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Vol. IV July, 191 7 No. i

LIFE HISTORY STUDIES ON
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ERNEST CARROLL FAUST

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VOLUME IV

Urbana, Illinois
1918-1919

s-.

Editorial Committee

Stephen Alfred Forbes William Trelease

Henry Baldwin Ward

TABLE OF CONTENTS

VOLUME IV

NUMBERS PAGES

1 Life History Studies on Montana Trematodes. By Ernest Carroll Faust.

With 9 plates and one text figure 1-120

(Distributed March 6, 1918)

2 The Goldfish (Carassius carassius) as a Test Animal in the Study of Toxicity.

By Edwin B. Powers. With graphs and tables 121-194

(Distributed July 28, 1918)

3 Morphology and Biology ot Some Turbellaria from the Mississippi Basin.

By Ruth Higley. With 3 plates 195-288

(Distributed December 31, 1918)

4 North American Pseudophyllidean Cestodes from Fishes. By Arthur Reuben

Cooper. With 13 plates 288-5^2

(Distributed May 31, 1919)

ILLINOIS BIOLOGICAL
MONOGRAPHS

Vol. IV July, 1917 No. I

Editorial Committee

Stephen Alfred Forbes William Trelease

Henry Baldwin Ward

Published under the

Auspices of the Graduate School by

THE University of Illinois

LIFE HISTORY STUDIES ON
MONTANA TREMATODES

WITH 9 PLATES AND
1 TEXT FIGURE

ERNEST CARROLL FAUST

Contributions from the

Zoological Laboratory of the University of Illinois

under the direction of Henry B. Ward, No. 98

111 III liiilllMll|lM

HH 738173

THESIS

SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE

OF DOCTOR OF PHILOSOPHY IN ZOOLOGY IN THE GRADUATE

SCHOOL OF THE UNIVERSITY OF ILLINOIS

1917

TABLE OF CONTENTS

Pages

Introduction 7

Methods of Investigation 7

Biology of the Bitter Root Valley 9

Morphology of Trematodes Foiind 13

Introduction 13

Embryology 14

Parthenitae (Sporocyst and Redia) 18

Cercaria General 23

Integument 27

Parenchyma 29

Musculature 30

Armature 31

Glands 32

Excretory System 36

Digestive System 43

Genital System 44

Nervous System 47

Description of the Trematodes Infecting Mollusks of the Bitter Root Valley 57

Introduction 57

Monostomata 58

Cercaria pellucida Faust 1917 58

Cercaria konadensis Faust 1917 61

olostomata 62

Cercaria flabelliformis Faust 1917 62

Tetracotyle pipientis nov. spec 64

Cercaria ptychocheilus Faust 1917 66

Distomata 68

Xiphidiocercariae 68

Cercaria crenata Faust 1917 68

Cercaria glandulosa Faust 1917 69

Cercaria diaphana Faust 1917 71

Cercaria dendritica Faust 1917 72

Cercaria micropharynx Faust 1917 74

Cercaria racemosa Faust 1917 75

Echinostome Cercariae 76

Cercaria trisolenata Faxist 1917 76

Cercaria biflexa Faust 1917 78

Furcocercariae 80

Cercaria gracillima Faust 1917 80

Cercaria tuberistoma Faust 1917 82

Pathology 84

Problems Presented 86

Interrelation of Trematodes 86

Relation of Trematodes to Other Groups 90

Life Cycle of the Digenetic Trematodes 92

Simamary 94

Species Described in this Paper 95

Bibliography .' 96

Explanation of Plates 1^2

71 LIFE HISTORY OP TREMATODES— FAUST

INTRODUCTION

During a two years' residence at Missoula, Montana, from 1914 to 1916
the writer became acquainted with the biology of the inter-mountain region
of the Bitter Root valley. The heavy trematode infection of the animals
in this locality has led to an investigation of the life history of the trematodes
of the region.

An opportunity is taken at this place to express appreciation to all who
have aided in this study, but especially to Professor Henry B. Ward whose
kindness and sincere interest have made the work possible.

METHODS or INVESTIGATION

This study is confined to the trematodes infecting moUusks. The majority
of the collections were made by Mr. Norbert Sager of Missoula. A sketch
map (text-fig. 1) indicates the location of each collection. The snails were
shipped in damp green moss and arrived in excellent condition.

These observations on living material gave data on the stages of develop-
ment within the mollusk, on the methods of locomotion, on encystment, and
on the excretory system.

The worms were removed from the infected tissue and placed in a watch
glass in 0.3 per cent saline solution. The change from the host tissue to the
sahne medium usually caused rapid movement.

It is essential that the excretory system be studied in the living material
as, aside from the vesicle and the main trunks of this system, very little can
be made out in the preserved material. The delicate structure of the flame
cells and the finer capillaries makes it necessary that these organs be examined
in living specimens, for in fixation they are likely to "collapse, even with the
most careful technic.

The organs of the digestive system come out equally well in living and
preserved mounts. Some systems, as a rule, can be made out only from pre-
served and stained material. The most important of these is the genital com-
plex. For all ordinary purposes the material was fixed in Gilson's reagent,
altho equally good results were obtained from a corrosive-acetic fixing agent.
From the preserved material toto mounts and sections were made, using Dela-
field's hematoxylin and EhrHch's acid hematoxyhn as stains. A strong
counter-stain of eosin in the sections brought out remarkably well the nerve
fibers of the worms. Wax models were made of the mature and immature
stages of the nervous system of cercariae and parthenitae.

Care was taken to keep the mounts acid-free, and for that purpose all
reagents except the destaining fluid were made slightly alkaline with dessicated

ILUNOIS BIOLOGICAL MONOGRAPHS

Text-figure 1. Sketch map of the Bitter Root Valley, Montana, showing
localities where collections were made.

9] UFE HISTORY OF TREMATODES— FAUST 9

potassium acetate. Some specimens were fixed without any acid fraction in
the reagent in order to preserve the excretory granules. These granules, as
well as the mucoid cyst membrane of the encysted worm, gave beautiful
biuret and xanthoproteic reactions, suggesting a tyrosine compound.

BIOLOGY OF THE BITTER ROOT VALLEY

The snails commonly found in the Bitter Root valley are Physa gyrina
Say, Lymnaea proxima Lea., and Planorbis irivolvis Say. They have been
identified by Mr. Bryant Walker of Detroit, Michigan. All of these snails
were collected from the lower part of the valley, but Planorbis trivolvis was
not found in the upper reaches of the river. These mollusks are the hosts
of the trematodes considered in this paper.

Two facts stand out predominantly in the study of these parasites: the
large munber of species of trematodes in the snails in the limited range of the
valley, and the high per cent of infection both among individuals of a species
and within the individual of the species.

There have been found in a single season's collection thirteen trematode
species in the snails of the valley, and one larval trematode in the squaw-fish,
Ptychocheilus oregonensis Richardson. A total of fifteen collections of snails
was made during the fall of 1916 and four collections during May 1917.
Seventeen of these collections contained trematode infection. Lymnaea
proxima was taken eight times from five different localities, Physa gyrina
was taken eleven times from eight different locaHties, and Planorbis trivolvis
was taken three times from two localities (Table I, see next page).

The infection record shows that the host is not specific. In the infection
of mollusks with Cercaria pellucida the host around Buckhouse Bridge was
Physa, while that up the valley was Lymnaea. Cercaria gracillima was found
both in Physa and in Lymnaea in the region of Buckhouse Bridge from
different collections. Cercaria trisolenata was found both in Physa and in
Lymnaea in the region of Buckhouse Bridge and in the vicinity of Fort
Missoula. While no parasite species was found in more than two of the three
snails common in the valley, there is reason to beUeve that the third species
of snail might be the host under proper conditions. This view is contrasted
with that of Thomas (1883:106) who found that only one EngHsh moUusk,
Lymnaea trunculata, "could serve as an intermediate host to the liver fluke,"
altho this writer suggested that other species of snails must serve in other
countries as hosts to the worm. This preference for a particular moUusk in a
particular locality, coupled with the abihty to select a different molluscan host
in another locality, has been found to hold true not only for Fasciola hepatica,
but also for Schistosoma haematobium (Leiper, 1916) and S. mansoni (Leiper,
1916; Lutz, 1916; Iturbe and Gonzalez, 1917). When two hosts so different
structurally as Physa and Planorbis are equally heavily infected, it seems
evident that the stimulus to which the miracidium of the fluke responds can

ILUNOIS BIOLOGICAL MONOGRAPHS

[10

TABLE I
DISTRIBUTION OF CERCARIAE IN THE BITTER ROOT VALLEY

•^

.52

"cS

•c

o
U

d
o

c73

173

^
■^

3
O

■1-1

^^^

■u

a
o

1-1

SPECIES

NUMBER OF COLLECTION

Monostomes

Cercaria pellucida

C. konadensis

Holostomes

C. flabelliformis

C. ptychocheilus

Distomes

C. crenata

C. glandulosa

C. diaphana

C. dendritica

C. micropharynx

C. racemosa

a
c

C. trisolenata

C. biflexa

a
a

c
a

C. gracillima

C. tuberistoma

a, Physa gyriru b, Lymnaea proxima

Compare with map on page 8.

c, Planorbis trivolvis d, Ptychocheilus oregonensis

not be specific. In the case of Cercaria trisolenata, where the infection ranged
from 22 to 100 per cent in Physa and from 50 to 100 per cent in Planorbis,
the host must be considered facultative.

In several instances the same species of snail from the same collection
harbored two or more cercariae (cf. collections nos. 3, 6, 7, 13, 16, 17, 18).
For example (Table I), at the Maclay Sloughs both Cercaria trisolenata and
C. gracillima were found in the same host species, Physa, in fact in the same
individual. This case is paralleled by the record of Cort (1915:55), where
the sporocysts of Cercaria polyadena and C. refiexae were found within the same
liver tissue of Lymnaea reflexa. However, Ssinitzin (1911) in an examination
of several thousand snails of six species, in which he discovered twenty-one
species of cercariae, makes no record of two species in the same host individual.

In the collection of Lymnaea proxima from Buckhouse Bridge three species
of trematodes were found as parasites, Cercaria dendritica, C. racemosa, and

11]

LIFE HISTORY OF TREMATODES— FAUST

C. gracilUma. In such a case as this, one species, C. dendritica, was present
in each host in large numbers, while C. racemosa was less frequent, and the
third species of worm, C. gracillima, constituted a very light infection in only
one of the thirty-two snails examined. Hausmann (1897:16) in referring to
the dominance of one parasite species in the individual host, regards this
phenomenon as a biological antagonism.

Turning to the per cent of infection in the snails collected in the fall of
1916 (Table II), a heavy parasitism is found to exist. The data are especially
significant when compared with the records of other investigators. Cort
(1915) gives detailed data for eleven species of moUusks collected from nine
localities. His collections were made in the fall of 1913. The least per cent
of individuals infected was 1.4, that for Pleurocerca elevatum, secured from
the Sangamon River at Mahomet, Illinois. This mollusk contained Cercaria
megalura. The heaviest infection recorded by Cort was that with C. isocotylea,
where an 18 per cent infection was found in Planorhis trivolvis from Urbana,
Illinois. The average infection from Cort's eleven species records is 8.5 per
cent. Ssinitzin (1911) has recorded data from twenty-one species of cercariae
described by him for the vicinity of the Black Sea at Sebastopol. In many
cases his records show a uniquely low parasitism, practically insignificant from
a pathological point of view. Out of 1159 individuals of Rissoa venusta he

TABLE II
INFECTION RECORD FOR CERCARIAE OF THE BITTER ROOT VALLEY

SPECIES

HOST

EXAMINED

INFECTED

PER CENT

1. Cercaria pellucida

a
b
b
a
a
a
d
b
a
b
b
b
b
b
a
c
a
a
c
a
a
a
a
a
b
a

18
16
16

34
10
12

6
22

5
16
14
29
32
29
12

8
18

2
71
12
18
29
71
32
19

5
5
5
3
3
6
3
2
5
5
3

18
3

12
1
2
4
1
5
1
1
5

33
1
1

5.5

2. Cercaria pellucida

31.3

3. Cercaria konadensis

31.3

4. Cercaria flabelliformis

14.7

5. Cercaria flabelliformis

30.0

6. Cercaria flabelliformis

25.0

7. Cercaria ptychocheilus

100.0

8. Cercaria crenata

13.6

9. Cercaria glandulosa

40.0

10. Cercaria diaphana

31.3

11. Cercaria dendritica

35.7

12. Cercaria dendritica

10.3

13. Cercaria micropharynx...-

56.3

14. Cercaria racemosa

10.3

15. Cercaria trisolenata

100.0

16. Cercaria trisolenata

100.0

17. Cercaria trisolenata

25.0

18. Cercaria trisolenata

22.2

19. Cercaria trisolenata

50.0

20. Cercaria biflexa

7.0

21. Cercaria gracillima

8.3

22. Cercaria gracillima

5.5

23. Cercaria gracillima

17.3

24. Cercaria gracillima

46.5

25. Cercaria gracillima

3.1

26. Cercaria tuberistoma

5.3

a, Physa gyrina b, Lymnaea prorima c, Planorbis trivoIvU d, Ptychocheilm oregoQenBU

12 ILLINOIS BIOLOGICAL MONOGRAPHS [12

found only one was infected with Cercaria cribrata and one with C. metentera,
or, in each case, only a 0.06 per cent infection. The heaviest infection found
by Ssinitzin among these twenty-one species of parasites was that of C. zernowi
in Cardium exiguutn, 7.0 per cent. The average for the twenty-one species is
only 1.34 per cent. In the cases of the worms found in Cerithiolum exile and
Rissoa venusta, the percentage of infection is so low that no parasites would
have been found had not a large number of snails been collected and examined.
The record of Iturbe and Gonzalez (1917) for the cercariae of Schistosoma
mansoni in Venezuela shows a heavy infection.

The infection in moUusks of the Bitter Root valley is decidedly heavy,
altho it varies within wide limits under different factors of place and season.
The lowest percentage of infection found was that with Cercaria gracillima in
Lymnaea proxima at Buckhouse Bridge, 3.1. From a different slough in the
same locaUty one month later a 46.5 per cent infection with this species was
found in Physa. Thus the percentage of infection is found to fluctuate with-
in a very circumscribed area. The least infection of Physa with C. gracillima
was from the Maclay Sloughs farther down the River, 5.5 per cent. On the
other hand, C. trisolenata was found as a hundred per cent infection in both
Physa and Planorbis collected from these same sloughs. Taken as a whole
the infection average during the fall of 1916 for the Bitter Root moUusks is
29.02 per cent. The average by host species is somewhat different, 24.8 per
cent for Lymnaea, 25.16 per cent for Physa, and 75.0 per cent for Planorbis.
Leaving Planorbis out of consideration because of the few specimens collected
there is an average infection of over 24 per cent in Lymnaea and in Physa.
The per cent infection for May 1917 (not included in table II) gives an average
of 11.5 for Lymnaea, 16.6 for Physa, and 50.0 for Planorbis.

131 LIFE HISTORY OF T REM ATODES— FAUST ' 13

MORPHOLOGY OF TREMATODES

INTRODUCTION

The progress in the morphological and histological knowledge of larval
trematodes is wrapped up in the development of discriminate observation
and interpretation on the part of investigators. This has been aided in no
small degree by the use of better technic and by better optical equipment, but
it is for the most part the observer's own expectation that differences must
exist in larvae, and his determination to discover faithfully and accurately
such a differentiation of structure, that has brought about progress in this
line of investigation. No clearer conception of the change in point of view
can be obtained than by a contrast of the statement of La Valette, a worker in
the field six decades ago, with the expression of Charles Sedgwick Minot just
ten years ago. In his S3Tnbolae ad Trematodum Evolutionis Historiam
La Valette (1855:34) recites: "nonnullae Trematodum larvae tam exiguam
offerunt differentiam ut discrimina earum characteristica vix commonstari
queant. " Minot (1897 :928) voices the modern point of view in his declaration
that "it is not true that all embryos are ahke; on the contrary they show class,
ordinal, and generic differences from one another."

While the writer fully agrees with the idea that the most natural way of
correlating larval trematodes with the adult forms is by a knowledge of their
Ufe histories, yet such a correlation is not always possible. Looss (1896)
probably had the cercaria of Schistosoma haematobium among some of the
furcocercariae that came under his observation, yet he was forced to admit
(p. 167) that "tons ces efforts ont ete, quant a la Bilharzia completement
negatifs, " The writer has attacked this part of the problem with the idea
in mind that not only the fundaments of the adult trematode are found in the
mature cercaria, but that even the main descriptive features of the adult
trematode are already present, so that the worker can recognize the adult
in the larva. While it has been impossible to show species correlations between
larva and adult it has been found in the course of the investigation that the
larva shows clearly the family features that hitherto have been inferred only
by the "blunderbuss method" of life-history investigations.

Probably none of the adult trematodes genetically related to the larvae
studied have been described. Moreover, the characters common both to
larva and adult have been overlooked in the study of many adidt species.
The writer has been confronted with the problem as to what characters of the
larva are ephemeral and what ones are common to cercaria and adult trematode.
A thoro analysis of the groups studied, including Monostomata, Holostomata,
and Distomata, gives convincing proof that the most constant systems in larva
and adult are the nervous, genital and excretory systems. Such systems and
organs as tail, cystogenous glands, and stylet are distinctly larval in nature
and may or may not show the same relationship as the natural grouping based
on characters common to both larva and adult.

14 ILLINOIS BIOLOGICAL MONOGRAPHS [14

EMBRYOLOGY

"Larval trematode" has been used for any phase of the life-history from the
fertilized egg to the adult trematode. This is truly a wrong conception in
the hght of the observations of investigators from early times down to the
present. Workers have recognized sporocyst and redia as "nurse" to the
progeny. In other words, they are parthenogenetic individuals. Ssinitzin
(1905, 1910, 1911) has made a wise separation of sporocyst and redia on the
one hand from the cercaria on the other. He groups the mature sporocyst
and redia together under the term parthenita, or parthenogenetic mother.
This term is used thruout this paper to define the mature sporocyst and redia
as distinguished from cercaria or other larval trematode of the hermaphroditic
generation.

The homology between cercaria, sporocyst and redia in their early stages
of development is recognized by Schwarze (1886:64), who compares his studies
on the cercaria's development with those of Schauinsland (1883) on miracidia.
Schwarze notes the similarity of the "cuticula," the sloughing off of the epider-
mis, the location of the solid entoblast, which divides so that a portion comes
to he next to the ectoderm and another part around the gut. He shows that
the homology is very apparent. "Die Keimzellen des Embryos entsprechen
den Genitalzellen der Cercarie, die etwas abgeplatteten Epithelzellen des
Embryo den MeristemzeUen der Cercarie." He observes the similarity of
the excretory system in miracidia, redia and cercaria, and adds "ferner sind
sie ebenfalls mit einem Nervensystem ausgestattet, welches die grosste Aehn-
lichkeit mit demjenigen der Cercarien hat."

Since the miracidium, redia, and cercaria are not, in last analysis, three
parts of one life-history, but more exactly three or more genetically related but
complete Hfe-histories, it would not be too much to expect, then, that the
origin of germ layers in miracidium, redia, and cercaria would be the same.
All three generations arise by the cleavage and development of a single germ
cell of mesodermal origin. In the miracidium the cell is always fertilized;
in the redia and cercaria it is always parthenogenetic. The observations on
the similarity of origin of these cells are extensive, yet mostly isolated, and
deserve re-emphasis.

The exact method of development of individuals within the sporocyst or
redia has been a matter of diversity of opinion. In general one of two views,
budding or parthenogenesis, has been supported by investigators. The
earHer writers who considered the origin of the germ balls described them as
arising endogenously. Thus Moulinie (1856:132) writes: "les Cercaires
naissent, comme nous I'avons vu en parlant des Sporocystes, de gemmes plus
ou moins arrondis qui se forment dans I'interieur de ses derniers lorsqu' ils
atteint leur developpement normal. " Then the question arose whether or not
the germ ball arose from the ordinary tissues lining the body cavity of sporocyst
or redia, or v^^hether special cells were set apart as a germinal epithelium.
Leuckart (1886:113-125) asserts that in all cases germ balls arise only from

151 LIFE HISTORY OF TREMATODES— FAUST 15

those cells which remain unquestionably embryonic. He distinquishes between
the condition in rediae and sporocysts, for in the former he found a specialized
germinal epitheHum, while in the latter all of the cells of the body wall remain
undifferentiated in character, and in consequence are capable of germ cell
production.

Thomas (1883:119) found for the sporocyst-redia generation of Fasciola
hepatica that the germ balls which develop into rediae arise in part from ger-
minal cells already present in the embryo (sporocyst), but that " they gain an in-
crease in their numbers by the proHferation of cells lining the body cavity. "
In the rediae he asserts (p. 125) that the majority of the embryos seem to be
formed from the transformation of cells at the posterior end. Cells from the body
wall become enlarged, and each of these cells undergoes segmentation, giving
rise to a morula. Looss (1892:156, 157) is definitely committed to the view
that any portion of the epitheUum lining the body cavity is capable of produc-
ing germ balls, but, as a matter of fact, only the posterior end (the vegetative
end) performs such service. Later in the same paper (p. 167) he speaks of the
developmental stages as a metamorphosis composed of several generations, in
no sense comparable to parthenogenesis. Haswell (1903:500, 501) describes
for the sporocyst of an echinostome larva the development of embryos from a
single ovarian mass at the posterior end of the body.

Within more recent years the problem of the origin of germ balls has been
centered around the criterion of the formation of polar bodies. Coe (1896:
562) found no polar bodies in the germinal epitheHum of the sporocyst and
redia of Fasciola hepatica. Because Reuss (1903 :470) found three small gran-
ular bodies attached to the germ balls of Distomum dupUcatum sporocysts, he
concluded that maturation occurred. Tennent's work on Bucephalus haimae-
nus (1906:649) supports the argument in favor of the origin of the germ cell
from the walls of the body cavity. After the germ cell passes into the body
cavity a "polar body" is cut off. Later Tennent has found that there are
three cells in the proximity of the germ cell, two of which seem to be the result
of division of the first cell. Rossbach (1906:433) finds no cells which he is
willing to call polar bodies. He concludes 1) that the small cells near the epithe-
lium are not polar bodies because their walls are not found in direct continuity
with the germ cells; 2) that the cells called polar bodies by Reuss are normally
present during development of the germ ball, in miracidia, in sporocysts, in
rediae, and even in the ovary of sexually mature trematodes; 3) that they are
more abundant in the younger sporocysts and rediae, and 4) that they are pre-
sent in larger numbers than three's. Finally Gary (1909), in his study of the
germ cells of an amphistome sporocyst, has found that the germ balls arise
from cells of the body wall which mature without reduction and throw off
one polar body.

The contribution to the problem of the meaning of the proHferation of germ
balls as described in this paper, is based on the development of the germ ceUs
in the rediae of the holostome, Cercaria fldbelliformis Faust 1917. In the

16 ILLINOIS BIOLOGICAL MONOGRAPHS [16

anterior part of the mother rediae large germ balls of both rediae and cercariae
are present. The germinal epithelium is confined to the posterior fourth of
the wall lining the body cavity. In some of the larval rediae within the
mother rediae the earlier stages of the history of the germ cells have been
studied. This has enabled the writer to secure a series of stages of the germ
cells all the way from the probable derivation of the mesoderm tissue from
the base of the gut up thru maturation and segmentation.

At a stage in the development of the redia when the archenteron is repre-
sented by about eight or ten large vesicular cells (Fig. 45), certain cells are
found wandering out from the bUnd end of the gut and spreading thru the
body cavity. Some of these cells come to he against the wall of the cavity
and at first appear as protrusions of the wall; later they seem to constitute a
loosely formed inner layer of the wall. Other cells of this type are found free
in the body cavity. The majority of these cells that have wandered out from
the base of the gut are oval in shape, and have attached to them on one side
a small, nodular protrusion, consisting of the film of cytoplasm around a densely
granular nucleus.

All of these cells, whether attached to the body wall or not, are to be re-
garded as germ cells, based on their present structure and future behavior.
The small nodules are polar bodies. Figure 46 H shows this body in process
of formation. The mitotic figure is in the anaphase stage, and was found in a
germ cell free in the body cavity of a young daughter redia. These data on
the origin of the germ cells from the specialized germinal mass at the blind
end of the gut support the thesis of Leuckart (1886:123) and Schwarze (1886:
48, 49), that the cells have preserved their original embryonic character. The
fact that the production of the polar body and consequent maturation of the
germ cells takes place in cells next to the body cavity as well as in those free in
the body cavity, explains the observations of Thomas (1883:115) that some
of the cells from which the germ balls are derived are "the germinal cells of
the embryo or cells derived from them by division, others are formed by a
proliferation of the epitheHum lining the cavity of the sporocyst," since these
two groups are traceable back to a common origin at the base of the gut.

A description is now given in support of the view that the germ cell is
a true ovum. In its unmodified condition the germ cell is moderately incon-
spicuous, similar in all respects to an undifferentiated parenchyma cell. As it
begins to change, the cell enlarges, the cytoplasm becomes granular, with
many interstitial vacuoles, and the nucleus comes to have a clearly outhned
membrane wall. Frequently the chromatin material is massed into a karyo-
some (Fig. 46 A). The chromatin mass now becomes oblong (B) and after
considerable growth becomes coiled into a thick skein (C). The next stage
(P) shows the division of the skein into eight chromosomes. These chromo-
somes arrange themselves in an equatorial plate, and soon show a longitudinal
sphtting. One of these (b) is precocious in its behaviour. It wanders toward
the edge of the nucleus and divides (6i, 62) while the other seven chromosomes

17] LIFE HISTORY OF TREMATODES— FAUST 17

remain with their halves still in contact. The precocious chromosomes take
up positions toward the poles of the cell (G). The other chromosomes then
divide and migrate to opposite poles {H), one of these daughter groups being
constricted off as a polar body (/). As a result of this process eight chromo-
somes separate by longitudinal splitting, so that half of each goes into the polar
body and half remains in the cell. The polar-body remains in cytoplasmic
connection with the ovum while the latter undergoes another division. As in
the previous division, simple mitosis occurs. The chromosomes ^i, 62 precede
the others in separation into component halves {{Fig. 46 /). In a late anaphase
of this second division (/) the polar body may divide, altho this is not always
the case.

This second division is not a part of the maturation, for that has been
accomplished by the expulsion of the single polar body: hence, it constitutes
the first division of the mature ovum. After this {K) the polar body is entirely
separated from the blastomeres (L) and disintegrates. Thus maturation
consists of a single mitotic division with the extrusion of a polar body, and
takes place without any reduction of chromosomes. In other words, the
process is one of true parthenogenesis.

The somatic chromosome count of the developing germ ball is eight, con-
sisting of seven ordinary chromosomes and the precocious individual. In
support of this statement is the count of each of the first two blastomeres
(JfiT, L), and the chromosome complex in the late metaphase of an endoderm
cell of a morula {M). In the latter the count is double, e.g., sixteen, in view
of the previous spHtting of the chromosomes antecedent to separation into the
daughter chromosome groups. The consistent tendency of the chromosome
b and its descendents to separate from the chromosome mass and to divide
before the other seven split, suggests the possibility that this chromosome is a
heterosome, two of which Lindner (1914) has found in the adults of Schistosoma
haematobium.

In the case of the germ balls that never reach the body wall, the process
of maturation takes place free in the body cavity. For those cells which
lodge against the wall and even fuse with the wall, the process of maturation
and cleavage into two blastomeres takes place while the ovum is still in con-
tact with the body wall. At this time it is set free and allowed to develop into
a germ ball.

In the older mature rediae (Fig. 44) the epithelial layer of the body wall
Hning the body cavity consists of a syncytium in which nuclei are arranged
irregularly. The cell boundaries become distinct only as maturation of the
cells approaches.

Leuckart (1886:124) has stated that it is relatively long after germ ball
formation before it is evident whether the embryo is to develop into a redia or
cercaria. While the chromosomal history in the rediae of Cercariaflabelliformis
shows no difference between cells which develop into daughter rediae or cer-
cariae, the cytoplasmic history of this species is indicative of the generation

18 ILUNOIS BIOLOGICAL MONOGRAPHS [18

of the offspring at an early date. The cytoplasm of the germ cells which
develop into rediae is granular altho quite transparent. It stains a delicate
lavender with Delafield's hematoxylin. On the other hand, from the very
outset the cytoplasm of the cercaria t3^e of cell is fibrillar, with many large
intermediate vacuoles. It stains a deep magenta with the same dye in the
same section as the rediae ova. Figure 46 L represents the first cleavage of the
cercaria embryo. The chromosome count is identical to that in each blastomere
in a redia-forming embryo. Subsequent divisions are difficult to follow on
account of the opacity of the cercaria germ-balls. It is very evident, never-
theless, that differentiation of layers and organs takes place much more rapidly
in the cercaria ovima than in the redia ovum.

The arguments produced by Rossbach (1906:433), to show that there are
no polar bodies given off by the germ cell, do not hold in the case of Cercaria
flabdliformis. The polar bodies have been found not only in cytoplasmic
continuity with the ovum, but in the actual state of mitosis preceding the
separation of the polar nucleus from the germ ball. Polar bodies are indeed
more mmaerous in the young rediae, since this is the period when the majority
of the germ cells free in the body cavity throw off the polar body and mature.
Altho Tennent has found three bodies similar to those designated by authors
as "polar bodies," no authentic proof is recorded of more than one polar
extrusion in the maturing germ cell of a redia or sporocyst.

In summary, it may be said that the study of the germ cells in the rediae
of Cercaria flabelliformis supports the thesis that true parthenogenesis takes
place here; that the germ cells are traceable to a mesodermal cell mass in the
region of the bUnd end of the gut; that a single polar body is extruded; and that
maturation takes place without reduction.

It is not surprising that the details of the germ layers have not been worked
out in the fertilized trematode egg, because of the yolk inclusions which ob-
scure developmental stages and no doubt modify the behavior of the segment-
ing cells. Yet it is regrettable that no attempt at the precise origin of the
germinal layers has been made on germ balls within the sporocyst or redia.
Without any effort at this exact study of the problem the writer has followed
in the Uving rediae of Cercaria pellucida and C. konadensis, and in the sporo-
cysts of C. dendritica the development of the germ balls from the single mature
ova, thru unequal divisions into two, three and five cells, up to the morula
stage.

PARTHENITAE (SPOROCYST AND REDIA)

Since the classic work of Thomas (1883) on the hfe-history of Fasciola
hepatica, it has been the common custom to define the sporocyst and redia
in terms of stages in the Hfe-history of the trematode. The sporocyst is the
metamorphosed miracidiimi, and the redia arises within the sporocyst. The
cercaria is the parthenogenetic offspring of the redia and develops into the
adult trematode. While this represents a so-called typical life-history, it is

191

LIFE HISTORY OF TREMATODES— FAUST

worth while to inquire into the facts and see if the outlined sequence of events
is always followed. In some cases the sporocyst is the mother of the cercaria,
in which case the redia cycle has been omitted. The accompanying table (III)
shows that of the fifteen species treated in this paper eight have cercariae
derived directly from the germ cells of the sporocyst. Of the seven remaining,
five are known to come from rediae, while the parthenitae of the other two
species of larvae are not known.

