distinct fluid vacuole can be made out surrounding it, but the
food appears to be simply lodged in the endoplasm itself ; the
vacuole is " virtual." When the digestion is completed, the in-
soluble faecal residues are cast out of the body.

In Protozoa in which the body consists of naked, non-corticate
protoplasm, the food is ingested, and the faecal remains are expelled,
at any point on the surface of the body. In corticate Protozoa,
on the other hand, in which the body is limited by a resistant
envelope or cuticle of a certain strength and thickness, food can-
not be ingested at any point, but is taken in through a special
aperture, a cell-mouth or cytostome. In such cases the organs of
food-capture are either flagella or cilia, and by their action the food
is wafted into the mouth. Primitively the mouth is a superficial
aperture in the cuticle, opening into the endoplasm by means of a
longer or shorter tube, the oesophagus or cytopharynx. In the
Peritricha (p. 433), however, the mouth and oesophagus are, as it
were, carried into the body at the end of an in-sinking of the ecto-
plasm, which forms a long tube or vestibule, comparable in its
mode of formation to the stomodseum of the Metazoa. In any case
the food-vacuoles are formed at the bottom of the oesophagus, in
the endoplasm. The mode in which the vacuoles arise, and the
processes of digestion and defaecation, are discussed in a subsequent
chapter (p. 189, infra).

2. In holophytic forms assimilation is carried on by cell-organs
of the same nature as those found in the green cells of ordinary
plants. Of primary importance are the chromatophores, or chromo-
plasts, bodies containing chlorophyll or allied pigments by means of
which the organism is enabled to decompose carbon dioxide in the
sunlight, setting free the oxygen and utilizing the carbon for build-
ing up the living substance. The chromatophores vary greatly
as regards size, form, and number present in the cell -body. Other
bodies of constant occurrence are pyrenoids, small glistening cor-
puscles which appear to serve as centres for the formation or storage
of starch or similar substances of amyloid nature produced in the
process of anabolism (see infra, p. 188).

In any Protozoa, whatever their mode of nutrition, the endo-
plasm contains usually various enclosures, which can be classed
generally as metaplastic — that is to say, as products of the upward
(anabolic) or downward (catabolic) metabolism of the living sub-
stance. Instances of anabolic products are the grains of starch or of
the allied substance, paramylum, found in the holophytic forms,
and the reserve food-materials — fat, " paraglycogen," and other
substances — often stored up in considerable quantity in prepara-

64 THE PROTOZOA

tion for developmental changes, especially in the female gamete,
in a manner analogous to yolk-grains in an ovum. Instances of
bodies resulting from catabolic activity are waste-products of various
kinds in the form of granules, crystals, pigment-grains, etc., often
present in great numbers, and giving the endoplasm an opaque and
coarsely-granular appearance. A familiar instance of such waste-
products is seen in the grains of melanin-pigment formed in the
bodies of the malarial parasites (Fig. 156) as a result of the absorp-
tion and decomposition of the haemoglobin of the red blood-cor-
puscle.

Many bodies present in the protoplasm of Protozoa may be con-
sidered as originally of metaplastic nature and origin, but as
utilized secondarily for various functions. Such are the oil-drops
in the intracapsular protoplasm of Radiolaria (p. 251), which appear
to have a hydrostatic function, and also to serve as reserve food-
material in the development. It is also highly probable that both
internal and external skeletons originated simply as excretions in
the first instance — that is to say, as waste - products of the
metabolism which have been utilized for the function of support,
and subsequently adapted and modified in accordance with the
special requirements of the organism.

Finally, as bodies of hydrostatic function, though not to be
included necessarily under metaplastic products, are the peculiar
gas-vacuoles of Arcella, bubbles of gas which can be secreted,
absorbed, and formed again, as circumstances may require, in and
by the living protoplasm.

Bibliography. — For references see p. 477.

CHAPTER VI

THE ORGANIZATION OP THE PROTOZOA (Continued)— THE

NUCLEAR APPARATUS— CHRO MATIN, NUCLEUS,
CHROMIDIA, CENTROSOMES, AND BLEPHAROPLASTS

OF all the parts or organs of the cell-body, there is none of greater
importance for the life and activities of the organism than the
so-called nucleus, a term which, understood literally, means simply
a kernel or central portion of the body, and conveys no idea of the
true nature of the structure in question or of its significance for the
life of the organism.

The cell-nucleus, in all its various modifications of form and
structure, is essentially and primarily a collection of grains and
particles of a peculiar substance which has received the name
chromatin, on account of its characteristic tendency to combine
with certain colouring matters and dyes. A nucleus may consist,
perhaps, in some cases of little more than a single mass of chromatin,
or of several such masses clumped together. In most cases, how-
ever, the chromatin is combined with other substances which may
be termed comprehensively achromatin, and which are built up with
the chromatin in such a way as to produce a complicated nuclear
structure, as will be described in detail presently.

The chromatin-substance is not necessarily, however, concen-
trated entirely in the nucleus in all cases. In many Protozoa,
especially amongst the Sarcodina, as, for example, Arcella (Fig. 32),
Difflugia, and many other genera, the cell-body contains, in addi-
tion to one or more nuclei, extranuclear granules of chromatin,
termed chromidia,* which may be scattered in the cytoplasm

* The term " chromidia," in the German form " Chromidien," was coined by
Hertwig (60) to denote the extranuclear grains of chromatin, and the whole mass
of them in the cell- body was spoken of as a " Chromidialnetz." Subsequent
authors, however, have used the word in its singular form, " chromidium," in a
collective sense, to denote the entire mass of chromidia present in a cellular organ-
ism, and not, as might have been expected, to mean the individual grains or
particles of chromatin which constitute the chromidial mass. In order to avoid
confusion, it is proposed in this work to use the term chromidiosome to denote the
smallest chromatin-particles of which the chromidial mass is made up, and which
grow and multiply by division like other elementary living bodies. It is clear,
however, that the chromidiosomes of which the chromidial mass scattered in the
cytoplasm is built up are in no way different in kind from the minutest granules
of chromatin contained in the nucleus. The term "chromidiosome" must there-
fore be applied to the ultimate, individual grain or particle of chromatin, alike
whether it be lodged inside or outside a nucleus.

65 5

66 THE PROTOZOA

throughout the cell, or may be aggregated in certain regions of
the body to form " chromidial masses " or " chromidial nets."
It is even found that in some species a true nucleus may be absent
temporarily during some phases of the life-cycle, all the chromatin
being then in the form of chromidia, from which nuclei arise by a
process of condensation and organization of the chromatin in com-
bination with achromatinic elements. Such a condition may be
regarded as a temporary reversion to a more archaic and ancestral
condition, since, as has been pointed out already (Chapter I.), the
Protista of the lower or bacterial grade of organization do not
possess, speaking generally, a true nucleus, but only scattered
grains of chromatin. Hence the chromidial condition of the
chromatin may be ranked as an earlier and more primitive state,
from which the strictly cellular grade of organization has been
evolved by concentration of some or all of the chromatin to form a
nucleus. In the tissue-cells of Metazoa, as a general rule, and in
many Protozoa, the chromatin is concentrated entirely in the nucleus
or nuclei, and chromidia do not occur.

Whatever view be taken as to the primitive or secondary nature
of the chromidial condition (a question upon which individual
opinions may differ considerably), the following facts can be stated
definitely with regard to the chromidia. In some cases the chromidia
can be observed to arise as extrusions of chromatin from the nucleus,
which either casts off a certain amount of chromatin into the cyto-
plasm, while preserving its individuality, or may undergo complete
fragmentation, becoming resolved entirely into chromidia, and
ceasing to exist as a definite nucleus. In other cases, chromidia
arise from pre-existing chromidia, by growth and multiplication
of the chromidiosomes, thus keeping up a chromidial mass or stock
which is propagated from cell to cell through many generations,
independently of the nuclei present in addition to them in the cell.
The chromidiar mass itself may vary considerably in structure
in different cases or at different seasons ; the chromidiosomes may
be arranged in clumps, strands, or trabeculse, on a protoplasmic
framework, and the mass is often vacuolated and contains substances
other than chromatin. In Difflugia, Zuelzer (85) has shown that
in the autumn the chromidial mass assumes a vacuolated or alveolar
structure, and in each alveolus grains are formed of a carbohydrate
substance allied to glycogen, which functions as reserve food-
material for the organism during the reproductive processes initiated
at that season.

On the other hand, as chromidia arise from nuclei, so nuclei may
arise from chromidia. In many Prolozoa, as, for example, Arcella
(Fig. 32), the formation of so-called " secondary " nuclei (which,
however, do not differ from other nuclei except in their mode of

THE NUCLEUS

67

origin), by concentration of chromidia into a clump or mass which
acquires gradually the structure and organization of a true nucleus,
is a frequent and normal occurrence in the life-cycle, as will be
seen in subsequent chapters. Those who regard the chromidial
condition as the more primitive will see in the formation of secondary
nuclei from chromidia the ontogenetic recapitulation of the phylo-
genetic origin of the nucleus as a structural element of the cell-body.
From the foregoing it is seen that nuclei, in the Protozoa, do not
necessarily arise from pre-existing nuclei ; the generalization " Omnis
nucleus e nucleo," though it probably holds good universally for
the cells of Metazoa, cannot be maintained for Protozoa if the term
" nucleus " be taken in its strict sense. On the other hand, there

A B

FIG. 32. — Arcdla vulgaris, to show formation of secondary nuclei from the chrc-
midia. A, Ordinary type of individual, with two nuclei and a ring of chromidia ;
B, example in which secondary nuclei are being formed in the chromidial
ring. N*-, Primary nucleus ; ^2, secondary nucleus in process of formation ;
chr., chromidial ring ; o, aperture of the shell. After R. Hertwig (65).

is no evidence that chromatin, within or without the nucleus, can
ever arise de novo or in any way except from pre-existing chromatin,
the particles of which grow and multiply as the result of processes of
assimilation such as constitute the most essential characteristic
of the living substance generally.

There is no doubt, however, that chromatin may itself give rise
to other substances of achromatinic nature, and probably of simpler
constitution, by a process of breaking down of its complex sub-
stance ; and also that there may be present in the cell various
substances very similar to chromatin in their properties and charac-
teristics, representing stages in the building-up of the complex
material of the chromatin-substance. In one or the other of these
two ways it is possible to account for bodies in the cell known by
various names, such as " metachromatinic grains," " chromatoid

68 THE PROTOZOA

grains," and so forth — bodies which are often mistaken for true
chromatin, but which must be carefully distinguished from it, just
as metaplastic bodies are to be distinguished from protoplasm.
Among such bodies must be mentioned more especially the so-called
" volutin-grains,"* which have attracted much attention of recent
years, and which occur in various bacterial or unicellular organisms.
The volutin-grains resemble chromatin in showing affinities for
so-called " nuclear stains," which they hold more firmly than the
chromatin itself, when treated with reagents that extract the stain.
According to Reichenow (78), volutin is a nucleic acid combination
which is to be regarded as a special reserve-material for the forma-
tion of the nucleo-proteins of the chromatin-substance ; during
phases of the life-cycle in which the chromatin in the nucleus
increases in quantity, the volutin in the cytoplasm diminishes, and,
conversely, when the quantity of chromatin is stationary, the
volutin-grains increase in number. Volutin-grains are thus seen
to be bodies of totally different nature from chromidia, with which
they are often confused on account of their similar appearance and
staining reactions ; chromidia are formed, typically, as extrusions
from the nucleus into the cytoplasm ; volutin-grains, on the other
hand, are formed in the cytoplasm, and represent, as it were, a
food-substance which is absorbed by the nucleus in the growth and
formation of the chromatin. In some cases, however, the meta-
chromatinic grains may represent chromidial extrusions from the
nucleus which are breaking down or being modified into other
substances ; compare, for example, the extrusion of vegetative
chromidia, which degenerate into pigment, from the nucleus of
Actinosphcerium during a depression-period (p. 209).

The occurrence in the cell-body of volutin and other substances
which resemble chromatin very closely may often render extremely
difficult the task of identifying and distinguishing the true chro-
matin, especially when it is not concentrated into a definite nucleus,
but is scattered in the cytoplasm in the form of chromidial grains.
The test upon which reliance is most usually placed for the identi-
fication of chromatin is its staining properties, and especially its
readiness for combining with basic aniline dyes and certain other
colouring matters. But this test is extremely inadequate and un-
reliable ; on the one hand, as has been stated above, there are
substances, such as volutin, which are coloured by " nuclear "
stains more intensely than the true chromatin itself ; on the other
hand, in cellular organisms which possess true nuclei containing
undoubted chromatin, the staining reactions of the nuclei may be
strikingly different in different cases. A good example of each of

* The name " volutin " was coined by A. Meyer in 1904, and is derived from the
fact that the substance was first studied by him in Spirillum volutans.

THE NUCLEUS

69

these statements is furnished by the trypanosomes parasitic in
vertebrate blood : on the one hand, these parasites often contain
in their cytoplasm so-called " chromatoid grains," probably of the
nature of volutin (Swellengrebel , 514), which stain in a similar
manner to the nucleus ; on the other hand, the nuclei of the
parasites react to stains in a manner very different from the
nuclei of the blood-cells amongst which they live. In short, it
is not possible to name any stain or class of stains which can be
relied upon either to combine with chromatin alone, or to stain
chromatin in the same manner and to the same degree, at all times
and in all cases* (compare Fig. 33). When,

therefore, the adjectives " chromatinic " and ,'" ^^^

" achromatinic " are used in the course of / \

this work, it must be clearly understood
that these terms signify that the bodies or
substances to which they are applied con-
sist or do not consist, as the case may be,
of chromatin, and not that they stain or
do not stain with certain dyes.

As regards the chemical nature of chro-
matin, it is characterized by containing
protein-substances more complex in com- FIG. 33. — Diagram to repre-

position than any other part of the cell ; it s^nt in a graphic manner

... / -, ~ ., , , the action of colouring

is not possible to say definitely, however, matters that stain chro-

whether it is to be regarded as a single
chemical substance or as a combination or
mixture of several. Its most salient feature
is its variability ; judged by microchemical
tests, no two samples of chromatin can be
considered identical in composition, whether
from different cells or even from the same
cell at different times. Certain substances,
especially phosphorus-compounds, are espe-
cially characteristic of nucleo-proteins, but
it is not possible at the present time to
define or identify chromatin by its chemical
properties or composition.

All experience at the present time tends to show that the final
test for the identification of chromatin in the cell is its relation to
the vital activities and life-history of the organism. The term
"chromatin" is thus to be regarded as denoting a biological or
physiological, but not a chemico-physical, unity. A given body

* Methyl-green, acidulated with acetic acid, has sometimes been indicated as a
most distinctively nuclear stain ; but Hertwig (64) has shown that in the nuclei
of Actinosphcerium this stain colours the plastin-framcwork, and not the chro-
matin, and this author casts doubt on the alleged value of this stain as a reagent
for demonstrating ehromatin in the nucleus.

matin. The circle drawn
with an uninterrupted line
is supposed to represent
a theoretically perfect
chromatin - stain, which
would stain chromatin
always, and nothing else
but chromatin ; the circles
drawn with interrupted
lines represent the action
of chromatin stains actu-
ally ; they will stain chro-
matin as a general rule,
though not in variably, but
they will also stain other
things which are not chro-
matin.

70 THE PROTOZOA

or grain in the cell cannot be definitely identified as chromatin, in
all cases, by any chemical or physical test, but only by its relation
to the life and development of the organism as a whole, and more
especially to the function of reproduction and the phenomena of
sex, as will be shown more fully by means of concrete instances in
subsequent chapters. The sum of modern knowledge with regard
to the vital activities of living bodies and the life-histories of
organisms, whether plants or animals, Protozoa or Metazoa,
indicates that the chromatin exercises a regulative and determina-
tive influence over the functions and properties of the cell-body.
Direct experimental proof of the all-importance of the nucleus for
the life of the cell is obtained by cutting Protozoa into pieces, some
containing portions of the nucleus, others consisting of cytoplasm
alone (p. 210, infra). Those pieces that contain nuclear substance
are able to regenerate the lost parts of the body and to perform
all the functions of life, and in particular those of assimilation,
growth, and reproduction ; those, on the contrary, that contain no
portion of the nucleus rapidly lose the power of assimilation, and
are unable to regenerate the body, to grow or to reproduce ; and
though they remain for a time irritable and capable of movement,
they soon lose these properties. There are a number of facts which
indicate that in the physiological activities of the cell the chief
function of the nucleus is the formation of ferments ; it is therefore
all-important in regulating the assimilative processes of the living
substance (p. 194).

The conception of chromatin as the directive and regulative centre
of the cell-body renders intelligible a number of phenomena con-
nected with it, such as the elaborate mechanisms which, as will be
described in the next chapter, are gradually evolved and perfected
for the exact partition of the chromatin in the reproduction of
the cell by division, and the relation of chromatin to the
sexual process. Further, the extremely variable nature of the
chromatin-substance becomes at once intelligible on this view of
its relation to the specific characters and properties of the organism ;
for since every species of living being — perhaps, even, every in-
dividual of the same species — differs to a greater or less extent
from every other : then, if such differences are determined by the
chromatin, it follows that the chromatin must also differ to a
corresponding degree in each case, and that consequently uni-
formity of character in different samples of chromatin cannot be
expected to occur.

Hertwig (67, 92) considers that a certain quantitative relation of
nucleus and cytoplasm is necessary in any cell for the normal
continuance of the vital functions. This nucleo-cytoplasmic ratio
(" Kernplasma-Relation ") is subject to variations at different

THE NUCLEUS 71

periods of life-history, but is the same, normally, for corresponding
phases of the life of the cell ; it can be influenced by external con-
ditions, such as food and temperature, and also by internal factors,
undergoing changes in a regular manner, in harmony with changing
functional conditions of the cell. In cultures of a given species
at a lower temperature, multiplication is slower and the organisms
grow larger and possess larger nuclei ; with increase of temperature
the reverse takes place (compare p. 206, infra). It has also been
observed that, in long-continued cultures of Protozoa, periods of
active assimilation and multiplication arc followed by periods of
depression, during which assimilation and reproduction are at a
standstill, even in the midst of abundant nutriment (see especially
Calkins, 5). The depression-periods are characterized by an in-
crease of the nuclear substance relatively to the cytoplasm, a
" hyperchromasy " of the cell, which may lead to the death of the
individual unless compensated by the elimination and absorption
of part of the nuclear substance (p. 209, infra) ; when the balance
has been thus restored, the organism becomes normal and feeds
and multiplies again. From this conception of a definite relation
between the mass of the nucleus, or rather of the chromatin, and
that of the cytoplasm, Hertwig has deduced a number of important
consequences to which reference will be made in subsequent chapters.

The influence exerted by the chromatin upon the life of the
organism may be manifested in two ways, which may be termed,
for convenience, actual and prospective, respectively. In the first
case it regulates the metabolism and functions, both trophic and
kinetic, of the cell in which it is contained, and is then commonly
termed vegetative chromatin, or trophochromatin. In the second case
it may be dormant and inactive in the cell that contains it, remaining
latent, as it were, until carried on to future generations in the
course of cell-reproduction ; at a later period the whole or a part
of this latent chromatin may become active, determining the nature
and properties of the offspring, and thus serving as the vehicle for
hereditary transmission of the characters of antecedent generations.
Such temporarily dormant chromatin is commonly termed genera-
tive chromatin, or idiochromatin. It is probable that in all Protozoa
the cell-body contains chromatin both in the active and inactive
state, the one regulating the vital functions of the living body,
the other remaining dormant, in reserve for future generations.

The validity of this conception, according to which the chromatin
present in an organism is regarded as being either vegetative or
generative in function, must be tested by its capacity to account
for the facts of the development and life-cycle which will be con-
sidered more fully in subsequent chapters. There are no means
of recognizing and distinguishing vegetative and generative chro-

72 THE PROTOZOA

matin except by their respective relations to the life-cycle, at certain
periods of which, as will be seen, the nuclear apparatus is entirely
reconstituted, effete vegetative chromatin being eliminated from
the organism, either cast out or absorbed, and its place taken by
reserve generative chromatin. It is only necessary to remark that
some authorities speak of vegetative and generative chromatin as
if they were two distinct kinds of substance, whereas they are
probably to be considered rather as two phases or states of one and
the same chromatin. Vegetative chromatin is that which is in a
state of functional activity, and which thereby tends to become
exhausted and effete in its vital powers, exhibiting in consequence
the phenomena of " senility." Generative chromatin, on the con-
trary, by remaining inactive, conserves its " youth " unimpaired,
and constitutes a reserve from which the worn-out vegetative
chromatin can be replaced. Generative chromatin of one genera-
tion may become vegetative chromatin in the next.

As regards their distribution in the cell-body, in some cases
vegetative and generative chromatin cannot be distinguished by
the observer as separate structural elements, but are mixed up
together in the same nucleus ; in other cases, however, they occupy
distinct situations in the body. Thus, in Sarcodina it is common
for the vegetative chromatin to be lodged in the principal nucleus
or nuclei, while the generative chromatin occurs in the form of
chromidia, as in Arcella (Fig. 32), or vice versa. In the Infusoria
there are two kinds of nuclei, which are shown by their behaviour
to consist, the one of vegetative, the other of generative chromatin.
Chromidia, when present in the cell, may also differ in kind, being
in some cases extrusions from the nucleus of purely vegetative
chromatin, in process of elimination, while in other cases, as
already mentioned, the chromidia, or a part of them, represent
the generative chromatin (see p. 150, infra).

The nuclei of Protozoa exhibit great variety of structure and
form as compared with the relatively uniform structure of the
nuclei of Metazoa. As stated already, the constituent substances
or structural elements in any nucleus may be distinguished broadly
as chromatinic and achromatinic : the former consisting of the
chromatin, the primary and essential element never absent in any
nucleus ; the latter comprising various accessory structures, an-
cillary to the chromatin, and not all of them invariably present
in any given nucleus. Amongst the principal achromatinic con-
stituents of nuclei in general must be mentioned the following :
(1) linin, occurring in the form of a framework, which stains feebly
or not at all by chromatin-stains, and which presents the appear-
ance of a delicate reticulum or network, the optical expression of
an alveolar structure ; (2) a fluid enchylema or nuclear sap, filling

THE NUCLEUS

73

the interstices of the linin-framework ; (3) plastin, a substance
which has staining reactions different to those of chromatin, and
which occurs in lumps or masses forming the ground-substance of
the nucleoli or karyosomes presently to be described. The whole
nucleus is commonly enclosed in a membrane, but this structure is
probably formed in different ways in different cases, and may be
absent. In addition to these
various constituents, there are
commonly present also in con-
nection with nuclei bodies of
kinetic nature. Such are the
centrosomes or centrioles, which
appear to control, or at least
to act as centres for, the move-
ments which the various parts
of the nucleus perform during
the process of reproduction by
division.

The structure and appear-
ance of nuclei depend chiefly
on the manner in which the
chromatin is distributed. Two
principal types of structure may
be distinguished : in the first
the chromatin is concentrated
into a single mass or grain, or, if
other grains are present in the
nucleus, they are smaller and
relatively insignificant in size ;
in the second a number of
grains are present which are
more or less equal in size. In
the condition with a single,
or one greatly preponderating,
mass of chromatin, the nuclear
space is not as a rule filled by
it, but presents the appear-
ance of a vesicle containing
the chromatin-mass at or near its centre ; consequently such nuclei
are commonly termed " vesicular " in type, and the chromatinic
mass may be termed generally, and without further determination
of its precise nature, an endosome (" Binnenkorper "). When, on
the other hand, the chromatin is in the form of numerous grains,
they are generally distributed more or less evenly throughout the
nuclear cavity ; such nuclei are termed " granular."

resting nuclei of Trichosphcerium sieboldi.

A, Stage with finely-meshed chromatic
network and large karyosome (see p. 76) ;

B, the meshes of the network widening,
the karyosome budding off blocks of
chromatin into it ; C, the same process
carried farther ; D, coarse network con-
taining scanty chromatin at the nodes,
karyosome wanting ; E to G, the chro-
matin increases greatly in quantity,
covering the linin-framework — in G the
meshes of the network are becoming
finer ; H, the network has become fine-
meshed again ; /, a karyosome is being
formed by condensation of the chro-
matin at certain points, leading to the
condition of A again. After Schaudinn,

X 2,250.

74 THE PROTOZOA

Every transition from the one type of structure to the other may
be found in the nuclei of Protozoa ; in a vesicular nucleus the prin-
cipal mass of chromatin may break up into smaller grains which
become distributed throughout the nuclear cavity ; in a granular
nucleus some or all of the grains of chromatin may be clumped
together, and become fused to form a principal or single mass of
chromatin. Such changes may take place during successive periods
of activity of one and the same nucleus (Fig. 34). It is usual to
speak of the condition of the nucleus as " resting " when it is not
actually undergoing the process of reproduction by division ; but
it must be borne in mind that, so long as the cell is in a state of
physiological activity of any kind, the nucleus also shares in this
activity, and, strictly speaking, cannot be said to be resting. The
activity of the nucleus is expressed in continual changes in its
structure and rearrangements of its chromatin-substance and other
constituents. In the gregarine Porospora gigantea, Leger and
Duboscq (72) have observed changes taking place rhythmically in

o to to •

FIG. 35. — Successive stages of the karyosomo (see p. 76) of Porospora gigantea,
showing the transformation of a hollow into a homogeneous karyosome by
expulsion of a vacuole of clear viscous fluid into the nuclear cavity, where it
forms a little mass of chromatin in front of the micropyle. After Leger and
Duboscq (72).

the living condition (Fig. 35) ; compare also Chagas (48'5). Hert-
wig (64) has shown that the structure of the nucleus of Actino-
sphcerium can be correlated with the functional activities of the
cell. Thus a condition with the chromatin all concentrated to
form a central endosome is found prior to division of the nucleus,
and is also found when the animal is being starved ; on the other
hand, when it is supplied with abundant nutriment and is feeding
actively, the chromatin-grains spread over the whole nuclear space.
Since, however, abundant food also leads to frequent nuclear
division, the condition with the chromatin concentrated at the
centre also occurs during active cell-metabolism, as well as during
hunger-periods.

In the simplest condition of the nucleus the grain or grains of
chromatin are lodged in a space or vacuole, containing a clear fluid
or nuclear sap, but not enclosed by a definite membrane. Nuclei
of this simple type of structure are seen in some of the primitive
forms, such as the small amoebae of the Umax-type, in which the

THE NUCLEUS 75

nucleus consists of a large mass of chromatin suspended in the
nuclear sap. In some cases no other structural elements can be
made out ; in others the nuclear sap contains granules of peripheral
chromatin varying in size from the most minute and scarcely
visible particles to distinct grains. For a simple nucleus of this
type the term " protokaryon " has been proposed ; it is just such
a nucleus as may be imagined to have arisen by a concentration
of chromidiosomes at one spot in the cell-body, and in many cases
such nuclei can be seen to be formed actually in this manner. The
kinetonucleus of trypanosomes may be considered as a nucleus of
this type in which the single mass of dense chromatin fills almost
or quite completely the space in which it lies. In other cases there
may be a clump of chromatin-grains more or less equal in size,
filling the nuclear cavity, as in the nucleus of hsemogregarines.
When there are numerous grains of chromatin, those placed super-
ficially may be united to form a limiting layer which may be termed
a "false" or " chromatinic " membrane, in distinction to a true
nuclear membrane, which is an achromatinic structure. Even in
nuclei of the most simple type, however, substances or structures
accessory to the chromatin are probably always present.

In the first place, it is very probable that the grain or grams of
chromatin do not lie loosely and freely in the nuclear vacuole, but
are suspended in it, in all cases, by a delicate achromatinic frame-
work, presenting the appearance of a fine network or reticulum, at
the nodes of which the chromatin-grains are lodged. It is true that
in many of the minute and primitive forms no such framework has
been made out, and is believed by many observers to be absent ;
but on that view it is difficult to account for the definite position
of the chromatin, its changes of position during division, and the
frequent appearance, during this process, of an achromatinic spindle,
phenomena that may be noted even in the simplest cases. The
achromatinic framework is often very fine and delicate, and its
substance stains feebly or not at all with the colouring matters
commonly employed in microscopical technique ; hence it is very
probable that it has often been overlooked in cases where it is
really present. When there is but a single mass of chromatin, or
one grain very much larger than all the others, the achromatinic
reticulum presents the appearance of very delicate threads of
linin radiating from the principal mass of chromatin to the
periphery. When, on the other hand, there are numerous grains
more or less equal in size, the reticulum is seen as fine lines passing
from each grain of chromatin to each of the grains adjacent to it.
In all probability the apparent " threads " of the reticulum are but
the optical expression of the walls or partitions separating alveoli,
and there is no reason for considering the achromatinic reticulum or

76 THE PROTOZOA

linin framework as different in any essential point from the
alveolar framework of the general protoplasm, with which, in nuclei
that lack a true membrane, it is perfectly continuous. Hertwig (66)
regards the cytoplasmic framework as achromatinic substance in
intimate combination with chromatin ; the nuclear framework, on
the other hand, as pure achromatinic substance (linin) from which
the chromatin has become separated out and organized into special
structures, independent of the framework in which they are lodged.
Similarly, the nuclear sap filling the nuclear space and the inter-
stices of the reticulum must be identified with the enchylema of
the body-protoplasm. As compared with the alveolar structure
of the general protoplasm, that of the achromatinic nuclear frame-
work is characterized chiefly by the larger size of the alveoli, and,
consequently, the greater distinctness of the apparent reticular
structure.

A true nuclear membrane, when present, is probably formed in
all cases from the achromatinic framework. In the nuclei of Actino-
sphcerium, according to Hertwig (64), the membrane is a super-
ficial condensation of the achromatinic reticulum. The membrane
may attain to a considerable thickness and appear doubly-con-
toured in optical section, separating the nuclear framework com-
pletely from the extranuclear protoplasm ; but it is always a structure
very readily absorbed and re-formed, and it appears to present
no obstacle to the passage of substance from the nucleus into the
cytoplasm, or vice versa. Awerinzew (47), on the other hand,
regards the nuclear membrane as a product of the cytoplasm.

In addition to the achromatinic framework, plastin is commonly, if
not invariably, present in the form of masses or bodies which receive
different names, according as they consist of pure plastin or of
plastin impregnated to a greater or less extent with chromatin.
In the vesicular type of nucleus, the endosome may perhaps consist,
in some cases, of pure chromatin, but in most cases, if not always,
it is composed of a matrix or ground-substance of plastin in which
the chromatin is lodged. An endosome of this kind is termed a
karyosome, or chromatin-nucleolus ; as a rule it has the form of a
rounded mass, occupying the centre of the nucleus, sometimes of
more than one such mass, but in a few cases it may have the form
of a crescent or cap (" calotte ") closely applied to the nuclear mem-
brane. In the granular type of nucleus, on the other hand, there
may be one or more masses of pure plastin containing no chromatin ;
such a body is termed a nucleolus simply, or a " plastin-nucleolus."
In the nuclei of the tissue-cells of Metazoa, true nucleoli occur
almost invariably ; in the nuclei of Protozoa, however, pure plastin-
nucleoli are not of common occurrence, but have been described
in a few instances — for example, in the haemogregarine-nucleus

THE NUCLEUS 77

(Reichenow, 78). As a general rule in the Protozoa, the plastin-sub-
stance is found as the matrix of karyosomes, but also as that of
other masses of chromatin, such as the chromosomes of the dividing
nucleus (see next chapter). Goldschmidt (41) observed that the
formation of generative chromidia in Mastigella (p. 265) was pre-
ceded by the extrusion of plastin from the nucleus into the cyto-
plasm, to serve as a matrix for the chromatin which passed out
from the nucleus subsequently. In Actinosphcerium, Hertwig has
shown that a karyosome or chromatin-nucleolus, present during
certain states or phases of nuclear activity, may give oft its chro •
matin-substance into the nuclear framework (re ticulum), leaving the
plastin-matrix as a body which is then seen to consist of a reticular
framework similar in structure to the achromatinic reticulum of the
nuclear framework, but distinguished from it by smaller meshes
(alveoli) enclosed by thicker walls, as well as by its different staining
properties. Certain phases of the development of Actinosphcerium
are further characterized by the formation in the nucleus of
numerous small plastin-nucleoli, each consisting of a single vesicle
(alveolus) of plastin containing nuclear sap.

Thus, a nucleus in its full compfication of structure, and apart
from the centrosomic elements, to be discussed presently, consists
of the following parts : (1) An achromatinic framework or nuclear
reticulum ; (2) a true membrane, formed from the achromatinic
framework, and separating the nuclear contents from the surround-
ing cytoplasm ; (3) nuclear sap, pervading the entire nuclear cavity ;
(4) plastin, in the form of one or more bodies or masses which may
consist either of pure plastin (nucleoli) or of plastin impregnated
with chromatin (karyosomes) ; and (5) the chromatin, which may
be present either in the form of granules lodged at the nodal points
of the reticulum, and scattered evenly or unevenly throughout the
nuclear framework, or may be concentrated in a karyosome, or
may combine both these two modes of distribution in various ways.
Achromatinic framework and nuclear sap may be considered as a
part of the general body-protoplasm, enclosed within the nuclear
space, and set apart from the cytoplasm as a special nucleoplasm ;
plastin, on the other hand, is probably to be regarded as a product
derived from the chromatin itself, either as a secretion or as a
modification of its substance, to form a cement-like material or
matrix in which true chromatin is carried. The two primary con-
stituents of a nucleus are chromatin and protoplasmic framework.

Nuclei, whatever their structure, are, as a general rule, bodies of
spherical or ovoid form ; but in some cases, especially amongst
Infusoria, the nuclei exhibit very varied forms in different species.
The nucleus may then be sausage-shaped, or in the form of a horse-
shoe, or resemble a string of beads (" moniliform "), or be branched

78 THE PROTOZOA

in a complicated manner. In the remarkable Acinetan Dendrosoma
radians a colony is formed by budding, which resembles super-
ficially a hydroid colony, each hydranth being represented by the
head of an Acinetan individual with suctorial tentacles ; the
branched nucleus is continuous throughout the whole colony, pass-
ing uninterruptedly from one individual to another.

Typically the cell-body contains a single nucleus, but in many
Protozoa two or more nuclei occur constantly. When there are
more nuclei than one, they may be all alike
and quite undifferentiated, or they may show
differences in size, structure, and function.
In many Sarcodina multiple nuclei without
differentiation are found to occur constantly
in certain species ; for instance, two in Amoeba
binudeata and Arcella ; several, perhaps a
dozen or so, in Difflugia (Fig. 16) ; from
twenty to forty up to some five hundred in
Actinosphcerium (Fig. 3) ; so also in Pelomyxa ;
and in the large plasmodia of Mycetozoa many
thousands of nuclei are found.

Differentiation of nuclei, when it occurs,
may be related to various causes. In trypano-
FIG. 36. — Trypano- somes and allied forms two nuclei occur con-
fronTthe btood^fthfi stantty — a principal nucleus, or trophonucleus,
pike (Esox Indus), so called because it appears to regulate the

a.fl., Anterior flagel- general metabolism and trophic activities of
mm; n, kmetonu- 7, ,, , , , 7 . . , , . , .

cleus ; N, trophonu- tne cell-body ; and a kinetonudeus , which is in
cleus -,p.ft., posterior special relation to the organs of movement,
edffoTthcT u±la! fl»g«ll». «>* undulating membrane. As a rule
ting membrane, and the kinetonudeus is smaller, in some cases very

ara^ver d sbhTtn?ree minute' and has a dense compact structure,
flagellum posteriorly, while the trophonucleus has a vesicular struc-
After Minchin (478), ture ; but in other cases (Trypanoplasma) the

kinetonudeus is the larger of the two (Fig. 36).
A nuclear differentiation of totally opposite character is seen
in the Infusoria, where two nuclei of different sizes, hence termed
" macronucleus " and " micronucleus," are constantly present ; the
behaviour of these two nuclei in relation to sexual phenomena and
reproduction (vide, p. 153, infra) shows that the macronucleus is
composed of vegetative chromatin, while the micronucleus contains
the reserve generative chromatin. In some cases — for example, in
Myxosporidia (p. 403) — nuclei of different sizes occur in relation to
sexual differences.

In some Protozoa — the so-called " Monera " of Haeckel — the
nucleus has been stated to be wanting entirely ; but this statement

THE NUCLEUS 79

is probably based on incomplete or erroneous observation, or on
defective technique. In all Protozoa that have been examined in
recent times, at least one nucleus has been found to occur without
exception, though in some phases of the development the nucleus
may temporarily disappear and resolve itself into chromidia.

There now remains for consideration the question of the centro-
some, the centre of the kinetic activity of the nucleus. Of all the
questions connected with the nuclear apparatus, those relating to
the centrosome are the most difficult to handle in a genera] manner,
largely on account of the minuteness of the bodies dealt with, and
the consequent difficulty of ascertaining their structure and com-
position, even their presence, in many cases. Hence, in the litera-
ture of the centrosome, there is found considerable confusion in
the terminology, different authors disagreeing entirely as to the
precise structures to which the name centrosome should be applied,
and opposed theories, which cannot be discussed adequately in a
short space, have been put forward as to the nature and origin of
the centrosome.

As the focus of the kinetic activities of the nucleus, the centro-
some is most apparent and recognizable when the nucleus is in
process of reproduction by division, and much Jess so when the
nucleus is in the so-called "resting state." Hence the study of the
nucleus during the process of division is alone decisive as to the
presence of a centrosome in any given case ; and since in many
cases nuclear division appears to go on without centrosomes being
present, it may be taken as equally probable that, in all such cases
at least, no centrosome is present in the resting state of the nucleus.
In many cases, however, the presence of a centrosome in, or in
connection with, the resting nucleus can be ascertained clearly ;
it may then lie either outside or inside the nucleus.

When the centrosome lies outside the nucleus, as it usually does
in the cells of Metazoa, it is found typically as a minute grain or
pair of grains (" diplosome ") close beside the nuclear membrane.
Its presence may be indicated by the radiate structure of the
surrounding protoplasm, giving the appearance of a system of rays
centred on the centrosome ; but such radiations are absent as a
rule during the resting state of the nucleus, and the appearance of
rays is often the first sign of impending activity and division of
the nucleus. In many cases the centrosome is found lying in a
mass of clear protoplasm termed archoplasm, a substance which
differs, apparently, from the rest of the cytoplasm only in being
free from granulations of all kinds. Archoplasm may, in short, be
regarded simply as pure cytoplasm, and it appears either perfectly
homogeneous, or traversed by striations which radiate from the
centrosome, through the archoplasm, and even beyond its limits;

80 THE PROTOZOA

the striations themselves being the optical expression of a radiate
arrangement of the protoplasmic alveoli (meshes of the " retic-
ulum "), indicating lines of force or tension centred in the centro-
some. In some cases it is probable that archoplasm showing
radiate striations may be present without any centres o me. In
Actinosphcerium Hertwig showed that rays were formed in the
archoplasm before a centrosome had been formed, and heralded its
appearance.

When the centrosome lies within the nucleus, it is found most
frequently, in Protozoa, within a plastin-body or karyosome, a
position which it may retain permanently during both the resting
and dividing conditions of the nucleus. The simple nuclei of
the protokaryon-type probably contain in most cases a centro-
somic grain lodged in the karyosome. In a few cases, however,
an intranuclear centrosome occurs without a karyosome, or outside
the karyosome if one is present. On the other hand, there are
many examples of the occurrence of extranuclear centrosomes in
Protozoa ; but these are for the most part cases in which the centro-
some is in relation, not only to the kinetic functions of the nucleus,
but also to those of other cell-organs, as will be described presently.
Nuclei containing centrosomes have been termed " centronuclei "
by Boveri.

The centrosome is seen, as a general rule, under the form of a
minute grain, or centriole. This is the form in which it occurs
invariably when it has an intranuclear position, lodged within the
karyosome. But when it occurs outside the nucleus, it exhibits
structural peculiarities which may vary at different periods, and
it often presents cyclical changes corresponding to different phases
of the activity of the nucleus. Thus, in Actinosphcerium, Hertwig
(64) describes the centrosome at its first appearance as a relatively
large body of spongy structure, formed at one pole of the nucleus from
extruded portions of the achromatinic reticulum (Fig. 37, A — E).
At this stage, in which the centrosome is termed a centrosphere, it
lies in a patch of archoplasm, and is the centre of a well-marked
system of radiations. The centrosphere then gives rise, by con-
densation of its substance, to two centrioles, or to one which divides,
and at the same time the archoplasmic radiations become fainter
and disappear (Fig. 37, -F, G). The centrioles then take part in
the division of the nucleus, and when this process is complete they
again become spongy centrospheres, which go through the same
series of successive changes that have already been described. Ana-
logous cyclical changes of the centrosome have also been described
in other cases, and have led to a conflict of opinion as to whether
the term " centrosome " should be applied to the whole centrosomic
complex, as it may be termed, or to the centrioles, of which many

THE NUCLEUS

81

may be present. It is simplest in theory, and probably correct in
fact, to regard the centriole as the primary, in many cases the sole,
constituent of the centrosome — an element which may be capable,
to a greater or less extent, of changes in size and structure, and
which multiplies by division. To the primary centrosome or

^mm^

QV \&t*^&-^fa

£iJKim&<
feJiSiiij^^x

£*
W

.

^•gfiiSSi^^

ai^miir

1

J^&:&^"

FIG. 37. — Actinosphcerium eichhorni: formation of the centrosome. A, Concentra-
tion of the nuclear reticulum towards one pole of the nucleus, near which
the cytoplasm appears free from granulations, forming the archoplasm ;
B, G, D, passage of a portion of the nuclear reticulum to the exterior to form
the " spongy centrosome " lying in the archoplasm ; E, spongy centrosome
with striations passing from it through the archoplasm to the nucleus ;
F, G, the centrosome passes back again to the vicinity of the nucleus and
undergoes a reduction of substance — the archoplasm also diminishes tem-
porarily in quantity ; H, division of the centrosome. After Hertwig (64).

centriole there may be added adventitious elements of protoplasmic
or nuclear origin, thus forming a centrosomic complex which may
attain a size relatively considerable in some cases.

So far the centrosome has been discussed only in its relation to

6

82

THE PROTOZOA

the kinetic activities of the nucleus, a function which may be re-
garded as its primary and most characteristic role. It may act
also, however, as the centre of other kinetic functions of the cell-
body, especially in relation to motile organs such as flagella ; it
then appears as the so-called " basal granule," from which the
flagella take origin. The basal granule appears as a thickening
at the base of the flagellum. It may be continued farther into
the cytoplasm, or connected with the nucleus, by means of one

or more root-like processes known
as the rhizoplast. A centrosome
which is in relation to a motor
cell-organ is termed generally a
blepharoplast. The rhizoplast may
have various origins ; in some cases
it represents the centrodesmose
(p. 103) which connects the bleph-
aroplast with the nuclear centro-
some, or the remains of such a
connection ; in other cases it repre-
sents the remains of the nuclear
spindle of the previous nuclear
division, as in the swarm-spores of
Stemonitis flaccida (Jahn, 69) and

FIG. 38. — Mastigina setosa, after Gold-
schmidt (41). n., Nucleus from which
the long flagellum arises ; the body
is full of diatoms and other food-
bodies. The surface of the body has a
covering of short bristle-like processes.

ABC

FIG. 39. — Connection of the flagellum
and the nucleus in Mastigina setosa.
A and B, As seen in the living
state ; C, after fixation and staining.
After Goldschmidt (41).

the collar-cells of Heteroccela (Robertson, 79) ; while in some
instances it may be formed by outgrowth of root-like processes,
of no special cytological significance, from the blepharoplast.

The relation of the nuclear to the kinetic apparatus is best
studied in the Flagellata, where three principal conditions may be
distinguished as follows :

1. The cell-body contains but a single centrosome, which functions
also as a blepharoplast ; these two names, then, denote two different
phases of activity of one and the same body, which is a centro-

THE NUCLEUS

83

-s n.

some when it is active in relation to the division of the nucleus,

and a blepharoplast when it is in connection with flagella or other

motile organs during the resting state of the nucleus. In this,

probably the most primitive state of things, there are, further, two

different structural conditions found to occur in different cases.

First, the centrosome- blepharoplast maybe within, or closely

attached to, the nucleus ; secondly, it may be quite independent

of the nucleus, and some

distance from it in the cell-

body, during the resting

state of the nucleus. In

the first case — of which an

example is seen in Mastigina

(Figs. 38, 39), paralleled by

collar - cells in the Leuco-

soleniid type of calcareous

sponges — the flagellum ap-

pears to arise directly from

the nucleus ; in the second

case, exemplified by Mas-

ligella (Fig. 40), and by

collar-cells of the Clathrinid

type, the flagellum takes

origin quite independently

of the resting nucleus. In

both cases alike, the flagel-

lum generally disappears

before division of the nucleus

begins; the blepharoplast

becomes the centrosome,

divides, and initiates the

division of the nucleus ; the

new flagella of the daughter-

cells grow out from the two

daughter - centrosomes dur-

ing or after division of the

nucleus, and in either case,

when the two daughter-cells are completely formed, their centro-

somes, as blepharoplasts, remain as the basal granules from which

the flagella arise.

2. The cell-body contains more than one body of centrosomic
nature — namely, a definitive centrosome, in relation to the single
nucleus, and, in addition to this, one or more blepharoplasts in
relation to motile organs. Then, when division of the cell takes
place, one of two things may happen.

Flo ^_Mastigdla vitrea, after
Goldschmidt (41). n, Nucleus,

the cytoplasm.

84

THE PROTOZOA

In the first place, the flagellum or flagella may disappear, together
with their blepharoplasts ; the nuclear centrosome divides into
two, which control the division of the nucleus in the usual way, and
the centrosome of each daughter-nucleus divides again into two,
one of which is the definitive centrosome, the other the blepharo-
plast, of the daughter-cell. The new flagella may either grow out
from the daughter-centrosomes before they divide, and be carried
off, as it were, by the product of division which becomes the

FIG. 41. — Stages in the division of Spongomonas splendida, to show different ways
in which the daughter-flagella arise. Compare the stages of S. uvella (Fig. 42).
A, Resting condition of the cell. B, Early stage of mitosis; the two flagella
of the parent cell are in process of absorption, together with their blepharo-
plasts. C, Daughter-flagella arising at the poles of the nuclear spindle ; the
flagella of the parent have disappeared. D, Nucleus completely divided ;
one pair of daughter-flagella are seen arising from the karyosome of a daughter-
nucleus, in which the blepharoplasts are still enclosed ; in the other daughter-
nucleus the blepharoplasts have become distinct and the flagella are given
off from them. E, Similar stage ; the two pairs of blepharoplasts, from which
the flagella arise, are quite independent of the two daughter-nuclei. After
Hartmann and Chagas (62), magnification about 2,400 diameters.

blepharoplast (Fig. 41, O, Z>, E ; Fig. 42, C), or they may not arise
from the blepharoplasts until a later period, after they have
separated off from the definitive centrosomes (Fig. 42, D, E, F).
The examples figured show that these differences in the origin of
the flagella may occur as developmental variations in one and the
same species.

In the second place, the blepharoplasts and flagella may persist
throughout the division of the cell ; then either the old flagellum
and blepharoplast are retained by one daughter-cell, while the other

THE NUCLEUS

85

forms a new blepharoplast from its centrosome, and subsequently
a new flagellum ; or the blepharoplast of the parent cell divides
independently to form the blepharoplasts of the daughter-cells
(Fig. 43). In this last type, the blepharoplast, though obviously
a body of centrosomic nature, acquires a more or less complete
independence of the definitive centrosome, and becomes a distinct
cell-organ, permanent for at least a certain number of cell-genera-
tions ; it may multiply and undergo various structural complica-
tions, to be described presently.

FIG. 42. — Stages in the division of Spongomonas uvella. A, Resting condition of
the cell ; two flagella arise, each from one of a pair of blepharoplasts (diplo-
some) ; the nucleus contains a large karyosome, in which the centriole is
lodged, and a few irregular grains of peripheral chro matin in the nuclear cavity.
B, Early stage of mitosis ; an achromatinic spindle is formed with the centrioles
at the poles, one centriole (on the right) having already divided into two ;
the chromatin, both peripheral and central, has united to form a dense
equatorial plate in which separate chromosomes cannot be discerned ; the
flagella have disappeared, together with their blepharoplasts. C, Similar
stage in which the daughter-flagella are growing out precociously from the
centrioles, one on the left, two on the right. D, Later stage in which the
equatorial plate has split into two daughter-plates, but no flagella have as
yet grown out from the centrioles, of which there are two at each pole. E,
Division of the nucleus nearly complete ; no flagella. F, Nucleus completely
divided, daughter-nuclei in process of reconstruction ; from each a pair of
blepharoplasts has been budded off, still connected by a centrodesmose with
the centriole contained in the karyosome ; a pair of daughter-flagella has
arisen from one pair of blepharoplasts, but not as yet from the other. After
Hartmann and Chagas (62), magnification about 2,400.

3. In certain flagellates- — for example, trypanosomes and allied
forms (" Binucleata ") — the cell-body contains two nuclei, as already
noted : a trophonucleus and a kinetonucleus. To what extent
these nuclei are provided with centrosomes is at present a little
doubtful ; probably this point is one which varies in different cases
(compare Wenyon, 84). There are, however, three chief possi-
bilities : (a) There may be but a single centrosome, that of the
kinetonucleus, which acts both as blepharoplast and division-centre

FIG. 43. — Stages in the division of PdLyiomdla agttis. A, Resting condition of the
cell ; the four flagella arise from four blepharoplasts which are connected
by a rhizoplast with the nucleus ; in the nucleus is seen a large karyosome,
which contains the centriole and is surrounded by a peripheral zone of
chromatin-grains in a nuclear reticulum. B, Early stage of mitosis ; the karyo-
some is dividing to form a bar of chromatin occupying the axis of the achro-
matinic spindle, at the equator of which a plate of chromosomes is formed
by the peripheral chromatin of the last stage. C, Later stage ; the karyosome
has divided completely, forming two masses at the poles of the spindle con-
nected by a centrodesmose. D, The spindle has become elongated, and the
equatorial plate has split ; the centrioles are seen connected by the centro-
desmose. E, Division advancing ; the polar masses have become cap-shaped,
and the daughter-plates of chromosomes have fused into conical masses ;
centrioles and centrodesmose still visible. F, Division of body beginning.
G, Centrodesmose broken through, the two daughter-nuclei separate. H, I, J ,
Division of cell complete, one daughter-cell only represented, to show the
reconstitution of the daughter-nucleus ; the polar cap becomes the karyosome,
enclosing the centriole ; the conical mass formed in Stage E by fusion of the
chromosomes in the daughter-plates becomes resolved gradually into
chromatin-grains again, and so forms the peripheral zone of the daughter-
nucleus ; each daughter-cell has two of the four blepharoplasts and flagella
of the parent, and the number is doubtless made up to four again by division
after the daughter-cells are set free. After Aragao (45).

THE NUCLEUS 87

for the cell ; then, when cell-division takes place, the kinetonucleus
first divides, and the two products of its division place themselves
on each side of the trophonucleus and act as its centrosomes, as
described by Franca and Athias (56)* ; (b) the trophonucleus may
have a centrosome of its own, lodged in the karyosome, in addition
to the centrosome-blepharoplast in connection with the kineto-
nucleus ; this is. probably the most usual condition with two sub-
ordinate variations, according as the centrosome-blepharoplast is
lodged within the kinetonucleus, as in Leishmania tropica (Wenyon,
84), or is situated close beside it, as in most trypanosomes ; in either
case the kinetonucleus and trophonucleus divide quite independently
of one another, as commonly seen ; (c) it is possible, but perhaps
not very probable, that in some cases there may be a blepharoplast
for the flagellum distinct from the centrosomes of the two nuclei ;
such a condition, perhaps, occurs in Trypanoplasma. In all cases
alike, division is initiated by the centrosome from which the
flagellum arises; next the kinetonucleus, and lastly the tropho-
nucleus, divide.

The various forms of flagellar insertion described in the foregoing para-
graphs admit of a simple and uniform phylogenetic explanation. Starting
with a non-flagellated organism in which a simple protokaryon contains a
single centriole (Fig. 44, Oa), we may suppose the flagellum at its first origin
to grow out from the centriole in the nucleus (0b). No such condition is
actually known amongst flagellates, though it may be compared to the origin
of the axopodia from a central grain in an Actinophrys-type of Heliozoon
(see below) ; in the flagellates the centrosome-blepharoplast always, ap-
parently, moves out of the nucleus, either remaining in close proximity to it
(la) or becoming quite independent of it (lb), the two variations of the first
type.

The second type may be derived by division of the centrosome-blepharo-
plast to form the definitive centriole and the blepharoplast ; the latter may
also remain in close proximity to the nucleus (2a) or become quite independent
of it (2b).

The third type may be supposed to arise from the hypothetical primitive
condition (On) by supposing that, not the blepharoplast -centrosome alone,
but the whole nucleus, divides to form two nuclei of unequal size and distinct
function, the trophonucleus and kinetonucleus, each with its own centriole
(3a, 3b). The centriole of the kinetonucleus, which is at the same time the
blepharoplast, may either remain within the kinetonucleus (3b) or come out
of it (3C) ; its relations to the kinetonucleus are parallel to those of the centro-
some-blepharoplast to the nucleus in types la and lb. Or, on the other hand,
the centrosome-blepharoplast may divide into a definitive kinetonuclear
centrosome and a true blepharoplast (3e). The condition with only a single
centriole for both the nuclei may, if it exists, be derived from 3a or 3h by
supposing that the trophonuclear centrosome becomes atrophied.

When a blepharoplast exists independently of the nuclear
apparatus, it may retain the form of a single grain or basal granule
of the flagellum, when this organ is single, or it may multiply to

* The statements of Franca and Athias are not, however, confirmed by Lebedeff
(468), and it may be doubted whether any species of trypanosomc or other ",b:nu-
cleate " exists which has but a single division-centre in the cell.

88

THE PROTOZOA

form two or more grains when there are numerous flagella. Thus,
in Lophomonas, which shows the extreme of complication, there are
numerous basal granules corresponding to the tuft of flagella
(Fig. 45). Each basal granule in this case is divided into a proximal

FIG. 44. — Diagrammatic representation of the possible phylogenetic origin of the
different types of flagellar attachment in flagellates. For the sake of sim-
plicity it is supposed that the animal has but a single flagellum. 0:i, Non-
flagellated cell with a centriole in the nucleus ; Ob, in a cell like the last a
flagellum arises from the centriole ; la, condition with a flagellum arising
close beside the nucleus ; lb, condition with the blepharoplast quite separate
from the nucleus ; 2a, division of the single centriole into a definitive centro-
some and a blepharoplast, which becomes quite independent (2h) of the
nucleus ; 3a, division of both nucleus and centriole to form distinct kinetic
and trophic nuclei, each with its own centriole ; 3b, the kinetonuclear centriole
remains within the nucleus ; 3C, the kinetonuclear centriole becomes distinct
from the nucleus ; 3d, condition with a single centriole in the cell ; 3C, condition
with a blepharoplast distinct from the centrioles of the two nuclei.

and a distal granule, and the pairs of granules are arranged in a
ring, interrupted at one point ; the tuft of flagelJa takes origin from
the distal granules of the ring. When the nucleus divides, the
daughter-centrosomes give rise to new rings of blepharoplasts,

THE NUCLEUS

from which daughter-tufts of flagella grow out ; the old tufts, with
their rings of blepharoplasts, persist for some time after the new
ones have been formed (Fig. 45, C), but ultimately they degenerate
and disappear. The ring of blepharoplasts in Lophomonas is

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supported on the edge of a membranous structure, or " calyx/'
which in its turn is surrounded by a peculiar striated body, the
" collar " of Grassi, or " parabasal apparatus " of Janicki (Fig. 45,
d.}. Janicki (71) has found a corresponding parabasal apparatus
in other flagellates, especially in Trichonymphidce ; the significance

90

THE PROTOZOA

of this peculiar structure remains for the present problematical.
In the spores of Derbesia, Davis (" Annals of Botany," xxii.,
pp. 1-20, plates i. and ii.) has described a condition very similar
to that of Lophomonas — namely, a double ring of blepharoplasts,
which, however, fuse together to form a ring of homogeneous
appearance. The blepharoplast-grains are given off from the
nucleus.

Centrosomic bodies may be related, not only to flagella, but also
to pseudopodia, especially in those cases in which the pseudopodia

FIG. 4G. — Actinophrys sol, showing the axial filaments of the pseudopodia centred
on the nucleus. N, Nucleus ; ps., pseudopodia ; ax., axial filament ; c.v.,
contractile vacuole ; f.v., food-vacuole. After Grenacher.

have become specialized in form and movement, as in the Heliozoa.
In this group the relationship of the nuclear apparatus to the
pseudopodia exhibits two types of arrangement, which are analo-
gous to the two arrangements described above in Mastigina and
Mastigella respectively, and which may be explained by supposing
that in the one case the kinetic centre lies within, in the other case
without, the nucleus itself. Thus, in Actinophrys (Fig. 46) the
numerous pseudopodia are all centred on the single nucleus, in
which the centrosome is contained. A variation of this type is
described by Schaudinn (43), in the peculiar multinucleate form

THE NUCLEUS

91

Camptonema nutans, in which a pseudopodium arises directly from
each nucleus (Fig. 47).* In Acanthocystis (Fig. 18) an example
is seen of the second type, the evolution of which can be traced
in the actual development ; in the buds of Acanthocystis a centriole
is contained in the karyosome of the nucleus, but during the growth

of the bud into the adult condition the centriole passes out of the
nucleus, and becomes the so-called " central grain " of the adult,
a corpuscle which occupies the centre of the body, and upon which

* In Aclinosphcerium, however, there is no relationship between the pseudopodia
and the nuclei. From the researches of Hertwig (64), it is evident that in this
form the centrosomes are lost altogether during the vegetative life, and are formed
only in certain phases of the development (p. 115).

92 THE PROTOZOA

the axial filaments of the pseudopodia are centred, while the nucleus
is displaced to one side and becomes excentric in position ; when
the cell enters upon division, the central grain becomes the centre -
some (Fig. 64).

From the condition seen in Acanihocystis, it is not difficult to explain the
state of things which has been described by Zuelzer (86) in the remarkable
form Wagner ella (p. 246). Here also the buds formed possess each a single
nucleus containing a centriole ; in this condition they may multiply by fission
with mitosis, in which the centriole functions as a centrosome. When the
buds develop into the adult form, a centriole is extruded from the nucleus
to form the central grain. The organism attaches itself, and the body becomes
divided into three regions — head, stalk, and basal plate (Fig. 48). The
nucleus travels down into the basal plate, while the central grain remains
in the head and functions as the kinetic centre of the pseudopodia, becoming
very complicated in structure. It consists of a centrosome surrounded by a
sphere, which is perhaps of the nature of archoplasm, but is stated to be
rich in plastin ; when tho pseudopodia are extended the sphere shows well-
marked radial striations. From the centrosome minute granules are budded
off. which pass along the striations of the sphere to its surface, and from these
granules arise the delicate axial filaments of the pseudopodia ; the basal
granules are therefore comparable to the ring of blepharoplasts in Lophomonas.
When the pseudopodia are retracted, the basal granules lie within the sphere,
immediately surrounding the centrosome, and the radial striations of tho
sphere vanish. The centrosome itself varies in structure at different times,
going through cyclical changes, but usually shows a distinct central granule or
centriole.

When Wagneretta divides by fission, the central grain and the nucleus
divide independently, and the central grain does not act as a centrosome
for tho dividing nucleus, which contains its own centriole. In this form,
therefore, the central grain, though centrosomic in origin and nature, loses
its primitive relation to the division of the nucleus, and becomes specialized
exclusively as a kinetic centre for the organs of locomotion, a course of evolu-
tion perfectly parallel to that which has been traced above for the blepharo-
plasts in their relation to flagella.

While there can be but little doubt as to the centrosomic nature
of the blepharoplasts or basal granules of the flagella, and of the
central grains on which the pseudopodia of the Heliozoa are centred,
the true nature of the basal grains of cilia, on the other hand, is
less certain. The majority of those who have studied them in
Ciliata are of opinion that they have nothing to do with centro-
somes (compare Maier, 73, and Schuberg, 44, and see p. 443, infra) ;
but there are certain observations which indicate that the basal
granules of the cilia have a connection with (Collin, 50), or an
origin from (Entz, 53), the nuclear apparatus, in which case they
may be of the same nature as the multiple blepharoplasts of such
a form as Lophomonas. Hertwig (66) considers that the basal
grains of the cilia may be of centrosomic nature, and that, if they
have no connection with the nucleus, they afford support for the
view that centrosomes can arise from the cytoplasm as well as
from the nuclear framework. In view of the great structural
similarity between cilia and flagella in other respects, it seems

THE NUCLEUS

93

hardly likely that the basal granules would be of a different nature
in the two cases. The whole question of the nature of the basal
granules has been discussed in a recent memoir by Erhard (54).

FIG. 48. — Wagnerella borealis, Mereschk. A, Whole specimen
seen under a low magnification: H., head containing
the central grain ; P, stalk ; N., nucleus contained in
the basal plate of attachment. B, Enlarged view of
the head, after fixation and staining with iron-haema-
toxylin : c., cuticle of the stalk ; ps., pseudopodia ;
ax., axial filaments of the pseudopodia, each arising
from a basal granule ; e.g., central grain. After
Zuelzer (86).

Few problems in cytology have been more discussed than the
question of the nature and origin of the centrosome, and three
opposed views have been put forward which may be termed, re-
spectively, the achromatinic theory, the nucleolo - centrosomic
theory, and the nuclear theory.

94

THE PROTOZOA

According to the achromatinic theory, the centrosome is "an
individualized portion of the achromatinic nuclear substance "
(Hertwig, 66), a kinetic centre on which the movements of the
framework are focussed. The essential and primary constituent
of the centrosome is the centriole, and so long as the centrosome
remains intranuclear, as in perhaps the majority of Protozoa, it
consists of the centriole alone. When, however, the centrosome
becomes extranuclear, as in many Protozoa and almost universally

H

FIG. 49. — Paramceba etthardi : stages of the life-cycle. A, Amoeba in the vegetative
stage: N., nucleus; n.L, " Nebenkern " ; d., ingested diatom. B, G, D,
Stages in the multiplication of the encysted amoeba ; in B the Nebenkern
has divided up, the nucleus is still undivided ; in G the nucleus has divided
up into a number of daughter-nuclei, each of which has paired with a daughter-
Nebenkern ; in D the body has divided into a number of daughter-cells, each
containing a nucleus and a Nebenkern. E, A free-swimming flagellula, derived
from one of the daughter-cells in D, and containing a nucleus and a Nebenkern.
F, G, H, I, Four stages of the division of a flagellula ; in F the Nebenkern is
dividing ; in G the two halves of the Nebenkern have placed themselves on
each side of the nucleus, which is preparing for division ; H, stage of the
nuclear spindle with the two halves of the Nebenkern at each pole ; in / the
nuclear division is nearly complete, and the body is beginning to divide. After
Schaudinn (81), all figures magnified about 500 diameters.

in the cells of the higher animals and plants, accessory cytoplasmic
elements may be added to the centriole to form a centrosomic
complex. A point still undecided, on the theory that centrosomes
are of achromatinic origin, is whether or no these bodies can be
formed, in some cases, in the cytoplasm also, as maintained by
some authorities. On Hertwig's view, mentioned above, that the
achromatinic substance of the nucleus is identical in nature with the
ground-substance of the general protoplasm, it follows that material
for the formation of the centrosome must be present in the cyto-

THE NUCLEUS 95

plasm no less than in the nucleus. Biitschli (3) considers it possible
that the centrosome might have been originally a cytoplasmic
structure, which had nothing to do with the nucleus, but became
included in it when a nuclear membrane was formed.

Attention must be drawn here to the remarkable genus Paramceba (Fig. 49)
founded by Schaudinn for the species P. eilhardi (see p. 228). In this form
there is present beside the nucleus a body which was termed the " Neben-
kern," consisting of a darkly-staining middle piece, at each end of which
is a cap of clear substance. The Nebenkern has generally been considered
to represent a centrosome, and Chatton (49) has put forward the suggestion
that it may correspond to a karyosome or a portion of a karyosome that has
passed out of the nucleus with the centrosome. Recently, however, Janicki
(71*5) has described two new species of Paramceba, and puts quite a different
interpretation upon the Nebenkern. He regards the middle piece as chro-
matin, the clear caps as archoplasmic masses, each of which contains a
centrosome ; and he considers the entire structure " as a second nucleus,
as it were, fixed in division, in which the state of division has become the
permanent form." He proposes to replace Schaudinn's term " Nebenkern "
by the term " nucleus secundus," and considers it especially comparable to
the " sphere " of Noctiluca (Fig. 65). Division of the nucleus and Nebenkern
takes place quite independently of one another.

On the nucleolo-centrosomic theory, the whole karyosome with
the contained centriole, as found in many Protozoa, is compared
with the complex extranuclear centrosome of the higher organisms.
It is clear, however, that the karyosome consists chiefly of plastin
which is impregnated to a greater or less extent with chromatin,
and in which the centriole is imbedded. As Chatton (49) has
pointed out, the three elements which compose the karyosome are
independent of each other. When the centriole and chromatin
have left the karyosome, the plastin-mass remaining behind is
homologous in every way with the nucleolus of the metazoan cell,
and the only element common to both the karyosome of Protozoa
and the centrosome of Metazoa is the centriole.

The nuclear theory of the centrosome is associated especially
with the names of Schaudinn and, in more recent times, of Hart-
mann and Prowazek (63). According to this view, the centrosome
represents a second cell-nucleus, and every cell is to be regarded
as primarily binucleate. The starting-point of the evolutionary
series would be such a form as Amoeba binucleata, which possesses
two similar and equivalent nuclei. In the next stage of evolution
one of the two nuclei became specialized more for kinetic, the other
for trophic, functions ; examples of this stage would be furnished
by Paramceba (Fig. 49), with its nucleus and " Nebenkern," and by
a trypanosome, with its trophonucleus and kinetonucleus, the
Nebenkern of the first and the kinetonucleus of the second repre-
senting the kinetic nucleus. The central grain of the Heliozoa or
the extranuclear centrosome of the Metazoa would represent the
final stage of evolution, namely, a kinetic nucleus deprived of all

96 THE PROTOZOA

chromatin-elements ; while the cell-nucleus proper would represent
the trophic nucleus deprived of all kinetic elements.

On the other hand, the condition in amoebae and similar or-
ganisms, where the cell appears to contain but a single nucleus
which includes the kinetic centres, is explained by supposing that
here the kinetic nucleus is encapsuled in the trophic nucleus, and
is represented by the karyosome with its centriole ; hence ^he
supporters of this theory term the type of nucleus characterized
by a large karyosome an " amphinucleus " or " amphikaryon,"
and, in their descriptions of such nuclei, they speak of the outer
nucleus (peripheral zone of chromatin) and the inner nucleus
(karyosome).

The reasons against homologizing the karyosome and the extra-
nuclear centrosome have been stated already. Against the theory
of binuclearity it may be urged further — First, that to regard the
protokaryon-type of nucleus seen in the most primitive forms of
Sarcodina and Flagellata as a secondary condition is a complete
inversion of what is, to all appearance, the natural series of evolu-
tion of the nuclear apparatus ; secondly, that the binucleate con-
dition of trypanosomes and allied forms is clearly, by comparison
with other Flagellates, a specialized condition ; the trophonucleus
of trypanosomes also contains a karyosome and centriole, and
would therefore be an " amphikaryon," on this theory ; thirdly,
that the binuclear theory still leaves the centriole as a kinetic
centre of achromatinic origin, which is present in both trophonucleus
and kinetonucleus of trypanosomes, in both nucleus and central
grain of Heliozoa (Wagner ella), etc. All that the binuclear theory
is capable of explaining is the secondary elements of the extra-
nuclear centrosomic complex. That the centriole is a body of
intranuclear origin and formation is shown clearly by its presence
in nuclei of the primitive karyosomatic type which arise, not by
division of pre-existing nuclei, but by aggregation and organization
of clumps of chromidia. It should be added that, in its most recent
exposition by Hartmann (61), the theory of binuclearity has
undergone considerable modification and restriction.

Having considered now the structure and composition of the
nucleus in its principal types and morphological variations, it
remains to attempt to establish a more precise conception as to
what exactly is meant by a nucleus. It is evident, in the first
place, that the essential component of a nucleus, never absent, is
chromatin ; but it is equally clear, in the second place, that a simple
mass, or several such masses, of chromatin, do not by themselves
constitute a nucleus in the true sense of the word. The word " chro-
matin " connotes an essentially physiological and biological con-
ception, as it were, of a substance, far from uniform in its chemical

THE NUCLEUS 07

nature, which has certain definite relations to the life-history and
vital activities of the cell. The word " nucleus," on the other hand,
as many authorities and more recently Dobell (52) have pointed
out, is essentially a morphological conception, as of a body, con-
tained in the cell, which exhibits a structure and organization of
a certain complexity, and in which the essential constituents, the
chromatin-particles, are distributed, lodged, and maintained, in
the midst of achromatinic elements which exhibit an organized
arrangement, variable in different species, but more or less constant
in the corresponding phases of the same species. If this standpoint
be accepted, and the nucleus be regarded as an essentially morpho-
logical conception, it seems to me remarkable that Dobell, in
his valuable memoir on the cytology of the bacteria, should apply
the term " nucleus " to a single grain of chroma tin, or to a collection
of such grains, and should speak of a nucleus " in the form of
chromidia scattered through the cell," or " in the form of a discrete
system of granules (chromidia)," phrases which are self-contra-
dictory on the principles that he himself has laid down.

We are confronted, nevertheless, with a considerable difficulty
when we attempt to state exactly what amount of organization
and structural complexity is essential to the morphological concep-
tion of a nucleus. If, as is probable in phylogeny, and certainly
occurs frequently in ontogeny (compare Fig. 32), the nucleus arises
from a primitive chromidial condition of scattered, unorganized
chromatin, at what point does the mass cease to be a chromidium
and become a nucleus ? This is a question very difficult to answer
at present, a verbal and logical difficulty such as occurs in all cases
where a distinction has to be drawn between two things which
shade off, the one into the other, by infinite gradations, but which
does not, nevertheless, render such distinctions invalid, any more
than the gradual transition from spring to summer does away with
the distinction between the seasons. Hartmann and his school
consider the possession of a centriole as the criterion of a nucleus
(see Nagler, 76) ; but it cannot be considered as established, in
the present state of knowledge, that all nuclei have centrioles or
centrosomes. All that can be said is that, as soon as a mass or a
number of particles of chromatin begin to concentrate and separate
themselves from the surrounding protoplasm, with formation of
distinct nuclear sap and appearance of achromatinic supporting
elements, we have the beginning at least of that definite organiza-
tion and structural complexity which is the criterion of a nucleus
as distinguished from a chromidial mass.

In the first chapter of this book a distinction was drawn between
organisms of the " cellular " grade, with distinct nucleus and
cytoplasm, and those of the " bacterial " grade, in which the

7

98 THE PROTOZOA

cliromatin does not form a distinct nucleus. In all Protozoa there
is a true nucleus in at least the principal stages of the life-history,
and it is obvious that the recognition of a cellular grade, charac-
terized by the possession of a true nucleus, postulates that the first
origin and evolution of the nucleus must be sought amongst those
organisms which have been classed, speaking broadly, as the
bacterial grade. We may expect, therefore, to find in organisms
which stand on the plane of morphological differentiation which
characterizes the bacteria the early stages of the evolution of the
nucleus from the primitive chromidial condition, and even cases
in which the condition of a true nucleus has been reached. The
matter cannot be discussed further here, where it must suffice to
establish the existence of true nuclei in Protozoa ; but Dobell (52)
has described an interesting series of conditions which may be
regarded as stages in the evolution of nuclei amongst bacterial
organisms.

Since the possession of a true nucleus has been regarded here
as the criterion of the cellular grade of organization, it is necessary
to discuss briefly the meaning and application of the term " cell."
By many, perhaps most modern writers, the cell has been regarded
as the elementary vital unit, than which there exists nothing
fcimpler amongst living beings. In this sense the word " cell " becomes
synonymous with the term " micro-organism," "protist," or any other
word used to denote living beings of the most primitive type :
" tout ce qui vit rtest que cellules " (Delage and Herouard, 6). The
word " cell " was, however, applied originally to the elements that
built up the tissues of animals and plants. At first, as the word
cell implies, it was used to denote only the enclosing membrane or
framework ; but when it became apparent that the membrane was
of secondary importance, it was transferred to the contained stuff,
and so came to signify a structural element in which the living
substance, protoplasm, is differentiated into two distinct parts-
nucleus and cytoplasm. If the term " cell " is not to become so
vague and indefinite in its significance as to be absolutely meaning-
less, it is best to restrict its application to living organisms which
have reached this degree of differentiation. Dobell considers that
all Protista are nucleated organisms ; in the preceding paragraphs
reasons have been advanced against accepting this proposition as
a statement of fact, and from the point of view of phylogenetic
speculation, I, at least, find it difficult to believe that the earliest
form of life could have been an organism in which the living sub-
stance was differentiated ab initio into distinct nucleus and cyto-
plasm.

In my opinion the cell, as defined above — that is to say, an
organism in which the living substance, protoplasm, has become

THE NUCLEUS 99

differentiated into two parts, a nucleus, in the morphological sense,
distinct from the cytoplasm — does not represent the primary and
universal form of the living organism or unit, but is to be con-
sidered as a stage in the evolution of living beings, a stage which
many living beings have not reached. Thus a bacterial type of
organism, in which the chromatin is scattered through the proto-
plasmic body in the form of chromidial granules, and which there-
fore does not possess a true nucleus, is not to be regarded as a cell,
but as representing a condition antecedent to the evolution of
the true cellular type of structure. In all Protozoa, on the other
hand, the entire plan of the organization is founded on the type of
the cell, which is to be regarded as the starting-point in the evolu-
tion of the entire animal and vegetable kingdoms (compare Min-
chin, 75). This point will be discussed further in a subsequent
chapter (p. 464).

Bibliography. — For references see p. 477.

LI 3R AR Yi=:

CHAPTER VII
THE REPRODUCTION OF THE PROTOZOA

THE methods by which reproduction is effected amongst the
Protozoa vary greatly in matters of detail, as will be seen ; but the
obvious diversity in method throws into greater relief the under-
lying unity in principle. In Protozoa, as in Protista generally,
reproduction takes place always by means of some form of fission —
that is to say, division or cleavage of the body into two or more
parts, which are set free as the daughter-individuals. An essential
part of the process is the partition amongst the daughter-individuals
of at least some part of the chromatin-substance possessed by the
parent. Hence fission of the cell-body as a whole is always pre-
ceded by division of the nucleus ; and if chrornidia are present, they
also are divided amongst the products of the fission of the body.
On the other hand, division of the nucleus is not necessarily
followed at once by division of the body.

Considering the methods by which fission is effected from a
general standpoint, we may distinguish three chief types of repro-
duction, each of which may show subordinate variations :

1. Division of the nucleus, or, if there are two differentiated
nuclei, division of each of them, is followed by division of the body ;
this is the commonest and most typical mode of reproduction,
known as simple or binary fission.

2. Division of the nucleus or of each of two differentiated nuclei
is not followed immediately by corresponding divisions of the body,
but may be repeated several times, and so give rise to a multi-
nucleate condition of the body, which may be —

(a) Temporary, and soon followed by cleavage of the body into
as many daughter-individuals as there are nuclei or pairs of dif-
ferentiated nuclei ; this method is known as multiple fission (Fig.
127) ; or it may be —

(6) Permanent, giving rise to a multinucleate body which is termed
a plasmodium. Then division of the body may take place at any
time by cleavage of the body into two or more multinucleate
parts ; this process is known as plasmotomy. Ultimately, however,
in all cases a plasmodium breaks up by multiple fission into uni-

100

THE REPRODUCTION OF THE PROTOZOA 101

nucleate individuals at the end of a longer or shorter vegetative
existence during which it may have multiplied frequently by
plasmotomy.

The process of fission must now be considered in more detail,
beginning with —

1. Division of the Nucleus. — As in the case of the cell-body as
a whole, the division of the nucleus is effected in various ways.
Probably the most primitive type is that in which the nucleus
becomes resolved into chromidia, from which, again, secondary
daughter-nuclei are reconstituted. This type of division may be
termed " chromidial fragmentation." It is of comparatively rare
occurrence, but examples of it are found among Sarcodina and
Sporozoa. In Echinopyxis two daughter-nuclei are formed in this
way (Hertwig, 66, p. 8). In other cases numerous daughter-nuclei
may arise, as in the formation of the nuclei of the microgametes
in Coccidium (Fig. 50), where the parent nucleus gives off into the
cytoplasm a fine dust of chromidial particles which travel to the
surface of the cell and become concentrated at a number of spots
to form the daughter-nuclei.

True nuclear division, in which the parent and daughter-nuclei
retain throughout the process their individuality and distinctness
from the cytoplasm, must be distinguished clearly from the above-
mentioned process of chromidial fragmentation. In the vast
majority of cases the nucleus divides into two halves by simple or
binary fission, which, as already stated, may be repeated several
times before cell-division takes place ; but in a few cases the nucleus
divides simultaneously into a number of portions by multiple
fission.

In the cells of Metazoa true nuclear division alone occurs, and
may follow one or the other of two sharply-marked types, termed
comprehensively direct and indirect. In direct division the nucleus
is constricted simply into two parts, without circumstance or
ceremony. In indirect division, on the other hand, the nucleus
goes through a complicated series of changes, following each other
in a definite order and sequence, the whole process being known as
karyokinesis or mitosis. In spite, however, of the intricate nature
of karyokinetic division, and the variations in matters of detail
that it exhibits in different cases, the whole process is perfectly
uniform in its general plan, and admits of being described without
difficulty in generalized terms. Such a description is found in
every textbook of biology at the present time, and need not be
repeated here ; it will be sufficient to analyze briefly the more
important events that take place.

In the process of "karyokinesis, the achromatinic elements of the
nucleus furnish the active mechanisms, while the chromatin-sub-

102

THE PROTOZOA

stance appears to be the passive subject of the changes that are
effected. With the achromatinic nuclear elements, extranuclear
cytoplasmic substances/such as archoplasm, may collaborate. After

FIG. 50. — Formation of microgametes in Coccidium schubergi. A, Full-grown
microgametocyte, with finely-granular cytoplasm and large nucleus con-
taining a conspicuous karyosome ; freed from the host-cell. B, The nuclear
membrane has disappeared, and the chromatin, in the form of minute chro-
midial granules, is passing out into the cell. C, The chromidia have collected
at the periphery of the body ; the karyosome is left at the centre, and has
become pale through loss of chromatin-substance. D, The chromidia, seen
on the surface of the body, are collecting together into irregular streaks and
clumps. E, The chromatin -streaks of the preceding stage are collecting
together into patches. F, The patches of chromatin of the preceding stage
have become dense and closely packed. G, H, The patches of chromatin
take on a definite form as the future nuclei of the microgametes. /, Two
flagella grow out from close to each microgamete-nucleus, and by their
activity the microgametes, consisting almost entirely of chromatin, break
loose from the body of the gametocyte and swim away. J, Three micro -
gametes, more highly magnified ; in each, two flagella arise from the thicker
cud ; one of the flagella (the shorter) becomes free at once, the other (the
longer) runs along the body and becomes free at the hinder end. n., Nucleus,
k, karyosome, of the microgametocyte ; n', n', nuclei of the microgametes.
After Schaudinn (99); A— E magnified 1,000, F— I magnified 1,500,
J magnified 2,250.

disappearance, as a rule, of the nuclear membrane, the achromatinic
substance, or the combination of achromatinic and archoplasmic

THE REPRODUCTION OF THE PROTOZOA 103

elements, assumes a characteristic bipolar form, like a spindle.
At each pole of the spindle a centrosome or centriole is to be found,
as a general rule. The two centrosomes have arisen by division of
the originally single centrosome, and may remain for some time
connected by a fibril or by a system of fibrils, forming what is often
termed a ' ; central spindle," but is better named a centrodesmose. The
axis of the achromatinic spindle is formed by the centrodesmose, if it
persists, and the remainder of the spindle is constituted by the so-
called ' ' mantle-fibres ' ' running from pole to pole. The mantle-fibres
are derived from the achromatinic reticulum of the nucleus and the
archoplasm ; they are probably in most cases the optical expression
of an arrangement of the protoplasmic alveoli in longitudinal rows,
under the influence of tensions or forces centred at the poles of the
spindle. Such an arrangement of the alveoli produces the optical
appearance of fibrils connected by cross- junctions, the apparent
fibril being formed by thickened walls of alveoli in line with one
another, while the cross-junctions are the transverse walls between
consecutive alveoli. On this view the apparent fibrils of the achro-
matinic spindle are in reality merely the indication of lines of force
in the protoplasmic framework ; but some authorities consider that
in certain cases at least true fibrils are formed, which may be
isolated from each other and without cross-connections (Hertwig,
64). The spindle-fibres, whether real or apparent, are centred at
the poles of the spindle on the centrosomes, from which other
striations may radiate out in all directions through the archo-
plasmic masses (" attraction-spheres "), and extend into the sur-
rounding cytoplasm.

While the achromatinic spindle-figure is in process of formation,
the chromatin of the nucleus has gone through a series of changes
which may differ in different cases, but which result in the forma-
tion of a number of masses of chromatin termed chromosomes. The
number, size, and shape, of the chromosomes vary greatly in dif-
ferent species, but in Metazoa these characters are generally con-
stant for the corresponding phases of the same species. Each
chromosome, when formed, consists of a great number of minute
grains of chromatin, chromidiosomes, cemented together in a matrix
or ground-substance of plastin. The chromosomes arrange them-
selves at the equator of the achromatinic spindle in the form of a
plate, hence termed the equatorial plate. The nucleolus disappears,
being absorbed or cast out, and does not contribute to the karyo-
kinetic figure, but a part at least of its substance probably furnishes
the plastin ground-substance of the chromosomes.

At this phase, when the achromatinic spindle is fully formed, with
the plate of chromosomes at its equator, the actual partition of the
chromatin between the two future daughter-nuclei usually begins,

104 THE PROTOZOA

though in some cases it is accomplished at an earlier stage ; it takes
place in one of two ways, known respectively as equating and re-
ducing division. In equating division each chromosome divides into
two daughter-chromosomes, a process which, in the finished and
perfect karyokinesis of the higher organisms, is effected by a longi-
tudinal splitting of the chromosome, and which may be interpreted
as a simple division into two of each of the component chromidio-
somes (compare Fig. 60). In reducing division, on the other hand,
the individual chromosomes do not divide, but are sorted out, half
of them going to one pole of the spindle, and eventually to one
daughter-nucleus, the other half to the other ; with the result,
finally, that each daughter-nucleus has half the number of chromo-
somes possessed originally by the parent nucleus. Equating
division is the usual type of karyokinesis seen in ordinary cell-
multiplication ; reducing division, on the other hand, is seen only
in certain phases of the maturation of the germ-cells, as explained
in the next chapter.

In either type of division, whether equating or reducing, the
equatorial plate of chromosomes as a whole divides into two
daughter-plates, which separate from one another and travel towards
the poles of the achromatinic spindle. As the daughter-plates move
away from each other, an achromatinic framework appears between
them, in which a longitudinal striation or fibrillation is seen in line
with, and continuing that of, the achromatinic spindle. Hence the
achromatinic spindle as a whole consists now of the older terminal
portions passing from the poles to the daughter-plates, and a new
median portion passing between the two daughter-plates ; the two
terminal portions constitute together what may be termed conveni-
ently the " attraction-spindle," the median portion the " separation-
spindle." As the daughter-plates travel further apart, the separa-
tion-spindle elongates more and more ; the attraction-spindle, on
the other hand, becomes shorter, usually to such a degree that the
daughter-plates are brought close up to the poles of the attraction-
spindle, which consequently is obliterated and disappears. When
full separation of the daughter.-plates is attained, the separation-
spindle breaks down and disappears gradually, the middle part
alone persisting in some cases ; the chromatin of the daughter-plates
becomes rearranged to form the daughter-nuclei, going through a
series of changes similar to those by which the chromosomes arose
from the parent-nucleus, but in inverse order. A nuclear mem-
brane is formed round each daughter-nucleus, and the process is
complete.

In the Metazoa, direct and karyokinetic division stand out as the
sole types of nuclear division, in sharp contrast and without inter-
mediate or transitional forms of the process. In Protozoa, on the

THE REPRODUCTION OF THE PROTOZOA 105

contrary, every possible form of nuclear division is found, from the
most simple and direct to karyokinesis as perfect as that seen in
the Metazoa. The nuclear division-processes of Protozoa are there-
fore exceedingly interesting as furnishing object-lessons in the
gradual evolution of the mechanism of nuclear division ; but the
extreme diversity in these processes makes it very difficult to deal
with them in the Protozoa in a general and comprehensive manner
in a short space and without excessive detail. Speaking generally,
the indirect nuclear division seen in Protozoa differs from that of
the higher organisms in a number of points which indicate that it
stands on a lower grade of evolution. As regards the achromatinic
elements, the nuclear membrane is usually persistent throughout
the process of division, a circumstance which enables a sharp dis-
tinction to be drawn between the portions of the division-mechanism
derived from the nuclear framework and the cytoplasm respectively.
In many cases it is then seen that the cytoplasm does not take any
share in the process at all, but that the nucleus divides in a per-
fectly autonomous manner, spindle and centrioles remaining intra-
nuclear throughout the whole process. As regards the chromatin,
the chromosomes when formed are often irregular in form, size,
and number ; they often appear imperfectly separated from one
another ; they are not always arranged in a definite equatorial plate,
but may be scattered irregularly along the spindle ; and they do
not always split in the exact manner characteristic of the nuclear
divisions of the higher organisms, but divide irregularly and often
transversely.

The principal types of nuclear division in Protozoa will now be
described with the aid of a few selected examples. We may begin
with those in which the division of the nucleus is autonomous,
without co-operation of cytoplasmic elements.

Division has often been asserted to be direct in cases in which
subsequent research has revealed a more elaborate type ; never-
theless, many typical cases of amitosis occur among Protozoa. In
some nuclei of the vesicular type, the chromatin appears to be
concentrated entirely in the karyosome, which may contain a
centriole also, and when the nucleus divides the karyosome becomes
dumb-bell-shaped, and is finally constricted into two halves, the
entire nucleus following suit ; as an example of this, almost the
simplest conceivable type of nuclear division, may be cited the
nuclei of the Microsporidia and allied organisms (Fig. 173, p. 416).

A type similar in the main to that just described, but slightly
more advanced in structural complication, is exemplified by the
division of the nucleus in the schizogony of Coccidium (Fig. 51, F — M) ;
here there is a peripheral zone of chromatin and a more distinct
nuclear membrane. After division of the karyosome, the peripheral

106

THE PROTOZOA

chromatin is halved irregularly ; no definite chromosomes are
formed, but the grains of peripheral chromatin form clumps and
masses of various shapes and sizes. A definite achromatinic spindle

FIG. 51. — Formation of the karyosome and division of the nucleus in the schizont
of Goccidium schubergi. A, Nucleus of the sporozoite, with scattered grains
of chromatin but no karyosome. B, C, D, Nuclei of young schizonts in which
larger grains of chromatin collect together at the centre to form the karyo-
some. E, Nucleus of older schizont with complete karyosome. F, Nucleus
of full-grown schizont. G — M , Division of the nucleus of the schizont ;
the chromatin of the nucleus becomes aggregated into larger clumps and the
karyosome becomes dumb-bell-shaped, with masses of chromatin at each
pole (G and H) ; the two daughter-karyosomes, at first connected by a fila-
ment or centrodesmose, travel apart, taking the polar clumps of chromatin
with them (/) ; the centrodesmose breaks through and disappears, and the
two daughter-nuclei travel apart, with formation of an intermediate body
on the filament between them (/ — L) ; finally the connecting filament breaks
down and the daughter-nuclei separate (M). k1, Karyosome ; &2, k2, daughter-
karyosomes ; i., intermediate body. After Schaudinn (99), magnified 2,250.

FIG. 52. — Direct division of the nuclei in the oocyst of Goccidium schubergi. A, The
resting nucleus ; B, G, D, clumping together of the chromatin-granuies
preparatory to division ; E, F, G, the nucleus elongates and becomes dumb-
bell-shaped ; H, the nucleus has just divided into two halves. After
Schaudinn (99), magnified 2,250.

also does not become differentiated. As the daughter-karyosomes,
connected by a centrodesmose, travel apart, half the peripheral
chromatin follows one karyosome, half the other. This method of

THE REPRODUCTION OF THE PROTOZOA

107

division is a very common one in the nuclei of Protozoa, and may
show a further advance towards a true mitosis in that the peri-
pheral chromatin may shape itself into more or less definite
chromosomes, as in Euglena.

Examples of granular nuclei which divide in the direct method
are seen in the division of the nucleus of the oocyst of
Coccidium (Fig. 52) to form the nuclei
of the sporoblasts (see p. 349, infra) and
in the corresponding divisions of the nuclei
of haemogregarines (Fig. 53). In these
two cases the presence of a centriole in
the nucleus is doubtful, but is affirmed
by Hartmann and Chagas (89) for hsemo-
gregarines ; a true nuclear membrane,

FIG. 53. — Direct division of the nucleus in the zygote
of Hcemogregarina stepanowi. $ , Degenerating
male elements attached to the zygote ; N., divid-
ing nucleus of the zygote, two successive stages
( A and B). After Reichenow (78). C.V.—

however, appears to be absent, and this
form of division is not much advanced
beyond the condition of chromidial frag-
mentation. In the macronucleus of
Infusoria (Fig. 54), in which a distinct
membrane is present, the division is also
direct, and centrioles are stated to be
absent as a general rule ; in some cases,
however, true centrioles appear to be
present (Nagler). When centrioles are
absent, the achromatinic framework of
the nucleus appears to be principally active in the division. In
some cases the division of the macronucleus of Infusoria is
not into two equal halves, but may take the form of budding
off a smaller daughter-nucleus from the main mass. Remark-
able instances of nuclear budding of this kind are seen in the
Acinetaria, where it is related to the formation of buds by the parent
individual. In some cases (Fig. 55), the nucleus may form a con-

FIG. 54. — Paramecium cauda-
tum : division showing the
macronucleus (N) dividing
without mitosis, the micro-
nucleus (n) dividing mito-
tically. c.v.1, Old, and c.v.2,
new, contractile vacuoles.
After Butschli and Sche-
wiakoff, in Lcuckart and
Nitsche's Zoologische Wand-
tafeln, No. Ixv.

108

THE PROTOZOA

siderable number of buds simultaneously, each of which becomes
the nucleus of a daughter-individual budded off from the parent.

The simplest types of mitosis show but little advance on the
processes of direct division that have just been described. Taking
first the vesicular type of nucleus with a large karyosome (" proto-
karyon "), the first stage in the process is the division of the karyo-
some, as in Coccidium ; its centriole divides first, then the karyo-
some becomes constricted and divides, the two halves often plainly
connected by the centrodesmose formed by the division of the cen-
trioles. Next an achromatinic spindle is formed between the two
daughter-karyosomes, and chromosomes make their appearance,

derived partly (perhaps
in some cases entirely)
from the peripheral zone
of chromatin, partly from
the chromatin contained
in the karyosome. A
good example of this
mode of division has
been described by Aragao
(87) in an amoeba named
by him A. diplomitotica
from the fact that two
types of mitosis occur in
this species. In the first
type (Fig. 56, A—G), the
little rod -like chromo-
somes are not arranged
FIG. 55. — Budding in Podophrya gemmipara. The
macronucleus of the parent has sent off a number

give rise to the nuclei of the daughter-individuals irrpaillar]v
about to be budded off. N1, Parent-nucleus ; ^regularly
N2, nuclei of buds. After Hertwig.

.e parent Has sent ott a number in a definite equatorial
of outgrowths, which extend into the buds and plate, but are scattered

ng the

spindle ; some travel to-
wards one pole, some

towards the other, and, after separation into two groups in this
manner, the chromosomes of each group fuse together to form an
apparently solid mass of chromatin, representing the daughter-
plates ; these masses of chromatin follow each their respective
karyosomes as they travel apart, and when the nucleus is finally
constricted into two daughter-nuclei, the chromatin-masses break
up again into their constituent chromosomes, which become dis-
tributed in the peripheral zone and karyosome of the daughter-
nuclei, where they can be distinguished plainly even during the
resting state (Fig. 56, A).

In the second type of mitosis seen in A. diplomitotica (Fig. 56,
H — K), the chromosomes arrange themselves in a definite equatorial

THE REPRODUCTION OF THE PROTOZOA

109

plate, which divides into two equally definite daughter-plates com-
posed of distinct chromosomes ; whether this division is brought
about by splitting of the individual chromosomes is not clear.
When the nucleus is finally constricted into the two daughter-
nuclei, the chromosomes are at first aggregated close beside their
respective karyosomes, but soon distribute themselves in the
manner already described.

The simple types of mitosis described in the two foregoing para-
graphs are examples of the so-called " promitosis " (Nagler, 95)

FIG. 56. — The two methods of nuclear division in Amoeba diplomitotica. A, Resting
nucleus ; B — G, first method ; H — K, second method. In F and G only
one of the two halves of the nuclear figure is drawn. After Aragao (87).

seen commonly in nuclei of the protokaryon-type. The nuclear
membrane in this type is a negligible quantity ; it may be scarcely
^r not at all developed in the resting nucleus, and when a distinct
membrane is present it may vanish entirely during the mitosis, as
in the form just described. In any case, however, the entire mitosis
goes on within the nuclear space. The chromosomes may show
every possible condition in different cases, from complete irregu-
larity in form, number, arrangement, and mode of division, to the

110

THE PROTOZOA

formation of a definite equatorial plate which splits into two
daughter-plates. The most striking and salient feature of this type
of mitosis is furnished by the relatively huge " polar masses," con-
sisting of the daughter-karyosomes with their contained centriolcs.
In the division of the nucleus of Arcella (Fig. 57), however, the
karyosome first breaks up into fine grains of chromatin, from which
the polar masses and the equatorial plate are formed. The karyo-
some, as has been pointed out in the previous chapter, consists of
three distinct elements — namely, plastin, chromatin, and centriole

FIG. 57. — Nuclear division in Arcella vulyaris: karyokinesis of
one of the two principal nuclei. A, Spireme-stage, resulting
from disruption of the karyosome ; B — D, formation of an
equatorial plate of minute chromosomes (?) which split ;
E, anaphase ; F, the two daughter-nuclei shortly after
division. After Swarczewsky (101), magnified 2,250.

— each independent of, and separable from, the
others. In proportion as the karyosome loses its
plastin and chromatin elements, and becomes reduced
to the centriole alone, so the primitive promitosis
will approach more ano^ more to the type of an
ordinary mitosis. Such a reduction of the karyo-
some could take place during the mitosis if, as
happens frequently, the whole of the chromatin
p contained in the karyosome passed out to join the

peripheral chromatin in forming the chromosomes,
the plastin-substance at the same time furnishing the required
ground-substance of the chromosomes (Fig. 58). On the other
hand, the karyosome may disappear from the resting nucleus
also ; Chatton (49) has brought together a number of instances
of nuclei showing a gradual reduction of the karyosome in
different species, and the evolution of a granular type of nucleus
in which the chromatin is scattered through the achromatinic
framework, leaving the centriole free or but slightly encumbered
by other elements in the nuclear cavity. When a nucleus of this
type divides by mitosis, a most typical and perfect karyokinetic

THE REPRODUCTION OF THE PROTOZOA

111

figure may be produced, as in Euglypha (Figs. 59, 60), only differing
from that of Metazoa in that the whole mitosis takes place within
the nuclear membrane, and consequently without any co-operation
of cytoplasmic elements. Chatton proposes for a mitosis of this
type the term " mesomitosis," as distinguished from the more ad-
vanced type, or " metamitosis," in which a collaboration of cyto-
plasmic and nuclear elements is effected, and the entire karyokinetic

FIG. 58. — Division of Hcematococcus pluvialis. A , Resting
condition, the nucleus with a conspicuous karyosome
and fine grains of chromatin in an achromatize reti-
culum ; B, C, preparations for nuclear division, the
chromatin passing from the karyosome into the
nuclear reticulum ; D, further stage, the karyosorne
in disruption and chromosomes beginning to be
formed ; E, nuclear spindle ; F, division of the
nucleus complete, the karyosomcs reconstituted in
• the daughter-nuclei, the cell-body beginning to
divide ; G, division of the cell, the daughter-nuclei
of the normal resting type. After Reichenow
(97'5).

figure lies free in the cytoplasm after disappearance of the nuclear
membrane. Before passing on, however, to this more advanced
type, account must be taken of the more simple types of mitosis
seen in granular nuclei.

Instructive examples of the division of nuclei, in which the
chromatin is not concentrated into a karyosome, but distributed
evenly throughout the achromatinic framework, are seen in the nuclei

112

THE PROTOZOA

FIG. 59. — Division of EuglypTia alveolata,
as seen in the living animal.

A, Condition of the animal when about
to divide. The protoplasmic body shows

three zones : (1) At the fundus of the shell is clear proto-
plasm containing the nucleus (N.) and the reserve shell-
plates (s.p.) ; (2) the middle region is occupied by granular
protoplasm containing ingested food- mate rials (/.)and the
contractile vacuole (c.v.) ; (3) near the mouth of the shell is a zone of hyaline
protoplasm from which the pseudo podia (ps.) are given off.

B, Early stage of division, about twenty minutes later than A. The proto-
plasm is streaming out of the shell-mouth to form the body of a daughter-
individual, into which the reserve shell-plates arc passing and arranging them-
selves at its surface to form a daughter-shell. In the nucleus chromosomes are
beginning to be formed.

C, About twenty-five minutes later than B. The body of the daughter and
its shell are further advanced in formation ; in the nucleus of the parent the
equatorial plate is forming, and the two centrosomes are becoming visible on
the two flattened sides of the nucleus (the centrosomes are probably derived from
the division of the karyosome, no longer visible in the nucleus at this stage, or
from a centriole contained in the karyosome). [Continued at foot of p. 113.]

THE REPRODUCTION OF THE PROTOZOA

113

FIG. GO. — Details of the structural changes of the nucleus of Euglypha alvedata
during karyokinesis, showing the formation of the chromosomes. A,
Coarsely - meshed condition of the nucleus ; the chromatin-granules
aggregated at the nodes of the reticulum. B, Later stage ; the nucleus
beginning to show a fibrous structure as a result of the irregular clumps
of chromatin-granules of the previous stage becoming arranged in linear
series. B2, Some of the fibrils of this stage more highly magnified.
0, Later stage ; the fibrils have become smoother and more parallel in
arrangement. C2, Fibrils more highly magnified ; they consist, as in the last
stage of darker and lighter parts (the former chromatin, the latter probably
plastin) ; between the individual fibrils are cross-connections, more regular
in this stage than in the last (remains of the nuclear reticulum). D, The
fibrils have become shorter and thicker, and are bending up to form the
U-shaped chromosomes. After Schewiakoff (100) ; magnification of A, B,
C, and D, about 1,200 diameters.

of ciliate Infusoria, such as Paramecium. The macronucleus divides
without mitosis, as stated already, but the micronucleus exhibits a
primitive type of mitosis (Fig. 61). When division begins, the

FIG. 59 — continued:

D, About fifteen minutes later than G. The daughter-shell is now com-
pletely formed, and the middle granular zone of the parent is passing over
into it ; the nucleus of the parent has assumed its definitive orientation, with
the centrosomes at the poles of an axis coincident with the longitudinal axis
of the animal, and the equatorial plate is definitely formed.

E, About thirty minutes later than D. The whole of the middle zone of
the parent has passed over into the daughter-shell ; the flattened form of the
nucleus is changing into an elongated spindle-form, and the equatorial plate
is splitting to form the two daughter- plates.

F, About five minutes later than E. The daughter-plates have travelled
apart, and the division of the nucleus is beginning.

G, About five minutes later than F. The division of the nucleus is com-
plete, and one daughter-nucleus has passed over into the body of the daughter-
Eiiglypha.

H, About twenty-five minutes later than G (about 125 minutes from the
beginning). Some of the protoplasm of the middle zone flows back into
the parent-shell, and each individual has its own contractile vacuole ; the two
daughter-nuclei are reconstituted, and the karyosome has reappeared in
each ; pseudopodia are being protruded from the mouths of the shells ; the
division is complete, and the animals are beginning to separate.

After Schewiakoff (100) ; magnification about 470 diameters.

8

114

THE PROTOZOA

amount of chromatin increases, and the nucleus becomes oval in
form. The chromatin forms a number of chromosomes shaped like
elongated rods or short threads, which arrange themselves at the
equator. At the same time the achromatinic framework shows a
longitudinal fibrillation or striation, the apparent fibrillse being
centred in thickenings of the achromatinic framework which appear
at the two poles of the nucleus within the persistent nuclear mem-
brane, hence termed the " polar plates." Centrosomic grains are
stated to be entirely absent, and their functions are performed by
the polar plates. The nucleus continues to elongate, and the
chromosomes divide transversely to their long axis to form the
daughter-plates, which travel apart ; as they do so the fibril! ated

FIG. 61. — Stages in the division of the micronucleus of Para-
mecium. A, B, Early stages ; 0, spindle-stage with equa-
torial plate of chromosomes ; D, spindle with the two
daughter-plates ; E — H, growth of the separation-spindle
and separation of the two daughter-plates ; /, reconstitu-
tion of the daughter-nuclei, which are widely separated,
but still connected by the greatly elongated separation-
spindle, the central part of which shows a dilatation prior to its final
absorption. After Hertwig. Figs A — E are drawn on a larger scale than
the other figures.

separation-spindle appears between them. The nucleus as a whole
now becomes dumb-bell-shaped ; the daughter-plates are lodged in
the terminal swellings, while the rapidly-growing separation-spindle
occupies the handle of the dumb-bell. The daughter-plates now
break up and reconstitute the daughter-nuclei, but the connecting
portion continues to elongate and to push the daughter-nuclei apart.
It is clear that the separation is effected by intrinsic growth of the
achromatinic framework constituting the separation-spindle, which
is often curved up into a horseshoe-figure, and shows bending or
twisting of its fibrils, as the result of the inert resistance of the sur-
rounding cytoplasm. Finally, however, a limit of growth is attained ;
the daughter-nuclei become constricted off completely from the
connecting bond, which is absorbed and disappears. The nuclear
membrane persists throughout the division.

In all the forms of nuclear division dealt with so far, nuclear
elements alone have been active in the process. A most instructive
series, showing how extranuclear elements come to collaborate in

THE REPRODUCTION OF THE PROTOZOA

115

the mechanism of division, is furnished by some examples of the
Heliozoa, and especially by the nuclear divisions of Actinosphcerium,
which have been the subject of extraordinarily thorough investiga-
tion by Hertwig (64). In this form there are three different modes
of karyokinesis, which, however, for present purposes may be
classified under two heads : karyokinesis without and with centro-
somes. In the ordinary nuclear division during the vegetative life
of the organism, and also in the divisions by which the primary

G

FIG. 62. — Actinosphcerium eichhorni : stages of the ordinary .'vegetative nuclear
division, without centrosomes.^of free-living individuals (not encysted).
A, B, Formation of the chromosomes within the nucleus, and of the "proto-
plasmic polar cones outside the nucleus ; G, spindle-stage with polar cones
K.C.), polar plates (p.p.), and equatorial plate of chromosomes (e.r.);
stage with daughter - plates of chromosomes which have travelled
towards the polar plates ; E — G, division of the nucleus, reconstitution of
the daughter-nuclei, and disappearance of the polar cones. After Hertwig (64).

cysts divide into the secondary cysts (p. 138), centrosomes are
absent, but they are present in the two divisions which produce
the two reduction - nuclei thrown off from each secondary
cyst.

In the ordinary karyokinesis of Actinosphcerium (Fig. 62) an
equatorial plate is formed composed of a large number of small,
rod-like chromosomes, imperfectly separated from one another,
which divide transversely. The spindle arises from the achromatinic
framework of the nucleus, and terminates in two conspicuous polar

&&•*,

m^-

gm^*M- .
4I1E '- B i

°?'!K;:;/K;?*i.7
."^ftilfiP

^s.-.

FMsMWSSW®

<^Hilli?

»ii^

^«^:^

f&Mpppl^

*.«y

•'' (fr

FIG. 03. — Actinosphcerium eichhorni: first reduction-division, with centrosomes
(the stages here shown follow those of the centrosome-formation in Fig. 37).
A, Centrosome with radiations in a mass of archoplasm at one pole of the
nucleus ; B, two centrosomes and archoplasmic cones, taking up positions
on opposite sides of the nucleus, in which chromosomes are beginning to appear ;
0, D, formation of the nuclear spindle and equatorial plate of chromosomes ;
E, division of the equatorial plate ; F, division of the nucleus beginning ;
G, H, division of the nucleus and reconstitution of the daughter-nuclei ; one
daughter-nucleus will degenerate and be rejected as a reduction-nucleus ;
the beginning of this is seen in //, where the upper darker daughte r- nucleus
is the one which degenerates. After Hertwig (64).

THE REPRODUCTION OF THE PROTOZOA 117

plates lying within the persistent membrane. External to the
membrane are two large conical masses of archoplasm, termed the
" polar cones." As in the micronucleus of Paramecium, the polar
plates represent functionally the centrosomes, towards which the
daughter-plates travel, and division of the nucleus is effected by
growth of the separation-spindle. The archoplasmic polar cones
appear to take little or no part in the mechanics of the division,
since their apices maintain their distance from one another, and
the growth of the separation-spindle pushes the daughter-nuclei
into their substance.

The reduction-karyokinesis is heralded by the formation of a
centrosome from the nucleus (Fig. 37 ; see p. 80, supra). The
centrosomes are at first close to the nucleus, external to its mem-
brane, but when the karyokinetic spindle is formed the centro-
somes travel to the apices of the cones. From the centrosomes
radiations extend through the polar cones, continuing the direction
of the longitudinal striations of the intranuclear spindle, though
separated from them by the intervening nuclear membrane. During
the division the apices of the cones move apart to a slight extent,
but the separation of the daughter-nuclei is still mainly the work
of the separation-spindle, which pushes them into the polar cones
and brings them close to the two centrosomes again ; hence the
activity of the polar archoplasm can be but slight. The chromo-
somes in the reduction-divisions are more distinctly separated from
each other as the result, apparently, of a reduction in the amount of
the plastin forming the ground-substance. The nuclear membrane
persists throughout the whole process.

In Actinophrys the karyokinesis appears to be of a type similar
to that of Actinosph cerium, with persistent membrane, but with
more activity in the extranuclear archoplasmic elements. In
Acanthocystis (Fig. 64), however, the nuclear membrane disappears
completely from the karyokinetic figure, and it is no longer possible,
in consequence, to distinguish the parts of the achromatinic spindle
which are of intranuclear and extranuclear origin respectively.
Nuclear and cytoplasmic elements are in complete co-operation, a
condition of things which has apparently been brought about and
rendered possible by the extrusion of the centrosome from the nucleus
in the first instance.

From the foregoing examples, it is seen that amongst the Protozoa
the material is to be found for illustrating the gradual evolution of
the mechanism of karyokinetic division, from the starting-point of
simple and direct division up to the most advanced type in which
a perfect karyokinetic figure is formed by co-operation of nuclear
and cytoplasmic substance. It is not necessary to suppose, how-
ever, that the course of evolution has always been in the direction

118

THE PROTOZOA

of that type of mitosis found in the cells of Metazoa ; it would be
more reasonable to expect that in some cases at least other distinct
types of division-mechanisms would have been evolved — side-

-^^-^--v^^^fcrr./? >*p

?e9;Wi^t<

v,

&

:P,-^

FIG. 64. — Division of Acanihocystis aculeata. A, Resting state of the animal.
N., Nucleus ; c., central grain ; a./., axial filaments of the pseudopodia, ps. ;
sp., spicules. B, Pseudopodia withdrawn ; nucleus in the spircme-stage ;
central grain dividing. C, Division of the central grain further advanced ;
nucleus showing distinct chromosomes. D, Central grain completely divided
into centrosomes, between which the nucleus is placed ; in the nucleus the
membrane is becoming dissolved, the rcticulum is becoming modified in
arrangement to form the achromathvc spindle (or a part of it), and the chromo-
somes are taking up their position in the equatorial plate. E, Complete
nuclear spindle, with centrosomes, achromatinic spindle, and equatorial plate.

F, Later stage with daughter-plates and division of the cell-body beginning.

G. Division of the nucleus and of the cell-body nearly complete. After
Schaudinn (82).

THE REPRODUCTION OF THE PROTOZOA 11§

branches, as it were, of the stem which culminates in the Metazoan
type. An example of this is seen in the peculiar karyokinesis of
Noctiluca (Fig. 65), in which the division is directed by a large
" sphere," consisting of a mass of archoplasm containing the cen-
trioles. The sphere divides and forms the axis of the karyokinetic
figure, of which the nuclear portion is placed asymmetrically to one
side.

In considering this remarkable process of evolution, consisting in
the gradual elaboration of a highly complicated mechanism for
division of the nucleus, the question naturally arises, What is the
object of a process so elaborate ? Or, if this method of posing the
problem offends as being too teleological, we may alter the phrase-
ology, and inquire, What is the result of the process ? The answer
is perfectly obvious. The result effected by equating karyokinesis

A

FIG. 65. — Stages in the nuclear division of Noctiluca miliaris. A, Early stage,
the "sphere" (sph.) beginning to divide, the nucleus wrapping round it;
B, later stage, the sphere nearly divided, the two poles of the nuclear spindle
in section attached to the two daughter-spheres ; G, section across B ; the
sphere contains a centriole (c.), to which the chromosomes (chr.) are attached
by achromatic fibrils. After Calkins (48).

in its most perfected forms is an exact halving, both quantitative
and qualitative, of the chromatin-substance of the nucleus — quanti-
tative, by division of each chromatin-granule or chromidiosome,
and the partition of the division-products equally between the two
daughter-cells ; qualitative also, if we suppose that different chro-
midiosomes may have different properties, and exert their own
peculiar influence on the life and activities of the cell ; then, since
each daughter-cell contains finally the sister-chromidiosomes of those
contained in the sister-cell, the qualities of its chromatin are the
exact counterpart of those of the sister-cell and also of the original
parent-cell. Hence karyokinesis may be regarded as insuring the
transmission to the daughter-cells of the distinctive properties of
the parent- cell, unimpaired and unaltered. The whole process indi-
cates clearly the immense importance of the chromatin-substance

120 THE PROTOZOA

in the life of the cell. It is probable, also, that the elaboration of
the process of karyokinetic division in Protista was an indispensable
antecedent to the evolution of multicellular organisms, since for
the formation of a tissue it is necessary that all the cells which
build it up should be perfectly similar in their constitution and
properties, and this condition could only be brought about, prob-
ably, by karyokinetic division of the nuclei in the process of cell-
multiplication.

In the foregoing paragraphs we have dealt only with simple
(binary) nuclear division, but, as already stated, in some cases the
nucleus divides by multiple fission into a number of daughter-
nuclei simultaneously. A simple instance of direct multiple division
of a nucleus, in which, apparently, no centrioles are present, has
been described by Lebedew (93) in the nuclei of Trachelocerca
(Fig. 66 ; see also p. 448). In this form partitions are formed
within the nucleus between the grains and masses of chromatin,
and finally the nucleus becomes segmented into a mulberry-like mass

of daughter - nuclei,
which separate from
one another.

In most cases, prob-
ably, of multiple
fission the nucleus

contains a centriole,
FIG. 66. — Four stages of direct multiple fission in •,,•• -,,- -, £ .

the nuclei of Trachelocerca phcenicopterus. After andtliemultlpJetlSSlon
Lebedew (93). is brought about in a

manner analogous to

the formation of a plasmodium by multiplication of the nucleus
in a cell which remains undivided — that is to say, the centriole
multiplies by fission a number of times without the nucleus as
a whole becoming divided. Thus, in a nucleus of the simple
protokaryon type, containing at first a single karyosome and cen-
triole, division of these structures may take place within the mem-
brane without the nucleus as a whole dividing, so that the nucleus
contains finally two or more karyosomes, each containing a cen-
triole. The karyosomes are ultimately set free from the nucleus,
either by being budded off singly from it, or by the nucleus as a
whole breaking up ; then each karyosome becomes the foundation
of a new nucleus. Division of this type, which may be termed a
multiple promitosis, has been described by Zuelzer (86) in Wag-
nerella. In cases where the division of the nucleus is of the karyo-
kinetic type, repeated divisions of the centriole result in the forma-
tion of a complicated multipolar mitotic figure, leading to a multiple
division of the nucleus, as seen in the divisions of the nuclei in the
male sporont of Aggregata (Fig. 67), as described by Moroff (94).

THE REPRODUCTION OF THE PROTOZOA 121

The presence of more than one centriole in a nucleus has led
Hartmann (60) to formulate the theory that such nuclei are to be
regarded as " polyenergid " nuclei.* Hartmann proposes to dis-
tinguish a nucleus with a single centriole as a " monokaryon " from
a polyenergid nucleus or " polykaryon " containing many cen-
trioles ; he interprets many cases, in which a nucleus appears to
become resolved into chromidia from which secondary nuclei are
formed, as being really a setting free of monokarya from a complex
polykaryon — an interpretation which certainly gets over the diffi-
culty of the formation
of centrioles in second-
ary nuclei (see further,
p. 255, infra).

In conclusion, men-
tion must be made of
the theory of cell-divi-
sion and of the causes
which bring it about,
put forward by Hertwig
(91, 92). This theory
is based on the sup-
position, of which men-

supra) — that for the

normal performance of FIG. 67.— Multiple nuclear division in the male

Vital functions a cer- sporont of Aggregate jacquemeti. The nucleus, of

. . which the outline has become irregular but is still

tain quantitative re- visible, is surrounded by eight centrioles, from

lation must be main- each of which striations pass towards and into

j -, A the nucleus. After Moroif (94), magnified 750

tamed between the iinear.

nuclear substance and

the cytoplasm. As a standard for the proportion of nuclear
mass and cytoplasm (" Kernpl as ma-Norm "), the individual im-
mediately after fission may be taken. Exact measurements made
on Infusoria show that, while the body grows continuously in size
from one division to the next, the nucleus at first diminishes slightly

* The conception of " energids " is due to Sachs, who coined the term to denote
" a single cell-nucleus with the protoplasm governed by it, so that a nucleus and
the protoplasm surrounding it are to be conceived of as a whole, and this whole
is an organic unity, both in the morphological and the physiological sense."
Hertwig (66) has criticized this conception, and has shown its untenability in the
case of Protozoa, which behave as single individuals whether they possess one
nucleus or many. Hartmann, considering the centriole as the criterion of in-
dividuality rather than the nucleus, has revived the energid theory in the manner
described above. It leads him to regard an ordinary Metazoan karyokinesis as
the division of a polykaryon, in which each separate chromosome represents a
distinct nuclear element or monokaryon — a conclusion which appears to lead rather
to a reductio ad absurdum of the theory.

122 THE PROTOZOA

ill size, and then grows slowly until the next division-period is
reached. As a result of the slow " functional growth " of the
nucleus, a disproportion between the mass of the nuclear substance
and that of the cytoplasm is brought about, producing a condition
of tension between the nucleus and the cytoplasm (" Kernplasma-
Spannung "). When the tension reaches a maximum, the nucleus
acquires the power of growing rapidly at the expense of the cyto-
plasm, and this " division-growth " leads to the fission of the cell,
restoring the standard balance of nucleus and cytoplasm. Relative
increase of the nuclear substance retards the cell-division, and
brings about increase in the size of the cell ; relative decrease of the
nuclear mass has the opposite effect.

2. Division of the, Cell. — A distinction has been drawn above
between binary fission, or division of the body into two, and mul-
tiple fission into many parts simultaneously. The daughter-indi-
viduals produced in either case may be similar to the parent-indi-
vidual in all respects except size, or may differ from it in lacking
more or fewer of its characteristic parts and organs, which are then
formed after the daughter-individuals are set free. In extreme
cases one or more of the daughter-individuals may possess, when
first liberated, no structure more elaborated than the essential
parts of a cell, cytoplasm and nucleus or chromidia ; in such cases
the daughter is termed a " bud," and the process of fission by which
it arises is termed " budding " or gemmation, distinguished further as
" simple gemmation " when only one bud is formed at a time, and
" multiple gemmation " when many arise simultaneously. In many
cases of multiple gemmation the parent- organism does not survive
the process, but breaks up almost completely into buds, leaving
only a greater or less amount of residual protoplasm, which degene-
ates and dies off ; budding of this kind is termed sporulation.

In binary fission, when the organism is of simple structure, as in
the case of amcebse, the division is equally simple. After division
of the nucleus, the two daughter-nuclei travel apart, and the body
follows suit, by flowing, as it were, in two opposite directions,
forming two smaller individuals each with a nucleus, and con-
nected at first by a protoplasmic bridge, which soon snaps and is
drawn in. The contractile vacuole, if present, is taken over by
one of the two daughter-individuals, while the other forms a new
vacuole ; in many cases the normal number of contractile vacuoles
is doubled before division begins.

In forms of more complicated structure, the division also becomes
a more complex process. Where the body-form is definite, the
plane of cleavage bears usually a constant relation to it. Thus, in
Ciliata the division of the body takes place typically transversely
to its longitudinal axis, except in the order Peritricha. In Flagel-

THE REPRODUCTION OF THE PROTOZOA

123

v^:l^^^Mx,^:>^

rv*.-..r-:;,t-o • • v -;;v

v^rh';«gF#&-;:..v:

»S:fesi

FKJ. 68. — Budding of Acanthocystis aculeata (compare Fig. 64, ^4). J, B, Division
of the nucleus, in which the central grain takes no part ; C, extrusion of a
bud ; D, three buds in process of extrusion, the nucleus of the parent dividing
again ; E, free bud ; F, flagellula, and G, amcebula, produced from buds ;
// and /, two stages in the extrusion of a centriole from the nucleus of a bud
to form the central grain of the adult form. After Schaudinn (82).

124 THE PROTOZOA

lata, on the other hand, the division of the body is usually longi-
tudinal. In any case, the two products of fission may be equal or
subequal in size, without perceptible difference of parent and
young ; or they may be markedly unequal, in which case parent
and offspring can be distinguished clearly.

The various organs of the body may be doubled before division :
either by splitting or new growth of one set ; or, if there are many
organs of a particular kind present, such as the cilia and tricho-
cysts of Ciliata, they may be simply shared between the two
daughter-organisms ; or, finally, any given organ present in the
animal before division may be retained by one of the two daughter -
individuals, while the other forms the organ in question anew after
division. Thus, in Ciliata one daughter-individual retains the old
peristome ; the other forms a new one for itself. The greater the
number of organs formed afresh in the daughter-individual, the
more advanced is the transition from ordinary fission towards
budding.

In typical gemmation small portions of the parent- organism
grow out, into which pass either nuclei, the products of the division
of the parent-nucleus (Fig. 68), or of budding from the nucleus of
the parent (Fig. 55), or chromidia, alone or together with a nucleus.
Such buds may arise on the surface of the parent-body, or they
may be cut off in the interior of the cytoplasm of the parent, and
may remain for some time within its body. Endogenous budding
of this kind is seen in the Neosporidia (p. 325), in the Acinetaria,
where it is combined with nuclear budding, and in Arcella (Fig. 80)
and some amoebae, where it is combined with formation of secondary
nuclei from chromidia.

Bibliography. — For references see p. 479.

CHAPTER VIII
SYNGAMY AND SEX IN THE PROTOZOA

Ki/rrpi papela,
Kvirpi vefj.e<Tffa.ra., Kvirpi dvarolcriv cbrex^7?*-

IT is a matter of common knowledge that amongst all the higher
animals and plants the phenomena of sexual generation and sexual
differentiation are of universal occurrence. Reduced to its simplest
terms, and stripped of all secondary complications, the sexual
process in an ordinary animal or plant consists essentially of the
following series of events : In the multicellular body certain cells
are produced which may be termed comprehensively and universally
the gametes. In the two sexes the gametes exhibit characteristic
differences ; those of the male sex, the spermatozoa, are typically
minute, active, and produced in large numbers ; those of the female
sex, the ova, are, on the contrary, relatively bulky, inert, and
produced in far fewer numbers. The gametes are set free from the
body, or, at least, from the organs in which they arise, and each
male gamete, if it finds a partner and if circumstances permit,
unites with a female gamete ; their bodies fuse completely, cell
with cell and nucleus with nucleus, and the product is a " fertilized
ovum," or zygote, a single cell which proceeds to multiply actively
by cell-division, the final result being a new multicellular individual.

In the Protista belonging to what has been termed in the first
chapter of this book the " cellular grade " — that is to say, in the
Protozoa and the unicellular plants sexual phenomena are also of
widespread, probably of universal, occurrence, and the process of
sexual union differs only in unessential points from that seen in
higher organisms.

In the first place, since the individual in Protozoa is a single cell,
the gametes themselves are also complete individuals, modifica-
tions merely of the ordinary individuals of the species produced at
certain periods or phases of the life-cycle.

Secondly, the differentiation of male and female gametes rarely
attains to the high degree seen in the Metazoa, and may be nil ;
the two gametes may be perfectly similar in all perceptible features
of structure or constitution, as, for example, Copromonas (Fig. 111).

125

126 THE PROTOZOA

Sexual union of similar gametes is termed isogamy ; of dissimilar,
anisogamy. When the gametes are differentiated, then one gamete
is generally smaller, more active, often with highly developed
motor mechanisms, and without reserve food-material in the
cytoplasm ; this is the microgamete, regarded as male. The other
gamete, on the contrary, exhibits a tendency, more or less pro-
nounced, to be large, inert, without motor mechanisms of any
kind, and to store up reserve food-material in the cytoplasm —
the macrogamete, regarded as female. The differentiation of the
gametes is seen to be a specialization of two kinds of cell-individuals,
the one rich in motile or kinetic protoplasm but poor in trophic
substance, the other rich in trophic protoplasm but poor in kinetic
substance. In some cases the sexual differentiation may affect
also the mother-cells of the gametes, the gametocytes, or may be
thrown back still farther in the series of generations preceding
the gametes ; in such cases a number of successive generations of
gamonts exhibiting sexual differentiation terminate in a gameto-
cyte generation from which the actual gametes arise.

Thirdly, in the process of sexual union, or syngamy, as it may
be termed comprehensively, the bodies of the two gametes do not
always fuse completely ; in some cases the two gametes come
together and merely interchange portions of their nuclear apparatus,
remaining separate and retaining their distinct individuality. The
nucleus which remains stationary in the one gamete then fuses
with the migratory nucleus derived from the other gamete.
Examples of this type of syngamy are seen in the Infusoria (Fig. 77).
The type of syngamy in which the two gametes fuse completely
is sometimes termed copulation (or total karyogamy) ; that in which
they remain separate and exchange nuclear material, is known as
conjugation (or partial karyogamy), and the two sexual individuals
themselves as conjugants (they should not, perhaps, be termed
" gametes," strictly speaking, for reasons explained below) ; but
the term " conjugation " is often used quite loosely for either type
and lacks precision.

These differences in the sexual process between Protozoa and
the higher organisms enable us to give a wider significance, and
at the same time a more precise definition, to the word " syngamy."
However varied in detail, syngamy is essentially nothing more
than an intermingling of chromatin-substance derived from two
distinct cell-individuals. Plus qa change, plus c'est la meme chose.
The chromatin that undergoes syngamic union may be in the
form either of chromidia or of nuclei ; in the former case the process
is termed chromidiogamy, in the second karyogamy. Chromidiogamy ,
though probably the most primitive type, is known to occur only
in a few Sarcodina (Difflugia, p. 230 ; Arcella, p. 148). In the vast

SYNGAMY AND SEX IN THE PROTOZOA

127

majority of Protozoa, as in all known cases amongst Metazoa and
plants, syngamy takes the form of karyogamy. The nuclei of
the gametes are termed pronuclei, and the nucleus that results
from fusion of the pronuclei in the zygote is termed a synkaryon.

In many Protozoa (e.g. Coccidium, Fig. 69) the fusion of the two pronuclei
is effected by means of a peculiar mechanism termed a " fertilization-
spindle." When the two pronuclei are in contact, the female pronueleus
first takes an elongated, fusiform shape, having its chromatin-grains spread
over an achromatinic framework. The chromatin of the male pronucleus
is then spread over the same structure. This mechanism has nothing to do
with nuclear division, but merely effects a complete intermingling of the
cliromatin of the pronuclei, after which the synkaryon assumes its normal
appearance and rounded form. In Infusoria the two pronuclei fuse in the
condition of the karyokinetic spindle in many cases.

FIG. 69. — Fertilization] of Coccidiumlschubergi. A, Pene-
tration of the macrogamete by] one of five micro-
gametes ; the female pronucleus has an elongated
form ; B, the favoured microgamete has passed into
the interior of the macrogamete, which has secreted a
membrane (ob'cyst) at the surface of the body, ex-
cluding the other microgametes ; C, the female pro-
nucleus has assumed an elongated, spindle-like form,
while the male pronuc^us lies at one pole of the
spindle in the form of a little mass of granules ; the
excluded microgametes are degenerating ; D, the granules of the male pronuqleus
have spread themselves over the spindle-figure formed by the female pronucleus ;
E, the fertilization-spindle soon in D has rounded itself off to form the synkaryon.
and fertilization is complete. 3 , Microgametes ; $ , macrogamete \ n$ , male
pronucleus; n% , female pronucleus; /.«., fertilization-spindle; c, oocyst ; n^ ,
synkaryon. After Schaudinn (99), magnified 2,250.

True sjTigamy, as defined above, must be distinguished carefully from
certain other phenomena which are likely to be confused with it ; it must
not be assumed that every fusion of cells, or even of nuclei, is necessarily a
case of syngamy. In some Protozoa the mother- cells of the gametes, the
gametocytes, enter into a more or less close association prior to the formation
of gametes, which are produced in due course and then perform the act of
syngamy in the normal manner. An example of such association is seen
in gregarines (p. 330), where association between adult gametocytes is the
rule. Sometimes the two gametocytes associate in the earliest stages of
their growth, as in Diplocystis (Fig. 70, A], and their bodies may then fuse
completely into one ; but their nuclei remain distinct, as in Cystobia
(Fig. 70, B), and give rise in due course to the pronuclei of distinct gametes.
Forms in which precocious association of this kind occurs are described as
being " neogamous " (Woodcock).

In many cases, union of distinct individuals can be observed which have
nothing to do with syngamy, since no fusion takes place of nuclei, but only

128

THE PROTOZOA

of cytoplasm. Such unions are distinguished as plastogamy (or plasmogamy)
from true syngamy. Plastogamic union may be temporary or permanent ;
in the latter case it leads to the formation of plasmodia, as in the Mycetozoa
(p. 239). The significance of plastogamy is obscure in many cases, but in
some it may perhaps be comparable to the association of gametes already
described, and in this way may throw light on some cases of so-called
" autogamy" (see p. 138, infra).

A further case of unions which are not in any way sexual in nature is seen
in the remarkable phenomena of agglomeration exhibited by some Protozoa —
for example, trypanosomes. In this case the organisms adhere to each other
by the posterior or aflagellar end of the body, apparently by means of a sticky
secretion formed by the kinetonucleus, so that large clumps are formed
composed of numerous individuals. The phenomena of agglomeration are
associated with conditions unfavourable to the parasite, and appear to be
due to the formation of special substances, agglutinins, in the blood of the
host. Similar phenomena are well known in bacteria as agglutination, since
in this case the agglutinated individuals are unable to separate, while in

FIG. 70. — Precocious association and neogamy of gametocytes in gregarines.
A, Diplocystis minor, parasite of the cricket: m., common membrane uniting
the two associates ; g., grains of albuminoid reserve-material. B, Cystobia
holothurice, parasite of Holothuria tubulosa, showing the two nuclei in an
undivided body. A after Cuenot, magnified about 120 diameters ; B after
Minchin.

the case of trypanosomes that are agglomerated it is possible for the indi-
viduals to become free again if the conditions are ameliorated. In other
Protozoa, also, phenomena of the nature of agglomeration are seen in de-
generating forms (see p. 209, infra).

Certain aspects of syngamy must now be discussed in more
detail — namely, the relation of syngamy to the life-history as a
whole ; its occurrence in the world of living beings ; its significance
for the life-cycle ; and its effects on the species and the individual.

1. Syngamy in Relation to the Life-History of the Organism. —
In any living organism the principal manifestation of vital activity
is the power of assimilation, resulting in growth. As a general
rule, however, the growth of an organism is not indefinite, but has
a specific limit ; an individual of a given species does not exceed
a certain size, which may be variable to a slight extent, but which
is fairly constant for normal individuals of the species in question
under similar environmental conditions. When the limit is

SYNGAMY AND SEX IN THE PROTOZOA 129

reached the organism tends to reproduce itself. In Protista, as
described in the last chapter, two principal types of reproduction
occur — namely, simple or multiple fission. In either case the
organism grows to its full specific size, and then divides into smaller
individuals ; the greater the number of daughter-individuals pro-
duced at each act of reproduction, the more minute those daughter-
individuals. Following the act of reproduction comes a period
of growth, during which the small forms grow up into full-sized
individuals which reproduce themselves in their turn.

Thus the life-history of a Protist may be described as an alterna-
tion of periods of growth and periods of reproduction. If, how-
ever, the life-history consists of only these two events in alternating
succession, it is an infinite series, not a cycle ; continuous, not
recurrent. Possibly such a condition, varied only by states of
repose interrupting the vital activity of the organism, is found in
Bacteria and allied forms of life, where true syngamy apparently
does not occur. But it is probable that in all Protozoa, as in all
Metazoa and plants, the life-history is a recurrent cycle, of which
an act of syngamy may be taken as the starting-point ; this point
will now be discussed.

2. The Occurrence of Syngamy in the Series of Living Beings. —
With regard to this question, there are two possibilities ; first, that
syngamy and sexuality constitute a fundamental vital phenomenon,
common to all living things ; secondly, that it is an acquisition at
some period or stage in the evolution of organisms, and not a
primary characteristic of living beings. The sex-philosopher
Weininger* has argued in favour of the first of these hypotheses,
and goes so far as to regard all protoplasm as consisting primarily
either of arrhenoplasm (male) or thelyplasm (female), standing in
fundamental antithesis to one another, and combined in varying
proportions in a given cell or sample of the living substance. A
view essentially similar has been put forward by Schaudinn, and
is discussed below.

It is beyond question that sexuality is a universal attribute of
all living beings above the rank of the Protista, whether animals
or plants. In Protista, however, syngamy has not been observed
to occur with certainty in the Bacteria and organisms of a similar
type of organization. It is true that certain rearrangements of
the chromatin, observed in some larger organisms of the bacterial
type at certain phases of their life-history, have been compared to
sexual processes, but such an interpretation is, to say the least,
highly doubtful. In Protozoa, syngamy has been observed to
occur in a vast number of forms, but by no means in all. In the

* Weininger, 0., " Sex and Character," chapter ii. London : W. Heinemann,
1906.

9

130 THE PROTOZOA

case of those species in which syngamy has not been observed,
there are three abstract possibilities : first, that it does occur,
but has not yet been seen ; secondly, that it is secondarily in
abeyance ; thirdly, that it is primarily absent — that is to say, that
it has never occurred either in the form in question or in its ancestral
lineage. On the whole, the first of these three possibilities is the
most probable, though the second must, perhaps, also be taken
into account, as will be shown later.

So far as a generalization is possible or permissible in the present
state of knowledge, it appears that sex and syngamy are phenomena
of universal occurrence in all truly cellular organisms, but we have
no certain knowledge that they exist in any organisms of the
bacterial type of organization. With the passage from the bacterial
to the cellular type of structure, syngamy became, apparently, a
physiological necessity for the organism, and was probably acquired
once and for all.

3. The Significance of Syngamy in the Life-Cycle. — In order
to appreciate the part that syngamy plays in the life-histories of
organisms generally, it is necessary to compare briefly and in
general outline the life-cycles of Metazoa and Protozoa in typical
cases.

In the Metazoa the cycle starts from a single cell, the zygote
or fertilized ovum, which multiplies by cell-division in the ordinary
way. Thus is produced a multicellular individual, composed
always of at least two classes of cells — tissue-cells (histocytes) and
germ-cells. The histocytes are differentiated in various ways,
related to various functions, to form tissues, and so build up the
soma. The germ-cells are not differentiated for any functions but
those of sex and reproduction, and occur primarily as a mass of
undifferentiated cells constituting the germen ; they are lodged
in the soma and dependent upon it — parasitic upon it, so to speak
— but in a sense distinct from it ; they draw their sustenance from
the soma, influence greatly its development and activities, but
contribute nothing to the work of the cell-commonwealth. Of
these two portions of the Metazoan individual, the soma is neces-
sarily mortal, doomed inevitably to ultimate senility and decay.
The cells of the germen, on the other hand, are potentially im-
mortal, since under favourable conditions they can separate
from the soma and give rise in their turn to a new individual of
the species with soma and germen complete again. This type of
generation is always found in every species, though ion-sexual
methods of generation may also occur in many cases.

In the life-cycle of the Metazoa, as sketched above in its most
generalized form, two individualities must be clearly distinguished,
the one represented by the soma together with the germen, con-

SYNGAMY AND SEX IN THE PROTOZOA 131

stituting the complex body of a Metazoan individual ; the other
represented by the single cells of which both soma and germen
alike are built up. The phrase " reproduction," whether sexual
or non-sexual, as applied to the Metazoa, refers only to the complex
multicellular body as a whole, and not to its constituent cells,
which reproduce themselves uninterruptedly by fission during the
whole life-cycle.

In the comparison of a typical Protozoan life-cycle with that of
the Metazoa, we may start in both cases alike from a single cell-
individual which is the result of an act of syngamy. In Protozoa,
also, the zygote multiplies, sooner or later, to produce numerous
cell-individuals ; but in this case the cells remain separate from
one another and independent, so that no multicellular body is
produced, except in the colony-building species, nor is there any
distinction of somatic and germinal cells, save in rare cases, such
as Volvox (p. 267). In Protozoa the phenomena of vital exhaustion,
so-called " senility " (Maupas) or " depression " (Calkins, Hertwig),
appear to be as inevitable as in the cells of the Metazoan body
(see pp. 135 and 208, infra) ; but if the derangement of the bodily
functions and the vital mechanism has not gone too far, the organism
is able to recuperate itself by self -regulative processes, of which
the most important and most natural are those involved in the
normal process of syngamy. Consequently no cell - individuals
among Protozoa are doomed necessarily and inevitably to decadence
and death, but r I possess equally potential immortality — that is
to say, the capacity for infinite reproduction by fission under favour-
able conditions. The Metazoan individual is represented in the
Protozoa only by the entire life-cycle, from one act of syngamy to
the next, and not by any living organic individual.

In the life-cycle of a Protozoon, as there is only one individuality,
so there is only one method of reproduction — that, namely, of the
cell, by fission ; and it must be made clear that the reproduction
of the cell-individual is not in any special relation to syngamy
in Protozoa, any more than in Metazoa.

It has been pointed out above that the life-history of a Protist
organism consists of alternate periods of growth and reproduction.
In those Protozoa in which syngamy has been observed, it is found
to take place sometimes at the end of a period of growth and before
a period of reproduction, sometimes at the end of a period cf
reproduction, and before a period of growth, and sometimes there
may be a difference between the two sexes of the same species
in this respect. In the first case, syngamy takes place between
full-grown individuals of the species, as in Actinophrys (Fig. 71) —
so-called macrogamy, which is almost always isogamous. In the
second case, syngamy is between the smallest individuals produced

132

THE PROTOZOA

by fission or gemmation, as in Foraminifera (p. 235), Arcella
(Fig. 80), etc. — so-called microgamy, which may be isogamous or
slightly anisogamous. In the third case, syngamy is between two
individuals showing the utmost disparity in size, a tiny micro-
gamete and a bulky macrogamete, as in Coccidium (Figs. 69, 152) ;
the result being anisogamy of the most pronounced type.

From these facts, it is abundantly clear that syngamy in the
Protista cannot be regarded as related specially to reproduction,
but as a process affecting the life-cycle as a whole, related equally

FIG. 71. — Copulation of Actinophrys sol. A, Two associated free-swimming
individuals. B, The two individuals are beginning to encyst themselves ; their
nuclei (N., N.) are preparing for karyokinesis ; an outer gelatinous envelope (g)
is secreted round the two gametes/ and also round each individual an inner
cyst-envelope (c. ), incomplete at the surface of contact. C, The nucleus of each
gamete is dividing by karyokinesis (first polar spindle, p.sp.). D, Formation
of the polar bodies or reduction-nuclei (r.n.) ; the reduced pronuclei (pn.)
take a central position in the body of the gamete ; the bodies of the gametes
are beginning to fuse. E, The pronuclei are fusing ; the reduction-nuclei have
passed through the wall of the inner cyst. F, The synkaryon (sk. ) is beginning
to divide by karyokinesis ; the degenerating reduction-nuclei have passed out
of the inner cyst. N., N., Nuclei of the gametes before reduction. After
Schaudinn, magnified about 850.

to all vital functions of the organism, and therefore only indirectly
to reproduction — that is to say, only in so far as reproduction may
result from renewed and invigorated vitality. This is equally
true of the Metazoa, where, however, the life-cycle begins and ends
with the production of a complex multicellular body, composed
of soma and germen. Hence, in the Metazoa syngamy is brought
into relation with the production of a higher individuality, the
body, comparable to the whole Protozoan life-cycle, and it is in
this sense that the phrase " sexual reproduction " must be under-

SYNGAMY AND SEX IN THE PROTOZOA 133

stood ; as already pointed out, syngamy has no special relation
in Metazoa to cell-multiplication. In Protozoa sexual reproduction
means simply reproduction following the sexual act ; but sex and
reproduction must be considered as two things entirely distinct.

The comparison instituted above between the life-cycles of the Protozoa
and Metazoa, according to which an entire Protozoan individual is the mor-
phological equivalent of a single constituent cell of a Metazoan body, is that
which I personally have always held and taught. It is, I believe, the pre-
vailing view among zoologists, and has been enunciated clearly by Calkins (5).
It has, however, been attacked vigorously by Dobell (110), who lays great
stress on the physiological analogy between the single Protozoon, as a com-
plete organism, and the entire Metazoan body. On this ground he expresses
the view that " a protist is no more homologous with one cell in a metazoon
than it is homologous with one organ (e.g., the brain or liver) of the latter " ;
he considers it " incredible that anybody could advocate the view that the
Metazoa have arisen from aggregated Protozoa," and he puts forward the
view that, if the Metazoa have arisen from protist forms, "it is far more
natural to suppose that they did so by developing an internal cellular structure,
and not by the aggregation of individuals to form a colony." Similar ideas
have been put forward also by Awerinzew (890). From these and other
considerations, Dobell draws the conclusion that the Protista are not to be
regarded as unicellular, but as " non- cellular " organisms.

So far as the word " cell " is concerned, I have already expressed the
opinion above that by the term should be understood a certain stage in the
evolution of the Protista, and that many protist organisms should not be
termed " colls," but only those which have reached what may be considered
as the truly cellular type of organization. I am not, therefore, concerned
with Dobell's attack on his own conception of the cell- theory so far as it
concerns Protists generally, but only in so far as it applies to the Protozoa.

It is not possible here to discuss in detail the ontogenetic development of
the Metazoa. It must suffice to state that in all primitive types of embryonic
development among Metazoa the cells which build up the body originate
by repeated binary fission of a single cell, the fertilized ovum ; and that the
only cases in which the ovum breaks up into cells by the development of cell-
limits internally are those in which the development is modified by the
presence of yolk, or where there is good reason to believe that yolk was
ancestrally present in the egg. For confirmation of these statements the
reader must be referred to the ordinary textbooks of embryology. I must
content myself with a single instance, that, namely, with which I am best
acquainted by personal study.

In the development of a simple Ascon sponge, such as Clathrina Uanca or
other species (see chapter " Sponges" in Lankester's " Treatise on Zoology,"
part ii., p. 68), the ontogeny may be divided into four phases or periods,
which indicate clearly, in my opinion, the general lines in the evolution of
the Metazoa from Protozoan ancestors.

1. Starting with the fertilized ovum, strictly homologous with a Protozoan
zygote, it divides by repeated binary fission into a number of cells (blasto-
meres), each similar to the ovum in every respect except size ; the process
is in every way comparable to the division of a Protozoan zygote into a
number of individuals which remain connected to form a colony, as, for
example, in many Phytomonadina.

2. Of the blastomeres thus formed, a certain number, variable in different
species, but relatively few, retain their original characteristics, while the rest
become differentiated into columnar flagellated cells forming the wall of a
cavity (blastoccele). The undifferentiated blastomeres give rise to the
archsGOcytes, from which ultimately the germ-cells and gametes arise. The
flagellated cells are the ancestors of the tissue-cells (histocytes) in the future
sponge. At this stage, in which the embryo is hatched out as a free-swimming

134 THE PROTOZOA

larva, it is perfectly comparable to a colony of flagellates such as Volvox, in
which the ordinary individuals have lost the power of becoming, or giving rise
to, gametes, which can only arise from certain special individuals.

3. The free-swimming larva, composed mainly of flagellated cells, with
the archaeocytes either at the hinder pole or in the internal cavity, undergoes
changes as it swims about, which consist in some of the flagellated cells losing
their flagcllum, becoming modified in structure, and migrating into the
interior of the larva ; in this manner the two germ-layers are established, and
the organism has then, so to speak, passed from the condition of a Protozoan
colony to that of a true Metazoon.

4. When the germ-layers are established, the larva fixes itself, and of the
subsequent development it is sufficient to state that the cells of the two
germ-layers become differentiated into the tissues of the adult sponge, and
that in the metamorphosis of the larva the cells undergo a complete rearrange-
ment, which shows clearly that every cell has an individuality as distinct
as that of any Protozoan individual, a conclusion fully borne out by the
recent experiments of Wilson and Huxley (Phil. Trans., B., ccii., pp. IBS-
ISO, pi. viii.) on the power of regeneration in sponges after complete separation
of the cells from one another.

I am unable, therefore, to accept the standpoint of Dobell with regard
to the relations of Protozoa and Metazoa, but consider that the comparison
of a Protozoan individual to a single cell in a Metazoan body is fully justified
both morphologically and physiologically, and is a reasonable phylogenetic
deduction from the ontogenetic data. The objection that there are no animals
known which correspond to the four-cell, eight-cell, and blastula stages in
embryological development misses the point and is not strictly true ; the
stage at which an embryo consists only of four or eight blastomeres is the
homologue of a Protozoan colony, and in the Flagellata species are known
in which the colony consists only of four, eight, sixteen, or thirty-two cell-
individuals (p. 275). To the query, " Has anyone ever found a metazoon
which is composed of nothing but coherent gametes ?" it may be replied
that in many Volvocineae the colony also consists only in part of gamete-
producing individuals. The theory that the Metazoa arise by cleavage of a
multinucleate plasmodium, equivalent to a single Protozoan individual, has
often been put forward, but has never found support from a general con-
sideration of the facts of Metazoan embryology. In Protozoa the plasmodial
phase is always temporary, and ends sooner or later by breaking up into
separate uninucleatc individuals.

4. The Effects of Syngamy — (1) upon the Individual, (2) upon
the Species. — 1. Of all Protozoa, the ciliate Infusoria are the
group in which syngamy is most easily observed and studied — in
the first place because in these organisms it is readily distinguished
from simple fission, which is transverse, while in syngamy the two
conjugants apply themselves laterally to one another ; in the
second place, owing to the fact that the species of Ciliata are
practically monomorphlc (p. 440), and can be identified without
difficulty. Hence in this group elaborate and exhaustive experi-
mental studies upon syngamy and its relation to the life-cycle
have been carried out by many investigators, more especially by
Maupas, Hertwig, Calkins, and Woodruff. The results of these
investigators is briefly as follows : After syngamy the fertilized
individuals appear vigorous, feed actively and multiply actively.
After many generations of reproduction by fission, however, the
race, if kept in an unchanged environment, becomes less vigorous

SYNGAMY AND SEX IN THE PROTOZOA 135

and shows signs of enfeeblement and " senility " or " depression " —
a condition which, with continued isolation, reaches such a pitch
that the organism is unable to assimilate, grow, or reproduce, but
dies off inevitably unless conjugation with another individual
takes place. At a result of syngamy, the vigour of the race is
renewed, and the organisms once more grow and reproduce them-
selves actively until senility supervenes again. From these and
many other facts it would appear as if syngamy produced a
strengthening or re-organizing effect upon the organism, restoring
vigour and activity to vital functions that have become, as it were,
worn out and effete.

One very important discovery has resulted from the experi-
ments of Calkins and Woodruff — namely, that the necessity for
syngamy can be greatly deferred by change of environment. A
strain which has become senile and exhausted can be stimulated
and revived by a change of food. Even this remedy appears to
have its limits, however, a degree of exhaustion being reached
sooner or later which nothing can restore to its pristine vigour.
The animals may even reach a pitch of exhaustion so great that
they are unable to conjugate, but die off in a helpless manner.
Calkins explains such cases as due to the senility having affected
not only the vegetative, but also the generative chromatin ; pro-
ducing generative senility, which is incurable, instead of mere vege-
tative senility, for which syngamy is a remedy. Nevertheless, the
fact that the advent of senility and exhaustion can be deferred by
the stimulation of changed conditions is a very important discovery.
It must be remembered that the Ciliata are organisms of extremely
complex organization, and it is not unreasonable to suppose that
in such forms the work thrown upon the vegetative chromatin is
much heavier, and therefore the tendency to exhaustion much
greater, than it would be in an organism of simpler constitution ;
in such a form the stimulus of change of environment might defer
the advent of senility very greatly, perhaps even for an indefinite
period (Woodruff, 141).* This suggestion applies particularly to
parasitic forms, in which the organization is always greatly simpli-
fied, and in which change of environment from generation to
generation is inseparable from their mode of life. It would not be
surprising, therefore, if syngamy were found to be completely in
abeyance in a parasitic form of simple structure.

