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THE UNIVERSITY
OF ILLINOIS
LIBRARY

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ILLINOIS BIOLOGICAL
MONOGRAPHS

Vol. XI July, 1927 No. 3

EDITORIAL COMMITTEE

STEPHEN ALFRED FORBES Homer Lr Roy SHANTZ

HENRY BALDWIN WARD

PUBLISHED UNDER THE
AUSPICES OF THE GRADUATE SCHOOL BY
THE UNIVERSITY OF ILLINOIS

CopyricHtT, 1928, By THE UNIVERSITY OF ILLINOIS
DISTRIBUTED NOVEMBER 17, 1928

THE STRUCTURE AND DEVELOPMENT
OF CORALLOBOTHRIUM

With Descriptions of Two New Fish Tapeworms

WITH FIVE PLATES

BY
HIRAM ELI ESSEX

Contributions from the
Zoological Laboratory of the University of Illinois
under the direction of Henry B, Ward
No. 323

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TABLE OF CONTENTS

Tn trod UCtion sane meer pieces 5 ce aie csacry ieton agieyiva tea sacs fee ven ieeesge Gio eae 7
MaterialsvandeWiethods so. cs 2 seroca.c deena tee Sad otre Hw wimawromnis cent ote no 8
The'Genus Corallobothrivm. «ccc. ccccc cscs ecwieacas ees ws ce gseeaw se eedes geese? 9
Corallobothrium giganteum NOV. SPEC... 2. eee ii
Reproductive Organs). (6 cise. fe cure nctewsaiGlem secs bas eaten eG cee secede 16
Amphitypy.2s2sc:-<s9ss-- Sein RE ON eee Dine aoe aioe eae 20
Corallobothrium fimbriatum nov. spec......... Nite Mee wsinar cease Ree e Ss 21
Reproductive Organs.................. Pe Fete rae eye 24
Distribution, Abundance and Seasonal Occurrence.................00000000 000000 30
Wiferbustory, of Corallobothrium’ 25. cvaiavaiiesani ea ayer teeta G.ewe sate stets ee werrtrenes 32
Observations Concerning the Eggs... 0... eee 33
SXperiments swith: thee eS 5.5 tang csinijensisss alae enesers ols eteye eps Orel ceeael@iepansleoe ce als 36
The: First. Intermediate Host: «cen cua cece s cote Sted cre hee ee neon so 37
Development of Corallobothrium fimbriatum in Cyclops.................. . 40
Development of Corallobothrium giganteum in Cyclops.................. . 4
The Second Intermediate Host............. 2... cece cece eect enn eee . 46
(Phe Plerocercoid Larvae aa oa ¢acac; emit ein ete see wets du eaclee eS, er 49
Comparison of Proteocephalus and Corallobothrium........................ ; fol
Comparison with Diphyllobothrium latum......0.0. 0000 oe ee ogee os)
Early Development in Bothriocephalids and Proteocephalids................ , 54
Afhnities of the Proteocephalids: :..2.:3..0ccc0s0cceesceeewsendweeeeewecnebecuies 57
Summary.......... ee ee oa lado ts tion Reese Re Tae er ee ee 58
Bibliography.................... RE On ear oN Ao ee eee eee .. 60

Explanation ofemlates tie sae: orektern curator yrds aieret or ey visnvenss oan) eames Sake once ORs 64

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261] STRUCTURE AND DEVELOPMENT OF CORALLOBOTH RIUM—ESSEX 7

INTRODUCTION

Representatives of the genus Corallobothrium from American fish
have never been described. Marshall and Gilbert (1905) report two
members of this genus taken from Ameiurus melas (black bullhead)
caught in the lakes at Madison, Wisconsin. La Rue (1914) refers to an
undescribed species of Corallobothrium encysted in the livers of A. melas
and A. nebulosus (common bullhead) from the Illinois River. Ward
(1918) noted the presence of a species of Corallobothrium in Ictalurus
punctatus (channel-cat) at Milford, Nebraska. Aside from these inci-
dental references, the American literature contains no information on
this interesting group of fish tapeworms.

The acquaintance of the writer with these cestodes began during
the summer of 1925 while a survey of the parasites of fish from the rivers
and lakes in the upper Mississippi and Missouri basin was in progress
(Essex and Hunter, 1926). At that time cestodes belonging to Corallo-
bothrium were found in the following hosts: Ameturus melas, Leptops
olivaris (mud-cat), and Ictalurus punctatus.

At the suggestion of Dr. Henry B. Ward an intensive study was begun
in the spring of 1926 on the species of Corallobothrium infesting 7. punc-
tatus. As the investigation progressed it came to assume three distinct
phases: (1) taxonomy and morphology; (2) seasonal occurrence; (3) life-
cycle. It was discovered that two new species of Corallobothrium were
represented in my collections. These two species are described and named
in the present paper. No work having been reported previously on the
seasonal occurrence of any fish tapeworm in America, an effort was made
to obtain all possible information on this phase of the problem. This
study has shed some light on the biological relations between the para-
sites and their hosts. Up to this time only a few experimental investiga-
tions on the life-cycle of fish cestodes have been reported by European
workers and none whatever by workers in America. Since such studies
are of especial biological significance, and since complete information
on the developmental history of fish parasites is of great assistance to
fish culturists in their efforts to combat parasitic diseases among fish,
all data that I have secured on this phase of the investigation are pre-
sented in this paper.

My most sincere thanks are extended to Professor Ward for his in-
spiration, guidance and helpful criticism in this work. I am deeply grate-
ful for the use of the zoological laboratories of Rockford College which
were made available to me, during the summer of 1926, through the

8 ILLINOIS BIOLOGICAL MONOGRAPHS [262

kindness of Dr. Ruth Marshall and the generosity of the college authorities.
I also acknowledge here the invaluable assistance rendered by Dr. David
H. Thompson of the Illinois Natural History Survey, who furnished me
several shipments of catfish for examination. Thanks are also due Mr.
R. E. Richardson for the identification of minnows and for a collection
of parasites from Ictalurus punctatus, and to Dr. S. A. Forbes for the
use of unpublished data on the food of I. punctatus collected by the Illi-
nois Natural History Survey.

MATERIAL AND METHODS

The parasites were killed in corrosive sublimate, Bouin’s solution and
4 per cent formol. The first two gave good results, but specimens killed
in formol were difficult to stain. Ehrlich’s or Delafield’s hematoxylin
was used for totos and sections. Counterstaining was done with eosin
or orange G.

Collection of the adult cestodes offers no difficulties, but it is a long
and tedious struggle to find the smallest larval forms. A method was
developed whereby plerocercoids which measured only 0.25 mm long
could be collected with a saving of time and effort. Briefly stated, the
procedure is as follows: (1) large parasites and particles of debris
are removed; (2) remainder of intestinal contents scraped into quart
jar of water and shaken thoroughly; (3) the mass is strained through a
small plankton net; (4) the plankton net placed under faucet, running
water allowed to play on contents until all possible material is washed
through the net; (5) the residue is turned into a watchglass and examined
under a binocular. This method is equally successful in collecting small
trematodes.

A rapid method of reconstruction was developed in connection with
the work on these cestodes. A plate of glass one foot square was placed
under the camera lucida. With a wax pencil the structure to be recon-
structed from a given section was traced on the glass. With plasticene
the tracings were modeled. The next section was then oriented accord-
ing to guide lines and the required tracings made from it. By means
of blocks of plasticene the structures modeled from the second, third,
and later sections were placed according to scale above those previously
modeled. When completed, the organs were represented in three di-
mensions and in their proper relation. This method was employed in
making the models represented by figures 39 and 41.

263] STRUCTURE AND DEVELOPMENT OF CORALLOBOTHRIUM—ESSEX 9

THE GENUS CORALLOBOTHRIUM

The genus Corallobothrium was created by Fritsch in 1886 to ac-
commodate a species of cestode from Malapterurus electricus, an elec-
tric catfish of Egypt. Because of the resemblance of the scolex to the
structure of an Oculina-like coral, he named the parasite Corallobothrium
and called the species C. solidum. It was his opinion that this genus
represented a connecting link between the Bothriocephalan and Taenian
cestodes. He gave the following diagnosis for the genus: ‘“‘Caput bothrio
uno terminali, fere plano, ovali lateribus attenuatis, superficie et margine
crispo. Acetabula quattuor cruciatim posita, in bothrii medio profunde
inserta. Collum nullum. Corpus articulatum, depressum, subaequale
vel retrorsum angustatum. Organa genitalia typica, orificia marginalia
involuta.’’ Fritsch says that the form of the scolex recalls that of Caryo-
phyllaeus, ‘‘nur ist die Sauggrube in ihrer ovalen nach beiden Seiten
leicht vershmalerten Gestalt, viel regelmassiger gebildet’’; that the ace-
tabular suckers are entirely obscured by the folds of the scolex and are
revealed only in sections. The suckers agree in structure and arrange-
ment with those of Taenia; the character of the whole body is strikingly
solid and strong.

No other species was referred to the genus Corallobothrium before
the work of Riggenbach (1896), who described a cestode from Pime-
lodus pati, a siluroid of Paraguay. This parasite was designated as Corallo-
bothrium lobosum. Fuhrmann (1916) redescribed this form and gave a
short redescription of C. solidum. On the basis of the cortical arrange-
ment of the testes and vitellaria he removed C. Jobosum from the genus
Corallobothrium and created for it a new genus, namely, Rudolphiella.
Later Fuhrmann and Baer (1925) reduced Rudolphiella to synonomy,
and placed R. Jobosa in the genus Ephedrocephalus.

Braun (1895) accepts the genus Corallobothrium and to Fritsch’s
diagnosis adds that neither hooks nor spines are present; that excretory
vessels have secondary openings in the proglottids; and that the hosts
are tropical or subtropical bony-fish. La Rue (1914) adds to Braun’s
diagnosis that the folds and lappets of the scolex may enclose the suckers
as in a corolla and that no rostellum is present. He omits the secondary
openings of the excretory system, given by Braun, and gives the habitat
as the intestinal tract of the Siluridae.

The validity of the genus Corallobothrium was never questioned
until the appearance of two papers by Woodland (1925, 1925a) in which
he proposes to delete such genera as Corallobothrium, Choanoscolex,

10 ILLINOIS BIOLOGICAL MONOGRAPHS [264

Acanthotaenia and Gangesia and make them synonyms of Proteocepha-
lus because they were founded on scolex characteristics. This author
regards such characters as of specific value only, and proposes that the
various arrangements of the reproductive organs with reference to the
inner longitudinal muscle sheath shall constitute the bases for the desig-
nation of genera. In Woodland’s opinion the scolex characters are of
secondary importance as compared to the structure of the proglottids.
However, if the early development of the cestodes is accepted as a guide
in determining the order of sequence which is followed in arriving at the
adult organization, and if those structures which appear first in the develop-
ment of the individual are considered as having arisen first in the phylo-
geny of the group, then the scolex must be acknowledged as one of the
most fundamental structures of the adult organism. In the development
of Taenia and related groups, the scolex and a more or less indifferent
neck are the only adult structures found in the cysticercus, and from them
arise allotheradult organs. In the development of the two new species des-
cribed in this paper the scolex is likewise the first adult structure to ap-
pear, being differentiated at the end of 10 to 12 days development. When
considered from this point of view, there is certainly sufficient reason for
attaching generic value to the character of the scolex. Fuhrmann (1916)
doubtless recognized this when he created a separate genus for Goezeella
siluri instead of referring it to the genus Monticellia; the only essential
difference between the two genera being that the former possesses a
scolex of the Corallobothrium type. Furthermore, the scolex has long
been used by helminthologists as a generic character, and to discard it
now would result in more confusion of the nomenclature than seems to
be justified. A recent publication by Stiles and Hassell (1926) contains
the following statement: ‘‘The genus Taenia, in its modern concept,
can be subdivided into at least three groups to which either subgeneric
or generic rank may be given (according to one’s personal point of view
in respect to generic values).”’ A key follows in which the genera Taenia,
Hydatigera and Taeniarhynchus are separated entirely on the basis of
the scolex while Taenia and Taeniarhynchus are separated on the nature
of the rostellum alone.