TABLE m
GERMINAL EPITHELIUM

Monostomata

1. Cercaria pellucida

2. Cercaria konadensis

Holostomata

3. Cercaria flabelliformis....

4. Cercaria ptychocheilus....

5. Tctracotyle pipieniis

Distomata

Xiphidiocercariae

6. Cercaria crenata

7. Cercaria glandulosa

8. Cercaria diaphana

9. Cercaria dendritica

10. Cercaria micropharynx..

11. Cercaria racemosa

Echinostome cercariae

12. Cercaria trisolenata

13. Cercaria biflexa

Furcocercariae

14. Cercaria gracillima

15. Cercaria tuberistoma

PARTHENITA

SPOROCYST REDIA

NON-LOCALIZED

LOCALIZl

X
X

rachis

?
?

Types of development are characteristic of certain groups. The Mono-
stomata, Holostomata, and Amphistomata and usually the echinostome cer-
cariae develop within rediae. The xiphidiocercariae and the furcocercariae
arise from sporocyst tissue. A considerable modification of a typical life-
history, such as is found in Fasciola hepatica, is displayed among various groups
of Digenea. In 1835 von Siebold described a viviparous monostome larva
under the name of Monostomum mutahile, in which the miracidium bursts the
egg-shell while it is still within the uterus. Within this miracidiimi, without
any metamorphosis into a sporocyst, there develops a single redia. Schistosoma
japonicum has two sporocyst stages, of which the former is covered with a
smooth and the latter with a spinous integvunent (Leiper and Atkinson,
1915:202). This worm has no redia stage, for the cercariae develop within
the secondary sporocyst. Cercariae and rediae develop side by side in the
rediae of Cercaria flabelliformis.

The sporocyst is much simpler than the redia. It is merely a sac with
ectoderm covering, and at times a secretory integimaent. Occasionally one
end is partially muscular. From the inner waU of this sac arise the germ balls

20 ILUNOIS BIOLOGICAL MONOGRAPHS [20

that grow into the parthenogenetic individuals. In the simplest types the
germinal cell mass consists of the entire internal layer lying next to the ecto-
derm. Such a type is seen in Cercaria diaphana (Fig. 79), and in C. micro-
pharynx (Fig. 94). In the majority of cases, however, the germinal tissue
is localized at one end of the sporocyst. In two cases at least there is the
differentiation of a muscular attachment organ at the antipodal end (C
dendriiica, Fig. 87; C. racemosa, Fig. 105). In the furcocercariae, C. gracUlima
and C. tuberistoma (Figs. 147, 157), there is a rhizoid-like attachment at the
germinal end. In these cases there seems to be some evidence for regarding
the germinal layer as localized at the end opposite the potential mouth.

The redia is the type of the life cycle normally developing within the
sporocyst. Its organization is much more complex than that of the sporocyst.
There is a well-developed oral aperture, a muscular pharynx, and a sac-like gut.
There is a birth-pore just behind the collar region, on the left side, sUghtly ven-
tral. Two projections, usually in the posterior part of the body, readily differ-
entiate the redia externally from the shapeless sporocyst. With some justifica-
tion Ssinitzin (1911:76) regards these projections as comparable to an originally
bifid tail of the cercaria as in Bucephalus. In the cephahc region aroimd the
pharynx there is a nerve complex of highly differentiated nerve cells and nerve
fibers. These are distinguishable as a central nerve ring, with four anterior
and four posterior tnmks. The posterior trunks do not develop far caudad.
The integimaent is well developed and thick, and muscular layers within it
play an important r61e in the movement of the redia, whereas the sporocyst
depends almost entirely for its movement on the motility of the larvae within
it. In the mature redia the germ tissue is always locah'zed at the posterior
extremity of the body.

The development of the germinal tissue of sporocyst and redia has been
shown to be the result of the maturation of parthenogenetic eggs. The sig-
nificant correspondence between the localized germinal epithelium of the
parthenita and that of the cercaria may be pointed out here. In most cercariae
the male germ cells are aggregated into a definite nimaber of testicular masses,
in most cases, two. In the apharyngeal furcocercariae (the probable larvae
of the Schistosomatidae) the niunber of germ masses is larger. The data
compiled in Table IV, on the better known Schistosomatidae, show that the
nimiber of the testicular follicles varies from four to five in Schistosoma haema-
tobium, the mammaUan parasite (Looss, 1899:658) to about 134 in Bilharziella
polonica, the avian parasite. The origin of these testes is not described in
any case. In all of the adults the sexes are separate. In Cercaria gracUlima
(Fig. 149) the testicular masses are proliferated from a germinal mass at the
posterior extremity of the body, ventral to the excretory bladder. They are
nimierous; some twenty-four or twenty-five masses are foimd in this region at
this stage of maturity. Moreover, the female cell masses are also present in
the species at this lar\'al stage, showing that the animal is not primitively
unisexual, but hermaphroditic. It would be only one step further back in
the phylogeny of the group to assume that the hermaphroditic cell masses and

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23] UPE HISTORY OF TREMATODES— FAUST 23

the germinal epithelium of the parthenitae arose from a common type of germ
cell. In other words, the germ cells of cercariae and parthenitae are homolo-
gous. Stages in the phylogenetic development of the germinal epithelium
may be outlined thus:

1. Germinal epithehum non-localized. Example, Cercaria diaphana
(Fig. 79), C micropharynx (Fig. 94). Sporocyst cycle.

2. Germinal epithelium localized; no mouth or suctorial apparatus. Ex-
ample, C. glandulosa (Fig. 67). Sporocyst cycle.

3. Germinal epithehmn localized; suctorial disc or attachment organ
opposite germinal cell mass. Example, C. dendritica (Fig. 87), C. racemosa
(Fig. 105). Sporcyst cycle.

4. Germinal epithehum localized opposite a true oral aperture, with phar-
ynx and gut present. Example, C flabelliformis (Fig. 43). Redia cycle.

5. Germinal epithelium locaHzed and specialized into two sorts of con-
jugating germ cells, male and female isogametes. (Theoretical.)

6. Male germ cells prohferated in numbers from the mass of germinal
tissue at the posterior end of the body; female germ cells more highly
differentiated. Example, C. gracillima (Fig. 149). Cercaria stage of
hermaphroditic cycle.

7. Germinal cells massed into a small number of speciaHzed glands, called
testes and ovaries. Example, C. pellucida (Fig. 18). Cercaria stage of
hermaphroditic cycle.

CERCARIA (general)

The cercaria is the offspring of the parthenita. It is a highly specialized
individual, homologous to the immature redia or the sporocyst. Its speciaU-
zation has been accounted for by Ssinitzin (1910:38-56) because of 1) a con-
siderable period of free-swimming hfe, during which it acquired a tail, and 2)
a change to parasitism in the vertebrate, which was at first facultative, but
later became obligatory. There are two types of modified characters to be
accounted for in the cercaria, in addition to the original characters common
to parthenita and cercaria. The tail, the well-developed muscle complex,
the nerves innervating the muscle system, together with the sahvary glands
and the sensory papillae — all of these bear evidence of a long period of indepen-
dent life. When the organism became parasitic, first ectoparasitic, later
endoparasitic, the highly developed muscular suckers with their nerve tracts
were further developed, while the stylet organs and cystogenous glands were
differentiated. The muscular specialization was of primary importance within
the host, while the cyst served to protect the worm during the period of transfer
from larval to definitive host.

The cercaria varies in size, altho it is fairly constant for a particular family
or genus. Holostome larvae reach a size of 0.63 mm. in length and 0.35 mm.
in width (C. ptychocheilus). On the other hand some of the xiphidiocercariae
are much more minute, 0. 18 mm. in length by 0.09 mm.in width.{C. micropharynx).

24 ILLINOIS BIOLOGICAL MONOGRAPHS [24

There are two types of movement in the cercaria aside from the apparent
contraction and expansion of the body. One of these is concerned with the
forward movement of the animal and depends on the cooperative action of
the suctorial organs and the general bodily musculature. The other is caused
by the flagellate action of the tail. The movement of the cercaria along a
forward path reminds one of the rythmic action of a measuring worm. The
oral sucker is always used as one organ of attachment, and the ventral or
caudal suctorial disc supplies the other anchorage. With these two organs
of attachment, the larval worm applies the oral disc to the object of contact,
while it draws the posterior portion of the body forward by the contraction
of all the longitudinal muscles. This places the posterior attachment advan-
tageously near the oral disc, so that a relaxing of the longitudinal muscles
and a synchronous contraction of the transverse muscles throws the cephalic
portion of the worm far forward. In the forms with well developed muscula-
ture, such as monostome and echinostome species, the larva may appear
discoid on contraction, while the expanded worm wiU assume a length several
times that of the normal body.

All groups of cercariae possess an oral suctorial organ. For the second
attachment organ there is a variety of accommodation. Undoubtedly the
most advantageously formed organ of this second typo, is the one found in the
Amphistomata, where there is a powerful suctorial disc at the posterior end of
the body.

Among the distomes there are many types of posterior suctorial organ,
ranging from those with a prominent acetabulum not far from the caudal
extremity, as in Stomylotrema pictum (Crep.) (Looss 1899:629), to those with
a poorly developed acetabulum more cephalic in position. In the latter case
there are frequently found auxiliary locomotor organs, such as those in the
posterior pockets of the xiphidiocercariae. In some species there is only
a suggestion of a paired suctorial organ, as in the larvae, Cercaria crenata (Fig.
55), and C diaphana (Fig. 76). In others there is the additional spinose
complement (C. glandulosa, C. dendritica, and C. micropharynx). These spines
are of important fimction on rough surfaces where the disc can take hold
with difficulty. Altho there is considerable difference in the rapidity of
movement of the various species studied, C. glandulosa was by far the most
rapid in movement of all the cercariae observed. The spinous outgrowth of
the acetabulum is of advantage in locomotion, catching hold where the un-
armed sucker can not operate (C glandulosa, Fig. 60 ; and C. gracillima, Fig. 142).

Muscular development in the holostome larva is confined entirely to the
suctorial apparatus, since there is no distinct tail portion. This type of sucker
is derived from the distome type. With the translocation of the genital opening
to the posterior end of the body, the primitive genital pore has come to be used
as an accessory suctorial organ (Cercaria ptychocheilus, Fig. 47). The most
unique modification is found in the tetracotyle type. Here there have arisen
two lateral accessory suctorial grooves (Fig. 41), and lappet modifications of

251 LIFE HISTORY OF TREMATODES— FAUST 25

the acetabulum. All of these come to be enclosed in a common pocket which
acts as a large sucking cup (Fig. 40). There is practically no locomotion in
these species, since movement is confined almost exclusively to the sucking
reflex.

In the monostome no acetabulum is present, yet the cercaria performs
the processes of locomotion par excellence. The pair of posterior locomotor
organs replaces the acetabulum in the measuring worm movement. In Cer-
caria pellucida and C. konadensis, as well as in C. urbanensis Cort, these organs
consist of posterior inpocketings of the integument. In C. imbricata, Looss
(1896, Fig. 151) there is an internal pocket. In C ephemera Nitzsch (Ssinitzin,
1905, Fig. 75, 76) there are hook-shaped spines. Cort (1915:15) finds that
they " apparently have no suctorial function, since no muscles are present and
the central cavity contracts while the projection is extended." A careful
study of living and preserved specimens of C. pellucida, C. konadensis, and
C. urbanensis shows that these three American species have no spinose or
other integumentary modifications. However, their function is found to be
distinctly suctorial, and not "analogous to setae," as Cort believes. Typical
drawings for the locomotor organs of any of these three species are shown
(Figs. 16, 17). As will be seen in figure 16, there are four muscles which are
attached to the pockets. By a contraction of the pair xx the pocket disc
is applied to the surface of the contact body; by a relaxation of xx and a con-
traction of yy the pocket is released and pulled forward by the general bodily
contraction. This has been observed repeatedly in so convincing a manner
that it leaves no doubt as to the structure or function of the organ. In addition,
in C. konadensis (Fig. 21) a group of glands just anterior to the locomotor
pockets pour out a mucous secretion at the time when the disc is applied
to the contact organ. The locomotor pockets perform a similar function
and in a similar manner to that of the secondary suctorial disc or acetabulum
of amphistome or distome, altho these organs are in no sense homologous.
The significance of the spines in connection with the caudal locomotor
pockets of distomes has been regarded by Leuckart (1886:128) as deserving
special consideration. In Cercaria armata he considers them as serviceable
in keeping the tail attached to the body after the constriction between the
two parts has become deep. Looking into the phylogenetic significance of
the spines of the same cercaria species, Ssinitzin (1911:68) regards them as
indicating a bifid ancestral appendage of a caudal nature. In view of the
fact that these pockets actually function similarly to the locomotor pockets
of the monostomes, and are more than likely the ancestors of the monostome
type of pocket (Fig. 12), it seems hardly worth while to find a more obscure
meaning in the structures.

The tail is the portion of the cercaria showing preeminently the adaptation
of the organism to free-swimming life. In such forms as C. setifera (Monticelli,
1914), C. pennata and C. plumosa (Ssinitzin, 1911, Figs. 76-79), the prolonged
free-swimming existence has given rise to setae, spines and scutes.

26 ILLINOIS BIOLOGICAL MONOGRAPHS [26

The tail arises as a median posterior protuberance, bilaterally symmetrical,
and is, according to the views of Ssinitzin, phylogenetically a paired organ.
This thesis is supported, in part at least, by the fact that the excretory trunks
arise as paired organs in both the body and the tail. In the furcocercariae
the caudal tubules remain separate in the rami of the tail and also in the
"eyelet anastomosis" at the junction of the body and the tail. There devel-
ops in the tail the usual complement of muscles, a transverse layer externally
and a longitudinal group more median. Within the cylinder of muscles is the
group of parenchyma cells surrounding the excretory tubule.

In the tails of distome cercariae (Figs. 99, 133) the excretory vessel is a
paired structure, separated in the middle by a parenchymatous partition with
one or two nuclei in each section of 7 /z thickness. Some schistosomatid larvae
have, in addition, eleven or twelve pairs of oblong cells just lateral to the
excretory vessel. The tail of the monostome is characterized by extra large
longitudinal muscles with prominent nuclei. The portion within the longi-
tudinal muscle cyHnder differs in structure in individual species. In C. pellu-
cida there is one ring of very large parenchyma cells situated around' the
excretory vessel. There are eight to ten cells to each transverse plane of 7/i.
In C. konadensis and C. urhanensis there are glandular cells within the paren-
chyma ring; they are large and crowded with granules. In both of these species
(Figs. 25, 32) these cells are arranged in six paired groups. In C. konadensis
there are many cells to each member of the group, arranged in pyramidal
fashion with the apex directed distally. Thus the largest cells in each group
(Fig. 27) are proximal. These cells He next to the excretory vessel. Cort
has described the cells of C. urhanensis thus: "extending the length of the
tail and forming a core are two rows of long cells which are close together and
have their long axes parallel with the length of the tail. . . , They are full
of heavy staining granules. . . There is nothing suggestive of the possible
function of these cells. " He has failed to observe the exact number of these
cells (six pairs) and is in error in considering them as a core extending the
whole length of the tail, for they alternate with non-glandular tissue in about
half of the extent of the organ. Their structure is probably glandular. In
C. urhanensis these cells arise from undififerentiated parenchyma cells (Fig. 2>2>).
They soon appear as falciform cells in trans-section (Fig. 34), separated in
a median sagittal plane by a partition arising between two intermediate
parenchyma cells, which soon differentiate into a muscular lamina. The
lamina arises before the excretory tubules differentiate as distinct lumina
among the parenchyma cells. Thus the bilateral symmetry along the median
sagittal plane is well show^n. The excretory vessel is single in the mature
C. pellucida and C. konadensis, but remains paired in C. urhanensis.

Looss (1893:24-28) cites the epithelial cells of the tail of cercariae as good
examples of " Blasenzellen, " where all cell elements of the mesenchyme usually
become " Blasenzellen ", and where no true glands take their place. The study
of C. konadensis, C. urhanensis, and C. gracillima, shows that axial cell glands
are present, and that they are derived from the parenchyma, Moreover

27] LIFE HISTORY OF TREMATODES— FAUST 27

where these special gland cells are not present, as in C. pellucida, the
parenchyma cells are more vesicular than where they are present. The writer
is in accord with Looss's view that there are no indifferent cells remaining
in the tail. Hence the tail, when separated from the body, can not meta-
morphose into a sporocyst or redia, as the older writers believed (Pagenstecher,
1857:15).

INTEGUMENT

The covering of trematodes and cestodes has been the subject of con-
siderable controversy. Four main theories have been proposed. The Bloch-
mann theory (1896) assumes that the cuticula of trematodes and cestodes is
a true morphological cuticula secreted by the hypodermis, as in other inver-
tebrates. A second theory, presented by Brandes (1892), postulates that
trematodes have no subcuticula in the true sense of the term, and what has
been considered as such is nothing more than the true parenchymatous con-
nective tissue. Nevertheless, the body covering is a true cuticula, secreted
by special glandular cells of epidermal origin just beneath the cuticula. The
presence of apparent nuclei in the cuticula has revived the old idea of Wagener
that the cuticula is a metamorphosed epithelium. Goto has subscribed to
this theory in his study of ectoparasitic trematodes (1894:6-13), defining
three layers, an outer cuticula, a subcuticula, and a basement membrane.
This is also the interpretation Monticelli has put on the body investment of
Cotylogaster michaelis (1892:189), which he claims to possess an "ectoderma
sinciziale di aspetto cuticuloide. " More recently Gary (1909:646) has ad-
vocated this view. Pratt (1909:721) is incHned toward Leuckart's theory
that the cuticula is of parenchymatous origin, a derivative of the peripheral
portion of the parenchyma.

The species of larval trematodes studied by the writer are uniform in
showing that the epidermal layer, developing into a syncytium in many cases,
is present in the early stages of the sporocyst, redia, and cercaria. In the
parthenitae, especially in the redia, this layer may persist until the germ
balls within are ripe and ready to escape. In the cercaria the epidermal
tissue is present in early life as a syncytial layer investing the larva. In the
mature cercaria it is sloughed off. The "cuticula," when present, arises
from below the epidermis. It is a discrete layer underneath the epidermis,
or it impregnates the epidermis from below. In the latter case the nuclei are
always superficial, usually rising above the surface as small tuberosities.

In the monostome group, the redia possesses a syncytium of ectodermal
cells impregnated here and there with granules of a secretory nature. The
cercaria develops a well-defined epidermis which later (Fig. 37) becomes
syncytial and is sloughed off. Underneath this the "cuticula" is distinctly
cut off from the epidermis on the outside and from the mesodermal tissue
beneath. Among the latter are the special parenchyma cells with aciculate
pseudopodia, corresponding to Blochmann's "Epithelzellen" (1896:7). These
differentiated parenchyma cells have no connection with the "cuticula" in

28 ILLINOIS BIOLOGICAL MONOGRAPHS [28

the developing or mature cercaria of this group. A non-nucleated epidermis
is shown in the process of sloughing off for the hemistome cercaria (C
ptychocheiliis, Fig. 54) . Underneath is a distinct layer of ' ' cuticula. ' ' B eneath
the "cuticula " is a lining of transverse and longitudinal muscle fibers. Median
to the complexes of the longitudinal muscles are the complexes of the con-
nective tissue. The whole structure, from the inner wall of the "cuticula"
thru to the free parenchyma, is infiltrated and bound together into a single
mass by a mucoid secretion. This secretion is indifferent to stains. The epi-
theHal cells of the complex send out long processes toward the integument, so
that the processes penetrate into the latter. These cells suggest gland cells,
concerned with the secretion of the "cuticula." They are not potentially
different from the underl>'ing parenchyma.

Among the distome larvae the writer has studied the "cuticula" problem
for echinostomes, schistosomes, and xiphidiocercariae. The redia of C. trisole-
nata possesses an ectodermal reticulum in which are foimd large vesicular
nuclei. This covering is impregnated with large granules which are indifferent
to stains. In the cercaria of this form (Figs. 128-133), there is an ectodermal
layer present, very thin, with the nuclei arising from the surface as minute
tuberosities. Beneath this is the thick layer of "cuticula." The epidermis
has been lost in the tail. No "Epithekellen" are visible in the mesenchyme
complex. For the schistosome larva, C. gracillima, there are definite nuclei
present as minute papillations rising above the surface of the epidermal layer.
The sporocyst of this form has no "cuticula." The body wall consists of
a single layer of ectoderm cells, arranged end to end, the nuclei of which are
oval to subspherical. In the distome, C. glanduLosa, the sporocyst wall is
composed of a single layer of epidermal cells, with falciform nuclei. In the
cercaria the epidermis is present only in individuals where the taU is still
attached. Here nuclei are present in the peripheral layer of the body, but
are not foimd in the covering of the tail. The "cuticula" is a thin envelope
around the circular layer of muscles.

The study of these trematodes with reference to the problem of the integu-
ment has led the writer to set aside the view that the "cuticula" is ectodermal
in origin, because the ectoderm is superficial, lying outside the "cuticula."
The impregnation of this layer with cuticular granules might lead one to be-
lieve that the two layers are one, but the earlier history of the layers shows
that this conception is erroneous. No hypodermis is f oimd in any of the species
studied. Consequently the Blochmann theory can not hold for these species.
No special gland cells have been foimd to support in its entirety the theor}' of
Brandes. On the other hand the evidence of this study points to the sus-
taining of Leuckart's theory of the parenchymatous origin of the basement
membrane on the following grounds. 1) In all the species the basement mem-
brane arises from tissue beneath the ectodermal layer. 2) In all cases where
there is an ectodermal layer only (in sporocysts), no basement membrane is
found. 3) The heaviest layer is foimd in species where the parenchj-ma has
a widely diversified potency, such as salivary, cystogenous, locomotor and

291 LIFE HISTOR Y OF TREMA TODES—FA UST 29

mucin glands, 4) The "Epithelzellen" of the monostomes and holostomes
(Figs. 37, 54) are characterized by large vesicular nuclei and vacuolated cyto-
plasm, similar to the "Blasenzellen" of Schwarze (1886) and Looss (1893).
They are modified parenchyma cells differing from the underlying layers not
in potency but in location. 5) As the secretory cells for the basement mem-
brane, these parenchyma cells have developed long acicular pseudopodia
toward the membrane and, in the larval holostomes, have penetrated into it.
All of these data point toward the parenchymatous origin of the basement
membrane.

PARENCHYMA

Soon after the fundaments of the digestive and nervous systems of the
cercaria are laid down, certain cells of mesodermal origin of the germ ball
become ovoid and are filled with milky white granules. These are cystogenous
cells, the "Stabenkornchen" of the German writers and the "cellules a
bS,tonnets" of the French. They develop most conmionly in monostomes,
amphistomes, and such distomes as form a heavy cyst.

Other portions of the mesoderm are differentiated as the germinal epithe-
lium and the muscle layers. The remainder of the mesodermal cells is for a
considerable time potentially great, and remains undifferentiated (Looss,
1893:29). They constitute the parenchyma. Looss has compared these
cells of the mesoderm to the cambium of the plant. They are the "nicht-
veranderten Zellen," on the multiplication of which depends the growth of
the minute larva to the relatively large adult. As the animal grows the cells
of this region become more vesicular, vacuoles appear within the cytoplasm,
and acidophilous granules appear within the cell. The intercellular spaces
become more and more prominent. The cells are held together by bands of
ragged connective tissue which, for the most part, is the outgrowth of the
interstitial cells. Within this parenchyma complex there appear large tubular
lumina in certain definite regions, and, leading into these, tubes and smaller
tubules. These are the excretory tubes; at the ultimate ends of these are
found the capillaries and the flame cells (Looss, 1892:162; Thomas, 1883:116-
118). In the schistosome cercariae studied the main group of cilia is not at the
extreme ends of the ducts, but in a pocket in the posterolateral part of the
main trunks (Figs. 143, 145). It is of importance to emphasize here that
these excretory trunks and tubes are not lined by a wall of specialized cells,
but are merely lumina among certain cells of the parenchyma. It seems
highly probable that Looss 's view is correct as regards the flame or "Trichter, "
that it, too, is an intercellular lumen, into which the parenchyma-cell cilia
protrude, and that it is not in a hoUowed-out cell. The cilia are definitely
outgrowths of the single cell at the head of the capillary (Fig. 138), a cell
which is differentiated from the sister cells of the parenchyma by the possession
of a much smaller nucleus and densely granular protoplasm.

30 ILUNOIS BIOLOGICAL MONOGRAPHS [30

MUSCULATURE

The muscle systems of the parthenitae and the cercariae are confined,
for the most part, to the peripheral and splanchnic regions. The peripheral
muscles consist of an outer series of radial muscle fibers and an inner series
of longitudinal fibers. A third series, the dorsoventral, which is common
in the adult forms, is suggested at times in the body of the cercaria. The
muscles of the intestinal tract consist of a longitudinal and a circular series.

The peripheral system Ues directly beneath the basement membrane. It
opens interstitially to permit the growth of the processes of the parenchyma
cells which secrete the basement membrane. The outermost layer is the cir-
cular series. It may consist of a single band one cell in thickness or it may in-
clude a cylindrical band several layers thick (Figs. 37, 54, 97, 128). Within this
is the longitudinal series. Usually here the individual fibers of the bundles
are separated from one another by a considerable interval. The fibers are
longer and fewer than those of the circular series. A section of an adult trema-
tode shows, in addition to these, an obUque series of fibers. These obHque fibers
give the appearance in section of a diamond pattern. In another type, the
dorsoventral, the fibers run at right angles to the frontal plane. In the holo-
stome cercaria (Fig. 54) no such series is found, altho the longitudinal series
is so arranged that the fibers are on edge and might be taken for the dorso-
ventral series. The view of Bettendorf (1897:315,316) that the "Epithelzellen"
of Blochmann are really longitudinal muscles, can not be considered vaUd,
since in the same sections the former are indifferent to stains and the latter
are deeply stained by the same methods of technic.

In the oral and acetabular suckers and frequently in the phar>-nx there
exist the transverse, longitudinal and obUque series of muscle fibers, inter-
woven into an inseparable complex. These are best developed in the Am-
phistomata. Since the redia which produces germ balls is an adult and the cer-
caria is an inunature individual, it is not surprising that the pharynx of the
redia is fibrous, with few nuclei and large vacuoles, while the pharjiix and
suckers of the cercaria are composed of cells practically undifferentiated. In
the rediae the fibers can be traced to the myoblasts.

The main deep-seated system of muscles for the cercaria consists of the
muscle band series of the digestive tract. In the holostome (Fig. 54) an
additional muscular activity has been assxmied by the cirrus pouch. Aside
from these no muscle striae are developed in connection with the genitalia in
the larva. The ceca of the digestive tract are covered with an outer and an
inner series. The former are longitudinal fibers and the latter are circular
fibers. This is in conformity with the muscular layer studies made on
other Platyhelminthes.

Histology of the muscle cells. When Bettendorf (1897) showed the
connection between the muscle fibers and the myoblasts an important step
was made in the knowledge of the intimate structure of the trematode muscle
cell. The present study corroborates Bettendorf 's work. The nuclei of

31] LIFE HISTORY OF TREMATODES— FAUST 31

the myoblasts are oval (Figs. 118, 119). The cells very early send out
long protoplasmic strands along well defined paths. While the processes
from the myoblasts may emerge from any part of the cell, the longitudinal
strands are always directed in a longitudinal plane, and the circular fibers
are always circular. A unique picture is presented at the point where the
furcae of the digestive tract arise (Fig. 118). Here there are two anterior
processes running cephalad, and three strands proceeding caudad along each
cecum. The chromatin in the nucleus of the myoblast is usually confined
to the karyosome.

^ ARMATURE OF THE TREMATODE

The miracidiimi and sporocysts are not ordinarily provided with hooks
or any piercing armature. The redia is usually conspicuous because of its oral
sucker, pharynx and gut, and not because of any armature. In the cercaria,
however, are found, even in some of the most delicate species, spines covering
the basement membrane, especially in the region of the head. In the special
group of the stylet cercariae the stylet is the larval organ which is of specific
systematic value.

It is not a universal rule, however, that all rediae and sporocysts are un-
armed. At times a modification of the posterior wall of the redia is produced
as in the redia of C. biflexa, where the terminal organ is spinose (Fig. 141).
Leiper and Atkinson (1915:202) found the second sporocyst generation of
Schistosoma japonicum to be covered with a spinous integument. More
conspicuous is the prepharynx organ of the redia of Cercaria pellucida (Fig. 7).
This organ is four-lobed, and has on the outer side of each lobe long spines
projecting forward and small spines directed laterad. The use of such a
weapon within the soft parts of the host tissue produces untold injury.

No armature has been observed on the body of any monostome cercaria.
The holostome, Tetracotyle pipientis (Fig. 47), has a spinose covering over the
entire body and special spines in the region of the acetabulum and accessory
suctorial grooves. Spinose modifications are common in the distome group,
and in some cercariae, setiferous modifications of the tail. The types which
the writer has examined have the armature confined to the body. They will
be discussed under the headings of 1) general body spines, 2) spines of the
oral aperture, 3) collar spines of the echinostomes, and 4) the stylet organ
of the xiphidiocercariae. In addition there are the spines at the posterior
end of the trunk in the caudal pockets. Their probable locomotor function
has made it necessary to consider them in another place.

In many cercariae there is a tendency for the entire bodily integiunent
to become modified so that the surface bristles with needle-like spines. These
are usually arranged in a regular diamond pattern, and are more fully devel- .
oped at the anterior end of the body than in the caudal portion (Figure 90).
This condition is found in some xiphidiocercariae and some echinostomes.
The spines are always pointed forward. They are more fully developed in
the anterior region of the body.

32 ILLINOIS BIOLOGICAL MONOGRAPHS [32

Of a somewhat more limited distribution is the oral armature of spines
in the schistosomatid C. gracillima (Fig. 142) . These spines are turned into the
body with the inpocketing of the oral sucker-pouch, so that the animal in the
condition of contraction appears perfectly aspinose except for the armature
of the acetabulum. But with its protrusion the oral sucker is crowned with
a sohd cap of spines.

The hood of spines of the echinostome group is specialized and valuable
in systematic work. It is usually an incomplete ring, consisting of a circlet
of spines around the dorsal side, extending ventrad into the middle half of
the body. Dietz (1910) has sketched 63 figures of spine characters and
numbers in his monograph on the Echinostomidae of birds. The adult echi-
nostomes of North America have received little attention and in consequence
of the difficulty in working out the exact spine number in the larva a descrip-
tion of the specific spine characters of the cercariae will not be worth while
until more attention is given to the adults of the family.

The stylet is the unique larval organ in the group of the xiphidiocercariae.
It might be more properly called a quill than a stylet, for its value as an organ
of piercing is questionable on account of its frailty and frequently disadvanta-
geous leverage. It is a mucoid structure, situated in the dorsal wall of the oral
pocket, well supplied with muscles to work it in any direction anteriad and
laterad. It is fully formed only in the mature cercaria, and is carried into
the cyst (Figs. 84, 85). Quite generally the stylet is recognized as of specific
systematic value, and is therefore figured in systematic descriptions (Liihe,
1909:189-200), but the stylets as they are figured are so generalized as to be
of little value in the identification of species. The stylet is of specific value,
but this value lies in the details of the organ rather than in the general out-
line. (See Figs. 57, 61, 77, 83, 91, 102).

The stylet is usually a weak organ mechanically and poorly levered.
However, it is resistent to chemicals and indifferent to dyes. The stylet of
Cercaria glandulosa is extremely delicate, so that it goes to pieces immediately
when a cover glass is pressed down on a water-mount of the worm. The
stylet, as a rule, is hard to observe in preserved mounts.