It should be noted here that examples of syngamy being in
abeyance are not wanting even in higher organisms. An instance

* In his most recent work on Paramecium, Woodruff (142) expresses the view
that " most, if not all, normal individuals have, under suitable environmental
conditions, unlimited power of reproduction without conjugation or artificial
stimulation." Compare also Woodruff and Baitsell (143).

136 THE PROTOZOA

is the banana-tree. In the wild-banana, seeds are produced from
flowers of a normal type by fertilization, just as in any other flower-
ing plant ; in the cultivated banana, however, the flowers are
sterile and incapable of fertilization, consequently the tree bears
fruit which are entirely seedless. Hence the cultivated banana-
tree is propagated entirely by a non-sexual method — namely, by
the production of suckers growing up from the roots, and in no
other way. Whether this complete abolition of sexuality will in
time lead to exhaustion of the cultivated race of banana remains
to be seen, but at present there seem to be no signs of loss of vigour
under cultivation.

If syngamy can be entirely dispensed with in an organism rela-
tively so high in the scale of life as a flowering plant, it seems
probable in the highest degree that the same may be true in many
cases for unicellular organisms of simple structure, and especially
for those parasitic forms which live, like cultivated plants, in a
medium rich in nutritive substances, and in an environment which
is changed at least once in each developmental cycle. Instances
of this are perhaps furnished by the various species of pathogenic
trypanosomes, strains of which have been brought to Europe and
propagated for many years from one infected animal to another
by artificial inoculation, without the natural agency of an inverte-
brate host. If it be true, as is generally believed, that in trypano-
somes syngamy takes place in the invertebrate host, then in the
long-continued artificial propagation of pathogenic trypanosomes
sexuality has been in abeyance for a vast number of generations
without any apparent loss of vital powers. The case of the patho-
genic trypanosomes cannot, however, be cited, in the present
state of our knowledge, as an absolutely conclusive example of
syngamy in abeyance, since it is by no means certain that this
process does not take place in the vertebrate host, where its
occurrence has frequently been affirmed (see p. 305, infra). But
it is certain that in trypanosomes generally, whether pathogenic
or non-pathogenic, syngamy is a rare phenomenon, since it has not
yet been demonstrated satisfactorily in a single instance, either in
the vertebrate or the invertebrate host, in all the many species
that have been studied. It is possible that, in these and many other
forms of life, sexual processes may intervene only at long intervals
in the life-history, and by no means in every complete cycle of
development or alternation of hosts. It then becomes necessary
to distinguish a developmental cycle, consisting of a recurrent
series of similar form-changes in regular succession, from a complete
life-cycle marked by the occurrence of an act of syngamy. In
such forms as the parasites of malaria, for example (p. 358), the
life-cycle and the developmental cycle coincide — that is to say,

SYNGAMY AND SEX IN THE PROTOZOA

137

syngamy occurs once for each complete cycle of development
with alternation of hosts, though it must not be forgotten
that the development in the vertebrate host comprises a vast
and quite indefinite number of generations of the parasite. On
the other hand, in such forms as trypanosomes, a complete life-
cycle, from one act of syngamy to the next, may comprise, ap-
parently, a great number of developmental cycles and alternations
of hosts.

From the foregoing considerations it is evident that syngamy,
though usually a necessity for the continued existence of uni-
cellular no less than of
multicellular organisms,
can be dispensed with for
a very large number of
generations, perhaps even
indefinitely, in some in-
stances or under special
circumstances. Two other
phenomena of apparently
widespread occurrence
point to the same con-
clusion — namely, the phe-
nomena of parthenogenesis
and autogamy. Partheno-
genesis is a mode of re-
production so common in
Metazoa of various classes FIG. 72. — Parthenogenesis of Plasmodium vivax.

, A female gametocyte, of wWch the nucleus
is dividing into a darker portion (n1) and a
lighter portion (n2); B, the separation of the
two Parts is complete ; C, the darker nucleus
has divided into a number of portions ; D, a
number of merozoites are formed from the
darker nuclei ; the lighter nucleus is abandoned
in the residual protoplasm (r.p.) containing
the meianin-pigment. After Schaudinn (130)

that it is unnecessary to

J
Cite instances of it here ;

it may be defined briefly

, , - J

as the power to develop

without syngamy possessed
i ,„ 11 T-ff ,. , j

by a sexually-differentiated

gamete, which under nor-
mal circumstances could do so only after syngamy with a
gamete of the opposite sex. To this it must be added that
the gamete which has this power is always the female ; but this
limitation receives an explanation from the extreme reduction
of the body of the male gamete and its feeble trophic powers,
rendering it quite unfitted for independent reproduction, rather
than from any inherent difference between the two sexes in
relation to reproductive activity. Parthenogenesis has been de-
scribed by Schaudinn for the human malarial parasite (Fig. 72)
and in Trypanosoma noctuce, and by Prowazek for Herpetomonas
muscce-domesticcB ; none of these cases, however, are entirely free

138

THE PROTOZOA

from doubt, and in any case parthenogenesis seems to be of much
rarer occurrence among Protozoa than among Metazoa.*

Autogamy, on the other hand, is a phenomenon which has been
frequently observed in Protozoa, chiefly, though not exclusively,
among parasitic forms ; it may be defined as syngamy in which the
two gametes, or at least the two pronuclei, that undergo fusion
are sister-individuals derived by fission of the same parent cell
or nucleus. Hartmann (116) has brought together the many cases
of autogamy known to occur among Protozoa and other Protist
organisms, and has classified them under a complex terminology.
It is sufficient here to mention two typical cases, those, namely,

of Actinosphcerium
and Entamceba coli,
made known by R.
Hertwig (64) and
Schaudinn (131) re-
spectively.

In Actinosphcerium
an ordinary indi-
vidual (Fig.} 3) be-
comes encysted as
a multinucleate
" mother - cyst ,"
which becomes di-
vided up into a num-
ber of uninucleate
"primary cysts,"
after absorption of
about 95 per cent, of
the nuclei originally
present. Each pri-
mary cyst then di-
vides completely into
two distinct cells —
" secondary cysts."

Each secondary cyst then goes through a process of nuclear re-
duction (see below), after which it is a gamete ; the two gametes
then fuse completely, cell and nucleus, to form the zygote.

* Prowazek (557) has described in Herpetomonas muscce-domesticce a process
interpreted by him as parthenogenesis (" etheogenesis ") of male individuals, but
the correctness both of his observations and of his interpretations are open to
the gravest doubt. According to Flu (536), the objects to which Prowazek gave
this interpretation are in reality stages in the life- history of a quite distinct
organism, named by Flu Octosporea muscce-domesticce, and now referred to the
Microsporidia. It is greatly to be deprecated that interpretations of such un-
certain validity should be used, as has been done, to support general theories in
the discussion of the problem of syngamy.

FIG. 73. — Autogamy in Entamceba coli. A, The amreba
at the beginning of encystation with a single nucleus ;
B, the nucleus dividing ; 0, the two daughter-nuclei
throwing off chromidia ; a space has appeared be-
tween them ; D, each nucleus has formed two re-
duction-nuclei, which are being absorbed ; E, a
resistant cyst-membrane has been secreted ; the
partial division in the protoplasm has disappeared,
and the two reduced nuclei are each dividing into
two ; F, each daughter-nucleus of the two divisions
in the last stage has fused with one of the daughter-
nuclei of the other division to form two synkarya.
After Hartmann (116), drawn by him from the de-
scription given by Schaudinn (131).

SYNGAMY AND SEX IN THE PROTOZOA 139

In Entamoeba coli (Fig. 73) the process starts in like manner
from a uninucleate individual, the nucleus of which divides into
two, but the cell divides incompletely and only temporarily. Each
nucleus then breaks up completely into chromidia and disappears
from view. Some of the chromidia are absorbed, while from others
a secondary nucleus is formed on each side of the cell, so that two
nuclei reappear again in the cyst, but smaller than before and
staining feebly. Each secondary nucleus now divides twice to
form three nuclei on each side, two of which degenerate as re-
duction-nuclei, while the third in each case persists as a gamete-
nucleus. As soon as the process of reduction is complete, the
incomplete separation of the two cells disappears, so that the two
gamete-nuclei lie in a single cell, which at this stage forms a tough
cyst. Now each gamete-nucleus divides into two pronuclei, those
of the same pair being slightly different from those of the other,
according to Schaudinn (133). Then a pronucleus of each pair fuses
with a pronucleus of the other pair, so that two synkarya result.
At a later stage each synkaryon divides twice, and eight amcebulse
are formed by division of the cell within the cyst.

From these two examples, it is seen that autogamy is a process
of extreme inbreeding as regards the gametes. In typical cases
of syngamy the two gametes must be derived from two distinct
strains, and those of the same strain will not conjugate ; Schaudinn
(131), for example, observed that the gametes of Polystomella
crispa would only copulate when a couple came together in which
each gamete was of distinct parentage. In a great number of
Protozoa the differentiation of the gametes and their mode of
formation makes it certain that the couple which join in syngamy
are derived from different parents. On the other hand, in many
cases of autogamy that have been described, it is equally certain
that the conjugating gametes and pronuclei have a common
parentage, and it is hardly possible to consider autogamy otherwise
than as a degeneration of the sexual process, evolved in forms in
which one feature of true syngamy — namely, the mixture of distinct
strains — is, for some reason, no longer a necessity ; we shall return
to this point when discussing the nature and origin of the syngamic
process. It is possible, moreover, to recognize progressive stages
of the degeneration, as shown by the two examples selected. In
the less advanced stage (Actinosph cerium] the parent cell divides
into two complete cells, each of which, after a process of matura-
tion, becomes a gamete. In the more advanced stage (Entamoeba
coli), the division of the parent-cell is checked, and only its nucleus
divides, each daughter-nucleus becoming a pronucleus after reduction.

The occurrence of autogamy has been asserted in a number of cases which
are, to say the least, extremely doubtful, as, for example, the Myxosporidia

140 THE PROTOZOA

(p. 407) and allied organisms, where it is far from certain that the two nuclei
or cells, from which ultimately the pronuclei or gametes arise, have a common
parentage. Autogamy has recently become very fashionable, and there is
a tendency to regard as such, not only many cases which are probably truly
heterogamous, but also nuclear fusions or appositions which are not in any
way sexual (e.g., Schilling, 134).

The essential point to consider, in cases of autogamy, is whether there is
a union of chromatin derived from distinct strains — amphimixis — or from
a common parentage — automixis. Thus, it has been pointed out above that
in gregarines two gametocytes may associate, and even fuse into one body,
but with the nuclei remaining distinct (Fig. 71, B). When gamete-formation
takes place in a " neogamous " species of this type, the gametes of one sex
derive their pronuclei from one gametocyte-nucleus, those of the opposite
sex from the other, with subsequent syngamy of a truly heterogamous type.
If the fusion of the gametocytes were to go farther, a plastogamic, non-sexual
union of the two nuclei might result, producing a single nucleus containing
chromatin from two distinct sources ; in that case, when gamete-formation
took place, the syngamy would be, to all intents and purposes, a typical case
of autogamy, and would certainly be so described if it were not known that
the single gametocyte-nucleus had arisen by fusion of two distinct nuclei.
If, however, in each couple of copulating gametes, one pronucleus contained
chromatin derived from one of the two original gametocyte-nuclei, the other
pronucleus, similarly, chromatin derived from the other nucleus, the result
would be a true amphimixis, just as in ordinary heterogamy.

In Actinosphcerium, plastogamic fusions of the ordinary vegetative, multi-
nucleate individuals are stated to be of common occurrence ; it is therefore
possible that an individual which encysts may contain frequently nuclei
from distinct sources. According to Brauer, fusion of nuclei takes place in the
mot her- cyst to form the nuclei of the primary cyst. There is therefore at
least a possibility that the autogamy of ActinospJicerium may be, in some
cases, combined with amphimixis.

In other cases, however, such as Entamoeba coli and Amoeba albida (Fig. 87),
there seems little reason to doubt that the autogamy is a true automixis.
Analogous cases of self-fertilization are well known in flowering plants, where
they are sometimes the rule, sometimes an alternative to cross-fertilization.
In free-living Ciliata, also, syngamy has been observed between cousins, the
descendants of an ex-conjugant after but four divisions (Jennings, 121),
which is not far removed from automictic autogamy.

The conclusion put forward above, on experimental grounds,
that syngamy has a strengthening or invigorating effect on the
cell-organism, receives further support from the many instances in
which it is observed to occur as a preliminary to the production
of resistant stages destined to endure unfavourable conditions of
life. Thus, in free-living Protozoa syngamy occurs commonly in
the autumn, previously to the assumption of a resting condition
in which the organisms pass through the winter. In Difflugia,
for instance, syngamy in the autumn is followed by encystment.
and the cysts remain dormant until the spring. This is strictly
comparable to the state of things known in many Metazoa, such as
Rotifers, Daphnids, etc., where in the summer soft-shelled eggs
are produced which develop parthenogenetically, but in the autumn
hard-shelled winter-eggs are produced which require fertilization.
In parasitic forms, such as Coccidia and Gregarines, syngamy is
related to the formation of resistant cysts which pass out of the host

SYNGAMY AND SEX IN THE PROTOZOA 141

and endure the vicissitudes of the outer world, until taken up by
a new host in which the parasite is set free from its cyst and starts
upon a fresh cycle of growth or multiplication without syngamy,
under the most favourable conditions of nutrition.

2. As regards the effects of syngamy upon the species, it must
be pointed out, in the first place, that a great difference exists
between multicellular and unicellular organisms as regards the
effects of external conditions of life upon the sexual process. In
Metazoa the germ-cells, as already pointed out, are a race of cells
apart, and are sheltered by their position in the body from the
direct effects of external conditions — at least, to a very large extent.
In Protozoa, on the other hand, there is no special race or strain
of germ-cells, but any individual may become a gamete or the
progenitor of gametes, and all alike are exposed to the direct
action of the environment. If, now, Protist organisms placed under
slightly different conditions of existence, tend to vary in their
characters as a direct consequence of environmental influences,
syngamy would check any such tendency, and would, on the con-
trary, tend to keep a given species constant and uniform in char-
acter, within narrow limits. Were there no intermingling of
distinct strains, such as syngamy brings about, individuals of a
species subject to different conditions of life would tend to give
rise to divergent strains and races ; syngamy levels up such diver-
gencies and keeps the tendency to variation within the specific
limits (compare Enriques, 112 and 113; Pearl, 124). If this sup-
position be correct, it would follow that no true species could exist
until syngamy had been evolved ; and if it be true that no syngamy
occurs in organisms of the bacterial type of organization, then such
organisms must be regarded as having diverged under direct
environmental influences into distinct races and strains, but not
as constituting true species. The " species " of bacteria would
then be comparable to the races of the domestic dog, rather than
to the natural species of the genus Canis. Not until syngamy
was acquired could true species exist amongst the Protista, a
condition which was probably first attained after the cellular grade
of organization had been evolved.

The conclusions reached in the foregoing paragraphs may be
summed up briefly as follows : Syngamy is a process of inter-
mingling, in a single cell-individual, of chromatin derived from two
distinct individuals, gametes, which may exhibit differentiation
into " male " individuals, characterized by preponderance of
kinetic activity, and " female," in which trophic activities are
more pronounced. Syngamy is probably of universal occurrence
in organisms of the cellular type of organization, and from them
has been inherited by the higher plants and animals, but apparently

142 THE PROTOZOA

it does not occur amongst organisms of the bacterial grade. Syn-
gamy is related to the life-cycle as a whole, and not specially to
cell-reproduction. In its effects on the cell-individual, syngamy
appears to have an invigorating effect, renewing vital powers that
have become effete and exhausted ; but in species that live in very
favourable conditions of nutrition, etc., whether such conditions
are due to artificial culture or to natural causes, such as parasitism,
syngamy may be deferred for a very long time, and may even be
completely in abeyance, or may degenerate into parthenogenesis
or autogamy. In its relation to the race, syngamy tends to level
down individual variations, and so produce true species amongst
the Protista.

Before proceeding to discuss the nature and probable origin of
the syngamic process, it is necessary to take into account a process
which appears to be a universal concomitant of syngamy — namely,
the process of nuclear reduction in the gametes. In all cases of
syngamy that have been carefully studied, it has been found that
the gametes differ from the ordinary cell-individuals of the species
in having undergone a process of so-called " maturation " which con-
sists essentially in nuclear reduction — that is to say, in a diminution
of the normal quantity of the chromatin by so-called "reducing "
divisions of the nucleus. Hence the pronuclei which undergo
syngamic fusion differ in their constitution from the nuclei of cells
not destined for this process, and do not multiply, as a rule, under
normal conditions so long as they remain single. In some cases
among plants, however, the cells that have undergone nuclear
reduction may multiply by fission and produce a multicellular
organism (gametophyte) from which gametes ultimately arise ; in
this way is brought about the well-known alternation of genera-
tions of the ferns and flowering plants. Since, moreover, in Metazoa,
ova that have undergone nuclear reduction can be stimulated
artificially to start their development without fertilization, it is
clear that the nuclear reduction does not in itself inhibit further
development or cell-multiplication.

True nuclear reduction in gametes must be distinguished clearly
from the process of elimination of effete or vegetative chromatin
which precedes the formation of the gametes or their nuclei, probably
in every case. As has been stated above (p. 72), vegetative and
generative chromatin may be combined in the same nucleus, or
may occur, the one in the form of a nucleus, the other in the form
of chromidia, or may constitute two distinct nuclei. When the
two are combined in one nucleus, a necessary preliminary to gamete-
formation is the purification of the generative chromatin of all
effete vegetative material. When the vegetative chromatin is
already separate from the generative, the latter alone takes a

SYNGAMY AND SEX IN THE PROTOZOA 143

share in syngamic processes, and the vegetative chromatin, whether
as chromidia or a nucleus, disappears from the life-history.

Nuclear reduction, in the strict sense, concerns simply the nuclei
composed of generative chromatin, and is a process which results
in the reduction of the chromatin to half the specific quantity, a
deficiency made up again to the full amount by the union of the
two pronuclei to form the synkaryon. It is therefore a process
which is seen in its most characteristic form in those cases where
it is possible to gauge the amount of chromatin in the nucleus
more or less accurately by the number of chromosomes formed
during division.

In the Metazoa, where each species is characterized by possessing
a number of chromosomes which is generally constant (the so-called
" somatic number "), the process of reduction appears to be ex-
tremely uniform in its essential details throughout the whole series,
from the Sponges and Co3lenterates up to man, and admits of a
description in general terms. The gametocyte (oocyte or sperma-
tocyte), when at the full term of its growth, has a large nucleus
which then goes through two maturative divisions in rapid succes-
sion. When the gametocyte-nucleus prepares for division, it
appears with half the somatic number of chromosomes ; but each
chromosome is in reality bivalent, and produced by the fusion or
close adherence of two separate somatic chromosomes. In the
first reduction-mitosis, the two adherent chromosomes in each case
separate from one another and travel to opposite poles of the
spindle ; hence this division is in reality a reducing, though it
simulates in some of its features an equating, division. Im-
mediately or very soon after the two chromosomes of each pair
have separated, they split longitudinally in preparation for the next
mitosis, which follows hard upon the first, and in which the two
sister-chromosomes of each pair go to opposite poles of the spindle.
Consequently the second reduction-division is in reality an equating
mitosis, though on account of the precocious splitting of the chromo-
somes it may simulate a reducing division. Thus, to sum up the
process briefly, the number of chromosomes in the germ-cells is
reduced to half the somatic number by two successive mitoses,
the first a reducing, the second an equating division. In the male
sex, the spermatocyte divides into four gamete-cells of equal size,
the spermatids, each of which becomes a spermatozoon. In the
female sex the oocyte-divisions are very unequal, producing the
ovum, ripe for fertilization, and three minute sister-cells of the
ovum which, as the so-called " polar bodies," are cast off and die
away. By syngamy between a ripe ovum and a spermatozoon,
each containing half the somatic number of chromosomes, the full
somatic number is restored.

144 THE PROTOZOA

In Protozoa the chromosomes are seldom so sharply defined as
. in Metazoa, and consequently it is difficult or impossible to deter-
mine their number. Many cases in which a fixed number of
chromosomes is alleged to occur, as in Trypanosoma noctuce (Schau-
dinn, 132), cannot be accepted without question in the present
state of our knowledge. On the other hand, in all groups of the
Protozoa, where the sexual processes have been carefully studied,
the union of the gamete-nuclei has been found to be preceded in
a great many cases by two successive divisions of each nucleus, with
one or the other of the following results : either the successive
formation of two reduction-nuclei,* which are cast out of the cell
or absorbed without dividing further, while the third persists as
the pronucleus of the gamete ; or the production of four nuclei, all
of which, or only one of them, persist as pronuclei. These reducing
divisions in Protozoa suggest forcibly a comparison with those of
the Metazoa, and from this analogy it may be further inferred that
in Protozoa also the chromatin of the conjugating pronuclei has
undergone a reduction to half the specific quantity ; but it is
seldom possible to confirm this inference by accurate enumeration
of the chromosomes. In the case which has been the most care-
fully studied of all others, that, namely, of Actinosphcerium, Her twig
(64) found the number of chromosomes in the first reduction-
spindle to be between 120 and 150 ; in the second reduction-spindle
the number was about the same, but the chromosomes were about
half the size of those in the first reduction-spindle. Moreover, in
both the reducing divisions of Actinosphcerium the chromosomes
in the equatorial plate divide to form the daughter-plates, as in
ordinary karyokinesis, whereas in the reducing divisions of Metazoa
the individual chromosomes are not divided, but merely sorted out.
Hence it would appear that in Actinosphcerium, and probably many
other Protozoa, the reduction of the chromatin in the pronuclei
is effected by more direct, though perhaps less exact, methods
than in the highly-perfected process seen in the Metazoa.

Nevertheless, a few cases are known among Protozoa in which
the small number of chromosomes permits of their being accurately
counted, and in which they are seen to be reduced to half the usual
number in the maturation-divisions of the gametes. In Pelomyxa
the first division reduces the chromosomes from eight to four ; the
second division, however, is equating, and no further reduction
takes place (p. 150). In some Infusoria it has been observed that

* These reduction -nuclei are sometimes termed " polar bodies," by analogy
with the maturative process of the Metazoan. ovum, but the term is to be avoided
in this connection, as it places upon these divisions an interpretation which is at
least highly doubtful ; the polar bodies of Metazoa are sister-cells of the ovum ;
the reduction- bodies in Protozoa are simply nuclei which are extruded or absorbed.
It is certainly not justifiable in fact, and probably no more so in theory, to regard
their formation as abortive cell-division.

SYNGAMY AND SEX IN THE PROTOZOA

145

the first division of the micronucleus is an equating division, the
second reducing ; so in Opercularia (Enriques, 112), Chilodon
(Enriques, 113), Carchesium (Popoff, 125), Didinium (Prandtl, 126),
and Anoplophrya (Fig. 74) ; in the last named the second division
of the micronucleus reduces the chromosomes from six to three,
and union of the pronuclei brings the number up to six again. In
Carchesium the number of chromosomes is reduced from sixteen to
eight. A similar reduction-process has been described by Mulsovv
(123) in gregarines (p. 335). Hence in these cases the pronuclei

FIG. 74. — Behaviour of the micronucleus during successive stages of the con-
jugation of Anoplophrya (Collinia) branchiarum. A, Micronucleus of one
conjugant preparing for division ; B, later stage, with six chromosomes dis-
tinct ; Q, nuclear spindle, with an equatorial plate of six chromosomes ;

D, diaster-stage, with six daughter-chromosomes at each pole of the spindle ;

E, later stage, with the chromosomes at each pole fused into one mass ;

F, G, H, reconstruction of the daughter-nuclei ; the remains of the spindle
between them disappears gradually ; /, the two micronuclei preparing for
division ; appearance of six chromosomes in each (one nucleus is seen in
profile, the other from one pole) ; J, diaster-stages, showing three chromo-
somes at each pole of the spindle (reducing division) ; K, later stage, the
chromosomes fused into masses of chromatin ; L, four granddaughter- micro -
nuclei ; M , one of them grows in size, the other three begin to degenerate ;
Nt division of the persistent micronucleus to form the two pronuclei ; 0, two
pronuclei and three degenerating micronuclei. After Collin (50), magnification
about 2.000 diameters.

have exactly half the amount of chromatin contained in the ordinary
nuclei, just as in the Metazoa.

Doflein (111) and Hartmann (116) consider that a process of
reduction is absolutely essential to the conception and definition
of syngamy, and regard reduction as a criterion whereby true
syngamic union of gametes and pronuclei can be distinguished
from plastogamic and nuclear fusions which have nothing to do
with the sexual process. " No fertilization without reduction "
(Hartmann). But it must be acknowledged that in a great many
cases of gamete-formation in Protozoa a reduction of the chromatin-

10

146

THE PROTOZOA

substance of the conjugating pronuclei cannot be deduced from
observation, and could only be inferred from analogy. In the
gamete-formation of Coccidium schubergi, so carefully studied by
Schaudinn (99), a large number of male pronuclei are formed
simultaneously by local condensations of chromidia thrown off
from the nucleus of the gametocyte, which is left behind in the
residual protoplasm, with its conspicuous karyosome (Fig. 50) ;
in the female gamete, also, the process of reduction appears to
consist of a simple elimination of the karyosome (Fig. 75), a process
which could be interpreted more naturally as elimination of effete
vegetative chromatin than as a process of true nuclear reduction.
In the case of Coccidium, as in others that might be cited, it must
either be assumed that reduction-processes, in the strict sense of

FIG. 75. — Four stages in the maturation of the female gametocyte of Coccidium
schubergi. A, Full-grown macrogametocyte contained in the host-cell ;
B, the macrogametocyte is beginning to round itself off and to expel the
karyosome from its nucleus ; C, the karyosome expelled from the nucleus of
the macrogametocyte has reached the surface of the body and broken up into
a number of fragments, which lie scattered in the body of the host-cell or are
extruded from it ; D, the macrogametocyte has now become a ripe macro-
gamete, having rounded itself off, eliminated the karyosome from its nucleus,
and divested itself entirely of the host-cell, n., Nucleus of the gametocyte ;
k., its karyosome ; n.', nucleus of the host-cell ; k.', k/, fragments of extruded
karyosome. After Schaudinn (99), magnified 1,000.

the phrase, occur but have been overlooked, or that the method of
reduction is one that can only be brought into line with the typical
method by theoretical interpretation founded on analogy.

It must therefore remain an open question, in the present state
of our knowledge, whether a process of nuclear reduction strictly
comparable to the process seen in Metazoa is essential to the
definition of true syngamy, or whether such a process has not been
evolved and perfected gradually as a consequence of the sexual
process. It is quite conceivable that syngamy may have been
at its first origin merely a process of intermingling of chromatin of
distinct cell -individuals ; that in this crude and primitive form
syngamy would tend to disturb the normal balance of nucleus
and cytoplasm, since it would lead to quantitative excess of the

SYNGAMY AND SEX IN THE PROTOZOA 147

nuclear substance ; that, consequently, by a regulative process
which may primitively have followed the syngamic union, the
chromatin of the zygote was reduced to the normal quantity by
elimination of half of its mass ; and that from this hypothetical
primitive process of regulation of the nucleo-cytoplasmic balance
a process of nuclear reduction preceding the syngamic act has been
gradually evolved until it reaches its perfection in the form seen,
in the Metazoa. On this view, it is to be expected that in Protista
a great diversity in the methods of nuclear reduction would occur,
from those of the roughest type to others highly elaborated and
perfected ; and this expectation certainly receives justification
from the data of observation. Hertwig (119), on the other hand,
compares the reducing divisions in the maturation of the gametes
to the so-called " hunger-divisions " in Infusoria, which exhibit
a great disproportion in the relative mass of nucleus and cytoplasm
as the result of starvation in artificial cultures ; in such forms the
body is smaller than in forms from a normal culture, but the nucleus
is not merely relatively, but absolutely, larger than that of
a normal form. The disturbance in the nucleo-cytoplasmic ratio
(see p. 70, supra) can, however, be regulated by reducing divisions
of the nucleus. On the ground of this comparison, Hertwig considers
that the maturative processes of the gametes are to be regarded as
the necessary consequences of antecedent events* in the life-history
— as processes which in their turn bring about syngamy, and not
such as have the object of preparing the nuclei for fertilization.

In order to give a more concrete idea of the processes of syngamy
and reduction in Protozoa, a few typical examples will now be
described, selected in order to illustrate the salient features of
these processes. The most convenient method of classification
of the examples chosen is to distinguish those cases in which chro-
midia are present in addition to nuclei from those in which nuclei
alone are present.

1. Syngamy and Reduction with Nuclei and Chromidia. — In a
great many Sarcodina, especially those belonging to the orders
Amoebsea (p. 218) and Foraminifera (p. 231), chromidia may be
present in the gamete-forming individuals as a permanent con-
stituent of the body-structure. In such cases the chromidia
represent, wholly or in part, the generative chromatin, and give
rise, by formation of secondary nuclei, to the nuclei of the gametes.
As an example Arcella may be taken, the life-cycle of which is
described in a subsequent chapter. In this form two distinct
forms of syngamy have been described.

* It is, of course, hardly necessary to point out that starvation is by no means
the only influence which can bring about a disturbance of the nucleo-cytoplasmic
equilibrium ; over-nutrition, for example, may have the same effect.

148 THE PROTOZOA

(a) Karyogamy. — The body of an Arcella gives rise by multiple
gemmation to a number of amcebulae, each containing a secondary
nucleus derived from the chromidia, while the primary nuclei of
the parent-form degenerate (Fig. 80). The number and size of
the amcebulae vary, however, in different individuals. In one
Arcella the number is Jess and the amcebulae are larger, eight or
nine macramoebce being produced. In another the amcebulae are
more numerous and smaller, about forty micramoebce being formed.
In either case the amoebulae swarm out of the parent-shell and are
the gametes. A micramceba copulates with a macramceba, the
two fusing completely to form a zygote with a synkaryon. The
amoeboid zygote thus produced is the starting-point in the growth
and development of an Arcella (Fig. 80, A).

In this example the karyogamy is a case of microgamy, which,
like other such cases, precedes a period of growth and follows a
period of active reproduction. It is possible that the syngamy
of the gametes is preceded by reducing divisions of the nuclei of
the amcebulae, but no such reduction has been observed in Arcella.
In Foraminifera (p. 235), in which the syngamy is perfectly isog-
amous, each secondary nucleus formed from the generative
chromidia divides twice to form the gamete-nuclei — divisions
doubtless to be regarded as reducing divisions. In C entropy xis,
according to Schaudinn (131), amcebulae, all of the same size, are
produced as in Arcella, by formation of secondary nuclei ; but in
some broods each amcebula divides into four micramcebae (micro-
gametes), while in other broods the amcebulse remain undivided as
macramcebae (macrogametes) ; copulation then takes place between
two gametes of different size.

(b) Chromidiogamy (Fig. 80, M — Q). — Two ordinary adult Arcellce
come together and apply the mouths of their shells. The proto-
plasm of one individual flows over almost entirely into the other
shell, taking with it both chromidia and primary nuclei, only so
much protoplasm being left in the one shell as suffices to hold the
two shells together. The primary nuclei now degenerate, and the
chromidia derived from each conjugant break up into a fine dust
of chromatin-particles and become intimately commingled. When
this process is complete, the protoplasm with the chromidia
becomes again distributed between the two shells, and the two
conjugants separate. Then in each individual secondary nuclei
are formed from the chromidia, and by a process of multiple gem-
mation a number of uninucleate amcebulae are formed which swarm
out of the shell, and, like the zygotes resulting from karyogamy,
become the starting-point of a new Arcella.

Thus chromidiogamy is here a case of macrogamy which, like
other similar cases, folloAvs a period of growth and precedes a

SYNGAMY AND SEX IN THE PROTOZOA

149

period of active reproduction. Chromidiogamy is a rare but very
interesting form of syngamy which, from the standpoint of general
notions with regard to the evolution of the nucleus, may be re-
garded as the most primitive type. It is known to occur also in
Difflugia (Zuelzer, 85), where also copulation of swarm-spores takes
place as an alternative method (p. 230).

A case must now be considered in which the chromidia represent
vegetative, while the nuclei contain the generative, chromatin.
An example of this state of things is furnished by Plasmodiophora
brassicce, a well-known parasite of cabbages, turnips, etc., in which

FIG. 76. — Gamete-formation and syngamy in Plasmodiophora brassicce. A, Normal
vegetative nuclei of the myxamoebse ; B, C, extrusion of chromidia from
the nuclei ; D, division of the nuclei by karyokinesis (first reducing division) ;
E, nuclei after reduction ; F, formation of gametes which are fusing in pairs ;
G, spore (zygote) containing two nuclei, one of which is going through a
further reduction-division ; H, fusion of the two pronuclei within the spore ;
/, ripe spore with synkaryon and two centrioles. After Prowazek (127),
magnified about 2,250 diameters.

it produces a disease known as " fingers and toes " (Kohlhernie).
According to the investigations of Prowazek (127) and others,
Plasmodiophora goes through a development which may be briefly
summarized as follows : At the end of the " vegetative " period of
growth and multiplication, there are found within the cells of the
infected plant a number of " myxamoebse," amoeboid individuals
(plasmodia) each with many nuclei containing distinct karyosomes
(Fig. 76, A). From the nuclei chromidia are given off into the cell,
and during this process the karyosomes disappear and centrosomes
make their appearance (Fig. 76, B, C). The chromidia are ab-

150 THE PROTOZOA

sorbed and disappear, and the nuclei divide twice by karyokinesis
(Fig. 76, D), so that their number is quadrupled. The myxamcoba
then undergoes multiple fission into as many cells as there are
nuclei in the plasmodium (Fig. 76, F), and each of these cells is a
gamete. The gametes now conjugate in pairs, and the zygotes
become encysted to form the spores. Within the spores the nuclei
of the gametes are stated to undergo a further process of reduction
before they fuse to form the synkaryon (Fig. 76, G). The syngamy
in Plasmodiophora is stated to be a case of autogamy, but this
allegation assumes that the nuclei of the myxamcebse are sister-
nuclei derived all from the division of one original nucleus ; they
may equally well be nuclei of different origins brought together by
plastogamic fusions.

The two examples selected, Arcella and PlasmodiopTiora, show
that the chromidia may represent generative chromatin in one
case, vegetative in another. Goldschmidt (57) has proposed to
distinguish these two conditions by a special terminology, retaining
the name " chromidia " (trophochromidia, Mesnil, 74) for those which
are purely vegetative, and coining a new term, sporetia (idio-
chromidia, Mesnil) for those of generative nature. It is more
convenient, however, to retain the term " chromidia " in its
original significance, to denote simply extranuclear particles of
chromatin, and to qualify the term by the adjectives " vegetative "
and " generative " when required (see also Goldschmidt, 41, p. 130).
The formation of vegetative chromidia, which are finally absorbed,
is a common phenomenon in many Protozoa ; it may take place
as a purely regulative process, as in Actinosphcerium during de-
pression-periods (p. 208), when hypertrophy of the nuclear apparatus
is corrected by the extrusion from the nuclei of chromidia, which
ultimately degenerate and become converted into masses of pig-
ment, and as such are eliminated from the protoplasm.

The account given by Bott (103) of gamete -formation in the common
Pelomyxa (Amoebcea nuda, p. 227) describes a condition in which chromidia,
extruded from the nuclei, are partly vegetative, partly generative ; secondary
nuclei are formed from them, which later cast out a portion of their chromatin,
then give rise to the gamete -nuclei. After the secondary nuclei have been
purified in this way of their vegetative chromatin, the generative chromatin
remaining in each of them forms a karyokinetic spindle with eight chromo-
somes, and a reducing division follows by which each daughter-nucleus obtains
four chromosomes. The " pro nuclei of the first order," resulting from the
first reducing division, divide again., forming a spindle with four chromosomes
which split, so that the " pronuclei of the second order " have also four chro-
mosomes. From the nuclei that have undergone reduction in this manner
the nuclei of the gametes arise in a somewhat remarkable fashion : the pro-
nuclei of the second order separate into two compact masses of chromatin ;
a vacuole is formed near them ; and the chromatin of the two masses wanders,
in the form of finely- divided granules, into the vacuole to form the definitive
pronucleus of the gamete, which forms a membrane when the process is
complete. When formed the gametes wander out as Heliozoon-like indi-

SYNGAMY AND SEX IN THE PROTOZOA 151

viduals, which copulate in pairs, and the uninucleate zygoto grows up into the
multinucleate Pdomyxa.

The conception of vegetative and generative chromidia has not been
accepted universally or without criticism. Hartmann, as pointed out above,
considers that many cases of generative chromidia are really the result of a
disruption of a polyenergid nucleus ; Awerinzew (47) is of opinion that, while
all Protozoa possess vegetative chromidia at some stage at least in the life-
cycle, generative chromidia are to be considered as a new acquisition, a hasten-
ing of the process of the formation of numerous gamete -nuclei ; Dobell (51)
puts forward a similar view with regard to generative chromidia. With
regard to the latter criticism, it may be pointed out that nuclei may become
resolved into chromidia in order to undergo simple binary fission. With
regard to Hartmann's view, there is at present, at least, little evidence that
it is an adequate explanation of the many cases of formation of secondary
generative nuclei from chromidia known amongst the Sarcodina. The ques-
tion is discussed further below (p. 255).

2. Syngamy and Reduction with Nuclei only. — A very simple
example is furnished by the common Actinophrys sol (Fig. 71), as
described by Schaudinn (129). Conjugation takes place between
two adult forms (macrogamy), which come together and become
enclosed in a common cyst. The nucleus of each individual then
divides by karyokinesis, and one nucleus of the pair thus produced
is expelled from the body and undergoes degeneration as a reduction
nucleus. The persistent nucleus of each individual then repeats
the process and forms a second reduction-nucleus. The nucleus
now remaining in each cell is the definitive pronucleus. The two
gametes now copulate, their pronuclei fusing to form the synkaryon,
after which the synkaryon divides by karyokinesis and the zygote
divides into two individuals which later escape from the cyst and
resume the free-living vegetative life. The course of syngamy in
Actinophrys is exactly similar to that performed by the two
" secondary cysts " derived from division of a " primary cyst " in
Actinosphcerium (see p. 138, supra). In both cases alike the nucleus
of the conjugants may be supposed to contain both vegetative
and generative chromatin mixed together. It is possible that the
vegetative chromatin is extruded from the nucleus in the form of
chromidia prior to the reducing divisions, but no elimination of
vegetative substance has been described.

The last example of syngamy in Protozoa that need be con-
sidered specially at this point is that of the Infusoria, which have
been the subject of numerous investigations. These organisms
present the highest degree of specialization of the body-structure
and elaboration of the nuclear apparatus found in any Protozoa.
Their syngamic processes vary in detail to some extent in different
cases (see p. 448), but the whole process is essentially as follows
(Fig. 77) : Two individuals come together and adhere, placing
themselves side by side. The two conjugants may be similar in
visible constitution, or may differ to a greater or less extent, and

152

THE PROTOZOA

FIG. 77. — Diagram showing the successive stages of conjugation in Infusoria.
A, The two conjugants attached, each with a macronucleus (N) and a micro-
nucleus (n) ; B, C, the micronucleus of each conjugant dividing ; D, each
conjugant has two micronuclei which are beginning to divide again ; E, each
conjugant has four micronuclei ; the macronuclei are beginning to become
irregular in form ; in later stages they degenerate, break up, and are absorbed ;
F, three of the four micronuclei of each conjugant are degenerating and
being absorbed ; the fourth is dividing ; G, one half of each dividing micro-
nucleus of the preceding stage has travelled over into the other conjugant
as the migratory pronucleus ; H, I, fusion of the stationary pronucleus of each
conjugant with the migratory pronucleus derived from the other conjugant
to form the synkaryon (S.) ; J, the two conjugants now separate ; in each
ex-con jugant the synkaryon (S.) divides ; the old macronuclei are now almost
completely absorbed ; K, L, the synkaryon has divided into two nuclei, one
of which grows large and becomes the new macronucleus, the other remains
small and becomes the new micronucleus, of each ex-conjugant. After Delage
and Herouard.

SYNGAMY AND SEX IN THE PROTOZOA 153

are sometimes markedly different in size (Doflein, 111). The
greatest amount of differentiation is seen in the order Peritricha
(p. 448), where microconjugants and macroconjugants can be dis-
tinguished. Each conjugant has a micronucleus and a macro-
nucleus. The macronucleus begins to degenerate, and finally dis-
appears completely. The micronucleus, on the other hand, en-
larges and divides by a simple form of karyokinesis (see p. 114,
supra). The division of the micronucleus is repeated twice as
a rule, but sometimes three times, and, as stated above, in one of
these divisions the number of chromosomes is halved in a great
many, possibly in all, cases. Of the four (or eight) micronuclei
thus formed, all but one represent reduction-nuclei which are
absorbed and disappear. The persistent micronucleus then divides
by equating division into two pronuclei, which may be distinguished
as migratory and stationary, respectively ; they sometimes exhibit
distinct structural differentiation. At this juncture the cuticle
of each conjugant is absorbed at the point of contact, and the
migratory pronucleus of each conjugant passes over into the
protoplasm of the other and fuses with its stationary pronucleus.
The gap in the cuticle is now repaired and the two individuals
separate, each " ex-conjugant " having a synkaryon constituted
by a fusion of one-eighth (or one-sixteenth) of its own original
micronucleus with the same fraction of the micronucleus of the
other partner. The synkaryon grows and divides into two nuclei,
one of which grows and becomes the macronucleus, while the other
remains small a,nd becomes the micronucleus, of the ex-conjugant,
which thereby becomes indistinguishable from an ordinary in-
dividual of the species, and proceeds to start on a course of vegeta-
tive growth and reproduction in the usual manner, until the next
act of syngamy initiates a fresh cycle. It has been observed that
the two ex-conjugants sometimes differ markedly in their capacities,
one of them multiplying much faster than the other.

In the syngamy of Ciliata it is seen clearly that the macronucleus
represents effete vegetative or " somatic " chromatin, which is
eliminated bodily from the life-history of the organism, while the
micronucleus represents reserve generative chromatin from which,
after reduction, the entire nuclear apparatus is regenerated. The
remarkable feature in the syngamy of Infusoria is the manner
in which the conjugants remain distinct, and merely exchange
pronuclei (so - called " partial karyogamy "). Versluys (137),
following Boveri, derives this from an ancestral condition of iso-
gamic copulation — that is to say, a condition in which the two
conjugants fused completely as gametes, both body and nucleus,
after which the zygote divided into two individuals ; on this view
the final division of the micronucleus which gives rise to the two

154 THE PROTOZOA

pronuclei is to be regarded as the equivalent of the division of
the synkaryon which took place ancestrally after syngamy. While,
however, there is a general agreement that partial karyogamy
(conjugation) is to be derived from total karyogamy (copulation),
it is very doubtful if the two conjugants in Infusoria represent
simple gametes ; it is more probable that the type of syngamy
characteristic of Infusoria is derived from an ancestral condition
in which each conjugant produced a number of minute gametes
(swarm-spores) which copulated (compare especially Popoff, 125,
and Hartmann, 116, and see p. 453, infra). On this view the
divisions of the micronucleus represent a primitively much larger
number of divisions which produced the numerous gametes, and
the conjugants themselves are not to be regarded as true gametes,
but rather as gametocytes or gamonts.

Having now illustrated by typical examples the various forms
which the syngamic process takes in Protozoa, we may conclude
this chapter by a consideration, necessarily brief, of the problem
of the significance and origin of syngamy and sex. This is a
problem which has a vast literature, and it is only possible here to
indicate in outline some of the theories that have been put forward,
none of which can claim to be a complete solution of one of the
profoundest mysteries of the living substance and its activities.

Considering first the fertilization of the Metazoa, it is evident
that the union of the spermatozoon with the ovum has two prin-
cipal results. In the first place the spermatozoon brings with it
a pronucleus, the equivalent of that contained in the ovum, but
derived from a distinct individual, and therefore possessing different
hereditary tendencies acquired from its own particular ancestral
history. The union of the male and female pronuclei brings about,
therefore, a process for which Weismann has coined the term amphi-
mixis— that is to say, a mingling of different hereditary tendencies
in one and the same individual. In the second place the spermato-
zoon produces a result which may be termed briefly " developmental
stimulus " (Entwicklungserregung) — that is to say, it produces
a disturbance in the equilibrium of the protoplasmic body of the
ovum which causes it to start on a course of cell-division oft-re-
peated, a process of cleavage which converts the unicellular ovum
into the mass of cells which supplies the material for the building
up of the multicellular body. It is very probable that the develop-
mental stimulus is supplied by the greatly-developed centrosome
of the spermatozoon, that of the ovum having completely atrophied,
apparently, after the completion of its maturative processes.

The introduction of a male pronucleus — that is to say, the process
of amphimixis — can be effected only by the spermatozoon. But
the researches of Loeb and others have demonstrated fully that the

SYNGAMY AND SEX IN THE PROTOZOA 155

spermatozoon is not indispensable for supplying a developmental
stimulus ; an unfertilized ovum can be induced by artificial stimuli
of various kinds to start upon a course of development similar to
that initiated, under natural circumstances, by fertilization with
a spermatozoon. Hence, of the two results produced in the fertiliza-
tion of Metazoa, amphimixis alone would appear to be that which is
essential and peculiar in the process, and which only fertilization
can bring about.

From the above considerations, amphimixis is regarded by many
thinkers as the essence of syngamy, a necessity for the evolution
of living beings in that it supplies, by the intermingling of different
hereditary tendencies, the conditions required for the production
of " innate " variations in organisms in which the germinal substance
is shielded from the direct influence of external conditions by its
position within a multicellular body. Apart from the question,
however, whether any such innate variations exist in the Protozoa,
where all cells alike are exposed equally to the direct action of the
environment, the criticism has often been made that amphimixis
gives only a teleological explanation of the sexual process, and as
such cannot be invoked as a causal explanation of its origin. The
intermingling of distinct hereditary tendencies, however useful to
the organism or important in the evolution of living beings generally,
cannot be regarded as the incentive to syngamy at its first appear-
ance in the Protista. In other words, amphimixis must be regarded
as a secondary consequence, not as a primary cause, of syngamy.

It is necessary, therefore, to seek some explanation for the
first origin of syngamy other than the benefits which it may confer
through amphimixis, and it is undoubtedly among Protist organisms
that the conditions under which syngamy first arose must be
sought. It has been pointed out above that syngamy appears to
have a strengthening or recuperating effect upon the cell-organism,
and upon such grounds has been founded the theory of " rejuven-
escence " (Verjiingung). According to this theory, connected
chiefly with the name of Maupas, the cell-protoplasm, after many
generations of reproduction by fission, tends to become effete and
senile to an ever - increasing degree, a condition which, if not
remedied, ends in the death of the organism ; the natural remedy
is furnished, however, by the process of syngamy, which has the
effect of renewing the " youth " of the cell and starting it upon
a fresh series of generations, until senility, once more supervening,
necessitates syngamy again.

The rejuvenescence-theory has been criticized by many critics
who have themselves done little more, in some cases, than give a
more precise meaning to the terms " youth " and " old age,"
terms that certainly stand in need of further explanation, since

156 THE PROTOZOA

it can hardly be supposed that the time-factor alone can account
for the exhaustion or depression of the vital faculties. It is gener-
ally admitted that unicellular organisms, such as the Protozoa,
tend, after a greater or less number of generations, to exhibit a
certain degree of exhaustion in their vital properties, or, it may be,
of derangement in their organization and vital mechanisms. Hert-
wig (164) is of opinion that " the conditions of death exist in the
living substance from the beginning, and are a necessary conse-
quence of its vital function " — a generalization which may be
accepted for those Protista in which the body exhibits the degree of
specialization and structural complication proper to a true cell
(as the term is understood in this book — see p. 98) ; but it is very
doubtful if it is tiue also for the simplest forms of life, such as the
bacteria and allied organisms. If it be further admitted that
syngamy is the natural remedy in unicellular organisms for a natural
disease, the problem before us is to discover, if possible, the precise
nature of the derangements, and of the method by which the
remedy restores them to the normal functional condition.

At the outset, attention must be drawn to a very constant and
general preliminary to syngamy in Protozoa — namely, the elimina-
tion of a large amount of chromatin which appears to have been
regulating the vital activities during previous generations (vegeta-
tive chromatin) , and its replacement by chromatin which has been
inactive and lying in reserve (generative chromatin). This process
is seen in its most striking form in the Ciliata, where the macro-
nucleus is entirely eliminated during the act of syngamy, and is
replaced in subsequent generations by a new macronucleus derived
from the micronucleus formed by fusion of portions of the micro-
nuclei of the partners in syngamy. Hence it might seem as
if the chief result of syngamy was to replace effete vegetative
chromatin by fresh generative substance which through inactivity
has retained its powers unimpaired. But in the first place it must
be pointed out that, to effect a replacement of this kind, the union
of two individuals is not necessary ; it would be sufficient for a
single individual to form a new nucleus from its store of generative
chromatin, and to get rid of its old, effete vegetative chromatin.
If we regard the chromidia of Arcella as composed of generative
chromatin, the buds produced by formation of secondary nuclei
from the chromidia would represent nuclear regeneration of this
kind. Secondly, it is open to doubt how far the theory of vegeta-
tive and generative chromatin can be applied throughout the whole
series. In such forms as Arcella the chromidial mass, although it
furnishes the gamete-nuclei, is a cell-element in a functional con-
dition, and in the more primitive forms the distinction between
vegetative and generative chromatin cannot be pressed so far as

SYNGAMY AND SEX IN THE PROTOZOA 157

in highly-organized forms, such as the Ciliata. Her twig (68) con-
siders that the separation of two kinds of chromatin is an adaptation
to particular conditions of life, evolved progressively, and attaining
its greatest perfection in the Ciliata ; whereby chromatin which
has become functionally effete is separated from that which has
retained its constitution.

According to the view put forward by Hertwig (118), syngamy
remedies the effete condition of the cell chiefly by regulating the
necessary quantitative balance between the nucleus and the cyto-
plasm. Such regulation may be effected also by internal re-
arrangements of the nuclear substance or by plastogamy, but is
brought about most efficiently by syngamy, since the definite and
necessary mutual relations between nucleus and cytoplasm are
better maintained by " arrangements which prevent disturbance,
than by arrangements which compensate for disturbances that
have already set in." The obvious criticism of this theory is that
it is difficult to understand why an internal regulative process of
the cell should require the co-operation of two individuals, and the
reason contained in the sentence just quoted from Hertwig scarcely
seems an adequate explanation.

The fact that two cells participate in syngamy indicates in itself
that the necessity for syngamy depends on a loss of balance between
two constituents or substances in the cell, and that the union of
the two gametes restores equilibrium. As Hertwig (119) has
pointed out, the quantitative relation of nucleus to cytoplasm is
more altered in the gametes of Metazoa than in any other cells,
and to opposite extremes in the two sexes ; in the ovum the quantity
of cytoplasm is enormous in proportion to the nucleus, while in
the spermatozoon the exact reverse is the case. The same argu-
ment applies to a greater or less degree in the case of anisogamous
gametes of Protozoa. It would not, however, apply to the many
cases of isogamy in Protozoa where the quantitative relations of
nucleus and cytoplasm are the same in each gamete ; in such cases
union of the gametes would leave the nucleo-cytoplasmic relation
exactly what it was before.

A theory of a different kind has been put forward by Schaudinn
(133) and his followers Prowazek (128) and Hartmann (116),
which is based on the notion that sex and sexual differentiation
are primary characteristics of living matter. A normally function-
ing cell is regarded as hermaphrodite, having male and female
elements equally balanced. The differentiation which leads to
the formation of gametes arises, as Biitschli originally suggested,
from inequalities in the results of cell- division, which may be
supposed to lead always to more or less imperfect partition of the
qualities of the parent-cell between the daughter-cells, As a result

158 THE PROTOZOA

of the defects in the process of cell-division, some cells acquire more
" male " properties, other more " female " ; the cells preponder-
atingly male show greater kinetic and motile energy, those that
have more female qualities show greater trophic activity. With con -
tinued cell-division these opposite tendencies tend to accumulate in
certain cells which in consequence become altogether one-sided in
their vital activities. Thus a want of balance in the vital functions
is brought about, which may reach such a pitch that the organism is
unable to continue to assimilate and reproduce, and must die unless
the balance is resorted by syngamy with an individual that has become
specialized in the opposite direction. By the union of two gametes
differentiated in this manner, equilibrium is restored and the vital
functions are rein vigor ated. No gametes, however, whatever their
degree of specialization, are to be considered as perfectly unisexual,
but only relatively so ; a male gamete will always contain a certain
amount of female substance, and a female gamete a certain amount
of male substance, thus accounting for the possibility of partheno-
genesis. Schaudinn's theory of sex is thus very similar to that
developed by Weininger on purely psychological grounds.

Schaudinn, whose work on Protozoa must secure full considera-
tion for any statement of his observations, however inherently
improbable the facts or the interpretations based upon them may
seem, founded his theory chiefly on data alleged to have been
observed by him in the development of Trypanosoma noctuce (Schau-
dinn, 132). According to him, an " indifferent " ookinete might
give rise either to male or female forms. In the formation of males,
certain nuclear elements were separated out to become those of
the daughter-cells, while certain other nuclear elements remained
behind and degenerated together with a quantity of residual
protoplasm. In the formation of females, the same two sets of
nuclear structures were separated out, but those proper to the
male sex degenerated, while those of the female sex, which were
just those which degenerated in the formation of males, in this
case persist and become the nucleus of the female gamete. Thus
the indifferent ookinete was supposed to be really hermaphrodite,
containing male and female elements mixed together, and giving
rise to individuals of one or the other sex by persistence of one set
of characters and atrophy of the other. It must be noted here
that these observations of Schaudinn's are entirely unconfirmed,
nothing similar having as yet been found by other investigators,
either in trypanosomes or in any other Protozoa ; and further that,
even if Schaudinn's observations be accepted as exact in every detail,
they will not bear the interpretations which he places upon them —
namely, that the small and large forms produced as he describes
are males and females, since, as he himself admits, they do not,

SYNGAMY AND SEX IN THE PROTOZOA 159

when developed, perform any act of syngamy. The alleged
sexuality of the forms described by Schaudinn lacks the only de-
cisive criterion of sexual differentiation — namely, sexual behaviour ;
and the differentiation exhibited by the two forms of trypanosomes
described by Schaudinn admits of an entirely different and far less
forced interpretation (see p. 176, infra).

There are two further criticisms that may be made of Schaudinn's
theory. The first concerns the alleged universality of sexual
differences in living matter. It must be pointed out that, as stated
above, at the present time we have no evidence whatever of the
occurrence of true syngamy in any organisms of the bacterial
grade. The processes that have been interpreted by Schaudinn
as autogamy in certain bacteria may be much more easily regarded
as processes of internal regulation of the chromatin-substance.
Nowhere yet has the union of two distinct gametes been observed
in any bacterial organisms. The theory that sex is a universal
characteristic, and syngamy an elementary function, of living things,
does not rest at the present time on any basis of established fact.

The second criticism is that the terms " male " and " female "
require definition and explanation, without which they remain
meaningless, connoting merely unknown, mystic properties, not
further analyzable, of the living substance. The characteristic
feature exhibited by male cells is the preponderance of kinetic
activity, and by female cells, of trophic functions, as Schaudinn and
many others have pointed out. Before Schaudinn, the same idea
was expressed in different language by Geddes and Thomson (114),
who regarded the male sex as characterized by katabolic, the
female sex by anabolic activities. It we suppose that these two
manifestations of physiological activity have each a distinct material
basis in the living cell, then it can easily be imagined that the
imperfections of cell-division may lead to the production of cells
in which one or the other substance predominates. This is the
view that Doflein (7) has developed in his very interesting critical
summary of the views that have been put forward upon the sexual
problem. He supposes, further, that these two different physio-
logical qualities depend upon substances which have intense mutual
interactions and attract each other strongly, and that a certain
equilibrium between them is necessary for the normal life of the
cell. When, therefore, one or the other substance preponderates
greatly in a cell, a functional derangement results ; but since cells
differentiated in opposite directions attract each other strongly,
they tend to unite, and by their union to restore equilibrium.

The question of the sexual differentiation of the gametes is one
that will be discussed at greater length in the next chapter. It is
only necessary to point out here that a clear distinction must be

160 THE PROTOZOA

drawn between intrinsic differences, not necessarily visible, and
structural or other differences which are more or less obvious.
The fact that gametes and pronuclei tend to unite proves that in
all cases there must be intrinsic differences between them which
stimulate them to do so ; in this sense, at least, we may endorse
fully the dictum of Hertwig, that " fertilization depends on a
fusion of sexually-differentiated cell-nuclei." On the other hand,
gametes of opposite sexes exhibit every possible condition from
complete similarity in structure and appearance to the greatest
possible contrast in every feature of their organization. There
can be no doubt that visible differentiation of the gametes is
largely, if not entirely, an adaptation to the functions that they
have to perform ; and this conclusion is by no means weakened
by the fact that there are many cases of isogamy which are un-
doubtedly secondary, in which a more primitive and phylogeneti-
cally older structural differentiation has gradually become annulled,
under circumstances in which adaptive differences in the gametes
are no longer necessary — as, for example, in gregarines (p. 173).

In Metazoa it is generally recognized that the two pronuclei
that undergo fusion are perfectly equivalent,* and that the dif-
ferences seen between them in the gametes are temporary and, in
the case of the spermatozoon, an adaptation to circumstances ; here
the real differentiation of the gametes affects only cytoplasmic
characters. In Protozoa, on the other hand, the conjugating
pronuclei often exhibit differences of structure when the cells
themselves appear perfectly similar. In the Infusoria, for instance,
differences have been noted between the migratory and stationary
pronuclei ; how far these differences may be correlated directly with
the differences in their activities must remain an open question.

In the foregoing paragraphs we have set forth and discussed
some of the attempts that have been made to solve the problem
of sex. It cannot be said that a perfectly satisfactory solution
has been attained, but at least certain conditions of the problem
may be laid down. In the first place, no theory of sex is satis-
factory which does not explain why the union of two cells should
be necessary in syngamy. In the second place a teleological inter-
pretation, such as amphimixis, can only state a secondary con-
sequence, not a primary cause, of sexual union ; but such a
consequence may suffice to explain the retention and persistence
of sexual phenomena after the conditions have ceased to exist under
which they came into existence.

In the simplest Protista of the bacterial grade, it may be supposed,
either that the living matter is not differentiated into localized
substances having distinct physiological qualities, or that in such

* Apart, that is to say, from the much -discussed question of the supernumerary
chromosome.

SYNGAMY AND SEX IN THE PROTOZOA 161

minute bodies reproduction by fission does not produce differentia-
tion in the fission-products. With increased size such differences
may arise, at first to a minor extent, and capable of being adjusted
by internal rearrangements of the living substance such as have
been described in the larger Bacteria. Not until the process of
natural evolution had gone so far as to produce the full complica-
tion of structure seen in a true cell would localized differences in
the living substance be brought about to a sufficient extent to
lead to differences between the daughter-cells produced by fission,
as a consequence of the imperfections of the process of cell-division.
The differences produced in this way might be changes in the
nucleo-cytoplasmic balance, as Hertwig supposes, or in the relative
proportions of substances exerting different physiological activities,
as suggested by Biitschli, Geddes and Thomson, Schaudinn and
Doflein, or possibly of all these and other changes yet unknown.
In any case it is reasonable to suppose that the imperfect character
of the primitive types of cell-division, described in the last chapter,
might produce accumulated material or structural inequalities in
the daughter-cells, such as could only be rectified by the union of
two cells differentiated in opposite directions, thus making syngamy
a necessity for the continued existence of the species. This theory
explains the necessity for syngamy recurring with greater frequency
in forms having a high degree of structural differentiation than in
forms of a primitive and simple type of organization.

With increasing perfection in the process of the division of the
cell, and especially of the nucleus, the primary cause of, or necessity
for, syngamy might be expected to disappear ; but at this stage in
evolution other benefits to the species consequent on the process
of amphimixis might be a sufficient cause for the retention of
a process already well established. This conclusion appears to
receive some support from the fact that intensive culture, whether
artificial, or natural as in parasitism, seems to diminish the necessity
for syngamy. It can hardly be supposed that intensive culture
can diminish consequences arising from defective cell-division ; but
it might conceivably produce a strengthening effect equal to, and
capable of supplanting, the benefits derived from amphimixis.
Enriques (113) has stated that in Infusoria ex-conjugants may
proceed to conjugation again, so that between one act of syngamy
and the next there may not be a single cell-division intervening.
In this case neither cell-division nor any consequences of cell-
division can be the factor bringing about sexual union, but some other
explanation must be sought. Enriques considers that the function
of syngamy in Infusoria is to maintain the fixity of the species.

Bibliography. — For references see p. 479.

CHAPTER IX
POLYMORPHISM AND LIFE-CYCLES OF THE PROTOZOA

A. POLYMORPHISM.

ONE of the most striking peculiarities of living beings is the infinite
variety of form, structure, and appearance, which they present.
There is, perhaps, no living individual of any kind which is exactly
similar, in all respects, to any other. Nevertheless, the most
uncultured intellect cannot fail to recognize that, in the case of
all ordinary, familiar plants and animals there is a pronounced
tendency to segregation into distinct kinds or species — that is to
say, natural groups of individuals which, though they may vary
greatly amongst themselves, yet resemble one another far more
than they do the individuals of another species. It is not necessary
to point out that species are not to be regarded as permanent or
immutable entities. It is certain that a species may in course
of time become modified so as to acquire characters different from
those it originally possessed, thus giving rise to a new species, or
that a single parent-species may become split up into a number of
groups which, by a similar process of modification, became so many
daughter-species differing from one another and from the parent-
species to a greater or less degree. The problem of the origin of
species is one that it is not necessary to discuss here ; it is sufficient
to point out that the mutability of species often makes it very
difficult to define or delimit a given species exactly, of which a
striking example is seen in the pathogenic trypanosomes of the
brucii - group, probably to be regarded, as pointed out above
(p. 27), as instances of species in an incipient or nascent condition.
Some species are sharply marked off from others, some are much
less so, and some are of questionable rank, regarded by one naturalist
as distinct, by another as mere races or varieties — a state of things
perfectly intelligible if existing species are regarded as having
arisen by descent, with modification, from pre-existing species.

In the Protozoa the existence of distinct species is just as marked
as in the higher plants and animals, and is universally recognized.
As has been pointed out in the previous chapter, it is probably
syngamy which is responsible for the segregation of individuals

162

POLYMORPHISM AND LIFE-CYCLES 163

into species, by blending the divergent characters that may be
supposed to arise from the influence of different conditions or
circumstances of life. Thus, syngamy in unicellular organisms
appears to have an effect which is the opposite, to a large extent,
to that which it produces in multicellular organisms, in which there
are special germ-cells, sheltered to a greater or less degree from
the direct influence of the environment, and in which amphimixis
appears rather to be a means by which variations arise.

The conception of a species is by no means incompatible with the
occurrence of a number of distinct forms in its life-history. Taking
well-known instances from the Metazoa, there may be, in the first
place, ontogenetic or developmental differences ; not only may the
individuals of the same species differ in size at different periods in
the development, but they may differ so greatly in appearance and
structure that only a knowledge of the life-history enables us to
assert that they belong to the same species — as, for example, a
caterpillar and a butterfly, or a hydroid and a medusa. Secondly,
the adult individuals may differ to an enormous extent in the two
sexes. Thirdly, there may be in many cases differences between
individuals of a species related to differences in the functions which
they perform, not merely at successive phases in the life-history,
as in some cases of ontogenetic differentiation already mentioned,
but even at corresponding phases of the life-history — a phenomenon
best seen in social or colony-forming organisms, as in the case of
ants and termites, or in the colonies of Hydrozoa.

In Protozoa, similarly, a given species may show distinct phases
or forms at different or corresponding periods of its life-history to
a greater or less extent. In some species the form-changes are very
slight, and the individuals occur always under a similar form and
aspect, at least during the active state, and are therefore recog-
nizable without difficulty as regards their specific identity ; such
forms may be termed monomorphic, and as examples the species
of ciliate Infusoria can be cited. Other Protozoa, on the other hand,
are extremely polymorphic — that is to say, they occur under a
variety of widely-differing forms at different stages in the life-cycle
or in response to variations in the conditions of life. Hence it is
often difficult or impossible to refer a given form to its proper
species without tracing out its life-history and following its develop-
ment step by step. The unravelling of the complicated life-cycles
of Protozoa is attended by far greater difficulties than in Metazoa,
since one important criterion fails us altogether in the Protozoa,
that, namely, of sexual maturity. A naturalist has no hesitation
in pronouncing a trochophore to be a larval form, and a rotifer to
be an adult organism, from the fact that the former is sexually
immature, while the latter produces ripe generative cells. In the

164 THE PROTOZOA

Protozoa, however, there is no visible criterion of any similar state
of maturity or the opposite which might be a guide in estimating
the significance of a particular form. It is certain that with in-
creasing knowledge many species of Protozoa now regarded as
distinct will prove to be developmental stages of others, as has
happened so frequently in the case of Metazoa.

The polymorphism of the Protozoa may be related directly or
indirectly to a variety of causes, which may be grouped generally
under three headings — life-conditions, growth and development of
the individual, and sex.

1. Polymorphism in Relation to the Conditions of Life. — Under
this heading are included all those cases where the individual is
forced to adapt itself to inevitable changes in the environment,
or else succumb to their effects ; hence this type of polymorphism
may be termed briefly adaptive. The animal may adapt itself to
such changes in one or the other of two ways : passively, by passing
into a resting state, in which vital activities are temporarily sus-
pended ; or actively, by changes of form, structure, and function,
adapted to the changed conditions.

Methods of passive adaptation to unfavourable conditions occur
probably in all Protozoa — perhaps it might be said in all Protista,
so that no species can be said to be absolutely monomorphic. The
commonest form of such adaptation is the process of encystment,
whereby the organism protects itself by secreting a firm, resistant"
envelope, or cyst, round its body.

The first preliminary to encystment in Protozoa is usually a
rounding off of the body-form. In the case of naked amoeboid
forms such a change of form follows naturally, as pointed out
above, from cessation of the locomotor activity. It is, however,
also observed that a similar change takes place in corticate forms,
a phenomenon which indicates that the cuticle or cortex must be
absorbed or softened, and that any internal form-giving elements
must be dissolved, so that the protoplasm is free to conform to
the natural physical tendencies of a fluid body. In the great
majority of cases, an individual in process of encystment becomes
perfectly spherical, whatever may have been the form of its body
in the active state, but in some cases the spherical form is not fully
attained, and the body becomes ovoid or pear-shaped. During the
process of rounding off, any food-particles or foreign bodies contained
in the cytoplasm are rejected or absorbed, as a rule ; the contractile
vacuoles, if there be any, cease to be formed and vanish ; and all
locomotor organs, such as cilia, flagella, and of course pseudo-
podia, are absorbed or cast off. At the same time the protoplasm
of the organism becomes less fluid and more opaque, and usually
diminishes appreciably in bulk, probably through loss of water ; it

POLYMORPHISM AND LIFE-CYCLES 165

thereby becomes denser in consistence, but of less specific gravity.
Lastly, the cyst-membrane itself appears round the body, if it
has not already done so ; it generally stands off distinctly from the
surface of the body, and may vary in nature in different cases,
from a soft, slimy or gelatinous coat to a firm membrane of variable
thickness, often exceedingly tough and impervious.

In the encysted state, Protozoa are able to withstand the many
vicissitudes to which they are naturally subject. They can then
be dried up, frozen, or sun-baked ; and since the protoplasm becomes
much lighter, they can be transported great distances by winds,
a fact which accounts for the appearance of Protozoa in infusions
exposed to the air in any situation — a peculiarity from which the
name Infusoria is derived. In general the function of encystment
is to protect the organism against unfavourable conditions or violent
changes in the environment — for instance, in freshwater forms,
against drought and climate, the cold of winter or the heat of a
tropical summer. In parasitic forms it is an adaptation commonly
connected with a change from one host to another.

In parasites two types of cysts can be distinguished. In the
first place, full-grown forms may produce relatively large, resistant
cysts (Dauerzysten) of the ordinary type, almost invariably
spherical or ovoid in form. In the second place, the smallest forms
in the developmental cycle, the products of multiple fission or
" sporulation," may secrete round themselves tough, resistant
envelopes, within which they may multiply further ; in this case
the envelope is termed a sporocyst, and the entire body a spore*

* The word " sporo " has come to be used in two distinct senses, as applied to
Protozoa, thereby producing a regrettable confusion and ambiguity. The word
itself is derived from the Greek <nr6pos, a seed, and was applied by botanists to
those cases where plants produce seed-like bodies which are not true seeds ; for
instance, the seed of an ordinary flowering plant is a complete embryo, with root
and shoot distinct, encapsuled in protective envelopes, but the " seed " of a fern
is merely a single cell enclosed in a protective membrane. Consequently the
term " spore " was used to distinguish the " seeds " of ferns, fungi, etc., from the
true seeds of flowering plants.

It was observed at a very early period that many parasitic Protozoa produced
minute seed-like bodies, which conveyed the infection ; for those of Myxosporidia
Johannes Miiller coined the term " psorosperms," but in general the term " spore "
was used for these bodies, and the group in which the production of such spores
is a very characteristic feature was named the Sporozoa.

With the progress of further investigation, it was found that in a great many
cases the essential part of the spore — namely, the encapsuled protoplasmic body —
arose by a process of multiple fission, hence termed " sporulation," from a larger
parent-body ; consequently the term " spore " has been used by many in a secon-
dary sense to denote a minute germ formed by multiple fission, as in the merozoites
of the malarial parasites. It is preferable to retain the word " spore " in its
original significance as a seed-like body contained in a resistant envelope or sporo-
cyst, and to use the word " germ " (equivalent to the German word Keim) for
the protoplasmic body formed by sporulation, whether enclosed in a sporocyst or
not. Unfortunately the word " germ " has become very much misused in popular
language, and a less ambiguous term would perhaps be the word gymnospore for
naked germs not enclosed in a protective envelope.

There is no essential difference between a cyst and a spore, except their relation

166 THE PROTOZOA

Sporocysts are often simply rounded or oval bodies, like cysts,
but in some cases they exhibit special forms, and may be prolonged
into spikes, tails, or processes of various kinds.

In many cases the purely protective uses of the cyst may be
combined with the performance of some special function within it.
The contained organism may remain merely in a resting state
within the cyst (hypnocyst) ; or it may utilize its leisure for the
digestion of large quantities of ingested food - material, or for
carrying on processes of reproduction or syngamy. As a process
of similar nature to encystment, the formation of " sclerotia " in
the Mycetozoa must be noted (see p. 240, infra).

Active adaptation to changed conditions is seen in those forms in
which the mode of life is bound up with changes of environment
during different periods of the life-history — that is to say, more
especially in parasitic forms, in which a change of hosts is necessary
for the continuance of the species. In such forms there are in
general two functions for which provision must be made : the first
is that of multiplying in the host itself and keeping up a stock of
the parasites in it ; the second is that of infecting a new host sooner
or later (see p. 20, supra). In the most primitive types of para-
sitic Protozoa there is no differentiation of form or structure corre-
sponding to these two distinct functions ; but as a general rule
a given parasite in a given host exhibits usually two forms or series
of forms, which may be termed " multiplicative " and " propagative "
respectively (Doflein). Multiplicative forms may be wanting in
some cases, as in the Eugregarines, but propagative forms are
always found, being an absolute necessity for the continuance of
the species.

As examples of multiplicative and propagative forms, we may
consider first species which are parasitic only on a single host in
the course of the entire life-cycle. A typical example is seen in
Coccidium (p. 342, Fig. 152), in which adult forms, " schizonts,"
multiply rapidly in the host by a process of multiple fission, " schi-
zogony," a process which takes place unaccompanied by any sexual
phenomena, and in which no resistant cysts are formed, since they
are quite unnecessary. Sooner or later, however, generations of
individuals, " sporonts," appear which do not multiply like the
schizonts, but which, as gametocytes, give rise to the gametes. After
a process of syngamy the zygote forms a resistant cyst within

to a developmental cycle ; the " spores " of Bacteria are for the most part simply
cysts, but are called spores on account of their small size.

In this book the word "spore, "when not qualified by any prefix, will be used
to denote a resistant seed-like body protected by a tough envelope, or sporocyst,
and the production or development of such bodies will be termed " spore-forma-
tion." On the other hand, the production of numerous small cells or germs by
multiple fission will be termed " sporulation."

POLYMORPHISM AND LIFE-CYCLES 167

which it multiplies to form a number of germs, which may or may
not be enclosed in sporocysts, in different species. Cysts and spores
pass out of the host, and do not develop further unless they are
devoured by a second host of a species in which they are able to
establish themselves ; if this event takes place, the spores germinate
in the new host and produce a fresh cycle of infection, each germ
when set free growing up into a schizont. In this case it is seen
that the schizonts represent the multiplicative, the sporonts the
propagative, phase, and that in the latter resistant cysts are pro-
duced as a protection against the vicissitudes of the outer world,
to which the parasite must expose itself during this phase of its
life-history.

An example of a parasite which infects two distinct species of
hosts in the course of its life-history is furnished by the malarial
parasites (p. 360, Fig. 156). In this case there are first of all
schizonts which, like those of Coccidium, reproduce themselves by
multiple fission, this part of the life-cycle being passed in the blood
of a vertebrate host. Later, sporonts are generated which under
normal circumstances are incapable of multiplication in the verte-
brate host, or, indeed, of any further development, unless taken up
by another host, in this case a mosquito, which takes them from
the vertebrate host by sucking its blood. In the stomach of the
new host the sporonts behave in a similar manner to those of
Coccidium — that is to say, they give rise as gametocytes to gametes,
which by syngamy produce zygotes. The zygotes grow and repro-
duce themselves by multiple fission, forming an enormous number
of minute germs or sporozoites, which do not develop further unless
they pass from the mosquito back into the blood of a suitable
vertebrate host, in which they start a fresh developmental cycle.

The life-cycle of the malarial parasites shows that a given phase
of a parasite is only to be regarded as multiplicative or propagative
in relation to a particular host. In the vertebrate blood the
schizont is the multiplicative, the sporont the propagative, phase.
As soon, however, as the sporont passes into the mosquito, it becomes
there the multiplicative phase which gives rise ultimately to the
sporozoites, representing the propagative phase in the mosquito.
The sporozoites in their turn, when they reach the blood of the
vertebrate, develop there into schizonts. Thus one and the same
stage in the life-cycle represents one phase in one host and another
in another, according to circumstances. It should be noted further
that in the life-cycle of the malarial parasites resistant cysts are
unnecessary, since the parasite never comes out into the open, but
passes the whole of its existence in one or the other of its two hosts ;
consequently such cysts are not formed at any stage of the life-
cycle in these forms.

168 THE PROTOZOA

Another example of a parasite with alternation of hosts, in which
the course of events is different from that of the malarial parasites,
is furnished by the species of the genus Aggregata (p. 353). Here
the schizonts are parasitic in crabs, and reproduce themselves by
multiple fission without encystment to form naked germs, mero-
zoites, which grow up into schizonts, and multiply again in the same
way. If, however, the crab is devoured by a Cephalopod, the
merozoites adapt themselves to their new surroundings and become
sporonts, which produce gametes. The zygotes form resistant
cysts in which they multiply to form spores enclosed in tough
sporocysts. The resistant phases pass out of the Cephalopod in its
faeces, and to develop further they must be devoured by a crab, in
which they become schizonts again. In this case there is no special
differentiation of propagative phases in the crab, but the same
stage can serve both functions ; on the other hand, in the
Cephalopod there is no multiplicative phase, but only a propagative
phase with resistant cysts.

2. Polymorphism in Relation to Growth and Development of the
Individual. — In Protozoa which multiply only by equal binary
fission, as, for example, many Infusoria, there is practically no
difference between young and old forms beyond a slight variation
in size. An individual feeds, and in consequence grows slightly
beyond the size characteristic of the species to which it belongs.
It then divides by equal binary fission into two individuals each
slightly below the specific size, and they in their turn feed and grow
and reproduce themselves by fission in due course.

In other cases, however, young and adult forms of a species can
be clearly distinguished, and may differ in structure as well as in
size. Beginning with reproduction by binary fission, the simplest
case is where the adult individual divides into two unequal portions,
so that parent and daughter can be distinguished, the former not
appreciably smaller than ordinary full - grown individuals, the
latter, however, very much smaller ; it may be relatively minute.
Examples of this type of reproduction are furnished by trypano-
somes, a group in which all gradations may be found between equal
and very unequal fission (Fig. 127). Still greater differences
between parent and young individuals are seen in cases of gemma-
tion— that is to say, where the offspring is set free in an undifferen-
tiated condition, and acquires after separation from the parent the
characters of the adult, as in Acinetaria.

The greatest differences between young and old forms are seen,
as might have been expected, in cases of reproduction by multiple
fission or gemmation. In such cases the young forms produced
often differ from the adult in structure and appearance, as well as
in size. An example of multiple fission is furnished by the common

POLYMORPHISM AND LIFE-CYCLES 169

Trypanosoma lewisi of rats, in which two types of such fission are
seen : either the multiplication of a small individual by repeated
binary fission to form a " rosette " composed of several daughter-
individuals (Fig. 127, J, K], or the separation of several small
daughter- individuals from a large one (Fig. 127, F, G, H). In both
cases the multiple fission is simply rapid and repeated binary fission.
The young individuals resulting from the fission are sometimes
crithidial in type (p. 294), and grow into the adult trypanosome-
form.

In multiple gemmation (sporulation) the parent body breaks up
into a number, sometimes very large, of small or even very minute
individuals, buds, or germs, usually given off from a more or less
considerable mass of residual protoplasm, which degenerates and
dies off. The buds when set free may become active at once, or
they may pass first into a resting state to which an active state
succeeds at a later period. In the latter case they may form
sporocysts, and become the spores already described. Within the
sporocyst the minute germ may multiply further by fission. In the
subclass Telosporidia of the Sporozoa, the contents of the spore
may divide up in this way to form a variable number of slender
sickle-shaped germs, for which Aime Schneider coined the term
sporozoites, a term which has since been frequently applied in senses
quite different to its original meaning.

An active germ produced by sporulation is termed a swarm- spore
or zoospore, whether or not the active phase is preceded by a resting
spore-stage. The swarm-spores of Protozoa may be of various
types in different cases. The swarm-spore may be amoeboid and
creep about by the aid of pseudopodia ; it is then termed an
ammbula (or pseudopodiospore). It may be provided with one or
more flagella as organs of locomotion, and is then termed a flagellula
(or flagellispore}. It may have a coat of cilia, as in the young stages
of Acinelaria, and may then be termed a ciliospore. Lastly, the
swarm-spore may be without organs of locomotion, whether perma-
nent or temporary, and may progress by twisting and wriggling
movements of the body as a whole, or by gliding forwards on its long
axis in a manner similar to the gliding movements of gregarines ;
swarm-spores of this type are specially characteristic of the Telo-
sporidia amongst the Sporozoa, arising either by sporulation of a
schizont (merozoites) or in the process of spore-formation after
syngamy (sporozoites), and may be termed gregariniform swarm-
spores or gregarinulce comprehensively.

In some cases the swarm-spore may pass through more than one
active phase, and exhibit different modes of locomotion in each.
This is well seen in the Mycetozoa (p. 239), where the germination
of the spore produces an amcebula, which may acquire a flagellum

170 THE PROTOZOA

and become a flagellula ; after a time the flagellula settles down and
becomes an amcebula again after loss of the flagellum.

A very interesting point, in connection with the question of young
and adult forms of Protozoa, is the occurrence of stages in the
development which may be interpreted as recapitulative in the
phylogenetic sense — that is to say, as representing past stages in the
evolution of the species, in a manner comparable to the recapitu-
lative larval or embryonic stages in the development of Metazoa.
It is probable that such recapitulative stages are commoner in the
development of Protozoa than has been generally supposed (compare
Awerinzew, 47). The best-known instance is furnished by the
ciliated larvae of Acinetaria (p. 459), indicating that this order is
descended from a ciliate ancestor of the order Peritricha, a relation-
ship fully confirmed by the similarity of their reproductive processes
to those of other Infusoria. The crithidial phase that occurs so
constantly in the development of trypanosomes (p. 299) is probably
to be regarded as a recapitulative form representing a type of
structure antecedent in evolution to that of the typical trypanosome-
form. The frequent occurrence of flagellated swarm-spores in the
development of Sarcodina (Foraminifera, p. 235 ; Radiolaria, p. 254)
probably has a phylogenetic significance, as pointed out by Biitschli.
Finally attention may be drawn to the remarkable series of forms
in the ontogeny of Arcella described in the next chapter ; first the
amcebula, then the Nuclearia-st&ge, followed by the Pseudochlamys-
stage, which grows finally into the adult Arcella-iorm. In the many
cases where young forms are markedly different from the adult, it
may be a difficult matter, as it often is in the case of Metazoa, to
decide whether a given larval form is to be interpreted as recapitu-
lative or merely adaptive ; but even in cases where the characters
of a larval form have an obvious adaptive importance, as in the
ciliated larvae of Acinetaria, atavism may be nevertheless a factor
determining the particular form taken by the adaptive characters in
question — that is to say, by the organs of locomotion in the example
chosen.

3. Polymorphism in Relation to Sex. — The phenomena of sexual
differentiation consist primarily of differences in size, structure, and
other characteristics between the gametes, the cells which are con-
cerned in the act of syngamy. Secondarily such differences may
extend to other cell-individuals, both in the life-cycle of a Protozoon
or in the body of a Metazoon. In the previous chapter it has "been
pointed out that, while in Metazoa the gametes at least are sharply
differentiated in all cases, in the Protozoa every condition is found
from perfect isogamy to a differentiation nearly as pronounced as
that in the Metazoa. The question has been discussed in the last
chapter whether or no sexual differentiation is to be regarded as

POLYMORPHISM AND LIFE-CYCLES 171

an inherent property of all living beings, as maintained by many
high authorities.

Whatever view be held with regard to the existence or non-
existence of inherent, intrinsic sexual differences in living organisms,
it seems clear that the apparent sexual differentiation of the gametes
is largely, perhaps purely, adaptive, and furnishes good examples
of the principle of morphological differentiation of structure in
relation to physiological division of labour. One gamete, termed
" female," tends to be bulky and inert, storing up reserve- material
in greater or less quantity, a provision (sit venia verbo /) for future
requirements ; it is economical of substance, and but few are
produced. The other gamete, termed " male," develops in the
opposite direction in every respect ; it tends to be small and active,
not weighted with superfluous material of any kind, but with motor
mechanisms strongly developed ; it is prodigal of substance, and
many are produced, but few are favoured by destiny. In extreme
cases the female gamete is a relatively huge, inert cell, incapable
of movement, crammed with foodstuffs ; the male is excessively
minute, and is practically nothing but a nucleus which has its
constituent parts packed into the smallest possible space, and with
motor mechanisms attached to it.

In reviewing the progressive differentiation of the gametes in
Protozoa, it is convenient to treat separately those forms in which
there is little or no ontogenetic differentiation from those in which
there is a more or less pronounced difference between the young
and adult forms. An example of the first type is seen in Copromonas
(Fig. Ill), in which the gametes are ordinary individuals of the
species, only differing in that their nuclei have undergone a process
of reduction. Good examples of monomorphic forms* are furnished
also by the Infusoria, a group in which a species may be free-swim-
ming, or may be more or less permanently attached and sessile in
habit.

In the free-swimming ciliate Infusoria, sexual differences in the
conjugants are frequently not discernible ; if they exist, they can
only be inferred from the fact that syngamy takes place, or from
subsequent behaviour of the individuals after conjugation, as, for
instance, the fact observed by Calkins, that in Paramecium one ex-
con jugant multiplies much more rapidly than the other. In other
cases differences of size more or less pronounced are exhibited by
the conjugants (Doflein, 111). As pointed out above, differences
of structure have also been noted in some cases between the
stationary and migratory pronuclei produced by a conjugant.
Collin (50), however, was unable to find the slightest morphological
differentiation of the conjugating pronuclei of Anoplophrya.

In the sedentary Infusoria, sexual differentiation may be as little

172

THE PROTOZOA

m.er

apparent as in the free-swimming species, as, for instance, in
Acinetaria, where conjugation can take place between two adjacent
individuals each on its own stalk. But in the Vorticellids special
free-swimming individuals, microconjugants, are developed which
are budded off from a sedentary individual, and then acquire
cilia, swim off, and conjugate with another sedentary individual
(Fig. 78). It seems obvious that this
state of affairs is an adaptation to the
exigencies of a sedentary life to insure cross-
fertilization analogous to the formation of
complemental males in the Cirripedes. The
free - swimming microconjugants of Vorti-
cellids are commonly termed " males," but
it is open to question whether, strictly
speaking, they deserve that title.

It is in species with marked differences
between young and adult forms that the
greatest differentiation of the gametes
occurs, though by no means universally even
in such forms. In polymorphic species of
this type, three different conditions can be
distinguished, to which reference has been
made in the previous chapter.

FIG. IS.—Vorticella micro- i Macrogamy — that is to say, syngamy
stoma, Ehrb. On the left , , -. ,? . ,. ., , /,- " .

an ordinary, sedentary between full-grown individuals of the species.

individual (macroconju- In this type the gametes appear to be always

fugante^n^^Ttached Perfectly similar, so far as is known; ex-

to it, one of which (to amples are seen in Actincphrys (Fig. 71),

the left) is in the act_of the chromidiogamy of Arcella (Fig. 80), and

conjugation,
right is an

On

2. Microgamy — syngamy between the

nucleus ; P,

and adoral ciliary spiral.

After Hickson.

individual possibly Noctiluca (p. 279).

with the stalk contracted
and the body enclosed
in a cyst. 'N, Macro- youngest individuals, products of the rapid

peristome multiplication of an adult. Conjugation of
swarm-spores is by far the commonest typo
of syngamy in Protozoa, and may be re-
garded as the normal type. In this case there is usually complete
iscgamy, as in Foraminifera (p. 235), sometimes slight anisogamy,
as in Radiolaria (p. 254, Fig. 108).

3. Mixed microgamy and macrogamy — that is to say, syngamy
between a full-sized adult individual on the one hand and a minute
individual, a swarm-spore, on the other hand. This type may be
regarded as derived from microgamy by progressive, and finally
complete, inhibition of the divisions that produce the swarm-spores
in one sex — possibly also with an enhanced tendency to such divisions
in the other sex. Thus in Arcella, as described in the previous

POLYMORPHISM AND LIFE-CYCLES 173

chapter, the macramcebae produced are fewer than the micramoebse,
showing that the tendency to division is more restricted in the
former case than in the latter. Again, in the development of Centro-
pyxis, as described by Schaudinn (131), formation of gametes is
initiated by a process of multiple fission combined with formation
of secondary nuclei from chromidia, as in Arcdla, and in this way
a number of amcebulse are produced. The amcebulse from one
Centropyxis remain undivided, as macramcebse, while those pro-
duced from another adult divide each into four micramcebae ;
syngamy takes place later between a micramceba and a macramceba,
after each has secreted for itself a shell.

When the inhibition of the gamete-forming divisions is quite
complete in one sex, the result is the most pronounced type of
anisogamy occurring in Protozoa ; and, conversely, it may be said
that all cases of extreme anisogamy in Protozoa are of this type.
In Metazoa the disproportion in the size of the gametes is mainly
due to the relatively enormous growth of the gametocyte, partly
also to the inequality of the four cells produced by the reducing
divisions, in the female sex. In Protozoa with extreme differen-
tiation of gametes, on the other hand, such as the Coccidia and
Hsemosporidia, the gametocytes do not differ greatly, sometimes
not at all, in size, though the female gametocyte may contain
more reserve food - material, and consequently less protoplasm.
The disproportion of the gametes is due almost entirely to the fact
that in the female sex the gametocyte does not divide, but becomes
a single macrogamete, while the male gametocyte sporulates to
produce a larger or smaller number of microgametes.

Very instructive in this respect is the comparison of the formation
of the gametes in the gregarines (p. 331) and the coccidia (p. 346)
respectively, two groups of Protozoa which are certainly closely
allied to one another. In such a form as Coccidium (Fig. 152), the
gametocytes remain separate one from the other, and the male
gametocyte forms numerous minute microgametes which swarm
away ; the female gametocyte, on the other hand, becomes a macro-
gamete after going through a process of reduction, and is fertilized
by a single microgamete. In gregarines, however, the gametocytes
associate in couples, either before or after attaining their full size,
and become surrounded by a common cyst, within which each
gametocyte sporulates to produce a large number of small gametes.
The gametes of gregarines can be arranged in a series, showing
marked anisogamy at one end, complete isogamy at the other.
Thus in PterocepTialus (Fig. 79, A, B) the gametes are very unequal
in size, and the microgametes are motile, the macrogametes not so.
In Stylorhynclms the gametes of opposite sexes are equal in size,
but in one sex the gametes are motile, in the other not (Fig. 79,

174

THE PROTOZOA

C, D}. In Monocystis (Fig. 79, G — L) the gametes differ slightly in
size in the two sexes, but have no organs of locomotion in either
case. In Urospora (Fig. 79, E, F) the gametes are not appreciably
different in size, but in those of one sex the nuclei are slightly
smaller than in those of the other. Finally, in Gregarina, Diplodina,
and many other genera, no difference whatever is perceptible
between the two gametes that perform syngamy. In those gre-
garines which have dimorphic gametes, syngamy is always between
two dissimilar individuals of distinct parentage, and it may be
inferred, therefore, that in all cases alike the gametes that unite are
derived from distinct gametocytes.

FIG. 79. — Gametes of different species of gregarines. A, Male, B, female, gamete
of Pterocephalus (Nina) gracilis. G and D, Stylorhynchus longicoUis : G, male
gamete ; D, male gamete attaching itself to a female. E, Male, F, female,

riete of Urospora lagidis, showing differences in the size of the nuclei.
L, Monocystis sp. : G, male gamete ; H, female ; /, union of the two
gametes, the nuclei still separate ; J , the two nuclei fusing ; K, the zygoto
becoming elongated ; L, the zygote has taken the form of the spore, and in
the synkaryon a centrosome has appeared, preparatory to division. A and
B after Leger and Duboscq ; G and D after Leger ; E — L after Brasil.

From a comparison of the life-cycles of the Coccidia and the
Gregarines respectively (see p. 354, infra], it is highly probable that
in the common ancestor of the two groups the gametocytes were
separate, as in Coccidium, and each produced numerous gametes,
as in Gregarines. Since the gametes had to find each other, by a
process of adaptation, those of one sex became smaller and more
motile (microgametes), while those of the other sex were more bulky
and inert (macrogametes).

In the course of their evolution from this primitive ancestral
type, the Coccidia, with some exceptions presently to be noted,
retained the habit of the gametocytes, remaining separate, and the
specialization of the gametes became greatly increased, as an adap-

POLYMORPHISM AND LIFE-CYCLES 175

tation to this condition, the female gametocyte ceasing to divide
and becoming a single macrogamete, while the male gametocyte
produced a swarm of minute, motile microga metes. Only in a
few Coccidia, exemplified by the genus Adelea (Fig. 154), did the
gametocytes acquire the habit of association before forming gametes,
a habit which led in this case to a reduction of the number of micro-
gametes produced to four, of which one fertilizes the macrogamete,
while the other three perish. It is clear that the formation of
microgametes in close proximity to the macrogamete increases
vastly the chance of the gametes finding each other, and renders
unnecessary the production of a swarm of microgametes.

In the gregarines, on the other hand, the gametocytes acquired
the habit of associating and forming their gametes in a common
cyst. Under these circumstances it becomes a certainty that a
gamete of either sex will find a partner if the gametes of each sex
are in equal numbers. Consequently there is seen in gregarines a
progressive tendency, illustrated by the examples cited above, to
disappearance of those characters of the gametes which are an
adaptation to the necessity of the sexes coming together, culminating
in production of gametes of opposite sexes which are perfectly
similar. On this view the isogamy seen in many gregarines is a
secondary condition brought about by the gradual obliteration of
adaptive differences between the gametes of opposite sexes, under
circumstances which render such differences unnecessary.

The comparison of the gamete -formation in different species of gregarines
furnishes an instance of a progressive levelling- down of structural differentia-
tion of gametes, under conditions in which no such differentiation is required,
until an anisogamy undoubtedly primitive has been reduced secondarily to a
perfect isogamy. This has led to the view expressed in many quarters, that
anisogamy is in all cases a primitive, isogamy a secondary, condition. The
case of the gregarines is by no means adequate, however, to support so
sweeping a generalization ; the only conclusion that can be drawn from it is
that adaptive differences tend to disappear when the conditions to which they
are an adaptation no longer exist ; and the very fact that the obvious structural
differentiation between the gametes vanishes in such a case is of itself a proof
that such differentiation is not the expression of intrinsic constitutional
differences between the gametes, for such differences could not be annihilated
merely by changed conditions of environment.

There can be no doubt that anisogamy in the form of visible structural
differences between the gametes of opposite sexes must have been acquired
very early by gametes as an adaptation to their functions. On the other
hand, it is highly improbable, to say the least, that the earliest gametes,
when the sexual process was first invented, so to speak, were structurally
differentiated. It must, of course, be postulated that the gametes possess
such intrinsic constitutional differences as would account for their behaviour —
that is to say, their mutual attraction and union ; and in this sense anisogamy
may be considered as a universal and primitive phenomenon. But the number
of cases in which gametes are perfectly isogamous, as regards visible struc-
tural or other differences, is a sufficient proof that purely constitutional
anisogamy does not necessarily express itself in perceptible differentiation
of the gametes.

176 THE PROTOZOA

So far only primary sexual differences — that is to say, those
between the actual gametes — have been discussed ; but, as has been
stated above, the sexual differentiation may be thrown back, as it
were, into generations preceding the gametes. Thus, it is by no
means uncommon, especially in Coccidia and Hsemosporidia, for
the gametocytes to be clearly distinguishable according to sex, the
female gametocyte having the cytoplasm loaded with reserve food-
material, and usually with a smaller nucleus, while the male gameto-
cyte has the cytoplasm clear and free from inclusions, and the
nucleus is relatively large. In Adelea the male gametocyte is
very much smaller than the female (Fig. 154). In Cydospora
caryolytica, parasitic in the mole, the sexual differentiation is carried
back through generations antecedent to the gametocytes, and,
according to Schaudinn (147), male and female merozoites can be
distinguished.

The various types of polymorphism that have been discussed in
this chapter may be classified as follows :

1. Adaptive polymorphism.

(1) Passive.

(2) Active.

2. Ontogenetic polymorphism.

(1) In size alone.

(2) In structure also.

(a) Recapitulative.

(b) Adaptive.

3. Sexual polymorphism.

(1) Primary (of gametes).

(2) Secondary.

(a) Of gametocytes alone.

(b) Of other generations also.

In the task of unravelling the complicated life-cycles of Protozoa,
it is of the greatest importance to distinguish clearly the significance
of the various forms that are seen, and there can be no doubt that
failure to do so has often been a source of error. With some writers
it is an obsession to ascribe all differences to sex, and to interpret,
for instance, in the development of trypanosomes, all bulky forms
as females, and all slender, active forms as males, quite regardless
of the behaviour of the forms thus designated. It is far more
probable that in the majority, at least, of such cases the bulky
forms are related to the multiplicative, the slender, active forms to
the propagative function, respectively, and that the differences

'••ween them have no relation whatever to sexual functions, either
forms themselves or in their descendants.

POLYMORPHISM AND LIFE-CYCLES 177

B. LIFE-CYCLES.

In the foregoing section the various forms have been described
under which one and the same species of Protozoon may occur in
the course of its life-history, and in response to the conditions of its
particular mode of life. In some species it has been seen that the
changes of form and structure are so slight that the species are
practically monomorphic, in the sense that they can be identified
without difficulty in any active phase of life ; no species is absolutely
monomorphic, since, in addition to resting states, differences in size
due to growth, at least, will always be found. Other species, on
the other hand, are polymorphic to such an extent that their specific
identity in different phases can only be determined by tracing their
development in a continuous sequence ; and in extreme cases of
polymorphism the life-history becomes a varied pageant of dis-
similar forms succeeding each other in more or less regular order,
determined largely, if not entirely, by the conditions of the environ-
ment. In a former chapter the distinction has been drawn between
a developmental cycle, consisting of a recurrent series of different
forms, and the complete life-cycle, consisting of the whole series
of forms or phases which appear between one act of syngamy and
the next. The complete life-cycle may comprise many develop-
mental cycles.

As a concrete example of a lif e-cycle comprising a great number of
different forms, and in which also the development may follow more
than one course, the life-cycle of Arcella vulgaris may be selected
(Fig. 80). The life-history of this form has now been made known
in detail by the combined labours of many investigators, amongst
whom Hertwig (65), Elpatiewsky (144), Swarczewsky (101), and
Khainsky (145), must be specially mentioned.

The form which may be taken as the starting-point of the life-
cycle is a minute, amoeba-like form, with a single nucleus (Fig. SO, A).
The amoebula, when set free, feeds, grows, and becomes after a
time spherical in form with radiate pseudopodia (Fig. 80, B) ; in
this stage it resembles a species of the genus Nuclearia. After a time
the Nudearia-foim secretes a shell, and now resembles an example
of the genus Pseudochlamys (Fig. 80, C). With further growth,
chromidia are given off from the nucleus into the cytoplasm, the
nucleus divides into two, and the animal thus assumes gradually the
characters of the adult Arcella (Fig. 32 ; Fig. 80, D). It has a
chitinous shell, circular in outline, flattened in profile-view, and
slightly concave on the under-side, in the centre of which is a large
circular aperture through which the pseudopodia stream out. The
body-protoplasm contains two nuclei situated approximately at

12

178

THE PROTOZOA

FIG. 80. — Combined diagram to show the different methods of reproduction and
syngamy in the life-cycle of Arcella.

^d.—D, The four stages in the ontogeny : A, the amoebula ; B, the Nuclearia-iorm ;
C, the PseudocMamys-torm ; D, the adult Arcella.

I)—G, Stages in the vegetative reproduction by fission : E, the protoplasm
beginning to stream out of the shell of the parent-individual ; F, division of the
nuclei of the parent, and formation of the shell of the daughter ; O, migration
of the daughter-nuclei into the daughter-individual and completion of the division.

[Continued at fool of p. 179.

POLYMORPHISM AND LIFE-CYCLES 179

the opposite ends of a diameter of the circular body, and an irregular
ring of chromidia forming a dense chromidial net. Under certain
conditions Arcella becomes encysted, forming a spherical cyst
with a tough impervious membrane within the shell, closing the
mouth of it.

The adult Arcella reproduces itself by a variety of methods,
which, however, may be reduced to two principal types : binary
fission, producing daughter-individuals (Arcellce) of approximately
equal size ; and gemmation, producing small amcebulse such as have
been described above as the starting-point of the ontogeny. The
production of the amcebulse may or may not be in relation to
syngamy, which, when it occurs, may be of one or the other of two
distinct types — karyogamy between amcebulae, or chromidiogamy
between adult Arcellce.

Binary fission (Fig. 80, D — G) is the ordinary type of reproduction
during the " vegetative " life in the summer months, when the
animal is actively feeding, growing, and reproducing itself. In
the process of binary fission, the two nuclei divide by a form of
karyokinesis (Fig. 57, p. 110). A quantity of the body-protoplasm
streams out through the mouth of the shell, together with some of
the chromidia, and one of the two daughter-nuclei of 6ach pair also
passes out of the shell. The daughter -Arcella thus formed secretes
for itself a new shell, and separates from the parent-individual,
which retains the old shell. Thus in binary fission both nuclei and
chromidia take part, the former dividing by mitosis, while the latter
are subjected to a roughly equal partition.

The ordinary binucleate form of Arcella may become multi-

FIG. 80 — continued:

All the figures below the level of D represent reproduction by gemmation :
those to the left are reproductive processes not combined with syngamy ;
those on the right show the methods of syngamy.

H, Formation of secondary nuclei and buds which are liberated singly
from the parent as amcebulso (a.).

/, Rapid bud-formation, leading to almost the whole protoplasm of the
parent being used up to form them.

J, Bud-formation external to the shell ; the protoplasm has streamed out,
leaving only a small residual portion, containing the primary nuclei, in the
shell ; the extruded protoplasm producing buds with formation of secondary
nuclei.

K, L, Formation of gametes and karyogamy : K, formation of macramoebiB
( ? ) ; L, formation of micramcebse ( c? ) ; the gametes ( ? and <$ ) pass out of
the shell and copulate ( ¥ ) to produce the zygote or amoebula (a.).

M — Q, Chromidiogamy : M , two Arcellce coming together ; N, the proto-
plasm, with" the chromidia and degenerating primary nuclei, of the one passes
over into the shell of the other ; 0, after intermingling of the chromidia, the
protoplasm becomes equally distributed between the two shells ; P, the
chromidia give rise to secondary nuclei ; Q, buds (amosbulae, a.) are formed
and liberated.

Other letters : n., nucleus ; n.1, primary nucleus ; n.2, secondary nucleus;
chr., chromidia ; sh., shell ; o, mouth of shell ; a., amcebulae.

Modified from a diagram by Swarczewsky.

180 THE PROTOZOA

nucleate by formation of secondary nuclei from the chromidia, as
described above (Fig. 32, p. 67). The secondary nuclei are entirely
distinct in their origin from the primary nuclei, which degenerate
when the secondary nuclei are formed. A multinucleate Arcella
may reproduce itself by binary fission after division of each secon-
dary nucleus by karyokinesis ; of each pair of secondary daughter-
nuclei, one goes to one daughter-ylrce^a, the other to the other, so
that each daughter-./4rce//a has the same number of nuclei exactly
(Hertwig, 65).

Gemmation takes place in multinucleate forms containing a
number of secondary nuclei. A portion of the body-protoplasm
becomes centred round each secondary nucleus, and thus a small
cell is formed, which becomes amoeboid, quits the parent-body, and
either grows directly into an adult Arcella by the successive stages
described above, or before doing so performs an act of syngamy.

Gemmation, as above described, takes place in three different
ways, as follows :

1. The buds are formed one at a time, and the parent-individual
persists and continues to reproduce itself (simple gemmation,
Fig. 80, H).

2. The whole body of the Arcella breaks up into numerous buds
which swarm out of the shell, leaving behind in it the two primary
nuclei, with a small quantity of residual protoplasm. The parent-
individual then dies off, apparently, but it is possible that it may in
some cases regenerate the body again. This process of multiple
gemmation differs only from the simple gemmation described in the
previous paragraph in being, as it were, greatly intensified, taking
place with such rapidity as to use up almost the entire protoplasm
at once (Fig. 80, /).

3. The protoplasm of the Arcella, with the chromidia, streams
out of the shell, leaving in it only the degenerating primary nuclei.
Outside the shell the amoeboid body forms secondary nuclei, and
breaks up by multiple fission into a number of amcebulae. This
process differs from that described in the foregoing paragraph only in
taking place outside the shell (Fig. 80, J).

As already stated, the amcebulse formed by multiple gemmation
may either be agametes, which develop directly into the adult form,
or gametes, which first go through a process of syngamy which has
been described in the previous chapter (Fig. 80, K, L). Both
agametes and gametes arise in the same manner ; the gametes,
however, show sexual differentiation as regards size. The zygote
is an amcebula which develops into the adult form in the same way
as an agamete. In addition to syngamy (karyogamy) between
amcebulse, chromidiogamy between adult Arcellce also occurs, as
already described ; the result in this case also is the formation of a

POLYMORPHISM AND LIFE-CYCLES 181

number of amoebulse which develop into the adult in the usual way
(Fig. 80, M—Q).

Arcella thus furnishes a surprising example of diversity both in
the courses taken by the development and in the methods of
syngamy. We may now consider some further complications of
the life-cycle, which in other Protozoa takes usually a more definite
and stereotyped course, less liable to the variations in one and the
same species seen in Arcella.

One of the commonest complications introduced into the life-
cycles of Protozoa is the differentiation of sexual and non-sexual
cycles. In the account given above of the life-cycle of Arcella, it
has been seen that an adult may produce amcebulse which as
agametes can grow up directly into the adult form without syngamy,
or which as gametes copulate before developing further. The
adult Arcellce, however, do not, so far as is known, exhibit any
differentiation in relation to these developmental differences, the
form that produces gametes being perfectly similar to that which
produces agametes. But in other cases there may be two distinct
forms of the adult individuals : the one, known as the sporont or
gamont, which gives rise to gametes ; the other, termed the schizont or
agamont, which produces agametes.* In this way an alternation of
generations is brought about in which the life-cycle as a whole
becomes a combination of two distinct types of developmental cycle
— one known as schizogony, in which no sexual processes occur ;
the other as sporogony, in which at one stage gamete-formation is
followed by syngamy.

An example of alternation of generations in a free-living form is
seen in the life-cycle of Trichosph cerium (Fig. 81), as described by
Schaudinn (146). The adult phase is a relatively large amoeboid
form, approximately spherical in contour, and having the body
surrounded by a gelatinous envelope in which at intervals there are
apertures through which the lobose pseudopodia are extruded ; the

* The word " sporont " was a modification suggested by Biitschli for the terra
" sporadin," originally coined by Aime Schneider to denote the adult spore-
forming phase in the cephaline Gregarines (p. 339), and to distinguish it from the
earlier phase which still bears the epimerite, known as a cephalont (" cephalin,"
Schneider). Since the production of resistant spores in Gregarines and allied
orders, such as the Coccidia, is accompanied by sexual phenomena, the word
" sporont " has undergone both an extension and a change in its original meaning,
and has come to be used to denote a gamete-producing form. In his memoir on
Trichosph cerium, Schaudinn used the word " sporont " in this sense, and coined
the term schizont to denote the agamete-producing form, and further coined the
words " schizogony " and " sporogony " to denote the non-sexual and sexual
cycles respectively. Since the word " sporont " in the secondary meaning thereby
given to it has reference solety to the occurrence of syngamy and not to the forma-
tion of resistant spores, and since these two processes are not always, though
frequently, combined in the same series of generations, it would perhaps be better
to replace the terms " schizont " and " sporont " by " agamont " and "gamont "
respectively, were it not that this leads to the substitution of the extremely cacopho-
nous words "agamogony " and "gamogony " for "schizogony" and "sporogony."

182

THE PROTOZOA

G

FIG. 81. — General life-cycle of Trichosphcerium sieboldi, as an example of dimor-
phism in the adult condition combined with alternation of generations.
A, Schizont or non-sexual form, distinguished by the possession of rod-like
bodies in the envelope (compare F) ; this form may multiply by simple or
multiple fission (plasmotomy) in a " vegetative " manner, or by the process
of sporulation (schizogony ) seen in B and 0, in order to give rise to the gamete-
producing form ; B, division of the body of the schizont into as many cells
(" sporogonia ") as there are nuclei ; 0, rupture of the envelope and escape
of the sporogonia as active amcebulse, each of which forms an envelope for

[Continued at foot of T. 183.

POLYMORPHISM AND LIFE-CYCLES 183

protoplasmic body is a multinucleate plasmodium. There are two
forms of the adult — the schizonts (agamonts), which are dis-
tinguished by the presence of rod-like spicules in the envelope
(Fig. 81, A) ; and the sporonts (gamonts), which have no spicules
(Fig. 81, F). The schizonts reproduce themselves either in the
free state or after encyst ment. In the free state the reproduction
is by simple or multiple plasmotomy — that is to say, by division of
the plasmodium into two or more portions. In the encysted con-
dition the schizonts divide by multiple fission into as many daughter-
cells as there are nuclei in the plasmodium (Fig. 81, B), and each
daughter-cell is set free as an amcebula (agamete), which may either
grow up into a sporont, or into a schizont which repeats the process
of multiplication by schizogony.

The sporont may reproduce itself in the free state in the same
manner as the schizont, by plasmotomy, or it may become encysted,
and then it multiplies in a manner totally different from that seen
in the corresponding phase of the schizont. The nuclei of the
encysted sporont multiply rapidly by karyokinesis (Fig. 81, G) until
there are a very large number of minute nuclei ; very probably the
final divisions in this process of multiplication are reducing divisions.
The protoplasmic body then becomes divided up into as many
minute cells as there are nuclei, and each of the daughter-cells
acquires two flagella, and is set free as a flagellula or gamete
(Fig. 81, H). The gametes, which are not differentiated in any way,
copulate with those derived from another sporont, and lose their
flagella (Fig. 81, / — L) ; the zygote is a small amcebula which grows
up into a schizont (Fig. 81, L, M, N, A).

An alternation of generations similar to that of Trichosphcerium
occurs also in the Fora minif era (p. 234). Here the schizont contains
numerous nuclei, which multiply by fission as the animal grows, and
also chromidia ; it reproduces itself by a process of multiple fission,
breaking up into a number of amcebulse (agametes), each with a
nucleus and chromidia. The amcebulse creep out of the old shell,
which is abandoned, and each amoebula secretes a shell for itself,

FIG. 81 continued,:

itself and grows, with multiplication of the nuclei (D and E) into the gamete-
producing form or sporont (F), similar in general structure to the schizont (^4),
but without rods in the envelope ; the sporont may also multiply in a vegeta-
tive manner by simple or multiple fission, or it may form gametes in the
manner seen in G and H ; G, active multiplication of the nuclei of the sporont
to form a great number of very small nuclei, after which the body divides
up into as many minute cells as there are nuclei ; these cells are the gametes,
and each gamete acquires two flagella ; H, rupture of the envelope to set free
the gametes, which swarm out and conjugate ; /, conjugation of two gametes,
more highly magnified ; J, after fusion of the bodies of the gametes the
flagella are thrown off ; K, fusion of the two pro nuclei ; L, complete zygote,
which forms an envelope and grows, with multiplication of the nuclei (M, N)
into the schizont (^4), which was taken as a starting-point of the life-cycle.
After Schaudinn (146).

184 THE PROTOZOA

and grows up either into a sporont or into a schizont again. The
sporont possesses only a single large nucleus, the primary nucleus
originally present in the amcebula, and a great number of chromidia.
When the sporont enters upon the reproductive phase, the primary
nucleus degenerates, and an immense number of secondary nuclei
are formed from the chromidia. Then the protoplasmic body divides
up to form as many cells as there are secondary nuclei. The cells
thus produced are the gametocytes, each of which divides by mitosis
to form four small cells, the gametes, which acquire flagella, swim
off, and copulate with gametes produced from another sporont ;
there appear, however, to be no differences exhibited by the gametes
of opposite sexes. The zygote forms a shell and grows into a
sporont. Since the zygote is very much smaller than the amcebula
produced by schizogony, the shell formed by it is also smaller. This
shell is later the initial chamber of the polythalamous adult, and
thus leads to a dimorphism in the adult shells, so-called " micro-
spha3iic " and " megalosphgeric " forms (p. 235) — a dimorphism
related, in this case, not to the manner in which the adult individuals
reproduce themselves, but to the manner in which they have been
reproduced.

In free-living forms the alternation of generations is related to
external conditions of the environment, as, for example, seasonal
changes ; the sexual generation may appear in the autumn, while
the non-sexual generations are found in the spring and summer.
In parasitic forms, on the other hand, alternation of generations is
of common occurrence in relation to a change of hosts. Thus, in
the life-cycle of the Coccidia (Fig. 152), described above, the multi-
plicative phases reproduce non-sexually by schizogony, as the so-
called " endogenous cycle " ; the propagative phases are preceded
by gamete-formation, leading to spore-formation, the so-called
" exogenous cycle." In Hsemosporidia, such as the malarial parasites,
for example (Fig. 156), the alternation of generations is related to
an alternation of hosts; the non-sexual, schizogoneus generations
take their course in the blood of the vertebrate host, in which the
gamonts are produced, but do not develop further unless taken up
by the invertebrate host, in which alone gametes are formed and
sporogony takes place.

The phrase " alternation of generations " must not be construed
into meaning that the sexual and non-sexual generations succeed
each other in a regular alternation. On the contrary, such regular
alternation, if it occurs at all, is rare, and as a rule a single sexual
generation is followed by several, or it may be by an immense
number, of non-sexual generations before the sexual cycle recurs.
The malarial parasite can multiply non-sexually in the blood for
many years without dying out ; and if propagated artificially from one

POLYMORPHISM AND LIFE-CYCLES 185

vertebrate host to another, it is probable that it could dispense alto-
gether with the sexual cycle, which occurs only in the invertebrate
host, so far as is known. In the suborder Eugregarinse of the
Gregarinoidea an opposite condition occurs, since these forms
possess only the sexual cycle, sporogony, and there is no non-sexual
schizogony. Whether this condition is to be regarded as a primitive
state of things, or whether the Eugregarines are to be regarded as
having dispensed with the non-sexual process of schizogony seen
in the allied suborder Schizogregarinse, must remain an open
question.

A further caution is also necessary with regard to the alternation
of generations in Protozoa. From the known facts of the malarial
life-cycle, in which an alternation of sexual and non-sexual cycles
is correlated with an alternation of hosts, it has often been assumed,
implicitly or explicitly, that a similar alternation of sexual and non-
sexual cycles must occur in other cases where there is an alternation
of hosts, as in the case of trypanosomes, and in particular that the
sexual cycle must occur in the invertebrate host. This assumption
is by no means justified, however, and has been the cause of much
unsound or unwarranted interpretation of the facts, especially as
regards the significance of the various forms of trypanosomes,
which are continually ascribed to sexual differentiation on no other
ground than the bare fact of form-differentiation, as pointed out in
the previous chapters. Up to the present there is not a single case
in which sexual phenomena in trypanosomes have been described
in a perfectly satisfactory manner, free from all doubt ; and, on the
other hand, it has been asserted that the syngamy occurs in the
vertebrate host in these parasites (Ottolenghi, 492).

Bibliography.— $ 'or references see p. 480.

CHAPTER X
THE GENERAL PHYSIOLOGY OF THE PROTOZOA

THE Protozoa, as has been seen in the previous chapters, exhibit a
wide range of structural differentiation, from forms which exemplify
a cell reduced to its simplest essential parts, nucleus and cytoplasm,
to others in which the cytoplasmic elements give rise in different
parts of the body to a great variety of structures and organs, each
subservient to some special function. In the Protozoa of simplest
structure, therefore, the study of the physiological activities of the
organism coincides, more or less, with that of the elementary
properties of the living substance, protoplasm, its peculiar powers
of metabolism and transmutation of energy ; while in Protozoa of
complicated organization the mechanism and mode of action of the
various cell-organs must be considered in relation to then" structure,
so far as it can be made out.

It is not possible to discuss adequately, in the limited space of a
chapter, the intricate problems, for the most part still very obscure,
of the vital mechanisms of elementary organisms. The matter can
only be dealt with here on broad general lines, and those desirous
of studying the subject further must consult the references given to
special works or memoirs.* On the other hand, the special functions
and mechanisms of the various cell-organs (" organellse") have been
considered in describing the structure of the organs themselves.
In this chapter, therefore, it is intended rather to fill the gaps left
in previous chapters ; and the physiological problems presented by
the Protozoa will be sketched in brief outline under the following
headings : (1) Nutrition and Assimilation ; (2) Respiration ; (3) Secre-
tion and Excretion ; (4) Transmutation of Energy ; (5) Reactions to
Stimuli and to Changes of Medium or Environment ; (6) Degenera-
tion and Regeneration.

* For works dealing with the physiology of Protozoa in a general way the student
should consult especially Verworn, " Allgemeine Physiologie, " Jena, 1907 (a trans-
lation of the second German edition, under the title " General Physiology," was
published by Macmillan, 1899) ; Prowazek, " Einfuhrung in die Physiologic der
Einzelligen," Leipzig (Teubner), 1910 ; the chapter on the general physiology of
the Protozoa in Doflein's " Lehrbuch der Protozoenkunde " ; and the excellent
summary of methods and results of physiological investigations upon Protozoa
given by Putter in Tigerstedt's " Handbuch der Physiologischen Methodik."

186

THE GENERAL PHYSIOLOGY OF THE PROTOZOA 187

1. Nutrition and Assimilation. — Living organisms, considered
generally, exhibit a great variety of methods of nutrition, which
may be classified into two main groups ; bearing in mind, however,
that in all classifications of living beings, or of their vital properties,
any groups or classes that can be distinguished are always connected
by gradual and imperceptible transitions, and that consequently
forms will present themselves which, owing either to their transi-
tional nature or to the imperfect state of our knowledge concerning
them, can only be assigned to one or the other group in a manner
as arbitrary as the statement that the 21st of June is the first day
of summer — a difficulty which in no way invalidates the distinction
between spring and summer. .

In the first place, many organisms can build up the complex
protein-substances, of which the living protoplasm is composed,
from simpler chemical materials. Of this type there are found
among Protozoa, as already stated, two types of nutrition : first, the
holophytic, or plant-like, in which the organism is able, by means of
special cell-organs, to utilize the energy of the sunlight in order to
synthesize its body-substance from the simplest chemical materials,
such as water, carbon dioxide, and mineral salts, through a series
of substances in an ascending scale of chemical complexity ;
secondly, the saprophytic type, in which the body contains no visible
organs subserving the function of nutrition, but the organism is
able to build up its protoplasm from food-materials consisting of
organic substances in solution which are far less complex chemically
than the body-proteins.

In the second place, many organisms cannot build up their body-
substance from materials of simpler chemical constitution, but are
entirely dependent on a supply of protein-substance ready-made,
which they obtain either by ingesting and digesting other living
organisms in the holozoic method, or by living as parasites at the
expense of other creatures. These two methods graduate into one
another, since many parasites simply devour portions of the bodies
of their hosts in a holozoic manner, but the majority of parasites
absorb fluid nutriment from their hosts in an osmotic manner ;
hence it is convenient to distinguish holozoic and osmotic parasites.

Considering these various methods of nutrition, it is seen that,
from the point of view of the nature of the food, those which ingest
solid food-particles (holozoic forms) can be distinguished from those
which absorb their food in a diffused or dissolved condition (holo-
phytic and saprophytic forms and osmotic parasites). From the
point of view of the structure of the organism, those which possess
special organs of nutrition (holozoic and holophytic forms) can be
distinguished from those which possess none (saprophytic forms and
osmotic parasites).

188 THE PROTOZOA

(a) Holophytic Nutrition. — The characteristic of this type of
nutrition is that the organism contains rpecial pigments by means
of which it is able to decompose CO2 in the sunlight, setting free
the oxygen and retaining the carbon,, which is built up in union
with other elements derived from water and mineral inorganic salts.
The pigments, termed comprehensively chromophyll, are contained
in bodies termed " chromatophores," which occur in diverse forms
and varying numbers in different species, and which multiply by
division when the cell divides. The chromophyll-pigments are of
various tints — yellow, brown, green, blue-green, etc. — but the
commonest tint is the green chlorophyll, similar to that character-
istic of plant-cells. A blood-red pigment, termed hcematochrome,
occurs in some flagellates — e.g., Hcematococcus ; it appears to be a
modification of chlorophyll produced under certain conditions (see
Reichenow, 97*5).

For the details of the complicated process of the synthesis of
chemical substances in the holophytic mode of nutrition, the student
is referred to botanical textbooks dealing with plant-physiology.
There appears to be no essential difference between the assimilative
processes of holophytic Protozoa and of ordinary plant-cells. A
characteristic product of holophytic nutrition is seen in the forma-
tion of amyloid substances, the most important of which are starch
(amylum), and an allied substance known as " paramylum," which
differs from starch in some of its reactions, notably in that it is not
coloured blue with iodine. Paramylum is of more frequent occur-
rence in Protozoa than true starch. The amyloid substances occur in
characteristic masses in the cytoplasm (see especially Butschli, 153).

The chromatophores of Protozoa contain usually small refringent
bodies termed farenoids, which also multiply by division. The
pyrenoids are often surrounded by a coat or envelope of paramylum,
and appear to be the centres of the production of amyloid substance.

Many flagellates with green chromatophores combine holophytic with
saprophytic nutrition. Examples of such " mixotrophic " forms are seen
in the genus Euglena (Zumstein, 223), the species of which flourish best in
a medium containing organic substances, and cannot maintain themselves
in pure water. Euglena viridis was shown by Khawkine to be able to live
for a considerable period in the dark in media containing organic substances,
but did not lose its green colour and did not multiply. E. gracilis, on the
other hand, in Zumstein' s experiments, lost its green colour and passed into
an Astasia-\\k& phase in the dark, or even in the light when placed in solutions
very rich in organic substances, nourishing itself as a saprophyte. When the
Astasia-iorm was exposed to the light, in solutions containing a small amount
of organic matter, it became green again and passed back into the Euglena-
phase. The degree to which the species of Euglena can adapt themselves
to a purely saprophytic life would appear to vary in different cases. In the
colourless forms the chromatophores lose their chlorophyll, and remain as
colourless leucoplasts.

The combination of holozoic and holophytic nutrition has been noted
above (p. 15).

THE GENERAL PHYSIOLOGY OF THE PROTOZOA 189

(6) Holozoic Nutrition. — In this type of assimilation three series
of events must be distinguished, each of which may be effected by
means of special organs : the capture and ingestion of the prey ; its
digestion ; and lastly the rejection from the body of the non-
nutritive residue (defsecation).

The methods of food-capture and ingestion have been dealt with
above in a general way. As regards food - capture, methods of
prehension by means of pseudopodia, or by special adhesive organs,
such as the suctorial and raptorial tentacles of Acinetaria (p. 457),
the tongue of Didinium (p. 442), etc., must be distinguished from
methods whereby the food is wafted towards the body in currents
produced by special vibratile organs such as flagella and cilia. As
regards ingestion of food, a distinction is imposed by the nature of
the outer surface of the body-protoplasm, whether naked or invested
by a firm cortex or cuticle.

In naked forms the food is ingested at any point, by methods
which vary in different forms. In Amoeba proteins the hinder end
of the body is most active in ingestion ; in Actinosphcerium all points
on the surface are equally active. Rhumbler (204) distinguishes
four methods of food-ingestion in amoebae : (1) By " import," when
the food is drawn into the protoplasmic body as soon as it comes
into contact with it, and with scarcely any movements on the part
of the amoeba (Fig. 23) ; (2) by flowing round, " circumfluence," in
which the protoplasm, as soon as it comes into contact with the
food-particle, flows round it on all sides and engulfs it ; (3) by
" circumvallation," when the amoeba, while still at some distance
from the object, sends out pseudopodia which flow towards each
side of the prey, and ultimately meet round it and surround it com-
pletely, without ever having been in actual contact with it ; (4) by
" invagination," in which the amoeba touches and adheres to the
object, and the portion of the ectoplasm in contact with it is
invaginated into the endoplasm like a tube, the walls of which
become liquefied and fused together, so that the food-particle is,
as it were, sucked into the endoplasm (Fig. 82). Of these various
methods, the process of circumvallation is most suggestive of a
conscious and purposeful act on the part of the amoeba ; but a
remarkable parallel to it is seen in the penetration of Lankesterella
into a red blood-corpuscle, as described by Neresheimer (see p. 378,
infra). In this case, as soon as the parasite comes within a certain
distance of the corpuscle, the latter opens its arms, as it were, to
the parasite, and engulfs it in a manner very similar to the
ingestion of food by circumvallation on the part of an amoeba.
In both cases the object that is ingested must give off some substance
which exerts at a certain distance an effect on the protoplasm of
the cell which ingests it.

190

THE PROTOZOA

According to Rhumbler (204), with a more fluid condition of the
ectoplasm, the food is ingested by import or circumfluence ; when
the ectoplasm is stiffened to a membrane-like consistence, the
ingestion is effected by circumvallation or invagination. Rhnmbler
maintains that all known methods of food- ingestion by amoebae, as
well as their movements, can be explained mechanically by differ-
ences of surface-tension in colloidal limiting membranes, and can
be imitated artificially in substances that are not living.

FIG. 82. — Ingestion of a food-particle by " invagination " in Amoeba terricola.
A — E, Five stages of the process, semi-diagrammatic ; F, diagrammatic
figure to show the direction of the currents on the surface of the body of the
amoeba during the process of ingestion. After Grosse-Allermann (245).

In corticate forms the ingestion of food is limited to one or more
special openings or organs, in which a direct communication is
established between the fluid endoplasm and the surrounding
medium, as in the cytostomes of Flagellata and Ciliata and the
suctorial tentacles of Acinetaria.

The digestion of the food is effected within the protoplasmic body,
and as a rule the prey is taken bodily into the cytoplasm ; but
the Acinetaria have the power, not fully explained, of sucking out

THE GENERAL PHYSIOLOGY OF THE PROTOZOA 191

the body-substance of their prey, probably by the aid of secreted
ferments. Together with the food a certain amount of water is
ingested, forming a drop or food-vacuole in which the actual
digestion takes place. The quantity of water ingested with the
food varies considerably, and, speaking generally, is inversely pro-
portional to the size of the object that is devoured ; that is to say,
small food-particles, such as bacteria, lie as a rule in a very distinct
vacuole, but large bodies, such as diatoms, usually appear as if
imbedded in the cytoplasm, with no liquid vacuole visible around
them. Amoebae not infrequently devour organisms larger than
themselves, so that the cytoplasm of the amceba appears like a
thin skin or envelope over the surface of the prey. According to
Greenwood (161), Amoeba proteus takes in but little fluid when it
ingests quiescent solid matter, such as starch-grains or yeast-cells,
but when actively- moving prey is dealt with an area of water not
inconsiderable surrounds it ; on the other hand, non-nutritious
particles are not surrounded by fluid when they lie in the endoplasm.

In forms in which food is ingested through a cytostome, as in
Ciliata, the food-particles, usually of small size, are wafted down
the oesophagus and collect at its proximal blind end, where a depres-
sion arises in the endoplasm, which gradually deepens, and finally
closes over and separates from the oesophagus as a closed vacuole
containing the food. According to Mrenstein (181), the food-
vacuole is detached from the oesophagus by suction of the endoplasm,
like a process of swallowing (" Schlingvorgang "). The vacuole is
at first immured in a thin layer of less fluid protoplasm, doubtless
as the effect of contact with water (see p. 44) ; consequently the
vacuole is not at first circular, but often spindle-shaped in its-
contours ; it soon, however, assumes a spherical form, indicating
that its protoplasmic envelope has become liquefied.

In cases where actively- motile organisms are devoured — as, for
example, flagellates by amoebae — the prey can often be seen to per-
form violent movements within the vacuole ; but soon the move-
ments become feebler and cease entirely. Bacteria ingested by
Paramecium become immobile about thirty seconds after the
vacuole has become detached from the oesophagus. In many cases,
however, the prey is killed when seized by the pseudopodia, and
before being ingested, as in Heliozoa and Foraminifera. After the
prey is killed it is slowly digested within the food-vacuole.

During the process of digestion the food-vacuole may perform
definite migrations within the body of the animal. In amoebae the
vacuoles are carried about by the currents of the protoplasm,
without, however, pursuing any definite course, and they tend to
become aggregated in the hinder end of the body, when the animal
is moving in a definite direction. In the Infusoria, on the other

192 THE PROTOZOA

hand, the endoplasm shows a constant rotating movement, known
as " cyclosis." In Paramecium the vacuoles are carried round by
the current of the cyclosis, and each vacuole may either do a short
course or a long course ; the short course is simply round the
nucleus, keeping close to it, while the long course travels the whole
length of the body, up one side and down the other. As a rule a
vacuole goes a short course two or three times, and then does a
long course (Nirenstein, 181). The path of the vacuole varies,
according to the nature of the contents ; but the tendency is to
keep them in the region posterior to the nucleus, where the contents
are either cast out through the anal pore, or the vacuole circulates
again in the cyclosis. In Carchesium the food- vacuoles, when
formed at the base of the oesophagus, pass down to one end of
the horseshoe-shaped nucleus, and then glide close along its concave
margin, passing round and up to the opposite end of the horseshoe
into the region near the upper end of the vestibule, from whence the
vacuole is finally emptied through an anal pore into the vestibule
itself (Greenwood, 162).

The process of digestion within the food- vacuole has been studied
by a number of investigators, amongst whom Le Dantec, Greenwood
(162), Metschnikoff (180), Metalnikoff (179), Nirenstein (181), and
Khainsky (170'5), must be specially mentioned. Their results are
not always in agreement, indicating that the process of digestion
is not always the same in different cases, even in the food- vacuoles
of one and the same species. According to Nirenstein (181), the
food-vacuoles of Infusoria exhibit changes which can be divided
nto two periods : in the first the vacuole shows an acid reaction,
and the ingested organisms are killed ; in the second the vacuole
has an alkaline reaction, and the albumens are digested. According
to Khainsky (170*5), however, the reaction of the food-vacuoles of
Paramecium is acid during the entire period of the proteolytic
process, and only becomes neutral and finally alkaline when the
solution of the food-substance is at an end.

In the first or acid period, according to Nirenstein (181), the
ingested food-particles — e.g., bacteria — after being rendered im-
mobile, are clumped together, enveloped in a turbid substance
which makes their outlines indistinct. The reaction of the vacuole
is strongly acid, due to the presence of mineral acid in the vacuole.
During this period, which lasts from four to six minutes, the vacuole
diminishes in size, till it is not more than one-third of its original size.
When the vacuole was first formed, its wall was surrounded by a
number of granules which stain very distinctly with neutral-red ;
these granules pass suddenly into the interior of the vacuole after
it has become diminished considerably in size. Nirenstein regards
the red -staining granules as bearers of a tryptic ferment.

THE GENERAL PHYSIOLOGY OF THE PROTOZOA 193

In the second or alkaline period the vacuole enlarges rapidly to
more than its original volume. The red colour produced by staining
with neutral-red disappears. The clumped food- mass breaks up into
smaller particles again. From the red-staining granules of the first
period deeply-staining spheres arise, homogeneous, refractile, and
apparently fluid (Nirenstein, 181). According to Khainsky (170*5),
the grains or droplets which are formed gather at the surface and
pass out into the endoplasm ; they represent the first products of
the assimilatory process in the vacuole, and their further chemical
transformation takes place in the endoplasm itself (compare the
refringent bodies formed in the process of digestion in acinetans,
p. 458) . According to Nirenstein, however, the spheres become smaller
and smaller, being reduced to tiny grains which vanish completely,
dissolved in the vacuole-contents. The vacuole now diminishes in
size a second time, and passes to the anal region, where it fuses with
other similar vacuoles, and is finally rejected from the anal pore.

In other cases, however, no acid reaction has been demonstrated
in the vacuoles at any time, as, for example, in ActinospJicerium — a
peculiarity which is perhaps to be correlated with the fact that in
this form the prey is killed when seized by the pseudopodia. It may
be supposed that the processes which, in Infusoria, etc., go on during
the first or acid period of the food- vacuole, take place in Actino-
sphcerium and some other forms before the vacuole is formed, in
which case the vacuole itself shows only the second or alkaline phase
of the digestion.

According to Greenwood and Saunders (163), any ingested particles excite
the secretion of acid, but the true digestive vacuole is only formed under the
stimulus supplied by nutritive matter. Metalnikoff (179), however, found
that in the same individual some of the food- vacuoles are first acid and then
alkaline, while others are alkaline throughout in their reactions, and others
again, but rarely, show an acid reaction throughout ; he concludes that the
living cell has the capacity of adapting itself to the food supplied, and of
altering the properties of its digestive juices in accordance with its require-
ments. The process is perhaps comparable to the manner in which the blood-
cells, produce different anti- bodies when brought into contact with different
pathogenic organisms or toxins.

The variety of ferments that have been isolated from different
Protozoa also indicates that the digestion takes a different course
in different cases. In the plasmodia of Mycetozoa, a peptic ferment,
which when acidulated dissolves fibrin, has been isolated ; but since
the protoplasm of the plasmodium has a distinctly alkaline reaction,
it was thought by some that the ferment must be without function.
Metschnikoff (180) showed, however, that the food- vacuoles formed
in the plasmodium had a strongly acid reaction, in contrast to the
protoplasm, and thus demonstrated the function of the peptic
ferment in the digestion. In other cases tryptic ferments have been
isolated (" amcebodiastase," etc.).

13

194 THE PROTOZOA

Some doubt has existed as to the power possessed by Protozoa
of digesting fats, and, according to Staniewicz (208). no digestion
of fat takes place in Infusoria. According to the recent investiga-
tions of Nirenstein (182), however, Paramecia under natural con-
ditions contain fat in more or less considerable quantities. By
choice of suitable food, the quantity of fat in the endoplasm can be
increased greatly. The fat-granules serve as reserve-nutriment,
and disappear under starvation. Paramecia which have lost their
fat in this way, if then fed with milk, oil-emulsion, or yolk of egg
lubbed up in water, show in a few hours the endoplasm full of fat-
granules ; if fed with starch or particles of egg-albumen, the same
result is obtained, but not to anything like the same extent.
Experiments on fatty substances ingested by the animals showed
that the fat remains unaltered during the first (acid) period of the
digestion in the food-vacuole, and is digested during the second
(alkaline) period. Feeding with fatty acid and glycerine also leads
to storage of fat in the endoplasm. If fed with oil-globules stained
with Soudan III., unstained oil-globules appear in the endoplasm.
Nirenstein concludes from his observations that the fat is broken
up into its soluble components in the vacuole, and synthesized again
to neutral fat in the endoplasm.

The indigestible residues of the food are ejected from the body
either at any point on the surface, in amoeboid forms, or through a
definite aperture, in corticate forms. A great accumulation of
faecal matter may take place in some cases, as in the " stercome "
of Foraminifera (p. 233), of which the animal purges itself
periodically.

(c) Saprophytic and Parasitic Nutrition. — In this type the
organism absorbs its nourishment by diffusion through the surface
of the body without the aid of any visible organs or structural
differentiations of any kind. Practically nothing is known of the
mechanism by which this is effected or of the chemical processes
involved, but it is probable that enzymes secreted by the organism
reduce the nutritive particles to a soluble form prior to absorption.
There is reason to believe that the nucleus is specially concerned
in the production of enzymes, and in many species, parasitic or
otherwise, the behaviour of the nucleus indicates a relationship
between it and the process of absorption of food-substance. In
Carchesium, as already stated, the path along which the food-
vacuoles travel runs close along the inner edge of the horseshoe-shaped
macronucleus (Greenwood, 162) ; in Euplotes, similarly, the large
macronucleus encloses an area containing all the food-vacuoles
(Fig. 182). According to Wallengren (214), the reactions of the
food-vacuoles of Paramecium change as they pass the nucleus, and
the function of the cyclosis in the endoplasm is to bring the food-

THE GENERAL PHYSIOLOGY OF THE PROTOZOA 195

vacuoles near, and under the influence of, the nucleus. In the
coccidian parasite Caryotropha (p. 352), the nucleus of the parasite
is connected by a kind of protoplasmic canal with the nucleus of the
host-cell (Siedlecki, 653). In the astomatous Ciliata (p. 451) a
diffuse nucleus is very commonly found, probably in relation to
absorption of nutriment by the osmotic method.

The process of nutrition in Protozoa may lead in some cases,
not to growth of the protoplasmic body directly, but to the produc-
tion and storage of reserve food-substances, which are precipitated
in the cytoplasm, and are utilized at a later period for rapid growth
during reproductive phases. The reserve- materials deposited in
this way vary considerably in nature in different cases. Examples
are the paramylum-grains of many flagellates ; the paraglycogen-
grains of gregarines and ciliates, similar in nature to glycogen, but
with certain distinctive reactions ; the plastinoid granules of
coccidia (p. 346) ; and other similar substances. In Radiolaria oil-
globules and albumen - spheres occur. An important substance,
acting apparently as reserve- material for the growth of the nucleus,
is volutin (p. 68).

The effects of starvation on Protozoa have been studied by a number of
investigators, most recently by Lipska (173), who gives a complete bibliog-
raphy and resume of previous work on the subject. Lipska found that
Paramecium died after five to seven days, a much shorter period than allowed
by Wallengren (214) and others, indicating that Lipska's methods were more
drastic and. sources of food were more thoroughly excluded in her experiments.
In the first period of starvation the reserves in the endoplasm are used up,
first the food-vacuoles and their contents, then the smaller endoplasmic
granules. After the fourth day the animal becomes deformed. Its dimensions
diminish progressively, and death supervenes when it has lost half its initial
volume. The ectoplasm with its cilia and trichocysts undergo no change,
but the endoplasm loses its food-vacuoles and a part of its crystals, and
becomes very transparent. The macronucleus becomes enlarged and breaks
up into two halves. The micronucleus undergoes no change of any kind.
Death is preceded by a progressive enfeeblement of all functions, such as
movements of the cilia and pulsation of the contractile vacuoles. According
to Wallengren, the reactions of the Paramecium (geotaxis, thermotaxis,
galvanotaxis) remain normal to the last. Wallengren described an excessive
vacuolation of the endoplasm as the result of starvation ; but according to
Lipska this phenomenon is not due to starvation, but to the chemical action
of ammoniacal products generated by bacteria present in the infusions, and
does not occur if they are excluded. Other observers noted the occurrence
of numerous conjugations during the first few days of starvation, but Lipska
was unable to confirm this ; in her experiments, however, the number of
Paramecia placed in each tube was small, not more than ten. Paramecia
containing symbiotic algae were more resistant to starvation than those
without them.

2. Respiration. — By respiration in its widest sense must be under-
stood all processes in the organism whereby the potential energy
stored up in chemical compounds of high complexity is set free to
furnish the energy required by the organism for its vital activities.
This object may be effected in two ways — by processes of oxidation,

196 THE PROTOZOA

or by the splitting up of complex chemical substances ; the result
in either case is the production of energy in various forms and of
simple chemical substances, such as water and carbon dioxide
(compare Barratt, 148). For the processes of oxidation the
organism may either absorb free molecular oxygen from its environ-
ment, or may produce it by internal molecular changes of substances
contained in its own body, as in anaerobic organisms living in a
medium in which free oxygen is lacking.

Many free-living Protozoa require oxygen, and are visibly and
rapidly affected by the lack of it, especially in their powers of
movement. No special organs of respiration are found in any
Protozoa, being unnecessary in animals of such small bulk, and in
which, consequently, the surface of the body is considerable in
proportion to the mass. The contractile vacuoles, when present,
are doubtless a means of eliminating carbon dioxide, together with
other waste products, from the body. It must be supposed, there-
fore, that as a general rule oxygen is taken up from the surrounding
water by the protoplasm, of which the limiting membranes are
freely permeable, and that the carbon dioxide is given off in a
similar manner. The experiments of Verworn (211) on /Spirostomum
show that the respiratory processes take place in the cytoplasm,
independently of the nucleus, which takes no share in respiration.

On the other hand, many sapropelic (p. 14) and parasitic forms
inhabit media lacking in free oxygen, and are anaerobic ; in such
forms the respiratory processes of the protoplasm can only take place
by intramolecular changes, in which the stored-up reserve- materials
are probably split up to supply the required oxygen.

The experiments of Putter (201) on a number of species of Ciliata, both
free -living and parasitic, showed that, when these animals were placed in
an anaerobic environment, different individuals of the same species reacted
very differently to the conditions, some dying very rapidly, others being
quite unaffected for a long time. It was shown further that this difference
was related to the amount of reserve -materials present in the body (proteins
and glycogen), which can be observed to vary greatly in different individuals
from the same culture. If Paramecia were first starved for some days and
then placed in anaerobic conditions, they succumbed much more rapidly
than normal individuals. Moreover, under anaerobic conditions the reserve-
materials were used up much more rapidly than under normal conditions,
and without resulting in increased production of energy. Opalina, when
placed in a culture-medium to which albumen was added by boiling up dried
white of egg in salt-solution, was able to make use of the energy of the albumen
without the help of free oxygen, and so to live for a much longer time. The
ciliates were found to succumb much more rapidly to the effects of anaerobic
conditions in smaller than in larger quantities of water, as the result of auto-
intoxication in consequence of the defective excretion of the products of
anaerobic metabolism. Spirostomum was found to be more affected by
anaerobic conditions in small quantities of water than Paramecium. The
differences between the two forms is to be ascribed to the system of the
contractile vacuoles, which is far more efficient in Paramecium than in
Spirostomum ; the contractile vacuoles tend to remove from the body the

THE GENERAL PHYSIOLOGY OF THE PROTOZOA 197

products of metabolism, a primary necessity of anaerobic life. The question
of size is also a factor, since deleterious substances may diffuse from the
surface of the body, and in a small body the surface is greater in proportion
than in a larger one. Consequently the conditions are more favourable for
a smaller species, such as Paramecium, than for a large form, such as
Spirostomum.

Excess of oxygen was found by Putter (198) to have an injurious effect
on Spirostomum, affecting, however, only the cytoplasm, and not the nucleus,
in the first instance.

On the current view that the symbiotic vegetable organisms present in
many Protozoa aid in the respiratory processes by absorbing the carbon
dioxide, breaking it up, and setting free the oxygen, the experiments of
Lipska (173) on a culture of Paramecia which contained green algae (Proto-
coccaceae) in their endoplasm are of considerable interest. In two glass
vessels of equal size there were placed, in the one Paramecia with, in the other
without, the algae in their body. Hydrogen was circulated through the vessels
to drive out the air, after which they were hermetically sealed and exposed
to the same conditions of light and temperature. After fifty hours the
vessels were opened. The Paramecia without algse were dead, but those
containing algse were still alive, though feeble in their movements, and they
revived completely in about twenty-four hours after air had access to them.
In another experiment two batches of Paramecia were kept in the dark ;
after eight days those without algae were dead, while those containing algse
were perfectly normal. Old cultures of Paramecia containing algae showed
no conjugation ; Lipska explains this as due to the influence of the algae,
since, by setting free oxygen, they prevent the development of anaerobic
bacteria which produce substances toxic to the Infusoria.

According to Popoff (185), the depression- periods of Protozoa (p. 208) are
partly due to derangements of the respiratory processes and to accumulation
of products of metabolism in the cell.

3. Excretion and Secretion. — The waste substances excreted from
the protoplasm may be either soluble or insoluble in nature. If
soluble, they may either pass out of the protoplasmic body by
diffusion from the surface, or may be removed by the agency of the
contractile vacuoles.

Contractile vacuoles are of common occurrence in free-living fresh-water
Protozoa, but are usually wanting in marine forms, or, if they occur in them,
they pulsate very slowly. They are generally absent also in entozoic and
parasitic Protozoa, but are found, however, in some internal parasites — for
example, in all Anoplophryince (p. 452 ; Cepede, 831).

Some authors (e.g., Degen, 154) have described an investing membrane
to the contractile vacuole, but it is practically certain that no such membrane
exists, and that the vacuole is simply a drop of watery fluid lodged in, and
bounded by, the more viscid protoplasm, without any special structural
differentiation (compare Khainsky, 170'5). The contractile vacuoles were
believed at one time to empty themselves internally, and to function simply
as circulatory organs ; but in all cases in which they have been studied care-
fully, it has been proved that they empty themselves to the exterior (compare
Jennings, 167, Khainsky, 170'5).

The effect of changes of temperature is noted below (p. 206). Increased
pressure makes the pulse slower (Khainsky, 170'5). Degen (154), experi-
menting with Glaucoma colpidium, found that oxygen produced at first an
increase in the frequency of the pulse, which soon became normal again.
Hydrogen and carbon dioxide diminished the frequency and caused a dilata-
tion of the vacuole ; both these gases were lethal in their effect, especially
carbon dioxide. Isotonic solutions of neutral salts had a retarding effect.

198 THE PROTOZOA

Substances that precipitate albumens have a retarding effect combined with
dilatation of the vacuole. Degen, following Hartog, regards the vacuole as
primarily a mode of compensation for the tendency of the protoplasm to take
up water by imbibition, a tendency checked or inhibited by changes in the
tonicity of the medium. Thus Zuelzer (222) found that Amoeba verrucosa,
if transferred gradually from fresh water to sea-water, lost its contractile
vacuoles ; at the same time its protoplasm shrank and altered in character,
and the nucleus acquired a different structure and appearance. When re-
stored to fresh water, the contractile vacuoles reappeared, and the nucleus
and cytoplasm became of normal character. These experiments indicate
that the formation of the contractile vacuoles depends on differences in the
tonicity of the protoplasm and the surrounding medium ; they also raise the
suspicion that many species of marine Protozoa may be only different forms,
due to change of medium, of fresh- water species, or vice versa.
For the excretory vacuole -system of Opalina, see p. 447.

Insoluble excretion- masses are often formed in great quantity in
the bodies of Protozoa. Such substances take the form of crystals
or grains of various kinds, and often of pigment. An example of
such a substance is the melanin-pigment of the haemamcebse (p. 359),
which appears to be a derivative of the haemoglobin of the infected
blood-corpuscle. Pigment may arise also by degeneration of
superfluous chro matin extruded from the nucleus, as in Actino-
sphcerium (p. 209), or by degeneration of nuclei, as in abnormal
oocysts of Cydospora caryolytica (p. 364).

The cytoplasm of Paramecium contains crystals which have been studied
by Schewiakoff (206), who finds that they consist of calcium phosphate, either
Ca3(P04)2 or Ca2H2(P04)2. When the Paramecia were starved, the crystals
disappeared completely in one or two days ; if then the Paramecia were
supplied with food again, the crystals reappeared. Schewiakoff was never
able to observe that the crystals were ejected from the anus, but they were
seen to collect round the contractile vacuole. He is of opinion that the
insoluble phosphate is dissolved in the enchylema, or is converted into the
soluble form CaH4(P04)2, and then eliminated by the contractile vacuole.