Since the characters which constitute a genus are considered largely
a matter of personal viewpoint, Woodland is hardly justified in deleting
genera which have been accepted previously by the leading workers in
helminthology because, from his point of view, he does not regard the
characters on which those genera were founded as of generic value. There-
fore, I have followed Braun, Fuhrmann and others in accepting the
genus Corallobothrium and the two new species described in this paper
have been referred to that genus.

265] STRUCTURE AND DEVELOPMENT OF CORALLOBOTHRIUM—ESSEX 11

Corallobothrium is closely related to the genus Proteocephalus. The
internal organization of the two genera is very similar. The scolex, how-
ever, is so distinctive that species belonging to the two genera can be
separated by an examination of the scolex alone. Another character
by which the species of Corallobothrium, which I have studied, may be
separated from those of Proteocephalus, is in the position of the vagina
with reference to the cirrus-pouch. In Corallobothrium giganteum and C.
jimbriatum, the vagina in successive segments varies and may be either
anterior or posterior to the cirrus-pouch. The descriptions of C. solidum
are silent on this point, but if this condition is true of it also, there exist
two distinct points of difference, scolex and position of vagina, between
the species of Corallobothrium and Proteocephalus. Regarding the latter
La Rue (1914) makes the following statement: ‘‘In Proteocephalus the
vagina is usually anterior to the cirrus-pouch although there are a few
species in which it is regularly posterior.”” Thus in the species of Proteo-
cephalus the position of the vagina with regard to the cirrus-pouch is
constant, while in the species of Corallobothrium it is inconstant.

The genus Corallobothrium may be defined as follows: With char-
acters of family. Scolex bears four suckers situated on anterior surface
surrounded by many irregular folds and lappets of tissue. Rostellum,
hooks and spines absent. Neck broad, short. Vagina inconstant in position,
anterior or poster to cirrus-pouch. Habitat: In Siluridae. Type species:
Corallobothrium solidum Fritsch.

CORALLOBOTHRIUM GIGANTEUM NOV. SPEC.

In life these cestodes are milky-white in color. The scolex is usually
attached in the region of the duodenum and the proglottids of a mature
specimen may extend almost to the posterior limit of the intestinal tract
of the host. They are strongly contractile and may draw themselves up
to less than half the fully extended length. The strobilization is indis-
tinct except in the posterior portion of the chain. The body surface is
excessively wrinkled in this species as is true of the whole genus. The
proglottids are so firmly joined that considerable force is required to tear
them apart. The proglottid number varies from 150 to 300 or more.

Among seventy-five adult individuals before fixation, 60 cm was the
greatest length observed. After fixation the longest individual was 44 cm.
The usual length of preserved specimens ranges between 15 and 30 cm. In
the largest living individuals mature proglottids are about 3 mm long
by 2.5 mm wide; ripe proglottids 4 to 8 mm long by 1 to 0.5 mm wide,
according to contraction. In the largest fixed specimen (44 cm) which
was not fully extended, immature proglottids were from 0.25 to 0.75 mm
long by 5 mm wide to 1 mm long by 3.5mm wide; mature proglottids from
1 mm long by 3.5 wide to 2 mm long by 2.25 mm wide; ripe proglottids

12 ILLINOIS BIOLOGICAL MONOGRAPHS [266

from 2 mm long by 2.25 mm wide to 5 mm long by 1 mm wide. In an
alcoholic specimen 22 cm long, containing about 225 proglottids, 3 cm
from the scolex, the proglottids are about 0.25 mm long by 2.5 to
2.75 mm wide; about 8 cm from the scolex they are 1 to 1.3 mm long by
2 to 1.5 mm wide; the last 20 proglottids measure from 1.5 to 2 mm long
by 1 to 0.5 mm wide. In four toto preparations of sexually mature speci-
mens which measure from 5 to 15 cm in length, immature proglottids are
0.10 to 0.84 mm long by 1.51 to 3.10 mm wide; mature proglottids 1 to
2.2 mm long by 1.3 to 1.89 mm wide; ripe proglottids 1.53 to 3.46 mm
long by 0.73 to 1.15 mm wide. The segments in the anterior portion are
always wider than long, but proceeding posteriad the length gradually
increases at the expense of the width and the posterior proglottids of the
chain are much longer than wide, the ratio begin from 2:1 to8:1 (Figs
6, 26). The shape of the cestode in toto recalls that of a whip.

The form of the scolex is highly variable owing to different states of
contraction. It may be globose (Fig. 15), quasi-conical (Fig. 5), quadrate
(Fig. 2), or it may in a measure resemble the head of C. fimbriatum (Figs.
10, 11). In living specimens it varies from 1 to 2.75 mm in diameter.
In six alcholic specimens, which are representative of the adult worms,
the scolex measures from 1 to 2.16 mm wide. The ratio of the width
to the length varies from about 1:1 to 2:1. Among four toto mounts
the diameter is 1.47 to 1.68 mm and the length is 0.9 to 1.5 mm. The
dorso-ventral dimension is usually slightly less than the transverse
diameter. The four strongly muscular suckers, which are directed an-
teriorly, are largely concealed beneath a heavy fold of the cortex. From
this fold project a large number of ridges and a few finger-like processes.
The folds and lappets are much less pronounced than those of C. fimbria-
tum and C. solidum (Figs. 5, 10, 15). At times the suckers are drawn in
and covered entirely (Fig. 11). When this occurs the scolex is drawn back
into the neck region (Fig. 10). This gives the anterior extremity a flat-
tened appearance. When the scolex is fully extended, the anterior extremity
is rounded and the bluntly pointed apex projects from the center (Fig.
5). There is no rostellum or rudiment of a fifth sucker revealed in five
sets of frontal and one set of transverse sections.

The suckers, which measure from 0.45 to 0.59 mm wide and from
0.53 to 0.59 mm long, vary in shape according to their contraction. In
some specimens they are nearly spherical while in others they are longer
than wide. One series of frontal sections shows each pair lying with their
inner margins touching in the posterior portions while the anterior por-
tions are quite widely separated, each one making an angle of about 30
degrees with the longitudinal axis of the worm (Fig. 33). In another
series of frontal sections, each pair of suckers is separated by a distance
of about 0.10 mm and they are directed anteriorly so that their longi-

267] STRUCTURE AND DEVELOPMENT OF CORALLOBOTHRIUM—ESSEX 13

tudinal axes are parallel with that of the scolex (Fig. 37). The first series
was made from a specimen that was fairly well extended, the second
from one that was much more contracted. The width of the openings
varies from 0.10 to 0.19 mm and the length of the cavity may be as much
as 0.33 mm.

At the apex of the suckers, surrounding the inner half of the opening,
is a massive set of muscle bands which pass from the margin of the open-
ing on one side in a circular course to the opposite side of the opening.
They form a semi-circle about the apex of the suckers. In transections
they appear as shown in figure 18; in frontal sections they are about
0.20 mm in diameter and resemble knobs (Fig. 37). Woodland (1925a)
has reported a similar structure for the suckers of Marsypocephalus rect-
angulus. This structure functions as a sphincter and, as Woodland has
suggested, doubtless aids in prehension. It was noted, in dealing with
the living C. giganteuwm that they were detached with great difficulty
when the scolex of one fastened itself upon another individual.

Besides the sphincter, each sucker is encircled by a very compact band
of muscle fibers 16u thick at the center. These fibers may be divided into
two groups: those which surround the sucker in the frontal, and those
which surround it in the sagittal plane. Within this band appears a layer
of muscle fibers about 0.30 mm thick in the center. These are much less
compact in their arrangement and all of them extend from the periphery
of the sucker to the lining of the cavity. Lining the cavity of the sucker
is a layer of cuticula which measures from 3 to 4u in thickness.

Anterior to the suckers there is a rhomboid of muscle fibers (Fig. 35)
and from the margins of the suckers many muscle fibers proceed into the
neck region (Fig. 37). Posterior to the rhomboid of muscle fibers is a trans-
verse cross of fibers. At the level of the sphincter a set of fibers pass from
one sucker to the next (Fig. 18). Transverse sections through the pos-
terior portions of the suckers show two bundles of muscle fibers, one
arising from each of the inner margins of the suckers. These bundles
pass diagonally to a member of the opposite pair. In their course they
cross each other near the median line to form an eight-rayed cross or
star (Fig. 28).

The neck in one set of frontal sections is about 1.60 mm long and
1.36 mm wide. It is easily recognized in frontal sections but it is not
evident in much contracted totos. There is frequently very little
constriction immediately posterior to the scolex. Thus the diameter of
the neck region, when a specimen is much contracted, may equal that of
the scolex (Figs. 10, 16, 37).

The cuticula, which varies from 4 to 9u in thickness, is composed of
two layers. A thin, more deeply staining layer about 1 thick, covers the
surface. Beneath it is a thicker, less deeply staining stratum at the inner

14 ILLINOIS BIOLOGICAL MONOGRAPHS [268

margin of which is found the very thin basement membrane, less than
iy thick. Beneath this is a layer of circular muscles about 3u thick. There
are longitudinal muscle fibers just below the circular muscles. The former
are interwoven with the outer ends of the spindle-shaped subcuticular
cells which form a phalanx beneath the subcuticular muscles. These cells
constitute a layer about 0.03 mm thick. They possess large nuclei which
vary in shape, some of them being spherical and others elliptical. Each
cell is drawn out into a fine process which can be followed as far as the
basement membrane.

In the strobila the inner longitudinal muscle sheath is exceptionally
well developed. In mature proglottids it measures from 0.05 to 0.07 mm
thick. The fibers are arranged in irregularly shaped bundles. Just within
this layer appears a band of inner circular fibers. This band constitutes
a stratum from 6 to 16u thick, which encircles the medullary parenchyma.
In immature segments transverse fibers are quite numerous. Passing
through the medullary region, as many as 60 bands of dorso-ventral
fibers were counted in a single section of a mature proglottid.

The nervous system consists of a ring and two nerve trunks. The former
is situated in the median region of the scolex at the level of the apices
of the suckers. In transections it has the form of a cross, the rays of which
project between the suckers (Fig. 35). Its greatest diameter in adults is
from 0.33 to 0.40 mm. Arising from the lateral portions of the ring two
trunks, which measure from 35 to 40u in diameter, pass off parallel to the
ascending excretory vessel and follow a course between the dorsal and
ventral pairs of suckers along the inner margin of the longitudinal muscle
layer (Fig. 30). In the scolex and throughout the proglottids these nerve
trunks maintain the same relation to the inner longitudinal muscle sheath,
and their diameter varies but little at any point in the chain.

