lose tentacles, flagella, and cytostomes, and conjugate ; after

mutual nuclear fertilization the
animals separate, while the proto-
plasm in each collects in a disc
which, by successive divisions, is
converted into numerous uni-
nucleate oval germs. These at first
project from the sphere, but later
separate and form small flagellate
spores whose later history is not
certainly known.

Leptodisciis medusoidcs of Eu-
rope (fig. 143) has the appearance
of a medusa 1 to 1.5 mm. in
diameter. Its gelatinous disc is
covered by a membrane, and at the
FIG. uz.-Leptodiscus medusoides, sur- highest point of the concave surface

face and optical section. /, nagellum; j s a mass O f protoplasm with a sin-
m, cytostome; n, nucleus; o, preoral

tract; p, protoplasmic band. gi e nucleus. On one side of this a

band goes to the mouth, on the other a canal bearing a fine
nagellum at its end. The animals swim well, like medusae, by
closing the umbrella, the motions of which are caused by delicate
muscles on the concave side.

Class III. Ciliata.

The Ciliata rival the Ehizopoda in numbers and variety of
form. They are so complicated in structure that they were long
held as multicellular, a view which was entirely abandoned only
in the last quarter-century. All have a form definite for the




III. CIL1ATA.



205



species; this in the ' ametabolous ' forms is unalterable, in the
4 metabola ' it can be pressed out of shape in passing through a
narrow space. This constancy of form is due to the 'development
of more or less cuticle on the outside of the body, which in the
' ametabola ' acquires an armor-like firmness; in the others is more
flexible. The cuticle is covered with cilia small vibrating pro-
cesses which move not singly but together in large numbers, and
serve not only as organs of locomotion, but by
creating vortices in the water bring food to the
organism. They furnish the most important
characteristic of the class (fig. 144).

The presence of a cuticle necessitates a
cytostome (except in the parasitic species),
since food particles cannot be taken in at any
point. At the cytostome the cuticle with its
cilia forms a funnel-like extension (cyto-
pharynx) into the protoplasm. At the bottom
the cuticle is interrupted so that water and pro-
toplasm are in contact. By the action of the
cilia food particles are taken into the cyto-
pharynx and pressed into the protoplasm,
formkiff a small enlargement which finally sinks FIG

J caudatum (half dia

into the substance as a lood vacuole (na),
which by the streaming of the protoplasm is
carried about in the body. The digestible por-
tions are absorbed, and those not capable of
digestion are cast out of the body at a fixed
point (cytopyge) usually not recognizable at other times (fig. 151).
Contractile vacuoles (cv) are lacking only in parasites and
marine species. They are constant in number and position, and
frequently have afferent ducts which empty into the vacuole, the
vacuole in turn forcing the fluid to the exterior. Trichocysts, nettle
bodies, and muscular fibrillse occur in some species. Trichocysts
are minute rods placed vertically to the surface in the cortical
layer, which under the influence of reagents (chromic acid is best)
elongate into threads penetrating the cuticula. These have been
compared by some to the nettle cells of coelenterates, and have
been ascribed defensive functions; others regard them as tactile
structures. They have no connexion with the cilia. Kettle
bodies are extremely rare. Muscle fibres are more common ; they
lie between ectosarc and cuticle, and cause quick convulsive motions
of the animal.




grammatic). cv, con-
tractile vacuole in
systole, cu', in dias-
tole; to, nucleus; na,
food vacuole, ?ia', iu
formation; nfc, micro-
nucleus; f, tricho-
cysts, at t' protruded.



206



PROTOZOA.



The nuclear relations are extremely interesting in that there are
two nuclei physiologically unlike. The larger of these (nucleus
of older writers, macronucleus} is a large oval, rod-like, or spiral
body, readily and deeply staining with microscopic stains, and sur-
rounded with a membrane. It appears to control all the common

vital functions of the animal (motion,
feeding, etc.). Beside it or in a depres-
sion in it is the much smaller micro-
nucleus (nucleolus or paranucleus of
older authors) which stains less deeply
and only plays a part in reproduction.
In all sexual processes it comes to the
front and can be called the sexual
nucleus.

Multiplication of Ciliata occurs by
binary fission (fig. 145); more rarely, and
then only in the encysted condition, by
division into numerous (up to 64) parts.
Budding is known in the Peritricha and
Suctoria. First the micronucleus divides

no. M-ParamKcium aurelia mitoticall y> and the * th macronucleus

in division, ft, macronucleus; separates bv elongation and construction.

n/r, micronuclei; o, cytostome J

of the separating individuals. The old cytostome persists in the anterior

At 2 an early stage of division

of cytostome. offspring, but often an outgrowth from

it (fig. 145, 2, o f ) passes into the posterior half and develops into
a new mouth.