Insoluble excretion- masses may be simply extruded from the
body, a process which commonly takes place at certain crises, as,
for example, prior to encystment. Or, on the other hand, they
may remain in the protoplasm, and are finally abandoned in the
residual masses left over during reproductive phases, as seen com-
monly in the sporulation of various types — for example, the
hsemamcebae already cited and other Sporozoa. In such cases the
young individuals are formed of protoplasm free from the coarse
excretion-granules, and the body of the parent, so much as is left
of it, dies off and disintegrates. In some cases, however, the young
individuals formed contain enclosures derived from the parent-bod}?-,
as, for example, the crystal-bearing swarm-spores of Radiolaria
(p. 254) ; but in such cases the enclosure is probably of the nature of
reserve-material.

Secretion, more or less rapid, of various substances can be
observed without difficulty in various Protozoa. Examples are the

THE GENERAL PHYSIOLOGY OF THE PROTOZOA 199

spicules and various skeletal structures ; the shells, houses, etc. ;
adhesive substances or stalks in sedentary forms, as, for example,
the non-contractile stalks of many Vorticellids (p. 441) ; and the
cysts or envelopes secreted round the body, such as the sporocysts,
etc. The pseudopodia of many Amcebaea, such as Difflugia, are
covered by a sticky slime which enables the animal to adhere to
surfaces over which it creeps, and which can be drawn out by
contact with a glass rod into threads, like the mucus of a snail
(Rhumbler, 34). In Foraminifera and Heliozoa the pseudopodia
appear to secrete a substance which holds the prey fast, and at the
same time kills it, as already mentioned. Some Protozoa — for
example, gregarines — leave a trail of mucilaginous substance behind
them as they move forwards, and by some authors this secretion
has been regarded as the mechanism by which locomotion is effected
(p. 327). Internal secretions in connection with the digestive
function have been mentioned in a previous section. Arcella has
the power of secreting gas-bubbles in its protoplasm for hydrostatic
purposes (compare also the Radiolaria, p. 252).

4. Transformation ot Energy — (a) Movement. — The different motile
organs of Protozoa have been described above. Considered from a
morphological standpoint, the protoplasmic body may exhibit, in
the first place, no specially differentiated organs of movement,
which then takes the form of currents and displacements in the fluid
protoplasm itself, manifested externally in the form of pseudopodial
processes or flowing movements of the entire body, internally as
streaming movements in the protoplasm. Secondly, there may be
special organs of movement, either external, in the form of vibratile
organs, such as cilia, flagella, or undulating membranes ; or internal,
in the form of contractile fibrils or myonemes.

Different as pseudopodia may appear at first sight from vibratile
organs, such as cilia or flagella, there is nevertheless a very gradual
transition from the one type to the other (see p. 53, supra). Of
pseudopodia there are two chief types of structure — the lobopodia,
in which a fluid core of endoplasm is enveloped by a superficial layer
of stiffer ectoplasm ; and the axopodia, in which, on the contrary, a
secreted axis of rigid or elastic nature is covered by a more fluid layer
of protoplasm. The axopodia are connected by transitions both
of structure and movement with organs of the vibratile type. In
both flagella and cilia the structure consists of a firmer elastic axis
covered over by a more fluid superficial layer (pp. 52, 54) ; many
axopodia exhibit swinging, nutating, or bending movements differ-
ing only in degree from those of flagella (p. 51). There are grounds
for believing the one type of organ to have been derived phylo-
genetically from the other.

The streaming movements of protoplasm have been the subject

200 THE PROTOZOA

of much investigation and discussion. The older view, which
ascribed them to contractility and assumed a complicated structure
in the protoplasm, has now been superseded generally bjr the theory
connected more especially with the names of Quincke, Berthold,
Butschli (37), and Rhumbler (34, 35, 40, etc.), according to which
differences of surface-tension are regarded as the efficient cause of
the streaming movements of the pseudopodia and the protoplasm.
The living substance is in a state of continual chemical change in
every part ; such changes are sufficient to account, in one way or
another, for the origin of local differences in the physical nature
(adhesion) of the surface of the body in contact with the surrounding
medium, or of internal protoplasmic surfaces in contact with
vacuoles or cavities filled with fluid ; and the resulting differences in
surface-tension cause flowing movements both in the protoplasm
and in the fluid with which it is in contact. The relation of such
currents to the movements of pseudopodia has been discussed above
(p. 47). Similar movements have been imitated artificially by
Butschli and Rhumbler in a manner which can leave no doubt that
the physical analogy is a reasonable interpretation of the mechanism
of amoeboid movement.

The close structural similarity between flagella and cilia on the
one hand, and the axopodia on the other, makes it highly probable,
to say the least, that the same explanation of the movement applies
to both. The axis of the vibratile organ is commonly regarded as
a firm, elastic, form-determining structure ; the more fluid sheath
as the seat of the motile activity. Chemical differences set up in
the limiting membrane, causing differences in the surface-tension of
the sheath along certain lines, have been supposed to be responsible
for a deformation of the sheath, bending the axis and the whole
organ with it ; with equalization and disappearance of such differ-
ences, the elastic axis straightens itself again. How such chemical
differences are set up remains to be explained ; possibly they origi-
nate in chemical changes taking place explosively in the basal
apparatus of the vibratile organs ; in any case it is clear that, as com-
pared with pseudopodia, they act with extreme rapidity, and, further,
that they are localized on the surface of the flagellum or cilium.
From the movements of these organs, the contraction appears to run
a spiral course as a general rule — at least in cilia (p. 54) ; flagella,
however, appear to be capable of various kinds of movements (p. 52).

According to Prowazek (192), the flagellum of a trypanosome only retains
its motility so long as it remains in connection with the kinetonucleus. Wer-
bitzki (526), however, has succeeded in producing strains of trypanosomes
without kinetonuclei, and with apparently no resulting loss of motility. It
has been observed frequently that detached cilia or flagella continue to
contract, for a time at least ; and Schuberg (44) denies that the basal granules
of the cilia function as centres of kinetic activity.

THE GENERAL PHYSIOLOGY OF THE PROTOZOA 201

With regard to the contractility of the myonemes, no detailed explanation
can be offered at present. Biitschli (37) has shown the possibility of explaining
the contractile mechanism of such structures by differences in surface-tension
arising between the walls and the contents of protoplasmic alveoli which
are disposed with a definite arrangement.

(6) Other Forms of Energy. — Light-production or phosphorescence
is a common phenomenon in marine Protozoa, a property expressed
in such names as Noctiluca (p. 279) and Pyrodinium (p. 278). The
magnificent phosphorescent effects often seen at night, especially
in warmer seas, is to be referred chiefly to swarms of Protozoa.
The source of the luminosity appears to reside in small globules of
fat or oil, and is probably the result of oxidation. It is easy to
observe that the production of light is stimulated by agitating or
stirring the water. For a general discussion of luminosity in living
organisms, see Putter (200).

From the analogy of the known facts in the physiology of animal
and plants, it may be inferred that in Protozoa also the vital
activities are accompanied by the production of heat and by
electrical changes ; but no exact determinations of such changes
have been made.

5. Reactions to Stimuli and Environment. — It can easily be
observed that Protozoa react in a definite manner to stimuli, and
behave in a particular way under certain conditions. In most
cases, however, these responses to external conditions must be
regarded as fundamental properties of the living protoplasm, and
not as functions of specially differentiated organs of the body.
This is well seen, for example, in amoebae, some species of which are
very sensitive to light, and cease feeding when exposed to the
bright illumination of the stage of the microscope (Rhumbler, 34).
In Arcella the nuclear division is stated to take place only at night,
between 1 and 5 a.m. (Khainsky, 145). In such cases, however,
there is nothing which can be identified as a special light-perceiving
organ.

In other cases Protozoa may possess organs which must be regarded
as sensory in nature. Pseudopodia appear to possess in many cases
a tactile or sensory function to a marked degree, and sometimes to
be specialized for such functions, as, for example, the anterior
pseudopodia of some Myxosporidia, such as Leptotheca agilis
(Fig. 165). The same is true to a much greater degree of flagella
and cilia ; anteriorly-directed flagella are perhaps always sensory in
function, especially when they are not the sole means of locomotion,
as in such forms as Rhizomastigina (p. £68) or Bodonidce (p. 270) ;
and in many Ciliata stiff tactile bristles occur (p. 446). In many
flagellates organs are found which appear to be specially sensitive
to light, in the form of pigment-spots or stigmata, which are
described further below.

202 THE PROTOZOA

The occurrence of a conducting nervous apparatus is more
doubtful ; it has been affirmed for Stentor by Neresheimer (p. 446),
but is not confirmed by other observers. It can at least be asserted
that in the more highly organized Ciliata a stimulus may lead to
sudden movements in which different sets of contractile structures
take a concerted part.

The reactions of Protozoa to stimuli have been the subject of a
great deal of experimental research by many investigators, amongst
whom Verworn, Loeb, Jennings (165), and Putter (199), deserve
special mention. The results of these investigations can only be
summarized briefly here. The various reactions are classified in the
first instance, according to the nature of the stimulus, by the use of
a terminology in which each principal category is denoted by a
word terminating in taxis, or in adjectival form— tactic. Thus we
can distinguish — (a) Chemotaxis, or reactions to chemical stimuli ;
(b) Phototaxis, or reactions to light ; (c) Thermotaxis, or reactions
to heat or cold ; (d) Barotaxis, or reactions to mechanical stimuli ;
and (e) Galvanotaxis, or reactions to electrical stimuli. A given
Protozoon may be quite unaffected by a particular stimulus ; or, on
the other hand, it may be affected by it in such a way that it tends
to move towards the source of the stimulus (positive taxis) or away
from it (negative taxis). The result depends, in many cases, on
the intensity of the stimulus applied ; thus, a Euglena will move
towards a moderate light (positive phototaxis), but away from a
too intense illumination (negative phototaxis). In each case an
optimum condition exists, in which the positive taxis reaches its
maximum.

In such experiments the Ciliata are the objects of choice, on
account of the definite polarity of their movements as compared
with forms less highly organized, such as amoeba. In the Ciliata
a negative taxis results in an " avoiding reaction " (Schreck-
bewegung), in which the animal shrinks back with reversal of the
ciliary movements, " turning towards a structurally-defined side,
followed by a movement forward " (Jennings). Repeated experi-
ments have shown that the forms taken by the avoiding movements
do not depend on the nature of the stimulus, but on the organization
of the animal itself, and are always the same for a given species.
An Oxytricha, for example, turns always to the right, whatever the
direction from which the stimulus comes. The movement is deter-
mined automatically by the structure of the body. " The same
symptom can be called forth by the most diverse stimuli " (Putter,
199).

'WCe various taxes may now be considered briefly :

(a) Chemotaxis and Effects of Environment. — This category in-
cludes reactions to liquids or gases diffused in the water ; reactions

THE GENERAL PHYSIOLOGY OF THE PROTOZOA 203

to gases may be considered as equivalent to a sense of smell in
higher organisms (osmotaxis).

It has been shown by many experiments that a given species is
attracted towards certain chemical substances, repelled by others.
Thus, Paramecium is attracted towards weak acids, but repelled by
them in greater concentration. If a drop of acid of suitable strength
is placed in the midst of a number of Paramecia distributed evenly
in the water under a cover-slip on a slide, they tend to gather round
the drop. As the drop diffuses in the surrounding water, the
Paramecia arrange themselves in a ring in the region of optimum
concentration. If, however, the drop of fluid employed is of a
strength which represents the optimum of chemotaxis for the species,

FIG. 83. — Diagram showing the course taken by a Paramecium which has entered
a drop of fluid to which it is positively chemotactic. The forward movements
of the Paramecium are indicated by arrows ; its backward movements by
dotted lines ; the outline of the drop of fluid by a circle. Each time the
Paramecium, in its forward movement, reaches the confines of the drop, it
comes into contact with fluid which is less positively chemotactic than the drop
into which it has entered ; it then shrinks backward (avoiding reaction), after
which it moves forward again with the same result every time it reaches the
edge of the drop. After Lang (10).

the Paramecia gather within it, and in such a case the position taken
up by each Paramecium depends on the avoiding reaction made by
it when it comes in contact with a less attractive medium. Thus,
if a Paramecium, swimming in a straight line, enters a drop of fluid
which is positively chemotactic to it, when it has crossed the drop
to its opposite boundary it comes to the region where it meets with
fluid which is less chemotactic to it ; it then shrinks back with an
avoiding movement ; after a time it again moves forward, and comes
again into the negatively chemotactic region, with the same result
as before. Thus its movements are as if caught in a trap (Fig. 83),
in which it is held by the automatic movements called forth by the
difference between the more and the less chemotactic fluids, until

204 THE PROTOZOA

the differences slowly disappear by the diffusion of the one liquid
into the other.

Chemotaxis is a phenomenon which is obviously of the greatest
importance in the natural life of the organism. It comes into play in
the search for food and in sexual attraction, for example. It has long
been known that certain Protozoa are attracted towards food-
substances, especially those species which feed more or less
exclusively upon certain particular foods. Plasmodia of Mycetozoa,
for example, "scent" their food from a considerable distance, and
move towards it.

Rhumbler (34, 204) has studied the ingestion of food by amoebae, and has
made a number of experiments on the manner in which drops of fluid take up
or cast out solid particles. Thus, a drop of chloroform suspended in water
draws into its interior a glass splinter coated with shellac when brought into
contact with it ; after a time the coating of shellac is dissolved in the chloro-
form, and the glass splinter is then ejected from the drop. This experiment
furnishes data for a mechanical explanation of the ingestion of food and
ejection of faecal matter ; and it might be expected that amoebae in Nature
would ingest mechanically, and as it were helplessly, many substances of a
useless kind with which they are brought into contact. This may occur
experimentally when amoebae are brought into contact with substances of
no nutritive value ; Rhumbler observed an amoeba which ingested carmine-
particles until it died. In Nature, however, there can be no doubt that
amoebae exercise a certain choice or selection in the food they ingest, doubtless
as the effect of chemotactic reactions (compare Jennings, 168). In the
Ciliata, however, there appears to be no selection of the food- particles wafted
down the oesophagus except as regards their size (compare Greenwood, 162).
Purely mechanical reactions, on the other hand, may possibly explain the
apparent selection which many Protozoa exhibit in building up houses of cer-
tain special materials (p. 34).

Chemotactic reactions to particular substances must play a large part
in determining the migrations of certain parasitic Protozoa towards particular
organs of the body in which they are parasitic, in so far as such migrations
are not purely passive on the part of the parasite, or determined to some extent
by rheotaxis (see below).

The attraction of gametes to one another can hardly be effected by any-
thing but chemotaxis. It is well known that the antherozoids of the fern-
prothallus are positively chemotactic to malic acid, which is secreted by the
oogonium. In Coccidium schubergi, Schaudinn (99) observed that the macro-
gamete, as soon as it had expelled its karyosome, but not before, became
attractive to the microgamete.

The effects of drugs and reagents on the activities of the Protozoa is a
field of investigation which cannot be dealt with in detail here. Some
reagents have a quickening effect on the movements, others the contrary.
Narcotics, on the other hand, such as alcohol, ether, etc., may at first have
a stimulating, later a deleterious, action on the vital activity. Minute doses
of alcohol, according to Woodruff (216), diminish the rate of division at one
period, augment it at another, of the life- cycle, but in the latter case the rate
is not continuous, but decreases again ; increase in the amount of alcohol
will, however, again cause a more rapid cell-division for a limited period.
Thyroid extract is stated to have an attractive effect on Paramecium, and also
increases its capacity for reproduction (Nowikoff, 183). For the effects of
other drugs and poisons, see Giemsa and Prowazek (159), and Prowazek
(191, 192, and 195). In the same culture different individuals often exhibit
different powers of resistance to the effects of reagents.

THE GENERAL PHYSIOLOGY OF THE PROTOZOA 205

(b) Phototaxis and Effects of Light and Other Rays. — Many Pro-
tozoa appear quite indifferent to light — at least of ordinary intensity ;
others show a very decided reaction, as already mentioned, either
negative or positive. Thus many amoebae, Pelomyxa, etc., are
negatively phototactic, and pass at once into a condition of rest
and inactivity when exposed to light. According to Mast (176), a
sudden increase in the intensity of the illumination inhibits move-
ment in Amoeba proteus ; but if the illumination remains constant,
movement begins again in a few moments.
If the illumination is very gradually in-
creased, it produces no response. In
strong light Amoeba proteus orientates
itself, producing pseudopodia only on the
less illuminated side.

Many flagellates, on the other hand, rn.~
especially the holophytic forms such as
Dinoflagellates, Phytomastigina, Eugle-
noids, etc., show the opposite reaction,
moving towards the light or becoming
active when exposed to it, and passing
into a resting state in the dark. The
positive photo taxis of the holophytic FIG. 84.— .4, Anterior end of
Protozoa has an obvious bionomical rig- £*%*£*$#€

nificance, since the holophytic nutrition
can only proceed in the presence of light.

thickening (blepharoplast ?)
on one of the two roots of the
flagellum ; St., stigma ; rh,
the two roots of the flagellum
passing through the reservoir
(R) of the contractile vacuoles,
two to be attached to its
opposite side. B, Stigma in
surface view, highly magni-
fied, showing the pigment-

grains imbedded in a proto-
plasmic basis. After Wager
(213).

In the majority of holophytic flagellates the
phototactic reaction is associated with the
possession of a special organ, the stigma or
"eye-spot." The stigma of Euglena consists
of a protoplasmic ground-substance forming a
fine network, in which is embedded pigment
in the form of drop-like bodies. The pigment
granules are brightly refractile, with a distinct
outline, and form a single layer. In some cases
the granules are spherical and all of the same
size ; in others they are more irregular in form and of different sizes. The
pigment appears to be a derivative of chlorophyll. The stigma is in close
contact with a well-marked thickening on one of the two branches into
which the flagellum bifurcates at its base. Wager (213) suggests that this
thickening (blepharoplast ?) is a specialized sensitive organ which is stimulated
by the light-absorbing pigment-spot, the stigma, and that in this way the
reaction of Euglena to light is determined. Euglena swims towards a moderate
light, but away from strong sunlight. If kept in bright sunlight it comes to
rest, rounds itself off, and ultimately becomes encysted.

The blue and violet parts of the spectrum exert the strongest stimulus
on flagellates. In the case of Amoeba proteus, Mast (176) found the blue rays
nearly as efficient as white light in causing reactions, but violet, green, yellow,
and red, to be but slightly active. Paramecium and some other Protozoa are
stated to react only to the ultra-violet rays.

The effect of radium-rays upon various Protozoa has been investigated
by Zuelzer (221). Some species are more affected by them than others;

206 THE PROTOZOA

Amoeba Umax, for example, was very resistant to the rays, while other Protozoa
were very soon injured by them. In all cases long exposure to the rays was
fatal. The first effect of the rays was generally to quicken the movements ;
the next was an injurious action. The rays appear to act more particularly
upon the nucleus in the first instance, with subsequent gradual deleterious
effects upon the cytoplasm.

In experiments on the effect of Rontgen-rays on Paramecium and Volvoyc
(Joseph and Prowazek, 169), these forms were found to exhibit a negative
taxis, collecting in ten to fifteen minutes in a part not exposed to the rays.
Exposure of Paramecium to the rays caused the pulse of the contractile
vacuoles to become slower to a marked degree as a rule, but individual
variations were observed in this reaction, the effect being inconsiderable in
some cases ; and the animals gradually regain the normal pulse. Intra vitam
staining of the nucleus of Paramecium exposed to the rays gave a result similar
to that obtained by staining Paramecia fatigued by being shaken evenly and
continuously for two hours. Long-continued action of the rays killed the
organisms.

(c) Thermotaxis and Effects of Temperature. — For a given species
of the Protozoa there is an optimum temperature at which its vital
activity is at its highest pitch, and above which the activity is
diminished until it reaches a point at which the vitality is impaired
and the animal is finally killed. A temperature, however, at which
the animal succumbs sooner or later may at first have a quickening
effect upon the vital functions. Thus, many experiments have
shown that a rise of temperature increases greatly the rapidity and
frequency of the pulsations of the contractile vacuoles ; and in the
case of Glaucoma colpidium Degen (154) found that, although the
animal was killed by a temperature above 30° C., the maximum
frequency of the pulsations was produced temporarily by a tempera-
ture of 34° C., above which the frequency was rapidly diminished
(compare also Khainsky, 170 -5).

The optimum temperature may, however, be different at different
stages in the life-cycle, as in parasitic Protozoa which infest a warm-
blooded and a cold-blooded host alternately ; in such cases a change
of temperature may perhaps be a factor in bringing about develop-
mental changes. In free-living Protozoa the phases of the life-cycle
are often related to seasonal changes, and are probably induced
largely by conditions of temperature.

Experimentally it has been shown that Protozoa tend to move towards
regions of more favourable temperature, and away from those less favourable.
Khainsky (170'5) found that rise of temperature produced a quickening of
the digestive processes in Paramecium, very marked at 24° C. or above. At
30° C. and above Paramecium takes up scarcely any more food ; the contents
of the food-vacuoles, which continue to be formed, then consist almost entirely
of water.

The effects of temperature on the development in cultures are very marked.
Popoff studied the growth of Frontonia leucas in cultures kept at 14° C. and
25° C. respectively ; at the lower temperature the animals divide once in
about eighty or ninety hours, in the warmer culture once in about seventeen
hours ; in the cold both the nucleus and the body grow to a size absolutely
larger than in the warmth, but in the former case the nucleus is about -^T,
in the latter about ^, the bulk of the whole body (Hertwig, 92). In the case

THE GENERAL PHYSIOLOGY OF THE PROTOZOA 207

of Actinosphcerium, the experiments of Smith (207), Mackinnon (174), and
Boissevain (151), show that increased temperature hastens on encystment,
and causes fewer and larger cysts to be formed in which the nuclei are larger
but poorer in chromatin ; while at lower temperatures the encystment is
retarded, and finally inhibited altogether, and the cysts produced are smaller
and more numerous, with nuclei smaller than the normal but rich in chromatin.

(d) Barotaxis and Effects of Mechanical Stimuli. — This category
includes Geotaxis, or reactions to gravity ; Thigmotaxis, or reactions
to the mechanical contacts of hard surfaces ; and Rheotaxis, or
reactions to the pressure of currents in the surrounding medium.
The influence of gravity is seen in the manner in which many
Protozoa, when placed in a vessel, seek of their own accord the
bottom in some cases, the surface-film in others. The plasmodia of
Mycetozoa exhibit often a well-marked rheotaxis, and move in the
opposite direction to currents of water. It has been suggested that
a similar rheotaxis may explain the passage of blood-parasites from
the invertebrate to the vertebrate host during the act of blood-
sucking ; but it is probable that such migrations are purely passive,
so far as the parasites are concerned.

Contact-stimuli acting from one side often have a marked effect
on the movements of Protozoa. An amoeba tends to adhere to, and
spread itself over, a firm surface with which it comes in contact.
The movements of Ciliata often cease when they come in contact
with a firm substance, and the animal remains still ; Putter (197)
has shown that the contact-stimulus may be sufficient to prevent
a Paramecium from reacting to thermal or electric stimuli, which
would otherwise produce a marked effect upon its movements.

Under effects of mechanical stimuli must be included those brought about
by changes in the tonicity of the surrounding medium. Such effects have
already been discussed above as regards their action on the contractile
vacuoles. For the remarkable experiments of Verworn on the change in
body-form and in the nature of the pseudopodia exhibited by amoebae under
the action of different media, see p. 217, infra. Free-living Protozoa are
probably seldom if ever subject to such changes, though they might well
occur in the environment of marine forms living near the upper limit of the
tide-marks, in rock-pools, or other places where the tonicity of the medium
might be lowered temporarily by influx of fresh water, as the result of rain
or other natural causes. On the other hand, parasitic forms, and especially
those which pass from one host to the other, may be subject to rapid changes
of tonicity in their environment. In this connection special interest attaches
to the experiments of Robertson (503) on fish-trypanosomes ; it was found
that in undiluted blood or in blood diluted with isotonic solutions the
trypanosomes underwent no change in vitro, but that when the blood was
diluted with water the trypanosomes multiplied by division, and went through
changes similar to the first stages of the natural development in the leech.
It was concluded, therefore, that the principal stimulus which initiates the
developmental changes in the organism was a lowering of the osmotic tension,
with consequent absorption of water by the protoplasm. Neumann (677)
also found that the " exflagellation " of the Profcosowa-parasite of birds was
greatly furthered by addition to the blood of not more than one-fifth of its
volume of water.

208 THE PROTOZOA

(e) Galvanotaxis and Effects of Electrical Stimuli. — Protozoa
placed in an electric field — that is to say, in a drop of water between
the two poles of a battery under a cover-glass on a slide — are
affected to a marked degree, but with opposite results in different
species. Opalina places itself parallel to the direction of the current,
with its anterior end towards the anode. With a current of
moderate intensity it swims towards the anode ; but with a stronger
current the speed at which the animal moves is diminished, and
with still more increased strength of current it is carried passively
towards the kathode, with its hinder end forward, as the result of
kataphoric action (Wallengren, 215). Chilomonas behaves in a
similar manner. Paramecium and Colpidium, on the other hand,
move towards the kathode. Spirostomum with a moderate
current also moves towards the kathode, but with stronger currents
it first contracts its myonemes spasmodically, and then takes up
a position transverse to the direction of the current, and remains
still.

According to Wallengren (215), the apparently different galvano-
tactic phenomena exhibited by different ciliates admits of a uniform
explanation, by a combination of two effects. In the first place,
in the half of the body turned towards the kathode the expansion-
phase of the ciliary movement is stimulated ; in the anodic half of the
body, the contraction-phase is stimulated. In the second place, the
turning movements of the ciliates are determined mechanically
(compare the " avoiding reactions " mentioned above), and may be
effected either by the expansion or by the contraction of certain
cilia. Consequently, if the turning movements are effected by
beats of expansion, the animal places itself automatically in a posi-
tion in which it moves towards the anode ; if beats of contraction
are effective in the turning movement, it moves towards the
kathode. According to Statkewitsch (209), the galvanotactic re-
action is one which overcomes chemotactic stimuli, and leads the
animals irresistibly into toxic media in which they are killed.

6. Degeneration and Regeneration. — The fact that under certain
conditions Protozoa undergo a process of physiological degenera-
tion, which may end in death, has been observed frequently by all
those who have kept cultures of Protozoa under observation for
a long time. It has been pointed out in a previous chapter (p. 135)
that the life-cycles of Protozoa exhibit depression-periods (Calkins)
which are characterized chiefly by cessation of feeding, metabolism,
growth, and reproduction, together with increase in the size of the
nucleus, and tendency to deposition of grains of fat or other sub-
stances in the protoplasm, giving the body a characteristic dark-
grey appearance. Such periods recur regularly and apparently
normally in the life-cycles both of Protozoan and Metazoan cells

THE GENERAL PHYSIOLOGY OF THE PROTOZOA 209

(Popoff, 184) ; they may also be induced artificially in various
ways by unfavourable conditions, such as overfeeding or starvation,
changes of temperature, or treatment with reagents (compare
Smith, 207 ; Popoff, 186 ; Boissevain, 151).

A state of depression may be regulated naturally by conjuga-
tion, or by restoration of the nucleo-cytoplasmic balance through
a process of self-regulation on the part of the organism. The
regulative processes consist of absorption of a large part of the
superfluous chromatin, so as to restore the normal quantitative
relation of the nucleus and cytoplasm. On the other hand, the
depression may lead to complete degeneration of the organism
without possibility of recovery, and death ensues by a process of
disruption of the protoplasm into granules — so-called " granular
disruption " (korniger Zerfall). Some examples are given below :

Actinosph cerium can be brought into a condition of depression either by
starvation or overfeeding (Hertwig, 164). In the depressed state a great
quantity of chromatin is extruded from the nuclei in the form of chromidia
which degenerate into pigment, so that the animal during a depression-period
has a characteristic brownish tint, more or less pronounced in proportion
to the degree of depression. In extreme cases the protoplasm is bereft of its
nuclei, and becomes incapable of continuing to live. The nuclei may become
entirely resolved into chromidia ; or some of the nuclei grow to a relatively
gigantic size and are cast out, while other nuclei break up ; or the entire
medullary layer surrounding the enlarged nuclei may be thrown off. The
pseudopodia may disappear altogether or become deformed in various ways,
the difference between cortical and medullary substance may be annulled
or abnormally increased, and the metabolism may be modified, all these
changes being in relation to nuclear alterations.

In Opalina, according to Dobell (155), physiological degeneration can be
induced by starvation of its host, the frog. The degenerating Opalince lose
their cilia and become irregular in form ; peculiar refringent eosinophile
globules appear in the cytoplasm ; the nuclei undergo increase in size and
modification in structure, give off chromatin, and undergo irregular fusions ;
and the body divides irregularly, sometimes producing buds which contain
no nucleus. Ultimately the Opalines disintegrate.

Prandtl (187) has described the degeneration of Amoeba proteus. The
nucleus increases in size and becomes hyperchromatinic. Chromidia are
extruded into the cytoplasm, and may there degenerate, with formation of
numerous small crystals. The chromatin in the nucleus also degenerates
to form a mass of brown pigment, which is extruded en bloc into the cyto-
plasm, or forms a ring of fine granules round the nucleus. The pigment may
also spread through the whole cytoplasm, giving it a brownish tinge. Finally
the nucleus breaks up and disappears altogether. Degenerating amoebae are
subject to the attacks of parasites. A noteworthy feature is the tendency
of the degenerating amoebae to associate in clumps, and plastogamic fusion of
two amoebae was observed by Prandtl. The tendency to fusion may be
compared with the agglomeration of trypanosomes, etc. (p. 128), which is
common also in degenerating forms or under unfavourable conditions.* It
is not improbable that many of the plastogamic unions of Sarcodina often

* The " conjugations " observed by Putter (201, p. 582) in Opalince kept
without oxgyen must have been also phenomena of the nature of agglomeration,
since in Opalina syngamy takes places between special gametes, and not in the
form of conjugation of adult forms as in other Ciliata (p. 453).

210 THE PROTOZOA

described may be phenomena of agglomeration associated with a similar
condition.

In Radiolaria, Borgert (152) describes fatty degeneration affecting the
nucleus as well as the protoplasm, both endoplasm and ectoplasm. The
nucleus becomes converted entirely into a vesicle filled with a mass of fat-
globules, or into a number of such vesicles.

In Tocophrya quadripartite, subjected to starvation, after the refringent
bodies (p. 458) have been absorbed, the nucleus becomes modified in structure,
the tentacles are retracted, active budding takes place, and with the last bud
formed the nucleus disappears and the remaining protoplasm dies away.

From a consideration of the various examples of degeneration
from different causes, it appears that the first part to be affected
is always the nucleus, and that the other derangements of the
structure and functions of the body are secondary consequences
of an abnormal condition of the nucleus.

The regeneration of lost parts of the cell-body of Protozoa has
been the subject of experiment by a great number of investigators.
The methods employed have consisted mainly in mutilating the
body or cutting it up in4o a number of pieces, in order to find out
to what extent the fragments possess the power of regenerating the
lost parts. The experiments have led to one very definite result,
which can be expressed briefly : no separate part of the body is
capable of continuing its vital activities indefinitely, or of regenera-
ting any of the deficiencies in the structure of the body, if it does
not contain the nucleus or a portion of the nucleus. Non-nucleated
fragments may continue to live for a certain time ; in the case of
amoeba such fragments may emit pseudopodia, the contractile
vacuole continues to pulsate, and acts of ingestion or digestion
of food that have begun may continue ; but the power of initiating
the capture and digestion of food ceases, consequently, all growth
is at an end, and sooner or later all non-nucleate fragments or
enucleated bodies die off. A Polystomella which possesses a nucleus
can repair breakages to the shell ; an individual deprived of its
nucleus cannot do so (Verworn). On the other hand, an isolated
nucleus, deprived of all protoplasm, dies off ; but a small quantity
of protoplasm containing the nucleus or a part of it is able in some
cases to regenerate the whole body, and to produce a complete
individual of small size.

In experiments on regeneration the Ciliata are the objects of choice ; their
complicated structure permits the regeneration that has taken place to be
estimated accurately ; their size renders the mutilation more easy to perform ;
and the large size and frequently extended form of the nucleus makes it
possible to divide up this body also. In recent experiments Lewin (171)
has succeeded in dividing Paramecium into a number of fragments (" mero-
zoa"), containing each a portion of the macronucleus. Only one of the
merozoa obtained in this manner contains the micronucleus, which is too
minute to be divided by a mechanical operation. Except when the Paramecium
was in process of division, only one merozoon recovered the normal body-
form and proceeded to divide ; and the interesting result was obtained that

THE GENERAL PHYSIOLOGY OF THE PROTOZOA 211

the merozoon which survived was not necessarily the one which contained the
micronucleus. Regenerated individuals multiplied for a number of genera-
tions, producing a culture of " amicronucleate " Paramecia. If, on the other
hand, a Paramecium in process of division was halved, each half regenerated
the entire body and was capable of division. These experiments indicate
that Paramecium contains a division- cent re independent of the nuclei, and
that its presence is necessary for regeneration of the body.

Prowazek (189) observed occasionally a certain power of regeneration in
non-nucleated fragments of Stentor, but considered it possible that extra-
nuclear chromatin might have been present. The same author (190) ob-
served abnormal regeneration, leading to monstrosities with three hinder ends,
in a culture of Stylonychia mytilus during a depression- period which led finally
to the extinction of the culture. The recent experiments of Lewin (172) on
Stylonychia mytilus show that, in the regeneration which follows artificial
mutilation, multiplication of micronuclei may occur, with the result that the
regenerated individual may have more micronuclei than the number typical
of the species or race.

Bibliography. — For references see p. 481.

CHAPTER XI
SYSTEMATIC REVIEW OF THE PROTOZOA : THE SARCODINA

As stated in Chapter I., the Protozoa are commonly divided into
four principal classes. Of these, two — namely, the Sarcodina and
Mastigophora — may be regarded as the more primitive groups,
comprising the main stock of less specialized and typical forms
from which the other two classes have been evolved. The Sporozoa
are an assemblage of exclusively endoparasitic forms exhibiting
clearly the modifications and adaptations induced by, or necessary
for, their particular mode of life ; and it is practically certain that
the Sporozoa are not a homogeneous class showing mutual affinities
based upon a common ancestry, but that one section of the group
is a specialized offshoot of the Mastigophora, the other of the
Sarcodina, and that the two sections are united only by characters
of convergence due to the influence of a similar mode of life. The
Infusoria, on the other hand, are a specialized group in which great
complexity of organization has been attained ; they are the highest
class of the Protozoa, and furnish examples of the most extreme
degree of structural differentiation of which a unicellular organism
is capable.

While there is but little difficulty, as a rule, in defining the classes
Sporozoa and Infusoria, or in assigning members of these groups
to their proper systematic position, the case is different, very often,
when we have to deal with the other two classes. The verbal
distinction between them is based chiefly on the use of the word
" adult ": Sarcodina are Protozoa which have no permanent organs A
of locomotion in the adult condition, but move by means of pseudo-
podia extruded from the naked protoplasmic body ; Mastigophora,
on the other hand, bear organs of locomotion in the form of flagella
in the adult condition, whether the protoplasmic body is naked
and amoeboid or corticate and of definite form. In both classes the
youngest stages may be flagellate ; if, in an amoeboid form, the
flagella are retained in the adult, the organism is classed in the
Mastigophora ; if lost in the Sarcodina.

The word " adult " when applied -to the Metazoa has a meaning
which can be defined clearly, as a rule, by the criterion of sexual

212

THE SARCODINA 213

maturity. In the Protozoa no such criterion is available, and the
distinction between young and adult is based on differences in size
and growth, or on phases of the life-cycle selected in an arbitrary
manner. In many cases the distinction presents no difficulty ; it
is perfectly easy to distinguish young from adult stages in such
forms as the Foraminifera and Radiolaria among Sarcodina, or the
genus Noctiluca among Mastigophora. But in other cases it is
purely a matter of opinion which phase in the life-cycle is to be
regarded as adult. Such a form as Pseudospora has a flagellated
and an amoeboid phase (Robertson), and can be placed in either
the Sarcodina or the Mastigophora with perfect propriety. The
amceba-like genus Mastigamoeba is placed in the Mastigophora
because the flagellum is retained ; but if any species of this genus
were to lose its flagellum when adult, rigid adherence to verbal
definitions would necessitate its being classed in the Sarcodina.

The difficulty of separating and defining the stems of the Sarco-
dina and Mastigophora at their root is only to be expected on the
theory of evolution. The two classes are undoubtedly descended
from a common ancestral type, which has become modified in
two divergent directions, giving rise to two vast groups of organisms
which may differ from one another very slightly or very greatly in
selected examples. The systematist may meet with many obstacles
when it is required to lay down verbal distinctions between the two
classes, but it is easy to recognize, in a general way, two principal
morphological types, round which each class is centred, and which
may be realized to a greater or less extent in given cases.

1. Sarcodine Type. — Protozoa which grow to a relatively large
size ; in the so-called " adult phase " permanent organs of loco-
motion are wanting, and the naked protoplasmic body moves or
captures food by means of pseudopodia ; the young stages may be
flagellate or amoeboid.

2. Mastigophoran Type. — Protozoa usually of minute size, seldom
with a large adult phase (as, for example, Nocti uca) ; flagella
retained throughout active life, only lost in resting phases ; body,
amoeboid or corticate.

THE SARCODINA.

The name Rhizopoda is sometimes used for this class but this
name is only applicable, strictly speaking, to the first four orders
recognized below, in which the pseudopodia are more or less root-
like, §,nd not to the orders Heliozoa and Radiolaria, characterized
by stiff radiating pseudopodia.

General Characteristics. — As stated above, the Sarcodina are Pro-
tozoa for the most part of relatively large size. Many Sarcodina

214 THE PROTOZOA

are visible to the naked eye, and some of the Radiolaria, Foramin-
ifera, and Mycetozoa, attain to a size that must be considered
gigantic for Protozoa. The more primitive forms, on the other
hand, are often very minute.

The body-form is of two principal types, related to distinct habits
of life — namely, the amoeboid type, characteristic of forms that
creep on a firm substratum ; and the radiate type, seen in floating
forms. Amoeboid forms are found aquatic, semiterrestrial, and
parasitic ; radiate forms are for the most part pelagic, living floating
or suspended in large masses of water, marine or fresh-water.

The protoplasmic body is in many cases distinctly differentiated
into clear motile ectoplasm and granular trophic endoplasm. The
surface of the protoplasm is naked, or may be covered in rare in-
stances (Amoeba verrucosa, A. terricola, etc.) by a very thin pellicle
which modifies, but does not restrain, the amoeboid movements.
A resistant cuticle or cell-membrane investing the body is not
formed, but an external shell or internal supporting skeleton is
frequently present.

The locomotor organs in the adult are always pseudopodia, which
may be of various types — lobose, filose, or reticulose (Chapter V.,
p. 46) ; they may lie in one plane, as in creeping forms, or may be
given off on all sides, as in pelagic forms. The youngest forms
(swarm-spores) may be flagellate or amoeboid. In some cases the
pseudopodia of the young forms may differ markedly in character
from those of the adult ; for example, the adult Amosba proteus has
fluid protoplasm with thick lobose pseudopodia, but the young
amcebula produced from the cyst of this species has viscid proto-
plasm with sharp, spiky pseudopodia (Scheel).

The free-living Sarcodina are almost without exception holozoic,
capturing other organisms by means of their pseudopodia, and
devouring them ; but the remarkable genus Chlamydomyxa (p. 243)
has chromatophores, and can live in either a holozoic or holophytic
manner, like some flagellates ; and the genus Paulinella, allied to
Euglypha, also possesses chromatophores.. and is capable of holo-
phytic nutrition (Lauterborn).

The nuclear apparatus consists of one or more nuclei, in addition
to which chromidia may be present. A single nucleus is charac-
teristic of the majority of species, even of many which grow to
very large size, such as many Radiolaria, in which the nucleus also
attains to proportions relatively gigantic. In other cases increase
in the size of the body is accompanied by multiplication of the
nuclei ; there may be two nuclei constantly, as in Amcsba binucleata
(Schaudinn), or several, as in Difflugia urceolata, or many hundreds,
as in Actinosphcerium and Pelomyxa, or even thousands, as in the
Mycetozoa. In such forms the adult is a plasmodium, but the

THE SARCODINA 215

numerous nuclei show no differentiation amongst themselves, and
appear to be perfectly equivalent both in structure and function.
Chromidia may be present as a permanent cell-constituent in many
Amcebaea, such as Arcella, Difflugia, and the Foraminifera ; in other
cases they are formed temporarily, as extrusions from the nucleus,
during certain phases of the life-cycle, either as a preliminary to
reproduction or as a regulative process under certain physiological
conditions.

The reproduction of the Sarcodina is effected either by binary
or multiple fission. Binary fission may be absent in some of the
larger, more specialized forms, as in many Foraminifera and Radio-
laria, but in most cases it is the ordinary " vegetative " method of
reproduction during the active trophic life of the organism. In
plasmodial forms it takes the form of plasmotomy (p. 100). Mul-
tiple fission or gemmation (sporulation) is in some cases the sole
method of reproduction ; in other case it is combined with binary
fission, and occurs only at certain crises in the life-cycle, in relation
to seasonal changes, or as a preliminary to syngamy. In this type
of reproduction the organism, breaking up rapidly into a large —
often an immense — number of minute individuals, is necessarily
put hors de combat as soon as the reproduction begins ; hence it is
not uncommon for the sporulation to take place within a cyst,
when a shell or protective envelope is not present, as in Amoeba
proten^ (Scheel). The minute germs produced by sporulation may
be set free at once as swarm-spores ; or they may form a pro-
tective envelope or sporocyst, and be liberated as resistant spores
which are disseminated passively, and germinate when conditions
are favourable, as in parasitic forms and in the semi-terrestrial
Mycetozoa.

The swarm-spores, whether produced directly by sporulation of
an adult or indirectly by germination of a spore, may be either
flagellulee or amoebula). In many forms two types of sporulation
occur — schizogony producing agametes, and sporogony producing
gametes. The agametes may be structurally or morphologically
distinguishable from the gametes. Thus, in Foraminifera the
agametes are amcebulse, the gametes are flagellulae. In Radiolaria
both alike are flagellulae, but the agametes produced in schizogony
• — the "isospores" — are distinguishable from the gametes produced
in sporogony — " aiiisospores."

In this class syngamy takes place rarely between adult indi-
viduals ; bat examples of this are seen in Actinophrys, where it takes
the form of karyogamy within a cyst (Fig. 71), and in Arcella (p. 148)
and Difflugia, where it takes the form of chromidiogamy between
free individuals, followed in Difflugia by encystmeiit. In the great
majority of Sarcodina the syngamy is microgamous, and takes place

216

THE PROTOZOA

between swarm-spores, either amcebulse or flagellulse. The microg-
amy is isogamous or slightly anisogamous ; macrogamy, as in other
cases, is perfectly isogamous. Microgamy occurs, as has been seen
(p. 148), in Arcella in addition to chromidiogamy ; and, according
to a recent note of Zuelzer (86, p. 191, footnote), syngamy between
free swarm-spores occurs in Difflugia also.

As regards the life-cycle of the Sarcodina, there remains still so
much to be discovered that to generalize is both difficult and
dangerous. Even in the commonest forms, such as Amoeba proteus,
the complete life-cycle has not been yet worked out. In some

FIG. 85. — Changes in the form of an amoeba under the influence of differences
in} [the [surrounding medium. A — C, In its natural medium (water) : A,
contracted ; B, beginning to throw out pseudopodia ; 0, Umax-form. D — F,
Forms assumed after addition of potash-solution : D, contracted, beginning
to throw out pseudopodia ; E, F, radiosa- forms. After Verworn.

cases the life-cycle appears to be of comparatively simple type, and
the species is monomorphic or nearly so, as in Actinosphcerium ;
in other cases there is a well-marked alternation of generations,
with dimorphism in the adult condition, as in Trichosphcerium
(p. 182), the Foraminifera, etc.

Classification. — The Sarcodina are subdivided into a number of
orders, the distinctions between which are based principally on the
characters of the pseudopodia and of the skeleton, when present ;
in more highly differentiated forms, such as Radiolaria, the internal
structure of the body is also taken into account. In the primitive

THE SARCODINA 217

forms of simple structure, however, in which no skeleton is present,
the subdivisions are defined entirely by the characters of the proto-
plasmic body and the pseudopodia, which furnish distinctions of
very doubtful validity. Not only may the characters of the
pseudopodia vary in different phases of the life cycle, as already
stated in the case of Amoeba proteus, but even in the same phase
under the influence of different media. Thus, no two forms of
amoeba could appear more distinct at first sight than the Umax
and radiosa forms, originally regarded as distinct species. In the
Umax-form the whole body flows forward as a single pseudopodium,
gliding along like a slug ; in the ra^'osa-form the spherical body
becomes star-like, sending out sharp-pointed pseudopodia on all
sides. Nevertheless, Verworn showed that the one form could be
changed into the other by differences in the medium (Fig. 85).
Doflein (238) obtained similar form-changes in Amoeba vespertilio.
and showed that the body-form and character of the pseudopodia
were quite inadequate features for distinguishing the species of
amoeba, depending as they do upon the conditions of the environ-
ment and the nature of the medium. Compare also Gruber (246)
on form- varieties of Amoeba proteus.

In view of the protean nature of these organisms, it is not sur-
prising that much diversity of opinion prevails as to the arrangement
of the groups and the exact position of some of their members. It is
usual to put a number of primitive organisms together in a group
termed Proteomyxa, the members of which probably have more
affinities with various members of other groups than with one
another. On the other hand, the more highly organized Sarcodina
are classified without difficulty into well-characterized orders ;
such are the Foraminifera, Mycetozoa, Radiolaria, and Heliozoa,
though even in these groups there are forms near the border-line and
of doubt "ul position.

The classification adopted here is mainly that of Biitschli (2),
with the addition of some forms not included in his great work, as
follows :

A. SUBCLASS RHIZOPODA. — Typically creeping forms with
branched, root-like pseudopodia.

I. Order Amoebcea. — Amoeboid forms of simple structure ;
skeleton lacking or in the form of a simple shell.

1. Suborder Reticulosa (Proteomyxa}. — With filose

or reticulose pseudopodia, without shell.

2. Suborder Lobosa. — With lobose pseudopodia.

(a) Section Nuda, without shell or skeleton.

(b) Section Testacea, with shells.

II. Order Foraminifera. — With reticulose pseudopodia and
shells.

218 THE PROTOZOA

III. Order Xenophyophora. — With skeleton of foreign bodies

and a peculiar internal structure.

IV. Order Mycetozoa. — Semi-terrestrial forms with repro-

duction by resistant spores and formation of plas-
modia.

B. SUBCLASS ACTINOPODA (Calkins). — Typically floating forms
with radiating, unbranched pseudopodia.

V. Order Heliozoa. — Principally fresh-water, without a

" central capsule."

VI. Order Radiolaria. — Exclusively marine, with a central
capsule.

I. AMCEBJEA.

1. Reticulosa. — In this suborder are comprised a number of
forms of doubtful affinities, sometimes ranked as a distinct order,
Proteomyxa. The only positive character which they have in
common is the possession of filose or reticulose pseudopodia, with
which is combined the absence of a shell and skeleton. Hence it
is not surprising that the position of many forms referred to this
suborder is extremely dubious, and some of them are referred to
distinct orders by many authorities.

In general two types of organisms are referred to this suborder :

(a) Large marine plasmodial forms ; an example is Pontomyxa
flava, described by Topsent from the Mediterranean and British
Channel. Pontomyxa is a multinucleate plasmodium of yellow
colour. It sends out branching root-like pseudopodia, which may
spread out and form a network extending over two or three inches
in length. Nothing is known of its development or life-cycle.

(b) Small forms with a s'ngle nucleus, marine or fresh-water,
which reproduce by process of multiple fission forming swarm-
spores. These forms have been subdivided into two families,
according to the type of swarm-spore found — Zoosporidce, pro-
ducing flagellulae ; and Azoosporidce, producing amoebulae. An
example of the Zoosporidce is furnished by the genus Pseudospora,
which preys upon algae, diatoms, Volvocineae, etc. The adult phase
is amoeboid, flagellate, or even Heliozoon-like. It feeds on the cell-
substance and chlorophyll of the prey, and multiplies by binary
fission. It can also break up by multiple fission into flagellate
swarm-spores, with or without previous encystment. Robertson
has observed syngamy between flagellulae thus formed, which are
therefore gametes ; in other cases the flagellulae are perhaps
agametes. As already pointed out above, the position of this form
amongst the Sarcodina is doubtful ; by many authorities it is
classified in the Mastigophora.

An example of the Azoosporidce is furnished by Vampyrella, a

THE SARCODINA

219

small amoeboid form which, like Pseudospora, preys upon algae
(Fig. 86), devouring the contents of the cell, and multiplying in the
free state by binary fission. It also encysts and breaks up within
the cyst by multiple fission to form a number of amcebulae, which
creep out and grow up into the adult form.

A large number of other genera are referred to the Reticulosa,
for the most part so little investigated as regards their develop-
ment and life-history that it is impossible to deal with them com-
prehensively in a brief space. For an account of them see Delage
and Herouard (6, p. 66), Hickson (248), and Rhumbler (288).

2. Lobosa. — This suborder comprises a great number of organisms,
which it is convenient to subdivide into — (a) Nuda (Gymnamoebae),

FIG. 86. — Vampyrella lateritia: various forms. A, Free Heliozoon-like phase;

B, creeping amoeboid phase ; G, amoeboid form attached to a Conferva-fila,-

. merit ; D, a similar form ; it has broken the algal filament at a joint, and has

emptied one cell of its contents. A and B after Hoogenraad ; G and D after

Cash and Hopkinson.

with no shell ; and (b) Testacea (Thecamoebae, Thalamophora), with
a shell or house.

General Characters. — Familiar examples of the Lobosa Nuda are
furnished b}^ the species of the genus Amoeba and allied forms. A
very large number of free-living amoebae have been described and
named, but it is very doubtful how far they are true species ; some
of them, with pronounced and constant characteristics, such as
Amoeba proteus (Fig. 2) and A. verrucosa (Fig. 23), are probably
"good" species; others, such as A. Umax and A. radiosa, are
probably forms that may occur as phases in the development of
other species of amoebae or of other organisms, such as Mycetozoa.

220 THE PROTOZOA

At the present time the life-history has been worked out satisfac-
torily in but few free-living amoebae, but in such protean organisms
it is quite unsafe to attempt to characterize or define a species
without a knowledge of the whole life-cycle. As regards the
familiar Amoeba proteus, for example, practically all that is known of
its life-cycle is that it encysts and multiplies within the cyst to
form a great number of small amcebulae, very different in appear-
ance from the parent-organism ; the amcebulae creep out of the cyst,
and probably grow up into the adult form (Scheel). Calkins
adduces arguments in favour of the occurrence of a sexual cycle,
which remains at present, however, purely conjectural.

The majority of free-living amoebae are aquatic in habitat. A
certain number, however, are semi-terrestrial, inhabiting damp
earth, moss, etc. Such is Amoeba terricola (vide Grosse-Allermann).
The " earth-amoebae," like other terricolous Protozoa, probably
play a great part in keeping down the numbers of the bacteria and
other organisms in the soil, and thereby lessening its fertility from
an agricultural standpoint (compare Russell and Hutchinson, 24 ;
Goodey, 16).

A great many species of amoebae are found living within the
bodies of animals of all kinds, for the most part in the digestive
tract. The entozoic amoebae are commonly placed in a distinct
genus, Entamoeba, distinguished from the free-living forms by little,
however, except their habitat and the general (but not invariable)
absence of a contractile vacuole. A common example is Entamceba
blattce, from the intestine of the common cockroach ; others are
E. ranarum of the frog (Dobell, 236, 237) ; E. muris of the mouse
(Wenyon) ; the species parasitic in the human intestine, presently
to be mentioned ; E. buccalis (Prowazek), from the human mouth ;
and many others. Chatton has described a species, Amoeba mu-
cicola, ectoparasitic on the gills of Labridce, and extremely patho-
genic to its host.

Life-History. — So far as it is possible to generalize from the scanty
data available at present, the development of many free-living
species of amoebae appears to be of a type very similar to that of
Arcella, described in a previous chapter (p. 179). In the free state
the organisms reproduce themselves in two ways : first, " vegeta-
tively," by simple binary fission, preceded by a division of the
nucleus, which varies 'n different cases from a promitosis (p. 109)
of the simplest type to very perfect mitosis ; secondly, by forma-
tion of chromidia and subsequently of secondary nuclei, round
which the cytoplasm becomes concentrated to form a number of
internal buds, destined to be set free as amcebulae, agametes, which
grow up into the adult form. In addition to these two methods of
reproduction in the free state, the animal may become encysted,

THE SARCODINA

221

and produce within the cyst a number of gametes in the same manner
as the agametes already described, but with the following differ-
ences of detail : the principal nucleus degenerates as soon as the
chromidia are formed ; the number of secondary nuclei produced is
much larger, and the gametes are much smaller than the agametes ;
and the cytoplasm of the parent is entirely used up in their forma-
tion. The gametes are ultimately set free from the cyst as amce-
bulse, and pair ; the zygote grows into the adult form of the amoeba.
Such a cycle has recently been described by Popoff (264) for a
species named by him Amoeba minuta ; the gametes in this species
are isogametes, without any sexual differentiation as in Arcella.
This type of life-cycle is probably very common in many amoebae,

FIG. 87. — Amoeba albida : autogamy in the encysted condition ; drawn in outline,
with nuclear details only. A, Encysted amoeba ; B, the nucleus of the
amoeba divides unequally into a larger vegetative and a smaller generative
nucleus ; the vegetative nucleus, as seen in the subsequent figures, travels
to the surface of the cyst, degenerates, and disappears ; the generative nucleus
gives rise to the gamete-nuclei ; 0, incomplete division of the generative nucleus ;
D, one half of the generative nucleus is budding off two reduction-nuclei
(on the right) ; E, four reduction -nuclei have been budded off, two from
each pole of the incompletely divided generative nucleus ; F, the reduced
generative nucleus completes its division ; the four reduction-nuclei are
degenerating ; G, the two pronuclei far apart ; H, the two pronuclei coming
together ; /, the pronuclei fusing. After Nagler (95).

with specific differences of detail in different cases, of which the
most important are, that in some cases, probably, the nucleus
divides to form the gamete-nuclei, instead of becoming resolved
into chromidia, and that autogamy within the cyst may occur,
instead of free gametes being formed, as A. albida (Fig. 87).
According to Nagler (95), autogamy of this type is characteristic
of all amoebae of the Umax-group ; in such cases only two gamete-
nuclei are formed in the cyst, which after going through reducing
divisions fuse to form a synkaryon. The zygote then leaves the
cyst and begins a fresh vegetative cycle.

A different type of life-cycle is exemplified by that which Schepo-
tieff has described in the case of a marine amoeba identified by him
as A. flava. In this case also the ordinary vegetative form is a

222

THE PROTOZOA

uninucleate amoeba, which reproduces itself by binary fission of the
ordinary type ; but large multinucleate forms occur which become
encysted. Within the cyst the nuclei break up into chromidia,
from which a great number of secondary nuclei are formed. The
protoplasm becomes concentrated round the secondary nuclei to
form a number of small cells, which acquire flagella and are set free
from the cyst as flagellulse, believed to be gametes and to copulate ;
the zygote is at first encysted, but becomes free from the cyst, and
develops into the uninucleate amoeba. The life-cycle of A. proteus
is possibly of this type, since in this species also multinucleate
amoebae are commonly observed (see especially Stole ; compare also
Paramceba (Fig. 49).

Fia. 88. — Amaha diploidea. A, The amoeba in the vegetative condition, with
its two nuclei ; B — F, the sexual processes within the cyst, drawn in outline
on a reduced scale ; B, two amoebae, each with its two nuclei, encysted together,
the nuclei beginning to give off chromidia ; C, the two nuclei of each amoeba
fused, numerous vegetative chromidia in the cytoplasm ; D, the bodies of
the amoebae fused, each synkaryon beginning its reduction-process ; E, the
synkarya giving off reduction -nuclei which are degenerating ; F, the reduction-
process complete ; the cyst contains a single amoeba with two nuclei (syn-
karya), ready to emerge and begin its vegetative free life. After Nagler (95).

Metcalf (257) describes " gemmules " budded from small free amoebae of
the proteus-type, each gemmule becoming detached and developing into a
flagellated gamete of a cercomonad type. The flagellulse were observed
frequently to lose their flagella and become amoeboid. Copulation of two
flagellulae took place to form an amoeboid zygote. Metcalf's observations
upon the syngamy in this case recall strongly the observations of Jahn (294)
on the sexual processes of Mycetozoa (p. 242). It is possible that the syngamy
observed by him did not form a part of the life-cycle of the amoeba, but of
some other organism.

The sexual process described by Nagler (95) in Amoeba diploidea is of a
remarkable kind (Fig. 88). In the ordinary vegetative condition the amoeba
possesses normally two nuclei, which divide simultaneously each time the

THE SARCODINA 223

animal reproduces itself by fission. The sexual process begins by two such
amoebae coming together and surrounding themselves with a cyst in common.
Within the cyst their nuclei first give off vegetative chromidia, which are
absorbed, after which the two nuclei in each separate amoeba fuse together
to form a single nucleus, a synkaryon. The protoplasmic bodies of the two
amoebae now fuse completely into one, after which each synkaryon goes
through two reducing divisions, producing each two reduction-nuclei, of
which the first may divide again, so that there may be in the cyst six reduction-
nuclei altogether, which are gradually absorbed. The two persistent synkarya,
after undergoing this process of reduction, approach each other, but remain
separate, and the amoeba is hatched out of the cyst to begin its vegetative
life with two nuclei representing gamete -nuclei that have undergone reduction
— that is to say, pronuclei — which remain separate and multiply by fission
throughout the vegetative life, and do not undergo syngamic fusion until the
end of it.

In Amoeba binudeata, described by Schaudinn, the vegetative phase also
contains two similar nuclei which multiply simultaneously by division each
time the animal divides ; but in this case the complete life-cycle is not known.

Owing to the practical importance of the entozoic amoebae, and
the attention that has been directed to them in consequence, their
life-cycles have been more studied and are better known than those
of the free-living species. According to Mercier, Entamosba blattce
multiplies by binary fission in the gut of its host, and later becomes
encysted, passing out of the body of its host in this condition.
Within the protective cyst it breaks up by multiple fission, follow-
ing repeated division of the nucleus, into a number of amcebulae,
which are set free from the cyst when it is devoured accidentally
by a new host. The amcebulae are gametes which copulate after
being set free, and the zygote grows into the ordinary vegetative
form of the amoeba. E. blattce thus furnishes a very characteristic
and primitive type of the life-cycle of an entozoic amoeba, and one
which differs only in points of specific difference from that of
Amoeba minuta, described above.

The question of the human entozoic amoebae is at present in a
somewhat confused state. The occurrence of amoebae in the hinder
region of the human digestive tract, especially the colon, has long
been known, and the name Amoeba coli was given by Losch to such
organisms (synonym, Entamceba hominis, Casagrandi and Barba-
gallo). It is, however, certain that more than one species of amoeba
occurs in the human bowel, and Losch's name must therefore be
restricted to one of these.

An epoch in the study of human entozoic amoebae was marked by the
researches of Schaudinn (131), who distinguished two species. The first, to
which he restricted the name Entamoeba coli, occurs commonly in Europe
and elsewhere as a harmless inhabitant of the intestine — that is to say, like
E. blattce and many others, it is not, under normal circumstances at least, a
parasite in any sense of the word, but a simple scavenger, feeding on bacterial
and other organisms, detritus, etc., in the colon and rectum. The second
species, to which Schaudinn gave the name E. Mstolytica, * is, on the contrary,

* Liihe has proposed to place E. histolytica in a separate genus, Poneramceba
n. g. (Schr. Physik. Ges. Konigsberg, vol. xlix., p. 421).

224

THE PROTOZOA

a parasite of a dangerous kind, which occurs in tropical and subtropical
regions, and is the pathogenic agent of amoebic dysentery and liver-abscess ;
it attacks and devours the tissues of the host, destroying the wall of the
intestine, whence it penetrates into the blood-vessels and is carried to the
liver, where it establishes itself and gives rise to liver-abscesses. These two
species of amoebae are distinguishable by structural characters. E. coli has
a relatively fluid body, with ectoplasm feebly developed and with a fairly
large spherical nucleus (or nuclei) lodged in the endoplasm. E. histolytica,

FIG. 89. — Entamceba coli. A and B, Living amoebae showing changes of form and
vacuolation in the endoplasm ; 0, D, E, amoebae showing different conditions
of the nucleus (n.) ; F, a specimen with two nuclei preparing for fission ;
G, a specimen with eight nuclei preparing for multiple fission ; H, an encysted
amoeba containing eight nuclei ; /, a cyst from which young amoebae
(al) are escaping ; J, K, young amoebae free. After Casagrandi and
Barbagallo.

on the contrary, has a relatively viscid body with greatly-developed ecto-
plasm, as is seen clearly in the formation of pseudopodia, which may consist
entirely of ectoplasm ; it is smaller than E. coli, and its nucleus has a com-
pressed form, stains feebly, and is lodged in, or immediately below, the
superficial ectoplasmic layer. The life-cycles of these two species are also
very different, as described by Schaudinn.
E. coli, in the amoeboid multiplicative phase, reproduces itself by binary

THE SARCODINA

225

fission of the ordinary type, and also by a process of multiple fission is
which the nucleus divides until there are eight nuclei in the body ; the
characteristic 8-nucleate plasmodium then divides up into eight small
amoebae, each of which grows into an ordinary adult form. Hence it in
characteristic of E. coli to occur in various sizes, from very small to full-grown
amoebae.

The propagative phase of E. coli is initiated by the formation of a gelatinous
envelope round a full-sized amceba possessing a single nucleus. The nucleus
then divides into two, and the process of maturation and autogamy takes place
that has been described on p. 139, supra (Fig. 73). When it is complete, a
tough resistant cyst is formed within the soft gelatinous envelope, and each
of the two synkarya divides twice to produce four nuclei. Thus is formed
the 8-nucleate resistant cyst which is characteristic, perhaps diagnostic,
of this species. Within the cyst no further changes take place until it is
swallowed by a new host ; then it
is believed that the contents of the
cyst divide up into eight uninucleate
amcebulae, which are set free in the
colon and are the starting- point of
a new infection. Schaudinn was
able to infect himself by swallowing
the 8-nucleate cysts of the amceba.

Prowazek (A.P.K., xxii., p. 345)
has described a variety of E. coli
under the name E. williamsi.

E. Jiistolytica reproduces itself in
the amoeboid phase by binary fission
and by a process of gemmation in
which the nucleus multiplies by
division, and then small amcebulae,
each with a single nucleus, are
budded off from the surface of the
body. In the process of gemma-
tion, however, the number of nuclei
in the body is irregular, and not
definitely eight, as in E. coli. In
its propagative phase E. Jiistolytica
does not form a cyst round the
whole body, but its nucleus becomes
resolved into chromidia, which
collect in patches near the surface
of the body. Little buds are then
formed as outgrowths of the body,
each bud containing a clump of
chromidia. Round each bud a
sporocyst is formed of so tough and
impervious a character that no
further cy^ological study of the
bud is possible. The resistant spores formed in this way separate from the
body, of which the greater part remains as residual protoplasm and dies off.
The minute spores are the means of infecting a new host, as shown by
Schaudinn in experiments on cats, which are particularly susceptible to the
attacks of this amceba.

Schaudinn's investigations, of which a brief summary has been given in
the foregoing paragraphs, first introduced clear ideas into the problem of the
human entozoic amoebae. Many of the works of subsequent investigators
have tended, however, rather to confuse and perplex the question, for various
reasons. In the first place, in cultures made from human faeces, free-living,
non- parasitic species of amoebae make their appearance, which have passed
through the digestive tract in an encysted condition, and emerge from their

15

FIG. 90. — Entamceba Jiistolytica. A, Young
specimen; B, an older specimen crammed
with ingested blood-corpuscles ; C, D, E,
three figures of a living amceba which
contains a nucleus and three blood-
corpuscles, to show the changes of form
and the ectoplasmic pseudopodia : n.,
nucleus ; b.c., blood-corpuscles. After
Jiirgens.

226 THE PROTOZOA

cysts in the cultures ;* such amoebae, for the most part of the Umax-type,
have been confused with the true entozoic amoeba, and have given rise to
erroneous ideas. Secondly, it is certain now that the two species of amcebse
recognized by Schaudinn does not exhaust the list of human entozoic amoebse.
Thirdly, it is possible that Schaudinn did not see the entire life-cycle of the
forms studied by him, or that hi some cases he confused stages of different
species in the same life-cycle (compare Hartmann, 247).

It is still doubtful how many species of entozoic amoebse occur in man.
Hartmann recognizes two dysenteric amoebse, in addition to the harmless
E. coli : E. histolytica, Schaudinn, and E. tetragena, Viereck (synonym, E.
africana, Hartmann). E. tetragena has been described from various parts
of the tropics ; it differs from E. histolytica in its characters, and more nearly
resembles E. coli, but is distinguished by the formation of resistant cysts
containing four nuclei. In addition to these species, many others have
been described by various investigators — for example, E. minuta, Elmassian,
which, according to Hartmann, is merely a variety of E. coli. A summary
of the various amoebse described from the human intestine is given by
Doflein (7) and Fantham (241). In Cochin China, Noc obtained from liver-
abscesses and dysenteric stools a small amoeba (not named) which in the
multiplicative phase reproduces in two ways : by binary fission of the ordinary
type ; and by budding off small amcebulse containing secondary nuclei formed
from chromidia. In the propagative phase Noc's amoeba encysts and breaks
up into amcebulse. Greig and Wells, in Bombay, obtained results very
similar to those of Noc. In cultures from liver-abscesses from Bombay,
Listen found two distinct forms of amoebse — a larger form containing a single
nucleus and numerous chromidia, and a smaller form containing a nucleus
only. The larger amoeba multiplies either by binary fission, with karyo-
kinesis of the nucleus and partition of the chromidia ; or by the formation of
endogenous buds containing chromidia from which a secondary nucleus is
formed, the bud being finally set free as a small amoeba with a nucleus and a
number of chromidia. The small amoeba multiples only by binary fission,
preceded by amitotic division of the nucleus. Both large and small amoebse
form resting cysts, in which, however, they remain unchanged, and from
which they emerge when circumstances are favourable. It is evident that
much of the life-cycle of these liver-abscess amoebse remains to be worked out.
From the foregoing it is clear that, with regard to the human pathogenic
amoebse, many important problems remain to be investigated, especially as
regards their specific distinctions, distribution, and life-history. Much
recent work has been carried on by culture-methods, with valuable results,
which, however, should be interpreted with caution, since it remains to be
ascertained whether the forms and phases assumed by these organisms in
cultures are identical in character with those which they exhibit under natural
conditions ; and until this point has been cleared up it is not safe to describe
the characters of a species of an amoeba, any more than of a trypanosome,
from cultural forms alone.

With regard to the life-cycle of the pathogenic amoebse, it is most important to
discover what are the phases of development or conditions of life under which
they occur outside the human body ; whether they exist only in an encysted,
resting condition, or in an active state also ; and, in the latter case, whether as
free-living organisms or within some other host. On general grounds it is un-
likely that an organism adapted to an entozoic life should be capable also of
living free in Nature, and it is more probable that the pathogenic amoebae out-
side the human body occur only in the condition of resting cysts or spores, which
produce infection through being accidentally swallowed with food or water
( compare Walker, 276'5). In that case unfiltered water, uncooked vegetables

* Whether this also applies to cultures made from the pus of liver-abscesses,
as asserted by Whitmore (279) and Hartmann (247), may well be doubted ; it is
not easy to understand how an encysted amoeba could be transported passively
from the intestine into a liver-abscess.

THE SARCODINA

227

and herbs, or fruit that grows near the ground, are likely sources of infection by
becoming contaminated with the resting stage of the amoebae scattered on the
ground or in manure. In this connection the further question arises whether
the human entozoic amoebae are specific parasites of man or not, and conse-
quently whether their infective stages would be derived only from human
feeces, or from the excreta of other animals also. From general considerations
of parasitism in Protozoa, it seems probable that the harmless E. coli is a
specific parasite of man, but that the pathogenic
forms are parasites of other animals also, and
perhaps only occasionally find their way into the
human body ; in which case garden-manure might
be a fruitful source of contamination, through
the medium of vegetables habitually eaten
uncooked, such as lettuce, celery, etc. None of
these questions can be answered decisively at
present, however, and there is a wide field of in-
vestigation open.

Greig and Wells found that in Bombay amoabic
infection shows a marked seasonal variation,
closely associated with variations in humidity,
but not corresponding with those of temperature,
and reaching its maximum in August.

In addition to the various species of Amoeba
and of allied genera and subgenera, a number of
other genera are included in the section under
consideration, for an account of which the reader
must be referred to the larger treatises ; but two
deserve special mention — namely, the genera
Pelomyxa and Paramceba.

The species of Pelomyxa (Fig. 91) are fresh-
water amoebae of large size and " sapropelic "
habit of life (p. 14). The body, which may be
several millimetres in diameter, is a plasmodium
in the adult condition, containing some hundreds
of nuclei ; it is generally very opaque, owing to
the animal having the habit of loading its
cytoplasm with sand and debris of all kinds, in
addition to food in the form chiefly of diatoms.
The pseudopodia are of the lobose type, blunt and
rounded, but the animal may also form slender
reticulose pseudopodia under certain conditions
(Veley). The cytoplasm is very vacuolated, and
contains a number of peculiar refringent bodies
(" Glanzkorper ") of spherical form, with an
envelope in which bacterial organisms (Cladothrix
pelomyxce, Veley) occur constantly. The bacteria
multiply by fission in a linear series in the form
of jointed rods, which may branch ; as a rule
they have five or six joints, or less, but at
least two. The refringent bodies are of albu-
minous nature (Veley). According to Gold-
schmidt (57), the refringent bodies arise from the
nuclei when they give off chromidia ; in this
process the chromatin is given off into the cytoplasm, and the plas tin -basis
of the karyosome is left as a spherical mass which becomes the refringent
body. At first the plastin-sphere is surrounded by the remains of the nuclear
membrane, which disappears, and the refringent body grows in size. Ke-
fringent bodies, with their bacteria, are seen frequently to be ejected by the
animal during life. Bott (103), on the other hand, states that the refringent
bodies are reserve food-stuff, their contents of the nature of glycogen, and

FIG. 91. — Pelomyxa palus-
tris : a specimen in which
the body is transparent
owing to the absence of
food-particles and foreign
bodies, showing the
vacuolated cytoplasm
and the numerous nuclei
and refringent bodies (the
refringent bodies are for
the most part larger than
the nuclei) in the living
condition. After Greeff,
magnified 60.

228

THE PROTOZOA

that they arise in the cytoplasm independently of the nuclei ; but their
rejection by the animal is more in favour of the view that they are waste -
products of the metabolism (Veley). It is not clear what is the role of the
bacteria, whether they are parasites or symbionts.

Pelomyxa reproduces itself by simple fission or by formation of gametes.
The sexual process, according to Bott, begins with extrusion of chromatin
from the nuclei into the cytoplasm to form chromidia, which may take place
so actively that sometimes the nuclei break up altogether. A similar extrusion
of chromidia may take place as a purely regulative process under certain
conditions, such as starvation ; but the vegetative chromidia formed in this
way, and absorbed ultimately in the cytoplasm, must be distinguished from

generative chromidia produced
as a preliminary to gamete-
formation. From the genera-
tive chromidia secondary nuclei
of vesicular structure arise,
which, after elimination of
chromatin followed by reduc-
tion (see p. 150, supra),
become the gamete -nuclei. The
gametes arise as spherical in-
ternal buds, each with a single
nucleus, to the number of 100
or more, and are extruded
when fully formed, causing
the parent-individual to break
up completely. Each free
gamete is Heliozoon-like, with
slender, radiating pseudopodia ;
they copulate in pairs, and the
zygote grows into a young
Pelomyxa, either directly or
after a resting period in an
encysted condition.

The genus Paramoeba (Fig.
49) was founded by Schaudinn
(81) for the species P. eilhardi
discovered by him in a marine
aquarium in Berlin.* In the
adult stage the animal occurs
as an amoeba, from 10 to 90 p,
FIG. 92.— Portion of a section through the body in diameter, of rather flattened
of Pelomyxa. N., Nucleus ; r.b., refringent form and with lobose pseudo-
bodies ; &., bacteria on the refringent bodies ; podia. It contains a single
s., sand and debris in the protoplasm. After nucleus, and near it a peculiar
Gould. body, the "Nebenkern" of

Schaudinn (see p. 95). In

this phase the amoeba multiplies by binary fission accompanied by
division both of nucleus and Nebenkern. It also becomes encysted and
through a process of multiple fission, which shows three stages ; in the
jt the Nebenkern multiplies by repeated division, the nucleus remaining
unchanged ; in the second the nucleus divides repeatedly to form as many
small nuclei as there are Nebenkerne present, and each nucleus attaches itself
to a Nebenkern ; in the third the protoplasmic body undergoes radial super-
ficial cleavage into a number of cells, each containing a nucleus and a Neben-
kern. Each of the cells thus formed becomes a swarm-spore with two flagella.

* The amoeba from the human intestine described by Craig under the name
Paramoeba hominis certainly does not belong to this genus. See Doflein (7),
pp. 602, 603.

THE SARCODINA 229

The swarm -spores are liberated from the cyst and live freely, feeding and
multiplying by binary fission, in which the nucleus divides by mitosis and the
Nebenkern acts like a centrosome. After a time, however, the swarm-spores
lose their flagella, and become amrebulae which develop into the adult phase.
Syngamy was not observed, but probably takes place between the flagellulae.
Two new parasitic species of Paramoeba have been described recently by
Janicki (71 "5) ; see p. 95.

To the order Amoebaea should be referred, probably, the parasite of the
Malpighian tubules of the rat-flea (Ceratophyllus fasciatus), described by
Minchin under the name Malpighiella refringens, and the parasite of Ptychodem
minuta, described by Sun under the name Protoentospora ptychoderce.

The section Lobosa Testacea or Thecamcebae contains a number
of free-living forms familiar to every microscopist, such as the
genera Difflugia (Fig. 16), Centropyxis, Arcella (Fig. 32), etc. The
majority of these forms inhabit fresh water, but Trichosphcerium
(Fig. 81) is marine. Their common distinctive feature, in addition
to the possession of lobose pseudopodia, is the formation of a shell
or house into which they can be withdrawn entirely. The shell may
be secreted by the animal, and then is chitinous (Arcella) or gelat-
inous (Trichosphcerium), or may be made up of various foreign
bodies cemented together (Difflugia). Typically the house has the
form of a chamber with a single large opening, through which the
pseudopodia are extruded at one pole.

When the animal multiplies by fission, the protoplasm streams
out through the aperture, and forms a daughter-shell external to
the old one, after which division of the nucleus takes place and the
two sister-individuals separate. In Trichosphcerium, however, the
house has the form of a gelatinous investment to the body, with
several apertures through which pseudopodia protrude, and when
the animal divides the investing envelope divides with it.

The protoplasmic body contains typically one nucleus — some-
times more than one — surrounded by a ring of chromidia. In
Arcella vulgaris there are constantly two primary nuclei ; in
Difflugia urceolata, from ten to thirty. Trichosphcerium possesses
many nuclei, but no chromidia.

The life-cycle, so far as is known, is of various types ; those of
Arcella and Trichosphcerium are described above (p. 177, Fig. 80,
and p. 181, Fig. 81). The latter, with an alternation of generations
combined with dimorphism in the adult condition, approaches that
of the Foraminifera in character.

In the testaceous amcebse the method of division varies in accordance
with the nature of the shell. In those in which the shell is soft and yielding,
as, for example, Cochliopodium and Cryptodifflugia, the division is longitudinal
— i.e., in a plane which includes the axis passing through the mouth and
apex of the shell (Doflein, 239) ; in Cryptodifflugia rapid division of this kind
may lead to colony-formation. In forms with a rigid shell, on the other hand,
such as Difflugia, Arcella, Centropyxis, etc., the shell sets a limit to the growth
of the animal, which, when it has filled the shell, ceases to grow for a while

230 THE PROTOZOA

and stores up reserve-material. Prior to division a sudden and rapid growth
takes place at the expense of the reserve-material and by absorption of water ;
as a result the protoplasm grows out of the shell-mouth, a daughter-shell is
formed, and the animal divides transversely (Fig. 50).

In Difflugia urceolata. Zuelzer (85) has described a process of chromidiogamy.
Two animals come together with the mouths of the shells in contact, and the
entire contents of one shell flow over into the other, the empty shell being
cast off. The chromidia of the two animals fuse into a single mass ; the
nuclei, however, remain separate. Copulation of this kind is a preliminary
to encystment, which takes place in Nature at the end of October or the
beginning of November. Prior to encystment the pseudopodia are retracted,
all foreign bodies, food-remains, excreta, etc., are cast out, and the proto-
plasmic body rounds itself off in the shell, and diminishes to about a quarter
of its former volume, becoming denser and more refractile. The cyst-
membrane is then secreted at the surface of the body. The old nuclei are
gradually absorbed, and new nuclei are formed from the chromidial mass.
The reconstitution of the nuclear apparatus takes place from January to
April ; in the spring the cyst is dissolved, and the rejuvenated Difflugia begins
to feed and to enter upon a summer course of vegetative growth and repro-
duction. In a recent note (86, p. 191, footnote) Zuelzer states that conjuga-
tion between free gametes also occurs in this species.

In Centropyxis aculeata, according to Schaudinn (131), the ordinary vegeta-
tive reproduction is by fission, the new shell that is formed being larger than
the old one, until the maximum size is reached. Sexual processes are
initiated by degeneration of the primary nucleus, which is single in this
species. Then the protoplasm with the chromidia creeps out of the shell,
and divides into a number of amcebulse, each containing chromidia which
condense into a single nucleus. Some amcebulae form a shell at once ; others
before doing so divide into four smaller amcebulae, and then form a shell.
The larger are macrogametes, the smaller the microgametes ; they copulate
and abandon their shells. The zygote forms a new shell, chromidia appear,
and a fresh vegetative cycle is started.

In a species of the genus Cryptodifflugia (" Allogromia") a remarkable
type of life-cycle has been described by Prandtl (265); see also Doflein (7),
p. 310, Fig. 283. In this form also the organism, at the time of gamete -
formation, quits its shell and penetrates into some other Protozoan organism,
such as Amoeba proteus, in the body of which it becomes parasitic and goes
through the process of gamete -formation. The nucleus breaks up into
chromidia, from which secondary nuclei are formed, producing a multinucleate
plasmodium which multiplies by plasmotomy until the host is full of them.
Ultimately the plasmodia break up into uninucleate cells, the gametes, which
are set free and copulate. The zygote becomes a flagellated Bodo-lika
organism, with two flagella, one directed forward, the other backward as a
trailing flagellum (p. 270, infra) ; it feeds and multiplies in this form for
several generations in the free state, but ultimately it loses its flagella, becomes
amoeboid, forms a shell, and develops into an adult Cryptodifflugia. Note-
worthy in this development are the alternation of generations between the
flagellated and the amoeboid phase, as in Pseudospora (p. 218), and the para-
sitism in the gamete -forming phases ; if, however, the Cryptodifflugia does
not succeed in finding a suitable host, the gamete -formation may take place
in the free state.

From the life-cycles and sexual processes of Arcella, Difflugia, Centropyxis,
etc., it is seen that the primary nuclei of all these forms are vegetative in nature,
while the chromidia give rise to the gamete -nuclei, and consist of, or at least
contain, the generative chromatin. The marine Trichosphcerium, however,
stands apart from the fresh- water genera in regard to its structure, sexual
processes, and life-cycle, in all of which it shows more similarity to the
Foraminifera.

THE SARCOBINA 231

II. FORAMINIFERA.

General Characters — Shell-Structure. — The characteristic features
of this group are the possession of reticulose pseudopodia and of a
shell or test. The Foraminifera are typically creeping forms,
moving slowly, and using their net-like pseudopodia chiefly for food-
capture. Certain genera, however, such as Globigerina, have taken
secondarily to a pelagic existence, and float on the surface of the
ocean, spreading their nets in all directions around them. On
the other hand, some forms have adopted a sedentary life, attaching
themselves firmly to some object. An example is seen in the genus
Haliphysema (Fig. 17), once believed to be a sponge, and in the
remarkable genus Polytrema and allied forms, recently monographed
by Hickson (282) — organisms which in many cases have a striking
and deceptive resemblance to corals.

The test may be secreted by the animal itself, and then is usually
either chitinous or calcareous, rarely siliceous or gelatinous (Myxo-
theca) ; or it may be made up of foreign bodies cemented together,
as in Haliphysema (Fig. 17), and is termed generally " arenaceous,"
but the materials used may be of various kinds, and the organism
sometimes exhibits a remarkable power of selection (see p. 34, supra).

The typical form of the shell, as in the Amcebaea Testacea, is a
chamber with a w'de aperture — sometimes more than one —
through which the pseudopodia are extruded, as in Gromia (Fig. 21).
In addition to the principal aperture, the wall of the shell may be
perforated by numerous fine pores, through which also the protoplasm
can stream out to the exterior. Hence the shells of Foraminifera
are distinguished primarily as perforate and imperforate, the former
with, the latter without, fine pores in addition to the principal
opening.

Whether perforate or imperforate, the shell remains a single
chamber in the simple forms, as in the Amcebsea Testacea. In some
cases, when the animal reproduces itself by binary fission, the proto-
plasm streams out through the principal aperture to give rise to
the body of the daughter-individual, which forms a shell for itself,
and, when the division is complete, separates completely from the
mother, which retains the old shell. Division of this type is seen
in Euglypha (Fig. 59). But in many species, when the animal out-
grows its original single-chambered shell, the protoplasm flows out
and forms another chamber, which, however, is not separated off
as a distinct individual, but remains continuous with the old shell,
so that the animal, instead of reproducing itself by fission, remains
a single individual with a two-chambered shell. By further growth ,
third, fourth, . . . nth chambers are formed successively, each newly-
formed chamber being, as a rule, slightly larger than that formed

232 THE PROTOZOA

just before. Hence a distinction must be drawn between mono-
tJialamous or single-chambered shells and polythalamous shells,
made up of many chambers formed successively. In the latter
type the new chambers may be joined in various ways to the old,

2.Lagena

4.Frondicularia aClobigerina
s.sJt,

7. Discorbina

Q.PIanorbulina 10 ILNummulires

FIG. 93. — Shells of various genera of Foraminifera. In 3, 4, and 5, a shows the
surface-view, and 6 a section ; 8a is a diagram of a coiled shell without supple-
mental skeleton ; 8&, of a similar form with supplemental skeleton (s.sk.} ;
10, of a form with overlapping whorls ; in lla half the shell is shown in hori-
zontal section ; & is a vertical section. In all the figures a marks the aperture
of the shell ; 1 to 15, the successive chambers, 1 being always the oldest or
initial chamber. From Parker and Haswell.

producing usually either a linear or a spiral series, and the utmost
variety of shape and pattern results in different species (Fig. 93).
Some polythalamous species exhibit a peculiar dimorphism (Fig. 94)

THE SARCODINA

233

in some individuals, hence termed microspheric, the initial chamber of
the shell is smaller than in others, which are known as megalospheric.
This point will be discussed further under the reproduction.

It may be noted that if, in this order, a species were to form no
shell, whether from having secondarily lost the habit or as a primi-
tive form which had never acquired it, then such a species would be
classed in the order Amcebaea Reticulosa. It is very probable that
many of the large marine " Proteomyxa " are allied to the true

FIG. 94. — Biloculina depressa: transverse sections of (a) the megalospheric form,
magnified 50 diameters, and (&) the microspheric form, magnified 90 diameters.
After Schlumberger, from Lister.

Foraminifera, as forms either primitively or secondarily without a
test ; and Rhumbler unites the Foraminif era proper with the naked
forms in the section Reticulosa.

The body-protoplasm exhibits no marked distinction of ecto-
plasm and endoplasm. Contractile vacuoles are present in some
of the fresh-water genera, but are not found in marine forms.
The protoplasm contains metaplastic bodies of various kinds, and
may become loaded with fsecal matter in the form of masses of
brown granules, termed by Schaudinn the " stercome " (compare also
Awerinzew, 281). Periodically a process of defsecation takes place,
whereby the protoplasm is cleared of these accumulations, often as
a prelude to the formation of a new chamber (Winter, 28). The

234

THE PROTOZOA

nuclear apparatus varies in different forms, even in the same species,
as will be seen in the description of the reproductive processes.

The marine Foraminifera, so far as they have been investigated,
show a well-marked alternation of generations in their life-history,

si.

FIG. 95. — Polystometta crispa : decalcified specimens to show the structure of the
two forms. A, The megalospheric type ; B, the microspheric type : b, the
central chambers of the latter more highly magnified ; r., retral processes ;
st, communications between the chambers. From Lister.

combined with dimorphism in the adult condition. An example is
Polystomella, which has been investigated by Lister (285) and

THE SARCODINA 235

Schaudinn (131) ; their results have been confirmed in the case of
Peneroplis by Winter, who gives a useful combined diagram of the
life -history (28, p. 16, text -fig. A). The microspheric form
(Fig. 95, B.} has many nuclei, which multiply by fission as the
animal grows, and which also give off chromidia into the body-
protoplasm. When reproduction begins, the nuclei become resolved
entirely into chromidia, and the protoplasm streams out of the
shell, which is abandoned altogether. Secondary nuclei are formed
from the chromidia, and the protoplasmic mass divides up into a
swarm of about 200 amcebulse (Fig. 96). Each amoebula contains
a nucleus and chromidia, and secretes a single-chambered shell,
which is the initial chamber of a megalo spheric individual. The
amcebulae separate, and each one feeds, grows, forms new chambers
successively, and becomes a megalospheric adult. Thus the micro-
spheric form is seen to be an agamont or schizont, which gives rise
by a process of schizogony or multiple fission to agametes (amce-
bulae). The megalospheric form, when full grown, has a single
large nucleus and numerous chromidia (Fig. 95, A). The nucleus
is that of the amoebula which was the initial stage in the develop-
ment of this form ; as it grows the nucleus passes from chamber to
chamber, and at the same time gives off chromidia into the cyto-
plasm. Finally the primary nucleus is resolved entirely into
chromidia, from which a great number of secondary nuclei are
formed. Round each such nucleus the protoplasm becomes con-
centrated to form a small cell, which may be termed a gameto-
cyte. By two divisions of the nucleus and cell - body of the
gametocyte four gametes are formed, each of which acquires two
flagella, and is set free as a biflagellate swarm-spore. In Peneroplis,
however, the gametes have a single flagellum, and in Allogromia
ovoidea the gametes are amce bulge (Swarczewsky). Gametes pro-
duced by different individuals copulate, losing their flagella in the
process, and the zygote secretes a minute single-chambered shell,
and thus becomes the starting-point of the growth of a micro-
spheric individual.

From the foregoing it is seen that the megalospheric form is the gamont,
which by multiple fission produces the gametocytes, and ultimately the
gametes. Thus, if m. represents the microspheric form and M . the megalo-
spheric, am. the amcebulse (agametes), and fl. the flagellulse (gametes), the
life -cycle may be represented thus :

m. — am. — M. — (fl. + fl.) — m. — am. . . .

In some cases, however, the life-cycle does not present a regular alternation
of sexual and non-sexual generations, but a number of non-sexual generations
may take place before a sexual generation intervenes ; that is to say, the
megalospheric forms may produce agametes and other megalospheric forms
again for several generations, before gametes are produced and the sexual
processes occur. Then the life-cycle may be represented thus :

m. — am. — M. — am. — M. — am. . . . M. — (fl. + fl.) — m. — am. — M. . . .

FIG. 96. — Stages in the reproduction
of the microspheric form of Poly-
stomdla crispa. In a the protoplasm
is streaming out of the shell ; in b
and c it is becoming divided up
into amcebulse ; in d the amcebulse,
having each formed a single-
chambered shell, are dispersing
in all directions, abandoning the
empty shell of the parent. From
Lister, drawn from photographs
of one specimen attached to the
walls of a glass vessel.

b

4

s

->f v £T

r-3 ^ j\ ,^-

i ^*

THE SARCODINA 237

Hence the dimorphism of the adults is due to their parentage, and is not
necessarily related to the manner in which they reproduce. A microspheric
form is produced sexually, and is always an agamont ; a megalospheric form
is produced non-sexually, and may be either a gamont or an agamont.

Very little is known of the life -cycle of the non-marine genera. The only
form of which the cycle is known with any approach to completeness is
Chlamydophrys stercorea, the only entozoic member of the order, which is
found in the faeces of various vertebrates ; a second species, C. schaudinni, is
distinguished by Schiissler (A.P.K., xxii., p. 366). The adult form has a
chitinous single-chambered shell, and its protoplasm contains a single nucleus
and a ring of chromidia. It reproduces itself vegetatively by binary fission,
and also by multiple fission producing gametes. In the gamete-formation,
according to Schaudinn (131), the nucleus is ejected from the shell together
with all foreign bodies, food-particles, etc. In the shell is left a small quantity
of protoplasm containing the chromidia, from which about eight secondary
nuclei are formed, and then the protoplasm concentrates round each nucleus
and divides up into as many cells, the gametes, each of which becomes a
biflagellate swarm-spore, and is set free. The gametes copulate and the zygote
encysts. In order to develop further, the cyst must be swallowed by a
suitable host and pass through its digestive tract. If this happens, the cyst
germinates in the hind-gut, setting free an amcebula which forms a shell and
becomes a young Chlamydophrys, living as a harmless inhabitant of the hind-
gut, and feeding on various organisms or waste products occurring there ; but
according to Schaudinn it may, under circumstances not yet defined or
explained, pass from the digestive tract into the peritoneal cavity, and
multiply there as an amoeboid form without a shell, thus giving rise to the
organism described by Leyden and Schaudinn, from ascites-fluid, under the
name Leydenia gemmipara.

The Foraminifera as a group comprise a vast number of genera
and species, both recent and fossil, for an account of which the
reader must be referred, to the larger works. They are classified
by Lister (286) into ten orders (suborders ?), containing in all thirty-
two families ; Rhumbler (288) recognizes ten families in all. The
vast majority are marine, but some of the simpler forms, such as
Euglypha, are found in fresh water, and can scarcely be separated
from the Lobosa except by the characters of their pseudopodia, a
feature upon which great weight cannot be laid as an indication
of affinity. Until the life-histories of these simpler forms have been
studied, their true systematic position must be considered as some-
what uncertain. But the affinities of such genera as Euglypha
and Chlamydophrys would seem to be with the Lobosa Testacea
rather than with the Foraminifera.

III. XENOPHYOPHORA.

This group was founded by F. E. Schulze (290) for a number of
curious organisms of deep-sea habitat, the zoological position of
which was a matter of dispute. By Haeckel they were believed
to be sponges allied to Keratosa, such as Spongelliidce, horny sponges
which load the spongin-fibres of the skeleton with foreign bodies of
various kinds. Schulze established definitely their relationship to

238 THE PROTOZOA

the Rhizopoda by showing that the soft body was a plasmodium
containing numerous nuclei and chromidia, and forming a
pseudopodial network, but with no cell-differentiation or tissue-
formation.

The body consists principally of a network of hollow tubes in
which the plasmodium is contained. The wall of the tubes con-
sists of a hyaline organic substance resembling spongin. In the
interspaces between the tubes great numbers of foreign bodies
(" xenophya," HaeckeJ) are deposited, such as sand-grains, sponge-
spicules, Radiolarian skeletons, and so forth. In one family
(Stannomidce) the xenophya are held together by a system of threads,
" linellse," in the form of smooth, refringent filaments, approxi-
mately cylindrical, which pass from one foreign body to another, and
are attached to them by trumpet-like expansions of their ends.
The substance of the linellse is doubly refractile. and allied to spongin
in its chemical nature. Schulze compares them to the capillitium
of the Mycetozoa (see p. 241, infra).

The protoplasmic body within the tubes contains, in addition
to nuclei and chromidia, enclosures of various kinds. Many tubes,
distinguished by the darker colour of their walls, contain quantities
of brown masses, apparently of faecal nature, and comparable to
the stercome of the Foraminifera (p. 233). In other tubes, lighter
in colour, there are found small, oval, strongly-refractile granules,
or " granellse," which consist chiefly of barium sulphate. Schulze
terms the system of stercome-containing tubes the " stercomarium,"
and those that contain granellse the " granellarium." The tubes
of each system are distinguishable by their mode of branching, as
well as by their colour and contents. In the tubes of the granel-
larium the protoplasmic bodies are often found to contain isolated
cells or groups of cells, each with a single nucleus, which are prob-
ably stages in the formation of swarm-spores. Hence the sterco-
marium probably represents the purely vegetative part of the body,
in which the waste products of metabolism are deposited, while the
granellarium is a differentiated region of the plasmodium in which
the reproductive elements are produced.

Nothing is known of the actual life-cycle of these organisms, but
from the appearances already described, seen in preserved speci-
mens, Schulze conjectures that they reproduce by formation of
swarm-spores, much as is known to take place in the Foram-
inifera.

The affinities of the Xenophyophora are seen to be with the
Foraminifera. In their habit of forming a skeleton of foreign
bodies they resemble the arenaceous Foraminifera, in which, how-
ever, the foreign bodies build up the house which directly encloses
the soft body, while in the Xenophyophora the soft body is en-

THE SARCODINA 239

closed actually within the system of tubes. Nothing similar to the
l.'nellse is known in any Foraminifera.

For the classification of the Xenophyophora and their genera see
Schulze (290).

IV. MYCETOZOA.

The Mycetozoa are a group of semi-terrestrial Rhizopods occur-
ring in various situations, especially on dead wood or decaying
vegetable matter of various kinds. Their most characteristic
features are the formation of plasmodia, which represent the adult,
vegetative phase of the life-history, and their method of repro-
duction, consisting in the formation of resistant spores very similar
to those of fungi. The Mycetozoa were originally classified amongst
the Fungi as a group under the name Myxomycetes, but the in-
vestigations of de Bary first made clear their Rhizopod affinities.

The life-history of a typical member of this group exhibits a
succession of phases, the description of which may conveniently
begin with the spore. Each spore is
a spherical cell with a single nucleus,
enclosed in a tough protective envelope
which enables it to resist desiccation.
It may be dormant for a considerable
period, and germinates when placed
in water. The envelope bursts, and
the contained cell creeps out as
an amcebula with a single nucleus FlG. 97._The Aching of a spore
(Fig. 97), the so-called " myxamceba.' of Fuligo septica. a, Spore; 6,

After a time the amcebula develops c> contents emerging and under-

„ * going amoeboid movements prior

a flagellum, and becomes a flagellula to the assumption of the flagel-

orzoospore(" my xoflagellate"), which lula-stage; d, flagellula. c.w..

f ^ T ij- T ^ r> • mi Contractile vacuole. After Lister,

feeds and multiplies by fission. The magnified 1,100.

flagellula (Fig. 98) retains its amoeboid

form, and sometimes also the amoeboid method of locomotion, the
flagellum appearing to act as a tactile organ. It captures bacteria
and other organisms by means of its pseudopodia, nourishing itself
in a holozoic, perhaps also in a saprophytic, manner. It also
may become temporarily encysted.

The flagellate phase is succeeded by a second amoeboid stage,
the flagellum being lost. The amcebulse of this stage tend to con-
gregate together in certain spots, and the groups thus formed fuse
together (their nuclei, however, remaining separate) to form the
plasmodium, the dominant vegetative stage, which feeds and grows,
its nuclei multiplying as it does so, until from the small mass of
protoplasm formed originally by the amoebulae, with relatively few
nuclei, it becomes a sheet or network of protoplasm, which may

240

THE PROTOZOA

FIG. 98. — Flagellula of
Stemonitis fusca, show-
ing successive stages in
the capture of a bacillus.
In a it is captured by
one of the pseudopodia
at the hinder end ; in c
it is enclosed in a diges-
tive vacuole. Another
bacillus is contained in
an anterior vacuole.
From Lister, magnified
800.

be several inches across and contain many thousands of nuclei.

The plasmodium moves about in various directions, showing
exquisite streaming movements of the proto-
plasmic body (Fig. 99). The nature of the
food varies in different species ; the majority
feed on dead vegetable matter, but some
attack and devour living fungi. The mode
of nutrition is generally holozoic, but in
some cases perhaps saprophytic . Contractile
vacuoles are present in large numbers in
the protoplasm, in addition to the innumer-
able nuclei, which are all similar and not
differentiated in any way. The plasmodia
are often brightly coloured.

From their mode of life, the plasmodia
are naturally liable to desiccation, and when
this occurs the plasmodium passes into the
sclerotial condition, in which the proto-
plasm breaks up into numerous cysts, each
containing ten to twenty nuclei. When
moistened, the .cysts germinate, the con-
tained masses of protoplasm fuse together,

and so reconstitute the active plasmodium again.

The plasmodium represents the trophic, vegetative phase, which

is succeeded by the reproductive phase, apparently in response to

external conditions, such

as drought, but more es-
pecially scarcity of food.

The reproduction begins

by the plasmodium be-
coming concentrated at

one or more spots, where

the protoplasm aggre-
gates and grows up

into a lobe or eminence,

the beginning of the

sporangium (Fig. 100),

the capsule in which the

spores are found. The

sporangium is modelled,

as it were, on the soft

protoplasmic body, and

takes the form of a

rounded capsule, attached to the substratum by a disc-like

attachment known as the hypothallus. Between the sporangium

FIG. 99. — Part of a plasmodium of Badhamia
utricularis expanded over a slide. From
Lister, magnified 8 diameters.

THE SA&CODINA

241

proper and the hypothallus the body may be drawn out into

a stalk.

The first events in the reproductive process are the formation of

the protective and supporting elements

of the sporangium. Over the surface

of the lobe a membrane or envelope is

secreted, the " peridium," and in the

interior of the protoplasmic mass a

network, or rather feltwork, of filaments,

the " capillitium," is produced, of

similar nature to the peridium, and in

continuity with it ; peridium and

capillitium contain cellulose or allied

substances, and the former may contain

carbonate of lime in some species.

During the formation of the pro-
tective peridium and the supporting

capillitium the protoplasmic mass

remains in the plasmodial condition,

but when the accessory structures are

completely formed the actual spore-
formation begins. According to recent

investigations, spore-formation is initi-
ated by the degeneration of a certain

number of the nuclei ; the nuclei that

persist then divide by karyokinesis simultaneously throughout the

whole plasmodium. The protoplasm then becomes divided up,

directly or indirectly, into as many
masses as there are nuclei. The cells
thus produced, lying in the interstices
of the capillitium, become surrounded
each with a tough membrane, and are
the spores (Fig. 101). They are
liberated by bursting of the peridium,
and the hygroscopic properties of the
capillitium are the cause of movements
in it which assist in scattering the
spores. With the formation of the
spores the life-cycle has been brought
round to the starting-point that was
selected. The spores are scattered in
all directions by the wind, and
germinate in favourable localities.

FIG. 100. — Badhamia utricularis.
a, Group of sporangia, magni-
fied 12 ; b, a cluster of spores ;
c, a single spore ; d, part of the
capillitium containing lime-
granules : b and d magnified
170. From Lister.

FIG. 101. — Trichia varia : part of
a section through a sporan-
gium after the spores are
formed ; threads of the capil-
litium are seen in longitudinal
and transverse section. From
Lister, magnified 650 dia-
meters.

The account given above may be taken as describing the typical series of
events in the life-history, which is liable to considerable variations in particular

16

242 THE PROTOZOA

types. In the subdivision termed the Sorophora~or Acrasiae there is no
flagellula-stage in the life-history, and the amcebulae which are produced
from the spores aggregate together, but form only a pseudo-plasmodium,
in which the constituent amcebulse remain distinct, without fusion of their
protoplasmic bodies, each amoabula multiplying independently. The details
of the reproductive process also vary greatly. In the division known as
the Exosporeae, represented by the genus Ceratiomyxa, no sporangium is
formed, but the plasmodium grows up into antler-like processes, sporophores,
over the surface of which the plasmodium divides up into a mosaic of cells,
each containing a single nucleus of the plasmodium. Each cell becomes
a spore, which is produced on the free surface of the sporophore, and drops
off when ripe. In the Sorophora the amoebae associated in the pseudo-
plasmodium are not all destined to become reproductive individuals ; some of
them join together to secrete a stalk, and develop no further ; others form
clusters (" sori ") of naked spores on the stalk.

The cytological details of the life-history of the Mycetozoa have been the
subject of a series of studies by Jahn, who, however, in his latest investigations,
has come to conclusions different from those at which he arrived in his earlier
works. According to the earlier accounts given by Jahn and Kranzlin, the
spore -formation was preceded by a fusion of nuclei in pairs throughout the
sporangium, a process which was regarded as the true sexual karyogamy,
and was followed by reducing divisions. According to Jahn's latest investiga-
tions (294), however, the nuclear fusions observed in the sporangium take
place only between degenerating nuclei, and are to be interpreted as purely
vegetative phenomena which have nothing to do with the true sexual process,
which is stated to be as follows : The nuclear division which immediately
precedes spore -formation is a reducing division, whereby the number of
chromosomes is reduced from sixteen to eight. Consequently the nuclei of
the spores, and also the swarm-spores produced from them, both flagellulae
and amoebulae, have half the full number of chromosomes. In Physarum
didermoides the amcebulae multiply by fission, with mitoses showing eight
chromosomes. After a certain number of such divisions, the amoebulse
copulate in pairs as gametes. The zygotes thus formed are the foundation
of the plasmodia ; when one zygote meets another it fuses with it, the nuclei
remaining separate, and by repeated fusions of this kind the plasmodia are
formed. When, on the other hand, a young plasmodium or a zygote meets
an amosbula (gamete), it devours and digests it. The nuclei of the plasmodia
multiply by mitoses which show sixteen chromosomes.

In Ceratiomyxa the reduction-division preceding spore -formation is followed
by degeneration of one of the two daughter-nuclei ; the other becomes the
nucleus of the spore. Within the spore the nucleus divides twice, forming
four nuclei, and as soon as the spore germinates the contents divide into four
amoebulae, which adhere in the form of a tetrahedron. Each amcebula has
eight chromosomes in its nucleus, and divides into two amcebulae, also with
eight chromosomes. Each of the amcebulae develops a flagellum and swims
off. Possibly in this genus the syngamy takes place between flagellulae.

From the investigations of Jahn, it is clear that the swarm-spores of
Mycetozoa, like those of other Sarcodina, are the gametes ; their nuclei have
undergone a process of reduction, and represent pronuclei, which after a
certain number of divisions give rise by syngamy to synkarya, from which
the nuclei of the vegetative phase, the plasmodium, takes origin.

The Mycetozoa are classified by Lister (297) as follows :

SUBORDER I. : EUPLASMODIDA (Myxogastres, Myxomycetes sens, strict.).—
Mycetozoa with a flagellula-stage and a true plasmodium formed by plasto-
gamic fusion of amoebulae. This suborder comprises forms with the full life-
cycle described above.

Section 1. Endosporece. — Spore-formation within a sporangium. Examples :
Badhamia, Fuligo (dBthalium), etc.

Section 2. Ectosporece. — Spores formed on the exposed surface of sporo-
phores. Example : Ceratiomyxa.

THE SARCODINA 243

SUBORDER II. : SOROPHORA (Acrasise, Pseudoplasmodida). — With no
flagellate stage in the life-history ; the amcebulse do not fuse completely to
form a true plasmodium ; the spores are formed in clusters (" sori "). Here
belong various genera, for the most part found in dung, such as Dictyostelium
and Copromyxa. Acrasis occurs in beer-yeast.

In addition to the typical Mycetozoa belonging to these two suborders,
there are a number of forms on the border-line, referred by some authorities
to the Mycetozoa, by others to other orders, such as the Proteomyxa. It
is only possible to refer very briefly to these genera here.

In the first place, there are a number of parasitic forms, placed together
by Doflein in the suborder Phytomyxince, Schroter. In this suborder no
sporangium is formed, the process of spore -formation being simplified,
probably, in correlation with the parasitic mode of life. The typical members
of this group are parasites of plants, but some recently-described parasites
of insects have been assigned to Phytomyxince. The best known example of
the group is the common Plasmodiophora brassicce, which attacks the roots
of cabbages and other Cruciferee, producing a disease known as " Fingers
and Toes " (" Kohlhernie "), characterized by knotty swellings on the roots.
Other genera parasitic on plants are Tetramyxa and Sorosphcera.

In Plasmodiophora the spores germinate to produce flagellulae, which are
liberated in water or damp earth, and which in some way penetrate into the
cells of the plant, and there appear as the myxamcebae after loss of the flagel-
lum. The youngest myxamcebae seen have two nuclei. They grow in the
cell-contents with multiplication of their nuclei, and fuse with one another
to form plasmodial masses which fill the cell after absorption of its contents.

In a diseased plant a number of cells are attacked by the parasite, and it is
not certain whether the myxamcebae can pass from one cell to another, and so
spread the infection, or whether all the infected cells are derived from the
multiplication of the first cell infected. The second view, maintained by
Nawaschin, is supported by Prowazek, and also by Blomfield and Schwartz,
with regard to the allied genus Sorosphcera.

When the host-cell is exhausted, the reproductive phase begins, according
to Prowazek (127), by the nuclei of the plasmodium throwing out numerous
chromidia, and becoming in consequence very indistinct. In Sorosphcera at
this stage (Blomfield and Schwartz) the nuclei disappear altogether, being
entirely resolved into chromidia from which secondary nuclei are formed.
Spore -formation, preceded by sexual processes, takes place in the manner
described above (p. 149, Fig. 76). In Sorosphcera, Blomfield and Schwartz
found that, after re constitution of the generative nuclei, the plasmodium
divides up into uninucleate cells, each of which divides twice by karyokinesis ;
after these divisions the cells become arranged as a hollow sphere, the " soro-
sphere," and each cell becomes a spore. No cell-fusions or syngamic processes
were observed.

As stated above, certain parasites of insects are referred to this order
by Leger. Such are the genera Sporomyxa, Leger (295), Mycetosporidium,
Leger and Hesse, and Peltomyces, Leger (C.R.A. S., cxlix., p. 239). Zoomyxa
legeri, Elmassian (637), parasite of the tench, is perhaps also to be referred
to the Mycetozoa. The position of these forms must, however, be considered
somewhat doubtful at present. Chatton has thrown out the suggestion
that the affinities of Peltomyces are rather with the Cnidosporidia (p. 409),
through the genus Paramyxa recently found by him (761).

Lastly, mention must be made of the remarkable genera Chlamydomyxa,
Archer, and Labyrinthula, Cienkowski, the affinities of which are still obscure.
By Lankester (11) they were ranked as an independent order of the Sarcodina
under the name Labyrinthulidea ; by Delage and Herouard (6) and others
they are placed as a suborder, Filoplasmodida, of the Mycetozoa.

Chlamydomyxa is a fresh-water genus occurring either free or encysted.
Its most remarkable feature is the possession of chromatophores which enable
it to live in a holophytic manner, and consequently to assimilate and grow
when encysted. On the other hand, when free it forms a network of long,

244 THE PROTOZOA

filamentous pseudopodia, by means of which it is able to digest food in the
ordinary holozoic manner. The body is a plasmodium containing, in addition
to numerous nuclei, chromatophores, and peculiar "oat-shaped bodies,"
"spindles," or "physodes," stated to consist of phloroglucin. The cyst-
envelope consists of cellulose, and has a stratified structure. In addition to
reproduction by fission (plasmotomy), Chlamijdomyxa appears to form flagel-
late swarm-spores, possibly gametes.

Labyrinthula occurs in marine and fresh water. In the active state it has
the form of a network of filaments, 1 millimetre or so in extent, over which
travel a great number of " units," each a nucleate cell or amcebula, sometimes
brightly coloured. When dried, each unit encysts and hatches out again
separately. The units multiply by fission. They were formally compared
erroneously with the " spindles " of Chlamydomyxa. Lister (298) regards
Labyrinthula as a colonial organism of which the units remain in connection
by their pseudopodia. He considers these two genera as related in ono
direction to certain members of the Foraminifera (Gromiidce), in other drections
to the Heliozoa and the Proteomyxa.

V. HELIOZOA.

The Heliozoa are characterized, as a group, by their spherical
form and stiff, radiating pseudopodia, whence their popular name
of " sun-animalcules." As in the case of the Radiolaria, these
peculiarities of form are generally correlated with a floating habit
of life, though in a few cases the animal is sedentary and attached
to a firm support. In contrast with the Radiolariai a "central
capsule" (p. 250) is absent from the body-structure. A skeleton
may be present or absent. The majority of species inhabit fresh
water, but a few are marine.

General Characters. — As in other orders of Sarcodina, a concise
statement of the characteristic features of the group is rendered
difficult by the occurrence of border-line forms, of which the exact
position is doubtful. It is best, therefore, to consider first typical
forms of which the position is incontrovertible, and then those
which link the Heliozoa to other groups of Protozoa.

The body-protoplasm exhibits commonly a vacuolated, frothy
structure, with distinct cortical and medullary regions. The cor-
tical zone, distinguished by vacuoles of larger size, disposed in a
radiating manner, is regarded as ectoplasm ; the medullary region,
with smaller vacuoles irregular in arrangement, as endoplasm ;
but it is open to doubt if these two regions correspond truly to the
ectoplasm and endoplasm of an amoeba. The cortex contains the
contractile vacuoles, and gives off the pseudopodia, which are
typically stiff, straight, and filamentous, ending in a sharp point
and supported by an axial organic rod (p. 48) ; but in some genera
the supporting axis is wanting. In the medulla are lodged the
nuclear apparatus, the food- vacuoles, and frequently also symbiotic
organisms, which are probably in most cases vegetative, non-
flagellate phases of holophytic flagellates (Chlamydomonads).

As regards the nuclear apparatus, there are two types of arrange-

THE SARCODINA 245

ment (compare p. 90). In the first or Actinophrys-type (Fig. 46)
the nucleus is central, and the pseudopodia are centred on it.
Actinosphcerium (Fig. 3) can be derived from this type by multi-
plication of the nucleus, originally single, until there may be some
hundreds present in large specimens. The marine form Campto-
nema nutans, Schaudinn, is perhaps also to be referred to this type
of structure ; it has as many pseudopodia as there are nuclei present,
each pseudopodium arising directly from a nucleus (p. 91, Fig. 47).

In the second or Acanthocystis-type (Figs. 18, 64) the centre of
the spherical body is occupied by a " central grain " (p. 91), on
which the axial rays of the pseudopodia are centred. The nucleus,
on the other hand, occupies an excentric position in the body. In
this type there is a tendency to a sessile habit of life, the animal
being attached by the surface of the body, which may grow out
into a stalk, as in Clathrulina (Fig. 19). In the interesting marine
genus Wagner ella (Fig. 48), the surface of attachment has become
drawn out in such a way that the body is divided into three parts —
basal plate, stalk, and head. The nucleus is situated in the basal
plate. The head contains the central grain, from which the pseudo-
podia radiate. Thus, in this genus the excentric position of the
nucleus is carried to an extreme ; it may be regarded as having
grown out from the body in a lobe or prolongation which forms the
basal plate and stalk, while the original body remains as the head
with the central grain and pseudopodia.

The skeleton, when present, may take various forms. It may
be a simple gelatinous investment, or may contain mineral (sili-
ceous) substance either in the form of loose, radiating spicules, as
in Acanthocystis, or of a continuous lattice-like investment, as in
Clalhrulina. In Wagner ella the basal plate and stalk are protected
by a tough yellowish organic membrane, replaced in the head by
a colourless gelatinous layer, and both head and stalk are further
protected by siliceous spicules, which are formed in the protoplasm
and transported by protoplasmic currents (Zuelzer, 86).

Life - History. — Reproduction in the free vegetative phase is
effected by binary fission or gemmation . Imperfect binary fission may
lead to colony -formation, as in Ehaphidiophrys. The sexual phases
are only known accurately in a few cases. In Actinophrys, Schaudinn
described copulation within a cyst (p. 132, Fig. 71), with subse-
quent division of the zygOte and liberation of two individuals from
the cyst. In Actinosphcerium (Hertwig), encystment of a large
multinucleate individual is followed by degeneration of about
95 per cent, of the nuclei ; the remainder appear to fuse in pairs,
and the body then divides into as many cells as there are nuclei.
Round each cell a separate " primary " cyst is secreted within the
gelatinous " mother-cyst " originally formed round the whole mass. .

246 THE PROTOZOA

Each primary cyst then divides into two secondary cysts, which
after nuclear reduction become the gametes and copulate. The
zygote develops into a young Actinosphcerium with several nuclei,
which emerges from the cyst and begins a vegetative life, but appears
to divide frequently at the start into uninucleate, Actinophrys-Mke
forms.

In other genera, on the other hand, and especially in those of the
Acanthocystis - type (Acanthocystis, Clathrulina, and Wagnerella),
flagellate swarm - spores are formed, which probably represent
gametes, as in many other Sarcodina.

The life-history of Wagnerella has recently been studied in detail by
Zuelzer (86) ; her investigations reveal a diversity in its modes of reproduction
almost as great as that seen in Arcella, and indicate that there is much yet
to be discovered with regard to the life-cycles of other forms.

Wagnerella exhibits, according to Zuelzer, dimorphism correlated with
alternation of generations. In June and July stout forms are observed,
which are believed to arise from the conjugation of gametes ; they reproduce
by binary fission, and by a process of schizogony giving rise to amcebulae
(agametes). The more usual form, on the other hand, is smaller and more
slender, and multiplies by binary fission, gemmation, and formation of
flagellate swarm-spores. Hence this peculiar form reproduces in a variety
of ways. In the process of binary fission the nucleus migrates from the
base up the stalk into the head, and places itself beside the central grain,
which divides, its two halves passing to opposite sides of the nucleus ; then
the nucleus follows suit and divides also. Divisions of the central grains,
and subsequently of the corresponding nuclei, may be repeated until eight to
ten nuclei and as many central grains are present. Each nuclear division
is followed by division of the head, at first incomplete, so that a condition
results resembling the colonial form Rhaphidiophrys, a number of daughter-
individuals united together, and each sending out pseudopodia (Fig. 102, D).
After a time the colony breaks up, the daughter-individuals separate, and
each one fixes itself and grows into the adult Wagnerella-form.

Bud-formation in Wagnerella (Fig. 102, A — C) is initiated by division
of the karyosome within the nucleus, which retains its position in the base.
The process is repeated until the nucleus contains a number of karyosomes,
each with a centriole. The nucleus then buds off one or more small daughter-
nuclei, each containing a single karyosome. Sometimes the nucleus breaks
up entirely into as many daughter-nuclei as there are karyosomes, in which
case the parent-individual dies off, in a manner similar to Arcella (p. 180),
after liberation of the buds. Each daughter-nucleus migrates up the stalk
into the head, where it becomes surrounded by a layer of protoplasm to form
the bud, which is set free at first as an amoeboid body. Before or after being
set free, the bud may multiply by binary fission with mitosis, in which the
centriole in the karyosome acts as a centrosome. Finally each amoeboid
body develops into a Wagnerella, and in the process the centriole passes out
of the nucleus and becomes the central grain, while the nucleus becomes
displaced from the centre. In the process of gemmation the central grain
of the parent-individual takes no share whatever.

In the formation of the swarm-spores, minute secondary nuclei arise from
chromidia near the principal nucleus in the base. Each secondary nucleus
forms a centriole and divides by mitosis ; the division is repeated until the
whole body, stalk and head as well as base, is filled with small nuclei, while
the primary nucleus degenerates. The body then divides up into as many
cells as there are secondary nuclei, each cell becoming a biflagellate swarm-
spore which is set free, while the parent -individual degenerates. The destiny
of the swarm-spores is uncertain, but they are believed to be gametes.

THE SARCODINA

247

In the " schizogony " of the stout forms the nucleus breaks up into a number
of daughter- nuclei, as in gemmation ; each daughter-nucleus grows, its karyo-
some multiplies by fission, and it breaks up in its turn into granddaughter-
nuclei. Continued multiplication of the nuclei in this manner proceeds
until the body is filled with vesicular nuclei ; it then breaks up into as many
amoebulse, which are set free, leaving a residual body with the central grain,
which degenerates.

Fia. 102. — Wagnerella borealis, showing budding and fission. A, Speoimen with
a single bud (6) : e.g., central grain ; B, specimen with four buds (6) ; G, en-
larged view of the head of a specimen containing two buds (6) in process of
extrusion ; D, specimen in which the head has multiplied by fission to produce
a Rhaphidiophrys-like colony ; six individuals are seen, five of them each
with nucleus and central grain, the sixth in process of fission, with two nuclei
and two central grains. After Zuelzer (86).

The Heliozoa are classified into four suborders :
SUBORDER I. : APHROTHORACA. — Body naked in the active state ;
envelopes, sometimes with siliceous spicules, only formed during

248

THE PROTOZOA

encystment. Examples : Actinophrys (Fig. 46), Actinosphcerium
(Fig. 3), Camptonema (Fig. 47), etc.

SUBORDER II. : CHLAMYDOPHORA. — Body protected by a soft gela-
tinous envelope, but without solid skeletal elements. Example :
Astrodisculus.

SUBORDER III. : CHALAROTHORACA. — Body invested by a soft
envelope containing isolated spicules, usually siliceous, sometimes
chitinous. Examples : Acanthocystis (Figs. 18, 64, 68), Wagnerella
(Figs. 48, 102), Heierophrys (Fig. 103).

SUBORDER IV. : DESMOTHORACA. — Body invested by a continuous,
lattice-like skeleton. Example : Clathrulina (Fig. 19).

^— -c.

FIG. 103. — Heterophrys fockei, Archer, c., c., Contractile vacuoles ; s., radial chiti-
nous spines surrounding the envelope. A nucleus is present in the body, but
is not shown ; the bodies in the protoplasm represent zooxanthellae. From
Weldon and Hickson, after Hertwig and Lesser.

A certain number of genera must be mentioned which are of doubtful
position, referred by some authorities to the Heliozoa, by others to other
orders. Some of these genera perhaps do not represent independent, " adult "
forms, but may be only developmental phases of other genera. Nuclearia,
classed by some in the Aphrothoraca, by others in the Proteomyxa, has an
amoeboid body and pseudopodia without axes. As described above (p. 177
and Fig. 80), a Nuclearia-stage occurs in the development of Arcella.

Especially remarkable are certain genera which indicate a close relation-
ship between Heliozoa and Flagellata. An account of several such forms is
given by Penard (302), in addition to which the following may be noted :
Ciliophrys, Cienkowski, has two phases ; in the one it appears as a typical
Heliozoon with stiff radiating pseudopodia ; in the other it is a typical
flagellate. In the process of transformation the Heliozoon-form retracts its
pseudopodia, its body becomes amoeboid, and a flagellum grows out ; finally

THE SARCODINA 249

the animal becomes a pear-shaped flagellate swimming by means of its
flagellum (Schewiakoff, 863 ; Caullery, 300). Ciliophrys thus recalls Pseudo-
spora in its two- phases (p. 218), and there can be little doubt that the two
forms are closely allied.

Dimorpha nutans, Gruber (Fig. 104), has radiating pseudopodia strengthened
by axial rods, and in addition a pair of flagella arising close together at one pole
of the body. Both flagella and pseudopodia arise from a centrosome situated
near the flagellated pole ; the single nucleus is also excentric and placed
close beside the centrosome. The animal uses one of its flagella for attach-
ment, while the other remains free (Schouteden).

These facts appear to indicate an origin for the Heliozoa from Flagellates
such as those of the genus Multicilia (p. 270, Fig. 113), in which the body
bears radiating flagella planted evenly over the surface ; transformation of
the flagella into stiff pseudopodia would produce the Heliozoon - type of
organism. On such a view two peculiarities of the Heliozoan pseudopodia
receive explanation : the power of nutation and bending which they fre-

FIG. 104. — Dimorpha nutans. After Schouteden.

quently possess ; and their insertion on a " central grain," which would then
represent the blepharoplast, pure and simple, of a flagellate. On this view
the pseudopodia of the Heliozoa would appear to be structures quite different
in nature from the similarly-named organs of Lobosa.

On the other hand the Heliozoa also show affinities towards forms classed
among the Reticulosa or " Proteomyxa," as already noted in the case of
Ciliophrys and Pseudospora. Przesmycki has described a species, Endophrys
rotatorium, parasitic in Rotifers, which he considers as a connecting-link
between Nuclearia and Vampyrella. The exact systematic position of such
genera must be considered at present an open question.

VI. RADIOLARIA.

General Characters. — The Radiolaria are characterized, speaking
generally, by the same type of form and symmetry that is so
marked a feature of the Heliozoa, though in many cases the internal

250

THE PROTOZOA

structure of the body, and especially the skeleton, may depart more
or less widely from the radiate symmetry which is to be regarded,
probably, as primitive for the group. Hence three principal types
of symmetry can be distinguished in these organisms : (1) Homaxon
(Figs. 13, 105, 107), in which all axes passing through the centre
are morphologically equivalent, the symmetry of the sphere ;
(2) monaxon (Fig. 109), in which the body has a principal or vertical
axis round which it is radially symmetrical, the type of symmetry of
the cone ; (3) bilaterally symmetrical (Fig. 106), in which the body

FIG. 105. — Acanthometra dastica, Haeckel. sp., Radiating spines of the skeleton
(twenty in number, but only twelve are seen in the figure) ; ps., pseudopodia ;
c., calymma ; c.c., central capsule ; N., N., nuclei ; x, yellow cells ; my., myo-
phrisks. After Butschli, Leuckart and Nitsche's " Zoologische Wandtafeln. "

can be divided along a principal plane into equivalent right and
left halves. With further modification the body may become
asymmetrical. Sedentary forms are not known in this group, the
species of which are exclusively marine, and occur on the open
surfaces of seas and oceans, reaching in many instances a re'atively
large size and a very high degree of structural differentiation.

In the internal structure, the most salient feature is the division
of the body by means of a membranous structure, termed the
central capsule (Fig. 13, CK), into a central medullary region and a
peripheral cortical zone — hence distinguished as the intracapsular

THE SARCODINA 251

and extracapsular regions of the body. The intracapsular medulla
contains the nucleus or nuclei, and is the seat of reproductive
processes. The extracapsular cortex is the seat of assimilation,
excretion, food-capture, and of such locomotor processes as these
organisms are able to perform, consisting chiefly of rising or sinking
in the water by means of changes in a hydrostatic apparatus
presently to be described.

The Radiolaria are an exceedingly abundant group represented by a great
number of species both at the present time and in past ages ; over vast
tracts of the ocean- floor their skeletons are the principal, almost the sole
constituents of the ooze ; and the same must have been true in past times,
since in many geological deposits the rocks are composed of the same materials.
Every microscopist is familiar with their skeletons, which on account of
their beauty and variety of form are favourite objects for microscopic study
and demonstration. Corresponding with the variety of forms and species,
the internal structure shows a range of variation and differentiation which
it is impossible to deal with adequately in a short space ; it must suffice,
therefore, to describe here the main structural peculiarities of this group
in a general manner, and to indicate briefly the principal variations of structure
which are of importance for the classification of the group. For further
information the reader must be referred to the larger treatises and special
monographs.

Structure. — The central capsule, absent in rare cases, may be a
thin, delicate structure, visible only after treatment with reagents,
or may be fairly thick. In homaxon forms it is generally spherical,
but may assume various shapes correlated with the general*body-
form, and even may be lobed or branched. It is perforated by
openings which place the intracapsular protoplasm in communica-
tion with the extracapsular ; the openings may take the form of
fine pores scattered evenly over the whole surface (Peripylaria) ; of
similar pores aggregated into localized patches, pore-areas or pore-
plates (Acantharia) ; of a single pore-plate at one pole of an asym-
metrical capsule (Monopylaria, Fig. 106) ; or of one principal and
two lateral apertures (Tripylaria).

The intracapsular protoplasm contains the nuclear apparatus,
either one nucleus of very large size or a number of smaller nuclei
(Fig. 105). In addition, various bodies of metaplastic nature,
serving as reserve-material for the reproductive processes, are
found in this region, in the form of fat-globules, oil-drops, concre-
tions, crystals, etc.

The extracapsular region consists of three zones, from within
outwards : (1) an assimilative layer or matrix immediately sur-
rounding the capsule ; (2) a vacuolated layer, known as the " cal-
ymma," hydrostatic in function ; (3) a protoplasmic layer from
which the pseudopodia arise.

1. The assimilative layer contains pigment, representing ex-
cretory substances and ingested food-material in the shape of small

252

THE PROTOZOA

organisms captured by the pseudopodia and passed into the body,
to be digested in this region. In the Tripylaria an aggregation of
food-material and excretory substances produces a characteristic
greenish or brownish mass concentrated round the main aperture
of the central capsule, and known as the phceodivm, whence this
suborder is sometimes known as the Phseodaria.

2. The calymma is composed for the most part of a great number
of vacuoles containing fluid, the function of which is hydrostatic ;
the contents of the vacuoles are stated to be water saturated with
carbon dioxide, causing the animal to float at the surface, and

enabling it to regulate its position
in relation to conditions of environ-
ment. In rough weather the vacuoles
burst or are expelled from the body,
and the animal sinks into deeper and
quieter layers of water; there fresh
vacuoles are formed, enabling it to
return again to the surface if the
conditions are favourable. Contractile
vacuoles of the ordinary type are not
present.

In addition to the vacuoles, the
calymma contains numerous " yellow
cells," generally regarded as sym-
biotic organisms of vegetable nature,

FIG. 106. — Lithocircus productus,
Hertwig, showing a bilaterally
symmetrical skeleton consisting
of a simple siliceous ring pro-
longed into spicnlar processes.
sk., Skeleton ; ex., central cap-
sule ; pf., pore-area, surmounted
by a conical structure (c.), the
so-called " pseudopodial cone " ;
N., nucleus ; o., oil-globule.
After Biitschli, Leuckart and
Nitsche's " Zoologische Wand-
tafeln."

and named " zooxanthellae " or

" zoochlorellae," according to their
colour. Absent in the Tripylaria,
these yellow cells are found, as a
rule, in the calymma, but in
Acantharia they occur in the intra-
capsular protoplasm (Fig. 105, x).
The nature of the yellow cells of
Acantharia has been much disputed,
and many observers have regarded
them as an integral part of the organism itself ; this view has
recently been revived by Moroff and Stiasny, who bring forward
evidence to prove that the yellow cells of Acantharia are a
developmental phase of the organism. Still more recently this
view has been extended by Stiasny to the colony-forming
Sphserozoa in the first place, and then to Radiolaria generally.
The difficulty in the way of such an interpretation which arises
from the co-existence, in Thalassicolla and other genera, of yellow
cells in the calymma, with an undivided nucleus in the host-
organism, is met by supposing that in such cases developmental

THE SARCODINA 253

stages of other Radiolarians have penetrated into the calymma,
and live there symbiotically — a supposition which is certainly in
need of further proof before it can be accepted.

3. The most external layer of the body is a protoplasmic envelope
from which the pseudopodia radiate. In Radiolaria, speaking
generally, the pseudopodia are straight, slender, and filamentous,
composed of motile protoplasm entirely (" myxopodia ") ; but hi
Acantharia some of the pseudopodia are, like those of Heliozoa,
axopodia supported by stiff axial rods of organic substance, which
originate deep within the central capsule and pass through the
calymma along the axis of the pseudopodium, bub without reaching
as far as its distal extremity. In some Acantharia (Acanthometrida)
are found also peculiar modifications of the bases of certain of the
pseudopodia in the form of groups of rod-like bodies, " myonemes "
or " myophrisks " (Fig. 105, my.), clustered round each of the
spicules of the skeleton. As their name implies, the myonemes are
contractile elements which, by their contraction or expansion, alter
the hydrostatic balance of the organism, and enable it to rise or
sink in the water. According to Moroff and Stiasny, the myonemes
are formed in the interior of the central capsule, and are derived
from nuclei.

In a certain number of Radiolaria a skeleton is absent altogether.
The Acantharia have a skeleton composed of a substance which
was formerly supposed to be of organic nature, and was termed
acanthin by Haeckel, but which consists of strontium sulphate
according to Biitschli (310). In other Radiolaria the skeleton,
when present, is siliceous. In Acantharia the skeleton invades the
intracapsular region, and consists typically of a system of twenty
spines or spicules radiating from the centre of the body (Fig. 105).
It is a simple and enticing view to regard such a skeleton as origin-
ating phylogenetically from a modification of the axis of pseudo-
podia. Union of outgrowths from radially-directed spicules gives
rise to a lattice-work forming a spherical perforated shell, and as
the animal grows in size several such concentric spheres may be
formed, one within the other, supported by radial bars which
represent the original radiating spicules (Fig. 107). In Radiolaria
other than Acantharia the skeleton is usually entirely extracapsular,
and exhibits a variety of form and structure which cannot be dis-
cussed further here. In some of the Tripylara foreign bodies are
utilized for building up the skeleton, either to form the basis
of spines secreted by the animal or to construct a coat of armour
on the exterior of the body (Borgert).

Life-History. — Reproduction of the Radiolaria is effected in
some instances by binary fission — namely, in those forms in which
a skeleton is lacking or consists of loose spicules. The nucleus

254

THE PROTOZOA

divides by a mitosis remarkable for the vast number of chromo-
somes, of which there may be over a thousand, and the apparent
absence of a centrosome. The more usual method of reproduction,
however, is formation of flagellated swarm-spores by a process of
rapid multiple fission within the central capsule. Two kinds of
swarm-spores are produced, which are known respectively as
" isospores " and " anisospores." The isospores (Fig. 108, A), which
are probably agametes, are all similar in size and appearance, and
frequently contain a crystal in their protoplasm, and are hence
sometimes termed " crystal-spores." The anisospores (Fig. 108,

FIG. 107. — Actinomma asteracanthion : semi-diagrammatic to show the mode of
growth of the skeleton. S.1, S.2, S.3, Three concentric lattice-work shells,
connected by sp., radial bars which are prolonged beyond the outermost shell
as spikes ; N., nucleus ; c.c,, central capsule ; ps., pseudopodia. After Biitschli,
Leuckart and Nitsche's " Zoologische Wandtafeln."

B, C), probably gametes, are of two kinds, smaller microspores and
larger macrospores ; they differ in structure from the isospores, and
lack the characteristic crystal. The swarm-spores vary in struc-
ture in different species, but usually have two flagella. Isospores
and anisospores are formed in different individuals, but it is still a
moot point whether an alternation of generations occurs. Micro -
spores and macrospores may be formed in the same individual in
some species ; in others they are produced by different individuals.
Previous to formation of the swarm-spores the extracapsular region
of the body disintegrates, and the central capsule with its contents

THE SARCODINA 255

sinks to a considerable depth. The swarm-spores are liberated by
the breaking-up of the central capsule. The subsequent develop-
ment of the swarm-spores when set free has not been made out.

While the main features of the reproductive process are as stated above,
the cytological details of the formation of the swarm-spores is still a matter
of dispute. The subject is dealt with in the recent memoirs of Moroff on the
one part, and Hartmann and Hammer, Hartmann (60), and Huth, on the
other. The formation of the anisospores is generally regarded as a breaking-
up of the primary nucleus into chromidia, from a part of which the secondary
nuclei arise, which become those of the swarm-spores (compare Foraminifera).
But according to Hartmann and his adherents, the huge primary nuclei seen
in many Radiolaria are polyenergid nuclei or polykarya (p. 121) containing
a vast number of nuclear energids or monokarya, consisting each of chromatin,
in the form of a twisted thread or so-called " chromosome," and a centriole.
In the gamete-formation a great number of such monokarya are set free
from the primary nucleus to become the gamete-nuclei ; hence the so-called
" generative chromidia " set free from the nucleus are interpreted as secondary
nuclei or monokarya already formed within the primary nucleus. A similar
interpretation is given to the mitosis seen in the process of binary fission ;
the huge mitotic figure, composed of more than a thousand chromosomes,
is interpreted as being in reality made up of as many mitotic figures as there
are chromosomes, since each so-called " chromosome " is regarded as a single

A B

c

FIG. 108. — Swarm-spores of Collozoum inerme. A, Crystal- bearing swarm-spores,
agametes ; B, C, swarm-spores without crystals, gametes ; B, microspores
(microgametes) ; C, macrospores (macrogametes). After Hertwig.

nuclear energid or monokaryon with its own centriole, the whole number of
energids dividing independently but synchronously to form the supposed
mitotic figure.

According to Moroff and Stiasny, in Acanthometra pellucida a process of
multiplication is proceeding continually within the central capsule, until it
is entirely filled up with cells, from which the swarm-spores arise. In this
multiplication, termed by the authors " schizogony," trophic nuclei (" macro-
nuclei") and generative nuclei (" micronuclei ") are formed. The trophic
nuclei are the " yellow cells," which ultimately degenerate. Hence the Acan-
tharia are considered not to be single individuals, but colonies of animals which
have the extracapsular protoplasm, pseudopodia and skeleton in common.

Finally, attention must be drawn to the peculiar organisms found in certain
Radiolaria, and regarded by some authorities as parasitic Flagellata (Silico-
flagellata, Borgert), by others as developmental stages, of the Radiolaria
themselves. See Delage and Herouard (6, p. 371).

The Radiolaria are classified as follows :

SUBORDER I. : PERIPYLARIA SEU SPUMELLARIA. — Central capsule spherical,
perforated by evenly-distributed pores. Extracapsular region well developed.
Skeleton wanting or consisting of scattered spicules or of lattice-work shells,
•developed in the extracapsular region, siliceous.

Legion 1 : Collodaria. — Skeleton wanting or simple in structure ; monozoic
forms. Five families. Examples : Thalassicolla (Fig. 13), Thalassophysa.

Legion 2 : Sphcerellaria. — Skeleton complex, usually with lattice-work
shell ; monozoic, generally small. Four families.

256

THE PROTOZOA

Legion 3 : Sphcerozoa seu Polycyttaria. — Colonial forms consisting of
numerous individuals embedded in a common jelly ; their central capsules
are distinct, but their extracapsular regions anastomose. The colonies reach
a length of several centimetres. Two families. Example : Collozoum.

SUBORDER II. : ACANTHARIA. — Skeleton composed of strontium sulphate,
typically in the form of spicules radiating from the centre of the body, within
the central capsule ; in addition lattice-work shells may be developed. Central
capsule with pores evenly developed, or grouped in areas.

A number of families are recognized, grouped in different ways by different
authorities. Example : Acanihometra (Fig. 105).

FIG. 109. — Eucyrtidium cranioides, Haeckel : entire animal as seen in the living
condition. The central capsule is hidden by the beehive- shaped siliceous
shell within which it is lodged. From Gamble, magnified 150.

SUBORDER III. : MONOPYLARIA SEU NASSELLARIA. — Central capsule monaxon
in form, with the pores aggregated at one pole into a pore-plate, and the
walls of the pores thickened to form a conical structure directed inwards
into the central capsule. Several families. Examples : Lithocircus (Fig. 106),
Eucyrtidium (Fig. 109).

SUBORDER IV. : TRIPYLARIA SEU PHJEODARIA. — Central capsule with a
principal aperture (astropyle) and two accessory apertures (parapyle). A
mass of pigment (phaeodium, p. 252) surrounds the principal aperture.
Divided by Hacker into six legions and numerous families. Example ;
Aulacantha.

Bibliography. — For references see p. 483.

CHAPTER XII

SYSTEMATIC REVIEW OF THE PROTOZOA : THE
MASTIGOPHORA

THE distinctive feature of the class Mastigophora is the possession
of one or more flagella as organs of locomotion and food-capture,
not merely during early stages of development, but in the active
phases of the adult organism also. In other classes, as has been
pointed out in a previous chapter, flagella may be present in the
young stages, but are absent in the adult phases. In the Masti-
gophora a flagellum is a permanent feature of the organization,
though even in this class it may be temporarily lost, either in
active phases, when the animal may become amoeba-like, or in
resting phases, especially in parasitic forms of intracellular habitat.
The Mastigophora are divided into three subclasses, of which
the first, the Flagellata, contains the more typical forms, and con-
stitutes the nucleus, so to speak, of the class ; while the two remain-
ing subclasses, the Dino flagella ta and Cystoflagellata, may be
regarded as specialized offshoots of the primitive flagellate stem.
It is convenient, therefore, to deal with the Flagellata in a general
manner first, and then to describe the special features of the other
two subclasses.

SUBCLASS I. : FLAGELLATA (EUFLAGELLATA).

General Characters. — The members of this group are for the most
part of minute size, and seldom attain to considerable dimensions ;
forms of relatively large size, such as the species of Euglena and
allied genera, are small as compared with the larger species of the
Sarcodina and other classes. As a rule the Flagellata are free-
swimming organisms ; a certain number, however, are sedentary in
habit, attaching themselves to a firm basis, and using their flagella
for food-capture alone. There is a great tendency to colony-
formation in this group. In the process of multiplication by fission
of the ordinary type, separation between the daughter-individuals
may be incomplete, so that they remain connected together, either
by means of a common envelope, house, or gelatinous matrix, or
by organic, protoplasmic union, or in both ways. Repeated fission

257 17

258 THE PROTOZOA

of this kind leads to the formation of a colony, which may attain
to dimensions relatively large, though composed of individuals
of minute size. The colony may be free-swimming or fixed, and
in the latter case is frequently arborescent in form. In many cases
the colonies of Flagellata show a differentiation of the constituent
individuals into vegetative and generative individuals — the former
not capable of reproduction, but purely trophic in function ; the
latter destined to be set free, and to produce new colonies, with or
without going through a process of syngamy.

Bionomics. — In their modes of life the Flagellata exhibit all the
four types described in Chapter II. (p. 13), different forms being
holozoic, holophytic, saprophytic, or parasitic ; and one and the
same form may live in different ways during different periods of its
life-history, according to circumstances.

The parasitic flagellates have attracted a great deal of attention of recent
years, on account of their importance in causing disease in man and animals.
Ectozoic parasites may occur in aquatic forms, as for example Costia, para-
sitic on the skin of fishes. The entozoic forms are parasitic for the most
part in the digestive tract, or in the blood and lymph of their hosts. Parasitic
flagellates are found in the intestines of practically all classes of the Metazoa,
and especially in arthropods and vertebrates ; those parasitic in blood and
lymph are found especially in vertebrates, and constitute an important
group commonly termed as a whole the Hsemoflagellates, to which a special
chapter will be devoted. From forms which were probably parasitic originally
in the blood have arisen secondarily forms parasitic in cells which in their
intracellular phase lose their flagellum entirely (Leishmania).

Many of the intestinal flagellates, especially in vertebrates, are probably
not true parasites at all, but for the most part scavengers. In any case their
pathogenic role appears to be very limited ; but in some cases a pathological
condition of the host may be combined in a suspicious manner with great
numbers of the parasites (compare Bohne and Prowazek, Noc). It is worthy
of note that in some cases an intestinal parasite may pass from the intestine
into the blood or lymph under pathological conditions of the host. This
condition seems to have been noticed first by Danilewsky, who described
cases of frogs and tortoises which had been kept long in captivity and were
in bad condition, thin, and with cedematous swellings in the muscles and
transudation of lymph into the peritoneal cavity ; in such animals there
were found in the blood and lymph, especially in the oedemata and trans-
udations, abundant flagellates of the genus Hexamitus ( =0ctomitus, Fig. 116),
of a species which in normal, healthy animals is found only in the intestine.
A number of similar cases have been recorded by Plimmer (383, and Presi-
dential Address to the Royal Microscopical Society, 1912), who found both
Octomitus and Trichomonas in the blood of various batrachia and reptiles.
The conditions under which these intestinal parasites pass into the blood
appears to be strictly comparable to those under which the Leydenia-iorm
of Chlamydophrys passes into the ascitic fluid (p. 237). Whether in such
cases the migration of the parasite is the cause of the diseased state of the
host, or whether, as seems more likely, the abnormal condition of the host
gives the parasite an opportunity of spreading into fresh pastures, must
remain for the present an open question ; but, according to Plimmer, the
presence of intestinal flagellates in the blood-circulation is associated with
definite and recognizable lesions of the intestinal wall. In any case, the
fact that intestinal flagellates can pass into the blood is a point which is
probably of phylogenetic as well as of practical importance (p. 322).

THE MASTIGOPHORA 259

Structure. — The body-form is of three principal types : (1) An
envelope or tough cortex may be entirely absent, and the body is
then amoeboid, as in the Rhizomastigina (Figs. 38, 40) ; (2) a thin
cuticle may be present, insufficiently rigid to inhibit changes of
body-form due to contractility of the living substance (Fig. 15) ;
(3) a thicker cuticle necessitates a constant body-form, which is
either rigid and unalterable or sinuous and permitting movements
of flexion and torsion. In the second type are comprised forms
termed commonly " metabolic," on account of the changes of form
they exhibit ; contractions of the superficial layer of the body pass,
as it were, in waves from the anterior to the posterior end of the
body, in a manner similar to the peristaltic contractions of the
intestine, producing rhythmic form-changes in the body.

In species in which the cuticle is thin or absent, a constant body-
form may nevertheless be maintained by internal form-giving
organs, such as the axostyle of Trichomonas (Fig. 5), Lophomonas
(Fig. 45), etc. True internal skeletons, however, do not occur. An
external shell or house may be present, enclosing the whole body.

The protoplasmic body shows, in the amoeboid forms such as
the Rhizomastigina (p. 268), distinct ectoplasm and endoplasm.
But as a general rule the thin ectoplasm is converted into a firm
cuticle, or periplast, enclosing the body and containing contractile
elements — myonemes. Hence the ectoplasm appears at first sight
to be absent, and the protoplasmic body to consist of endoplasm
alone. In larger forms the myonemes can be made visible by
suitable treatment (Fig. 28), but as a general rule in such minute
organisms the existence of myonemes or other contractile mechan-
isms can only be inferred from the movements of contractility or
flexibility which the body exhibits.

The flagella may perform various functions in different cases ;
they may serve as organs of locomotion and of food-capture, as
organs of temporary attachment, and as tactile organs. As stated
above (p. 52), they may be distinguished by their relation to the
progression of the organism, as tractella, anterior, and pulsella,
posterior in movement. The flagella vary in number and in arrange-
ment in different species, and for the different types of the flagellar
apparatus a number of technical terms are in use : monomastigote,
with a single flagellum (Fig. 38) ; isomastigote, with two or four
flagella of equal length (Fig. 43) ; paramastigote, with one long
principal flagellum and a short accessory flagellum (Fig. 15) ;
heteromastigote, with one or more anterior flagella directed forwards,
and a " trailing flagellum " directed backwards (Figs. 5, 25) ;
polymastigote, with a tuft of flagella (Fig. 45) ; and holomastigote,
with numerous flagella scattered evenly over the body (Fig. 113).
Of these various types of arrangement, the heteromastigote con-

260

THE PROTOZOA

dition, with a backwardly-directed trailing flagellum (" Schlepp-
geissel"), deserves special attention, since by attachment of the
trailing flagellum to the body an undulating membrane (p. 56)
may arise ; and that it has actually so arisen in some cases is
indicated by the existence of pairs of similar forms, in which a

FIG. 110. — Codonosiga botrytis. A, Young specimens
attached singly to the stalk of a Vorticella ; B, colony
of six individuals on a common stalk ; C, stalked
individual which has recently divided into two, pro-
ducing a dichotomous division of the stalk, c.v.,
Contractile vacuole. After Stein.

trailing flagellum, free from the body, in the one form is represented
by the marginal flagellum of an undulating membrane in the
other — as, for example, Trichomastix and Trichomonas (Fig. 5) ,
Prowazekia (Fig. 141), and Trypanoplasma (Fig. 36).

In one group of flagellates — hence known as the Choanoflagellata

THE MASTIGOPHORA 261

or Craspedomonads (Fig. 110) — a peculiar structure occurs, known
as the " collar," a delicate protoplasmic tube or funnel which
arises along a circular base-line of which the insertion of the flagellum
is the centre, and so forms a cup, sleeve, or collar-like structure
surrounding the flagellum for about a third or a half of its length.
It is stated, both for Choano flagellates and for the very similar
collar-cells of sponges, that the collar is a membrane folded in a
spiral manner, its insertion running along the body and round the
base of the flagellum ; but the spiral structure is not easy to make
out. The Choano flagellates are sedentary forms which, if set free
temporarily from their attachment, swim with the flagellum
directed backwards, doubtless the mechanical result of the presence
of the collar. The function of the collar is probably connected
with the capture and absorption of food-particles wafted towards
the body by the flagellum. The collar is retractile, but is not capable
of active movements such as are seen in an undulating membrane.

The organs of nutrition must be considered in connection with
the four modes of life already mentioned.

(a) In holozoic forms the organism captures and ingests other
organisms of various kinds. In some forms the ingestion of food-
particles may take place at any point on the body-surface ; examples
of this are the amoeboid forms, such as Mastigamceba, which capture
their food by means of their pseudopodia, like an amoeba ; the holo-
mastigote genus Multicilia (Fig. 113) ; the parasitic Lophomonas
(Fig. 45), and possibly others. But in most cases food-particles
are ingested at the base of the flagellum, the spot towards which
they are propelled by the activity of the flagellum itself. There
may, however, be no special aperture for food-ingestion, particles
which impinge upon the soft protoplasmic body being simply
absorbed directly with formation of a food-vacuole. With a more
advanced type of organization, a special aperture or cytostome for
the ingestion of food-particles is found at the base of the flagellum.
The cytostome may be a simple aperture leading through the cuticle
directly, or by means of a funnel-shaped depression, into the proto-
plasmic body, or it may, in more highly organized forms, lead into
a special tube, termed an " oesophagus " or " cytopharynx," which
receives the evacuations of the contractile vacuoles, and serves for
excretion as well as ingestion (Fig. 84). In any case the oesophagus
ends blindly in the fluid endoplasm. There is no special anal aper-
ture for expulsion of faecal material, which is expelled at any point
of the body-surface in primitive forms, or through the oesophagus
and cytostome in those more highly organized.