The excretory tubules are very prominent in sections of this species.
Four principal tubules are easily seen in sections of proglottids which
are immature. When the reproductive organs are fully developed the
excretory system is so crowded that at times it is difficult to distinguish
it clearly. The four main longitudinal trunks are located in the lateral
regions of the medullary parenchyma roughly parallel to the longitudinal
nerve trunk of each side, the descending lying nearer the center than
the ascending vessels.

The ascending tubules, which measure from 12 to 18u in diameter,
lie only 5 to 15u from the nerve trunk, both in the neck region and in the
immature proglottids. In these regions they follow a straight course with
only slight deviations. The descending tubules are much larger in the
regions just named, as they measure from 24 to 40u. Their course is much
more tortuous and their position with reference to the nerve trunk is
much less definite.

269] STRUCTURE AND DEVELOPMENT OF CORALLOBOTHRIUM—ESSEX 15

The structure of the ascending and descending trunks is very different.
Transections of the former showa heavy wall of hyaline material about
1p thick surrounded by what appears to be a single layer of muscle fibers.
Also the parenchymal cells are compactly arranged about these tubules
(Fig. 40). The descending trunks lack the hyaline wall and also the layer
of muscle fibers, and they are surrounded by a less compact arrangement
of the parenchymal cells.

In a larval specimen about 4 mm long, cut in transverse section, the
ascending trunks arise 0.14 mm from the posterior end of the individual
where they measure from 2 to 5uin diameter. They are found in the lateral
medullary parenchyma. As they proceed anteriorly they increase slightly,
measuring 8 to 10u at a point about 0.8 mm from the scolex. As they
enter the scolex they measure about 8u in diameter. Upon reaching the
scolex they pass laterally between the suckers and the longitudinal muscle
layer of the scolex, following the outer margins of the suckers until the
anterior level of the latter is reached, when they proceed inward toward
the median line where they follow a tortuous course between the suckers
before uniting with the descending trunks.

Branches of the descending trunks are more numerous in the central
region of the scolex. The apex is ramified with both ascending and descend-
ing branches, but about the bases of the suckers there occur numerous
coils of the descending tubules. Upon reaching the neck region, the main
vessels proceed laterally, the ascending running dorsal and the descending
ventral to the nerve trunk. In the neck the ascending trunks measure
about 0.02 mm, or twice the diameter of the ascending ones. Through-
out the length of the individual there is little difference in the diameter
of the descending tubules since they measure from 20 to 25y in the pos-
terior region. There are no cross trunks apparent between the vessels
of the same or opposite sides in the parasites at this stage of develop-
ment. Furthermore, they follow practically a straight course throughout.
About 0.08 mm from the posterior end, the two descending trunks empty
into an excretory bladder. Just below the point of union with the de-
scending tubules, the bladder measures 20u dorso-ventrally and 27 trans-
versely. It narrows posteriorly and empties through a small duct at the
extreme posterior end of the individual.

Frontal sections were made of a strongly contracted individual, about
15 mm long, in which a large number of proglottids had been differentiated.
Here the excretory system is much more highly developed than in the
individual just discussed. The position of the ascending and descending
trunks with reference to each other has been slightly altered. At this
stage they are parallel in a horizontal plane, with the ascending trunk
more lateral or nearer the longitudinal nerve on each side. The diameter
of the ascending is less than that of the descending trunks throughout

16 ILLINOIS BIOLOGICAL MONOGRAPHS [270

their extent. Both are more or less coiled in this individual. With the
differentiation of proglottids an addition to the descending system has
occurred. At the posterior limit of each proglottid is found a cross-trunk
which in many instances equals in diameter the descending tubules.
Also a small duct, 8u in diameter, arises near the confluence of the des-
cending and cross trunks. This passes to the posterio-lateral margin of
the proglottids and empties to the outside through a small duct and pore
(Figs. 34, 38). These same features are found also in the fully mature
segments, but owing to the pressure of the reproductive organs they are
more difficult to distinguish. The excretory system of this species agrees’
in all essential features with the description of Riggenbach (1896) for
Ephedrocephalus lobosus (=Corallobothrium lobosum).

A study of frontal sections of the scolex and strobila in an extended
and contracted condition has lead me to the conclusion that this system
has more than an excretory function. When the scolex and strobila are
contracted, the vessels are greatly diminished (Figs. 16 and 38). When
the opposite is the case, the vessels are much distended (Figs. 21 and 34).
This suggests the probability that the excretory vessels aid in the exten-
sion of the scolex and strobila.

Reproductive Organs

A common genital sinus, which measures about 64 in diameter?
occurs on the lateral margin of the proglottid from one-quarter to one~
half the proglottid length behind the anterior margin. The usual position
is within the anterior one-quarter of the proglottid. It is irregularly
alternate in successive segments. The cortical wall surrounding the sinus
protrudes sufficiently to be seen with the naked eye in toto mounts.
This constitutes a genital papilla. The character and arrangement
of the reproductive organs, for the most part, is identical with that of
the other Proteocephalids. Each sexual unit occurs within the inner
longitudinal muscle sheath (Fig. 20).

The male system will be considered first. The testes vary considera-
bly in shape. Some of them are almost spherical, others pear-shaped,
but the majority are elliptical. They measure from 0.05 mm to 0.08 mm
in length, and from 0.03 to 0.06 mm in diameter. The number present
in a single proglottid is from 80 to 100. They lie in a continuous field
between the vitelline glands, extending from the anterior margin of the
proglottid posteriad to the level of the ovary. Between the vitelline
glands and the uterus they occur in two or three layers, but dorsal to the
uterus only a single layer is present. Vasa efferentia were not observed
in any of the preparations. In many sections the vas deferens passed
among the testes and often there appeared to be a connection between
the walls of the two. This relation could not be established for a sufficient
number to warrant the statement that such is the usual condition.

271] STRUCTURE AND DEVELOPMENT OF CORALLOBOTHRIUM—ESSEX 17

At the level of the cirrus the thin-walled vas deferens, which measures
from 0.03 to 0.05 mm in diameter, forms a compact mass of 15 to 20
coils that almost completely fill the medullary space between the vitel-
laria and uterus and extend anteriad and posteriad from 0.25 to 0.33 mm.
(Figs. 7, 26). In mature proglottids they are usually distended with
spermatozoa. At the point of entrance into the cirrus-pouch the vas
deferens ends abruptly and at this point the ductus ejaculatorius takes
its origin. After describing two or three coils it passes into the cirrus.
The duct at the point of entrance into the cirrus-pouch measures about
16u. A short distance beyond its point of entrance it doubles in diameter.
Upon entering the cirrus it narrows again. Its lumen varies from 8 to 12u
in diameter. Its structure is almost identical with that of the cirrus.

The cirrus-pouch is usually elongate-oval in shape when the cirrus is
inverted, but its form varies when the cirrus is everted. Apparently the
extent of protrusion of the cirrus affects the shape of the cirrus-pouch.
It assumes a variety of forms in successive segments. Some appear wedge-
shaped, while others recall the form of a gourd (Fig. 7, 26). When the
cirrus is inverted, the pouch measures from 0.26 to 0.33 mm long by 0.09
to 0.13 mm in greatest diameter. The wall of the pouch is from 3 to 5y
in thickness and is composed of longitudinal muscle fibers. Between the
wall of the pouch and the cirrus is a loose network of connective tissue fibers
with scattered nuclei. Immediately surrounding the cirrus is a compact
layer of cells about 8u thick. Wagner (1917) in his description of Proteo-
cephalus torulosus calls a group of cells similarly located, subcuticular
cells. Benedict (1900) in his description of P. filicollis and P. amblop-
litis designates them as gland cells.

When the cirrus is inverted it measures from 0.20 to 0.23 mm in length
and about 0.02 mm in greatest diameter and about the same at its point
of union with the ductus. It is roughly cone-shaped, the base of the cone
being adjacent to the genital sinus. In transections the wall of the cirrus
shows a series of closely applied folds which almost close the lumen. The
inverted cirrus is lined with a cuticular layer that extends to the ductus.
Surrounding this layer are found longitudinal and circular muscles.
When completely everted the cirrus reaches a length of 0.5 mm. Its dia-
meter just outside the genital sinus is about 0.1mm, while its distal por-
tion has a diameter of about 0.05 mm (Fig. 17).

In the female system the vagina opens into the genital sinus beside
the cirrus in the same horizontal plane. Frontal sections of two indi-
viduals showed that the vagina may be either anterior or posterior to the
cirrus. In one individual the vagina opened anterior to the cirrus on the
right side in 14 proglottids, and on the left side anterior to the cirrus, in
12 proglottids. It opened posterior to the cirrus on the right side in 10
proglottids and posterior to the cirrus on the left side also in 10 proglottids.

18 ILLINOIS BIOLOGICAL MONOGRAPHS [272

In another specimen the relation was as follows: anterior to cirrus, right
side, 18; anterior to cirrus, left side, 20; posterior to cirrus, right side, 10;
posterior to cirrus, left side, 13. In these two specimens there is a close
approach to equality in the dextral and sinistral position, and antero-
posterior relation of the vagina and cirrus. For a distance of about 0.10
mm from the sinus the diameter of the vagina may almost equal that
of the cirrus, and like the latter has a lining of rather heavy cuticula. A
sphincter vaginae is present but weakly developed. At the end of the
distance just mentioned the vagina narrows, and from there to the semi-
nal receptacle it measures from 11 to 24y and its lumen varies from 6 to
204 in diameter. The greater diameter is only reached when the vagina
is distended with spermatozoa. Since the vaginal opening may lie either
anterior or posterior to the opening of the cirrus, the course of the vagina
will vary somewhat. From the level of the genital sinus it may pass an-
teriorly for a short distance before proceeding toward the median line,
or it may run between the coils of the vas deferens in a direct course to-
ward the median line of the segment. At the same time it is directed
ventrad. It passes through the ventral region of the medullary cortex
for a short distance, then turns dorsally and for the remainder of its course
to the seminal receptacle, it lies above the uterus. It is found in this
last position throughout about two-thirds of its length. Anterior to
the ovarian commissure when the proglottid is much extended, and
posterior to it in contracted segments, the vagina widens gradually for about
0.10 mm, then it narrows suddenly, giving rise to a pear-shaped seminal
receptacle which equals the width of the vagina at ifs narrowest point
and is about 0.04 mm at its widest portion (Fig. 23). Leading from this
structure is a narrow duct, the lower vagina, which joins the oviduct.
This portion may be straight (Fig. 23) or coiled (Fig. 39). The position
of the duct is dependent upon the contraction of the proglottids. Aside
from a cuticular lining for a short distance from the genital sinus, the
wall of the vagina is composed of muscle fibers and measures from 3 to
5u in thickness. Only longitudinal fibers were distinguished. Like the
cirrus, it is surrounded by a layer of gland cells throughout its length.