The periods of fission are interrupted from time to time by the
sexual process of conjugation, which will be described as it occurs
in Paramcecium (fig. 146). Two individuals touch at first in front,
and then by their whole ventral surfaces, so that their cytostomes
come together. In the neighborhood of the latter a plasma bridge
connects the two. Later the individuals separate. While these
easily observable external processes are occurring there is a com-
plete modification of the nuclear apparatus in the interior. The
macronucleus increases in size, and breaks into small portions
which disappear within the first week after copulation (probably
absorption), and give place to a new nucleus derived from the
micronucleus. At the beginning of copulation the micronucleus
becomes spindle-shaped, divides and repeats the process, the result
being the formation of four spindles, three of which break down,
thus recalling the polar globules in the maturation of the egg
(p. 146). The fourth or primary spindle places itself in the neigh-




III. CILIATA.



207



borhood of the cytostome at right angles to the surface and divides
into two nuclei, the superficial being called the wandering or




FIG. 146. Conjugation in Paramcecium. fc, macronucleus; ?i

stomes.



micronucleus; o, cyto-



I. Changes of micronucleus; left sickle stage, right spindle stage.

II. Second division of micronucleus into primary spindles (1, 5) and secondary
spindles (2, 3, 4; 6, 7, 8).

III. Degeneration of secondary spindles (2, 3, 4; 6, 7, 8); division of primary spindle
into male (1m, 5m) and female spindles (I?/;, 5w).

IV. Exchange of male spindles nearly complete (fertilization), one end still in the
parent animal, the other united with the female spindle, 1m with 5w and 5m with Ito;
macronucleus broken up.

V. The cleavage spindle t formed by male and female spindles dividing into the
secondary cleavage spindles t', t".

VI. VII. End of conjugation. The secondary cleavage spindle dividing into the
anlage of the new micronucleus (nfc') and that of the new macronucleus, pt
(placenta). The fragments of the old macronucleus begin to degenerate.

Since P. caudatum shows the earlier and P. aurelia the later stages better, these
forms have been used, P. caudatum for I-III, P. aurelia for the rest. The differences
consist in the existence of one micronucleus in P. caudatum, two in P. aurelia^ and
that in the latter the nuclear degeneration begins in I.

male nucleus, the deeper, the stationary or female nucleus. The
male nuclei of the two copulating animals are exchanged, travers-



208 PROTOZOA.

ing the protoplasmic bridge in their course. Both male and
female nuclei become spindle-shaped, and the immigrant male
.spindle fuses with the female spindle, forming a single spindle of
division. At last the division spindle produces (usually by indi-
rect means) two nuclei, one of which becomes the new macronu-
cleus, the other the new micronucleus.

In a comparison of the fertilization of the Metazoa, the female
nucleus corresponds to the egg nucleus, the male nucleus to that
of the spermatozoa. As the fusion of egg and sperm nuclei forms
a segmentation nucleus, so here the division nucleus is formed in
a similar manner. As the egg cell through fertilization acquires
the capacity not only to produce sex cells but somatic cells cells
which carry on the common functions of the body the fertilized
micronucleus forms not only the new micronucleus, but also the
macronucleus which controls the body processes, and hence is the
somatic nucleus. In other words, fertilization in the Ciliates
leads to a complete new formation of the nucleus and thus to a
new organization of the organism.

In most Ciliata the conjugating individuals are equivalent,
the fertilization is mutual, and the individuals separate later. In
the Peritricha (mostly sessile forms, fig. 147), on the contrary, the




Fio. \it.-Epistylis umbellnria. (After Greeff.) Part of a colony in 'bud-like ' conju-
gation r, microspores arising by division; fr, microspore conjugating with a
macrospore.

resemblance to fertilization in the Metazoa is strengthened in that
there is a sexual differentiation and a permanent fusion of the
conjugating individuals. Some animals the macrospores retain
their size and sessile habits; others by rapid division produce



III. CILIATA: HOLOTRICHA, HETEROTRICHA.



209



groups of markedly smaller microspores. The latter separate and
fuse completely with the macrospores, only a small cuticular sac
persisting to indicate the fusion. The nuclear phenomena are
much the same as with Paramcecium, allowance being made for
the permanance of the fusion.

Order I. Holotricha.