GLANDS OF THE LARVAL TREMATODE

Glandular organs in the trematode may be distinguished as dermal, salivary,
mucin, cystogenous, genital, and locomotor. The dermal glands are those
imbedded in the subdermal tissues, are unicellular, usually flask-shaped, and
have a small duct opening to the exterior. The saUvary glands include all of
the unicellular glands which open into the digestive tube. Mucin glands are
paired, right and left groups of one to several gland cells emptying into the
oral pocket thru long attenuate ducts. Since mucin is a constituent of salivary
glands, these glands are modified salivary glands. Cystogenous glands are
imbedded in the parenchyma and are usually filled with rhabditiform granules
which superficially resemble the dermal rhabdites of the Turbellaria but are

33] LIFE HISTORY OF TREMATODES— FAUST 33

not to be confused with them. The cystogenous glands function in the for-
mation of the larval cyst at the time when the transfer to the secondary or
definitive host is to be made. Genital glands, in the sense employed here,
include only the auxiUary gland elements of the genital system and do not
refer to the sex glands themselves. Locomotor glands arise in connection
with the locomotor organs in the posterior part of the body.

The dermal glands are of adult significance. Looss (1894:125) has found
them in all groups of adult trematodes studied, but he does not later (1896:
219, Fig. 176, glcu) record them for any cercariae except C. vivax Sons.
No dermal glands have been found by the writer in the course of the present
study.

Salivary glands are probably present in all groups of cercariae and in
some rediae. In the simplest form they are nothing more than pyriform cells
in the region of the digestive tube. Thus the monostome cercaria, C. imbricata,
described by Looss (1896:195) as having a pharynx without a bulb, has unicell-
ular glands massed around the tube in the pharynx region. The f urcocercariae,
with no true pharynx, have a similar group of cells in the pharynx region,
so closely massed together as to lead Looss to considering them a true phar)mx
(1896:220, Fig. 176, ph). In structure these masses of glands in the f urco-
cercariae look superficially like a pharynx (Fig. 142), but on cross-
section the cells of the complex are found to be unmistakably glandular
(Fig. 152).

A modification of the type of sahvary gland just described has been ob-
served in Cercaria micropharynx, C. diaphana, and C. glandtdosa. In these
species the cercariae show not only the muscular pharynx, but also a large
group of gland cells around the digestive tract. In C micropharynx (Fig. 93)
the glands are prepharyngeal, grouped in a spherical mass around the oral
chamber. They are minute cells, about 3/x in trans-section. The glands of
C diaphana (Fig. 76) exhibit a maximum glandular growth in the vicinity
of the pharynx proper. Several hundred gland cells about 3/i in diameter
surround the pharynx. A case of secretion along the entire digestive tract
is found in C. glandulosa (Fig. 60). In this species the glands are much larger
than in the two preceding species, about 6/i in cross section and 12/i to 25)u in
length. They are formed along the entire course of the lumen, from the ori-
fice to the blind end of the ceca, altho they are best developed in the region of
the pharynx.

A distinctly different type of gland is that termed the "stylet gland."
It is so-named because of its frequent occurrence coincidently with the stylet
organ of the xiphidiocercariae. But since it occmrs, too, in furcocercariae
and in echinostome cercariae, where there is no trace of a stylet, the evidence
supports the view that this type of gland is more generalized and more primi-
tive than the stylet organ.

These glands are found in the cercariae of the distome groups examined
by the writer, and in the redia of the holostome, C. flabelliformis. They are
bilaterally symmetrical, lying outside the intestinal furcae, behind the region

34 ILLINOIS BIOLOGICAL MONOGRAPHS [U

of the pharynx. They open thru long-necked ducts into the oral pocket. The
glands are in masses; they vary in the number of cells from four in each lateral
mass of some furcocercariae (Fig. 144), to eight or ten in the stylet cercariae,
while in the echinostomes they run as high as 1 10 on each side of the esophagus
(Fig. 134). In general the cells are characterized by a densely staining gran-
ular protoplasm and a highly refractive nucleus, which remains hyaline when
treated with hematoxyhn dyes. Most interesting is the type presented in
Cercaria crenata (Fig. 55), where there is a differentiation of inner and outer
groups of the glands on each side of the gut. These groups have individual
canals to their exit at the oral pocket. The outer series consists of six glands,
comparatively small, Sfx to 9/i in diameter, goblet-shaped, extending caudad
to the midacetabular region. They are finely granular and are best studied
in living mounts. The inner series consists of five cells, two of which are
situated just behind the pharynx and the other three postacetabular, thus
causing the inner series to be divided into an anterior and a posterior group.
These inner gland cells are llju to 15ju in diameter, and coarsely granular.
Their difference in structure suggests a functional difference.

The mucin glands of the redia of C. flabelliformis are paired structures,
lateral and dorsal to the digestive pouch, consisting of a single series of six
cells which open thru a common tube into the pharynx region of the redia.
The cells are similar in structure to the mucin cells of the cercariae of other
groups, altho no such glands have been recorded from the cercariae of the
holostome group. Only one other case has been reported for the redia, that
for the parthenita of Cercaria equitator by Ssinitzin (1911:52, Fig. 50). In
this redia the gland cells consist of a single cell with a wide duct to the pharynx
region. A similar pair of unicellular salivary glands is figured by Looss for
the miracidium of Schistosoma haematobium (1896, Fig. 113, glcph) and by
Miyairi and Suzuki for the miracidium of S. japonicum (1914, Taf, 2, Figs.
1, 2). This occurrence of the mucin glands in the miracidium, redia, and cercaria
of various groups, and the fact that they pass into the intermediate host along
with the larva (La Rue, 1917), show that these organs are of fundamental
importance in the economy of the worm.

That these glands are of more specific character than the ordinary salivary
and epidermal cells of the trematodes is demonstrated by their differential
staining reaction. The usual hematoxylin dyes show a great nimiber of
granular protein inclusions. Recently La Rue (1917) has shown that these
glands in Cercaria marcianae have "mucus" in their ducts, because of, the
staining reaction with toluidin blue and thionin. However, since the glycopro-
tein of salivary digestion is mucin (Mathews, 1915:323), it is more exact to
designate these structures as mucin glands.

A t3^e of gland undoubtedly common to all cercariae is the cystogenous
gland. It is a unicellular organ in the parenchyma just beneath the integument.
In some groups this cell may be small and in the midst of parenchyma
cells (C glandulosa, Fig. 62). In other groups the cystogenous cell is very
large and conspicuous as in the species C pellucid a (Fig. 14), C dendritica

35] LIFE HISTOR Y OF TREMA TODES—FA UST 35

(Fig. 85), and C. trisolenata (Fig. 132). The material within the cyst cell is
usually milky, semi-opaque, either homogeneous or granular. In most cases
the contents consist mainly of the rhabditiform granules, which are indif-
ferent to dyes. These granules are not attacked by weak acids or alkalies,
but are digested by strong acids or bases. It seems probable that they are
of a derived protein nature.

The formation of the cyst varies in the types studied. In the majority
of the species the cyst is a firm envelope with a free space around the embryo,
more or less filled with a watery fluid (Figs. 41, 84, 118). On the other hand,
some of the cysts are more mucoid in structure, with a granular viscous inner
portion and an outer jell (Fig. 11),

The method of encystment differs in different species. In the monostome
where the encystment is rapid and an entire lot of mature cercariae encysts
in two or three minutes after they are freed from the redia, the process is so
rapid that the tail is not entirely cut off until the major portion of the cyst
as formed (Figs. 9-11). Where the time of encystment is considerably longer,
OS in C. trisolenata and C. dendritica, the tail is discarded long before the process
of encystment actually begins. Encystment is an adaptation on the part
of the larva to the change in environment. In two cases studied it takes place
within the liver of the primary host (C. micropharynx and C. biflexa). It is
highly probable that in these forms encystment was the result of temperature
stimuli, since the worms were secured in November when the winter had
already set in. It is apparently an adaptation for "wintering over."

In only one group, the furcocercariae, has there been no record of encyst-
ment of the cercaria. Here the tail is dropped only under the pressure of the
cover slip or when the worm begins to disintegrate. La Valette (1855:34)
expresses this condition for his forms when he writes of the larvae: "Cercariae
cystibus non indutae in animalium vertebratorum intestinis pereunt."

The phenomenon of encystment is one which has been observed by many
investigators. It has been seen and described very accurately by La Valette,
Moulinie (1856), Pagenstecher (1857), and a long line of later investigators.
Moulinie refers to the studies of earlier workers on encystment, mentioning
von Siebold (1835) and Steenstrup (1842). But the credit for the first record
of encystment undoubtedly belongs to Nitzsch (1807). Later (1816) this
writer records his observations on the encystment of Cercaria ephemera.
The review of Nitzsch in Isis describes the process of decaudation and en-
cystment as observed by Nitzsch, and shows that this worker expected the
cyst to develop the following year. Fantham 's criticism of Nitzsch is essen-
tially unjust (1916:12), since Nitzsch considered the cyst to be dormant ands set
dead.

The process of encystment has been described in detail by Thomas in
his work on Fasciola hepatica (1883:129). Encystment here conforms to the
rapid type described for the monostome C. pellucida. "The tail is sometimes
shaken off before encystment begins, but, as a rule, the tail remains in con-
nection with the body during the process, and continues to be energetically

36 ILLINOIS BIOLOGICAL MONOGRAPHS [36

lashed from side to side, until finally a more vigorous movement detaches
it. The whole process is very rapid, and in a few minutes a layer of consid-
erable thickness is formed, whilst its substance begins to harden. "

EXCRETORY SYSTEM

The excretory system is the most dehcate of the four important systems
o the trematode. It can be worked out with precision in the Uving animal,
but in preserved material it is impossible to find more than the main trunks
of the system. In all of the cercariae and parthenitae described in this paper
the excretory systems have been studied from living material. Altho there
are many individual differences within groups, yet the fundamental uniformity
of groups is evident.

A. The Monostomata. The main features of the excreton,-^ system of the
Monostomata are the two main trunks arising from a common point just behind
the median eye-spot or median pigment center, and proceeding posteriad and
laterad to the posterior part of the body, where they join one another in the
common vesicle. The bladder opens to the outside thru the excretory pore,
which is not terminal but slightly dorsal.

The main excretory trunks are filled with large refractor}' granules, more
extensively described on p. 42. The continuous circuit of the system provides
for the transfer of granules and other waste products from right to left and
reversely, dependent on the contraction and expansion of the several parts of
the animal.

The bladders of the various species differ considerably in size and structure,
but as a whole they may be placed in two sub-groups. In the trioculate forms,
such as Cercarin pdlucida, in dorsal view the bladder is distinctly trilateral
when relaxed, with the excretory pore at the posterior horn. This same type
is found in C. ephemera Nitzsch (Ssinitzin, 1905, Fig. 76), and in C. imbricata
Looss (18%, Fig. 148), and also in C. zostera (Ssinitzin 1911, PI. 1, Figs. 14,
15).

In action, however, due to the muscular movements of the posterior portion
of the body, the anterior portion of the bladder may seem to be a separate
organ opening into the bulbous posterior portion of the vesicle thru a con-
stricted area. In the binoculate tj'pes, on the other hand, the bladder is spheri-
cal, with the excretory trunks emptying into the extreme lateral reaches of the
vesicle. The excretory pore in these species is subterminal rather than termi-
nal. The only binoculate species known are C. lophocerca (de FiUppi, 1857, PI.
1, Fig. 3), C. itrbanensis (Cort, 1915, Fig. 5), and C. konadensis. Lebour
(1907:443, PL X, Fig. B) describes the bladder of C. lophocerca as semilunar,
but from her figure it appears more reniform than lunar. Cort does not
describe the shape of the bladder of C. urbanensis, or state its size. The writer
has found it to measure 50/i to 60/i in median sagittal line and 60ju in transverse
section for preserved material. The excretor)'^ pore of this species is large,
some 20^1 in diameter; it is weakly muscular (Fig. 35). In C. konadensis (Fig.
29) the bladder is smaU, 14)ii to IS/x in diameter. The excretor)' pore is cor-
respondingly small, 3n to 4^i in diameter, and weakly muscular.

37] LIFE HISTOR Y OF TREMA TODES—FA UST 37

The excretory system in the tail of monostomes is simple. It consists
of a median tubule, with tributary laterals, which swell in the proximal
region and empty into the common bladder of the trunk.

B. Holostomata. The excretory systems of Holostomidae and Hemi-
stomidae are sufficiently different to require separate treatment.

1. Holostome type. No accurate or detailed description of the tetracotyle
type of excretory system exists. De Filippi (1857, Fig. 26) has pictured two
laterals for C. vesiculosa, arising from nimoierous tubules in the anterior part
of the body. The connection of these tubes in the region of the bladder is not
clear. Altho his sketch was made ''to show particularly the lateral vessels,"
it gives no adequate conception of the fundamental vessels of the system.
Brandes (1891:569) merely states that the "system reaches into all parts of
the cone; an especially large canal passes longitudinally thru the anterior wall
of the cone. " Only a faint suggestion of the system is figured by Rosseter
(1909, Fig. 17), for Holostomum excisum (von Linstow). Brown (1899, Fig,
11) has worked out an interesting but unusual type. In view of the lack of
definite data concerning the excretory vessels of the holostomid group, it
seems advisable to describe the system for the species Cercaria flabelliformis.

The excretory system of Cercaria flabelliformis is shown in figure 39. At the
extreme posterior end of the worm, situated slightly dorsally, is the excretory
pore. It is the opening of a relatively small bladder no larger than the pore
itself. At its antero-lateral horns two large trunks arise, considerably inflated
in their posterior portion. They may be traced forw^ard along the inner
reaches of the digestive ceca until they reach a place about two-fifths the dis-
tance from the anterior end of the larva. Here a transverse canal is found,
with a median connection between the two trunks, and lateral transverse
tubules. The lateral tubules drain the part of the larva posterior and lateral
to them. Between them and the main longitudinal trunks are found a great
number of anastomoses. Anterior to the median transverse canal the tubules
spread out in fan-like arrangement, running to the sides and front of the worm.

Apparently this system was originally distome in character, but was made
over to suit the needs of a modified distome larva. The longitudinals are
clearly those of the Y-type so common to the excretory system of the distomes.
On the other hand, the transverse tubes and the anastomoses of the postero-
lateral reaches are new structures.

The entire system is filled with minute refractory granules which facilitate
the tracing of the courses of the various vessels.

2. Hemistome type. This type has been worked out in faithful detail
both in the larva (Diplostomulum) and in the adult. Hence a discussion of
the excretory system of C. ptychocheilus will be limited to the points of diver-
gence from the previously described species.

The earliest larvae of this group to be accurately figured are Diplostomulum
clavatum (Nordmann) and D. volvens (Nordmann) (1832, Taf. II-IV). From
the elongated bladder there arises a bicornuate structure which proceeds
forward and outward for a short distance. A bifurcation of each cornu then

38 ILLINOIS BIOLOGICAL MONOGRAPHS [33

takes place, so that there are two pairs of vessels to proceed forward, an inner
and an outer pair. They run forward to a plane in front of the middle of the
body, where they unite and run cephalad as a single vessel. A transverse
vessel is found posterior to this union; this vessel connects the two sides of
the system. Brandes' diagram for the excretory system of D. abbreviaium
(1891, Taf. 39, Fig. 17) differs from this type only in the details and not in
the main features.

The system of Cercaria ptychocheilus (Fig. 49) has a long, attenuate non-
muscular bladder dorsal to the posterior genital apparatus. It does not pair
but gives off a single median longitudinal vessel, which proceeds forward to
the midacetabular region, where it gives off the transverse vessel. The median
longitudinal trunk then runs forward to the origin of the ceca. Here it gives
rise to three antero-lateral vessels. These bend outward and backward, with
numerous anastomoses, and finally imite with the lateral traces of the trans-
verse vessel. The outer reaches of the transverse vessel give rise to many
anastomoses which are conspicuous in the postero-lateral portion of the body.

The fundamental vessels of the holostome tv-pe are the paired laterals and
the transverse vessel. Anastomoses and modifications have altered the
system appreciably, but not beyond the ability to recognize in them a conmion
type underlying the system, probably reducible to the Y-type of the distomes.

The entire system contains many mediimi-sized refractor\' granules which
oscillate back and forth thru the vessek at every movement of the animal.
By imusual contraction of the worm, the granules are forced into the bladder
and out thru the excretor}^ pore.

C. Distomata. The distome cercaria has a simple type of excretory
system, consisting of a posterior median bladder with two lateral longitudinal
vessels in the body of the cercaria and a median longitudinal vessel in the tail.

1. The xiphidiocercariae. The excretory system of the stylet cercariae
consists of a bladder, usually muscular, and a pair of lateral longitudinal
vessels which arise from lateral cornua of the bladder. The primitive lateral
system consists of three tubules, which emerge from the common lateral soon
after the latter leaves the bladder. One of these tubules proceeds posteriad,
while the other two run forward as inner and outer tubules. The single
median tail vessel ends blindly near the posterior end of the tail; it sometimes
receives tributaries, but this is not always the case.

The bladder is a median posterior structure opening to the exterior thru
the dorsal pore. It is usually muscular, unpaired. It v^aries greatly as to
size and shape. It may be p3Tiform (Fig. 90), obo\^te (Fig. 93), crenate
(Figs. 55, 81), truncate or obtnmcate (Figs. 60, 100), falciform (Looss, 1896,
Fig. 146), or lunar (Looss, 1896, Fig. 179).

The physiological and morphological bladders are not always the same.
The former may encroach on the lateral tubules in order to increase its capa-
city. This may consist of mere enlargements of the cornua without any change
in structure (C glandidosa, Fig. 60; C micropharynx, Fig. 90). On the other

391 LIFE HISTORY OF TREMA TODES—FA UST 39

hand the needs for a muscular enlargement sometimes cause the musculariza-
tion of the cornua (C. dendritica, Fig. 81; C. crenata, Fig. 55; and C. racemosa,
Fig. 100). In C. diaphana (Fig. 76) the modification of structure has taken
place before the enlargement of the long median vessel and the lateral tubes.

The capillaries tributary to the lateral tubules are represented in their
most simple form in C. micropharynx. The internal anterior vessel may
move forward, as in C. crenata, or become rudimentary, as in C. glandulosa.
The external anterior tubule is usually the most fully developed.

It is important to note that the lateral systems of the xiphidiocercariae
never anastomose or coalesce in any way. Thus the median sagittal plane
acts as a "watershed."

In the forms studied no large flame cells were found in the course of the ex-
cretory system. If any minute flame cells were present they were concealed
by the thick integument.

The literature shows a paucity of observations on the flame cells of larval
and adult distomes. Ssinitzin (1905) shows the details of the flame cells
in Gorgordera pagenstecheri and in Phyllodisiomum folium. They consist of an
ameboid cytoplasm in which is imbedded a spheroid nucleus with rich chro-
matic inclusions. This cell is the terminus of the capillary (cl). It is ordi-
narily funnel-shaped, but when distended becomes deeply reniform. The
junction of the flame cell and the capillary is marked by a considerable number
of cilia which vibrate rythmically, giving rise to Ssinitzin 's characterization,
"vibratile tip cell of the excretory system."

A detailed study of the flame cell of the adult distome is given by Looss
(1896:110; Figs. 72, 77) for Distomum sanguineutn Sons. The details of the
cell per se are not appreciably different from those given by Ssinitzin, but
the distribution of the flame cells thru the body of the distome is described.
There are four symmetrically paired groups of three cells each in the middle
of the body, and one pair of two cells each in the anterior and posterior reaches
of the body, making sixteen pairs of flame cells and capillaries in all (Fig. 77).
This probably gives an indication of the arrangement of the flame cells in the
typical distome. In Distomum isoporum (Looss, 1894, Fig. 103) six paired
groups of ultimate tubules are figured with four flame cells to each group,
making forty-eight flame cells in all. In Distomum cylindraceum (Fig. 163)
there are six paired groups of capillaries with three flame cells to each group,
totalling thirty-six flame cells. Thus the number of flame cells is not constant
in different species but ordinarily remains constant for each species.

Looss (1894:249, 250; Fig. 186) suggests that the fundamental larval system
is the fundamental system of the adult. Extension and modification occur
thru a dichotomy of the existing capillaries and flame cells, and an encroach-
ment of the tubules upon the capillaries. The greatest modification takes
place during encystment, altho this is in no sense a metamorphosis.

Among adult American distomes the excretory system of Microphallus
opacus Ward alone has been worked out with the exactitude of the Euro-
pean workers (Wright, 1912, PL 17, Figs. 1, 2). This form has the distome

40 ILLINOIS BIOLOGICAL MONOGRAPHS [40

Y-shaped bladder and cornua. There are only eight paired capillaries,
and only sixteen flame cells. This condition constitutes a reduction of flame
cells from the average types, a reduction which can not be entirely accounted
for by the small size of the species.

2. The Echinostome type. This family of distomes is characterized by
simplicity of detail in the excretory system except at the head of the main
lateral vessel. The bladder is not markedly muscular. The pair of lateral
vessels arise from the anterior median region of the bladder, and not from the
horns of this vesicle as in the xiphidiocercariae. The main trunks do not
divide but proceed to the cephalic extremity along the lateral margins. They
sometimes receive small tributaries along their course. In the cephalic region
the vessel commonly flexes back on itself. Such flexure may continue back to
the posterior extremity of the body, as in C reflexae (Cort, 1915, Fig. 43), or
may continue caudad only a short distance, reflexing a second time (C. biflexa,
Fig. 135). An intermediate form, C. echinata, has been described by Looss
(1894:191), where the first flexure continues caudad while another part is
reflexed cephalad.

A modification of the type represented by C. biflexa, where the double
flexure is entirely within the cephalic region, is seen in C. trisolenata (Fig. 109).
Either the end of the flexure has been fused to the most anterior part of the
main vessel, or the middle portion of the system has been modified. As a
result a triangular channel system has been formed at the anterior end of this
excretory system.

The characteristic feature of the excretory system in the two species of
echinostomes is the triplet of flame cells at the anterior part of the system.
A detailed study of the flame cells in C. biflexa is found in figure 138. The cells
are situated in the pockets communicating with the ultimate part of the re-
flexed tubule. Cell a is found in the sinus between the secondary and tertiary
vessel. It points upward and outward. It is the smallest of the three cells.
Cell c occupies the swollen end of the tertiary vessel. It is the largest of the
three vessels; its ciUa are the most rythmical of the group. Cell b Hes midway
between cells a and c. It points downward and inward. Cells a and b func-
tion in bringing the excretory wastes into the vessel from the surrounding
tissue and cell c directs the excretory material along the vessel.

The excretory system of certain species of echinostome cercariae contain
granules. These granules have been found in all C. trisolenata examined;
they are found in the lateral vessels from the region of the pharynx posteriad
to the acetabulum. They have not been seen in C. biflexa.

The excretory system in the tail of echinostome cercariae is not uniform.
In C. trisolenata there is a single median tube with no prominent tributaries.
In C. biflexa a median tube runs two-fifths the distance posteriad, where it
divides to form two tubules which proceed distad. In C. trivohis and C.
reflexae (Cort, 1915, Figs. 39, 43) the median vessel of the tail courses back-
ward about one-fifth way and ends there in a bifurcation, the ends of which

41] LIFE HISTORY OF TREMATODES— FAUST 41

open to the sides. The hiflexa type seems to be intermediate between the
echinostome type described by Cort and the more common distome type. It
is highly probable that the excretory system of the echinostome, with three
flame cells in the anterior portion of the system and possibly several smaller
ones further caudad, has arisen from the primitive distome type. In most
cases, the posterior flame cells have become fused into larger ones, so that only
three flame cells remain in the anterior part of the system in C. trisolenata and
C. biflexa.

3. The Furcocercaria type. The mature apharyngeal distome cercaria
of the furcocercous type (i.e. schistosome) has a very small bladder in the
posterior part of the body and two lateral vessels running cephalad. The
unpaired portion of the tail has a single median canal, which is united to the
system of the trunk thru an "eyelet anastomosis." The median tubule of
the tail forks to enter the rami. The origin of the caudal vessels has been
worked out by Looss (1896, Figs. 172-174) for C. vivax Sonsino. These tubules
arise as the posterior extension of the paired body excretory tubes. Their
fusion in the common portion of the tail occurs after the rami have become
well differentiated. The "eyelet" is an index of the original paired system
in both body and tail.

A study of the species C gracillima (Fig. 143) and C. tuberistoma (Fig. 155)
shows the main features of the vivax type. The small bladder, the lateral
canals, the median caudal tube, bifurcating distally to proceed into the rami,
the "eyelet" at the junction of the body and the tail — all of these seem to be
constant for the entire group. Beyond these characters the features of the
several species are divergent.

In C. gracillima (Figs. 143, 145) the caudal portion is extremely simple,
containing only the common median tubule and the forked tubule system
entering the rami. Unlike C. vivax with its three pairs of flame cilia in the
common caudal tubule, this species has no flame cells in the caudal portion
of the worm. The system in the body of the cercaria has a non-muscular
trilateral bladder, small posterior tubes arising from the lateral tubes, and
a ciliary pocket about one-fourth way from the posterior margin of the body, on
the inner wall of each lateral tube (Fig. 145). At the posterior margin of
this ciliary pocket small tributary canals from the median plane flow into the
main canal. Slightly cephalad is another pocket, somewhat larger than the
ciliary pocket, filled with small granules of various sizes and shapes. Into
this pocket four or five small canals empty, the median ones of which anstomose
with their mates from the opposite side. No ciliary cells have been found in
the terminations of the capillaries.

In C. tuberistoma the caudal portion of the worm is characterized by five
transverse canals. Another pair, anterior to these, is conspicuous because
it runs forward for a short distance and is then reflexed backward for some
distance (Fig. 155). The eyelet and the bladder are both muscular. In the
body portion there are no pockets for the lodgement of granules and no
transverse anastomoses. No flame cells have been found in this larva.

42 ILLINOIS BIOLOGICAL MONOGRAPHS f42

A comparison of the furcocercous larvae with the Schistosomatidae shows
the striking similarity of the excretory systems of these forms. Looss (1895)
finds the system of male and female Schistosoma haematobium alike, altho
that of the female may be sUghtly better developed, due to a minimization
of the musculature. The bladder is median, non-muscular, except for a
weak sphincter at the pore. It receives the two longitudinals at its antero-
lateral reaches. There is no median canal (p. 72). Many of the laterals are
dendritic, altho they do not anastomose. Small flame ciMa are at the heads
of the capillary tubes of Sn to 4/1 diameter. These flame cells and capil-
laries are intra-cellular, and not surrounded by an epithelial lining.

D. Excretory system of the Parthenitae. Details are given only in ob-
servations of Looss (1892:158-161) for the excretory system of young parthe-
nitae. The "protonephridia" of Ssinitzin (1911:77-80; PI. 1, Figs. 24, 25),
described by him in connection with the birthpore of the redia, have not been
proved to have an excretory function.

According to Looss the excretory sytem both in the sporocyst and redia
arises as a paired structure, from which capillaries and flame cells soon arise.
The observations of the writer have been confined to the adult sporocyst and
redia of the species studied, in which the system is strikingly different from
the embryonic condition. In many cases the excretory system consists
of a diamond pattern of intercellular channels, without any clue to the former
bilateral symmetry. The same amount of modification holds for both sporo-
cyst and redia. Even in the holostome redia (Fig. 42) this diamond pattern
is found. No flame cells have been found in adult parthenitae. This distinct
modification of the excretory system in parthenitae is not surprising in view
of the extraordinary degeneration of the animal that has resulted from its
endoparasitic habits during its entire life.

Excretory granules. The excretory granules of the cercaria and parthenita
are spheroidal and have the general appearance of glass beads. Their re-
fractive index is very high. The size of the concretions is variable in different
groups and even in the same individual. As a rule the granules are largest
in the monostomes and holostomes.

Few writers have given consideration to these excretory granules. Thomas
(1883:117) says for Fasciola hepatica larvae that "the yellowish granules. . .
appear to be excretory products formed within the cells of the sporocyst and
then ejected. They are partially soluble in acids, leaving an organic basis. "
Looss refers to them as opaque concrement-granules which on first sight throw
the boundaries of the tubules into black rehef (1894:165). They are insoluble
in alcohol and color beautifully in stained mounts. Reference is made to
these granules by Cort (1915:16) to the effect that the tubules of the mono-
stomes are filled thruout their entire length "with small round concretions
which disappear in the process of preservation." The writer has found that
these granules are not usually preserved in the corrosive-acetic fixing fluids.
However, if fixation is done without the acid fraction of the fluid the granules

43] LIFE HISTOR Y OF TREMA TODES—FA UST 43

are preserved. Application of strong acid to the granule causes an evolution
of gas. The granules are negative to inorganic CO2 tests, and are non-crystal-
line, as determined by the petrographic microscope. They take hematoxylin
stains readily, altho they do not stain deeply. They give no Molisch reaction.
The xanthroproteic test is positive, indicating a benzene nucleus. It is
probable that they consist of a conjugate protein before fixation. Fixation
with mercuric chlorid alters them, since they are then acid and alkali re-
sistent.

Generalizations on the excretory sytem. The excretory system of the
trematodes, including both cercariae and parthenitae, is essentially a bilateral
system. It arises as two paired tubules, which fuse in the bladder region of
the cercaria to form the vesicle. The mature system of the parthenitae is
highly modified from the primitive type. The system as found in the cer-
caria is carried into the adult without very profound modification.

Most individuals of all generations contain within their excretory systems
spheroidal concretions, which are waste organic products, quite probably
derived proteins. They lodge in the main tubes and are expelled thru the
excretory pore.

DIGESTIVE SYSTEM

The most uniform system in the Digenea is the digestive tract. With the
exception of the sub-order Gasterostomata and the super-family Prostomata,
the enteric canal is triclad in character. The main features of difference in
the various families of the group is the modification of the esophagus region of
the gut. In most forms there is a pharynx sphincter just within the oral
pocket. In other species the pharynx is small and inconspicuous. In still
others there is no bulbus around the esophagus, but in its stead a group of
gland cells.

The digestive system in the cercaria is not distinctly a larval system but
practically a fully matured system. In some cases it is not functional, as in
the Monostomata, where the paired ceca are still filled with a jell (Fig. 13) ;
in the Schistosomatidae there is the interesting phenomenon of short ceca in
some species {Cercaria gracilUma) and entire absence in others (C tuheristoma) .
While the larval digestive glands of the cercaria may not be retained or may be
metamorphosed in the mature worm, nevertheless they are functional in
most larvae.

The forking of the ceca is not constant, varying in different species. Even
the relative length of the parts of the tract varies greatly in the same individual
at different times, due to the extreme limits of contraction and expansion of
the larva, so that this relation of parts can not be entirely depended on as a
basis for diagnosis. As a whole the digestive tract is remarkably uniform and
simple, which might be expected in a larva in which the food supply is so
accessible.

The sporocyst has no digestive tract, but takes its nourishment directly
thru the body wall. In consequence the cells of the epidermis are thin and
at times apparently glandular, as in the stylet cercariae.

44 ILLINIOS BIOLOGICAL MONOGRAPHS [44

The redia has a gut-pouch for a digestive system, with a pharynx sphincter
around the anterior end. Hence the epidermis is not used in the capacity
of food transference, and is heavily Kned beneath with an integvmientary
secretion. For securing food the redia of Cercaria pdlticida is provided with
an oral piercing organ. The redia of C. flabelliformis is equipped with paired
mucin-salivary glands.