The bi-lobed ovary lies in the posterior portion of the proglottids.
In fully extended ripe proglottids it is H-shaped. The two wings are broad
and bluntly rounded posterior to the commissure, but anterior to it they
taper to a rather sharp point and measure from 0.86 to 1.32 mm in length.
The width of the ovary at the level of the commissure is from 0.33 to
0.46 mm (Figs. 23, 26). In fully extended ripe proglottids the structure
of the ovary has a latticed or corded appearance as it is made up of a
network of thin-walled tubules which are interwoven with one another.
In mature proglottids the lobes of the ovary are much shorter and more
compact, measuring from 0.46 to 0.80 mm in length and from 0.75 to
1.06 mm in width at the level of the commissure (Fig. 26).

273] STRUCTURE AND DEVELOPMENT OF CORALLOBOTHRIUM—ESSEX 19

As revealed by sections, the two lobes lie just beneath the inner longi-
tudinal muscles in the dorsal region of the medullary parenchyma but the
commissure dips ventrally. Near the median line, it connects with the
muscular oocapt which is spherical in shape and measures about 20y in
diameter. It is surrounded by a layer of gland cells about 4u thick. From
the oocapt in mature proglottids the oviduct usually changes direction
three or four times before reaching the posterior margin of the segment
where it turns laterad and dorsad. Near its lateral limit it empties into
the ootype. The greatest diameter of the oviduct is about 24u. The lower
vagina joins the oviduct at its last bend before the ootype is reached
(Fig. 39).

The ootype, which is about the same diameter as the oviduct, passes
laterally and dorsally for a short distance and then proceeds anteriorly.
Near the anterior level of the vitelline receptacle it empties into the uter-
ine passage. The wall of the ootype is very similar to that of the oviduct.
The only striking difference between the two structures is the presence
of the shell gland about the former, some cells of which measure 48 long
by 16u wide. The processes of these cells pass into the wall of the ootype.

The uterine passage, which leads from the ootype, measures about 16
in diameter. After bending upon itself once or twice it passes dorsal
to the vagina and empties into the uterus near the median line ata point
near the middle of the proglottid.

In mature proglottids the uterus has a diameter equal to about half
the proglottid width. It is separated from the vitellaria on each side
and from the dorsal musculature by the testes. It extends from the an-
terior margin to near the level of the ovarian commissure. It opens to
the exterior through two or three uterine pores near the ventral median
line. In mature proglottids the uterus possesses from 10 to 15 lateral
pouches (Fig. 26). Their beginnings are very distinct in immature pzo-
glottids. In fully extended, partially spent proglottids the lateral pouches
are relatively greatly reduced, giving the uterus the character of a tube
with irregular borders (Fig. 6).

The vitellaria form two columns of a diameter of 0.08 mm which
extend from the anterior to the posterior margin of the proglottid. They
crowd the longitudinal nerve trunks close to the inner muscle sheath,
They are follicular in structure, the follicles emptying into a central
tubule. Near the level of the ovarian commissure a duct 16u in diameter
leads inward from each side. The two unite anterior to the oocapt, form-
ing a common vitelline duct which proceeds posteriorly for about 0.05 mm
and then widens to form the vitelline reservoir, which is from 40 to 56u
Jong and from 28 to 36u wide. From the reservoir a narrow duct leads
into the ootype near its point of union with the oviduct (Fig. 39).

20 ILLINOIS BIOLOGICAL MONOGRAPHS [274

AMPHITYPY

Amphitypy, or complete organ reversal, occurs in the position of all
the interovarian organs in successive segments. This condition is not
correlated with the position of any of the other organs of the reproductive
system. For example, the genital sinus may be on the left margin with
the vagina anterior to the cirrus and with the interovarian organs dis-
posed as shown in figure 39. In another segment the genital sinus will
be on the right with the vagina posterior to the cirrus and the
interovarian organs will be arranged the same as in the figure just cited,
or they may be just the reverse. The following data were taken from
seven successive segments cut in frontal section.

Right | Right} Left | Right} Right) Left | Right

Genital sinus

Vagina anterior to cirrus + AF

Vagina posterior to cirrus” + + + + oh
Oviduct right + + + oF

Oviduct left +
Seminal receptacle right + oF

Seminal receptacle left
Vitelline reservoir right
Vitelline reservoir left

Amphitypy has been observed among the Trematoda by many in-
vestigators (Looss, 1902: 789) but I have not discovered any reference to
such a condition among the Cestoda.

A description of the living eggs is given later in this paper conse-
quently only the ova within the uteri of sectioned specimens are considered -
here. The outer egg covering is so variable in amount and so irregular
in shape that it is difficult to distinguish in preserved material. The
second membrane is spherical and measures from 14 to 19u in diameter.
This membrane is closely applied to the oncosphere which measures
from 8 to 13u in diameter. The eggs of this species are the smallest pro-
duced by any of the species of Corallobothrium thus far described.

Because of the tremendous difference in the length as compared with
the other two species, the smaller number of testes, and the great dif-
ference in the egg measurements, besides the other distinct characters
to be pointed out, I regard the parasite under consideration as a new
species which I shall designate as Corallobothrium giganteum. This name
was given not only because it is the largest species of its genus but also
because it is one of the largest known cestodes infesting fresh-water fish.

Max. Sucker No. of Second egg Size of

length sphincter testes membrane oncosphere
C. solidum 4 cm. absent 140 to 180 20 to 24u 13 to 16u
C. giganteum 44 cm. present 80 to 100 14 to 19u 8 to 13u

C. fimbriatum 8 cm. absent 100 to 125 28 to 36u 16 to 24y

275] STRUCTURE AND DEVELOPMENT OF CORALLOBOTHRIUM—ESSEX 21

Only a superficial examination is necessary to separate this species
from Corallobothrium solidum or C. fimbriatum. Besides the points con-
sidered in the preceding comparison, C. gigantewm is distinct from the other
species in the character of the scolex (Figs. 5, 10, and 15), the size and shape
of the proglottids, shape of the ovary, and in the less extensive develop-
ment of the uterus. The measurements in the preceding comparison
were made on preserved material.

CORALLOBOTHRIUM FIMBRIATUM NOV. SPEC.

This cestode is usually found in the anterior portion of the intestine
of Ictalurus punctatus, Leptops olivaris, or Ameiurus melas. The length,
when ripe proglottids are present, varies from 15 to 80 mm among pre-
served specimens. The maximum breadth reaches 2.6 mm. Living in-
dividuals frequently reach a length of 70 to 90 mm when well extended.
The strobilization is very distinct and the segments are more easily de-
tached than those of C. giganteum. The number of proglottids ranges
from 40 to 90. They vary in shape and size according to the state of con-
traction and the body size of the individual. The following measurements
in millimeters were taken from 6 prepared specimens:

Immature proglottids
length 0.09, 0.16, 0.41, 0.19, 0.53, 0.16, 0.31, 0.27, 0.21
breadth 0.78, 0.46, 2.40, 1.57, 1.89, 1.68, 1.36, 1.15, 0.56
Mature proglottids
length 1.00, 0.95, 1.05, 0.50, 0.63, 0.73, 0.73, 0.63
breadth 1.9, 1.26, 1.36, 0.59, 1.26, 1.26, 2.60, 1.05
Ripe proglottids
length 1.05, 1.05, 1.01, 1.05, 1.00, 0.94, 1.05, 1.36, 1.36, 0.84
breadth 1.78, 2.60, 1.01, 1.01, 1.20, 1.36, 1.05, 0.73, 0.73, 0.84

The thickness varies from 0.5 to 0.7 mm. The immature and mature
proglottids are almost invariably broader than long, while the ripe seg-
ments are longer than broad. In transections some ripe proglottids are
flattened dorsally but rounded ventrally; in others the reverse is true.

In the descriptions of C. solidum, with which this form agrees very
closely, that of Fuhrmann (1916) is the only one containing adequate
measurements. He records the length of first proglottids as 0.09 mm;
5 mm behind the scolex as 0.23 mm and posterior segments as 0.65 mm.
He gives the same maximum length and breadth as did Fritsch (1886)
since he used the latter’s preparations. Janicki (1926) gives the maximum
length as 60 mm and maximum breadth as 3.5mm but fails to record
any other measurements for the proglottids. I have been unable to find
in any C. jfimbriatum specimens the definite surface structure which
Janicki describes and figures for C. solidum. He states, “Von den zwei

22 ILLINOIS BIOLOGICAL MONOGRAPHS [276

mir vorliegenden Exemplaren weist das grdéssere eine sehr eigentiimliche
Gestaltung der Kérperobeflache auf, indem die Rindenschicht durch tiefe
longitudinal wie transversal verlaufende Einkerbungen das Bild einer mosai-
kartigen Tafelung hervorruft.’”’ There are, to be sure, longitudinal and
transverse grooves which are largely the result of contraction (Fig. 1),
but they are never as regular in occurrence as Janicki indicates for C.
solidum.

This species possesses the same type of scolex as C. solidum and Goe-
zeella silurt Fuhrmann 1916. It measures from 1.26 to 3.75 mm in trans-
verse diameter The latter measurement was found in only one case and
then the scolex was completely expanded. Figure 4 represents the scolex
in a more expanded condition. Among 15 individuals bearing ripe pro-
glottids the scolex usually measured about 2 mm in transverse diameter.
The dorso-ventral is always less than the transverse diameter. In one
fully expanded scolex the former is 2.31 mm and the latter is 2.61 mm.
It is evident that the scolex of this species is subject to such ex-
tremes that many individuals must be studied to establish the
range in size. When fully expanded, the scolex appears as a disc surmount-
ing the proglottids and is set off sharply from the neck. In some con-
tracted specimens the scolex is not thus sharply set off (Fig 1). The
collar-like structure which surrounds the suckers may be folded over
them laterally and dorso-ventrally, thus concealing them from view.
Extending from each of the suckers toward the periphery of the scolex
are deep grooves which mark the limits of the folds just described. The
anterior surface of the scolex thus frequently resembles that of Ephed-
rocephalus lobosus as figured by Riggenbach (1896, Pl. 8, fig. 23b). The
apex may be protruded as shown in figure 22, or it may be invaginated
as indicated by figure 19. A rostellum is lacking, and hooks of any kind
are absent.

Four suckers are situated in the anterior surface of the scolex. Their
form and size vary according to the state of contraction. The following
measurements in millimeters were made on sectional material:

Length 0.36, 0.43, 0.41, 0.37, 0.37, 0.38, 0.33, 0.45, 0.33, 0.53
Diameter 0.56, 0.53, 0.51, 0.37, 0.41, 0.40, 0.41, 0.38, 0.43, 0.60
Diameter of opening 0.13, 0.19, 0.21, 0.06, 0.06, 0.06, 0.12, 0.18, 0.18, 0.23

The measurements which follow were taken from toto-mounts:
Length 0.30, 0.23, 0.23, 0.19, 0.26, 0.39, 0.51

Diameter 0.38, 0.26, 0.26, 0.23, 0.23, 0.53, 0.88

Diameter of opening 0.16, 0.09, 0.06, 0.11, 0.13, 0.13, 0.41

A description of the musculature of the scolex and its suckers is un-
necessary, since there is no apparent difference in this regard between
C. fimbriatum and E. lobosus as described by Riggenbach. The peculiar,

277] STRUCTURE AND DEVELOPMENT OF CORALLOBOTHRIUM—ESSEX 23

knob-like structure or sphincter found in the suckers of C. giganteum is
wanting here. In the three descriptions of C. solidum the size of the
suckers is not given. From Fritsch’s figure which was drawn to scale, I
estimated the length of the suckers as 0.6 mm and the width as the same.