(6) In holophytic forms the organs of nutrition are those of the
plant-cell (p. 188) — namely, chromatophores, or corpuscles contain-
ing chlorophyll or allied pigments ; pyrenoids, small glistening bodies

262 THE PROTOZOA

embedded in the chromatophores, the centres of the formation of
amyloid substances ; and grains of amyloid nature formed by the
constructive metabolism of the organism. It is also common to
find in the holophytic flagellates a peculiar red spot, or stigma,
placed near the anterior end of the body, and probably sensitive
to light (p. 205).

In general, two types of holophytic flagellates can be recognized :
first, forms in which, in addition to the organs already mentioned,
those pertaining to the holozoic mode of nutrition are also present ;
secondly, those possessing only the holophytic apparatus. The
first type may be regarded as more primitive forms in which the
holophytic habit of life has not become so engrained as to exclude
any other mode of nutrition ; but a change is still possible, and the
organism can combine or vary the holophytic with the holozoic
or saprophytic method. In the second type the organism has be-
come plant-like, to the complete exclusion of other methods of
nutrition ; the body is generally enclosed completely in a firm cellu-
lose envelope, allowing diffusion of liquids and gases, but without
apertures through which foreign bodies can pass into the interior.
Such forms, if they lose their flagellum in the adult state, are classed
as unicellular Algse, and the young flagellated individuals are termed
" zoospores." The transition from holophytic flagellates to plants
is a gradual one, and the border-line is simply fixed by the characters
of the " adult," and is therefore as arbitrary as that between Sar-
codina and Mastigophora discussed in a previous chapter.

(c) In saprophytic and parasitic forms no special organs of nutri-
tion are present, since the food is absorbed in a fluid condition from
the surrounding medium.

Contractile vacuoles are commonly present in those flagellates
which inhabit fresh water. In the more primitive forms the
vacuoles empty themselves direct to the exterior. In more highly
organized types the vacuoles open into the oesophagus. In
Euglena the two contractile vacuoles open into a reservoir-vacuole,
which, according to Wager (213), is in open communication with
the oesophagus (Fig. 84).

The nuclear apparatus consists, as a rule, of a single nucleus of
vesicular type, with a distinct karyosome. Chromidia are generally
absent, but are found in a few cases (Rhizomastigina).

The relations of the nuclear apparatus and the flagella have been dis cussed
above, and are briefly as follows :

1. There is a single nucleus with a single centriole, which functions at the
same time as centrosome and blepharoplast. Then either (a) the centriole
is within, or connected intimately with, the nucleus, in which case the fla-
gellum appears to arise directly from the nucleus, as in Mastigina (Fig. 38) ; or
(6) the centriole, and the flagellum it gives off, are quite independent of the
nucleus, as in Mastigdla (Fig. 40).

THE MASTIGOPHORA 263

2. There is a single nucleus with its centrosome, and in addition one or
more blepharoplasts in relation to the flagellar apparatus. Then (a) at
division the old blepharoplasts and flagella are lost, and new blepharoplasts
arise during or after nuclear division from the centrosomes ; or (6) the blepharo-
plasts and flagella persist, and the former divide independently to form
daughter- blepharoplasts from which new flagella arise (Fig. 43).

3. In a certain number of Flagellata, grouped provisionally as Haemo-
flagellates or Binucleata (see next chapter), two nuclei, each probably possess-
ing its own centrosome, are present : a principal or trophic nucleus and an
accessory or kinetic nucleus.

In Type 2 the blepharoplast attains to a greater or less degree of indepen-
dence of the centrosome, and divides independently of it for many generations
of ordinary vegetative reproduction by fission. But there are probably in
all cases periods in the life-cycle when the entire nuclear apparatus is reduced
to a single nucleus and centriole, from which the condition in the adult,
whatever it may be, arises. For the so-called fourth type of Hartmann and
Chagas (62), see below (p. 273).

Reproduction and Life-Cycle. — The commonest method of repro-
duction is simple or binary fission in the free state. The products
of the fission are of equal size, and the division of the body is in-
variably longitudinal (Senn, 358) — that is to say, along an axis
continuing the direction of the principal flagellum or flagella. In
addition to this, the typical method of reproduction, other types of
division occur. Multiple fission in the free active condition is
known in some parasitic forms, such as Trypanosoma lewisi and
Lophomonas blattarum (Janicki, 70). On the other hand, fission
may sometimes take place in a resting, non-flagellated condition, or
within a cyst ; in the first case it is frequently, in the second
perhaps always, of a multiple type.

The occurrence of syngamy in the life-cycle is a point which
has been disputed, probably owing to the fact that in forms of
simple structure it takes place only at long intervals in the life-
cycle, or under special conditions. Moreover, the longitudinal
division prevalent in this group makes it practically very difficult
to decide, except by continuous observation, whether two conjoined
flagellates are individuals about to fuse in syngamy or to separate
after fission. In the colonial Phytomonadina, where highly-differ-
entiated gametes are found, the occurrence of syngamy has long
been known, but the existence of sexual processes in other flagel-
lates has been doubted by high authorities. In recent years, how-
ever, it has been observed in a number of forms, and there can be
no doubt of the existence of sexual processes in flagellates generally.
A summary of recent observations, with full references, is given by
Dobell (335, pp. 109-111). The available data are as yet insufficient
to make it possible to give a connected account of syngamic pro-
cesses in Flagellata generally, and only a few typical cases can be
dealt with here.

A simple type of syngamy has been described in Copromonas

264

THE PROTOZOA

subtilis (Fig. Ill) by Dobell (335). In this species the two gametes
appear perfectly similar to each other, and are not, in fact, distin-
guishable in any way from ordinary individuals of the species. Two
such individuals come together and unite by their anterior or flagellar

extremities. In one
gamete the flagellum is
lost, and the couple swims
about by means of the re-
maining one ; this is the
only difference between
the two gametes which
could be interpreted as
one of sex. While fusion
of the bodies is still
incomplete, the nucleus
of each gamete divides
by a simple type of
promitosis (p. 109). One
of each pair of sister-
nuclei thus produced is
a reduction - nucleus,
which degenerates ; the
other persists. The per-
sistent nucleus of each
gamete then divides a
second time, but into
two very unequal halves ;
the smaller nucleus in
each case degenerates as
a reduction -nucleus,
while the larger persists
as the pronucleus. The
bodies of the gametes are
now completely fused,
and the fusion of the
pronuclei follows. The
zygote may become en-
cysted at once, or may
continue to live a free
life. In the first

FIG. 111. — Life-cycle of Copromonas subtilis. A,
Ordinary adult form ; B, C, D, " vegetative "
reproduction by binary fission ; E — J, stages of
reduction and syngamy : F, G, H, reduction ;
I, J, fusion of the two pronuclei ; the zygote
(/) may develop into an ordinary free-swimming
individual, or (J) may retract its flagellum and
become encysted ; K, cyst ; L, liberation of an
adult form from the cyst. After Dobell (335).

case

the fusion of the pro-
nuclei takes place within the cyst, from which it is ultimately set
free as an ordinary individual which feeds and multiplies vegeta-
tively. In the second case the zygote becomes an ordinary free
individual at once, the interlude of encystment being omitted.

THE MASTIGOPHORA 265

The syngamy of Copromonas is thus seen to be a case of perfect
isogamy, and is probably to be regarded as representing a very
primitive type, whence the more complex sexual processes of other
Flagellata have been evolved — (1) by greater specialization and
differentiation of the gametes in their relation to other phases of
the life-cycle (gamete-formation) and to one another (sexual differ-
entiation) ; (2) by correlation of the sexual phases with definite
crises, to which they become restricted, in the general life-cycle.

In the Rhizomastigina sexual processes occur of a type resembling those
found in the Sarcodina to such an extent as to indicate that the affinities of
this group is rather closer to some of the primitive Rhizopods than to typical
Flagellata. The life-cycle (Fig. 112) has been worked out in full detail in
Mastigdla vitrea by Goldschmidt (41). Vegetative reproduction in the free
state is by binary fission of the ordinary type, and occurs when food is abun-
dant ; a falling-off in the supply of nutriment leads to gamete-formation and
syngamy. In the earliest stages of the sexual generation a differentiation
of the individuals into macrogametocytes and microgametocytes is to be
observed, though externally they are similar to ordinary individuals and
continue their vegetative life during the early stages of gamete-formation.
In the macrogametocyte, first a quantity of nucleolar substance, and then of
chromatin, is set free from the nucleus ; these two substances unite to form
a chromidial mass from which a number of secondary nuclei are formed.
The secondary nuclei become scattered through the cytoplasm, and each
becomes surrounded by a protoplasmic body. The small cell thus formed
is a macrogamete, which goes through reducing divisions. The still active
macrogametocyte, which has its cytoplasm crammed with the small gametes,
now becomes encysted. Within the cyst the gametes acquire fiagella and
become motile. At this stage the original nucleus of the gametocyte breaks
up and disappears rather suddenly. Finally the cyst -wall is ruptured and the
flagellated gametes escape.

The formation of the microgametes takes place in a manner essentially
similar to that already described for the macrogametos, but with a few
differences in detail. The microgametocytes become encysted at the very
beginning of the process ; then formation of chromidia begins, and as soon
as it is completed the primary nucleus degenerates ; the microgametes have
no flagella, and are shot out of the cyst when it bursts.

The free macrogametes measure on the average about 3*6 p diameter,
and have a flagellum 15 to 18 p. in length ; the microgametes are 2'8 /* in
diameter, and have no flagellum. A macrogamete seeks out a microgamete
and fuses with it, cytoplasm and nucleus. The zygote retains the flagellum
of the macrogamete, and becomes a small, monad-like individual which
multiplies by fission as such. After several generations the monads cease
to multiply, and each grows up into an adult Mastigdla. A development
similar in the main is described by Goldsohmidt for Mastigina, but some of
the phases escaped his observation.

Comparing the sexual cycle of Mastigella (Fig. 112) with that of
Copromonas (Fig. Ill), the chief difference is seen to be that in
the former an ordinary individual does not become a gamete directly
but a gametocyte, which by a process of multiple fission gives rise
to a generation of minute swarm-spores, the gametes. In the two
sexes a slight differentiation of the gametes is seen. Further, in the
life-cycle of Mastigella considered as a whole, there are two forms
of individuals, each capable of multiplying vegetatively for many

266

THE PROTOZOA

generations — namely, the monad form, product of syngamy, and
the adult, mastigamoeba-form, which ultimately produces the
monad-like gametes. Hence the life-cycle in such a type is an
alternation of generations (metagenesis), which, as in so many other

FIG. 112. — Life-cycle of Mastigdla vitrea, diagrammatic. 1, 2, and 3, Different
forms assumed by the adult " vegetative " type of individual ; 3a, 3&, repro-
duction by binary fission; 4 — 10, gamete - formation ; a (in each case),
microgamete-formation, &, macrogamete-formation ; in the former the gamont
becomes encysted, and the principal nucleus degenerates early in the process ;
in the latter the gamont remains motile and the principal nucleus persists
to the last : 4 — 6, extrusion of chromidia from the nucleus and formation
of secondary nuclei ; 7, 8, formation of the gametes round the secondary
nuclei ; 9, extrusion of the gametes ; 10a, the small, non-flagellated micro-
gametes ; 106, the larger, flagellated macrogametes ; 11, copulation of the
gametes ; 12, 12a, 12&, multiplication by binary fission of the monad-like
zygote ; 13, 14, growth of the monad-form, after a period of multiplication,
into the adult mastigamoeba-form. After Goldschmidt (41).

cases in the animal kingdom, appears to have come about by mul-
tiplicative processes taking place in a larval type, phylogenetically
older — namely, the monad form, the only form of individual that

THE MASTIGOPHORA 267

occurs in the life-cycle of Copromonas. In Mastigina, on the other
hand, the monad form developed from the zygote apparently does
not multiply by fission, but develops directly into the adult form —
perhaps a more primitive state of affairs.

A very instructive series is furnished by the colony-forming
Phytomonads of the family Volvocidce. At one end of the series
are primitive types, such as Stephanosphcera, where the colony is
composed of eight monad individuals, all alike, which may be
agamonts in one colony or gamonts in another. Each agamont
multiplies by fission to form eight small cells, which remain con-
nected together and grow into full-sized monads, thus giving rise
directly to new colonies. In the gamont-colonies each gamont
(gametocyte) gives rise by multiple fission to a large number of
minute biflagellate swarm-spores, the gametes, which are set free and
copulate. The syngamy is perfectly isogamous. The zygote grows in
size, and finally multiplies to form the eight monads of a new colony.

At the other end of the series are the species of the genus Volvox,
in which the colony is composed of a great number of individuals,
which may be of three kinds, not necessarily all present in the same
colony : (1) The ordinary " somatic " monads, locomotor and
trophic in function, which do not reproduce themselves in any way ;
(2) agamonts, so-called " parthenogonidia," which multiply by
fission to form daughter-colonies ; (3) gamonts or gametocytes,
which are sexually differentiated as " microgonidia " and " macro-
gonidia." The microgonidia produce by multiple fission a swarm of
small biflagellate microgametes, comparable to the gametes of
Stephanosphcera. In the macrogonidia, on the other hand, multi-
plicative processes are in abeyance, and each becomes a single, ovum-
like macrogamete, which is fertilized by the relatively minute
microgamete. Thus, the syngamy in Volvox is anisogamous to
the highest degree ; and, as in other cases among Protozoa, this
condition appears to have arisen from a primitive isogamy in which,
in both sexes, the gametocytes sporulated to produce a swarm of
minute gametes, by the process of sporulation becoming altogether
suppressed in one sex — namely, the female — while retained in its
primitive form in the other. The colonies of Volvox, with their
differentiation of individuals, exhibit a condition transitional to
that of the Metazoa. The trophic, non-reproductive individuals,
taken as a whole, may be compared to the Metazoan soma, the repro-
ductive individuals to the germen. In Pleodorina calif ornica dis-
tinct male, female, or parthenogenetic colonies occur (Chatton), as
is the case in some species of Volvox.

Classification. — The Flagellata are classified in different ways by different
authors, and in the present state of our knowledge of the group no system
can be regarded as in any way final. As in other groups of Protozoa, there

268 THE PROTOZOA

are a certain number of well-defined orders and families characterized by
the possession in common of certain features of organization which leave
no doubt as to their taxonomic homogeneity. On the other hand, there are
a large number of primitive forms whose characteristics are mainly of a
negative order, and of which the affinities are in consequence vague and
uncertain, the systematic position debatable. There is, moreover, frequently
an element of uncertainty, in the case of many forms, as to whether they
represent truly specific adult forms, or merely developmental stages of some
other species of the Flagellata or Sarcodina. Finally there are a certain
number of species and genera concerning which it is still debated whether
they should be assigned to the Mastigophora or some other class of Protozoa.

Hartmann and Chagas (62) have proposed to utilize the relations of the
flagellar to the nuclear apparatus for systematic classification of the Flagellata,
as suggested also by Prowazek (354). But, apart from the fact that these
relations have as yet been investigated in very few flagellates, and that in
such minute objects the details are very difficult to make out and liable to
be a subject of dispute, it may be doubted whether these points of structure
are sufficiently constant to be of classificatory value in this subclass, since
they appear to vary considerably in allied forms. Thus in Copromonas
subtilis, according to Dobell (335), the blepharoplast persists through division-
phases, and divides independently of the nucleus ; but in C. major, according
to Berliner, the old blepharoplast and flagellum are lost at each division,
and a new blepharoplast, from which the new flagellum grows out, is formed
by division of the nuclear centriole in each daughter-individual. Again, the
third type of flagellar insertion (p. 263) is found in the Trypanosomidce, allied
to the Cercomonadidce, and in the trypanoplasms, which belong to the family
Bodonidce, as shown in the next chapter. Classification by these characters
is, therefore, at least premature, if not fallacious. Compare also Senn (358).

The classification adopted here is in the main that of Doflein (7), with
certain modifications. For convenience a number of forms are put together
in the Pantastomina, without, however, claiming that this order is anything
more than a cataloguer's makeshift for disposing of a number of forms of
dubious position and uncertain affinities.

ORDER I. : PANTASTOMINA. — Holozoic, with no definite mouth-opening ;
food-particles ingested at any point on the surface of the body.

Suborder 1 : Khizomastigina. — Body amoeboid ; food captured and ingested
by means of pseudopodia.

Several genera, only known as yet from fresh water, are referred to this
very interesting group ; such are Mastigamwba, F. E. Schulze, Mastigina,
Frenzel (Fig. 38), and Mastigdla. Frenzel (Fig. 40), distinguished from one
another by the nature of their amoeboid movement and the characters of their
pseudopodia. In appearance the species resemble amoebae which possess a
long and well- developed flagellum, or in Dimastigamceba two, in Trimastig-
amoeba (Whitmore, 280) three flagella. Locomotion and food-capture are
carried on for the most part as in an amoeba, and the flagellum appears to
function chiefly as a tactile organ in the adult mastigamceba-phase ; in the
young monad-phase, on the other hand, the flagellum is the sole organ of
locomotion and food-capture, as in an ordinary flagellate. The relation of
the flagellum to the nucleus is of Type 1 described above (p. 263), a single
centriole which functions both as centrosome and blepharoplast ; in Mastigina
and Mastigamceba the flagellum arises from the nucleus (Type la) ; in Masti-
gdla the origin of the flagellum is distinct from the nucleus (Type 16). The
life- cycle of Mastigdla is described above (p. 265). In many points, especially
in the formation of secondary gamete-nuclei from chromidia, the develop-
ment resembles more that of the Sarcodina than that of the Flagellata, and
by many authorities the affinities of the Rhizomastigina are considered to be
rather with the first of these two classes. The mastigamcebee certainly link
the true flagellates with the Proteomyxa and Mycetozoa ; and if the flagellum
were lost in the adult phase, they would be classed in the Sarcodina without
hesitation.

FIG. 113. — A, Mvlticilia lacustris, after Lauterborn. ft., Flagella, one of which
is curled up into a loop ; ps., pseudopodium-like process ; N., one of the
nuclei (the others are hidden by the ingested food-masses) ; 0,, ingested
Chlamydomonads ; c., chlorophyll- bodies, the remains of other Chlamydo
monads in process of digestion. B, Multicilia palustris, after Penard. N., The
single central nucleus.

270 THE PROTOZOA

Suborder 2: Holomastigina. — With numerous flagella radiating from a
spherical or approximately spherical body.

This suborder contains the single genus Multicilia, Cienkowski, to which
several species, some fresh-water, some marine, have been referred. The
number of flagella varies in different species, and their precise relation
to the nuclear apparatus remains to be made out. M . lacustris, Lauterborn
(Fig. 113, A), is multinucleate ; M. palustris, Penard (Fig. 113, B), has a single
nucleus. The body is not covered by a cuticle, and may throw out pseudo-
podia, or even become amoeboid (Lauterborn). Nothing is known of the
life-cycle, but in M. lacustris Lauterborn observed reproduction by simple
fission (plasmotomy ?). In the present state of our knowledge adequate data
are lacking for discussion of the affinities of this genus. Doflein (7) regards
it as a form lying at the root of the Infusorian stem, and derives the most
primitive Ciliata from a form similar to Multicilia, in which the numerous
flagella become specialized in structure and movement to give rise to an even
coat of cilia ; Penard (302), on the other hand, considers Multicilia allied to
the Heliozoa (p. 249). It is clear that the genus is one which would repay
further study.

ORDER II. : PROTOMONADINA.— Flagellates for the most part of small or
minute size ; with a single flagellum ; or with a principal and one or two acces-
sory flagella ; or with two flagella, one directed anteriorly, the other pos-
teriorly as a trailing flagellum. Nutrition holozoic, saprophytic, or parasitic ;
in the first case the food- par tides are ingested at the base of the flagellum,
where a definite mouth-opening may be present or absent, but without a
distinct oesophagus in any case. The contractile vacuole is generally single,
if present, and empties itself direct to the exterior.

This order comprises a vast assemblage of genera and species, subdivided
by Doflein into eight families, one of which, the Trypanosomidce, including
the important parasitic genus Trypanosoma, is discussed in detail in the next
chapter. The cuticle is generally thin, and the body is often capable of
amoeboid or metabolic movements ; if amoeboid, however, the flagellum is
the organ of locomotion, so long as it is present, and not the pseudopodia.
The relations of the flagellum to the nuclear apparatus are, in general, of the
second type (p. 263), according to Hartmann and Chagas (62) — that is to say,
with distinct centrosome and blepharoplast ; but it is extremely probable
that in the simpler forms Type 1 occurs also (compare Alexeieff, 327), and in
the Trypanosomidce the distinctive feature is the possession of Type 3, with
trophonucleus and kinetonucleus, as also in some of the Bodonidce (Prowa-
zekia). The life-cycle of the free-living forms is probably in general of a
simple type, similar to that described above in Copromonas (Fig. Ill) ; but
observations on the sexual processes are at present very scanty.

For a detailed description of the forms included in this order the reader
must be referred to the larger treatises, especially Butschli (2) and Senn (320) ;
it must suffice here to mention some of the more typical forms. Cercomonas,
type of the family Cercomonadidce (Fig. 114). has a single flagellum ; the hinder
end is frequently drawn out into a long tail-like process, and is capable of
change of form. (Ecomonas (Oikomonas) differs in having the body rounded.

Monas, type of the family Monadidce, has a principal flagellum and one
or two accessory flagella. Cladomonas and Spongomonas (Figs. 41, 42) form
arborescent colonies ; the constituent monads have two flagella of equal
size, both directed forwards. Alexeieff (327) considers that the Monadidce
should be placed in the suborder Chrysomonadina (see below).

Bodo (Fig. 115), type of the family Bodonidce, has two flagella, one directed
forwards, the other backwards as a trailing flagellum ; the species of this
genus are free -swimming and do not form colonies ; they occur both free-
living and parasitic, for the most part in the digestive tracts of various animals.
Bodo lacertce, from the cloaca of Lacerta spp., has been studied by Prowazek
(354), who has described a process of autogamy, but doubt has been cast upon
his observations by Dobsll (335). Note also the oocurrenoj of Bodo-liko
forms in the developonnb of Orgptodiffl*yix (p, 230, supra). The flagellate

THE MASTIGOPHORA

271

recently described by Wenyon (361) from a culture of human faeces, and
referred by him to the genus Cercomonas, would appear rather to belong to
the genus Bodo. To the family Bodonidce must be referred also the genera
Prowazekia and Trypanoplasma, dealt with in greater detail in the next chapter.
Hdcomastix, Senn (358), is to
be referred to the Bodonidce or
made the type of a distinct
family ; its two flagella of
unequal length are both
directed backwards in move-
ment.

Finally, mention must be
made of the group of flagel-
lates characterized by the pos-
session of a collar (see p. 261,
supra], and hence commonly
known as " choanoflagel-
lates1' or " craspedomonads."
They are sedentary forms,
attached by the end of the
body opposite to the flagellum,
and may remain single, but
more usually form colonies
often of considerable extent
(Fig. 110). The flagellum is
used mainly for food-capture,
in which the collar also pro-
bably plays an important FIJ. 114. — Cercomonas crassicauda, Dujardin,
part ; but an individual may showing amosboid changes of form. After
become detached from its Stein,
support, and swim freely, the

flagellum being then directed backwards. The systematic position of the
choanoflagellates has been differently estimated by different authors ; by some
they have been ranked as a primary subdivision of the Flagellata, which are
then divided as a whole into Choanoflagellata and Lissoflagellata, the second
of these divisions being used to include all other flagellates. Since, however,
the choanoflagellates scarcely differ from ordinary monads
except in the possession of the characteristic collar, a
specialization of the food- capturing function related to
a sedentary life, they are now generally ranked as a
family of the Protomonadina, the Choanoflagellidce.

ORDER III. : POLYMASTIGINA. — Flagella from three to
eight in number, usually all more or less equal in size ;
in other points of structure similar to the last -mentioned
order. Two families, which are sharply marked off from
one another, are referred to this order.

1. Tetramitidce, with three or more flagella, which all
arise at the anterior end close together. The flagella
may all be directed forwards, or one of them may be
turned backwards as a trailing flagellum ; in the latter
case the trailing flagellum may or may not be united to
the body by an undulating membrane.

The species referred to this family are for the most
part parasitic. Endoparasitic forms of common occur-
rence, especially in the digestive tracts of vertebrates,
are Trichomastix, with three anterior flagella and a free
trailing flagellum, and Trichomonas (Fig. 5), with the same number and arrange-
ment of the flagella, but having the trailing flagellum united to the body by an
undulating membrane. These two forms occur frequently in the same host,
and are pernaps to be interpreted as two developmental phases of the same

FIG. 115.— A, Bode
saltans.Ehren-
berg. B, Bodo
gracilis, Stein.
After Stein.

272

THE PROTOZOA

organism rather than as distinct generic types. Trichomonas hominis is
entozoic in the human intestine, T. vaginalis in the human vagina ; they
appear to be harmless scavengers rather than parasites. The encystment
of Trichomonas has been the subject of some controversy. According to
Alexeieff (326), the supposed cysts of Trichomonas described by various
authors are in reality independent vegetable organisms, of the nature

of yeasts. In some species of Trichomonas the
anterior flagella are four in number (Alexeieff,
323) ; for such forms Parisi (A.P.K., xix.,
p. 232) has founded a subgenus Tetratricho-
monas. The genus Macrostoma, according to
Wenyon (362), differs from Trichomonas in
having the undulating membrane wedged in
a deep groove ; M . mesnili occurs in the
human intestine. According to Alexeieff (324),
Macrostoma is a synonym of Tetramitus. Mono-
cercomonas, including a number of common
intestinal parasites, has four anterior flagella
of equal length, or two longer, two shorter
(Alexeieff, 325).

Costia necatrix, also referred to this family,
is ectoparasitic on the skin of fishes. According
to Moroff, it has four flagella in two pairs, two
larger and two smaller, all of which serve for
locomotion ; but the larger pair are used also
for fixation, and the smaller pair for wafting
into the mouth the food-particles, which consist
chiefly of dead epithelial cells torn away from
the epidermis (see also Neresheimer).

2. Octomitidce.* — With six or eight flagella,
arranged in pairs ; the body is bilaterally
symmetrical in structure. Entozoic forms, for
the most part of intestinal habitat.

The remarkable bilateral symmetry of the
species of this family is not merely an external
characteristic of the body, but affects the
internal structure as well, and the entire
nuclear structure is doubled, with right and left
halves. Octomitus (synonym, Hexamitus ; see
Dobell, 236), with four pairs of flagella (Fig. 116),
includes a number of entozoic species — e.g.,
0. intestinalis, from the cloaca of the frog and
other animals. Lamblia intestinalis (synonym,
Megastoma entericum, Fig. 117) is a common
inhabitant of the human intestine. It becomes
encysted, and is probably disseminated in this
form. Within the cyst it divides into two
(Rodenwaldt). L. sanguinis, described by
Gonder (A.P.K., xxi., p. 209) from the blood
of a falcon, is probably an intestinal parasite
gone astray (vide p. 258).
The order Polymastigina differs little from the Protomonadina except in
the complication of the flagellar apparatus, correlated probably with the
entozoic habit. Hartmann and Chagas propose to merge the Polymastigina

* Doflein terms this family the PclymastigidcB, but the name is clearly in-
admissible, since the genus Polymastix belongs to the preceding family, and is
closely allied to Trichomonas, but has six anterior flagella and no trailing
flagellum (compare Alexeieff, 325).

FIG. 116. — Octomitus dujar-
dini. W.1, Anterior blep-
haroplast, from which the
first and second flagella of
that side of the body arise ;
bl.2, second blepharoplast,
giving off the flagellum of
the third pair ; .$"., left-hand
nucleus ; ax., left axostyle ;
bl.3, third blepharoplast, at
the extremity of the axo-
style, giving off one of the
flagella of the fourth pair.
All the structures indicated
are paired, and the letters
indicate the member of each
ir on the left side of ths
y. After Dobell (236).

par
bod.

THE MASTIGOPHORA

273

in the Protoinonadina, and then to divide the order into two suborders ; the
first, entitled the Monozoa, would include the Protomonadina as constituted
above, with the exception of the Trypanosomidce (" Binucleata "), and with
the addition of the Tetramitidce. The second suborder, Diplozoa, would in-
clude only the Octomitidce. This arrangement certainly seems more natural
than that which is usually adopted, so far as the Tetramitidce and Octomitidce
are concerned.

ORDER IV. : EUGLENOIDINA. — Larger forms, with mouth-aperture and
oesophagus ; with a complex vacuole-system opening into the oesophagus ;
often with holophytic apparatus, chromatophores, stigma, etc.

This order represents, so far as structural complication of the individual
is concerned, the highest type of organization among Flagellata. The body
may be metabolic, or of definite contours, with thick cuticle. The free-living

FIG. 117. — Lamblia intestinalis. A, Ventral view ; B, side view. N., One of the
two nuclei ; ax., axostyles ; fl.1, fl.2, fl.3, fl.*, the four pairs of flagella ; s., sucker-
like depressed area on the ventral surface ; x, bodies of unknown function.
After Wenyon (277).

forms are either holozoic or saprophytic, if colourless, or holophytic if pro-
vided with chromatophores, in which case they may be capable of nourishing
themselves by more than one method. The flagellum may bo single, or there
may be a second flagellum, usually smaller than the principal flagellum,
and sometimes directed backwards as a trailing flagellum. The attachment
of the flagellum is of the second type (p. 263), with blepharoplast distinct
from the centrosome. According to Hartmann and Chagas (62), in Peranema
trichophorum the centrosome first divides to furnish a blepharoplast, and
the latter, having become completely independent of the nucleus, divides
into two, a distal blepharoplast or basal granule of the flagellum, connected
by a rhizoplast (centrodesmose) with the proximal blepharoplast or anchoring
granule. The authors consider that this should be regarded as a fourth typo

18

274

THE PROTOZOA

of flagellar insertion, characteristic of this order ; but it is simplest to regard
it merely as a secondary complication of the second type, and one which is
not universal in this order, since in Copromonas subtilis the blepharoplast
remains undivided, so that this species shows a flagellar attachment strictly
of the second type. In Euglena, according to Wager (213), the flagellum
passes through the oesophagus and becomes attached to the wall of the
reservoir- vacuole by a bifurcate base. On one of the branches is a distinct
thickening in close contact with the stigma (p. 205). The thickening is prob-
ably the blepharoplast, and the two branches represent the rhizoplast.

The sexual processes of the Euglenoidina are but little known, and Copro-
monas is the only genus in which the complete life -cycle has been worked out ;
in this species it is of a simple type (p. 264, Fig. 111).

The order comprises three families. The first, Euglenidce, contains forms
provided with chromatophores, ho]ophytic, saprophytic, and parasitic
(Haswell) in habit. Examples: Euglena (Fig. 4), Phacus (Fig. 118). The
second family, Astasiidce, contains the genus Astasia (Fig. 15), colourless
and saprophytic or parasitic. The third family, Per-
anemidce, contains numerous genera without chro-
matophores. holozoic or saprophytic. Examples :
Peranema, Copromonas (Fig. 111). The subfamilies
Heteronemince and Anisonemince are heteromastigote.
Example : Anisonema (Fig. 25).

OBDEBV. : CHBOMOMONADINA. — Small forms, with-
out oesophagus or vacuole-system, with delicate cuticle
and one or two flagella ; their characteristic feature is
the possession, usually, of one or two conspicuous
chromatophores, green, yellow, or brownish, in colour.
The nutrition, for the most part holophytic, may
be also holozoic or saprophytic. Divided into two
suborders.

Suborder 1 : Chrysomonadina. — With one or two
flagella and one or two yellowish-brown chroma-
tophores ; body often amoeboid or metabolic ; colony-
formation frequent ; nutrition holozoic and holophytic.
Three families. Examples : Chrysamoeba, Chromulina,
Dinobryon, etc. According to Scherffel, Chrysamoeba
is the amoeboid, non-flagellated phase of Chromulina ;
compare also Lauterborn (345'5). To this suborder
must be referred also the Coccolithophoridce. marine
flagellates which secrete the calcareous shells known as
coccoliths (vide Lohmann).
Suborder 2 : Cryptomonadina. — Small forms with one or two flagella, colour-
less, or with chromatophores ranging in colour from yellowish- brown to olive-
green or blue-green. Holophytic or saprophytic, not holozoic. Examples :
Chilomonas, colourless ; Cryptomonas, some species of which are symbiotic in
Sarcodina (p. 15). Doflein refers the Silicoflagellata to this order (p. 255).

OBDEE VI. : PHYTOMONADINA SEU PHYTOFLAGELLATA. — Completely and
exclusively holophytic, with cellulose envelope and without mouth-aperture.

This order comprises the most plant-like flagellates, to all intents and
purposes unicellular algae which retain throughout life their flagellar apparatus
4and their motility. The individual is generally small, and the body is, except
in one family, of definite form and enveloped in a rigid cellulose envelope
which may stand off from the body, and is perforated by pores through which
the flagella pass out to the exterior. The flagella are usually two in number,
sometimes four, of equal size. The cytoplasm generally contains a large
green chromatophore and a red stigma. The flagellar insertion, according
to Hartmann and Chagas, is of the second type, as in Protomonadina. The
reproduction may take the form of multiple fission within the body-envelope
to form numerous swarm-spores, which when set free may be gametes or
agametes. Colony-formation is frequent in this order (p. 257).

FIG. 118. — Phacus
triqueter. ces., (Eso-
phagus ; c.v., con-
tractile vacuole ; st.,
stigma ; N., nucleus.
After Stein.

THE MASTIGOPHORA

275

Three families are recognized. The first, represented by the genus Pyra-
mimonas, contains primitive forms in which the body is metabolic and the
cellulose envelope is absent. The second family, Chlamydomonadidce, com-
prises non-colonial forms such as Uhlamydomonas, Hcematococcus, etc. Nephro-

B

FIG. 119. — Gonium pectorale: colony of sixteen individuals, each with two flagella.
A, In surface view ; B, in side view. N., Nuclei ; c.v., contractile vacuoles ;
st., stigmata. After Stein.

selmis, referred by Senn (358) to this family, has two flagella, on which it
creeps like a Bodo. The third family, Volvocidce, comprises colony-forming
species in which the individual is similar in structure to the Chlamydomonads,
and the colony is composed of individuals ranging in number from four, eight,

276 THE PROTOZOA

sixteen, or thirty-two, up to many thousands. Examples are Gonium
(Fig. 119), Stephanosphcera, Volvox, etc.

In addition to the six orders of flagellates enumerated above, there remain
some peculiar parasitic forms, the systematic position of which is extremely
doubtful. Such are the family Lophomonadidce, represented by Lophomonas
blattarum, a common parasite of the end-gut of the cockroach and other
Orthoptera, and the Trichonymphidce. including the genus Trichonympha and
allied forms, parasitic in the end-gut of termites of various species.

Lophomonas blattarum, which has recently been studied by Janicki (70),
bears a tuft of flagella arising at the anterior pole of the body from a double
ring, or rather horseshoe, of blepharoplasts, situated at the edge of a funnel-
shaped or cup-like structure, the calyx, which is prolonged into an axostyle
(Fig. 45). The nucleus lies within the calyx, which is surrounded in its turn
by a peculiar thickening or support, termed tho " collar," consisting of free,
radially-disposed rods crowded together to form an aureole-like figure, approxi-
mately spherical. The nutrition is holozoic, and food-particles are ingested
at any point on the body-surface, as in the Pantastomina. Multiplication
takes place by binary or multiple fission in the free state ; and division of the
nucleus up to eight within a cyst has been observed, but the entire life -cycle
has not been worked out. Associated with L. blattarum, another form,
L. striata, occurs, but it is doubtful if this is a distinct species, or a phase or
condition of L. blattarum.

The group or family Trichonymphidce comprises a number of peculiar
parasites found in the digestive tract of various species of Termitidce ; such
are the genera Joenia, Lophophora, Calonympha, Devescovina, etc., and finally
the genus Trichonympha, from which the family takes its name. The chief
peculiarity of these forms is the possession of numerous flagella, which may
be disposed in tufts at the anterior end of the body, in a manner similar to
Lophomonas (which by some authorities is included in this family), or may
be distributed over the whole body, like a coat of cilia, as in the genera
Trichonympha, Dinenympha, etc.

According to Hartmann, Trichonympha hertwigi occurs under two forms,
which he believes to represent male and female gamonts. They multiply
by binary fission, and also by a process of sporulation to produce swarm-
spores which are believed to be gametes. Dinenympha also exhibits sexual
dimorphism, according to Comes (333).

From Janicki's investigations, there can be no doubt that Lophomonas is a
true flagellate, possibly allied to Trichomonas, possibly, however, to the Pan-
tastomina. The genus Joenia, parasitic in Calotermes fiavicollis, was thought
by its discoverer, Grassi, to connect Lophomonas and Trichonympha ; the
recently-described genus Lophophora (Comes, 332) also has points of resem-
blance to Lophomonas, but is remarkable for the presence of undulating mem-
branes running the length of the body. By some authorities, however, the
Trichonymphidce have been placed with the Ciliata, while Harlmann considers
that they should rank as an independent class of the Protozoa.

SUBCLASS II. : DINOFLAGELLATA SEU PERIDINIALES.
The characteristic feature of this subclass is the possession of
two flagella, which arise close together about the middle of the
body. One flagellum (Fig. 120, e) runs longitudinally backwards
as a trailing flagellum ; the other (Fig. 120, d) runs transversely
round the body. It is further characteristic of this group for the
cuticle to be greatly thickened, forming a tough cuirass, or lorica,
investing the body. The two flagella are usually lodged in grooves
in the cuirass, the longitudinal flagellum in a longitudinal groove
or sulcus, the transverse flagellum in a circular groove, or annulus.

THE MASTIGOPHORA

277

The transverse flagellum executes undulating movements whicii
were formerly mistaken for those of a ring of cilia ; hence the name
Cilioflagellata formerly applied to this group.

The cuirass, composed of c?llulose or an allied substance, is in its
typical form a perfectly rigid structure, and is
often prolonged into spikes and processes which
cause the body as a whole to assume strange or
even monstrous forms (Fig. 121). Detailed
studies on the skeleton have been published by
Kofoid in a series of memoirs (374-383). The
nutrition is for the most part holophytic, but
in some species ingestion of solid food has been
observed. A great many parasitic forms have
been made known of recent years (Chatton,
366-369 ; Caullery, 364) ; these are for the most
part forms which, in the vegetative, parasitic
phase are inert bodies with no sign of locornotor
organs, often fixed and pedunculate when ec to-
parasitic ; but in their reproductive phases
they betray their affinities by the formation
of numerous flagellated swarm-spores exhibiting
the typical Dinoflagellate structure.

The pelagic species generally possess chroma-
tophores, and frequently a red stigma, which in
some genera — Pouchetia (Fig. 31), Erythropsis — is modified into an
eye-like organ. The deep-sea forms, on the other hand, are colourless.

In many Dinoflagellates a peculiar system of vacuoles is found (Fig. 122),
consisting of two sacs containing watery fluid, each of which empties itself
to the exterior by its own duct. They differ from
ordinary contractile vacuoles in possessing a dis-
tinct envelope and in not performing rhythmical
contractions, and have hence been given the
special name of " pusules " (Schiitt). One of these
organs, termed the " collecting-pusule, " consists of
a reservoir-vacuole surrounded by a ring of smaller
vacuoles which empty themselves into it ; the
other, termed the " sack-pusule, " is a large cavity
which takes up a great part of the interior of the
cuirass. The function of these organs is probably
hydrostatic.

The commonest method of reproduction is
binary fission in the transverse plane of the body,
in which each daughter-individual receives a half
of the cuirass of the parent and regenerates the
half that is wanting. Fission rapidly repeated may
lead to the formation of chains of individuals. In
other cases multiple fission within the cuirass has been observed, leading to the
formation of swarm-spores which are possibly gametes ; but little is known of
the sexual processes of these organisms.
The Dinoflagellates are an exceedingly abundant and widespread group,

FIG. 120. — Glenodi-
nium cinctum,
Ehrenberg. a,
Amyloid granules ;
6, stigma ; c, chro-
matophores ; d,
flagellum of the
transverse groove ;
e, flagellum of tho
vertical groove ; v.,
vacuole. From
Lankester.

FIG. 121. — Ceratocorys
horrida: cuirass. After
Stein, from Lankester.

278

THE PROTOZOA

~cp.

FIG.

highly differentiated as regards forms and species. The vast majority are
pelagic in habit, and constitute an important element of the plancton-fauna,
both marine and fresh-water. A certain number of species are adapted to

parasitic life. They are divided into two
orders.

ORDER I. : ADINIDA (Prorocentraceae). —
Primitive forms in which the typical peculi-
arities of Dinoflagellate organization are not
fully developed. The body-envelope consists
of a bivalve shell without furrows. The two
fiagella emerge through an aperture between
the two valves, and one flagellum projects
freely into the water, while the other twists
round it at the base. Example : Prorocentrum.
ORDER II. : DINTFERA. — With the typical
characters of the subclass, as described above.
Families: (1) Gymnodinidce, without a well-
developed cuirass — example : Gymnodinium ;
the marine genus Oxyrrhis (Fig. 123) is referred
to this family by Senn (358) ; it is holozoic
in habit. (2) Peridinidce, with a well- developed
cuirass made up of definite plates — examples :
Glenodinium (Fig. 120), Ceratium, Ceratocorys
(Fig. 121), Peridinium, etc. ; Pyrodinium
(Plate, 385) is remarkable for its intense phos-
phorescence ; at the hinder pole, between the
chromatophores, the cytoplasm contains a body,
the "Nebenkorper" of Plate, surrounded by
numerous oil-drops, which are perhaps the
seat of the luminosity. (3) Dinophysidce,
oceanic species with the cuirass divided by a
sagittal suture, often of extraordinary form —
example : Dinophysis, etc. (4) Blastodinidce,

a family created by Chatton (366, 367) for certain parasitic forms ; such
are Blastodinium, an internal parasite of various cope pods, and Apodinium
mycetoides, an ectoparasite of appendicularians (Fritillaria). The parasitic,
vegetative form, without organs of locomotion,
gives rise by periodic segmentation of mother-
cells to successive generations of swarm-spores, JPP^lk fir
which in their structure resemble Gymnodinium. • *•- M^^tL-?*"

SUBCLASS III. : CYSTOFLAGELLATA SEU
RHYNCHOFLAGELLATA .

This group comprises a small number of
forms all marine and pelagic in habitat.
Their chief peculiarity is that, like so
many other pelagic organisms of all classes,
the body is inflated, as it were, writh
watery gelatinous substance, so that it
attains to a size which far exceeds the
actual bulk of the living substance con-
tained in it. In consequence of the
secondary increase in size, the powers of locomotion are feeble, and
these organisms float more or less helplessly on the surface of the sea.

122. — Peridinium diver-
ventral view showing
the vacuole-system. c.p.,
The collecting-pusule sur-
rounded by a rosette of still
smaller pusules which open
into it ; s.p., the large sac-
pusule, or reservoir ; both
opening into the fundus (/.),
from which both the trans-
verse flagellum (£.), lying in
the annulus (a.), and the
longitudinal flagellum (L),
arise. After Schiitt, from
Lankester.

nucleus; f.v., food-
vacuoles ; ex., excretory
mass about to be ejected.
After Blochmann, from
Senn (slightly modified) ;
magnification 1,000.

THE MASTIGOPHORA 279

The best known form is the common Noctiluca miliaris of our coasts. The
adult Noctiluca is about the size of an ordinary pin's head (1 to 1'5 millimetres
in diameter). The spherical body consists chiefly of jelly, with at one pole
a superficial concentration of the protoplasm containing the nuclei and giving
off the locomotor organs. From this central mass of protoplasm strands extend
in an irregular network through the whole body, which is limited by a thin
pellicle. The central protoplasm bears the so-called " peristome," a deep groove
containing the mouth-aperture near one end. The mouth is bordered by pro-
jections known as the " tooth " and the " lip," and near it arise two motile
organs — a small flagellum, and a large tentacle-like process which shows a
transversely striated structure and performs twisting and lashing movements.
The tentacle is sometimes named the " flagellum," and the true flagellum
the " cilium " ; the former probably serves as the organ of locomotion, the latter
for food- capture. The nutrition is holozoic.

Noctiluca reproduces itself by binary fission, and also by multiple fission
producing a brood of small flagellate swarm-spores. The formation of the latter
has been stated to be preceded by isogamous conjugation of the adults, but
the matter is open to doubt, and it is possible that the swarm-spores them-
selves represent the gametes. Other genera of Cystoflagellata are Leptodiscus
and Craspedotdla (Kofoid, 373), both remarkable for their superficial resem-
blance to medusae. No tentacle like that of Noctiluca is present in either of these
forms, and locomotion is effected by rhythmic contractions of the disc-like
body.

Bibliography. — For references see*p. 486.

CHAPTER XIII
THE H^IMOFLAGELLATES AND ALLIED FORMS

General Characters and Principal Types. — Under the term "Hsemo-
flagellates " are grouped together a number of forms of which the
characteristic, though by no means invariable, habit is alternating
parasitism in the blood of a vertebrate and in the digestive tract
of a blood-sucking invertebrate host. The group must be regarded,
however, as one founded on practical convenience rather than oil
natural affinity — as a method of classification comparable to that
of the gardener rather than of the botanist. The existence of a
parasitic habit common to a number of different forms is in itself
no proof of genetic affinity or community of descent, and it is highly
probable that more than one line of ancestry has contributed,
through divergent adaptation, to the composition of the group
Hsemo flagellates. The name itself has, moreover, lost much of its
significance, since closely allied to the forms parasitic in blood, and
inseparable from them in a natural scheme of classification, are
other forms parasitic only in invertebrates, or even free-living.

The chief morphological characteristic of the Haemo flagellates is
the possession of two nuclei, a trophonucleus and a kinetonucleus,
and the relation of the locomotor to the nuclear apparatus is of the
third type distinguished in the preceding chapter (p. 263) ; on this
account they are ranked by Hartmann and Jollos (390) as a distinct
order of the Flagellata termed the Binucleata.

The Hsemo flagellates as a group comprise a number of forms
which represent in some cases distinct generic types, in others
merely developmental phases alternating with other forms in the
life-cycles of particular species. The following six generic names
represent the more important of these types :

1. Trypanosoma (Fig. 126, etc.), with a single flagellum which
arises near the kinetonucleus, at the extremity of the body which is
posterior in progression, and runs forward as the marginal flagellum
of an undulating membrane. At the anterior end of the body the
flagellum is usually continued as a free flagellum, but in some cases
it ends with the undulating membrane. A vast number of species
parasitic in the blood of vertebrates and in the digestive tract of

280

THE H^MOFLAGELLATES AND ALLIED FORMS 281

invertebrates alternately are comprised in this genus. Trypano-
some-forms also occur as developmental phases in the life-cycle of
species parasitic solely in the digestive tracts of insects.

2. Trypanoplasma (Figs. 36, 134), with two flagella arranged in
a heteromastigote manner, and with the posterior trailing flagellum
united to the body by an undulating membrane for the greater part
of its length. A number of species are known, which by their dis-
tribution fall into three sections : (1) Species parasitic in the blood
of fresh-water fishes, with alternating parasitism in the digestive
tract of leeches ; (2) species parasitic in the digestive tract of marine
fishes ; (3) species parasitic in various invertebrates.

3. Crithidia (Fig. 135), with a single flagellum which arises near
the kinetonucleus, at about the middle of the body, in front of or
close beside the trophonucleus, and runs along the pointed anterior
end of the body to form the marginal flagellum of a relatively
short, often rudimentary, undulating membrane, beyond which
it is continued as a free flagellum. As an independent genus this
type comprises species parasitic in the digestive tracts of various
insects ; but the majority of the so-called species of Crithidia arc
merely phases in the developmental cycle of trypanosomes.

4. Leptomonas (Herpetomonas — Figs. 124, 136), with a single
flagellum arising at the anterior end of the body, and with no trace
of an undulating membrane. As an independent generic type
this form occurs as a parasite of invertebrates, chiefly insects ;
secondarily also in the latex of plants (Euphorbiacese). It occurs
also as a developmental form of the next genus in the invertebrate
host or in cultures.

5. Leishmania (Fig. 138), with an oval body containing a tropho-
nucleus and kinetonucleus, but with no flagellum. As a generic
type this form is an intracellular parasite of a vertebrate host,
multiplying there by fission and developing into a typical Lepto-
monas-ioim. On the other hand, as a developmental phase this form
represents simply a non-flagellated, resting stage which may occur
in the life-cycle of either Trypanosoma, Crithidia, or Leptomonas.

6. Prowazekia (Fig. 141), with two flagella arranged in the hetero-
mastigote manner, as in Trypanoplasma, but with the trailing
flagellum quite free from the body, without an undulating mem-
brane. Prowazekia is therefore quite similar in its morphology to
Bodo, with which it was formerly confused, if, indeed, it is really
distinct, and it differs from Bodo only in the possession of a kineto-
nucleus. Several species are described, free-living or intestinal in
habitat.

Considering the above six types as a whole from a morphological
standpoint, it is seen that there are two types of structure amongst
them — the cercomonad or monomastigote type, represented by

282

THE PROTOZOA

Trypanosoma, Crithidia, and Leptomonas, of which Leishmania may
be regarded as the resting, non-flagellated phase ; and the bodonid
or heteromastigote type with two flagella, seen in Trypanoplasma
and Prowazekia. We shall return to this point in considering the
affinities of the group as a whole and of its constituent genera.

The six types enumerated above are given with the nomenclature and
definitions most commonly accepted, but it is necessary to state that the
application and significance of the names Crithidia, Leptomonas, and Herpeto-

monas, are much disputed and are far from
being settled. The type of the genus Herpeto-
monas of Saville Kent is a species found in
the digestive tract of house-flies, H. muscce-
domesticce (Fig. 124). According to Prowazek
(557), this form possesses normally two
flagella, which are connected together by a
membrane ; according to Patton (551) and
many others, the biflagellate condition is due
to precocious division of the normally single
flagellum as a preparation for division of the
body (compare Strickland, 558 ; Wenyon, 84).
Those who follow Prowazek in regarding the
biflagellate condition of Herpetomonas as its
normal adult form employ the older genus
Leptomonas of Saville Kent* for forms with a
single flagellum (Chatton,Roubaud, Prowazek).
The main source of the confusion in the nomen-
clature arises from the uncertainty which still
exists in many cases as to whether a given form
or structural type is to be regarded as an in-
dependent specific or generic type, or as a
developmental phase of another species. This
applies especially to the genus Crithidia,
founded by Leger (543) for a species, C.
fasciculata, from the intestine of Anopheles
maculipennis, and defined as a small uniflagel-
late form shaped like a grain of barley (Greek,
Kpi6r}). Such forms, however, occur as
developmental forms of trypanosomes or of
leptomonads, and it is extremely probable that
the species on which Leger founded his genus
was simply a phase of this kind, which Wood-
cock (527) has proposed to call the " trypano-
monad" phase, in the development of a
trypanosome. On this ground Dunkerly
(535), who has recently discussed the whole
question, considers that the name Crithidia
cannot be used as a generic name at all, but must be merged in Leptomonas,
the name that should be used for all the uniflagellate parasites of insect -guts ;
while Herpetomonas should either become a synonym of Leptomonas, or should
be used solely for Prowazek's biflagellate type, if that prove to be a distinct
generic type. On the other hand, Leger and Duboscq (646, p. 232, footnote)
consider that Crithidia should be retained, and Leptomonas ranked as a

* The genus Leptomonas was founded by Saville Kent, <; Manual of Infusoria,"
vol. i., p. 243, for L. biitschlii, parasite of the nematode worm Trilobus gracilis ;
the genus Herpetomonas was founded on p. 245 of the same work for H. muscce-
domesticce and H. lewisi ( = Trypanosoma lewisi). Leptomonas is therefore techni-
cally the older genus.

B

FIG. 124, — H erpetomonas
muscce-domesticce (Burnett).
A, Motile individual with
two flagella ; B, cyst : n.,
nucleus ; bl, kinetonucleus.
After Prowazek.

THE H^EMOFLAGELLATES AND ALLIED FORMS 283

synonym of it. The question has given rise to a controversy which has been
carried on by some of the participants in an acrimonious and even unseemly
manner, and which it would be unprofitable to discuss further here, since
the question is one which must be decided ultimately by facts, and not by
personal opinions or tastes.

The various forms comprised in the Hsemoflagellates may now
be considered in detail, beginning with the most important type.

I. THE GENUS TRYPANOSOMA.

Occurrence. — Trypanosomes were first discovered as blood -
parasites of cold-blooded vertebrates — fishes and batrachia ; the
type-species of the genus Trypanosoma is T. rotatorium (synonyms,
T. sanguinis, Undulina ranarum) of the frog (Rana esculentd).
Trypanosomes are now known, however, to occur commonly as
blood-parasites in all classes of vertebrates. In a wild state many
species of mammals, birds, and other vertebrate animals, are often
found to harbour trypanosomes in their blood, though frequently
in such scanty numbers as to render the detection of the parasites
extremely difficult. It may be almost impossible in some cases to
find trypanosomes in the blood of an animal by direct microscopic
examination, owing to their great scarcity ; but in such cases an
artificial culture made from the blood may reveal the presence of the
parasites, since in a few days the trypanosomes originally present
in small numbers in the blood multiply, under favourable conditions,
to produce a swarm of flagellates. The cultural forms are quite
different, as a rule, from the blood-forms which gave rise to them,
and appear generally as crithidial or trypanomonad types ; thus,
cultures furnish evidence of the existence of a trypanosome in a
given host, but give no indication whatever of the type of parasite
actually present in the blood.

In some cases the trypanosomes appear to be present in the
peripheral circulation of the vertebrate host only at certain periods,
and at other times they are only to be found in the internal organs
or tissues of the host, such as the spleen, bone-marrow, liver, lungs,
etc. The trypanosome of Athene noctua — T. noctuce, for example —
is to be found during the winter only in the bone-marrow of its host,
and appears in the peripheral circulation during the summer months,
and then most abundantly in the night-time (Minchin and Wood-
cock, 42). Hence, for various reasons, it may often be extremely
difficult to decide whether a given animal is infected with trypano-
somes or not ; and in recent years trypanosomes have been dis-
covered in animals in which their presence was previously quite
unsuspected — for instance, in calves (Crawley, Carini, 423, Stockman ;
see also Bulletin of the Sleeping Sickness Bureau, No. 29, p. 320)
and in sheep (Woodcock, 527, p. 713, footnote).

-ft:

B

FIG. 125. — Trypanosoma mega, from the blood
of African frogs, ft.1, Marginal flagellum of
the undulating membrane ; fl.2, free flagellum ;
m., myoneme-striations (it is doubtful whether
the granular streaks or the clear interspaces
correspond exactly to the actual myonemes);
n, kinetonucleus ; N, space in which
the trophonucleus lies, but, not being
stained, it is not clearly defined in
the preparation. After Minchin, magni-
fied 2,000; compare Figs. 11 and 12 at
the same magnification.

THE H^EMOFLAGELLATES AND ALLIED FORMS 285

Effects on the Host. — The trypanosomes found infesting wild
animals in Nature are, as a rule, quite specific to a particular host,
and, so far as can be observed, perfectly harmless to it. If the
relations between host and parasite had always been of this type
in all cases, our knowledge of trypanosomes would be in a much
more backward state even than it is. Of recent years a vast
amount of attention has been attracted to these parasites owing to
the diseases of man and animals caused by certain species of trypano-
somes, and hence termed comprehensively " trypanosomiases."
The greater number of these pathogenic species belong, from the
structural point of view, to a type which may be called the brucii-
type (Fig. 12) ; such are T. brucii, cause of tsetse-fly disease ; T. gam-
biense, of sleeping sickness ; T. evansi, of surra ; T. equiperdum, of
dourine ; and many others. The structural similarity of these
species renders their identification a matter of extreme difficulty.
Of a slightly different type is T. equinum, of " mal de caderas " in
South America, with a very minute kinetonucleus ; but the recently-
described T. hippicum of " murrina " (Darling, 428) appears to be
a typical member of the brucii-group. T. theileri, on the other
hand, from cattle, is very distinct in size and appearance from the
members of the brucii-gjtoup. Finally, T. cruzi, the cause of human
trypanosomiasis in Brazil, stands apart from all the others in
peculiarities of reproduction and development, which have led to
its being ranked in a distinct subgenus, Schizotrypanum.

The problem of the pathogenic trypanosomes has been touched
upon in Chapter II. From a survey of trypanosomes in general, it
is clear that the normal type of these parasites is one which is specific
to one or to a limited number of species of hosts, to which it is quite
harmless. The pathogenic species are to be regarded as aberrant
forms not yet adapted to their hosts, as an instance of a disharmony
in Nature. They are species which have probably established
themselves but recently in the hosts to which they are pathogenic.
As contrasted with the natural, non-pathogenic forms, their most
striking peculiarities are that they are not specific to one host, but
can flourish in a great number of different species of hosts, and that
in susceptible animals their power of multiplication has no limit.
T. brucii, so deadly to many domestic animals, is known to occur
also as a natural parasite of wild animals, to which it is harmless.

Structure. — The constitution of the trypanosome-body is of a
very uniform type in its general traits, though subject to great
variation in different cases as regards size, form, and minor details
of structure. The body is typically long and sinuous, with the
anterior end tapering gradually to a fine point, while the posterior
extremity is usually broader, and tapers more abruptly, or ends
bluntly ; but in different forms, even of the same species, there may

286 THE PROTOZOA

be great variation, from long, slender to short, stumpy types, and
in some cases the posterior end is also greatly drawn out and attenu-
ated. The principal nucleus or trophonucleus is usually situated
near the middle of the body. The kinetonucleus is almost invariably
behind the trophonucleus,* sometimes close behind it, but more
usually near the posterior extremity, separated from the tropho-
nucleus by about half the length of the body.

The flagellum arises from a centriole (blepharoplast) which is in
connection with the kinetonucleus. In the more primitive type of
arrangement the blepharoplast is lodged within the kinetonucleus
itself, and then the flagellum appears to arise from the kineto-
nucleus directly (Wenyon, 84). In most cases, however, the
blepharoplast is situated close beside, and usually in front of, the
kinetonucleus, connected with it by a delicate rhizoplast. When
the blepharoplast is distinct from the kinetonucleus, it is at present
an open question whether the kinetonucleus contains a centriole
of its own, in addition to the blepharoplast, or whether the blepharo-
plast represents a centriole which belongs to the kinetonucleus, but
has migrated to the exterior of this body.

Passing from the blepharoplast to the surface of the body, the
Hagellum forms the free border of the undulating membrane, which
runs forward from the vicinity of the kinetonucleus to the extreme
anterior end of the body as a fin-like ridge or fold of the periplast,
of variable width (cf. Fig. 126). The flagellum may in some cases
end with the undulating membrane at the anterior end of the body,
but more usually it is prolonged forward beyond this point, so that
a free portion of variable length is to be distinguished from the mar-
ginal portion contained in the undulating membrane. The sinuous
body, the undulating membrane, and the flagellum, are alike in a
state of incessant movement during life, and in larger forms con-
tractile myonemes are clearly visible in the periplast of the body
(Fig. 28, p. 58) ; in the more minute individuals the presence of such
elements must be inferred from their movements, but cannot always
be demonstrated optically.

The movements of a trypanosome, speaking generally, are of two types :
travelling movements, when it progresses with the free flagellum forwards,
sometimes very fast, shooting across the field of the microscope in a straight
line (mouvement en fleche), sometimes, on the other hand, pushing its way
s lowly through the blood- corpuscles, with the flagellum directed either forwards
or backwards in movement ; and wriggling movements, when the animal
writhes incessantly in serpentine contortions with little or no displacement

* The only known exceptions are furnished by certain forms of the recently-
described T. rhodesiense (vide Stephens and Fantham), and by some of the small
forms seen during the multiplication of T. lewisi (Fig. 127, L). It is needless to
point out that the statement made above applies to the typical trypanosome-form
as found in the vertebrate blood, and not to the developmental forms through which
they pass in the invertebrate host (crithidial and other types).

THE H^MOFLAGELLATES AND ALLIED FORMS 287

from a given spot. Many trypanosomes, especially the large stout forms,
are very sluggish in their movements, and show but little power of progression.
At the opposite extreme, in this respect, is the African parasite of cattle, well
named by Ziemann T. vivax, which, according to Bruce and his collaborators
(411, iii.), " dashes across the field of the microscope with such rapidity that
it is impossible to follow its movements, cyclone-like leaving a clear path, the
corpuscles in its track having been flung on either side. If it remains at the
same spot for a time, as it sometimes does, it has an appearance of great
energy and power, throwing the surrounding red blood- corpuscles about in
wild confusion."

In the foregoing paragraphs the terms " anterior " and " posterior," as
applied to the trypanosome-body, have been used strictly with reference to
its mode of progression. It is pointed out below, in the comparison
with other types such as Trypanoplasma and Crithidia, that the extremity

FIG. 126. — A, Trypanosoma tincce of the tench ; note the very broad undulating
membrane in this species ; B, C, T. percce of the perch, slender and stout
forms. After Minchin, X 2,000.

of the body which is anterior, in the strictly morphological sense, in one
species, may conceivably be posterior in another case. Hence some writers
avoid the use of the words " anterior " and " posterior," and substitute for
them " flagellar " and " aflagellar " respectively, to denote the two poles of
the body,, There is as yet, however, no concrete evidence for regarding the
flagellar extremity as morphologically posterior in any known species of
trypanosome.

The undulating membrane is to be regarded as a fold of the periplast or
ectoplasm, into which the granular endoplasm may extend a short way in
some cases ; it arises from the body along a line which is sometimes spoken of
as " dorsal," an unnecessary refinement of terms. The free edge of the
membrane, with its marginal flagellum, can be shown by direct measurements
to exceed considerably in length that portion of the body to which it is at-
tached ; consequently its free edge is thrown into folds or pleats more or less
marked. In preparations, trypanosomes are seen to lie, speaking generally,

288 THE PROTOZOA

in one of the three ways ; a certain number show the body extended nearly
in a straight line, with the free edge of the membrane much pleated, but as a
rule the body is curved, and then either with one principal bend, like a C, or
with several S-like serpentine bends. In either case the undulating membrane
is seen almost invariably to run on the convex side of each curve. In C-like
forms (Fig. 125, A) the membrane runs evenly along the outside of the principal
curve, and the myoneines parallel to it. In S-like forms (Fig. 125, B] the
membrane is often seen distinctly to be spirally twisted round the body, the
myonemes also exhibiting the same twist. In life the undulating membrane
performs, as its name implies, movements like those of a sail napping in the
wind. Wave-like undulations run along it from one end to the other, but not
always in the same direction ; it has been observed that reversals of the move-
ments may take place, the waves first running in one direction for a time,
and then suddenly undergoing a change and running in the opposite direction
(Minchin and Woodcock, 42).

Much confusion exists in the nomenclature of the parts of the trypanosome-
body, more especially with regard to the small body for which Woodcock's
term " kinetonucleus " (" Geisselkern ") is here used — a confusion due to
differences of cytological interpretation. While it has never been doubted
that the larger body (N.) is a true nucleus, various views have been held
with regard to the smaller body (n.), which, summarized briefly, are as
follows : The older writers regarded it merely as an organ of the periplast
from which the flagellum arose. Stassano and Bradford and Plimmer re-
garded n. as a body of nuclear nature, and termed it the " micronucleus,"
comparing it with the similarly-named body of Infusoria. Laveran and
Mesnil (464, 391), on the other hand, regarded n. as the " centrosome," the
name by which it is generally known in France. Schaudinn (132) emphasized
strongly its nuclear nature, and stated that n. was not a centrosome, but
nevertheless used for it the term " blepharoplast," by which it is still generally
known in Germany, although a true blepharoplast is a body of centrosomic
nature. Moore and Breinl (484) reverted to the centrosomic view, and termed
n. the " extranuclear centrosome," believing that it arose by division of the
intranuclear centrosome contained in the principal nucleus (N.). Hartmann
and Prowazek (63), on the basis of their nuclear theory of the centrosome (see
Chapter VI., p. 95), regarded n. as a body both of nuclear and centrosomic
nature, using for it the term " blepharoplast " ; so also Rosenbusch. Finally,
Doflein (7), who is not convinced of its truly nuclear nature, continues to
employ for n. the term " blepharoplast." With these many conflicting views
with regard to the nature of n., the basal granule has been either ignored or
overlooked, or considered as a mere " end-bead " of no particular importance,
or ranked as a centriole, as it doubtless is. The nomenclature used here is
based on the general theory that a centrosome, or its equivalent, a blepharo-
plast, is an achromatinic body of nuclear origin, but not equivalent to an entire
nucleus, and on the conviction that n. is a true nucleus, and therefore is not
to be regarded either as a centrosome or a blepharoplast. For a fuller dis-
cussion of these points, see Robertson and Minchin (80).

The trophonucleus of a trypanosome is typically a vesicular nucleus con-
taining a karyosome in which is lodged a centriole. The karyosome varies
in size in different species, and is sometimes double or multiple ; in T. granu-
losum the smallest forms have a single karyosome which buds off others as
the animal increases in size (Minchin, 478). By the method which is most in
vogue, however, for making permanent preparations of trypanosomes —
namely, the various modifications of the Romano wsky- stain — this structure
is seldom to be made out, and the trophonucleus appears generally as an
evenly-stained mass or as a dense clump of stained granules. It contains
a centriole, difficult to make out in the resting condition, owing to its being
embedded in the substance of the nucleus. The kiuetonucleus consists
mainly of a mass of plastin impregnated with chromatin, staining very
deeply, rounded, oval, or even rod-like in shape. According to Rosenbusch,
the chromatinic mass of the kinetonucleus is to be regarded as representing

THE H^EMOFLAGELLATES AND ALLIED FORMS 289

a karyosome, and it is surrounded by a space, sometimes purely virtual,
which represents the nuclear vacuole, bordered by a delicate nuclear mem-
brane, on or close to which the basal granule of the flagellum is lodged.

In some species of the brucii-group, an axial filament, apparently a sup-
porting structure of the nature of an axostyle, has been described (cf. Swel-
lengrebel, 514). The system of fibrils, however, with which Prowazek
decorates the trypanosome-body are probably artefacts (cf. Minchin, 479).

Many trypanosomes contain granules in their cytoplasm which stain
similarly to chromatin, so-called " chromatoid grains." According to Swel-
lengrebel (514), they are of the nature of volutin (p. 68, supra).

The division of a trypanosome is initiated, as a rule, by the division of the
blepharoplast or basal granule of the flagellum, and following close on this
a reduplication of the flagellum takes place, the exact method of which is
disputed. In some cases the old flagellum appears to split ; in others the
parent -flagellum remains unaltered, and a daughter-flagellum grows out
from the daughter- blepharoplast. It is asserted by some that in all cases
the new flagellum really arises as an independent outgrowth of a blepharoplast,
and that the splitting of the old flagellum is only apparent, and due to the
daughter-flagellum growing out at first in its sheath, from which it separates
later (cf. Wenyon, 84). The division of the kinetonucleus follows hard
on that of the blepharoplast, and next, as a rule, the trophonucleus divides.
When the division of flagellum and nuclei is complete the body divides, begin-
ning to do so at the flagellar end ; the two sister-trypanosomes are often
connected for a time by the posterior extremities.

The division of the kinetonucleus is a simple constriction into two ; that of
the trophonucleus is of a simple type, in which first the centriole and then the
karyosome divides. The two daughter- karyosomes travel apart, and the
nucleus follows suit. The two daughter-nuclei sometimes remain connected
for a time by a long centrodesmose, which is finally severed. Such, at least,
is the mode of division of the two nuclei as it has presented itself to the majority
of investigators, and the nuclear division of trypanosomes is to be regarded
as amitotic, or at least not further advanced towards mitosis than that of
Coccidmm described above (p. 108, Fig. 51). According to Rosenbusch,
however, the division of the nuclei, both trophic and kinetic, takes place by
true mitosis. This author is in advance of his contemporaries upon this
point, and his statements require independent confirmation before they can
be accepted unreservedly, since in objects of such minuteness, requiring
delicate and elaborate technique, imagination may all too readily outrun
perception.

Life-History. — The transmission of trypanosomes from the blood
of one vertebrate host to another is effected, probably for every
species of these parasites, by the agency of a blood-sucking inverte-
brate of some kind. When the host is a terrestrial vertebrate, the
transmitting agent is generally an insect, such as a mosquito or
some biting fly or bug, or an ectoparasite of the host, such as a
flea, louse, or possibly a tick in some cases ; the trypanosomes of
aquatic vertebrates, on the other hand, are transmitted by leeches
in all cases that have been investigated. In addition to inoculative
transmission (p. 24) of this kind, trypanosomes may pass directly
from one vertebrate host to another during coitus ; this is known to
occur in the case of the parasite of " dourine " in horses (T. equi-
perdum), and has been suspected, but not proved, to take place in
other cases also. It is also possible for the vertebrate to become
infected by devouring animals containing living trypanosomes,

19

290 THE PROTOZOA

whether it be the blood-sucking invertebrate, or possibly the flesh
or organs of another vertebrate infected with trypaiiosomes.

Two methods of inoculative transmission of trypanosomes have
been distinguished ; in the one, known as the " direct " or " mechan-
ical" method, the parasites merely become contained in or adhere to
the proboscis of the blood-sucking intermediary when it sucks blood
from an infected animal ; and when it feeds a second time the try-
panosomes pass directly, and without having undergone any change
or development, into the second host ; in the other, known as the
" indirect " or " cyclical " method, the trypanosomes, when taken up
by the blood-sucking invertebrate, go through a developmental cycle
in it, at the end of which, but not before, they are " ripe " for inocu-
lation into a suitable vertebrate host. Comparing natural with
artificial processes of infection, in the direct method the blood-
sucking invertebrate may be said to play the role merely of an
injection-syringe, but in the indirect method it acts also as a culture-
medium, in which the parasite passes through various phases and
assumes forms quite different from those occurring in vertebrate
blood. Patton (393) has put forward the view that transmission
is always by the direct method, and that the crithidial and other
forms found in the blood-sucking invertebrate are parasites of the
invertebrate alone, and have no connection with the trypanosomes
found in vertebrates ; but the number of cases in which it has
now been shown clearly that trypanosomes go through a definite
cycle in the invertebrate host disproves Patton's contention, and
renders it unnecessary to discuss it further. It is rather the
direct method that stands in need of further demonstration ; though
undeniably possible as a laboratory-experiment, it may be doubted
if it ever really occurs in Nature, and in any case it is probably to
be regarded as a purely accidental rather than a normal occurrence.

It has been frequently asserted or assumed that trypanosomes
can pass from parent to offspring, by so-called " hereditary trans-
mission," in the invertebrate host, but convincing proof of this state-
ment is as yet lacking entirely. Attempts to prove hereditary trans-
mission by direct experiment have given, for the most part, negative
results, and the observation so frequently made, that leeches, tsetse-
flies, fleas, mosquitoes, etc., bred from the egg and not exposed
to infection, are entirely free from parasitic flagellates, affords cumu-
lative evidence against the existence of any such method of trans-
mission (cf. Kleine and Taute, 459). Brumpt (419), however, asserts
that T. inopinatum is transmitted hereditarily from parent to off-
spring of the leech Hdobdella algira. According to Porter (554),
" Crithidia " melophagia of the sheep-ked is also transmitted from
parent to offspring in this insect ; and if, as is extremely probable,
the flagellate in question is the developmental phase of the trypano-

THE H^MOFLAGELLATES AND ALLIED FORMS 291

some of the sheep, it would furnish another instance of hereditary
transmission. Hence this mode of transmission must, apparently,
be reckoned with in some instances, though it is evidently an ex-
tremely rare phenomenon in trypanosomes generally.

Just as a given species of trypanosome is, in Nature, capable of
maintaining itself only in a particular species, or limited group of
species, of vertebrate hosts, so it may be said, as a general rule,
that in transmission by the cyclical method the parasites are
specific in the same way to certain invertebrate hosts, in which
alone they are able to go through their full natural cycle. Amongst
the many blood- sucking invertebrates which may prey upon the
vertebrate, we may distinguish " right " and " wrong " hosts ; in
the right host or hosts the parasite establishes itself more or less
easily, and passes through a full and complete developmental
cycle ; in the wrong host it either dies out immediately or goes
through only a part of its cycle. The distinction between right
and wrong hosts must not, however, be taken in an absolute sense,
but as implying only that, amongst many possible hosts, there is
one at least to which the parasites have become better adapted
than to any other ; but the trypanosomes may sometimes succeed
in maintaining themselves in other than the right host sufficiently
long to pass back again into the vertebrate. Thus, in the case of
the rat-trypanosome (T. lewisi) the right host is a rat-flea (Cerato-
phyllus fasciatus, or possibly other species) ; but it may persist in
the rat-louse (Hcematopinus spinulosus), and even pass from it,
though rarely, back into the rat again.

The following are a few well-established examples, in addition
to that of T. lewisi already cited, of trypanosomes and their right
hosts. Many pathogenic species of trypanosomes in Africa are
transmitted by tsetse-flies — e.g., T. gambiense and T. vivax by
Glossina palpalis, T. brucii by G. morsitans* etc. The recently -
described T. cruzi of Brazil was discovered in its invertebrate host,
a blood-sucking hemipterous insect, Gonorhinus megistus, before it
was found in the blood of human beings. The trypanosomes of
certain fresh-water fishes — namely, goldfish, perch, etc. — pass
through their developmental cycle in the leech Hemiclepsis mar-
ginata (Robertson, 503). T. mice of skates and rays develops in
the leech Pontobdella muricata (Robertson, 500, 502). The trypano-
some of African crocodiles, T. grayi, develops in the tsetse-fly
Glossina palpalis (Kleine, 458 ; Kleine and Taute, 459), and stages
in its life-cycle have consequently been confused with those of
T. gambiense in the same fly. The trypanosomes of birds are prob-
ably transmitted for the most part by mosquitoes, but the details of

* According to Taute, G. morsitans can act as a true host for T. gambiense, and,
conversely, according to Fischer, 0. palpalis can do the same for T. brucii.

292 THE PROTOZOA

their transmission have not yet been worked out in a satisfactory or
conclusive manner.

It must be considered for the present an open question whether true try-
panosomes occur as parasites of an invertebrate host exclusively ; the answer
to the question will depend on the significance given to the expression " true
trypanosome." It is now practically certain that many leptomonads have a
trypaniform phase in their development (see p. 314, infra), so-called " lepto-
trypanosomes." In Drosophila confusa, a non-biting, muscid fly, Chatton
and Alilaire (compare also Chatton and Leger) found in the Malpighian tubules
a trypaniform type of flagellate which they consider as a " eutrypanosome,"
as a species of Trypanosoma distinct from the Leptomonas occurring in the
gut of the same fly (Fig. 137). Wenyon (84) also found similar forms in the
Malpighian tubules of house-flies in Bagdad, and considered that they might
belong to the cycle of the Leptomonas (Herpetomonas) in the same host. In
both cases the phase in the Malpighian tubules is a little stumpy trypanosome -
like form, very similar in its characters to T. nanum. The fact that these
" eutrypanosomes " are so far known only to occur in flies which are infected
also by a species of Leptomonas indicates that, like the " leptotrypanosomes,"
they are merely a phase in the cycle of the Leptomonas.

From the foregoing it is seen that the complete life-cycle of a
trypanosome is an alternation of generations corresponding to an
alternation of hosts. One part of the cycle is passed in the blood of
a vertebrate, in which the predominant form is the trypanosome-
type of flagellate ; the second part is passed in the digestive tract
of an invertebrate, and here the predominant form is the crithidial
or trypanomonad type. We may consider the life-history, therefore,
under these two principal phases :

1. As a type of the life-cycle in the vertebrate host, that of the
common rat-trypanosome may be taken. After infection, natural
or artificial, of the rat, the trypanosomes make their appearance
in the blood about the fifth, sixth, or seventh day. What the para-
sites have been doing during this time, the so-called " incubation-
period " in the rat, cannot as yet be stated definitely ; it may be
that the relatively few trypanosomes inoculated by the flea or
syringe have merely been multiplying steadily, in the manner
presently to be described, until they become sufficiently numerous
in the blood to be detected by microscopic examination ; there may,
on the other hand, be phases of the parasite as yet unknown during
this period, and, according to recent statements (Carini, 422), a
process of schizogony takes place in the lung similar to that dis-
covered by Chagas in Schizotrypanum cruzi (see below).

When the trypanosomes first appear in the blood, their most
striking peculiarity is the extraordinary diversity in type which they
exihibit. Besides " ordinary " individuals of the normal dimensions
of the " adult " form, there are others smaller or larger, the extremes
of size being relatively huge in one direction, very minute in the
other. These differences of size are due to the fact that the try-
panosomes are multiplying actively, the large forms being those

FIG. 127. — Various forms of multiplication in Trypanosoma lewisi from the blood
of the rat. A, Trypanosome of the ordinary type ; B, small form resulting
from division ; G, stage in equal binary fission ; the nuclsi have divided and
two flagella are present, but division of the body is beginning, and is indicated
by a lighter streak down the middle of the body ; D, final stage of binary
fission, which is complete except for a bridge of protoplasm, much drawu
out, connecting the hinder ends of the two sister-trypanosomes ; E, form
with hinder end drawn out (longocaudense type), the result of binary fission
as seen in the last figure ; F, unequal binary fission of a large trypanosome ;
G, H, continued fission of the same type ; in G a parent and three daughter-
individuals, in H a parent and seven daughter- individuals, can be distin-
guished ; the parent-individual in each case is marked by the possession of
a flagellum of the full normal length, while the daughter-individuals, formed
by successive divisions, have flagella varying in length ; /, a small form,
similar to B, but with the kinetonucleus in front of the trophonucleus ; J,
binary fission of a form similar to / ; K, further division of a similar form
producing a rosette of seven individuals still connected together. From
preparations made by Dr. J. D. Thomson ; magnified 2,000 diameters.

294 THE PROTOZOA

which are about to reproduce themselves by some form of fission,
while the small forms are those which have resulted from a recent
act of reproduction.

The multiplication of T. lewisi in the rat's blood takes various forms
(Fig. 127). In some cases a trypanosome divides by equal binary fission
(O, D), but this is comparatively rare. More usually the fission is markedly
unequal, and of a multiple type. Small daughter-forms are split off from
large parent -individuals, and usually many at a time; the nucleus of the parent-
form divides several times, and subsequently the body divides into as many
portions as there are nuclei, thus producing rosette -like forms (Fig. 127,
F, G, H) in which the original parent can usually be distinguished by its long
flagellum from the small daughter-individuals with their flagella growing
out. The small forms are sometimes set free with a crithidial type of struc-
ture, the kinetonucleus in front of the trophonucleus (Fig. 127, L), and these
immature forms may proceed to reproduce themselves rapidly again by
either binary or multiple fission, in the latter case forming rosettes in which
no large parent-form can be distinguished (Fig. 127. K).

A curious type of trypanosome found during the multiplication-period of
T. lewisi is a form with the posterior end prolonged to a great length, so
that it almost resembles a second flagellum (Fig. 127, E), and has sometimes
been mistaken for such. This form has been described by Lingard as a dis-
tinct species under the name T. longocaudense. These forms appear to arise
by binary fission (Fig. 127, D] ; they are of constant occurrence and very
numerous at a certain stage of the multiplication-period.

The multiplication of T. lewisi in the rat's blood is most active
from the eighth to the tenth day after infection, after which it is
on the decline and gradually ceases. The relative number of forms
of ordinary size increases steadily, while those of unusual dimen-
sions, whether great or small, become continually scarcer, until
about the twelfth or thirteenth day the trypanosomes, now usually
present in vast numbers in the blood, are of uniform size and
appearance, exhibiting, apart from occasional abnormalities, indi-
vidual variations only of a comparatively slight character ; and all
multiplication has ceased entirely, never to recommence in the
same host. The trypanosomes swarm in the blood of the rat for
a certain time, which varies in different cases, but is usually one
or two months. The infection of the rat is sometimes spoken of as
" acute " when the trypanosomes are multiplying, and as " chronic "
when multiplication has ceased, not, however, very well-chosen
terms, since the trypanosomes soon begin to dimmish in number,
and finally disappear altogether ; sometimes the diminution is very
gradual and slow, sometime? it takes place with great rapidity. In
either case the rat gets rid of its infection entirely sooner or later,
without having suffered, apparently, any marked inconvenience
from it,* and is then immune against a fresh infection with this
species of trypanosome.

* Instances are on record of lethal epizootics of rats ascribed to T. lewisi ; but
the proof that this parasite was really the cause of the disease is lacking. Under
normal circumstances rats show no perceptible pathological symptoms whatever

THE H^MOFLAGELLATES AND ALLIED FORMS 295

A type of development in the vertebrate, host contrasting in many points
with that described in the foregoing paragraphs is seen in T. cruzi (Fig. 128),
the cause of human trypanosomiasis in Brazil. In this case the ordinary or
adult forms of the trypanosome found in the general circulation do not
multiply there ; but the investigations of Chagas and of Hartmann have
made known two types of multiplication which take place in the internal
organs of the body.

The first type of multiplication proceeds in the capillaries of the lung
(Fig. 128, 6 — e). An adult trypanosome loses its flagellum, and in some cases
its kinetonucleus also ; its body then becomes rounded off into an oval mass ;
the trophonucleus, and also the kinetonucleus, if present, multiply by sue
cessive divisions to form eight nuclei of each kind ; and finally the body
divides within its own periplast into eight minute daughter-individuals, so-
called "merozoites." The merozoites are stated to exhibit a dimorphism

//.

~" f
FIG. 128. — Phases of T. (Sckizotrypanum) cruzi in vertebrate blood, a, The two

forms of the adult trypanosome, " male " (upper) and " female " (lower), from
human blood ; &, preparations for schizogony ; c, schizont ; d, division of the
nucleus of the schizont ; e, division of the schizont into eight merozoites ;
/, merozoite in a blood-corpuscle ; g, intracorpuscular phase in late stage
of growth ; h, similar phase escaping from a corpuscle, the flagellum not yet
formed ; t, similar phase, the flagellum in process of formation. Stages
6 — e are found in the lung, the others in the peripheral blood. After
Chagas (425).

which Chagas regards as sexual ; those produced by trypanosomes which
retained their kinetonucleus have both trophic and kinetic nuclei and a
rudiment of a flagellum (male forms) ; those derived from trypanosomes which
lost both flagellum and kinetonucleus have only a trophonucleus (female
forms) ; in the latter case the single nucleus divides into two unequal parts,
of which the smaller becomes the new kinetonucleus, and a flagellum is
formed subsequently. In either case the merozoites penetrate into blood-

f rom even the most swarming infection with T. lewisi (for the action of the " ren-
forces " strains see p. 28). Those who study habitually the lethal species of
trypanosomes often display a natural bias, not in the least justified, to assume
that a similar virulence is an inseparable attribute of all other species of these
parasites. If that were so, it would be necessary to consider practically every
specimen of pike, bream, perch, or tench, in the Norfolk Broads, for instance, to be
in a diseased condition.

296 THE PROTOZOA

corpuscles, and so pass into the general circulation. Within the corpuscle
they grow into the adult form, which is finally set free from the corpuscle as
a trypanosome of normal structure. The adult trypanosome (Fig. 128, a),
swimming freely in the blood-plasma, may either be taken up by the inverte-
brate host in which it develops, or may repeat the process of multiplication
by schizogony.

'The second type of multiplication was first described by Hartmann from
hypertrophied endothelial cells of the lung ; Chagas (426) has since found it
in the tissues of the body, more especially in the cardiac muscle, central nervous
system, and striped muscle. In this type the parasite is intracellular, and has
the appearance and structure of a Leislimania (cf. Fig. 138), a rounded
body containing a trophonucleus and a kinetonucleus, but no flagellum or
undulating membrane.

On account of its power of multiplication by schizogony, Chagas has made
T. cruzi the type of a special genus, Schizotrypanum ; the type of multiplication
observed in the lung- capillaries is not essentially different, however, from that
of T. lewisi in the blood, except for its alleged sexual dimorphism ; and, accord-
ing to Carini (424), similar processes of schizogony occur in other trypanosomes
The intracellular multiplication in the tissues, however, recalls strongly that
of the parasite of kala-azar (see p. 316, infra}. Schizotrypanum thus forms
an important link between a typical blood-trypanosome, such as T. lewisi,
and a tissue-parasite, such as the species of Leishmania, in which the free
trypanosome -phase no longer exists, apparently.

Chagas considers the multiplication of Schizotrypanum cruzi in the tissues as
non-sexual, and serving to increase the number of parasites in the host, but that
which takes place in the lung- capillaries as a process of gametogony whereby
the sexually differentiated adult forms are produced. His grounds for this
interpretation are, first, that in human blood the adult trypanosomes exhibit
a dimorphism rarely found in guinea-pigs infected artificially, in which also
schizogony in the lung is seldom observed ; secondly, that the invertebrate
host, Conorhinus, is always rendered infective if fed directly on infected
human blood, but very rarely becomes infective if fed on guinea-pigs, even
when these animals show an intense infection. He suggests that the greater
resistance of the human organism to the parasite stimulates the production
of sexual forms which the trypanosome may cease to produce in a less resistant
host.

In the more familiar pathogenic species, such as T. brucii, T. gambicnse,
etc., the development in the vertebrate host takes the form mainly of continued
multiplication by binary fission simply. Reproduction of this kind may pro-
ceed until the trypanosomes swarm in the blood ; or, on the contrary, the
trypanosomes may be at all times relatively few in number, even when
fatal to their host. T. brucii, for example, may produce in different hosts
an acute or a chronic form of disease ; in the latter case the infected animal
may live a long time, and the parasite exhibits very limited powers of multi-
plication. The behaviour of the parasite in the natural hosts to which it is
harmless has not been studied.

In many pathogenic species, periods of multiplicative activity, during
which the trypanosomes are abundant, alternate with periods during which
the parasites pass into a resting condition in the internal organs, and become
scarce or disappear in the general circulation. In this phase they are alleged
to lose their flagellum, diminish in size, and become small, rounded " latent
bodies," which, according to Moore and Breinl (484), have only a single nucleus ;
but according to Fantham they are Leishmania-like, with distinct tropho-
. nucleus and kinetonucleus. From resting stages of this kind the active
trypanosomes are developed again. Laveran (462), however, denies that there
is a non-flagellated stage of development in the vertebrate host, and considers
that the elements described as "latent bodies" represent involution-stages of
the parasites — that is to say, forms which have become deformed in structure
owing to unfavourable conditions, but not to such an extent as to be incapable
of recovery if the conditions improve.

THE ILEMOFLAGELLATES AND ALLIED FORMS 297

In the vast majority of trypanosomes in their natural hosts, such as birds,
fishes, etc., the mode of multiplication and the developmental cycle remains
a mystery, although the sizes of the individual trypanosomes and their numbers
are observed to vary at different times in the same host. Considerable light
has been thrown upon this question by the recent investigations of Machado
upon the multiplication of Trypanosoma rotatorium of frogs, a species re-
markable for the polymorphism it exhibits. The results obtained by Machado
may be summarized briefly as follows : Trypanosomes of any size may divide
by binary fission when free in the blood (supposed " non-sexual " reproduction).
On the other hand, trypanosomes of large size may become rounded, flattened,
leaf -like forms, losing their flagellum ; such forms undergo a process of
schizogony in the internal organs, chiefly in the liver or kidneys, sometimes in
the spleen, sometimes even in the circulating blood. The kinetonucleus
approaches the trophonucleus, and may (1) remain distinct from it, so-called
" male " type ; or (2) may pass into the trophonucleus, in which the karyo-
some breaks up to form a small secondary karyosome ; the kinetonuclear
karyosome then fuses with, or becomes closely adherent to, the secondary
trophonuclear karyosome — so-called " female " type. A multiplication of
the nuclei then takes place : in the " male " type by independent divisions
of the kinetonucleus and trophonucleus ; in the " female " type by divisions
of the single mass formed by fusion of the kinetonuclear and trophonuclear
karyoeomes, followed by budding off of small nuclei from the originally
single nucleus. Thus the body of the rounded-off trypanosome becomes
filled, within its periplast, with nuclei varying in number from five to seven-
teen ; then round each nucleus ("female ") or each pair of dissimilar nuclei
(" male ") the protoplasm becomes condensed to form as many merozoites,
which are finally set free by rupture of the periplast. The merozoites of
" male " type develop a flagellum ; in those of " female " type the single
nucleus divides into two nuclei of unequal size, a larger trophonucleus and a
smaller kinetonucleus, and from the latter a basal granule is budded off
from which the flagellum grows out (Fig. 30, G). In either case the mero-
zoites (which may divide further after being liberated from the parent body)
become transformed finally into the smallest forms of trypanosomes, which
then grow up into the larger forms found in the blood. Machado's observa-
tions of fact, apart from his theoretical interpretations, explain the many
different forms found in the frog's blood, which have recently been studied
in detail by Lebedew ; compare also Mathis and Leger.

In other cases there may be three well-marked types of form — long and
slender, short and stumpy, and intermediate or indifferent forms, as in
T. gambiense (Fig. 12 ; cf. Minchin, 477, Kindle, 450, Bruce, 405) ; or there
may be every gradation in size from small to large forms, as in T. granulosum
of the eel (Fig. 129) ; or, finally, the trypanosomes may be practically uniform
in size and structure, as in T. lewisi after the multiplication- period, T. vivax,
etc. A satisfactory explanation of the polymorphism has not been found
in all cases ; the various forms may be in some instances stages of growth
related to multiplication, as in T. lewisi during the multiplication- period ; in
other cases the polymorphism — for example, of T. gambiense — may be sexual
differentiation which is related to the subsequent development in the in-
vertebrate host ; a third possibility is that in some cases the propagative
forms, destined for multiplication in the invertebrate host, are differentiated
from the other forms found in the vertebrate host, as in T. noctuce (Minchin
and Woodcock, 42). Different explanations must probably be sought in
different cases.

2. The cycle in the invertebrate host always takes place entirely
or mainly in the digestive tract, though the extent to which this
region is invaded varies greatly. In the development of T. lewisi
in the flea the parasites pass down as far as the rectum, and there

298

THE PROTOZOA

undergo the principal phase of their cycle. In the development of
the trypanosomes of fresh- water fish in the leech Hemiclepsis, the
parasites do not pass farther back than the crop (Robertson, 503).
Finally, in the many species of pathogenic trypanosomes which are
transmitted by tsetse-flies of various species, two types of develop-
mental cycle can be distinguished : in the one, the parasite invades

Fid. 129. — Trypanosoma granulosum of the common eel : four different sizes,
probably stages of growth. After Minchin (478), x 2,000.

the whole alimentary canal of the fly ; in the other it undergoes the
greater part of its development in the proboscis and pharynx alone.
The details of the developmental cycle in the invertebrate host
are very inadequately known, and have only been studied in a
very few instances. As a rule the characteristic form of this
part of the life-history is a crithidial or trypanomonad type, repre-

THE H^MOFLAGELLATES AND ALLIED FORMS 299

senting the principal multiplicative phase in the invertebrate host ;
it is a form in which the kinetonucleus is placed in front of, or close
beside, the trophonucleus, and in which, consequently, the undu-
lating membrane is confined to the anterior region of the body,
and may be quite rudimentary. As a rule the body of the trypano-
monad is shorter, stiffer, more pear-shaped, than in the typical try-
panosome-form ; no longer sinuous and flexible, it is held straight
and rigid in progression, which is effected almost entirely by the
flagellum. In many cases, however, the free flagellum is very short,
and used to attach the organism to the lining of the digestive tract.
Besides the trypanomonad form, the developmental cycle may also
include many other types of form, and often exhibits a degree of
polymorphism which is most bewildering, and compared to which
the diversity of form seen in the vertebrate host is but slight.

Taking the development of T. lewisi in the rat-flea as a typical
example, the parasites when taken up by the flea pass with the
ingested blood into the stomach (mid-gut) of the insect. In this
part they multiply actively in a peculiar manner, not as yet de-
scribed in the case of any other trypanosome in its invertebrate host
(Fig. 130) ; they penetrate into the cells of the epithelium, and in
that situation they grow to a very large size, retaining their flagellum
and undulating membrane, and exhibiting active metabolic changes
in the form of the body, which in early stages of the growth is
doubled on itself in the hinder region, thus becoming pear-shaped
or like a tadpole in form, but later is more block-like or rounded.
During growth the nuclei multiply, and the body when full-grown
approaches a spherical form, and becomes divided up within its
own periplast into a number of daughter-individuals, which writhe
and twist over each other like a bunch of eels within the thin envelope
enclosing them. When this stage is reached, the flagellum, which
hitherto had been performing active movements and causing the
organism to rotate irregularly within the cell, disappears altogether,
and the metabolic movements cease ; the body becomes almost
perfectly spherical, and consists of the periplast-envelopa within
which a number of daughter-trypanosomes are wriggling very
actively ; the envelope becomes more and more tense, and finally
bursts with explosive suddenness, setting free the flagellates, usually
about eight in number, within the host-cell. The products of this
method of multiplication are full-sized trypanosomes, complete in
their structure, and differing but slightly in their characters from
those found in the blood of the rat. They escape from the host-cell
into the lumen of the stomach.

To the intracellular multiplicative phase in the stomach a
crithidial phase in the rectum succeeds (Fig. 131). In the fully-
established condition the rectal phase consists of small pear-shaped

300

THE PROTOZOA

forms with the flagellum very short, in some cases projecting
scarcely at all from the body at its pointed end. These forms are
found attached by means of their flagella, often in vast numbers,
to the wall of the rectum, sometimes also in the intestinal or pyloric
region ; they multiply by binary fission, and form a stock, as it were,
of the parasites, which persists for a long time in the flea — probably,
under favourable conditions, for the whole life of the insect. Experi-
ments have shown that a flea once rendered infective to rats can

FIG. 130. — Trypanosoma lewisi: developmental phases from the stomach of the
rat-flea. O, Ordinary form from the blood of the rat ; A — F, intracellular
stages : A, a trypanosome curled on itself ; B, similar form in which the body
has become rounded ; C, multiplication beginning, division of kinetonucleus
and trophonucleus, daughter-flagellum growing out ; D, further stage — three
nuclei of each kind, two short daughter- flagella, and a long pa rent- flagellum
wrapped round the body ; E, six nuclei of each kind, five daughter-flagella,
parent-flagellum wrapped round the body ; F, eight nuclei of each kind, the
daughter-flagella running parallel with the parent-flagellum ; G, the type of
trypanosome resulting from the process of multiplication seen in the fore-
going figures ; this is the form which passes down the intestine into the rectum.
Magnified 2,000.

N.B. — The drawings in this figure and in Fig. 131 are made from prepara-
tions fixed wet with Schaudinn's fluid and stained with iron-hsomatoxylin ;
in such preparations the trypanosomes always appear appreciably smaller
than in films stained with the Romano wsky-stain (see Minchin, 479) ; con-
sequently these figures, though drawn to the same magnification as Figs. 11,
127, etc., are on a slightly smaller scale ; compare the trypanosome drawn in
0 with those in Figs. 11, A, and 127, A.

remain so for at least three months, without being reinfected.
From the rectal stock trypaniform individuals arise by a process of
modification of the crithidial forms, in which the flagellum grows
in length, the anterior portion of the body becomes more drawn out,
the kinetonucleus migrates backwards behind the trophonucleus,
taking with it the origin of the flagellum, and an undulating mem-

THE H^EMOFLAGELLATES AND ALLIED FORMS 301

brane running the length of the body is established. The trypani-
form individuals thus formed are of small size and broad, stumpy
form ; they represent the propagative phase which passes from the
flea back into the rat. From the rectum they pass forwards into
the stomach, and from the stomach they appear to be regurgitated
into the rat's blood when the flea feeds.

Experiments show that the flea becomes infective to the rat in
about six days after it first took up the trypanosomes from an
infected rat. The intracellular phase is at the height of its develop-
ment about twenty-four hours after the flea takes up the trypano-
somes ; the rectal phase begins to be established towards the end of

FIG. 131. — Trypanosoma lewisi: developmental phases from the rectum of the rat-
flea. A, Early rectal form ; B, crithidial form attached to wall of rectum ;
0, D, division of crithidial form ; E, clump of crithidial forms detached from
wall of rectum, hanging together by their flagella, one of them beginning to
divide ; F, G, H, crithidial forms without free flagella ; /, rounded form
without flagellum ; /, K, L, M, series of forms transitional from the crithidial
to the final trypaniform type ; N, the last stage in the flea. Magnified 2,000.

the first or beginning of the second day ; and the stumpy, trypani-
form, propagative phase is developed in the rectum towards the end
of the fifth day.

The account of the development of T. lewisi in the flea given in the fore-
going paragraphs is based upon investigations, some of them as yet unpub-
lished, carried on in conjunction with Dr. J. D. Thomson by the author
(480-482). Some of the phases of the parasite have also been described by
Swellengrebel and Strickland (517). A number of investigators — namely,
Prowazek (497), Breinl and Kindle, Baldrey (396), Rodenwaldt, and others-
have studied the development of this trypanosome in the rat-louse (Hcemato-
pinus spinulosus). Experiments have shown that this insect is also capable
of transmitting the trypanosome from rat to rat, but only, to judge from the

302

THE PROTOZOA

published results, in rare instances, in striking contrast with the ease with
which the transmission is effected by the rat-flea. The rat-louse may be
regarded, therefore, as a host in which the trypanosome establishes itself
only exceptionally, and by no means as the host to which it is best adapted.
Crithidial and other forms have been seen in the louse, but the intracellular
phase has not been observed, and it is probable that most of the forms de-
scribed from this host are degenerating forms maintaining a feeble and pre-
carious existence under adverse conditions, and destined to die_o£Tand dis-
appear sooner or later.

The developmental cycle of Schizotrypanum cruzi in the bug Conorhinus
megistus has been described by Chagas,* and is briefly as follows (Fig. 132) :

FIG. 132. — Phases of Schizotrypanum cruzi in the bug Con-orhinus megistus.
a, b, and c, Forms transitional from the ordinary trypanosomes to the rounded
forms ; d, clump of rounded forms ; e and /, change of rounded into crithidial
forms ; g and h, crithidial forms ; i, trypaniform type from the salivary
glands ; j, encapsuled form from the intestine. After Chagas (425).

The trypanosomes taken up by the bug into its stomach change in about
six hours ; they lose their flagellum and contract into rounded, Leishmania-
like forms, which multiply actively by fission. After a time multiplication
ceases, and the rounded forms become pear-shaped, develop a flagellum at
the pointed end, and change into typical crithidial forms which pass on into
the intestine, and there multiply by fission. In this way the characteristic
condition of the infected bug is produced, with the intestine containing a
swarm of trypanomonad individuals multiplying actively. The final stage
in the insect is a small trypaniform type which is found in the body- cavity
and salivary glands, whence it doubtless passes into a vertebrate host again.

* A critical summary and review of the memoir of Chagas is given by Minchin
in Nature, vol. Ixxxiv., pp. 142-144 (August 10, 1910), with three text-figures.

THE H^MOFLAGELLATES AND ALLIED FORMS 303

The three principal phases in the development of T. cruzi in the bug may be
compared, without difficulty, with those of T. lewisi in the flea, though
differing in minor details ; in both cases an early multiplicative phase in the
stomach is followed by a crithidial phase, also multiplicative and constituting
the principal stock of the parasite, in the hinder part of the digestive tract ;
to this succeeds a propagative trypaniform phase, which in the case of T. leurisi
passes forwards to the stomach, but which in the case of T. cruzi appears to
pass through the wall of the alimentary canal into the body- cavity, and so
into the salivary glands. Other developmental forms have been described
by Chagas, but their relation to the cycle of the parasite, if indeed they really
belong to it, is not clear.

The developmental cycle of the trypanosomes of fresh- water fishes in the
leech Hemiclepsis marginata (Robertson, 503) begins also by active multi-
plication in the crop about six to nine hours after the flagellates have been
ingested. The trypanosomes divide by repeated binary fission of unequal
type, budding off small individuals which are crithidial in type and multiply
in their turn. In a few days the crop is populated by a swarm of trypano-
monad forms of various sizes, multiplying actively. Towards the end of the
digestion, the propagative phase begins to appear in the form of long, slender
trypaniform individuals which arise directly from the crithidial forms, and
pass forwards in great numbers from the crop into the proboscis-sheath,
whence they are inoculated by the leech into a fresh host. A certain number
of the crithidial forms remain behind in the crop, however, where during
hunger- periods they may pass into a resting Leishmania-iorm ; when the
crop is again filled with fresh blood, these forms begin to multiply again,
repopulating the crop with crithidial forms, from which a fresh batch of
trypaniform propagative individuals arise towards the end of digestion
again.

In the development of T. raice in the leech Pontobdella muricata (Robertson,
500, 502), the ingested trypanosomes multiply in the crop in a similar manner
by unequal binary fission, budding off small individuals which, however, are
rounded and leishmanial in type, and which pass down from the crop into the
intestine, where they develop a flagellum, become crithidial in type, and
multiply actively. During hunger- periods they become leishmanial, resting
forms which persist when all other forms have succumbed and died out, becom-
ing crithidial again when the supply of food is renewed. From the crithidial
forms arise the long, slender trypaniform individuals of the propagative phase,
which pass forward into the proboscis to be inoculated into the fish. The
development of T. vittatce, from the blood of the Ceylon tortoise, Emyda vittata,
in the leech Glossiphonia sp., is of a similar type, but takes place almost entirely
in the crop (Robertson, 501).

The development of T. gambiense in the tsetse-fly, Glossina palpalis, so far
as it has been described by Kleine (457), Kleine and Taute (459), and Bruce
and his collaborators (415), presents some peculiar features not quite intelli-
gible at present. The whole development takes a long time, about eighteen
to twenty- five days or more, a fact which, together with the low percentage
of flies which become infected, accounts for the existence of a developmental
cycle having been missed by so many investigators, until it was first dis-
covered by Kleine. From five to seven days after the infection of the fly the
trypanosomes disappear or become scarce in its digestive tract, indicating,
possibly, an intracellular stage yet to be discovered. Later, in a small
percentage of the flies, the trypanosomes reappear in the digestive tract in
enormous numbers. The flagellates at this stage vary greatly in size, form,
and appearance, but crithidial forms are stated to be very rare, a feature
in which the development contrasts with the usual type seen in other trypano-
somes. Finally an invasion of the salivary glands takes place, though in what
way it is brought about is not clear ; short, stumpy trypaniform individuals
are found in the glands, which represent the ripe, propagative phase destined
to be inoculated into the vertebrate host. These ripe forms first make their
appearance, according to Kleine, in the intestine.

304 THE PROTOZOA

In many species of trypanosomes transmitted by tsetse-flies, a peculiar
mode of development occurs, as already stated, in the proboscis, termed
by Roubaud, who discovered it, a culture d'attente. The trypanosomes
taken up from the vertebrate change very rapidly into trypanomonad
(" leptomonad," Roubaud) forms, with the kinetonucleus far forward, and
attach themselves by the tip of the flagellum to the wall of the proboscis tube.
In this situation they multiply in the salivary fluid by binary fission, until
great numbers are present. In some cases this culture in the proboscis appears
to be the sole form of developmental cycle in the fly, as, for example in
T. cazalboui (Roubaud, 506, Bouffard), T. vivax (Bruce, 411, iii.) ; this type
is termed by Roubaud evolution par fixation directe. In other species
(T. dimorphon, T. pecaudi) the parasite multiplies first in the digestive tract
of the fly, and then spreads forward into the proboscis — evolution par fixation
indirecte of Roubaud ; in this case, however, the possibility does not seem
to be excluded that the forms seen in the digestive tract may have belonged
to the developmental cycle of a distinct trypanosome. Development of this
kind has only been observed in tsetse-flies.

According to Bouffard, T. cazalboui can be transmitted mechanically by
Stomoxys, but goes through its developmental cycle only in the proboscis of
Glossina palpalis ; Stomoxys may therefore cause epidemics of the disease
("souma"), but endemic areas are always in regions where O. palpalis
occurs. The tsetse-fly is not infective until six days after first feeding on an
infected animal, and it then remains infective permanently, or at least for the
greater part of its existence. Hence the proboscis- cycle is a rapid develop-
ment, comparable, as regards the time it requires, to that of T. lewisi in the
flea rather than to that of other trypanosomes in the digestive tract of the
tsetse.

Finally,* mention must be made of the cysts of T. grayi, described by
Minchin (476), occurring in the hind- gut of Glossina palpalis. The cysts result
from the encystment of a crithidial form, and are very similar to the cysts of
Herpetomonas, described by Prowazek (Fig. 124), from the hind-gut of the
house-fly ; their mode of formation indicates that they are destined to pass
out of the rectum to the exterior with the faeces, and Minchin has suggested
that a contaminative method of spreading the infection may occur in addition
to the usual inoculative method. The possibility must be reckoned with,
Jiowever, that the cysts in question may be part of the cycle of a distinct
flagellate parasite, perhaps peculiar to the fly alone, and may not belong at all
to the life- cycle of T. grayi, which has now been shown to be the developmental
form of the trypanosome of the crocodile (cf. Cystotrypanosoma, Roubaud,
557 '5). According to Kleine and Taute, trypanosomes, not encysted, may
be found in the faeces of infected tsetses.

Apart from the somewhat aberrant development of the members
of the &mcu-group, which require further elucidation, the cycle
of a trypanosome in the invertebrate host appears to consist typically
of three principal phases : (1) An initial multiplicative phase, which
may be trypaniform, as in T. lewisi, or Leishmania - like, as in
T. cruzi, or may take the form of unequal division of large trypani-
form individuals to produce either small crithidial forms directly,
as in fish-trypanosomes in the leech Hemiclepsis, or rounded
Leishmania-toTms which later become crithidial, as in T. raice
and T. vittacet ; to this initial phase succeeds (2) a crithidial phase,
which may pass farther down the alimentary canal, and which in any
case multiplies by fission and constitutes the principal stock of the

* The development described by Schaudinn (132) for T. noctuce is dealt with in
a subsequent chapter (p. 390).

THE H.EMOFLAGELLATES AND ALLIED FORMS 305

parasite, keeping up the infection of the invertebrate host. In
hunger-periods the flagellates may persist as simple, rounded,
Leishmania-like forms. Sooner or later many, it may be the greater
number, but not all, of the crithidial forms become modified into the
trypaniform individuals, which represent (3) the propagative phase
of the parasite, and pass forwards to be inoculated into the verte-
brate host. Those crithidial forms which do not become trans-
formed into the propagative individuals remain to multiply and
replenish the stock.

A very much debated question in this development is that relating to the
occurrence of sexual phases and syngamy, which, purely on the analogy
of the malarial parasites, are assumed almost universally to occur in the
invertebrate host. Not in a single instance as yet, however, has the sexual
act been proved satisfactorily to take place in the development of trypano-
somes. The fertilization described by Schaudinn (132) in " T. noctuce " is
the well-known conjugation of Halteridium, which can be observed without
difficulty ; and though Schaudinn described so-called " male " and " female "
types of trypanosomes in the mosquito, he expressly stated that they did not
and could not conjugate. The process of syngamy described by Prowazek
(497) for T. lewisi in the rat-louse, though " confirmed " by Baldrey (396),
Gonder (445*5), and Rodenwaldt, is almost certainly the agglomeration of
degenerating forms (Swellengrebel, 516 ; compare Reichenow, 78, p. 268).
Less biassed investigators, who have studied the developmental cycle of
trypanosomes with great care, such as Chagas, Robertson, and others, have
been quite unable to observe sexual processes of any kind. The liability to
error in the interpretation of observations is greatly increased, first by the
fact that trypanosomes divide longitudinally and often unequally, secondly
by the phenomena of agglomeration (p. 128), which occur readily under un-
favourable conditions. Consequently the adhesion together of two trypano-
somes may be due to quite other causes than sexual affinity. In some cases
the alleged occurrence of syngamy has been based merely on the fact that
non- flagellated forms have been seen, which, on the analogy of the malarial
parasites (p. 362), are termed " ookinetes " and interpreted as zygotes.

It is certainly remarkable, in view of the paucity of data, that so many
investigators, following Schaudinn's lead, should persist in ascribing all form-
differentiation in trypanosomes to sex, and should be unable, apparently, to
conceive of any other cause of polymorphism in parasites which have to adapt
themselves, in the course of their life- cycle, to a great diversity of conditions
(compare also Doflein, 430). It must be emphasized that the only true
criterion of sexual polymorphism is sexual behaviour, and until that has been
established it is premature to speak of sexual differentiation.

Some investigators have upheld the unfashionable view that the syngamy of
trypanosomes occurs in the vertebrate host ; so Bradford and Plimmer, and
more recently Ottolenghi, who has described in T. brucii, T. equinum,
T. gambiense, and T. equiperdum, the following process of sexual conjugation :
Two trypanosomes of very different size and appearance attach themselves
to one another by their hinder ends. One, regarded as the microgamete, is
more slender, and contains one trophonucleus or a larger nucleus of this kind
and two smaller (reduction-nuclei) ; the other, the macrogamete, is much
larger, and contains also a larger nucleus near the kinetonucleus and two or
more other nuclei in process of degeneration. The macrogamete also has
usually three, sometimes two or four, flagella and undulating membranes.
After the two gametes have united by their hinder ends, a small nucleus is
budded off from the principal nucleus of the microgamete, passes over into the
body of the macrogamete, and fuses with its principal nucleus. Subsequently
the microgamete appears to degenerate, and the fertilized macrogamete to

306 THE PROTOZOA

divide up into trypanosomes of the ordinary type. Those who consider that
syngamy can only occur in the invertebrate host will doubtless regard the
process described by Ottolenghi as phenomena of agglomeration and de-
generation. In the present state of our knowledge, however, it is best to keep
an open mind on this question, and to await further investigations.

In T. gambiense, Moore and Breinl (484) have described a process of fusion
between the kinetonucleus and trophonucleus in the formation of the " latent
bodies," and have interpreted this as a sexual process, a suggestion hardly
to be taken seriously. A similar process alleged to occur in the multiplication -
forms of T. lewisi has been interpreted by Schilling as the inevitable autogamy.

All that can be said at present, with regard to sexual processes in trypano-
somes, is that, on the analogy of other Protozoa generally, syngamy may be
expected to occur in some part of the life -cycle. It remains, however, for
further research to establish definitely the conditions under which syngamy
takes place, and the nature of the process in these organisms ; nor can it be
considered as sound reasoning, in the absence of concrete observations, to at-
tempt to limit the possible occurrence of syngamy, or to infer the exact form
it takes, either by analogies more or less far-fetched with one or another
group of Protozoa, or by the mere existence of form-differentiation, and still
less by the arbitrary interpretation of certain forms as zygotes or ookinetes.

A very variable feature in the development of trypanosomes is the sus-
ceptibility of the invertebrate host. In the case of T. lewisi, only about
20 per cent., approximately, of the fleas fed experimentally on infected rats
become infective in their turn, and in the case of tsetse-flies and pathogenic
trypanosomes the percentage is much smaller. There are also grounds for
suspecting that a certain condition or phase of the trypanosome in the blood
of the vertebrate is sometimes necessary for establishing the developmental
cycle in the invertebrate ; compare the observations and conclusions of Chagas
with regard to Schizotrypanum cruzi, mentioned above (p. 296). In Trypano-
soma noctuce the summer form which appears in the blood is of a type distinct
from the winter forms found in the bone-marrow (Minchin and Woodcock, 42).
On the other hand, in the case of the trypanosomes of fresh- water fishes, Robert-
son (503) found that every leech became infected that was fed on an infected
fish ; so that the simplest method of determining whether a fish was infected
was to feed a newly-hatched Hemiclepsis on it.

A question often discussed is whether trypanosomes in any part of their
development may pass through " ultramicroscopic " stages. Schaudinn (132)
expressed the opinion that some stages of trypanosomes investigated by him
were small enough to pass through bacterial filters ; though he did not put
this suggestion to an experimental test, it is often quoted as a proved fact.*
Moore and Breinl (484) also asserted, without experimental data, that infected
blood remained infective after filtration. On the other hand, attempts by
Bruce and Bateman to obtain experimental verification of these statements
gave negative results (compare also Report XI., p. 122, of the Sleeping Sickness
Commission).

Recently it has been asserted by Fry that T. brucii can throw off granules
which, when liberated, possess a certain motility of their own in the blood ;
this process is regarded as " essentially of a vital and not a degenerative
nature." That a trypanosome or any other living cell might excrete grains
which when set free could exhibit movements due to molecular or other
causes is highly probable ; but that such grains represent a stage in the life-
history of a trypanosome is far from being so ; nor can analogy with spiro-
chaetes be considered as a legitimate argument in favour of any such con-
clusion.

There remains for consideration the development which trypanosomes
undergo in artificial cultures, in which they exhibit a series of forms quite
different from those seen in the blood of the vertebrate, and so far resembling
the cycle in the invertebrate host in that the predominant phase is a crithidial

* It is doubtful whether the forms of which Schaudinn made this statement were
really trypanosomes or spirochaetes.

THE H^EMOFLAGELLATES AND ALLIED FORMS 307

or trypanomonad type of flagellate. Until the cultural development of a
trypanosome has been compared in detail with its natural development in
the invertebrate host, it is impossible to estimate precisely the bearing of the
cultural series of stages from the point of view of the physiology and mor-
phology of the parasite. The only investigator who has attempted this is
Chagas (425), who found in cultures of Schizotrypanum cruzi the same three
principal phases— namely, rounded, crithidial, and trypaniform — that occur
in the natural cycle, and in the same order of sequence. At present, therefore,
it would be unprofitable to discuss in detail the series of forms occurring
in artificial cultures, and it must suffice to refer the reader for further infor-
mation to the principal works on the subject, namely, those of Novy and
McNeal (489), Bouet, Franga (438, 443), Rosenbusch, Thomson (525), Wood-
cock (527), Lebedew, and Doflein (431). As already pointed out above, the
cultural method is often of the greatest practical value in determining whether,
in a given case, an animal is infected with trypanosomes or not.

Lebedew has described what he believes to be syngamy in the cultural
phases of T. rotatorium ; compare also the account of Leishmania below
(p. 319).

The genus Trypanosoma comprises a vast number of species,
parasitic in the blood of animals throughout the vertebrate series ;
and several attempts have been made to subdivide and classify

Fia. 133. — Endotrypanum schaudinni from the blood of Chdcepus didactylus.
A — E, Various forms of the intracorpuscular parasite ; F, trypanosome
from the blood of the same host. After Mesnil and Brimont, magnified about
1,500 diameters.

this comprehensive genus into smaller groups. Such attempts
have either taken the course of splitting off particular forms, char-
acterized by some special peculiarity, from the main group, or of
subdividing the group as a whole on some principle of morphology
or development. An example of the first method is the foundation
by Chagas (425) of the genus Schizotrypanum, as already mentioned,
for T. cruzi, on the ground that it multiplies by schizogony and
possesses intracorpuscular phases. The genus Endotrypanum was
proposed by Mesnil and Brimont for a peculiar form which was
discovered by them within the red blood-corpuscles of a sloth
(Cholcepus didactylus), and which is very probably an intracorpus-
cular phase of a trypanosome found free in the blood-plasma of
the same host. The life-cycle of Endotrypanum is not yet known.
Chagas considers it not improbable that it should be placed in the

308 THE PROTOZOA

same genus as T. cruzi, in which case the name Endotrypanum has
the priority over Schizotrypanum. In the present state of know-
ledge, data are lacking for deciding how far it is possible to employ
either multiplication by schizogony or an intracorpuscular habitat
as characters for defining genera of trypanosomes. An intra-
corpuscular habitat is probably commoner in trypanosomes than
has usually been supposed. It has been described quite recently
by Buchanan in T. brucii.

Attempts to subdivide the genus Trypanosoma as a whole have
been based on the possibility that the trypaiiosome-type of structure
may have had two distinct phylogenetic origins, one through
Leptomonas and Crithidia from a cercomonad ancestor, the other
through Trypanoplasma from a heteromastigote or Bodonid type.
The trypanosome-form might be imagined to have arisen from
either of these two types. It could be derived from a form like
Trypanoplasma by loss of the free anterior flagellum, in which
case the flagellum of a trypanosome is to be regarded as posterior ;
on the other hand, if, in a form like Leptomonas, the kinetonucleus
and with it the origin of the flagellum, be shifted backwards to the
neighbourhood of the trophonucleus, and if at the same time the
flagellum runs forwards along the body connected to it by an un-
dulating membrane, a Crithidia-like form results, from which, by
still further displacement backwards of the kinetonucleus and
flagellum to near the posterior end of the body, a trypanosome-
form is produced in which the single flagellum is to be regarded as
anterior. It is therefore conceivable that the trypanosome-form
may comprise two morphological types, structurally indistinguish-
able, but entirely different in origin, and opposite in morphological
orientation of the body.

From this point of view, Woodcock (395) subdivided trypano-
somes into two genera : Trypanomorpha, with cercomonad ancestry
and flagellum morphologically anterior ; and Trypanosoma, in a
restricted sense, with heteromastigote ancestry and flagellum
morphologically posterior. The genus Trypanomorpha included
only one species, T. noctuce of Athene noctua ; all other species of
trypanosomes were left in the genus Trypanosoma sens, strict.
Liihe put forward a classification based on similar conceptions with
different interpretations, and proposed three genera of trypano-
somes : Hcematomonas (Mitrophaiiow) for the trypanosomes of fresh-
water fishes believed to have a heteromastigote ancestry ; Trypano-
zoon for the trypanosomes of mammals, such as T. lewisi, T. brucii,
etc., regarded as having a cercomonad ancestry and an anterior
flagellum ; and Trypanosoma sens, strict, for the trypanosomes of
frogs and reptiles. T. noctuce,, on the other hand, he regarded, in
agreement with Schaudinn (see p. 390, infra], merely as a develop-

THE H.EMOFLAGELLATES AND ALLIED FORMS 309

mental stage of Hcemoproteus. Although, however, it is quite
possible that some trypanosomes may have a heteromastigote
ancestry, all the developmental facts hitherto discovered indicate
a cercomonad ancestry with a single anterior flagellum, and there
is no concrete evidence of a heteromastigote origin for any species
that has been studied up to the present. Trypanoplasms, so far
as they have been studied, preserve their biflagellate, heteromastigote
type of structure throughout their development in all active phases,
and never pass through a trypaniform or crithidial phase. Try-
panosomes, on the other hand, show constantly a crithidial phase
in the invertebrate host, but have not been observed in any case
to be heteromastigote or even biflagellate, except temporarily during
division, in any phase of the life-history. Consequently, attempts
to subdivide trypanosomes on a morphological or phylogenetic
basis must be regarded at present as premature (compare also
Laveran, 461).

II. THE GENUS TRYPANOPLASMA.

The peculiar distribution and occurrence of the species of this
genus has been pointed out above. Originally founded for forms
parasitic in the blood of fishes, it now comprises a somewhat
heterogeneous collection of species, some of which were formerly
referred to other genera of Flagellates. Of recent years, the
number of species known to be parasitic in invertebrate hosts has
increased, and is increasing rapidly. Such are T. (" Trypano-
phis ") grobbeni, found in the gastro vascular system of Siphonophora
(Keysselitz, 453) ; T. (" Bodo ") helicis, from the receptaculumseminis
of Helix pomatia and other snails (Friedrich) ; T. dendroccdi, from
the digestive tract of Dendrocodum lacteum (Fantham and Porter,
P.Z.S., 1910, p. 670) ; T. vaginalis, from the female genital organs
of leeches (Hesse, C.R.A.8., cli., p. 504) ; and T. gryllotalpce, from
the end-gut of Gryllotalpa vulgaris (Hamburger). These examples
show that the genus, as at present defined, is of widespread occur-
rence. It may be doubted, however, if the various species described
should all be placed together.

The species of Trypanoplasma parasitic in blood are only known
as yet from fresh-water fishes ;* they have an alternation of hosts,
being transmitted by leeches. The life-history of the intestinal
trypanoplasms has not been investigated, but in all probability they
have but a single host, which acquires the infection by swallowing
accidentally their cysts or other resting stages passed out from a

* The " Trypanoplasma " stated by Bruce and his colleagues (412, pp. 495, 496)
to occur in the blood of birds and in the digestive tract of tsetse-flies was in reality
a Leucocytozoon.

310

THE PROTOZOA

former host. T. helicis, according to Friedrich, passes from one
snail to another mechanically in the spermatophores during coitus.
The following account refers mainly to the blood-inhabiting species :
The body of a trypanoplasm is relatively broader and shorter,
less sinuous and serpentine, than that of a trypanosome, and is
at the same time softer and more plastic, being limited by an
extremely thin periplast. The contractile, often slightly metabolic,
body yields readily to pressure, and exhibits in consequence
passive form-changes when moving among blood-corpuscles or

FIG. 134. — A, Trypanoplasma abramidis from the blood of the bream ; B and C,
T. keyssditzi from the blood of the tench : B, small ordinary form ; C, large
form. After Minchin, magnified 2,000.

other solid particles. The principal structural feature is the
possession of two flagella, which arise close together at the anterior
extremity from a pair of blepharoplasts or diplosome, or from a
single basal granule (Martin). One flagellum projects freely for-
wards ; the other turns more or less abruptly backwards, and passes
down the side of the body at the edge of an undulating membrane
to the hinder end, beyond which it projects freely backwards to
a variable extent in different species. In T. gryllotalpce the un-

THE H^MOFLAGELLATES AND ALLIED FORMS 311

dulating membrane only extends along two-thirds of the length of
the body, after which the posterior flagellum becomes free. The
kinetonucleus, situated at the extreme anterior end of the body,
is relatively very large, usually exceeding the trophonucleus in
size, and is sometimes constricted into two or three portions, but
is generally a compact mass which stains deeply in preparations.
In T. helicis, according to Jollos, it is prolonged backwards into
fibrils, usually two in number, which extend some way down the
body, and are probably comparable to an axostyle. The tropho-
nucleus has a vesicular structure with a conspicuous karyosome. Its
position in the body varies, being in some species close behind the
kinetomicleus, in others near the middle of the body. It often
appears to be lodged completely in the undulating membrane, which
in this genus is often very broad and less sharply defined than in a
trypanosome, appearing as the border of a flattened body. The
cytoplasm frequently contains numerous " chromatoid grains."

Trypanoplasms in the blood of fishes often exhibit marked
polymorphism, with two extremes of size, small and large (Fig. 134,
B, G). According to Keysselitz (454), the large forms are the
gametes which conjugate in the leech, and are distinguishable as
male and female forms, but the statement requires confirmation.
From the investigations of Robertson (503) on the development,
it appears more probable that the large forms are simply full-grown
individuals, ripe for multiplication by fission. Unfortunately,
next to nothing is known of the reproduction of the parasites in
the vertebrate host, though it has been observed that their numbers
are subject to considerable fluctuations, and that a fish showing
at one time a very scanty infection of the blood may have a
" relapse," and appear later well infected. Keysselitz accuses
these parasites of pathogenic properties, but this charge is founded
on observations on fish in captivity, in which weakened powers of
resistance may lead to abnormal activities on the part of the parasite
(compare also Neresheimer).

The development of blood - trypanoplasms in the invertebrate
host, which is in all known cases some species of leech, appears to be
of a comparatively simple type as compared with that of trypano-
somes, and consists of little more than rapid multiplication by
binary fission to produce a swarm of relatively small trypano-
plasms, some of which, more slender and elongate in form, pass
forwards into the proboscis, and are inoculated by the leech into
a fish. Conspicuous in this development, as compared with that
of trypanosom.es, is the entire absence of any uniflagellate forms,
crithidial or other. So long as a trypanoplasm is in an active state,
it is invariably biflagellate. Resting forms without a locomotor
apparatus may occur. In T. helicis, Friedrich describes winter

312

THE PROTOZOA

forms with a single nucleus, which is in some cases the tropho-
nucleus, in others the kinetonucleus.

The accounts given of the process of division are somewhat conflicting.
According to Martin, division of T. conger -i is initiated by the division of the
single basal granule of the flagella, followed by splitting of each flagellum
longitudinally. Next the trophonucleus divides amitotically, the karyosome
becoming first drawn out into a band, after which the nucleus as a whole is
constricted into two. Lastly the kinetonucleus becomes elongated, and
divides simply by a transverse constriction into two pieces. Jollos, however,
following Rosenbusch's statements for trypanosomes, affirms that the division
of both nuclei is mitotic in T. helicis. Alexeieff, on the other hand, denies
that the kinetonucleus of Trypanoplasma is a nucleus at all. This author also
describes a series of chromatinic blocks at the base of the undulating membrane
of T. intestinalis, similar to those seen in Trichomonas (compare Fig. 5).

Keysselitz (454) has described syngamy in the development of T. " borreli"
in the leech Piscicola, but the description and figures are unconvincing, and the
matter requires reinvestigation. No other investigators have found sexual
processes of any kind in trypanoplasms.

III. THE GENUS CBITHIDIA.

The distinctive structural feature of Crithidia (Fig. 135, A) is
the relatively short undulating membrane which, with the single
flagellum, arises in the middle of the body from the vicinity of a
kinetonucleus situated beside, or in front of,
the trophonucleus. The form of the body varies
from a relatively long, slender type to the short,
" barley-grain " form from wrhich the name of
the genus is derived.

As already pointed out, the application of
the name Crithidia as the denomination of a
genus is involved in considerable confusion
and perplexity — partly because the distinctive
morphological characters shade off by imper-
ceptible gradations into those of trypanosomes
on the one hand, and leptomonads on the other,
but stilt more because a certain number of the
" species of Crithidia " are unquestionably de-
velopmental stages either of trypanosomes or
leptomonads, and others are justly suspected
of being so. In the present state of know-
ledge, it is safest to presume that any
" Crithidia " from the digestive tract of a
blood-sucking insect is a stage of a trypano-
some from the blood of a vertebrate, until the contrary has been
clearly established. At the same time the possibility must always
be taken into account that a blood-sucking invertebrate may
harbour flagellate parasites peculiar to itself in addition to those

— bl

FIG. 135. — Crithidia
minuta, Leger, from
the gut of Tabanus
tergestinus. A, Or-
dinary motile indi-
vidual; B, O, young
forms, with flagel-
lum short or rudi-
mentary. After
Leger.

THE H^EMOFLAGELLATES AND ALLIED FORMS 313

which it takes up in vertebrate blood, and that in this way stages
of the life-cycle of two or more distinct parasites may be confused
together. Up to the present, however, no blood-sucking insect has
been proved satisfactorily to harbour flagellate parasites not derived
from vertebrate blood.

After deducting doubtful species of Crithidia, there remains a
residue which appears to comprise genuine, independent species,
parasites of the digestive tract of insects. As examples of such
species may be cited C. campanulata, recorded from the digestive
tract of Chironomus plumosus (Leger, A.P.K., ii. 1903, p. 180),
from that of the larva of Ptychoptera (Leger and Duboscq) and
of caddis-worms (Mackinnon, 547) ; O. gerridis, from Gerris spp.
(Patton, 550 ; Porter, 555) ; and possibly others. The life-cycle
of C. gerridis has been investigated by Patton and Porter. The
parasite appears under two principal phases : an active, flagellate
phase, which grows to a large size, and multiplies by fission,
sometimes very actively, forming rosettes ; and a resting, non-
flagellate Leishmania - form. The flagellate forms may be free
in the digestive tract, or may attach themselves to the lining
epithelium of the gut by their flagella. The non- flagellate forms
are found in the crop, where they grow into the adult phase,
and in the rectum, where they become encysted. The flagellate
phase is found throughout the digestive tract and in the ovaries,
but has not been observed to pass into the ova The encysted
forms pass out of the rectum, and infect new hosts by the
contaminative method.

IV. THE GENUS LEPTOMONAS (HERPETOMONAS).

The genus Leptomonas comprises typical intestinal parasites
of insects, especially Diptera and, above all, Muscidce. Several
species are also known in Hemiptera. They are in most cases
parasites of the insect alone, having no alternate host, and infection
is brought about by the contaminative method, so far as is known,
cysts dropped by one host being accidentally devoured by another.
But some species are found as parasites of the latex of Euphor-
biacese, and in this case an alternation of hosts occurs. The para-
sites are taken up from the plants by bugs (Hemiptera) which
suck their juices, and by the agency of the bugs the flagellates
are inoculated into other plants again (Lafont ; Bouet and Roubaud,
530 ; Franca, 537, 538). There can be little doubt that in this case
the bug is the primary, the plant the secondary host. The plants,
or the parts of them that are infected by the Leptomonas, suffer
considerably. The term " flagellosis " has been proposed for the
disease.

314

THE PROTOZOA

The distinctive structural features of this genus are the possession
of a single flagellum, arising from close beside a kinetonucleus
which is placed far forwards in the body, and the entire absence
of an undulating membrane (Fig. 136, B ; Fig. 137, d). As already
stated above, however, the application of the names Leptomonas
and Herpetomonas is much disputed, and the morphological defini-
tion of the genera in question is attended with considerable diffi-
culties, chiefly owing to the fact that in one and the same host a
great variety of forms may occur, with regard to which it is not
possible, in the present condition of knowledge, to state with cer-
tainty whether they represent distinct species of flagellates, refer-
able even to distinct genera, occurring fortuitously in the same
host, or whether they are all merely developmental phases of the
same species. The following are the principal forms which may

A ^D v\* U' t.^ r 6

FIG. 136. — Leptomonas jacidum, Leger, from the intestine of Nepa cinerea. A, B,
Monad forms ; G, division of a monad form ; D, monad form with short
flagellum ; E, F, 0, gregarine-like forms : E, in division, F, attached to an
epithelial cell by the rudimentary flagella, which resemble the rostra of gre-
garine sporozoites. After Leger/

occur together in the same host : (1) Large, biflagellate individuals
(Fig. 124, A), often with a distinct pair of rhizoplasts connected
with the two flagella, the type to which, according to one set of
opinions, the name Herpetomonas should be restricted, but which
on another view represents merely an early stage in binary fission,
with a daughter-flagellum precociously formed ; (2) smaller flagel-
lates with a single flagellum (Fig. 136, B ; Fig. 137, d), the type for
which the name Leptomonas is employed by those who regard the
true Herpetomonas as typically biflagellate, while by those who hold
the contrary view the two genera are ranked as synonyms ; (3) cri-
thidialforms (Fig. 137, g) ; (4) trypaniform flagellates (Fig. 137, j, k),
with the kinetonucleus at the posterior end, and the flagellum
running the whole length of the body with a more or less distinct
undulating membrane — the " leptotrypanosomes " of Chatton. In

THE H^EMOFLAGELLATES AND ALLIED FORMS 315

addition to these four types of active flagellates, there may occur
also non-flagellated individuals or with the flagellum rudimentary —
namely, (5) long " gregariniform " individuals (Fig. 136, E — G ;
Fig. 137, q) and (6) oval or rounded Leishmania-iorms. The latter
may become encysted and function as the propagative stages. If
the four active forms are all distinct species, one and the same host
may have intestinal flagellates belonging to four different genera ;
if they are all phases in the development of one species, it becomes
a subtle point for discussion which of the four forms is to bs regarded
as the " adult " generic type.

n.

FIG. 137. — Flagellates from the digestive tract and Malpighian tubules of Dro-
sophila confusa. a, b, c, Trypanosoma drosophilce, three forms, from the
Malpighian tubules; d — q, various forms of Leptomonas drosophilce from
the intestine : d, e, f, leptomonad forms ; g, crithidial form ; h, i, transitional
forms from the preceding to j, k, the leptotrypanosome-forms ; m, n, small
crithidial (" barley-grain ") forms ; o, p, forms transitional from the preceding
to q, gregariniform individuals attached to the epithelium by a rudimentary
flagellum, the middle one of the three in process of division. After Chatton
and Leger (533).

Not in every case, however, does such complexity of form occur in the
same host. The development of a typical leptomonad, such as L. (H. ) jaculum
of Nepa cinerea, as described by Porter (556), is of a comparatively simple
type, like that of Crithidia gerridis described above. Non- flagellated Leish-
mania-like individuals give rise to flagellates of the true leptomonad type,
which multiply by fission ; these in their turn pass into a non- flagellated
condition in the hind-gut, there becoming encysted and being cast out with the
faeces to infect new hosts. Prowazek (557) has described in H. muscce-domes-
ticcB an extraordinary complication of male and female types — autogamy,
parthenogenesis of female forms, and " etheogenesis " of male forms ; none
of these statements can be accepted as even probable until the weighty super-
structure of theoretical interpretation is supported by a more substantial
foundation of observed facts. Many of the stages described by Prowazek,
especially his so-called "etheogenesis," represent stages in the development of
distinct parasitic organisms not belonging to the group Flagellata ; compare
Flu, Dunkerly.

316

THE PROTOZOA

V. THE GENUS LEISHMANIA.

This genus was founded by Ross to include two human parasites :
the so-called Leishman-Donovan bodies, cause of the disease
known in India as " Kala-azar " ; and Wright's bodies (L. tropica),
cause of boils known by various local names, but termed compre-
hensively " Oriental sore." To these a third species — namely,
L. infantum — has been added by Nicolle (570), causing a disease in
children in Tunis, Algeria, and Italy, and found also in dogs, which
are regarded by Nicolle as the primary host of the parasite and the
source of the infection in human beings. In all cases the type of
parasite found in the vertebrate host is very uniform (Fig. 138) —
small bodies, usually rounded or oval, contained within cells and

Fia. 138. — Leishmania donovani in cells. A, A macrophage ; B and 0, endothelial
cells containing the parasites (p.) ; n., nucleus of the infected cell. After
Christophers.

multiplying by fission (Fig. 139). Each parasite possesses two
distinct nuclear bodies, which the development shows to be a tropho-
nucleus and a kinetonucleus respectively. The cells which harbour
the parasite are mainly, if not exclusively, of two classes — namely,
leucocytes and endothelial cells ; the latter become greatly hyper-
trophied, forming the so-called " macrophages " (Fig. 138, A), which
may contain 150 to 200 parasites at a time. L, donovani was
believed originally to occur also in red blood-corpuscles, and was
first described as a species of the genus Piroplasma (p. 379). The
balance of evidence, however, is against their occurrence in the
h?ematids. If set free by the disintegration of their host-cell, they

THE H.EMOFLAGELLATES AND ALLIED FORMS 317

are probably taken up by leucocytes, and in them they may be
carried into the general circulation.

Although the diseases caused by these parasites are termed
comprehensively " leishmanioses," they are not all of one type.
L. donovani produces a systemic disease, very deadly in its effects,
and the parasite is found in immense numbers in the spleen, bone-
marrow, liver, etc. L. infantum is similar in its effects. L. Iropica,
on the other hand, produces a purely local infection, manifested
in the form of one or more boils on the skin, each of which, accord-
ing to Wenyon (84), represents either a single infection by the
insect, as yet not known with certainty, which transmits the
disease, or a secondary infection by a house-fly or by the in-
dividual himself from another boil on the skin. The infection by
L. Iropica has an incubation-period of about two months. The
disease lasts from twelve to eighteen months, and one attack, after
it is healed spontaneously, confers absolute immunity for the
rest of the patient's life. Corresponding with these differences in

B

D

FIG. 139. — Leishmania donovani. A, Three parasites in the ordinary condition,
each showing a larger trophonucleus and a smaller kinetonucleus ; B, C, D,
stages of binary fission ; E, multiple fission into three parts. After Chris-
tophers.

the effects produced by the parasites, there are also slight structural
differences to be made out in them. L. donovani (Fig. 138) is very
uniform in shape, being rounded or ovoid ; L. tropica (Fig. 140),
on the other hand, shows more variety of form, with every transition
from elongated, narrow forms with one end pointed to the typical
oval body (Row, Wenyon).

No other stage than that described above is known from the
human body ; but it was first discovered by Rogers (576) for
L. donovani, and subsequently confirmed by other investigators
for this and other species, that in artificial cultures the parasite
develops into a typical leptomonad form (Fig. 140). The Leish-
mania-ioYms in the cultures grow considerably in size, and at the
same time multiply by fission. The relatively large rounded forms
become pear-shaped, and a flagellum is developed at the blunt end
of the body ; finally the organism assumes the typical elongated form
of a leptomonad, with a long flagellum arising close beside the kine-
tonucleus, which is situated near the anterior end of the body.
Leishman and Statham have described a further stage in the

318

THE PROTOZOA

development in which slender, so-called " spirillar " forms are split
off from the large leptomonad forms.

There can be little doubt but that the cultural development observed in
all the species of Leishmania represents the natural development which the
parasite goes through in some invertebrate host. As regards, first, L. dono-
vani, arguments have been brought forward incriminating the bed-bug as the

Fio. 140. — Leishmania tropica. A, Parasites from the sore, showing different
forms ; B and G, development in cultures : B, parasites growing and multi-
plying prior to the formation of the flagellum ; 0, adult flagellated leptomonad
forms, with a couple probably the result of binary fission ; D, adult leptomonad
form ; E, similar form with the kinetonucleus dividing ; F, G, stout forms,
two stages of division ; note the flagella arising direct from the kinetonuclei,
which are connected by a centrodesmose, indicating that the centriole is con-
tained within the kinetonucleus (compare p. 87). A — 0, after Row, from
preparations stained by the Romanowsky method, magnified 2,000 ; D — G,
after Wenyon (84), from preparations stained with iron-hsematoxylin after
wet fixation.

transmitting agent, and Patton (573) has found that the parasite goes through
the same stages of development in the digestive tract of the bug (Cimex rotun-
datus) as in the artificial cultures ; but Donovan believes the true intermediate
host in Madras to be another species of bug, Conorhinus rubrifasciatus, and
Wenyon (84) considers that the development in the bug obtained by Patton
is, like the development in artificial cultures, only an imitation of the develop-
ment in the true host, and not a proof of transmission by the bug. Basile

THE H^MOFLAGELLATES AND ALLIED FORMS 319

claims to have transmitted L. infanlum by fleas. In the case of L. tropica,
Wenyon points out that the sores occur almost invariably on parts of the
person not covered or protected by clothing, a fact which is strongly against
the infection being effected by fleas, bugs, or ticks, and indicates that the
invertebrate host is some biting fly, probably either a species of mosquito or
a sand-fly (Phlebotomus). Experimental evidence of transmission, however,
is as yet lacking.

It is clear from the development that the species of Leishmania are non-
flagellated phases of a true leptomonad, and it has been proposed by Rogers
to abolish the genus Leishmania, and to place the parasites in question in the
genus Herpetomonas. The life- cycle of a Leishmania is, however, so different
from that of a typical Herpetomonas (Leptomonas), which is parasitic solely
in the digestive tract of an insect, that the genus Leishmania may well be
allowed to stand.

So long as the development is only known from artificial cultures, the
significance of the " spirillar " forms of Leishman cannot be determined.
Assuming that they are not merely degenerative forms, they may possibly
represent the propagative stage in which the invertebrate host inoculates
the parasite back into the vertebrate ; the fact that L. donovani causes a sys-
temic disease rather suggests that the initial phase in the vertebrate may be
a flagellated form which is carried all over the body in the circulation, and
from which the typical Leishmania-iph&se is developed. Another possible
explanation of the spirillar forms is that they may be gametes, perhaps of
male sex ; but there is no evidence in support of this interpretation either
from observation or analogy, since sexual phenomena in leptomonads have
not been observed. Marzinowsky claims, however, to have observed copula-
tion of male and female gametes in cultures of L. tropica.

Darling has described under the name Histoplasma capsulatum an organism
causing a disease in human beings, and believed to be allied to Leishmania.
It is stated to develop flagellated phases in lung-smears. For Toxoplasma,
referred by some to a position near Leishmania, see p. 387. " Leucocytozoon "
piroplasmoides, found in epizootic lymphangitis of horses in Senegal (Thiroux
and Teppaz), is possibly a Leishmania, but only a single mass of chromatin
appears to be present in the body, and no flagellated forms were obtained
in cultures ; possibly, therefore, its proper systematic position is near Toxo-
plasma.

VI. THE GENUS PROWAZEKIA.

This genus was created by Hartmann and Chagas (62) for P. cruzi, a species
discovered in a culture from human faeces on an agar-plate in Brazil. Two
other species have also been described from human faeces — namely, P. wein-
bergi, Mathis and Leger (Fig. 141, A and B), and P. asiatica, Whitmore.
It would appear, therefore, that several species (or possibly a single species) of
this genus occur in various parts of the world in human faeces. Martini considers
P. cruzi to be a cause of human diarrhoea and intestinal catarrh in China.
Nagler has described a species P. parva (Fig. 141, C), which is free-living, and
Dunkerly has found a Prowazekia in the gut of the house-fly. The form which
Walker has described under the name " Trypanoplasma ranee " very possibly
should be referred to Prowazekia ; it was obtained from cultures of the
intestinal contents of the frog.

In its structure, Prowazekia resembles the genus Bodo in the heteromastigote
arrangement of the flagella, and in its nuclear apparatus it resembles Trypano-
plasma, with trophonucleus and kinetonucleus. It differs structurally from
Trypanoplasma only in the fact that the backwardly- directed flagellum is free
from the body, not united to it by an undulating membrane ; it bears, in fact,
the same structural relation to this genus that Trichomastix has to Trichomonas.
Alexeieff (388) denies that the genus is distinct from Bodo, and considers that
the name Prowazekia should be cancelled ; he identifies P. cruzi with B. edax,
Klebs, and P. parva with B. saltans, Ehrenberg.

320

THE PROTOZOA

Affinities and Phylogeny of the Hcemo flagellates. — Two opposite
views have been held with regard to the origin of the Flagellates para-
sitic in blood and their allies : First, that they have a double origin
along two distinct lines of descent, some being derived from hetero-
mastigote, the others from cercomonad ancestors (Woodcock,
Doflein, Senn) ; secondly, that the Haemo flagellates are closely
allied to certain forms hitherto classed as Hsemosporidia (p. 388),
and form with them a homogeneous group or order of the Flagellata,
the so-called Binucleata (Hartmann).

The question of the Haemosporidia will be discussed below
(p. 389). It is sufficient here to deal with the Hsemo flagellates alone.
From the general survey of the " forms " or " genera " dealt with
in this chapter, it is very evident that Trypanosoma, Crithidia,
Leptomonas (Herpetomonas), and Leishmania, are very closely

FIG. 141. — A and B, Prowazekia weinbergi, Mathis and Leger (473), magnified
2,400 ; G, Prowazekia parva, Nagler (585), magnified about 2,250.

related to one another. Structurally the first three types shade
off insensibly into one another, the dividing line between Trypano-
soma and Crithidia, or between Crithidia and Leptomonas, being
quite arbitrary, and far less definite in reality than it appears when
reduced to words ; while Leishmania is a resting non-flagellated
phase of any of the three. Developmentally the four types, or any
two of them, may occur as phases in the life-history of a single
species, so that the selection of a given form as the " adult " in-
dividual, by means of which the generic name is to be determined,
is also, in many cases, quite arbitrary. Phylogenetically an evolu-
tionary series can be recognized beginning with Leptomonas, and
passing through Crithidia to Trypanosoma, of which the central
feature is the gradual development of an undulating membrane,
which finally runs the whole length of a more or less sinuous and

THE H.EMOFLAGELLATES AND ALLIED FORMS 32i

serpentine body, probably as an adaptation to life and movement
in a broth-like medium, containing numerous suspended bodies,
such as occurs in the gut of an insect, especially a blood-sucking
insect, or in the blood-fluid of a vertebrate. Leishmania, on the
other hand, represents an offshoot from the main stem in which the
resting, non-flagellated phase has become the most prominent stage
in at least one part of the life-cycle.

On the other hand, the Haemo flagellates of the biflagellate type,
Trypanoplasma and Prowazekia, stand sharply apart from the
uniflagellate genera. The orientation of the body, and of the undu-
lating membrane, when present, in particular, is entirely different in
the two types. The development in the invertebrate host of Trypano-
plasma and Trypanosoma, respectively, are quite distinct in type,
neither form passing through any stages which suggest the slightest
affinity with the other. The only feature common to the two types
is the possession of a kinetonucleus in addition to the principal
nucleus, and it is questionable to what extent this structure can
be relied upon to indicate affinity. The large kinetonucleus of
Trypanoplasma is very different in appearance from that of the
uniflagellate genera ; and, according to Alexeieff (324), it is a struc-
ture of quite a different order from the cytological point of view.
Finally it should be remarked that it is only in the biflagellate
genera that parasitism in the gut of vertebrates is known to occur.

With regard to the origin of the forms parasitic in blood, two
theories have been put forward. Leger (545) and Brumpt (389)
have upheld the view that they were originally parasites of the
digestive tracts of invertebrates, as many allied forms still are ;
that in many cases their invertebrate hosts acquired the blood-
sucking habit, whereby the intestinal flagellates became accus-
tomed and adapted to life in blood ; and that, finally, forms so
adapted passed from the invertebrate host into the blood of the
vertebrate itself. Minchin (476), on the other hand, suggested
that possibly the ancestral forms may have been parasites of the
digestive tract of vertebrate hosts, and may have passed from the
digestive tract into the blood, whence they were taken up by blood-
sucking invertebrates and transmitted to fresh hosts, acquiring
finally the power of being parasitic upon, and establishing themselves
in, the invertebrate host.