The Holotricha are doubtless the most primitive Ciliates, since
the cilia on all parts of the body are similar; being at most slightly
stronger at one end of the body or on the inside of the cytostome.
Best known are the species of Paramcecium* (fig. 144) occurring
in stagnant water. Opalina ranarum * lives in the intestine of the
frog. It lacks mouth, has numerous similar nuclei, no micronu-
oleus and no conjugation. The small encysted Opalines pass out
with the faeces, and are eaten by the tadpoles, which thus become
infected.

Order II. Heterotricha.

Like the Holotricha the Heterotricha
are everywhere ciliated, but they have a
tract of stronger cilia, the adoral ciliated
spiral. This is a band of cilia beginning
at some distance from the cytostome and
leading in a spiral course into the mouth.
It consists of rows of cilia united into
' membranellse ' placed at right angles to
the course of the spiral. In the best-
known heterotrichans, the Stentors * (fig.
148), the peristomial area, surrounded by






FIG. 148. FIG. 149.

FIG. 148. Stentor polymorphus. (After Stein.) a, peristomial area; b, roof of hypo-

storae; 0, contractile yacuole; n, nucleus; o, cytostome; r, adoral ciliated spiral;

t, hypostome (excavation for mouth).
FIG. UU.Balantidiuni coli. (After Leuckart.)



210



PROTOZOA.



the spiral, forms the broader end of the body, which gradually
tapers toward the other end, by which the animal may attach
itself by small plasma threads. Muscle fibres which run length-
wise immediately under the cuticle produce energetic move-
ments. Stentor polymorphus * when attached builds a gelatinous
case. S. cceruleus.* Balantidium coli (fig. 149) appears in the
large intestine of men ill with diarrhrea; it also occurs in swine
without causing sickness. Other parasites of man are B. minu-
tum and Nyctotherus faba.

Order III. Peritricha.

In the Peritricha there is always a broad peristome area with
the cytostome; the opposite end has a corresponding pedal disc
or is narrowed like a goblet and ends in a stalk (fig. 150). Only




FIG. 150. Carchesium polypinum. (After Biitschli.) Left, a single animal; right, three
stages of division, cv, contractile vacuole; n, macronucleus: n', micronucleus;
JVv, food vacuoles: os, cytopharynx; per, peristome; vs, reservoir of contractile
vacuole; *, undulating membrane ; vst, vestibule; wk, ring on which a posterior
circle of cilia may develop.

the adoral ciliated spiral is constant. It arises from the swollen
margin of the peristomial area, and continues on the ' operculum/
a ciliated disc which projects free from the peristomial area, but
in contraction is drawn close against it, tliQ peristome lips folding
over all. Besides, there may be a temporary or permanent circle
of cilia near the hinder end. The nucleus is usually sausage-
shaped, much bent, and with the small micronucleus in its hinder
angle (fig. 150, n f ).

The best known representatives are the VORTICELLID^E (figs. 147, 150),
attached by a long stalk which is usually hollow and contains a slightly



///. CILIATA: HJPOTRICHA.



211



spiral muscle. This extends into the body and divides up into fine fibrilla3
which extend under the cuticle to the peristome. When the muscle in the
stalk contracts it becomes coiled into a corkscrew spiral, drawing back the
animal, and folding in the anterior end. Vorticella* is solitary; Carche-
sium* forms colonies with dichotomously branched stalks; Zoothamnion*
colonies imbedded in a common jelly ; Epistylis* (fig. 147), branched col-
onies with rigid stalks, the muscle being confined to the base of the body.

Order IV. Hypotricha.

In this order the body is more or less flattened and a ventral
and a weakly arched dorsal surface are differentiated. The back
lacks cilia, but often bears spines and tactile bristles. On the ven-
tral side are several longitudinal rows of cilia, and besides straight




ID 1 ..




FIG. 151. FIG 152.

FIG. 151. Stylonychfa mytilns. (After Stein.) , anal hooks; 6, ventral hooks; c, con-
tractile vacuole: rf, frontal ridge; g, canal leading to contractile vacuole; I, upper
lip; 71, nucleus with micronucleus: p, adoral ciliated spiral; r, marginal cilia; s,
caudal cilia; .sf, frontal spines; z, anus (cytopyge).

FIG. 152. Division of Sti/ionychia mytilns. (After Stein ) c, c', contractile vacuoles of
the two individuals; n, ?V, nucleus and micronucleus; p, p', adoral ciliated spiral;
r, ', marginal cilia; w;, ;', ciliated ridges.

spines and hooked cilia composed of united cilia. These latter are
of use in creeping. The strongly developed adoral cilia are of use
in locomotion and in producing vortices which bring food. The
macronucleus is often divided into two oval bodies connected by a
thread; the micronuclei vary in number from 2 to 4 in the same



212



PROTOZOA.



species. These are the best forms for studying the micro nuclei.
The species of Stylonychia* (figs. 151, 152) are best known.