A neck is present, but its dimensions are dependent upon the state
of contraction and the size of the specimen. Among eight individuals
the neck in three was longer than wide, but in five cases it was wider
than long. In millimeters the necks measure as follows:

Length 0.46, 0.63, 0.46, 0.53, 0.72, 0.96, 1.05, 1.26

Breadth 0.33, 1.89, 0.36, 0.56, 0.86, 1.21, 1.57, 0.94

In his description of C. solidum Fritsch states, ‘‘Man erkennt ohne
Schwierigkeit, dass die schmalen, ohne Vermittelung eines Halses dem
Kopf angefiigten Glieder, sehr bald geschlechtsreif werden.”’ Fuhrmann,
using the same preparations, reports a short neck, while Janicki states
that no neck is present in the specimens examined by him.

The cuticula of this species varies from 5 to 9u in thickness which
corresponds very closely to that of Corallobothrium giganteum. It is
divided into two layers, an inner which stains deeply with hematoxylin,
and an outer layer which stains very little. Beneath the cuticula courses
the very thin basement membrane (less than 1u). The subcuticular
musculature shows a variation from the usual condition since the longi-
tudinal fibers, which are present in a single layer, lie closely applied to
the basement membrane. The usual layer of circular fibers was not dis-
tinguishable. Beneath the muscle fibers just described occur the spindle-
shaped subcuticular cells which constitute a layer about 0.03 mm thick.
The cortical parenchyma is very loosely constructed. In some sections
it reveals a network of rounded spaces which measure from 6 to 35y.

The musculature of this form is highly developed, but less so than
in C. giganteum. Separating the cortical and medullary parenchyma are
found the inner longitudinal muscles which constitute a layer from 16 to
30u thick. These fibers are arranged in irregularly shaped bundles, but
the bundles are not grouped in layers (Fig. 27). In C. solidum both Fuhr-
mann and Janicki report that laterally the muscles are more highly
developed. This is also the case in C. fimbriatum. In this species trans-
verse bundles, within the longitudinal muscle layer, are very numerous
in immature proglottids; but in mature segments they are crowded against
the longitudinal bundles by the growth of the reproductive organs. Many
dorso-ventral bundles are present between the pouches of the uterus and
in the lateral margins of the medullary parenchyma.

The nervous system consists of a nerve ring situated in the apex of
the scolex near the anterior level of the suckers. A nerve trunk which
measures 0.03 mm in diameter arises from each side of the ganglion and

24 ILLINOIS BIOLOGICAL MONOGRAPHS [278

passes posteriad between the outer margins of the two pairs of suckers.
These trunks extend throughout the strobila in the lateral margin of the
medullary parenchyma close to the longitudinal muscle sheath, as in
C. giganteum and most Proteocephalids.

The excretory system is highly developed, but less so than in C.gigan-
teum. It represents the typical condition as there are two pairs of vessels,
a dorsal or ascending pair, and a ventral or descending pair. The former
are more lateral in position and are found throughout the strobila closely
applied to the nerve trunks. Their course is much less tortuous than
that of the descending vessels. No branches could be found issuing from
them. In ripe proglottids they measure about 4y in diameter, but pro-
ceeding anteriorly the diameter increases until in the neck region it may
attain as much as 24u. The structure of the wall of the ascending trunk
is very similar to that described for C. giganteum (Fig. 40). Frequently
in ripe proglottids the vitellaria surround the dorsal vessel and it might
be mistaken for a longitudinal vitelline duct.

The descending trunks, as already mentioned, describe a tortuous
course. Their position is less rigidly fixed than that of the ascending
vessels, because of the crowding of the reproductive organs, but they
are always found in the ventral medullary parenchyma proximal to the
ascending vessels. Their diameter varies from 24 to 40u. Their walls
are much thinner than those of the ascending vessels. The cross com-
missure which connects the descending vessels and the small vessels
leading to the exterior which have been described for C. giganteum, are
wanting in C. fimbriatum. Likewise I have been unable to discover any
such vessels as Janicki has described for C. solidum. He states: ‘Die
Foramina secundaria gelangen im hinteren Teil der Proglottis auf der.
ventralen Seite zur Entwicklung und stehen vermittelst besonderer
Zweiggefissen mit den zwischen den grossen Ventralstimmen sich
ausspannenden und vielfach secundir anfgelésten Commissuren in Ver-
bindung.” At no point can I find any vessels passing beyond the inner
ongitudinal muscle sheath. The behavior of the ascending and descend-
ing vessels in the scolex is almost identical with that already described
for C. giganteum.

Reproductive Organs

The common gential sinus occurs irregularly alternate on the lateral
margin of the proglottid, almost invariably within the anterior fourth
of the segment. A genital papilla is lacking in this species. The character
and arrangement of the reproductive organs is typically Proteocephalid,
as all the sex organs are contained within the inner longitudinal
muscle sheath.

279] STRUCTURE AND DEVELOPMENT OF CORALLOBOTHRIUM—ESSEX 25

In immature proglottids where the testes are not crowded upon them-
selves or upon other organs, they are typically spherical and measure
from 0.02 to 0.04 mm in diameter. In the mature proglottids, their shape
varies from spherical to elongate oval, the form being dependent on the
degree of pressure to which they are subjected (Fig. 32). The spherical
testes measure from 60 to 72y in diameter while the others range from
64 long by 48 wide to 80u long by 724 wide. The number of testes
present in mature proglottids ranges from 100 to 125. Before the uterus
has undergone a great deal of development the testes occupy all the
available space in the medullary parenchyma (Fig. 14), but as the uterus
grows it crowds the testes dorsally and laterally (Fig. 31). In mature
proglottids only a single layer is present dorsal to the uterus, and only
two or three layers are usually found lateral to it. In ripe proglottids the
testes are crowded out of the lateral portions of the medullary parenchyma
by the uterus, which extends to the vitellaria on each side (Fig. 31).
They are found between the uterine pouches and frequently in the ven-
tral portion of the medullary parenchyma. In the fully ripe segments
they have almost completely disappeared.

Vasa efferentia were not distinguishable in any of the preparations.
The vas deferens which measures from 16 to 50u in diameter is extremely
well developed. Its coils, from 25 to 30 in number, extend from the mid-line
of the segment to the cirrus-pouch (Fig. 14). In immature segments
they occupy nearly the anterior fourth of the medullary parenchyma,
but when the segments become mature they are forced dorsally or between
the pouches of the uterus (Fig. 29). Spermatozoa are present in the
vas deferens when the uterus is in a very early stage of development
(Fig. 14), ie., in proglottids which are otherwise immature. Upon reach-
ing the cirrus-pouch the vas deferens passes over into the ductus ejacu-
latorius. In immature segments it proceeds to the cirrus without coiling
but in mature and ripe proglottids it describes three or four coils before
emptying into the cirrus. Its diameter, upon entering the cirrus-pouch
is about 16u, but it widens as it proceeds, and frequently it may reach a
diameter of 30 to 40u before emptying into the cirrus. As it enters the
cirrus it narrows again to about 16y in diameter.

When inverted, the cirrus measures from 0.13 mm long by 25u wide
to 0.19 mm long by 36 wide. It is typically club-shaped, with the narrow
end at the proximal portion of the cirrus-pouch. When everted the cirrus
measures from 0.16 to 0.23 mm in length and from 40 to 44 in greatest
diameter. It tapers gradually from its proximal to its distal end, where
it measures about 0.02 mm in diameter. .A terminal dilatation is wanting
(Fig. 36). The cirrus-pouch varies from elongate oval, when the cirrus
is inverted, to gourd-shape, when the cirrus is everted. It measures
from 0.17 to 0.24 mm in length and from 0.07 to 0.09 mm in greatest

26 ILLINOIS BIOLOGICAL MONOGRAPHS [280

diameter. None of the descriptions of C. solidum record the size of the
cirrus inverted or everted. The cirrus-pouch according to Fuhrmann is
pear-shaped and measures 0.5 mm long by 0.22 mm wide. Janicki makes
no reference to the shape but reports the length as 0.34 mm. The struc-
tural details of the vas deferens, cirrus and cirrus-pouch do not vary
from those described for C. giganteum.

As in C. giganteum, the vagina opens into the genital sinus beside
the cirrus in a horizontal plane, and may be either anterior or posterior
to the latter. Both the cirrus and vagina pass into the medullary paren-
chyma between the dorsal and ventral excretory vessels and ventral to
the longitudinal nerve trunk.

From the genital sinus the vagina passes along the ventral margin
of the medullary parenchyma for about one-fourth of the proglottids
diameter; then it courses dorsally and posteriorly to the mid-line of the
proglottid, which it follows to the level of the ovarian commissure (Fig.
29). The course of the lower vagina will be discussed presently.

A sphincter vaginae is absent, or only weakly developed. The first
part of the vagina, or the portion that usually extends from the genital sinus
to about the mid-line of the segment, measures from 11 to 16u in diameter.
Its walls are somewhat heavier than those of the succeeding portion. The
second portion of the vagina is thin-walled, and frequently reaches 32u
in diameter, but in such cases it is distended with spermatozoa. This
portion of the vagina functions as a receptacle for spermatozoa. A dis-
tinct seminal receptacle, such as is found inC. giganteum is not present.
Fuhrmann states that a seminal receptacle is wanting in C. solidum. Near
the level of the ovarian commissure the second portion of the vagina is
greatly reduced in diameter, giving rise to the narrow, more muscular,
lower vagina which measures from 8 to 124 in diameter. It passes dorsal
to the ovarian commissure and follows along the lateral margin of the shell
gland. Near the posterior margin of the segment it empties into the
oviduct (Fig. 41).

The bi-lobed ovary lies in the posterior portion of the proglottids
midway between the dorsal and ventral longitudinal muscles. In some
transections the ovary presses against the dorsal and ventral longitudinal
muscles thus filling much of the medullary space in the posterior end of
the segment. Its shape may be roughly omegoid (Fig. 9) or it may be
pyramidal (Fig. 8). The contraction of the segment affects the shape
very materially. When much contracted, each wing of the ovary shows
several secondary lobes (Fig. 12), which are less evident when the seg-
ment is fully extended (Fig. 13). A commissure joins the inner anterior
margins of the two wings of the ovary. The inner posterior margins pass
around the shell gland and proceed toward the median line but do not
join. From the shell gland the two wings extend laterally. The pos-

281] STRUCTURE AND DEVELOPMENT OF CORALLOBOTHRIUM—ESSEX 27

terior margin of each wing parallels the septum of the segment, but the
anterior margin dips down gradually until near the vitellaria on each
side the two margins meet in a rather acute angle. Figures 8, 9, 12 and 13
represent some of the variations in the shape of the ovary. In an ex-
panded ripe segment 1.58 mm wide the ovary measures 0.79 mm in dia-
meter and only 66y at the point of greatest length. In an expanded mature
segment 1 mm wide the ovary measures 0.56 mm wide and 0.01 mm
through the region of greatest length.