GENITAL SYSTEM

This system of organs has been the most constant basis of classification
of adult trematodes. It is also the best specific criterion for the larvae, altho
a more deUcate technic is required for differentiation of the genital organs in the
cercaria than in the adult worm. Because these organs have failed to come
out in the ordinar>^ preparations, no attempts have been made to use them as
basis for correlating larvae and adults. Cell masses have been figured by Looss
(1896), Ssinitzin (1905, 1911) Miyairi and Suzuki (1914) and Cort (1915), but
these workers have not in any case showTi them in detail. By means of a
lengthy staining in a weak solution of Delafield's hematoxylin, followed by
rapid differentiation and then neutralization with potassium acetate solutions
in the higher alcohols, the genital organs of the cercariae have been traced
with a degree of detail not previously attained. These organs have been found
to offer valuable data for correlating cercariae and adult trematodes.

A. Monostomata. All three species of monostomes on which observations
have been made, Cercaria pellucida, C. kanadensis, and C. urbanensis Cort are
characterized by the symmetrically arranged testes, the presence of Laurer's
canal, the location of the vitelline glands in a double series on each side of the
body, and the courses of the uterus and vas deferens. Ssinitzin (1905, Fig.
76) shows the inner series of five paired vitellaria for C. ephemera Nitzsch, but
he has figured no outer series of three glands, such as are found in the three
species worked out by the \NTiter. He is in error in considering them cj'sto-
genous glands, because their connection is traceable thru filiform ducts to the
ootype. All these species are provisionally referred to the Notocotyhdae.
With the growth of the cercaria to the adult monostome the originally distinct
and readily recognizable vitelline elements becomed fused in part. Looss 's
figure (1896, Fig. 94) of Notocotyle verrticosa (Froel.) shows five rather poorly
defined foci of vitelline elements in each of the lateral series. It is possible
that the five inner elements of the series have become fused to the three outer
elements of the series, thus causing the indefinite outline of the elements in
the adult worm. The vitelline glands of Notocotyle quinqueseriale are ap-
parently eight to the side. Here the three glands of the outer series may have
been introduced between the five glands of the inner series (Barker and Laugh-
lin, 1911, PI. 1, Fig. 10). A symmetrical pair of \dtelline ducts, between the
inner and outer series of glands, leads to the ootype.

The cercariae which the writer has studied in this group are readily dis-
tinguished by a comparison of their genital systems.

45] LIFE HISTORY OF TREMATODES— FAUST 45

In Cercaria pellucida the well-developed cirrus pouch and the poorly de-
veloped vagina reach the confines of the excretory trunk just behind the median
eye. In C. konadensis the cirrus pouch and the vagina are both equally devel-
oped. The former is falciform, the later pyriform. The vagina is lateral
to the cirrus pouch but is somewhat posterior to it. The genital pore in
C. pellucida is not as far posterior as that in C. konadensis. In this species,
as well in C. urhanensis, the testes are marked by definite cell masses, while
in C. konadensis the testicular masses are much more indefinite. They are
small in each case and lie ventral to the vitelline organs. The course of the
vasa efferentia is clearly outlined.

On the basis of the structure of the vitellaria alone these species can be
differentiated in the cercaria stage. In C. pellucida the glands are actually
spiculate in outline, flattened dorsoventrally. The vitelline material is
finely granular and closely massed. In C. konadensis the glands are decidedly
dendritic, and the granules are diffuse. In C. urhanensis the glands are lobate
and the fine granules are included within a dense mucoid matrix.

B. Holostomata. The genitalia of the Holostomidae and Hemistomidae
will be considered separately.

1. Holostomidae. The thickness of the tetracotyle larva, together with
the thickness of the cysts, in which the majority of these individuals have been
found, has prevented a study of the genital system from stained toto mounts.
However, these organs come out clearly in frontal sections of 7/i thickness
(Fig. 39). In Cercaria flabelliformis the ovary is situated just caudal to the
posteriormost muscular lappet. A short oviduct proceeds dorsad to the
ootype. The uterus winds posteriad to the genital pouch. The vitelline
glands are long paired cords. In C. flabelliformis they are composed of large
vesicular glands (Fig. 39) ; in Tetracotyle pipientis (Fig. 47) they are loosely
follicular. The testes are paired structures which may occupy positions from
the plane of the ovary (T. pipientis) to the plane of the genital pouch (C.
flabelliformis). The pouch is muscular and opens posteriad, ventral to the
excretory pore.

Thus these genital organs are tj^ically holostome in character, correspond-
ing to the main features described for the adults by Brandes (1891), Thoss
(1897), and Johnston (1904). They are sufficiently detailed in this stage of
the species development to be of diagnostic value.

2. Hemistomidae. In this family all of the genital organs are situated
entirely posterior to the acetabulum. The primitive genital pore, anterior
to the acetabulum, has lost its connection with the genitalia, and with the
addition of muscular elements has assumed a suctorial function.

The species Cercaria ptychocheilus has an ovary elongate in a transverse
plane, nearly spatulate, situated just behind the acetabulum. It is granulate,
compact, and stains deeply with hematoxylin dyes. At its left it merges
into the oviduct, a large coiled tubule, which bends on itself three times just
behind the margin of the ovary, then empties into the ootype just anterior

46 ILLINOIS BIOLOGICAL MONOGRAPHS [46

to the bursa copulatrix. The densely massed cells of the glands in the vicinity
of the ootype lie just above this organ. The testes are situated at the right
side just ventral to the ovary. They are small compact glands, and have no
ducts at this stage of development. The vitelline ducts from the diffuse
vitelline follicles meet the other genital products in the ootype. The genital
bursa is very large and muscular, and hes just ventral to the excretory bladder.
Symmetrically arranged glands, with glandular nuclei and hyaUne cytoplasm,
empty into it from the postero-lateral reaches. They vary in number from
seven to ten on each side.

With the exception of these glands emptying into the bursa, all of the genital
organs of this larva lie in the anterior patelliform region. With the exception
of the later formation of a uterine duct between the oot}^e and the bursa, all
of the organs are in the approximate location where they wUl be in the adult
worm. The massing of the organs in the anterior portion of the animal is
undoubtedly correlated with the abbreviation of the appendicular portion of
the species.

The literature on larval hemistomes (Diplostomulum) shows that von
Nordmann (1832:34-35, PL III, Fig. 1) has described an egg pouch for D.
volvens and two symmetrically arranged testes, with ducts, in the region of
the acetabulum. Leidy (1904:111) describing D. grande (Diesing), speaks of
"ovaries, dusky yellow." Since the ovary in the Holostomata is single, the
organs thus described are possibly testes.

The bursa is the muscular organ par excellence in Cercaria ptychocheilus.
Muscle elements protrude into the atriiun, so that a constriction exists between
the anterior and posterior portions of the organ.

The genital systems of the holostome and the hemistome are similar in
those features in which they differ from the distomes. They have modified
their primitive genital pore so that it has either become rudimentary or has as-
sumed a muscular function. The sperm ducts and the uterine duct empty
into the pouch at the posterior end of the animal, instead of the atrium an-
terior to the acetabulum. The new genital p)ore is posterior to the ootype,
and ventral to the excretory pore.

C. Distomata. The genital organs of the distomes are different in various
families.

1. Xiphidiocercariae. The genital organs in these cercariae are readily
defined with reference to the acetabulum. They are mostly situated in the
middle of the ventral side of the larva just behind the acetabulum or shghtly
posterior to this position. The ootype is posterior and dorsal to the acetabulum.
The uterus coils around the right side of the acetabulimi. It ends in a blimt
or tapering ceU mass. Laurer's canal is on the left of the median line, just
behind the middle of the acetabulum. It is present in all of the species of
stylet cercariae examined. Only in two species are the testicular cell masses
outlined. In C. crenata (Fig. 59) these glands consist of two large ovate masses.

47] LIFE HISTOR Y OF TREMA TODES—FA UST 47

In C. dendritica (Fig. 86) the testes are small, situated closely behind the oo-
type. In no case is the ovary clearly differentiated from the region of the
00 type.

The vitellaria are definitely outlined. These glands in C. glandulosa
(Fig. 66), C. diaphana (Fig. 78), and C. micro pharynx (Fig. 96) are much more
alike than those in the remainder of the stylet species. The vitelline follicles
of C. dendritica (Fig. 86), and C. crenata (Fig. 59) are noticeably dissimilar,
having on the one hand, a system extending the entire length of the body,
and, on the other hand, a system confined to the immediate vicinity of the
ootype.

The genital organs and ducts of C. racemosa, the lateral fin type (Fig. 104),
bear some resemblance to those of C. dendritica (Fig. 86). However, Laurer's
canal is very prominent in this fintail species, while in C. dendritica it is not
so prominent. Instead of coiUng around the right side of the acetabulum,
the uterus in C. racemosa makes four double obHque coils dorsal to the acetabu-
lum. The ovarian cell mass is dorsal to the ootype and connects with that
organ thru a short duct. The testes masses have not been observed.

2. Echinostomidae. The two species of this group which have been
studied, C. trisolenata and C. hiflexa, vary in the structure of their genital
organs most markedly. In view of this diversity it does not seem advisable
to take them up in detail in this comparative phase of the study.

3. Furcocercariae. The material of Cercaria gracillima was studied with
especial reference to the genital cell masses, both in the totos and the section
mounts. The main system consists of the ovary-uterus mass on the right
and the cirrus mass on the left, both in the vicinity of the acetabulum. The
vitellaria are lateral and empty into the ootype thru transverse ducts (Fig. 149).
The testicular follicles are numerous, 24 or 25 having been counted. They
are proUferated from a posterior germ mass, which is ventral to the bladder

NERVOUS SYSTEM

One of the earlier and better known system of the adult trematode was
the nervous system. Leuckart (1863:462) states that Bojanus and Mehlis
were famihar with the gross anatomy of the nervous system of the larger flukes,
and that von Laurer, Diesing and Siebold as well as the elder van Beneden
were acquainted with the nervous systems of both large and small worms.
Leuckart described the sy tem for Fasciola hepatica and Dicrocoelium lanceatum-.
He states that there are two or three stems, the anterior dorsalis and an-
terior lateralis and the thick posterior ven trails. Somewhat later Lang (1880:
46-50), substantiates the work of Leuckart and, in addition describes the dor-
sal posterior and acetabular innervation. Gaffron (1884) and Looss (1892,
1894, 1895) have placed the nerve anatomy of the adult trematode on a
firm foundation. Hofmann (1899), Wright (1912), and Monticelli (1914) have
confirmed the work of earlier workers. Nor has the finer work on the nerve
endings and the ganglion cells been overlooked. Many of the earlier writers

48 ILUNOIS BIOLOGICAL MONOGRAPHS [48

made out the ganglion cells of the pharynx region and recorded their ob-
servations on the nuclei. Bettendorf (1897), working on Fasciola hepatica
with intra vitam methylene blue and Golgi methods, has brought out clearly
and convincingly the nervous sytem of this worm. This study has been aug-
mented by the work of Zailer (1914).

In view of the extensive study of the nervous system of the adult tre-
matode, it is a matter of no Httle surprise that so Uttle has been done on the
nervous structure of the cercaria and the parthenita. Looss (1894:245) has
confessed the difficulty in making such a study and had observed that "ein,
wie es scheint, nicht unbetrachtUcher Theil derselben fallt in die Zeit der
Cercarienentwicklimg, imd weiterhin, ist auch der ganze Apparat wahrend
seiner AusbUdungzeit, dass es mitimter recht schwer ist, zu entscheiden was
zu ihm und was zu dem umgebenden Parenchyme gehort. " However, Looss
depended on Hving mounts for his study and did not use preserved material
or avail himseh" of intra vitam methylene blue technic. By the use of an
eosin coimterstain against a hematoxyhn background the writer has been
able to secure remarkably clear sections showing with extraordinary deUcacy
the nerve branches as well as the central nervous system. It is the purpose
of this section of trematode morphology to present data and observations
on the development and structure of the nervous system in parthenita and
cercaria.

The central nervous system of the adult trematode consists of two central
ganglion masses, situated dorsal and lateral to the pharynx and yoked together
by a transverse commissure passing dorsal to the pharynx. The appearance
of this structure has been aptly described by Lang (1880:46) as a saddle
between oral sucker and pharynx. In cross section it is lunar. Here are
centered the most of the gangUon cells, altho they are frequently found poster-
iorly, and often in the sensory apparatus of the oral and ventral suckers. The
system also has a subesophageal commissure which differs in size and shape in
different species of flukes. Extending forward into the region of the oral
sucker are three pairs of nerve trunks, the dorsalis, lateraUs, and ventraHs.
Of these three the latter is the most fully developed. It has a ramus muscular-
is which is both motor and sensory (Zailer), and an extensive connection with
the oral ner\'e ring. The anterior laterahs is also a strongly developed trunk,
with a ramus muscularis and a ramus palpaUs, and transverse commissures
to the anterior dorsahs and posterior lateralis. The anterior dorsaUs is a
weakly developed nerve which innervates the apical sensory field. A trans-
verse commissure connects the two dorsales above the head muscle sheath.
In addition to these three primary trunks, the palatinus, a weak motor nerve,
lies internal to the anterior ventrahs. Posterior to the central nervous system
are the three posterior trunks, the dorsahs, laterahs, and ventrahs. The ven-
tral trunk is by far the most strongly developed. In addition to these is the
small but conspicuous internal branch of the ventrahs known as the pharyn-
geahs. It occupies a posterior position, corresponding to the palatinus anter-
ior to the central nervous system.

49J LIFE HISTORY OF TREMATODES— FAUST 49

Braun (1893:683) considers the ventralis, dorsalis, and pharyngealis to be
the three pairs of posterior nerves. However, the consistent course of the
lateralis to the posterior extremity of the body, its early appearance
in the embryology of the worm, and its conmiissural connections with the
anterior lateralis and posterior dorsalis surely prove its right to a place in the
rank of the primary posterior nerve trunks.

The nervous system of the monostomes has been worked out by Jager-
skiold (1891) for Ogmogaster plicatus (Crepl.), and by Monticelli and Looss
for Catatropis verrucosa (Frol.). Looss (1896:149) considers the system similar
to the distome type. "Je n'hesite pas a attribuer au systeme nerveux de
notre ver une construction analogue a celle que nous avons deja signalee chez
un bon nombre de Trematodes digeneses." However, Looss (1896:11-16)
was not able to make out clearly the anterior trunks. Jagerskiold (1891 :14-16)
describes the cerebral ganglion masses with the transverse commissure, the
posterior ventralis, dorsaUs, and lateralis, and the three anterior trunks, short
and thorn-like, the homologs of the dorsalis, lateralis, and ventralis. A stem,
designated as the "fourth," arising from the anterior reaches of the cerebral
masses, passes ventrad to the region below the oral sucker; it seems probable
that it is the palatinus. The only real modification from the distome type
is the absence of the acetabular innervation, due to the loss of this organ.

In the Amphistomata adults among the earlier writers Lejtenyi (1881 :142-
144), working on Gastrodiscus polymastos Leuck!, described two ganglion centra
with the dorsal commissural bridge, but with only one anterior and one poster-
ior pair of trunks. In contrast to this incomplete description is that given
by Looss (1896:21, 22) for Gastrodiscus aegyptiacus (Cobb), where the usual
distome nerve trunks, were found, and, in addition, a median anterior and a
median posterior nerve. Looss has worked out the nerve anatomy for Am-
phistomum suhclavatum Rud. in even greater detail (1892:151; Taf. 19,
Figs. 1, 2, ), and finds that they correspond to the distome type, except for
the innervation of the posterior sucker.

The one group of the Digenea where the nervous system has been almost
entirely neglected is the Holostomata. Brandes (1891) states that none of
the workers of the nervous system up to his day have worked on the holosto-
mids. He has observed only the central nerve center lying above the posterior
portion of the pharynx, an anterior and a posterior pair of nerve trunks, the
tracings of which he has found in sections. Thoss (1897), working on Holo-
stotnum cucullus, finds the main nerve center lying dorsal to the origin of the
esophagus, with two pairs of anterior and one pair of posterior nerve trunks.

The central nervous system of Cercaria trisolenata, the echinostome,
consists of two masses of ganglion cells and the dorsal commissure lying con-
cavely on the dorsal side of the large muscular pharynx. The commissure is
broad and flat. The dorsal surface of the gangUon masses and the commissure
present a smoothly curved surface, but on the ventral side the ganglia bulge
out against the pharynx. The anterior trunks consist of the dorsalis, lateralis,
ventralis, and the palatinus. The paired dorsales arise together with the

50 JLUNOIS BIOLOGICAL MONOGRAPHS [SO

laterales and proceed forward with them for some distance. After separation,
the dorsalis runs more median, then flexes outward and dorsalward over the
oral hood, proceeding toward the apical sensory center. The lateralis at the
point where it leaves the dorsalis proceeds outward and forward, so that it
reaches a level slightly below the plane of the central nervous system. SUghtly
after diverging from the dorsaUs the lateralis gives back a commissure to the
dorsalis. This dorsolateral connective fuses with the dorsaUs just behind
the posteriormost branching of this trunk. Arising from the most ventral
reaches of the gangUon center is the ventralis, a broad flat trimk, which courses
outward and downward to the oral Hp of the oral sucker. Internally it gives
oflF the palatine, which Ues just lateral to the pharynx.

Caudal to the central nervous system arise the four pairs of posterior
trunks, the dorsales, the laterales, the ventrales, and the pharyngeales. The
dorsaUs branch arises dorsal and slightly lateral to the junction of the gangHon
and the commissure. It runs straight backward, slightly dorsal to the plane
of the central nervous system. The lateralis arises sUghtly lateral to the
dorsaUs; its path Ues outward and backward. The ventralis arises from
the very heart of the gangUon mass. It spreads outward and then runs back-
ward paraUel to its mate. The ventral commissure, arises just median to the
origin of the posterior ventraUs flexing below the prepharyngeal opening. It
is stout and bowed considerably downward. Between the commissure and
the ventraUs arises the pharyngeaUs.

In a germ ball of Cercaria trisolenata some 45^4 by 60ai in size, the central
nervous system is weU developed. This may be called the butterfly stage
(Fig. 121). At this period there are two pairs of main tnmks anterior and
four pairs posterior to the central gangUon mass. The anterior trunks are
the ventrales and the laterales. By reference to the next stage in the devel-
opment (Fig. 122), the dorsales are found to arise from the sinus between the
laterales buds of figiu-e 121. They arise at first as a single bud and bifurcate
later. CaudaUy the most conspicuous trunks are the dorsales, which arise
in a median plane and conspicuously dorsal to the other posterior trunks. The
dorsal commissure at this period is practicaUy negligible. The outer-
most ventral tnmk-buds are the laterales, short and stubby at this
period of growth. The ventral trunks arise from the ventral portion of the
cerebral masses. Between them and the laterales arise trunks which are
present in the embryonic stage only. They may be designated as the posterior
intermedins nerves.

In stage 11 (Fig. 122) a very decided change has occurred in the outline of
the central nervous system, altho the fundaments of the first stage described
are present. Anteriorly the intermediate space between the laterales has
disappeared and from that region has arisen a wedge which is the fundament
of the paired dorsales. The ventral trunks have been set off to themselves by
a lateral growth and elongation of the intermediate fibers. On the caudal side
of the gangUon the posterior dorsalis has been separated frorn its mate by the
growth of the dorsal saddle commissure. Most noticeable, however, is the

51] LIFE HISTOR Y OF TREMA TODES—FA UST 51

change that has taken place in the ventral portion of the system. Here the
space between the ventrales has become exceptionally wide and a prominent
commissure has grown out from the trunks, commonly known as the subesopha-
geal commissure. It is the homolog of the transverse commissure occuring
along the entire ventral side. The intermedins trunk has become fused with
the posterior lateralis, in part, and then crosses over to the ventralis. This
is the connection known in adult nerve anatomy as the ventrolateral com-
missure, a strong and important intercommunicating trunk (Fig. 123). In
the developmental stages no trace of palatinus or pharyngealis has been found.

Cercaria glandulosa, a xiphidiocercaria, is favorable material for the study
of the minute structure of the nerve fibers and endings. In the anterior
end of this larva there occur in five frontal sections of 8/i thickness all of the
fundamental nerve endings of this region. In section 1 of the worm (the
most dorsal section), there are no nerve structures save a few sensillae to the
dorsal lip of the oral sucker. They receive innervation from the anterior
dorsalis, and derive that innervation from the anteriormost fibers seen beneath
in section 2, just in front of the musculuspreoralis. Section 2 (Fig. 68) shows
the trunk of the dorsalis descending into the oral musculature. It has three
main branches, one coursing to the preoral region to supply the conductive
strands for the preoral sensory endings, one becoming the short superficalis,
and a longer one, the profundus, passing under the endings of the superficialis.
In the region of the musculus preoralis, the apical sensory field is continuous
across the sucker from right to left. In section 3 (Fig. 69) are illustrated the
main outlines of the central nervous sytem, together with the anterior trunks.
Here is the dorsal portion of the gangUon cells. Anterior and dorsal is the
dorsal commissure and ventral is the subesophageal commissure. The for-
ward traces are the trunks of the laterales with the outermost superficial ramus
palpalis and the more deeply situated ramus muscularis. The latter branch
innervates the musculus preoralis and the anterior lip of the oral sucker. On
the left is the trunk of the anterior ventraHs, arising from below the mass
of the ganglion cells. At the anterior extremity is the apical sensory field.
The dorsolateral commissure is very clearly shown in this section. Section 4
(Fig. 70) shows the remainder of the central gangUa with the left anterior
ventralis passing forward. This is a large trunk, with an especially important
ramus palpalis leading to the apical sensory field, and a small oral nervus
communicans supplying the oral nerve ring. This ring completely encircles
the superficial region of the oral sucker and connects with the superficial
branch of the dorsahs. The ramus muscularis of the ventralis and the palatine
branch of the ventraHs are found in section 5 (not figured).

Passing caudad all the posterior roots are well defined. Four posterior
roots are visible in section 3 (Fig. 69). These include the posterior dorsales,
laterales, ventrales, and pharyngeals. In a fortunately cut section of the
same species the innervation of the acetabulum is beautifully demonstrated
(Fig. 71). The two main longitudinal trunks, the ventrales and the laterales,

52 ILLINOIS BIOLOGICAL MONOGRAPHS [52

are connected by commissures. Those around the acetabulum are of especial
importance. The preace tabular commissure arises from the lateral trunk
and proceeds in a posterior oblique course, then around the anterior reach of
the acetabulum to meet the branch from the other side. The postacetabular
branch arises from the lateralis also, but continues caudad along the course
of the ventralis. Behind the acetabulum it meets the branch from the oppo-
site side to form the span. From these trunks circumscribing the acetabulum
two ring commissures arise, a superiicialis and a profundus, of which the latter
with the nerve endings is found in the section (Fig. 71).

The nervous system of the monostome, as worked out by Jagerskiold (1891,
Taf. I) for Ogmogaster plicatus (Crepl.), has been substantiated for the most
part in the study of Cercaria pellucida (see figure 23). The three paired
posterior trunks are evident. The posterior ventralis is the most important
of these and can be traced to the caudal extremity of the animal in all cercariae
of this species, as well as in C. konadensis and C. urhanensis. The dorsalis is
less conspicuous, yet it is usually traceable far caudad. The posterior lateralis
is delicate. It arises near the origin of the ventralis and swings out laterad in
a great bov/. It, too, can usually be traced to the posterior extremity of the
body.

The anterior trunks can also be definitely traced. The ventralis arises
from the extreme lateral horn of the ganglion center in conjunction with the
posterior ventralis. More median, the anterior lateralis is found. The two
anterior dorsales arise as a single structure along the median line. Their
primary function in the cercaria is the innervation of the median pigment eye,
altho branches may be traced farther anteriad. Likewise, an important
branch of each posterior dorsalis constitutes the nerve tract to the lateral eye.

The ganghon cells in the monostomes are superficial to the nerve strands.
A considerable number of them are not even in intimate contact with the
fibers, but have fibrillar communications with them. The ganglion masses
from which the nerves arise are distinctly cornuate, with a wide dorsal com-
missure.

Pigmentation and eye-spots in the monostomes. The monostome cer-
cariae that have come under the direct observation of the writer, together
with those described in the literature, may be placed in two groups according
to their eye-spots, namely, those with a single pair of eye-spots, disposed
laterally to the brain center, and those with an additional median eye, anterior
to the central nervous system. The amount of pigmentation is considerably
larger in the trioculate species than in the binoculate type. Figures 1 to 3
show in dorsal view a series of stages in the pigmentation of Cercaria pellucida.
The pigment originates anteriorly over the brain center and proceeds caudad
along six lines of growth. A very careful study of the pigmentation in these
species indicates that a very simple but reasonable relation exists between
the pigmentation and the underlying nervous system. The pigmentation is
found to be a delicate superficial index of the underlying nerve fibers. This

531 LIFE HISTOR Y OF TREMA TODES—FA UST S3

pigmentation is present in the subintegumentary areas and follows with pre-
cision all the ramifications even to the nerve endings. Figure 37 shows the
nerve endings in the anterolateral reaches of Cercaria pellucida.

In the paired eye-spot a definite subspherical "lens" is found in the region
of the concentration of the pigment. In the median eye of the trioculate type
a "lens" is sometimes present. The origin of the eye is simple. At an early
stage in the germ ball (60 n to 80 ju), when the cell masses of the nerve trunks
are definitely outlined as they emerge from the ganglion center (Fig. 36), a
branch of the posterior dorsalis, larger than any other nerve, pushes out
obliquely. It meets an invagination of the ectodermal layer, which may be
considered an "optic cup." There soon forms in the hollow of the cup a
group of dark brown refractory granules, which entirely lines the optic
cup several layers deep and leave but a small cavity within. The optic branch
of the dorsalis bends back into the cavity at the place where it first comes in
contact with the cup and here ends in a pyriform enlargement, the nerve cell.
The structure of this end organ is such that it might be interpreted as a " lens, "
if the connection with the nerve is not made out. Cort (1915:15) has placed
that sort of an interpretation on the eye structure of C. urbanensis and C.
inhabilis. For the former he states that " each true eye is formed by a mass
of pigment in the form of a cup, the bottom of which is thicker than the sides.
A lens fits into the opening of the cup, leaving a space between its lower sur-
face and the bottom of the cup." And again, for C. inhabilis, "the large
eyespots . . . are composed of the lens and the cone of pigment like those
already described for the monostome, Cercaria urbanensis.'' The writer has
studied some of Cort's material and has found sections where such an inter-
pretation might be made from a single section. But in the preceding or fol-
lowing section the connection of this "lens" with the optic nerve is plainly seen.

The eye structure as studied in this monostome is similar to that found
in the Monogenea, especially the type in the posterior eye of Tristommn molae
(Hesse, 1897:559; Taf. 28, Fig. 29).

The nervous system of the monogenetic trematode was first studied in
detail by Lang (1880), who made out the pigment cup, a refractory body
(Uchtbrechender Korper), a ganglion cell, the retina, and eye muscles (p. 41;
Taf. I, Fig. 2, Taf. II, Fig. 2). Most later investigators mention only theper-
ceptory body and the accessory apparatus, altho Andre (1910:217) has iden-
tified the muscle fibers of Lang. The writer believes that the movement of
the eyes depends largely on the general bodily movement.

In the adult Monogenea studied the pigment cup is found to lie between
the refractory bulb of the eye and the possible source of light (Goto, 1894:81).
In the monostomes, as in Dendrocoelium lacteum (Hesse, 1897, Taf. 27, Fig.
10), the hollow of the cup is directed outward, so that light falling on the eye
must pass thru the end organ before reaching the inner portion of the pigment
complex.

The pigment of the organism is probably the waste product in the metabolic
economy of the worm. Its close association with the nerve endings in the

54 ILLINOIS BIOLOGICAL MONOGRAPHS (54

monostome cercariae seems to indicate that it is the melanoidin fraction of
the oxidative processes in the nervous system. The possibility of utility as
a receptor of light or heat is a secondary item and must not be confused with
the primary meaning of the pigmentation.

In the free-Uving Platyhelminthes the fully developed eye is present in the
mature individual. In the ectoparasitic trematodes the eye-spot is well
developed in the young animal (Hesse, 1897:560, 561), but degeneration takes
place as the animal matures. Goto (1894:81), speaking of Tristomum, ob-
serves: "Morphologically speaking they are certainly degenerate eyes; and
have probably been derived from such eyes as are found in Turbellaria; but
I do not think they are functional. In the first place the pigment granules
are situated on the dorsal side and thus prevent the light from reaching the
lens, since the dorsal side is the only direction from which light can come. In
the second place there is not always a distinct retina. If these 'eyes' are
really still useful to the animal, they may possibly be a temperature sense
organ; and for that purpose their structure seems to answer well." Goto
goes on to show that the more degenerate condition of the eyes in Tristomum
ovale is due to the greater degree of internal parasitism of this species than
that of Tristomum molae. In the monostome, the eyes are well developed in
the cercaria but become fully degenerate, with a loss of all the pigment in the
adult, so that the adult of one species has been described by Creplin as "albi-
dus" (Jagerskiold, 1891 :4). In some species of Allocreadiidae {Crepidostomum
farionis O. F. M. and C. cornutum (Osborn)), pigment eye-spots are found in
the adult. A still further stage of degeneracy is found in Cercaria racemosa
(Fig. 100) and C. gracillima (Fig. 144), where the optic nerve is still present
but the pigmentation is absent.

In Cercaria gracillima, the representative of the furcocercariae, the ner-
vous system is narrow, in correspondence with the attenuate condition of the
animal. The posterior laterales are not found in the mature cercariae, altho
the bud is present in the germ ball (Fig. 151). One is struck by the significant
resemblance of the main nerve complex of this cercaria and that of Schistosoma
haematobium, described in detail by Looss (1895). The three pairs of anterior
trunks are readily made out, altho, in addition, a prominent dorsolateralis is
found (Fig. 150). The posterior dorsalis arises from the dorsal side of the
ganglion cell mass and proceeds caudad to the region of the acetabulum, where
it fuses with the ventral trunk. A prominent subesophageal commissure and
a small pharyngealis are present. The fundamental resemblance between
the system described for this cercaria and that for the schistosome adult
seems to the writer to be sufficient morphological evidence for the correlation
of these apharyngeal furcocercariae with the Schistosomatidae.

A study of the nervous system of the Holostomata has been made of Cer-
caria ptychocheilus, based on both toto mounts and sections (Fig. 53). No
adequate idea of the nervous system of this group can be secured from the
meager data of Brandes (1891) and Thoss (1897). The dorsal commissure is

55] LIFE HISTORY OF TREMATODES— FAUST 55

indistinct and thoroly fused with the ganghon masses. The latter are wide,
with a construction in each in the region of the origin of the lateral trunks.
The trunks figured by Thoss are probably the ventrales, since they supply the
main innervation of the animal. The anterior ventralis arises along with
the posterior ventraHs just anterior to the latter. The anterior trunk soon
divides. The major portion runs around the oral sucker, while the external
branch is traceable anterolaterad. The anterior lateralis is represented by a
blunt stock just outside the pharynx. It rims cephalad but soon ends in two
delicate branches. There is no posterior dorsal of posterior lateral. The
posterior ventral is stout and thick. It gives off one prominent branch ex-
ternally soon after it reaches its most external position. At regular intervals
it gives off branches internally which have the indication of rudiments of
commissures. These transverse trunks just anterior and posterior to the
acetabulum are still well developed; they are similar to those described for
the distome.