Order V. Suctoria (Acinetaria).

The Suctoria differ from other Infusoria in the absence of cilia
from the adult and consequently have no means of locomotion.
They are fixed to some support either by the base or by a slender
stalk. The body is usually spherical and is covered with a cuticle,
which in the genus Acineta is produced into a cup-like lorica.
There is no mouth, but in its place tentacles or sucking feet, very
fine tubes with contractile walls which begin in the protoplasm and
protrude through the cuticle (fig. 153, F). The Acinetaria kill
other animals, especially infusoria, with their tentacles, and then




FIG. 153. Forms of Suctoria. (After various writers.) A, Dendrosoma; B, Rhyncheta;
C, Opliryodendron; D, Tokophrya; ", ciliated young of Sphceroplirya; F, diagram of
structure showing capitate and styliform tentacles arising from the ectosarc
and corresponding canals in the entosarc.

suck the substance through these tubes. The contractile vacuole,
rarely lacking, lies near the compact macronucleus; micronuclei
are generally present.

In contrast to the immobile adults the young which are ciliated
(fig. 153, E) after the pattern of ciliates, are good swimmers.
They arise either as buds from 'the surface of the mother or as
( embryos 9 in her interior. This latter condition is only a modifi-
cation of the other, for parts of the outer surface become pushed
into the interior, and there form a brood cavity in which the
embryos arise. After swimming for a while the young come to
rest, lose the cilia, and develop the tentacles.

Some species of Podoplirya are widely distributed in fresh water, also
Sphcerophrya, parasitic in Infusoria. The species of Acineta as well as
Podophrya gemmipara (fig. 20) are marine, living on hydroids and Poly-
zoa.



IV. SPOROZOA: OREGARINA.



213



Class IV. Sporozoa.

Under the name Sporozoa are united several groups of Protozoa
which, while they differ much in structure, have much in common
in life and development. They are parasites in Metazoa, many of
them in the cells themselves, causing their degeneration (Cytospo-




FIG. 154. Sporozoa. -4, cyst of Clepsidrina with sporoducts; B, Clepsidrina, two indi-
viduals (after Schneider); C, Eimeriafalcifonnis, from mouse; >, same, falciform
embryos: JK, Hoplorhynchus dujnrdinii^ from Litkobius; F, Gregarina atgantea. from
lobster; Cr, Sarcocystis miescheri, from pig; H, Myxidium (after Th6olan); I,Rhopa-
locephalus, alleged cause of cancer (after Korotneff).

ridae). They take no solid food, but are nourished by fluid mate-
rial absorbed through the whole surface. In reproduction they
form a large number of l sporoblasts/ which when enveloped with
a membrane are called ' spores/ the contents of which usually
break up into several small bodies or ' sporozoites/ The sporozo-
ites for their development must leave the host. The resemblances
to the Rhizopods (Mycetozoa) are unmistakable, especially those
Sporozoa which have pseudopodia for much of their life.

Order I. Gregarina.

The typical and longest known sporozoa are the Gregarines,
parasites of oval or thread-like form (recalling round worms),
usually somewhat flattened, which so far have only been found in
invertebrates, where they live in the intestine or gonads, more
rarely in the body cavity. The protoplasm (fig. 155, /) is sepa-
rated more sharply than in other Protozoa into a clear ectosarc
(elc) and a granular entosarc (en). The ectosarc is covered by
a cuticle (not always easily seen, but frequently with a double con-
tour) (cu), which must be permeable by fluid food, for no cyto-
stome exists. In many (perhaps all) there is a double striping
of the body, a longitudinal recognizable by furrows on the outer
surface and hence cuticular, and a transverse marking in the



PROTOZOA.



ectosarc, produced by circular or spiral muscle fibrillae. These
muscles explain the peristaltic motion and the occasional sharp
bending of the body, but not the peculiar gliding motion like that
of diatoms by which locomotion is usually effected. This is



pm.




I.



en.



FIG. 155. Development of Gregarina blattarum. I, conjugation ; II, A-C, a cyst in
transformation into pseudonavicellae; III, A, a pseudonavicella greatly enlarged;
B, same with sickle-formed sporozoites; CM, cuticle; dm, deutomerite; ek, ecto-
sarc; en, entosarc; ?i, nucleus; pm, protomerite; pn, pseudonavicellae; rJc, re-
sidual body; sfc, sickle-form sporozoites.

explained by the view that the gregarines secrete stiff gelatinous
threads from the posterior end, and the elongation of these forces
the body forward.