The following measurements in millimeters were made on mature
segments which were more or less contracted:

Width of segment: 1.15, 1.11, 1.19, 1.26, 1.26

Width of ovary: 0.45, 0.46, 0.53, 0.54, 0.53

Length of ovary: 0.22, 0.23, 0.24, 0.21, 0.23
These measurements indicate that the width of the ovary is a little less
than half the proglottid diameter.

Near the median line, and on the ventral surface, the commissure
empties into the oocapt which measures from 28 to 38y in diameter and
is surrounded by a layer of gland cells about 16 thick (Fig. 29). Fuhr-
mann gives the diameter of the oocapt of C. solidum as 28u. From the
oocapt the oviduct, whose maximum diameter is about 24u, proceeds
along the lateral margin of the interovarian space. Just before reaching
the intersegmental septum it changes direction and crosses the inter-
ovarian space. Near the opposite side it bends posteriad and dorsad.
After receiving the lower vagina it passes along the posterior margin of
the proglottid. Upon reaching the middle of the interovarian space it
turns anteriorly. Near this point it receives the vitelline duct and empties
immediately into the ootype (Fig. 41).

The ootype, which measures from 12 to 16u in diameter, lies in the
dorsal portion of the medullary parenchyma. It is surrounded by the
shell gland which is highly developed and measures from 0.09 to 0.16 mm.
in diameter (Fig. 32). From its connection with the oviduct the ootype
continues anteriorly from 0.09 to 0.10 mm, then it empties into the ute-
rine passage. The uterine passage is a very thin-walled tube measuring
from 16 to 20u in diameter. From the ootype it proceeds anteriorly
and dorsally. After making several coils it empties into the uterus near
the middle of the proglottid.

The uterus begins growth in the ventral region of the medullary
parenchyma but as it develops takes up more and more space, until
in the ripe proglottids it crowds the vitellaria, excretory vessels and longi-
tudinal nerves at each side, and occupies all possible space (Figs. 25, 31).
The testes, vas deferens and other organs are crowded between the ute-
rine pouches or flattened against the longitudinal muscle layer. The
ovary is frequently pressed against the posterior limit of the segment

28 ILLINOIS BIOLOGICAL MONOGRAPHS [282

to such an extent that it is distorted in shape and may be difficult to
distinguish (Fig. 25). At this stage the proglottid is hardly more than
an egg-sac. From the main uterine stem arise from 10 to 14 uterine pouches,
each of which in turn produces from 2 to 5 secondary pouches (Figs.
29, 32). On the ventral surface of the ripe proglottids occur one or two
uterine pores.

The vitellaria form two lateral columns which extend from the an-
terior to the posterior region of the segment. They are more dorsal than
ventral in position. The ventral excretory vessels lie beneath them. Their
transverse diameter, whichis dependent on theamountof contraction, ranges
from 0.06 to 0.19 mm. At the level of the ovary or near the posterior
limit of the proglottid each column turns inward until it comes in con-
tact with the wings of the ovary (Fig. 14). From these inward-directed
portions arise two vitelline ducts, one from each side, which run ventrad
and meet lateral to the oocapt, forming the common vitelline duct, this
proceeds dorsally and empties into the oviduct near its union with the
ootype. The diameter of the two ducts just mentioned depends on the
presence of vitelline cells; when empty they are indistinguishable, but
when they contain vitelline cells the lumen measures from 11
to 16u. At the point where the lateral ducts empty into the common
vitelline duct a diameter of 32y is frequently attained. From this region
to its union with the oviduct the common vitelline duct measures only
from 16 to 24y in diameter. A distinct vitelline reservoir, like that in
C. giganteum, is lacking in this species (Fig. 41). The vitelline cells pre-
sent in the ducts are ovoid in form and measure from 11 to 14y through
their long axes.

This species shows amphitypy, the same irregularity in the arrange-
ment of the organs of the interovarian space as described for C. gigan-
teum; that is, in successive segments a complete reversal occuts. This
reversal is not correlated with the right or left position of the genital
pore, nor with the position of the vagina with reference to the cirrus.
The organs may be arranged as shown in figure 41 or they may be just
the reverse. In five successive segments the arrangement of the organs
as shown below was observed.

Left Left

of

Genital Pore

Vagina anterior
Vagina posterior
Oviduct right
Oviduct left
Vitelline duct right
Vitelline duct left
Lower vagina right
Lower vagina left

+
+

283] STRUCTURE AND DEVELOPMENT OF CORALLOBOTHRIUM—ESSEX 29

A description of the living egg of the species is given later. Only the
interuterine eggs of prepared specimens will be considered here. The outer
membrane, which is so prominent just after the eggs have been discharged
into the water (Fig. 42), is very difficult to see in sectional material.
The second membrane is clear and since it is rather heavy its size is not
affected greatly by preservatives. Its form is not spherical but is some-
what longer than broad. Through the long axis it measures from 28 to
36u, the average being about 344. The contained oncosphere measures
rom 16 to 24u in diameter, the average being about 20u.

The eggs of this species are larger than those of C. giganteuwm. Fuhr-
mann reports the eggs of C. solidum as being small; ‘“‘die Oncosphaere
hat einen Durchmesser von 0.013 to 0.016 mm, die dussere Schale einen
solchen von 0.020 to 0.024 mm” Janicki remarks: “Die reifen Eier von
C. solidum sind ausserordentlich klein, sie messen nur 0.020 mm im Durch-
messer, erscheinen aber sehr charakteristisch, so dass sie nicht leicht mit
Eiern eines anderen Cestoden verwechselt werden kénnen.”’

The foregoing description indicates that C. fimbriatum bears a close
resemblance to C. solidum, but the following comparison shows some
very outstanding differences between the two forms.

Foramina No. testes Size of second Size of

secundaria egg membrane oncosphere
C. solidum Present 140 to 180 20 to 24u 13 to 16p
C. jimbriatum Absent 100 to 125 28 to 36u 16 to 24y

A lack of specific information on a great many points in the descrip-
tions of C. solidum prevents a more complete comparison. The above
data, however, are sufficient to mark the cestode under consideration
as distinct from C. solidum. It is therefore regarded as a new species,
which is designated as Corallobothrium fimbriatum because of the fringed
character of the scolex.

30 ILLINOIS BIOLOGICAL MONOGRAPHS [284

DISTRIBUTION, ABUNDANCE AND SEASONAL
OCCURRENCE

Corallobothrium giganteum and C. fimbriatum have been found associ-
ated in the intestinal tract of Ictalurus punctatus, Ameiurus melas and
Leptops olivaris taken from the Rock, Mississippi and Illinois rivers.
An intensive study was made only of J. punctatus from the Rock River,
130 of that species being examined during 1926. Nearly 70 per cent
showed infection with one or both species of Corallobothrium. The
following table is confined to the data on the adult parasites.

TaBLeE I
OccURRENCE OF ADULT CORALLOBOTHRIUM

Number Number
Wate oct Number Stream C. fimbriatum | C. giganteum
Examined
Present|Average|Present|Average
October, 1924 | A. melas 3 Rock River 0 0 0 0
é # I. punctatus 5 € 0 0 0
June, 1925 | I. punctatus 8 € . 16 2 21 2.6
y “ | I. punctatus 1‘ |Mississippi R. 10 | 10 8 8
July, 1925 | L. olivaris 1 « e 1 1 1 1
December, 1926 | A. melas 2 Illinois River 0 0 0 0
November, 1927 | A. melas 5 & « 0 0 0 0
April, 1926 | I. punctatus 14 Rock River 0 0 0 0
June, : = c 10 e 25 2:5 15 5
July, is ie a 46 « oy 42 0.95 61 ai)
August, 6 « ae 25 “ o 12 0.48 6 0.24
September, “ « « 6 i « 0 0 4 0.66
November, “ é < 11 é ss 0 0 0 0
December, “ é “ 18 € # 0 0 0 0

It is evident from the preceeding data that the adult form of Cor-
allobothrium appears in the late spring or early summer, reaches its
maximum during June and July, and disappears entirely the latter part
of October or the first part of November. Additional data on the sea-
sonal occurence of Corallobothrium giganteum and C. fimbriatum have been
secured by an examination of the parasites collected by Mr. R.E. Richard-
son of the Illinois Natural History Survey, in connection with his studies
on the food of Ictalurus punctatus. Only the stomach and about 5 cm
of the intestine of each fish were preserved for his investigation. From
such a limited portion of the intestinal tract, at best, only a small per

285] STRUCTURE AND DEVELOPMENT OF CORALLOBOTHRIUM—ESSEX 31

cent of the parasites present in each fish could be secured. In all, 1252
individuals were examined. From 954 J. punctatus, which were collected
from June to September, 35 showed the presence of either one or both
species of Corallobothrium. Among 278 of the same species of fish, col-
lected from October to May, no parasites were recorded. While to be sure,
a much larger number was examined during the period from June to
September nevertheless a sufficient number was studied throughout the
months from October to May to warrant the expectation of a proportionate
percentage of parasitized fish, had the cestodes been present to the same
degree during the whole year. Taken independently, these data would
not be significant, but in connection with the evidence shown in Table
1 there can remain little doubt that the adult form of both species of
Corallobothrium occurs only from spring to fall in J. punctatus.

Meggitt (1914) in his study of Proteocephalus filicollis states: ‘‘Almost
every fish in autumn was infected with one or more of these parasites,
75 per cent of which were adult; in winter, the number of infected fish
was considerably smaller, and adults were rare; while in spring, the pro-
portion of adults again increased.” He goes on to say that von Linstow
failed to find adult P. filicollis at all in winter, and Zschokke noticed it only
three times. Wagner (1917) makes the following statement regarding P.
torulosus: ‘‘Wie verschiedene Autoren (Zschokke, v. Linstow, Kraemer,
Riggenbach) iibereinstimmend berichten, fillt die Reife der Geschlechts-
produkte der Fishtaénien in Zeit zwischen Friihling und Herbst. Im
Winter sind immer nur junge, noch nicht geschlechtsreife Tiere gefunden
worden, was auch meine Erfahrungen an /. torulosa bestatigen.” Thus
my findings for Corallobothrium agree, for the most part, with those
or Proteocephalus filicollis and P. torulosus as just quoted.

32 ILLINOIS BIOLOGICAL MONOGRAPHS [286

LIFE HISTORY OF CORALLOBOTHRIUM

Gruber, (1878) in his study of the copepods of Lake Constance, was
the first to discover a larval cestode in the body cavity of a Cyclops.
He found and described a procercoid from C. brevicaudatus and made
the following conjecture: ‘‘Die Entwicklung zur Taenia erfahrt der
Wurm ohne Zweifel im Darme eines der zahlreichen Fische welche sich von
den kleiner Krustern des Sees ernéhren und es méchte wohl am wahrschein-
lichsten sein, der Jungendzustand der TJ. torulosa ist, welche nach Ru-
dolphi und Dujardin in Cyprinoiden unser Siisswasserseen lebt, obgleich
es mir bis jetzt noch nicht gelungen ist, dieselbe aufzufinden.” Following
Gruber’s discovery papers appeared by Mrazek, v. Linstow, and others,
which described procercoids from Cyclops, Diaptomus, Gammarus and
various ostracods. In many instances the larvae were identified with
known adult parasites, but such studies usually admit of considerable
doubt. Schmidt (1894) was the first to feed tapeworm eggs experiment-
ally to the smaller aquatic crustacea. He succeeeded in infecting Cypris
ovata with the eggs of the duck tapeworm, Taenia anatina, and described
the development of the latter species from the oncosphere to the mature
procercoid (Cysticerkoide).