It must be admitted that all evidence which has accumulated
of recent years is in favour of the view of Leger and Brumpt. so
far as the uniflagellate forms are concerned. The types denoted
by the generic names Leptomonas. Crithidia, and Trypanosoma,
form a perfect evolutionary series, beginning with monogenetic
parasites of invertebrates and culminating in digenetic blood-
parasites. From the same stem other forms of parasitism are seen

21

322 THE PROTOZOA

to arise in other directions, as in the digenetic flagellate parasites
of Euphorbiacese.

The biflagellate genus Trypanoplasma , on the other hand, com-
prises species which, like those of Prowazekia, appear to have been
primarily parasites of the vertebrate digestive tract, and which
in some cases have established themselves in the blood and have
acquired an alternation of hosts (they can hardly be said to have
an alternation of generations), having become parasitic in an inter-
mediate host, always, so far as is known, a leech, in which they
pass through a simple type of development, consisting of little more
than simple multiplication by fission. Their structure indicates
affinities with heteromastigote types such as Bodo and Trichomonas,
common intestinal parasites, rather than with uniflagellate forms.

The suggestion is, therefore, that the flagellates parasitic in the
blood of vertebrates have two distinct lines of ancestry : the one
from heteromastigote forms such as Bodo and Trichomonas, origin-
ally parasitic in the gut of the vertebrate and culminating in the
genus Trypanoplasma ; the other derived from uniflagellate cer-
comonad* ancestors originally parasitic in the digestive tracts of
invertebrates, and culminating in the genus Trypanosoma (compare
also Senn, 358). It must be emphasized strongly, however, that
any such conclusions are of a tentative nature, and can have no
finality, but are liable to modification with every increase of know-
ledge concerning these organisms.

Bibliography. — For references see p. 488.

CHAPTER XIV
THE SPOROZOA : I. THE GREGARINES AND COCCIDIA

UNDER the common denomination Sporozoa are grouped together
a great number of parasitic organisms extremely varied in form,
structure, habitat, and life-history, but of which the most general
though not invariable characteristic is that the propagation of the
parasite from one host to another is effected by means of spores,
in the primary sense of the word (see p. 165, footnote) — that is to
say, resistant seed-like bodies within which one or more parasitic
germs are protected by a firm envelope or capsule, wheretiy they are
enabled to resist the vicissitudes of the outer world until they pass,
in one way or another, into the body of a suitable host ; when this
end is attained, the spore germinates — that is to say, the contained
organisms are set free and a fresh infection is started.

It is very obvious that propagation by means of resistant spores
is a character very inadequate for diagnosing an extensive group
of Protozoa. In the first place, many organisms, parasitic
or free-living, which are not included in the class Sporozoa, are
propagated by means of resistant spores. In the second place,
many forms included in the Sporozoa do not produce resistant spores,
being propagated by methods which render any such phase un-
necessary. The class therefore ceases to be amenable to strict
verbal definitions, and it is not surprising that the limits
assigned to it have varied at different times, and are even now
debated. The class Sporozoa was originally founded by Leuckart
to comprise two closely allied orders — the Gregarines and the
Coccidia. To this nucleus other groups were added, in particular
the various forms termed vaguely " psorosperms "* — a word
coined originally by Johannes Miiller to denote the spores of the
Myxosporidia, but soon extended to other parasitic organisms.
Thus " Sporozoa " and " psorosperms " became practically
synonymous terms, and the class to which these names were
applied became a most heterogeneous assemblage of organisms

* From the Greek \f/wpa, mange, and (TTrfy/xa, a seed, on account of the
sores and ulcers of the skin of fishes produced by Myxosporidia, and the resemblance
of their spores to little seeds.

323

324 THE PROTOZOA

having nothing in common except the parasitic habit and the
adaptations arising from it, more especially the propagation by
spores.

The modern tendency is rather to split up this vast assemblage
into smaller groups, and to abolish the Sporozoa as a primary
subdivision of the Protozoa. It is practically certain, at least, that
the two main subclasses into which it is always divided are per-
fectly distinct in their origin. The class Sporozoa is retained here
solely in deference to custom and convenience, and without preju-
dice to the affinities and systematic position of its constituents,
a question which will be discussed when the group as a whole has
been surveyed.

The life-cycle of a Sporozoon may be started conveniently from
the minute germ or sporozoite which escapes from the spore, or
from the corresponding stage when spores are not formed. The
sporozoite may have one of two forms : it may be an amoebula,
a minute amoeboid organism ; or it may be of definite form, a little
rod-like or sickle-shaped animalcule (" falciform body," " Sichel-
keim ") which is capable of twisting or bending movements, but
retains its body-form, and progresses by gliding forwards ; for this
second type of sporozoite the term " gregarinula " has been proposed
in a previous chapter (p. 169).

The sporozoite, whatever its form, is liberated in the body of
the new host, and begins at once its parasitic career ; it nourishes
itself and grows, often to a relatively huge size, at the expense of
the host. This phase of the life-history is termed the " trophic
phase," and the parasite itself during this phase a trophozoite,
by which term is understood a parasite that is actually absorbing
nourishment from the host. The trophozoite may be lodged within
cells (cytozoic), or in tissues of the body amongst the cells (histo-
zoic), or in some cavity of the body in which it either lies free or
is attached to the wall (ccelozoic). Whatever their habitat, the
trophozoites of Sporozoa never exhibit any organs or mechanisms
for the ingestion or digestion of food, but absorb their nutriment
in all cases in the fluid state, by osmosis through the surface of
the body, from the substance of the host ; if pseudopodia or flagella
are possessed by these parasites, they are never used for food-
capture, except in so far as pseudopodia, by increasing the surface
of the body, may augment its absorptive powers.

The parasite may exhibit multiplicative phases in which it
reproduces itself actively, so that there may be many generations
of trophozoites within one and the same host, which may thus be
quite overrun by swarms of the parasites. Multiplication of this
kind, which is non-sexual, is known as schizogony ; the trophozoites
which multiply in this manner are termed schizonts ; and the minute

THE GREGARINES AND COCCIDIA 325

daughter-individuals, products of schizogony, are termed mero-
zoites, to distinguish them from sporozoites which they may resemble
closely. Sooner or later, however, the propagative phase, destined
to infect new hosts, makes its appearance ; so-called sporonts (see
p. 330, infra) multiply by sporogony, which is combined with
sexual phases, to produce the sporozoites. The life-cycle of the
parasite may be passed entirely in one host, or there may be an
alternation of hosts of different species, with a distinct series of
phases of the parasite in each. When there is but a single species
of host, the method of infection of new hosts is usually contamina-
tive (p. 24), by means of resistant spores and cysts ; when there is
an alternation of hosts, the infection may be inoculative (p. 23),
without resistant phases, as in malarial parasites, or contamina-
tive, with resistant phases, as in Aggregata (p. 353).

Whether the life-cycle be of simple or complex type, it ends
with the production of sporozoites, bringing it back to the starting-
point again ; and in the vast majority of cases the sporozoites are
enclosed, one or more together, in tough sporocysts to form the
characteristic resistant spores. As a rule each spore arises from
a single spore-mother-cell or sporoblast.

The Sporozoa fall naturally into two subclasses, which have
received various names, according as one or another of their char-
acteristic features has been considered diagnostic. It is best to
define each subclass by a number of characteristics, since none by
itself is sufficiently distinctive.

In the first subclass the trophic and reproductive phases are
typically distinct — that is to say, the animal becomes full-grown,
and ceases to grow further, before reproduction begins, hence
Telosporidia (Schaudinn) ; reproduction takes place usually by
a process of multiple fission in which the daughter-individuals are
budded or split off on the outer surface of the parent-body,
hence Ectosporea (Metchnikoff) ; and the germs or sporozoites
produced are gregarinulae, hence Rhabdogenise (Delage and
Herouard).

In the second subclass the trophic and reproductive phases
usually overlap — that is to say, the still-growing or even quite
young trophozoite may begin to form spores, hence Neosporidia
(Schaudinn) ; the spore-mother-cells are formed by a process of
internal gemmation, being cut off within the cytoplasm of the
parent, hence Endosporea (Metchnikoff) ; and the sporozoites
produced are amcebulae, hence Amcebogenise (Delage and
Herouard).

Of the three contrasted characters by which the two subclasses
are distinguished, the most absolutely diagnostic is probably the
form of the sporozoite. The names Telosporidia and Neosporidia

326 THE PROTOZOA

are, however, in more common use than the other names of the
subclasses given above.*

The subclass Telosporidia, as mentioned above, includes the
three orders Gregarinoidea, Coccidiidea, and Hsemosporidia.

ORDER I. — GREGARINOIDEA.

The chief characteristics of this order are — First, that the tropho-
zoites are parasites of epithelial cells in the earlier stages of their
growth, but in later stages they become entirely free from the cells,
and lie in cavities of the body ; their most frequent habitat is the
digestive tract, but sometimes they are found in the body-cavity or
the haemoccele. The full-grown trophozoite is of relatively large size
and definite form, with a thick cuticle as a rule. In addition to
these characters, the reproduction and spore-formation, presently
to be described, are quite distinctive in type, the most diagnostic
feature being that each spore is the product of a single zygote.

The Gregarines are an extremely abundant order of the Sporozoa,
highly differentiated in structure, and comprising a great number
of species classified into genera and families. They occur most
commonly as parasites of the digestive tract or body-cavity of
insects, but also as parasites of other classes, such as Echinoderms
and Annelids ; in Molluscs they are comparatively rare, and, though
they occur commonly in Prochordata (Ascidians), they are not
known from any class of Vertebrata in the strict sense of the word.

In the early phases of development, during which the tropho-
zoite is a cell-parasite, it may be entirely enclosed in the cell, or
only attached to it by one extremity of the more or less elongated
body. In the latter case the sporozoite may have the anterior
end of the body modified into a definite rostrum, by which it attaches
itself to the host-cell, and from which is developed a definite organ
of attachment, termed an epimerite (Fig. 142, ep.), often of com-
plicated structure, and provided with hooks and other appendages.
When the cytozoic phase is past and the host-cell is exhausted, the
parasite drops off, shedding its epimerite as a rule. In the earlier
phase, in which an epimerite is present, the parasite was termed
by Aime Schneider a cephalont (" cephalin "), and in the later
phase a sporont (" sporadin "), the original use of this term, now
applied in a wider sense to denote in this and other orders of Sporozoa
those individuals about to proceed to spore-formation. The body
of the Gregarine-sporont always contains a single nucleus, but may
be divided into partitions or septa formed as ingrowths of the
ectoplasm, and is then said to be " septate " or " polycystid."

* The subclass Rhabdogenise, as instituted by Delage and Herouard, included
the Sarcosporidia, which, however, are almost certainly true Amoebogeniae.

THE GREGARINES AND COCCIDIA

327

As a rule, in such cases there is but a single septum, which divides
the body into two parts termed respectively protomerite and deuto-
merite (Figs. 7, 142) ; but in the curious genus Tceniocystis (Leger,
616) there are a number of septa,
giving the parasite a superficial
resemblance to a segmented worm.

The body of a gregarine consists
typically of distinct ectoplasm and endo-
plasm. The ectoplasm may be further
differentiated into three layers : an ex-
ternal cuticle or epicyte, a middle layer
or sarcocyte, and a deeper contractile
layer or myocyte containing myonemes
(Fig. 29. p. 58). The epimerite, with
its hooks and processes, is derived from
the epicyte ; the septa, if present, from
the sarcocyte. The endoplasm is usually
extremely granular, and contains great
quantities of stored-up food material in
reserve for the reproductive processes ;
chief amongst these substances are para-
glycogen - spherules, extremely charac-
teristic of these parasites.

A remarkable feature of gregarines is
the power possessed, by many species, of
gliding forward, often at a great pace,
without any visible organs of locomotion.
Two explanations have been given of
these movements: (1) by Schewiakoff,
that they are due to extrusion of
gelatinous fibres from the hinder end of
the body, secreted between the epicyte
and sarcocyte ; (2) by Crawley. that the
movements are produced by contrac-
tions of the myonemes which are only
present in motile forms. In motionless
forms the ectoplasm is very thin, and
consists of epicyte alone.

The nucleus of a gregarine is usually
very large, spherical, and vesicular in
type, with one or more distinct karyo-
somes. It is typically single, except in
the cases of precocious association men-
tioned below — exceptions, however, which
are only apparent, since in such cases
the gregarine represents in reality two
individuals fused into one. In the
septate forms the nucleus lies in the

deutomerite normally. In Pterocephalus (Nina), however, a second nucleus,
which appears to be of transitory nature and to take no share in the repro-
ductive processes, has been discovered in the protomerite (Leger andDuboscq,
621). The nucleus-like body observed by Siedlecki in Lankesteria ascidice,
and by Wenyon (84) in L. culicis, occurring at the point of contact of the two
associated sporonts in the cyst, is perhaps a body of similar nature. The
nucleus of Callyntrochlamys phronimce is remarkable for being surrounded
by a halo composed of radiating processes, each a thin tubular evagination

FIG. 142. — Examples of gregarines
in the " cephalont " condition.

A, Actinocephalus oligacanthus /

B, Stylorhynchus longicollis. ep.,
Epimerite ; pr., protomerite ; d.,
deutomerite. After Schneider.

328 THE PROTOZOA

of the nuclear membrane (Dogiel, 605) ; as a rule the surface of the nucleus
is perfectly smooth.

Chromidia are stated to occur in the cytoplasm of some gregarines (compare
Kuschakewitsch). According to Comes, they are scarce in normal individuals,
but become abundant with over-nutrition ; since he states, however, that
they arise in the cytoplasm, it is possible that they represent grains of the
nature of volutin rather than true chromidia. According to Drzewccki,
however, the nucleus of Monocystids may, during the early growth of the
trophozoite, break up into chromidia and be re-formed again, or may throw
out vegetative chromidia which are absorbed in the cytoplasm ; Kuschake-
witsch, however, regards this as a degenerative process.

Drzewecki affirms that Stomatophora (Monocystis) coronata, from the vesiculre
seminales of Pheretima sp., possesses a mouth-opening in a peristome, and an
anal aperture, and takes up solid food in the form of the spermatozoa of its
host. If so it is quite unique, not only among gregarines, but among Sporozoa
generally. The ingested spermatozoa are stated to be taken up and digested
by the nucleolus (karyosome). According to Hesse, the supposed mouth and
peristome are parts of a sucker-like organ of attachment. The alleged
nucleolar digestion is perhaps a misinterpretation of the extrusion of chroma-
tinic particles from the karyosome.

The Gregarines are subdivided at the present time into two
suborders characterized by differences in the life-cycle. In the
first suborder, known as the Eugregarinse, the parasite has no
multiplicative phase, but the trophozoites proceed always as
sporonts to the propagative phase by a method of reproduction
(sporogony) which is combined with sexual processes, and leads
to the formation of resistant spores. In the second suborder, the
Schizogregarinse, the trophozoites which arise from the sporozoites
become schizonts which multiply for several generations non-sexually,
by schizogony, before a generation of sporonts (gamonts or gameto-
cytes) is produced which proceed to reproduce themselves by sexual
sporogony. Stated briefly, the Eugregarinse have only a propaga-
tive phase, sporogony, in their life-cycle ; the Schizogregarinae have
both a multiplicative phase, schizogony, and sporogony. The
sporogony is of essentially the same type in both orders. It is
simplest, therefore, first to describe the life-cycle of a eugregarine,
and then to deal with the multiplicative phases of the schizogre-
garine. The complete life-cycle of a eugregarine may be divided
into eight phases.

1. The sporozoites are liberated from the spores in the digestive
tract of the host in all cases known, and usually proceed at once to
attach themselves to, or penetrate into, the cells of the lining
epithelium of the gut ; but in a few cases the sporozoites pass through
the wall of the gut into other organs, as does, for example, the
common Monocystis of the earthworm, which penetrates into the
vesicula seminalis, and finally into sperm-cells.

2. In the early cytozoic phase the trophozoite may be con-
tained completely within a cell (Fig. 143, A, B,) or merely attached
to it; the former condition, speaking generally, is characteristic

THE GREGARINES AND COCCIDIA

of the Acephalina, the latter of the Cephalina. In either case,
the first effect of the parasite is to produce a hypertrophy, often
very great, of the cell attacked (Fig. 143, B) ; later, however, the
cell atrophies, dies, and shrivels up (Fig. 143, C).

(a) In the Acephalina the intracellular parasite is set free from
the cell by its dissolution, and, if lodged in the epithelium of the
gut, may pass out of the epithelium either on its inner side, into the
lumen of the gut again, or on its outer side, into the bloodvessels
or body-cavity.

(6) In the Cephalina the relation of the parasite to the host-

FIG. 143. — Lankesteria ascidice, parasite of Ciona intestinalis.

A, Young intracellular stages in the intestinal epithelium;

B, older intracellular stage ; C, extracellular trophozoite
attached by a process of the anterior end of the body to
a withered epithelial cell, ep., Normal epithelial cell ; ep. ,
hypertrophied epithelial cell containing (6r.)the young grega-
rine ; n., nucleus of normal cell ; n.', nucleus of infected cell.
After Siedlecki, magnified 750.

cell varies greatly, and has been studied in detail by Leger and
Duboscq (618 and 620). The sporozoite may merely prick the
surface of an epithelial cell with its rostrum (e.g., Pterocephalus) ,
or may dip a short stretch of its anterior end into the cell (e.g.,
Pyxinia), or may penetrate so far that the nuclear region of the
parasite is within the cell (e.g.,Stylorhynchus), or, finally, may become
completely intracellular (e.g.,Stenophora). Ultimately, in all cases,
the chief mass of the body of the gregarine projects from, or grows out
of, the host-cell into the cavity of the digestive tract, and becomes
the protomerite and deutomerite in septate forms ; the attached

330 THE PROTOZOA

portion of the body develops into an epimerite which may acquire
a large size and a complicated structure. Originally attached to
one cell, which it destroys, the epimerite may acquire a secondary
attachment to other cells of the epithelium, which in this case are
not injured by it, as in Pterocephalus. Ultimately the epimerite
breaks off, and the body of the sporont drops into the cavity of
the digestive tract. In some cases (Pyxinid) the early attached
stages may free themselves from the epithelium several times,
and attach themselves again.

3. When liberated from the host-cell, the trophozoite grows
into the adult sporont, which, as its future history shows, is a gamont
or gametocyte. A remarkable feature of gregarines at this stage
is the tendency to associate together (Fig. 7), a habit from which
the name Gregarina is itself derived. In some cases quite a number
of individuals may adhere to one another in strings ; such associa-
tions, known as " syzygies," are, however, of a temporary nature,
passing flirtations, as it were, which have no significance for the
life-cycle or development. On the other hand, a true association
of individuals destined to form gametes always, apparently, occurs
at one time or another in the life of the sporont. In the majority
of cases, however, the sexual association does not take place till
the end of the trophic phase, when the sporont is full-grown and
ripe for reproduction. But in a number of instances the associa-
tion takes place early in the trophic phase, between quite young
free trophozoites ; and " neogamous " association of this kind may
lead to almost complete fusion of the bodies of the two individuals,
only their nuclei remaining separate, thus producing the appear-
ance of a binucleate trophozoite (Fig. 70, p. 128).

In general, the two trophozoites which associate are perfectly
similar in appearance, and exhibit no differentiation ; this is so
in all cases where they pair side by side. In some cases where
there is an early association end to end — that is to say, where one
sporont attaches itself by its protomerite to the deutomerite of
another (Fig. 7, p. 9), as is common in polycystid forms — the two
sporonts may be differentiated one from the other. In Didy-
mophyes, for instance, the protomerite of the posterior individual
disappears ; in Ganymedes the two sporonts are held together by
a ball-and-socket joint (Huxley). It is not known whether these
differences stand in any constant relation to the sex of the sporonts.
In Stylorhynchus the two partners attach themselves to one another
by their anterior extremities (Leger, 614).

4. As soon as growth is completed, the reproductive phases are
in iated by the formation of a common cyst round the two asso-
ciated sporonts, which together form a spherical ma.ss (Fig. 144, a).
The parasite is now quite independent of its host ; it is, in fact, a

THE GREGARINES AND COCCIDIA

331

parasite no longer, and may now be ejected with the faeces. The
nucleus of each sporont then divides by repeated binary fission
(Fig. 144, b) into a large number of nuclei, which place themselves
at the surface of the body (Fig. 144, c).

A question much debated with regard to the life-history of gregarines is
whether a single sporont can encyst by itself, without association with another,
and then proceed to the formation of spores. It has been asserted frequently
that this can occur, and the suggestion has been put forward that the differences
in the size of the spore observed in some species may be correlated with double
or solitary encystment. Schellack (630) has discussed the question in detail,
and is of opinion that in septate eugregarines solitary encystment either does

Fro. 144. — Schematic figures of syngamy and spore-formation in gregarines.
a, Union of two sporonts in a common cyst ; 6, various stages of nuclear
division in each sporont ; c, formation of gametids beginning (" pearl-stage ") ;

d, stages in the copulation of the gametes : in the left upper quadrant of the
figure, separate gametes are seen ; in the left lower quadrant the gametes are
uniting in pairs ; the right lower quadrant shows fusion of the pronuclei ;
and in the right upper quadrant complete zygotes (sporoblasts) are seen ;

e, stages in the division of the nuclei of the sporoblasts, which assume an
oval form ; a different stage is seen in each quadrant, eight nuclei being
present in the final stage ; /, cyst with ripe spores, each containing eight
sporozoites ; two spores are seen in cross-section. Modified after Calkins and
Siedlecki.

not occur, or leads to nothing if it does, but that amongst the Acephalina and
schizogregarines it can take place ; a clear case has been described by Leger
in Lithocystis schneideri, parasite of Echinocardium ; and in Monocystis
pareudrili solitary encystment leading to spore -formation is described by
Cognetti de Martiis. In some species cysts containing three sporonts have
been seen ; Woodcock also found a specimen of Cystobia irregularis with three
nuclei. With regard to the differences in the size of the spores, the possi-
bility has to be taken into account that in some cases they may be developed
parthenogenetically — that is to say, the gametids may each become a sporo-
blast directly, without copulation with another.

332

THE PROTOZOA

The first division of the nucleus of the sporont has given rise to considerable
discussion and has been the object of much study. In the resting state the
sporont-nucleus is a body of relatively huge size, but the first spindle formed
in the sporont is, like all the subsequent mitoses, a minute structure. Some
authors have believed that the sporont contains two nuclei, comparable to
those of Infusoria — namely, a very large macronucleus of purely vegetative
nature, which takes no part in the subsequent development ; and a minute
micronucleus of generative nature, from which the first and subsequent

FIG. 145. — Stages in the formation of a generative nucleus (" micronucleus ")
from the primary nucleus of Pterocephalus (Nina) gracilis. A, Primary
nucleus showing the first appearance of the micronucleus in a clear space ;

B, disruption of the primary nucleus ; appearance of the micronucleus in the
form of a few chromosomes in the centre of a little island of nuclear substance ;

C, further stage in the formation of the micronucleus ; D, micronucleus com-
plete with the first centrosome ; the remainder of the primary nucleus in process
of absorption. After Leger and Duboscq (621) ; A magnified 800, B, C, D,
1,000, diameters.

mitoses arise. Recent researches, however — more especially those of Schnitzler
on Gregarina ovata, Schellack (629) on Echinomera hispida, Leger and Duboscq
(621) on Pterocephalus, Robinson on Kalpidorhynchus, Duke on Metamera,
and especially Mulsow (123) on Monocystis rostrata — leave no doubt but that
the sporont contains a single large nucleus, which consists chiefly of vegetative
chromatin and other substances, but contains also the generative chromatin,
relatively minute in quantity in proportion to the whole bulk of the nucleus.

THE GREGARINES AND COCCIDIA

333

The generative chromatin may organize itself into a definite secondary nucleus
(" micronucleus ") during the break-up of the sporont-nucleus, as in Ptero-
cephalus (Fig. 145) ; or the first spindle arises within the sporont-nucleus
before it breaks up, as in G. ovata (Fig. 146) ; or a number of distinct chromo-
somes are formed in the sporont-nucleus during the process of its disintegration,
which pass to the exterior of the nucleus and form the equatorial plate of a
spindle of which the achromatinic elements appear to arise chiefly outside the
nucleus, as in Monocystis rostrata. In either case the first spindle consists
only of the generative chromatin ; the remainder of the original sporont-nucleus
is disintegrated and absorbed, or is left over in the residual protoplasm of the
cyst. The statement of Kuschakewitsch, to the effect that the primary
nucleus of the sporont may break up into a mass of chromidia, from which
a number of secondary (generative) nuclei are re-formed, has not received
confirmation in any quarter.

The mitoses in the sporont are remarkable, in most cases, for the very
distinct centrosomes (Fig. 147), which appear at the side of the nucleus before

FIG. 146. — Two stages in the formation of the first division-spindle of Gregarina
ovata, showing its origin from a very small part of the primary nucleus. In
A the spindle is seen within the primary nucleus ; in R the spindle is becoming
free from it at one point, after which the remainder of the primary nucleus
degenerates. After Schnitzler ; magnification 850 diameters.

division begins as a grain or a pair of grains placed at the apex of a " cone
of attraction" ; in Monocystis rostrata, however, centrosomes appear to be
absent. The number of chromosomes in the equatorial plate is usually four ;
but in Monocystis rostrata the number appears to be eight, and in Pterocephalus
and the allied genus Echinomera there are five chromosomes, four of ordinary
size and one large unpaired chromosome. Unlike the unpaired chromosome
of Metazoa, that of the gregarines is present in both sexes ; it gives rise, during
the reconstitution of the daughter nucleus, to the karyosome ; and the karyo-
some is eliminated from the nuclear spindle at the subsequent mitosis.
The significance of the unpaired chromosome is far from clear, and requires
further elucidation.

5. Each of the nuclei of the preceding stage grows out from the
surface of the body surrounded by a small quantity of protoplasm,
and thus a great number of small cells are budded off over the

334

THE PROTOZOA

whole body of each sporont. The small clear cells produced stud
the opaque body of the sporont like pearls ; hence this stage is often
spoken of as the " pearl-stage " (perlage, etc.). The remainder of
the body of the sjforont is left over as residual protoplasm, which
may contain nuclei, but which takes no further direct share in the
development. The cells that are produced are known as the "primary

^

*»s

-;. r / »• v\x..\ •

Wi

FIG. 147. — Stages of nuclear division in the cyst of Pterocephalus (Nina) gracilis.
A, Resting nucleus with a centrosome at one pole ; B, division of the centro-
some ; 0, D, formation of the nuclear spindle and equatorial plate ; ejection
of the karyosome ; E, nuclear spindle, with the unpaired chromosome on the
left, also the remains of the karyosome ; F, diaster-stage, with the unpaired
chromosome stretching across, the karyosome on the left ; the centrosomes
have each divided again ; O, H, later stages of division ; /, J, K, reconstruction
of the daughter-nucleus ; the unpaired chromosome forms the karyosome.
After Leger and Duboscq (621); magnification of the figures, 1,200 diameters.

sporo blasts," but a better name for them is the gametids, since each
one is destined to become a gamete. The amount of transforma-
tion which a gametid undergoes in becoming a gamete may be
very considerable, or it may be practically nil. In some cases the
male gamete develops a special structure, while the female remains

THE GREGARINES AND COCCIDIA 335

unmodified ; in other cases both male and female remain in the
undifferentiated condition of the gametid. For an account of the
gametes of gregarines, see above (Fig. 79, p. 174).

Reduction has been described in several cases in the formation of the
gametids. In the genus Gregarina the nucleus of the gametid divides twice
to form two reduction-nuclei (Leger and Duboscq, 621); Paehler and
Schnitzler have also described a reduction- division hi the gametids of Gre-
garina ovata. In Monocystis rostrata, on the other hand, the reduction takes
place, according to Mulsow (123), in the last nuclear division in the sporont-
body, prior to the budding off of the gametids. In this case the ordinary
number of chromosomes is eight, as seen in all the divisions of the nuclei ;
in the final division the eight chromosomes associate to form four pairs, those
of each pair being in close contact, but not fused ; in the mitosis that follows
one chromosome of each pair goes to each pole of the spindle, thus reducing
the number of chromosomes in each gametid-nucleus from eight to four.

6. When the gametes are ripe, they copulate in pairs, and
probably in every case the gametes of each pair are of distinct
parentage. This is certainly the case when the gametes show any
trace of sexual differentiation, since those of one sex can be seen
to arise from one sporont, and of the other sex from the other.
In many cases the two sporonts are separated from one another
by a partition dividing the cyst into two chambers, in one of which
the male gametes are formed, in the other the female ; when the
gametes are ripe, the partition breaks down and pairing of the sexes
takes place.

7. The zygote becomes oval or spindle-shaped, and a membrane
is secreted at its surface to form the sporocyst, which becomes
an exceedingly tough and impervious envelope, and is generally
composed of two layers — epispore and endospore. Within the sporo-
cyst the nucleus (synkaryon) divides usually three times to form
eight nuclei, and then the protoplasm of the sporoblast divides up
into as many slender, sickle-shaped sporozoites, leaving over a
small quantity of residual protoplasm. The sporozoites are usually
arranged longitudinally in the spore, with the residual protoplasm
at the centre. The number of sporozoites in the spore is almost
invariably eight ; exceptions to this rule are only known amongst
the schizogregarines.

The spores of gregarines differ enormously in different species
in form and appearance, and often have the sporocyst prolonged
into tails, spines, or processes of various kinds. Various mechanisms
may be developed for liberating the spores from the cyst ; for
instance, in the genus Gregarina (Clepsydrina) the cyst is provided
with sporoducts, and the residual protoplasm derived from the
sporonts swells up when the spores are ripe, and forces them out
through the sporoducts in long strings.

8. The ripe spore with its contained sporozoites passes out of

336 THE PROTOZOA

the body to the exterior. Usually it passes out per anum with the
faeces, but when the spores are formed in some internal organ of
the body, as in the Monocystis of the earthworm, it may be necessary
for the host to be eaten by some other animal, which then scatters
the spores broadcast in its faeces. In all cases, so far as is known,
the new host is infected by the casual or contaminative method,
and in its digestive tract the spores germinate and liberate the
sporozoites. In the case of Cystobia minchinii, parasite of Cucu-
maria, it is extremely probable that the host acquires the infection
by taking up the spores per anum into its respiratory trees, where
the spores germinate (Woodcock).

The schizogony characteristic of the schizogregarines takes
place during either the second or third of the phases described in
the foregoing paragraphs, in trophozoites derived from the sporo-
zoites by growth, and it takes various forms which cannot be
described in general terms ; a few examples must suffice.

1. Selenidium caulleryi (Fig. 148) : The sporozoite penetrates into a cell
of the intestinal epithelium, and grows to a large size, remaining uninucleate.
When full-grown, the intracellular parasite gives rise by a process of multiple
fission to a great number of motile merozoites which penetrate into epithelial
cells, grow, and finally become free sporonts. The schizogony of Merogre-
garina amaroucii (Porter) is of a similar type, but fewer merozoites are produced
by the schizont.

2. In Schizocystis gregarinoides (Fig. 149) the sporozoite attaches itself by
its rostrum to an epithelial cell, and as it grows in size its nuclei multiply ;
it finally becomes a multinucleate schizont of very large size, which may be
either vermiform, and is then attached by an anterior sucker-like organ to
the epithelium, or massive in form, and quite free. When full-grown, its
body divides up into as many small merozoites as there are nuclei. The
merozoites may probably repeat this development and multiply by schizogony
again ; or a merozoite may grow, without multiplication of its nucleus, into a
sporont, which proceeds to sporogony of a typical kind. In Schizocystis
sipunculi (Dogiel, 603) the schizont has a principal nucleus near its anterior
end, and forms a number of secondary nuclei near the hinder end of the body,
apparently from chromidia given off from the principal nucleus, which loses
its chromatin. Round the secondary nuclei protoplasm aggregates, and
finally about 150 to 200 merozoites are formed, lodged in a cavity in the cyto-
plasm of the schizont. The principal nucleus and the maternal body of the
schizont now degenerate, and the merozoites are set free.

3. In Porospora gigantea of the lobster, the largest gregarine known, the
full-grown individuals round themselves off, become encysted singly, and divide
up to form an immense number of so-called " gymnospores " (Fig. 150), each of
which consists of a cluster of merozoites grouped round a central mass of
residual protoplasm. The subsequent development and the sporogonj- are
unknown ; the schizogony was formerly mistaken for the sporogony (Leger and
Duboscq, 621).

In the species Porospora legeri, recently described by Beauchamp (592)
from the crab Eriphia spinifrons, a similar process of schizogony is recorded ;
but in this case an associated couple or syzygy of two trophozoites becomes
encysted together, to undergo a similar process of non sexual multiplication.
The association is one of two septate trophozoites closely attached, with loss
of the protomerite in the posterior individual, as in Didymophyes ; the subse-
quent development and sporogony are unknown. Leger and Duboscq (622)

THE GREGARINES AND COCCIDIA

337

have described recently a number of new species of Porospora from various
Crustacea ; they suggest that the genus Porospora represents the schizogony.
the genus Cephcloidophora the sporogony, of the same cycle.
4. In the peculiar genus Ophryocystis (Fig. 151), parasitic in the Malpighian

FIG. 148. — Selenidium caulleryi. A, Full-grown intracellular schizont, x 850 ;
B, stage in the multiplication of the nuclei of the schizont, X 1,200 ; G, schi-
zogony complete, showing the merozoites, X 1,000 ; D, young sporont embedded
in an epithelial cell, x 700 ; E, free, adult sporont, x 700. After Brasil (596).

tubules of certain beetles (Tenebrionidce, Curcidionidce, etc.), and formerly
regarded as a distinct order of Sporozoa, the Amcebosporidia, a double
schizogony takes place ; there are first of all multinucleate schizonts which can

22

338

THE PROTOZOA

reproduce their like for many generations, but which finally produce mero-
zoites which grow up into paucinucleate schizonts, and these produce mero-
zoites which grow up into sporonts. The sporogony of this genus is also
peculiar. Two sporonts associate, and the nucleus of each sporont divides
into three ; the body of each sporont then divides into a smaller cell with one
nucleus and a larger cell with two nuclei ; the small cell is a gamete, which is

FIG. 149. — General diagram of the life-cycle of Schizocystis gregarionides, after
Leger (617, ii.). A, Sporozoite escaping from the spore ; B, C, D, E, growth
of the sporozoite into the multimicleate schizont, of which there are two
types": the vermiform schizont (a), which attaches itself to the epithelium by
its anterior end, and the massive schizont (6), which lies free in the gut of the
host ; F, division of the schizont into a number of merozoites, which may
either grow into schizonts again (CP-, G2), or may grow into sporonts (GP) ;
H , young sporonts ; /, association of two full-grown sporonts ; J, formation of a
common cyst by two associated sporonts ; K, division of the nuclei in the
sporonts ; L, formation of the gametes by the sporonts ; M, copulation of the
gametes ; N, each zygote becomes a sporoblast and forms a spore.

enveloped by the larger binucleate cell. The two gametes copulate, and
the zygote becomes a single spore with the usual eight sporczoites ; the two
binucleate envelope- cells form a protective envelope to the spore during its
development, and die off when it is ripe (Leger, 617, i.).
(For Schaudinndla see p. 355.)

THE GREGARINES AND COCCIDIA 339

The Gregarinoidea are classified as follows :

Suborder I. — Eugregarince (without Schizogony).

Tribe I : Acephalina. — Without an epimerite and non-septate ;
typically, though by no means invariably, " ccelomic " parasites.
Example : Monocystis, with several species parasitic in the vesiculse
seminales of earthworms, and many allied genera and species ;
see especially Hesse. Also many other genera parasitic in various
hosts — echinoderms, ascidians, arthropods, etc.

Tribe 2 : Cephalina. — With an epimerite in the early stages, at
least, of the trophic phase ; in one family, Doliocystidce, non-septate,
but all others septate, with protomerite and
deutomerite, or with many segments (Tcenio-
cystis, Metamera). Typically parasites of the
digestive tract, most common in insects.

This tribe comprises a great number of

families, genera, and species ; see Minchin FIG. 150. — " Gymno-

(589). The type-genus Gregarina (Clepsy- spore" of Porospora

7 • x . • 1 gigantea, consisting of

anna) comprises many common species, such a number of sporo

as G. ovata of the earwig, G. blattarum of zoites arranged radi-
the cockroach, G. polymorpha of the meal- SJt; ThSh
worm (Fig. 7, p. 9), etc. Other well-known contains a chromatinic
species we—Pterocephalus (Nina) nobilis, from
the centipede (Scolopendra spp.) ; Stylo-
rhynchus longicollis (Fig. 142), from the cellar- beetle, Blaps mortisaga,
and many others. The family Doliocystidce contains species parasitic
in marine Annelids.

Suborder II. — Schizogregarince (with Schizogony).

Various methods of classifying the Schizogregarines have been
proposed. Leger and Duboscq (645) divide them into Monospora,
which produce a single spore in the sporogonic cycle (example :
Opkryocystis) ; and Polyspora, which produce many spores. Fantham
proposes to divide them into Endoschiza, in which the schizogony
takes place in the intracellular phase, as in Selenidium and Ecto-
schiza, in which the schizont is a free trophozoite, as in Ophryo-
cystis and Schizocystis ; the aberrant genus Siedleckia is probably
to be referred here also (see Dogiel, 606). The present state of
knowledge is hardly ripe, however, for a comprehensive classifica-
tion of the schizogregarines, and it may well be doubted whether
they are to be considered as a homogeneous and natural suborder ;
some of the families of the Schizogregarinae appear to be more
closely allied to particular families of Eugregarinse than to one
another. Leger (617, ii.) points out that the family Schizocystidce
shows close affinities with the eugregarine family Actinocephalidce.

340

THE PROTOZOA

Pf eff er asserts that the young intracellular stages of the mealworm-
gregarine multiply by fission. Porospora, with its remarkable
schizogony, is apparently a septate cephaline gregarine of the

FIG. 151. — Diagram of the life-cycle of Ophryocystis, after Leger (617, i.). A, The
spore setting free^sporozoites ; B, the sporozoite attached by its rostrum to
the epithelium of^the Malpighian tubule ; 0, multiplication of the nucleus
of the sporozoite, and] growth to form D, the multinucleate or " mycetoid "
schizont ; E, division of the multinucleate schizont into a number of mero-
zoites (F), each of which may become a multinucleate schizont again, or
(G, H) may become a paucinucleate or " gregarinoid " schizont ; H, division
of the paucinucleate schizont to form young sporonts (/, J) ; K, association
of two sporonts ; L, formation of a common cyst round the associated sporonts,
and division of their nuclei ; M , formation of three nuclei in each sporont ;
N, separation of a gamete (g.) within the body of each sporont, while the
rest of the body, with two nuclei, becomes an envelope-cell ; 0, the two gametes
have fused to form the zygote (z.) or sporo blast ; P, the sporo blast has as-
sumed the form of the spore, and its nuclei have divided into four ; ultimately
eight nuclei and as many sporozoites are formed. ^

ordinary type. A character such as the possession of the power
of multiplication by schizogony is clearly one of great adaptive
importance in the life-history of a parasitic organism, and therefore

THE GREGARINES AND COCCIDIA 341

not likely to be of classificatory value. The classification of the
future will probably be one which divides all gregarines into Cepha-
lina and Acephalina, and distributes the schizogregarines amongst
these two divisions.

At present the following families of schizogregarines are recog-
nized : Ophryocystidce, Schizocystidce , Selenidiidce, Merogregarinidce,
and Porosporidce. For the family Aggregatidce see p. 353.

ORDER II. — COCCIDIA.

The chief characteristics of the Coccidia are that, with very few
exceptions, the parasites are of intracellular habitat during the
trophic phase, and that a number of spores or sporozoites are
produced within a cyst, all of which are the offspring of a single
zygote. Further, there is always an alternation of generations,
non-sexual multiplicative schizogony alternating with sexual
propagative sporogony. As a general rule the entire life-cycle is
confined to a single host, but in one family (Aggregatidce) an alterna-
tion of hosts occurs, corresponding with the alternation of genera-
tions ; that is to say, the schizogony takes place in one host, the
sporogony in another.

Coccidia are found as parasites of various groups of the animal
kingdom. In contrast to gregarines, they are found sparingly in
Insects, and, indeed, in Arthropods generally with the exception
of Myriopods ; but they occur commonly in Molluscs, and especially
in Vertebrates of all classes. They are found also in Annelids, but
not abundantly, and in Flat- Worms (Turbellaria) and Nemertines.
A parasite of the gregarine Cystobia chiridotce has been identified
by Dogiel (602) as a coccidian, and given the name Hyalosphcera
gregarinicola.

The intracellular trophozoite is typically a motionless body,
spherical, ovoid, or bean-shaped, often with a considerable resem-
blance to an ovum ; hence these parasites were formerly spoken of
as egg-like psorosperms (" eiformige Psorospermien "), and the
same idea is expressed in such a name as Coccidium oviforme, given
by Leuckart to the familiar parasite of the rabbit now generally
known as C. cuniculi (or C. stiedce). The same deceptive resemblance
extends to the propagative phases, and the eggs of parasitic worms
have before now been mistaken for coccidian cysts, or vice versa.

The infection of the host takes place in every case, so far as is
known at present, by the casual or contaminative method. Resis-
tant spores or cysts of the parasite are swallowed accidentally with
the food, and germinate in the digestive tract. The sporozoites
escape and are actively motile ; in the majority of cases they pene-
trate into cells of the intestinal epithelium, but they may under-

342

THE PROTOZOA

FIG. 152. — Life-cycle of Coccidium schubergi. A — E, Schizogony ; F — 7, gametog-
ony ; K, L, syngamy ; L — 0, sporogony. A, Sporozoite liberated from
the spore ; B, three epithelial cells to show three stages of the parasite ; in
the first (to the left) a sporozoite (or merozoite) is seen in the act of pene-

[Conlinued at foot of p. 343.

THE GREGARINES AND COCCIDIA 343

take more extensive migrations, and find their way into some other
organ of the body, of which they are specific parasites, such as the
liver, fat-body of insects, genital organs, kidneys, and so forth.
When they have reached the cell, of whatever tissue it may be,
which is their destination, they penetrate as a rule into the cyto-
plasm, and come to rest there, but in some cases they are intra-
nuclear parasites. The trophozoite grows slowly at the expense
of the host-cell, which is at first greatly hypertrophied as a rule,
but is ultimately destroyed ; and when full-sized the parasite
enters upon the multiplicative phase as a schizont. After several
generations of schizogony, a generation of trophozoites is produced
ultimately, which become sexually - differentiated sporonts and
proceed to sporogony.

The great power of endogenous multiplication possessed by these
parasites renders them often pathogenic, or even lethal, to their
hosts, in contrast to the usually quite harmless gregarines. As a
rule, however, the production of a pathological condition in the host
reacts on the parasite, and stimulates, apparently, the development
of propagative phases, which, by passing out of the host, purge it
of the infection. In this way the disease — " coccidiosis," as it is
termed generally — may cure itself, and the host recuperates its
health, but without acquiring immunity against reinfection.

As a typical coccidian life-cycle may be taken that of Coccidium
schubergi (Fig. 152), from the common centipede, Lithobius forficalus,
described by Schaudinn (99) in a classical memoir. The complete
life-history may be divided into eight phases, which are described

FIG. 52 continued :

trating the cell ; the other two cells contain parasites (p.) in different stages
of growth (schizonts) : n., nucleus of the host-cell ; 0, D, multiplication
of the nuclei of the full-grown schizont; E, the schizont has divided
into a number of merozoites (mz.) implanted on a mass of residual proto-
plasm ; the merozoites, when set free, may either penetrate into epithelial
cells and become schizonts again, as indicated by the long arrow, or may
develop into sporonts (gametocytes) ; F, epithelial cell containing two young
sporonts, the one male ( $ ), with fine granules, the other female ( ? ), with
coarse plastinoid granules in its cytoplasm : G$ , full-grown male sporont ;
G <j? , full-grown female sporont : k. , its karyosome : H <£ , male sporont with nuclei
divided up ; the remains of the karyosome are seen at the centre of the body ;
// $ , female sporont which has expelled the karyosome : k.2, fragments of the
karyosome in the host-cell ; / $ , ripe male gametes round the residual mass
of the body of the sporont ; / ? , female gamete ripe for fertilization, throwing
out on one side a cone of reception towards the male gametes ( c? ) swarming
round it ; J, fertilized zygote which has surrounded itself by an ocicyst (ooc. ) ;
inside the body the female pronucleus ( ? ) has taken the form of a spindle,
at one pole of which is seen the chromatin of the male pronucleus ( <? 1) ;
outside the oocyst is seen a clump of degenerating male gametes ( $ 2) ; K, the
fertilization-spindle complete, with male and female chromatin spread over
it ; L, synkaryon dividing ; M , the synkaryoii has divided into four ; N, four
sporoblasts are formed, each of which has surrounded itself with a sporocyst,
lying in a mass of residual protoplasm (cystal residuum) ; O, ripe oticyst
containing four spores, each enclosing two sporozoites and a small quantity
of residual protoplasm (sporal residuum). After Schaudinn (99).

344 THE PROTOZOA

in the sequel, together with a brief summary of the chief variations
which each phase may exhibit in other coccidia.

1. The sporozoites, liberated in the digestive tract, are small
gregarinulae which move by gliding movements, and penetrate
into epithelial cells by means of their pointed anterior end
(Fig. 152, A, B).

2. In the cytoplasm of the cell they grow into the large rounded
schizonts, distinguished by the absence of reserve food-materials in
their cytoplasm, and by the large vesicular nucleus with a karyosome
(Fig. 152, B).

In a few rare instances — namely, Coccidium mitrarium, Lav. et Mesn.,
Cryptosporidium muris, Tyzzer, and the recently-described Selenococcidium
intermedium (see p. 351, infra), the trophozoite is free as in gregarines. In
Barroussia spiralis, from Cerebratulus sp., the schizont during its early phases
of growth is vermiform and spirally twisted, but becomes rounded off when
full grown (Awerinzew, 47). In the intranuclear parasite of the mole, Cydo-
spora caryolytica, the schizonts are stated by Schaudinn (147) to be sexually
differentiated, as also the merozoites to which they give rise. In the case oi Adelea
ovata, however, a sexual differentiation of the schizonts alleged by Siedlecki
(Fig. 153) is stated by Schellack and Reichenow to be due to a confusion of two
distinct species ; the supposed microschizonts, giving rise to microgametocytes, of
Siedlecki, are stated to be in reality the schizonts of Barroussia alpina, Leger,
while Siedlecki's macroschizonts alone represent the true schizonts of Adelea
ovata; compare also Debaisieux. Chagas, however, describes in Adelea
hartmanni (Chagasia hartmanni, Leger, 644) distinct male and female genera-
tions, microschizonts and macroschizonts, multiplying by microschizogony
and macroschizogony respectively.

3. In the full - grown schizont (agamont) the nucleus divides
repeatedly by binary fission (Fig. 51, p. 106 ; Fig. 152, C, D, E)
until a variable number of nuclei, about thirty or forty as a rule,
are produced. The body of the schizont then divides into as many
segments as there are nuclei, leaving a certain quantity of residual
protoplasm, and each segment becomes a merozoite (" schizozoite,"
Leger).

The schizogony takes place without any formation of resistant membranes
by the parasite, but the remains of the host-cell may furnish an envelope or
cytocyst within which the multiplication of the parasite proceeds. As a general
rule the merozoites produced are arranged like a barrel round the residual
protoplasm (Fig. 153, F), forming a so-called corps en barillet. In Caryo-
tropha a double process of schizogony occurs, recalling somewhat that of
Porospora ; the schizont divides into a number of cells, " schizontocytes " or
** cytomeres," each of which divides in its turn into a cluster of merozoites
arranged in a corps en barillet.

The nuclear multiplication in the schizont is not always effected by simple
binary fission, as in Coccidium schubergi. In Adelea ovata binary or multiple
fission of the nucleus occurs (Jollos). First the centriole contained in the
karyosome, and then the karyosome itself, divides into two ; the whole nucleus
may then divide into two also, or the division of the karyosome may be re-
peated several times, until the nucleus contains a number of karyosomes.
In the later nuclear divisions the karyosome becomes very small, consisting
of little more than the bare centriole, while the peripheral chroma! in increases

THE GREGARINES AND COCCIDIA

345

greatly in amount, forming the characteristic star-shaped figures that have so
often been depicted. According to Schellack and Reichenow, however, Jollos'
observations relate to Barroussia alpina, and not to Adelea ovata, and his state-
ments with regard to cytological details are criticized, and contradicted in
part, by these authors and also by Debaisieux. In Caryotropha the nucleus

FIG. 153. — Schizogony of Adelea ovata. A — C, Multiplication of a female schizont
to produce a cluster of merozoites (C) in which the nucleus has no karyosome ;
D — F, multiplication of male schizont to produce a cor^s en barillet (F)
of merozoites, in each of which the nucleus has a conspicuous karyosome
placed at one end of the nucleus. (According to Schellack and Reichenow,
however, the figures A — C alone represent the schizogony of Adelea ovata,
and the figures D — F represent that of a distinct species, Barroussia alpina.)
After Siedlecki.

of the schizont resolves itself into a mass of chromidia, which is then constricted
simply into two masses, then again into two, and so on (Siedlecki, 653).

Non-sexual multiplication has long been known to occur in Coccidia, but
the schizogonous generation was regarded formerly as a distinct genus and

346 THE PROTOZOA

species from the prbpagative, spore-producing phase, and was given the
generic name Eimeria, with type E. falciformis of the mouse. When the true
connection between the two forms was discovered, Eimeria became a synonym
of Coccidium, or of whatever the generic name of the sporont might be (e.g.,
Eimeria nepce, from Nepa cinerea, =Barroussia ornata). The nomenclature -
purists have, however, sought to abolish the generic name Coccidium, and to
replace it by Eimeria, on the ground of priority — a procedure which, in my
opinion, is contrary to public policy, and should not be followed, anything in
the law of priority notwithstanding.

4. The merozoites (agametes), the daughter-individuals produced
by schizogony, are set free from the remains of the host-cell (cyto-
cyst). Each merozoite is very similar to a sporozoite in form,
structure, and movements, differing only in minor points of detail ;
for instance, in C. schubergi the nucleus of the merozoite has a distinct
karyosome, wanting in that of the sporozoite. The merozoites
penetrate into epithelial cells, and become trophozoites which may
develop in one or the other of two ways — (1) into schizonts again,
repeating the schizogony already described ; (2) into sporonts
(gamonts), destined to produce gametes and resistant propagative
phases.

5. The growth of the sporonts is slower than that of the schizonts,
and differs in the two sexes ; in the male sporont (Fig. 152, G £)
the cytoplasm remains clear, free from enclosures, but in the female
(Fig. 152, G ? ) it becomes crowded with reserve nutriment, stored
up as a provision for the reproductive phases, in the form chiefly
of so-called " plastinoid spherules."

In C. schubergi the female sporonts differ also from the spherical male form
in being bean-shaped, but this is a specific peculiarity. In some species the
female sporonts are very much larger than the male, as in Adelea ovata
(Fig. 154), Orcheobius herpobdellce, etc. In the last-named species, parasitic in
the testis of the leech Herpobdella alomaria, the trophozoites which become
schizonts are parasitic in the cytophores ; but the merozoites destined to become
sporonts are quite motionless, and lie free in the lymph, whence they are
taken up passively by the lymphocytes, often several by one such cell. In the
lymphocytes they associate in couples, a male and a female sporont together,
and the female sporonts grow into long, monocystid-like bodies (Kunze).

6. When full-grown, the sporonts proceed to gamete-formation:
(a) In the male sporonts (Fig. 50, p. 102 ; Fig. 152, H J , / 3) the

nucleus gives off chromidia into the cytoplasm, and the chromidia
collect at the surface of the body ; the old nucleus, now much poorer
in chromatin, and with its karyosome still distinct, remains in the
centre of the body. The chromidia become condensed and con-
centrated into patches to form secondary nuclei, which finally take
shape as elongated compact bodies consisting of dense chromatin ;
each such nucleus, together with an almost imperceptible quantity
of cytoplasm, forms the body of a male gamete (micro gamete), and is
set free, while the greater part of the body of the sporont, together
with its old nucleus, degenerates and dies off as residual protoplasm.

THE GREGARINES AND COCCIDIA

347

(6) The body of the female sporont rounds itself off and bursts
the host-cell. At the same time the karyosome is expelled from
the nucleus (Fig. 75, p. 146 ; Fig. 152, #?,#?). It is then ripe
for fertilization as a complete and mature macrogamete.

The process of gamete -formation varies considerably in its details in other
coccidia, though similar in all essential points to that of C. schubergi. The
most important difference is that in many coccidia — as, for instance, in Addea

FIG. 154. — Addea ovata: association of sporonts and gamete-formation. A, The
two sporonts associated ; in the male ( <J ) the nucleus beginning to break
up into chromidia ; B, the nucleus of the male sporont resolved into chro-
midia ; G, formation of four secondary nuclei from the chromidia ; D, in the
male gametocyte four microgametes are formed from the four secondary
nuclei of the previous stage ; in the female gamete the nucleus has taken the
form of a fertilization-spindle. After Dobell.

ovata (Fig. 154) — the two sporonts do not remain separate, as in C. schubergi ',
but associate in pairs ; a small male sporont (gametocyte) attaches itself to
the larger female form, and the gametes are then produced. In correlation
with this habit, a great reduction in the number of the male gametes takes
place, four only being produced. In Addea (Chagasia) hartmanni, Chagas
states that two or even four microgametocytes attach themselves to the
female gametocyte ; Dobell also figures attachment of two male sporonts
in A. ovata.

348 THE PROTOZOA

The maturation of the female gamete does not necessarily take the form of
expulsion of the karyosome ; on the contrary, the karyosome may be retained
throughout the development. In the macrogamete of Cydospora caryolytica
the nucleus divides twice to form two reduction-nuclei, which are cast off,
and a third nucleus which persists as the pronucleus. A similar reduction-
process has been described by Chagas in Adelea hartmanni. In Adelea ovata,
according to Jollos, a reducing division occurs in the female gametocyte before
association with the male takes place ; this is denied, however, by Schellack
and Reichenow and by Debaisieux.

In Caryotropha the male sporont does not divide at once into microgametes,
but first into a number of microgametocytes, each of which then produces
microgametes. The process of gamete-formation is thus seen to be exactly
parallel to the schizogony, in which the schizont first divides into cytomeres,
which in their turn produce merozoites. It is obvious that in coccidia, as in
Protozoa generally, schizogony and gametogenesis are strictly homologous
processes ; the only difference, primarily, is in the nature and destiny of the
swarm-spores produced in each case, merozoites or gametes. This comparison
accentuates the fact, which will be discussed further below, that in the coccidia
multiple reproduction to produce gametes is entirely in abeyance in the
female sex.

7. The fully-formed microgamete (Fig. 50, p. 102) is a minute,
slender, serpentine organism, the body of which consists almost
entirely of chromatin ; the cytoplasm is represented by the two
flagella, which arise close together at one end of the body. One
flagellum is entirely free, the other runs along the body to the hinder
end, from which it is continued freely ; thus the structure of the
male gamete recalls that of a trypanoplasm in the heteromastigote
arrangement of the flagella.

The male gametes swarm round the inert female gamete, and one
of them penetrates into it and fertilizes it. As soon as the entrance
of a microgamete is effected, the macrogamete secretes a tough
membrane, the oocyst, at the surface of the body, preventing the
penetration of any other microgametes. A fertilization-spindle
(Fig. 69, p. 127 ; Fig. 152, J, K) is then formed in the zygote. The
female pronucleus becomes spread out into a fusiform figure con-
sisting of grains of chromatin on an achromatinic framework. When
the spindle is complete, the male pronucleus breaks up into granules
of chromatin which spread over the spindle, and are thus com-
mingled intimately with the chromatin of the female pronucleus.
When this has taken place, the spindle contracts to form the rounded
synkaryon, and the syngamy is complete.

The structure of the microgamete varies in different species. In some
cases (Adelea, Klossia, Legerella, Barroussia spiralis) flagella are wanting,
and the microgamete is a slender, spirochaete-like organism, consisting entirely,
so far as can be seen, of chromatin, but actively motile. When flagella are
present, they are usually two in number. In Orcheobius herpobdellce, Bar-
roussia (Minchinia) caudata, and some other species, the microgamete ter-
minates anteriorly in a point or rostrum, close behind which two flagella are
given off, and are directed obliquely backwards, quite free from the body.
In Aggregate, Moroff (94) describes the microgametes as long and slender,
with a nucleus of peculiar form, sometimes greatly drawn out, and with

THE GREGARINES AND COCCIDIA 349

two flagella, both arising at the anterior end and directed forwards. In
Coccidium rouxi, Elmassian describes two forms of microgametes differing
greatly in size.

In forms in which the sporonts associate, as in Adelea and Orcheobius, one
of the four microgametes produced penetrates the macrogamete ; the other
three die off. In some species — e.g., Coccidium proprium of the newt — the
oocyst is formed prior to fertilization, and the male gamete enters through a
minute aperture or micropyle, which is closed as soon as one has entered.
In Cydospora caryolytica, however, numerous microgametes penetrate into
the macrogamete, but only one of them furnishes a male pronucleus, which
copulates with the female pronucleus ; the remaining male nuclei are absorbed.

A fertilization-spindle appears always to be formed in the process of
syngamy, but may differ considerably in appearance from that seen in
C. schubergi ; compare Kunze's description of the fertilization of Orcheobius
herpobdellce.

8. The zygote is enclosed, as stated above, in an oocyst
(Fig. 152, J) secreted at its surface as a membrane delicate at first,
but very soon becoming thickened to a tough impervious capsule,
in which the parasite can pass out of the body of the host and brave
the vicissitudes of the outer world. The synkaryon divides in the
genus Coccidium into four nuclei (Fig. 52, p. 106), and the body
of the zygote then divides into as many sporo blasts, each with a
single nucleus, leaving over a certain amount of residual protoplasm
(" cystal residuum "). Each sporoblast secretes a sporocyst at
its surface (Fig. 152, AT), and within the envelope the sporoblast-
nucleus divides into two. after which the cytoplasm segments round
each nucleus to form two sporozoites (Fig. 152, 0), leaving a small
amount cf residual protoplasm (" sporal residuum "). These
residua are slowly absorbed. When sporogony is complete, there-
fore, the tough oocyst contains four spores, each consisting of a
tough sporocyst containing two sporozoites. In order to develop
further, the cyst must be swallowed by a new host, in the digestive
tract of which the oocyst dissolves, and the spores split open, libera-
ting the sporozoites.

In other species of coccidia the details of the spore -formation may vary
enormously as compared with the example described. The contents of the
oocyst may divide into only two, or into a very large number of sporoblasts.
In the genus Caryospora (Leger, 644) and Cryptosporidium (Tyzzer). the
oocyst does not divide into sporoblasts, but gives rise to a single spore, contain-
ing eight sporozoites in Caryospora, four in Cryptosporidium. In Paracoccidium
prevoti sporocysts are formed in the oocyst. but absorbed again, so that the
sporozoites finally lie free in the oocyst, as in the genus Legeretta, in which no
sporocysts are formed at all, but the body of the zygote divides directly into
sporozoites. With these exceptions, resistant spores are always formed, in
numbers varying from two to some thirty or so in different genera.

The spore may contain one. two, three, four, or n sporozoites, and is then
said to be monozoic, dizoic, trizoic, tetrazoic, or polyzoic ; it is rarely octozoic,
as in gregarines, but Caryospora is so. In Caryotropha mesnilii the spore
contains twelve, in Angeiocystis audouinice about thirty sporozoites (Brasil,
597). In contrast also with gregarines, the spores of coccidia are generally
smooth, round, or ovoid bodies, but in a few cases (e.g., Minchinia chitonis)
bear tails or spikes.

350

THE PROTOZOA

FIG. 155. — For description see foot of opposite page.

THE GREGARINES AND COCCIDIA 351

The germination of the spore takes place always, apparently, in the digestive
tract of the specific host, and there alone ; it may be in some special part of
it, as in C. cunicidi, the spores of which, according to Metzner. germinate in
pancreatic, but not in gastric, juice.

The remarkable form Selenococcidium intermedium (Fig. 155), parasitic
in the intestine of the lobster, described by Leger and Duboscq (646), differs
from all other known coccidia in the character of its trophozoites and its
schizogony. The trophozoites are vermiform, nematode-like organisms,
extremely active in their movements, and frequently coiling themselves up
and wriggling like worms (Fig. 155, A — D). The anterior end of the body is
blunt, the posterior pointed ; the surface of the body contains myonemes
running spirally, visible in the living state at the anterior end as oblique
striations. The youngest trophozoites have a single nucleus, but as they
grow the nuclei multiply, until in the full-grown organism there are eight.
The trophozoite is now a schizont, and penetrates into an epithelial cell of the
intestine in order to multiply by schizogony. The vermiform body rolls up
within the cell into a compact oval mass (Fig. 155, E), and then each of its
eight nuclei grows out into a tongue-like cytoplasmic process. In this way
eight merozoites are formed round a central residual mass. The merozoites
are set free as the uninucleate trophozoites (Fig. 155. F, G). This " in-
different " type of schizogony may continue for several generations, until a
final generation appears in which the schizonts are sexually differentiated ;
smaller, slender trophozoites with eight nuclei give rise to eight merozoites
which grow into male sporonts, and larger, stouter forms with four nuclei
produce four merozoites which become female sporonts.

The male sporonts (gametocytes) arise from vermicules with clear cytoplasm,
which penetrate into an epithelial cell and roll up into an ovoid mass
(Fig. 155. H) ; they may do this when they have but a single nucleus, but
usually not until the nuclei have increased to eight. In the compact, intra-
cellular gametocyte the nuclei multiply rapidly in a manner similar to that
described above for the schizont of Adelea, by binary or multiple fission
following division of the karyosome. In later stages of multiplication the
karyosomes become very small, and the peripheral chromatin of the nuclei
increases greatly, so that they have the appearance of patches of granules
(Fig. 155, 7). When the multiplication is complete, each such patch of granules
forms the dense, comma-shaped nucleus of a microgamete (Fig. 155, J). An
enormous number of microgametes arise from each gametocyte, but the
structure of the free microgametes has not been made out.

The female gametocytes arise from stout vermicules which penetrate into
a cell and become rounded off, the nucleus remaining single all the time
(Fig. 155, K, L, M). The oval gametocyte grows, and its cytoplasm becomes
full of chromatoid grains. When full-grown it appears to go through a process
of maturation, in which, as in Adelea, the karyosome divides into two, and one
half is expelled. The full details of the fertilization have not been made
out, but macrogametes have been seen with the nucleus placed superficially,
and with a small corpuscle, apparently a microgamete, adherent to the body
(Fig. 155, N). After fertilization the zygote becomes spherical and surrounds

FIG. 155. — Selenococcidium intermedium: various phases in the life-cycle. A, B,
G, D, Vermicules with one, two, five, and eight nuclei respectively ; E, vermi-
cule rolling up prior to schizogony ; F, schizogony nearly complete ; eight
pear-shaped merozoites, each with a single nucleus, budded off from a mass
of residual protoplasm to which they are still attached by long stalks ; G,
schi/ogony complete ; eight uninucleate vermicules rolled up together ; H , I, J,
formation of microgametes : H, the nuclei of the microgametocyte at an early
stage of division ; 1, later stage ; J, formation of a great number of comma-
shaped microgametes ; K, L, vermicule rolling up to become a macrogameto-
cyte ; M , fully-formed macrogametocyte, its cytoplasm full of patches of
chromatoid granules that stain deeply with iron-hjematoxylin ; N, macro-
gamete at the moment of fertilization ; 0, oocyst with very numerous chroma-
toid grains. After Leger and Duboscq (646).

352 THE PROTOZOA

itself by a tough oocyst (Fig. 155, 0} ; in this stage it is expelled from the
body with the faeces. The subsequent development of the oocyst, spore-
formation, etc., are not known.

From these data it is sufficiently clear that Sdenococcidium is perfectly
gregarine-like in its trophic phase and in its schizogony ; the trophozoites are
free vermicules which multiply just as in Schizocystis. The parasite only
penetrates into a cell when it enters upon reproductive phases. On the other
hand, the sporogony, so far as it is known, and especially the sexual processes,
are entirely coccidian in type. Selenococcidium links the gregarines and
coccidia in a striking and convincing manner, as will be discussed further
below.

Classification. — The Coccidia have been classified in various ways at different
times, as increased knowledge of these organisms has shown older schemes
to be artificial or unnatural. The following classification is in the main that
of Liihe (392), with certain modifications. Some genera have not, however,
been investigated sufficiently to make their systematic position certain.

Suborder I. : Prococcidia.

Trophozoites free, vermiform, motile ; schizogony similar in type to that
of Schizogregarines. The only genus known at present is Selenococcidium.
The genus Siedleckia should perhaps be placed here, perhaps in the Schizo-
gregarines near Schizocystis ; its sporogony is as yet unknown.

Suborder II. : Eucoccidia.

Trophozoites typically intracellular, motionless, oviform, rarely free or
vermiform ; schizogony of coccidian type.

SECTION A. — Forms in which the sporonts do not associate prior to gamete-
formation, and numerous microgametes are produced :

Family 1 : Coccidiidce (Eimeridce). — The schizogony is of a simple type,
as described in C. schubergi. Examples : Coccidium (Eimeria) and allied
genera ; Barroussia (Barrouxia), with type B. ornata, from the gut of Nepa
cinerea ; Cyclospora, including C. caryolytica, from the intestine of the mole ;
and other genera. Cryptosporidium muris, from the gastric glands of the
mouse, has free trophozoites and produces a single tetrazoic spore.

Family 2 : Caryotrophidce. — With double multiple fission in the schizogony.
Example : Caryotropha mesnilii, parasite of the Annelid Polymnia nebulosa
(Siedlecki, 653). Klossiella muris,* from the kidney of the mouse, should
perhaps be referred to this family, possibly also Merocystis kathce (Dakin).

SECTION B. — Forms in which the sporonts (gametocytes) associate prior
to gamete-formation, and the number of male gametes is reduced to four :

Family 3 : Adeleidce. — With sporocysts. Examples : Adelea, with several
species, of which the best known is A. ovata, parasite of the intestine of
Lithobius ; Klossia, with type K. helicina, from the kidneys of Helix spp. ;
Orcheobius herpobdellce, from the testis of the leech Herpobdella (Kunze) ;
and Caryospora simplex, from the intestine of Vipera aspis, in which the
contents of the oocyst form a single octozoic spore (Leger, 644). Minchinia
chitonis, from the liver of Chiton and Patella spp., should perhaps be referred
to this family, but the gamete-formation is not yet known.

Family 4 : Legerellidce. — Without sporocysts. Example : Legerella nova,
parasite of the Malpighian tubes of Glomeris.

A classification similar in the main to the above has been put forward by
Leger (644). who terms Section A the Eimeridea, Section B the Adeleidea.

* My friend Dr. A. C. Stevenson, of the Pathological Department, University
College, who has studied Klossiella, informs me that he considers it possible that
it may represent a stage of H cemogregarina musculi (p. 377).

THE GREGARINES AND COCCIDIA 353

Leger proceeds to divide the two sections further by the number of sporozoites
produced in the oocyst, but we venture to doubt if this is a method of classi-
fication which is natural. In the section Adeleidea, Leger includes the haemo-
gregarines as a family, Hcemogregarinidce, characterized by producing one
octozoic spore ; but this is true only of two species, so far as is known at
present, and certainly not of many others (see p. 378, infra).

There remains for mention the family Aggregatidoe, comprising certain
organisms, generally regarded as coccidia, parasitic upon Cephalopods of
various genera (Sepia, Eledone, Octopus, etc.). These parasites fall into
numerous species, of which Moroff (94) enumerates . twenty-one, but they
are comprised in a single genus which has gone through many vicissitudes of
nomenclature, having figured at different times under the names Benedenia,
Legeria, Legerina, and Eucoccidium ; but when it had, apparently, settled
down under the last of these names, it was discovered that the schizogony,
formerly supposed to be absent in this genus of parasites, occurs in a distinct
host — namely, a crab — where it had been seen by Frenzel and named by him
Aggregate, ; this name stands, therefore, as the " correct " name of this genus
of parasites.

Not less debatable than the name of these parasites is their systematic
position. While, up to a comparatively recent time, their schizogonous
phases in crabs had been regarded as those of ccelomic gregarines, their
sporogonous cycle in Cephalopods was accepted as that of a coccidian.
Siedlecki (652) investigated the sexual phases, and found a type of sporogony
quite in accordance with that of coccidia — namely, sporonts (gametocytes)
separated from one another, the male gametocyte producing a great number
of microgametes, one of which fertilized a macrogamete, with subsequent
division of the zygote to form a number of sporoblasts and spores.

Recently, however, Moroff published a note in which ho maintained that the
fertilization was of a type quite different from that described by Siedlecki.
He asserted that the macrogametocyte gave rise before, not after, fertilization
to a number of sporoblasts, and that the sporoblasts in question were the true
macrogametes, each of which, after being fertilized, gave rise to a single
spore. In other words, Moroff described the fertilization as being of the
gregarine-type, and not that characteristic of coccidia. Consequently these
organisms have been classified by Fantham and by Leger and Duboscq (645)
amongst the schizogregarines.

In his latest work, however, Moroff (94) acknowledges that the proofs of
the process of fertilization alleged by him are inadequate to establish the
point at issue, and that further investigations are necessary ; he is no longer
prepared to insist on the gregarine-nature of these organisms. Until, there-
fore, the question has been settled by fresh observations, the account of the
sporogony and sexual phases given by Siedlecki must stand. These parasites
may be regarded as a distinct family of the coccidia, the Aggregatidce,
characterized by an alternation of hosts corresponding to an alternation of
generations. The life -cycle in its general outline is as follows: The spores
are produced in the bodies of Cephalopods ; the dead bodies of the Cephalopods,
killed in various ways (by porpoises, for example), are eaten by crabs, which
thus infect themselves ; the spores germinate in the intestine of the crab and
liberate the sporozoites, which traverse the wall of the intestine and come to
rest in the subepithelial connective-tissue layer. There the parasite grows
to a large size, forming a cyst which bulges into the body-cavity, and repro-
duces itself by schizogony, a process which has been studied exhaustively by
Leger and Duboscq (645). The final result is a vast number of merozoites.
If now the crab be eaten and digested by a Cephalopod, the merozoites resist
the digestive juices and establish themselves in their new host.

The cycle in the Cephalopods has been studied by Moroff. The merozoites
grow into sporonts or gametocytes which are not sexually differentiated, but
when their growth is complete sexual differences are seen in the mode of
gamete-formation. Whatever the method of fertilization, a number of
sporoblasts are formed from which the spores arise ; each spore has a tough

23

352 THE PROTOZOA

itself by a tough oocyst (Fig. 155, 0) ; in this stage it is expelled from the
body with the faeces. The subsequent development of the oocyst, spore-
formation, etc., are not known.

From these data it is sufficiently clear that Selenococcidium is perfectly
gregarine-like in its trophic phase and in its schizogony ; the trophozoites are
free vermicules which multiply just as in Schizocystis. The parasite only
penetrates into a cell when it enters upon reproductive phases. On the other
hand, the sporogony, so far as it is known, and especially the sexual processes,
are entirely coccidian in type. Selenococcidium links the gregarines and
coccidia in a striking and convincing manner, as will be discussed further
below.

Classification. — The Coccidia have been classified in various ways at different
times, as increased knowledge of these organisms has shown older schemes
to be artificial or unnatural. The following classification is in the main that
of Liihe (392), with certain modifications. Some genera have not, however,
been investigated sufficiently to make their systematic position certain.

Suborder I. : Prococcidia.

Trophozoites free, vermiform, motile ; schizogony similar in type to that
of Schizogregarines. The only genus known at present is Selenococcidium.
The genus Siedleckia should perhaps be placed here, perhaps in the Schizo-
gregarines near Schizocystis ; its sporogony is as yet unknown.

Suborder II. : Eucoccidia.

Trophozoites typically intracellular, motionless, oviform, rarely free or
vermiform ; schizogony of coccidian type.

SECTION A. — Forms in which the sporonts do not associate prior to gamete-
formation, and numerous microgametes are produced :

Family 1 : Coccidiidce (Eimeridce). — The schizogony is of a simple type,
as described in C. schubergi. Examples : Coccidium (Eimeria) and allied
genera ; Barroussia (Barrouxia], with type B. ornata, from the gut of Nepa
cinerea; Cyclospora, including C. caryolytica, from the intestine of the mole ;
and other genera. Cryptosporidium muris, from the gastric glands of the
mouse, has free trophozoites and produces a single tetrazoic spore.

Family 2 : Caryotrophidce. — With double multiple fission in the schizogony.
Example : Caryotropha mesnilii, parasite of the Annelid Polymnia nebulosa
(Siedlecki, 653). Klossiella muris,* from the kidney of the mouse, should
perhaps be referred to this family, possibly also Merocystis kathce (Dakin).

SECTION B. — Forms in which the sporonts (gametocytes) associate prior
to gamete-formation, and the number of male gametes is reduced to four :

Family 3 : Adeleidce. — With sporocysts. Examples : Adelea, with several
species, of which the best known is A. ovata, parasite of the intestine of
Lithobius ; Klossia, with type K. helicina, from the kidneys of Helix spp. ;
Orcheobius herpobdellce, from the testis of the leech Herpobdella (Kunze) ;
and Caryospora simplex, from the intestine of Vipera aspis, in which the
contents of the oocyst form a single octozoic spore (Leger, 644). Minchinia
chitonis, from the liver of Chiton and Patella spp., should perhaps be referred
to this family, but the gamete-formation is not yet known.

Family 4 : Legerellidce. — Without sporocysts. Example : Legerella nova,
parasite of the Malpighian tubes of Glomeris.

A classification similar in the main to the above has been put forward by
Leger (644). who terms Section A the Eimeridea, Section B the Adeleidea.

* My friend Dr. A. C. Stevenson, of the Pathological Department, University
College, who has studied Klossietta, informs me that he considers it possible that
it may represent a stage of Hcemogregarina musculi (p. 377).

THE GREGARINES AND COCCIDIA 353

Leger proceeds to divide the two sections further by the number of sporozoites
produced in the oocyst, but we venture to doubt if this is a method of classi-
fication which is natural. In the section Adeleidea, Leger includes the hsemo-
gregarines as a family, Hcemogregarinidce, characterized by producing one
octozoic spore ; but this is true only of two species, so far as is known at
present, and certainly not of many others (see p. 378, infra}.

There remains for mention the family Aggregatidce, comprising certain
organisms, generally regarded as coccidia, parasitic upon Cephalopods of
various genera (Sepia, Eledone, Octopus, etc.). These parasites fall into
numerous species, of which Moroff (94) enumerates . twenty-one, but they
are comprised in a single genus which has gone through many vicissitudes of
nomenclature, having figured at different times under the names Benedenia,
Legeria, Legerina, and Eucoccidium ; but when it had, apparently, settled
down under the last of these names, it was discovered that the schizogony,
formerly supposed to be absent in this genus of parasites, occurs in a distinct
host — namely, a crab — where it had been seen by Frenzel and named by him
Aggregata ; this name stands, therefore, as the " correct " name of this genus
of parasites.

Not less debatable than the name of these parasites is their systematic
position. While, up to a comparatively recent time, their schizogonous
phases in crabs had been regarded as those of coelomic gregarines, their
sporogonous cycle in Cephalopods was accepted as that of a coccidian.
Siedlecki (652) investigated the sexual phases, and found a type of sporogony
quite in accordance with that of coccidia — namely, sporonts (gametocytes)
separated from one another, the male gametocyte producing a great number
of microgametes, one of which fertilized a macrogamete, with subsequent
division of the zygote to form a number of sporoblasts and spores.

Recently, however, Moroff published a note in which he maintained that the
fertilization was of a type quite different from that described by Siedlecki.
He asserted that the macrogametocyte gave rise before; not after, fertilization
to a number of sporoblasts, and that the sporoblasts in question were the true
macrogametes, each of which, after being fertilized, gave rise to a single
spore. In other words, Moroff described the fertilization as being of the
gregarine-type, and not that characteristic of coccidia. Consequently these
organisms have been classified by Fantham and by Leger and Duboscq (645)
amongst the schizogregarines.

In his latest work, however, Moroff (94) acknowledges that the proofs of
the process of fertilization alleged by him are inadequate to establish the
point at issue, and that further investigations are necessary ; he is no longer
prepared to insist on the gregarine-nature of these organisms. Until, there-
fore, the question has been settled by fresh observations, the account of the
sporogony and sexual phases given by Siedlecki must stand. These parasites
may be regarded as a distinct family of the coccidia, the Aggregatidce,
characterized by an alternation of hosts corresponding to an alternation of
generations. The life -cycle in its general outline is as follows: The spores
are produced in the bodies of Cephalopods ; the dead bodies of the Cephalopods,
killed in various ways ( by porpoises, for example), are eaten by crabs, which
thus infect themselves ; the spores germinate in the intestine of the crab and
liberate the sporozoites, which traverse the wall of the intestine and come to
rest in the subepithelial connective-tissue layer. There the parasite grows
to a large size, forming a cyst which bulges into the body-cavity, and repro-
duces itself by schizogony, a process which has been studied exhaustively by
Leger and Duboscq (645). The final result is a vast number of merozoites.
If now the crab be eaten and digested by a Cephalopod, the merozoites resist
the digestive juices and establish themselves in their new host.

The cycle in the Cephalopods has been studied by Moroff. The merozoites
grow into sporonts or gametocytes which are not sexually differentiated, but
when their growth is complete sexual differences are seen in the mode of
gamete-formation. Whatever the method of fertilization, a number of
sporoblasts are formed from which the spores arise j each spore has a tough

23

354 THE PROTOZOA

sporocyst, and contains, in different species, from three to twenty-four
sporozoites. The various species of Aggregata appear to be specific to par-
ticular hosts, whether crabs or cephalopods.

If the Aggregatidce are coccidia, they differ from other coccidia in having
an alternation of hosts, and in the absence of an oocyst formed round the
zygote. If, on the other hand, they are gregarines, they differ from all other
known gregarines (with the exception of the doubtful form Schaudinnella,
see p. 355, infra), not only in the alternation of hosts, but also in the fact
that the gametocytes remain separate and produce gametes without previous
association. If the view put forward by Moroff is the true one, they are to
be regarded rather as forms derived from the ancestral form of gregarines and
coccidia (see below), before the habit of association of gametocytes, so charac-
teristic of gregarines, had been acquired.

Comparison of the Life-Cycles of Coccidia and Gregarines. — It is seen that a
typical coccidian, such as Coccidium schubergi, differs from a typical gregarine
mainly in the following points : (1) The trophozoites are intracellular ; (2) the
gametocytes are more or less widely separated from one another at the time
they produce gametes ; (3) the female gametocyte does not divide into a
number of gametes, but remains undivided to form a single macrogamete,
disproportionately large as compared with the male gametes ; (4) the zygote
undergoes a process of division, with the result that all the spores produced
within the cyst are the offspring of a single zygote, while in gregarines the
cyst contains many zygotes and each zygote gives rise to a single spore.

When, however, the coccidia are considered as a whole, it is seen at once
that the first two points do not furnish absolute distinctions ; in Sdenococ-
cidium the trophozoites are motile and extracellular, and in Adeleidce the game-
tocytes associate together. There remains only the sporogony which stands
out as the distinctive feature of each group. It is by no means difficult to
understand, however, the manner in which the two types of sporogony,
different as they may appear, could have arisen from a common source.

The common ancestral form, from which the two groups arose by divergent
evolution and adaptation to different modes of parasitism, may be supposed
to have been a parasitic organism in which the trophozoites that grew into
gametocytes were separated from one another, as in coccidia, and consequently,
when full-grown, produced their gametes separately ; and each gametocyte
produced a number of gametes which differed only slightly from one another,
as in gregarines.

From such a form the coccidia arose by the acquisition of an intracellular
habitat on the part of the trophozoites, whereby the gametocytes remained
more or less widely separated when they produced gametes. As a result of
this condition the gametes have to seek each other out, and may easily miss
one another ; consequently there was a tendency to greater specialization of
the gametes. The male gametes became very smaU and very motile, and were
produced in large numbers. The female gametocyte, on the other hand, no
longer divided up into a number of gametes, but became a single large macro -
gamete. As soon, however, as fertilization is effected, the suppressed divisions
of the female gametocyte take place in the zygote, which divides into the
sporoblasts produced formerly by the division of the gametocyte.

The gregarine-type, on the other hand, arose from the ancestral form by
the trophozoites which grow into sporonts being free and motile in the later
stages of their growth ; consequently, gametocytes of different sexes were able
to come together and produce their gametes in close proximity, and finally
to associate intimately and produce their gametes within a common cyst.
In such a condition it was impossible that the gametes should miss one
another ; consequently there was no tendency to increased specialization of
the gametes, but, on the contrary, a tendency for the gametes to lose even
the slight degree of specialization inherited from the ancestral form, with the
result that a more or less perfect isogamy was developed ; and instead of the
microgametes being produced in excess, the numbers of each kind of gamete
produced are approximately equal.

THE GREGARINES AND COCCIDIA 355

It follows, from the course of evolution sketched in the foregoing paragraphs,
that in both gregarines and coccidia the cyst is to be regarded as a secondary
acquisition. In the ancestral form there were simply scattered zygotes
from which the spore with its contained sporozoites arose ; the spore may, in
fact, be regarded as representing the primary form of the encysted parasite,
comparable to an encysted zygote of the Flagellata. It is indeed obvious
that the cyst of gregarines and coccidia respectively are quite different
things. In gregarines the cyst is formed round the two associated gameto-
cytes — it is a " copularium," asLeger has termed it ; in coccidia the cyst is
a protective membrane formed round the zygote, immediately after fertiliza-
tion. In the genus Legerdla among coccidia, however, the cyst is the sole
protective membrane formed to enclose the sporozoites, no sporocysts being
produced, a condition which is of interest, since it leads on to that found
in the Hsemosporidia.

In both coccidia and gregarines secondary departures from the primary
type of the life- cycle occur. In coccidia the gametocytes of certain forms
(Addeidce) have acquired the habit of association prior to gamete-formation ;
this has not led, however, to a development in the direction of isogamy, as
in gregarines, but merely to a reduction in the number of male gametes formed.
In some gregarines, on the other hand, notably in those forms of " coelomic "
habitat, or parasitic in the haemoccele, the sporonts in the later stages of growth
are inert and motionless ; this condition has led to neogamous association
of young sporonts while still motile and capable of coming together proprio
motu.

Here mention must be made of the remarkable form Schaudinndla de-
scribed by Nusbaum (624), parasitic in the gut of an oligochaete worm. The
full-grown trophozoites of Schaudinndla are gregarine-like, and may be either
free in the lumen of the gut or attached to the epithelium by an epimerite ;
the body is non-septate. Temporary associations (syzygies) may be formed
which have nothing to do with sexual conjugation, since the associates part
again and produce gametes separately and independently. The full-grown
sporonts are distinguishable as male and female forms. The female sporonts
divide up into eight or ten spherical cells, the macrogametes. The male
sporonts divide up into a great number of minute spindle-shaped elements,
the microgametes. Copulation takes place between a microgamete and a
macrogamete. The zygote may become encysted and cast out with the
faeces, or may penetrate into the wall of the intestine. In the first manner
infection of new hosts is brought about ; in the second, multiplication of the
parasite in the same host. The zygotes in the wall of the intestine grow in
size, and divide each into a number of sporozoites.

Some doubt may be felt as to whether the life-history of Schaudinndla has
been interpreted correctly throughout ; it is unusual for endogenous mult--
plication to be preceded by sexual processes, and the development requires
further examination. If, however, the account of the gamete-formation be
correct, Schaudinndla is a form which in this respect stands very near to the
hypothetical ancestral form of gregarines and coccidia.

There can be no doubt that the gregarines and coccidia are closely allied
in every respect, and that the two groups are distinguished by points of
difference which can be referred quite simply to adaptation to slightly different
habits in their parasitic life.

Bibliography. — For references see p. 494.

CHAPTER XV
THE SPOROZOA: II. THE HJEMOSPORIDIA

IN the order Hsemosporidia are comprised a number of organisms
characterized by the following peculiarities : They are parasites of
the blood-corpuscles, red or white, of vertebrates during a part of
the life-cycle ; like the Coccidia, they exhibit an alternation of
generations, non-sexual schizogony and sexual sporogony ; and, in
all cases thoroughly investigated up to the present, the alternation
of generations corresponds to an alternation of hosts, the schizogony
taking place in the blood or internal organs of a vertebrate, the
sporogony in the digestive tract or other organs of an invertebrate ;
lastly, resistant spores are not, as a rule, produced in this order,
being rendered unnecessary by the fact that the parasite is never,
so to speak, in the open, but always sheltered within the body of
one or the other of its two hosts during its entire life-cycle.

The Hsemosporidia, as the name is generally understood, are a
group which comprises a number of forms differing considerably
amongst themselves. Some of the types referred at present to
this order will, perhaps, when thoroughly investigated, be removed
from the order altogether. The existence of these dubious forms
renders the precise limits of the group uncertain and ill-defined.
All that can be said at present is that the order contains a nucleus
of true Hsemosporidia presenting very obvious and close affinities
with the Coccidia, and, in addition to such forms, certain others,
the true affinities of which remain to be determined, but which can
be ranked provisionally in the group.

Under these circumstances, the occasion is not yet ripe for treating
the group in a comprehensive manner, as has been done with
Gregarines and Coccidia. The difficulty of dealing with these
blood-parasites is enhanced by the fact that there is perhaps no
group in the animal kingdom in which the nomenclature-purist has
wrought such havoc as in the Hsemosporidia. Matters have reached
such a pitch that in some cases the popular names of certain forms
are more distinctive than their strictly scientific appellations, so
that the very raison d'etre of a scientific terminology has been
stultified.

356

THE ILEMOSPORIDIA 357

In the sequel, therefore, the Hcemosporidia will be discussed
under five principal types, each of which comprises several forms.
So far as possible, the " correct " names of these forms will be
stated. Finally an attempt will be made to discuss the position
and affinities of the group as a whole. The following is a summary
of the distinctive characters of the types in question :

1. The Hcemamoeba-Type. — The trophozoites of the schizogonous
cycle occur within red blood-corpuscles, and are amoeboid ; they
produce a characteristic pigment, termed " melanin." When the
blood is drawn and cooled down on a slide, the male sporonts, if
present, form filamentous male gametes resembling flagella, and
are consequently said to " exflagellate." The invertebrate host,
so far as is known, is a mosquito.

2. The Halteridium-Type. — The intracorpuscular trophozoite is a
characteristic halter-shaped parasite of red blood-corpuscles, which
is amoeboid, and which, like the last, produces melanin-pigment,
and " exflagellates " on the slide. Only known from the blood of
birds ; the invertebrate host, so far as is known, is a Hippoboscid fly.

3. The Leucocytozoon-Type. — The full-grown sporonts are found
within white blood-cells, which are greatly altered by the parasite.
They are not amoeboid, and do not produce pigment, but they
" exflagellate " when the blood is drawn. Only known in birds ;
the invertebrate host is unknown.

4. The Hcemogregarine-Type. — Parasites usually of red blood-cor-
puscles, sometimes of white ; they are not amoeboid, do not produce
pigment, and do not " exflagellate." They occur throughout the
whole vertebrate series, but are most abundant in cold-blooded
vertebrates. Those of fishes, amphibia, and reptiles, are trans-
mitted generally by leeches ; those of mammals and some reptiles
apparently by ectoparasitic Arthropods.

5. The Piroplasma - Type,. — Parasites of red blood - corpuscles,
amoeboid or of definite form ; they do not produce pigment and
do not " exflagellate "; generally very minute. They are known
only in mammals, and the invertebrate host is always a tick.

These five types will now be considered in more detail.

1. The Hcemamcebce. — The characteristic form of parasite in this
section is a minute, amoeba-like organism contained within a red
blood-corpuscle ; as it grows it gradually exhausts and destroys the
corpuscle, and at the same time produces the characteristic melanin-
pigment. Such are the well-known malarial parasites of mammals
and birds. Unfortunately, the accepted rules of nomenclature
render it obligatory to use the generic name Plasmodium for these
parasites, a most unsuitable name, since they are not plasmodia
in any phase except very temporarily, when they are sporulating.
They may, however, be termed familiarly " hsemamoebse," pro-

358 THE PROTOZOA

vided the word be not written in italics or with an initial capital
letter ; anything is better than to speak of them as " plasmodia."

In human beings three distinct species at least of hsemamcebse
are recognized — namely, the parasites of tertian, quartan, and
pernicious or tropical malaria, now generally named Plasmodium
vivax, P. malarice, and P. falciparum, respectively ; the last-named
is distinguished from the other two by the sporonts being crescent-
shaped, and was put formerly in a distinct genus, Laverania, which
has been abolished . Hsemamcebse similar to those causing malaria
in man have been described from other mammals — for example,
monkeys, several species ; bats ; and squirrels. The human
malarial parasites go through their sporogony in mosquitoes of the
subfamily Anophelinse ; the life-cycle of those of other mammals
has not been yet fully investigated.

In birds hsemamcebse are of very common occurrence. For
these Labbe created the genus Proteosoma, a name still in use
unofficially as a distinctive appellation ; but the correct name of
the avian malarial parasites, commonly assumed to belong all to
one species, is variously stated to be Plasmodium prcecox or P. re-
lictum. In contrast with the human malarial parasites, those of
birds are transmitted by mosquitoes of the subfamily Culicinse.

Lastly, parasites are known, from certain reptiles, which are
intracorpuscular in habitat, amoeboid in form, and produce pig-
ment. Hence they appear to be genuine hsemamcebae, but they
do not exflagellate when the blood is drawn,* and very little is
known of their life-cycle. By some authorities these reptilian
forms are referred also to the genus Plasmodium, but it is best
for the present to maintain the genus Hcemocystidium, Castel-
lani and Willey, for these reptilian forms. Examples are H. metsch-
nikovi (Simond), from an Indian tortoise, Trionyx indicus ; H.
simondi, Castellani and Willey, from a Ceylon gecko, Hemidactylus
leschenaulti ; and various other species.

Since the transmission of the malarial parasites by mosquitoes
was first discovered by Ross in his experiments on the Proteosoma-
parasite of birds, the development of human malarial parasites
has been studied in full detail by numerous investigators, amongst
whom Grassi and Schaudinn (130) must be specially mentioned.
Consequently the life-cycle of these parasites is better known than
that of almost any other Protozoa, and is now to be found described
in every textbook. It will be sufficient, therefore, to describe the
life-cycle of the species parasitic in human beings in brief outline,
as typical of this class of parasites (Fig. 156).

* Aragao and Neiva have observed in Plasmodium (Hcemocystidium) diploglos.si
that, in the male gametocytes on the slide, violent streaming movements occur,
such as are the prelude, in other haemamcebaa, to exflagellation ; but formation of
gametes was not seen.

THE H^MOSPORIDIA 359

The sporozoites introduced into the blood by the proboscis of
a mosquito are minute active organisms of slender form (Fig. 156,
XIX.). Each sporozoite attacks a red blood-corpuscle and pene-
trates into it. Within the corpuscle it becomes a small, amoeboid
trophozoite, which grows at the expense of the corpuscle (Fig. 156,
I. — V.). A characteristic feature of the young trophozoite is the
possession of a large space — probably a vacuole — in the body,
which gives the parasite an appearance which has been compared
to a signet-ring. As the parasite grows, this space disappears and
the body becomes compact. The characteristic pigment is formed
within the body of the parasite at an early stage of its growth,
and as it increases in size the pigment-grains become more numerous.
When the parasite is full-grown it is a schizont, and proceeds to
multiply by schizogony (Fig. 156, 6 — 10). The body becomes
rounded by cessation of the amoeboid movement, and the nucleus,
hitherto single, multiplies by repeated division. Then as many
small daughter-individuals (merozoites) as there are nuclei are
budded off round the whole periphery of the schizont, leaving at
the centre a small quantity of residual protoplasm containing the
pigment-grains ; this is the characteristic rosette-stage, or corps
en rosace. The corpuscle now disintegrates, setting free the
merozoites.

The three species of human malarial parasites are distinguished by differ-
ences in their amoeboid activity, their effects on the corpuscles, the number
of merozoites produced, and other points, but more especially by the time
required for a complete schizogonous generation. Thus, in Plasmodium vivax
the growth and multiplication of the schizont requires about forty-eight
hours ; in P. malarice, seventy-two hours ; in P. falciparum, twenty- four
hours or an irregular time. The attacks of fever produced by the parasites
occur when the rosettes are breaking up and setting free the merozoites,
probably because the disintegration of the body of the parasite sets free
toxic substances contained in it. Hence in the tertian ague caused by
P. vivax the fever returns every third day ; in quartan ague of P. malarice,
every fourth day ; while P. falciparum causes irregular or quotidian fevers,
more or less continuous.

The schizogony of the tertian and quartan parasites proceeds in the
peripheral blood, but that of the pernicious parasite takes place mo're
generally in the internal organs. The amoeboid trophozoites present them-
selves under the most varied forms in the corpuscles ; especialy noteworthy
in the quartan parasite is the occurrence of haemogregarine-like forms
(Billet, 664).

There is some doubt as to whether the trophozoites are in all cases within,
or merely attached to, the corpuscles. Schaudinn (130) held at first the view
that in all cases the parasites were intracellular, and that appearances tending
to prove the contrary were the result of alterations due to manipulation in
making preparations. It is nevertheless maintained by many authors that
some stages, at least, of the parasites are attached to the corpuscles ; Halber-
staedter and Prowazek, for example, believe that in P. pithed the trophozoites
which develop into female sporonts are extracellular, whilst those which
become schizonts are intracellular.

Different species of haemamcebse differ also in the effects they produce on

360

THE PROTOZOA

.

FIG. ]56. — Life-cycle of a malarial parasite: combined diagram (the figures are
not in all cases from the same species, and some of them are schematic).
All the figures above the dotted line represent stages passed in human blood ;
those below are the stages that are found in the mosquito.

I. — V. and 6 — 10, Schizogony of the tertian parasite, Plasmodium vivax, after
Schaudinn (130), magnified about 1,500 diameters. L, Youngest intracor-
puscular stage, which has arisen either from a sporozoite (XIX.) or a merozoite
(10) that has penetrated into, or is attached to, the corpuscle (represented
by a circular outline). II. — IV., Further stages of the growth of the para-
site ; a vacuole is formed in its body which gives it the characteristic " signete
ring " appearance (IV.). V. and 6, Later stages of growth ; the vacuol-

[Continued at foot of p. 361.

THE H^MOSPORIDIA 361

the corpuscles. An effect commonly seen is the so-called " stippling "
(Tiipfelung) of the corpuscles, which exhibit a dotted appearance (Scjiuffner's
dots).

I
The merozoites, when set free, penetrate into other corpuscles,

and become in their turn trophozoites, which may either grow
into schizonts again and repeat the process of multiplication by
schizogony, or may grow into sporonts. As in Coccidia. a number
of generations of schizogony succeed each other before sporonts
are produced. At first the parasites are not sufficiently numerous
to be perceptible in the blood or to evoke febrile symptoms, and
during this, the so-called " incubation-period," schizogony alone
.occurs, in all probability ; but when the numbers of the parasite
are sufficient to affect the health of the host, the reaction of the
host against the parasite probably stimulates the production of
the propagative phases. The trophozoites which grow into sporonts

FIG. 156 continued :

disappears ; in 6 the parasite is full-grown and its nucleus is beginning to
divide. 7, 8, Progress of the nuclear divisions, complete in 8. 9, Division
of the body of the parasite to form the merozoites ; the blood-corpuscle
beginning to degenerate. 10, The parasite has divided up into sixteen mero-
zoites, leaving the pigment-grains in a small quantity of residual protoplasm ;
the corpuscle has completely disappeared and the merozoites are set free.

VI., Vila., VII6., Formation of the gametocytes of pernicious malaria
(Plasmodium falciparum) ; the gametocytes arise from the intracorpuscular
parasites by a series of stages similar to those represented in II. — V., but
without a vacuole in the body. In P. falciparum the ripe gametocytes have
the form of crescents, as shown, but in the tertian and quartan parasites the
gametocytes are simply rounded, as Villa, and VIII&. Vila., Male crescent
with larger nucleus and scattered pigment ; VII6., female crescent, with a
smaller nucleus and the pigment more concentrated round it. (N.B. — Vila,
and VII6. are drawn on too small a scale ; the crescent should be as large
as XIII.)

VIII. — XIII., Stages of the sexual generation of the tertian parasite in
the stomach of the mosquito, after Schaudinn. a, Male forms; &, female
forms. (In pernicious malaria the crescents round themselves off, become
free from the corpuscle, and assume forms similar to VIII. a and &.) VIII.,
Rounded - off parasites free from the corpuscle. IX., Gamete-forma-
tion ; in a the nucleus is divided into eight ; in 6 the nucleus has passed to
the surface of the body. X., Further stage ; in a the body of the gametocyte
is throwing off the long slender microgametes, one of which is represented
free ; in 6 the nucleus is dividing to throw off a reduction-nucleus. XI.,
Process of syngamy ; a male gamete is seen penetrating the body of a female
gamete. XII., Zygote shortly after fertilization ; the body is growing out
and becoming vermiform, with the synkaryon at the hinder end ; male and
female chromatin still distinct ; near the zygote is seen a clump of degenerating
microgametes. XIII., Motile ookinete formed from the zygote ; the syn-
karyon, with male and female chromatin still distinct, is seen near the middle
of the body ; the pigment- grains are at the hinder end of the body, whence
they are soon rejected.

XIV. — XVIII., Sporogony: diagrammatic. The ookinete (XIII.) pene-
trates the stomach-wall and becomes encysted (XIV.) ; its nuclei multiply
(XV.), and it forms a number of sporo blasts so called (XVI.) ; in each sporo-
blast the nucleus divides to form a great number of small nuclei, which grow
out in tongue-like processes from the surface to form the sporozoites (XVII.) ;
the ripe cyst contains great numbers of sporozoites with a certain amount of
residual protoplasm ; the sporozoites when set free (XIX.) pass into the
salivary glands, and thence through the proboscis into the blood of the
vertebrate again.

362 THE PROTOZOA

have, according to Schaudinn (130), no signet-ring stage in their
development, but are of compact form, and grow more slowly than
the trophozoites which become schizonts. The sporonts are of
two types, male and female (Fig. 156, Villa., VIII&.) ; the male
forms have a large nucleus and lightly-staining, clearer cytoplasm ;
the female forms have a smaller nucleus and more deeply staining
cytoplasm. In the tertian and quartan parasites the sporonts are
distinguishable from the schizonts by their greater size and more
abundant pigment in larger grains. In the parasite of pernicious
malaria, the sporonts are further characterized by their sausage-
like form (Fig. 156, Vila., Vltt.), and are thereby easily dis-
tinguishable from the rounded schizonts.

The sporonts only undergo further change if taken up by a mos-
quito of a species capable of acting as the specific host of the para-
site. When human blood containing various stages of the parasite
is ingested by a culicine mosquito, ah1 stages of the parasite are
digested with the blood ; but if taken up by an anopheline, the ripe
sporonts resist the action of the digestive juices of the mosquito,
and develop further in its stomach, while all other stages succumb.
The sporonts burst the corpuscle in which they are contained, and
round themselves off. In the male sporont the nucleus undergoes
rapid fragmentation into some four or six nuclei (Fig. 156, IXa.),
leaving a residual karyosome at the centre of the body, as in
Coccidium (Schaudinn, 99). The daughter-nuclei place themselves
at the surface of the body, and grow out with explosive suddenness
into fine filaments of chromatin, ensheathed in a scarcely perceptible
layer of cytoplasm (Fig. 156, Xa.). Each such filament is a micro-
gamete, of slender, spirochsete-like form, without flagella, but
endowed with powers of active movement. The micro gametes
lash about violently, often dragging the body of the sporont after
them, and presenting a superficial resemblance to flagella, which,
indeed, they were formerly thought to be ; hence the process of
microgamete-formation, which can be observed without difficulty
in freshly-drawn blood, was thought to represent a flagellated
" Polymitus " stage of the parasite, and was termed " exflagella-
tion." The microgametes by their movements finally become
detached, and swim away from the body of the sporont, which
perishes as residual protoplasm.

In the female sporont the nucleus divides to give off a reduction-
nucleus (Fig. 156, X6.) ; it is then ripe for fertilization by a micro-
gamete (Fig. 156, XI.), which penetrates the body and fuses with
the female pronucleus. The zygote then changes from a rounded
form into an elongated vermicule, termed an " ookinete " (Fig. 156,
XII., XIII.), which moves by gliding movements, like a gregarine.
The ookinete bores its way through the lining epithelium of the

THE H^MOSPORIDIA 363

gnat's stomach, and comes to rest in the subepithelial tissue ; here
it rounds itself off and forms an oocyst (Fig. 156, XIV.), becoming
surrounded by a delicate membrane, which is not, however, of a
tough and impervious naturelike a coccidian oocyst, since the parasite
continues to absorb nutriment and to grow in size, bulging out the
stomach-wall towards the body-cavity. As it grows, the originally
single nucleus of the zygote multiplies by binary fission, and the
cytoplasm becomes concentrated round each nucleus to form a
" sporoblast," so called (Fig. 156, XV., XVI.). In each sporoblast
the nucleus divides repeatedly, and then the surface of the sporo-
blast grows out into slender tongue-like processes, each carrying
out one of the nuclei in it (Fig. 156, XVII.). Thus a vast number
of minute sporozoites are formed by a process of multiplication
recalling that seen in the schizogony of Aggregate or Porospora.
Finally the cyst contains some hundreds, or even thousands, of
sporozoites, together with a certain amount of residual protoplasm,
in which the melanin-pigment of the macrogamete is contained
(Fig. 156, XVIII.). The ripe cysts burst and scatter their contents
in the body-cavity (haemocoele) of the mosquito ; the sporozoites
pass by means of the blood-currents to the salivary glands, in
which they collect in vast numbers. The mosquito is now infective ;
at its next feed, which is usually the fourth, counting as the first
that by which it first took up the parasites in the infected blood,
the tiny sporozoites pass with the salivary secretion down the
proboscis into the blood of the man on whom the mosquite feeds,
and so produce a new infection.

A disputed point in the life- cycle is the manner in which relapses are brought
about in malarious persons ; as is well known, persons who have had malaria
may have fresh attacks of the disease under conditions which preclude infec-
tion by mosquitoes, and leave no doubt but that the parasite has been present
in the body in a latent or inconspicuous condition, and has for some reason
reacquired the power of multiplication until its presence becomes perceptible
again. Two views have been put forward to explain relapses. According
to Schaudinn (130), in the healthy intervals all forms of the parasite have
died off except the female sporonts, which are the most resistant forms of the
parasite, and maintain their existence in a resting state ; when, however, the
conditions occur, whatever they may be, which favour a relapse, the female
sporonts multiply parthenogenetically (Fig. 72, p. 137), and produce a brood
of merozoites which are the starting-point of a fresh series of schizogonous
generations. Ross, on the other hand, believes that in the healthy intervals
the number of parasites in the blood merely falls below that sufficient to pro-
duce febrile symptoms, and that a relapse is brought about simply by an
increase in the numbers of the parasites present.

The number of cysts formed in the stomach of the mosquito may be very
large, 500 or more ; and the cysts themselves vary in size considerably, some
developing only a few hundreds of sporozoites, while in others they are to be
counted in thousands. Even in mosquitoes of a species susceptible generally
to a particular species of malarial parasite, however, the sporonts do not
succeed in every case in passing through their sexual stages and developing
normally (compare Darling, 669). In many cases also the cysts degenerate

364 THE PROTOZOA

and form masses of pigment, the so-called " black spores " of Ross. Similar
degeneration-phenomena have been observed by Schaudinn (147) in the
oocysts of Cydospora caryolytica, and may be compared to the transformation
of chromidia into pigment in the degeneration of Actinosphcerium in cultures
(p. 209).

The " exflagellation," or formation of microgametes, which takes place,
under normal circumstances, in the stomach of the mosquito, can be seen also
in blood freshly drawn and examined on a slide, if ripe sporonts are present.
The process is greatly furthered by lowering the density of the blood — for
example, by adding to it not more than one-fifth of its volume of ordinary
water, or by simply breathing on the blood when drawn (compare Neumann,
677).

It is curious that, while so many experimenters have established absolutely
beyond all doubt the transmission of haemamoabae by mosquitoes, those of man
by anophelines, and those of birds by culicines, no experiments seem to have
been performed to determine how long a mosquito, once infected, remains
infective without being reinfected. In other cases of similar transmission,
such as that of trypanosomes, yellow fever, etc., it is known that the inverte-
brate host, once rendered infective, remains so for a very long time, probably
for the rest of its life. In the case of malarial parasites this point remains to
be tested experimentally.

The hsemamcebse of Primates have been studied by a number of investigators,
and several species distinguished : Plasmodium kochi (Laveran) from the chim-
panzee and various African monkeys ; P. pithed from the orang-outang, and
P. inui from Macacus spp. (Halberstaedter and Prowazek, Mathis and Leger,
473) ; P. cynomolgi from Macacus cynomolgus (Mayer, A.P.K., xii., p. 314) ;
and P. brasilianum from the ouakari, Brachyurus calvus (Berenberg-Gossler).
The schizogony appears to be generally similar to that of the species parasitic
in man ; ring-stages occur, and the multiplication is in some cases similar
to the tertian, in other cases to the quartan parasite. Binucleate trophozoites
are of common occurrence, and binary fission also occurs (Flu, A.P.K., xii.,
p. 323). A -striking feature of monkey- malaria is the comparative rarity
of multiplicative phases, which may be in relation to the fact that these
parasites cause no appreciable symptoms of disease in their hosts ; in both
respects they are comparable to non- pathogenic trypanosomes. Transmission
is probably effected by anopheline mosquitoes (Mayer).

In bats two distinct forms of intracorpuscular parasites have been described
under distinct generic names : Polychromophilus, from Vespertilio and Miniop-
terus spp., and Achromaticus, from Vesperugo spp. These two genera are
distinguished by the fact that Polychromophilus produces melanin-pigment,
and Achromaticus does not. Polychromophilus is apparently an ordinary
hsemamceba which should be included in the genus Plasmodium. Achro-
maticus, on the other hand, appears, from the recent investigation of Yakimoff
and others (753), to be a true piroplasm (see below).

Plasmodium vassali from squirrels has ring-like young trophozoites, and
its schizogony takes place by binary or multiple fission, more commonly the
former (Vassal) ; some forms of the parasite figured resemble Piroplasma.

The life-history of the Profeosoraa-parasite of birds has been studied in
detail by Neumann ; the principal phases of the parasite are essentially similar
to those of the haemamcebae parasitic in man. Experimenting with canaries,
Neumann transmitted the infection by means of Stegomyia fasciata, but this
mosquito was found to be less efficient as a host for Proteosoma than the
species of Culeyc. Of Stegomyia only 11*4 per cent, developed ripe cysts, as
against 85 per cent, of Culex ; the development of the parasite is accomplished
in nine to eleven days in Culex, in thirteen to fifteen days in Stegomyia ; and
a far smaller number of the parasites succeed in developing in Stegomyia, in
which the maximum number of cysts seen in the stomach of any mosquito
was thirty-six, while in Culex much larger numbers, 500 to 1,000, are recorded.

But little is known of the life-cycle of the reptilian hsemamoebae of the
genus Hcemocystidium. Aragao and Neiva have described schizogony of the

THE ILEMOSPORIDIA 365

ordinary multiple type, taking place in the blood-corpuscles, in H. tropiduri
and H. diploglossi. According to Dobell, however, the schizogony of
H. simondi consists simply of binary fission as a rule, sometimes of division
into four. The male and female gametocytes, sharply differentiated by their
staining properties in this as in other species, are stated also to have the
nucleus divided into two when mature ; Woodcock (687), however, disputes
the correctness of Dobell' s interpretations. In no case as yet is the inverte-
brate host of any Hcemocystidium known.

2. The Halteridia. — The characteristic form of parasite in this
section, only known to occur in the blood of birds, is an organism
which is found within the nucleated red corpuscle, and which does
not displace the nucleus of the corpuscle, but grows round it into a
halter-like form, whence the name Halteridium given to it by
Labbe. Hence the parasite is easily distinguisbed from Proteosoma,
which is more compact in form, and which displaces the nucleus of
the corpuscle. Halteridium is amoeboid, but the form-changes
are generally slight ; it produces the characteristic melanin-pigment
in abundance ; and when the blood is drawn, " exflagellation " of
the ripe male sporonts takes place very readily. Not merely the
gamete-formation, but the subsequent fertilization and the for-
mation of the ookinete, can be observed on the slide. It is in this
form that Macallum first followed out the whole process, and so
made clear the true significance of the " Polymitus " stage in the
malarial parasites.

The correct generic name for the Halteridium-paTasite is believed
to be Hcemoproteus. Labbe considered the halteridia of different
birds to be all one species, to which he restricted the specific name
danilewskyi (Grassi and Feletti). By other naturalists several
species have been distinguished and named after the birds in which
they occur, as H. noctuce of the little owl, H. columbce of pigeons,
etc. The halteridia of different birds show considerable differences
in form, structure, and appearance, and there can be no doubt that
there are many species of these parasites ; but it by no means
follows that a given species is restricted to a particular host. It is
probable that in some cases one and the same species may be
capable of infecting several species of avian hosts. The Sergent
brothers were unable, however, to infect canaries with H. columbce
of pigeons.

The life-cycle of these parasites has been the subject of con-
flicting statements. We shall consider first the type of develop-
ment made known by the Sergent brothers (686) in part, and more
fully by Aragao (Fig. 157). The development described by Schau-
dinn (132), to which the utmost doubt attaches, will be dealt with
later (p. 390).

The invertebrate host of H. columbce is a biting fly of the genus
Lynchia, of the dipterous family Hippoboscidce. These flies, though

366

THE PROTOZOA

FIG. 157. — For description see foot of opposite page.

THE H^EMOSPORIDIA 367

provided with wings (some genera of this family, such as Melophagus,
the common sheep-ked, are wingless), are extremely louse-like in
appearance, and creep in the plumage of birds ; they attack nest-
lings as well as adults — a fact which explains the appearance of the
infection in pigeons before they have left the nest.

When blood containing the parasites is taken up by a Lynchia,
the ripe gametocytes burst the corpuscles in which they are con-
tained, round themselves off, and form gametes, in the manner
already described for hsemamcebae, in the stomach of the fly
(Fig. 157, D, E). Fertilization then takes place, and ookinetes are
formed (Fig. 157, F — J). Practically the only difference from the
hsemamcebae is that the o okinetes get rid of their melanin-pigment,
which is cast off in a small bead of protoplasm at the hinder end.

The ookinete grows considerably larger than the full-grown
halteridia of the blood. The development of the parasite does not
proceed further, apparently, than this stage in the fly, and it is the
ookinete which is inoculated back into the bird's blood by the
Lynchia.

At this point there is a gap in the development which it remains
for further observations to fill up. Thirteen or fourteen days after
the actual infection by the fly the parasite makes its first recorded
appearance in the pigeon, within a leucocyte which is adherent to
the wall of a blood-capillary, so that possibly the previous develop-
ment of the parasite has taken place in an endothelial cell (Aragao).
The parasite has the form of a small round body contained in the
cytoplasm of a leucocyte (Fig. 156, K] ; it has a single nucleus of

FIG. 157. — Developmental cycle of Hcemoproteus columbce, after Aragao (683).
A, Youngest halteridia in the blood-corpuscles: a, female; 6, male; B, 0,
growth of the gametocytes, female (a) and male (6) ; D, gamete-formation :
a, reducing division in the female gametocyte ; 6, division of the nucleus of
the male; E, ripe gametes: a, female; b, male (" Polymitus " stage); F,
copulation of male and female gametes ; G, the zygote beginning to assume
the ookinete-form ; H, the ookinete with pigment in the body ; /, the pigment
passing to the hinder end of the body ; J, the ookinete after it has got rid of
the pigment.

K, Youngest stage in the leucocyte in the lung of the pigeon ; L, the pre-
ceding stage has divided into a number of small individuals, each with one
nucleus, and the leucocyte has increased in size ; M , the individuals of the
last stage have grown in size and become multinucleate ; the leucocyte still
further enlarged ; N, further advance on the last ; 0, the greatly hypertrophied
leucocyte contains a number of multinucleate masses ; P, Q, further multi-
plication of the nuclei ; the leucocyte beginning to break down ; R, the multi-
nucleate masses become divided into a vast number of small uninucleate
individuals, which are set free from the leucocyte by its disintegration, and
which penetrate into blood-corpuscles and there become the youngest halteri-
dia, as in A.

The stages D — J are passed through in the fly (Lynchia), the stages K — 0
in the pigeon. Between J, the last stage seen in the fly, and K, the earliest
stage yet found in the pigeon, is a gap which it remains for further investigation
to till.

The stages H — J are drawn rather too small in proportion to those pre-
ceding.

368 THE PROTOZOA

irregular form, often seen in process of division. The parasite
grows, its nucleus multiplies, and it divides into a number of small
bodies, twelve to fifteen in number, each with one nucleus
(Fig. 156, L). During this process the leucocyte also increases
in size. Each of the small bodies produced by division grows
rapidly in its turn, and its nucleus divides repeatedly to produce a
very large number of nuclei, which become arranged in clumps
resembling the sporo blasts of a malarial parasite (Fig. 156, M — O).
Finally each mass becomes divided up into a great number of
minute " merozoites " of irregular form (Fig. 156, P — R). During
this process the leucocyte first becomes greatly hypertrophied, and
finally breaks down altogether, setting free the merozoites, which
pass into the blood and attack the blood-corpuscles, into which they
penetrate and become the young halteridia (Fig. 156, A). The
development in the lung that has been described takes about
twelve days, so that the youngest parasites make their appearance
in the circulating blood about the twenty-sixth day after infection
by the fly.

In the blood - corpuscles the youngest halteridia are minute
bodies with a single nucleus, which grow into the adult form, and
become male or female gametocytes, readily distinguishable by the
characters of the cytoplasm, which is darker in the female, and of
the nucleus, which is larger in the male (Fig. 156, B, C). No multi-
plication takes place in the red corpuscle ; the sole multiplicative
stage known with certainty is that in the lung. Consequently, in
the pigeon the infection dies out after a time, unless re-infections
take place, and the degree to which parasites abound in the blood is
related directly to the number of infected flies fed on the bird. This
may not be equally true, however, of other species of these parasites.

From Aragao's account it would appear that in H. columbce only male and
female halteridia (sporonts) occur. In other species, however, indifferent
forms occur also, which, it may be supposed, are destined as schizonts to
repeat the process of schizogony, and so to maintain the infection in the
bird, like the schizonts of the malarial parasites. Anschutz has described
in H. oryzivorce (of Padda oryzivora) a process of schizogony taking place in
the circulating blood.

The development of the halteridia in the leucocytes may be considered,
probably, as equivalent to the schizogony of the malarial parasites. On this
interpretation the missing part of the development is that which corresponds
to the sporogony of the malarial parasite, and which in this case is either
suppressed entirely (" aposporogony," Aragao), or takes place in the verte-
brate host, in some manner yet to be described, instead of in the invertebrate.
The absence of sporogony, and of any but the sexual phases, in the Lynchia,
doubltess explains the short duration of the infectivity of the fly ; according
to Aragao, if the flies are fed for three days on clean pigeons, they cease to be
infective. Some of the stages in the lung show a certain resemblance to the
sporogony of the malarial parasites, especially the formation of sporoblast-
like masses, which, however, are probably more comparable to the schizonto-
cytes of Caryotropha than to true sporoblasts.

THE H^EMOSPORIDIA

369

• Labbe described for halteridium a process of multiplication in the red
corpuscle which has never been confirmed. He stated that the nucleus of
the parasite divided into a number of small nuclei placed at the two ends of
the halter-shaped body, which then divided up into two bunches of small
merozoites. It is, of course, possible that the development may differ
in different species. But it is more probable that the supposed nuclei at
the ends of the body are merely metachromatinic grains, possibly the
" alkaliphilous " granules described by Mayer (685, p. 234).

3. The Leucocytozoa. — The true leucocytozoa — that is to say,
the species of the genus Leucocytozoon of Danilewsky — are only
known to occur in the blood of birds, as stated above ; they must be

B

FIG. 158. — Leucocytozoon ziemanni from the blood of the Little Owl, Athene noctua.
A, Male, B, female, 0, young form. N., N., nucleus of the parasite ; N1, N1,
nucleus of the host-cell. Original ; magnification 2,000.

distinguished clearly from the pseudo-leucocytozoa of mammals,
which are in reality hsemogregarines, and will be dealt with as such
below. The leucocytozoa of birds are found in the blood as bodies
usually elongated and spindle-shaped, sometimes, however, rounded
in form, which represent each a gametocyte, male or female, con-
tained in its host-cell (Fig. 158). The exact composition of these
bodies is, however, a little doubtful ; it is not quite certain where
the host-cell ends and the parasite begins. The centre of the body

24

370 THE PROTOZOA

is occupied by an oval, compact mass of cytoplasm containing a
nucleus. By some this mass is regarded as the whole parasite, by
others as its endoplasmic region alone. In the female forms the
cytoplasm is dense and stains deeply, and the nucleus is relatively
small, with a distinct karyosome sometimes placed eccentrically.
In the male forms the cytoplasm is paler, and the much larger
nucleus stains feebly, with a diffuse granular structure and with-
out a conspicuous karyosome. Stretched along one side of the
body of the parasite is the nucleus of the host-cell, compressed,
usually more or less drawn out, and staining deeply. The surface
of the body is covered by a thin membrane, which is prolonged
usually into two horn-like processes at the two poles of the body.
It is doubtful whether these two processes consist solely of the
substance of the host-cell, or whether they contain ectoplasmic
extensions of the parasite also. In any case it is certain that the
parasite modifies the host-cell in a singular manner. It is also
disputed whether the host-cell itself is an erythroblast or a mono-
nuclear leucocyte. Most recent investigators, however, incline
to the latter view ; but Keysselitz and Mayer (A.P.K., xvi., p. 237)
state that the host-cell is an erythroblast. No melanin-pigment is
formed.

The young forms of the parasite are compact, rounded, or
hsemogregarine-like, contained in white cells with a large nucleus,
and without the horn-like processes characteristic of the adult.
Fantham (689) has described in L. lovati of the grouse multiplica-
tion by schizogony taking place in the spleen. The schizonts pro-
duce a number of merozoites which escape into the blood, and
doubtless give rise to the young forms of the leucocytozoa. The
periodicity of the sexual forms in the blood observed by Mathis
and Leger (473) depends, probably, on successive schizogonous
generations occurring in the internal organs, such as Fantham has
described.

The method of transmission and the invertebrate host are as yet
unknown. If blood containing the parasites in the condition of
ripe gametocytes be drawn, the sexual phases and fertilization can
be studied without difficulty on the slide. The female gametocytes
round themselves off, losing their spindle-like form, and burst their
envelope. The male gametocytes contract themselves into two or
three rounded masses, which give off about eight thread-like
microgametes altogether, in a manner similar to the " exflagel-
lation " of the malarial parasites. The microgametes become de-
tached and fertilize a female.

Schaudinn (132) gave an account of the development of these parasites
which cannot be accepted as correct. According to him, L. ziemanni of
Athene noctua is in reality the resting stage of a large trypanosome, which

THE H^MOSPORIDIA 371

when full-grown attaches itself to an erythroblast and develops into the
leucocytozoon, losing its locomotor apparatus. The large trypanosomes in
question were supposed to be the sexual, propagative phases, male and
female, of a very minute spirochaete-like trypanosome, which represented the
indifferent, multiplicative form of the parasite. The existence, however, of
young forms of the leucocytozoon, no less than the schizogony discovered by
Fantham, disprove entirely any such origin from trypanosomes.

In correspondence with his ideas upon the nature and orgin of leucocytozoa,
Schaudinn regarded the nucleus of the female forms (Fig. 158, B) as con-
sisting of a trophonucleus with a kinetonucleus (" blepharoplast ") close
beside it ; while the nucleus of the male leucocytozoon (Fig. 158, A) was sup-
posed to consist of a cluster of small trophonuclei, each with a small kineto-
nucleus beside it, precocious division of the two nuclei of the " male trypano-
some " being supposed to have produced a number of couples of nuclei in readi-
ness for gamete -formation. These cytological interpretations cannot be upheld.
There is nothing in the structure of the nucleus of the male leucocytozoon to
support the notion that it is not a single large nucleus, and the " blepharo-
plast " of the female form appears to be simply the karyosome, eccentric in
position.

Schaudinn also described what he believed to be the development of
Leucocytozoon (or, as he named it, Spirochceta) ziemanni in Culeyc pipiens.
According to his account, the ookinete became an elongated, worm-like body
which divided up to produce an immense number of spirochaetes, or very
slender trypanosomes. The spirochaetes were stated to find their way into the
Malpighian tubules, where they multiplied and occurred in vast numbers.
The spirochaetes, inoculated by the mosquito into the blood of the owl, there
became the " indifferent form of the leucocytozoon."

The statements of Schaudinn with regard to the development of Leucocyto-
zoon have received no confirmation, in spite of the efforts of the Sergent
brothers to find experimental proof for them. These investigators wero
unable to obtain any development of the leucocytozoon in Culex, or to
transmit the parasite from owl to owl by the agency of mosquitoes. They
found, however, that mosquitoes were commonly infected with spirochaetes
in the Malpighian tubules, but injection of these spirochaetes into the owl
produced no infection with Leucocytozoon, and there can be no doubt that
the spirochaetes in question were true spirochaetes, not connected in any way
with either trypanosomes or leucocytozoa. Mayer (685) obtained only
ookinetes, apparently similar to those of halteridium, but non-pigmented
and slightly larger, in mosquitoes fed on owls infected with leucocytozoa, and
observed no sign whatever of nuclear multiplication in the ookinetes ; Wood-
cock's unpublished results were practically the same as those of Mayer.
Mathis and Leger (473) obtained no development of L. sabrazesi in mosquitoes,
bugs, and leeches, fed on well-infected fowls, nor could they bring about
transmission by means of mosquitoes.

4. The Hcemogregarines. — Parasites of this type have been
found in the blood of all classes of vertebrates, and are especially
common in cold-blooded animals, such as fishes and reptiles.
Until quite recently, hsemogregarines were not known to occur in
birds ; but Aragao (692) has described a number of species para-
sitic in the leucocytes of various species of birds in Brazil. It is
a curious anomaly of the distribution of these parasites that,
while common in marine fishes, they are not known in fresh-
water fish, with the sole exception of the eel. While in other
classes they are parasitic in the red corpuscles, in mammals they are
parasitic in either the red or the white corpuscles, but more com-

372 THE PROTOZOA

monly in the latter as the so-called " leucocytozoa," not to be con-
fused with the true leucocytozoa dealt with in the last section.

Hsemogregarines present themselves usually as more or less
elongated parasites of quite definite form, sausage-shaped or worm-
like, not amoeboid, lying within the blood-corpuscle. The middle
of the body is occupied by a conspicuous nucleus, and there are
often numerous metachromatinic grains in addition, but no melanin-
pigment is produced. The parasite may be liberated from the
corpuscle as a free vermicule, the resemblance of which to a small
gregarine is accentuated by its active gliding movements ; liberation
of the vermicules may often be seen when the blood is drawn, but
no " exflagellation " ever occurs, since, as will be seen when the
development is described, the microgametes are formed in a manner
totally different from that characteristic of the hsemamcebse.

In many haemogregarines the body of the parasite, when lodged
within the blood-corpuscle, is enclosed in a distinct capsule or mem-
brane, which may be of considerable thickness, and often stains
deeply. When the parasite is liberated from the corpuscle, the
capsule may be left behind as a conspicuous enclosure of the cor-
puscle, which has puzzled some observers, and has even been
described as a distinct form of parasite (compare Sambon and
Seligmann) . In H. bicapsulata the capsule is thickened at the two
extremities of the sausage-shaped body to form two caps, plainly
visible in the living condition, and staining a bright red colour in
preparations made with the Romanowsky-stain (Franca, 712).

Different species of haemogregarines differ considerably in their
appearance and size relatively to the blood-corpuscle in which they
are lodged, and distinct genera have been founded on these differ-
ences ; but as yet the complete life-cycle is known in so few cases
that it is not possible at present to draw up a classification of these
parasites that can have any pretence to be natural.

The following are the principal genera that have been suggested for these
parasites. Lankesterella (Drepanidium) is of very small size, the full-grown
vermicule being not more than two- thirds of the length of the blood- corpuscle ;
type, L. ranarum (minima), parasitic in the blood- corpuscles of the frog.
In Karyolysus the parasite is about the same length as the corpuscle, or
slightly shorter ; the generic name is derived from the action of the parasite
on the nucleus of the host-cell, which is often broken up and " karyolysed,"
though not invariably. This form of parasite is especially common in Reptilia
Squamata, lizards and snakes ; type, K. lacertarum. In the genus Hcemo-
gregarina (sens, strict.) the full-grown vermicule is much longer than the
corpuscle, within which it is doubled on itself in the form of the letter U,
with the nucleus situated at the bend ; type, H. stepanowi of European water-
tortoises, Emys lutaria and Cistudo europcea. Finally there are the " leuco-
cytozoa " of mammals, for which the generic names Hepatozoon, Miller, and
Leucocytogregarina, Porter, have been proposed ; if it becomes necessary to
separate them from the genus Hcemogregarina, Miller's name has the priority,
as Wenyon (690) has pointed out. The fact, however, of parasitism in a white

THE H^MOSPORIDIA 373

corpuscle, instead of a red, does not of itself supply adequate grounds for a
generic, or even for a specific, distinction, since in some species — for example,
H. agamce — the parasites may occur either in white or red corpuscles (Laveran
and Pettit). For the present, therefore, these leucocytozoa, so called, may
remain in the genus Hcemogregarina, until greater knowledge of the life-histories
of haemogregarines makes possible a natural classification of these organisms.
A hsemogregarine of leucocytic habitat has been described also from a frog
by Carini (Rev. Soc. Sci., Sao Paulo, 1907, p. 121).

As a type of the life-cycle of the haemogregarines may be taken
H. stepanowi (Fig. 159), which has been studied by Reichenow (78).
The chief points in this author's account of the life-history are con-
firmed in essential details, but with specific variations, by that
given by Robertson (725) for the life-cycle of H. nicorice* In both
cases the developmental cycle in the tortoise comprises two forms
of schizogony, the one producing schizonts, the other sporonts ;
and the invertebrate host is a leech.

(1) The sporozoite penetrates into a blood-corpuscle, and grows
into a long vermicule, which is at first doubled on itself (Fig. 159, F).
The two limbs of the U-shaped body within the corpuscle fuse
together to produce a bean-shaped parasite — the macroschizont.

(2) The macroschizont of H. stepanowi, remaining within the
blood-corpuscle, goes through its schizogony in the bone-marrow
of the tortoise, producing some thirteen to twenty-four macromero-
zoites (Fig. 159, B, C}. The number produced is larger in the earlier
stages of the infection than in older infections (Fig. 159, D — H).
In H. nicorice, however, the macroschizont is set free in a capillary
of the lung, and there produces about seventy macromerozoites.

In the account of the schizogony given by Reichenow, the significance of the
recurved vermicules is not clear. In drawn blood they can be observed to
be set free from the blood- corpuscles, and then, as free vermicules, to
exhibit active powers of movement, which indicate the existence of some sort
of locomotor apparatus, probably of myonemes. According to Reichenow,
however, liberation from the corpuscle never occurs normally within the
body of the tortoise, but the recurved vermicule remains within the blood-
corpuscle in which it has grown up, and its two limbs fuse to form the body
of the bean-shaped macroschizont. If that is so, it is difficult to understand
why the motile vermicule is ever developed. One is inclined to suspect that
it becomes free from the .corpuscle in which it has developed, and as a " schizo-
kinete " (Minchin and Woodcock, 483) finds it way as a motile vermicule
to the bone -marrow (or lung in H. nicorice), where it penetrates another
corpuscle (or remains free in a capillary vessel, H. nicorice) and becomes the
macroschizont.

(3) The macromerozoites produced penetrate into blood-cor-
puscles, and may (a) repeat the development already described, and
become macroschizonts again ; or they may (b) develop into micro-
schizonts, which produce micromerozoites in small numbers,

* Nothing in the work of these authors confirms in any way the peculiar account
of the life-history of H. stepanowi given by Hahn, whose work is criticized by
Reichenow.

376 THE PROTOZOA

different type. In these cases the invertebrate host appears to be always
an ectoparasitic arthropod. The only life-cycle of such forms which has been
described completely is that of the parasite of the leucocytes of rats, which
has been described by Miller under the name Hepatozoon perniciosum. This
parasite appears to be identical with that named by Balfour (694) Leucocyte-
zoon muris and by Adie L. ratti ; its correct name, therefore, is Hcemogregarina
(Hepatozoon) muris. According to Miller, this parasite causes lethal epidemics
amongst tame rats, but in London it occurs commonly in the blood of wild
sewer-rats, and appears to be quite harmless to them. It is a parasite of world-
wide distribution, apparently, having been recorded from rats in the Punjaub
(Adie), Khartoum (Balfour), North America (Miller), Brazil (Carmi), and various
other parts of the world (see Franca and Pinto, A. I. B.C. P., iii., p. 207).

The life-cycle of H. muris, according to Miller, is in the main as follows:
The sporozoites are liberated in the intestine of the rat, and pass through the
wall of the gut into the blood- stream ; they may be found in the circulation
twenty-four hours after infection. Ultimately the sporozoites reach the
liver and penetrate into liver- cells ; in this situation they grow into schizonts,
which when full-grown sporulate to produce some twelve to twenty, usually
about sixteen, merozoites. The merozoites may penetrate into liver- cells
again and repeat the schizogony, or they may pass out into the capillaries
of the liver ; in the latter event they are taken up by leucocytes, doubtless
as an act of phagocytosis. The merozoites are able, however, to resist any
digestive action of the leucocytes ; they become encapsuled in the leucocytes,
and in this state they are carried into the general circulation. They do not
increase in size in the leucocytes, and their further development, so far as the
rat is concerned, is at an end. Hence the " leucocytozoon " of the rat is an
encapsuled merozoite of a hsemogregarine which, strictly speaking, is a para-
site of the rat's liver, and not of the blood at all ; in the leucocytes its role is
one merely of passive resistance. These merozoites represent at the same time
the sporonts, the propagative phase which develops further in the inverte-
brate host, in this case a rat-mite, Lcelaps echidninus, which sucks the rat's
blood, and so takes up the parasite into its stomach.

In the stomach of the mite the hsemogregarines are set free as motile vermi-
cules which associate in couples. According to Miller, this association is a
true copulation of two gametes which fuse into a zygote ; from the analogy
of the life- cycle described above, it is more likely that some stages have been
overlooked, and that the vermicules are gametocytes which associate, with
subsequent production of gametes by the male and fertilization of the female
by a microgamete.

The zygote, however formed, becomes a motile ookinete which passes
through the wall of the gut into the body- cavity of the mite, and there forms
an oocyst which, like that of the malarial parasites, has a thin wall, permitting
the parasite to absorb nourishment from the surrounding tissues and to grow
to a large size. When full-grown, the contents of the oocyst divide up into a
large number of sporoblasts, each of which becomes surrounded by a delicate
sporocyst. The contents of the spore divide up into some twelve to twenty
sporozoites, and then the development of the parasite is at an end so far as
the mite is concerned. The cyst and spores are the propagative phase, and
in order that they may develop the mite must be eaten by a rat ; if this occurs,
the sporozoites are liberated in the stomach and the cycle is complete.

In the case of other mammalian heemogregarines, fragments of the develop-
ment are known which indicate a life-cycle similar in the main to that of
H. muris, allowing for specific differences. Forms parasitic in the red blood-
corpuscles are H. gerbilli of Gerbillus indicus (Christophers, 699) ; H. balfouri
(jaculi) of the jerboa (Balfour, 693) ; and the three species recently described
by Welsh and others (Journ. Path. Bact., xiv.) from marsupials, one of which
(H. peramelis) is remarkable for having been found only in the free, extra-
corpuscular condition. The schizogony of H. gerbilli has not been described,
but that of H. jaculi takes place in the liver, and is of two types, producing
in the one case a large number of small merozoites, in the other a small

THE ILEMOSPORIDIA 377

number of large merozoites (compare H. cam's, below). In both H. gerbilli
and H. jaculi free vermicules occur, and are set free readily in vitro ; those of
H. gerbilli are recurved when contained in the blood-corpuscle. Stages of
the development of H. gerbilli were found in a louse, Hcematopinus stephensi ;
first free vermicules in the stomach and intestine, later large cysts in the
body- cavity containing a great number of spores, each of which encloses
six to eight sporozoites. It seems impossible that the parasites encysted in
the body- cavity of the louse should get back into the gerbille in any other
way than that of being eaten by the gerbille. Christophers found that, though
the sporozoites were liberated in the intestinal juice of the gerbille, they soon
died in it, but that in the blood- plasma of the gerbille they became extremely
active ; this observation may perhaps be interpreted as indicating that the
spores germinate in the intestine, and the sporozoites, when liberated, pass at
once through the wall of the intestine into the blood- circulation.

The crithidial forms seen by Balf our in Pulex cleopatrce can have no connec-
tion whatever with the haemogregarine of the jerboa ; the flea is probably not
the right host for this parasite.

A number of leucocytic gregarines have been described from various mam-
mals, amongst which may be mentioned H. canis (Christophers, 700), H.
funambuli (Patton, 721), and H. musculi (Porter). The life-cycle of H. canis
has been described by Wenyon (84). The schizogony takes place in the bone-
marrow and the spleen of the dog, and is of two distinct types. In the one
case the schizont divides into a small number of merozoites, usually three,
of large size. In the second case the schizogony results in the production of
a large number of small merozoites. The larger merozoites grow up into
schizonts again ; the small merozoites pass into the blood, are taken up by
the leucocytes, and become the gametocytes, as in H. muris. The sporogony
takes place in the tick, Khipicephalus sanguineus, and is similar throughout
to that of H. muris. The sexual phases were not observed by Wenyon, but
according to Christophers (701) the vermieules become free in the stomach,
and penetrate the epithelial cells, in which they multiply by fission to form
gametes ; probably this applies to the male sex alone. The next stage is an
oocyst in the tissues of the tick. The oocyst grows in size, its nuclei multiply,
some thirty to fifty uninucleate sporoblasts are formed, and each secretes
a sporocyst and becomes a spore containing on the average sixteen sporozoites.
The oocyst- wall dissolves, and the ripe spores are set free in the body of the tick.
Wenyon considers it possible that the dog acquires the infection by eating
infected ticks.

Free vermicules of H. funambuli were seen in a louse by Patton, and a similar
observation was made for H. musculi by Porter. H. musculi also reproduces
by schizogony in the bone-marrow of its host.

The haemogregarines of birds described by Aragao (692) appear to be very
similar to those parasitic in the leucocytes of mammals. The schizogony
takes place in the epithelial cells of the gut or in the cells of the liver, lung, or
bone-marrow; it results in the formation of a number of small, comma-
shaped merozoites, which escape from the cell and are taken up by the mono-
nuclear leucocytes. They do not, however, remain in a resting phase in the
leucocytes, but grow within them to a fair size. When set free from the
leucocyte, they perform active movements. The intermediate host and the
mode of transmission remain, however, to be discovered.

The schizogony of haemogregarines parasitic in snakes has been studied
by Sambon and Seligmann, Hartmann and Chagas (89), and Lave ran and
Pettit (716). It takes place in the capillaries of the liver and lung or in the
bone-marrow. The parasite becomes free from the corpuscle in the capillary,
and grows to a large size. In H. sebai the number of merozoites formed
varies from two or four to over thirty, but is more often from four to eight.
The merozoites are larger when a smaller number is produced. Possibly the
variation is related to the age of the infection, as in H. stepanowi, or to the destiny
of the merozoites, whether to become schizonts or gametocytes, as in H. canis.

The sporogony of the haemogregarines of terrestrial reptiles is practically

378 THE PROTOZOA

unknown in its details, but the transmission appears to be effected by ticks ;
so Karyolysus lacertarum by Ixodes ricinus (Schaudinn, A.P.K., ii., p. 339,
footnote), H. mauritanica by Hyalomma cegyptium (Laveran and Pettit,
718), and the hsemogregarines of snakes (Flu, 707).

The minute " drepanidia " of frogs and newts appear to stand rather apart
from the true hsemogregarines ; beyond the fact that they multiply by
schizogony in the red blood- corpuscles, but little is known of their develop-
ment. According to Hintze, Lankesterella ranarum has no invertebrate host,
but passes from the blood into the wall of the intestine, where it forms re-
sistant cysts like a coccidian parasite. The cysts were believed to pass out
of the frog with the faeces and infect other frogs by the direct contaminative
method. It is, however, very doubtful if the cysts described by Hintze really
belong to the cycle of the Lankesterella ; from other observations it is possible
that the drepanidia are not haemogregarines at all, but stages in the life-cycle
of a trypanosome (compare Billet, 696). According to Fra^a (709), " Dacty-
losoma " splendens of the frog produces Leishmania-like merozoites, with
distinct kinetonuclei (compare also Seitz). Until further researches have
been undertaken, the position of the drepanidia must remain uncertain.

Neresheimer (720) has described the penetration of the red blood- corpuscles
of frogs by Lankesterella sp., a process in which remarkable phenomena are
exhibited. When a Lankesterella, in approaching a blood- corpuscle, is within
a distance from the corpuscle about equal to the length of the parasite, the
edge of the corpuscle turned towards the parasite shows distinct amoeboid
movements. As the parasite comes still nearer, two long processes are
thrown out by the corpuscle, forming a deep bay, into which the parasite enters ;
as soon as it does so, the two processes approach each other, fuse and engulf
the parasite, just as an amoeba ingests its prey. The parasite, after this point
is reached, appears to be drawn into the corpuscle without further exertion
on its part ; the protoplasm of the corpuscle closes up behind it, and the
corpuscle regains its normal smooth contour, with the parasite lying within
it. The whole process of penetration takes one or two minutes. Neresheimer
compares the activity of the corpuscle to the " cone of reception " formed
by an ovum when approached by a spermatozoon.

From the foregoing account of the life- cycles of haemogregarines, it is seen
that the sporogony varies greatly, from the production of eight sporozoites
in the oocyst of H. stepanowi and H. nicorice, to the condition of H. canis,
H. muris, and H. gerbilli, in which a large number of spores are formed with a
variable number of sporozoites. It is impossible, therefore, to accept as
adequate the diagnosis given by Leger (644) of the " Hcemogregarinidce " as
producing a single octozoic spore (see p. 353, supra).

5. The Piroplasms. — The parasites of this type are minute
organisms, capable of amoeboid movement, but generally of a
definite form, which is usually pear-shaped or rod-like. They are
contained, sometimes as many as a dozen or more together, within
a mammalian red blood-corpuscle. They produce no pigment, but
destroy the corpuscle in which they are contained, and set free the
haemoglobin, which is then excreted by the kidneys of the host. In
consequence of this, the diseases produced by these parasites,
termed generally " piroplasmoses " (or " babesioses "), are of a very
characteristic type, the most striking symptoms being an enormous
destruction of blood-corpuscles and a red coloration of the urine
by haemoglobin (haemoglobinuria). From this peculiarity are
derived popular names, such as " redwater," etc., applied to
diseases caused by piroplasms.

THE ILEMOSPORIDIA

379

The best-known member of this group of organisms is a parasite
of the blood of cattle (Fig. 160), which has been most unfortunate
in its nomenclature, and has appeared under a variety of generic
names (Hcematococcus, Pyrosoma, Apiosoma, Piroplasma), but of
which the correct name is probably Babesia bovis (or bigemina).
The typical form of this parasite is a pear-shaped body within the
blood-corpuscle. It multiplies by binary fission, and is often
double in consequence — whence the specific name bigemina.

Many other species are now known, parasites of domestic animals in
various parts of the world, and of recent years a number of species have
been made known from wild animals, but our knowledge of piroplasms
in a natural state is not very extensive. No species is known with
certainty to be parasitic upon human beings, but a disease known
as " spotted fever of the Rocky Mountains " has been stated to be
caused by Piroplasma hominis, and it is possible that the organisms

FIG. 160. — Piroplasma, bigeminum (Babesia bovis) in the blood-corpuscles of the
ox. a, b, Youngest forms ; c — /, binary fission ; g — j, various forms of
the twin parasites ; k, I, doubly-infected corpuscles. After Laveran and
Nicolle.

described from the blood of yellow fever patients by Seidelin (757),
and named by him Paraplasma flavigenum, may be allied to
the piroplasms.

The investigations upon these organisms carried on during the
last few years have led to their being divided up into a number of
genera based on differences of form and structure. The following
enumeration of the genera of " Piroplasmidoe " may serve at the
same time to indicate the structural varieties exhibited by these
parasites (compare Fraii9a, 736).

(1) Piroplasma, Patton (Babesia, Starcovici). — Pear-shaped forms,
dividing by a process of gemmation — hence commonly found in
pairs in the corpuscle. Species are known from oxen, sheep, horses
(P. caballi of " biliary fever "), dogs, monkeys, rats, and various
wild animals.

(2) Theileria, Bettencourt, Fran9a and Borges. — Bacilliform or
rod-shaped parasites arranged in a characteristic figure of a

380 THE PROTOZOA

cross.* T. parva is the parasite of " East Coast fever " of cattle in
Africa. Other species have been described from the fallow-deer and
from Cephalolophus grimmi.

(3) Nicollia, Nuttall. — Oval or pear-shaped parasites with peculiar
nuclear structure (see below), and with quadruple division, pro-
ducing a figure at first like a fan, then like a four-leaved clover.
One species, N. quadrigemina, from the gondi, Ctenodactylus
(Nicolle, 746).

(4) Nuttallia, Fran$a. — Parasites oval or pear-shaped (not rod-
shaped) ; multiplication-forms like a cross. N. equi, of equine
piroplasmosis ; N. herpestidis, of a mongoose (Herpestes ichneumon).

(5) Smithia, Fran9a. — Pear-shaped forms, occupying the whole
diameter of the corpuscle, not in pairs ; quadruple multiplication
in the figure of a cross. 8. microti from Microtus arvalis.

Future research will, no doubt, determine the value of these
generic distinctions, some of which seem to rest upon a somewhat
slender foundation.

As is evident from the foregoing classification, the form of the para-
site varies considerably in different species, and even in the same
species. In many cases the body may show amoeboid changes of
shape, and may throw out long pseudopodial processes. The two
principal types of form of the full-grown parasite are the pear-
shaped and the bacillary forms ; but the smaller parasites may be
ring-like, with the nucleus excentric, and placed near the margin
of the body in some cases. The relation of these forms to one
another, and their significance in the life-cycle, are not clear, but the
annular forms appear to be young stages of either the pear-shaped
or bacillary forms. Kinoshita claims to be able to distinguish
indifferent (schieonts) from sexually-differentiated forms (sporonts)
(compare Theileria, p. 382, infra).

The minute structure of the body is very simple, since the cyto-
plasm has as a rule no enclosures except the nucleus, which is
single. In some cases, however, the cytoplasm may be vacuolated
to some extent, and in the ring-like forms has a large central
vacuole. The nucleus itself appears to be of a simple type of

* A confusion has arisen between two parasites very similar as regards the
appearances they present in the blood, but differing in every other respect — namely,
Theileria parva, the true parasite of " East Coast fever " of cattle, and Babesia

(Piroplasma) mutans, also found in cattle. In both parasites alike the charac-
teristic cross-forms appear in the blood. In Theileria parva, however, the cross-
forms are an aggregation of four distinct gametocytes (see p. 382, infra] which
have invaded the same corpuscles, while in Babesia mutans the cross-forms are
produced by quadruple fission of an ordinary multiplicative individual ; this
difference has the consequence that, since the gametocytes of T. parva are not
capable of further development in the blood of the ox, direct inoculation of blood
from an infected to a healthy ox does not produce an infection in the latter, as
happens always when a healthy ox is inoculated with blood containing Babesia
mutans. The diagnosis of the genus Theileria given by Franca would appear to
apply to B. mutans rather than to T. parva. See especially Gonder (739).

THE ILEMOSPORIDIA 381

structure, a compact mass of chromatin or karyosome contained
in a vacuole-like space — in other words, a protokaryon of the simplest
type (compare Breinl and Hindle, 730). The remarkable form
Nicollia quadrigemina has an oval nucleus at the blunt end of the
body, with two karyosomes, a larger one placed close to the surface,
and a smaller one nearly at the centre of the pear-shaped body
(Nicolle, 746).

With the unreliable method so much in vogue until quite recently, of
making preparations by drying blood-smears and staining them with the
Romanowsky stain, the nucleus may show various appearances about which
much has been written, and which cannot be interpreted with certainty until
they have been examined by better cytological methods. In such prepara-
tions the appearance is usually presented of a deeply-stained karyosome
lying at the edge of, or near to, a diffuse, more or less irregular chromatin-
mass ; or the nucleus as a whole may appear as an evenly-stained mass lying
usually at one end of the body in bacillary forms, or near the rounded ex-
tremity in the pear-shaped forms. In other cases, in addition to the principal
chromatinic mass, some specimens may exhibit a grain or dot, which from its
staining reactions appears to be chromatin. Many efforts have been made
to establish on this slender basis a theory of nuclear dimorphism for piro-
plasms, and to interpret the second grain as a kinetonucleua ; but it bears no
resemblance to any such body in its structural and cytological relations, and is
inconstant in its occurrence, being entirely absent as a general rule.