Contrary to the opinion of Looss (1894:245, 246), the writer has found
without exception that the general trematode nerve anatomy can be traced
from the early germ balls up thru various stages of growth, and that the
cercaria shows not only the potentialities of the adult system, but actually
the details of this system. Moreover, the study of various groups of cer-
cariae has demonstrated that the fundamental deviations and modifications
from type are recognizable in the mature cercaria. Thus this study has
shown that the nervous system of the cercaria is constant for the group to
which it belongs, and is a definite basis for the natural classification of the
groups.

In contrast to the highly developed nervous system found in the cercaria
is that of the parthenita. In the sporocyst no definite nerve complex is found,
altho Looss (1892) has observed nerve elements in miracidia of Amphistomum
subdavatum. In the redia, however, with the continued functioning of the
highly muscular pharynx, there is a nerve complex practically embracing the
entire anterior portion of the gut (Fig, 125). Viewed from the dorsal, ventral,
or lateral aspect, the system in surface view appears as an H. It is resolvable
into four anterior trunks, four posterior trunks, and a ring commissure. On
the dorsal side are two swellings, the rudiments of the cerebral ganglion masses
of the cercaria. The nerve cells of the system are very prominent. They
are usually bipolar or multipolar (Fig. 126), but, as might be expected, the
more superficial ones are more often the multipolar cells.

This redia nervous system constitutes a very primitive type, in which the
nerve cells are much more frequently diffuse and more discrete than in the
systems in the cercariae. It is probable that the pharynx is responsible for
keeping the system from total degeneration.

The size, number, and location of the ganglion cells vary according to indi-
vidual species of cercariae. They may be situated within the ganghon centers,
as in Cercaria micropharynx (Fig. 97) and C. glandulosa (Figs. 69, 70); they

56 ILUKOIS BIOLOGICAL MONOGRAPHS {56

may be scattered around the ganglia altho not imbedded in the fibers. In
the redia of C. trisolenata the fibers are less conspicuous than the ganglion
cells. Species closely related may have ceUs of different numbers and different
sizes. In C. micro pharynx there are always just two ganghon cells, imbedded
in the fibers, just above the esophagus. Their nuclei are large, pyriform,
and usually containing conspicuous refractory nucleoli. They measure 5.5^i
to 6ju in short diameter by 8.5^ to 9/i in long diameter. The nucleoli are
about 2/i in diameter. Cercaria glandulosa presents a case where there is a
definite number of minute ganghon cells within the ganghon masses. There
are fifteen cells in each of the two masses. The cell walls are not well defined,
but the nuclei are readily distinguished. They measure 1/x to 1.5/x in short
diameter by 1.5m to 2/i in long diameter. The ganghon cells of C. pellucida
are numerous; it has not been ascertained whether they are constant in ntmi-
ber. They are subspherical at times, but are usually multipolar. The entire
cell averages 3.Zti by 6n while the nuclei measure Iju to \.6n. The ceUs of the
redia of C. trisolenata are usually multipolar in the region of the epidermis.
They range from 6n to 22/i in diameter. The nuclei are inconstant in size,
varying from 2/i to 6/i in diameter. The nuclei of the ganghon cells of C.
gracillima are so minute in the nerve complex in the germ balls (Fig. 151) that
they are barely visible under 1,000 magnification. Yet these nuclei are
definitely set off from the surrounding matrix. They measure about 0.4/*
in diameter.

In cell-studies of adult trematodes the nerve cells have been measured in
many cases. The measurements range from 80/i (Lejtemd, 1881:41) in Gas-
trodiscus polymastos to 6/x (Fischer, 1883:17) in Opisthotrema cochleare. The
nuclei range from 12/x (Juel, 1889:41) in Hemiurus excisus to l.tfi'va. Opistho-
trema cochleare (Fisher). A comparison of these measurements in adult
trematodes with those for the cercariae, shows that the nuclei of the adult
cercariae are as large as those of the adult trematode. It is evident, however,
that the cells are much smaller in the cercariae. Ageing of these cells consists,
then, in the growth of the cytoplasm rather than an increase in size of the
nucleus.

S7J LIFE HISTORY OF T REM ATODES— FAUST 57

DESCRIPTION OF THE TREMATODES INFECTING MOLLUSKS
OF THE BITTER ROOT VALLEY

INTRODUCTION

On account of the biological isolation of the Bitter Root Valley, it is little
wonder that it contributes new species of trematodes. The fourteen species
of trematodes found in the valley are not thot to comprise the entire trematode
fauna of the region, but are the representative species for the year and season
when the study was made. Of the fourteen species found in the Bitter Root
River, two are larval Monostomata, two are Holostomata, and the remaining
ten are Distomata. In addition to these, a larval holostome, Tetracotyle
pipientis nov. spec, from the vicinity of Chicago, Illinois, is included in the
study for the sake of comparison.

Previous to the writers' preliminary report (Faust 1917) the following
larval trematodes have been described for North America.
Monostomata Distomata

Cercaria hyalocatida Haldemann 1842 Cercaria polyadena Cort 1914

Glenocercaria liicania Leidy 1877 Cercaria hemilophura Cort 1914

Cercaria urbanensis Cort 1914 Cercaria trigonura Cort 1914

Amphistomata Cercaria trivohis Cort 1914

Cercaria inhabilis Cort 1914 Cercaria rubra Cort 1914

Cercaria diastropha Cort 1914 Cercaria douthitti Cort 1914

Cercaria gorgonocephala Ward 1916 Cercaria wrightii Ward 1916

Distomata Cercaria anchoroides Ward 1916

Cercaria agilis Leidy 1858 Cercaria marcianae La Rue 1917

Rhopalocerca tardigrada Leidy 1858 (Really a Distomulum)

Gymnocephala ascoidea Leidy 1877 Cercaria vergrandis La Rue 1917

Cercaria platyura Leidy 1890 (Really a Distomulum) .

Cercaria reflexae Cort 1914 Holostomata

Cercaria megalura Cort 1914 Diplostomulum cuticula (v. Nordmann 1832)

Cercaria leptacantha Cort 1914 Diplostomulum grande (Diesing 1850)

Cercaria caryi Cort 1914 Diplostomulum volvens (v. Nordmann 1832)

Cercaria isocotylea Cort 1914 Tetracotyle typica (Diesing 1858)

Cercaria brevicaeca Cort 1914 Diplostomulum parmdum (Stafford 1904)

Cercariaetim

Cercariaeum helicis (Leidy 1847) Later recorded by Leidy as C. vagans (1850).

In addition, there is the doubtful form, Cercaria bilineata Haldemann 1840.

According to Stiles and Hassall (1908:157), Leidy is credited with the
record of a species, Diplostomulum rhachiaeum (Henle). Investigation of the
literature shows this to be an error, owing to the confusion of the names
Leidy and Leydig. Fr. Leydig described the species D. rhachiaeum for Europe
in 1853 (Leydig, 1853:383).

Of the thirty-two forms listed, it is doubtful if any except those described
by Cort (1914), Ward (1916) and LaRue (1917) could be recognized by their
descriptions, since in the majority of cases the data are so indefinite as to leave
the systematist a wide range of choice in determining the species. An excellent

58 ILUNOIS BIOLOGICAL MONOGRAPHS [58

example of this valueless type of description is afforded in the form Diplosto-
mulum cuticula (von Nordmann 1832), reported by four American investigators
from various localities east of the Rocky Moimtains. The descriptions include
larvae encysted with pigment and without it, some specimens found subder-
mally, others taken from the peritoneum of the body cavity, all secured from
a great variety of teleost fishes. In none of the descriptions is there mention
of the course of the excretory system or of the genital cell masses, both of which
are essential to the exact determination of the species. It seems reasonably
certain that a careful revision of these forms described as Diplostomulum
cuticula (von Nordmann) would result in the discovery of several new species
of Diplostomulvun.

The species of cercariae and parthenitae described in this section of the
paper have been studied with special reference to the excretory, genital, and
nervous systems.

MONOSTOMATA

Cercaria pellucida Faust 1917

This larval trematode is a muscular cercaria, characterized by heavy
anterior pigmentation on the dorsal surface, centered around three foci, the
paired lateral eye-spots and the median eye. It is a member of the trioculate
group of the Monostomata. The pigmentation tends to spread caudad from
the pigment center along six Hues of growth, two dorsal, two lateral and two
ventral. These lines of pigment have been shown (p. 53) to be the superficial
index of the underlying nerve trunks. The worm is characterized by 1) a
transparent body, 2) a circuit of refractory granules that marks the excretory
system, 3) a small oral sucker, and 4) large longitudinal muscle bimdles of
the tail.

Cercaria pellucida was obtained from Lymnaea proxima Lea in the Bitter
Root River in the vicinity of Corvallis, Montana, and from Physa gyrina Say
near Buckhouse Bridge. The snails were examined in October, 1916.
Lymnaea proxima contained a heavy infection with this species, along with a
lesser infection with the monostome cercaria, C. konadensis, and a distome
larva, C. diaphana. Physa was heavily infected with an echinostome, C.
trisolenata, and contained only a hght infection with the monostome. In all
cases the infected organs were the Uver ceca.

The mature C. pellucida has an average measurement of 0.4 mm. to
0.7 mm. in length and 0.18 mm. to 0.2 mm. in width. The tail is about 0.5
mm. long and has a diameter of 0.07 mm. at the base. Most usually the
animal has an eUiptical constricted outline, such as is shown in figiu-e 4, but
when relaxed it assumes the elongate-ovoid or spatulate condition, shown in
figures 1 to 3.

The parthenita is a large conspicuous redia, measuring 2.2 mm. by 0.5 mm.
(Fig. 6). Within the redia is a large rhabdocoel gut extending almost the
entire length of the animal and measuring 0.3 mm. in cross section. The gut
empties anteriad thru a muscular bulbus 15m in length and 12/x in cross sec-

591 LIFE HISTOR Y OF TREMA TODES—FA UST 59

tion. It is spinose internally (Fig. 20). In the prepharynx region is a unique
piercing organ (Fig. 17), probably of ectodermal origin. It is four-lobed and
is covered with spines. A rythmic eversion of the organ against the host tissue
and redrawal within the pharynx region of the parthenita is a characteristic
movement of the redia. Around the muscular pharynx is a ganglion mass
consisting of a fibrous matrix and a network of ganglion cells. Behind the
head region is a neck-like constriction, and behind the neck is a sacculate
body. At the extreme posterior end is a large papilla. The redia is covered
with a non-cellular basement membrane, and imbedded in this superficially in
the form of minute tuberosities are the remains of the epidermal nuclei
(Fig. 22).

The walls of the redia are well-supplied with muscular layers, longitudinal
and transverse, so that the parthenita is capable of extraordinary distension
and contraction, altho it has no specific locomotor organs.

The germ balls of the redia arise from the matured ova, derived from four
cells localized at the posterior extremity of the parthenita. Altho the cells
lying next to the wall around this quartet may be potentially germ cells, they
take no part in the ordinary proliferation of germ cells (Fig. 22). From these
cells arise the germ balls, thru cleavage into 2, 3 and 5 cells, after which cer-
tain cells of the ball appear much smaller than the others and grow over the
latter, giving rise to the gastrula by epiboly. The young germ balls usually
lie en masse behind the gut, while the more advanced cercariae are crowded
anteriorly. They appear strangely grotesque, with their pigment eyes and their
snout-like bodies oscillating back and forth within the body wall of the par-
thenita.

Aside from the larger size of the body and the trioculate anterior end,
Cercaria pellticida might be at first confused with Cercaria urhanensis Cort.
While the size and eye-spots are sufficient to separate these two species, a
more careful examination shows that there has not been a separation of two
species at all, but more correctly two groups of species. The group of smaller
species is binoculate and ranges around 0.3 mm. to 0.46 mm. in length by 0.1
mm. to 0,16 mm. in width, while the group of larger species is trioculate and
averages around 0.5 mm. in length by 0.15 mm. to 0.2 mm. in width. Con-
sequently from a description of external characters alone there is no means of
separating Glenocercaria lucania Leidy from the Bitter Root species Cercaria
pellucida. It is such a problem as this that has caused the writer to believe
that there are characters more deeply seated in the larva that will readily
set it off from others of the same group.

Sufficient care in technic makes it possible to bring out very clearly and
convincingly the genital organs of the Bitter Root species. Here are characters,
constant both in the larva and the adult that readily differentiate these mon-
ostome cercariae. These have been described in detail in the section devoted
to morphology (p. 45) and need only to be summarized at this point. The
median ovary just in front of the excretory bladder opens out thru a short
duct at its left (Fig. 18), and after receiving the common vitelline duct, opens

60 ILLINOIS BIOLOGICAL MONOGRAPHS [60

anteriad into the uterus. This organ has an outlet just behind the median
eye. It ends in a poorly developed vagina. No Laurer's canal has been
definitely made out in the totos but there is evidence of such an organ in sec-
tions. From the sides and sUghtly caudad to the ovary the closely massed
testes open into filiform vasa efferentia which unite anterior to the ovary to form
the vas deferens. This canal is directed forward parallel to the uterus, ending in
a bulbous cirrus pouch just to the left of the vagina. The three paired outer
vitelline follicular masses and the five paired iimer masses occupy a dorsal
position. They are irregular in contour (Fig. 4), with aciculate margins, and
are finely granular with close massing of the granules. Inconspicuous com-
mon viteUine ducts connect the vitellaria with the ootype just dorsal to the
ovary.

The excretory trunks are similar to those of the entire group of monostomes.
The bladder is quite small, 48/i in section, moderately muscular, superficially
triangular, with the excretory pore posterior. The excretory tube in the tail
is vesicular at the base and narrows down distad (Fig. 4). The tubes of the
tnmk are crowded with large excretory granules.

The digestive system is t3T)ically triclad, with ceca extending to the sub-
distal extremity. They are filled with a jell, and are crowded with granules
imbedded in the jell. No pharynx has been observed. The oral sucker is
directed ventrad. It is small but powerful.

The parenchyma is filled with cystogenous granules, included in one-celled
cystogenous glands, probably of mesodermal origin (Fig. 14). Between the
cystogenous cells are angular parenchyma cells, more commonly known as
vesicular cells (Blasenzellen), with processes extending to the integiunent and
possibly functioning in the capacity of secretory ducts for the basement mem-
brane.

The locomotor organs at the posterior angles of the tnmk are neither spicu-
late nor spinose. They possess no cement glands. The tail has no central
pair of gland elements such as axe found in binoculate cercariae of the mono-
stome group. However, the ordinarj' parenchyma cells of the tail of C. pelltt-
cida are remarkably large and vesicular and suggest a glandular function
(Fig. 19.).

Large, isolated bands of transverse muscle fibers are present thruout the
body just within the basement membrane. Longitudinal muscles are not so
large in the tnmk as are the transverse series, but constitute the important
muscle system of the tail. The transverse muscles of the tail frequently give a
moniliform appearance to that organ, such as is described by Leidy (1877) for
Glenocercaria Iticania.

The nervous system of C. pellucida (Fig. 23) varies from the distome nervous
system only in its relation to pigmentation and the eye-spots. There are six
anterior tnmks and six posterior trunks arising from a paired brain center.
They constitute the dorsal, lateral and ventral nerve lines. These trunks are
carefully followed by the melanoidin pigment fraction. The eye-spots receive

61] LIFE HISTORY OF TREMATODES—FAUST 61

innervation from the dorsal trunks; the paired eyes are innervated from the
posterior trunks and the median eye from the fused branch of the anterior
dorsales. The optic nerve runs forward from its origin in the dorsalis and
enters the pigment cup from above, ending in a sensory cell (Fig. 24). The
general anatomy and histology of this eye-spot is similar to that described for
all Turbellaria and Monogenea. However, no previous account has been
found for the structure of the eye-spot of the Digenea showing its relation to the
central nervous system.

Locomotion is brought about thru a cooperation of the body musculature
together with the special functioning of the oral sucker and the posterior loco-
motor pockets. The tail serves as a swimming organ, with a peculiarly rapid
and nervous lashing.

Encystment occurs as a fmal step in the larval stage of the life-history of
the hermaphroditic generation, in preparation for entering the definitive host.
The process is rapid and the mucoid cyst is secreted by the cystogenous glands
before the tail has been thrown off. This organ is freed from the cyst by the
violent wriggling which it produces. The cyst is spherical; it encloses the now
quiescent larva. The outer portion of the cyst is an opaque mucoid, which
gives the cyst an appearance of a white grain, about the size of a pin-head.
The larva now waits transfer to the definitive host.

Cer carta konadensis Faust 1917

Cercaria konadensis is a species of monostome cercaria of the binoculate
type. The species is more graceful than C. pellucida. Its bodily contour
is most usually spa tula te, while the long tail reaches far behind. The small
amount of pigmentation around the two eye-spots and the less usual pigmenta-
tion along the nerve trunks caudad serve to indicate the superficial differences
between the binoculate group to which this form belongs and the trioculate
group.

Cercaria konadensis was found in Lymnaea proxima Lea, collected from the
Bitter Root River at Corvallis Montana in October 1916. It occurred as an
infection along with the larger species, C pellucida. Of the snails examined,
31.3 per cent were infected with this cercaria in the connective tissue be-
tween the liver ceca. The cercaria measures 0.4 mm. to 0.46 mm. in length
and has a bodily width of 0.1 mm. to 0.16 mm. (Fig. 25). The tail is of equal
length under conditions of relaxation, but may be extended so as to*exceed
by far the bodily length. At its base it has a transverse diameter of 30/x to
40jU. The posterior locomotor organs are not so conspicuously lateral as
those of C. pellucida (Fig. 4). Considered together with the younger stage
of C. pellucida (Fig, 12), these pockets suggest an origin from the caudal
pockets found in certain distome cercariae. Unlike those of C. pellucida, the
posterior locomotor pockets of C. konadensis are provided with about ten
gland cells surrounding the lumen, cells probably of a secretory nature (Fig.
21).

62 ILLINOIS BIOLOGICAL MONOGRAPHS [62

The parthenita (Fig, 26) is a relatively small, elongate redia, 1.7 mm. in
length and 0.35 mm. in transverse section near the middle. It is attenuately
obtruncate, with the posterior end sloping down to a blunt point. The
pharynx is muscular but small, 60)u in cross section, and aspinose internally
(Fig. 31). The rhabdocoel gut extends posteriad about three-fifths the body
length. The posterior end is filled with cells, composed of a central rachis
with apex directed posteriad, and an outer cell complex of goblet cells (Fig. 30).
The central rachis comprises the germinal epitheUum, the proliferating region of
which is situated sub terminally. From this epithelial mass the matured
parthenogenetic eggs are proliferated forw'ard so that the germ balls come to
lie in the lumen posterior to the gut. Similarly to those in C. pdlucida, only
the maturing cercariae come to lie around the gut.

The excretory system of C. konadensis consists of the circuitous trunk
system, opening posteriorly into a non-muscular vesicular bladder. This
vesicle measures 16)Lt to 17/i in width and 14/i to 15^ along the longitudinal
axis of the cercaria. The excretory pore is dorsal, opening from the middle
of the bladder (Fig. 29).

The digestive system is of the usual triclad tjpe, with no distinct pharyn-
geal region.

The genital organs are notocotyhd in character, but different in several fea-
tures from those of C. pellucida. The ovary (Fig. 28) is skull-cap shaped, with a
distinct Laurer's canal. A short oviduct leads into the ootype. The uterus,
emerging from the ootype, runs cephalad, ending in a swollen vagina some
distance behind the line joining the paired eye-spots. The vitellaria consist
of a double series of five inner and three outer follicular masses. The indi-
vidual glands are very diffuse and dendritic.

The testes are small, lateral, and posterior to the ovary, with the vasa
efferentia describing a broad crescent anteriad around the ovary and meeting
in a common tube, the vas deferens, which runs forward to the left and parallel
to the uterus. The vas deferens ends in a swollen cirrus pouch (Fig. 25).

The nervous system corresponds to the monostome type described for C.
pellucida, except that the dorsal trunk to the median pigment eye-spot is
lacking.

In the tail six paired groups of gland cells, derived from parenchyma,
occupy places just lateral to the median canal of the excretory system, each
group dove-tailing into the one next proximal. These caudal glands indicate
a much closer kinship of this worm to Cercaria urbanensis than to C. pellucida.

Encystment is brought about by the pouring out of the contents of the
cystogenous cells and by subsequent decaudation.

HOLOSTOMATA

Cercaria flabelliformis Faust 1917

Cercaria flabelliformis is the first larval holostomid to be described in
detail for North America. Leidy has listed Tetracotyle typica Diesing from

63] LIFE EISTOR Y OF TREMA TODES—FA UST 63

Lymnaea catascopium and Fkysa heterostropha (1890). Rettger (1897) has
mentioned a larval tetracotyle in connection with a life-history study, but he
has failed to identify the species.

Cercaria flabelliformis was found in three collections of Physa gyrina Say,
taken from the Bitter Root River in the vicinity of Corvallis, Montana, in
October 1916. Practically every snail from these collections bore evidence
of infection with the parthenita of this species, altho only 14.7 per cent of the
snails examined contained the tetracotyle. The mature cercaria has a length
of 0.48 mm. to 0.56 mm., and a width of 0.44 mm. It is about 0.2 mm. thick.
While the anterior end is not clearly set oflf from the posterior end as is usual
in holostomids, it does have the suctorial cup which includes all the ventral
suctorial apparatus, including among the rest the lateral suctorial grooves.
In the young larva these lateral organs are discoidal (Fig. 41); in the mature
tetracotyle they have become modified into lateral lappets (Fig. 40).

The larva was found maturing within the redia, free in the liver interstices,
and encysted in the Hver tissues. It was seldom found free in the tissues.

The parthenita (Fig. 42) is a redia which measures 0.5 mm. in length by
0.052 nun. in transverse section. The head is set off from the trunk by a collar
prominence, while in the posterior third of the body are found the "walking
feet, " which protrude ventrolaterad to support the redia. The posterior end
of the body is produced into a large knob, in which are parenchyma and
germinal epithelium ceUs. At the oral end is a wide muscular organ. It is
not clear whether it is a pharynx or an oral sucker. It is about 40/i in trans-
section and surrounds the fore-end of a gut 0.18 mm. long. On the ventral
side are two groups of saHvary glands, six cells to each group, opening into the
anterior region of the gut thru a common duct for each group (Fig. 43).
Around the anterior end of the gut, just behind the muscular organ, is a nerve
complex (Fig. 42), differentiated into two ganghon masses on the dorsal side,
four nerve trunks, and a circimiintestinal commissure. A birth-pore is
here ventral and shghtly sinistral. The wall of the parthenita is heavily
covered with an integimient of non-cellular material, beneath which are
muscle and parenchyma elements. Running thru the parenchyma is a com-
plex diamond-pattern excretory system.

The germinal epithehum is localized at the posterior end of the redia.
It offers an unusually fine opportunity for study of the maturation of the ova.
The detailed description of this maturation is found in the section on morpho-
logy (p. 16).

The germ balls may differentiate into a second generation of rediae and cer-
cariae at the same time. These larvae are about equal in size as they develop,
but the cercariae differentiate much more rapidly than do the rediae so that
the two are readily distinguished. Usually only three or four cercariae are
found developing at one time in the redia, along with many daughter redia.
This fact seems to indicate that the animals have come to depend largely on
parthenogenetic propagation. The cercariae escape thru the birth-pore and

64 ILLINOIS BIOLOGICAL MONOGRAPHS [64

soon encyst in the free tissue of the host. The second generation redia is
aheady producing germ balls before it comes to take up a free existence out-
side the first generation redia.

The internal systems of organs of Cercaria flabelliformis are of considerable
interest. However, since they are described in detail in the respective sections
in the morphological division of this paper (pp. 37, 45, 54) they will not be
treated here.

Valuable data on holostomid anatomy are obtained by a comparison of
Cercaria flabelliformis with the following species:

Tetracotyle pipientis nov. spec.

This species of larval trematode was found in March 1917 in the mesentery
and pericardium of a large number of Rana pipiens collected in the vicinity
of Chicago, Illinois. All of the frogs were more or less infected with this
holostome. The infection consisted of creamy oval yellow cysts, either single
or in grape-like clumps. Each cyst consisted of many lamellae, and innermost,
a tough cyst membrane. The inner membrane stains a deep brown with
iodine in 70 per cent ethyl alcohol. The gross measurement of the cyst ranges
from 0.5 mm. to 0.76 mm. in lesser diameter and 0.7 mm. to 1.0 mm. in greater
diameter, while the inner membrane is about 0.3 mm. by 0.5 mm. Within the
inner membrane is the larva, tightly coiled at one end of the cavity, while
the remainder of the cyst, often two-thirds of the volume, is filled with accum-
ulations of large excretory granules. Some of these granules have fused to
form single clumps as large as the larva

WTien the lamellae and cyst membrane are teased open and the larva is
allowed to work its way out, the body becomes expanded and flattened. It
then measures 0.5 mm. in length by 0.37 mm. in trans-section (Fig. 47). The
oral sucker is 75)U in diameter. It lies in an anterior cone of the body. Antero-
lateral prominences and the blunt posterior portion of the body give a lyrate
outline to the worm. The primitive genital pore, 80;u in diameter, lies in a
plane where the anterior and posterior portions of the body join, just within
the suctorial pocket. The free ventral wall of this pocket is often folded
backward so that it fits down snugly against the body. At other times it
bulges out so that the pocket cavity is a large ovoid atrium. The acetabulum
is represented by a single lappet situated behind the primitive genital pore.
The non-muscular accessory suctorial grooves consist of long narrow slits,
directed obliquely inward toward the acetabulum. The entire worm is covered
with minute anterior and posterior spines, equally prominent. The primitive
genital pore is crowned with a ring of fused spines. The lateral suctorial
organs are surrounded by a band of discrete spines imbedded in the tissues.

The worms examined were all filled with excretory granules. A careful
study of the larva showed the main course of the excretory trunks to appear
as shown in figure 48. The median posterior excretory pore, sUghtly dorsal,
conmiunicates with the bladder which merges imperceptibly with the paired

65] LIFE HISTORY OF TREMA TODES—FA UST 65

lateral trunks. These tubes lie just within the margins of the larva and unite
with one another in a large transverse vessel at the anterior end of the body,
so that a complete circuit is formed. If a rent is produced in the body near
the oral sucker, it is customary for the excretory granules to be poured out
there rather than thru the natural channel. A tube from the lateral trunks
crosses thru the ventral pocket wall at its anterior end. Tributary tubules,
bisymmetrically arranged, empty into the main trunks, mostly at the anterior
and posterior margins of the body.

The digestive tract is simple and inconspicuous. A small swelling within
the oral sucker marks the pharynx, just behind which is the esophagus. The
ceca barely clasp the anterior margin of the primitive genital pore.

The genital organs are readily recognized as holostome in type (Fig. 47).
They open posteriad. A small spherical ovary lies median. Dorsal to this
is the ootype, into which come the short oviduct and the transverse vitelline
ducts. The vitellaria are diffuse bands of large follicles extending from the
anterior face of the acetabulum to the posterior margin of the genital pouch.
They lie strictly ventral. Two large oval testes lie to the sides of the ovary,
the one (ti) slightly anterior to the other (t,). They have individual ducts
(efferent) which reach the genital pouch and fuse into a common vas deferens
just before entering the genital pouch. This organ is muscular, oval in con-
tour, with the transverse diameter longer than the longitudinal.

A survey of the literature shows that only one tetracotyle has been re-
ported for Amphibia, Tetracotyle crystallina (Rud.), from the mesentery cysts
in Rana temporaria, R. esculanta, Bufo igneus, B. viridis, and Vipera berus
(Rudolphi, 1819:380-382). The formation of the cysts is not clearly de-
scribed, but the large size of the Europen tetracotyle, together with its oval
contour, aspinose body and oval accessory sucking discs, clearly separates it
from Tetracotyle pipientis. The new species conforms much more to the type
represented by T. cohibri v. Linstow, but differs from it in the relative sizes
of the oral and ventral suckers, and the possession of small spines all over
the body instead of a few broad spines (Linstow, 1877:192; Fig. 22).

While the excretory system is one of the best systems of organs to use in
systematic work with trematode larvae, in the absence of such data for other
tetracotyles. described, the comparative data actually afforded are sufficient
in this case to justify the establishment of Tetracotyle pipientis as a distinct
species.

Observations on the anatomy of Tetracotyle pipientis present an oppor-
tunity for comparison with Cercaria flabelliformis, the parasite of the Bitter
Root moUusk, Physa gyrina.

The two larvae are about equal in length, but C. flabelliformis is consider-
ably the wider. The widest region in T. pipientis is in the anterior region of
the body; the widest portion of C . flabelliformis is in the middle of the body.
The suctorial pocket in the former species has grown over the ventral sur-
face so that a true pocket is formed with the opening anterior; in the latter

66 ILUNOIS BIOLOGICAL MONOGRAPHS [66

species the suctorial pocket is hemispherical with the opening ventral. The
lateral accessory suctorial grooves in T. pipientis are non-muscular oblique
slits; in C. jlabelliformis they are at first oval depressions which are modified
later into a pair of lateral lappets. The primitive genital pore in C. fiabelli-
formis is 0.05 mm. in diameter; in T. pipientis it is 0.08 mm. wide, with a
crown of heavy spines. The homologies between the lateral excretory trunks
of the two species are apparent, altho the median transverse trunk is much
farther anterior in T. pipientis than in C. Jlabelliformis. The tributar}' tubules
are entirely different in the two species. The digestive ceca of the Bitter
Root species conform to the family type in extending well into the posterior
part of the body; those of T. pipientis are short and rudimentary. The geni-
tal organs of the two species occupy the same relative position, altho individual
variations in size and shape of organs are evident.

In concluding the study of the tetracotyle larvae, emphasis must be placed
on the maturation of the parthenogenetic ova, which shows that these larvae
do not develop in miracidia, without the intercalation of parthenitae as
Brandes (1891:572) and Fantham (1916:224) beUeve. This fact, previously
recorded by the writer (1917), makes the morphological evidence complete
in support of the view of true alternations of hermaphroditic and partheno-
genetic generations among Holostomata.

Cer carta ptychocJieUus Faust 1917

This form, really a Diplostomulum, is elongate ovate in outline, with dorso-
ventral flattening, sHght ventral concavity, and a more or less distinct sepa-
ration of body into anterior and posterior portions. In addition, the
group to which this worm belongs lacks the lateral auxiHary sucking grooves
which are characteristic of the tetracotyle forms. Several species of Diplosto-
muliun have been weU described and their excretory system beautifully traced
by von Nordmann (1832). These include the species Z>. volvens,D.cuticula,
D. clavaium, and D. breoicaudaium. Of the forms found in North America
there have been recorded D. cuticula, D. volvens, and D. grande of the Old
World species, and D. parvulum (Stafford), new to North x\merica. However,
as has been previously suggested, none of these American records give suf-
ficient data to distinguish accurately the species.

The general outline of the body of Cercaria ptychocheilus is such as to dis-
tinguish it readily from the described species. Broadly oblong-ovoid in
contour, with the anterior half laminate and the posterior portion fleshy,
this cercaria might at first be confused with distome cercariae. Such a con-
fusion is caused, further, by the abbreviated appendiculate portion of the
larva, which, on extension into a caudal cone, may reach one-third of the body
length, but on contraction barely protrudes behind the anterior part of the
body. The concavity of the anterior part is found only in the fleshy region
behind the acetabulum. Here in this area is foimd the muscular complex
comparable to the cup-shaped suctorial apparatus of the tetracotyle.