Linton (1891) published a contribution to the life-history of Di-
bothrium cordiceps in which he says, ‘I have found a large Dibothrium
in the white pelican (Pelecanus erythrorhynchus) which is evidently the
adult form of D. cordiceps, of which the trout (Salmo mykiss) is
the intermediate host.’’ Linton gives no experimental evidence to sub-
stantiate his supposition. Consequently his conclusions are largely con-
jectural. No experimental work was done on the first intermediate hosts
of fish cestodes until the work of Schneider (1903) who infected Gam-
marus locusta with the eggs of a species of Proteocephalus, Barbieri
(1909) described a new cestode from Alsosa finta var. lacustris which
he called Ichthyotaenia agonis. On insufficient evidence he gives the inter-
mediate hosts for his cestode as Bythotrephes and Leptodora.

A successful study of the complete life-cycle of a fish cestode was
made by Meggitt (1914), who traced the complete development of Pro-
teocephalus filicollis by experimental methods. Cyclops varius was found
to be the first and only intermediate host. P. filicollis is parasitic in the
stickleback. The latter is infected by ingesting Cyclops which contain
mature procercoids of P. filicollis.

Wagner (1917) made a splendid experimental study of the develop-
mental cycle of Proteocephalus torulosus, for which he discovered Cyclops
strenuus and Diaptomus castor as the first intermediate hosts. The fish

287] STRUCTURE AND DEVELOPMENT OF CORALLOBOTH RIUM—ESSEX 33

host, Cyprinus orfus, is infected with P. torulosus by feeding on cope-
pods, some of which are infected.

Janicki and Rosen (1917) published the results of their successful
study on the manner in which fish were infected with the plerocercoid of
Diphyllobothrium latum.

Following this work, Rosen (1918) elucidated the life-history of two
other species, viz., Triaenophorus nodulosus and Abothrium infundi-
buliforme. A year later the same worker outlined the development of
Ligula simplicissima. It was found that the life-cycles of these forms were
almost identical, excepting in A. infundibuliforme, the mature egg gives
rise to a ciliated larva; the egg of that species, however, produces in the
water an unciliated larva. In each case these larvae are eaten by some
species of Cyclops and the subsequent development is practically the same.
All of these cestodes except A. infundibuliforme require a second inter-
mediate host, which is found among the young fish inhabiting the same
waters. The adult host of D. /atum is man, the dog, or possibly the cat;
that of T. nodulosus and A. infundibuliforme is found among the fish,
while that of L. simplicissima is some species of aquatic bird.

The literature contains no further studies on the life cycles of fish
cestodes until the appearance of a fine paper by Kuczkowski (1925).
This worker succeeded in infecting Cyclops strenuus, C. serrulatus and
C. oithonoides experimentally with the eggs of Proteocephalus percae
which is parasitic in Gasterosteus aculeatus, and likewise C. strenuus
and C. serrulatus with the eggs of P. longicollis which is parasitic in Core-
gonus albula. In this study, Kuczkowski, gave particular attention to
the development of the bladder appendage, or ‘‘cercomer,”’ and its bear-
ing on the “‘cercomer theory.” Bangham (1925), in his studies of the
cestode parasites of the black bass, reports that the procercoids of P.
pearsei were found in a species of Cyclops and also in Epischura lacustris.
Since no experimental work was done to establish the identity of the lar-
vae there remains considerable doubt whether they were the procer-
coids of P. pearsei or some other Proteocephalid.

The papers just mentioned represent the work that has been done
on the life-cycles of fish cestodes in Europe and America up to the present
time. Therefore the study of the developmental history of fish cestodes
from American hosts offers a nearly unexplored field. The investigation
reported here was undertaken in the hope that some definite information
might be obtained on the developmental cycle of the two species of Ameri-
can fish cestodes just described.

OBSERVATIONS CONCERNING THE EGGS

After the cestodes were removed from the intestine of the fish, they
were washed immediately in tap water. This was done by grasping the

34 ILLINOIS BIOLOGICAL MONOGRAPHS [288

worm near the middle with a pair of forceps and rapidly raising and lower-
ing it in the water. Each adult individual was then placed in a separate
watchglass and covered with cold water. The excessive contractions of
the worms caused the eggs to be ejected in milk-colored streams from
the uterine pores of all the ripe proglottids. It was estimated that upward
of a million eggs were emitted by an average-sized adult Corallobothrium
gigantewm, and one-half million or more by an adult C. fimbriatum. Ac-
cording to LaRue (1914) the eggs of the Proteocephalids usually have
three membranes. The outermost membrane is thin, hyaline and spheroi-
dal in form. The middle membrane is thick and granular. The inner-
most membrane is a clear, delicate but tough structure which is closely
applied to the embryo.

The eggs of Corallobothrium fimbriatum are typically spherical, usually
flattened and depressed at each pore. In their general outline they recall
the form of an apple. The diameter varies from 0.08 to 0.14 mm. The
outer membrane encloses a thick layer of transparent, gelatinous sub-
stance wich is responsible for the unusually large size of these eggs (Fig.
42). At the center of the gelatinous material is found a second membrane
which is ovoidal in form, varying in size from 36 to 38u by 30 to 32u.
The structure of this membrane is homogeneous and firm. It does not
have a granular appearance in the living material nor in the eggs sec-
tioned in the uterus. It presents rather the character of a chitinous cover-
ing which closely resembles, and is doubless homologous to, the shell of
the Bothriocephalan egg. Meggitt (1914) reports an aperture in the second
membrane of the eggs of P. filicollis. I have not observed such an open-
ing in the eggs of either species of Corallobothrium. Lying beneath the
second membrane of the eggs of Corallobothrium fimbriatum is a dense layer
of granular substance about 0.10 mm thick. This material is doubtless
composed of vitelline granules and other substances, either stored for
the nourishment of the oncosphere or cast off during its formation. Sur-
rounded by the granular layer just mentioned is found the six-hooked
embryo. A third membrane could not be distinguished in either living
or sectional material. The membranes of the living egg are so trans-
parent that the oncosphere, which is about 20y in diameter, can be seen
distinctly. By a series of gliding movements it turns itself about within
the shell or second membrane. Coincident with the movements of the body,
the hooks are repeatedly extended and withdrawn. Observations made
successively on the same individual for 12 hours showed that the onco-
sphere continued its apparent efforts to escape from its enclosing mem-
branes. Its movements were rather spasmodic and intermittent. A period
of vigorous contortions, during which it would frequently turn itself
completely about, would be followed by a longer period of inactivity. On
several occasions oncospheres were observed to work their way through

289] STRUCTURE AND DEVELOPMENT OF CORALLOBOTHRIUM—ESSEX 35

the granular layer and reach the shell, against which they repeatedly
brought their hooks with all possible force but without apparent effect.
The second membrane or shell seemed impervious to the action of the
hooks. These observations indicated clearly that the oncospheres could
not escape from the egg membranes by their own efforts.

Frequently in studying the eggs the rupture of the shell was noted. This
permitted the escape of the oncosphere into the gelatinous covering (Figs.
43, 46). I could not always attribute the ruptured shell to the pressure of
the coverglass. Meggitt (1914) who observed the same phenomenon in
the eggs of P. filicollis offers the following explanation: ‘The cause of its
[the oncosphere’s] escape may be possibly due to osmosis, but it is more
probable that it is due to the oncospheric movements.” That is, the
oncosphere forces its way out of the shell through the aperture which has
already been mentioned. My observations on the structure of the shell
and the activity of the oncosphere of Corallobothrium fimbriatum make the
latter explanation untenable. When the oncosphere is found free in the
gelatinous covering its structure and movements are more easily observed.
The body of the oncosphere is covered by a very delicate membrane in
which the proximal ends of the hooks are embedded. Within this mem-
brane is the plasma, a grayish mass of homogeneous substance containing
extremely fine granules. The plasma vividly recalls the color and structure
of the protoplasm found in Amoeba proteus. Cell boundaries could not be
distinguished, and it was quite impossible to detect the presence of any
structures that might be interpreted as muscle fibers.

To determine the method by which the hooks of the oncosphere were
brought into action, a long series of observations was necessary. The hooks
are arranged in three pairs near the periphery of one pole of the embryo.
Two pairs are placed laterally, while the third pair lies between. Usually
the proximal ends of the hooks lie close together while the distal ends,
bearing the hooks proper, are more widely separated. Before being thrust
out the lateral pairs are brought up close to the middle pair. When this
movement is completed the hooks of each pair are parallel with each other
(Fig. 46). After watching their movements for hours, it became quite
evident that the hooks were incapable of independent action; that their
extension only occurred when the body of the oncosphere was elongated
(Fig. 43); and that their return to a position of rest occurred only when the
oncosphere again assumed a spherical form, i.e., the elongation of the
oncosphere extended the hooks and its contraction withdrew them. The
presence of muscle fibers attached to the hooks is extremely doubtful.
My observations lead me to the conclusion reached by Janicki and Rosen
(1917) in their study of Diphyllobothrium latum, viz., that the hooks,
embedded in the membranous covering of the oncosphere, are brought into
action as a result of the movements of the plasma rather than through the
agency of muscle fibers.

36 ILLINOIS BIOLOGICAL MONOGRAPHS [290

In Corallobothrium giganteum only a glance at the eggs is needed to
distinguish them from those of C. fimbriatum (Figs. 42, 50). The differ-
ences in shape and size are noticed at once. They are much smaller, measur-
ing only from 30 to 60u in diameter. Their shape is extremely irregular
and varied. These differences are due largely to the distribution of the
gelatinous material which surrounds the shell. It usually covers the shell
in varying degrees of thickness, with here and there a finger-like projection
which may give the egg a star shape. In some instances these projections
are absent or less pronounced (Figs. 49, 50). The thickness of the gela-
tinous material is then more uniform (Fig. 49). The shell itself is almost a
perfect sphere, measuring from 21 to 24y in diameter, which is considerably
smaller than that of C. fimbriatum. A layer of finely granular material is
present within the shell, but its thickness is much less than in C. fimbriatum.
The oncosphere, which ranges from 13 to 16u in diameter, is not sur-
rounded by a third membrane.

Although the structure of the eggs of the two species of Corallobothrium
is identical, there is wide variation in the amount of the differentiated
parts. Thus the ova of C. giganteum have less of the outer gelatinous sub-
stance, less of the granular material within the shell, and a much smaller
oncosphere. Also, the shape and size of the egg as a whole, and the shape
and size of the shell are quite different in the two species.

Experiments with the Eggs

To determine whether or not the eggs would hatch, watchglasses
containing several thousand eggs were placed in the dark at room tempera-
ture. As a control another watchglass containing a like number of eggs
was placed in the light at room temperature. Neither batch of eggs hatched.
This experiment, together with observations on the structure of the eggs
of each species, indicated that they did not give rise to free larvae but must
be ingested in toto by the first host.