A question much discussed is that of the occurrence of flagellated forms of
piroplasms in the blood of the vertebrate host. In a few rare cases, in parasites
preserved by the defective method mentioned in the last paragraph, irregular
streaks of substance similar to chromatin in its staining properties have been
seen extending from the karyosome even some way beyond the body of the
parasite (Fantham, 735; Kinoshita, 741), and these appearances have been
interpreted as flagella ; but the published figures of these structures do not
in the least favour any such interpretation. Kinoshita suggests that the
" flagella " figured by him may represent formation of microgametes. Of
more value are the observations of Nuttall and Graham-Smith (748) on the
living parasites. They observed that a pear-shaped parasite, when free in
the blood- plasma, is capable of moving very rapidly, with the blunt end
forwards, while the posterior pointed end exhibits active vibrations which they
compare to those of a fish's tail. In some cases the hinder end was observed
to be prolonged into a flagellum-like process. The authors cited explain the
absence of flagellated forms in permanent blood- preparations by supposing that
the flagellum becomes retracted when preserved ; if so, it is a structure of a
very different kind to a true flagellum, such as that of a trypanosome, and its
relations to the progression of the parasite also differ.

Breinl and Hindle (730) have figured biflagellate organisms from the blood
of dogs dying from piroplasmosis. The flagellates in question were of transi-
tory appearance, and were only found in the blood of the dog the day before
its death. The authors interpret these forms as a phase of the piroplasm ;
but a consideration of the figures given, and of the circumstances under which
the flagellates were found, leave hardly any doubt but that the forms seen
were intestinal flagellates, Bodo or Prowazekia sp., which, in the pathological
condition of the host, had passed into the blood (see p. 258).

The development of the parasite in the vertebrate host appears
to consist solely of multiplication by fission (Figs. 160, 161), usually
either binary or quadruple, within the corpuscle ; though the
presence of the annular forms, apparently representing young

382 THE PROTOZOA

individuals, would seem to indicate the existence of some form of
schizogony, yet to be discovered, in the tissues or internal organs
of the body. When the parasite or parasites have destroyed the
corpuscle in which they are lodged, they are set free in the blood-
plasma and penetrate other red corpuscles.

Theileria parva stands apart from other piroplasms in its developmental
cycle in the vertebrate host. According to Gonder (738, 740), the minute
sporozoites injected by the tick collect in the spleen and lymphatic glands,
where they penetrate into lymphocytes, in which they grow rapidly. The
originally single nucleus divides repeatedly, and large multinucleate plasmo-
dial masses are formed which finally divide up into as many minute mero-
zoites, " agamonts," as there are nuclei ; the process recalls strongly the
schizogony of Hcemoproteus columbce (Fig. 157, K — R), and leads to the break-
up of the lymphocyte. The first schizogonous generation may be repeated
several times, but at last a generation of " gamonts " is produced, which
are distinguished from the agamonts by characteristic differences in the
nuclear structure. The gamonts multiply by a process of schizogony, the
final or " gamogenous " generation, ending in the production of gametocytes,
minute parasites which do not multiply further, but penetrate into the red
blood- corpuscles, where they grow into adult gametocytes of two kinds — male
gametocytes, which are long, slender, " bacillary " forms ; and female gameto-
cytes, which are plump, rounded, or pear-shaped forms. The gametocytes
can only develop further in 'the tick Rhipicephalus (see below).

The forms found in the red corpuscles in the peripheral blood are either
gamonts or gametocytes, incapable of developing beyond the latter stage
except in the tick ; this explains a peculiarity of this parasite, namely, that
inoculation of infected blood into a healthy animal does not produce an
infection.

The position of the genus Achromaticus, founded by Dionisi for A. vesperu-
ginis, parasitic in the blood of bats of the genus Vesperugo, is still doubtful.
It occurs under a number of different forms, some free in the blood- plasma ;
others, more common, within the corpuscles. The free forms are rounded or
spindle-shaped ; the intracorpuscular parasites may be also of these two
forms, but are more often pear-shaped. Within the corpuscles the rounded
and pear-shaped forms divide into two or four by a process of schizogony.
According to Gonder (737), the parasite has a double nucleus in all stages,
but this is not confirmed by Yakimoff and Co. (753), who regard the parasite
as a true Piroplasma. Neumann (745) states that in the bat- mite (Pteroptus
vespertilionis) the parasites undergo a transformation into flagellated organisms,
and considers Achromaticus allied to trypanosomes. It is not improbable
that stages of Achromaticus, both in the vertebrate and invertebrate hosts,
have been confused with stages of the trypanosome found in the blood of the
same vertebrate hosts.

The process of division in Piroplasma canis (Fig. 161) has been studied in
great detail by Nuttall and Graham-Smith (748), and by Christophers (732).
The small rounded forms divide by simple binary fission of the ordinary type.
In the larger forms the division takes place in a peculiar manner, more akin
to gemmation than to ordinary fission. Before division the parasites become
amoeboid and irregular in form, and the nucleus has the form of a compact
mass. The nucleus then sends out two buds which grow towards the surface
of the body, and at this point two protoplasmic buds grow out into which
the nuclear buds pass. The buds increase in size until they become two pear-
shaped piroplasms, joined at their pointed ends by the continually- diminishing
remains of the body of the original parent- individual. The connecting mass
dwindles to a mere point, and finally the two daughter- individuals separate.
A modification of this method leads to the quadruple fission producing four
buds and four daughter-individuals, as in Babesia mutans.

THE H^MOSPORIDIA

383

The piriform parasites escape from the corpuscle when it is exhausted,
and approach other corpuscles, moving with considerable rapidity. The
parasite attacks the corpuscle with its blunt extremity foremost, and " rapidly
indents its surface. Then violent movement of the thin end of the parasite
occurs, and the side of the corpuscle becomes greatly distorted. . . . Gradually
the parasite sinks more deeply into the corpuscle, and finally disappears within
it, when the movements of the corpuscle cease and it resumes its rounded
shape " (Nuttall and Graham-Smith, 748, vi., p. 235 ; compare the penetra-
tion of blood- corpuscles by Lankesterella described above). Only piriform or
long parasites enter corpuscles, never the round forms ; but immediately after
its entry into the corpuscle the parasite becomes rounded. If rounded para-
sites are set free from a corpuscle by its rupture, they die off, as do also the
pear-shaped forms if they do not succeed in penetrating into a corpuscle.

FIG. 161. — Diagrams showing the mode of division of Piroplasma cam's in the
blood-corpuscle. A, Parasite about to divide ; B, the nucleus budding off a
smaller mass ; C, the nuclear bud has grown out into a forked strand ; D, the
forked ends of the strand are growing out into protoplasmic buds ; E, F, G,
growth of the buds at the expense of the main body ; //, /, J, final stages of
the division of the body. After Nuttall and Graham-Smith.

A peculiar parasite, perhaps allied to the true piropasms, is Anaplasma
marginale, which occurs in the blood of cattle, and causes a disease charac-
terized by destruction of the red corpuscles and production of high fever,
leading to a degeneration of the large parenchymatous organs. The parasite
occurs within the red corpuscles, and is described as consisting solely of
chromatinic substance, without a cytoplasmic body; hence the parasites
were formerly described as " marginal points." The parasite has the form
of a round or oval coccus-like body which multiplies by simple fission. It is
transmitted by a tick, Rhipicephalus decoloratus. See especially Theiler (752).

The transmission of piroplasms was first discovered by the
American investigators Smith and Kilborne, who in a classical

384 THE PROTOZOA

memoir showed that the parasite of Texas cattle-fever (Babesia
bows or bigemina) was transmitted from sick to healthy oxen by
the agency of ticks. The method of transmission is of a peculiar
type, which finds its explanation in the habits and life-history of
ticks. These arachnids have typically three stages in their life-
history — (1) the minute six-legged larva hatched from the egg,
which, after growing to its full size, sheds its skin and appears as
(2) the nymph, eight-legged, but sexually immature ; the nymph
after another moult becomes (3) the adult tick, sexually mature and
with four pairs of legs. In each of these three stages of the life-
history the tick feeds, as a rule, but once. Consequently, if the
parasites are taken up by the tick at one stage of its existence, they
cannot be reinoculated into another host until a later stage of the
tick. Smith and Kilborne found that the parasites taken up by the
adult female ticks passed through their ova into the next generation
of the ectoparasites, so that the minute larval ticks, progeny of an
infected mother, were the infective agents which spread the disease
amongst the cattle.

Subsequent investigations have confirmed and extended the dis-
covery made by Smith and Kilborne, and in every case the in-
vertebrate host of any species of piroplasm appears to be a tick.
In P. boms (bigeminum) the parasites develop only if taken up by
an adult female tick (Koch), but this is not so in other cases. The
parasites may be taken up by the tick at various stages, and returned
to the vertebrate host at a later one ; for instance, by the larva and
returned by the nymph, or by the nymph and returned by the adult,
or by the adult and returned by the larva of the next generation.

Although the transmission of piroplasms by ticks is well established, the
developmental cycle of the parasite in the tick is known only in a fragmentary
and incomplete manner. The most complete accounts are those given by
Christophers (732) for Piroplasma canis, and Koch (743) for P. bovis, whose
observations supplement each other, since Koch studied chiefly the earlier
stages, while Christophers' investigations appear to be more complete for
later phases of development. Stages in the tick are also described by
Dschunkowsky and Luhs (734), but in a disconnected manner, and observa-
tions on the development in cultures have been published by Kleine (742)
and by Nuttall and Graham-Smith (750). Accounts differ chiefly as to the
events at the beginning of the development. So far as it is possible to make
a connected story out of the published observations, the development in the
tick appears to comprise six principal phases :

1. The piroplasms taken up in the blood pass into the stomach of the
tick, and there the pear-shaped forms are set free from the corpuscles,
these forms alone being capable of further development. After
about twelve to eighteen hours they become amoaboid, sending out in all
directions slender, stiff, sharply- pointed pseudopodia which are slowly re-
tracted and emitted again. Usually the pseudopodia are given off chiefly
from the thicker end of the pear-shaped body, but in some cases the form is
spherical and the appearance of the parasite strikingly Heliozoon-like (Fig. 162,
A — C). The nucleus of the parasite divides into two parts — a larger mass,

THE H^MOSPORIDIA

385

staining more deeply, on which the pseudopodia are centred ; arid a smaller,
paler body placed more excentrically. In the pear-shaped forms the large,
dark nucleus is placed at the blunt end, the small, pale body near the pointed
end. Forms similar to these have been obtained in cultures, and evidently

H

Fia. 162. — Stages in the development of Piroplasma in the tick. A — G, Amoeboid
forms (gametes ?) : A, pear-shaped, with the pseudopodia given off at the
thicker end of the body ; B, G, spherical or Heliozoon-like, with the pseudo-
podia radiating out on all sides ; D — F, fusion of the gametes (?) ; G, result
of fusion (?) ; H — J, globular bodies (zygotes ?) ; K — M, motile vermicules
(ookinetes ?). A—J after Koch (P. bovis) ; K— M , after Christophers
(P. canis).

represent the first stages of the development ; but they appear to have been
missed by Christophers, unless it is to be assumed that these forms occur in
P. bovis, and not in P. canis.

The star-like forms would appear to represent the gametes ; they congregate

25

386 THE PROTOZOA

in clusters, and according to Koch they fuse in pairs (Fig. 162, D — 0} ;
cytological details of the syngamy, if such it be, are lacking (but compare
Theileria, infra).

2. The stellate stage is succeeded by a spherical stage, very possibly repre-
senting the zygote. This body grows in size, but its development, as de-
scribed by Koch, is difficult to understand, and requires further elucidation.
The final result is a globular mass with a single nucleus, found in great numbers
on the third day, according to Koch (Fig. 162, J). Whether these bodies have
arisen by division of the zygote, or represent simply the zygotes, is not clear,
but the latter alternative seems the more probable.

3. The globular stage is succeeded by a club-like or retort-shaped stage.
According to Christophers, whose account of the life-cycle appears to begin
at this stage, a split appears in the globular body, whereby a portion contain-
ing the nucleus is divided off incompletely from a portion which has no
nucleus. Tho non-nucleated portion then swings round and forms the tail-
piece of the complete club-shaped body, which has a single nucleus at the
swollen extremity. The club-shaped bodies appear to represent the ookinetes
(Fig. 162, K — M). They are motile and gregarine-like, and in some cases
have an organ resembling an epimerite, regarded by Christophers as a boring
organ, at the anterior extremity. Their size is about four times that of the
piroplaswns in the blood.

4. The club-shaped bodies pass from the gut of the tick into the ovary
and oviduct, and penetrate into the ova. There they become again globular
in form, and are found in the yolk of the egg, and later in the cells of the
embryo developed from the egg. When, however, the parasites have been
taken up by a nymph, as may happen in P. canis, the globular bodies are
found in the tissue-cells of the body. This globular stage, termed " zygote "
by Christophers, very probably corresponds to the oocyst of the hsemamcebae.

5. The globular body of the previous stage divides up by multiple fission
into a number of " sporoblasts," which do not remain aggregated together,
but scatter themselves through the tissues of the tick, larva, nymph, or adult,
as the case may be.

6. The sporoblasts divide in their turn into a great number of sporozoites,
small bodies with a single nucleus similar in appearance to the piroplasms in
the blood. The sporozoites collect in vast numbers in the salivary glands
of the tick, and pass into the vertebrate when next the tick feeds. According
to Gonder, ticks infected with Theileria parva purge their salivary glands com-
pletely of the parasites when they feed, and are only infective for a single meal.

The development of Theileria parva in the tick has been described by
Gonder (740). Within an hour after passing into the stomach of the tick
the parasites become free from the corpuscles. The immature gametocytes
die off, but the adult forms proceed to gamete -formation. The free parasites
are at first rounded off, but soon send out processes and become amoeboid.
The male gametocytes send out a single process, and creep about actively
like a limax-amosbz ; their nucleus goes through an unequal division, after
which the gametocyte becomes a gamete. The female gametes, which are
inactive, go through a similar reduction- process. Pairing of two gametes
and fusion of the cytoplasmic bodies takes place, but before the nuclei fuse
each nucleus goes through a second reduction-division. After copulation of
the nuclei the zygote becomes an active ookinete, first retort-shaped and then
gregariiiiform, which penetrates into the salivary glands, and there goes
through a multiplicative process, very similar to that of Halteridium in the
lung of the pigeon (cf. Fig. 157), producing a swarm of sporozoites which are
inocuated into the vertebrate host by the tick. Thus in Theileria also
there is no flagellated stage at any part of the life-cycle — a fact which does
not, however, prevent Gonder from seeing " blepharoplasts," and even crith-
idial forms on every possible occasion ; he seems to consider nuclear reduction
and blepharoplast -formation as the same thing. It is a pity that the effect
of such excellent work should be marred by so much theoretical bias. Aber
tvie die Alien sungen . . . !

THE ILEMOSPORIDIA 387

From the foregoing it is seen that the development of piroplasms
appears to be of a type essentially similar to that of the hsem-
amcebse and haemogregarines. In the present fragmentary state of
our knowledge, however, it would be premature to generalize con-
cerning the development of these forms. The most noteworthy
feature of the development is the entire absence of flagellated forms
from the life-cycle. The alleged flagellate forms of P. canis in
the dog's blood described by Breinl and Hindle have been dealt
with above ; it only remains to be mentioned that Miyajima
obtained trypanosomes in cultures of the blood of calves suffering
from piroplasmosis, an observation which led to the discovery of a
trypanosome in calves not previously known to exist (see p. 283).

Doubtful Genera of Hcemosporidia. — A certain number of blood-
parasites have been described which at present are not sufficiently
well known to make it possible to assign to them a definite systematic
position. When more thoroughly investigated, many of them may
turn out to belong to other groups than the Heemosporidia ; it is
even possible that some of these bodies are not parasites at all, but
merely some forms of cell-enclosures.

The genus Toxoplasma was founded by Nicolle and Manceaux (754) for
T. gondii, a parasite of the gondi (Ctenodactylus gondii) ; other species have
since been described — namely, T. cuniculi, Carini, from the rabbit, T. canis,
Mello, from the dog, and T. talpce, Prowazek, from the mole. The organisms
in question are parasites of the white blood- corpuscles, and occur most
abundantly in the spleen or liver, causing a disease which is frequently fatal.
The parasite is a crescent-shaped body, with one end thicker than the other,
and containing a single nucleus ; they multiply by binary or multiple fission.
Nicolle and Manceaux regarded them as allied to LeisJimania, but their
resemblance to this genus appears to be purely superficial, since in Toxoplasma
no kinetonucleus is present, and in cultures no flagellated stage is developed.

Elleipsisoma ihomsoni is the name given by Fran£a (441) to a parasite of
the blood of moles discovered by Thomson (524). It occurs as an amoeboid
intracorpuscular parasite with a single nucleus situated at the margin of the
body, which contains no melanin-pigment. Multiplication takes place ex-
clusively in the lung, and is by binary or multiple fission, according to Fran$a ;
the young forms are either vermiform, with the nucleus drawn out, or oval,
with a compact nucleus ; they penetrate into the corpuscles and grow there.
Fran9a considers this form to be allied to Toroplasma.

The name Toddia bufonis is given by Franca (440) to certain bodies in the
red blood-corpuscles of batrachia, first described by Todd. The earliest stage
in the corpuscle is a small globule of chromatin ; Franca believes that the
parasite when it penetrates the corpuscle is reduced to its nucleus alone, and
that it gradually forms a cytoplasmic body which becomes substituted for
that of the corpuscle. As the cytoplasmic body is formed, crystals appear
in it, one large crystal or as many as three smaller ones. Finally the corpuscle
is seen with a si ightly hypertrophied nucleus pushed to one side, and its contents
consisting chiefly of substance which stains intensely blue with the Roman-
owsky stain, in which are the crystals and the nucleus of the parasite, now
3 to 3 '5 p. in diameter. No multiplication-stages have been observed.

Globidium multifidum is the name given by Neumann (488) to a parasite
of the red blood- corpuscles of Gobius minutus and Arnoglossus grohmanni. It
was met with in the form of a cluster of some thirty to sixty merozoite-like
bodies, each 2'5 /* in length by 1*5 p. in breadth ; similar bodies were seen in

388 THE PROTOZOA

blood-corpuscles singly, but their growth and multiplication were not ob-
served. The parasite appears to develop in red corpuscles, which it finally
fills completely, breaking up the nucleus ; no pigment is formed. The youngest
forms show sometimes a grain near the nucleus, possibly a kinetonucleus.
With the bodies desciibed by Neumann may be compared those observed
by Mathis and Leger (473, pp. 417-419, Plate XIIL, Figs. 12-16) in a fish,
Clarias macrocepholus ; possibly they have some connection with the trypano-
some found in the same host.

Immanoplasma scyUii, Neumann (488), is a parasite of the red blood-
corpuscles of Scyllium canicula. It grows to a size of 30 by 20 , and in life
is feebly amoeboid. Its protoplasm stains very deep blue by the Romano wsky
stain, and its nucleus appears usually as if separate from the rest of the body
of the parasite, lying apparently free from it in the blood- corpuscle. Some
forms of the parasite have paler protoplasm with a larger nucleus, others
darker protoplasm with a smaller nucleus ; the two forms are possibly male
and female. No pigment is produced. The development of the parasite
remains at present unknown.

Finally mention must be made of the so-called " Kurloff-Demel bodies,"
found in the leucocytes of the guinea-pig. According to Patella (755) they
are true "leucocytozoa," but according to Mathis and Leger (473) they are
not of parasitic nature. A memoir will be published shortly by Dr. E. H. Ross,
however, in which it will be shown that the Kurloff-bodies are true parasites,
representing, apparently, a stage of a motile organism, probably a spirochsete,
found free in the blood. The author proposes for this parasite the name
Lymphocytozoon cdbayce.

Affinities of the Hcemosporidia. — Two opposed and conflicting
theories with regard to the systematic position of the Haemosporidia
hold the field at the present time.

1. The older and more generally accepted view is that the
Hsemosporidia are closely allied to the Coccidia, sufficiently so,
in fact, to be classed with them in a single order. Thus, Doflein
divides the Telosporidia into two orders, the Gregarinoidea and
the Coccidiomorpha, the latter comprising two subdivisions, Coc-
cidia and Haemosporidia ; while Mesnil placed the Haemosporidia,
together with the genus Legerella, amongst the Coccidia in an
order Asporocystea, characterized by the absence of sporocysts
in the oocyst, a character that cannot be utilized in this manner
now that some haemogregarines have been shown to form sporocysts.

2. Hartmann and others (e.g., Awerinzew) maintain that the
Hsemosporidia should be removed altogether from the Sporozoa,
and should be classed, together with the Haemoflagellates, as an
order of the Flagellata, for which the name Binucleata is pro-
posed, since the chief structural feature common to all members of
the order is supposed to be the possession of two differentiated
nuclei, a kinetonucleus and a trophonucleus, distinct from each
other.

It must be clearly understood that the theory of the Binucleata, as pro-
pounded by Hartmann and his school, is not merely one of a general relation-
ship between Haemosporidia and Flagellata. This wider point of view will
be discussed when the affinities of the Telosporidia as a whole are considered.
The question at present under discussion is whether the Haemosporidia, more

THE HvEMOSPORIDIA 389

than the other Telosporidia, are allied specially to the Haemoflagellates, more
so than to other Flagellata ; whether, in short, the Haemosporidia should
be removed from the Telosporidia altogether, and should be classified, together
with the Hsemoflagellates, in one natural order, family, or other systematic
category. In dealing with the Hsemoflagellates in a previous chapter, cause
was shown for believing them to have two distinct lines of ancestry, the one
from a Cercomonad, the other from a Bodonid type of Flagellate ; in that
case it is the Cercomonad section — that is to say, the trypanosomes and their
allies — to which the Haemosporidia must be considered to be specially related
on the theory now to be discussed.

Leger and Duboscq (646), recognizing distinct Bodonid and Cercomonad
stems in the Haemoflagellates, derive the Gregarines, Coccidia, and Haemo-
gregarines, from the Bodonid stem (trypano plasms), the Hsemamoebae and
Piroplasms from the Cercomonad (trypanosome) type.

The close relationship of the Haemosporidia and the Coccidia
seems at first sight so obvious, from a general consideration of the
life-histories of typical members of each group, that any theory
to the contrary must justify itself by convincing and cogent argu-
ments. The chief grounds upon which affinities between Haemo-
sporidia and Haemoflagellates are alleged are found, when analyzed,
to be of three kinds — namely : first, developmental data ; secondly,
structural — that is to say, mainly cytological — peculiarities ;
thirdly, resemblances between certain forms which appear to be
sufficiently close to link the two groups together by a series of gradual
transitions. The evidences of affinity between Haemosporidia and
Haemoflagellates based on these three classes of facts must be
considered separately.

1. Developmental Data. — Beginning with the first of the five types of
Haemosporidia which have been recognized above — namely, the haemamcebae
or malaria] parasites, it is very evident, as Schaudinn (658) first pointed out,
that their life-cycle resembles in the closest manner that of the Coccidia.
With one exception, every phase in the life-cycle of a malarial parasite has a
corresponding phase in that of a coccidian, and the same terminology can be
used throughout for describing the stages of the development ; the one ex-
ception to this statement — the only phase that requires a special name — is
the ookintte-stage of the malarial parasites, which is not known to occur
in any coccidian. It is clear, however, that the points in which the life-
cycles differ from one another in the two cases are such as can be correlated
with the differences in the mode of parasitism — that is to say, with the fact
that in Coccidia, speaking generally, there is a single host, and the mode of
infection is contaminative, while in the haEmamcebae there are two hosts,
and the vertebrate is infected by the inoculative method. Corresponding
with this difference, the zygote in the Coccidia prepares at once for leaving
the body of the host and passing out into the open, and protects itself by a
firm envelope ; while that of the haemamcebae, produced in the body of an
intermediate host, does not encyst itself, but is actively parasitic, continuing
to absorb nourishment from the host and to grow. Further, in the hsemamcebae
the parasite is always in the body of one or the other of its two hosts, and
consequently tough, impervious cysts and spores like those of Coccidia are
superfluous and are never formed ; the oocyst is a thin membrane through
which soluble foodstuffs can diffuse, and sporocysts are not secreted, as is the
case also in some Coccidia. The adaptive significance of these differences
is so obvious that it does not require further elucidation or discussion.

The development of the halteridium-type, as described by Aragao, can be

390 THE PROTOZOA

derived without difficulty from that of the hsemamcebse ; and, in spite of
the hiatus in what is known of the life-cycle, there is no difficulty in comparing
and homologizing the phases of Hcemoproteus columbce with those of a malarial
parasite, and consequently with those of a coccidian. The development of
Leucocytozoon requires investigation, but the little that is known — namely, the
schizogony, sexual phases, and ookinete -formation — is entirely of the
hsemamoeba -type.

More striking than in any other type of the Hsemosporidia are tha coccidian
features of the hsemogregarines. In such a form as H. stepanowi the life-cycle
is seen to exhibit not merely a general similarity to that of the Coccidia, but
even a special resemblance to particular forms. The mode of gamete-forma-
tion is that which characterizes the family Adeleidce among Coccidia, and the
many developmental similarities between H. stepanowi and the only known
coccidian parasite of a leech, Orchedbius herpobdellce, have led Reichenow
to derive them from a common form. In many hsemogregarines, apparently,
the parasite obtains an entry into the vertebrate host, not by the inoculative
method, but by the contaminative, through the vertebrate devouring the
invertebrate host. In such cases (H. muris, H. gerbilli) the characteristic
coccidian sporocysts reappear in the spprogony. It is not necessary, however,
to dilate further on the coccidian affinities of the hsemogregarines, since they
are recognized by Hartmann and his school, and the latest revisions of the
order Binucleata do not comprise the hsemogregarines, which are left in the
Telosporidia.

As regards the piroplasms, it is perhaps unsafe to generalize in the present
fragmentary state of our knowledge of the life-cycle, and in particular of the
sexual phases ; but so far as it is known, the phases of the development appear
to correspond closely with those of the typical Hsemosporidia. But at least
it can be said that the development of piroplasms does not afford the slightest
support to the view that they are in any way allied to Hsemoflagellates ;
indeed, it can be affirmed, on the contrary, that, of all the forms included in
the Hsemosporidia, the piroplasms exhibit the least indications of flagellate
affinity.

From a general consideration of the life-cycles of the typical Hsemosporidia,
such as the hsemamcebse and hsemogregarines, and omitting doubtful forms,
it is very clear that what may be called the nucleus of the group bears a close
and unmistakable resemblance to the Coccidia. One section, comprising the
hsemamcebse. halterldia, and leucocytozoa of birds, are to be derived from an
ancestor which formed gametes after the manner of Coccidium, and in these
types the phenomena of " exflagellation " can be observed readily. In the
other section, comprising at least the hsemogregarines, gamete-formation is
of the type of that seen in Adeleidce, and does not take place until the gameto-
cytes have associated ; consequently exflagellation in vitro does not occur,
but coupling of the sporonts, as in gregarines, has often been described, but
wrongly interpreted as copulation (cf. Sambon and Seligmann).

In the face of such profound homologies with Coccidia, what are the argu-
ments from the developmental cycle in favour of a contrary opinion ? The
case for the alleged Hsemoflagellate affinities of the Hsemosporidia rests on
the famous memoir of Schaudinn (132) on the blood-parasites of the Little Owl,
a work which must now be considered briefly.

The Little Owl (Athene noctua) harbours the full number of known avian
blood-parasites — namely: (1) a proteosoma ; (2) a halteridium ; (3) a small
form of trypanosome ; (4) a large form of trypanosome ; (5) a leucocytozoon :
(6) a spirochsete.

According to Schaudinn, these six forms belong to the life-cycle of three
species of parasites. First, the proteosoma (1) is a distinct form, not related
to any of the others. Secondly, the halteridium ( 2) and the small trypanosome
(3) are alleged to be two phases of the same parasite. Thirdly, the large
trypanosome (4), the leucocytozoon (5), and the spirochsete (6), are supposed
to represent different phases of one and the same life-cycle.

The halteridium (Hamoproteus noctuce) was stated by Schaudinn to be the

THE H^EMOSPORLDIA 391

resting intracorpuscular diurnal phase of a trypanosome which at night
developed a locomotor apparatus, became free from the blood- corpuscle, and
swam freely in the plasma ; in the morning the trypanosome penetrated into
a corpuscle, lost its locomotor apparatus again, and became a halteridium.
Male, female and indifferent forms were distinguished. The smallest in-
different forms went through a six-day development and growth, in the
corpuscle as a halteridium by day, free in the plasma, as a trypanosome by
night, until full grown ; then they multiplied rapidly by repeated fission to
produce trypanosomes of the smallest size. These young forms might grow
up into indifferent forms in their turn, or might become male or female forms ;
in the latter event their development was slower, and in its later stages the
parasite lost the power of forming a locomotor apparatus or of leaving the
corpuscle. Thus arose the adult male and female halteridia, which, in order
to continue their development, required to be taken up by a gnat, Culev
pipiens. In the stomach of the gnat the parasites formed gametes which
copulated and produced zygotes in the well-known manner. Each ookinete,
according to Schaudinn, formed a locomotor apparatus (see Fig. 30, p. 59) and
either became a trypanosome which might be of female or indifferent type,
or gave rise to several trypanosomes in the male sex. The trypanosomes
of each type multiplied in the digestive tract of the gnat to produce a swarm
of trimorphic individuals, but no further copulation of the male and female
forms occurred or could occur (Schaudinn, 132, p. 401). Ultimately, after
complicated migrations, the trypanosomes were inoculated by the gnat into
the owl again ; the male and indifferent forms passed through the proboscis,
but the female forms were too bulky to do so, and, as the male forms were
stated to die off in the blood, there was effective inoculation of indifferent
forms only, which start on the cycle of development already described.

These remarkable statements, the origin and significance of which have
been, for the last seven years, a veritable riddle of the sphinx, have met with
general scepticism except from a few devoted partisans, who have been
striving continually to find corroborative evidence for Schaudinn's theories,
in spite of the mass of evidence to the contrary that has been steadily accu-
mulating. Recently Mayer (685) has affirmed that in owl's blood containing
only halteridia, kept under observation in hanging drops under the micro-
scope, trypanosomes make their appearance which could only have come
there by transformation of halteridia. These experiments are supposed to
prove conclusively one part, at least, of Schaudinn's statements — namely,
that the halteridia are merely intracorpuscular stages of trypanosomes.

Against Schaudinn's views, on the other hand, two principal objections,
out of many, may be urged :

First, that the development of Hcemoproteus columbce, as made known by
the Sergent brothers and by Aragao, is of a totally different type to that
described by Schaudinn ; it comprises no trypanosome-phases at any point
of the life-cycle, and the invertebrate host is not a gnat, but a biting fly of an
altogether different kind. To meet this objection, Mayer proposes to restrict
the name Hcemoproteus to forms which develop after the manner of H. columbce,
and to revive the name Halteridium (in italics and with an initial capital
letter) for parasites that, on the Schaudinnian theory, are really trypanosomes.

Secondly, that the small trypanosomes of Athene noctua are connected
by every possible transitional form with the largest found in the same bird,
and there is every reason to suppose that in this case, as in other birds or
vertebrates of all classes, they are all merely forms of one polymorphic try-
panosome (Minchin and Woodcock, 42).

It may be added that the whole mystery receives a complete solution on a
simple supposition — namely, that the trypanosome of the Little Owl, like other
known species of trypanosomes (see p. 308), has intracorpuscular forms
which have been confused with the true halterida ; on such an assumption,
so eminent an investigator as Schaudinn can be acquitted of having made
what would appear at first sight to be a gross error of observation, and Mayer's
observations are easily explained. Mayer seems, in fact, to have figured

392 THE PROTOZOA

such forms on his Plate XXII., Figs. 2-4— small intracorpuscular forms, more
or less LeisJimania-\ike, without pigment, and with, apparently, distinct tro
phonucleus and kinetonucleus.

It is not necessary to deal with Schaudinn's statements concerning Leiico-
cytozoon further than has been done above (p. 370). It is now as certain as
anything can ever be in such matters that Leucocytozoon has nothing whatever
to do with either trypanosomes or spirochsetes. The six forms of bicod-
parasites of the Little Owl may be regarded as belonging to five species,
namely: A proteosoma (1), a halteridium (2), a trypanosome (3 and 4), a
leucocytozoon (5), and a spirochsete (6). Of these five, it is probable that only
the proteosoma, the trypanosome, and possibly the spirochsete, can develop
in, and be transmitted by, a gnat ; the halteridium and the leucocytozoon
require, probably, quite different intermediate hosts. If, therefore, a Culex
were fed on an owl containing in its blood halteridia and leucocytozoa abun-
dantly, and trypanosomes and spirochsetes in scanty numbers, the first two
parasites might be expected to die out after the ookinete-stage, while the
trypanosomes, and possibly the spirochsetes, would multiply, and thus produce
very easily the impression that they were derived from the intracorpuscular

Even less cogent for the theory of Hsemoflagellate affinities than the argu-
ments deduced from the development of Hsemosporidia are those based on
the development of Hsemoflagellates. Thus the schizogony of ScJiizotry-
panum discovered by Chagas has been compared to that of a malarial parasite,
and has been adduced seriously as an additional proof of the alleged affinities
between trypanosomes and hsemamcebse. But " schizogony :' — that is, repro-
duction by simple or multiple fission without concomitant sexual phenomena,
— occurs throughout the whole range of the Protozoa, and affords no proof
whatever of genetic affinities. Those who bring forward such an argument
must surely have forgotten that the word " schizogony " was originally
coined by Schaudinn for the non-sexual multiplication of TricJiospJicerium
sieboldi. a marine Rhizopod (p. 181).

2. Cytological Data. — The theory of the Haemoflagellate affinities of the
Hsemosporidia has led to the most laborious and painstaking efforts to discover
in the body of each and every Hsemosporidian parasite, in at least some of
its phases, a second nucleus, the homologue of the kinetonucleus ; and any
little granule, however minute, that can be coloured like chromatin is pro-
claimed triumphantly to be the inevitable kinetonucleus, or any streak of
similar staining properties to be a flagellum.

Consider first by itself the case of a cell in which, in addition to the nucleus,
there is seen a grain which, by some particular dye, is stained in a manner
similar, or nearly so, to the chromatin of the nucleus. This is not by itself
a decisive proof that the grain in question is chromatin, since, as pointed out
above, other grains may take up so-called " chromatin-stains " ; the body
in question may therefore be chromatin or some other substance. If it be
cliromatin, it may be a chromidial granule extruded from the nucleus ; or it
may be a body of the nature of a karyosome, situated close to the edge of the
nucleus, or possibly, in some cases, where the nucleus has no limiting mem-
brane, a little way from the main mass of the nucleus ; or it may be a true
kinetonucleus. If it be not chromatin, it may be a centrosome or blepharo-
plast ; or a grain of metachromatinic substance, such as volutin ; or, lastly, some
other kind of metaplastic body. There are therefore many possible alterna-
tives before a grain that stains like chromatin can be identified definitely as
being a kinetonucleus and nothing else.

What are the criteria by which a grain that stains like chromatin can be
identified as a kinetonucleus, to the exclusion of other possible interpretations
of its nature ? In the first place, according to modern views (see p. 288,
supra, and compare especially Rosenbusch, 505), a kinetonucleus is not a
simple granule, mass or lump of chromatin, but it is a true nucleus with
centriole, karyosome, and a nuclear cavity, actual or virtual, containing
nuclear sap at least, if not peripheral chromatin also. Secondly, a kineto-

THE H^MOSPORIDIA 393

nucleus when present is a permanent cell-element which, like the principal
nucleus, divides when the cell divides, and is propagated by fission equally
with the cell itself. Thirdly, and this is the most important criterion of all,
the kinetonucleus is in relation with a flagellum during at least some phases
of the development, though for a time the locomotor apparatus may be
temporarily absent, its existence indicated only by the kinetonucleus during
resting phases.

The smaller chromatinic body of Leishmania may be cited as an example of
a body which fulfils these conditions, and which can be identified unhesita-
tingly as a true kinetonucleus, homologous in every way with that of a try-
panosome. But with the alleged kinetonuclei of Hsemosporidia the matter
stands quite otherwise. It is not possible to discuss fully here every separate
instance, but a few typical examples of such bodies may be dealt with
briefly.

In female halteridia and leucocytozoa (Fig. 158), a large grain is seen by
the side of the nucleus, and often interpreted as a kinetonucleus. Until this
body has been shown conclusively to be related in some phase of the life-
history to a flagellum, it is far simpler to regard it as a karyosome which,
like that of the merozoites of Adelea (Fig. 153, F), is excentric, or possibly
extranuclear in position ; assuming, that is, that the body in question is a
true chromatinic nuclear element.

In the merozoites of Proteosoma, Hartmann (675) has discovered a flagellum-
like process at the anterior end, arising from a grain which he regards as a
kinetonucleus (" blepharoplast " in the German use of the term), thus con-
firming certain obiter dicta of Schaudinn (132, p. 436) with regard to the mero-
zoites and sporozoites of the tertian parasite. It may be pointed out that the
rostrum of the sporozoites of Gregarines appears to be a perfectly similar
structure, which very possibly represents a rudimentary flagellum arising
from a true blepharoplast of centrosomic nature. Hartmann's discovery is
therefore more proof of the affinities of proteosoma with other Telosporidia
than with Haemoflagellates.

The supposed kinetonuclei of piroplasms have been mentioned above ; the
entire absence (pace Hartmann) of flagellated stages throughout the life-
cycle make it impossible to accept any such interpretation of the nature of
these granules so highly inconstant in their occurrence.

Lastly it should be mentioned that Schaudinn, and recently Hartmann,
have maintained that the microgametes of halteridia and other Hsemosporidia
have the structure of a trypanosome. Inasmuch as Schaudinn also pointed
out the great structural similarity between trypanosomes and spermatozoa,
this point might not count for much, even if it were true ; unless the Metazoa
also are to be classified amongst the Binucleata, a conclusion which, indeed,
seems to follow from the nuclear theory of Hartmann and Prowazek (63).
In objects of such extreme minuteness, however, statements ascribing to them
complicated details of structure must be regarded with great scepticism until
thoroughly substantiated. It is a sufficient warning of the need of caution
to bear in mind the controversy that has raged over the question of the minute
structure of spirochaetes, with regard to which Schaudinn was obliged to
retire from the position he took up at first — namely, that their structure was
similar to that of a trypanosome.

3. Possible Transitional Forms. — The parasite of kala-azar was originally
described by Laveran under the name Piroplasma donovani,* in the belief that
it was a true piroplasm ; and many writers have been struck by the external
similarity of the two parasites, in spite of the difficulty in finding in Piroplasma
a satisfactory representative of the constant and definite kinetonucleus of
Leishmania. In fact these two genera are often cited as the connecting link
between Hsemoflagellates and Hsemosporidia, and are supposed to indicate
the course of evolution whereby serum-parasites of the first type became

* On the other hand, the parasite of Oriental Sore was first described by Wright
under the name Helcosoma tropicum, and referred to the Microsporidia.

394 THE PROTOZOA

cell- parasites of the second (compare Leger and Duboscq, 646). However
enticing such a view may seem when only the forms parasitic in the verte-
brate hosts are taken into consideration, the facts of the development in the
invertebrate hosts must dispel completely any notion of affinity between
the two types. Nothing could be imagined more different than the develop-
ment of Leishmania, with its typical leptomonad forms (Fig. 140), and that
of Piroplasma (Fig. 162), with no flagellated stages at all in its life-cycle. It
becomes evident at once that any apparent resemblance between the two
genera is due to convergent adaptation induced by a similar mode of parasitism,
and that the two forms are in reality poles apart, with no more real affinity
than porpoises and fishes, or bats and birds. It is certainly not at this
point that any transition from one group to the other is to be sought.*

In the foregoing paragraphs an attempt has been made to sum
up the arguments for and against the theory that the Hsemosporidia
are to be removed from the vicinity of the Coccidia, and classified
with the trypanosomes and allied forms in an order of the Flagellata.
When the evidence on each side is weighed in the balance, in one
scale must be placed the complete similarity of the life-cycles of
typical Coccidia and Hsemosporidia, a similarity seen in every phase
of the life-cycle, and extending even to minor developmental
details ; and in the other scale certain cell-granules of doubtful
significance. It is almost inconceivable that more importance
should be attached to cytological details, the genetic and classifi-
catory value of which is at present quite uncertain, than to the
homologies of the life-cycle as a whole, in estimating the affinities
of the orders of Protozoa ; the more so since even in the HoBmo-
flagellates themselves the possession of the binucleatc type of
structure does not, apparently, indicate a common ancestry for all
members of the group.

The conclusion reached is, then, that the Hsemosporidia as a
group, excluding doubtful forms insufficiently investigated at
present, are closely allied to the Coccidia. It is, indeed, probable
that there are two lines of evolution in the group — the one repre-
sented by the haemamcebse, halteridia, and true leucocytozoa,
descended from a Coccidium-like ancestor ; the other represented
by the haemogregarines, from an ancestral form similar to Adelea
or Orchedbius. Leger (644) has classified the hsemogregarines in
the section Adeleidea of the Coccidia, and one may regret that
the distinguished French naturalist did not go one step farther and
place the haemamcebaa in his section Eimeridea (see p. 352, supra).

On the other hand, any resemblances which the Haemosporidia
exhibit to trypanosomes and allied forms are due to convergent
adaptation on the part of the Flagellates themselves, and more
especially to the secondary acquisition by the latter of intracellular

* Leger and Duboscq (646), who derive Leishmania and Babesia directly from
Crithidia as a common ancestor, do not seem to have taken the development of
Babesia (Piroplasma) into consideration at all ; they neither refer to it in their
text nor cite any of the relevant memoirs in their bibliography.

THE H^EMOSPORIDIA 395

parasitism, and consequent temporary loss of the locomotor
apparatus. It may well be, therefore, that some forms now
generally included amongst the Haemosporidia (e.g., possibly the
drepanidia) may prove, when better known, to be stages of Hsemo-
flagellates, and to have in reality nothing to do with the true
Hsemosporidia .

Affinities of the Telosporidia. — From the foregoing discussion, the
conclusion has been drawn that the Coccidia and the typical
Hsemosporidia are closely allied, sufficiently so to be grouped
together in a single order, for which the name " Coccidiomorpha "
may be used. In a former chapter (p. 354) the relationship of the
Gregarines and Coccidia was discussed, and it was pointed out
that there was no difficulty in assuming a common ancestral origin
for the two groups — a conclusion which, indeed, has never been
called in question. The Telosporidia, taken as a whole, may be
regarded, therefore, as a homogeneous and natural group, in which
the close affinity existing between its constituent members mayfcbe
regarded as indicating a common phylogenetic origin. If this
conclusion be accepted, it remains to discuss the affinities of the
Telosporidia as a whole to other groups of Protozoa. It is not
unreasonable to suppose that a parasitic group of this kind has been
evolved from free-living, non-parasitic ancestors, and the question
to be discussed is to which of the groups of Protozoa the ancestral
form of the Telosporidia belonged. Of the three great classes of
the Protozoa, the Infusoria may almost certainly be excluded
from consideration in regard to this question, since, in view of the
very specialized and definite features of this group, there are no
grounds whatever for connecting them with the Telosporidia.
There remain, therefore, only the Sarcodina and Mastigophora to
be considered.

At different times two opposed theories have been put forward
with regard to the affinities and ancestry of the Sporozoa. One
view sees in them the descendants of typical forms of Sarcodina,
such as Amoeba (Awerinzew, 890) ; the other derives them from
flagellate ancestors such as are represented at the present day by
Euglena or Astasia. It is no longer possible, however, to regard the
Sporozoa as a whole as a homogeneous group, and the two so-called
" subclasses," Telosporidia and Neosporidia, must be considered
separately, each on its own merits. The Neosporidia are considered
at the end of the next chapter. The question here is of the Telo-
sporidia alone. For this group opinion is practically unanimous at
the present day in favour of a flagellate ancestry, a theory which
must be considered critically.

One of the main arguments generally put forward for the theory
of the flagellate origin of the Telosporidia is the existence of flagel-

396 THE PROTOZOA

lated stages in the life-history. In the first place, the micro-
gametes are very often flagellated, as has been stated frequently
in the two foregoing chapters. In the second place, the youngest
stages in the development — the merozoites or sporozoites — exhibit
structural features which are either those of a flagellate swarm-
spore (Hartmann, 675 ; Schaudinn, 132), or can readily be derived
from a flagellula in which the flagellar apparatus has become rudi-
mentary, as in the sporozoites of gregarines, where the rostrum may
be interpreted, with a high degree of probability, as representing
a rudimentary flagellum. The existence of flagellated stages of
the kinds mentioned in the development of the Telosporidia is by
no means, however, a cogent argument for a flagellate ancestry for
the group, since quite typical Sarcodina of all orders exhibit flagel-
late swarm-spores and gametes. It may be urged that in the case
of these types of Sarcodina, also, the existence of flagellate stages
indicates a flagellate ancestry ; but such an argument merely
evades the question at issue, which is not whether the Telosporidia
are derived from Flagellata indirectly through Sarcodine ancestors,
but whether or not they are descended directly from ancestors
that were typical Flagellata. The existence of flagellated swarm -
spores and of gametes representing a modification of such swarm-
spores is not sufficient of itself to prove a flagellate ancestry for the
Telosporidia.

Far more cogent arguments for the flagellate affinities of the
Telosporidia maybe drawn from the characters of the adult forms,
especially from the gregarine-type of body, elongated and ver-
micular in character, and perfectly definite and constant in form,
which occurs in every group of the Telosporidia at one point or
another in the life-history. Such a type of body can be readily
derived, as Butschli (2) pointed out, from an organism similar to
Astasia or Euglena, in which the flagellar apparatus has been lost,
and all special organs of nutrition, whether holozoic or holophytic,
have disappeared in relation with the parasitic mode of life. On
the other hand, the gregarine-type of body cannot be derived from
the adult forms of the Sarcodina, which are typically amoeboid,
and without any definite body-form other than that imposed by
the physical nature of their body-substance.

We may therefore consider the ancestral form of the Telosporidia
to have been a flagellate organism with an elongated form of body,
with a definite form, owing to the presence of a cuticle of a certain
degree of thickness and toughness, and with a flagellar apparatus
at the anterior end. Such a form would have been not unlike the
leptomonads now found commonly as parasites of insect-guts ;
but there is no reason to suppose the ancestral form to have had
a kinetonucleus and the third type of flagellar insertion. Such a

THE ILEMOSPOKIDIA 397

form probably used its flagellum for the purpose of attaching itself
to the epithelium of the digestive tract, as leptomonads do now
(compare Figs. 136, 137) ; and from this primitive type of attach-
ment the epimerite of the gregarines may have been derived by
secretion of chitin round the attaching flagellum, just as the
primitive tuft of fixing cilia, the " scopula" of the primitive
Vorticellids appears to become converted into the chitinous stalks
of such forms as Epistylis (p. 441).

The conclusion drawn from these various considerations is,
therefore, that the Telosporidia may be regarded as a group de-
scended from flagellate ancestors modified in adaptation to a para-
sitic mode of life ; not, however, specially from flagellates of the
" binucleate " type of structure.

Bibliography. — For references see p. 496.

CHAPTER XVI
THE SPOROZOA : III. THE NEOSPORIDIA

A TYPICAL member of the subclass Neosporidia is a parasite of
which the life-cycle is initiated by the liberation from the spore
of one or more amcebulse within the body of the host, in the digestive
tract in all known cases. For this initial amcebula-phase Stempell's
term, planont (i.e., " wanderer "), may be employed conveniently,
since in no case does it remain in the lumen of the digestive tract,
but penetrates into the wall of the gut, and in most cases migrates
thence into some organ or tissue of the host, where it lives and
multiplies actively, being usually at this stage an intracellular
parasite, in some cases, however, occurring free in the blood or
lymph.

The planont-phase is succeeded typically by a plasmodial phase,
which arises in some cases by simple growth of the amcebula
(probably then a zygote), accompanied by multiplication of its
nuclei ; in other cases by association together and cytoplasmic
fusion of at least two distinct amcebulse, of which the nuclei remain
separate. The plasmodial stage is very characteristic of this sub-
class ; it represents the principal or " adult " trophic phase of the
parasite, and is also the spore-forming phase ; and, as the name
Neosporidia implies, the production of spores begins, as a rule,
when the plasmodium is still young, and continues during its
growth.

In some cases, however, no plasmodium is formed, but the
planont-phase is succeeded by uninucleate " meronts " or schizonts,
which multiply by fission and give rise ultimately to sporonts in
which spore-formation sets a limit to the growth. In such forms
the general course of the life-cycle is not essentially different in
any way from that of a member of the Telosporidia, such as Coc-
cidium. The tendency, therefore, of many Neosporidia to form
spores during the trophic phase cannot be used to frame a rigorously-
exact definition of the group. A more distinctive characteristic
of the subclass is the complete absence of flagellated phases in
any part of the life-cycle, and more especially the fact that

398

THE NEOSPORIDIA

399

the sporozoites are always, apparently, amcebulse, and never
gregarinulse.*

The Neosporidia are divisible into two sections, known re-
spectively as the Cnidosporidia and the Haplosporidia. The
Cnidosporidia are distinguished by the possession in the spore of
peculiar structures termed polar capsules, which are lacking in the
Haplosporidia.

A polar capsule (Fig. 163) is a hollow, pear-shaped body, with a
tough envelope, probably chitinoid in nature. It is situated at one
pole of the spore, with its pointed end immediately below the
surface, in continuity with a minute pore in
the sporocyst. Coiled up within the capsule
is a delicate filament, often of great length,
probably of the same nature as the capsule,
and continuous with it. Under suitable stimu-
lation the polar filament is shot out through
the pore in the sporocyst. In their structure
the polar capsules resemble the nematocysts
of the Ccelentera. Each polar capsule is
formed within a capulogenous cell.

The Cnidosporidia comprise four orders —
the Myxosporidia, Actinomyxidia, Micro-
sporidia, and Sarcosporidia. The Haplo-
sporidia constitute an order apart.

Order /. : Myxosporidia. — This order is
characterized chiefly by the following points :
The principal trophic phase is a multinucleate
plasmodium of relatively large size, resembling
an amoeba in its appearance and movements.
The spores are also relatively large, and
exhibit typically a binary symmetry, having
a sporocyst composed of two valves and
usually two polar capsules, sometimes increased
in number to four, rarely reduced to one.

The Myxosporidia comprise a great number of genera and species,
parasitic for the most part in cold-blooded vertebrates, especially
fishes, in which they are found very commonly. They are not as
yet known as parasites of birds or mammals, but a few species are
known from invertebrate hosts.

Myxosporidia are typically tissue-parasites, occurring hi various
tissues of the body, by preference muscular or connective, but also

* A possible exception to this statement is furnished by the family Codospor-
idiidce of the Haplosporidia (p. 424). But the position of all the forms in this order
is more or less questionable, and their attachment to the typical Neosporidia is
still probationary.

FIG. 163. — Polar cap-
sules of the spores
of Myxosporidia. a,
Polar capsule with
the filament coiled
within it ; 6, with the
filament partly ex-
truded ; c, d, with the
filament completely
extruded. After
Balbiani.

400

THE PROTOZOA

other classes of tissue. A few species are known to attack the
nervous system — for instance, Lentospora (Myxobolus) cerebralis ,
cause of " Drehkrankheit " in Salmonidce (Plehn), and Myxobolus
neurobius of trout (Schuberg and Schroder). In the tissue attacked
the parasite may be concentrated at one spot, so as to form a dis-
tinct cyst visible to the naked eye ; or parasite and tissue may be
mixed up together in a state of " diffuse infiltration " such that
microscopic examination is required to detect the parasite, and as
its body becomes used up, to form spores, the tissue becomes in-
filtrated with vast numbers of spores lying singly or in groups
between the cells.

In many species of Myxosporidia, on the other hand, the spore-
forming plasmodial phase is found in
cavities of the body — not in any
known instance in the lumen of the
digestive tract, but frequently in the
gall-bladder or urinary bladder of the
host. In such cases the parasite
may lie quite freely in the cavity it
inhabits, or may be attached by
its pseudopodia to the lining epi-
thelium ; in the latter case the
attachment is purely mechanical,
and does not involve injury to the
epithelial cells.

As might be expected, the Myxo-
sporidia parasitic in tissues are
often very deadly to their hosts,
and are sometimes the cause of
severe epidemics among fishes.
Those species, on the other hand,
which inhabit cavities with natural
means of exit from the body appear to be as harmless to their
hosts as are the majority of parasitic Protozoa in nature.

The adult trophic phase is usually a large amoeba-like organism
with a distinct ectoplasm and endoplasm. In some species the
ectoplasm, which appears to be purely protective in function, ex-
hibits vertical striations, or is covered by a fur of short, bristle-like
processes, the nature and significance of which are uncertain — as,
for example, Myxidium lieberkuhni, the common parasite of the
urinary bladder of the pike (Esox lucius). The form of the body
changes constantly, with extrusion of pseudopodia, which are
used for locomotion to a limited extent, more often for fixation,
but never for food-capture. They may, however, by increasing
the body-surface, increase also the power of absorption of food-

FIG. 164. — Chloromyxum leydigi,
parasite of the gall-bladder of the
dogfish, skate, etc. ; trophozoite
(plasmodium) in an active state.
ect., Ectoplasm ; end., endoplasm ;
y., yellow globules in the endo-
plasm ; sp., spores, each with four
polar capsules. After Thelohan,
from Minchin, magnified 525.

THE NEOSPOBIDIA

401

B

stuffs by diffusion, the method by which the organism, like other
sporozoan parasites, obtains the required nourishment. The pseu-
dopodia vary in form in different species, from coarsely lobose
and blunt to fine filaments ending in sharp points. In some species
the formation of pseudopodia is localized at one pole of the body,
termed " anterior," and in such cases a peculiar propulsive pseudo-
podium (" Stemm-pseudopodium ") may be developed at the
posterior pole like a tail, which
by its elongation pushes the body
forward.*

The endoplasm is distinguished
from the ectoplasm by its coarsely
granular appearance. In addition
to numerous nuclei and stages of
spore-formation, the endoplasm
may contain various metaplastic
products, such as crystals, pig-
ment-grains, fat-globules, etc. ;
but never food-vacuoles or solid
ingested food-particles.

The plasmodial trophozoite
forms spores in its endoplasm,
as a rule, during the whole period
of growth, but may also multiply
by plasmotomy. In Myxidium
Ueberkiihm, for example, plas-
motomy proceeds actively during
the summer months, and leads
to the wall of the pike's bladder
being carpeted with the slimy,
orange - coloured plasmodia, the
presence of which can generally
be detected at a glance ; spore-
formation, on the other hand,
takes place almost exclusively during the colder months of the year.

Spore-formation in the Myxosporidia is a somewhat complicated
process, and is accompanied by sexual phenomena, which are
commonly stated to be autogamous, but which are probably
nothing of the sort. There is a slight difference between the
mode of spore-formation in the Disporea, in which each
trophozoite produces but two spores, and the Polysporea, which
produce many.

* Auerbach (758, p. 11) seems to have mistaken altogether the significance of
Doflein's " Stemm-pseudopodium," and applies the term to the anterior pseudo-
podia, which appear to be rather tactile in function in such cases.

FIG. 165. — Leptotheca agttis: young
plasmodial trophozoites in which
the spore-formation has not begun.
A, Individual moving forward by
means of the " Stemm-pseudopo-
dium " (st. ps.) ; B, individual in
which only the anterior pseudopodia
are developed. After Doflein.

402

THE PROTOZOA

errv

FIG 166. — For description see foot of opposite page.

THE NEOSPORIDIA 403

An example of the Disporea is Ceratomyxa drepanopsettce, of which the
spore-formation is described by Awerinzew (759). The trophozoite has at
first only two nuclei, which are considered by Awerinzew to be derived,
" beyond all doubt," from division of a single nucleus ; it seems far more
probable, on the contrary, that the binucleate trophozoite is to be derived
from the association and fusion of two distinct planonts. In the binu-
cleate trophozoite each nucleus divides by karyokinesis into two nuclei,
a larger and a smaller (Fig. 166, A). The two smaller nuclei are vegetative,
the two larger generative, in function. Round each of the two generative
nuclei the protoplasm becomes concentrated so as to form two cells which
lie embedded in the endoplasm of the trophozoite. These two cells are usually
of distinctly different sizes, and represent a microgametocyte and a macro-
gametocyte respectively. Each gametocyte next divides into two gametes
(Fig. 166, B, C, D), and in each gamete a certain amount of chromatin is
extruded from the nucleus, first into the cytoplasm of the gamete, and then
into the endoplasm of the mother-trophozoite. Then each microgamete
copulates with one of the two macrogametes (Fig. 166, E, F). The two
zygotes thus formed represent the sporoblasts, each of which forms a spore
independently of the other.

Each sporoblast divides into two cells, a larger and a smaller (Fig. 166, G),
and the smaller divides again into two (Fig. 166, H) ; the result is an aggregate
of three cells : a larger, which gives rise ultimately to the two parietal cells
which form the valves of the sporocyst, and may be termed the " sporocyst-
mother-cell " ; and two smaller cells, one of which is the mother- cell of the
two capsulogenous cells, the other the future sporozoite or amcebula. The
sporocyst-mother-cell may become temporarily separate from the capsule-
mother-cell and the amcebula.

The three cells of the previous stage build up the spore in the following
manner : The sporozoite grows in size, and its nucleus divides into two. The
capsule -mother- cell divides into two capsulogenous cells, each of which
forms a polar capsule in its interior. The amcebula and the two capsulogenous
cells are placed close together and arranged in a definite manner (Fig. 166, /).
The sporocyst-mother-cell divides into two parietal cells (Fig. 166, J), which
place themselves on either side of the cell-complex composed of the associated
amcebula and capsulogenous cells (Fig. 166, K), and each secretes one valve
of the sporocyst enveloping the whole complex.

Thus the trophozoite consists finally of an amoeboid body containing two

FIG. 166. — Spore-formation in Ceratomyxa drepanopsettce. A, Trophozoite sketched
in outline, showing in the plasmodium two generative nuclei (g.), each sur-
rounded by a cell-body, and two vegetative nuclei (v.), which lie in the pro-
toplasm of the body (left blank) ; note that the generative cells are of different
sizes ; B, C, the two generative cells have divided each into two, so that
there are now two macrogametes ( ? ) and two microgametes ( c? ) ; chromatin
is being given off from the nuclei of the gametes into the cytoplasm ; D, each
microgamete is apposed to a macro-gamete ; the chromatin-bodies given off
by the gamete-nuclei are now extruded into the plasmodial body ; E, Ft
stages in the synganiy between the gametes ; in E the cell-bodies are fused,
in F the zygotes (z.) are complete ; G, each zygote (sporoblast) has divided
into a larger (p) and a smaller cell ; H, the smaller cell in each sporoblast
has divided into two, the capsule-mother-cell (c.m.) and the sporozoite (am) ;
the larger cell (p.) is the mother-cell of the parietal cells ; /, a single sporoblast
showing the parietal mother-cell (p.) still undivided, the sporozoite (am)
with its nucleus divided into two, and two capsulogenous cells (e.g.) derived
from division of c.m. in H ; J, a trophozoite showing the two parietal mother-
cells of H each divided into two parietal cells (p/) but still separate from the
cell-complex consisting of the binucleate sporozoite (am) and the two capsu-
logenous cells (e.g.) ; K, union of all the cell-elements of the spore ; the two
parietal cells (p/) surround the cell-complex (drawn on a smaller scale than
the last figure) ; L, spore nearly fully formed : n.p., nucleus of a parietal
cell ; am, sporozoite with two nuclei (n.g.) ; p.c., polar capsules. After
Awerinzew (759).

404

THE PROTOZOA

FIG. 167. — Spore-formation in Sphceromyxa sabrazesi. A, Propagative cell with
two nuclei of different sizes ; B, two such propagative cells undergoing fusion
to form C, a pansporoblast with four nuclei, two smaller, peripheral, the
nuclei of the two envelope-cells, and two larger, central, the nuclei of the
spore-forming elements ; D, pansporoblast with fourteen nuclei, eight peri-
pheral, six central ; two of the latter, smaller than the others, represent reduc-

[Continued at foot of p. 405.

THE NEOSPORLDIA 405

vegetative nuclei and two spores. Each spore (Fig. 166, L) consists of (1) a
sporocyst composed of two valves, each secreted by a parietal cell ; (2) two
polar capsules, each secreted by a capsulogenous cell ; (3) a binucleate amcebula,
the sporozoite or sporoplasm. When the spore is fully formed, the cells which
form the valves and polar capsules are used up and degenerate, remnants
only of their nuclei being visible. The spores represent the propagative
phase, and the trophozoite with its vegetative nuclei degenerates.

The Myxosporidia Polysporea differ from the Disporea in that the plasmo-
dium contains a great number of nuclei, some of which are purely vegetative
in function, others generative ; and the plasmodium produces in its interior
numerous spores, which are always formed in couples. This peculiarity is
due to the fa~t that the two sporoblasts arise from a cell- complex which is
termed a "pansporo blast," producing two sporoblasts and two spores.

Spore -formation in Polysporea has been studied in Sphceromyxa sabrazesi
(not labrazesi), from the gall-bladder of Hippocampus, by Schroder (767 and 768),
and in Myxobolus pfeifferi, a deadly tissue-parasite of the barbel, by Keysselitz.
Their results are almost identical in each case, except for minor details, and
are in the main as follows (Fige. 167, 168).

The generative nuclei of the plasmodium become the centres of a condensed
patch of protoplasm (Fig. 168, A], forming a " propagative cell " (Keysselitz).
These cells may multiply with mitosis of the nuclei for a while, but finally
proceed to spore-formation. The nucleus of a propagative cell divides into
two, a larger and a smaller, and division of the cell follows sooner or later
(Fig. 167, A ; Fig. 168, B, C). Two such couples of cells become associated, and
the two smaller cells form an envelope surrounding the two larger cells, which
by their association form the pansporoblast (Fig. 167, B, C ; Fig. 168, D). Hence
the pansporoblast is from the first a complex of two distinct cells, and not,
as was formerly supposed, a single cell. The two cells of the pansporoblast
may be termed gamonts, since they give rise ultimately to gametes, but not
to gametes alone, like the gametocytes of Ceratomyxa. The cytoplasm of
the two gamonts may fuse into one mass, but the nuclei remain separate and
undergo repeated divisions, until the pansporoblast within its envelope
contains twelve nuclei, and may consist of as many separate cells (Fig. 167, D ;
Fig. 168, E). The nuclei or cells then become arranged in a definite manner ;
eight of them take up a peripheral position, four of them place themselves
more centrally (Fig. 167, E). The four central cells are the gametes ; their
nuclei undergo reducing divisions, and the four cells then pair off into two
couples ; in each couple the cytoplasmic bodies of the two cells fuse together,
but their nuclei remain distinct. It is probable that in each couple one
nucleus is descended from that of one of the two original propagative cells, the
other nucleus from that of the other.

At this stage the pansporoblast divides into two masses, the sporoblasts

FIG. 167 continued:

tion-nuclei beginning to degenerate ; the envelope-nuclei are not represented ;
E, the pansporoblast beginning to divide into two sporoblasts ; within the
envelope are seen also some small bodies of doubtful nature ; F, the two
sporoblasts completely separated, between them two residual nuclei ; each
sporoblast has six nuclei, four peripheral, two central ; at the two extremities
of the sporoblast the polar capsules are beginning to be formed ; 0, one of
the two sporoblasts at a later stage, showing two parietal cells, situated
superficially ; two nuclei of the capsulogenous cells, each near a polar capsule ;
the two germinal nuclei close together at the centre ; and a residual nucleus
attached to the surface ; H, I, further stages in the development of the
sporoblast ; J, pansporoblast with two spores almost fully formed, and the
two residual nuclei ; each spore has a polar capsule (p.c.) at each end, and near it
a nucleus of the capsulogenous cell (n.c.) ; two large parietal nuclei (n.p.), in
process of degeneration ; and two germinal nuclei (n.g.) ; K, L, M, fully-
formed spores ; in K and M the two germinal nuclei are still separate, in
L they have undergone fusion ; in M the two polar filaments are extruded.
After Schroder (767 and 768).

406

THE PROTOZOA

each containing six nuclei — namely, four peripheral and two central
(Fig. 167, F ; Fig. 168, F). The reduction-nuclei are left out in the cold,
and die off. From each sporoblast a spore is formed in the following way
(Fig. 167, G — J ; Fig. 168, G) : Of the four peripheral cells, two are parietal cells
which give rise to the two valves of the sporocyst, the other two as capsu-
logenous cells produce the two polar capsules ; the two central nuclei with the
mass of protoplasm in which they lie become the amo3bula or sporozoite of
the spore. The sporozoite is thus at first binucleate, but when the spore
is fully formed its two nuclei fuse into one. There can be no doubt that this
fusion represents a karyogamy, and that the single nucleus is a synkaryon.
The cells which form the valves of the sporocyst and polar capsules degenerate
when the spore is completely formed.

H

FIG. 168. — Spore-formation in Myxobolus pfeifferi. A, Propagative cell from the
plasmodium ; B, division of the propagative cell into two unequal halves ;
C, the smaller cell of the preceding stage applies itself as a flattened envelopc-
cell to the larger ; D, a mass formed by union of two couples of cells similar
to those of the preceding stage — the pansporoblast ; E, pansporoblast with
fourteen nuclei, two representing the envelope -cells, and twelve arisen by
division of the two larger cells of the preceding stage ; F, the pansporoblast
divided into the two envelope-cells and two masses, sporoblasts, each con-
taining six nuclei, which are arranging themselves so that two nuclei are
more central, four more peripheral in position ; G, spore in process of forma-
tion ; the sporocyst is formed by two parietal cells (p. ) ; at the upper pole arc
the two polar capsules (p-c.) in their capsulogenous cells ; and the lower part
of the spore is occupied by the binucleate amoebula (am.) ; H, ripe spore ;
in the amoebula the two nuclei have fused into one ; lettering as in the last.
After Keysselitz.

Mercier (765*5), on the other hand, who has also studied the spore -formation
of Myxobolus pfeifferi, differs from Keysselitz in his account, more especially
with regard to the sexual processes. He affirms that the plasmodium contains
four zones: (1) A peripheral zone, without nuclei or spores; (2) a zone of
nuclei, all similar amongst themselves, which multiply by mitosis ; (3) a zone
containing nuclei of different sizes and early stages of spore -formation ; and
(4) a central region containing ripe spores. In the third zone differentiation
of microgametes and macrogametes takes place. The gametes copulate, and
the zygote is a pansporoblast. Its nucleus (synkaryon) divides to form
fourteen nuclei, two of which are rejected, while from the remaining twelve
arise two sporoblasts, each with six nuclei, and finally two spores.

THE NEOSPORIDIA 407

According to Awerinzew (760), in Myxidium sp. a propagative cell may
give rise sometimes to a single spore, as in Ceratomyxa, in other cases to three
spores ; this must doubtless be interpreted to mean that a propagative
cell may become a sporoblast without entering into association with another
propagative cell, and that in other cases three propagative cells may form
an association ; these variations present an analogy with the solitary encyst-
ment or triple associations of gregarines (p. 331).

The process of syngamy in these parasites has been described as being a
process of autogamy, but whether it is so or not depends entirely upon the
manner in which the plasmodium arises ; if a single, uninucleate amcsbula
becomes a plasmodium by growth accompanied by nuclear multiplication,
then the sexual process is a case of autogamy ; but if, as is more likely, two
or more distinct amcebulse become associated to form a plasmodium, then
the two nuclei of the gametocytes in Disporea, of the " pansporoblast " of
Polysporea, may well be of distinct parentage, and in that case the sexual
process is not autogamous.

Comparing the different modes of spore-formation, it is seen that
in all cases alike the spore arises from a sporoblast which divides
into several cells : two to form the sporocyst, which consists of two
distinct valves meeting in a suture, and thus denning a sutural
plane in the spore ; two (or four in Chloromyxidce) to form the
polar capsules ; and a fifth to furnish the binucleate sporozoite.
The spores of Myxosporidia have, as has been seen, a complex
structure, and are highly characteristic bodies — the original psoro-
sperms of Johannes Miiller. In minor details of form and structure
they vary enormously in different species. The greatest diameter
of the spore may lie in the sutural plane, as in Polysporea generally,
or in a plane at right angles to it, as in Disporea (Fig. 169). The
sporocyst may be prolonged into tails and processes of various
kinds ; the polar capsules may be close together at one pole of the
spore, or at opposite poles. In all cases, so far as is known, the
spores germinate in the intestine of the new host, which becomes
infected casually by taking in the spores with its food. Other
methods of infection have been imagined, but have never been
demonstrated experimentally.

The most complete account of the germination of the spore and of the early
development of the parasite in its new host is that given by Auerbach (758)
for Myxidium bergense, parasite of the gall-bladder of Oadus virens. The
spores from the gall-bladder pass through the rectum to the exterior. To
develop further, they must be taken up by the new host, in the stomach of
which, however, the spores undergo very little change ; the sporozoite rounds
itself off, and in some cases its nuclei copulate, in others they remain apart.
From the stomach the spores pass into the duodenum, and as soon as they
are acted upon by the bile the polar filaments are extruded, the valves of the
sporocyst split apart, and the amoeboid sporozoite creeps out. When the
amcebula becomes free, its two nuclei fuse into one if they have not done so
already.

The free amcebula wanders actively up the bile-duct, and penetrates into a
cell of the lining epithelium. Within the cell the nucleus of the parasite
undergoes a change, becoming looser in texture. The amcebula leaves the
cell and becomes free in the bile again, where it multiplies by fission, producing
in this way very numerous amcebulae, which may occur singly or in clumps.

408 THE PROTOZOA

The amcebulse next associate in couples. In each couple the cytoplasm of
the associates undergoes partial fusion. In one associate the loosely-textured
nucleus remains unaltered ; in the other the nucleus divides by mitosis, and
one of the two daughter-nuclei, with a small quantity of the cytoplasm, is
cast off. The bodies of the two associates now fuse completely into a single
mass containing two nuclei, a large and a small. The larger nucleus represents
the unaltered nucleus of one of the two original associates ; the smaller
nucleus is the reduced nucleus of the other associate.

The binucleate stage formed by the association of two amcebulse (planonts)
is the foundation of the plasmodium. The two nuclei remain separate and
multiply independently, maintaining their difference in size. Hence the
young plasmodia consist of nuclei of two sizes, small and large ; and this
difference in size, which has often been noted in the plasmodia of other
species, is due, according to Auerbach, to the fact that the smaller nuclei are
derived from a nucleus which has undergone reduction, while the larger nuclei
are derived from one which has not done so.

So far as it is possible to generalize from the few recorded observa-
tions and experiments, the germination of the Myxosporidian spore
probably takes place always in the digestive tract of the new host.
The first act in the process is the rounding off of the amoeboid
sporozoite ; next the polar capsules are discharged, the function of
these organs being, apparently, that of fixing the spore to the wall
of the gut. Then the two valves of the sporocyst separate, and
the amoebula creeps out ; its two nuclei copulate to form the syn-
karyon, if they have not done so already. In this way the planont-
phase arises from the sporozoite, and is set free in the digestive
tract, whence it migrates to the organ or tissue of which it is a
specific parasite. When its destination is an organ which, like the
gall-bladder, is in open communication with the gut, the migration
may be comparatively simple and direct ; but in the majority of
cases the journey to be accomplished is a complicated one. It is
probably safe to assume that in most cases the planont passes
through the wall of the gut into the channels of the blood or lymph,
and by this route arrives ultimately at its destination. In the
organ or tissue which the parasite attacks, the planont probably
passes through a period of cell-parasitism and proliferation by
binary fission ; ultimately the plasmodial phase is initiated by
association of two planonts, of which the bodies fuse, but the nuclei
remain separate. Growth of the body with independent multipli-
cation of its nuclei to four (Disporea) or many (Polysporea) produces
the spore-forming plasmodium characteristic of the order.

The Myxosporidia are classified as follows :

SUBORDER I. : DISPOREA. — Only two spores formed in the plasmodium.
The greatest diameter of the spore is at right angles to the sutural plane
(Fig. 169).

One family, Ceratomyxidce, with two genera : Ceratomyxa, with several
species parasitic in the gall-bladders of fishes; Leptotheca (Fig. 165), in-
cluding several species from gall-bladders of fishes, but L. ranarum occurs
in the kidneys of frogs (Eana spp.).

THE NEOSPOE1DIA 409

SUBORDER II. : POLYSPOREA. — Numerous spores formed in the plasmodium.
The greatest diameter of the spore lies in the sutural plane.

Three families : (1) Myxobolidce, with two polar capsules (sometimes reduced
to one), and with a peculiar vacuole, which stains with iodine, in the amcebula.
Typically tissue-parasites of fishes ; principal genera Myxobolus, with round
or oval spores, and Henneguya, with tail-like processes to the spore.

(2) Myxidiidce ; spores with two polar capsules, no iodinophilous vacuole ;
typically "free" (i.e., ccelozoic) parasites. Principal genus Myxidium,
with the polar capsules at opposite poles of the spore ; M . lieberkuhni, the
common parasite of the pike.

(3) CMoromyxidce, with four polar capsules ; the best known species is
CJdoromyxum leydigi (Fig. 164), from the gall-bladder of various Elasmobranch
fishes.

To the typical Myxosporidia enumerated in the above summary must be
added two genera recently described :

Coccomyxa morovi (Leger and Hesse, 765), from the gall-bladder of the
sardine ; the plasmodium has only two nuclei, a large and a small, and forms
a single spore with two valves and two parietal cells, one polar capsule, and
an amcebula with two nuclei. This form seems to be transitional between
Myxosporidia and Microsporidia, and should perhaps form the type of a third
suborder, the Monosporea.

Paramyxa paradoxa (Chatton, 761), a parasite of the intestine of a pelagic
Annelid larva ; the multiplicative amcebula stage is succeeded by a plasmodial

FIG. 169. — Spore of Ceratomyxa sphcerulosa. p.c., Polar capsules ; sp.p., sporo-
plasm ; s., suture of the sporocyst ; x, " irregular, pale masses of undetermined
origin." After Thelohan, magnified 750.

stage with two nuclei of unequal size, which multiply by fission. Finally
the plasmodium produces four spores, each with a single parietal cell and no
polar capsule. Chatton is of opinion that this species is the type of a new
order of Cnidosporidia, to be named Paramyxidia.

Order II. : Actinomyxidia. — The members of this group are
only known, up to the present, as parasites of oligochsete worms,
fresh-water or marine. They were discovered originally by Stole,
who found, in the intestinal epithelium of different species of Tubi-
ficidce, the spores of three genera of these parasites, named by him
Synactinomyxon, Hexactinomyxon, and Triactinomyxon, respectively.
The nature and affinities of these organisms remained for some time
doubtful ; but the investigations of Caullery and Mesnil (769) on
Sphceractinomyxon stolci, a species found by them in the coelome of
several species of Tubificidce, established indisputably the position
of these parasites amongst the Cnidosporidia. Their distinctive
features are — first, that the plasmodial stage is represented only by
a binucleate amcebula, which is the spore-forming phase ; secondly,
that the spore is of very large size and exhibits a ternary symmetry,
with three valves and three polar capsules.

410

THE PROTOZOA

The development of Sphceractinomyxon (Fig. 170) begins with a uninucleate
amcebula (Fig. 170, A), which represents the planont phase, and doubtless
multiplies by fission, since these parasites, though rare generally, occur abun-

FIG. 170. — Stages in the development of Sphceractinomyxon stolci. A, Amcebula
with a single nucleus ; B, binucleate amoebula ; 0, the two nuclei of the
preceding stage have each divided, and the body is divided into four cells,
two peripheral envelope- cells and two central germinal cells ; D, the space
enclosed by the envelope- cells has become greatly enlarged, and the two
germinal cells have divided into four ; E, the germinal cells have increased in
number by repeated division into sixteen, which as gametes are copulating
in eight pairs ; F, G, two stages in the fusion of two gametes ; H, the zygote
has divided into two cells ; in one of these (on the left), which will form the
germinal mass of the spore, the nucleus is at this stage undivided ; in the
other (on the right), which will form the accessory structures of the spore, the
nucleus has divided to form six nuclei ; /, further stage of the preceding ;
in the germinal cell (on the left) the nucleus has divided into several nuclei
of unequal sizes ; the sporal tissue (on the right) is represented by six cells,
three peripheral, the parietal cells, and three central, the capsulogenous cells ;
J, ripe spore, enclosed by a sporocyst composed of three valves meeting in
sutures ; the germinal mass (g.), separate in the preceding stage, has migrated
into the interior of the spore, and contains an immense number of nuclei ;
at the upper pole of the spore are seen the three polar capsules (p.c.). After
Caullery and Mesnil (769).

dantly in the infected animals. The planont phase is succeeded by a binu-
cleate stage (Fig. 170, B), the origin of which is uncertain, but which most
probably arises from an association and plastogamic fusion of two planonts,
and which represents the spore-forming phase.

THE NEOSPORIDIA 411

The binucleate amcebula is succeeded by a stage with four cells (Fig. 170, C),
the result of the division of each nucleus, with subsequent division of the
cytoplasm of the amrebula. Two of the cells take up a superficial position
and form an envelope for the other two, which are the gametocytes. The
two enveloping cells do not develop further, but the two internal cells proceed
to multiply by repeated division to form sixteen gametes (Fig. 170, D, E), eight
derived from each of the gametocytes. The gametes now copulate in pairs,
those of each couple being slightly different from one another, chiefly an
regards the size of their nuclei. It is very probable that in each couple one
gamete is descended from one of the two original gametocytes, the other
from the other (Fig. 170, F, G). In this way eight zygotes are formed, each
of which represents a sporoblast and proceeds to form a spore.

Each sporoblast now divides into two cells, which may be distinguished
as Cell A and Cell B respectively. Cell A is the mother- cell of all the accessory
elements of the spore — namely, parietal cells and capsulogenous cells. Cell B
is the mot her- cell of the germinal elements. The development of these two
sets of elements proceeds at first quite independently. Cell A divides into
six cells (Fig. 170, H, I, right), three parietal cells which secrete the three
valves of the sporocyst, and three capsulogenous cells which produce the
three polar capsules. Cell B is at first a cell with a single large nucleus, which
now begins to divide, and when it does so Cell B separates from the six cells
derived from Cell A (Fig. 170, H, I, left). As a result of the nuclear division
in Cell B, it becomes a large multi nucleate plasmodium, the germinal mass,
containing larger central nuclei, and smaller towards the periphery. The
larger nuclei are perhaps trophic in function, the smaller germinal.

As a result of these changes, the body now consists of two envelope-cells,
destined to degenerate, containing sixteen cell-masses ; eight, consisting each
of the six spore -forming cells, which take up a more central position, and
eight multinucleate germinal masses, which lie at the periphery of the body.
Each central mass forms the sporocyst and polar capsules of the spore, and
when these parts are completely formed the germinal masses migrate bodily
into the spores, each germinal mass occupying the cavity of one of the spores
(Fig. 170, J). Within the spore the germinal mass remains for a time in the
condition of a multinucleate plasmodium, but divides ultimaely into a vast
number of uninucleate sporozoites. The spore germinates, doubtless, in the
digestive tract of a new host, setting free a swarm of amoebulse which as
planonts pass through the intestinal epithelium and initiate a fresh develop-
mental cycle.

The spore-formation in Actinomyxidia is seen to agree in all
essential details with that of the Myxosporidia, and inasmuch as
each zygote becomes a sporoblast, and gives rise to an entire spore,
with all its accessories, the process is similar to that of the Disporea.
The chief points in which the Actinomyxidia differ from the Myxo-
sporidia are the absence of the large trophic plasmodial stage, the
ternary symmetry of the spore, and the enormous number of sporo-
zoites contained in the relatively huge spore.

Order III. : Microsporidia. — The characteristic feature of this
order is furnished by the spores, which are minute oval refringent
bodies in which no polar capsule is visible in the fresh condition ;
but when treated with reagents the spores are seen to contain,
with one exception, a single polar capsule, from which, after suit-
able stimulation, a polar filament of very great length is extruded.
The existence of the polar capsule in the Microsporidian spore was
discovered by Thelohan, who in consequence of this discovery

412 THE PROTOZOA

united the Microsporidia with the Myxosporidia into a single order
— the Myxosporidia (sensu latiori) — which was divided by him into
two suborders : Phsenocystes ( = Myxosporidia sensu strictiori) and
Cryptocystes (= Microsporidia). This classification is found in
many textbooks ; but in view of the possession of polar capsules by
other orders of the Cnidosporidia, it is more convenient to maintain
the old order Microsporidia of Balbiani.

The Microsporidia first attained an unenviable notoriety through
the ravages caused by Nosema bombycis, the cause of " pebrine," or
silkworm-disease ; hence the spores are often spoken of as " pebrine-
corpuscles." The silkworm-disease was investigated by Pasteur,
who found that the silkworms acquired the infection in two ways :
first, by the contaminative method, by eating leaves contaminated by
the faeces of other infected caterpillars, and thus infecting themselves
with the spores of the parasite byway of the digestive tract; secondly,
by the so-called " hereditary " method — that is to say, through
the parasite penetrating into the ovaries and eggs of the female
silkworm-moth, and, in the form of spores, remaining dormant in
the egg through its embryonic development until the hatching of
the caterpillar, which in this way is born infected with the disease.
In contrast with the Myxosporidia, the Microsporidia are chiefly
parasites of arthropods, especially insects, and are comparatively
scarce in fishes, from which, however, a few species are known —
e.g., Glugea stephani of the flounder, G. anomala of the stickleback,
etc. Two species are known which are parasitic in gregarines.
No species of Microsporidia are known as yet from warm-blooded
vertebrates, though their occurrence in such hosts has often been
alleged erroneously ; for instance, Leishmania tropica (p. 316), para-
site of Oriental Sore, was referred originally to the Microsporidia
by Wright (581) under the name Helcosoma tropicum. In addition
to Nosema bombycis already mentioned, other highly pathogenic
species are known — Thelohania contejeani, cause of destructive
epidemics amongst river-crayfishes in parts of France ; and Nosema
apis, cause of the recent destructive epidemic among hive-bees in
England (vide Fantham and Porter, P.Z.S., 1911, p. 625).

As a general rule the parasites of this order are cell-parasites,
which multiply and form their spores within cells, and the trophic
phase of the parasite is typically minute and microscopic in size.
Usually some particular tissue is attacked, but the pathogenic
species owe their lethal powers to the fact that they infest all the
tissues of the body. In a few cases, however, the parasites produce
cysts of relatively large size, visible to the naked eye in the tissues
of the host — as, for example, the species of the genus Glugea.

The most marked effect of the parasites is to produce, in many
cases, an extraordinary hypertrophy of the host-cell, and in par-

THE NEOSPORIDIA

413

ticular of its nucleus, which becomes of gigantic size, and multiplies
by division, usually in a direct and irregular manner (Fig. 171).
Hypertrophied nuclei may also come into contact with one another,
and fuse into irregular masses ; and the nuclear hypertrophy affects
not only the infected host-cell, but also neighbouring cells (Schuberg).
According to Mercier, a species of Pleistophora parasitic in the cells
of the fat-body of the cockroach stimulates the cells to multiply,
with mitosis of the nuclei, and so form neoplasial growths. These
facts are of considerable interest from the point of view of the
growth of tumours.

i-p

FIG. 171. — Section of a testis-tubule of a barbel infected by Pleistophora longifilis,
showing the cysts of the parasite (P., P.) and the greatly hypertrophied tissue-
nuclei (N., N.). After Schuberg.

Corresponding with the two types of the parasite mentioned above, there
are two methods of development to be distinguished in the trophic phase.
As an example of the first, Nosema bombycis, of which the development has
recently been described in full detail by Stempell (785), may be selected ;
while Glugea anomala (Stempell, 784) is an example of the second type.

The development of Nosema bombycis in the silkworm (Fig. 172) begins
with small uninucleate amoabulse, which are found first free in the digestive
tract, and later in the lymph- channels (Fig. 172, 5-8) ; they multiply by
simple fission and wander all over the body, and are hence termed planonts
(i.e., wanderers) by Stempell. After a time the planonts penetrate into cells,
and there grow larger, assume a definite oval or spherical form, and
become " meronts " or schizonts, which multiply by binary or multiple
fission until they have filled and exhausted the host-cell (Fig. 172, 9-13) ;
but they do not pass into other cells. The multiplication of the meronts may

414

THE PROTOZOA

FIG. 172. — Diagram of the life-cycle of Nosema bombycis. All the stages to the left
of the dotted^line are passed within a single cell, in which the parasite goes
through its sporogony after active multiplication by schizogony. 1, 2, Spores
showing the division of the two nuclei of the sporozoite ; 3, 4, germination
of the spore, showing first the extrusion of the polar filament, and then the
escape of the sporozoite, which leaves two nuclei behind in the empty sporo-
cyst and comes out with two nuclei ; 5, uninucleate planont ; 6, multiplication
of the planont by fission ; 7, 8, planonts, the latter entering the host-cell !

[Continued at foot of p. 415.

THE NEOSPORIDIA 415

be very similar in its general appearance to that of yeast-organisms, and
may result in the formation of chains of cells. When the host- cell is used up,
the meronts do not multiply further, but produce a final generation of uni-
nucleate cells which, as sporonts (Fig. 172, 13), give rise in this genus each
to a single spore.

In the development of a spore, the nucleus of the sporont (sporoblast)
buds off three small nuclei (Fig. 172, 14), two of which, as parietal nuclei,
form the sporocyst, while the third is concerned with the formation of the
single polar capsule, and the fourth or principal nucleus remains as the nucleus
of the amcebula (Fig. 172, 15). Doubtless there are divisions of the proto-
plasm corresponding to the divisions of the nuclei, but in such minute bodies
they cannot be made out clearly. The sporocyst, when formed, is a tough
capsule, which, though produced by two cells, does not show any indications
of a double composition, but appears to be cast in one piece. In some species
only a single parietal cell has been seen. The spore as a whole (Fig. 172, 16,
1, 2, 3) is egg-shaped, with one end, commonly termed " anterior," narrower
than the other. It contains two vacuoles, one near the anterior, the other
near the posterior end. The single polar capsule is of relatively large size ;
situated axially in the spore, it occupies its whole length, and contains a polar
filament of immense length, wound spirally in its interior. In Glugea anomala
atoore 6 A* in length may eject a polar filament 150 n long (Stempell, 784) ;
whue in Pleistophora longifilis the filament may measure as much as 510 /*,
more than forty-one times the length of the spore (Schuberg). The existence
of a polar capsule is denied by Schuberg, who maintains that the filament
is coiled up within the posterior vacuole of the spore.

The amcebula occupies the middle region of the spore, between the two
vacuoles, and apparently separating them ; but in reality it has the form of a
ring or girdle, wrapping round the axial polar capsule and filament, and
placed slightly nearer the anterior pole of the spore. The amcebula contains
at first a single nucleus, which, according to Stempell, divides into two and
then into four. Schuberg, however, maintains that the amcebula, and indeed
the entire spore, contains but a single nucleus ; he denies the existence of
parietal and capsulogenous nuclei, and in his opinion the bodies that have
been interpreted as such are in reality metachromatinic grains. Stempell's
description of the development of the spore is, however, in accordance with
that given by other investigators.

When the spore germinates in the intestine of a new host, the polar filament
is shot out, and the amcebula creeps out through a pore at the anterior end ;
there would appear to be at this point a small cap which closes the spore, and
which is blown off by the explosion of the polar capsule (Fig. 172, 4). Accord-
ing to Stempell, the amoebula emerges from the spore with two nuclei, leaving
the other two behind in the sporocyst as reduction-nuclei ; then the two nuclei
of the amcebula copulate, in an autogamous manner, to form a synkaryon,
and the uninucleate amcebula that results initiates the generation of planonts.
It seems, however, not improbable that some process of copulation with other
amcebulse, liberated from other spores, may occur at this stage, and remains
to be described.

A life-cycle similar in the main to that described for Nosema bombycis,
with planonts, meronts, and sporonts, as successive phases, is probably

FIG. 172 continued:

9 — 13, multiplication of the meront (schizont) in the cell, in two different
ways, the one shown in the series 9a, lOa, lla, 12a, 13a, the other in the series
9&, 10&, 11&, 12&, 12c, I2d, 13& : 13, a and &, young sporonts ; 14, divisions
of the nucleus of the sporont ; two small nuclei which have been budded
off at the lower end are the future parietal nuclei ; from the principal nucleus
the nucleus of the polar capsule is being budded off ; 15, 16, formation of
the spore, with two parietal nuclei, one capsulogenous nucleus applied to
the polar capsule, and the nucleus of the sporozoite, at first single (15), later
double (16). After Stempell (785), slightly modified.

416

THE PROTOZOA

characteristic of Microsporidia generally. Its most important variations are
exhibited in the mode of spore-formation and in the vegetative or multiplicative
stages. Only in the genus Nosema does the sporont give rise to a single
spore. In Thelohania chcetogastris, studied by Schroder (781), for example,
the sporonts are distinguished from the meronts by being enclosed in a
delicate cyst, within which the sporont multiplies by successive divisions
into eight uninucleate sporoblasts (Fig. 173), connected at first by a central
mass of protoplasm like a rosette ; but as soon as the sporocyst is formed
the sporoblasts become separate. The nucleus of each sporoblast divides
until there are five, two for the amcebula, one for the polar capsule, and two
for the sporocyst, and the development is similar to that of the spore of
Nosema bombycis already described.

A noteworthy feature of many Microsporidia is that the spores formed are
of .two sizes, microspores and macrospores, which may differ considerably in
their dimensions. In Pleistophora longifilis the macrospores are 12 /* in
length by 6 M in breadth, while the microspores are 2 or 3 /* in length and
broad in proportion (Schuberg). It is very probable that these differences
are related to differences in sex of the contained amoebulse, and that the two
kinds of spores produce macrogametes and microgametes respectively.

H

FIG. 173. — Stages in the spore-formation of Thelohania chcetogastris. A, Uri-
nucleate sporont ; B, G, division of its nucleus into two ; D, E, F, 0, division
of the nucleus and body into four ; H, division into eight sporoblasts ; /, eight
sporoblasts, each with the nucleus dividing again ; J, two sporoblasts from a
clump, showing further divisions of the nuclei ; K, young spore showing two
parietal and three central nuclei (nucleus of the capsulogenous cell and two
nuclei of the amoebula). After Schroder (781).

In Pleistophora periplanetce, according to Shiwago, several planonts
(" amceboids ") fuse into a plasmodium ; their nuclei become resolved into
chromidia which become mixed together — a process interpreted by Shiwago
as chromidiogamy. From the chromidia secondary nuclei are formed, which
become the nuclei of the sporonts (" daughter-amceboids "). The sporonts
become free from the plasmodium and form spores. If this account be con-
firmed, it is clear that the alleged autogamy of the Microsporidia, if it occurs,
is not necessarily an autogamy without amphimixis. In Thelohania mcenadis,
according to Perez (778), the nucleus of the sporont becomes resolved into a
cloud of chromidia, from which the eight nuclei of the sporoblasts are recon-
structed.

The greatest difference in the vegetative phase from the condition described
for Nosema bombycis is seen in the genus Glugea, where the multiplication of
the meront leads to the formation of a multinucleate plasmodium — a result
easily explained on the supposition that the nucleus of the meront divides
repeatedly, but the body as a whole does not do so. In this way a relatively
large plasmodial trophozoite, comparable to that of the Myxosporidia, is pro-

THE NEOSPORIDIA 417

duced, which may form a conspicuous cyst. From the plasmodial stage
sporonts arise by separation of a mass of protoplasm round a nucleus within
the body of the parasite, and thus distinct cells are formed lying in vacuoles
in the plasmodium. Such cells are commonly termed " pansporoblasts," but
the use of this term is best avoided, since the cells in question are in no
way equivalent to the pansporoblasts of Myxosporidia, which are associa-
tions of two gamonts ; but they correspond exactly to the sporonts of
Nosema and other genera, and proceed to the formation of spores in the
manner that has been described already, dividing first into several
sporoblasts.

The plasmodia of the Glugea-type lead, as already stated, to the forma-
tion of conspicuous cysts, visible to the naked eye, in the tissues of the
host ; but the composition and nature of these cysts are at present a matter
of dispute. According to Stempell (784), in Glugea anomala, the body of the
parasite is sharply defined and marked off from the tissues of the host by a
thick membrane or autocyst (" Eigencyst ") formed by the parasite itself
(Fig. 174, e). Within the autocyst is contained the plasmodium, consisting of

e —

psp.

FIG. 174. — Glugea anomala, Moniez : part of a section of a cyst, e,, Envelope
(autocyst) ; bn% vegetative nuclei ; sp., spores ; psp, sporont lying in a space
in the protoplasm. After Stempell.

protoplasm containing many nuclei, amongst which the most conspicuous
are large — indeed, relatively gigantic — vegetative nuclei, which multiply by
direct division. From the vegetative nuclei the minute nuclei of the sporonts
are stated to arise, while in other case vegetative nuclei break up and de-
generate.

Schroder (781) and Schuberg, on the other hand, maintain that the large
vegetative nuclei of Stempell are in reality tissue -nuclei of the host, greatly
hypertrophied and mixed up with the plasmodium of the parasite. Schuberg
found that Pleistophora longifilis, from the testis of the barbel, causes a hyper-
trophy, not only of the host-cell in which it is contained, but also of neigh-
bouring cells, the effect of which is to produce a sort of host -plasmodium, as
it were, containing gigantic host-nuclei of irregular form (Fig. 171), amongst
which the sporonts and spores of the parasito are scattered. Mrazek also
interprets the supposed vegetative nuclei of Myxocystis as hypertrophied
host-nuclei (see below). This interpretation of the composition of the plas-
modium greatly diminishes, or even abolishes, the principal distinction between
Glugea and the other genera of Microsporidia. In opposition to this view,

27

418 THE PROTOZOA

Stempell (786) brings forward a number of arguments, the most cogent of
which is the existence of the autocyst separating the plasmodium of the
parasite, containing the nuclei of disputed nature, from the tissues of the
host.

The most recent investigations of Awerinzew and Fermor confirm com-
pletely Stempell' s interpretation of the cysts of Glugea anomala ; compare also
Weissenberg. These authors find nuclei of various sizes in the protoplasm of
the cyst, larger or smaller. The larger nuclei are found in the outer, non-
vacuolated protoplasmic layer of the Glugea ; they grow in length and become
sausage -shaped, and are ultimately segmented into smaller nuclei, which
may form chains at their first origin, like the meronts of Nosema and other
forms. In this way arise the smaller nuclei, which either become sporonts,
or remain as vegetative nuclei in the protoplasmic walls of the vacuoles
containing the spores, where they ultimately degenerate and break up. The
sporonts are stated to arise in toto from nuclei, without visible participation
of the protoplasm of the cyst ; they become enclosed separately in vacuoles,
within which each sporont forms a cluster of spores. Thus, in older cysts
the central part of the body becomes divided by fine protoplasmic partitions
into a mass of separate chambers or vacuoles, each containing ripe spores.
Glugea anomala is to be regarded, therefore, as a colonial organism in which
meronts and sporonts, homologous with those of Nosema, etc., lie embedded
in the protoplasm of their own cyst — the meronts in the peripheral zone of
growth, the sporonts and spores in the central protoplasmic region of the
cyst.

Classification. — The two types of the trophic phase that have been de-
scribed in the foregoing paragraphs have been utilized by Perez (779) to sub-
divide the Microsporidia into two suborders, as given below. Stempell
(785), on the other hand, divides the group into three families ; the un-
certainty that prevails at present with regard to the exact structure of the
trophic phases in some forms is a hindrance to finality in the classification
of this order.

SUBORDER I. : SCHIZOGENEA (seu Oligosporea). — The principal trophic phase
is a uninucleate meront which multiplies Jby fission, and from which the sporont
finally arises. Several genera, characterized by the number of spores produced
by the sporont : One spore, Nosema ; two spores, Perezia ; four spores, Gurleya ;
eight spores, Thelohania ; sixteen spores, Duboscqia (see below) ; n spores,
Pleistophora ; but Stempellia (Leger and Hesse, 775), for S. mutabilis, parasite
of the fat-body of Ephemerid larvse, produces spores to the number of eight,
four, two, or one indifferently; Oclosporea, the species of which are parasitic
in Muscidce, produces eight spores in one species, one in another. These
anomalies indicate that the classification by the number of spores produced
by the sporont is purely artificial (Chatton and Krempf). Telomyxa glugei-
formis (Leger and Hesse), also from the fat-body of Ephemerid larvse, pro-
duces eight, sixteen, or n spores, and stands apart from all other known
Microsporidia in possessing two polar capsules in the spore.

SUBORDER II. : BLASTOGENEA (seu Polysporea). — The principal trophic phase
is a multinucleate plasmodium producing sporonts by internal cleavage ;
example : Glugea. To this section, also, the peculiar form Myxocystis has
been referred, which was discovered by Mrazek in the body-cavity of Oligo-
chsetes. Myxocystis occurs in the form of large masses floating freely in the
body-cavity, each mass remarkable for an envelope composed of a fur of
vertical filaments, not unlike stiff cilia, and enclosing nuclei and spores in
various stages of development. According to the most recent investigations
of Mrazek, however, each of these masses represents in reality a lymphocyte
containing numerous parasites, which multiply and form spores, and provoke
a great hypertrophy of the host-cell, accompanied by multiplication of its
nucleus. Hence the true Myxocystis is an intracellular parasite referable,
apparently, to the order Schizogenea, and characterized chiefly by the peculiar
form of its spores. Duboscqia legeri, Perez (780), from the body-cavity of
Termes lucifugus, is perhaps an organism of similar nature ; it is described

THE NEOSPORIDIA 419

as a floating plasmodium in which sporonts arise, each of which produces
sixteen spores ; it has, however, been referred by its discoverer to the Blasto-
genea.

Order IV. : Sarcosporidia. — The parasites of this order are con-
sidered at present to constitute a single genus, Sarcocystis, with
numerous species. In contrast to the three orders of Cnidosporidia
dealt with in the foregoing pages, the Sarcosporidia are pre-eminently
parasites of the higher vertebrates, more especially of mammals,
occurring occasionally, though rarely, in man (see Darling) ; but
they are known also to occur in avian and reptilian hosts, though
sparingly. On the other hand, no Sarcosporidia are known to be
parasitic in invertebrate hosts of any kind. In their hosts the
Sarcosporidia are tissue-parasites, occurring principally in the
striped muscles, but occasionally in unstriped. In a few cases they
are found in connective tissue, but this appears to be a secondary
condition in which a parasite living first in the muscle-fibres becomes
free from them at a later period. As a general rule the Sarco-
sporidia appear to be harmless parasites, which do not make their
presence known by any symptoms of disease, and can only be
detected by post-mortem examination. Some species, however, are
an exception to this rule, and are extremely pathogenic to their
host — for example, Sarcocystis muris of the mouse. The extent to
which the health of the host is impaired appears to be directly pro-
portional to the numbers of the parasite in the body, and conse-
quently to the power which a given species may possess of
multiplying and overrunning the host. In most species the
capacity for endogenous multiplication appears to be extremely
limited.

In spite of the fact that Sarcosporidia are very common parasites
of domestic animals, and have been found frequently in man, our
knowledge of their structure and life-history is in a very backward
state. As a rule Sarcosporidia present themselves as opaque,
whitish bodies, usually elongated and cylindrical in form, encysted
in the muscle-fibres of the infected animal, and known commonly
as " Miescher's tubes." They are distinctly visible to the naked
eye, and often very large. Sarcocystis tenella of the sheep reaches
a length of 16 millimetres, while in the roebuck (Cervus capreolus)
cysts of 50 millimetres in length are recorded. The Miescher's
tube, when examined microscopically, is seen to be a body of
complex structure, and consists chiefly of vast numbers of sickle-
shaped spores — " Rainey's corpuscles " — lying in clumps or bunches
contained in chambers separated off from one another by partitions.
The whole organism is enclosed by a distinct envelope, often ex-
hibiting vertical striations, and the partitions between the chambers
containing the spores are continuations of the envelope. The exact

420 THE PROTOZOA

structure of the spores is still a matter of dispute, and it is
possible that there is more than one kind of spore even in the
same species of parasite. A remarkable feature of the spores —
in some species, at least — is that they are motile when set free :
for example, in S. muris. They are also extremely delicate
structures, easily injured by external media, in marked contrast to
the spores of the other orders of Cnidosporidia. The spores of
8. muris, S. bertrami (of the horse), and $. tenella, reproduce them-
selves by division (Negri, Fiebiger, Teichmann). Finally it must
be mentioned that the spores of Sarcosporidia contain a true toxin,
which was named by Laveraii and Mesiiil " sarcocystine." Its
properties have been investigated recently by Teichmann (25) and
Teichmann and Braun (26).

The natural mode of transmission of the Sarcosporidia remains
to be discovered. It was found by Theobald Smith that mice could
be infected experimentally with S. muris by feeding them with the
flesh of other infected mice ; but it is extremely unlikely that
cannibalism is the method whereby sheep and other ruminants
become infected with these parasites. All experiments indicate
that the spores germinate in the digestive tract of the new host ;
but the delicate nature of the spores seems to preclude any possi-
bility of the occurrence of ordinary contaminative infection, as in
other Cnidosporidia. In this connection attention should be drawn
to the statement of Watson, that the spores are to be found in the
circulating blood, indicating the possibility of transmission by an
intermediate host.

In spite of several recent investigations upon the structure and develop-
ment of the Sarcosporidia, the subject is in a confused state, even the structure
of the spores being still disputed. It is therefore difficult to obtain a clear
notion of the course of the life-cycle in these organisms.

According to Laveran and Mesnil, the spores of S. tenella (Fig. 175) are
sausage-shaped bodies, curved, with one end more pointed than the other.
At the pointed end is a striated structure representing a polar capsule, and
at the blunt end is a nucleus, while the middle of the body is occupied by
coarse, deeply-staining, metachromatinic grains. Watson also figures a large
nucleus near the blunt end of the spore, and places the polar capsule at the
pointed end. Negri also describes the spores of S. muris and S. bertrami as
having the nucleus near tha blunt end, while the opposite extremity appears
hyaline and homogeneous for a certain distance. Betegh, again, describes
a nucleus at the blunt end of the spore, and one or two " centrosomes " in the
middle region. Erdmann (790), on the other hand, places the nucleus in the
middle of the body amongst the metachromatinic grains, and describes it as
consisting of a large dense karyosome lodged in a small vacuole ; she does not
seem to be decided, however, whether the polar capsule is at the pointed or
the blunt end of the spore. Teichmann describes a large nucleus at the
blunt end of the body, and is doubtful as to the existence of a polar capsule.
So far as it is possible to draw any conclusions from so many contradictory
statements, the clear description given by Laveran and Mesnil seems to be,
on the whole, confirmed. But according to Crawley, the spores of 8. rileyi
are binucleate; compare those of Gastrocystis (Fig. 179, p. 428). It is not

THE NEOSPORIDIA 421

clear which part of the spore contains the amcebula which is liberated
from it, as presently to be described.

In addition to spores having the complicated structure described for those
of S. tenella, there appear to be also spores of much simpler structure, as,
for example, in S. muris. Apparently the more complicated spore is propa-
gative in function, serving to infect new hosts, while the simpler form, which
should perhaps be regarded rather as a sporoblast, as a simple cell not differ-
entiated as a spore, serves for spreading the infection in the same host. The
occurrence of the simpler type of spore in S. muris would account for the
manner in which this parasite overruns its host, and is usually lethal to it,
while S. tenella, which appears to produce chiefly propagative spores, is a
harmless parasite. How far these suggestions are true must be determined
by future investigations.

The discovery made by Smith, mentioned above, that mice could be infected
with S. muris by feeding them with the flesh of other infected mice, has been
confirmed and extended by other observers. According to Negre, the faeces
of mice which have been fed with infected muscular tissue are infective to other
mice if ingested by them ; they possess this power about fifteen to sixty days
after the mouse was fed with muscle containing Sarcosporidia, and retain
their infectivity even if kept dry in an open bottle for a month, or heated to
65° C. for fifteen minutes. Negri was able to infect
guinea-pigs with S. muris by feeding them with the
flesh of infected mice, and found that in the guinea-
pig the parasite appeared with quite different char-
acters from those which it presents in the mouse, so
that it might be taken easily for a distinct species.
Darling also infected guinea-pigs with S. muris in
the same way, and points out the resemblance
between the experimental sarcospori diesis of the
guinea-pig and a case of human sarcosporidiosis
observed by him; it is suggested that the sarco- «J T ?°reS7,

sporidia occasionally observed in the human subject ^arcocys "Jj^**^"^
are those of some domestic animal undergoing a condition • B after
modified or abortive development in a host that is staining with iron-
not their usual one. Erdmann also infected mice hsematoxylin: N.,
with 8. tenella in a similar manner. It is remarkable nucleus ; c, striated
that parasites generally so harmless should be so body (polar capsule?),
little specific to particular hosts, and the results of After Laveran and
Negri render the value of the characters used for Mesnil.
distinguishing species of Sarcosporidia as doubtful in
their validity as the distinctions founded on their occurrence in certain hosts.

According to Erdmann (791), the spore germinates in the intestine of the
new host, and the first act in the process is the liberation from the spore of
its toxin, sarcocystine, which causes the adjacent epithelium of the intestine
to be thrown off. At the same time an amcebula is set free from the spore ;
and, owing to the intestine being denuded of its lining epithelium, the amcebula
is able to penetrate into the lymph-spaces of the submucous coat and establish
itself there. Before this happens, however, the metachromatini c grains of the
spore disappear, and it is suggested that this disappearance is related to the
secretion of the sarcocystine, and that the toxin is contained in the metachro-
matinic grains. If, however, a polar capsule be discharged during the germina-
tion of the spore, as in other Cnidosporidia, it might well be that the toxin
is contained in the polar capsule, and is set free by its discharge, like the
poison in the nematocysts of the Ccelentera. However that may be, it would
appear as if the sarcocystine were a weapon, as it were, the function of which
is to facilitate the invasion of the germ, the amcebula, by destroying the lining
epithelium of the gut.

The liberation of the amcebula from the spore initiates the first period
of the development, which is passed in the lymph- spaces of the intestine,
and which lasts, according to Erdmann, some twenty-eight to thirty days.

422

THE PROTOZOA

Analogy with other Neosporidia would lead us to identify this with the
planont- phase, initiated, possibly, by sexual processes between different
amcebulso and subsequent active multiplication. The second period of
the development begins with the penetration of the amcebula into a
muscle-fibre, in which the parasite grows into a Miescher's tube and forms
spores.

The intramuscular development of the parasite begins by multiplication
of the nuclei to about twelve, forming a plasmodium (Pig. 176, A). This next
becomes divided up, in parasites about thirty- three days old, into separate cells,

pansporoblasts or sporonts, which multiply
actively by division. The form of the para-
site now becomes elongated; this stage
is reached in from forty-eight to sixty
days (Fig. 176, B). At this point the para-
site may disintegrate, setting free the
sporonts, or may develop into a Miescher's
tube. In the first case the sporonts
wander out and establish themselves in
other muscle- fibres, where each sporont
initiates a fresh development, thus spread-
ing the infection in the tissues of the host.
In the second case a membrane is secreted
round the body, which forms the striated
envelope prolonged inwards to form the
chambers. The striated envelope of the
Miescher's tube has generally been com-
pared to the striated ectoplasm of some
Myxosporidia — e.g., Myxidium lieber-
Icuhni ; but according to Fiebiger it is
not ectoplasm, but altered muscular
tissue. The nuclei of the muscle-fibres
are stimulated by the parasite to multi-
plication and migration. The body then

FIG. 176. — Four stages in the de-
velopment of a " Miescher's tube "

of Sarcocystismuris in the pectoral consists of a peripheral zone of sporonts,
muscles of white rats infected ex- multiplying actively, and a central

perimentally. A, Parasite 25 /u in
length, fifty days after infection ;
the contents of the body beginning
to divide into separate cells ; B,
parasite of the same age, 35 ^ in

region in which spores are differentiated.
In the development of the spore, the
sporont becomes sausage-shaped, and
multiplies by division. Finally the
sausage -shaped bodies become spores,

length, division of the contents an(j a°e stated to be at first binucleate ;

further advanced ; C, parasite of
the same age, 60 /* in length, con-
taining separate cells ; at the
centre the division of a sporont
into two sickle-shaped bodies is
seen to be taking place ; D, middle

probably one nucleus is that of the
amcebula, the other that of the capsu-
logenous cell, parietal cells being absent ;
but these statements are at present hypo-
thetical and require substantiation. Fully-

portion of a tube about 450 /* formed spores are found in parasites
in length, seventy days after in- eighty to ninety days after the infection

of the host.

In old infections the parasites may have
destroyed the muscle-fibre completely,
so that the Miescher's tube lies in the
connective tissue. In such forms the

centre of the body may consist of granular debris, derived from the
disintegration of spores which are past their prime and have degenerated.

So far as it is possible to draw conclusions in the present state
of knowledge, the Sarcosporidia would appear to be true Cnido-
sporidia, with spores which contain each a single polar capsule,

fection, showing two couples
of sickle-shaped bodies formed
by division of a sporont. After
Negri.

THE NEOSPOR1DIA 423

and from which an amcebula is liberated, as in other Neosporidia
(Amoebogenise).

Order V. : Haplosporidia. — The distinctive features of this order
are for the most part of negative character, and, as the name im-
plies, the tendency is towards simplicity in structure and develop-
ment. The spores are without the polar capsules which are so
marked a peculiarity in the four previous orders, and have the
form of simple cells, each with a single nucleus, and with or without
a sporocyst, which, however, when present, is not formed by distinct
parietal cells.

In organisms of such simple structure, the absence of distinctive
peculiarities renders the limits of the group indefinite, and the
affinities of its members vague and undecided, and it is possible
that the order Haplosporidia, as generally understood, is a hetero-
geneous assemblage, many members of which present only develop-
mental analogies to the true Neosporidia — that is to say, a simi-
larity in the life-history which is an adaptation to a similar mode
of life, and not a true indication of genetic affinity. Leger and
Duboscq (646) point out that the characters — " peu limitatifs " —
of the Haplosporidia would suit Protista of the most diverse affini-
ties, and scarcely mark them off from yeasts or Chytridinese. With
the exception of the family Haplosporidiidce, they regard the group
Haplosporidia as purely provisional, and comprising heterogeneous
forms with undecided affinities.

The life-cycle of a typical Haplosporidian parasite is very simple.
The initial phase is an amcebula or planont, which multiplies by
fission, division of the nucleus being followed by division of the
body to form two planonts, which may continue to divide for many
generations. From a planont arises ultimately a plasmodial phase,
the result of divisions of the nucleus without corresponding divisions
of the body, which grows to a relatively large size. The plasmodium
is the principal trophic phase. It may multiply by plasmotomy or
by schizogony, or may proceed to spore-formation, and then it
divides into as many cells as there are nuclei. The cells formed in
this way are either sporoblasts, each of which becomes a single
spore (Oligosporulea), or they represent sporonts (" pansporo-
blasts "), which give rise each to a cluster of spores (Polysporulea).
The spores are usually simple rounded bodies invested by a
more or less distinct protective membrane, which in rare
instances becomes a definite sporocyst prolonged even into tails
or spikes.

The Haplosporidia were divided by Caullery and Mesnil (802)
into three families. In order to include forms more recently dis-
covered, Ridewood and Fantham have extended the classification,
and recognize two suborders :

424 THE PROTOZOA

SUBORDER I. : OLIGOSPORULEA. — The plasmodium divides at once into
sporoblasts, each of which becomes a single spore.

Family Haplosporidiidce. — Spores with a double envelope, the outer some-
times prolonged into tails or processes. Genera : Haplosporidium, Urospor-
idium, and Anurosporidium ; all the known species are parasitic in Annelids.

Family Bertramiidce. — Spores with a simple envelope, or with none.
Bertramia, with several species : B. capitellce, parasite of the coelome of
Capitella capitata ; B. asperospora, a common parasite of the body-cavity
of Rotifers. B. kirkmanni, described by Warren from Rotifers in Natal,
is stated to have several nuclei and a vacuole in the spore, and appears to
belong to a distinct genus.

In this family the genus Ichthyosporidium is ranked provisionally, as the
mode of spore -format ion is unknown as yet. Ichthyosporidium is a common
parasite of fishes, often lethal to an extreme degree. It occurs in the form
of plasmodia, sometimes irregular, sometimes more or less spherical in form,
scattered in various organs, but usually in the muscles or the connective
tissue ; the plasmodium contains numerous vesicular nuclei with distinct
karyosomes, and may be naked at the surface, or marked off from the sur-
rounding tissues by a membrane or envelope, often of considerable thick-
ness. The plasmodia multiply actively by plasmotomy, and an intense
infection is produced. Parasites with a single nucleus are also found, which
may cither represent the planont stage, or may be derived from the division
of a plasmodium ; from them the plasmodial stage arises by multiplication
of the nuclei. No other stage of the parasite is known, and the method of
transmission remains to be discovered.

Bertramia bufonis, described by King (Proc. Acad. Sci. Philad., 59, p. 273),
is possibly a species of Ichthyosporidium or allied to this genus.

Family Ccelosporidiidce, for the genera Cwlosporidium, Mesnil and Marchoux
and Polycaryum, Stempell : All the species known are parasites of Crustacea
(Phyllopoda and Cladocera). The plasmodium forms globules of fatty
substance in the interior ; it becomes encysted as a whole, and breaks up into
sporozoite-like bodies within the cyst.

Caullerya mesnili, Chatton (803), parasite of the epithelium of the mid- gut
of Daphnia spp., produces, by fragmentation of the plasmodium, spores
with resistant envelopes containing each about thirty nuclei. Chatton
considers it to be intermediate between the Haplosporidiidce and Ccelo-
sporidiidce ; possibly it should be referred to the next suborder.

Blastulidium pcedophthorum, Perez, referred to this family, is, according
to Chatton (804), a Chytridinian. Codosporidium blatellce, Crawley, is
referred by Leger (C.R.A.S., cxlix., p. 239) to the genus Pdtomyces (Myce-
tozoa, p. 243).

SUBORDER II. : POLYSPORULEA. — The plasmodium divides into sporonts,
each of which produces a cluster of spores.

Two genera, each with a single species : Neurospcridium cephalodisci, from
the nervous system of Cephalodiscus nigrescens (Ride wood and Fantham) ;
and Rhinosporidium kinealyi, from the septum nasi of human beings in India
(Minchin and Fantham ; Beattie) ; a case has also been observed in America
(Wright).

Rhinosporidium causes vascular pedunculated growths or tumours,
resembling raspberries, in the septum nasi or floor of the nose. In
sections of the growth, great numbers of the parasite are found embedded
in the connective tissue, while the mature cysts may be in the stratified
epithelium (Wright). The youngest parasites are rounded cells with a
single nucleus and a distinct envelope (Beattie). By division of the
nucleus -the parasite becomes a multinucleate plasmodium, the so-called
" granular stage," often of irregular form, but this may be due to the action
of the preserving reagents. Older parasites are spherical, with the
envelope thickened to form a thick transparent cyst, external to which
a nucleated envelope is formed by cells of the connective tissue (Beattie).
The contents of the cyst (Fig. 177, A) become divided up into numerous

THE NEOSPORIDIA

425

e

uninucleate sporonts (" pansporoblasts ") towards the centre or at one
pole, while the peripheral zone or the opposite pole remains in the
plasmodial condition. The sporonts grow in size, and at the same time
multiply by repeated fission to form a cluster of about sixteen spores,
a " spore-morula " (Fig. 177, B), enclosed by a membrane. Between
the spore-morulse an indefinite framework is formed by the residual
protoplasm in which the sporonts have developed (Beattie). Hence the
full-grown parasite exhibits three zones, which may be concentric or polar
in arrangement : a plasmodial region, peripheral or polar ; an intermediate
zone of spore -f ormation ; and a central or polar region containing ripe
spore-morulse. The process of spore -formation continues until the whole
cyst is full of spore-morulse. The ripe cysts burst and scatter their
contents in the tissues. It is possible that spores set free in this way
may germinate in the tissues and give rise to fresh cysts ; but it is more
probable that the spores, if they
escape the phagocytes, are dis-
charged from the surface of the
epithelium. From the analogy of
other Neosporidia, it is reasonable
to suppose that the youngest uni-
nucleate forms of the parasite are
the multiplicative phase in the
tissues, and that the spore-morulse
represent the propagative phase.
Nothing is known, however, of the
mode of transmission of the para-
site or of the manner in which the
infection is acquired.

A parasite is described by
Laveran and Pettit from Salmo
irideus, which in the opinion of
the authors presents affinities
with Rhinosporidium and Neuro-
sporidium. It causes a disease
in the fish, termed in German
" Taumelkrankheit."

FIG. 177. — Rhinosporidium kinealyi. A,
Segment of a section through a cyst :
e., hyaline envelope ; p.z., peripheral
zone of pansporoblasts ; i.z., inter-
mediate zone of pansporoblasts contain-
ing a few spores ; c.z., central zone of
ripe spore-morulaa; B, ripe spore-morula ;
m., membrane ; sp., spores. After
Minchin and Fantham.

In addition to the more or less
typical genera of Haplosporidia
mentioned in the foregoing para-
graphs, a number of other forms
have been described, of which the
affinities and systematic position re-
main for the present uncertain. Such are the " Serumsporidia " of Pfeiffer, and
other forms, for a review of which the reader must be referred to the comprehen-
sive memoir of Caullery and Mesnil (802) or to the original descriptions. The
remarkable form, Scheiviakovella schmeili, however, presents peculiarities which
deserve special mention. It is a parasite of the body-cavity of Cyclops spp.,
and was the subject of detailed study by Schewiakoff. In the active con-
dition it occurs as an amoeba with a single nucleus and a contractile vacuole, or
as a plasmodium formed by fusion of such amcebse. Encystment of either the
amoebae or the plasmodia occurs, and within the cyst a number of simple,
uninucleate spores are formed, which, although possessing a distinct envelope,
multiply further by fission, with mitosis of the nucleus. Germination of the
spores sets free small amcebulse. In many points this form is unique amongst
the Sporozoa, and should perhaps be classed rather with the parasitic
amcebse.

Incertce Sedis. — In conclusion a number of forms must be mentioned which
have been referred to the Neosporidia, but of which the position and affiinities
are quite doubtful.

426 THE PROTOZOA

Under the generic name Microklossia, Krassiltschik has described
certain cell-parasites of caterpillars, which appear to belong to the Neo-
sporidia, though it is not possible to assign the genus to a definite position,
since the structure of the spores has not been made out, and the account
given of the life -cycle requires revision. According to Krassiltschik, the cycle
begins with non-sexual schizogony ; the nucleus of the schizont divides into
four or eight nuclei, and as many merozoites are produced within the body
of the schizont. Schizogony is succeeded by formation of " macronts " and
" micronts " which give rise to gametes ; the macront by a process of fission
similar to the schizogony produces four to eight macrogametes, while the
micront produces in a similar way two, four, or eight, microgametes. The
nucleus of the macrogamete divides to form two reduction-nuclei. The
microgamete attaches itself to one pole of the macrogamete, and its nucleus
passes over into the cytoplasm of the latter and fuses with the female pro-
nucleus. In the zygote the synkaryon buds off daughter-nuclei, round
which the cytoplasm of the zygote is condensed to form internal buds — " pro-
toblasts." The protoblasts are set free, and produce in their turn " deuto-
blasts," which are set free, become amoeba-like, multiply in the blood of the
insect, and infect the tissues and organs of the host, especially the fat-body
and the wall of the digestive tract. In the fat-body the deutoblasts produce
a generation of " tritoblasts " which multiply actively and spread amongst
the tissue. From the tritoblasts arise finally a generation of " teloblasts,"
which divide each into a rosette of small cells, the definitive sporo blasts,
round a central residual mass. Each sporoblast produces a spore, a smooth,
strongly refractile body, ellipsoidal or egg-shaped, in which no details of
structure could be made out. The spores appear to be produced in the wall
of the digestive tract, whence they are set free with the faeces. The concluding
phases suggest a Nosema-type, but the earlier part of the life-cycle, if correctly
described, appears to be a type sui generis.

Under the name Lymphocystis johnstonei, Woodcock (824) described a
parasite of plaice and flounders, which forms conspicuous cysts in the lymph-
spaces of the skin and mesentery. Each cyst (Fig. 178) contains a single
parasite, which may attain 1 '5 millimetres in diameter, and shows a remarkable
structure. The body is enclosed by a thick, structureless membrane, and
contains at the centre a very large nucleus, irregular in shape, staining feebly,
and containing a number of karyosomes in a faintly- staining reticulum.
Surrounding the nucleus is a chromidial network forming a ring or zone of
considerable thickness, filling the greater part of the cytoplasm between the
nucleus and the envelope. The outermost zone of the chromidial net may
contain a series of small, clear " spherules."

According to Awerinzew (815 and 816), the youngest stages of Lymphocystis
are minute cells with a single nucleus which grow very rapidly, and as they
do so the chromatin passes out of the nucleus to form the chromidial ring.
The spherules are masses of plastin which separate from the chromidial net.
From the chromidia secondary nuclei are formed, round which a portion of
the cytoplasm is cut off to form small cells, termed by Awerinzew " secondary
amceboids," and compared by him to the sporonts of Glugea. Within the
secondary amceboids spores are formed, of which, however, the structure
has not been made out clearly. In teased-up preparations of Lymphocystis,
Awerinzew found spores similar to those of Henneguya, and proposed to place
the parasite in that genus. He has now become doubtful, however, whether
the Henneguya-spores belong to the Lymphocystis or to a distinct parasite,
since he was unable to demonstrate a similar structure in the spores found
in the secondary amoeboids. Awerinzew is of opinion, nevertheless, that
Lymphocystis should be referred to the Cnidosporidia, but this form requires
further investigation.

Toxocystis homari, Leger and Duboscq (646), is a parasite of the posterior
intestinal caecum of lobsters. In appearance it resembles a haemogregarine,
motionless, with granular cytoplasm and a small karyosomatic nucleus at
the middle of the body ; there are also usually two, sometimes one, " para-

THE NEOSPORIDIA

427

nuclear bodies," round masses larger than the nucleus, and staining very in-
tensely with nuclear stains. The parasite occurs between the basal membrane
and the epithelium, or in the epithelial cells, or occasionally free in the lumen
of the caecum. Multiplication appears to take place by longitudinal fission.
No other stages are known.

Gastrocystis gilruthi, Chatton (819), is a parasite of sheep and goats dis-
covered by Gilruth in Australia, but of common occurrence in Europe. The
parasite appears as a cyst, visible to the naked eye, in the mucous membrane
of the stomach. The cyst has an envelope formed by a single cell with a
large nucleus ; the envelope is concentrically striated, and bears externally a
fur of short, stiff, bristle-like processes, recalling the covering of Myxidium
lieberkuhni, Myxocystis, and Sarcosporidia. The younger cysts contain a
plasmodium with a vast number
of nuclei, some of them in groups
of two, three, four, and so on up
to a large number, which are then
arranged in a single layer en-
closing a blastula-like sphere or
blastophore. The blastophore
becomes separated off from the
interstitial protoplasm of the

plasmodium, and each nucleus f.'f/ Mgggf^ -^IgPI &- N

grows out from the surface in a Wf pff&' =^^jT

tongue-like process to form a \ pl^K'^^V.ifep \L~/»Af

cluster of sporozoite-like bodies ^f^A^-»ff^ /

or germs in a manner very
similar to the sporulation of a
malarial parasite or of Porospora
or Aggregata. The ripe cyst is
full of an enormous number of
these germs (Fig. 179), each of
which is a fusiform body, about ~,
10 /A in length, with one end
pointed and terminating in a
rostrum, the other blunter.
Near the blunt end is a
largo nucleus, and at about
the middle of the body is a
deeply-staining mass resembling
a separate karyosome or a kinetonucleus. The surface of the germ is
clothed by a delicate pellicle. The germs are set free from the cyst by
dehiscence.

The affinities of Gastrocystis remain for the present quite uncertain.
Negre reports the occurrence of a similar cyst in the duodenum of a mouse
of which the faeces infected other mice with sarcosporidiosis (see p. 421),
and suggests that Gastrocystis may be a stage in the development of
Sarcosporidia.

Pansporella perplexa, Chatton (818), is a parasite of the intestine of Daphnia
spp., occurring in the form of amoeboid bodies, reaching 80 fj- in diameter,
adherent, but not permanently attached, to the epithelium of the intestinal
wall. The amoeboid movement may be active, but does not serve for food-
capture, since nutrition is effected by the osmotic method. The cytoplasm
is divided into hyaline ectoplasm and granular endoplasm containing a single
large nucleus in which the karyosome has the form of one or two caps adherent
to the nuclear membrane. The amoeboid phase does not multiply by fission,
but becomes encysted, and then the nucleus divides repeatedly until a large
number of small nuclei are present. The body then becomes divided into a
number of spores, each containing eight nuclei, of which six degenerate,
so that the ripe spore is binucleate. Germination of the spore sets free a
binucleate amcebula which divides, apparently, into two, each of which has

lei : section
though one" of the parasites lying in the
mesentery. N., The large nucleus of the
parasite ; chr., the ring of chromidia ; l.s.,
lymph - space ; I., layer of lymphocytes
adherent to the parasite. After Woodcock
(824), magnified 45 diameters.

428 THE PROTOZOA

a single nucleus and grows up into the adult amoeba-like phase. Sexual phe-
nomena have not been observed, though their occurrence is indicated by the
development described. Chatton considers that the parasite has resemblances
to Amcebspa, Mycetozoa, and Sporozoa.

Chytridiopsis, Schneider. — Leger and Duboscq (823) describe several species
parasitic in the intestine of insects, and have followed out the development of
G. socius. The youngest form is a minute amcebula which penetrates into
an epithelial cell, and grows, with multiplication of its nuclei, to form a
plasmodium or schizont, which then divides up to form a mass of uninucleate
" schizozoites," each one at first crescent-shaped, then amoeboid. The
schizozoites are set free in the intestine, and penetrate other cells ; they either
grow" into schizonts, which repeat the process of schizogony, or into gameto-
cytes. Certain schizozoites grow within the cells without multiplication
of the nuclei till they attain a diameter of about 10 /* ; then the nucleus divides
rapidly, and a number of microgametes are formed. Other schizozoites become
macrogametes, which are about 8 /* in diameter and appear to be fertilized
each by a microgamete. The nucleus of the zygote divides into a great
number of nuclei, three or four of which travel to the
surface of the spherical body and form a cyst-
envelope ; the remaining nuclei retain their central
position, and the body of the zygote divides into . uni-
nucleate spores. In this way resistant cysts are formed
containing a large number of spores, each containing
a single nucleus and a vacuole. The cysts are cast out
of the body and infect new hosts.

Leger and Duboscq consider that Chytridiopsis may
be allied to the Microsporidia ; but having found no
polar filament in the spore, they prefer to regard it as
FIG. 179. — Spores of having affinities with Mycetozoa.*

Gastrocystis gtiru- The genera Amcebidium and Siedleckia were held

thi. After Chatton formerly to constitute a distinct order of the Sporozca,

(819). which was named the Exosporidia. Amcebidium has

been shown clearly by Chatton (817) to be an organism

of the nature of a fungus ; while Siedleckia is now generally referred to the
schizogregarines, as suggested by Minchin (589) ; see Dogiel (606). Compare
also Capillus intestinalis, Granata, parasite of the intestine of Millepedes.

Affinities of the Neosporidia. — It is sufficiently apparent, from the
structure and development of typical examples of any order of this
subclass, that their affinities are wholly with the Sarcodina. In the
case of many of the more primitive forms, it is an open question
whether they should be classed in the Neosporidia or in one of the
orders of the Sarcodina. Comparing them with the Telosporidia,
it is seen that the two characteristics of that subclass which indi-
cate affinities with the Flagellata are absent altogether in the
Neosporidia — namely, the possession of flagellated swarm-spores or
gametes, and the definite, gregarine-like body-form of the adults.
No flagellated stages are known to occur at any period of the life-
history in any member of the Neosporidia, and the body-form of
the adult in this group is typically that of an amoeba. Many of the
Myxosporidia might almost be regarded as parasitic amoebae with
a peculiar type of reproduction. Even more remarkable is the

* It is not clear on what grounds Schepotieff (269, p. 516) considers Chytridiopsis
to be a Flagellate.

THE NEOSPORIDIA 429

regularity with which the sporozoite in the Neosporidia has the form
of an amoebula, as contrasted with the equally-constant gregarinula-
form of the Telosporidian sporozoite. The characters implied in
the terms Amcebogeniae and RhabdogeniaB appear to be more
diagnostic of the two groups than any other. There can be little
doubt, therefore, that the union of the Telosporidia and Neosporidia
in one class — the Sporozoa — is a quite artificial arrangement, and
that the two subclasses in question show distinct affinities, and are
descended from distinct ancestral forms — the Telosporidia from
Flagellata, the Neosporidia from Sarcodina.

Bibliography. — For references see p. 449.

CHAPTER XVII
THE INFUSORIA

THE term Infusoria had originally a much wider application than
at present, being used to denote the various microscopic animalcules
which make their appearance in infusions exposed to the air. Hence
the Infusoria included any Protozoa, and even organisms distinct
from them, such as Rotifers. Just as the word " insect " has been
restricted in its zoological application to a single class — the Insecta
Hexapoda — so the term Infusoria has become narrowed down to
denote the Infusoria Ciliata and Suctoria, which constitute, taken
together, one of the most definite and sharply-marked classes of the
Protozoa, characterized by two principal structural features : first,
the possession of cilia during the whole or a part of their active life ;
secondly, the differentiation of the nuclear apparatus into a vegeta-
tive macronucleus and a generative micronucleus (p. 153).

The Infusoria fall naturally into two subclasses : the Ciliata
proper, in which the cilia are retained throughout life ; and the
Acinetaria or Suctoria, in which cilia are present only during
the early or larval phases of the life-history, and are lost in the
adult organism, which is of sedentary habit, and in which food-
capture is effected by special organs — suctorial tentacles.

SUBCLASS I. — CILIATA.

The Ciliata, the most abundant and familiar of microscopic forms
of life, may be considered in a sense the highest of the Protozoa,
since in no other class does the cell -body attain to so great a com-
plication of parts and organs or to so high a degree of structural
differentiation. Not even in the Metazoa are single cells to be
found of such visibly complicated structure, since in the Metazoa
the cell is specialized usually for one particular function of a living
body, while in the Ciliata the single cell performs all the functions
of life. Moreover, the differentiation of the nuclear apparatus into
generative and vegetative portions may be considered analogous
with, and parallel to, the differentiation of germen and soma in the
Metazoa ; and Lewin (172) regards the micronucleus as living inde-

430

THE INFUSORIA

431

pendently during the asexual cycle, with the cell as its environment.
In contrast to the extreme elaboration in the structure of the indi-
vidual, the life-cycle as a whole is generally of
a simple type, and the majority of the free-
living species are practically monomorphic ;
but some of the parasitic forms show a
succession of form-changes in their life-cycle.
Habits, Mode of Life. — The majority of
Ciliata are free-living aquatic forms, marine
or fresh-water, probably without exception
holozoic in the mode of nutrition ; but a
great number of parasitic forms are known.
A ciliate, whatever its mode of life, may be
free or sedentary. The free forms may be
of swimming or creeping habit, using their
cilia in the one case to move freely through
the water or to glide along firm surfaces, in
the other to creep over solid objects or on
the surface film of the water. The sedentary
forms may be attached temporarily or more
or less permanently to some object, which is
often the body of some larger animal. Para-
sitic forms may be, as in other cases, epizoic
or entozoic ; but the word " parasitic " must l|W/?Hi- __ N
be taken in a wide sense, since many Ciliata
living in or upon other organisms are not
parasitic in the strict sense of the word,
though many truly parasitic forms occur.

Body-Form. — Correlated with the diversity
in the habit of life, the body-form and
external structure show many [ variations.

*

The primitive type of ciliate may be con-
sidered to be an ovoid, gooseberry-shaped
organism with -a principal axis parallel to the
direction of movement, consequently with an

~~0. 1/jAycn/vX*

FIG. 180. — Spirostomum ambiguum, one of the largest
free-living Ciliata, reaching a length of 3 millimetres,
consequently a favourable object for physiological
experiments. N, Macronucleus, greatly elongated,
in shape like a string of beads or sausages (so-called
" moniliform " type) ; o, mouth at the hinder end of
the elongated peristome ; c.v., contractile vacuole,
supplied by a very long feeding'-canal (/.c.) ; the
micronucleus is not shown. After Stein.

anterior and a posterior pole (Fig. 14, p. 32). The mouth is terminal
at the anterior pole. The cilia clothe the whole body evenly, being

432

THE PROTOZOA

arranged in meridional rows running from the anterior to the
posterior pole, and are of equal length in all parts of the body.
An ideally-simple type of this kind is very nearly realized in some
of the primitive forms, but as a rule is modified in various ways.

In the first place, the mouth does not remain anterior, but is
shifted to the. side of the body, as far as, or even farther than, half-
way to the posterior pole (Fig. 181) ; consequently the rows of
cilia become displaced from their primitively meridional arrange-
ment, and tend to run obliquely round the body. S^^ndly, a
differentiation is set up between the general coaj£^|BKclothing
the body and locomotor in function, and special cilia ji^Hor around
the mouth, which are usually much longer than tyjj&kliers, and
modified in various ways in connection with the function of food-
capture. The mouth itself becomes surrounded by a special area

termed the "peristome," in
which are found the special
food-capturing cilia.

In forms of creeping habit
the form becomes still more
modified. The body becomes
flattened, and a ventral sur-
face, turned towards the
substratum and bearing the
mouth and peristome, is
distinguished from the oppo-
site or dorsal surface. Even
more marked are the adapta-
tions of the coat of cilia to
this mode of life (Fig. 182).
The locomotor cilia become

restricted to the ventral surface, and those on the dorsal side either
tend to disappear altogether or persist with a purely tactile function.
The cilia of the ventral surface tend to form tufts which fuse into
cirri (p. 55), with which the animal creeps as if on legs.

Sedentary forms may be attached temporarily by means of special
cilia or adhesive organs, or more or less permanently by a portion
of the body-surface on the side opposite to the mouth. In such
forms (Fig. 183) the general coating of cilia may be retained, or
may disappear entirely, only the peristomial cilia persisting ; but
locomotor cilia may be developed temporarily, enabling the animal
to become detached from one spot, and to swim away and attach
itself again elsewhere. In sedentary forms the point of attachment
may be drawn out into a stalk, which may be of great length rela-
tively, and may be a secreted structure or a portion .of the body
drawn out. In. the second case the stalk may contain highly-per-

ABC

FIG. 181. — Diagram illustrating the shifting
of the mouth, and the consequent displace-
ment of the rows of cilia, in Cilia ta, from a
form in which the mouth is at the anterior
pole and the rows of cilia run a meridional
course (A), to a form in \vhich the mouth is
shifted to the side of the body (G). After
Delage and Herouard.

THE INFUSORIA

433

fected contractile mechanisms, enabling the animal to stretch out
a long way from the base of attachment, or to retract itself close to
it. Sedentary forms may also secrete round themselves a protec-
tive sheath or tube.

Structure of the Body. — The mouth, or cytostome, is an aperture
leading into a longer or shorter oesophagus, or cytopharynx, which
ends blindly in the endoplasm. The indigestible remains of the
food are cast out through a pore in the cuticle — a cell-anus, or
cytopyge, which, though a permanent structure, is usually only
visible at the moment of defecation ; but in some cases there is a
distinct anal tube leading to an anal pore, visible at all times. In
the Gymnostomata (see p. 439, infra) the mouth can be closed or
opened by a system of rods contained in the wall of the oesophagus
(Fig. 184), which contains no vibratile apparatus ; but in all other

A B C

FIG. 182. — A and B, Euplotes patella : A, ventral view ; B, dorsal view ; G, Euplotes
harpa. In all the figures : N, macronucleus ; n, micronucleus ; c.v., contractile
vacuole ; crh, cirri ; p.m., peristomial membranellse ; F, area containing food-
vacuoles enclosed by the macronucleus. After Stein, the micronucleus added
from original preparations.

Ciliata the mouth (if present) is permanently open, and the oeso-
phagus has no rod-apparatus, but contains one or more undulating
membranes. In the orders Heterotricha, Hypotricha, and Peritricha
(see pp. 439, 440, infra), the peristome contains a spiral zone of
cilia modified in various ways, leading to the mouth, and continuous
with the undulating membrane in the oesophagus. In the two first
of these orders the cilia in the adoral zone are generally fused in
transverse rows to form membranellae. In the Peritricha the adoral
zone is composed of two parallel undulating membranes, and in
this order the mouth, together with the anus and the contractile
vacuoles, are sunk into a funnel-shaped or tubular depression called
the "vestibule" (Fig. 183, F.)- The two undulating membranes, after
describing a spiral which varies from one and a quarter to five com-

28

434

THE PROTOZOA

epl.

—st.

FIG. 183. — Campandla umbellaria. p.g., Peristomial* groove in which" runs the
adoral spiral zone of cilia, which in this species takes 4| turns ; p.r., peri-
stomial ridges between the peristomial grooves ; a.sp., the two undulating
membranes, each made up of three rows of cilia fused, which compose the
adoral spiral, seen in optical section ; the two undulating membranes pass
down into the vestibule (V.), and run down inside it spirally as far as its
termination at m., which represents the true mouth, leading into the short
cytopharynx or oesophagus (ces.) ; n, micronucleus ; N, macronucleus ;
c.pl., cortical ectoplasm, thick at the base of the body, thin at the sides ;
st.c., " collar " of the stalk ; st., stalk ; gr., granules in the endoplasm which
stain red with neutral red in the living condition ; f.v., food-vacuoles ; c.v.,
contractile vacuole opening by two canals into the vestibule. After
Schroder (864).

THE INFUSORIA

435

N—

plete turns, pass down into the vestibule, at the bottom of which
is the mouth, leading into a short oesophagus (Fig. 183, m, ORS.}. The
vestibule, into which the faeces and the excretions of the contractile
vacuoles are evacuated, forms a sort of cloaca, combining, as it
were, the functions of a stomodseum and a proctodaeum.

The body of a ciliate Infusorian is composed of ectoplasm and
endoplasm, the first of these two regions being highly differentiated
and complex in structure. The surface of the entire body is clothed
by a pellicle (Fig. 185, p.) — the most superficial differentiation of the
ectoplasm — usually in the form of a thin, delicate membrane, which
is sometimes, however, greatly thickened to form a cuirass or
lorica. In addition to the mouth and anal pore already men-
tioned, the pellicle is perforated
by the openings of the contractile
vacuoles, one or more in number.
The cilia also pass through the
pellicle.

Beneath the pellicle the ecto-
plasm, in its full development,
may be differentiated into four
layers, which, however, are not all
of them invariably present. The
most external layer of the ecto-
plasm is the so-called alveolar layer
(Fig. 185, al.}, consisting of the
outermost stratum of the alveoli
of the protoplasmic framework,
which take a regular arrangement,
the walls between contiguous
alveoli being disposed vertically
to the pellicle, thus giving the
appearance of a radially-striated
layer. Within the alveolar layer
is found commonly a protoplasmic zone containing small, spindle-
shaped bodies — the so-called trichocysts (Fig. 185, tm.) — from which a
long, stiff thread is discharged upon suitable stimulation. Within the
trichocyst-layer comes a contractile layer, containing myonemes
which run primitively beneath, or parallel to, the rows of cilia at
the surface. The cilia themselves take origin from basal granules
placed externally to, or between, the myonemes, and pass to the
exterior between the alveoli of the alveolar layer. The most
internal stratum of the ectoplasm is a spongy protoplasmic zone
traversed by irregular spaces and channels containing fluid, and
representing an excretory layer. The liquid from this region drains
into the contractile vacuole or vacuoles. The smaller channels

FIG. 184. — ChUodon cucullidus. o,
Mouth ; ph., pharynx surrounded
by a supporting apparatus of rods ;
N, macronucleus ; c.v., c.v., con-
tractile vacuoles ; an., anus, tem-
porarily visible during the extrusion
of fsecal matter (ex.). After Stein.

CV-,

FIQ. 185. — Paramecium caudatum : semi-diagrammatic figure to show the structure.
P., peristomial groove ; o, mouth ; ais., oesophagus, containing an undulating
membrane (a.m.) ;f-v.', food-vacuole forming at the base of the oesophagus ;
/.«., f.v., other food-vacuoles circulating in the endoplasm ; c.v., c.v., the two
contractile vacuoles, showing a different condition in each, the upper one full
and ready to empty itself, the lower one beginning to fill after a contraction ;
ex., excretory crystals in the endoplasm ; N, macronucleus ; n, micronucleus ;
tm., trichocysts ; a/., alveolar layer; p., pellicle. After Lang (10), slightly
modified.

THE INFUSORIA 437

unite usually into more or less conspicuous main ducts — so-called
" feeding-canals " — which empty themselves into a contractile
vacuole.

The arrangement of the contractile vacuoles and canals varies
considerably in different species. Thus, in Stentor (Fig. 8) there is
a single contractile vacuole, with a feeding-canal running the length
of the body ; so also in Spirostomum (Fig. 180, f.c.). In Paramecium
(Fig. 185) there are two contractile vacuoles near each end of the
body. The vacuole contracts suddenly, diminishing to a tiny
globule, and then some six or eight feeding-canals make their
appearance, arranged round the vacuole in a star-like figure, but
at first distinct from the central vacuole. The inner ends of the
feeding-canals gradually swell, and, after reaching a certain size,
burst through and empty themselves into the central vacuole, which
grows slowly to its full size, and as it does so the feeding-canals
disappear by degrees from view. When the vacuole has reached
its full size, it empties itself to the exterior, and the process begins
again. The contractile vacuole itself may be considered as a cen-
tralized portion of the canal-system, and though when full it
bulges into the endoplasm, it belongs strictly to the ectoplasm.

The endoplasm is the seat of nutrition, and also, as containing
the nuclear apparatus, of reproductive processes. It is of fluid
consistence, and exhibits streaming movements, termed " cyclosis "
— that is to say, currents of protoplasm which flow round constantly
in one direction, as if the endoplasm was being stirred round and
round. The endoplasm contains enclosures of various kinds, chief
amongst which are the food- vacuoles, containing ingested food-
particles in process of digestion. The food- vacuoles are formed at
the base of the oesophagus, down which food-particles are wafted
by the action of the adoral cilia and membranes. When full-sized,
the food- vacuole becomes detached from the end of the oesophagus,
like a soap-bubble from a pipe, and passes round the body in the
currents of the endoplasm, the indigestible faecal residue being
expelled finally from the anal pore (p. 433, supra). In addition to
food- vacuoles, the endoplasm contains various metaplastic grains,
excretory granules, " spheroplasts " (see p. 448), and sometimes
symbiotic algae.

The nuclei are typically two in number — a large, conspicuous
macronucleus, staining deeply ; and a micronucleus of much smaller
size, often very inconspicuous, and difficult to stain. In primitive
forms the macronucleus is a compact body, and the micronucleus
appears as a small refringent globule close beside it, often lodged
in a depression of the surface of the macronucleus (Fig. 185, N, n).
But the nuclei show very great variation in form, number, and
appearance. The macronucleus may be drawn out into the shape

438 THE PROTOZOA

of a sausage or of a horseshoe, as in Vorticellids (Fig. 183, N), or
exhibit the form of a string of beads, as in Stentor (Fig. 8) and
Spirostomum (Fig. 180) ; or there may be two macronuclei con-
nected by a delicate filament, with a micronucleus beside each, as
in Stylonychia ; or, finally, the macronucleus may be broken up
to form a diffuse network or a great number of small nuclei. The
micronucleus may be single or multiple, but does not vary in form
to any marked extent.

Life-History. — Reproduction takes the form of binary fission,
usually in the free state ; but some species become encysted prior to
division, and then divide into two, four, eight, or a large number
of small individuals within the cyst. Binary fission in the free
state is, with few exceptions, transverse to the long axis of the
body ; but in the fixed, sedentary forms the fission is usually in the
vertical plane, or slightly oblique to it, and often takes the form of
very unequal fission or budding. In some of the entozoic species
of Astomata (p. 439), repeated transverse division of the body
without complete separation of the daughter-individuals from one
another leads to the formation of chains of individuals, of which
the most anterior may be larger than the others.

As in other Protozoa, colonies may be formed in Ciliata as the
result of imperfect separation of sister-individuals produced by
fission. This is especially common in the sedentary Peritricha,
leading usually to the formation of arborescent growths ; but some-
times the colony takes other forms, as, for example, in Ophrydium,
where it consists of a great number of individuals embedded in a
common mass of jelly which floats freely.

Encystment is related in various ways to the life-conditions of
the Ciliata. Most frequently it appears to take place as a protec-
tion against desiccation in free-living forms, or as an adaptation
to a change of hosts in parasitic forms. But in some cases it is
related to the digestion of food, in others to reproductive processes.
In some species it is stated to take place if the supply of food fails,
and it can be induced artificially in various ways.

The process of syngamy has been described above (p. 152, Fig. 77).
Summarized, it consists essentially of the following processes ; some
exceptions are described below :

1. Degeneration and ultimate absorption of the macronucleus of
each conjugant.

2. Reducing divisions of the micronucleus to form four micro-
nuclei, three of which are absorbed.

3. Division of the single remaining micronucleus into two pro-
nuclei, one stationary, the other migratory.

4. Passage of the migratory pronucleus of each conjugant across
into the body of the other conjugant, where it fuses with the
stationary pronucleus.

THE INFUSORIA 439

5. Separation of the conjugants '; division of the synkaryon to
form a new micronucleus and macro nucleus.

Classification. — The Ciliata are divisible into two sections, which
comprise in all four orders :

Section A. — Aspirigera.