In many gregarines (Poly cyst idae) the body is divided by a cir-
cular incision into a smaller anterior part, the protomerite, and a
larger deutomerite. Internally this division is marked by a bridge
of ectosarc across the entosarc. The vesicular nucleus (there is
but one in any gregarine) lies in the deutomerite. An epimerite
a structure connected with the peculiar type of parasitism occurs
in many species. All gregarines are parasitic in youth inside of
cells. They later leave these, but many remain for a long time
with a process of the protomerite imbedded in the cells. This
process the epimerite is provided with threads or hooks for



IV. SPOROZOA: COCCIDIAE. 215

anchorage, and is lost when the animal gives up its connexion
with the host cell. Among the intestinal gregarines frequently
occur l associations ' where two or more animals are fastened to-
gether head to tail in a row. Perhaps these associations are prep-
arations for conjugation which occurs in development.

Eeproduction occurs exclusively in an encysted condition (fig.
155, II, ^4). Usually two animals (sometimes one, rarely more than
two) occur in a cyst. A fusion of the two encysted animals does
not take place, but it is probable that a nuclear exchange (recalling
that of ciliates) takes place. After each individual has become
polynucleate by division of its nucleus, it divides at first super-
ficially, later internally into small particles, the sporoblasts (II, B),
which change into spores, here called pseudonavicellae. The
pseudonavicellae are inononucleate bodies with firm membrane and
usually spindle form in shape (III, AA). In these processes a
part of the gregarine takes no part. This residual body appears
under proper conditions to swell up and rupture the cyst, thus
freeing the pseudonavicellae. In many gregarines there are sporo-
ducts for the escape of the pseudonavicellae (fig. 154, A). The
contents of the pseudonavicellae divides into (usually eight) sporo-
zoites or falciform spores which must pass out from the spores and
into the cells of the host in order to form gregarines. This escape
of the sporozoites depends upon entrance into the proper host.
Often the transformation of the contents of the cysts into pseudo-
navicellae takes place when the cysts have left the original host.

Best known are the Monocystis tenax of thespermatheca of earthworms,
and Gregarina (Clepsidrina) Uattarum of the cockroach. The American
species have scarcely been touched. One species is abundant in the intes-
tine of Geophilus.

Order II. Coccidiae.

The gregarines of all Sporozoa are nearest the Coccidiae, which
are also cell parasites with a single nucleus, but without either cell
membrane or division into protomerite and deutomerite. In most
species, as in Coccidium cuniculi, there are two types of reproduc-
tion, an endogenous, leading to ' autoinfection/ and an exogenous,
concerned in the transfer of the germs to other hosts. In the
first (lacking in many species) the Coccidium divides into many
falciform germs which separate from each other and, without
alternation of hosts, enter other cells. The second type is begun
by fertilization. Certain individuals, by rapid division form
microgametes, small bodies swimming with serpentine motions or
by one or two flagella. Other individuals do not divide, but form



216



PROTOZOA.



macrogametes which are fertilized by the microgametes, and then
encyst, pass to the outside, and serve for the infection of other
animals. The contents of the cyst begin to divide, sooner or
later, into sporoblasts (in Coccidium, four) containing spores, the




FIG. 156. Coccidium cuniculi, from the liver of the rabbit (from Wasielewski. a, & r
young Coccidia in the epithelial cells of bile duct, the nucleus of the cell in the
upper process; c, encysted; d, e, contraction of protoplasm; t, h, g, spore forma-
tion; /, ripe spore with two germs and a residual body.

process being completed only after entrance into a new host.
Each spore forms one or more sporozoites, a portion of the sub-
stance being left behind. Coccidium cuniculi (oviforme) in the
liver of mammals, especially rabbits (rare in man), producing
cheesy granules. C. perforans in the intestine of rabbits, rare in
man.

Order III. Haemosporida.

In structure and development these are much like the Coccidiae ;
they live in blood corpuscles. The forms occurring in man pro-
duce malaria. Here, also, there are endogenous (autoinfecting)
and exogenous generations transferring the parasites to other
hosts. The parasites in the corpuscles (fig. 157, a to d) grow and

abed e f g




FIG. 157. Plasmodium laverni, var. quartana (from Wasielewski, after Labb6), from
the blood of a malarial man. a, newly infected blood corpuscle; b, somewhat
larger germs; c, full-grown parasite with strong pigmentation; d, rounded form
with large nucleus; e, beginning of germ formation; /, rosette of germs around a
residual body; g, germs set free by degeneration of corpuscle.

divide, producing ( daisy-like forms' characterized by little accu-
.mulations of pigment derived from the haemoglobin of the blood.



IV. SPOROZOA: MYXOSPORIDA.