67] LIFE HISTOR Y OF TREMA TODES—FA UST 67

The Diplostomulum (Fig. 49) measures 0.48 mm. to 0.63 mm, in length
by 0.17 mm. to 0.37 mm. in width, and about 30^ thick in the fleshly portion
of the body. The oral sucker is small but powerful, and is directed strictly
anteriad. Behind this oral region the esophagus is enlarged into the pharynx,
about 40/x in section. Behind the pharynx is an equal portion of the esopha-
gus which is non-muscular, posterior to which the ceca rise, spreading out
into a broad furculum.

The acetabulum is large and circular; it is situated somewhat posterior
to the middle of the body. At times of extreme contraction the acetabulum
becomes narrowed antero-posteriorly, with a transverse wrinkling. This disc
measures 70ju in diameter. The primitive genital pore, situated just in front
of the acetabulum, has lost its connection with the genital system and has
become modified into a muscular sucking disc.

The excretory, genital, and nervous systems have been treated on pages
37, 45, 54, as types for the hemistome larva. A comparison of these data
with V. Nordmann's observations on Diplostomulum cuticula, D. volvens, and
D. clavatum, and with the work of Blanchard (1847) on Hemistomum alatum
(Goeze) shows the fundamental conformities and differences of the excre-
tory systems of the group. However, the nervous system (Fig. 53) is worked
out thoroly in this paper for the first time in the Hemistomidae. The genitalia
bear a fundamental resemblance to those of the adult species, as described by
Brandes (1891), but differ in size, shape and position of the respective organs.
This difference may be accounted for in part by the immaturity of some of
the organs, but there are undoubtedly specific differences, such as the lamellae
of muscular nature in the genital pouch and the glandular cells emptying into
the pouch.

The larva Cercaria ptychocheilus was taken from mesentery cysts of Pty-
chocheilus oregonensis Richardson, caught in the Bitter Root River in April
1915 in the vicinity of Stevensville, and Carlton, Montana. Thousands of
cysts were found. The cysts are much larger than the larvae (Figs. 50, 51)
and are filled with a limpid milky fluid which bathes the larva and serves as
a liquid cushion. The cyst is oblong, and flattened. It is composed of a
thin, tough membrane, and it is attached to the mesentery by a discoid annulus
in the middle of one of the flattened sides. Within the cyst the worm works
around and grows, so that it comes to fill the cyst in later life. At frequent
intervals there is extruded from the excretory bladder a considerable quantity
of granules which pile up at the posterior end of the larva within the cyst,
but are soon dissolved and absorbed by the fluid medium.

The encysted animal when placed in a normal saline solution soon increases
its activity and bursts thru the cyst. This rent usually occurs at one end
of the membrane. The larva then crawls out with a "measuring worm move-
ment. " After several hours of activity it settles down on the bottom of the
container and remains quiescent, altho sUght mechanical disturbances activate

68 ILLINOIS BIOLOGICAL MONOGRAPHS [68

it again. In a modified Ringer's solution ninety per cent of these larvae were
kept alive for forty-eight hours.

It seems probable that Cercaria ptychocheilus is in an intercalated host.

DISTOMATA

Xiphidiocercariae (St}'let Larvae)
The xiphidiocercariae are grouped together because of their possession in
common of a larA^l stylet. The writer beHeves that the features of the geni-
tal and excretory systems of the group are more fundamental characters
which will hold the members of the group together.

Cercaria crenata Faust 1917

Cercaria crenata is a delicate larva, with an ovate bodily outline and a
short lanceolate tail (Fig. 55). The body measures 0.25 mm. in length by
0.13 mm. in width, and the tail, 0.15 mm. to 0.16 ram. in length by lOjx to
30/1 at the base. The entire body except the tail is covered with minute hair-
like spines. A large median spine, the stylet organ (Figs. 56, 57) hes in the
dorsal wall of the oral hood. This organ is about SO/z long by 5/x in width at
its base. It has the general shape of a quill pen, with reinforcements at its
base and also in the distal portion toward the acute point. The distal third
of the stylet is bent ventrad about 20 degrees. There are two prominences
in the anterior portion of this organ, one where the shaft joins the quill and
a less prominent one-half way between this position and the quill point.

The oral sucker is relatively large, 20^ in diameter, while the acetabulum,
situated three-fifths the way from the anterior end, measures just half that
diameter. The tail is inserted in the posterior caudal pocket which has no
spinous projections.

Cercaria crenata was found in large numbers in 13.6 per cent of Lymnaea
proxima Lea, taken from the springs at Fort Missoula, Montana, in October
1916. It occurs in oval sporocyst sacs, 0.5 mm. in length and 0.35 mm. in
diameter. At one end the germinal epithelium, is localized and from this end
the ova are proliferated. Only cercariae have been found to develop within
the sporocysts.

When the cercaria is mature its breaks thru the wall of the sporocyst and
swims thru the surrounding medium. The tail is retained for a consider-
able time, and encystment is slow. This seems to indicate a considerable
period of free-swimming Hfe.

The internal structure of Cercaria crenata is such as to distinguish it readi-
ly from the other stylet cercariae. The excretory system is characterized pos-
teriorly by a subspherical vesicle, deeply crenate. It measures 20/i long and
30/i wide. Anterior to the bladder a bicornuate trunk empties into the ves-
icle thru a common median tube. The horns of the U are widely separated.
At the place where each main lateral turns forward there is given off a small
dendritic tubule, directed posteriad. Some distance ahead of the acetabulum

69] LIFE HISTOR Y OF TREMA TODES—FA UST 69

the main lateral trunk divides into inner and outer tubes, each of which has
a number of branches and capillaries. The main tube of the tail is median,
with no prominent tubules.

The digestive system consists of an esophagus provided with a pharynx for
most of its way, and, behind the pharynx, a typical gut extending to the
posterior plane of the acetabulum.

The salivary-mucin glands in C. crenata are of a unique type. An outer
series of eight small vesicular cells, with a common duct system into the oral
pocket, corresponds to the usual salivary-mucin gland system of cercariae.
These glands are readily made out in the living worm. An inner series of
five cells, two of which are just behind the pharynx and three behind the ace-
tabulum, empty thru a common duct system into the oral pocket. This
series is not seen in the living larva, but in stained specimens the cells show
small vesicular nuclei with deeply staining cytoplasm and numerous chromo-
philic granules. This inner series probably consists of a type of salivary
gland different histologically and suggests a correspondingly different function.

The genital cell masses are prominent and are well differentiated early in
development. Their structure and position are indicated in figure 59. The
ovary lies posterior to the acetabulum and median whereas Laurer's canal
lies anterior and to the left. The uterus is characterized by a double coil,
which ends in a moderate sized vagina, just anterior to the acetabulum. The
vitellaria are limited to three cords which lie in a transverse plane just
posterior to the ovary. The large flask-shaped testes lie behind the ovary.
This genital system suggests the Plagiorchiine arrangement. The distribution
of vitellaria is similar to that described by Poirier for Plagiorchis sauromates
(1886, pi. 2).

Cercaria glandulosa Faust 1917

A stylet cercaria characterized by a multiplicity of glands has received
the name of Cercaria glandulosa. It is somewhat larger than C. crenata, is
more oblong-ovate, and is a much more active larva (Fig. 60). The body
measures 0.45 mm. in length and 0.2 mm. in width. The tail is slightly
shorter than the body, 0.35 mm. in length, by 50/i to 60/i in section at the base.
The tail is set within the caudal pocket. This pocket is provided with a
pair of locomotor grooves, in which are set a number of stiff spines. Below
the insertion of the tail is a small lappet (Fig. 63), provided with three spines
directed posteriad. A mucoid secretion is present in the sinuses of the pocket,
lateral to the base of the tail.

The stylet organ measures 39yii in length by 5m in width at the base of the
shank. It is reinforced all thru, but especially at the base of the shank, and
thruout the quill. The point of the stylet is blunt. The stylet, as well as
the entire body, is very delicate, and is shattered by the slightest pressure of
the cover slip. The oral sucker is directed downward; it measures 86^ in
diameter, while the acetabulum, in the middle of the ventral side, is smaller,
with a diameter of 66//.

70 ILUNOIS BIOLOGICAL MONOGRAPHS 170

The cercaria was found in the liver tissues of Physa gyrina Say from the
Bitter Root River in the xdcinity of Hamilton, Montana, in October 1916.
Forty per cent of the physas examined were infected with the parasite. The
cercaria develops within a very simple sporocyst, which has a length of 0.34
mm. and a width of 0.17 mm. (Fig. 67). The wall of the sporocyst is delicate,
consisting of a single layer of very thin epidermal ceUs, with no basement mem-
brane and no muscular complement. The genital epithehum is localized at one
end, and from this only a few cercariae are developed at any one time.

The excretory system of Cercaria glandulosa presents some interesting
features. The bladder is flattened, truncate, and subterminal instead of
terminal. A narrow canal communicates with the excretory pore which is
median posterior. The four angles of the bladder are muscular. When the
bladder is emptied these corners lie close together, so that the cavity of the
bladder is small. Then by the expansion of the bladder this organ is filled
from the trunks (Figs. 64, 65). Two vesicular cornua empty into the bladder.
Each cornu is directed laterad and sKghtly anteriad; it soon constricts to
form the lateral tube. The common tube divides soon to form the posterior
tubule and the anterior tube. The anterior vessel then divides in the region
of the acetabulum to form a trifurcate system. Just behind the region of
this division there is a small vesicular swelling where granules of the system
accumulate. The excretory system in the tail consists of the common medi-
an vessel and several tributaries.

The digestive system is characterized by an abundance of glands, so that
the entire tract is surrounded with gland cells. A small pharynx surrounds
the esophagus near the anterior end of the tube. The esophagus extends to
the preacetabular region, at which place it forks to form short furcae which
barely clasp the anterior end of the acetabulum. Along this entire course
there are many gland cells in clusters, especially abundant in the pharynx
region. Their relation to the pharynx and nerve gangha is shown in figure 72.
The individual gland ceU is ovate, with a short neck. The cytoplasm is
chromophilous. There is no recognizable duct connection thru the myoblasts
of the pharynx to the lumen. The nuclei of these cells are large and studded
with granules.

In addition to the grape-like clusters of gland cells surrounding the entire
digestive tract there are right and left paired gland groups of the salivary-
mucin type. They consist of nine large cells to each group, usually situated
in the acetabular region, but capable of extension, so that they may He as
far caudad as the bladder (Fig. 62). Figures 73 and 74 show sections passing
thru the anterior tip of the excretory vesicle. In each of these a right and a
left gland are visible. In these glands not only is the nucleus granular, but
the cytoplasm is densely granular, the granules being assembled in little
climips. Frequently (Fig. 73) there are vacuoles within the cytoplasm.
'i%^ The genital organs are represented by cell masses which show clearly the
location of the mature organs, but as yet show little differentiation (Fig.

71] LIFE HISTORY OF TREMATODES— FAUST 71

66). Ovary, Laurer's canal, vagina, uterus — all are recognized in the midace-
tabular region, with vitelline follicles extending from the oral aperture to the
posterior end. They are divided into anterior and posterior portions. No
testes are yet to be found. The genital organs as a whole seem to indicate
Plagiorchid relationship.

Conspicuous thruout the body are the large bundles of longitudinal muscle
fibers. They are scattered thruout the parenchyma at the anterior end
(Fig. 72), while they are much larger and more concentrated laterad in the
region of the acetabulum. Still further caudad they become fewer and less
conspicuous (Fig. 74).

The nervous system has been described in detail on page 51.

This cercaria lives a free-swimming existence for only a short time. When
placed in a watch-glass in tap water, it soon drops its tail, preparatory to
encystment. The tail is helpful in locomotion, yet after decaudation this
species is more active and able to cover considerably more ground than most
other species v/ith the aid of the tail. This movement is due in no small
measure to the spines in the locomotor grooves of the caudal pockets. After
moving about for a little while the cercaria settles down and pours out an
abundance of shme within which it coils up and becomes quiescent until a
transfer to the new host is effected.

Cercaria diaphana Faust 1917

Cerceria diaphana is closely related to C glandulosa. When contracted,
it is broadly ovate (Fig. 78), but on extension it assumes an elongate ovoid
contour (Fig. 76). The measurement of the body when at rest is 0.2 mm. to
0.26 mm. in length by 0.1 mm. to 0.12 mm. in width. Under pressure of a
cover slip the internal organs are beautifully worked out and the delicate
mist of the parenchyma in which they are imbedded suggests the term "dia-
phanous. " The tail is broadly lanceolate, 0.15 mm. in length by 0.04 mm. at
the base. It is inserted into a caudal pocket provided with spinose locomotor
pocket grooves. The spines are few in number (8 to 10) and well developed.
They are directed meso-caudad. As in C. glandulosa the two sinuses of the
caudal pocket are thickened by a mucoid lamination. The acetabulum is
situated in the middle of the ventral side; it has a diameter of about 32/i. The
larger and more powerful oral sucker has a diameter of 44/i. The stylet organ
(Fig. 77) is a delicate but firm quill of 39/i length and Sn width at the base
of the shank. It is entirely without any reinforcement in the region of the
shank but has thin ventral plates at the junction of the shank and quill, while
inserted in the quill point, directed posteriad, is a minute spine, 5/* long and
0.5^1 in diameter.

Cercaria diaphana was found in the liver tissues of Lymnaea proxima in
the Bitter Root River near CorvaUis in October 1916. The infection was
heavy. The cercaria develops in an oblong sporocyst (Fig. 79), frequently
drawn out or contorted at one end (Fig. 80). The unique feature of the

72 ILUNOIS BIOLOGICAL MONOGRAPHS [72

sporocyst is that the germinal epithelium is not localized; consequently germ
balls may be derived from any portion of the body. Whether or not the germ
cells arise parthenogenetically has yet to be determined. This type of germ
ball production represents a structural simplicity previously not recorded for
the sporocyst.

The excretor\' system differs from that of other stylet cercariae mainly
in the shape of the bladder and of the essential tubes. The bladder is small,
hea\'ily muscular, flattened antero-posteriad. Leading out from it in a median
plane is a non-muscular shank of some length, which opens into two cornua
a considerable distance in front of the bladder. Caudad these cornua are
vesicular, but further cephalad they become constricted into a system of
tubules similar to those of C. glandulosa, w^hich nm thru the body to collect
the excretor\' wastes.

The digestive system consists of a long esophagus, with pharjTix at the
anterior end, and a wide bifurcation somewhat anterior to the acetabulum.
The entire digestive tract is very attenuate in outline. It is not supplied
with glands along the furcae but has an even more abundant supply
than C. glandulosa in the region of the pharynx (Fig. 76). Altho the pharynx
itself measures only 15/x in cross section, the glandular area as a whole em-
braces a sphere 65ju in diameter. The rest of the tract is free from gland
cells of this nature. The saUvar\--mucin glands are situated in the upper outer
reaches of the furcae. Each group consists of eight cells, relatively very small,
granular, with a common duct system opening into the oral pocket.

The genital organs are similar to those of C. glandulosa (Fig. 78). They
differ from the genital cell masses of that form in the more limited vitellaria, and
the more conspicuous Laurer's canal. This form is probably a Plagiorchid larva.

Unlike C. glandulosa this cercaria is slow to drop its tail and much slower
to encyst, in spite of the fact that there is an equally good pair of posterior
locomotor pockets with spines and an equally good supply of c}'stogenous.
material. We have here, then, e\'idence of a physiological adaptation to
different conditions of the en\-ironment, where the structure of the two t}'pes
would lead one to expect similar habits and reactions.

Cercaria dendritica Faust 1917

Cercaria dendritica is a species of cercariae readily recognized by its obovate
structure, large suckers, large muscular phar\'nx, and large muscular excre-
tor\- vesicle. The body as a whole is heavily muscular. The tail is short
and almost conical (Fig. 81). The body measures 0.33 mm. to 0.4 mm. in
length by 0.13 mm. to 0.17 nmi. in wadth. The tail is about half the body
length, 0.16 mm. and is 0.04 mm. wide at the base. It is inserted into a typi-
cal caudal pocket, the whole ca\"ity of which is lined with stiff spines. The
large oral and ventral suckers are nearh' equal in size. The former has a
diameter of 62^ and the latter of 60;/. The stylet (Figs. 82, 83) is short and
stout, heavily reinforced at the shank, with a flat deltoid quill. The quill

73] LIFE HISTORY OF TREMATODES— FAUST 73

is pointed at the tip. It is directed ventrad by about ten degrees more
than the shank. The stylet has a length of 44/i and a breadth at the base
of the shank of 14/x.

Cercaria dendritica was secured from two collections of Lymnaea proxima
taken from the chara sloughs at Fort Missoula, Montana, in October 1916.
The infection was in the liver interstices. The parthenita (Figs. 87-89) is a
well-developed sporocyst, with an attachment disc, but without any indica-
tion of a digestive tract. It seems to approach a redia more nearly in its
structure than any other described sporocyst. The sporocyst is muscular and
heavily covered with integument. The parthenogenetic eggs develop from
a germinal epithehum situated at the antipodal end from the disc. The
stages of cleavage are clearly made out from the study of the germ cells pro-
liferating from the germinal epithelium (Fig. 89). This layer is closely
pressed against the epidermis. As the cells mature they increase in size.
The increase continues thruout the cleavage, so that a three-cell stage is
larger than a one-cell stage, and a morula is larger than a five-cell stage. This
continued growth of the embryo is accounted for by the nourishing medium
which bathes the sporocyst. This is a special case of nurture, where the
growth stimulus is reacted to immediately. The germ ball attains a con-
siderable size before it begins to differentiate, altho epiboly has occurred soon
after the morula stage has been reached. The animal is mature before it
breaks thru the wall of the sporocyst and swims out into the inter-cecal spaces.

The larva has an interesting excretory system (Fig. 81). An immense
spheroid bladder, somewhat crenate, opens dorso-posteriad thru a small pore.
Anterior it receives the contents of two large muscular comua thru a common
opening. These cornua extend laterad to the extreme margin of the animal.
At the outside of each, at the margin of the worm, arise three tubes, one
directed posteriad and two directed anteriad. The capillaries are dendritic.
The caudal tube is a median canal without any prominent tubules.

The alimentary system consists of a pharynx with muscular fibers developed
early. It has a width of 30^ and a length in section of 36ijl. A short, attenuate
esophagus opens posteriad into two vestigial furcae. Anterior and lateral
to the acetabulum are the salivary-mucin glands, eight to each group. They
are moderately large (Fig. 85), and empty thru common duct systems into
the oral pocket.

The conspicuous features of the genital system (Fig. 86) are the large swollen
vagina, and the prominent Laurer's canal, the latter extending out on the
left side of the acetabulum under its posterior margin. In the mid-area,
just behind the acetabulum, are two small pyriform testes. The vitelline
glands extend from the extreme anterior margin of the worm to the extreme
posterior end; they are attenuate, sparsely branching serpentine chords,
composed of a long anterior and a short posterior portion. The vitelline
ducts run in from the postero-lateral regions to the ootype, which is just
anterior to the testes. This type is suggestive of Plagiorchid relationships.

74 ILLINOIS BIOLOGICAL MONOGRAPHS [74

Soon after the cercaria is set free into the water, it drops its tail. Ahnost
before the observer is aware it secretes a thin membrane from the abundance
of cystogenous material contained in the large cyst cells which pack the paren-
chyma of the worm. The oval c>'st with the worm coiled up inside is shown
in figure 84. This type of cyst offers only a temporary lodgement for the
cercaria, and it is evident that the worm must reach the definitive host soon
if the infection is' to be successful.

Cercaria micropJiarynx Faust 1917

Cercaria micropJiarynx is a minute larva of the xiphidiocercariae, oval in
contour, with small clavate tail (Fig. 93). The body is covered with minute
spines arranged in diamond pattern, progressively less prominent toward
the caudal end. The spines are probably constant characters of the adult
as weU as of the larva, since the entire trunk is well suppHed with these spines
while the tail is naked. The body measures 0.18 mm. in length and 0.09 mm.
in width. The tail is 0.14 mm. long and 0.03 mm. at the base. It is inserted
into a caudal pocket provided with a group of spines on the lateral lappets
ventral to the tail. The oral sucker is large for the bod}'- size, 35^1 in diameter,
while the acetabulum is shghtly smaller, 30/i in diameter. Inserted in the
hood of the oral sucker is the stylet organ (Figs. 91, 92), 34fi long and 5n to
6fi in breadth along the shaft. The organ is reinforced all around and has a
velum stretched across the ventral surface of the quiU.

The cercaria was secured from the infected Uver tissues of a large number
of Lymnnea proxima, taken from Rattlesnake Creek, Missoula, in Novem-
ber 1916 and in May 1917. The cercariae develop in oval irregular sporo-
cysts, measuring 0.24 mm. along the long axis and 0.18 mm. along the short
axis (Fig. 94). The body wall of the sporocyst consists of a single layer of
epidermal cells, between which are found numerous excretory granules, lying
in irregular grooved channels. There is no localization of the germinal epi-
theUum, so that germ balls arise from aU portions of the body wall and, when
mature, break out into the body lumen. Not only do the cercariae develop
to maturity in the sporocyst, but in some cases they drop their tails and
encyst in the sporocyst (Fig. 95). Thus the larval host, the snail, is the food
of the intercalated or of the definitive host, since no free-living stage is com-
monly found. In case the cercaria is pressed out of the sporocyst before
encystment, it swims about for a very brief period, then drops the tail and
enc>^sts.

The excretory system consists of a subspherical vesicle and bellows-shaped
comua, which open into the vesicle thru a common cylinder. The three
usual tubes of the excretory system are present, the single posterior and the
two anterior ones. The tail tube is single median, with a few inconspicuous
lateral tributaries. The comua are filled with excretory fluids; they are
Imed with cells (Fig. 98).

The digestive system consists of the very minute pharynx in the mid-
region of the esophagus, and two vesicular f urcae considerably anterior to the

75] LIFE HISTOR Y OF TREMA TODES—FA UST 75

acetabulum. No glands occur in the pharynx or cecal regions, but in the
prepharynx region, just within the oral aperture, is a band of about fifty gob-
let cells of a glandular nature. The salivary-mucin glands are found at the
sides of the acetabulum. They consist of eight cells for each group. They
are relatively large, vesicular, and have common ducts opening into the oral
pocket. In addition to the usual transverse and longitudinal systems just
within the integument (Fig. 97, 98), large muscle elements are scattered
thruout the parenchyma.

The genital organs (Fig. 96) consist of a prominent vagina, a well-defined
Laurer's canal, and a group of massed organs in the vicinity of the ootype.
In addition, there are the yolk follicles, distributed over a wide range of the
dorsal side of the animal. The follicles are closely massed together. This
species suggests a Plagiorchid genital system.

Cercaria racemosa Faust 1917

Cercaria racemosa belongs to that group of stylet cercariae usually desig-
nated as cercariae ornatae, by virtue of their possession of a fin-fold structure
to the tail. While this separation may be concomitant with a deeper, more
fundamental difference of type, it is well to bear in mind that fin-folds occur
in other groups, such as in monostomes, Cercaria lophocerca (Fihppi, 1857:5;
Fig. 3), echinostomes, Cercaria echinatoides Fil. (La Valette:1855,Taf. I, C),
and among the furcocercous larvae, Cercaria cristata (La Valette, 1855,Taf.
II, K). It may be looked on as a modification of the caudal organ for swim-
ming.

The body of Cercaria racemosa is elongate ovoid, measuring 0.29 mm. in
length by 0.11 mm. in width (Fig. 100). It is characteristically broadest
just ahead of the acetabulum. The tail consists of a central lanceolate region
and a lateral ruffled fringe, which is most conspicuous at the distal end. The
tail measures 0.22 mm. in length and 0.04 mm. in width at the base. It is
inserted into the posterior extremity of the trunk, altho there are no lateral
sinuses to be found in this caudal pocket. The acetabulum is sHghtly caudal
to the middle of the body. It measures 26/i in diameter, while the larger oral
sucker has a diameter of 36iu. The stylet organ (Figs. 101, 102) is delicately
attenuate, with a reinforced tip. It is 27/i long and about 5^ wide at the base.

The species was found in the liver of Lymnaea proxima in the chara sloughs
of the Bitter Root River at Fort Missoula, Montana, in October 1916. It
occurred as a minor infection along with C. dendritica and C. gracillima. The
parthenita is an irregular polygonal sporocyst about 0.62 mm. long and 0.38
mm. thick (Figs. 104, 105). At one end is situated a pocket of glandular
cells which attach the sporocyst to the host. This is done by the exudation
of a mucus. It is doubtful if these cells are at all muscular. At the antipodal
end is the germinal epithehum, from which germ balls arise. Only a few
cercariae develop within the sporocyst at any one time.

The bladder of the excretory system is truncate, with a common median
vessel leading into it from the anterior end. Lining the vesicle at the anterior

76 ILLINOIS BIOLOGICAL MONOGRAPHS [76

end are six gland cells, paired right and left. They appear as small tubercules
suspended from the anterior wall of the vesicle. Anterior to the median vessel
are two cornua, elongate, yet swollen, reaching antero-laterad around the
acetabulum. Near the acetabulum there are received the common posterior
and the two anterior tubules. The pattern of the capillaries is racemose.
The tail trunk system consists of a common median vessel with many lateral
tubules. The entire system is filled with minute excretory granules.

The digestive system consists of a very long esophagus, near the anterior
end of which is the small sphincter, and from the posterior end of which the
furcae arise. They extend partly around the acetabulum. The salivary-mucin
glands consist of right and left paired groups of cells, eight to the group, with
long ducts leading in a common bundle to the oral pocket.

In the region of the cerebral ganglion a pair of oval bodies, the non-pig-
mented eye-spots are located. They are degenerate, similar to those eyes
described for Cercaria gracillima (p. 52).

The genital cell masses are found in the region of the acetabulum (Figs.
104, 107). To the left is Laurer's canal, and running dextro-laterad is the
closely coiled uterus. The genital pore is on the right of the mid-ventral line,
anterior to the acetabulum. Running into the ootype from the postero-
lateral angles are the vitelline ducts, connecting the vitellaria with the ootj'pe.
The testes are not well defined. The relationship of the cercaria is not evi-
dent from the genital cell masses.

Cystogenous cell glands are present, altho not as conspicuous as in C.
glandulosa or C. micro pharynx. Encystment takes place after a considerable
period of free swimming life. Decaudation always precedes encystment.
The cyst wall is thin ; the animal is easily viewed thru the cyst.

Echinostome Cercariae
Cercaria trisolenata Faust 1917

Cercaria trisolenata represents a unique type of echinostome larva (Fig.
109). It is more attenuate than the average species of this family, and has
an unusually short tail. The body has an average length of 0.45 mm. and a
width at the preacetabular region of 0 1 mm. The tail is about 0.2 mm. long,
lanceolate, and measures 0.06 mm. at the base. An anterior region of the
trunk, measuring 0.06 mm. along the median line, constitutes the head region,
behind which is a neck-like constriction. There is a collar of 36 spines along
the margin of the head, arranged in a single irregular series (Figs. 110, 111).
These spines are bluntly rounded at the base and taper to a rounded point
at the distal end. They are from 12/x to 14jLt in length. The body as a whole
is usually covered with minute spines. The acetabulum is beset with an
irregular arrangement of crooked spines (Fig. 112). The oral sucker is small
but powerful, Z^ti in diameter. The acetabulum, situated behind the mid-
plane of the body, measures 42)u.

These cercariae, together with Cercaria gracillima, are the most cosmopoli-
tan species of the Bitter Root River. They occur in Physa gyrina from the

77] LIFE HISTORY OF TREMATODES— FAUST 77

upper and lower reaches of the Valley, and in Planorbis trivolvis from the region
of Buckhouse Bridge. The infection of the host is always heavy, both
as relates to numbers of individuals infected and the number of parasites in
the individual host. The per cent of infection ranges from 22 to 100. The
parasite is located primarily in the interstices of the liver, but frequently
invades the cecal walls and does great injury to the tissues.

The cercaria develops in a redia of well-marked characters (Fig. 117).
The redia measures about 1.0 mm. in length and has a mid-diameter of 0.22
mm. and a gross width of 0.35 mm. across the region of the locomotor feet.
A small powerful pharynx at the anterior end opens into the rhabdocoel gut
which fills the greater part of the body cavity, extending almost to the posterior
extremity. The germinal epithehum is at the posterior end. From this
layer the ova develop, which grow into cercariae. The first character of the
germ ball to become diflferentiated superficially is the oral sucker (see series
of stages in figure 114), Later the tail and the acetabulum become marked
off, and finally the oral hood.

At the posterior end a small, non-muscular, truncate bladder is situated.
It opens anteriad into two simple unbranched tubes. These can be traced
cephalad inside the intestinal ceca to the head of the worm. The cephalic
end of the excretory system is unique. Lateral to the pharynx, a triangular
channel-system is found. From the anterior angle a small capillary leads
forward to a single flame cell. From each of the other two angles a small
capillary leads back to a flame cell. This constitutes the trisolenate sys-
tem at the anterior terminus of the excretory tract. The tail excretory tube
is a single median structure and has no laterals or terminal outlet. This
fact necessitates a revision of the scheme proposed by Cort (1915:37), in
which this writer characterizes the excretory system of echinostome cercariae
as "opening on each side of the anterior part of the tail. " It seems from the
present investigation that the three flame cells in the anterior part of the
trunk may be a more reasonable criterion for distinguishing the excretory
system of this group. Further work on other forms must be done before this
can be definitely proposed.

Excretory granules fill the lateral excretory trunks from the pharynx
region as far caudad as the acetabulum.

The digestive system is simple. It consists of a long esophagus, with a
very small pharynx sphincter about in its middle, and two very long furcae,
extending to the sub-caudal region.

The genital cell masses are yet very immature. There are four cell masses
present, one on the upper right of the acetabulum (Fig. 130), the vagina; one^
behind the acetabulum (Fig. 131), the ovary, and two tandem masses in front
of the bladder (Fig. 120), the testes. In the vicinity of the ovary are num-
erous viteUine follicles, but they have not been found to follow any definite
pattern.

78 ILLINOIS BIOLOGICAL MONOGRAPHS [78

The nervous system of this species has been made the basis of the dis-
cussion on page 49, and needs no further consideration here.

The musculature is ahnost all parietal, except for the walls of the intestinal
tract. Parietal and splanchnic muscles are similar in structure. The former
consist of external transverse and internal longitudinal bundles, while the
latter consist of external longitudinal and internal transverse fibers (Figs.
118, 119). Each fiber can be traced to a myoblast, the central figure of which
is the large oval nucleus, with karyosome and radiating processes, so that
the whole figure appears stellate. There are several fibers originating from
each myoblast; they always nm along a single axis. The longitudinal mus-
cles of the tail are prominent (Fig. 133).

The body is filled with a parenchyma complex, consisting of undifferen-
tiated cells, connective tissue fibers, and cystogenous gland cells. In the tail
of an immature cercaria (Fig. 133), there is a partition of parenchyma cells,
separating the caudal excretory canals into right and left tubules. This
condition disappears as the animal matures, altho vestiges of these cells may
be found in the mature cercaria.