Without a spiral zone of adoral cilia or membranellae.

ORDER I. : HOLOTRICHA. — Cilia of approximately even length all over
the body, forming a continuous, evenly- distiibuted coat in more primitive
forms, arranged in bands or restricted to special regions in more specialized
forms.

Suborder 1 : Astomata. — Mouthless forms of parasitic habit. Opalina,
Anoplophrya, Discophrya, etc. (see p. 451).

Suborder 2: Gymnostomata. — Mouth a simple pore, near or at the anterior
pole of the body, leading into a simple, usually straight oesophagus without
cilia or undulating membranes, often with a rod-apparatus by which the mouth
is closed and opened for food-ingestion.

Classified in various ways ; three families recognized by Doflein (7) :

(1) Enchelidce, including Holophrya, Prorodon (Fig. 14), Coleps, Didinium,
etc. ; Buetschlia, parasitic in the rumen of ruminants. To the family Enche-
lidce must be referred, apparently, the remarkable form described by Meunier
under the name Gymnozoum viviparum, which is stated to have the following
characteristics : The surface of the body bears no cilia, which appear to be
wanting altogether in this form ; the mouth- opening is at one extremity of
the ovoid body, and contains an extrusible proboscis, used for the capture
of prey (see p. 442) ; the micronucleus is contained within the macronucleus ;
reproduction is by transverse fission, and also by internal budding, producing
embryos which may produce in their turn other embryos in a similar manner
before being liberated from the parent body, from which they are set free by
dehiscence. (2) Trachelidce, including Trachelius, Trachelocerca, Amphileptus,
Lionotus, Loxodes, Dileptus, etc. (3) Chlamydodontidce, including Chilodon
(Fig. 184), Nassula, etc. (4) F cettingeriidce (Chatton, 831'5): F ccttingeria,
Perikaryon.

Suborder 3 : Hymenostomata. — Mouth usually at the side of the body and at
the bottom of a peristomial depression, leading into a short oesophagus never
supported by a rod-apparatus, but containing an undulating membrane;
consequently not capable of being closed, but permanently open.

Families: (1) Chiliferidce : Leucophrys, Glaucoma,, Frontonia, Colpoda,
etc. (2) Paramecidce : Paramecium (Fig. 185), etc. (3) Pleuronemidce :
Pleuronema (Fig. 27), etc. (4) Isotrichidce : Isotricha, parasitic in the rumen
of ruminants ; and other families. (5) Microthoracidce : Microthorax, Con-
chophrys (Chatton, 831 -5).

Section B. — Spirigera.

With a conspicuous spiral zone of larger cilia or vibratile membranes leading
to the mouth ; oesophagus as in Hymenostomata.

ORDER II. : HETEROTRICHA. — Generally of swimming habit, sometimes
sedentary.

Suborder 1 : Polytricha. — Body covered with an even coat of cilia.

Principal families: (1) Plagiotomidce ; example: Spirostomum (Fig. 180).

(2) Bursaridce; examples: Bursaria ; Nyctotherus (Fig. 9), with species
entozoic in various animals; Balantidium, also entozoic. (3) Stentoridce;
example : Stentor (Fig. 8). (4) Tintinnidce (compare Entz, 53) ; examples :
Tintinnus, etc.

Suborder 2 : Oligotricha. — Body-cilia greatly reduced or absent.

Families: (1) Halter idee ; example: Halteria. (2) Ophryoscolecidce, with
numerous genera parasitic in the stomachs of ruminants ; examples : Ento-
dinium, Ophryoscolex, Cycloposthium.

440 THE P&OTOZOA

ORDER III. : HYPOTRICHA.— Ciliata typically of creeping habit ; the body
flattened, with dorsal and ventral surfaces, the ciliation highly modified
and specialized, usually with cirri on the ventral surface.

Principal families: (1) Peritromidce, with cilia on the ventral surface ;
example : Peritromus. (2) Oxytrichidce, with cirri ; examples : Oxytricha, Uro-
styla, StylonycMa. (3) Euplotidce ; example : Euplotes (Fig. 182).

ORDER IV. : PERITRICHA.— Typically of sedentary habit, the locomotor
cilia reduced to a single ring or absent temporarily or permanently ; the
adoral spiral runs down into a deep depression, the vestibule, into which
open the anus and contractile vacuoles, and at the base of which is the mouth,
leading into the oesophagus.

Suborder 1 : Scaiotricha.—The adoral zone describes a left-handed spiral.

Two families: (1) Spirochonidce : Spirochcna, ectozoic on the gill-plates
of Gammarus pulex, has a non- contractile body which bears at the upper
extremity a spirally-folded membranous funnel, on the inner side of which
is a zone of cilia. Allied genera are Kentrochona and Kentrochonopsis, both
ectozoic on the gill-plates of Nebalia. (2) Licnophoridce ; example : Licnophora,
ectozoic on various marine animals (one species entozoic in the respiratory
trees of Holothurians) ; attachment by a sucker-like disc.

Suborder 2 : Dexiotriclia.—The adoral zone describes a right-handed spiral.

Family : Vorticellidce, with three subfamilies : (a) Urceolarince, unstalked,
attached temporarily by a sucker or disc, surrounded by a persistent zone
of locomotor cilia; examples: Trichpdina, Cydochceta. (6) Lagenophryince ;
example : Lagenophrys. (c) Vorticdlince, with numerous genera : Vorticdla,
Carchesium, Zoothamnium, etc., with contractile stalks ; Epistylis, Opercu-
laria, Campandla (Fig. 183), Ophrydium, etc., with non-contractile stalks ;
Cothurnia, Vaginicola, with sheaths ; Scyphidia, free-swimming.

The entozoic Ciliata exhibit two different methods of. nutrition : first, the
holozoic method, in which the animals ingest solid food- particles, like the
free-living species, and possess in consequence a distinct mouth and contain
food- vacuoles in their interior ; secondly, the osmotic method, seen in the
astomatous forms, which absorb fluid nutriment by diffusion from their host,
and in which a mouth is rudimentary or absent and food-vacuoles are not
found. The Ciliata of the astomatous type represent the truly parasitic
forms, a familiar example of which is the genus Opalina, with species parasitic
in the common frog and other vertebrates. Common entozoic genera of the
holozoic type are Balantidium and Nyctotherus, found in the digestive tracts
of various animals ; such forms are perhaps for the most part scavengers ;
according to Comes (A.P.K., xv., p. 54), Balantidium nourishes itself exclu-
sively on red blood-corpuscles, which are set free in the intestine from wounds
caused by other parasites, especially Trematodes. Species which inhabit
the human intestine are Balantidium coli, B. minutum, and Nyctotherus fdba.

On the other hand, ciliates may crop up in cultures of human fasces, which,
like the amoebae and flagellates found there, are not to be regarded as in-
habitants of the human intestine, but as free-living forms which have passed
through the digestive tract in an encysted condition without being destroyed,
and germinate when set free from the gut. An example is Chilodon dentatus
(undnatus], described by Guiart from human fseces ; possibly also the ciliates
described by Martini (850) in a case of dysentery. 1

The free-living Ciliata exhibit, as a rule, great uniformity of character
in the active state, occurring constantly in one specific form which only
varies slightly in size under natural conditions ; they are, in fact, as nearly
as possible monomorphic. Some of the parasitic forms exhibit, how-
ever, a well-marked recurring cycle of forms in relation to the special
necessities of their mode of life, as is described below (p. 450). In some
free-living forms also different forms occur in the same species. The small
free-swimming conjugants (gametes, so called) of the sedentary Vorticellids
have been noted above (p. 172). In Leucophrys patula, a free-swimming
species, large and small individuals occur; but, according to Prowazek (861),

THE INFUSORIA 441

this dimorphism has no relation to sex, but only to differences in the sur-
rounding medium ; he states that by the addition of quinine (1 : 80,000) to a
culture of the small forms he was able to bring about the appearance of the
large forms.

The body of a ciliate is often prolonged into processes, spikes, etc., giving
the animal a curious appearance. The most bizarre forms are found amongst
the species entozoic in the digestive tracts of ruminants, such as Ophryoscolep,
Entodinium, etc. ; but some free-living species also exhibit peculiarities of
external form. Actinobolus radians (Hplotricha) has the body covered with
tentacle-like processes, each bearing a trichocyst at the extremity. Legendrea
loyezce (Faure-Fremiet), allied to Prorodon, bears on the left side of the body
about twenty digitiform processes of variable length, flexible but not motile ;
each process is composed of clear protoplasm enveloped by the pellicle, and
at its slightly dilated extremity is lodged a bundle of trichocysts. Hastatella
radians is a free-swimming Vorticellid which bears two circlets of pointed
" fulcra," or spines, one circlet on the external border of the peristome, the
other about the middle of the body (Collin).

The pellicle may be greatly thickened to form a lorica, as in Coleps, where it
is composed of a series of plates ; or may be decorated with warts or sculpturings
of various kinds, formed as local thickenings, as in some species of Vorticella, etc.

The body is often enveloped in a protective sheath or envelope secreted
by the animal, especially in sedentary forms. The animal may then be capable
of protruding its body from the sheath, and retracting itself back again into
it, and when retracted the aperture of the sheath may be closed by a special
lid, or operculum. In the Tintinnidce, some species of which are free-swimming,
others sedentary, the body secretes a shell or house, to which foreign bodies
may be added, derived for the most part from the faecal pellets of the animal
itself ; the structure of these shells has been studied in detail by Eritz (53).

The sedentary habit of life occurs in species of all orders, though especially
characteristic of Peritricha. The mechanism of fixation varies greatly, in
different cases. Stentor attaches itself by cilia, and also by pseudopodial
processes thrown out from the point of fixation, and from this type is to be
derived that of the Tintinnidce (Faure-Fremiet, 836).

The hypotrichous genus Ancystropodium (Oxytrichidce) swims freely or
attaches itself by its posterior cirri ; the body is then drawn out at the hinder
end into a long stalk (Faure-Fremiet, 837). Trachdius ovum possesses a
conspicuous, sucker-like organ by means of which it attaches itself to the
stalks of Epistylis-colonies, in order to devour the members of the colony
(Hamburger, 841).

In the Peritricha the attachment may be permanent or temporary ; in the
latter case the animal fixes itself by a sucker-like organ of the aboral pole.
In Trichodina the adhesive organ is surrounded by a ring of cilia ; in Cyclo-
chceta there is an additional circlet of stiff bristles ; in LicnopJiora the disc of
attachment is in the form of a cup surrounded by four concentric ciliary
membranes (Stevens, 872) ; these three genera, and others with similar modes
of attachment, are ectozoic forms, attaching themselves to the skin of various
aquatic animals. Faure-Fremiet (834) has traced the evolution of the per-
manently fixed Vorticellid type from temporary fixation by an aboral sucker.
As a starting-point is taken Hemispeira asterice, which attaches itself to the
gills of Asterias by a bundle of fixative cilia. In Scyphidia fixation is by a cup-
like sucker containing a circular brush of rod-like processes, equivalent,
apparently, to the fixative cilia of Hemispeira. For this brush-like organ
the term " scopula " is proposed; the cilia in it have lost their motilityand
secrete a terminal chitinous knob. Episiylis fixes itself in a similar way by
means of a scopula, of .which each rod forms a secretion of albuminoid nature
(Schroder, 865), which grows continually, forming a bundle of delicate tubes
composing the stem, and ensheathed by an outer covering secreted by a
rim round the scopula ; the stem that results is a non-contractile structure
representing a secretion of the body, and not a prolongation of the body
itself. The contractile stalk of Vorticella, Carchesium, etc., arises by an out-

442 THE PROTOZOA

growth of the central part of the scopula on a prolongation of the body-
substance, leaving a peripheral ring of scopular rods surrounding a central
protoplasmic cord, which furnishes the contractile muscular stalk.

The mouth and cytopharynx, whether capable of being closed, as in the
Gymnostomata, or permanently open, as in other forms, constitute together
a conspicuous organ in the holozoic Ciliata, sometimes showing remarakble
adaptations to special modes of feeding. In the gymnostomatous genus
Didinium the cytopharynx contains a peculiar tongue-like organ, a prolonga-
tion of the endoplasm, which shows a longitudinal striation due to the presence
of fine rods — " trichites." The tongue of Didinium is used for capturing prey,
consisting chiefly of Paramecium and other Ciliata, and the manner in which
it is used recalls the tongue of a chameleon. If the Didinium comes into
contact with its prey, the tongue is shot out by a violent contraction of the
pharynx, and adheres to the victim, which, according to Thon, is killed in-
stantly ; but according to Mast larger Ciliata sometimes escape, and in doing
so may break off and carry away the tongue of the Didinium. A Paramecium
when thus attacked emits a cloud of trichocysts, but none are discharged by
the Didinium. The prey when mastered is drawn into the endoplasm by the
retraction of the tongue. The recently- described genera Proboscidium and
Gymnozoum (Meunier) possess similar organs. The hymenostomatous genus
Pleuronema and allied forms are remarkable for the huge size of the un-
dulating membrane (Fig. 27). The animal, after swimming freely for a time,
comes to rest, with its body-cilia sticking out stiff and straight ; the undulating
membrane is then protruded from the mouth, and by its active movements
serves to waft food- particles into the pharynx.

The peristome, or region round the mouth, exhibits a wide range of special
adaptations in relation to the function of food-capture, as is apparent from
the classification given above. Absent or scarcely developed, as a rule, in
the Gymnostomata, in the Hymenostomata it has the form, usually, of a
simple groove leading to the mouth (Fig. 185, P.) ; in the Spirigera, on the other
hand, it is generally disc-like, bearing the adoral zone which terminates in
the mouth ; the extreme type of complication is seen in the Peritricha, where
the peristomial disc can be contracted completely over the mouth by means
of circular myonemes situated in the margin of the disc like a sphincter
(see below), while a central funnel-shaped portion is prolonged inwards, with
the mouth at its extremity to form the vestibule, in a manner analogous to
the stomodaeum of the Metazoa. The adoral ciliary spiral may consist simply
of longer cilia, more powerful than those of the general body- covering, the
most primitive condition ; or of transversely- planted, comb-like mem-
branellae or " pectinellae," the usual arrangement in Heterotricha and Hypo-
tricha ; or of a pair of undulating membranes running parallel to one another
in the spiral, as in Peritricha. These various structures, seen in optical section
in the living state, have often produced erroneous impressions of bristles,
cirri, etc. The adoral spiral varies greatly in extent, and the peristomial
region shows numerous modifications which cannot be described or sum-
marized briefly ; the reader must be referred to the beautiful descriptions of
Schroder (864-867), amongst recent witers. In the remarkable peritrichous
form Opercularia (Cochlearia) faurei, the adoral spiral takes five complete
turns, running like a screw round a sort of retractile proboscis (Collin, 832).

The ciliary apparatus and its modifications (Fig. 186) have been the subject
of much minute and detailed study ; among recent investigators must be
mentioned especially Maier (73) and Schuberg (44). The body-cilia run in
rows with a meridional, spiral, or other arrangement ; they arise in depressions
of the body-surface which have usually the form of furrows, but in some
cases (Paramecium, Frontonia) each cilium arises from the centre of a small
depressed area of the surface. In Paramecium the areas are for the most
part hexagonal in form, but in places they are rhombic (cf. Khainsky, 170'5).
The points of the trichocysts are situated in the angles of the polygons, and
also in the broader edges between the areas in each row.

Each cilium takes origin from a basal granule situated at the level of the

THE INFUSORIA 443

myonemes, or just external to this level, below the alveolar layer (Fig. 186,
B, D) ; the cilium passes outwards in the edges of the alveoli — that is to say,
along the lines in which the walls of contiguous alveoli touch at their corners —
and pierces the pellicle to pass to the exterior. In Anoplophrya, Collin (50)
describes root-like fibrils which pass inwards through the endoplasm, and
are inserted on the membrane of the macronucleus. Khainsky (170-5) also
describes fibrils passing inwards from the basal granules of the cilia of Para-
mecium. In the remarkable form Pycnoihrix monocystoides, which possesses
an ectoplasm of great thickness and distinctness, there are, according to
Schubotz (868), two layers of basal granules, one more superficial, the other
deeper. Each granule of the outer layer gives off a cilium on its outer side,
and on its inner side a fibril connecting it to a granule of the deeper layer,
from which, again, a fibril passes inwards and becomes directly continuous
with a myoneme.

The free cilium shows, according to Schuberg (44), a distal " end-piece,"
which stains more lightly and is of finer calibre, and a basal, thicker, and
darkly-staining portion (Fig. 186, A) ; the basal portion is of even thickness,
and is about double the length of the distal end-piece, which tapers to a fine
point. Motile cilia are not stiff, but change their form by bending in a heli-
coid spiral, or in a portion of such a spiral, like the flagella of the Flagellata
and of spermatozoa. Cast-off cilia often coil up at their proximal end into a
fine loop.

A cilium is composed of two different parts — an elastic axial filament of
firm consistence covered by a sheath of more fluid contractile substance.
According to Khainsky (170'5), the sheath of the cilium is in continuity with
the substance of the pellicle. The end-piece represents the axis exposed and
continued beyond the sheath. The axis is compared by Schuberg to that of
the axopodia (p. 48), and is the form-determining element for the fluid
sheath. Cilia perform active movements even when separated from their
basal granules, which are not to be regarded, in Schuberg's opinion, as kinetic
centres ; the movements caused by the fluid envelope are probably due to
alterations in surface-tension (p. 200, supra).

The basal granules of the cilia are not regarded by Maier or Schuberg as
centrosomic in nature. Maier considers that they probably arise as cytoplasmic
bodies at the surface of the cell, and are to be interpreted as special thicken-
ings at the roots of the cilia ; Khainsky (170'5) takes a similar view. In this
connection, however, attention should be drawn to the observations of
Entz (53), who finds that in the division of Tintinnidce the new peristomo
arises in the interior of the cytoplasmic body as a split or cavity, and that
the basal granules appear first, the pectinellae later ; the basal granules are
stated to be formed in connection with the nuclear apparatus, and their
substance to be formed either from the macronucleus or micronucleus. The
connection between the basal granules and the macronucleus described by
Collin (50) would seem also to indicate a nuclear origin for them. The
question of their centrosomic nature must remain, therefore, open for the
present. According to Schuberg, the basal granules of each row of cilia are
connected with one another by a fine longitudinal fibril.

The typical motile cilia described above become modified in various
ways, chiefly by fusion of separate cilia to form more complex structures.
The stiff, tactile bristles have precisely the same structure and mode of
insertion as the ordinary cilia (Fig. 186, H, t.c.), and in this case the change
is purely one of function or substance rather than of perceptible cytological
structure. The undulating membranes found in the pharynx of the Hymeno-
stomata are formed by fusion or adhesion of a single row of cilia, of which
the basal granules are ranged in a series to form a " basal rim " (Basalsaum)
from which the membrane takes origin (Fig. 186, E, u.m.}. According to
Schuberg, the fibrils of which the membranes, membranellae, etc., are made
up correspond, not to a whole cilium, but to its axial portion alone. Some-
times, however, more than one row of cilia contribute to the formation of
an undulating membrane ; the two membranes which compose the adoral

444

THE PROTOZOA

B

TIG. 186. — Details of the structure of the ciliary and contractile apparatus of
Ciliata. .4, Two isolated cilia of <Sfewfor coeruleus, showing the deeply-stained
proximal portion, of even thickness throughout, and the lighter distal portion,
tapering to a point ; magnified 2,250 diameters ; B, section through the surface
of the body of Prorodon teres, showing the cilia arising from basal granules
(b.g.), situated above canals (c.w.), at the base of which run the myonemes (m.),
seen in transverse section ; 0, section through the mouth of Prorodon teres
(Fig. 14), showing the rod-apparatus (#.). each rod with two myonemes
(m.r., m.r.1) ; N., nucleus ; D, section of the body-surface of Paramecium
caudalum, showing the cilia arising from basal grains : T., trichocysts ; f.v.,
food-vacuole ; E, section through the mouth and oesophagus of Paramecium
caudatum, showing the undulating membrane (u.m.) in the oesophagus :
other letters as in D ; F, section through the adoral zone of Nyctotherus
cordiformis, showing the membranellse (ml.) cut across, each composed of two
cilia arising from a pair of basal granules ; G, section of the adoral zone of
Stentor niger, showing a membranella (ml.), composed of fused cilia arising

[Continued at foot of p. 445.

THE INFUSORIA 445

spiral of Vorticellids are formed each by the concrescence of three rows of
cilia (Fig. 186, K, u.m.) ; in Glaucoma, scintillans there is a " peroral " mem-
brane built up of five rows, an " endoral " membrane of ten rows of fused cilia
(Maier, 73).

The membranellae of the adoral zone are formed each by the concrescence
of two transverse rows of cilia (Fig. 186, G, ml.). In some genera (Stentor,
Spirostomum) the basal rim of each membranella is continued down into the
endoplasm in the form of a fibrillar plate, triangular in form, with the apex
continued into a terminal filament, which is attached at its proximal ex-
tremity to a fibril running longitudinally, parallel to the row of membranellse.
The nature of this basal fibril has been much discussed ; it has been regarded
as a nervous element, co-cordinating the movements of the membranellae ;
Maier, on the other hand, regards the basal lamella and its terminal filament as
serving for the firmer attachment of the membranellae, and considers the
basal fibril to be a contractile element ; Schroder states that the basal fibril
is really a broad band, and believes its function to be purely mechanical ;
Schuberg rejects the nervous theory of the basal system of the adoral zone of
Stentor, but comes only to negative conclusions with regard to its function.

The cirri of the Hypotricha are formed by concrescence of a tuft of cilia
arising from a number of basal granules which are arranged to form a basal
plate (Fig. 186, H, C.). The posterior ciliary ring of Vorticellids is composed
of " membranulae " (Maier), each formed by concrescence of a single row of
cilia, three in each row. The two circlets of Didinium are also membranulae
(Thon).

Closely connected with the bases of the cilia in position, and with the
ciliary apparatus in their general arrangement, are the myonemes. The most
superficial study of the Ciliata suffices to convince the observer that these
animals have in many cases an extremely efficient contractile system. Such
forms as Stentor, Vorticella, etc., contract with such lightning rapidity that
it is almost impossible to kill and preserve them expanded ; the spasmodic
action of their contractile organs contrasts sharply with the slow contractility
of lower Metazoa, such as polyps. Trachelocerca, according to Lebedew (93),
contracts in an instant to one-twelfth of its length when expanded.

In their primitive arrangement the myonemes run parallel to the rows of
cilia, immediately beneath the basal granules or close beside them (Fig. 186,
B, m.). In Stentor the myonemes are broad and band-like, and composed of
alternating light and dark portions (Fig. 186, J) ; they are lodged in canals
below the alveolar layer, running in the intervals between the "ribs" or
pigmented strips of the body-surface ; the rows of cilia run above each
myoneme-canal, slightly to the side of it (Fig. 186, 7). The myonemes run
the length of the body, from the foot to the adoral zone of membranellae.
At the extremity of the foot they bend inwards and form a cone or " foot-

FIG. 186 continued:

from a number of basal granules in a row forming the basal rim (b.r.) ; below
the basal rim is the basal lamella (b.l.), continued at its apex into the end-
fibril (e.f.), which passes down to the basal fibril (&./.), seen cut in transverse
section : Z, zoochlorellse ; H, part of a section of the body of Stylonychia
histrio, showing two tactile cilia (i.e.) on the dorsal surface, and on the ventral
surface two cirri (C.), each composed of a fused tuft of cilia arising from a basal
plate of granules ; /, section of the body-surface of Stentor cceruleus, showing
the longitudinal myonemes (l.m.) lodged in canals (c.m.) between the pig-
mented " ribs " (p.) of the outer surface ; J, one of the longitudinal myonemes
of Stentor in surface view, showing the alternating light and dark portions ;
K, detail from a longitudinal section of Epistylis plicatilis, showing the two
undulating membranes (u.m.) of the peristome in transverse section, each
composed of three fused cilia arising from three basal granules (b.g.) fused
together ; from each basal plate arises a fibril ; the two fibrils join and become
continuous with one of the longitudinal myonemes running down the body
to the stalk.

A after Schuberg (44) ; B—H after Maier (73) ; /, J, after Schroder
(867) ; K after Schroder (865).

446 THE PROTOZOA

plate." At the upper end of the body fine continuations of the longitudinal
myonemes can be traced to the adoral zone, ending in the basal rims of the
membranellaB (Schroder, 867).

Stentor may be taken as a type showing the contractile system highly
developed in functional efficiency, but more or less primitive in arrangement.
Canals lodging the myonemes are not present universally, even in highly
contractile forms ; they are absent, according to Lebedew (93), in Trachdo-
cerca, but they are figured by Maier (73) in Prorodon teres (Fig. 186, B). In their
general form the myonemes are simple fibrillse, often beaded when contracted.

In the more specialized forms the contractile system acquires a more com-
plicated arrangement. In Campanella, Schroder (864) describes five systems
of myonemes : ( 1 ) Annular myonemes of the basal part of the body ; (2) longi-
tudinal myonemes of the outer body- wall, doubtless representing the primitive
system (Fig. 186, K) ; (3) annular myonemes forming the sphincter-like
muscle of the margin of the peristome ; (4) a spiral myoneme running under
the adoral spiral, and continued down the wall of the vestibule ; (5) a series
of retractor-myonemes of the peristomial disc. In Epistylis plicatilis, on the
other hand, Schroder (865) found only three systems : The longitudinal
myomenes (2), the annular peristomial myonemes (3), and the vestibular
myoneme (4). To these systems found in the Vorticellids with non-con-
tractile stalks must be added, in the genera Vorticella, Carchesium, etc., the
powerful stalk-muscle (" spasmoneme ?:) formed by the union of the longi-
tudinal myonemes (Schroder, 866). In Vorticella monilata fine connections
run from the hinder ciliary ring upwards and downwards to the longitudinal
myonemes when the cilia are developed, but disappear when these cilia dis-
appear. In Licnophora, according to Stevens, the fibril that runs under the
adoral spiral is continued down to the disc or cup of attachment and ramifies
in its walls.

In the aberrant form Pycnothrix monocystoides, Schubotz describes a re-
markable development of the myonemes in the form of a dense plexus of
fibrils at the inner limit of the ectoplasm. The fibrils are connected with the
basal granules of the cilia, and run in two directions, forming a deeper layer
of circular myonemes and a more superficial layer of longitudinal myonemes.

The question has been much discussed whether the contractile system,
often so highly developed, is accompanied by any conducting elements of
nervous nature. That many ciliates react with extreme rapidity to stimuli
has been noted above, and that their movements are co-ordinated is suffi-
ciently apparent. Neresheimer (856) describes in Stentor filaments believed
to be of nervous nature, neuronemes which take origin from the foot and
run about halfway up the body, at which point each neuroneme either ends
in a bulbous swelling or becomes thinner and disappears. The neuronemes
are situated externally to the myonemes, and run parallel to them. By
experiments with various drugs, Neresheimer tried to prove the existence
in Stentor of true nervous elements, as compared with Paramecium and other
forms in which neuronemes were not found, and concluded that the elements
described by him were truly nervous in nature. Schroder (867) casts doubt
on the existence of neuronemes and criticizes Neresheimer's technique.
Lebedew (93), however, describes fibrils, possibly nervous in nature, running
parallel to the myonemes in Trachelocerca.

For the present the existence of nervous elements in Ciliata must remain
doubtful. But of the sensory function of the cilia there can be hardly any
doubt, and the fact that their basal granules are always in close proximity
to the myonemes is extremely significant. Such a direct contact between the
sensory and contractile mechanisms may render conducting elements of
nervous nature unnecessary, except for purposes of co-ordination of move-
ments. In some cilia, as already stated, the motile function is lost, and only
the sensory function remains. The genus Mycterothriyc (Trichorhynchus) is
characterized by a rostrum bearing a number of stiff, tactile cilia (Faure-
Fremiet, 839). In some cases, however, sensory organs occur which appear
not to be derived from cilia, as, for example, the tentacle-like or club-shaped

THE INFUSORIA

447

organs, probably tactile, between the membranellae of the adoral spiral of
Tintinnidce (Schweyer).

The nature and mechanism of the peculiar trichocysts remains to be ex-
plained. The trichocyst in the unexploded state is a spindle-shaped body
with a fine, hair-like process at its outer end which reaches to the pellicle
(Fig. 186, /), T.). The exploded trichocyst tapers gradually to a sharp point
at its proximal end ; distally it shows a cap-like swelling (Fig. 187, D — G).
According to Khainsky (170'5) the trichocyst consists of two portions : a distal
or outer part which stains deeply, and a proximal or inner part which stains
a lighter colour (Fig. 187, A—C).
The unexploded trichocyst consists
entirely or almost entirely of the
darker substance ; in the process of
explosion the dark substance is con-
verted into the ]ight,?K> that in the
exploded trichocyst only a small
portion of the dark substance
remains to form the distal cap.
The notion, recently upheld by
Mitrophanow (855), that the tricho-
cyst consists of viscid fluid con-
tained in a cavity in the ectoplasm,
whence it is expelled by a sudden
contraction of the ectoplasm, and
stiffens to a solid thread under the
action of the watery medium,
cannot be maintained (Schuberg,
44) ; nor does there seem to be
any ground for comparing it to a
Ccelenterate nematocyst or to a
polar capsule of a Cnidosporidian
spore. According to Mitrophanow,
the substance of the trichocysts
appears first near the nucleus in
the endoplasm as small grains which C D E •

B

FIG. 187. — Trichocysts of Infusoria.
A — E, Stages in the explosion of the
trichocysts of Paramecium caudatum,
showing the manner in which the tricho-
cyst grows in length, with conversion of
a darkly-staining substance into a lighter
material ; the fully-exploded trichocysts
are seen in D and E. After Khainsky
(170'5). F, 0, Exploded trichocysts
of Frontonia leucas. After Schuberg,
magnified 1,500 diameters.

pass out into the ectoplasm. Tricho
cysts do not occur in any Peritricha,
but in one species, Epistylis umbel-
laria, large oval nematocysts occur,
arranged in pairs — a phenomenon
unique amongst the Ciliata.

The contractile vacuoles open to
the exterior as a general rule, but
in the Peritricha, as already stated,
they open into the vestibule ; in
this order there is usually a reservoir-
vacuole into which one or two con-
tractile vacuoles empty themselves, and which in its turn voids its
contents into the vestibule. In Campanella, however, there is no reservoir -
vacuole, and the single contractile vacuole opens by two canals into the
vestibule (Schroder, 8G4). In Opalina there are no contractile vacuoles,
and in some species (e.g., 0. ranarum) no excretory organs are to be found ;
but in other species the endoplasm contains an axial series of more or less
irregular vacuoles, opening one into the other and to the exterior by a pore at
the posterior end of the body. These vacuoles are sometimes in close relation
with the nuclei, often enveloping them to form a perinuclear space (Metcalf ,
852). In Pycnothrix monocystoides the endoplasm is traversed by a branched
system of excretory canals, which unite into a single efferent duct opening at
the surface of the body near the posterior end by a pore ; the duct is ciliated,
and is homologized by Schubotz with the cytopyge, which in Nyctotherus is

448 THE PROTOZOA

also ciliated. These excretory systems of Opalina and Pycnoihrix differ in
being endoplasmic from the ordinary contractile vacuoles, which are always
formed in the ectoplasm.

The endoplasm of the Ciliata may contain enclosures of various kinds :
food -vacuoles ; metaplastic bodies in the form of excretory grains, crystals,
pigment-grains, etc. ; zoochlorellae, and occasionally parasites of one kind or
another, etc. Special attention has been drawn by Faure-Fremiet (38'5 and
835) to the bodies termed by him spheroplasts, and considered by him to be
homologous with the mitochondria (p. 41). The bodies in question are
small spherules, which multiply by fission when the cell- body divides ; they
are permanent cell-organs to the same extent as the nuclear apparatus, of
which, however, they are entirely independent.

As pointed out above, the form of the macronucleus and the number of
nuclei vary greatly in different species. The cases will be considered below
in which the micronucleus appears to be wanting (Opalina), or is contained
in the macronucleus in the ordinary condition of the body (Trachdocerca,
Ichthyophthirius). As a rule the macronucleus has a finely granular appear-
ance, with the chromatin distributed evenly over the nuclear framework ;
but in a few cases it has a distinctly vesicular structure, with a large karyo-
some, as in Loxodes (Joseph, Kasanzeff), Chilodon (Nagler, 96), etc. The
macronucleus divides by binary fission of a simple and direct type (Fig. 54).
The micronucleus, on the other hand, divides by mitosis (Fig. 61). In
Trachdocerca, a form which may possess one or many nuclei (but no separate
micronuclei), Lebedew (93) describes a peculiar mode of multiplication of the
nuclei, which divide by multiple fission to form a morula-like body consisting
of a mass of small nuclei which separate from one another (Fig. 66). In
Loxodes, another form in which the number of nuclei varies greatly in different
specimens, the macronuclei do not divide, but only the micronuclei do
so, and the macronuclei arise by growth and modification of the micro-
nuclei (Kasanzeff). In many cases in which the macronucleus is of the
elongated moniliform type, or in which the body in the ordinary state contains
two or more macronuclei, they come together to form a single compact
macronucleus prior to division; but in other similar cases this does not occur,
and when the body divides the nuclei are distributed irregularly between the
two daughter-individuals, as in Trachdocerca, Opalina, etc. The distributed
form of nucleus is especially characteristic of the astomatous parasitic forms,
and in the opinion of Pierantoni (A.P.K., xvi., p. 99) is correlated with nutri-
tion by the osmotic method.

The micronucleus is less variable in form or number, as a general rule,
than the macronucleus, but is not infrequently multiple, especial! y when there
is more than one macronucleus ; but in Trachdius ovum a single large macro-
nucleus is combined with thirteen micronuclei (Hamburger, 841).

The conjugation of the Ciliata conforms, as a general rule, in its main
outlines to the scheme sketched out above (Fig. 77), but some important
variations must be noted. In the first place, the conjugation is often pre-
ceded% by active division of the animals, so that the conjugants* are much
smaller than the ordinary individuals of the species. When the two conju-
gants come together, the micronucleus of each usually divides into four, but
sometimes into eight, as in both conjugants of Euplotes and the microconju-
gant of Peritricha ; in either case, however, only one micronucleus persists,
and furnishes the two pronuclei.

The Peritricha exhibit in their conjugation certain peculiarities which are
clearly of a secondary nature and correlated with their sedentary habit.
Certain individuals divide two or three times successively to produce four or
eight microconjugants (" microgametes ") which acquire a ring of locomotor

* It is preferable not to speak of two conjugating Infusoria as gametes, since
it is very doubtful if they correspond to the gametes in the other classes of Protozoa.
It is on the whole more probable that the conjugants correspond rather with
gamonts or gametocytes, which originally produced a number of gametes, reduced
now to two, represented in each conjugant by the two pronuclei.

THE INFUSORIA 449

cilia and swim off. Each microconjugant attaches itself to a macroconjugant
— that is to say, to an ordinary sedentary individual ; each of the conjugants
has a single micronucleus and macronucleus, but as soon as they become
associated the changes preparatory to syngamy begin. In the microconjugant
the micronucleus divides three times to produce eight micronuclei. In
Carchesium the first of these divisions is an equating division ; the second
reduces the number of chromosomes from sixteen to eight ; and the third
division is again an equating division (Popoff, 125). Meanwhile the macro-
nucleus is in process of degeneration, and is breaking up into fragments.
Of the eight micronuclei, seven degenerate, one persists and divides into two
pronuclei. In the macroconjugant, meanwhile, similar events are taking
place, but the micronucleus only divides twice, first by a reducing, then by an
equating division, to produce four micronuclei, of which three degenerate,
while the fourth persists and divides into the two pronuclei.

Of the two pronuclei now present in each conjugant, one degenerates in
each case ; the persistent pronucleus of the microconjugant passes over into
the macroconjugant and copulates with its persistent pronucleus. The frag-
ments of the macronucleus also pass over into the macroconjugant, but are
there absorbed slowly. The body of the microconjugant then falls off and dies ;
only the macroconjugant is fertilized.

Variations of minor importance are seen in the behaviour of the synkaryon
of the exconjugant after fusion of the pronuclei has taken place. For example,
in Paramecium bursaria the synkaryon divides to form four nuclei, two of
which become macronuclei, whereupon the exconjugant divides into two
ordinary individuals (Hamburger, 842) ; in Licnophora the synkaryon divides
into eight, which become a micronucleus and a macronuclear chain of seven
segments (Stevens, 872) ; in Carchesium the synkaryon divides also into eight
to furnish a micronucleus and seven separate macronuclei, but the micro-
nucleus then divides six times, with subsequent divisions of the body and
sorting out of the macronuclei, until seven individuals, each with a single
micronucleus and macronucleus, are produced (Popoff, 125) ; in Anoplophrya
the synkaryon divides into four nuclei, two of which degenerate, the remaining
two becoming a micronucleus and a macronucleus respectively. The method
of nuclear reconstruction may vary even in the same species, as shown by
Prandtl (126) in the case of Didinium.

The most important deviations from the usual scheme of conjugation are
seen in those forms in which there is no separate micronucleus in the ordinary
condition. The cases of Opalina and Ichthyophthirlus, parasitic forms and
therefore open to the charge of degeneration, are dealt with below. In
Trachelocerca phoenicopterus, a free-living species, conjugation has been
described by Lebedew (93) between individuals containing many nuclei all
similar in appearance, each with a large karyosome. Pmor to conjugation
the chromatin passes out of the karyosome into the nuclear cavity of each
nucleus (Fig. 188, A, B), which then divides into four. The chromatin forms
a compact mass at one pole of each nucleus. During conjugation these masses
of chromatin pass out of the nuclei, and lie free in the cytoplasm between
them (Fig. 188, C — G) ; each such mass is now to be regarded as a micro-
nucleus and lies in a clear area, finally becoming a vesicular nucleus with a
distinct alveolar structure ; the old nuclei can now be considered as macro-
nuclei. All the nuclei now collect in a mass near the middle of the body.
The macronuclei ultimately degenerate ; the micronuclei multiply by fission,
but ultimately, according to Lebedew, they all degenerate with the exception
of one in each conjugant ; the persistent micronucleus divides into two pro-
nuclei which conjugate in the usual way ; unfortunately, the author's observa-
tions contain so many gaps that this statement cannot be considered estab-
lished so decisively as could be desired. The exconjugants contain each a
single synkaryon which divides by successive divisions into a number of nuclei
not differentiated into micronuclei and macronuclei.

The case of Trachelocerca, as it is described, furnishes an important clue
to understanding the origin of the heterokaryote condition of Infusoria from

29

450

THE PROTOZOA

that found in other Protozoa. In this case, during the ordinary vegetative
condition, the generative chromatm representing the micronucleus of. other
Infusoria, and the vegetative chromatin representing the macronucleus, are
contained in one and the same nucleus, and become separate only when
syngamy is about to take place. The first sign of the separation is the forma-
tion of chromidia from the karyosome within the nucleus, resulting in the
formation of a secondary nucleus which becomes separate and which behaves
exactly as an ordinary micronucleus ; thus indicating a clear homology between
the micronuclei of Infusoria and the secondary generative nuclei of Sarcodina.
The production of numerous micronuclei in the conjugation of Trachelocerca

N'

FIG. 188. — Formation of micronuclei in Trachelocerca phcenicopterus. A, B, A
nucleus has divided into two, and from the karyosome (k. ) of each daughter-
nucleus masses of chromatin are being given off into the nuclear cavity ;
C, D, the two nuclei of the preceding stages have divided again, to form a
group of four, and the chromatin-masses (n) have acquired a compact struc-
ture and are passing out of the nuclei to form the micronuclei ; in C crystals
are seen in the cavities of the old nuclei, probably a sign of degeneration ;
E, F, two groups of nuclei, both from the same specimen ; the micronuclei
given off from the old nuclei become surrounded by a vacuole (n' in F), and
then acquire an alveolar structure (n' in E) ; G, portion of a preparation of
the body of a conjugant, the wavy contour on the right being the surface of
the body which is in contact with the other conjugant ; numerous micronuclei
(n) are seen, -and also macronuclei, some of which still appear normal (N),
others degenerating (N'). After Lebedew (93).

is noteworthy, and would appear to favour the theory (see p. 154) that primi-
tively numerous gametes (swarm-spores) were produced in the conjugation
of Infusoria.

Examples of a complicated life cycle are to be found in Ciliata chiefly,
perhaps solely, among parasitic forms. As an example may be taken Ich-
ihyophthirius multifHiis, a parasite of the skin of various species of fresh-water
fishes. In aquaria, where, owing to the limited space, the parasites, if present,
find their way to the fish very easily, and where, consequently, a fish becomes
infected with vast numbers of the ciliates, the parasites are usually lethal to
the host, and cause its death, according to Buschkiel, in about fourteen days.
In Nature, on the other hand, " ichthyophthiriasis " is seldom observed, prob-

THE INFUSORIA 451

ably owing to the fact that under natural conditions only a very small propor-
tion of the young parasites succeed in establishing themselves on a fish, and
consequently the infections produced are so slight that they are overlooked,
and the fish is unharmed.

The life-cycle of Icliihyophthirius is as follows : The youngest parasites
hatched out from a cyst are very small, and have a macronucleus and a micro-
nucleus. They seek out a fish and bore into its epidermis, attaching them-
selves by one end of the club-shaped body and rotating actively, with the
result that epithelial cells are displaced, and either cast off into the water or
form a ring-like wall round the parasite. In this way the infusorian works
its way gradually into the deeper layers of the epidermis, which closes over it,
so that the parasite lies finally in a closed hollow space in the epidermis. In
this position it grows in size, and at a certain point the micronucleus disappears,
passing into the macronucleus to form a nucleolus-like body within it. The
parasite appears to the naked eye as a little white spot on the skin, occurring
on any part of the body-surface or on the gills. It retains its cilia, and can be
seen rotating within the cavity in which it lies.

The full-grown Ichthyophthirius may reach 1 millimetre in diameter, but is
usually less, about 0'75 millimetre. When full-grown the ciliate breaks out
of the cavity in the epidermis and sinks to the bottom, attaching itself to the
ground or to water- weeds, and becomes encysted. Within the cyst it multi-
plies by binary fission repeated eight times, producing 256 small ciliates ;
sometimes this multiplication takes place without encystment. During this
process of multiplication the micronucleus reappears, being extruded from
the macronucleus of each individual when not less than four are present in
the cyst ; but the exact period at which the micronuclei appear varies in
different cases. In addition to the micronucleus, one or two other extrusions
from the macronucleus take place (Buschkiel) ; but whether these represent
other micronuclei or expelled vegetative chromatin is not clear ; in any case
they degenerate and disappear. When the micronucleus makes its appearance,
it divides by mitosis at each division of the cell-body, as in ordinary Ciliata,
while the macronucleus divides in the usual way by direct division.

When the full number of tiny ciliates is formed, each with a macro-
nucleus and micronucleus, sexual phenomena occur, but the events that
take place are described differently by different investigators. According to
Neresheimer (858), in each individual the micronucleus divides twice, and
three of the four micronuclei produced degenerate ; the fourth then divides
again. The reduction- process is, therefore, according to this account, similar
to that of other Ciliata, and the organism appears to be ready for con jugation,
with two pronuclei ; but Neresheimer was unable to observe conjugation taking
place either in the cyst or after the organisms have become free ; he observed,
however, sometimes two micronuclei, sometimes one, both in free forms and
in those attached to the fish, and from this it was inferred that the two pro-
nuclei fuse autogamously, leaving the possibility open, however, that heter-
ogamous conjugation might sometimes occur. According to Buschkiel, on
the other hand, the micronucleus of each individual divides twice, and, of the
four thus produced, two degenerate, and the remaining two fuse autoga-
mously while still within the cyst.

The little ciliates are set free from the cyst, and seek out a new host in their
turn. From the time that the full-grown parasite leaves the fish to the time
that the brood is liberated from the cyst is, according to Buschkiel, about
twenty hours, more or less. If an infected aquarium be kept empty of fish
for sixty hours, it becomes disinfected, since the parasites all die off if they
cannot attach themselves to a fish very soon after they are hatched out.

The entozoic Ciliata, in which adaptation to a purely parasitic life has led
to the degeneration of the apparatus of a holozoic mode of nutrition — that is
to say, of the mouth, peristome, and accessory cilia — are sometimes classified
as an order, Astomata, of the Holotricha ; but there can be little doubt this
group, like others founded on negative characters, is a heterogeneous collection
of forms in which the characters they possess in common are due to convergent

452 THE PROTOZOA

adaptation to their mode of life (c/. Leger and Duboscq, 848). The best-
known genera are Anoplophrya, a typical ciliate with micronucleus and
macronucleus and with a rudimentary cytostome, constituting with Hopli-
tophrya, Herpetophrya Discophrya, etc., the group Anoplophryince ; Chromidina
and Opalinopsis, parasitic in Cephalopods, are probably allied to the fore-
going (cf. Dobell, 833). The species of Opalina, constituting the group
Opalinince, are parasitic in frogs and various cold-blooded vertebrates ;
their nuclei vary in number in different species from two to an indefinitely
large number, but are all similar and without differentiation into micronuclei
and macronuclei at any period of the life-cycle. Cepede has monographed
the section Anoplophryince, and has described a number of new genera and
species, distributed amongst eleven families. The Astomata are internal
parasites of their hosts, especially of the digestive tract. Protophrya ovicola
occurs in the brood-sac of the mollusc Littorina rudis, and is parasitic upon
its eggs, causing their disintegration (Kofoid).

The remarkable form Pycnotkrix monocystoides, from the gut of Hyrax
capensis, described by Schubotz, deserves special mention. It reaches a length
of 3'2 millimetres, and contains parasitic nematodes. The animal itself has
a great superficial resemblance to a nematode or to a monocystid gregarine ;
it has a very thick and distinct ectoplasm, covered by an even coat of short
cilia, and with two longitudinal grooves which Schubotz regards as equivalent
to the perisbomial grooves of other Ciliata. Each groove contains a series of
pouch-like depressions, which open down into the endoplasm, and are provided
with special tracts of myonemes. Schubotz regards these pouches as a series
of cytostomes, but no food-particles or vacuoles are found in the endoplasm ;
the interpretation, therefore, of these openings as cytostomes can only be
taken in a phylogenetic sense ; actually they appear to represent perforations
of the tough ectoplasm which may facilitate absorption of food by the osmotic
method. For the cilia, myonemes and excretory system of this form see
above (pp. 443, 446 447) ; the micronucleus and macronucleus are each
single and of the ordinary type. Pycnothrix stands at present quite
isolated.

The species of the genus Opalina differ in certain peculiarities of structure
and life-history from all other ciliates. The life-history of the common
species of Opalina parasitic in the rectum of the frog has been studied by
Metcalf (853) and Neresheimer (857), whoec accounts agree as regards the
general life-cycle, but differ in some cytological details.

Opalina ranarum multiplies in a vegetative manner during the summer
and autumn months, but in the spring a special propagative cycle occurs in
relation to change of hosts and is followed by sexual processes.

The vegetative reproduction increases the numbers of the parasite in the
host ; it consists of two processes, multiplication of the nuclei and division
of the body, which go on independently. The animal contains a great many
nuclei, and when it reaches a certain size the body divides either longi-
tudinally or transversely to produce two daughter-individuals, each of which
grows again to the full size. The multiplication of the nuclei is effected by
a simple mitosis, similar to that of the micronucleus of other Infusoria, and
without centrosomes.

In the spring the parasites divide rapidly and repeatedly, without growing
to full size between the divisions, so that they become continually smaller in
size. A few individuals, however, do not undergo this process of rapid
fission, but remain of the ordinary type, forming a stock which persists and
carries on the infection in the frog, while those which divide up are de -tined
to pass out of it. At the beginning of the process of rapid division, the nuclei
extrude chromidia, some of which are absorbed, while from the remainder
secondary nuclei are formed (Neresheimer). Finally the old nuclei are
absorbed. The secondary nuclei also multiply by mitosis ; and, according
to Metcalf, in the later mitoses preceding encystment the number of chromo-
somes is reduced to one- half the ordinary number (in O. intestinalis from eight
to four, in 0. caudata from six to three). The result of the repeated division

THE INFUSORIA 453

is to produce small individuals containing, as a rule, from three to six secondary
nuclei. Such individuals become encysted (infection-cysts), and pass out of
the frog in the faeces. The animal at first fills the cyst completely and shows
no cilia, but after a time the body shrinks within the cyst, and the animal is
then seen to have a ciliary covering.

The faeces of the frogs are readily devoured by tadpoles, which thus become
infected with cysts. In the gut of the tadpole the Opalina emerges from its
cyst. It at once divides up into uninucleate individuals, the gametes,
elongated club-shaped forms with a sparse coat of cilia over the flattened
body. Under unfavourable circumstances the gametes undergo agglomera-
tion in rosettes, adhering by their pointed ends (Neresheimer). Under
normal circumstances they copulate in pairs as isogametes, according to
Neresheimer, mO. ranarum ; butMetcalf describes smaller uninucleate micro-
gametes and larger macrogametes with one or two nuclei, in other species ;
the male pronucleus then fuses with one of the two nuclei of the macrogamete.
The zygote of 0. ranarum, with the two pronuclei still separate, rounds itself
off and becomes encysted (copulation-cyst) ; within the cyst the two pronuclei,
which have passed into a spindle-stage, undergo fusion. The zygote emerges
from the cyst with a synkaryon, and it becomes an adult Opalina.

Neresheimer considers that the life-cycle of Opalina proves that its affinities
are with Flagellata rather than with Infusoria. In deciding this question,
it must be considered, in the first place, whether in such a form the life-cycle,
or the structural features of the body, are most likely to indicate affinity —
that is to say, least likely to exhibit secondary peculiarities due to adaptation.
Opalina is a parasitic form, and its life-cycle shows very obviously a direct
daptation, of a type very common in parasitic Protozoa, to its mode of life ;
multiplicative reproduction increasing its numbers within the host, and prop-
agative reproduction, combined with sexual phenomena, leading to the
infection of new hosts. On the other hand, its minute structure is that typical
of Ciliata, a character hardly likely to be due to the influence of parasitism,
as Popoff (125) has well pointed out.

The chief difference between Opalina and other Ciliata, which requires
special consideration, is the fact that the animal contains but one kind ot
nucleus. This, however, is a character known in other genera of Ciliata
also — e.g., Trachelocerca, Ichihyophihirius. There can be but little doubt
that the " heterokaryote " condition of the Infusoria, with distinct generative
and vegetative nuclei, must have been derived phylogenetically from a condi-
tion in which, as in other Protozoa, the two kinds of chromatin were contained
in one and the same nucleus ; and to find this condition still retained in some
Infusoria would not be remarkable. In such forms it is to be expected that
prior to gamete-formation the vegetative chromatin, equivalent to the
macronucleus, would be expelled, and the pronuclei would be formed from
generative chromatin.

There is nothing, therefore, to be said against the view of Popoff, that
Opalina shows the most primitive type of gamete -formation* known at present
amongst the Ciliata. Its nuclei contain generative and vegetative chromatin
combined, and in preparation for syngamy nuclei are formed which are purely
generative, out of chromidia expelled from the primary nuclei. The forma-
tion of uninucleate gametes which copulate (total karyogamy) has been re-
garded by almost all those who have theorized on the subject as being probably
the most primitive type of syngamy from which the conjugation (partial
karyogamy) of the Ciliata has been derived (p. 154).

In Trachelocerca (p. 450) the gamont produces in a similar manner a number
of generative nuclei (micronuclei) prior to the syngamic process ; but here,-
as in Ciliata generally, the gamont no longer divides into a number of gametes ;
only one micronucleus in each gamont persists to form the two pronuclei, and
the usual process of partial karyogamy takes place. These considerations
indicate that the monomorphic character of the Infusorian life- cycle is a
secondary feature ; as the structural complication of the body has increased,
so the tendency to divide up into relatively minute swarm-spores has been

454

THEJPROTOZOA

A

suppressed, and has been replaced by the peculiar type of syngamy charac-
teristic of the group.

The question of the exact systematic position of Opalina cannot be decided
until more is known of the life-cycles of other parasitic Ciliata ; but at present
there do not seem to be any cogent reasons for removing this genus from the
Ciliata.

Affinities of the Ciliata. — A typical ciliate, such as Paramecium, with its
even coat of fine cilia, its heterokaryote nuclear apparatus, and its peculiar
type of syngamy with partial karyogamy, stands apart and apparently
isolated from the typical members of other classes of the Protozoa. Never-
theless, even within the limits of the class Ciliata,
examples are to be found in which the heterokaryote
condition is not developed, or only appears prior
to syngamy in the form of a separation of generative
from vegetative chromatin (Trachelocerca, Opalina),
and in which the syngamy takes the form of total
karyogamy between minute gametes, swarm-spores
(Opalina). Such cases, while they minimize the gap
between Ciliata and other Protozoa, do not bring the
ciliates nearer to any particular class, since a similar
type of syngamy and of preparations for it may occur
either in Sarcodina or Mastigophora.

As the most distinctive feature of the Ciliata there
remains that which is
implied in the name —
that is to say, the posses-
sion of cilia. As has been
pointed out above, how-
ever, a cilium is similar
to a flagellum in every
essential point of structure
and function. There can
be no doubt that the
ciliary covering represents
a large number of flagella
specialized in respect to
size, number, arrange-
ment, and co-ordination.
It has been mentioned
abovs that some flagel-
lates, such as the Tricho-
nymphidce and allied
forms, are regarded by
some authorities as transi-
tional from the FJagellata
to the Ciliata. It is per-
haps improbable, how-
ever, that the transition
from the one group to
the other should have been

through endoparasitic forms ; and it is on the whole more likely that free-
living forms, such as the holomastigote genus MuUicilia, are the nearest
representatives of the earlier ancestral forms of the Ciliata.

Two interesting forms have been described which combine in some respects
the characters of both Flagellata and Ciliata.

Maupasia paradoxa (Fig. 189, B) is described by its discoverer, Schewiakoff
(863), as having the body metabolic, with cilia in the anterior part of the
body, and the remainder covered with long flagella. At the hinder end of the
body is a longer flagellum implanted close beside the aperture of the efferent
duct of the contractile vacuole. The mouth -opening, on the ventral side of

a,

FIG. 189. — A, Monomastix ciliatus : ft., flagellum ;
o, mouth ; N, macronucleus ; n, micro-nucleus ;
c.v., contractile vacuole ; a., anus, near which opens
the efferent canal of the contractile vacuole. After
Roux, magnified 1,000. B, Maupasia paradoxa :
CBS., oesophagus ; other letters as in A. After
Schewiakoff, magnified 1,300.

THE INFUSORIA 455

the body, leads into a short oesophagus. The nucleus is single, without a
micronucleus. Schewiakoff makes Maupasia the type of a distinct order of
the Ciliata — the Mastigotricha.

Monomastix ciliatus (Fig. 189, A), described by Roux (862), and referred by
him also to the Mastigotricha, has an even coat of cilia all over the body, and
possesses two macronuclei, near each of which is a micronucleus ; its most
remarkable feature is the possession of a long flagellum implanted at the
anterior end of the body close to the mouth.

From these various considerations, it seems highly probable that the Ciliata
are descended from flagellate ancestors ; but it is not possible at present to
indicate with any approach to exactness the line of descent.

SUBCLASS II. — ACINETARIA (Suctoria, Tentaculifera).

The Acinetaria are distinguished from the Ciliata by the posses-
sion of the following characters in combination : The adult organism
is of sedentary habit, and has no cilia, though the youngest stage
in the life-history is typically a free-swimming ciliated organism ;
there is no mouth, but both the capture and ingestion of food is
effected by means of special organs peculiar to this subclass, and
known as tentacles.

An acinetan may be attached to various objects, and is frequently
epizoic. Some species attach themselves indifferently to a living
or a lifeless object ; others are constantly epizoic, and occur always
attached to some particular animal, frequently to a particular
organ of it. Very few species, however, are truly parasitic in the
adult condition ; on the other hand, many species are parasitic in
the early larval stages of their life-history, and frequently so within
the bodies of Ciliata (Fig. 192). The marine genus Ophryodendron,
however, is a true ectoparasite of hydroids, according to Martin,
and contains nematocysts derived from its hosts. In this case the
parasitism is correlated with a peculiar dimorphism of " proboscidi-
form " and " vermiform " individuals, the former possessing a tuft
of tentacles on a proboscis-like process, the latter being without
tentacles altogether. The vermiform individuals are budded from
the proboscidiform, and either form can produce ciliated buds,
which develop into proboscidiform individuals again ; but the
vermiform type does not grow into the proboscidiform. In Den-
drosomides paguri, however, Collin (881) finds that similar vermi-
form individuals become transformed into the tentacle- bearing
form. In Ehabdoplirya trimorpha, ectozoic on a Copepod (Cletodes
longicaudatus), there are three forms of individuals — namely, in
addition to tentaculated and vermiform specimens, peculiar " unci-
form " individuals, which are also without tentacles (Chatton and
Collin, 876).

The form of the body varies greatly, but may be said to be
typically vase-like, with or without a stalk or peduncle. In sessile
forms the body is attached by a broad base to the substratum. In

456

THE PROTOZOA

stalked forms the body is raised up from the point of attachment
on a straight, non-contractile stalk of secreted substance, similar to
that of many Vorticellids, and the animal as a whole may resemble
in its general contours an Epistylis or other Vorticellid (Figs. 10,
190). Collin (877) finds that the stalk consists of a sheath, a cor-
tical layer thickest at the base, and a medullary substance stratified
longitudinally to the longitudinal axis. The base of the stalk rests
on a cushion of secreted substance — the portion which is first
formed, and which is produced by a special organ of the larva
comparable to the scopula (p. 441) of the Vorticellids.

The body is often protected by a secreted house or theca, con-

FIG. 190. — A, Podophrya mollis ; B, Tocophrya quadripartita, two specimens
attached to the stalk of Epistylis plicatilis ; C, Podophrya fixa, two specimens
conjugating. After Saville Kent.

tinuous with the stalk in the pedunculate forms. In Asirophrya
arenaria the house is built up of foreign particles of various sizes
(Awerinzew). As in the attached ciliates, colonies may be formed
of considerable size and extent, and of various forms. The non-
pedunculate genus Dendrosoma produces spreading colonies, which
bear a considerable resemblance to a polyp-colony.

The characteristic tentacles are stiff protoplasmic processes con-
sisting of a parietal layer of ectoplasm in the form of a tube en-
closing a canal containing fluid. The apex of the tentacle usually
terminates in a sucker-like knob ; suctorial tentacles (" Saugten-

THE INFUSORIA

457

takel ") of this type are always present. In the genus Ephelota
there are present in addition prehensile tentacles (" Greiftentakel "),
which end in a fine point. The exterior of the tentacle is clothed
by a delicate pellicle, continuous with that of the body, and forming
in the suctorial tentacles a sheath or tube, from the end of which
the sucker protrudes. The tentacles are slowly retractile. When
expanded they appear homogeneous ; but in the process of retrac-
tion they exhibit a spiral marking, due apparently to creases and
folds in the pellicle, and not to be interpreted as indicating the
presence of myonemes. The tentacles are used for the capture of
prey, which consists chiefly of ciliates. As soon as the sucker-like
extremity of a tentacle touches a ciliate it is held fast ; the substance
of the prey is then
slowly absorbed by the
tentacle, and passes as
a stream of granules
down the axis of the
tentacle. During this
process the ciliate re-
mains alive, with cilia
movin gand contractile
vacuoles pulsating, until
about half its substance
is absorbed (Filipjev).

In the genus Rhyn-
cheta there is but a
single tentacle of great
length ; in Urnula (Fig.
191), one or two. Other
genera bear usually
many tentacles, which
may be distributed
evenly over the body-
surface, or, more commonly, occur in special regions of the body
or are distributed in tufts and patches. In Dendrocometes the
tentacles occur in bunches borne on branches or arm-like processes
of the body-wall.

Ishikawa describes in the larger prehensile tentacles of Ephelota buetschliana
a system of filaments, consisting of fine threads running parallel to one
another in pairs and continued into the body as far as its base. The filaments
stain deeply with iron-haematoxylin. According to Collin (877), each such pair
of filaments is in reality the optical section of a fine tube. A suctorial tentacle,
according to Collin, represents a deep invagination of the ectoplasm, opening
at its innermost end into the endoplasm like the cytopharynx of a ciliate.
The prehensile tentacles, on the other hand, are special formations of a
different kind, simple evaginations of the body-wall, pseudopodial in nature,
and containing from one to three axial filaments, the number increasing with
the age of the tentacle.

FIG. 191. — Urnula epistylidis, epizoic on Dendro-
soma radians. A, B, Individuals with one or two
tentacles respectively ; 0, formation of a bud
(g) ; D, the same seen in transverse section
passing through the bud and the macronucleus
of the parent ; E, free -swimming larva ; F, en-
larged view of the single tentacle, showing the
spiral striation. After Hickson and Wads-
worth (886).

458 THE PROTOZOA

When a ciliate — for example, a Paramecium — is captured by the tentacle,
its protoplasm streams down the tentacle to form a mass in the endoplasm
of the acinetan. Before the process of suction is complete the mass breaks
up into smaller masses, and these again into still smaller ones, which are
carried away by the cyclosis of the endoplasm, and other masses of small
size continue to be formed at the base of the tentacle. Round each of these-
food-masses a fluid vacuole is formed, in which the ingested protoplasm is
for the most part dissolved, becoming reduced to a few granulations. The
vacuole then gives off fluid and diminishes in size, and the contents are con-
centrated to form a refractile body. Three kinds of such refractile bodies are
formed: so-called "colourless bodies" which stain feebly with nuclear stains,
and are derived from the protoplasm of the prey ; " tinctin-bodies," staining
deeply, and originating, as described by Martin, from the chromatin of the
prey ; and others, found in some acinetans, derived from the chlorophyll of
green ciliates and algal spores devoured by the animal. If a Tocophrya bo
starved, the refringent bodies are slowly absorbed, and the protoplasm becomes
quite clear (Filipjev). Hence the refringent bodies that arise from the diges-
tive vacuoles represent reserve -material ; there appears to be no defsecation
of indigestible residues.

The nature and origin of the tentacles of acinetans have been much dis-
cussed, and some authors have sought to derive them from cirri or cilia.
Schuberg (44) points out, however, that the structure of the tentacles is quite
the opposite of that of the cilia ; in a cilium the axial portion is of firm con-
sistence, the superficial layer is fluid, while in a tentacle the axis is fluid and
the superficial sheath is of firm texture. Collin (877) considers that the pre-
hensile tentacles are modifications or adaptations of a pseudopodium-like
process ; on the other hand, he regards the suctorial tentacles as organs of
quite a different kind, more like the cytostome of a ciliate than anything
else ; they may be considered each as a cytostome which has grown out from
the body on a slender process or stalk (compare also Hickson, 826).

In correlation with their sedentary habits, the organization of the
Acinetaria is greatly simplified as compared with the Ciliata, and
the remarkable structural and functional differentiation of the
ectoplasm seen in the Ciliata is wanting altogether in Acinetaria,
in which the ectoplasm is relatively a feebly-developed layer. Con-
tractile vacuoles are usually present, one or more in number. As
in Ciliata, the macronucleus exhibits a great variety of forms. One
of the most remarkable is seen in the colonial form Dendrosoma,
where the macronucleus is branched to the same degree as the
colony, throughout which it extends continuously.

The methods of reproduction are more varied, and exhibit a
greater specialization, in the Acinetaria than in the Ciliata. Simple
binary fission in the adult condition is rare in acinetans. Collin (881 ) ,
however, has observed division into two or four within a cyst in
Podophrya fixa. The fission usually takes the form of bud-forma-
tion. The buds may be formed either on the exterior of the body
or in the interior in special brood-cavities, and they may be pro-
duced in either case singly and successively or in batches or relays
of several at a time. The bud is usually a simple outgrowth of the
cytoplasm containing a prolongation budded off from the macro-
nucleus, and one of the daughter-nuclei derived from a division of
the micronucleus. At first a simple cell without structural differ-

THE INFUSORIA

459

entiation, the bud is set free with a complete or partial coat of
cilia as a free-swimming " embryo," " larva," " swarm-spore "
(Schwarmer), or " gemmula." The larva often becomes parasitic
within the body of another Infusoriaii (Fig. 192), multiplying there
by binary fission. Finally it becomes free again, swims away,
attaches itself in a suitable locality, and develops into the adult
form.

The ciliated larvae of acinetans exhibit various types of ciliation,
commonly classed as peritrichous (Fig. 193, A, B}, holotrichous
(Fig. 191, E), and hypotrichous. Collin (882) has studied recently
the morphology of the different types of larvae.

c.e

FIG. 192. — A and B, Stylonychia mytilus infested by parasitic Acinetans. N, N,
Maeronuolei of the Stylonychia ; P, parasitic Acinetan embryo from which
arise small ciliated larvae (c.e) which swim off and develop into the adult
free -living Acinetan. After Stein.

The most primitive and commonest larval type of larva amongst the
Acinetaria is very similar to a free-swimming stage of a Vorticellid. It has
a principal axis round which the body is radially symmetrical, with an upper
pole (posterior in movement) bearing a rudimentary adoral zone, and a lower
(anterior) pole bearing a mass of secretion or a sucker, indicating the future
point of fixation and representing the scopula of the Vorticellid ; the body is
surrounded by several rings of cilia forming a zone more or less equatorial
in position. Such a form, while retaining its radiate symmetry, may become
either lengthened or shortened to a remarkable degree in the direction of the
principal axis ; in the elongated forms the rings of cilia may increase in
number until they cover the whole body, thus producing the holotrichous
type. On the other hand, the body may become elongated in the morpho-
logically transverse plane, and acquire a bilateral symmetry, with a dorsal
surface representing the primitive upper pole and bearing the rudimentary
adoral zone, and a ventral surface, with the sucker in the middle of it, repre-
senting the primitive lower pole ; secondary anterior and posterior extremities
are now distinguishable in relation to progression, but representing opposite

460

THE PROTOZOA

points of the primitive transverse plane. In such a type the zones of cilia
run obliquely along the sides of the body, or may be confined to the ventral
surface, where they run a more or less elliptical course round the sucker,
thus producing the hypotrichous type seen in Ephelota gemmipara and in the
persistent larval form Hypocoma acinetarum. Examples of holotrichous
larva? are seen in Tocophrya limbata and Urnula epistylidis (Hickson and
Wadsworth, 886). In all cases the principal or dorsiventral axis of the larva
becomes the principal axis of the adult ; in the process of budding, however,
the principal axis of the bud arises at right angles to that of the parent, accord-
ing to Collin ; Filipjev, however, does not confirm this for Tocophrya quadri-
partita.

The remarkable form Tachyblaston described by Martin lives in the adult
condition attached to the stalk of Ephelota ; it produces buds each with a
single tentacle, which creep up the stalk of the Ephelota and penetrate into
the body, becoming parasitic in it and multiplying by fission to produce
ciliated larva?, which in their turn swim out, attach themselves to the stalk
of the Ephelota, and become adult forms.

The conjugation of the Acinetaria conforms in general to the
type of the process seen in Ciliata, as regards cytological details.
Conjugation may take place between two individuals fixed near

FIG. 193. — Free-swimming larva of Dendrosoma radians. A, Side veiw ; B, viewed
from above ; G, older larva with the first rudiments of the tentacles beginning
to appear. After Hickson and Wadsworth (886).

together (Fig. 190, G) ; then a lobe or outgrowth may be formed
from one individual, which meets a similar outgrowth from the
other, thus establishing contact. On the other hand, as in Peri-
tricha, conjugation may take place between a fixed, ordinary indi-
vidual and a free-swimming bud or larva liberated from another
adult individual (Martin ; Collin, 879). In Dendrocometes the
macronuclei come into contact during conjugation, but separate
again (Hickson and Wadsworth).

Classification. — The Acinetaria are divisible into eight families (cf.
Doflein, 7).

1. Hypocomidce, for the single, somewhat aberrant genus Hypocoma, which
is free-swimming, ciliated on one surface, and with a single suctorial tentacle —
possibly a persistent larval form (see Collin, 877).

2. Urnulidce. — With or without a house, with one or few tentacles. Rhyn-
cheta, Urnula (Fig. 191).

3. Metacinetidce. — With a stalked house opening at the upper end for the
exit of the tentacles. Metacineta.

THE INFUSORIA 461

4. Podophryidce. — Stalked or sessile, with no house and with numerous
tentacles. Sphcerophrya, Podophrya (Fig. 190), Ephelota.

5. Acinetidce. — Stalked or sessile, with a house of simple form and wide
aperture, and with numerous tentacles, all knobbed. Tocophrya (Fig. 190),
Acineta (Fig. 10).

6. Dendrosomidce (Trichophryidce). — Sessile, without a house ; tentacles
knobbed, arranged in tufts or branches. Trichophrya, Dendrosoma, Lernceo-
phrya (Perez), Ehabdophrya (Chatton and Collin), Astrophrya (Awerinzew).

7. Dendrocometidce. — Flat forms with numerous branched arms on the ends
of which the suckers occur. Dendrocometes.

8. Ophryodendridce. — Marine stalked forms with numerous short tentacles
concentrated on proboscis-like processes. Vermiform individuals also occur
(p. 455). Ophryodendron.

Affinities of the Acinetaria. — The presence of cilia in the young stages, the
possession of distinct vegetative macronuclei and generative micronuclei, and
the process of conjugation, similar in all essential details to that of the Ciliata,
can leave no doubt as to the position of the Acinetaria in the class Infusoria,
and their affinities with the Ciliata. Collin, in a series of interesting studies,
has drawn attention to many points indicating a close relationship between
Acinetaria and Vorticellids, more especially the structural homologies between
the larvae of the one and the free-swimming stages of the other group ; for
example, the peritrichous arrangement of the cilia, the rudimentary adoral zone
at the posterior pole, and the fixation by means of a scopula like organ at the
anterior pole, points especially well seen in the larva of Tocophyra cyclopum.

Bibliography. — For references see p. 502.

CHAPTER XVIII

AFFINITIES AND CLASSIFICATION OF THE MAIN
SUBDIVISIONS— DOUBTFUL GROUPS

IN the foregoing chapters the Protozoa have been dealt with
systematically, grouped in a somewhat conservative manner under
the four old-established and generally-recognized classes. At the
same time it has been pointed out that one class at least — namely,
the exclusively-parasitic Sporozoa — comprises two subclasses which
are quite distinct from one another, and are descended, in all
probability, from ancestors differing greatly in characters and
affinities. And in the case of the three remaining classes, con-
sisting mainly of free-living, non-parasitic forms, two which exhibit
more primitive characters — namely, the Sarcodina and Mastigophora
— are connected with one another by transitional forms which
render the distinction between them very arbitrary (p. 213) ; while
the third, the highly-specialized Infusoria, are linked closely by
structural characters and by transitional forms to the Mastigophora.
Many authorities on the Protozoa have put forward schemes of
classification which are intended to express the affinities and inter-
relationships of the chief groups in a clearer and more satisfactory
manner than the fourfold classification generally recognized. The
systems proposed have taken the form either of subdividing the
Protozoa into more than four classes or of uniting the recognized
subdivisions into a smaller number of categories.

Rolleston and Jackson (15) divide the Protozoa as a whole into three groups :
(1) the Rhizopoda (= Sarcodina) ; (2) the Endoparasita (=Sporozoa); and
(3) the Plegepoda, " referring to their mode of progression by means of a
rapidly - repeated stroke (rr\rjyrj) of vibratile processes," to comprise the
Mastigophora and Infusoria.

Doflein (891) recognizes two principal stems in the Protozoan phylum:
(1) the Plasmodroma, to include the Sarcodina, Mastigophora, and Sporozoa,
organisms that make use of locomotor organs which represent true pseudo-
podia, or their derivatives or modifications ; and (2) the Ciliophora, comprising
the Ciliata and Suctoria, in which the locomotor organellse are cilia. The
obvious criticism of this scheme is that, whatever opinion may be held as to
the desirability of drawing a line between the Infusoria, so highly specialized in
many respects, and other Protozoa, the distinctive character chosen is not a
happy one, since whatever may be predicated of flagella as derivatives of pseu-
dopodia applies, apparently, with equal force to cilia.

462

CLASSIFICATION OF THE MAIN SUBDIVISIONS 463

Hartmann (892) recognizes six classes of the Protozoa : Class I., the Sarco-
dina, including four subclasses — namely, Rhizopoda, Heliozoa, Radiolaria,
and Mycetozoa ; Class II., the Cnidosporidia, including Microsporidia, Sarco-
sporidia, Myxosporidia, and Actinomyxidia ; Class III., the Mastigophora,
including the Rhizomastigina, Protomonadina, Binucleata, Chromomonadina,
Euglenoidea, and Phytomonadina, the order Binucleata including the Haemo-
flagellatcs and the Haemosporidia with the exception of the haemogregarines ;
Class IV., the Telosporidia, including the gregarines, coccidia, and haemo-
gregarines ; Class V., the Trichonymphida ; Class VI., the Infusoria. With
regard to this classification, the order Binucleata has been dealt with at
length above ; it only remains to say that the isolated position given to the
Trichonymphida appears to express the defective state of knowledge con-
cerning the affinities of these peculiar parasites, rather than their true taxo-
nomic importance.

A number of radical changes in the classification of the Protozoa are pro-
posed by Awerinzew (890). With Hartmann he unites the Haemoflagellates
and Haemosporidia in an order Binucleata to be placed in the Flagellata.
The class Sporozoa is to be entirely abolished. The order Amcebina
(Amoebaea) is removed by him entirely from the Sarcodina, which will then
comprise only the Foraminifera and some Heliozoa. The Amcebina are to be
put with the Flagellata as the Amceboflagellata, a group from which all other
Protozoa are supposed to have arisen, and from which the Amcebina branch
off in one direction, the Flagellata and Dinoflagehata in another. The gre-
garines are believed by Awerinzew to be connected on the one side with the
Amcebina, on the other with the Coccidia. In the Neosporidia, the Sarco-
sporidia are regarded as allied to Flagellata ; the Myxosporidia, Microsporidia,
and Actinomyxidia, are considered not to be Protozoa at all ; the Haplo-
sporidia are to be placed provisionally as an independent group taking origin
from Amcebina. For the Infusoria, it is suggested that they take origin from
amceboflagellate ancestors rather than from true Flagellata.

The object of what is termed a natural as opposed to an artificial
system of classification is to endeavour to express by the arrange-
ment of the groups the affinities of the living organisms concerned,
and more especially the genetic relationships of one to another on
the theory of evolution — that is to say, on the assumption or belief
that forms now existing are descended from older ancestral forms,
and that any two existing forms are descended from a common
ancestral form more or less remote, according as the two existing
forms in question have diverged more or less widely from one another.
The foundation of a natural classification is therefore the phytogeny
of the groups dealt with — that is to say, their pedigrees and lines
of descent, so far as they can be traced. Phylogeny must, however,
always be a matter of speculation, and to a large extent of personal
opinion, rather than of direct observation. It is only possible to
infer from the study of existing species what the ancestral forms
may have been like, since it is unnecessary to point out that no
form can be the ancestor of another species existing at the same
time. The most that can be said of two co-existing species is
that one of them may be believed to have diverged much less in
its characters from the common ancestral form than the other.
When, therefore, a given form is said to have an amoebic or a cer-
comonad ancestry, it is not intended to imply by that statement

464 THE PROTOZOA

that the ancestor was Amoeba proteus or Oercomonas crassicauda,
but only that it was a form such that, if it existed at the present
day, it would be referred by its characters to the genus Amoeba or
Cercomonas, as the case might be.

The data for drawing phylogenetic conclusions in Protozoa con-
sist entirely of comparisons between the structure and life-history
of the various existing forms. Palaeontology gives no assistance,
since only skeletons are preserved as fossils. All that can be
learned from the geological record is that the differentiation of the
main groups must have taken place at an immeasurably remote
period of the earth's history, since skeletons of Foraminifera and
Radiolaria — groups of which the structure and life-history indicate
a long pedigree — are found in the earliest fossiliferous strata. It is
little wonder, therefore, that the phylogeny of the Protozoa is a
subject on which the most opposite opinions are held, as is apparent
from the classificatory systems cited above. There can be no
finality in a phylogenetic theory, nor, consequently, in any scheme
of classification put forward. Both the one and the other express
merely the state of current knowledge, and may be expected to
undergo modification as knowledge advances.

It is impossible to discuss here at length the phylogeny and
classification of the Protozoa, and only a few guiding principles
can be put forward. From a general survey of the phylum, it may
be claimed first of all that the Protozoa constitute a compact group
with definite characters, not a mere receptacle into which can be
put anything and everything of microscopic dimensions which is
not a bacterium, a fungus, or a parasitic worm, as some writers
seem to think. Common to all Protozoa in at least the principal
stages of the life-cycle is the differentiation of the body into distinct"
nucleus and cytoplasm — that is to say, the possession of that type
of organization to which I have proposed to restrict the application
of the term cell. Doubtless there are, or have been, transitions
from this type to the simpler grade of organization characteristic
of the bacteria and allied organisms, but such transitions must be
sought for outside the phylum Protozoa.

The essential unity and homogeneity underlying the innumerable
differentiations of form and structure in the Protozoa may be taken
to mean that the phylum as a whole is descended from a common
ancestral form, and the first problem is, then, to attempt to form
some notion of what the ancestor was like. In dealing with the
more specialized forms, such as those constituting the Infusoria or
the two principal subdivisions of the Sporozoa, it has been pointed
out that each group appears to be derived either from flagellate or
sarcodine ancestors. In reviewing the Mastigophora and Sarcodina,
it was further pointed out that, greatly as the typical representa-

CLASSIFICATION OF THE MAIN SUBDIVISIONS 465

tives of the two classes may differ, there are forms of which the
systematic position is quite arbitrary. In such a form as Pseudo-
spora, it becomes almost purely a matter of opinion or taste which
phase of the life-cycle is to be regarded as the " adult " form
determining the class in which the genus is to be placed.

Thus, all paths of evolution in Protozoa appear to lead back-
wards to one or the other of the two forms that occur so frequently
in the actual development as the earliest phases — the amcebula
and the flagellula. Most of those wha have speculated on the
phylogeny of the Protozoa have, consequently, regarded the an-
cestral form of the phylum as one combining amoeboid and flagellate
characters. Biitschli (2) considered that the Rhizomastigina re-
present more nearly than any other existing group the primitive
type of Protozoon. Since then, however, the life-cycle of the
mastigamcebse has been studied, and it is seen that the adult
amoeboid form is preceded in development by a simpler monad
form (p. 266, Fig. 112), which makes it very doubtful if the mastig-
amceba itself can be taken as a primitive type. Awerinzew (890)
also regards an " amceboflagellate " type as the primitive stock
of Protozoa, which gave rise to all existing groups, and became
differentiated into the Amcebina on the one hand, the Flagellata
on the other.

If an organism possesses two kinds of locomotor organs — pseudo-
podia and flagella — it is reasonable to suppose that a still more
primitive and ancestral form would have possessed only one of
these two kinds of organs. It has been seen that there is a gradual
transition from pseudopodia to flagella, the intermediate type of
organ being a pseudopodium (axopodium) with a firm, rigid, or
elastic secreted axis. The question then arises, Which end of the
series is to be put first, the flagellum or the pseudopodium ? Inas-
much as flagella are found commonly in bacteria, it might be argued
that they represent the most primitive type of locomotor organella,
and that a simple flagellate monad would represent most nearly the
ancestral type of organization in Protozoa. Then it must be sup-
posed that the formation of pseudopodia is a secondary character,
acquired by the ancestral form, and the pseudopodia themselves
would represent either simple outgrowths of the naked body (lobo-
podia) or modifications of flagella (axo podia).

Having regard, however, to the manner in which flagella them-
selves arise — as simple outgrowths from the body — and to the fact
that their structure and mode of action are apparently of a much
more specialized type than those of pseudopodia, the conclusion
seems irresistible that pseudopodia preceded flagella in evolution.
We may, then, regard as the most ancestral type in the Protozoa
a minute amoebula-form, in structure a true cell, with nucleus and

30

466 THE PROTOZOA

cytoplasm distinct, which moved by means of pseudopodia ; but
it must be supposed that some of the pseudopodia very soon under-
went modifications which resulted in the acquisition of true flagella,
and thus arose at a very early stage of evolution the flagellula or
monad-form. In all probability these earliest monads were forms
with an amoeboid body, most nearly represented at the present
day by such forms as Cercomonas (Fig. 114) or the flagellulae of
Mycetozoa (Fig. 98). From such forms arose the Sarcodina and
their derivatives (Neosporidia) by loss of flagella and specialization
of the amoeboid form in the adult, and the Mastigophora and their
derivatives (Telosporidia, Infusoria) by specialization of the flagellar
apparatus combined with the acquisition of a cortex and loss of
amoeboid movement.

If the foregoing phylogenetic speculations be accepted, it is clear
that in a natural classification of the Protozoa the Sporozoa must
be abolished as a class, and the two groups comprised in them
must either be raised to the rank of independent classes or dis-
tributed amongst the others — the Telosporidia placed near the
Mastigophora, the Neosporidia near the Sarcodina. The primary
subdivision of the Protozoa, if it is to represent the first branching
of the ancestral stem, should be one which places on one side the
Mastigophora, Telosporidia (better Rhabdogenise), and Infusoria,
on the other the Sarcodina and Neosporidia (better Amcebogeniaa).
Beyond this point it is scarcely profitable at the present time to push
phylogenetic speculations farther.

In conclusion, two groups of organisms require brief mention —
the Spirochaetes and the Chlamydozoa — since by many authorities
they have been referred to a position in or near the Protozoa.

THE SPIROCHAETES.

Under the name " Spirochaetes " are grouped a number of or-
ganisms, free-living or parasitic, with flexible bodies of slender,
thread-like form, concerning the nature and systematic position of
which a great deal of confusion has existed of recent years, due
chiefly to conflicting statements with regard to the facts of their
structure and methods of reproduction. The group comprises five
principal types, regarded each as of generic rank :

1. Spirochceta sens, strict., a name given by Ehrenberg in 1833
to a relatively large, free-living form, S. plicatilis. Other species
of the genus have been described. For a full account, see Zuelzer
(904).

2. Cristispira, a name proposed by Gross (897) for a number of
species parasitic in the digestive tract or crystalline style of Lamelli-
branch molluscs, and characterized by the possession of a crest or

.

CLASSIFICATION OF THE MAIN SUBDIVISIONS 467

ridge, commonly but wrongly termed an " undulating membrane,"
running the length of the body. The type of the genus is C. bal-
bianii, originally named by Certes Trypanosoma balbianii, from the
crystalline style of the oyster.

3. Saprospira, Gross (898), for free-living, saprophytic forms
similar in structure to Cristispira, but without the crest.

4. Spiroschaudinnia, the name proposed by Sambon for the
many species of minute spirochaetes parasitic in the blood of verte-
brates and in various invertebrates. Such are $. recurrentis
(=obermeieri), parasite of human relapsing fever; S. duttoni,
parasite of African relapsing fever ; S. gallinarum of fowls ; S.
anserina of geese ; and numerous other species from various hosts.
In structure the body of these species appears to be little, if any-
thing, more than a flexible thread of chromatin ; but the develop-
ment indicates rather that, as in the genus Cristispira, the interior of
the body is divided into minute segments or chambers. The species
parasitic in blood are transmitted by the agency of blood-sucking
arthropods. S. duttoni, for example, is transmitted by a tick— -
Ornithodoros moubata — which lives in the mud-floors of huts or in
the soil in spots where caravans camp habitually. The spirocheetes
are taken up from human blood by the adult ticks, and pass through
the egg into the next generation of nymphs,* which transmit the
infection to human beings.

5. Treponema, the name proposed by Schaudinn for T. pallidum,
the spirochsete of syphilis discovered by him. A second species —
T. pertenue, the parasite of yaws (frambcesia) — is also recognized.
Structurally this type is very similar to the last.

Some authors — for instance, Gross (899) and Dobell (895) — consider that
there is " no valid reason for drawing a generic distinction between Treponema
pallidum and such forms as ' Spirochceta'' recurrentis, etc." Gross combines
Types 4 and 5 under the name Spironema proposed by Vuillemin ; but
since this name is preoccupied, Dobell places them together in Schaudinn's
genus Treponema.

The forms parasitic in the blood of human beings and other vertebrates
were generally regarded as Bacteria of the genus Spirillum, or at least of the
section Spirillacea, until quite recent years, and the diseases caused by them
were spoken of as spirilloses. The chief points of difference between the
spirilla of relapsing fevers and those of the ordinary type were the flexibility
of the body in the former and the failure to grow them in cultures. The con-
fusion prevailing at present originated with Schaudinn's famous memoir on
the blood- parasites of the Little Owl (132). While, on the one hand, it is to
Schaudinn's credit to have recognized the affinities of the parasitic " spirilla "
to Ehrenberg's free-living genus Spirochceta he was, on the other hand, misled
by the superficial resemblance between spirochsetes and certain small, slender
forms of trypanosomes, which again he connected, quite erroneously, with
the life-cycle of Leucocytozoon (see p. 370). Schaudinn therefore regarded
the spiroghajtes as Protozoa allied to trypanosomes, and endeavoured to
prove a similar type of organization in both classes of organisms : a nuclear

* The six -legged larval stage is suppressed — that is to say, passed through in
the egg — in this species of tick.

468 THE PROTOZOA

apparatus with kinetonucleus and trophonucleus, and a locomotor apparatus
with flagellum and undulating membrane. Schaudinn further constructed
a hypothetical form of " Urhaemoflagellat " connecting the spirochaete and
trypanosome type of organization ; he put forward the suggestion (903) that
"as the general structural plan of a trypanosome (nuclear and locomotor
apparatus) may be found realized in various groups of Protozoa as a transitory
developmental condition (comparable somewhat to the gastrula- condition
in the Metazoa), so also the spirochaete may crop up occasionally as a morpho-
logical type in the development of Protozoa, and as a developmental stage
may indicate to us phylogenetic relations."

Schaudinn lived long enough, fortunately, to retract many of his state
ments with regard to the structure of spirochaetes, and acknowledged that the
trypanosome-type of structure was not to be made out in the minute parasitic
spirochaetes. Nevertheless, since his time the investigators of these organisms
have been divided into two camps — those who hold fast to Schaudinn's theory
of the spirochaetes as Protozoa, and those who class them with Bacteria,
respectively ; it being generally assumed, for some unknown reason, that it
they are not Protozoa they must be Bacteria, or vice versa. A third set of
authorities compromise by placing the spirochaetes in an intermediate position
between the two groups.

In considering the question of the affinities of the spirochsetes, attention
has been directed not only to their structure, but also to their life-history ;
and a hot controversy has raged with regard to their mode of fission, whether
it takes place longitudinally, as in a trypanosome, or transversely, as in a
bacterium. Investigators contradict each other flatly with regard to this
point ; but from the most recent investigations it seems probable, at least,
that the division is always transverse, and that the appearance of longitudinal
division is due to the peculiar method of " incurvation :' described by Gross
(Fig. 194). A spirochaete about to divide grows greatly in length, and one
end of the body doubles back on itself, continuing to do so until the recurved
limb of the body is of the same length as the remainder ; the two halves twist
round each other and produce an appearance which may be mistaken easily
for longitudinal fission ; but the actual division of the body takes place at the
point where it is bent over, and is transverse.

With regard to the development, nothing has been found in the least con-
firmatory of Schaudinn's statements with regard to " Spirochceta ziemanni,"
with the sole exception of the statements of Krzysztalowicz and Siedlecki (901),
who profess to have seen trypanosome-stages in the development of Treponema
pallidum ; but their statements are entirely unconfirmed by other investi-
gators. Of a very opposite type are the statements of Leishman (902) with
regard to the development of S. duttoni in the tick. The spirochaete appears
to break up into minute masses of chromatin, " coccoid granules," in the
ova and tissue-cells of the tick. The coccoid granules appear to develop into
spirochaetes again.

The observations of Leishman have recently been fully confirmed by the in-
vestigations on the development of Spiroschaudinnia gallinarum published by
Hindle (900), who gives a useful diagram of the entire life-history. Bosanquet
(894) also observed the formation of coccoid bodies in Cristispira anodonice
by the segmentation of the elongated body into a number of coccoid bodies
like a string of beads. A development of this type suggests very strongly
affinities with bacteria, but none whatever with Protozoa of any class. The
coccoid grains may be compared with the spore -formation in bacteria, and
with that described by Gross (898) in Saprospira grandis. In all cases, through-
out the series of living beings, wherever an organism exhibits in its fully-
developed " adult " stage peculiarities of a special kind, it is above all to
the early developmental forms that the naturalist turns for indications of the
true affinities of the organism in question.

Recently the structure of spirochaetes has been studied carefully by Gross
(897, 898), Zuelzer (904), and Dobell (895), by means of proper cytological
methods of technique. The results show a complete difference in every

CLASSIFICATION OF THE MAIN SUBDIVISIONS 469

respect between spirochaetes and trypanosomes and other flagellates. In the
words of Dobell, " the nuclear and cytoplasmic structures are wholly different ;
a trypanosome has a flagellum, a spirochaete has none ; the crista is not an
undulating membrane ; the cell-membranes are not similar ; and, moreover,
the method of division is quite different in the two organisms."

Doflein (7) places the spirochsetes as a group named the Pro-
flagellata, supposed to be transitional from bacteria to flagellates.
Zuelzer (904) takes a similar view, rejecting, however, any affinity
between spirochsetes and Hartmann's " Binucleata." Awerinzew
(890) puts forward the remarkable suggestion that the Flagellata
" pass on into different Binucleata, and end with the Spirochceta

FIG. 194. — Stages in the division of Cristispira pcctinis. A, B, Two successive
stages of the incurvation ; 0, incurvation complete ; D, division of the body
at the point where it is bent back ; E, F, separation of the two daughter-
spirochsBtes. After Gross (897).

(sic)" from which it would appear that he regards the spirochsetes
as the last product of the line of evolution that produced the
trypanosomes and allied forms.

For the various reasons that have been set forth above, it appears
impossible to include the spirochsetes any longer in the Protozoa.
Dobell regards them as "an independent group of unicellular
organisms which show very little affinity to any other group."
Gross, on the other hand, considers that the Spironemacea — i.e.,
the genera Cristispira, Saprospira, and Spironema, in the sense in
which this genus is understood by him (see above)— form a family
which can be ranked in the bacteria, but which is related to the
Cyanophycese, especially the Oscillatorise.

470 THE PROTOZOA

THE CHLAMYDOZOA.

The name Chlamydozoa of Prowazek (Strongyloplasmata, Lip-
schiitz) was proposed in order to include in the first place a class of
highly problematic organisms believed to be the causes of certain
diseases of man or animals. It is not yet certain exactly what
diseases are to be referred to Chlamydozoa. According to Hart-
mann (909), undoubted chlamydozoal diseases are vaccinia and
variola, trachoma, and molluscum contagiosum, amongst human
beings, and in birds epithelioma contagiosum and diphtheria.
Further diseases probably attributable to Chlamydozoa are hydro-
phobia, scarlet fever, measles, foot-and-mouth disease of animals,
and " Gelbsucht " of silkworms. In all theue diseases the virus has
certain common properties, while exhibiting specific peculiarities
in each case. It can pass through ordinary bacterial filters without
losing its virulence, and it produces characteristic reaction-products
or cell-inclusions in the infected cell.

In order to understand why these organisms should be men-
tioned hi a book dealing with Protozoa, the subject is best dealt
with in an historical manner. The advances in the knowledge of
the diseases mentioned may be summarized briefly in four principal
stages :

1 . Various investigators at different times have made known the
existence of peculiar cell-inclusions in the infected cells in a certain
class of diseases, inclusions which have been known by the names
of their discoverers — for instance, in trachoma (Prowazek's bodies),
vaccinia (Guarnieri's bodies), scarlet fever (Mallory's bodies),
hydrophobia (Negri's bodies), etc.

.2. By many investigators the characteristic cell-inclusions were
identified as the actual parasitic organisms causing the disease.
They received zoological names, were referred to a definite position
in the ranks of the Protozoa, and attempts were made to work out
and construct a developmental cycle for them. The supposed
parasites of molluscum contagiosum were referred to the coccidia ;
those of vaccinia and variola were given the name Cytoryctes ; of
hydrophobia, Neuroryctes ; of scarlet fever, Cyclasterium.

Calkins (908) studied in great detail the cell-inclusions of vaccine
and smallpox, and described a complete developmental cycle, in its
main outlines as follows : The primary infection is brought about,
probably, at some spot on the mucous membrane of the respiratory
or buccal passages by air- borne germs (spores). After active pro-
liferation at the seat of the primary infection, the parasites are
carried to all parts of the body in the circulation, probably during
the initial fever. These two early phases are hypothetical. The
third Jphase is the appearance of the parasites in the cells of the

CLASSIFICATION OF THE MAIN SUBDIVISIONS 471

stratified epithelium of the epidermis. In this situation they run
through two cycles — the one cytoplasmic, the other intranuclear.
The first is the vaccine-cycle, and is the only part of the develop-
ment of which the harmless vaccine-organism is capable ; the
variola-organism, however, after passing through a vaccine-cycle,
proceeds to the extremely pathogenic intranuclear cycle.

The vaccine-cycle, according to Calkins, begins with the appear-
ance of " gemmules " in the cytoplasm of the cells affected. Each
gemmule is a minute grain of chromatin without cytoplasm of its
own at first, but as it grows a cytoplasmic body is formed. When
full-grown, the parasite sporulates by fragmentation of its nucleus
into a great number of grains, which, as gemmules, pass into other
cells and repeat the development already described. Several
generations of this type may succeed each other before giving rise
to the next type.

The intranuclear variola-cycle begins in the same way with
gemmules, which, however, penetrate into the nucleus, and develop
a cytoplasmic body. According to Calkins, they become sexually
differentiated, and produce gametes which conjugate. The final
result is the production of numerous spores, which are probably the
means of spreading the infection.

Calkins referred Cytoryctes to the Microsporidia. Now, however,
he inclines to the opinion that the genus should be placed amongst
the E/hizopods (4).

Negri (910) also describes a developmental cycle for Neuroryctes
hydrophobice, which he regards as a true Protozoon, and which
Calkins refers also to the Rhizopoda. Siegel (914) describes under
the name Cytorhyctes organisms of a type perfectly different from
those described by Calkins. He distinguishes four species — Cyto-
rhyctes vaccinice of vaccine and smallpox, C. luis of syphilis, G. scarla-
tinas of scarlet fever, and C. aphtharum of foot-and-mouth disease.

3. The parasitic life-cycles described by Calkins and others have
been criticized by a number of investigators, who have maintained
that the bodies in question are not Protozoa, nor even independent
living organisms at all, but merely degeneration-products of the cell
itself, provoked by a virus yet to be found. Thus, with regard to
Guarnieri's bodies (Cytoryctes) of vaccine, it is maintained by Foa,
Prowazek, and others, that they consist of nucleolar substance
(plastin) extruded from the nucleus ; that they have no definite
developmental cycle ; and that infection can be produced by lymph
in which Guarnieri's bodies have been destroyed, or by tissue in
which they are not present. With regard to the Negri bodies,
Acton and Harvey (906) come to the same conclusions, and state
that similar nucleolar extrusions can be brought about also by
other stimuli than the rabies- virus.

472 THE PROTOZOA

4. The foregoing sceptical phase has been succeeded by the positive
belief that the true parasitic organism in these diseases consists of
certain minute bodies — the Chlamydozoa or strongyloplasms.*

The chief characteristics of the Chlamydozoa, according to
Prowazek and Lipschiitz (913), are, first, their minute size, smaller
than any bacteria hitherto known, enabling them to pass the
ordinary bacterial filters ; secondly, that they develop within cells,
in the cytoplasm or nucleus, and produce characteristic reaction-
products and enclosures of the cell (their position within the cell
is not the result of phagocytosis) ; thirdly, that they pass through
a series of developmental stages, and are specially characterized by
their mode of division, which is not a simple process of splitting,
as in bacteria, but is effected with formation of a dumb-bell-shaped
figure, as in the division of a centriole. Two dots are seen con-
nected by a fine line like a centrodesmose, which becomes drawn out
until it snaps across the middle, and its two halves are then re-
tracted into the body. Chlamydozoa have not yet been grown
successfully in cultures, but infections can be produced with pure
colloid- filtrates, free from bacteria, but containing the minute
bodies themselves. They are characteristically parasites of epi-
blastic cells and tissues.

As an example of the development of a chlamydozoon may be
taken that of the vaccine- virus, which, according to Prowazek (913)
and Hartmann (909), is briefly as follows :

1. The infection begins and ends with numerous "elementary
corpuscles " (gemmules of Calkins ?), which occur both within and
amongst the cells. They are very minute, and can pass bacterial filters.

2. Within the cells the elementary corpuscles grow into the
larger " initial bodies."

3. The infected cell extrudes nucleolar substance — plastin — from
its nucleus, which envelops the parasites as in a mantle (hence the
name Chlamydozoa, from x^a/*vs, a mantle), thus producing in the
case of vaccine the characteristic Guarnieri's bodies, in which the
parasites multiply. It is this mantle of nucleolar substance,
apparently, which represents the " cytoplasm " of Cytoryctes, as
described by Calkins.

* The name Chlamydozoa, as denoting a class of microscopic organisms, must
on no account be confused with the names Cytoryctes, Neuroryctes, etc., which
represent the generic names of the supposed parasites of variola and rabies re-
spectively. To those who regard Cytoryctes, etc., as true organisms, the Chlamydo-
zoa are merely chromidia or dots of chromatin in the body of the parasite ; to
those who believe in the Chlamydozoa as complete organisms, Cytoryctes, etc.,
are cell-inclusions or degeneration-products of the nucleus. The conceptions
implied in the words Chlamydozoa and Cytoryctes respectively are antagonistic
and mutually destructive ; if the one is a reality, the other is non-existent. It is
altogether incorrect to speak of Cytoryctes, Neuroryctes, etc., as genera of Chlamv-
dozoa.

CLASSIFICATION OF THE MAIN SUBDIVISIONS 473

4. Finally, the Guarnieri's body breaks up, and the cell becomes
full of initial corpuscles, which divide up in their turn into numerous
elementary corpuscles, and the cycle is complete.

An interesting problem, from both the medical and biological points of
view, is that of the relation of the organism of vaccinia (cow-pox) to that of
variola (small-pox). It is well known that an inoculation with vaccine-lymph
(vaccination) produces a transitory local disturbance which confers partial
immunity against infection with variola. It does not seem to be quite clear
whether the organisms of vaccinia and variola are to be regarded as two
distinct species or as two phases or conditions of the same species of or-
ganism ; the latter is the view of Calkins, as stated above. Manson has
suggested (Brit. Med. Journ., 1905, ii., p. 1263) that the relationship between
the organisms of vaccinia and variola may be similar to that between
Leislimania troptca, of Oriental Sore, and L. donovani, of Kala-azar. No
evidence has been brought forward as yet, however, to show that an infection
with Oriental Sore confers any immunity against Kala-azar.

The Chlamydozoa have been most studied in those cases where
their power of producing disease has forced them upon the atten-
tion of medical investigators, but it is not to be supposed that as a
group of organisms they occur solely as parasites of higher animals.
It is probable that they are of widespread occurrence, and that the
peculiar nuclear parasite of Amoeba known as ffucleophaga, Dan-
geard, for instance, should be referred to the Chlamydozoa (com-
pare SchepotiefT, 269), and perhaps also the similar parasite of
Paramecium described by Calkins under the name Caryoryctes.
No Chlamydozoa are known, however, to occur as free-living, non-
parasitic organisms, but this circumstance may be due to their
extreme minuteness ; the species known owe their detection to the
disturbances they cause in their hosts. FinaUy, it must be men-
tioned that the parasitic theory of cancer, sometimes thought to be
long since defunct, has been revived recently by Awerinzew (907),
who is of opinion that cancer is caused by intranuclear parasites of
the nature of Chlamydozoa.

Such, briefly summarized, is the present position of the problem.
Future research must decide the truth or falsity of one or the
other of the solutions that have been advocated. It only remains
to discuss briefly the nature of the Chlamydozoa, if the interpreta-
tion of Prowazek and his adherents be accepted. According to
Prowazek and Lipschiitz (913), the Chlamydozoa belong neither to
the Bacteria nor to the Protozoa. Hartmann (909), however, seems
to consider that their development and their characteristic mode of
division are Protozoan characteristics. The " development," how-
ever, seems to consist of little, if anything, more than growth in size.
As "elementary corpuscles" they are smaller, as "initial bodies"
larger. The dumb-bell-shaped figure seen in division may mean

474 THE PROTOZOA

simply that their substance is of a viscid or semifluid nature, and
that their bodies are not limited by a membrane ; consequently,
when the two halves travel apart in the process of division, the
substance of the body is drawn out into a connecting thread until
its surface tension overcomes its cohesion. On the other hand,
they exhibit nothing of cell-structure or of any other characteristics
which indicate any affinity to the Protozoa. Their type of organiza-
tion seems to be the simplest possible in a living body — a mere
grain of chromatin without cytoplasm, and without a membrane
or envelope of any kind. In the latter respect they appear to be
of a simpler type of organization than any bacterium, and perhaps
represent more nearly than any other known organism the simplest
possible form of living being.

Bibliography. — For references see p. 504

Ite domum, saturce, venit Hesperus, ite capellce.

BIBLIOGRAPHY

The references to literature are numbered consecutively, but are grouped according

to the chapters.
An asterisk (*) attached to a reference indicates that the work in question contains

full references to the previous literature of the subject.
Memoirs in which only new species are described are not cited, unless there is some

special reason for doing so. All new species are recorded in the " Zoological

Record," published annually by the Zoological Society of London ; the last volume

published up to date is that for 1910 / the volume for 1911 will appear towards

the end of 1912.
The titles of the subject-matter of articles are in many cases not given verbatim, but

in abbreviated form.
The abbreviations employed for the titles of periodicals are given below. (In other

cases the titles of periodicals are abbreviated in a manner which does not require

special explanation.)

A. I.C. P. Archives do Institute Bacteriologico Camara Pestana (Lisbon).

A.I.P. Annales de 1'Institut Pasteur (Paris).

A.K.G.A. Arbeiten aus dem kaiserlichen Gesundheitsamte (Berlin).

A.P.K/ Archiv fur Protistenkunde (Jena).

A.S.T.H. Archiv fiir Schiffs- und Tropenhygiene (Leipzig).

A.T.M.P. Annals of Tropical Medicine and Parasitology (Liverpool).

A.Z.E. Archives de Zoologie experimental et generale (Paris).

B.A.S.C. Bulletin Internationale de 1'Academie des Sciences a Cracovie.

B.B. Biological Bulletin (Woods Holl, Mass.).

B.C. Biologisches Centralblatt (Leipzig).

B.I.P. Bulletin de 1'Institut Pasteur (Paris).

B.S.P.E. — de la Societe de Pathologic Exotique (Paris).

B.S.Z.F. — de la Societe Zoologique de France (Paris).

C.B.B.P.K. Centralblatt fiir Bakteriologie, Parasitenkunde und Infections-

krankheiten (Jena).

C.Pv.A.S. Comptes-rendus hebdomadaires des Seances de 1'Academie des
Sciences (Paris).

C.R.S.B. des Seances et Memoires de la Societe de Biologic (Paris).

J.E.M. Journal of Experimental Medicine (Baltimore).

J.E.Z. — of Experimental Zoology (Baltimore).

J.H. — of Hygiene (Cambridge).

J.L.S. — of the Linnean Society : Zoology (London).

M.I.O.C. Memorias do Institute Oswaldo Cruz (Rio de Janeiro).

P.R.S. Proceedings of the Royal Society of London.

Py, Parasitology (Cambridge).

P.Z.S. Proceedings of the Zoological Society of London.

Q.J.M.S. Quarterly Journal of Microscopical Science (London).

S.B.A.B. Sitzungsberichte der koniglich-preussischen Akademie der Wissen-

schaften zu Berlin.

S.B.G.B. • — der Gesellschaft naturforschender Freunde zu Berlin.

S.B.G.M.P. — der Gesellschaft fiir Morphologic und Physiologic in Munchen.

S.M.I. Scientific Memoirs by Officers of the Medical and Sanitary Depart-
ments of the Government of India (Calcutta).

V.D.Z.G. Verhandlungen der deutschen zoologischen Gesellschaft (Leipzig).

Z.A. Zoologischer Anzeiger (Leipzig).
Z.a.P. Zeitschrift fiir allgemeine Physiologie (Jena).

Z.H. — fiir Hygiene und Infectionskrankheiten (Leipzig).

Z.w.Z. — fiir wissenschaftliche Zoologie (Leipzig).

475

476 THE PROTOZOA

CHAPTER I
General Works on Protozoa.

(1) BRFMPT, E. (1910). Precis de Parasitologie. Paris : Masson et Cie.
*(2) BUTSCHLI, 0. (1882-1889). Protozoa. Bronri's Klassen und Ordnungen die
Thier-Reichs, I.

(3) — (1910). Vorlesungen iiber vergleichende Anatomic, 1. Leipzig :

W. Engelmann.

(4) CALKINS, G. N. (1901). The Protozoa. New York : Macmillan and Co.
*(5) — (1909). Protozoology. New York and Philadelphia : Lea and Fiebiger.
*(6) DELAGE, Y., and HEROUARD, E. (1896). Traite de Zoologie Concrete, I.

Paris : Schleicher Freres.

*(7) DOFLEIN, F. (1911). Lehrbuch der Protozoenkunde. Third edition. Jena:
Gustav Fischer.

(8) HARTOG, M. (1906). Protozoa. Cambridge Natural History, vol. i. London:

Macmillan and Co.

(9) KENT, W. S. (1880-1882). A Manual of the Infusoria. London : David

Bogue.

*(10) LANG, A. (1901). Lehrbuch der vergleichenden Anatomic der wirbellosen
Thiere, 2te Auflage. Jena : Gustav Fischer.

(11) LANKESTER, E. R. (1891). Protozoa. Encyclopaedia Britannica, ninth

edition ; reprinted in Zoological Articles. London : A. and C. Black.

(12) — (1903 and 1909). A Treatise on Zoology. Part I., Fascs. 1 and 2.

London : A. and C. Black.

(13) MINCHIN, E. A. (1907). Protozoa. Allbutt and Rolleston : A System of

Medicine, vol. ii., part ii., p. 9.

(14) PROWAZEK, S. V., and others (1911). Handbuch der Pathogenen Protozoen.

Leipzig : J. A. Barth. Lief. 1 and 2.

(15) ROLLESTON, G., and JACKSON, W. H. (1888). Forms of Animal Life. Second

edition. Oxford : Clarendon Press.

CHAPTER II

In addition to the general works cited under the previous chapter, see especially :

(16) GOODEY, T. (1911). A Contribution to our Knowledge of the Protozoa of

the Soil. P.R.S. (B.), Ixxxiv., p. 165.

(17) LAUTERBORN, R. (1901). Die " sapropelische " Lebewelt. Z.A., xxiv., p. 50.

(18) LAVERAN, A., and MESNIL, F. (1899). De la Sarcocystine, toxine des Sarco-

sporidies. C.R.8.B., 1L, p. 311.

(19) — and PETTIT, A. (1911). Les trypanotoxines. B.S.P.E., iv., p. 42.

(20) MESNIL, F. (1905). L'Heredite dans les Maladies a Protozoaires. B.I. P.,

iil, p. 401.

(21) MINCHIN, E. A. (1910). Phenomena of Parasitism amongst Protozoa.

Journ. QueTcett Microscop. Club (2), xi., p. 1.

(22) ROUDSKY, D. (1910). Le Trypanosoma lewisi Kent renforce. C.R.8.B.,

Ixix., p. 384.

(23) — (1911). La possibilite de rendre le Trypanosoma lewisi virulent pour

d autres rongeurs que le rat. G.R.A.S., clii., p. 56. (See also Bulletin of
the Sleeping Sickness Bureau, vol. iii., pp. 81 and 265, for further references
on this subject.)

(24) RUSSELL, E. J., and HUTCHINSON, H. B. (1909). The Effect of Partial

Sterilization of Soil on the Production of Plant Food. Journ. Agric. Sci.,
iii., p. 111.

(25) TEICHMANN, E. (1910). Das Gift der Sarcosporidien. A.P.K., xx., p. 97.

(26) — and BRAUN, H. (1911). Ein Protozoentoxin (Sarcosporidiotoxin). A.P.K.,

xxii., p. 351.

(27) WENDELSTADT and FELLMER, T. (1910). Einwirkung von Kaltbliiterpas-

sagen auf Nagana- und Lewisi-Trypanosomen. Zeitschr. f. Immunitats-
forschung, v., p. 337.

(28) WINTER, F. W. (1907). Untersuchung iiber Peneroplis pertusus (Forskal).

A.P.K., x., p. 1.

BIBLIOGRAPHY 477

CHAPTER III

In addition to the general works cited under Chapter L, see especially :

(29) HERON-ALLEN, E., and EARLAND, A. (1909). A New Species of Technitella.

Journ. Quekett Microsc. Club (2), x., p. 403.

(30) KOLTZOFF, N. K. (1903). Formbestimmende elastische Gebilde in Zellen.

B.C., xxiii., p. 680.

(31) — (1906). Die Gestalt der Zelle. Arch. mikr. Anal., Ixvii., p. 364.

(32) PROWAZEK, S. v. (1908). Biologic der Zellen, I. B.C., xxviii., p. 782.

(33) — (1909). Theorie der Cytomorphe. Z.A., xxxiv., p. 712.

(34) RHUMBLER, L. (1898). Physikalische Analyse von Lebenserscheinungen der

Zelle, I. Arch. Entwicklungsmech. , vii., p. 103.

(35) — (1902). Die Doppelschalen von OrUtolites. A.P.K., i., p. 193.

(36) VERWORN, M. (1888). Biologische Protisten-Studien. Z.w.Z., xlvi., p. 455.

CHAPTER IV

In addition to Nos. 34 and 35, see :
*(37) BUTSCHLI, 0. (1894). Microscopic Foams and Protoplasm. (Translation

by E. A. Minchin.) London : A. and C. Black.
(38) FATJRE'-FREMIET, E. (1908). La Structure des Matieres Vivantes. B.S.Z.F.,

xxxiii., p. 104.
*(38'5) — (1910). Les Mitochondries des Protozoaires et des Cellules sexuelles.

Arch. d'Anat. Microsc., xi., p. 457.
*(39) FISCHER, A. (1899). Fixirung, Farbung und Bau des Protoplasmas. Jena :

Gustav Fischer.

(40) RHUMBLER, L. (1902). Der Aggregatzustand und die physikalischen Beson-

derheiten des lebenden Zellinhalts. Z.a.P., ii., p. 183.

CHAPTER V

In addition to the references cited above for Chapters I. and III., and those
cited below for Chapter X., see :

(41) GOLDSCHMIDT, R. (1907). Lebensgeschichte der Mastigamoben. A.P.K.,

Suppl. L, p. 83.

(42) MINCHIN, E. A., and WOODCOCK, H. M. (1911). The Trypanosome of the

Little Owl (Athene noctua). Q.J.M.S., Ivii., p. 141.

(43) SCHATJDINN, F. (1894). Camptonema nutans. S.B.A.B., Hi., p. 1227. Re-

printed, Schaudinn's Arbeiten, 1911, p. 50.

(44) SCHUBERG, A. (1905). Cilien und Trichocysten einiger Infusorien. A.P.K.,

vi., p. 61.

CHAPTER VI

In addition to the works cited here, see also the bibliographical references for
Chapter VII.

(45) ARAGAO, H. DE B. (1910). Ueber Pdytomdla agilis. M.I.O.C., ii., p. 42.

(46) AWERINZEW, S. (1907). Struktur des Protoplasma und des Kerns von Amoeba

proteus (Pall.). Z.A., xxxii., p. 45.

(47) — (1909). Entwicklungsgeschichte von Coccidien aus dem Darme von

Cerebratulus sp. (Barrouxia spiralis). A.P.K., xviii., p. 11.

(48) CALKINS, G. N. (1903). The Protozoan Nucleus. A.P.K., ii., p. 213.
(48'5) CHAGAS, C. (1911). Die zyklischen Variationen des Caryosoms bei zwei

Arten parasitischer Ciliaten. M.I.O.G., iii., p. 136.
*(49) CHATTON, E. (1910). La structure du Noyau et la Mitose chez les Amcebiens.

A.Z.E. (5), v., p. 267.
(50) COLLIN, B. (1909). La Conjugaison d' Anoplophrya branchiarum (Stein)

(A. circulans, Balbiani). A.Z.E. (5), i., p. 345.
*(51) DOBELL, C. C. (1909). Chromidia and the Binuclearity Hypothesis.

Q.J.M.S., liii., p. 279.

478 THE PROTOZOA

*(52) DOBELL, C. C. (1911). Contributions to the Cytology of the Bacteria.
Q.J.M.S., Ivi., p. 395. " Autorreferat " in A.P.K., xxiv., p. 84.

(53) ENTZ, G. (1909). Organisation und Biologic der Tintinniden. A.P.K., xv.,

p. 93.

(54) ERHABD, H. (1911). Die Henneguy-Lenhosseksche Theorie. Ergebn. Anat.

Entwick., xix. (second half), p. 893.

(55) FAURE-FREMIET, E. (1910). Appareil nucleaire, Chromidies, Mitochondries.

A.P.K., xxi., p. 186.

(56) FRANCA, C., and ATHIAS, M. (1907). Les Trypanosomes des Amphibiens, II.

Le Trypanosoma rotatorium de Hyla arborea. A.I.G.P., i., p. 289.
^(57) GOLDSCHMIDT, R. (1904). Die Chromidien der Protozoen. A.P.K., v.,p' 126.

(58) — and POPOFF, M. (1907). Die Karyokinese der Protozoen und der Chromi-

dialapparat der Protozoen- und Metazoenzelle. A.P.K., viii., p. 321.

(59) GUILLERMOND, A. (1910). Corpuscules metachromatiques ou Grains de Volu-

tine. A.P.K., xix., p. 289.

(60) HARTMANN, M. (1909). Polyenergide Kerne. B.C., xxix., pp. 481 and 491.

(61) — (1911). Die Konstitution der Protistenkerne. Jena : Gustav Fischer.

(62) — and CHAGAS, C. (1910). Flagellatenstudien. M.I.O.O., ii., p. 64.

(63) — and PROWAZEK, S. v. (1907). Blepharoplast, Caryosom und Centrosom.

A.P.K., x., p. 306.

(64) HERTWIG, R. (1898). Kerntheilung, Richtungskorperbildung und Befruch-

tung von Actinosphcerium Eichhorni. Abhandl. bayer. Akad. (II. Cl.),
xix., p. 631.

,(65) — (1899). Encystierung und Kernvermehrung bei Arcella vulgaris. Kup-
ffer's Festschrift, p. 567.

(66) — (1902). Die Protozoen und die Zelltheorie. A.P.K., i., p. 1.

(67) — (1903). Das Wechselverhaltnis von Kern und Protoplasma. 8.B.O.M.P.,

xviii., p. 77.

(68) — (1907). Der Chromidialapparat und der Dualismus der Kernsubstanzen.

Ibid., xxiii., p. 19.

(69) JAHN, E. (1904). Kernteilung und Geisselbildung bei den Schwarmern von

Stemonitis flaccida. Ber. Deutsch. Bot. Ges., xxii., p. 84.

(70) JANICKI, C. (1910). Parasitische Flagellaten, I. Lophomonas blattarum,

L. striata. Z.w.Z., xcv., p. 243.

(71) — (1911). Der Parabasalapparat bei parasitischen Flagellaten. B.C.,

xxxi., p. 321.

(71'5) — (1912). Parasitische Arten der Gattung Paramceba. Verh. Natur-
forsch. Ges. Basel, xxiii.

(72) LE'GER, L., and DUBOSCQ, 0. (1911). Deux Gregarines des Crustaces. A.Z.E.

(5), vi., " Notes et Revue," p. lix.

(73) MAIER, H. N. (1903). Der feinere Bau der Wimperapparate der Infusorien.

A.P.K., ii., p. 73.

(74) MESNIL, F. (1905). Chromidies et Questions connexes. B.I. P., iii., p. 313.

(75) MINCHIN, E. A. (1911). Some Problems of Evolution in the Simplest Forms

of Life. Journ. Quekett Microsc. Club (2), xi., p. 165.

(76) NAGLER, K. (1911). Protozoen aus einem Almtumpel, I. Amoeba hartmanni,

n. sp. Anhang : Zur Centriolfrage. A.P.K., xxii, p. 56.

-77) POPOFF, M. (1909). Die Zellgrosse, ihre Fixierung und Vererbung. Arch.
Zellforschung, iii., p. 124.

(78) REICHENOW, E. (1910). Hamogregarina stepanowi. Die Entwicklungsge-

schichte einer Hamogregarine. A.P.K., xx., p. 251.

(79) ROBERTSON, M. (1911). The Division of the Collar-Cells of the Calcarea

Heterocoda. Q.J.M.8., Ivii., p. 129.

(80) — and MINCHIN, E. A. (1910). The Division of the Collar-Cells of Clathrina

coriacea. Q.J.M.S., lv., p. 611.

(81) SCHAUDINN, F. (1896). Der Zeugungskreis von Paramceba, eilhardi. S.B.A.B.,

p. 31. Reprinted, Schaudinn's Arbeiten, 1911, p. 115.

(82) — (1896). Das Centralkorn der Heliozoen. V.D.Z.G., vi., p. 113. (With

discussion by Lauterborn and Biitschli.)

(83) SIEDLECKI, M. (1905). Die Bedeutung des Karyosoms. B.A.S.C., p. 559.

(84) WEN YON, C. M. (1911). Oriental Sore in Baghdad, together with Observa-

tions on a Gregarine in Stegomyia fasciata, the Hsomogregarines of Dogs,

and the Flagellates of House Flies. Py., iv., p. 273.
.(85) ZUELZER, M. (1904). Difflugia urcedata. A.P.K., iv., p. 240.
(86) — (1909). Wagnerella borealis. A.P.K., xvii., p. 135.

BIBLIOGRAPHY 479

CHAPTER VII

In addition to the works cited here, see also Nos. 45, 48, 49, 50, 56, 58, 60, 62,
64, 66, 69, 70, 71, 71'5, 78, 79, 80, 81, 82, and "86 above.

(87) ARAGAO, H. DE B. (1904). Amoeba diplomitotica. M.I.O.C., i., p. 33.

(88) AWERINZEW, S. (1904). Teilung von Amoeba proteus. Z.A., xxvii., p. 399.

(89) HARTMANN, M., and CHAGAS, C. (1910). Schlangenhamogregarinen. A.P.K.,

xx., p. 351.
(90) (1910). Die Kernteilung von Amoeba Jiyalina. M.I.O.C., ii., p. 159.

(91) HERTWIG, R. (1903). Korrelation von Zell- und Kerngrosse. B.C., xxiii.,

pp. 49 and 108.

(92) — (1908). Neue Probleme der Zellenlehre. Arch. f. Zdlforschung, i., p. 1.

(93) LEBEDEW, W. (1908). Trackelocerca phcenicopterus. A.P.K., xiii., p. 70.

(94) MOROFF, T. (1908). Die bei den Cephalopoden vorkommenden Aggregata-

Arten. A.P.K., xi., p. 1.

(95) NAGLER, K. (1909). Entwicklungsgeschichtliche Studien iiber Amoben.

A.P.K., xv., p. 1.

(96) — (1911). Caryosom und Centriol beim Teilungsvorgang von Chilodon

uncinatus. A.P.K., xxiv., p. 142.

(97) PROWAZEK, S. v. (1903). Die Kernteilung des Entosiphon. A.P.K., ii.,

p. 325.
(97'5) REICHENOW, E. (1909). Hcematococcus pluvialis. A.K.G.A., xxxiii., p. 1.

(98) SCHAUDINN, F. (1894). Kerntheilung mit nachfolgender Korpertheilung bei

Amoeba crystalligera. S.B.A.B., 1894, p. 1029. Reprinted, Schaudinn's
Arbeiten, 1911, p. 95.

(99) — (1900). Der Generationswech.se! bei Coccidien. Zool. Jahrbiicher (Abth.

f. Anat.), xiii., p. 197. Schaudinn's Ar' eiten, 1911, p. 208.

(100) SCHEWIAKOFF, W. (1887). Die karyokinetische Kerntheilung der Euglypha

alveolata. Morph. Jahrbuch, xiii., p. 193

(101) SWARCZEWSKY, B. (1908). Die Fortpflanzungserscheinungen bei Arcella

vulgaris. A.P.K., xii., p. 173.

CHAPTER VIII

In addition to the works cited here, see also Nos. 41, 47, 50, 51, 57, 64, 67, 68,
74, 75, 81, 85, 92, 93, 99, and 101.

(102) BAITSELL, G. A. (1911). Conjugation of Closely Related Individuals of

Stylonychia. Proc. Soc. Exper. Biol. Med., viii., p. 122.

(103) BOTT, M. (1907). Fortpflanzung von Pelomyxa. A.P.K., viii., p. 120.

(104) CALKINS, G. N. (1904). Studies on the Life-History of Protozoa, IV.

J.E.Z., i., p. 423.

(105) — (1906). The Protozoan Life-Cycle. B.B., xi., p. 229.

(106) — and CULL, S. W. (1907). The Conjugation of Paramecium aurelia

(caudatum). A.P.K., x., p. 375.

(107) DANGEARD, P. A. (1911). La Conjugaison des Infusoires cilies. C.R.A.S.,

clii., p. 1032.

(108) — (1911). La Fecondation des Infusoires cilies. C.R.A.S., clii., p. 1703.

(109) DEHORNE, A. (1911). Permutation nucleaire dans la Conjugaison de Col-

pidium colpoda. G.R.A.S., clii., p. 1354.

(110) DOBELL, C. C. (1911). The Principles of Protistology. A.P.K., xxiii.,

p. 269.

(111) DOFLEIN, F. (1907). Die Konjugation der Infusorien. S.B.G.M.P., xxiii.,

p. 107.

(112) ENRIQUES, P. (1907). La Coniugazione e il Differenziamento sessuale negli

Infusori. A.P.K., ix., p. 195.

(113) — (1908). Die Conjugation und sexuelle Differenzierung der Infusorien.

A.P.K., xii., p. 213.

(114) GEDDES, P., and THOMSON, J. A. (1901). The Evolution of Sex. Revised

edition. London.

(115) HAMBURGER, C. (1908). Die Conjugation von Stentor coeruleus. Z.w.Z.,

xc., p. 423.

(116) HARTMANN, M. (1909). Autogamie bei Protisten. A.P.K., xiv., p. 264.

480 THE PROTOZOA

(117) HARTOG, M. (1910). Apropos of Dr. Hartmann's " Autogamie bei Proto-

zoen." A.P.K., xviii., p. 111.

(118) HERTWIG, R. (1902). Wesen und Bedeutung der Befruchtung. Silzber. k.

Akad. Wiss. Munchen., xxxii., p. 57.

(119) — (1905). Das Problem der sexuellen Differenzierung. V.D.Z.G., 1905,

p. 186.

(120) HICKSON, S. J. (1910). The Origin of Sex. Ann. Rep. Trans. Manchester

Microsc. Soc., 1909, p. 34.

(121) JENNINGS, H. S. (1910). What Conditions induce Conjugation in Para-

mecium ? J.E.Z., ix., p. 279.

(122) MAUPAS, E. (1889). Le Rajeunissemcnt karyogamique chez les Cilies.

A.Z.E., (2) vii., p. 149.

(123) MULSOW, K. (1911). Fortpflanzungserscheinungen bei Monocystis rostrata.

A.P.K., xxii., p. 20.

(124) PEARL, R. (1907). A Biometrical Study of Conjugation in Paramecium.

Biometrika, v., p. 213.

(125) POPOFF, M. (1908). Die Gametenbildung und die Conjugation von Car-

chesium polypinum. Z.w.Z., Ixxxix., p. 478.

(126) PRANDTL, H. (1906). Die Konjugation von Didinium nasutum. A.P.K.,

vii., p. 229.

(127) PROWAZEK, S. v. (1905). Der Erreger der Kohlhernie, Plasmodiophora

brassicce. A.K.G.A., xxii., p. 396.

(128) — (1907). Die Sexualitat bei den Protisten. A.P.K., ix., p. 22.

(129) SCHAUDINN, F. (1896). Copulation von Actinophrys. 8.B.A.B., p. 83.

(130) — (1902). Krankheitserregende Protozoen, II. Plasmodium vivax.

A.K.G.A., xix., p. 169.

(131) — (1903). Die Fortpflanzung einiger Rhizopoden. A.K.G.A., xix., p. 547.

(132) — (1904). Generations- und Wirtswechsel bei Trypanosoma und Spiro-

chcete. A.K.G.A., xx., p. 387. Reprinted, with " Nachtrag," in Fritz
Schaudinn's Arbeiten, 1911.

(133) — (1905). Die Befruchtung bei Protozoen. V.D.Z.G., xv., p. 16.

(134) SCHILLING, C. (1910). Autogamie bei Trypanosoma lewisi. A.P.K., xix.,

p. 119.

(135) STEMPELL, W. (1906). Die neuere Protozoenforschung und die Zellenlehre.

S. B. Med.-naturwiss. Ges. Miinster i. W., June 13.

(136) STEVENS, N. M. (1910). The Chromosomes and Conjugation in Boveria

subcylindrica, var. concharum. A.P.K., xx., p. 126.

(137) VERSLUYS, J. (1906). Die Konjugation der Infusorien. B.C., xxvi., p. 46.

(138) WOODRUFF, L. L. (1905). Life-History of Hypo trichous Infusoria. J.E.Z.,

ii., p. 585.

(139) — (1908). Life-Cycle of Paramecium. Amer. Nat., xlii., p. 520.

(140) — (1909). Further Studies on the Life-Cycle of Paramecium. B.B., xvii.,

p. 287.

(141) — (1911). Two Thousand Generations of Paramecium. A.P.K., xxi.,

p. 263.

(142) — (1911). The Adaptation of Paramcecia to Different Environments.

B.B., xxii., p. 60.

(143) — and BAITSELL, G. A. (1911). Rhythms in the Reproductive Activity of

Infusoria. J.E.Z., xi., p. 339.

CHAPTER IX

In addition to the works cited here, see also Nos. 41, 65, 78, 85, 86, 99, 101,
130, and 131.

(144) ELPATIEWSKY, W. (1907). Fortpflanzung von Arcella vulgaris. A.P.K.,

x., p. 441.

(145) KHAINSKY, A. (1910). Tiber Arcellen. A.P.K., xxi., p. 165.

(146) SCHAUDINN, F. (1899). Der Generationswechsel von Trichosphcerium sieboldi.

Anhang. Abhandl. Preuss. Akad. Wiss.

(147) — (1902). Cydospora caryolytica. A.K.G.A., xviii., p. 378. Reprint in

Fritz Schaudinn's Arbeiten, 1911, p. 318.

BIBLIOGRAPHY 481

CHAPTER X

In addition to the works cited below, see also 34, 35, 36, 37, 40, and 237.

(148) BARRATT, J. 0. W. (1905). Die Kohlensaureproduktion von Paramecium

aurelia. Z.a.P., v., p. 66.

(149) — (1905). Der Einfluss der Konzentration auf die Chemotaxis. Z.a.P.,

v., p. 73.

(150) BASS, C. C. (1911). A New Conception of Immunity : its Application to

the cultivation of Protozoa and Bacteria. Journ. Amer. Med. Assoc.,
Ivii., p. 1534.

(151) BOISSEVAIN, M. (1908). Kernverhaltnisse von Actinosphcerium eichhorni^

bei fortgesetzter Kultur. A.P.K., xiii., p. 167.

(152) BORGERT, A. (1909). Erscheinungen fettiger Degeneration bei tripyleen

Radiolarien. A.P.K., xvi., p. 1.

(152'5) BOVARD, J. F. (1907). Structure and Movements of Condylostoma patens.
Univ. California PubL, iii., p. 343.

(153) BUTSCHLI, 0. (1906). Zttr Kenntnis des Paramylons. A.P.K., vii., p. 197.

(154) DEGEN, A. (1905). Die kontraktile Vacuole und die Wabenstruktur des

Protoplasmas. Bot. Zeitung, Ixiii., p. 163.

(155) DOBELL, C. C. (1907). Physiological Degeneration in Opalina. Q.J.M.S.,

li., p. 633.

(156) ERDMANN, R. (1910). Depression und facultative Apogamie bei Amoeba

diploidea. Hertwig's Festschrift, i., p. 323.

(157) GARBOWSKI, L. (1907). Gestaltsveranderung und Plasmoptyse. A.P.K.,

ix., p. 53.

(158) GIEMSA, G. (1911). Fixierung und Farbung der Protozoen. Vide Prowazek

(14), p. 7.

(159) — and PROWAZEK, S. v. (1908). Wirkungdes Chinins auf die Protistenzelle.

A.S.T.H., xii., Beiheft 5, p. 188.

(160) GREELEY, A. W. (1902). Artificial Production of Spores in Monas by a

Reduction of the Temperature. Univ. Chicago Decennial PubL, x.,
p. 73.

(161) GREENWOOD, M. (1886-1887). Digestive Processes of some Rhizopods, I.

Journ. Physiol., vii., p. 253. II., ibid., viii., p. 263.

(162) — (1894). Constitution and Formation of " Food-Vacuoles " in Infusoria,

etc. Phil. Trans. (B), clxxxv., p. 355.

(163) — and SAUNDERS, E. R. (1894). The Role of Acid in Protozoan Digestion.

Journ. Physiol., xvi., p. 441.

(164) HERTWIG, R. (1904). Physiologische Degeneration bei Actinosphcerium

eichhorni. Haeckel's Festschrift (Jena, G. Fischer), p. 301.

*(165) JENNINGS, H. S. (1904). The Behaviour of the Lower Organisms.
Washington : Carnegie Institute.

(166) — (1904). The Behaviour of Paramecium. Journ. Comp. Neurology, xiv.,

p. 441 ; Contr. Zool. Lab. University of Philadelphia, xi., 1905.

(167) — (1904). The External Discharge of the Contractile Vacuole. Z.A.,

xxvii., p. 656.

(168) — (1904). Physical Imitations of the Activities of Amoeba. Amer. Natural ,

xxxviii., p. 625.

(169) JOSEPH, H., and PROWAZEK, S. v. (1902). Die Einwirkung von Rontgen-

Strahlen auf einige Organismen. Z.a.P., i., p. 142.

(170) KANITZ, A. (1907). Der Einfluss der Temperatur auf pulsierenden Vakuolen

der Infusorien. B.C., xxvii., p. 11.

(170-5) KHAINSKY, A. (1910). Morphologie und Physiologic einiger Infusorien
(Paramecium caudatum). A.P.K., xxi., p. 1.

(171) LEWIN, K. R. (1910). Nuclear Relations of Paramecium caudatum during

the Asexual Period. Proc. Cambridge Phil. Soc., xvi., p. 39.

-(172) — (1911). Behaviour of the Infusorian Micronucleus in Regeneration.
P.R.S., Ixxxiv., p. 332.

(173) LIPSKA, I. (1910). L'lnfluence de 1'Inanition chez Paramecium caudatum.

Eev. Suisse Zool., xviii., p. 591.

(174) MACKINNON, D. (1908). Encystation of Actinosphcerium eichhorni under

Different Temperatures. Q.J.M.8., Hi., p. 407.

(175) McLENDON, J. F. (1909). Protozoan Studies. J.E.Z., vi., p. 265.

(176) MAST, S. 0. (1910). Reactions of Amoaba to Light. J.E.Z., ix., p. 265.

31

482 THE PROTOZOA

(177) MESNIL, F., and MOTTTON, H. (1903). Une Diastase Proteolytique Extraite

des Infusoires Cilies. C.R.S.B., lv., p. 1016.
(178) (1903). L' Action Antiproteolytique Comparee des Diverses Serums

sur 1'Amibodiastase etc. C.R.8.B., lv., p. 1018.

(179) METALNIKOFF, S. (1903). Die intracellulare Verdauung. Bull. Ac. St.

Petersbourg, xix., p. 187.

(180) METSCHNIKOFF, E. (1889). La Digestion Intracellulaire. A.I. P., iii., p. 25.

(181) NIRENSTEIN, E. (1905). Ernahrungsphysiologie der Protisten. Z.a.P., v.,

p. 434.

(182) — (1910). Fettverdauung und Fettspeicherung bci Infusorien. Z.a.P.,

x., p. 137.

(183) NOWIKOFF, M. (1908). Die Wirkung des Schilddriisenextrakts auf Ciliaten.

A.P.K., 3d., p. 309.

(184) POPOFF, M. (1907). Depression der Protozoenzelle und der Geschlechtszellen

der Metazoen. A.P.K., Suppl., i., p. 43.

(185) — (1909). Der Einfluss chemischer Reagentien auf der Funktionszustand

der Zelle. S.B.G.M.P., xxv., p. 55.

(186) — (1909). Einige Ursachen der physiologischen Depression der Zelle.

Arch. Zellforschung, iv., p. 1.

(187) PRANDTL, H. (1907). Die physiologische Degeneration der Amoeba proteus.

A.P.K., viii., p. 281.

(188) PROWAZEK, S. v. (1903). Studien zur Biologic der Zelle. Z.a.P., ii.,

p. 385.

(189) — (1903). Regeneration und Biologic der Protozoen. A.P.K., iii., p. 44.

(190) — (1903). Degenerative Hyperregeneration bei den Protozoen. A.P.K.,

iii., p. 60.

(191) — (1908). Das Lecithin. B.C., xxviii., p. 382.

(192) — (1908). Einfluss von Saurelosungen niedrigster Konzentration auf die

Zell- und Kernteilung. Arch. Entwicklungsmech., xxv., p. 643.

(193) — (1909). Biologic der Zellen. II. Zelltod und Strukturspannung. B.C.,

xxix., p. 291.

(194) — (1910). Die Physiologic der Einzelligen. Leipzig : Teubner.

(195) — (1910). Giftwirkung und Protozoenplasma. A.P.K., xviii., p. 221.

(196) — (1910). Biologie der Protozoen, V. A.P.K., xx., p. 201.

(197) PUTTER, A. (1900). Thigmotaxis bei Protisten. Arch. Anal. PhysioL,

Physid. Abt., Suppl. Band, p. 243.

(198) — (1903). Die Wirkung erhohter Sauerstoffspannung auf die lebendige

Substanz. Z.a.P., iii., p. 363.

(199) — (1903). Reizbeantwortung der ciliaten Infusorien. Z.a.P., iv., p. 406.

(200) — (1905). Leuchtende Organismen. Z.a.P., v., Referate, p. 17.

(201) — (1905). Die Atmung der Protozoen. Z.a.P., v., p. 566.

(202) — (1908). Vergleichende Physiologic des Stoffwechsels. Abh. k. Ges. Wiss.

Gdttingen (n.F.), vi., p. 1.

*(202) — (1908). Erforschung des Lebens der Protisten. Tigerstedt, Handbuch
der physiologischen Methodik.

(203) RHUMBLER, L. (1905). Die Oberflachenkrafte der Amoben. Z.w.Z.,

Ixxxiii., p. 1.

(204) — (1910). Die verschiedenen Nahrungsaufnahmen bei Amoben als Folge

verschiedener Colloidalzustande ihrer Oberflachen. Arch. Entwicklungs-
mech., xxx., p. 194.

(205) ROESLE, E. (1902). Die Reaction einiger Infusorien auf einzelne Induk-

tionsschlage. Z.a.P., ii., p. 139.

(206) SCHEWIAKOFF, W. (1893). Die Natur der sogennanten Excretkorner der

Infusorien. Z.w.Z., Ivii., p. 32.

.(207) SMITH, G. (1903). Actinosphcerium eichhorni : A Biometrical Study in the
Mass Relations of Nucleus and Cytoplasm. Biometrika, ii., p. 241.

(208) STANIEWICZ, W. (1910). La Digestion de la Graisse dans les Infusoires

Cilies. B.A.S.C., p. 199.

(209) STATKEWITSCH, P. (1905). Galvanotropismus und Galvanotaxis der Ciliata.

Z.a.P., v., p. 511.

(210) — (1904). Zur Methodik der biologischen Untersuchungen iiber die Pro-

tisten. A. P. K., v., p. 17.

(211) VERWORN, M. (1904). Die Localisation der Atmung in der Zelle. Dtnkschr.

Ges. Jena, xi., p. 561.

(212) — (1907). Allgemeine Physiologie. Jena. Fourth edition.

BIBLIOGRAPHY 483

(213) WAGER, H. (1900). On the Eyespot and Flagellum of Euglena viridis.

J.L.S., xxvii., p. 463.

(214) WALLENGREN, H. (1902). Inanitionserscheinungen der Zelle. Z.a.P., i.,

p. 67.

(215) — (1902). Zur Kenntnis der Galvanotaxis. Z.a.P., ii., p. 341.

(216) WOODRUFF, L. L. (1908). Effects of Alcohol on the Life-Cycle of Infusoria.

B.B., xv., p. 85.

(217) — (1911). The Effect of Excretion Products of Paramecium on its Rate

of Reproduction. J.E.Z., x., p. 559.

(218) — and BAITSELL, G. A. (1911). The Reproduction of Paramecium aurelia

in a " Constant " Culture Medium of Beef Extract. J.E.M., xi., p. 135.

(219) (1911). The Temperature Coefficient of the Rate of Reproduction

of Paramecium aurelia. Amer. Journ. Physiol., xxix., p. 147.

(220) — and BUNZEL, H. H. (1909). The Relative Toxicity of Various Salts and

Acids towards Paramecium. Amer. Journ. Physiol., xxv., p. 190.

(221) ZUELZER, M. (1905). Die Einwirkung der Radiumstrahlen auf Protozoen.

A.P.K., v., p. 358.

(222) — (1907). Der Einfluss des Meerwassers auf die pulsierende Vacuole.

S.B.G.B., p. 90.

(223) ZUMSTEIN, H. (1899). Morphologic und Physiologic der Euglena gracilis.

Pringsheim's Jahrbucher f. wiss. Botanik, xxxiv., p. 419.

CHAPTER XI
SARCODINA

(a) General Works.

(224) CASH, J., and HOPKINSON, J. (1905, 1909). The British Freshwater Rhizo-

poda and Heliozoa. London, Ray Society, vol. i. (1905) and ii. (1909).

(225) HARTOG, M. (1910). Rhizopoda. Encydop. Brit., eleventh edition, xxiii.,

p. 244.

(226) LEIDY, J. (1879). Freshwater Rhizopods of North America. Rep. U.S.

Geol. Survey, xii.

(b) Amcabsea.

See also Nos. 32, 34, 36, 46, 49, 65, 71-5. 76, 81, 85, 87, 88, 90, 95, 98, 101 ,
103, 131, 144-146, 156, 161, 168, 176, 178, 187, 203, 204, 222.

(227) ALEXEIEFF, A. (1911). La Division nucleaire et 1'Enkystement chez

quelques Amibes, I.-III. C.R.S.B., Ixx., pp. 455, 534, 588.

(228) AWERINZEW, S. (1907). Die Struktur des Protoplasma und des Kerns von

Amoeba proteus. Z.A., xxxii., p. 45.

.(229) — (1906). Die Struktur und die chemische Zusammensetzung der Gehause
bei den Siisswasserrhizopoden. A.P.K., viii., p. 95.

(230) — (1906). Zur Kenntnis der Siisswasserrhizopoden. A. P. K., viii., p. 112.

(231) CALKINS, G. N. (1904). Evidences of a Sexual Cycle in Amoeba proteus.

A.P.K., v., p. 1.

(232) — (1907). Fertilization of Amoeba proteus. B.B., xiii., p. 219.

(233) CASAGRANDI, 0., and BARBAGALLO, P. (1897). Entamceba hominis, s.

Amoeba coli. Ann. Igiene Sperimental., vii., p. 103.

(234) CHATTON, E. (1910). Protozoaires parasites des Branchies des Labres :

Amoeba mucicola, Trichodina labrorum. A.Z.E. (5), v., p. 239.

(235) CRAIG, C. F. (1908). The Amoebae in the Intestine of Man. Journ. Infect.

Diseases, v., p. 324.

(236) DOBELL, C. C. (1909). The Intestinal Protozoa of Frogs and Toads.

Q.J.M.S., liii., p. 201.

(237) — (1909). Physiological Degeneration and Death in Entamceba ranarum.

Q.J.M.S., liii., p. 711.

(238) DOFLEIN, F. (1907). Amobenstudien. A.P.K., Suppl. i., p. 250.

(239) — (1907). Der Teilungsvorgang bei den Siisswasserthalamophoren.

S.B.G.M.P., xxiii.

(240) FANTHAM, H. B. (1910). The Protozoa Parasitic in the Red Grouse, etc.

P.Z.S., 1910, p. 692.

484 THE PROTOZOA

(241) FANTHAM, H. B. (1911). The Amoebae Parasitic in the Human Intestine.

A.T.M.P., v., p. 111.

(242) GAUDICHEAU, A. (1908). Formation de Corps spirillaire dans une Culture

d'Amibe (Entamaba phagocytoides). C.R.S.B., Ixiv., p. 493.

(243) GOULD, L. J. (1894). The Minute Structure of Pelomyxa palustris. Q.J.M.S.

xxxvi., p. 295.

(244) GREIG, E. D. W., and WELLS, R. T. (1911). Dysentery and Liver Abscess

in Bombay. 8. M.I., 47.

(245) GROSSE-ALLERMANN, W. (1909). Amoeba terricola. A.P.K., xvii., p. 203.

(246) GRUBER, K. (1911). Eigenartige Korperformen von Amoeba proteus.

A.P.K., xxiii., p. 253.

*(247) HARTMANN, M. (1911). Die Dysenterie-Amoben. Vide PROWAZEK (14),
p. 50.

(248) HICKSON, S. J. (1909). The Proteomyxa. Lankester's Treatise on Zoology,

i., fasc. 1.

(249) — (1909). The Lobosa. Ibid.

(250) HOOGENRAAD, H. R. (1907). Vampyrdla lateritia. A.P.K., viii., p. 216.

(251) — (1907). Uyalodiscus rubicundus. A.P.K., ix., p. 84.

(252) JURGENS (1902). Die Darmamoben und die Amobenenteritis. Veroff.

Militdr-Sanitdtswesens, xx., p. 110.

(253) LISTON, W. G., and MARTIN, C. H. (1911). Pathogenic Amoebae from

Bombay. Q.J.M.S., Ivii., p. 107.

(254) McCARRisoN, R. (1909). Amcebce in Intestines of Persons suffering from

Goitre in Gilgit. Q.J.M.S., liii., p. 723.

(255) MARTIN, C. H. (1911). Nuclear Division of the Large Amoeba from Liver

Abscess. Q.J.M.S., Ivii., p. 279.

(256) MERCIER, L. (1910). L'Amibe de la Blatte (Entamceba blattce). A.P.K.,

xx., p. 143.

(257) METCALF, M. M. (1910). Studies upon Amoeba. J.E.Z., ix., p. 301.

(258) MINCHIN, E. A. (1910). Parasites observed in the Rat-Flea (Ceratophyllus

fasciatus). Hertwig's Festschrift, i., p. 289.

(259) MUSGRAVE, W. E., and CLEGG, M. T. (1904). Amoebas : their Cultivation

and Etiologic Significance. Manila, Dept. of the Interior, Bureau of
Govt. Laboratories, Bid. Lab., xviii.

(260) NERESHEIMER, E. (1905). Vegetative Kernveranderungen bei Amoeba

dofleini. A.P.K., vi., p. 147.

(261) Noc, F. (1909). La Dysenteric amibienne en Cochinchine. A.I.P., xxiii.,

p. 177.

(262) PfiNARD, E. (1902). Faune Rhizopodique du Bassin du Leman. Geneva :

Kundig.

(263) — (1905). Les Amibes a Pellicule. A.P.K., vi., p. 175.

(264) POPOFF, M. (1911). Der Entwicklungscyclus von Amoeba minuta, etc.

A.P.K., xxii., p. 197.

(265) PRANDTL, H. (1907). Der Entwicklungskreis von Allogromia sp. A.P.K.,

ix., p. 1.

(266) ROBERTSON, M. (1905). Pseudospora volvocis. Q.J.M.S., xlix., p. 213.

(267) SCHAUDINN, F. (1895). Teilung von Amoeba binudeata. S.B.G.B., 1895,

p. 130. Reprinted, Schaudinn's Arbeiten, 1911, p. 101.

(268) SCHEEL, C. (1899). Fortpflanzung der Amoben. Kupffer's Festschrift,

p. 569.

(269) SCHEPOTIEFF, A. (1910). Amobenstudien. Zool. Jahrbucher (Anat. u.

Ontog.), xxix., p. 485.

(270) SCHUBOTZ, H. (1905). Amoeba blattce und Amxba proteus. A.P.K., vi., p. 1.

(271) STOLC, A. (1906). Plasmodiogonie, eine Vermehrungsart der niedersten

Protozoen. Arch. Entwicklungsmech., xxi., p. 111.

(272) SUN, A. (1910). Uber einen Parasiten aus der Korperhohle von Ptychodera

minuta. A.P.K., xx., p. 132.

(274) TOPSENT, E. (1893). Pontomyxa flava. A.Z.E. (3), i., p. 385.

(275) VAHLKAMPF, E. (1905). Biologic und Entwicklungsgeschichte von Amciba

Umax. A.P.K., v., p. 167.

(276) VELEY, L. J. (nee GOULD) (1905). Pelomyxa palustris. J.L.S., xxix., p. ^74.
(276-5) WALKER, E. L. (1911). Amoeba; in the Manila water-supply, etc. Philip-
pine Journ. Sci., vi. (B), p. 259.

(277) WENYON, C. M. (1907). Protozoa in the Intestine of Mies. A.P.K.,

Suppl., i., p. 169.

BIBLIOGRAPHY 485

(278) WERNER, H. (1911). Entamceba cdi. Vide PROWAZEK (14), p. 67.

(279) WHITMORE, E. (1911). Parasitare und freilebende Amoben aus Manila und

Saigon. A.P.K., xxiii., p. 71.

(280) — (1911). Kulturamoben aus Manila. Ibid., p. 81.

(c) Foraminifera.
See also Nos. 28, 29, 35, 100, and 131.

(281) AWERINZEW, S. (1910). Gromia dujardini. Z.A., xxxv., p. 425.

(282) HICKSON, S. J. (1911). Polytrema and some Allied Genera. Trans. Linn.

Soc. London (2), xiv., p. 443.

(283) LAUTERBORN, R. (1895). Paulindla chromatophora. Z.iv.Z., lix., p. 537.

(284) LEYDEN, E. v., and SCHATJDINN, F. (1896). Leydenia gemmipara. 8.B.A.B.,

p. 951.

(285) LISTER, J. J. (1895). Life-History of the Foraminifera. Phil. Trans. (B),

clxxxvi., p. 401.

(286) — (1903). The Foraminifera. Lankester's Treatise on Zoology, i., fasc. 2,

p. 47.

(287) — (1906). Life-History of the Foraminifera. Pres. Address Zool. Sec.

Brit. Assoc., York, 1906.

(288) RHTJMBLER, L. (1903). Systematische Zusammenstellung der recenten

Reticulosa. A.P.K., iii., p. 181.
(288-5) SWARCZEWSKY, B. (1909). Attogromia ovoidea. A.P.K., xiv., p. 396.

(d) Xenophyophora.

(289) ANON. (1909). The Xenophyophoridae, F. E. Schultze (sic). Lankester'a

Treatise on Zoology, i., fasc. 1, p. 284.

(290) SCHULZE, F. E. (1905). Die Xenophyophoren. Wiss. Ergebn. Expedition

" Valdivia," xi.

(291) — (1906). Die Xenophyophoren der Siboga-Expedition. Uitkomst. Siboga,

iv. bis.

(e) Mycetozoa.
See also Nos. 69 and 127.

(292) BLOMFIELD, J. E., and SCHWARTZ, E. J. (1910). The Tumours on Veronica

Chamcedrys caused by Sorosphcera Veronicce. Ann. Botany, xxiv., p. 35.

(293) JAHN, E. (1908). Myxomycetenstudien. 7. Geratiomyxa. Ber. Deutsch.

Bot. Ges., xxvia., p. 342.

(294) — (1911). Myxomycetenstudien. 8. Der Sexualakt. Ibid., xxix., p. 231.

(295) LE'GER, L. (1908). Sporomyxa scauri. A.P.K., xii., p. 109.

(296) — and HESSE, E. (1905). Un Parasite des Otiorhynques (Mycetosporidium).

G.R.S.B., Iviii., p. 92.

(297) LISTER, J. J. (1909). The Mycetozoa. Lankester's Treatise on Zoology,

i., fasc. 1, p. 37.

(298) — (1909). Chlamydomyxa and Labyrinthula. Ibid., p. 274.

(299) MARCHAND, E. F. L. (1910). Le Plasmodiophora brassicce. G.R.A.S.,L\.,

p. 1348.

(£) Heliozoa.
See also Nos. 43, 64, 66, 82, 86, 129, 151, 161, 164, 174, and 207.

(300) CAULLERY, M. (1910). Un Protozoaire Marin du Genre GUiophrys Cien-

kowsky (C. marina, n. sp.). G.R. Assoc. Franc. Sci., Lille, 1909, p. 708.

(301) HARTOG, M. (1910). Heliozoa. Encyclop. Brit., eleventh edition, xiii.,

p. 232.

(302) PE'NARD, E. (1903). Quelques Protistes Voisins des Heliozoaires ou des

Flagelles. A.P.K., ii., p. 283.

(303) — (1904). Les Heliozoaires d'Eau Douce. Geneva : Henry Kiindig.

(304) PRZESMYCKI, A. M. (1901). Parasitische Protozoen aus dem inneren der

Rotatorien. B.A.S.G., 1901, p. 358.
*(305) SCHATJDINN, F. (1896). Heliozoa. Das Tierreich., Berlin, 1896.

(306) SCHOUTEDEN, H. (1907). Quelques Flagelles. A.P.K., ix., p. 108.

(307) WELDON, W. F. R., and HICKSON, S. J. (1909). The Heliozoa. Lankester's

Treatise on Zoology, i., fasc. 1, p. 14.

486 THE PROTOZOA

(g) Radiolaria.
See also No. 152.

(308) BORGERT, A. (1911). Fremdkorperskelete bei tripyleen Radiolarien.

A.P.K., xxiii., p. 125.

(309) BRANDT, K. (1902). Die Colliden. A.P.K., i., p. 59.

(310) BUTSCHLI, 0. (1906). Die chemische Natur der Skeletsubstanz der Acan-

tharia. Z.A., xxx., p. 784.

(311) GAMBLE, F. W. (1909). The Radiolaria. Lankester's Treatise on Zoology,

i., fasc. 1, p. 94.

(312) HARTMANN, M., and HAMMER, E. (1909). Die Fortpflanzung von Radio-

larien. S.B.G.B., 1909, p. 228.

(313) HARTOG, M. (1910). Radiolaria. Encydop. Brit., eleventh edition, xxii.,

p. 802.

(314) HUTH, W. (1911). Fortpflanzung von Thalassicolla. S.B.G.B., 1911, p. 1.

(315) MOROFF, T. (1910). Vegetative und reproduktive Erscheinungen bei

Thalassicolla. Hertwig's Festschrift, i., p. 73.

(316) — and STIASNY, G. (1909). Bau und Entwicklung von Acanthometron

pdlucidum. A.P.K., xvi., p. 209.

(317) SCOTT, R. (1911). On Traquairia. Ann. Botany, xxv., p. 459.

(318) STIASNY, G. (1910). Die Beziehung der sog., " gelben Zellen " zu den

kolonie-bildenden Radiolarien. A.P.K., xix., p. 144.

CHAPTER XII
MASTIGOPHORA

(a) General Works.

(319) HARTOG, M. (1910). Flagellata. Encydop. Brit., eleventh edition, x., p. 44.
*(320) SENN, G. (1900). Flagellata. Engler and Prantl, " Die natilrlichen Pflan-
zenfamtiien," I. Teil, 1. Abth., a, p. 93.

(321) WILLEY, A., and HICKSON, S. J. (1909). The Mastigophora. Lankester's

Treatise on Zoology, i., fasc. 1, p. 154.

(b) Flagellata.
See also Nos. 41, 45, 62, 70, 71, 97, 97-5, 153, 160, 213, 223, 236, and 277.

(322) ALEXEIEFF, A. (1909). Les Flagelles Parasites de 1'Intestin des Batraciens

Indigenes. C.R.S.B., Ixvii., p. 199.

(323) — (1909). Trichomonas a Quatre Flagelles Anterieurs. C.R.S.B., Ixvii.,

p. 712.

(324) — (1910). Les Flagelles Intestinaux des Poissons Marins. A.Z.E. (5),

vi., Notes et Revue, p. i.

(325) — (1911). Notes sur les Flagelles. Ibid., p. 491.

(326) — (1911). " Kystes de Trichomonas intestinalis." C.R.S.B., Ixxi., p. £96.

(327) — (1911). La Position des Monadides dans la Systematique des Flagelles,

etc. B.S.Z.F., xxxvi., p. 96.

(328) BENSEN, W. (1909). Trichomonas intestinalis und vaginalis des Menschen.

A.P.K., xviii., p. 115.

(329) BERLINER, E. (1909). Flagellaten-Studien. A.P.K., xv., p. 297.

(330) BOHNE, A., and PROWAZEK, S. v. (1908). Zur Frage der Flagellatendysen-

terie. A.P.K., xii., p. 1.

(331) CHATTON, E. (1911). Pleodorina calif ornica a Banyuls-sur-Mer. Bull. Sci.

Franc. Bdg. (7), xliv., p. 309.

(32) COMES, S. (1910). Lophophora vacuolata. Boll. Ace. Gioen. Catania (2),
xiii., p. 11.

(333) — (1910). A Proposito del Dimorfismo sessuale riscontrato in Dinenympha

gracilis. Ibid., p. 20.

(334) DANILEWSKY, W. B. (1886). Une Monado (Hexamitus), Parasite du Sang.

Arch. Slav. Bid., i., p. 85.

(335) DOBELL, C. C. (1908). Structure and Life-History of Copromonas subtilis.

Q.J.M.S., lii., p. 75.

BIBLIOGRAPHY 487

(336) DOBELL, C. C. (1908). The" Autogamy "of Bodolacertce. B.C., xxviii., p. 548.

(337) FOA, A. (1905). Due nuovi Flagellati parassiti (Galonympha grassii and

Devescovina striata}. Rend, Ace. Lincei, xiv. (2), p. 542.

(338) GRASSI, B., and FOA, A. (1904). Processo di Divisione delle Joenie e Forme

affini. Ibid., xiii. (ii.), p. 241.

(339) HAASE, G. (1910). Euglena sanguinea. A.P.K., xx., p. 47.

(340) HAMBURGER, C. (1905). Dunaliella salina und eine Amobe aus Salinen-

wasser von Cagliari. A.P.K., vi., p. 111.

(341) — (1911). Euglena ehrenbergii, insbesondere die Korperhiille. Sitz-ber.

Heidelberg. Ak. Wiss., 1911.

(342) HARTMANN, M. (1910). Bau und Entwicklung der Trichonymphiden

(Trichonympha hertwigi). Hertwig's Festschrift, i., p. 349.

(343) HASWELL, W. A. (1907). Parasitic Euglenae. Z.A., xxxi., p. 296.

(344) KEYSSELITZ, G. (1908). Studien iiber Protozoen. A.P.K., xi., p. 334.

(345) LATJTERBORN, R. (1895). Eine Siisswasserart der Gattung Multicilia

(M. lacustris). Z.w.Z., lx., p. 236.
(345'5) — • (1911). Psoudopodien bei Chrysopyxis. Z.A., xxxviii., p. 46.

(346) LIEBETANZ, E. (1910). Die parasitische Protozoen des Wiederkauermagens.

A.P.K., xix., p. 19.

(347) LOHMANN, H. (1902). Die Coccolithophoridse. A.P.K., i., p. 89.

(348) MARTIN, C. H., and ROBERTSON, M. (1911). Csecal Parasites of Fowls, etc.

Q.J.M.S., Ivii., p. 53.

(349) MOROFF, T. (1903). Einige Flagellaten. A.P.K., iii., p. 69.

(350) NERESHEIMER, E. (1911). Costia necatrix. Vide PROWAZEK (14), p. 98.

(351) Noc, F. (1909). Le Cycle evolutif de Lamblia intestlnalis. B.S.P.E., ii.,

p. 93.

(352) PASCHER, A. (1910). Chrysomonaden aus dem Hirschberger Grossteiche.

Leipzig : Werner Klinkhardt.

(353) PLIMMER, H. G. (1909). Report on Deaths at the Zoological Gardens during

1908. P.Z.S., 1909, p. 125.

(354) PROWAZEK, S. v. (1903). Flagellatenstudien. A.P.K., ii., p. 195.

(355) — (1904). Einige parasitische Flagellaten. A.K.Q.A., xxi., p. 1.

(356) RODENWALDT, E. (1911). Trichomonas, Lamblia. Vide PROWAZEK (14),

p. 78.

(357) SCHERFFEL, A. (1911). Die Chrysomonadineen. A.P.K., xxii., p. 299.

(358) SENN, G. (1911). Oxyrrhis, Nephroselmisund einige Euflagellaten. Z.w.Z.,

xcvii., p. 605.

(359) STEIN, F. (1878, 1883). Der Organismus der Infusion sthiere. III. Leipzig:

Wilhelm Engelmann.

(360) STEVENSON, A. C. (1911). The Protozoa parasitic in Bufo regularis in

Khartoum. Rep. Wellcome Lab. Khartoum, iv., p. 359.

(361) WENYON, C. M. (1910). A Flagellate of the Genus Oercomonas. Q.J.M.S.,

Iv., p. 241.

(362) — (1910). Macrostoma mesnili from the Human Intestine. Py., iii., p. 210.

(c) Dinoflagellata and Cystoflagellata.

(363) BORGERT, A. (1910). Kem- und Zellteilung bei marinen Ceratium-Aiten.

A.P.K., xx., p. 1.

(364) CATJLLERY, M. (1910). Ellobiopsis chattoni, Parasite de Calanus helgolandicus

Bull. Sci. Franc. Belg. (7), xliv., p. 201.

(365) COUTIERE, H. (1911). Les Ellobiopsis des Crevettes bathypelagiques.

O.R.A.8., clii., p. 409.

(366) CHATTON, E. (1906). Les Blastodinides. C.R.A.8., cxliii., p. 981.

(367) — (1907). Nouvel Apercu sur les Blastodinides (Apodinium mycetoides).

C.R.A.S., cxliv., p. 282.

(368) — (1910). Sur 1'Existence de Dinoflagelles parasites ccelomiques. Les

Syndinium chez les Copepodes pelagiques. C.R.A.S., cli., p. 654.

(369) — (1910). Paradinium poucheti, Flagelle parasite d'Acartia dausi.

C.R.S.B., Ixix., p. 341.

(370) DOGIEL, V. (1906). Die Peridinien. Mitth. Zool. Stat. Neapel, xviii., p. 1.

(371) DUBOSCQ, 0., and COLLIN, B. (1910). La Reproduction sexuee d'un Pro-

tiste parasite des Tintinnides. C.R.A.S., cli., p. 340.

(372) JOLLOS, V. (1910). Dinoflagellatenstudien. A.P.K., xix., p. 178.

(373) KOFOID, C. A. (1905). Craspedotdla, a New Genus of the Cystoflagellata.

Bull. Mus. Harvard, xlvi., p. 163.

488 THE PROTOZOA

(374) KoFOtt), C. A. (1906). Asymmetry in Triposdenia. Univ. California Pull.

Zod., iii., p. 127.

(375) — (1906). Structure of Gonyaulax triacantha. Z.A., xxx., p. 102.

(376) — (1907). Structure and Systematic Position of Polykrikos. Ibid., xxxi.,

p. 291.

(377) — (1907). The Plates of Ceratium. Ibid., xxxii., p. 177.

(378) — (1908). Exuviation, Autotomy, and Regeneration, in Ceratium. Univ.

California Publ. Zool., iv., p. 345.

(379) — (1909). On Peridinium steini. A.P.K., xvi., p. 25.

(380) — (1909). Morphology of the Skeleton of Podolampas. Ibid., p. 48.

(381) — (1909). Mutations in Ceratium. Bull. Hus. Harvard, Iii., p. 211.

(382) — (1910). A Revision of the Genus Ceratocorys. Univ. California Publ.

Zool., vi., p. 177.

(383) — (1910). Forms of Asymmetry of the Din o flagellates. Proc. Internal.

Congr. Zool., vii.

(384) KUSTER, E. (1908). Eine kultivierbare Peridinee. A.P.K., xi., p. 351.

(385) PLATE, L. (1906). Pyrodinium baJiamense. A.P.K., vii., p. 411.

(386) SCHUTT, F. (1895). Die Peridineen der Plankton-Expedition. Ergebn.

Plankton- Exped., iv.

(387) STEIN, F. (1883). Der Organismus der Infusorien. III. (ii.) Die Natur-

geschichte der Arthrodelen Flagellaten. Leipzig : W. Engelmann.

CHAPTER XIII

H^EMOFLAGELLATES

(a) General Works.

See also the Bulletin of the Sleeping Sickness Bureau, London, for abstracts
and reviews of literature.

(388) ALEXEIEFF, A. (1911). La Structure des " Binucleates " de Hartmann.

C.R.S.B., Ixix., p. 532.

(389) BRUMPT, E. (1908). L'Origine des Hemoflagelles du Sang des Vertebres.

C.R.8.B., Ixiv., p. 1046.

(390) HARTMANN, M., and JOLLOS, V. (1910). Die Flagellatenordnung " Binu-

cleata." A.P.K., xix., p. 81.

*(391) LAVERAN, A., MESNIL, F., and NABARRO, D. (1907). Trypanosomes and
Trypanosomiases. London : Bailliere, Tindall and Cox.

*(392) LTJHE, M. (1906). Die im Blute schmarotzenden Protozoen. Mense's
Handbuch der Tropenkrankheiten, iii., p. 69.

*(393) PATTON, W. S. (1909). Our Present Knowledge of the Hsemoflagellates
and Allied Forms. Py., ii., p. 91.

*(394) THIMM, C. A. (1909). Bibliography of Trypanosomiasis. London : Sleep-
ing Sickness Bureau.

*(395) WOODCOCK, H. M. (1909). The Hsemoflagellates and Allied Forms. Lan-
kester's Treatise on Zoology, i., fasc. 1, p. 193.

(b) Trypanosoma and Trypanoplasma.
See also Nos. 19, 22, 23, 27, 42, 56, 132, 134, 686, and 696.

(396) BALDREY, F. S. H. (1909). Die Entwicklung von Trypanosoma lewisi in der

Rattenlaus Hcematopinus spinulosus. A.P.K., xv., p. 326.

(397) — (1911). Evolution of T. evansi through the Fly : Tabanus and Stomoxys.

Journ. Trop. Veterin. Sci., vi., p. 271.

(398) Bosc, F. J. (1904). La Structure etl'Appareil Nucleaire des Trypanosomes.

A.P.K., v., p. 40.

(399) BOUET, G. (1906). Culture du Trypanosome dela Grenouille (T. rotatorium).

A.I. P., xx., p. 564.

(400) — and ROTJBATJD, E. (1910). Transmission des Trypanosomes par les

Glossines, I. and II. A.I. P., xxiv., p. 658. III., B.8.P.E., iii., p. 599.
IV., Ibid., p. 722.

(401) BOUFFARD, G. (1910). Glossina palpalis ct T. Cazalboui. A.I. P., xxiv.,

p. 276.

BIBLIOGRAPHY 489

(402) BRADFORD, J. R., and PLIMMER, H. G. (1902). The T. brucii found in

Nagana, or Tse-tse Fly Disease. Q.J.M.8., xlv., p. 449.

(403) BREINL, A., and KINDLE, E. (1910). Life-History of T. lewisi in the Rat-

Louse. A.T.M.P., iii., p. 553.

(404) BRTJCE, D. (1911). Morphology of T, evansi. P.R.S. (B), Ixxxiv.,

p. 181.

(405) — (1911). Morphology of T. gambiense. Ibid., p. 327.

(406) — and BATEMAN, H. R. (1908). Have Trypanosomes an Ultramioroscopical

Stage in their Life-History ? (No /) P.R.S., (B), Ixxx., p. 394.

(407) — HAMERTON, A. E., BATEMAN, H. R., and MACKIE, F. P. (1909).

T. ingens, n. sp. P.R.S. (B), Ixxxi., p. 323.
(408) (1909). Development of T. gambiense hi Glossina palpalis.

Ibid., p. 405.
(409) — • (1909). A Trypanosome in the African Elephant. Ibid.,

p. 414.
(410) (1910). Development of Trypanosomes in Tsetse Flies.

Ibid., Ixxxii., p. 368.
(411) (1910, 1911). Trypaiiosome Diseases of Domestic Animals in

Uganda, I-V. Ibid., Ixxxii., p. 468 ; Ixxxiii., pp. 1, 15, 176, and 180.
(412) (1910). The Natural Food of Glossina palpalis. Ibid.,

Ixxxii., p. 490.
(413) — (1910). Mechanical Transmission of Sleeping Sickness by the

Tsetse Fly. Ibid., p. 498.
(414) (1911). Experiments to Ascertain if T. gambiense during

its Development within Glossina palpalis is Infective. Ibid., Ixxxiii.,

p. 345.

(415) (1911). Further Researches on the Development of T. gam-
biense in Glossina palpalis. Ibid., p. 513.
(416) and BRUCE (LADY) (1911). T. gallinarum. Rep. Sleeping

Sickness Comm., xi., No. 32, p. 170.

(417) — • (1911). A Trypanosome found in the Blood of a Crocodile.

Ibid., No. 36, p. 184.

(418) BRUMPT, E. (1906). Le Mode de Transmission des Trypanosomes et des

Trypanoplasmes par les Hirudinees. C.R.S.B., Ixi., p. 77.

(419) — (1907). L'Heredite des Infections a Trypanosomes et a Trypanoplasmes

chez les Hotes intermediaires. Ibid., Ixiii., p. 176.

(420) BUCHANAN, G. (1911). Developmental Forms of T. brucei (pecaudi) in

the Internal Organs of the Gerbil. P.R.S. (B), Ixxxiv., p. 161.

(421) CARINI, A. (1910). Stades Endoglobulaires des Trypanosomes. A.I. P.,

xxiv., p. 143.

(422) — (1910). Formas de Eschizogonia do T. lewisi. Soc. de Med. e Cir. de

Sao Paulo, August 16, 1910 (quoted from B.I. P., ix., p. 937).

(423) — (1911). Presence de Trypanosomes chez les bovides, a Sao Paulo.

B.S.P.E., iv., p. 191.

(424) — (1911). Schizogonien bei Trypanosomen. A.P.K., xxiv., p. 80.

(425) CHAGAS, C. (1909). Eine neue TrypanosonTiasis des Menschen. M.I.O C ,

i., p. 159.

(426) — (1911). Le Cycle de " Schizotrypanum cruzi" chez 1'Homme et les

Animaux de Laboratoire. B.S.P.E., iv., p. 467.

(427) CRAWLEY, H. (1910). T. americanum from the Blood of American Cattle.

Journ. Comp. Path. Therap., xxiii., p. 17.

(428) DARLING, S. T. (1911). Murrina. Journ. Infect. Diseases, viii., p. 467.

(429) — (1911). Mode of Infection and Methods of Controlling an Outbreak of

Equine Trypanosomiasis in the Panama Canal Zone. Py., iv., p. 83.

(430) DOFLEIN, F. (1909). Problem der Protistenkunde. I. Die Trypanosomen.

Jena : G. Fischer.

(431) — (1910). Experimentelle Studien iiber die Trypanosomen des Frosches.

A.P.K., xix., p. 207.

(432) DUTTON, J. E., TODD, J. L., and TOBEY, E. N. (1906, 1907). Certain Para-

sitic Protozoa observed in Africa. Part I., Liverpool Trop. Med.
Memoirs, xx., p. 87. Part II., A.T.M.P., i., p. 287.

(433) ELDERS, C. (1909). Trypanosomiasis beim Menschen auf Sumatra.

C.B.B.P.K. (I Abth. Orig.), liii., p. 42.

(434) FANTHAM, H. B. (1911). Life-History of T. gambiense and T. rliode-

siense as seen in Rats and Guinea-pigs. P.R.S. (B), Ixxxiii., p. 212.

490 THE PROTOZOA

(435) FISCHER, W. (1911). Zur Kenntnis der Trypanosomen. Z.H., Ixx., p. 93.

(436) FRANCA, C. (1908). La Biologic des Trypanosomes. A.I.C.P., ii., p. 43.

(437) — (1908). Le Cycle Evolutif des Trypanosomes de la Grenouille. Ibid.,

p. 89.

(438) — (1908). Le Trypanosome de 1'Anguille (T. granulosum). Ibid., p. 113.

(439) — (1910). Un Trypanosome du Lerot (T. elyomis). Ibid., iii., p. 41.

(440) — (1911). Hematozoaires de la Guinee Portuguaise. Ibid., pp. 201, 229.

(441) _ (1911). Les Hematozoaires des Taupes. Ibid., p. 271.

(442) — (1911). Relation autogenetique entre les grands et les petits Trypano-

somes de la Grenouille. C.E.S.B., Ixx., p. 978.

(443) — (1911). La Transformation "in vitro" des Formes crithidiennes de

" T. rotatorium " en Formes trypanosomiques. B.S.P.E., iv., p. 534.

(444) FRIEDRICH, L. (1909). Bau und Naturgeschichte des Trypanoplasma helicis.

A.P.K., xiv., p. 363.

(445) FRY, W. B. (1911). The Extrusion of Granules by Trypanosomes. P.R.S.

(B), Ixxxiv., p. 79.

(445*5) GONDER, R. (1911). Arzneifeste Mikroorganismen. I. T. lewisi.
C.B.B.P.K. (I Abth. Orig.), Ixi., p. 102.

(446) HAMBURGER, C. (1911). Einige parasitische Flagellaten. Verh. Heidelberg.

Naturhist.-Med. Ver. (n. F.), xi., p. 211.

(447) HARTMANN, M. (1910). Eine weitere Art der Schizogonie bei Schizotrypanum

cruzi. A.P.K., xx., p. 361.

(448) KINDLE, E. (1909). Life-History of T. dimorphon. Univ. California Publ.

Zool., vi., p. 127.

(449) — (1910). Degeneration Phenomena of T. gambiense. Py., iii., p. 423.

(450) _ (1910). A Biometric Study of T. gambiense. Ibid., p. 455.

(451) — (1911). The Passage of T. gambiense through Mucous Membranes and

Skin. Ibid., iv., p. 25.

(452) JOLLOS, V. (1910). Bau und Vormehrung von Trypanoplasma helicis.

A.P.K., xxi., p. 103.

(453) KEYSSELITZ, G. (1904). Trypanophi* grobbeni. A.P.K., iii., p. 367.

(454) — (1906). Generations- und Wirtswechsel von Trypanoplasma borreli.

A.P.K., vii., p. 1.

(455) — (1907). Die undulierende Membran bei Trypanosomen und Spirochaten.

A.P.K., x., p. 127.

(456) — and MAYER, M. (1908). Die Entwicklung von T. brucei in Glossina

fusca. A.S.T.H., xii., p. 532.

(457) KLEINE, F. (1909). Positive Infectionsversuche mit T. brucei durch

Glossina palpalis. Deutsch. Med. Wochenschr., xxxv., p. 469. Die
Entwicklung von Trypanosomen in Glossinen. Ibid., p. 924. Die
Aetiologie der Schlafkrankheit. Ibid., p. 1257. Tsetsefliegen und Try-
panosomen. Ibid., p. 1956.

(458) — (1910). Trypanosomenbefunde am Tanganyika. Ibid., xxxvi., p. 1400.

(459) — and TAUTE, M. (1911). Erganzungen zu unseren Trypanosomenstudien.

A.K.G.A., xxxi., p. 321. Reprinted as " Trypansomenstudien."

(460) KOCH, R., BECK, M., and KLEINE, F. (1909). Die Tatigkeit der zur Erfor-

schung der Schlafkrankheit im Jahre 1906-07 nach Ostafrika entsandten
Kommission. A.K.G.A., xxxi., p. 1.

(461) LAVERAN, A. (1911). Identification et Classification des Trypanosomes des

Mammiferes. A. I. P., xxv., p. 497.

(462) — (1911). Les Trypanosomes, ont-ils des Formes latentes chez leurs Hotes

vertebres ? C.E.A.8., cliii., p. 649.

(464) — and MESNIL, F. (1902). Des Trypanosomes des Poissons. A.P.K., i.

p. 475.

(465) — and PETTIT, A. (1910). Des Trypanosomes du Mulot et du Campagnol

(T. grosi et T. microti). C.R.S.B., Ixviii., p. 571.

(466) (1910). Le Trypanosome du Lerot (Myoxus nitela) et la Puce qui

parait le propager (T. blanchardi). Ibid., p. 950.

(467) LEBAILLY, C. (1906). Les Hematozoaires parasites des Teleosteens marins.

Arch. ParasitoL, x., p. 348.

(468) LEBEDEFF, W. (1910). T. rotatorium, Gruby. Hertwig's Festschrift, i., p. 397.

(469) MACHADO, A. (1911). Zytologische Untersuchungen iiber T. rotatorium,

Gruby. M.I.O.C., iii., p. 108.

(470) MANTEUFEL (1909). Studien iiber die Trypanosomiasis der Ratten.

A.K.G.A., xxxiii., p. 46.

BIBLIOGRAPHY 491

(471) MARTIN, C. H. (1910). Trypanoplasma congeri — I. The Division of the

Active Form. Q.J.M.S., lv., p. 485.

(472) MARTIN, G., LEBOBUF, A., and ROTJBATJD, E. (1908). Transmission du

" Nagana " par les Stomoxes et les Moustiques. B.S.P.E., i., p. 355.

(473) MATHIS, C., and LEGER, M. (1911). Parasitologie et Pathologie humaines

et animales au Tonkin. Paris : Masson et Cie.

(474) MESNIL, F. (1910). L'Identification de quelques Trypanosomes pathogenes.

B.S.P.E., iii., p. 376.

(475) — and BRIMONT, E. (1908). Un Hematozoaire nouveau (Endotrypanum)

d'un Edente de Guyane. C.R.S.B., Ixv., p. 581.

(476) MINCHIN, E. A. (1908). The Development of Trypanosomes in Tsetse-Flies

and Other Diptera. Q.J.M.S., Hi., p. 159.

(477) — (1908). Polymorphism of T. gambiense. Py., i., p. 236.

(478) — (1909). The Flagellates parasitic in the Blood of Freshwater Fishes.

P.Z.S., 1909, p. 2.

(479) — (1909). Structure of T. lewisi in Relation to Microscopical Technique.

Q.J.M.8., liii., p. 755.

(480) — and THOMSON, J. D. (1910). Transmission of T. lewisi by the Rat-Flea

(Ceratophyllus fasciatus). P.R.S. (B.), Ixxxii., p. 273.

(481) (1911). Transmission of T. lewisi by the Rat-Flea. Brit. M ed. Journ. ,

1911, i., p. 1309.

(482) — • — (1911). An Intracellular Stage in the Development of T. lewisi in

the Rat-Flea. Ibid., ii. (August 19), pp. 361-364.

(483) — and WOODCOCK, H. M. (1910). Blood-Parasites of Fishes occurring at

Rovigno. Q.J.M.8., lv., p. 113.

(484) MOORE, J. E. S., and BREINL, A. (1907). Cytology of the Trypanosomes,

part i. A.T.M.P., i., p. 441.

(485) , (1908). T. equiperdum. P.R.S. (B.), Ixxx., p. 288.

(486) and HINDLE, E. (1908). Life-History of T. lewisi. A.T.M.P., ii.,

p. 197.
*(487) NERESHEIMER, E. (1911). Die Gattung Trypanoplasma. Vide PROWAZEK

(14), p. 101.

(488) NEUMANN, R. 0. (1909). Protozoische Parasiten im Blut von Meeresfischen.

Z.H., Ixiv., p. 1.

(489) NOVY, F. G., and McNEAL, W. J. (1905). Trypanosomes of Birds. Journ.

Infect. Diseases, ii., p. 256.

(490) — — and TORRE Y, H. N. (1907). Trypanosomes of Mosquitoes and Other

Insects. Ibid., iv., p. 223.

(491) OTTOLENGHI, D.( 1908). T. Irucei und T. equinum. C.B.B.P.K. (I. Abth.

Orig.), xlvii., p. 473.

(492) — (1909). Die Entwicklung einiger pathogener Trypanosomen im Sau-

getierorganismus. A.P.K., xviii., p. 48.

(493) PATTON, W. S., and STRICKLAND, C. (1908). The Relation of Blood-sucking

Invertebrates to the Life-Cycles of Trypanosomes. Py., i., p. 322.

(494) PETRIE, G. F. (1905). The Structure and Geographical Distribution of

Certain Trypanosomes. J.H., v., p. 191.

(495) — and AVARI, C. R. (1909). On the Seasonal Prevalence of T. lewisi in

Mus rattus and in Mus decumanus. Py., ii., p. 305.

(496) POLICARD, A. (1910). Sur la Coloration vitale des Trypanosomes. C.R.S.B.,

Ixviii., p. 505.

(497) PROWAZEK, S. v. (1905). Studien iiber Saugetiertrypanosomen. A.K.G.A.,

xxii., p. 351.

(498) — (1909). Kritische Bemerkungen zum Trypanosomenproblem. A.S.T.H.,

xiii., p. 301.

(499) ROBERTSON, M. (1906). Certain Blood-inhabiting Protozoa. Proc. R.

Phys. Soc. Edinburgh., xvi., p. 232.

(500) — (1907). A Trypanosome found in the Alimentary Canal of Pontobdella

muricata. Ibid., xvii., p. 83.

(501) — (1909). Life-Cycle of T. vittatce. Q.J.M.S., liii., p. 665.

(502) — (1909). A Trypanosome found in the Alimentary Tract of Pontobdella

muricata. Q.J.M.S., liv., p. 119.

(503) — (1911). Transmission of Flagellates living in the Blood of Fishes. Phil.

Trans. (B.), ccii., p. 29.

(504) RODENWALDT, E. (1909). T. lewisi in Hcematopinus spinulosus. C.B.B.P.K.

(I Abth. Orig.), Iii., p. 30.

492 THE PROTOZOA

(505) ROSENBUSCH, F. (1909). Trypanosomen-studien. A.P.K., xv., p. 263.

(506) ROUBAUD, E. (1909). Les Trypanosomes pathogenes et la Glossina palpalis.

Rapport de la Mission d* Etudes de la Maladie du Sommeil au Congo Fran-
c.ais (Paris, Masson et Cie.), p. 511.

(507) — (1910). Phenomenes morphologiques du Developpement des Trypano-

somes chez les Glossines. C.R.A.S., cli., p. 1156.

(508) STASSANO, H. (1901 ). La Fonction et Relation du petit Noyau des Trypano-

somes. C.R.S.B., liii., p. 468.

(509) STEPHENS, J. W. W., and FANTHAM, H. B. (1911). Peculiar Morphology of

a Trypanosome from a Case of Sleeping Sickness (T. rhodesiense). P.R.S.
(B.), Ixxxiii., p. 28.

(510) STOCKMAN, S. (1910). A Trypanosome of British Cattle. Journ. Comp.

Pathcl. Therapeut., xxiii., p. 189.

(511) STKICKLAND, C. (1911). Mechanism of Transmission of T. lewisi by the Rat-

Flea. Brit. Med. Journ., 1911, p. 1049.

(512) — and SWELLENGREBEL, N. H. (1910). On T. lewisi and its Relation to

Certain Arthropoda. Py., iii., p. 436.

(513) STUHLMANN, F. (1907). Die Tsetsefliegen (Glossina fusca und 01. tachinoides).

A.K.G.A., xxvi., p. 301.

(514) SWELLENGREBEL, N. H. (1909). Bau und Zellteilung von T. gambiense

und T. equinum. Tijdscnr. Ned. Dierk. Ver. (2), xi., p. 80.

(515) — (1910). Fixation and Staining of T. lewisi. Py., iii., p. 226.

(516) — (1910). Normal and Abnormal Morphology of T. lewisi. Ibid, p. 459.

(517) — and STRICKLAND, C. (1910). The Development of T. lewisi outside the

Vertebrate Host. Ibid., p. 360.

(518) (1911). Remarks on Dr. Swingle's Paper, "The Transmission of

T. lewisi by Rat-Fleas," etc. Ibid., iv., p. 105.

(519) SWINGLE, L. D. (1907). On T. lewisi. Trans. Amer. Micr. Soc., xxvii.,

p. 111.

(520) — (1911). Transmission of T. lewisi by Rat-Fleas. Three New Herpeto-

monads. Journ. Infect. Diseases, viii., p. 125.

(521) TAUTE, M. (1911). Die Beziehungen der Glossina morsitans zur Schlaf-

krankheit. Z.H., Ixix., p. 553.

(522) THIROUX, A. (1905). T. paddce. A.I.P., xix., p. 65.

(523) — (1905). T. duttoni. Ibid., p. 564.

(524) THOMSON, J. D. (1906). Blood -Parasites of the Mole. J.H., vi., p. 574.

(525) — (1908). Cultivation of the Trypanosome found in the Blood of the Gold-

fish. Ibid., viii., p. 75.

(516) WERBITZKI, F. W. (1910). Blepharoplastlose Trypanosomen. C.B.B.P.K.
(I Abth. Orig.), liii., p. 303. (See also Bulletin of the Sleeping Sickness
Bureau, vol. iii., pp. 221, 313, and 458, for further references.)

(527) WOODCOCK, H. M. (1910). On Certain Parasites of the Chaffinch (Fringilla

coelebs) and the Redpoll (Linota rufescens). Q.J.M.S., Iv., p. 641.

(528) YAKIMOS-F, W. L., KOHL-YAKIMOFF, N., and KORSSAK, D. W. (1910).

T. korssaki of Mus agrarius, Piroplasmoses of Mus agrarius, Reindeer,
Yak, and Bears. C.B.B.P.K. (I Abth. Orig.), Iv., p. 370.

(529) ZTJPITZA, M. (1909). Die Vogel- und Fischtrypanosomen Kameruns.

A.S.T.H., xiii., Beiheft 3, p. 101.

(c) Crithidia, Leptomonas, Herpetomonas, etc.
See also No. 84.

(530) BOUET, G., and ROUBAUD, E. (1911). La Presence au Dahomey et Trans-

mission du Leptomonas davidi. C.R.8.B., Ixx., p. 55.

(531) CHATTON, E. (1909). Un Trypanosomide nouveau d'une Nycteribie, et les

Relations des Formes Trypanosoma, Herpetomonas, Leptomonas et
Crithidia. C.R.S.B., Ixvii., p. 42.

(532) — and ALILAIRE, E. (1908). Coexistence d'un Leptomonas et d'un Trypano-

soma chez un Muscide non vulnerant, Drosophila confusa. C.R.S.B.,
Ixiv., p. 1004.

(533) — and LE'GER, A. (1911). Eutrypanosomes, Leptomonas et Leptotrypano-

somes chez Drosophila confusa (Muscide). C.R.S.B., Ixx., p. 34.
(534) (1911). Quelques Leptomonas de Muscides et leurs Leptotrypano-

somes. Ibid., p. 120.
(535) DUNKERLY, J. S. (1911). Life-History of Lepf. muscce-domesticce. Q.J.M.8.,

Ivi., p. 645.

BIBLIOGRAPHY 493

(536) FLTI, P. C. (1911). Die im Darm der Stubenfliege vorkommenden proto-

zoaren Gebilde. C.B.B.P.K. (I Abth. Orig.), Ivii., p. 522.

(537) FRANCA, C. (1911). L'Existence en Portugal de Lept. davidi dans le Latex de

Euphorbia peplus et E. segetalis. B.8.P.E., iv., p. 532.

(538) — (1911). Notes sur Lept. davidi. Ibid., p. 669.

(539) GEORGEWITCH, J. (1909). Le developpement de Crithidia simulice. C.R.S.B.,

Ixvii., p. 517.

(540) LAFONT, A. (1910). La Presence d'un Leptomonas . . . dans le Latex de

Trois Euphorbiacees. A. I. P., xxiv., p. 205.

(541) — (1911). La Transmission du Lept. davidi des Euphorbes par un Hemip-

tere. C.B.S.B., Ixx., p. 58.

(542) LEGER, L. (1902). La Structure et Multiplication des Flagelles du Genre

Herpetomonas Kent. O.R.A.S., cxxxiv., p. 781.

(543) — (1902). Un Flagelle Parasite de I' Anopheles maculipennis. C.R.S.B.,

liv., p. 354.

(544) — (1904). Un nouveau Flagelle, Parasite des Tabanides. C.R.S.B., Ivii.,

p. 613.

(545) — (1904). Les Affinites de Y Herpetomonas subulata et la Phylogenie des

Trypanosomes. C.R.S.B., Ivii., p. 615.

(546) — and DUBOSCQ, 0. (1909). Parasites de 1'Intestin d'une Larvede Ptychop-

tera. Bull. Acad. Belgique, No. 8, p. 885.

(547) MACKINNON, D. L. (1910). New Parasites from Trichoptera. Py., iii., p. 245.

(548) — (1910). Herpetomonads from Dung-Flies. Ibid., p. 255.

(549) — (1911). More Protozoan Parasites from Trichoptera. Ibid., iv., p. 28.

(550) PATTON, W. S. (1908). Life-Cycle of a Species of Crithidia parasitic in

Gerris fossarum. A.P.K., xii., p. 131.

(551) — (1908). Herp. lygcei. A.P.K., xiii., p. 1.

(552) — (1909). Life-Cycle of a Species of Crithidia parasitic in Tabanus hUarius

and Tabanus sp. A.P.K., xv., p. 333.

(553) — (1910). Infection of the Madras Bazaar Fly with Herp. muscce-domesticce.

B.8.P.E., iii., p. 264.

(554) PORTER, A. (1910). Crithidia melophagia. Q.J.M.S., Iv., p. 189.

(555) — (1909). Crithidia gerridis. Py., ii., p. 348.

(556) — (1909). Life-Cycle of Herp. jaculum. Ibid., p. 367.

(557) PROWAZEK, S. v. (1904). Die Entwicklung von Herpetomonas. A.K.G.A.,

xx., p. 440.

(557'5) ROTJBAUD, E. (1911). Cyslolrypanosoma intestinalis. C.R.S.B., Ixxi.,
p. 306.

(558) STRICKLAND, C. (1911). A Herpetomonas parasitic in the common Green-

bottle Fly, Lucttia sp. Py., iv., p. 222.

(559) SWELLENGREBEL, N. H. (1911). Morphology of Herpetomonas and

Crithidia, etc. Ibid., p. 108.

(560) WERNER, H. (1908). Eine eingeisselige Flagellatenform im Darm der

Stubenfliege. A.P.K., xiii., p. 19.

(d) Leishmania, etc.

See also No. 84. For references to literature and critical summaries and reviews,
see Kola Azar Bulletin (Royal Society, London).

(561) BASILE, C. (1910). Leishmaniosi del Cane e 1'Ospite intermedio del Kala-

Azar infantile. Rend. Ace. Lincei (5), xix. (2), p. 523.

(562) — (1911). Trasmissione delle Leishmaniosi. Ibid. (5), xx. (1), p. 50.

(563) — (1911). Leishmaniosi e suo Modo di Trasmissione. Ibid. (5), xx. (2),

p. 72.

(564) — LACAVA, F., and VISENTINI, A. (1911). L' Identita delle Leishmaniosi.

Ibid., p. 150.

(565) DARLING, S. T. (1909). Histoplasma capsulatum and the Lesions of Histo-

plasmosis. J.E.M., xi., p. 515.

(566) DONOVAN, C. (1909). Kala-Azar in Madras. Bombay Medical Congress,

February 24, 1909.

(567) LEISHMAN, W. B., and STATHAM, J. C. B. (1905). Development of the

Leishman Body in Cultivation. Journ. R. A. Med. Corps, iv., p. 321.

(568) MARSHALL, W. E. (1911). Pathological Report, Kala-Azar Commission.

Rep. Wellcome Lab., iv., p. 157.

(569) MARZINOWSKY, E. J. (1909). Cultures de Leishmania tropica. B.8.P.E.,

ii., p. 591.

494 THE PROTOZOA

(570) NICOLLE, C. (1909). Le Kala-Azar infantile. A.I.P., xxiii., p. 361.

(571) — and COMTE, C. (1908). Origine canine du Kala-Azar. C.R.A.S., cxlvi.,

p. 789.

(572) NOVY, F. G. (1909). Leishmania infantum. B.S.P.E., ii., p. 385.

(573) PATTON, W. S. (1908). The Leishman-Donovan Parasite in Cimex rotun-

datus. S.M.I., xxxi.

(574) — (1908). Inoculation of Dogs with the Parasite of Kala-Azar (Herpeto-

monas [Leishmania] donovani). Py., i., p. 311.

(575) — (1909). The Parasite of Kala-Azar and Allied Organisms. Trans. Soc.

Trop. Med. Hygiene, ii., p. 113.

(576) ROGERS, L. (1904). Trypanosomes from the Spleen Protozoic Parasites of

Cachexial Fevers and Kala-Azar. Q.J.M.S., xlviii., p. 367.

(577) — (1907). The Milroy Lectures on Kala-Azar. Brit. Med. Journ.,

February 23, March 2 and 9.

(578) Row, R. (1909). Development of the Parasite of Oriental Sore in Cultures.

Q.J.M.S., liii., p. 747.

(579) THIROUX, A., and TEPPAZ, L. (1909). La Lymphangite epizootique des

Equides au Senegal. A. I. P., xxiii., p. 420.

(580) VISENTINI, A. ( 1910). La Morfologia ed il Ciclo di Sviluppo della Leishmania.

Istituto d. Clin. Med. d. It. Univ. Roma.

(581) WRIGHT, J. H. (1903). Protozoa in Tropical Ulcer (" Delhi Sore "). Journ.

Med. Research, x. (n.s. v.), p. 472.

(e) Frowazekia.

(582) ALEXEIEFF, A. (1911). La Morphologic et la Division de Bodo caudatus.

C.R.S.B., Ixx., p. 130.

(582-5) DUNKERLY, J.S.(1912). Thelohania and Prowazekia in Anthomyid Flies.
G.B.B.P.K. (I Abth. Orig.), Ixii., p. 136.

(583) HARTMANN, M. (1911). Die Flagellatenordnung Binudeata und die

Gattung Prowazekia. A.P.K., xxii., p. 141.

(584) MARTINI, E. (1910). Pr. cruzi und ihre Beziehungen zur Atiologie von

ansteckenden Darmkrankheiten zu Tsingtau. Z.H., Ixvii., p. 275.

(585) NAEGLER, K. (1910). Pr. parva. A.P.K., xxi., p. 111.

(586) WALKER, E. L. (1910). Trypanoplasma ranee. Journ. Med. Research, xxiii.,

(n.s. XVIII.), p. 391.

(587) WHITMORE, E. R. (1911). Pr. asiatica. A.P.K., xxii., p. 370.

CHAPTER XIV
SPOROZOA— TELOSPORIDIA

(a) General Works.
*(588) HAGENMULLER (1899). Bibliotheca Sporozoologica. Ann. Mus. Nat.

Hist. Marseille (2), i.
*(589) MINCHIN, E. A. (1903). The Sporozoa. A Treatise on Zoology (Lankester)

(London, A. and C. Black), p. 150.

(590) WOODCOCK, H. M. (1910). Sporozoa. Encydop. Brit., eleventh edition,

xxv., p. 734. Coccidia. Ibid., vi., p. 615. Gregarines. Ibid., xii.,
p. 555. Hsemosporidia. Ibid., xii., p. 806. Endospora. Ibid., ix.
p. 383.

(b) Gregarines.
See also Nos. 72, 84, and 123.

(591) AWERINZEW, S. (1909). Die Vorgange der Schizogonie bei Gregarinen aus

dem Darm von Amphiporus sp. A.P.K., xvi., p. 71.

(592) BEATJCHAMP, P. de (1910). Une Gregarine nouvelle du Genre Porospora.

C.R.A.8., cli... p. 997.

(593) BERNDT, A. (1902). Die im Darme der Larve von Tenebrio molitor lebenden

Gregarinen. A.P.K., i., p. 375.

(594) BRASIL, L. (1905). La Reproduction des Gregarines monocystidees.

A.Z.E. (4), iii., p. 17.

BIBLIOGRAPHY 495

(595) BRASIL, L. (1905). La Reproduction des Gregarines monocystidees.

A.Z.E. (4), iv., p. 69.

(596) • — (1907). La Schizogonie et la Croissance des Gametocytes chez /Se/emctatm

caulleryi. A.P.K., viii., p. 370.

(597) — (1909). Documents sur quelques Sporozoaires d'Annelides. A.P.K.,

xvi., p. 107.

(598) COGNETTI DE MARTIN, L. (1911). Le Monocistidee e loro Fenomeni ripro-

duttivi. A.P.K., xxiii., p. 205.

(599) COMES, S. (1907). Der Chromidialapparat der Gregarinen. A.P.K., x.,

p. 416.

(600) CRAWLEY, H. (1905). Movements of Gregarines. Proc. Acad. Philadelphia,

Ivii., p. 89.

(601) CUNNINGHAM, J. T. (1907). Kalpidorhynchus arenicdce. A,P.K., x., p. 199.

(602) DOGIEL, V. (1906). Cystobia chiridotce. A. P.K., vii., p. 106.

(603) — (1907). Schizocystis sipunculi. A.P.K., viii., p. 203.

(604) — (1909). Die Sporocysten der Colom-Monocystidese. A.P.K., xvi., p. 194.

(605) — (1910). Callynthrochlamys phronimce. A.P.K., xx., p. 60.

(606) — (1910). Einige neue Catenata. Z.w.Z., xciv., p. 400.

(607) DRZEWECKI, W. (1903, 1907). Vegetative Vorgange im Kern und Plasma

der Gregarinen des Regenwurmhodens. A.P.K., iii., p. 107. II. Stomato-
phora coronata. Ibid., x., p. 216.

(608) DUKE, H. L. (1910). Metamera schubergi. Q.J.M.S., Iv., p. 261.

(609) FANTHAM, H. B. (1908). The Schizogregarines. Pi/., i., p. 369.

(610) HALL, M. C. (1907). A Study of some Gregarines, with especial Reference to

Hirmocystis rigida. Stud. Zool. Lab. Univ. Nebraska, vii., p. 149.

(611) HESSE, E. (1909). Les Monocystidees des Oligochetes. A.Z.E. (5), iii.,

p. 27.

(611'5) HOFFMANN, R. (1908). Fortpflanzungserscheinungen von Monocystideen
des Lumbricus agricola. A.P.K., xiii., p. 139.

(612) HUXLEY, J. S. (1910). Ganymedes anaspidis, Q.J.M.S., Iv., p. 155.

(613) KUSCHAKEWITSCH, S. (1907). Vorgange bei den Gregarinen des Mehlwurm-

darms. A.P.K., Suppl. L, p. 202.

(614) LEGER, L. (1904). La Reproduction sexuee chez les Stylorhynchus. A.P.K.,

iii., p. 303.

(615) — (1904). Sporozoaires Parasites de YEmbia Sdieri. Ibid., p. 358.

(616) — (1906). Tceniocystis mira. A.P.K., vii., p. 307.

(617) — (1907, 1909). Les Schizogregarines des Tracheates : I. Ophryocystis.

A.P.K., viii., p. 159. II. Schizocystis. Ibid., xviii., p. 83.

(618) — and DUBOSCQ, 0. (1902). Les Gregarines et l'Epithelium intestinal chez

les Tracheates. Arch. Parasitol., vi., p. 377.

(619) — • — (1903). Le Developpement des Gregarines Stylorhynchides et Steno-

phorides. A.Z.E. (4), i., Notes et Revue, p. Ixxxix.
(620) (1904). Les Gregarines et I'Epitheliuin intestinal des Tracheates.

A.P.K., iv., p. 335.

(621) (1909). La Sexualite chez les Gregarines. A.P.K., xvii., p. 19.

(622) (1911). Deux nouvelles Especes de Gregarines appartenant au Genre

Porospora. Ann. Univ. Grenoble, xxiii., p. 401.
*(623) LUHE, M. (1904). Die Sporozoiten, die Wachstumsperiode und die ausge-

bildeten Gregarinen. A.P.K., iv., p. 88.

(624) NUSBAUM, J. (1903). Fortpflanzung einer Gregarine — Schaudinella henlece.

Z.w.Z., lxxv.,p. 281.

(625) PAEHLER, F. (1904). Die Morphologie, Fortpflanzung und Entwicklung von

Gregarina ovata. A.P.K., iv., p. 64.

(626) PFEFFER, E. (1910). Die Gregarinen im Darm der Larve von Tenebrio

molitor. A.P.K., xix., p. 107.

(627) PORTER, A. (1909). Merogregarina amaroucii. A.P.K., xv., p. 228.

(628) ROBINSON, M. (1910). On the Reproduction of Kalpidorhynchus arenicolce,

Q.J.M.S., liv., p. 565.

(629) SCHELLACK, C. (1907). Die Entwicklung und Fortpflanzung von Echinomera

hispida. A.P.K., ix., p. 297.

(630) — (1908). Die solitare Encystierung bei Gregarinen. Z.A., xxxii., p. 597.

(631) SCHNITZLER, H. (1905). Die Fortpflanzung von Clepsidrina ovata. A.P.K.,

vi., p. 309.

(632) WOODCOCK, H. M. (1906). Life-Cycle of " Cystobia " irregularis. Q.J.M.8.

\., p. 1.

496 THE PROTOZOA

(c) Coccidia.

Sec also Nos. 47, 83, 94, 99, and 147.

*(033) BLANCHARD, R. (1900). Les Coccidies et leur Role pathogene. Causeries
Sci. Soc. Zod. France, p. 133.

(634) CHAGAS, C. (1910). Adelea haftmanni. M.I.O.C., ii., p. 168.

(635) DAKIN, W. J. (1911). Merocystis kathce. A.P.K., xxii., p. 145.

(635'5) DEBAISIEUX, P. (1911). Recherches sur les Coccidies. La Cellule, xxvii.,
pp. 89 and 257.

(636) DOBELL, C. C. (1907). Life-History of Adelea ovata. P.R.S. (B.), Ixxix.,

p. 155.

(637) ELMASSIAN, M. (1909). Coccidium rouxi, Zoomyxa legeri. A.Z.E. (5), ii..

p. 229.

(638) FANTHAM, H. B. (1910). Eimeria (Coccidium) avium. P.Z.S., 1910, p. 672.

(639) — (1910). Avian Coccidiosis. Ibid., p. 708.

(640) HADLEY, P. B. (1911). Eimeria avium. A.P.K., xxii., p. 7.

(641) JOLLOS, V. (1909). Multiple Teilung und Reduktion bei Adelea ovata.

A.P.K., xv., p. 249.

(642) KUNZE, W. (1907). Orcheobius herpobdellce. A.P.K., ix., p. 382.

(643) LAVERAN, A., and PETTIT, A. (1910). Une Coccidie de Agama colonorum.

(Cocc. agamce). C.R.S.B., Ixviii., p. 161.

(644) LEGER, L. (1911). Caryospora simplex, et la Classification des Coccidies.

A.P.K., xxii., p. 71.

(645) — and DTJBOSCQ, 0. (1908). Involution schizogonique de YAggregata

(Eucoccidium) eberthi. A.P.K., xii., p. 44.
(646) (1910). Selenococcidium intermedium. A.Z.E. (5), v., p. 187.

(647) METZNER, R. (1903). Coccidium cuniculi. A.P.K., ii., p. 13.

(648) MOROFF, T. (1906). Adelea zonula. A.P.K., viii., p. 17.

(649) — and FIEBIGER, J. (1905). Eimeria subepithelialis. A.P.K., vi., p. 166.

(650) PEREZ, C. (1903). Le Cycle evolutif de 1' Adelea mesnili. A.P.K., ii., p. 1.

(651) SCHELLACK, C., and REICHENOW, E. (1910). L^o&ms-Coccidien. Z.A.,

xxxvi., p. 380.

(652) SIEDLECKI, M. (1898). La Coccidie de la Seiche. A.I. P., xii., p. 799.

(653) — (1907). Caryotropha mesnilii. B.A.8.C., 1907, p. 453.

(654) STEVENSON, A. C. (1911). Coccidiosis of the Intestine of the Goat. Rep.

Wellcome Lab. Khartoum, iv., p. 355.

(655) TYZZER, E. E. (1910). Cryptosporidium muris of the Common Mouse.

Journ. Med. Research, xxiii, (n.s. XVIII.), p. 487.

(656) WOODCOCK, H. M. (1904). On Klossietta muris. Q.J.M.S., xlviii., p. 153.

CHAPTER XV
H^EMOSPORIDIA

(a) General Works.

*(657) LAVERAN, A. (1905). Hsemocytozoa. B.I. P., iii., p. 809.
*(658) SCHAUDINN, F. (1899). Der Generations wechsel der Coccidien und Haemo-
sporidien. Zool. Centralbl., vi., p. 765.

(659) WASIELEWSKI (1908). Studien und Mikrophotogramme zur Kenntnisse der

pathogenen Protozoen. II. Untersuchungen iiber Blutschmarotzer.
Leipzig : Barth.

(b) Hsemamceboe.
See also Nos. 130 and 686.

(660) ARAGAO, H. DE B., and NEIVA, A. (1909). Intraglobular Parasites of

Lizards. PI. diploglossi and PI. tropiduri. M.I.O.C., i., p. 44.

(661) BERENBERG-GOSSLER, H. v. (1909). Naturgeschichte der Malariaplas-

modien. A.P.K., xvi., p. 245.

(662) BERTRAND, D. M. (1911). Les Parasites endoglobulaires pigmentes des

Vertebres. Paris : Jouve et Cie.

(663) BILLET, A. (1905). Une Forme particuliere de 1'Hematozoaire du Palu-

disme decrite par MM. Ed. et Et. Sergent. C.R.S.B., Iviii., p. 720.

(664) — (1906). La Forme hemogregarinienne du Parasite de la Fievre quarte.

C.R.S.B., Ix., p. 891.

BIBLIOGRAPHY 497

(665) BILLET, A. (1906). Diagnose differentielle des Formes annulaires des

Hematozqaires du Paludisme. C.R.S.B., Ixi., p. 754.

(666) — (1910). Evolution chez le meme Sujet du Paludisme tierce primaire en

Paludisme tierce secondaire. B.8.P.E., iii., p. 187.

(667) CARDAMATIS, J. P. (1909). Le Paludisme des Oiseaux en Gr£ce. Etude du

Parasite de Danilewsky. C.B.B.P.K. (I Abth. Orig.), Iii., p. 351.

(668) CASTELLANI, A., and WILLEY, A. (1904). Hsematozoa of Vertebrates in

Ceylon. Spolia Zeylanica, ii., p. 78.

(669) DARLING, S. T. (1910). Transmission and Prevention of Malaria in the

Panama Canal Zone. A.T.M.P., iv., p. 179.

(670) DOBELL, C. C. (1910). Life-History of Hcemocystidium simondi. Hertwig's

Festschrift, i., p. 123.

(671) FLU, P. C. (1908). Affenmalaria. A.P.K., xii., p. 323.

(672) GILRUTH, J. J., SWEET, G., and DODD, S. (1910). Proteosoma biziurce and

Hcemogregarina megalocystis. Proc. Roy. Soc. Victoria (n.s.), xxiii., p. 321.

(673) GRASSI, B. (1901). Die Malaria, Studien eines Zoologen. Jena : Gustav

Fischer.

(674) HALBERSTAEDTER, L., and PROWAZEK, S. v. (1907). Die Malariaparasiten

der Affen. A.K.G.A., xxvi., p. 37.

(675) HARTMANN, M. (1907). Das System der Protozoen. Zugleich vorlaufige

Mitteilung iiber Proteosoma. A.P.K., x., p. 139.

(676) MAYER, M. (1908). Malariaparasiten bei Affen. A.P.K., xii., p. 314.

(677) NEUMANN, R. O. (1908). Die Ubertragung von Plasmodium prcecox auf

Kanarienvogel durch Stegomyiafasciata. A.P.K., xiii., p. 23.

(678) Ross, R. (1910). The Prevention of Malaria. London : John Murray.

(679) SERGENT, ET., and SERGENT, ED. (1910). L'lmmunite dans le Paludisme

des Oiseaux, etc. G.R.A.8., cli., p. 407.

(680) THIROTJX, A. (1906). Des Relations de la Fievre tropicale avec la Quarte et

la Tierce. A.I. P., xx., pp. 766 and 869.

(681) VASSAL, J. J. (1907). L'Hematozoaire de 1'Ecureil (Hoemamaeba vassali).

A.I.P., xxi., p. 851.

(c) Halteridia.
See also No. 132.

(682) ANSCHUTZ, G. (1910). Uebertragungsversuche von Hcemoproteus oryzivoros

und Trypanosoma paddce. C.B.B.P.K. (I Abth. Orig.), liv., p. 328.

(683) ARAGAO, H. DE B. (1908). Der Entwicklungsgang und die Ubertragung von

Hcemoproteus cdumbce. A.P.K., xii., p. 154.

(684) MAYER, M. (1910). Die Entwicklung von Halteridium. A.S.T.H., xiv.,

p. 197.

(685) — (1911). Ein Halteridium und Leucocytozoon des Waldkauzes. A.P.K.,

xxi., p. 232.

(685'5) MINCHIN, E. A. (1910). Report on Blood-Parasites collected by the
Commission. Rep. Sleeping Sickness Comm., x., p. 73.

(686) SERGENT, ED., and SERGENT, ET. (1907). Les Hematozoaires d'Oiseaux.

A.I.P., xxi., p. 251.

(687) WOODCOCK, H. M. (1911). An Unusual Condition in Halteridium. Z.A.,

xxxviii., p. 465.

(d) Leucocytozoa (Vera).
See also Nos. 132, 473, and 686.

(688) BERESTNEFF, N. (1904). Das Leucocytozoon Danilewskyi. A.P.K., iii.,

p. 376.

(689) FANTHAM, H. B. (1910). Parasitic Protozoa of the Red Grouse. P.Z.S.,

1910, p. 692.

(690) WENYON, C. M. (1910). On the Genus Leucocytozoon. Py., iii., p. 63.

(e) Hsemogregarines.
See also Nos. 78, 84, and 89.

(691) ADIE, J. R. (1906). "Leucocytozoon " ratti. Journ. Trop. Med., ix., p. 325.

(692) ARAGAO, H. DE B. (1911). Hamogregarinen von Vogeln. M.I.O.C., iii.

p. 54.

(693) BALFOUR, A. (1906). H. balfouri. Rep. Wellcome Lab. Khartoum, ii., p. 96.

(694) — (1906). " Leucocytozoon " muris. Ibid., p. 110.

32

498 THE PROTOZOA

(695) BERESTNEFF, N. (1903). Eine neue Blutparasiten der indischen Frosche.

A.P.K., ii., p. 343.

(696) BILLET, A. (1904). Trypanosoma inopinatum et Drej.anidium. C.R.S.B.,

Ivii., p. 161.

(697) BOUET, G. (1909). Hemogregarines de 1'Afrique occidentale frangaise.

C.R.S.B., Ixvi., p. 741.

(698) CARINI, A. (1910). " H. muris." Rev. Soc. Sci. Sao Paulo, v.

(699) CHRISTOPHERS, S. R. (1905). H. gerbilli. S.M.I., 18.

(700) — (1906). Leucocytozoon canis. S.M.I., 26.

(701) _ (1907). Leucocytozoon canis in the Tick. S.M.I., 28.

(703) DANILEWSKY, B. (1886). Lea Hematozoaires des Lezards. Arch. Slav.

Bid., i., p. 364.

(704) — (1887). Les Hematozoaires des Tortues. Ibid., iii., pp. 33 and 370.

(705) — (1889). La Parasitologie comparee du Sang. I. Nouvelles Recherches

sur les Hematozoaires du Sang des Oiseaux. II. Recherches sur les
Hematozoaires des Tortues. Kharkoff.

(706) FANTHAM, H. B. (1905). Lankesterella tritonis. Z.A., xxix., p. 257.

(707) FLIT, P. C. (1909). Hamogregarinen im Blute Surinamischer Schlangen.

A.P.K., xviii., p. 190.

(708) FRANCA, C. (1908). Une Hemogregarine de 1'Anguille (H. bettencourli).

A.I.C.P., ii., p. 109.

(709) — (1908). H. splendens (Labbe). Ibid., p. 123.

(710) _ (1909). Hemogregarines de Lacerta ocellata. Ibid., p. 339.

(711) — (1910). Parasites endocellulaires du Psammodromus algirus. Ibid.,

iii., p. 1.

(712) — (1910). Hemogregarines de Lacerta muralis. Ibid., p. 21.

(713) HAHN, C. W. (1909). H. stepanowi in the Blood of Turtles. A.P.K., xvii.,

p. 307.

(714) KOIDZTJMI, M. (1910). H. sp. in Clemm^s japonicus. A.P.K., xviii., p. 260.

(715) LAVERAN, A., and PETTIT, A. (1909). Les Hemogregarines de quelques

Sauriens d'Afrique. B.S.P.E., ii., p. 506.
(716) (1910). Les Formes de Multiplication endogene de H. sebai.

C.R.A.S., cli., p. 182.

(717) (1910). H. agamce. C.R.S.B., Ixviii., p. 744.

(718) (1910). Le Role d'Hyalomma Mqypiium L. dans la Propagation de

H. mauritanica. O.-R. Assoc. France (Lille), p. 723.

(719) MILLER, W. W. (1909). Hepatozoon perniciosum and its Sexual Cycle in

the Intermediate Host, a Mite (Lelaps echidninus). Hygienic Laboratory
Bulletin, No. 46 (June, 1908).

(720) NERESHEIMER, E. (1909). Das Eindringen von Lankesterella spec, in die

Froschblutkorperchen. A.P.K., xvi., p. 187.

(721) PATTON, W. S. (1906). On a Parasite found in the Blood of Palm Squirrels.

S.M.I., 24.

(722) — (1908). The Hsemogregarines of Mammals and Reptiles. Py., i., p. 319.

(723) PORTER, A. (1908). Leucocytozoon musculi. P.Z.S., 1908, p. 703.

(724) PROWAZEK, S. v. (1907). Ueber Hamogregarinen. A.K.G.A., xxvi., p. 32.

(725) ROBERTSON, M. (1910). Life-Cycle of H. nicorioe. Q.J.M.S., lv., p. 741.

(726) SAMBON, L. W.,and SELIGMANN, C. G. (1907). Hsemogregarines of Snakes.

Trans. Pathol. Soc. London, Iviii., p. 310.

(727) SEITZ (1910). Die Hartmannsche Binukleaten. C.B.B.P.K. (I. Abth.

Orig.), Ivi., p. 308.

(£) Piioplasms.
See also No. 528.

(728) BETTENCOTJRT, A., FRANCA, C., and BORGES, I. (1907). Piroplasmose

bacilliforme chez le Daim. A.I.O.P., i., p. 341.

(729) BOWHILL, T. (1905). Equine Piroplasmosis, or "Biliary Fever." J.H., v.,

p. 7.

(730) BREINL, A., and KINDLE, E. (1908). Morphology, etc., of Piroplasma canis.

A.T.M.P., ii., p. 233.

(731) BRUCE, D., HAMERTON, A. E., BATEMAN, H. R., and MACKIE, F. P. (1910).

Amakebe : a Disease of Calves in Uganda. P.R.S. (B.), Ixxxii., p. 256.
*(732) CHRISTOPHERS, S. R. (1907). P. canis and its Life-Cycle in the Tick.

S.M.I., 29.
(733) DSCHUNKOWSKY, E., and LUHS, J. (1909). Protozoenkrankheiten des Blutes

des Haustiere in Transkaukasien. Ber. IX. Int. Tierarztl. Kongr. Haag.

BIBLIOGRAPHY 499

(734) DSCHUNKOWSKY, E., and LUHS, J. (1909). Entwickelungsformen von

Piroplasmen in Zecken. Ibid.

(735) FANTHAM, H. B. (1907). The Chromatin-Masses of P. bigeminum (Babesia

bovis. Q.J.M.S., li., p. 297.

(736) FRANCA, C. (1910). La Classification des Piroplasmes et Description de

deux Formes. A.I.G.P., iii., p. 11.

(737) GONDER, B. (1906). Achromaticus vesperuginis. A.K.O.A., xxiv., p. 220.

(738) — (1910). Die Entwicklung von Theileria parva. A.P.K., xxi., p. 143.

(739) — (1911). Th. parva und Babesia mutans Kiistenfieberparasit und Pseudo-

kiistenfieberparasit. Ibid., p. 222.

(740) _ (1911). Die Entwicklung von Th. parva. II. A.P.K., xxii., p. 170.

(741) KINOSHITA, K. (1907). Babesia cants. A.P.K., viii., p. 294.

(742) KLEINE, F. K. (1906). Kultivierungsversuch der Hundepiroplasmen.

Z.H., liv., p. 10.

(743) KOCH, R. (1906). Entwicklungsgeschichte der Piroplasmen. Ibid., p. 1.

(744) MAYER, M. (1910). Das ostafrikanische Kiistenfieber der Kinder. A.8.T.H.

xiv., Beiheft 7, p. 307.

(745) NEUMANN, R. 0. (1910). Die Blutparasiten von Vesperugo. A.P.K.,

xviii., p. 1.

(746) NICOLLE, C. (1907). Une Piroplasmose no'uvelle d'un Rongeur. C.R.S.B.,

Ixiii., p. 213.

(747) NUTTALL, G. H. F., and FANTHAM, H.B. (1910). Theileria parva. Py.,

iii., p. 117.

*(748) — and GRAHAM-SMITH, G. S. (1906, 1907). Canine Piroplasmosis V. and
VI. J.H., vi., p. 585 ; vii., p. 232.

(749) (1908). Multiplication of Piroplasma bovis, P. pithed in the circu-
lating Blood compared with that of P. canis. Py., i., p. 134. *

(750) (1908). Development of P. canis in Cultures. Ibid., p. 243.

(751) SMITH, T., and KILBORNE, F. L. (1893). Southern Cattle Fever. U.S.

Dept. of Agriculture, Eighth and Ninth Reports Bureau Animal Industry,
1891, 1892, p. 77.

(752) THEILER, A. (1910). Texasfieber, Rotwasser und Gallenkrankheit der

Rinder. Zeitschr. f. Infektionskrankheiten der Haustiere, viii., p. 39.

(753) YAKIMOFF, W. L., STOLNIKOFF, W. J., and KOHL- YAKIMOFF, N. (1911).

L. Achromaticus vesperuginus. A.P.K., xxiv., p. 60.

(g) Incertae Sedis.

(754) NICOLLE, C., and MANCEAUX, L. (1909). Un Protozoaire nouveau du Gondi.

C.R.A.8., cxlviii., p. 369.

(755) PATELLA, V. (1910). Corps de Kurloff-Demel dans quelques Mononucleaires

du Sang des Cobayes. La Genese Endotheliale des Leucocytes Mono-
nucleaires du Sang (Siena, Imprimerie St. Bernardin), p. 211.

(756) SEIDELIN, H. (1911). Protozoon-like Bodies in Yellow-Fever Patients.

Journ. Pathol. Bacteriol., xv., p. 282.

(757) — (1911). Etiology of Yellow Fever. Yellow Fever Bureau Bulletin, i.,

p. 229.

CHAPTER XVI

SPOROZOA— NEOSPORIDIA
A. CNIDOSPORIDIA

(a) General Works.
*(758) AUERBACH, M. (1910). Die Cnidosporidien. Leipzig : Werner Klinkhardt.

(b) Myxosporidia.

(759) AWERINZEW, S. (1909). Die Sporenbildung bei Ceratomyxa drepanopsettce.

A.P.K., xiv., p. 72.

(760) — (1911). Sporenbildung bei Myxidium sp. aus der Gallen blase von Gottus

scorpius. A.P.K., xxiii., p. 199.

(761) CHATTON, E. (1911). Paramyxa paradoxa. C.R.A.8., clii., p. 631.

(762) DOFLEIN, F. (1898). Myxosporidien. Zool. Jahrbiicher (Abth. f. Anat. u.

Ontog.), xi., p. 281.

500 THE PROTOZOA

(763) KEYSSELITZ, G. (1908). Die Entwicklung von Myxdbclus pfeifferi, I. and II-

A.P.K., xi., p. 252.

(764) LEGER, L., and HESSE, E. (1906). La Paroi sporale des Myxosporidies.

C.R.A.8., cxlii., p. 720.

(765) (1907). Coccomyxa morovi. C.R.A.S., cxlv., p. 85.

(765*5) MERCIEB, L. (1910). La sexualite chez les Myxosporidies et chez les

Micro sporidies. Acad. Roy. Belgique, Mim. 810. (2), ii., No. 6.

(766) PLEHN, M. (1904). Die Drehkrankheit der Salmoniden (Lentospora cere-

brates). A.P.K., v., p. 145.

(767) SCHRODER, 0. (1907). Entwicklungsgeschichte der Myxosporidien.

Sphceromyxa labrazesi (sdbrazesi). A.P.K., ix., p. 359.

(768) — (1910). Die Anlage der Sporocyste (Pansporoblasten) bei Sphceromyxa

sabrazesi. A.P.K., xix., p. 1.

(c) Actinomyxidia.

(769) CAULLERY, M., and MESNIL, F. (1905). Sphceractinomyxon stolci. A.P.K.,

vi., p. 272.

(d) Microsporidia.

(770) AWERINZEW, S., and FERMOR, K. (1911). Die Sporenbildung bei Olugea

anomala. A.P.K., xxiii., p. 1.

(771) CHATTON, E., and KREMPF, A. (1911). Les Protistes du genre Octosporea.

B.8.Z.F., xxxvi., p. 172.

(772) HESSE, E. (1904). Le Developpement de Thdohania legeri. G.R.8.B.,

Ivii., p. 571.

(773) _ (1905). Myxocystis mrazeki. C.R.8.B., Iviii., p. 12.

(774) LEGER, L., and DUBOSCQ, O. (1909). Perezia lankesterice. A.Z.E. (5),

i., Notes et Revue, p. Ixxix.

(775) — and HESSE, E. (1910). Cnidosporidies des Larves d'Ephemeres.

C.R.A.8., cl., p. 411.

(776) MERCIER, L. (1908). Neoplasie du Tissu Adipeux chez les Blattes Parasitees

par une Miorosporidie. A.P.K., xi., p. 372.

(777) MRAZEK, A. (1910). Auffassung der Myxocystiden. A.P.K., xviii., p. 245.

(778) PEREZ, C. (1904). Une Microsporidie parasite du Carcinus mcenas.

C.R.S.B., Ivii., p. 214.

(779) _ (1905). Microsporidies Parasites des Crabes d'Arcachon. Bull. Stat.

Biol. Arcachon, viii.

(780) — (1908). Duboscqia legeri. C.R.S.B., Ixv., p. 631.

(781) SCHRODER, 0. (1909). Thdohania chcetogastris. A.P.K., xiv., p. 119.

(782) SCHUBERG, A. (1910). Microsporidien aus dem Hoden der Barbe. A. K.Q.A.,

xxxiii., p. 401.

(783) SHIWAGO, P. (1909). Verrnehrung bei Pleistophora periplanetce. Z.A.,

xxxiv., p. 647.

(784) STEMPELL, W. (1904). Nosema anomalum. A.P.K., iv., p. 1.

(785) _ (1909). Nosema bombycis. A.P.K., xvi., p. 281.

(786) — (1910). Morphologic der Microsporidien. Z.A., xxxv., p. 801.

(787) WEISSENBERG, R. (1911). Einige Mikrosporidien aus Fischen (Nosema

lophii, Olugea anomala, 01. Hertwigii). S.B.G.B., p. 344.

(787-5) WOODCOCK, H.M. (1904). On Myxosporidia in Flatfish. Trans. Liverpool
Bid. Soc., xviii., p. 126.

(e) Sarcosporidia.
See also Nos. 18, 25, and 26.

(788) BETEGH, L. v. (1909). Entwicklungsgange der Sarcosporidien. C.B.B.P.K.

(I Abth. Orig.), lii., p. 566.

(788-5) CRAWLEY, H. (1911). Sarcocystis rileyi. Proc. Acad. Philaddphia, 1911,
p. 457.

(789) DARLING, S. T. (1910). Experimental Sarcosporidiosis in the Guinea-Pig.

J.EM., xii., p. 19.

(790) ERDMANN, R. (1910). Kern und metachromatische Korper bei Sarko-

sporidien. A.P.K., xx., p. 239.

(791) _ (1910). Sarcocystis muris in der Muskulatur. S. B. G. B., p. 377.

(792) FIEBIGER, J. (1910). Sarkosporidien. Verh. Zod.-Bot. Oes. Wien, Ix.,

p. (73).

BIBLIOGRAPHY 501

(793) LAVERAN, A., and MESNIL, F. (1899). La Morphologic des Sarcosporidies.

O.R.S.B., II, p. 245.

(794) NEGRE, L. (1910). Le Stade intestinal de la Sarcosporidie de la Souris.

C.R.S.B., Ixviii., p. 997.

(795) NEGRI, A. (1908, 1910). Ueber Sarkosporidien, I. and II. C.B.B.P.K.

(I Abth. Orig.), xlvii., pp. 56 and 612 ; III., Ibid., lv., p. 373.

(797) TEICHMANN, E. (1911). Die Teilungen der Keime in der Cyste von Sarco-

cystis tenella. A.P.K., xxii., p. 239.

(798) VUILLEMIN, P. (1902). Sarcocystis tenella. C.R.A.S., cxxxiv., p. 1152.

(799) WATSON, E. A. (1909). Sarcosporidiosis : Its Association with Loco-

Disease, etc. Journ. Comp. Pathol. Therapeut., xxii., p. 1.

B. HAPLOSPORIDIA.

(800) BEATTIE, J. M. (1906). Rhinosporidium kinealyi. Journ. Pathol. Bacterial.,

xi., p. 270.

(801) CAULLERY, M., and CHAPPELLIER, A. (1906). Anurosporidium pelseneeri.

G.R.S.B., lx., p. 325.

(802) — and MESNIL, F. (1905). Les Haplosporidies. A.Z.E. (4), iv., p. 101.

(803) CHATTON, E. (1907). Cautterya mesnili. C.R.S.B., Ixii., p. 529.

(804) — (1908). Blastulidium posdoyhthorum. O.R.8.B., Ixiv., p. 34.

(805) CRAWLEY, H. (1905). Caelosporidium blatellos. Proc. Acad. Philadelphia,

Ivii., p. 158.

(806) KING, H. D. (1907). Fertramia lu/onis. Ibid., lix., p. 273.

(807) LAVERAN, A., and PETTIT, A. (1910). Une Epizootic des Truites. C.R.A.S.,

cli., p. 421.

(808) MINCHIN, E. A., and FANTHAM, H. B. (1905). Rhinosporidium kinealyi.

Q.J.M.S., xlix., p. 521.

(809) RIDEWOOD, W. G., and FANTHAM, H. B. (1907). Neurosporidium cephalo-

disci. Q.J.M.S., li., p. 81.

(810) ROBERTSON, M. (1908). A Haplosporidian of the Genus Ichthyosporidium.

Proc. R. Phys. Soc. Edinburgh, xvii., p. 175.

(811) — (1909). An Ichthyosporidian causing Disease in Sea-Trout. P.Z.S.,

1909, p. 399.

(812) STEMPELL, W. (1903). Die Gattung Polycaryum. A.P.K., ii., p. 349.

(813) WARREN, E. (1906). Bertramia kirkmanni. Ann. Natal. Govt. Mus., i., p. 7,

(814) WRIGHT, J. (1907). Rhinosporidium kinealyi. New York Med. Journ.,

December 21.

C. INCERT^E SEDIS.

(815) AWERINZEW, S. (1909). Lymphocystis johnstonei. A.P.K., xiv., p. 335.

(816) — (1911). Die Entwicklungsgeschichte von Lymphocystis johnstonei.

A.P.K., xxii., p. 179.

(817) CHATTON, E. (1906). La Biologie, etc., des Amoebidium. A.Z.E. (4), v.,

Notes et Revue, p. xvii.

(818) — (1907). Pansporella perplexa. O.R.S.B., Ixii., p. 42.

(819) — (1910). Gastrocystis gilruthi. A.Z.E. (5), v., Notes et Revue, p. cxiv.

(820) GILRUTH, J. A. (1910). Gastrocystis gilruthi. Proc. Roy. Soc. Victoria (n.s.),

xxiii., p. 19.

(821) GRANATA, L. (1908). Capittus intestinalis. Biologica, ii., p. 1.

(822) KRASSILSTSCHIK, J. M. (1909). Neue Sporozoen bei Insekten. A.P.K.,

xiv., p. 1.

(823) LEGER, L., and DUBOSCQ, 0. (1909). Les Chytridiopsis. A.Z.E. (5), i.

Notes ct Revue, p. ix.

(824) WOODCOCK, H. M. (1904). Lymphocystis johnstonei. Trans. Bid. Soc.

Liverpool, xviii., p. 143.

502 THE PROTOZOA

CHAPTER XVII
INFUSORIA

(a) General Works.
(825) HABTOG, M. (1910). Infusoria. Encyclop. Brit., eleventh edition, xiv.,

p. 557.
*(826) HICKSON, S. (1903). The Infusoria. A Treatise on Zoology (Lankester)

(London : A. and C. Black), p. 361.

(b) Ciliata.

See also, Nos. 16, 32, 33, 38'5, 44, 50, 53, 73, 93, 96, 102, 104, 106-109, 111-113.
115, 121, 122, 124-126, 136-143, 148, 149, 155, 162, 165-167, 170-173, 177, 181-183,
197-199, 201, 205, 206, 208, 209, 211, 214-220, and 346.

(827) BEAUCHAMP, P. DE, and COLLIN, B. (1910). Sur Hastatella radians.

A.Z.E. (5), v., Notes et Revue, p. xxviii.

(828) BFSCHKIEL, A. L. (1911). Ichthyophthirius multifiliis. A.P.K., xxi., p. 61.

(829) CAULLEBY, M., and MESNIL, F. (1903). La Structure nucleaire d'un Infu-

soire Parasite des Actinies (Fcettingeria actiniarum). C.R.8.B., lv., p. 806.

(830) (1907). L'Appareil nucleaire d'un Infusoire (Rhizocaryum concavum).

C.R.Ass. Franc. Reims.

(831) CEPEDE, C. (1910). Les Infusoires astomes. A.Z.E. (5), iii., p. 341.
(831-5) CHATTON, E. (1911). Perlkaryon c:sticola and Conchophrys davidoffi.

A.Z.E. (5), viii., Notes et Revue, p. viii.

(832) COLLIN, B. (1909). Deux Formes nouvelles d'Infusoires Discotriches.

A.Z.E. (5), ii. Notes et Revue, p. xxi.

(833) DOBELL, C. C. (1909). Infusoria parasitic in Cephalopoda. Q.J.M.S., liii.,

p. 183.

(834) FATTBE-FBEMIET, E. (1905). L'Appareil fixateur chez les Vorticdlidce.

A.P.K., vi., p. 207.

(835) — (1907). Mitochondries et Sphere plastes chez les Infusoires cilies.

C.E.S.B., Ixii., p. 523.

(836) — (1908). Tintinnidium inquUinum. A.P.K., xi., p. 225.

(837) — (1908). UAncystropodium maupasi. A.P.K., xiii., p. 121.

(838) — (1909). Le Macronucleus des Infusoires cilies. B.8.Z.F., xxxiv., p. 55.

(839) — (1910). Le Mycterothrix tuamotuensis. A.P.K., xx., p. 223.

(840) GONDEB, R. (1905). Kernverhaltnisse bei den in Cephalopoden schmarot-

zenden Infusorien. A.P.K., v., p. 240.

(841) HAMBTJEGEB, C. (1903). Trachelius ovum. A.P.K., ii., p. 445.

(842) — (1904). Die ^Conjugation von Paramcecium bursaria. A.P.K., iv., p.199.

(843) — and BUDDENBBOCK, v. (1911). Nordische Ciliata mit Ausschluss der

Tintinnoidea. Brandt and Apstein, Nordisches Plankton.

(844) JOSEPH (1907). Kernverhaltnisse von Loxodes rostrum. A.P.K., viii.,

p. 344.

(845) KASANZEFF, W. (1910). Loxodes rostrum. A.P.K., xx., p. 79.

(846) KIEBNIK, E. (1909). ChUodon hexastichus. B.A.S.C., p. 75.

(847) KOFOID, C. A. (1903). Protophrya ovicda. Mark Anniversary Volume,

p. 111.

(848) LEGEB, L., and DUBOSCQ, 0. (1904). Les Astomata representent-ils un

Groupe naturel ? A.Z.E. (4), ii., Notes et Revue, p. xcviii.
(849) (1904). Les Infusoires endoparasites. A.Z.E. (4), ii., p. 337.

(850) MABTINI (1910). Uber einen bei amobenruhrahnlichen Dysenterien vor-

kommenden Ciliaten. Z.H., Ixvii., p. 387.

(851) MAST, S. 0. (1909). The Reactions of Didinium nasutum. B.B., xvi., p. 91.
(851-5) MAUPAS, E. (1888). La Multiplication des Infusoires cilies. A.Z.E. (2),

vi., p. 165.

(852) METCALF, M. M. (1907) . Excretory Organs of Opalina. A.P.K., x., pp. 183,

365.

(853) — (1909). Opalina : Its Anatomy, etc. A.P.K., xiii., p. 195.

(854) MEUNiEPv, A. (1910). Microplankton des Mers de Barents et de Kara.

Due d'Orleans, Campagne Arctique de 1907. Brussels.

BIBLIOGRAPHY 503

(855) MITROPHANOW, P. (1905). La Structure, etc., des Trichocystes des Para-

meeies. A.P.K., v., p. 78.

(856) NERESHEIMER, E. R. (1903). Die Hohe histologischer Differenzierung bei

heterotrichen Ciliaten. A.P.K., ii., p. 305.

(857) NERESHEIMER, E. (1907). Die Fortpflanzung der Opalinen. A.P.K.,

Suppl. i., p. 1.

(858) — (1908). Fortpflanzung eines parasitischen Infusors (Ichthyophthirius),

8.B.O.M.P., xxiii.

(859) PROWAZEK, S. v. (1904). Der Encystierungvorgang bei DUeptus. A.P.K.,

iii., p. 64.

(860) — (1909). Conjugation von Lionotus. Z.A., xxxiv., p. 626.

(861) — (1909). Formdimorphismus bei Ciliaten Infusorien. M.I.O.O., i., p. 105.

(862) Roux, J. (1899). Quelques Infusoires cilies des Environs de Geneve. Rev.

Suisse Zool., vi., p. 557.

(863) SCHEWIAKOFF, W. (1893). Die geographische Verbreitung der Susswasser-

Protozoen. Mem. Acad. Imp. St.-Petersbourg (vii.), xli.

(864) SCHRODER, O. (1906). Campandla umbdlaria. A.P.K., vii., p. 75.

(865) — (1906). Epistylis plicatilis. Ibid., p. 173.

(866) — (1906). Vorticella monilata. Ibid., p. 395.

(867) — (1906). Stentor cceruleus und St. rceselii. A.P.K., viii., p. 1.

(868) SCHUBOTZ, H. (1908). Pycnothrix monocystoides. Denkschr. Ges. Jena, xiii.,

p. 1.

(869) SCHWEYER, A. (1909). Tintinnodeenweichkorper, etc. A.P.K., xviii.,

p. 134.

(870) SIEDLECKI, M. (1902). UHerpetophrya astoma. B.A.S.C., p. 356.

(871) STEIN, F. v. (1859, 1867). Der Organismus der Infusionthiere : I. Hypo-

tricha ; II. Heterotricha. Leipzig : W. Engelmann.

(872) STEVENS, N. M. (1904). On Licnophora and Boveria. A.P.K., iii., p. 1.

(873) THON, K. (1905). Bau von Didinium nasutum. A.P.K., v., p. 281.

(874) WALKER, E. L. (1909). Sporulation in -the Parasitic Ciliata. A.P.K.,

xvii., p. 297.

(c) Acinetaria.

(875) AWERINZEW, S. (1904). Astrophrya arenaria. Z.A., xxvii., p. 425.

(876) CHATTON, E., and COLLIN, B. (1910). Un Acinetien commensal d'un

Copepode, Rhabdophrya trimorpha. A.Z.E. (5), v., Notes et Revue,
p. cxxxviii.

(877) COLLIN, B. (1907). Sur quelques Acinetiens. A.Z.E. (4), vii., Notes et

Revue, p. xciii.

(878) — (1908). Sur ToTcophrya cydopum. A.Z.E. (4), viii., Notes et Revue,

p. xxxiii.

(879) — (1909). La Conjugaison gemmiforme chez les Acinetiens. C.R.A.S.,

cxlviii., p. 1416.

(880) — (1909). Les Formes hypertrophiques et la Croissance degenerative chez

quelques Acinetiens. C.R.A.S., cxlix., p. 742.

(881) — (1909). Sur deux Acinetiens. Ibid., p. 1407.

(882) — (1909). La Symetrie, etc., des Embryons d'Acinetiens. A.Z.E. (5), ii.,

Notes et Revue, p. xxxiv.

(883) FILIPJEV, J. (1910). Tocophrya quadripartite. A.P.K., xxi., p. 117.

(884) HARTOG, M. (1902). Notes on Suctoria. A.P.K., i., p. 372.

(885) HICKSON, S. J., and WADSWORTH, J. T. (1902). Dendrocometes paradoxus.

Q.J.M.8., xlv., p. 325.
(886) (1909). Dendrosoma radians. Q.J.M.S., liv., p. 141.

(887) ISHIKAWA, C. (1897). Eine in Misaki vorkommende Art von Ephdota.

Journ. Cdl. Sci. Tokyo, x., p. 119.

(888) MARTIN, C. H. (1909). On Acinetaria. Parts I. and II. Q.J.M.S., liii.,

p. 351. Part III. Ibid,, p. 629.

(889) PEREZ, C. (1903). Lernceophrya capitata. C.R.S.B., lv., p. 98.

504 THE PROTOZOA

CHAPTER XVIII

(a) Classification.

(890) AWERINZEW, S. (1910). Die Stellung im System und die Klassifizierung der

Protozoen. E.G., xxx., p. 465.

(891) DOFLEIN, F. (1902). Das System der Protozoen. A.P.K., i., p. 169.

(892) HARTMANN, M. (1911). Das System der Protozoen. Vide Prowazek (14),

p. 41 ; and No. 675.

(b) Spirochsetes.

*(893) BOSANQUET, W. C. (1911). Spirochsetes. Philadelphia and London :
W. B. Saunders Company.

(894) — (1911). Sp. anodontce Keysselitz. Q.J.M.S., Ivi., p. 387.

(895) DOBELL, C. C. (1911). On Cristispira veneris and the Classification of Spiro-

chsetes. Q.J.M.8., Ivi., p. 507.

(896) FANTHAM, H. B. (1911). Life-Cycle of Spirochsetes. A.T.M.P., v., p. 479.

(897) GROSS, J. (1910). Cristispira nov. gen. Mitt. zool. Stnt. Neapel, xx., p. 41.

(898) — (1911). Freilebende Spironemaceen. Ibid., p. 188.

(899) — (1911). Nomenclatur der Sp. pallida. A.P.K., xxiv., p. 109.

(900) KINDLE, E. (1912). Life-Cycle of Sp. gallinanim. Py., iv., p. 463.

(901) KRZYSZTALOWICZ, F., and 'SIEDLECKI, M. (1905). La Structure, etc., de

Sp. pallida. B.A.S.C., p. 713.

(902) LEISHMAN, W. B. (1910). Mechanism of Infection in Tick Fever and Heredi-

tary Transmission of Sp. duttoni in the Tick. Trans. Soc. Trop. Med.
Hyg., iii., p. 77.

(903) SCHAUDINN, F. (1905). Sp. pallida. Deutsch. Med. Wochenschr., xxxi.,

p. 1665.

(904) ZUELZER, M. (1911). Sp. plicatUis. A.P.K., xxiv., p. 1.

(c) Chlamydozoa.

(906) ACTON, H. W., and HARVEY, W. F. (1911). Negri Bodies. Py., iv., p. 255.

(907) AWERINZEW, S. (1910). Die Krebsgeschwiilste. C.B.B.P.K., Ivi. (I Abth.

Orig.), p. 506.

(908) CALKINS, G. N. (1904). Cytoryctes variola, Guarnieri. Journ. Med. Research

(Special Variola Number), xi., p. 136.

(909) HARTMANN, M. (1910). Chlamydozoen. O.B.B.P.K. (I Abth. Kef.),

xlvii., Beiheft, p. 94.

(910) NEGRI, A. (1909). Die Morphologic und der Entwicklungszyklus des Para-

siten der Tollwut. Z.IL, etc., Ixiii., p. 421.

(911) PROWAZEK, S. v. (1907). Chlamydozoa. A.P.K., x., p. 336.

(912) — and ARAGAO, H. DE B. (1909). Variola-Untersuchungen. M.I.O.O.,

i., p. 147.

(913) — LiPSCHtJTZ, B., and Others (1911). Chlamydozoa, etc. Vide Prowazek

(14).

(914) SIEGEL, J. (1905). Die Atiologie der Pocken und der Maul- und Klauen-

seuche : des Scharlachs : der Syphilis. Abhandl. k. preuss Akad. Wiss.
(Anhang. )

INDEX TO TECHNICAL TERMS AND
ZOOLOGICAL NAMES

The numerals printed in heavier black type refer to pages on which the moaning
of the svord or the systematic position of a genus, family, or order are fully explained.

AOANTHARIA, 251, 256

Acanthin, 37, 253

Acanthocystis, 37, 48, 91, 245, 248

— aculeata, 117, 118 (Fig. 64), 123

(Fig. 68)

— chwtophora, 37 (Fig. 18)
Acanthometra, 256

— elastica, 250 (Fig. 105)

— pellucida, 255
Acanthometrido}, 37
Acephalina, 339
Achromaticus, 364, 382

— vesperuginis, 382
Achromatin, 65
Acineta, 4-61

— grandis, 11 (Fig. 10)

— papillifera, 16
Acinetaria, 430, 455
Acinetidco, 461
Acrasise, 243
Acrasis, 243
Actinobolus radians, 441
Actinocephalidce, 339
Actinocephalusoligacanthus, 327 (Fig. 142)
Actinomma asteracanthion, 254 (Fig. 107)
Actinomyxidia, 409

Actinophrys, 117, 215, 245, 248
- sol, 90 (Fig. 46), 132 (Fig. 71), 151

Actinopoda, 218

Actinosphmrium, 43, 50 (Fig. 22), 68,
74, 77, 78, 80, 91, 138, 144, 150, 193,
198, 207, 209, 214, 216, 245, 248

— eichhorni, 7 (Fig. 3), 81 (Fig. 37), 115

(Fig. 62), 116 (Fig. 63)
Adaptive polymorphism, 164
Adelea, 175, 176, 348, 352, 393

— hartmanni, 344, 347, 348

— ovata, 344, 345 (Fig. 153), 346, 347

(Fig. 154), 352
Adeleida), 352, 354, 355
Adeleidea, 352, 394
Adinida, 278
Adoral spiral, 442
Adult, 212
JEthalium, 242
Aflagellar, 287
Agamotes, 180, 181
Agamogony, 181
Agamont, 181

Agglomeration, 128, 209, 305
Agglutination, 128
Agglutinin, 128
Aggregata, 23, 168, 325, 348, 353

— jacquemeti, 121 (Fig. 67)
Aggregatida, 353

Alcohol, effects of, 204
Allogromia, 230

— ovoidea, 235

Alternation of generations, 181
Alveolar layer, 435

Alveoli, 42
Amicronucleate, 211
Amitosis, 105
Amoeba, 219

— albida, 221 (Fig. 87)

— Unucleata, 78, 95, 214, 223

— diploidea, 222 (Fig. 88)

— diplomitotica, 108, 109 (Fig. 56)

— flava, 221

— Umax, 46, 47 (Fig. 20), 206, 217, 219

— minuta, 221, 223

— mucicola, 220

— proteus, 6 (Fig. 2), 47, 191, 205, 209,

215, 216, 217, 219, 220, 222, 230

— radiosa, 217, 219

— terricola, 48, 190 (Fig. 82), 214, 220

— verrucosa, 32, 45, 48, 50, 51 (Fig. 23),

198, 214, 219

— vespertilio, 217

Amoeba, form-changes, 216 (Fig. 85)
Amoebaea, 217
Amcebidium, 428
Amosbo diastase, 193
Amosboflagellata, 463
Amoebogeniee, 325, 466
Ainosboid, 30
Amoebula, 169
Amphikaryon, 96
Amphileptus, 439
Amphimixis, 150, 154
Amphinucleus, 96
Amylum, 188
Anaerobic, 196
Anaplasma marginale, 383
Ancystropodium, 441
Angeiocystis audouinics, 349
Anisogamy, 126, 132, 175
Anisonema, 274

— grande, 53 (Fig. 25)
AnisonemincB, 274
Anisosporo, 215, 254
Annulus, 276
Anophelinae, 358

Anoplophrya, 171, 439, 443, 449, 452

— branchiarum (reduction), 145 (Fig. 74)
AnoplophryincB, 197,452
Anurosporidium, 424
Aphrothoraoa, 247

Apiosoma, 379
Apodinium, 278

505

506

THE PROTOZOA

Aposporogony, 368

Arcella, 64, 65, 72, 78, 126, 148, 173, 199,
201, 215, 216, 229

— vulgaris, 67 (Fig. 32), 110 (Fig. 57),

177, 178 (Fig. 80)
Archaeocytes, 133
Archoplasm, 79, 103
Arenaceous, 34, 231
Asporocystea, 388
Aspirigera, 439
Arrhenoplasm, 129
Artificial classification, 463
Assimilation, 187
Association, 127, 330
Astasia, 274
- tenax, 33 (Fig. 15)
Astaxiidco, 274
Astomata, 438, 439, 451
Astrodisculus, 248
Astrophrya, 461

— arenaria, 456
Athene noctua, 390
Attraction-sphere, 103
Attraction-spindle, 104
Aulacantha, 256
Autocyst, 417
Autogamy, 138, 306
Automixis, 140
Autophya, 34
Avoiding reaction, 202
Axopodium, 48, 53, 60, 87, 199, 465
Axostyle, 36, 259, 289, 311
Azoosporida?, 218

Bdbesia, 357, 379, 394

— boms (bigemina), 379, 384

— rmtians, 380, 382
Babesioses, 378
Bacteria, 5, 98
Badhamia, 242

— utricularis, 240 (Fig. 99), 241 (Fig. 100)
Balantidium, 439, 440

— coli, 440

— minutum, 440
Banana-tree, 136
Barroussia, 352

— alpina, 344, 345 (Fig. 153)

— caudata, 348

— ornata, 346, 352

— spiralis, 344, 348
Barotaxis, 202, 207

Basal granule, 82, 92, 200, 443

— rim, 443
Benedenia, 353
Bertramia, 424

— asperospora, 424

— bufonis, 424

— capitelloB, 424

— kirkmanni, 424
Bertramiidce, 424
Bilateral symmetry, 31, 250
Biloculina depressa shells, 233 (Fig. 94)
Binary fission, 100

Binuclearity, 96
Binucleata, 85, 280, 388
Bioblast, 40, 41
Bionomics, 15
Black spores, 364
Blastocoelo, 133
BlastodinidcB, 278
Blastodinium, 278
Blastogenea, 418

Blastomere, 133

Blastulidium pcedopTithorum, 424

Blepharoplast, 52, 59, 82, 262, 286, 288,

289
Bodo,270, 281, 319

— edax, 319

— gracilis, 271 (Fig. 115)

— lacertw, 270

— saltans, 271 (Fig. 115), 319
Bodonidce, 268, 270

Body -form, 29
Bud, 122
Buetschlia, 439
Bursaria, 439
Bursaridce, 439

Catty ntrochlamys phronimw, 327

Calonympha, 276

Calymma, 251, 252

Calyx, 89

Campanella, 440, 446, 447

— umbcllaria, 434 (Fig. 183)
Camptonema, 51, 248

— nutans, 91 (Fig. 47)
Cancer, 473
Capillitium, 241
Capillus intestinalis, 428
Capsulogenous cell, 399, 403
Carchesium, 145, 192, 194, 440, 441, 449
Caryoryctes, 473

Caryospora, 349, 352

— simplex, 352
Caryotropha, 195, 344, 348, 352

— mesnilii, 349, 352
Caryotrophidco, 352
Caullerya, 424

— mesnili, 424
Cell, 1, 98, 464
Cell-anus, 433
Cell-division, 121
Cell-membrane, 45
Cell-mouth, 63
Cell-theory, 133
Central capsule, 250

— grain, 91

— spindle, 103
Centriole, 73, 80, 97, 262
Centrodesmose, 36, 58, 59, 82, 103
Centropyxis, 148, 173, 229

— aculeata, 36, 230
Centrosomo, 58, 59, 73, 79, 262, 288
Centrosphere, 80

Cephalina, 339
Cephaloidophora, 337
Cephalont, 181, 326
Ceratiomyxa, 242
Ceratium, 278
Ceratocorys, 278

— horrida, 277 (Fig. 121)
Ceratomyxa, 408

— drepanopsetto), 402 (Fig. 166), 403

— sphcerulosa, 409
Ceratomyxida$, 408
Ceratophyllusfasciatus, 291
Cercomonadido), 268, 270
Ccrcomonas, 270, 271

— crassicauda, 271 (Fig. 114)
Chagasia hartmanni, 344, 347
Chalaiothoraca, 248
Chomotaxis, 202
Chiliferida), 439

Chilodon, 145, 439, 448

INDEX

507

Chilodon cucullulus, 435 (Fig. 184)

— dentatus, 440
Chilomonas, 208, 274
Chlamydodontidce, 439
Chlamydomonadidcc, 275
Chlamydomonas, 275
Chlamydomyxa, 214, 243, 244
Chlamydophora, 248
Chlamydophrys, 237

— schaudinni, 237

— stercorea, 17, 237
Chlamydozoa, 470
Chloromyxidce, 407, 409
Chloromyxum, 409

— ZeT/digri, 400 (Fig. 164), 409
Chlorophyll, 13, 63, 188, 261
Choauoflagollata, 261, 271
Choanoflagellidce, 271
Chondriosome, 41
Chromatin, 65, 69
Chromatoid grains, 67, 289, 311
Chromatophore, 13, 63, 188, 261
Chromidia, 6, 65, 97, 150, 215, 328
Chromidial fragmentation, 101
Chromidina, 452
Chromidiogamy, 126, 416
Chromidiosome, 65, 103
Chromomonadina, 274
Chrornophyll, 188
Chromoplast, 13, 63
Chromosome, 103
Chromulina, 274

— • flavicans, 15
Chrysamceba, 274
Chrysomonadina, 14, 274
Chytridiopsis, 428

— socius, 428

Ciliary apparatus, 442, 444 (Fig. 186)
Ciliata, 430, 432 (Fig. 181)
Cilioflagellata, 277
Ciliophora, 462
Ciliophrys, 248
Ciliospore, 169

Cilinm, 12, 53, 92, 199, 200, 442, 454
Ciroumfluence, 189
Circumvallation, 189
Cirrus, 55, 445
Cladomonas, 270
Cladothrix pelomyxce, 227
Classification, 462
Clathrulina, 39, 245, 248

— elegans, 38 (Fig. 19)
Clepsydrina, 335, 339
Cnidosporidia, 399
Coccidia, 341, 389
Coccidiidm, 352
Coccidioides immitls, 17
Coccidiornorpha, 388, 395
Coccidiosis, 343

Coccidium, 101, 166, 173, 174, 346, 352

— cuniculi, 341, 351

— mitrarium, 344

— oviforme, 341

— rouxi, 349

— scJtubcrgi, 102 (Fig. 50), 106 (Figs.

51, 52), 127 (Fig. 69), 146 (Fig. 75),
204, 342 (Fig. 152), 353, 354

— sticda), 341
Coccoid bodies, 468
Coocolith, 274
Coccolithophorido), 274
Coccomyxa, 409

Coccomyxa morovi, 409
Cochlearia faurei, 442
Cochliopodium, 229
Codonosigabotrylis, 260 (Fig. 110,
Ccelosporidiidco, 399, 424
Ccelosporidium, 424

— blatellce, 424
Coelozoic, 324
Coleps, 439, 441
Collar, 57, 89, 261
Collecting-pusule, 277
Collodagia, 255
Collozoum, 256
Colpidium, 208
Colpoda, 439
Conchophrys, 439
Conjugant, 126, 448
Conjugation, 126, 448
Conorhinus megistus, 291, 302
Contact-stimulus, 207

Contractile vacuole, 60, 196, 197, 262,
437, 447

— system, 445, 446
Contractility, 200, 201
Copromonas, 171, 274

— major, 268

— subtilis, 264 (Fig. Ill), 268
Copromyxa, 243
Copularium, 355
Copulation, 126

Corps en barillet, 344
Cortex, 45
Cortical layer, 32
Corticate, 45
Costia, 258, 272
— necatrix, 16, 272
Cothurnia, 440
Craspedomonads, 261, 271
Craspedotella, 279
Cristispira, 466, 469

— anodontce, 468

— balbianii, 467

— pectinis, 469 (Fig. 194)

Crithidia, 281, 282,-287, 308, 312, 320,
321

— campanulata, 313

— gerridis, 313

— melophagia, 290

— minuta, 312 (Fig. 135)
Cryptocystes, 412
Cryptodifflugia, 229, 230
Cryptomonadina, 15, 274
Cryptomonas, 274

— schaudinni, 15
Cryptosporidium, 349, 352

— muris, 344, 352
Crystal-spores, 254
Cuirass, 33, 45, 276
Culicinse, 358
Culture d'attente, 304
Cuticle, 45
Cyclasterium, 470
Cyclical transmission, 290
CyclochcBta, 440, 441
Cycloposthium, 439
Cyclosis, 192, 194, 437
Cyclospora, 352

- caryolitica, 176, 198, 344, 348, 349,

352

Cyst, 154

Cystal residuum, 349
Cystobia chiridotce, 341

508

THE PROTOZOA

Cystobia holothurice, 128 (Fig. 70)

— irregularis, 331

— minchinii, 336
Cystoflagellata, 257, 278
Cystotrypanosoma, 304
Cytocyst, 344
Cytomere, 344
Cytomicrosome, 41
Cytopharynx, 63, 261, 433, 442
Cytoplasm, 6, 7, 99
Cytopyge, 433
Cytorhyctes, 471

— aphtharum, 471

— luis, 471

— scarlatina}, 471

— vaccincc, 471
Cytoryctes, 470, 471

Cytostome, 63, 190, 191, 261, 433, 452
Cytozoic, 324

Dactylosoma splendens, 378
Defalcation, 233
Degeneration, 208
Dendrocomctcs, 457, 460, 461
Dendrocomctida), 461
Dendrosoma, 456, 458, 461
- radians, 78, 460 (Fig. 193)
Dendrosomidco, 461
Dendrosomides paguri, 455
Depression, 131, 135, 197, 208
Derbesia, 90
Desmothoraca, 248
Deutoblast, 426
Deutomcritc, 327
Deutoplasmic, 41
Dcvcscovina, 276
Dexiotricha, 440
Dictyostelium, 243
Didinium, 145, 439, 442, 449
Didymophyes, 330

Difflugia, 34, 35, 50, 65, 66, 78, 126, 140,
149, 199, 215, 216, 229

— spiralis, 34 (Fig. 16)

— urceolata, 214, 229, 230
Diffuse infiltration, 400
Digestion, 192
Dileptus, 439
Dimastigamoeba, 268
Dimorpha, 249

— nutans, 249 (Fig. 104)
Dinenympha, 276
Dinifera, 278
Dinobryon, 274
Dinoflagellata, 257, 276
Dinophysida), 278
Dinophysis, 278
Diphtheria, 470
Diplocystis minor, 128 (Fig. 70)
Diplodina, 174
Diplosome, 79
Diplozoa, 273
Direct division, 101
Direct transmission, 290
Discophrya, 439
Discorbina, 232 (Fig. 93, vii)
Disporea, 408
Dizoic, 349
DoliocystidcB, 339
Dourine, 26, 285, 289
Drehkrankhoit, 400
Drepanidia, 395
Drepanidium, 372

Duboscqia, 418

— legeri, 418

Earth-amoebae, 220
Echinomera, 333
Echinopyxis, 101
Ectoplasm, 43, 45, 435
Ectosarc, 43
Ectoschiza, 339
Ectosporea, 325
Eimeria, 346, 352

— faldformis, 346

— nepce, 346
Eimerido}, 352
Eimeridea, 352, 394
Electrical stimuli, effects of, 208
Elementary corpuscles, 472
Ellcipsisoma, 387

— thomsoni, 387
Enchelidw, 439
Enchylcma, 41, 72
Encystmont, 164
Endogenous budding, 124

- cycle, 184
Endoparasita, 462
Endophrys rotatorium, 249
Endoplasm, 43, 62, 437
Endoral membrane, 445
Endosarc, 43
Endoschiza, 339
Endosome, 73
Endospore, 335
Endosporere, 242, 325
Endotrypanum, 307

— schaudinni, 307 (Fig. 133)
End-piece, 443

Enorgid, 121
Entamceba, 220

— africana, 226

- blattco, 47, 220, 223

— buccalis, 220

— coli, 18, 138 (Fig. 73), 139, 223, 224

(Fig. 89), 225

— histolytica, 18, 46, 223, 224, 225

(Fig. 90)

— minuta, 226

— muris, 220

— ranarum, 220

— tetragena, 226

— williamsi, 225
Entodinium, 439, 441
Entozoic, 16

Enzymes. See Ferments
Ephelota, 457,461

— buetschliana, 457

— gemmipara, 460
Epicyto, 45, 327
Epimerito, 45,326
Epispore, 335
Epistylis, 440, 441

— plicatilis, 444 (Fig. 186, K), 446

— umbellaria, 447
Epithelioma contagiosum, 470
Epizoic, 16

Equating division, 104
Equatorial plate, 103
Ergastoplasm, 41
Erythropsis, 277
Etheogenosis, 138, 315
Eucoccidia, 352
Eucoccidium, 353
Eucyrtidium, 256

INDEX

509

Eucyritidium cranioides, 256 (Fig. 109)

Euflagellata, 257

Euglena, 14, 33, 52 (Fig. 24), 107, 202, 274

— gracilis, 188

— spirogyra, 8 (Fig. 4)

— viridis, 188, 205 (Fig. 84)
Euglenida), 274
Euglenoid movement, 33
Euglenoidina, 273
Euglypha, 34, 35, 214, 237

- alveolata, 111, 112 (Fig. 59), 113

(Fig. 60)

Eugregarinte, 328, 339
Euplasmodida, 242
Euplotes, 194, 440, 448

— harpa, 433 (Fig. 182)

— patella, 433 (Fig. 182)
EuplotidcB, 440
Eutrypanosome, 292
Ex-conjugant, 153
Excretion, 197
Excretory canals, 447
Exflagellation, 357, 362, 364, 365, 390
Exogenous cycle, 184

Eye-spot, 205

Falciform body, 324

Fat, 194

Fatty degeneration, 210

Feeding canals, 437

Female sex, 159

Ferments, 193, 194

Fertilization-spindle, 127, 348

Filoplasmodida, 243

Filose, 48

Fission, 100

Fixation, 441

Flagollar, 287

Fiagellata, 82, 257

Flagellispore, 169

Flagellosis, 313

Flagollula, 169

Flagellum, 6, 51, 199, 200, 289, 454, 465

Fcettingeria, 439

Fcettingeriidce, 439

Food-vaouole, 50, 62, 191, 194, 437

Foot-and-mouth disease, 470

Foraminifera, 217, 231

Form-production, 31

Framboesia, 467

Frondicularia, 232 (Fig. 93, iv.)

Frontonia, 439, 442

— leucas, 206, 447 (Fig. 187)
Fulcra, 441

Fuligo, 242

— septica, 239 (Fig. 97)

Galvanotaxis, 202, 208

Gamete, 125, 448

Gametid, 334

Gametocyte, 126

Gamogony, 181

Gamont, 126, 181

Ganymedes, 330

Gas-vacuole, 64

Gastrocystis gilruthi, 427, 428 (Fig. 179)

Gemmation, 122

Gemmula, 459

Gemmule, 471

Generative chromatin, 71

Geotaxis, 207

Germ, 165

Germ-cells, 130
Germen, 130

Germinative infection, 24
Glaucoma, 439

— colpidium, 197, 206

— sdntillans, 445
Glenodinium, 278

— cinctum, 277 (Fig. 120)
Globidium, 387

— multiftdum, 387
Globigerina, 231, 232 (Fig. 93, vi.
Glossina morsitans, 291

— palpalis, 291, 303, 304
Olugea, 412,417,418

— anomala, 411, 415, 417 (Fig. 174), 418

— stephani, 412
Gonium, 276

— pectorale, 275 (Fig. 119)
Granelte, 238
Granellarium, 238
Gregarina, 174, 335, 339

— blattarum, 339

— munieri, 58 (Fig. 29>

— ovata, 332, 333 (Fig. 146), 335, 339
• — polymorpha, 9 (Fig. 7), 339
Gregarines, sporogony, 331 (Fig. 144)
Gregariniform phases, 315
Gregarinoidea, 326
Gregarinula, 169, 324

Gromia, 231

— oviformis, 49 (Fig. 21)
Guarnieri's bodies, 470
Gurleya, 418
Gymnamoabee, 219
Gymnodinidai, 278
Gymnodinium, 278
Gymnospore, 165
Gymnostomata, 439, 442
Gymnozoum, 439, 442

— mviparum, 439

Heemamo3bce, 357, 389
Heematochrome, 188
Hcematococcus, 188, 275, 379

— pluvialis, 111 (Fig. 58)
Hcematomonas, 308
Hcematopinus spinulosus, 291, 301
Hcemocystidium, 358, 364

- diploglossi, 358, 365

— metschnikom, 358

— simondi, 358, 365

— tropiduri, 365
Heemoflagellates, 258, 280
Hcemogregarina, 372

— agamce, 373

— balfouri, 376

— bicapsulata, 372

— canis, 377

— funambuli, 377

— gerbilli, 376, 377, 390

— jaculi, 376

— muris, 23, 376, 390

— musculi, 352, 377

— nicorico, 373, 375

— peramelis, 376

— sebai, 377

— stepanowi, 107 (Fig. 53), 372, 373,

374 (Fig. 159), 375, 390
Heemogregarines, 357, 371, 390
HcBmogregarinida}, 378
Hcomoproteus, 365, 391

— columbce, 365, 366 (Fig. 157), 390, 391

510

THE PROTOZOA

Hwmoproteus danilewskyi, 365

— noctuco, 365, 390

— oryzivorce, 368
Hsemosporidia, 356
Haliphysema, 35, 231

— tumanowiczii, 35 (Fig. 17)
Halterla, 439

Halteridce, 439
Halteridia, 389, 391
Halteridium, 357, 365, 391
Haplosporidia, 399, 423
Haplosporidiidce, 423, 424
Haplosporidium, 424
Hastatella radians, 441
Helcosoma tropicum, 393, 412
Holiozoa, 90, 218, 244
H emiclepsis marginata, 291, 298, 303
Hemispeira asterice, 441
Henneguya, 409, 426
Hepatozoon, 372

— muris, 376

— pemidosum, 376
Hereditary transmission, 24, 290
Herpetomonas, 281, 282, 292, 313, 319,

320

— musccB-domestica}, 137, 138, 282

(Fig. 124), 315
Herpetophrya, 452
Hotorokaryote, 449, 453
Hoteromastigoto, 259
Heteronemincc, 274
Heterophrys, 248

— fockei, 248 (Fig. 103)
Hoterotricha, 433
Hexactinomyxon, 409
Hexamitus, 258, 272
Histocytos, 130, 133
Jlistoplasma, 319

— capsulatum, 319
Histozoic, 324
Holomastigina, 270
Holomastigote, 259
Holophrya, 439
Holophytic, 13, 187, 188, 261
Holotricha, 439
Holotrichous larvee, 459
Holozoic, 8, 13, 187, 261
Homaxon, 39, 250
Hoplitophrya, 452

House, 33, 45

Hyalosphcera gregarinicola, 341

Hyalosphenia, 34

— cuneata, 34 (Fig. 16)
Hydrophobia, 470
Hymenoetomata, 439, 442
Hyperchromasy, 71
Hypnocyst, 166
Hypocoma, 460

— acinetarum, 460
Hypocomidce, 460
Hypothallus, 240
Hypotricha, 433, 440
Hypotrichous larvee, 459, 460

Ichthyophthiriasis, 450
Ichthyophthirius, 448, 453

— multifiUis, 16, 21, 450, 451
Ichthyosporidium, 424
Idiochromatin, 71
Idiochromidia, 150
Immanoplasma, 388

— scyllii, 388

Imperforate, 231
Import, 189

Incubation-period, 292, 361
Incurvation, 468
Indirect division, 101

— transmission, 290

Infusoria, 2, 12, 152 (Fig. 77), 153, 430

Ingestion, 204

Initial body, 472

Intestinal flagellates, 258

Invagination, 189

Involution stages, 296

Isogamy, 126, 175

Isomastigote, 259

Isosporo, 215, 254

Isotricha, 439

Isotrichidw, 439

Jcenia, 276

Kala-azar, 316
Kalpidorhynchus, 332
Karyogamy, 126
Karyokinesis, 101, 119
Karyolysus, 372

— lacertarum, 372, 378
Karyosome, 76, 288
Kataphoric action, 208
Kentrochona, 440
Kentrochonopsis, 440
Kinetonucleus, 78, 85, 200, 286, 288, 289 ,

392
Klossia, 348, 352

— helicina, 352
Klossiella, 352

— muris, 352
Kurloff-Domel bodies, 388

Labyrinthula, 243, 244
Labyrinthulidoa, 243
Lagena, 232 (Fig. 93, ii.)
Lagenophryince, 440
Lagenophrys, 440
Lamblia, 272

— intestinalis, 31, 272, 273 (Fig. 117)

— sanguinis, 272
Lankesterella, 189, 372, 378

— ranarum, 372, 378

Lankesteria ascidice, 327, 329 (Fig. 143)

— culieis, 327
Latent bodies, 296
Laverania, 358
Legendrea loyezce, 441
Legerella, 348, 349, 352, 355, 388

— nova, 352
Legerellidce, 352
Legeria, 353
Legerina, 353

Leishmania, 258, 281, 316,, 320, 321,
393,394

— donovani, 316 (Fig. 138), 317 (Fig.

139), 473

— infantum, 316, 317

— tropica, 87, 316, 317, 318 (Fig. 140),

412, 473

Lentospora cerebralis, 400
Leptodiscus, 279
Leptomonas, 52, 281, 282, 292, 308, 313,

319, 320, 321

— butschlii, 282

— jaculum, 314 (Fig. 136), 315
Leptotheca, 408

INDEX

511

Leptotheca agilis, 201, 401 (Fig. 165)

— ranarum, 408
Leptotrypanosome, 292, 314
Lemccophrya, 461

Lethal, 19

Leucocytogregarina, 372
Leucocytozoa, 372
Leucocytozoon, 357, 369, 390, 392

— lovati, 370

— muris, 376

— piroplasmoides, 319

— ratti, 376

— sabrazesi, 371

— ziemanni, 369 (Fig. 158), 370, 371
Leucophrys, 439

- patula, 440
Loucoplasts, 188
Leydenia gemmipara, 237
Licnophora, 440, 441, 446, 449
Licnophoridce, 440
Life-cycle, 129, 130
Light-perception, 201
Light-production, 201
Linellse, 238
Linin, 72
Lionotus, 439
Lithocircus, 256

— producing, 252 (Fig. 106)
Lithocystis schneideri, 331
Lobopodia, 47, 199
Lobosa, 217, 219

— testacca, 229
Lobose, 47
LopJiompnadidco, 276
Lophomonas, 36, 88, 261, 276

— blattarum, 17, 18, 89 (Fig. 45), 263,

276

— striata, 276
Lophophora, 276
Lorica, 33, 45, 276, 441
Loxodes, 439, 448
Luminosity, 201
Lymphocystis, 426

— johnstonei, 426, 427 (Fig. 178)
Lymphocytozoon, 388

— cobaycs, 388
Lynchia, 365

Macramceba, 148
Macroconjugant, 153, 449
Macrogamete, 126
Macrogamy, 131, 151, 172
Macrogonidiee, 267
Macromerozoito, 373
Macront, 426

Macronucleus, 78, 107, 430, 437, 448, 458
Maoroschizogony, 344
Macroschizont, 344, 373
Macrospores, 254, 255, 416
Macrostoma, 272

— mesnili, 272
Mai de caderas, 285
Malaria, 358, 359
Male sex, 159
Mallory's bodies, 470
Malpighiella refringens, 229
Mantle-fibres, 103
Mastigcemceba, 213, 261, 268
Mastigella, 77, 268

— vitrea, 83 (Fig. 40), 265, 266 (Fig. 112)
Mastigina, 265, 267, 268

— setosa, 82 (Figs. 38, 39)

Mastigophora, 12, 257
Mastigotricha, 455
Maturation, 142
Maupasia, 454

— paradoxa, 454 (Fig. 189, B)
Measles, 470

Mechanical stimuli, effects of, 207
Mechanical transmission, 290
Megalosphseric, 184, 233
Megastoma, 272

— entericum, 272, 273 (Fig. 117)
Melanin, 64, 198, 357
Membrane (nuclear), 76
Membranollse, 55, 443, 445
Membranulee, 445
Merocystis, 352

— kathcB, 352

Merogregarina amaroucii, 336
Merogregarinidce, 341
Meront, 398, 413
Merozoito, 169, 325
Merozoon, 210
Mesomitosis, 111
Metabolic, 33

Metachromatinic grains, 67, 420, 421
Metacineta, 460

Metacinetidce, 460

Metagenesis, 266

Metamera, 332, 339

Metamitosis, 111

Metaplastic, 40, 63

Metazoa, 2

Micramcfiba, 148

Microconjugant, 153, 172, 448

Microgamete, 126, 448

Microgamy, 132, 172

Microgonidia, 267

Microklossia, 426

Micromerozoite, 373

Micront, 426

Micronucleus, 78, 113, 114 (Fig. 61), 288,

332, 333, 430, 437, 448
Microschizont, 344, 373
Microsomo, 40
Microspheric, 184, 233
Microspore, 254, 255, 416
Microsporidia, 411
Microthoracidce, 439
Microthorax, 439
Miescher's tubes, 419, 422
Minchinia, 352

— caudata, 348

— chitonis, 349, 352
Mitochondria, 41, 448
Mitosis, 101
Mixotrophic, 188
Molluscum contagiosum, 17, 470
Monad, 466

Monadidce, 270
Monas, 270
Monaxon, 39, 250
Monera, 78
Monilif orm, 77
Monocercomonas, 272
Monocystis, 23, 174 (Fig. 79), 328, 336,
339

— coronata, 328

— pareudrili, 331

— rostrata, 332, 333, 335
Monokaryon, 121, 255
Monomastigote, 259
Monomastix, 455

512

THE PROTOZOA

Monomastix ciliatus, 454 (Fig. 189, A),

455

Monomorphic species, 163
Monopylaria, 251, 256
Monospora, 339
Monosporea, 409
Monothalamous, 36, 232
Monozoa, 273
Monozoic, 349
Mother-cyst, 138
Movement, 199
Movements of gregarines, 327
Multicilia, 249, 261, 270, 454

— lacustris, 269 (Fig. 113), 270

— palustris, 269 (Fig. 113), 270
Multiple fission, 100, 120

— gemmation, 122

— promitosis, 120
Multiplicative phase, 20, 166
Multipolar mitosis, 120
Murrina, 285
Mycetosporidium, 243
Mycetozoa, 218, 239, 268
Mycterothrix, 446
Myocyte, 327

Myonemes, 57, 201, 253, 259, 286, 445
Myophrisks, 253
Myxamoeba, 239
Myxidiidce, 409
Myxidium, 409

— bergense, 407

— lieberkuhni, 400, 401, 409

— sp., 406

Myxobolidce, 22, 23, 409
Myxobolus, 409

— cerebralis, 400

— neurobius, 400

— pfeifferi, 405, 406 (Fig. 168)
Myxocystis, 417, 418
Myxoflagellate, 239
Myxogastres, 242
Myxomycetes, 239, 242
Myxopodia, 253
Myxosporidia, 399
Myxotheca, 231

Nagana, 19

Narcotics, effects of, 204
Nassellaria, 256
Nassula, 439

Natural classification, 463
Nebenkern, 95
Nebenkorper, 278
Negri's bodies, 470
Nematocyst, 447
Neogamous, 127, 330
Neosporidia, 325, 398, 466
Nephroselmis, 275
Nervous system, 446
Neuronemes, 446
Neuroryctes, 470

— hydrophobia, 471
Neurosporidium, 424

— cephalodisci, 424
Nicollia, 380

— quadrigemina, 380, 381
Nina. See Pterocephalus
Noctiluca, 201, 213, 279

— miliaris, 119 (Fig. 65), 279
Nodosaria, 232 (Fig. 93, 3)
Nosema, 418

— apis, 412

Nosema bombyds, 24, 411, 413, 414 (Fig.

172)
Nuclear membrane, 76

— sap, 72
Nuclearia, 248
Niiclearia-st&ge, 177
Nucleo-cytoplasmic ratio, 70
Nucleolo-centrosome, 95
Nucleolus, 76, 103
Nucleophaga, 473
Nucleus, 6, 7, 65, 96

— secundus, 95
Nuda, 217,219
Nummulites, 232 (Fig. 93, 11)
Nutation, 51

Nutrition, 187
Nutlallia, 380

— equi, 380

— herpestidis, 380
Nyctotherus, 439, 440, 447

— cordiformis, 10 (Fig. 9), 444 (Fig.

186, F)

— faba, 440

OctomitidcB, 272
Octomitus, 36, 258, 272

— dujardini, 272 (Fig. 116)
Octosporea, 418

— musccs domesticce, 138
Octozoic, 349
GEcomonas, 270
(Esophagus, 261, 433
Oikomonas, 270
Oligosporea, 418
Oligosporulea, 424
Oligotricha, 439
Oocyst, 348

Oocyte, 143
Ookinete, 305, 362

Opalina, 196, 198, 208, 209, 439, 440,
447, 448, 452, 454

— caudata, 452

— intestinalis, 452

— ranarum, 447, 452, 453
Opalininw, 452
Opalinopsis, 452
Opercularia, 145, 440

— faurei, 442
Operculum, 441
Ophrydium, 438, 440
Ophryocystidce, 341
Ophryocystis, 337, 339
Orcheobius, 352
Ophryodendridce, 461
Ophryodendron, 455, 461
OphryoscolecidcB, 439
Ophryoscolex, 439, 441

Orcheobius herpobdella), 346, 348, 349, 352

Organella, 1

Oriental sore, 316

Osmotaxis, 203

Ovum, 125

Oxyrrhis, 52, 278

— marina, 278 (Fig. 123)
Oxytricha, 202, 440
Oxytrichidce, 440

Pansporella perplexa, 427
Pansporoblast, 405, 417, 423
Pantastomina, 268
Parabasal apparatus, 89
Paracoctidium prevoti, 349

INDEX

513

Paraglycogen, 41, 63, 195, 327

Paramastigote, 259

Paramecidce, 439

Paramecium, 61, 114 (Fig. 61), 171, 191,
192, 194, 196, 197, 198, 203 (Fig. 83),
205, 206, 208, 210, 437, 439, 442, 443

— bursaria, 449

— caudatum, 107 (Fig. 53), 436 (Fig.

185), 444 (Fig. 186, D, E), 447 (Fig.
187)
Paramceba, 228

— eilhardi, 94 (Fig. 49), 95, 228

— hominis, 228
Paramylum, 63, 188, 195
Paramyxa, 243, 409

— paradoxa, 409
Pararayxidia, 409
Paraplasma flavigenum, 379
Parasite, 8, 14

Parietal cell, 403
Parthenogenesis, 137
Parthenogonidia, 267
Partial karyogamy, 126, 153, 453
Pathogenic, 19

— amoebae, 226
Paulinella, 214
Pearl-stage, 334
Pebrine, 24, 411
Pectinellae, 442
Peduncle, 31
Pellicle, 32, 45, 435

Pelomyxa, 78, 144, 150, 205, 214, 227

— palustris, 227 (Fig. 91)
Peltomyces, 243
Peneroplis, 15, 235
Peranema, 274

— trichophorum, 273
Peranemidco, 274
Perezia, 418
Perforate, 231
Peridiniales, 276
Peridinidce, 278
Peridinium, 278

— diver gens, 278 (Fig. 122)
Peridium, 241
Perikaryon, 439
Periplast, 45, 259
Peripylaria, 251, 255
Peristome, 433, 442

Peritricha, 433, 438, 440, 441, 442, 448
Peritrichous larvae, 459
Peritromidce, 440
Peritrorjius, 440
Pernicious malaria, 358
Peroral membrane, 445
Phacus, 274

- triqueter, 274 (Fig. 118).
Phaenocystcs, 412
PhtBodaria, 258
Phaeodium, 252
Phosphorescence, 201, 278
Phototaxis, 202, 205
Phylogeny, 483
Physarum didermoides, 242
Physodes, 244
Phytoflagellata, 274
Phytomonadina, 274
Phytomyxince, 243
Piroplasma, 24, 357, 379, 393, 394

— bigeminum (bovis), 379 (Fig. 160),

384, 385 (Fig. 162)

— cabatti, 379

Piroplasma canis, 382, 383 (Fig. 161),
384, 385 (Fig. 162), 387

— donovani, 393
— hominis, 379

Piroplasmoses, 378
Piroplasms, 378, 390
Plagiotomidcc, 439
Planont, 398, 408, 413, 423
Planorbulina, 232 (Fig. 93, 9)
Plasmodiophora, 243

- brassicce, 149 (Fig. 76), 243
Plasmodium, 100, 128, 240, 398, 423
Plasmodium, 357

— brasilianum, 364

— cynomolgi, 364

— diploglossi, 358

— falciparum, 358, 359, 360 (Fig. 156)

— inui, 364

— kochi, 364

— malarias, 358, 359

— pithed, 359, 364

— prcecor, 358

— relictum, 358

— vivax, 137 (Fig. 72), 358, 359, 360

(Fig. 156)

- vassali, 364
Plasmodioma, 462
Plasmogamy, 128
Plasmotomy, 100
Plastin, 73, 103

Plastinoid granules, 41, 195, 346
Plastogamy, 128, 209
Plegepoda, 462
Pleistophora, 418

- longifilis, 413 (Fig. 171), 415, 416

— periplanetoe, 416

— species, 413
Pleodorina calif ornica, 267
Pleuronema, 55, 439, 442

— chrysalis, 56 (Fig. 27)
Pleuronemidce, 439
Podophrya, 461

— flxa, 456 (Fig. 190, C), 458

— gemmipara, 108 (Fig. 55)

— mollis, 456 (Fig. 190, A)
Podophryidce, 461

Polar bodies, 143

— capsule, 399 (Fig. 163)

— cones, 117

— filament, 399

— masses, 110

— platos, 117
Polycaryum, 424
Polychromophilus, 364
Polycystid, 326
Polycyttaria, 256
Polyenergid nuclei, 121, 151, 255
Polykaryon, 121, 255
Polymastigidcc, 272
Polymastigina, 271
Polymastigoto, 259
Polymastix, 272

Polymoiphism, 162, 163, 297, 311
Polyspora, 339

Polysporea, 409, 418
Polysporulea, 424
Polystomella, 210

— crispa, 139, 234 (Fig. 95), 235, 236

(Fig. 96)

Polythalamous, 36, 232
Polytomella ayUis, 86 (Fig. 43)
Polytrema, 231

33

514

THE PROTOZOA

Polytricha, 439
Polyzoic, 349
Poneramceba, 224
Pontdbdella murlcata, 291, 303
Pontomyxa flava, 218
Porospora, 337, 340

— gigantea, 74 (Fig. 35), 336, 339 (Fig. 150)

— legeri, 336
Porosporidce, 341
Pouchetia, 62

— cornuta, 61 (Fig. 31)
Prehensile tentacle, 457
Proboscidiform individuals, 455
Proboscidium, 442
Prococcidia, 352
Proflagellata, 469
Promito'sis, 109
Pronucleus, 127
Propagativo cell, 405

- phase, 21, 166
Propulsive pseudopodium, 401
Prorocentraccae, 276
Prorocentrum, 278
Prorodon, 439

— teres, 32 (Fig. 14), 444 (Fig. 186, B,

C), 446

Proteomyxa, 217, 268
Proteosoma, 358, 364, 365, 393
Protista, 4, 5
Protoblast, 426
Protccoccaceae, 15
Protoentospora ptychoderce, 229
Protokaryon, 75, 87, 108
Protomcrito, 327
Protomonadina, 270
Prolophrya, 452

— ovicola, 452
Protophyta, 8
Protoplasm, 29, 40
Protozoa, 2, 10, 464
Prowazek's bodies, 470

Prowazekia, 260, 271, 281, 319, 321, 322

— asiatica, 319

— cruzi, 319

— parva, 319, 320 (Fig. 141)

— weinbergi, 319, 320 (Fig. 141)
Pseudochlamys-staga, 170, 177
Pseudoplasmodida, 243
Pseudoplasmodium, 242
Pseudopodiospore, 169
Pseudopodium, 30, 46, 90, 199, 214, 400,

465

Pseudospora, 213, 218, 249
Psorosperm, 165, 323
Pterocephalus, 173, 327, 329, 330, 339

— graeilis, 174 (Fig. 79), 332 (Fig. 145),

334 (Fig. 147)

— nobilis, 339
Pulsellum, 52, 259
Pusulo, 277
Pycnothrix, 452

— monocystoides, 443, 446, 447, 452
Pyramimonas, 275
Pyronoid, 63, 188, 261
Pyrodinium, 201, 278
Pyrosoma, 379
Pyxinia, 329, 330

Quartan malaria, 358, 359

Radiolaria, 218, 249
Radium-rays, effects of, 205

Raincy's corpuscles, 419
Reactions of protozoa, 201
Recapitulative forms, 170
Reducing division, 104
Reduction, 142, 145, 335
Reduction-nuclei, 144
Redwater, 378
Regeneration, 208, 210
Rejuvenescence, 155
Relapse (malarial), 363
Reserve-materials, 195, 196
Reservoir-vacuole, 262
Respiration, 195
Reticulosa, 217, 218
Roticulosc, 48
Reticulum (nuclear), 75, 103

— (protoplasmic), 41
Rhabdogeniae, 325, 466
Rhabdophrya, 461

— irimorpha, 455
Rhaphidiophrys, 245
Rheotaxis, 207
Rhinosporidium, 424

— kinealyi, 424, 425 (Fig. 177)
Rhizomastigina, 265, 268, 465
Rhizoplast, 82
Rhizopoda, 213, 217
Rhyncheta, 457, 460
Rhynchoflagellata, 278
Right hosts, 291
Rod-apparatus, 433, 439
Rontgen-rays, effects of, 206
Rostrum, 326

Saccamina, 232 (Fig. 93, 1)

Sack-pusule, 277

Sapropelic, 14

Saprophytic, 8, 14, 187, 194, 262

Saprospira, 467, 469

— glandis, 468
Sapro/oic, 14
Sarcocystinc, 20, 420, 421
Sarcocystis, 20, 419

— bertrami, 420

— muris, 419, 420, 421, 422 (Fig. 176>

— rileyi, 420

— tenella, 419, 420, 421 (Fig. 175)
Sarcocyte, 327

Sarcode, 40
Sarcodina, 11, 213
Sarcosporidia, 20, 419
Scaiotricha, 440
Scarlet fever, 470
Schaudinnella, 355
Schewiakovella schmeili, 425
Schizocystidce, 339, 341
Schizocystis, 339

— gregarinoides, 336, 338 (Fig. 149)
Schizogcnea, 418

Schizogony, 166, 324, 392
Schizogregarinae, 328, 339
Schizokinete, 373
Schizont, 166, 181, 324
Schizontocyte, 344
Schizotrypanum, 285, 307, 392

— cruzi, 28, 295 (Fig. 128), 296, 302.

(Fig. 132), 307
Schizozoite, 344, 428
Sclerotium, 166, 240
Scopula, 441, 456, 459
Scyphidia, 440, 441
Secondary nuclei, 66

INDEX

515

Secretion, 197, 198
Selenidiidce, 341
Selenidium, 339

— caulleryi, 336, 337 (Fig. 148)
Selenococcidium, 352, 354

- intermedium, 344, 350 (Fig. 155), 351
Senility, 131, 135, 155

Sensory organs, 201, 446

Separation-spindle, 104

Septate, 326

Serumsporidia, 425

Sex, 154

Sexual differentiation, 160, 170, 176

— phases of trypanosomes, 305
Shell, 33, 45, 232 (Fig. 93)
Siedleckia, 339, 352
Silicoflagcllata, 274
Sleeping sickness, 26
Smithia, 380

— microti, 380
Soma, 130

Somatic number, 143
Sorophora, 243
Sorosphcera, 243
Sorus, 242
Souma, 304
Spasmoneme, 446
Species, 141, 162
Spermatocyte, 143
Spermatozoon, 125
SphcGractinomyxon, 409

— stolci, 409, 410 (Fig. 170)
Sphsercllaria, 255

Sphceromyxa sabrazesi, 404 (Fig. 167),

405

Sphcerophrya, 461
Spheerozoa, 256
Sphere, 95
Spheroplast, 41, 448
Spicule, 36

Spindle (nuclear), 103
Spirigera, 442
Spirillacea, 467
Spirillar forms, 319
Spirillum, 467
Spirochceta, 466

— plicatilis, 466

— ziemanni, 371, 468
Spirocheetes, 466
Spirochona, 440
Spirochonidce, 440
Spiroloculina, 232 (Fig. 93, 5)
Spironema, 487, 469
Spironemacea, 469
Spiroschaudinnia, 467

— anserina, 467

- duttoni, 467, 468

— gallinarum, 467

— obermeieri, 467

— recurrentis, 467

Spirostomum, 196, 197, 208, 438, 439, 445

— ambiguum, 431 (Fig. 180)
Spongomonas, 270

— splendida, 84 (Fig. 41)

- uvella, 85 (Fig. 42)
Sporal residuum, 349
Sporangium, 240, 241
Spore, 165, 166, 323
Spore -formation, 166
Sporetia, 150
Sporoblast, 325
Sporocyst,k165

Sporocyst-mother-cell, 403
Sporoduct, 335
Sporogony, 181, 325
Sporomyxa, 243
Sporont, 166, 181, 325, 325
Sporophoro, 242
Sporoplasm, 405
Sporozoa, 12, 323, 462, 466
Sporozoito, 169, 324
Sporulation, 122, 165, 166
Spumollaria, 255
Stannomidcc, 238
Starvation, 195, 210
Stemonitis flaccida, 82

— fusca, 240 (Fig. 98)
Stemm-pseudopodium, 401
Stempellia, 418

— mutabilis, 418
Stenophora, 329

Stentor, 61, 202, 211, 437, 438, 439, 441,

445, 446
— cceruleus, 444 (Fig. 186, A, I)

— niger 444 (Fig. 186, O)

— roeselii, 10 (Fig. 8)
Stentoridce, 439
Stephanosphcera, 267, 276
Stercomarium, 238
Stercome, 194, 233
Stigma, 61, 205, 262
Stomatophora coronata, 328
Streaming movements, 199
Strongyloplasmata, 470
Stylonychia, 438, 440

— histrio, 444 (Fig. 186, H)

— mytilus, 211, 459 (Fig. 192)
Stylorhynchus, 173, 329, 330, 339

- longicollis, 174 (Fig. 79), 327 (Fig.

142), 339
Suctoria, 455

Suctorial tentacle, 190, 458
Sulcus, 276
Surface-tension, 200
Surra, 26

Swarm-spore, 169, 396
Symbiosis, 15
Symbiotic algee, 197
Synactinomyxon, 409
Syngamy, 126, 438
Synkaryon, 127
Syphilis, 467
Syzygy, 330

Tachyblaston, 460
Tactic, 202
Tactile bristles, 443

— organs, 201
Twniocystis, 327, 339
Taxis, 202

Technitella thompsoni, 34
Teloblast, 426
Telomyxa, 418

— glugeiformis, 418
Telosporidia, 325, 395, 466
Temperature, effects of, 206
Tentaculifera, 455
Tertian malaria, 358, 359
Test, 33

Testacea, 217,219
Tetramyxa, 243
Tetratrichomonas, 272
Tetrazoic, 349
Thalamophora, 219

516

THE PROTOZOA

Thalassicolla, 255

— pelagica, 30 (Fig. 13)
Thalassophysa, 255
Thecamoebee, 219, 229
Theileria, 379

— parva, 380, 382, 386
Thelohania, 418

— chcetogastris, 416 (Fig. 173)

— contejeani, 412

— mcenadis, 416
Thelyplasm, 129
Thermotaxis, 202, 205
Thigmotaxis, 207

Thyroid extract, effects of, 204
Tinctin-body, 458 N*
Tintinnidco, 439, 441, 443, 447
Tocophrya, 461

— cyclopum, 461

— limbata, 460

— quadripartita, 210, 456 (Fig. ICO, B)

460
Toddia, 387

— bufonis, 387
Tolerant, 21
Tonicity, effects of, 207
Total karyogamy, 126, 453
Toxocystis homari, 426
Toxoplasma, 319, 387

— cants, 387

— cuniculi, 387

— gondii, 387

— talpce, 387
Trachelidce, 439
Trachelius, 439

— ovum, 441, 448
Trachelocerca, 439, 448, 453

— phcenicopterus, 120 (Fig. 66), 449, 450

(Fig. 188)
Trachoma, 470
Tractellum, 52, 259
Trailing flagellum, 53, 260
Transmission of trypanosomes, 289
Transmutation of energy, 199
Treponema, 467

— pallidum, 467, 468

— pertenue, 467
Triactinomyxon, 409
Trichia varia, 241 (Fig. 101)
Trichites, 442

Trichocyst, 46, 435, 447 (Fig. 187)
Trichodina, 440, 441
Trichomastix, 260, 271
Trichomonas, 17, 36, 56, 258, 260, 271

— eberthi, 8 (Fig. 5), 36

— hominis, 272

— vaginalis, 272
Trichonympha, 276

— herhvigi, 276
Trichonymphida, 463
TrichonympMdcc, 89, 276, 454
Trichophrya, 461
Trichophryidce, 461
Trichorhynchus, 446
TrichosphcBrium, 51, 216, 229

— sieboldi, 73 (Fig. 34), 182 (Fig. 81)
Trimastigamceba, 268

Tripylaria, 251, 256
Tritoblast, 426
Trizoic, 349
Trophic phase, 324
Trophochromatin, 71
Trophochromidia, 150

Trophonucleus, 78, 85, 286, 288
Trophozoite, 324
Tropical malaria, 358
Trypanomonad, 282, 298, 299
Trypanomorpha, 308
Trypanophis grobbeni, 309
Trypanoplasma, 56, 78, 87, 260, 271, 281,
287, 308, 309, 321, 322

- abramidis, 310 (Fig. 134)

- borreli, 312

- confirm, 312

— dendrocceli, 309

— gryllotalpoe, 309, 310

— gurneyorum, 78 (Fig. 36)

- helicis, 309, 311, 312

— intestinalis, 312

- keysselitzi, 310 (Fig. 134)

— ranee, 319

— vaginalis, 309

Trypanosoma, 270, 280, 283, 308, 320,
321

— balbianii, 467

— blanchardi, 25

— brucii, 19, 25, 26, 27 (Fig. 12), 285,

291, 296, 305, 306, 308

— cazalboui, 304

— cruzi, 285, 295, 296

— cuniculi, 25, 26 (Fig. 11)

— dimorphon, 304

— drosophilce, 315 (Fig. 137)
-»• duttoni, 25, 26 (Fig. 11)

— elyomis, 25, 26 (Fig. 11)

— equinum, 285, 305

— equiperdum, 22, 26, 285

— evansi, 26, 27 (Fig. 12), 285

— gambiense, 19, 26, 27 (Fig. 12), 285,

291, 296, 297, 303, 304, 305, 306

— granulosum, 288, 297, 298 (Fig. 129)

— grayi, 304

— hippicum, 285

— inopinatum, 290

— lewisi, 19, 25, 26 (Fig. 11), 28, 263,

286, 291, 292, 293 (Fig. 127), 297,
299, 300 (Fig. 130), 301 (Fig. 131),
305, 306, 308

— longocaudense, 294

— mega, 284 (Fig. 125)

— microti, 25, 26 (Fig. 11)

— nanum, 27 (Fig. 12)

— noctuce, 59 (Fig. 30), 137, 144, 158,

283,297, 305, 306, 308,391

— pecaudi, 304

— perccB (myonomos), 58 (Fig. 28)

— rabinowitschi, 25

— raice, 291, 303

— remaki, 9 (Fig. 6)

— rhodesiense, 26, 286

- rotatorium, 59 (Fig. 30), 283, 297, 307

— sanguinis, 283

- vittatce, 303

— vivax, 27 (Fig. 12), 287, 291, 304
Trypanosomes, syngamy, 136
Trypanosomidce, 268, 270
Trypanotoxin, 20
Trypanozoon, 308

Ultramicroscopic stages, 306
Uncif orm individuals, 455
Undulating membrane, 55, 2 CO,

443

Undulina ranarum, 283
Unicellular, 1, 3

>, 287.

INDEX

517

Urceolarince, 440
Urhsemoflagcllat, 468
Urnula, 457, 460

— epistylidis, 457 (Fig. 191), 460
Urnulldce, 460

Urospora lagidis gametes, 174 (Fig. 79)
Urosporidium, 424
Urostyla, 440

Vaccinia, 470
Vacuole, 43
Vaginicola, 440
Vampyrella, 218

— lateritia, 219 (Fig. 86)
Variola, 470

Vegetative chromatin, 71
Vermiform individuals, 455
Vestibule, 433

Volutin, 68, 1*95, 289
Volvocidce, 267, 275
Volvox, 3, 131, 206, 267, 276
Vorticella, 440S 441, 445, 446

Vorticella microstoma, 172 (Fig. 78)

— monilata, 446
Vorticellidoe, 440
Varticellince, 440

Wagnerella, 48, 51, 92, 120, 245, 246, 248

— borealis, 93 (Fig. 48), 247 (Fig. 102)
Wrong hosts, 291

Xenophya, 34, 238
Xenophyophora, 218, 237

Yaws, 467
Yellow cells, 252

Zoochlorellse, 15, 252
Zoomyxa, 243
Zoospore, 169, 262
ZoosporidcB, 218
Zoothamnium, 440
Zooxanthellee, 15, 252
Zygote, 125

THE EN"D

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