The cystogenous cells are differentiated parenchyma cells, filled with a
mucoid in the form of oval granules. In the ordinary cystogenous cell (Fig.
113), the granules are about l/i by 0.6/i in section. There is a central nucleus
to each of these cells, with poorly defined membrane separating it from the
cytoplasm. It is conspicuous because of its large number of chromatic gran-
ules, composed of elongate flecks. These flecks are also present in considerable
numbers thruout the cytoplasm; they are especially massed against the cell
walls. The glands are best developed in the middle of the body (Fig, 109,
sections hb and dd). Since the cystogenous glands are well developed, the
cyst wall is heavy (Fig. 115, A-C). In crawling over the surface of any object
the mature cercaria squeezes off the tail by a constriction of the posterior
transverse muscles. A final jerk of the tail frees it from the body. Immedi-
ately the cystogenous glands pour out a mucus aroimd the contracting worm,
so that at first an oval cyst is formed. Later, as it hardens, it assumes a more
spherical outline (Fig. 116). Thru this cyst membrane the excretory and
digestive systems of the body and the collar spines are readily distinguished.
The cysts are so well walled and so numerous that they suggest a considerable
period of wintering over.

Cercaria biflexa Faust 1917

Cercaria biflexa belongs to a type of echinostome cercariae distinguished
by a smooth body outline, a long powerful taU, blunt oral hood spines and a
reflexed excretory tube. The excretory system worked out by Looss (1894:
Fig. 191c) for Distomum echinatum approaches the system in this species to
some extent, but differs from it in many details.

The body of Cercaria biflexa is elongate ovoid, with a slight constriction
just behind the oral hood (Figs. 134, 135). Both the body and the tail are
extraordinarily muscular. The body measures 0.45 mm. to 0.5 mm. in length

79] UFE HISTORY OF T REM ATODES— FAUST 79

and 0.13 mm. to 0.15 mm. in width. The tail is at least as long as the body
or slightly longer. Its width is about 0.05 mm. at the base. The oral sucker
has a diameter of 55At and the ventral sucker, situated at the beginning of the
posterior third of the body, measures 65/* in diameter. Around the oral hood
is a circlet of collar spines, 42 in number, ovoid elongate, bluntly rounded at
both ends, with a length of 10/t to 15/1 and a thickness of 3/i.

The worm was found in Physa gyrina in November 1916, and in Planorhis
trivolvis in May 1917, in the neighborhood of Buckhouse Bridge, near
Fort Missoula, Montana.

The parthenita is a redia with a length measurement of 0.4 mm. and a
thickness of 0.088 mm. (Fig. 137). The locomotor feet are short, blunt pro-
cesses in the posterior third of the body, and have a gross span of 0.1 mm.
In contrast to the large gut-pouch of Cercaria trisolenata parthenitae, the
rediae of this species have short inconspicuous rhabdocoel guts, only 0.1 mm.
in length. One-third of this is occupied by the pharynx. The body wall
is covered with a thick integument, within which is a heavy muscular layer.
At the posterior end are a number of small spinous projections (Fig. 141).
The germinal epithelium also is at the posterior end. A noticeable feature
of the cleaving ova is their flattened condition (Fig. 141). Stages in matura-
tion and cleavage are seen in this figure and may be compared with similar
stages of maturation and development in C. trisolenata (Fig. 140.) The cer-
cariae, when mature, escape thru the birth-pore situated ventrolaterad.

A prominent excretory system is foimd in this cercaria (Fig. 135). The
vesicle is a cylindrical organ inflated posteriorly. It is not muscular to any
marked degree. Tubular cornua empty into the anterior end of the bladder.
As these cornua are traced forward lateral tributaries are found to empty
into them at regular intervals. In the region of the pharynx the tubes become
attenuated and bend twice upon themselves (Fig. 138) . The detailed descrip-
tion of this anterior end of the system of Cercaria biflexa is found in the section
on morphology (p. 40). It may be noted here that there are three flame cells
along the course of the ultimate tubule of the system, and that these seem
comparable to the three flame cells found in C. trisolenata. The excretory
tube in the tail is a single median tube for about two-fifths of the way distad,
at which point it forks and continues double the remainder of the way distad,
with numerous cross-anastomoses. It does not open to the outside either
on the sides or end.

The digestive system consists of an extremely long esophagus, extending
all the way to the acetabulum; furcae which end at the caudal end of the
animal; and salivary-mucin glands, developed to a very high degree. These
latter consist of an inner and an outer series of right and left groups (Fig. 134).
There are from fifty to sixty cells in each group, in oblong clusters, with a
common duct anterior to each series leading cephalad. The two ducts of each
side fuse to form a single lateral duct which leads into the oral pocket. These
glands are different from the majority of mucin glands in being differentiated

80 ILUNOIS BIOLOGICAL MONOGRAPHS ^

into inner and outer series. The condition is similar in part to that in Cer-
carta crenaia (Fig. 55), in which species there is also a double series of glands
on each side of the esophagus. But in this case the glands of the inner and
outer series are not different in structure and function as in C. crenata. Here,
too, the ducts are not composed of a bundle of separate ducts, as is found in
C. marcianae (La Rue, 1917:5), but consist of a single common duct for the
entire group of gland cells.

The genital system is much further developed in this species than in C.
trisolenata (Fig. 139). Behind the acetabulum is the ovary, from which a
uterus leads around the acetabulum, ending in a swollen vagina in the pre-
acetabular region. Only the transverse ducts of the vitelline system are
differentiated. Behind these are the two testes, unequal in size, one above
the other.

The encystment of Cercaria biflexa is similar to that of C. trisolenata in
that it depends on the secretion of mucoids from a large number of cystogenous
glands in the parenchyma. It differs, however, in the two species both as to time
and place of encystment. Cercaria trisolenata encysts only after it has escaped
from the liver tissues of the host. C. biflexa encysts within the host, immedi-
ately upon breaking thru the birth-pore of the redia. Thus a section of
Planorbis trivolvis liver tissue shows the interstices of the Hver ceca filled with
encysted cercariae, which continue to grow and differentiate within the pri-
mary host (Fig. 159).

Furcocercariae
Cercaria graciUima Faust 1917

Cercaria graciUima is a furcocercous cercaria more slender than those
previously described. This species, together with C. tuberistoma (p. 82),
constitute the second instance of furcocercous cercariae to be described for
North America, the first being C. douthiUi Cort (1915:50-52; Figs. 55-64).
In addition to the forked-tail character of these three species, they lack a
pharynx, and have paired salivary-mucin glands leading into the oral pocket,
composed of four or more cells to each group. The "eyelet" excretor>' ana-
stomosis, connecting the excretory system of the body and the tail is also a
common character.

Cercaria graciUima has an oblong cylindrical body (Fig. 142). The
branched portion of the tail is elongate lanceolate. The body length varies
from 0.13 mm. to 0.16 mm. and the diameter of the worm varies from 0.02
mm. to 0.03 mm. The unbranched portion of the tail is about 0.16 mm. long
and the caudal rami are of equal length. The former is 0.02 mm. to 0.03 mm.
in diameter and the ramus has a width of 0.01 mm. The trunk is characterized
further by the absence of a true oral disc, while in its place there is an invertible
sucker. A ventral sucker, 12fi in diameter, varies in location, according to
the movements of the animal, from the middle of the ventral side to a position
considerably farther forward. The cephalic region is ovately rounded when
the sucker is fully distended and is crowned by a cap of small spines. A

81] LIFE HISTORY OF TREMATODES— FAUST 81

feature of this cercaria, in common with that of C. douthitti, is the possession
of eye-spots (Figs. 144, 150). But the eye-spots of C. gracillima are the more
vestigial, for they have no pigment.

This species was found in the livers of Fhysa gyrina Say, collected from
the lower reaches of the Bitter Root River near Maclay Bridge, Buckhouse
Bridge, and the sloughs at the Roadhouse, near Fort Missoula, in the fall of
1916. In addition it was found in the livers of Lymnaea proxima Lea from
Rattlesnake Creek, Missoula. The infection in most cases was not exceed-
ingly heavy, except in the collection from the sloughs at the Roadhouse,
where thirty-three out of seventy-one individuals were infected, or 46.5 per
cent.

The cercariae develop in long cylindrical sporocysts, varying in length
from 0.25 mm. to 0.1 mm., but most frequently averaging about 0.5 mm.
(Figs. 146, 147). In diameter the sporocysts vary from 0.2 mm. to 0.4 mm.
The parthenita is a simple structure, non-muscular, depending on the daughter
cercariae for its movement. At one end (Fig. 147) is a non-muscular attach-
ment area; at the other end, merely a rounded non-differentiated cap. The
germinal epithehum is localized at the attachment end. From this mass the
daughter worms develop. Internal pressure from the developing larvae
increases the length and diameter of the parthenita. In development (Fig,
148), the ovoid germ ball first differentiates a tail portion; later the rami
appear. It is not until considerably later that the acetabulum is found. The
oral spines appear only when the larva is mature.

The movement of the cercaria is characteristic for furcocercariae. The
main movement consists in a very strenuous beating and lashing of the rami,
so that the head is pushed into the object with which it comes in contact.
In case the head is not forced into the object, the worm is set free by a back-
ward movement of the tail and the entire worm squirms around until it comes
in contact with another object, when the same boring movement is again
attempted. The oral end of the cercaria is much better adapted to this type
of invasion of the tissues to be infected than if it possessed an oral disc.

The excretory system of C. gracillima is embryologically a single paired
system for both body and tail. As development and differentiation of parts
progress the tubes in the posterior extremity of the trunk and the anterior
region of the tail fuse, to form a median bladder and the common tube of the
proximal region of the tail. There remains the bifurcated portion in the
laterals of the trunk and the rami of the tail, and in addition, the "eyelet
anastomosis." This eyelet structure has been observed by Looss (1896:172-
174; PL 15), m Cercaria vivax Sons, and by Cort (1915, Fig. 57) in C. douthitti.

The excretory system in the body consists of two lateral tubes that diverge
from the bladder and can be traced forward, together with dendritic tubules
and capillaries, the internal ones of which frequently form chiasmic anasto-
moses across the median plane of the body. Slightly posterior to the middle
of the body the lateral tube expands and opens into a pocket provided with

82 ILLINOIS BIOLOGICAL MONOGRAPHS [82

dlia (Fig. 145). These cilia come from a flame cell bordering on the lumen
of the lateral tube. A second pocket somewhat anterior is an atrium into which
many of the capillaries empty; it is filled with small excretory granules, in
this way acting as a secondary reservoir.

The digestive system of C. gracillima consists of an unbranched esophagus
without a pharynx sphincter, a pair of short degenerate furcae extending
posteriad beyond the acetabulum, and a ring of gland cells in the region of the
esophagus where the pharynx might be expected. Opening into the oral
atrium thru common bundles of ducts are the salivary-mucin glands (Fig. 144).
These glands are very large with vesicular nuclei. They are situated in the
posterior third of the body. In cross section the ducts are similar to those
described by Cort (1915, Figs. 59-62) for C. douthUti.

The nervous system has been discussed on page 54.

The genital cell masses in the cercaria are hermaphroditic (Fig. 149).
Anterior to the acetabulum are the vagina and the cirrus pouch buds, and
lateral, extending both anteriad and posteriad, are the viteUine foUicles. In
the posterior extremity is a conical germinal mass, from which are proliferated
anteriad a number of small testicular folMcles.

The general features of this fluke make it possible to refer it to the Schis-
tosomatidae.

Cercaria tuberistoma Faust 1917

This species of cercaria is shorter and much more muscular than C. gracil-
lima. The body is elongate ovoid, with the anterior end slightly constricted
and crowned with a pair of tuberosities (Fig. 155). The body length is about
0.2 mm. and the width 0.05 mm. to 0.06 mm. The tail measures about 0.32
mm. as a whole, equally divided into common portion and rami. There is
no oral suctorial disc, but instead the oral invertible proboscis. The acetabulum
measures 0.03 mm. in diameter.

The cercaria was secured from a single Ught infection of Physa gyrina
collected in the Bitter Root River at Corvallis, Montana, in October 1916.
Out of nineteen snails examined only one was infected. Only a few cercariae
were secured, and these were studied as Hve mounts. From this study the
excretory, digestive and general body features were worked out.

The cercaria develops in an elongate, dumb-bell-shaped sporocyst, spread-
ing out at one end to form an attachment disc (Figs. 157, 158). At the end
opposite the attachment organ the cercariae develop from the maturation
of the germinal epithehum. They escape thru a rent in the wall of the sporo-
cyst. Stages in development (Fig. 158, A-E) are similar to those described
for C. gracillima (Fig. 143). On the whole the embryos of this species are
stouter than those of C. gracillima.

The excretory system has the features common to all furcocercariae. The
bladder and the eyelet are muscular (Fig. 155). The lateral tubes are of
small diameter, with anterior and posterior tubules. No anastomoses take

83] UFE HISTORY OF TREMA TODES—FA UST 83

place in the cercariae of this species. The median tail tube receives six lateral
tributaries, the anteriormost of which is reflexed. The rami have each
an unbranched tubule.

The cephalic region is marked by a large invertible sucker, extending
thru the anterior third of the body. No intestinal ceca whatever have been
observed in this species. No glands surround the esophagus as a distinct
ring, altho the entire esophageal tube lining is glandular in nature. Four
small salivary-mucin glands are situated in the posterior third of the body
(Fig. 155). Their thick ducts empty into the oral cavity as heavy
bundles. The cells of this system are filled with closely aggregated, deeply
staining granules. The nucleus of the salivary-mucin gland cell is extremely
small.

This species possesses neither pigment eye nor eye-spot without pigment.

Encystment has not been observed in this species.

Cercaria tuberistoma is probably a schistosomatid larva.

84 ILLINOIS BIOLOGICAL MONOGRAPHS [84

PATHOLOGY

The infection in any case of internal parasitism suggests an inquiry as
to the effects of the parasite on the host. The injury on the human sub-
ject produced by trematode infections has been the subject of numerous
observations and records. Notable among these are the contributions of
Looss (1913) on Schistosoma haematobium, Katsurada (1914) on Schistosoma
japonicum, and Ward (1909) on Fasciolopsis spp. Again, the effect of tre-
matodes on their host has been the subject of considerable study in fish infec-
tion, on account of the economic importance of the problem. But -where the
special incentives to the problem have been lacking, very little study has been
made on the pathological significance of trematode infection.

The helminth parasite causes a two-fold injury to the host, mechanical
and chemical. The inclusion of parasites within the organs of the host is the
occasion for distension of the organs and consequent irritation; the piercing
of organs of the host by the armature of the worm, an actual mechanical,
injury. These injuries are accompanied by the formation of fibromata within
the organs and, usually, attempts to isolate the parasite by the secretion of a
cyst around it, as in schistosomiasis (Bovaird and Cecil, 1914:191). In the
ordinary infection a toxin is secreted by the parasite, and frequently an anti-
thrombin and a hemolysin are produced. Such injuries as these in higher
animals are diagnosed by the blood-picture, where excessive hemocytolysis
and eosinophilia are found.

The infected organs of the molluscan hosts of the Bitter Root Valley are
the liver ceca. Altho these Ue next to the testes, the worms have never been
found to invade these organs. Thomas (1883:114) found that the cercariae
of Fasciola hepatica live normally in the pulmonary chamber of the snail
Lymnaea trunculata. Cort (1915) found the infected organs of the Campelomas
were the gills, but in other species, the Hver tissues were the seat of the infec-
tion. The infected tissue of the Venezuelan snail, Planorhis guadelupensis,
is the testicle according to observations made by the writer.

The liver ceca consist of polygonal lymphocytoidal cells grouped around
the liunina of the ceca, with an epithelial Uning surrounding the ceca. Among
the ceca are large interstices filled with lymph. These intercecal spaces are
the places where the worms are first found, suggesting invasion thru the blood
stream. In light infections, the parthenitae lie here, absorbing the nourish-
ment from the surrounding liquid in which the worm is bathed. Ths only
mechanical injury up to the time of the activity of the cercariae is caused by
the agitation of the developing larvae encysted within the host. But in the
case of heavy infection, especially where the larva does not encyst within the
host, where it works its way out into the water, even a few worms may cause
considerable mechanical harm to the host.

In an examination of living material and sections of infected moUusk Uver
tissue, no infection was found to be so light that the host was unharmed. In

85] LIFE HISTORY OF TREMA TODES—FA UST 85

the Cercaria hiflexa infection of Physa gyrina (Fig. 159), where the cyst mem-
brane is moderately heavy, many ceca are uninjured, yet some betray the
marks of injury. One such injury is shown in the figure. In this case the
cells of the ceca have undergone only a little change. A comparison of this
condition with that of C. micropharynx infection in Lymnaea proxima (Fig.

160) and C. gracillima infection in Physa gyrina (Fig. 161), shows a compara-
tively small injury in the former tissue and a severe injury in the latter tis-
sues. Both the latter cases show tissue degeneration. The chemical change
in Lymnaea proxima is evinced by 1) fatty bodies that have accumulated in
some of the cells (a), showing as highly refractive inter-cellular inclusions;
2) large vacuoles in the cells (6), especially around the nuclei; 3) cytolysis and
karyolysis (c, d), including a sloughing of the tissues in the region of the lumina
of the ceca. The condition of C. gracillima infection in Physa gyrina (Fig.

161) pictures a further degeneration of the tissues. Fatty globules {b), are
common, usually accumulated as spherules within the wall. Vacuolization
{d) has progressed to an advanced stage. Cytolysis and karyolysis (a, c)
have gone so far that the outlines of the majority of the cells are indistinct
and no difference exists longer between the epitheUal and the lymphocytoidal
cells. An indefinite, irregular margin marks off the ceca from the interstices
in which the cercariae lie. A further change consists in the formation of
fibromata {e) and granulomata within the degenerating ceca. Finally the
epithehum surrounding the entire liver mass has been penetrated by sand
granules (/), and other foreign bodies have had access to the tissues.

In the infection of Planorbis irivolvis with C. trisolenata the mass of the
worms was about twice that of the Uver tissue infected. The tissue was so
distended with the parasites that a prick of the needle was sufficient to cause
the liver membrane to burst, upon which the rediae and cercariae fairly poured
out of the tissue.

The data on the effect of the trematode infection on the molluscan host
are significant. No infection is so light that mechanical and chemical injuries
are not inflicted. In the heavy infections such as are conmion to the moUusks
of the Bitter Root Valley, the injury is so heavy that it must alter appreciably
the Hfe of the host. The mechanical pressure tends to inhibit or increase the
functioning of the glandular organs and cramps the tissues within unusual
confines. The presence of foreign proteins in close association with the lymph
sinuses is sufficient to alter the vital economy of the host. The boring of the
worm destroys the tissues locally and in general irritates the mechanism,
exposing it to bacterial infection. The secretion of digestive juices by the
parasite, and of anti-thrombins and possibly specific poisons, upsets the
entire physiological equilibrium of the organism.

86 ILUNOIS BIOLOGICAL MONOGRAPHS [86

PROBLEMS PRESENTED

INTERRELATION OF TREMATODES

In working out new species of organisms, especially from new geographi-
cal areas, there are often physiological and morphological facts that are
of general significance in the light of previous studies. Relationship is the
ultimate problem for all workers in morphology. While light is shed on
phylogeny by the discovery of new species, it is futile to expect to found a
system of phylogeny on a single species. With these limitations in mind the
writer presents some of the more important questions that arise from the
study of the trematodes of the mollusks of the Bitter Root Valley.

In the early days cercariae and rediae were considered as different groups
of the animal kingdom, and it was not until the life-history studies of Leuckart,
La Valette (1855), and Ercolani (1881, 1882) had been pubUshed that the
genetic relationships of cercariae and parthenitae were established. The
germ layers of all generations of trematodes have a similar origin, and impor-
tant structures of the group present the same problem.

Certain investigators of recent time have come to regard the trematodes
as a polyphyletic group. Their conclusion has resulted, perhaps, from their
lack of study and consequent inability to recognize the fimdamental resem-
blance of the genital, excretory and nervous systems of the various sub-divi-
sions of the group, especially dming the developmental stages.

From more convincing observations Odhner (1907) has concluded that the
Monostomata are poU'phyletic. He has noted among certain monostomes a
structure comparable to the pharyngeal pockets of amphistomes, and among
others a primitive acetabulum (1911). In a study of monostome cercariae
from the Bitter Root Valley, the similarity of the nervous system and genital
cell masses of Cercaria peUucida and of those systems in Gastrothylax gre-
garius Looss has been investigated.

Both Cercaria peUucida and Gastrothylax gregarius show paired brain
ganglia closely set together with only slight constriction of the dorsal com-
missure. In both species the nerve cells lie superficially upon the central
nerve gangUon masses. IVIoreover, relatively large posterior ventral and
smaller lateral and dorsal tnmks, together with their respective positions,
constitute a series of similarities not to be overlooked. The lack of pharyn-
gealis, palatinus, and dorsolateral commissure (Figs. 123, 124) serves to
show that the nerve complex of the monostome larva Cercaria pdlucida is
not t>'pically distomate. Its nerve structures are much more readily referred
to the Gastrothylax type.

In the second place certain features of the genitalia of Cercaria peUucida
and Gastrothylax suggest a common ancestry. The median ovar>' in the
subcaudal region; the paired testes lateral to the ovary; the dendritic vitel-
laria, located in two series, and, finally, the parallel course of the uterus and

87] LIFE HISTOR Y OF TREMA TODES—FA UST 87

the vas efferens to the genital pore far cephalad — ^all of these show in common
a genital system quite distinct from the usual distome types.

The similarity of the nervous and genital complexes of larval monostomes,
such as Cercaria pellucida and C. konadensis, and the amphistome, Gastro-
thylax gregarius, suggest a common origin of certain monostomes and amphi-
stomes.

Among adult distomes there is great variety of structure, yet only in one
family, the Schistosomatidae, has the nervous system been fundamentally
altered. The structures of the two furcocercous larvae, Cercaria gracilUma
and C. tuberistoma, demonstrate their relationship to the Schistosomatidae.
The reasons for this beUef are these:

The characters which distinguish the apharyngeal furcocercous cercariae
are as follows: 1) a forked tail (larval character only); 2) paired groups of
salivary-mucin glands (larval); 3) absence of an oral suctorial disc, and in
its place 4) an invertible suctorial proboscis; 5) an apharyngeal esophagus, pro-
vided with glands in the region usually occupied by a pharynx. The nervous
system, more deeply seated, is modified by the degeneration of the posterior
laterales during early embryonic development, and the fusion of the posterior
dorsales with the posterior ventrales about one-third the body length back
from !the anterior end (Fig. 150). All of these, except the forked tail and
the saUvary-mucin glands, are both larval and adult characters. In addi-
tion, the larva of Cercaria gracilUma has several testicular follicles proliferated
from the testes-mass at the posterior end of the body.

Certain of the structures of this group also characterize the larvae of other
groups of trematodes. For example, Cercaria cristata La Val. (1855:23; Taf.
II, Fig. K), has a bifid tail and apparently lacks a pharynx, but the fact that
it lacks an acetabulum probably separates it from the distome f urcocercariae.
Among the Gorgorderinae there are apharyngeal cercariae with several testes.
However, Ssinitzin (1905:46-51; Taf. I, II) has shown for four Gorgordera
species, that the cercariae are characterized in common by 1) a stylet, 2)
salivary glands only in the cephalic region of the body, 3) a large glandular
excretory vesicle, almost filling the posterior third of the body, and 4) a dis-
proportionately large tail, showing the cystocercous relation of the larvae of
the group. Moreover, the nervous system of the Gorgorderinae is typically
distomate (Zailer 1914:386).

It may be stated with considerable probabihty that all of the fundamental
organs of the f urcocercariae, namely, the apharyngeal esophagus, the multiple
testes, and the uniquely modified nervous system, are found in only one
family, the Schistosomatidae. All described Schistosomatidae are charac-
terized by the absence of a true oral suctorial disc and by the presence of an
invertible oral suctorial pouch. They have no pharynx, but in its stead
glands that line the wall of the esophagus. Looss has described the modified
nervous system of the family in his study of Schistosoma haematobium (1895:

88 ILLINOIS BIOLOGICAL MONOGRAPHS [88

60-68; Taf. II, Fig. 18). It corresponds in detail to the system in Cercaria
gracilUma previously described.

Coupled with these morphological likenesses are the experimental data
of Leiper (1915, 1916), Miyuri and Suzuki (1914), and Iturbe and Gonzalez
(1917) on Schistosoma life-histories. Leiper has found that the three
schistosome species known to infect man, Schistosoma haematobium, S. man-
soni, and S. japonicum, give rise to miracidia which have a certain attraction
for certain snails in the districts infected. Within the tissues of these snails
the miracidia metamorphose into sporocysts, and the second generation sporo-
cysts give rise internally to bifid cercariae with a ventral sucker but without
a true pharynx. Furthermore, these cercariae introduced thru the skin of
experimental animals, mice and monkeys, give rise to typical unisexual adult
schistosomes.

This two-fold evidence favors the view that the furcocercous apharyngeal
distome cercariae, including Cercaria gracillima and C. tuberistoma of the Bitter
Root fauna, develop, under proper conditions, into adult schistosomes. One
character figured by Leiper for all of his apharyngeal bifid cercariae, yet not
used by him as a diagnostic character, is the presence of saUvary-mucin glands.
On the other hand, one character used by Leiper for cercariae of the group,
namely, the absence of a pigment eye, holds for his three species of schistosome
larvae, but does not hold for Cercaria ocellata La Val., C. douthitti Cort, or C.
gracillima. It has been shown that the eye-spot may be present without
pigment (C gracillima). Likewise the failure of Looss to mention an eye-
spot for C. vivax Sons. (1896:216-223; Figs. 172-174) does not necessarily
imply the absence of pigmentless eye-spots in that species.

The relationship of the forked tail apharyngeal distome cercariae will
be made much clearer by a consideration of the genital organs. The adult Schis-
tosomas into which the larvae of Leiper develop are characterized by a relatively
small number of testicular folUcles, 4 to 5 for S. haematobium, 6 to 8 for .5.
japonicum, and 8 for S. mansoni. On the other hand, the testicle prolifera-
tion in Cercaria gracillima (Fig. 149) shows twenty-four or twenty-five fol-
licles already differentiated from a posterior germ mass. The large number
of testicular follicles has been found to be characteristic of the adult Schisto-
somatidae of the genera Bilharziella (Kowalewski,1895; 1896), Gigantobil-
harzia (Odhner, 1912), and Ornithobilharzia (Odhner, 1912). None of these
genera and in fact no Schistosomatidae have been reported from North
America.

From these considerations it seems probable that Cercaria gracillima is
the larva of a schistosome genus, such as Bilharziella, Ornithobilharzia or
Gigantobilharzia, all of which are bird parasites.

Since the germinal masses of Cercaria gracillima are hermaphroditic, and
any marked differentiation of the organs does not take place while the larva
is outside the definitive host, differentiation of sex in Schistosomatidae takes
place in these species comparatively late in their metamorphosis. This view

89] LIFE HISTORY OF TREMA TODES—FA UST 89

is in keeping with the studies of Odhner (1912), who points out the fundamen-
tal morphological relationship of the hermaphroditic species Liolope and
Haplometra to the unisexual BUharziella, Gigantobilharzia, Omithobilharzia,
and Schistosoma.

The discussion leads to the conclusion that the furcocercous larvae possess
in common 1) a bifid tail, 2) a ventral sucker, 3) an oral suctorial pouch which
can be inverted, 4) a glandular esophagus without sphincter muscles, 5)
paired groups of salivary-mucin glands, four or more to the group, 6) multiple
testes, and 7) a specifically modified nervous system. In the light of present
knowledge all of these species fall within the limits of the family Schistoso-
matidae.

Of all the known groups of trematodes the Holostomata have been the
group of least genetic study and most erroneous interpretation. On account
of their large size the adult holostomes have been known for many years and
dozens of species have been described. Nothing, however, has been known
of the parthenitae and their development. Without sufficient evidence
Brandes (1891:573) has interpreted the sketch of a miracidium of Strigea
(Holostomum) cornucopiae Molin (von Linstow,1877, Fig.30) as a metamorphos-
ing tetracotyle. In other words, Brandes concludes that the holostome has
a direct development without the intercalation of a parthenogenetic cycle.
Ercolani (1881:284-290; Tav. II, Figs. 16-22) has worked out the life-history
of Strigea erratica (Duj.) from the tetracotyle to the adult form, by infecting
Anas sp. with Tetracotyle typica cysts from the mollusk Planorhis corneus.
Altho Ercolani found a tetracotyle in a sporocyst (Tav. II, Fig. 18), he inter-
preted it as the invasion of the tetracotyle into the sporocyst of Cercaria
ocellata La. Ya\. Ssinitzin (1910:22, 23) has justly criticized Brandes' con-
clusion of the monogenetic development of holostomes, but in lieu of true
holostome evidence in support of the digenetic view he has substituted evidence
from Cercaria plicata, a peculiar distome larva which he has found to bear
certain relationships to the holostomes.

It has been shown in this paper (p. 16) that there are parthenogenetic
cycles in Cercaria flabelliformis, a typical holostome, and that several genera-
tions of rediae are intercalated between the miracidium and the tetracotyle.
Thus, there is conclusive proof that the holostome has an alternation of genera-
tions, hermaphroditic and parthenogenetic, similar in kind to such alternation
in other Digenea.

In spite of the strangely modified suctorial apparatus and posterior genital
organs of the holostomes, there seem to be good grounds for beUeving that
they originated from the distomes. They have an acetabulum, and frequently
the muscular rudiment of a genital pore just in front of the acetabulum (Fig.
52). On the other hand it is very doubtful if the lappets (Zapfenlappen of
Brandes 1892, Taf. 41, Figs. 5-15) bear any homology to the genital pore
rudiment. It has been shown, in fact, that the lateral lappets in Cercaria
flabelliformis arise from a pair of oval suctorial grooves (Fig. 41), and that in

90 ILLINOIS BIOLOGICAL MONOGRAPHS pO

Tetracotyle pipientis (Fig. 47), where these grooves remain rudimentary, no
I ateral lappets develop.

As von Linstow (1877:189) pointed out, species characters in Strigea
(Holostomum) have been treated very superficially, since the group members
are not readily distinguished by external markings and the internal anatomy
is difficult to interpret. Yet the writer has found that even in the early
larva the points of differentiation are well marked. The parthenogenetic
egg of the holostome developing into the cercaria is at the time of matura-
tion structurally different from the ova developing into a redia. Thus the
actual phylogenetic history of the group is hidden by its precocity and the
developmental stages of the holostome show only in telescopic fashion the
actual ancestral history.

Extraordinary nerve modification in the holostomes (Fig. 53) is related
directly to the modification of the muscle complex. This modification con-
sists usually in the degeneration of the posterior dorsales and laterales, and
a relative increase in size and importance of the posterior ventrales. The
other systems of the holostomes, especially the genital and excretory organs,
are equally highly modified and equally well formed in the larva. Ssinitzin
(1910, 1911) has suggested that the change in the genital pore from the pre-
acetabular position to the posterior ventral extremity has come about thru
the formation of a new opening rather than thru a shifting of the old pre-
acetabular pore. The original pore is still present in the larvae, altho in most
cases there is no clue to its former connection or function. The extent of
these changes indicates a long period of gradual adjustment to a modifying
environment.

The study of the cercariae of the various groups of the Digenea not only
serves to supplement relationship studies in adult hermaphroditic generations
of trematodes, but also brings out structural relationships very considerably
if not entirely hidden in the adult. The most constant of all the systems in
the group Digenea is the nervous system. Any marked modification from
the characteristic distomate type is indicative of a considerable period of
divergent growth.

The fundamental systems of the hermaphroditic generation of the tre-
matode are deep seated; they are well formed in the cercaria, and little signi-
ficant differentiation takes place during metamorphosis.

RELATION OF TREMATODES TO OTHER GROUPS

Among the early systematists Trematoda were classified with the Hiru-
dinea because of the common superficial resemblance of the two groups.
Even as late as 1871 Schmarda separated the Trematoda from the Turbellaria
and Cestoda, and placed them with the Hirudinea in the Cotylidea. Balfour
(1881:316, 317) considered a direct relationship of all Metazoa above Coel-
enterata entirely unsatisfactory and conceived the idea of referring them
all back to the trochophore larva which possessed radial symmetry. In his

91] LIFE HISTOR Y OF TREMA TODES—FA UST 91

monograph on Amphistomum subclavatum, Looss (1892:156, 157) com-
pared the proHferation of the germ-balls from the body wall of the parthenita
to the production of eggs and spermatozoa in the marine polychaetes, and
suggested that other embryonic structures of the trematode were comparable
to annelid structures, so that they might be considered of phylogenetic value.
Recently Ssinitzin (1911:86) has spoken of the resemblance of the Trematoda
to Arthropoda and Trochelminthes, in view of the absence of any ciliary integ-
ument, in place of which, he says, the cuticula and the external skeleton
develop.

During this time the theory of the common descent of the Trematoda,
Cestoda and Turbellaria has been gaining ground, not because they are all
"flatworms, " as Ssinitzin insists, but on the homologies of the genital, excretory
and nervous systems. The observations of Leuckart (1886:140), Schulze
(1853:178-195), and Schneider (1864:590-597) all support this view, while
Leuckart even saw the analogy between the gutless sporocyst and the Acoela.
Lang (1884:669) showed that the nervous system of the Trematoda and
Turbellaria was homologous.

With the work of Haswell on Temnocephala (1888) the close affinities
of the Trematoda and the Turbellaria became evident. In this group the
excretory system, the three anterior and posterior nerve trunks, the anterior
mouth, and the dorsal pigment eyes — all these bridged the way for the ac-
ceptance of the thesis that the Trematoda and the Turbellaria have a common
ancestry.

The study of the parthenogenetic generations of the Digenea, to which
this paper is devoted, stands in support of this thesis and contributes the
following facts towards its further acceptance.

1. The body cavity of the hermaphroditic generations of trematodes and
of Turbellaria is filled with differentiated mesenchyme and connective tissue.
In the parthenitae the parenchyma is confined to the body wall because it is
less diJGferentiated.

2. Both Trematoda and Turbellaria are typically flat, with a pronounced
bilateral symmetry. The cylindrical appearance of the parthenitae is a
secondary modification due to parasitism.

3. The epidermis of Trematoda and Turbellaria consists of a single layer
of cells. In the sporocyst larva, the miracidium, and in the Turbellaria, the
epithelial layer is ciliated. In the rediae and in the cercariae the layer is
usually sloughed off before maturity and in its place the basement membrane of
mesodermal origin, serves as the integument.

4. The nervous system of the Monogenea, the Digenea, and the Turbellaria
is reducible to a common type. Two brain gangha with a transverse commis-
sure, three anterior pairs of nerve trunks, and three anterior pairs of nerve
trunks — these are common to all three groups. Moreover, the pigment eye-
spots of the Turbellaria, Monogenea, and Digenea are not only homologous,
but practically identical in detail (Hesse 1897; and page 52 this paper). In

92 ILLINOIS BIOLOGICAL MONOGRAPHS [92

each case one or more ganglion cells fill the optic cup. In each it can be
traced to the brain center. Parasitism has caused the pigment eye to degen-
erate in most adult Digenea. Even in the cercariae it is pigmented only in
certain species; other species have lost all traces of pigment, but the optic
nerve is still present and can be traced to the brain center. In many cases
it has been lost, even in the cercariae. Eye-spots are common in miracidia,
but are lost on metamorphosis into the sporocyst. There are no records of
eyes in rediae.

5. The digestive tract of the cercariae and the adult hermaphroditic genera-
tions of trematodes is usually triclad. In the redia the gut is rhabdocoel;
there is a pharynx and saUvary glands have been described (Ssinitzin, 1911,
and pp. 63, this paper). In the miracidium, there is an indication of a
rhabdocoel gut and salivary glands (Looss, 1892; Miyuri and Suzuki, 1914),
altho these are usually lost in the adult. In the Turbellaria the gut is triclad,
polyclad, rhabdocoel or acoel. The pharynx is ordinarily present and salivary
glands are common.

6. The excretory system in the two groups is at first a single pair of pro-
tonephridia. This condition is found in miracidia, rediae, cercariae and Tur-
bellaria alike. The capillaries, whether in the larva or adult, end in flame
cells.

7. The genital system was one of the first in which investigators recog-
nized the relationship between the Trematoda and the Turbellaria. The
hermaphroditic condition in the hermaphroditic generation of the Trematoda is
strikingly similar to that of the Turbellaria, with the common genital atrium
in all groups except Acoela. Parthenogenesis in parthenitae is the result
of the great change in environment of these cycles.

Thus the main trend of investigation has come to support the common
origin of the Trematoda and the Turbellaria.

LIFE CYCLE OF THE DIGENETIC TREMATODES

The life-history of the trematode of the order Digenea consists not in an
alternation of sexual and asexual generations, but rather of successive sexual
generations which are parthenogenetic and hermaphroditic.

A problem which has arisen in connection with the genitaUa of the Digenea
is the significance of Laurer's canal. Looss (1893a) considers it homologous
to the uterus of Cestoda, while Goto (1893) beHeves it to be the homolog of
the blind vagina of AmphiUna and the genito-intestinal canal of Monogenea.
According to Liihe (1909) a Laurer's canal is present in Monostomes, and in
some groups of the distomes, including Plagiorchiidae and Echinostomidae.
It has not been recorded for holostomes or Schistosomatidae. Except for the
Echinostomid cercariae, a Laurer's canal has been found in all cercariae of
the groups studied by the writer, where the adult trematode has the canal.
Absence of the canal in Echinostomid cercariae can be explained on the
basis of late development of the genital organs in this family. On the other

93 J LIFE HISTOR Y OF TREMA TODES—FA UST 93

hand, no Laurer's canal has been found in the groups where no canal is present
in the adult. Students of cercariae have not as a rule recorded the canal
in trematode larvae. Ssinitzin (1905, Figs. 62, 67, 74) has found it in the three
xiphidiocercariae, Cercaria gibba de Fil., C. prima, and C. secunda. The
constant development of this organ in the several groups described in this
paper shows that the canal originally had an important place in the genital
processes of the Digenea.

The pronounced difference in structure between parthenogenetic ova which
develop into rediae and those which develop into cercariae has been discussed
(p. 18). This difference has been found to bear no relation to the phenomenon
of maturation, since the chromosome count in the mature cells is the same,
whether redia or cercaria is to be produced. In fact, it seems probable that
the differentiation occurs before maturation. It is significant that the ova
which develop into redia are comparatively simple while the ova which develop
into cercariae are extremely complex. In this connection it has been observed
that embryos developing from germ-balls produced from ova free in the
body cavity produce daughter rediae. The maturing ova from the germinal
epithelium lodged in the body wall of the parthenita develop either into rediae
or cercariae.

In his experiments on planarians Child (1915) has shown that starvation
and fragmentation (fission) secure a rejuvenescence for the individual. The
less differentiated individual is on the whole the younger one. From the
present study on the life-history of trematodes there is justification for the
belief that the undifferentiated eggs produce daughter parthenitae because
they are simple, i.e., yoimger, while the more highly differentiated eggs grow
into cercariae because they are physiologically old. Interpreted in this light,
the parthenitic individuals of the Digenea are physiologically younger than the
cercariae and the adult hermaphroditic forms because their structure is
simpler. They have sacrificed complexity of structure to meet the needs of
the parasitic life, and in so doing have become remarkably rejuvenated. In
two species, Cercaria diaphana and C. micropharynx extreme simplicity has
been assumed in the sporocyst, for the germ-balls develop from any cell of
the body wall.

The writer believes that the abihty of the parthenita to reproduce daughter
rediae or sporocysts for two or more generations rests on the simplicity of the
ovum and the relative simplicity of the parthenita, especially as regards the
undifferentiated mesoderm cells. If this rejuvenation can be continued
indefinitely, the parthenogenetic generations can also continue indefinitely
without the intercalation of the hermaphroditic cycle.

Child (1915:407) has stated that "in many cases parthenogenetic eggs
are apparently less highly differentiated morphologically, and younger phy-
siologically, than zygogenic eggs of the same species." The present study
makes it necessary to add that in cases where the parthenogenetic eggs may
develop into parthenitae or cercariae, the eggs which develop into the former

94 ILLINOIS BIOLOGICAL MONOGRAPHS [94

individuals are apparently less highly differentiated morphologically and
younger physiologically than those which develop into cercariae.

Finally the present study causes the writer to support the \'iew that the
hermaphroditic phase of the life cycle of the Digenea is more closely
related to the ancestral group than the parthenita, and that the simplicity of
the parthenita has been assumed secondarily. This conclusion is based on
the evidence that the original type was a highly complex Platyhelminth with
ciliary integimient and eye-spots, characters found only in the miracidium.
The modification of the parthenita has come about as the direct result of
parasitism. It has lost its mesenchymatous matrix, its excretory tract has
been extraordinarily modified, and its germ cells have become uniquely sim-
ple. The nervous system of the redia has been simplified while the sporocySt
lacks a nervous system entirely. In the sporocyst even the muscle cells have
remained undifferentiated. Thus complexity in the hermaphroditic genera-
tion of Digenea is an index of the unmodified condition of the group most
early related to the prototype.

SUMMARY

1. Trematode infection of mollusks of the Bitter Root Valley, Montana,
is heavy.

2. The history of the germ cells of the sporoc}'^st and redia show them to
arise parthenogenetically.

3. Parthenitae and adult hermaphoditic trematodes are comparable in-
dividuals: likewise their germ cells can be referred to a common type of ger-
minal epithehum.

4. The integimient of trematodes is mesodermal in origin.

5. The fundamental systems of the adult hermaphroditic trematode are
well developed in the cercaria.

6. The excretory, genital and nervous systems of the cercaria may be used
to show the natural relationships of the larvae.

7. Holostomes, like dis tomes, monostomes and amphis tomes, have an al-
ternation of hermaphroditic and parthenogenetic generations.

8. Holostomes are probably of distome origin.

9. Parthenitae are well adapted to their parasitic life because their struc-
ture is simple, in consequence of which they have become physiologically
young.

95] LIFE HISTORY OF TREMATODES— FAUST 95

SPECIES DESCRIBED IN THIS PAPER.

MONOSTOMATA

Cercaria pellucida Faust 1917
Cer carta konadensis Faust 1917

HOLOSTOMATA

Cercaria flabelliformis Faust 1917
Tetracotyle pipientis nov. spec.
Cercaria ptychockeilus Faust 1917

DiSTOMATA

Xiphidiocercariae

Cercaria crenata Faust 1917
Cercaria glandulosa Faust 1917
Cercaria diaphana Faust 1917
Cercaria dendritica Faust 1917
Cercaria micropharynx Faust 1917
Cercaria racemosa Faust 1917

Echinostome Cercariae

Cercaria trisolenata Faust 1917
Cercaria biflexa Faust 1917

Furcocercariae
Cercaria gracillima Faust 1917
Cercaria tuberistoma Faust 1917

96 ILUNOIS BIOLOGICAL MONOGRAPHS [96

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102

ILLINOIS BIOLOGICAL MONGRAPHS

[102

EXPLANATION OF PLATES
Abbreviations

anterior dorsalis nerve

nerrve ending

anterior lateralis nerve

nervus palatinus

anterior sensory field

nph

pharyngealis nerve

anterior ventralis nerve

subesophageal commissure

b, be

genital atrium

nerve trunk

bursa glands

ovum

cerebral ganglion

oviduct

c, ce

cecum

oral nerve ring

caudal pocket

optic nerve cell

ceg

cercaria germ-ball

ope

optic cup

caudal gland cells

opn

optic nerve

cirrus pouch

oral sucker

collar spines

oot3^e

d.dl

salivary gland duct

ovary

dorsal commissure

phar>-nx

die

dorsolateral commissure

parenchyma

profundus of dorsalis nerve

polar body

superficialis of dorsalis nerve

preacetabular commissure

epithelium

posterior dorsalis nerve

ectoderm

preoral sense endings

excretory granules

primitive genital pore

evertible prepharynx

Pgl

locomotor pocket glands

excretory pore

posterior lateralis nerve

esophagus

postacetabular commissure

excretory tube

posterior ventralis nerve

excretory vesicle

pvc

postero-ventrolateraJis commissure

excretory tubule

pvi

postero-ventral intermedius nerve

flame cell

rhabdocoel gut

genital pore, birth pore

ramus muscularis of the lateralis nerve

germ-ball

ramus palpalis of the lateralis nerve

gle

cystogenous cell

salivary gland cell

intermedius nerve

acetabular spine

igl

digestive gland

stylet

longitudinal muscle cell

basement membrane

Laurer's canal

te, t],2 testis

lateral eye

transverse muscle fiber

localized germinal epithelium

uterus

posterior locomotor pocket

vagina

lateral suctorial groove

vas deferens

myoblast

vas ef ferens

median eye-spot

vitelline follicles

musculus preoralis

vitelline duct

n.ne

nerve cell

acetabulum

The lines in figures 6, 26, 51, 146, 147 have a value of 0.5mm; in figures 5, 7, 13-17, 19-20,
27-29, 31-34, 36, 37, 44-46,54, 56, 57, 61, 68-75, 77, 82, 83, 89, 91,92,97-99, 101, 102, 104, 107,
108, 111-113, 118, 119, 121-133, 136, 138, 140, 141, 145, 150-154, a value of 0.01 mm; in all
other figures, a value of 0.05 mm.

103] UFE HISTORY OF TREMATODES— FAUST 103

PLATE I

104 ILUNOIS BIOLOGICAL MONOGRAPHS (104

DESCRIPTION OF PLATE

Figs. 1-3. — Cercaria pellucida; sketches of progressive stages of pigmentation; dorsal view,

showing two lateral eye-sp>ots and one median spot. X 100.
Fig. 4. — Cercaria pdlucida; dorsal view, somewhat contracted. X 100.
Fig. 5. — Cercaria pdlucida; anterior tip, figuring details of pigmentation and contents of the

excretory tube. X 330.
Fig. 6. — Cercaria pellucida; redia,^characteriz€d by extensive rhabdocoel gut and spinous

prepharynx. X 34.
Fig. 7. — Cercaria pellucida; detail of the spinous prephar^Tix of the redia. X 540.
Fig. 8. — Cercaria pdlucida; young redia; precocious development of the cercariae before the

redia is mature. X 38.
Figs. 9-11. — Cercaria pellucida; three stages in encystment. X 38.
Fig. 12. — Young Cercaria pdlucida; origin of posterior locomotor pockets within the caudal

pocket. X 170.
Fig. 13. — Cercaria pellucida; transverse section thru the middle of the body. X 330.
Fig. 14. — Cercaria pdlucida; detail of cystogenous gland cells in the region of the lateral eye-

spot. X 330.
Fig. 15.— Cercaria pdlucida; contracted excretory bladder and posterior locomotor pockets.

X 238.
Figs. 16, 17. — Cercaria pellucida; details of the posterior locomotor pocket; Fig. 16, con-
tracted; Fig. 17, relaxed; xx, retractor muscles; yy, reflexor muscles. X 540.
Fig. 18. — The genitalia of Cercaria pdlucida; r^ons of ootype and metraterm. X 238.
Fig. 19. — Cercaria pellucida; transverse section thru tail, indicating arrangement of ordinary

parenchyma cells. X 540.
Fig. 19a. — Cercaria pdlucida; oblique section thru tail, indicating arrangement of muscle

fibers. X 540.

ILLINOIS BIOLOGICAL MONOGRAPHS

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LIFE HISTORY OF TREMATODES

PLATE I

1051 UFE HISTORY OF TREMATODES— FAUST 105

PLATE II

105 ILLINOIS BIOLOGICAL MONOGRAPHS [106

DESCRIPTION OF PLATE

Fig. 20. — Cercaria pellucida; sagittal section thru pharynx and gut of redia, with prepharynx

organ retracted. X 330.
Fig. 21. — Cercaria pellucida; transverse section thru body in region of posterior locomotor

pocket glands. X 170.
Fig. 22. — Cercaria pellucida; optical view of the proliferation of the germ-balls from the

posterior germinal epithelium of the redia. X 330.
Fig. 23. — Cercaria pellucida; central nervous system, typical for the trioculate species of

monostome cercariae. X 330.
Fig. 24. — ^Yoimg Cercaria pellucida; oblique section thru ganglion mass, sho';nng connection

of eye-spots with brain center. X 330.
Fig. 25. — Cercaria konadensis; dorsal view. X 105.
Fig. 26. — Redia of Cercaria konadensis. X 34.

Fig. 27. — Cercaria konadensis; detail of paired group of caudal gland cells. X 540.
Fig. 28. — Cercaria konadensis; genital cell masses in region of ootype. X 540.
Fig. 29. — Cercaria konadensis; detail of excretory bladder and posterior locomotor pockets.

X 238.
Fig. 30. — Cercaria konadensis; optical view of the germinal rachis of the redia. X 330.
Fig. 31. — Cercaria konadensis; sagittal section thru aspinose prepharynx of the redia. X 330.
Fig. 32. — Mature Cercaria urbanensis Cort; transverse section thru tail, showing caudal gland

cells. X 330.
Figs. 33, 34. — Cercaria urbanensis; stages in differentiation of caudal gland cells from ordinary

parenchyma cells. X 330.
Fig. 35. — Cercaria urbanensis; detail of excretor>' vesicle and posterior locomotor pockets.

X 238.
Fig. 36. — Early germ-balls of Cercar /a «rJa»e«5J5; oblique section thru brain mass and lateral

eye-spot, showing ectodermal origin of pigment cup, and connection with optic cells

of brain. X 730.
Fig. 37. — Oblique longitudinal section thru Cercaria pellucida, showing detail of nerve

endings. X 730.

ILLINOIS BIOLOGICAL MONOGRAPHS

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FAUST

LIFE HISTORY OF TREMATODES

PLATE II

[107 LIFE HISTORY OF TREMATODES— FAUST 107

PLATE III

108 ILUNOIS BIOLOGICAL MONOGRAPHS [108

DESCRIPTION OF PLATE

Fig. 38. — Cercaria fldbdliformis; ventral view of worm freed from cyst; U, lateral lappets

X 80.
Fig. 39. — Cercaria flabelliformis; dorsal view, giving details of the excretory system and

genitalia. X 80.
Fig. 40. — Cercaria flabelliformis; lateral view, showing suctorial cup in anterior portion of

worm; U, lateral lappets. X 80.
Fig. 41. — Immature Cercaria flabelliformis within cj'st. X 54.
Fig. 42. — Cercaria flabelliformis; yoimg redia, detailing the excretory chaimels in the worm.

X 54.
Fig. 43. — Cercaria flabelliformis; redia showing paired salivary glands emptying into the

oral pocket. X 54.
Fig. 44. — Cercaria flabelliformis; mid-frontal section thru young daughter redia in region of

germinal cell maturation. X 330.
Fig. 45. — Cercaria flabelliformis; median frontal section thru yoimg daughter redia, showing

proliferation of germinal epithelium at posterior end of gut. X 330.
Fig. 46 a-m. — Cercaria flabelliformis rediae; matiu-ation of parthenogenetic ova; A, resting

cell; B, C, formation of spireme; D, division of spireme skein into eight chromosomes; E.

P, G, longitudinal splitting of chromosomes at equatorial plate; H, mitosis, with forma.

tion of polar body and preparation of ovum for second mitosis; /, polar body almost

constricted off, chromosome b excentric; /, ovum preparing for second division, polar

body also dividing; K, cell cleavage, with precocious chromosomes bi, b2 excentric;

L, first cleavage of a cercaria-ov\mi, with polar body degenerating; M, metaphase of a

somatic cell in process of division. X 1620.

ILLINOIS BIOLOGICAL MONOGRAPHS

VOLUMES

FAUST

LIFE HISTORY OF TREMATODES

1091 LIFE HISTORY OF T REM ATODES— FAUST 109

PLATE IV

no ILLINOIS BIOLOGICAL MONOGRAPHS [110

DESCRIPTION OF PLATE

Fig. 47. — Tetracotyle pipientis; ventral view, showing digestive tract and genital system.

X 105.
Fig. 48. — Tetracotyle pipientis; diagram of the excretory system, with excretory granular

inclusions. X 105.
Fig. 49. — Cercaria ptychocheilus; ventral view, including digestive, excretory and genital

systems. X 105.
Fig. 50. — Cercaria ptychocheilus; sketch of encysted worm. X 25.

Fig. 51. — Cercaria ptychocheilus; sketch of ruptured cyst with attachment annulus. X 25.
Fig. 52. — Cercaria ptychocheilus; detail of genital system. X 165.
Fig. 53. — Cercaria ptychocheilus; nervous system. X 330.

Fig. 54. — Cercaria ptychocheilus; transverse section thru middle of body. X 540.
Fig. 55. — Cercaria crenata; dorsal view. X 170.

Figs. 56, 57. — Cercaria crenata; ventral and lateral views of stylet. X 540.
Fig. 58. — Cercaria crenata; sporocyst. X 54.
Fig. 59. — Cercaria crenata; detail of genitalia. X 170.
Fig. 60. — Cercaria glandulosa; ventral view. X 370.
Fig. 61. — Cercaria glandulosa; ventral view of stylet. X 370.
Fig. 62. — Cercaria glandulosa; salivary and cystogenous glands. X 75.
Fig. 63. — Cercaria glandulosa; detail of caudal pockets, showing insertion of tail, spinose

lateral grooves, and three-spined ventral flap. X 100.
Figs. 64, 65. — Cercaria glandtilosa; outline of excretory vesicle, open and closed. X 200.
Fig. 66. — Cercaria glandulosa; genital cell masses, dorsal view. X 110.
Fig. 67. — Cercaria glandulosa; sporocyst. X 170.

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LIFE HISTORY OF TREMATODES

PLATE IV

Ill] UFE HISTORY OF TREMATODES— FAUST 111

PLATE V

112 ILLINOIS BIOLOGICAL MONOGRAPHS [112

DESCRIPTION OF PLATE

Figs. 68-70. — Cercaria glandnlosa; consecutive frontal sections, giving details of the nervous
system anterior to the brain. X 540.

Fig. 71. — Cercaria glandtdosa; frontal section, with details of innervation of acetabulum.
X540.

Fig. 72-75. — Cercaria glandulosa; transverse sections thru levels aa to dd oi Fig. 60. X 540.

Fig. 76. — Cercaria diaphana; ventral view, considerably flattened by cover slip. X 170.

Fig. 77. — Cercaria diaphana; ventral view of stylet. X 540.

Fig. 78. — Cercaria diaphana; ventral view, giving details of glands and genital cell masses.
X 170.

Figs. 79, 80. — Cercaria diaphana; sporocysts. X 80.

Fig. 81. — Cercaria dendritica; ventral view. X 170.

Figs. 82, 83. — Cercaria dendritica; lateral and ventral views of stylet. X 250.

Fig. 84. — Cercaria dendritica; encysted worm. X 150.

Fig. 85. — Cercaria dendritica; salivary and cystogenous glands. X 170.

Fig. 86. — Cercaria dendritica; genital system. X 150.

Fig. 87. — Cercaria dendritica; yoimg sporocyst. X 150.

Fig. 88. — Cercaria dendritica; mature sporocyst. X 150.

Fig. 89. — Cercaria dendritica; posterior end of mature sporocyst, showing origin of germ-
balls from localized germinal epithelium. X 330.

ILLINOIS BIOLOGICAL MONOGRAPHS

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LIFE HISTORY OF TREMATODES

PLATE V

113] LIFE HISTORY OF TREMATODES— FAUST 113

PLATE VI

114 ILLINOIS BIOLOGICAL MONOGRAPHS [114

DESCRIPTION OF PLATE

Fig. 90. — Cercaria micro pharynx; ventral view. X 170.

Figs. 91, 92. — Cercaria micropharynx; ventral and lateral views of stylet. X 540.

Fig. 93. — Cercaria micropharynx; distribution of glands. X 170.

Fig. 94. — Cercaria micropharynx; sporocyst with non-localized germinal epithelium. X

Fig. 95. — Cercaria micropharynx; cercariae encysted in old sporocyst. X 54.

Fig. 96. — Cercaria micropharynx; genital cell masses. X 170.

Fig. 97. — Cercaria micropharynx; transverse section thru brain center. X 540.

Fig. 98. — Cercaria micropharynx; transverse section thru excretory comua. X 540.

Fig. 99. — Cercaria micropharynx; transverse section thru tail. X 540.

Fig. 100. — Cercaria racemosa; ventral view. X 150.

Figs. 101, 102. — Cercaria racemosa; ventral and lateral views of stylet. X 330.

Fig. 103. — Cercaria racemosa; detail of salivary glands. X 150.

Fig. 104. — Cercaria racemosa; genital cell masses. X 330.

Figs. 105, 106. — Cercaria racemosa; sporocysts, showing localized germinal epithelium and

attachment organ, ao. X 54.
Fig. 107. — Cercaria racemosa; lateral view of genital cell masses in region of acetabulum.

X 330.
Fig. 108. — Cercaria racemosa; optical view of the sporocyst in region of birth-pore, bp; arrow

points toward attachment organ. X 330.
Fig. 109. — Cercaria trisolenata; ventral view. X 150.
Fig. 110. — Cercaria trisolenata; dorsal view of collar spines. X 170.
Fig. 111. — Cercaria trisolenata; lateral view of collar spines. X 330.
Fig. 112. — Cercaria trisolenata; sketch of acetabular spines. X 540.
Fig. 113. — Cercaria trisolenata; typical cystogenous cell glands, showing granules and chro-

midia. X 540.
Fig. 114.4-E. — Cercaria trisolenata; sketches of developmental stages. X 80.
Fig. 115 A-C. — Cercaria trisolenata; stages in encystment. X 80.

ILLINOIS BIOLOGICAL MONOGRAPHS

-st

VOLUME 4

LIFE HISTORY OF TREMATODES

PLATE VI

1151 LIFE HISTORY OF TREMATODES— FAUST 115

PLATE VII

116 ILLINOIS BIOLOGICAL MONOGRAPHS [116

DESCRIPTION OF PLATE

Fig. 116. — Cercaria trisolenata; encysted worm. X 150.

Fig. 117. — Cercaria trisolenata; redia. X 50.

Fig. 118. — Cercaria trisolenata; longitudinal and transverse muscle fibers of the digestive
tract, showing myoblast connections. X 730.

Fig. 119. — Cercaria trisolenata; peripheral muscle fibers of longitudinal system. X 730.

Fig. 120. — Cercaria trisolenata; genital cell masses. X 220.

Fig. 121. — Cercaria trisoleruUa; butterfly stage in development of the central nervous system.
X 330.

Fig. 122. — Cercaria trisolenata; differentiating stage in development of central nervous system.
X 330.

Figs. 123, 124. — Cercaria trisolenata; lateral and dorsal views of central nervous system of
mature cercaria. X 330.

Fig. 125. — Cercaria trisolenata; central nervous system of the redia. X 220.

Fig. 126. — Cercaria trisolenata; distribution of nerve cells in the redia, median sagittal sec-
tion. X 330.

Fig. 127. — Cercaria trisdenata; detail of the peripheral nerves of the redia. X 540.

Figs. 128-133. — Cercaria trisolenata; traiisveTst sections at levels aatofol Fig. 109. X 330.

ILLINOIS BIOLOGICAL MONOGRAPHS

VOLUME 4

LIFE HISTORY OF TREMATODES

PLATE VII

117] UFE HISTORY OF TREMATODES— FAUST 117

PLATE VIII

118 ILLINOIS BIOLOGICAL MONOGRAPHS [118

DESCRIPTION OF PLATE

Fig. 134. — Cercaria biflexa; ventral view, showing salivary gland cells. X 105.

Fig. 135. — Cercaria biflexa: ventral view, showing excretory system. X 105.

Fig. 136. — Cercaria biflexa; lateral view of collar spines. X 330.

Fig. 137. — Cercaria biflexa; redia of worm. X 170.

Fig. 138. — Cercaria biflexa; detail of three flame cells in cephalic region. X 540.

Fig. 139. — Cercaria biflexa; genital cell masses. X 170.

Fig. 140. — Cercaria trisolenata; posterior end of redia. X 540.

Fig, 141. — Cercaria biflexa; posterior end of redia. X 540.

Fig. 142. — Cercaria gracillima; ventral view. X 230.

Fig. 143.— Cercaria gracillima; excretory system. X 350.

Fig. 144. — Cercaria gracillima; dorsal view of trunk, showing eye-spots and salivary glands

X 350.
Fig. 145. — Cercaria gracillima; detail of flame cell of excretory system. X 750.
Figs. 146, 147. — Cercaria gracillima; sporocysts; Fig. 146, x 14; Fig. 147, X 21.
Fig. 148 A-G. — Cercaria gracillima; stages in development. X SO.

ILLINOIS BIOLOGICAL MONOGRAPHS

VOLUME 4

FAUST

LIFE HISTORY OF TREMATODES

PLATE VIII

119] UFE HISTORY OF TREMATODES— FAUST 119

PLATE IX

120 ILLINOIS BIOLOGICAL MONOGRAPHS [120

DESCRIPTION OF PLATE

Fig. 149. — Cercaria graciUima; genital cell masses. X 270.

Fig. 150. — Cercaria graciUima; nervoiis system. X 540.

Fig. 151. — Cercaria graciUima; central nervous system in a very yoimg germ-ball. X 540.

Fig. 152. — Cercaria graciUima; transverse section thru esophagus glands. X 540.

Fig. 153. — Cercaria graciUima; transverse section thru region slightly posterior to that shown

in Fig. 152. X 540.
Fig. 154. — Cercaria graciUima; transverse section thru salivary glands. X 540.
Fig. 155. — Cercaria tuberisloma; ventral view. X 170.
Fig. 156 A-F. — Cercaria tuberisloma; stages in development. X 75.
Figs. 157, 158. — Cercaria tuberisloma; sporocysts. X 54.
Fig. 159. — Cercaria biflexa; section thru liver tissue of Physa gyrina Say, showing infection;

a, disintegrating cecvmi; b, broken down connective tissue; c, section of worm. X 170.
Fig. 160. — Cercaria micropharynx; section thru liver tissue of Lymnaea proxima Lea, infected

with the worm; a, fatty bodies in degenerating cecimi; b, vacuoles; c, sloughing tissue;

d, karyolysis; e, section of worm. X 170.
Fig. 161. — Cercaria graciUima; section thru liver tissue of Physa gyrina Say infected with

the worm; a, cytolysis; b, fatty globules; c, karyolysis; d, vacuoles; e, fibromata;/, sand

inclusions; g, section of worm. X 240.

ILLINOIS BIOLOGICAL MONOGRAPHS

VOLUME 4

FAUST

LIFE HISTORY OF TREMATODES

PLATE IX

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