It was difficult to determine the viability of the eggs because of the
action of bacteria. Thirty-six to forty-eight hours after the isolation of
the ova myriads of bacteria began their destructive action upon them
but feeding experiments with eggs which had been isolated for four days
showed positive results. Eggs liberated in nature would very probably
remain viable for a much longer period, since the bacteria should be less
numerous in the open waters than under the restricted conditions in the
watchglasses. In a medium containing a minimum number of bacteria
it is probable that the ova remain viable for eight or ten days, and possibly
for a longer period. :

To ascertain the manner in which the eggs were disseminated—whether
discharged from the proglottid before or after leaving the host—a series
of observations were made on live fish. Adult Ictalurus punctatus were

291] STRUCTURE AND DEVELOPMENT OF CORALLOBOTHRIUM—ESSEX 37

placed in the laboratory aquaria, and for three or four successive days
after their arrival the feces were examined once or twice a day. The feces
were obtained by placing the fish on its back and firmly stroking the ab-
domen in the direction of the anus. The feces forced out in this way were
inspected for the presence of cestode proglottids, eggs, etc. In such exam-
inations of adult fish, eggs were present, but no detached proglottids were
found. Furthermore, in post mortem examinations of over 100 adult
I. punctatus, not a single detached ripe proglottid was recorded. From this
evidence and that gained from the study of the adult worm (uterine pore,
firmly attached proglottids, etc.), it is concluded that the eggs are forced
through the uterine pores and pass out with the feces into the water, where
they float about for a time and then sink to the bottom.

THE FIRST INTERMEDIATE HOST

In attacking the problem of the life-cycle of these parasites, two
methods of approach were considered. First, it seemed reasonable to
suppose that some clue to the intermediate hosts of the parasites might
be gained by a thorough examination of the stomach and intestinal con-
tents of the fish. Since the larvae of the cestodes probably must enter their
final host passively with its food, a systematic study of the food of the fish
was made a part of the routine of examinations. Secondly, the inter-
mediate host might be discovered through direct experiment, i.e., by
feeding ripe proglottids or eggs to any invertebrate animals which might
possibly serve as the first intermediate host of the parasites.

The diet of 55 Ictalurus punctatus examined during the months of June
and July consisted almost exclusively of crayfish, Cambarus propinquus,
larval and adult Hexagenia bilineata, other insect larvae, and portions of
mollusks and fish. The first two of these forms were considered as possible
intermediate hosts, and macroscopical and microscopical examinations
were made of the remains of those obtained from the stomachs of the fish,
but with negative results. It was thought advisable, however, to attempt
an infection by feeding them ripe proglottids or eggs.

Experiments with the crayfish, Cambarus propinquus, were carried on
from July fifth to fourteenth. Crayfish secured from Rock River were
placed in laboratory aquaria. After they had been allowed to fast for two
or three days, living adult individuals of C. giganteum and C. fimbriaium
were fed to them. Although they did not show a decided preference for
the worms, they did eat them. At intervals varying from a few hours to a
week after the worms had been ingested, the crayfish were examined. The
intestine was removed, its contents teased out on a slide and inspected
for the presence of oncospheres that might be in the lumen or for more
advanced stages of the larvae encysted in the intestinal wall. Likewise,
all the organs contained in the body-cavity were examined, and also the
surrounding musculature. The results were negative.

38 ILLINOIS BIOLOGICAL MONOGRAPHS (292

Experiments with the Mayfly, Hexagenia bilineata, were made between
July twentieth and August fifteenth. While the work with the crayfish
was in progress, experiments were conducted on the larvae of Hexagenia
bilineata. To obtain uninfected material adults were caught and stripped
of their eggs, which were placed in large Petri dishes in the laboratory where
they were allowed to stand. The water on them was changed every 24
to 48 hours. Seventeen days incubation produced hundreds of small larvae.
Eggs of C. giganteum and C. fimbriatum were placed in two Petri dishes
containing fifteen to twenty of these larvae and water-plant. Observations
of the larvae under the binocular showed them swimming about or clinging
to the vegetation in the containers. None of them seemed to be attracted
to the tapeworm eggs. Subsequent examination of the larvae showed no
trace of infection with the cestode larvae.

Experiments with Cyclops albidus also were conducted during July;
these were coincident with the experiments just described. A supply of
Cyclops albidus was collected from a lagoon near Rock River. A single
individual was placed in each of six watchglasses, along with a spray of
water-plant. After three or four days it was decided that they could live
under such restricted conditions, as all of them were alive and very active.
Then a drop of water containing the eggs of Corallobothrium giganteum
was added to each of three watchglasses; and to each of the other three,
a drop of water containing the eggs of C. fimbriatum. My observations of
the Cyclops under the binocular convinced me that they were not attracted
to the cestode eggs. They would, however, readily devour protozoa which
were placed with them. On one occasion fork-tailed cercaria, obtained
from a snail of the genus Physa, were placed in a watchglass with a C.
albidus. To my great astonishment the Cyclops pounced upon one after
another until fourteen were devoured.* Since efforts to observe the in-
gestion of the eggs by this species of Cyclops resulted negatively, and
since no oncospheres or larvae were found when all of the individuals were
afterward examined, it was concluded that further experiments with this
species would be futile. It was evident that such a process of elimination
applied to each animal which might be suspected of being an intermediate
host of these cestodes, would consume much more time than I had at my
disposal. Therefore, a more comprehensive method was conceived and
pursued.

Mass infection of plankton was accordingly tried from July twentieth
to August second. Not far from the Rockford College campus Rock River
is obstructed by a dam. By holding a plankton net in the water that poured
over this dam, it was possible in a few minutes to collect samples of a large
number of the pelagic forms, as well as some bottom organisms that were

* This may account for the infrequency with which cercaria are met in plankton samples.

293] STRUCTURE AND DEVELOPMENT OF CORALLOBOTHRIUM—ESSEX 39

caught in the current and carried over the dam. A large quantity of the
material gathered by this means was placed in each of two crystalizing
dishes. Water-plant of the genus Cladophora taken from the face of the
dam was placed in each dish. The bottom of one dish was strewn with the
eggs of Corallobothrium giganteum and that of the other with the eggs of
C. fimbriatum. Under these conditions all species were subjected to identi-
cal conditions; each was given an equal opportunity to ingest the eggs.
It was hoped by an examination of the species contained in these cultures
that the primary host of each worm might be discovered. After the
cultures had stood for eight days, an examination of the different species
present was begun. Since among the Copepoda a number of species had
been discovered as the primary hosts of cestodes, representatives of that
group were examined first. Each copepod was placed on a slide in a small
drop of water, then excess water was drawn off with a fine pointed pipette
so that only enough water was left to cover the specimen. This procedure
minimized its movements and anchored it to the spot so that it could be
examined successfully under the microscope. By this method several
hundred copepods were examined.

From the culture in which C. giganteum eggs were placed, Cyclops
serrulatus were found to be infected with from 1 to 6 larvae each, while
C. prasinus were infected with from 1 to 3 each. From the culture inocu-
lated with C. fimbriatum eggs, infected individuals were found among
C. bicuspidatus and C. serrulatus, the former usually showing much heavier
infection. No infection was observed among the copepods, C. albidus,
C. fuscus, C. bicolor, or Diaptomus, nor among the Cladocera examined.

Since these results were accepted as a clear indication of the true first
intermediate hosts of Corallobothrium giganteum and C. fimbriatum, further
group infections were discontinued and a series of experiments were carried
on with isolated groups of the species that had shown infection under mass
conditions.

To determine the species and to prevent the inclusion in the experi-
mental groups of individuals infected in nature each Cyclops was examined
microscopically. Because of the transparency of the Cyclops, a cestode
larva, when present, could be detected without great difficulty. The un-
infected C. serrulatus and C. prasinus were placed together, and uninfected
C. bicuspidatus and C. serrulatus were also allowed to occupy the same
container.

Experimental infection of Cyclops was successfully attempted in
August. These copepods were placed in a fingerbowl of tap water to which
were added a few sprays of water-plant that had previously been rinsed
thoroughly to reduce the protozoa in the fingerbowls as much as possible
and likewise to prevent the entrance of uninspected Cyclops. On August
twentieth at 11:30 a.m. the eggs of C. fimbriatum were placed in with

40 ILLINOIS BIOLOGICAL MONOGRAPHS [294

them. Oncospheres were found at 3:45 p.m. of the same day in the body-
cavity of the Cyclops examined. Thus in a little more than four hours the
oncospheres had migrated from the intestine into the body-cavity.

To determine whether or not the ingestion of the tapeworm eggs was
selective or accidental, a study of the feeding habits of the Cyclops was
andertaken. A fingerbowl containing C. bicuspidatus and C. serrulatus and
the eggs of Corallobothrium fimbriatum was observed under the binocular.
It was noted that the Cyclops foraged over the sprays of water-plant in
the bottom of the fingerbowl and browsed on the particles of debris ad-
hering to the vegetation and to the bottom. Any of the smaller protozoa
which came near were instantly consumed. The outer gelatinous portion
of the tapeworm eggs was repeatedly trimmed off and eaten, while the
inner membrane (shell) containing the oncosphere was rejected. By con-
tinuous observation it was revealed that occasionally the inner portion
also was taken in with the rest, which indicated that the eggs were eaten
only incidentally, along with other organic material on which the Cyclops
fed. This condition is in striking contrast with that of Diphyllobothrium
latum and related forms in which the eggs give rise to ciliated larvae that
successfully simulate protozoa and therefore constitute real objects of
prey, attracting the Cyclops by their movements and tempting them to
pursuit and capture.

The mass infection experiments had shown that Cyclops serrulatus
could be infected by feeding the eggs of either species of Corallobothrium,
but this point was not settled in respect to Cyclops bicuspidatus and
C. prasinus. Therefore the eggs of Corallobothvium giganteum were fed to
Cyclops bicuspidatus and those of Corallobothrium fimbriatum to Cyclops
prasinus. The eggs of Corallobothrium giganteum were eaten by Cyclops

, bicuspidatus and the oncospheres migrated to the body-cavity, but no
development was observed. The oncospheres, five days after the eggs were
fed, measured only 16u in diameter, their original size. The number present
ranged from 2 to 15. This condition was noted in 15 different individuals
examined from 1 to 5 days after feeding. The infection of C. prasinus with
Corallobothrium fimbriatum larvae was light; only 2 individuals out of 10
harbored the larvae. The latter, however, were well developed.

Development of Corallobothrium fimbriatum in Cyclops

When Cyclops bicuspidatus and C. serrulatus had been identified as the
first intermediate hosts of Corallobothrium fimbriatum, a study of the
successive developmental stages in these copepods was begun. All observa-
tions were made on living material and within the period from August
twentieth to September fourth. Beginning from one to four hours after
feeding, the progress of development was traced through all of the stages
found in these animals. As has already been stated, oncospheres were

295] STRUCTURE AND DEVELOPMENT OF CORALLOBOTHRIUM—ESSEX 41

first observed in the body-cavity of the Cyclops about four hours after
the eggs had been placed in the watchglasses. Immediately following their
liberation in the intestine of the Cyclops, the oncospheres increased
slightly in diameter. While contained in the egg membranes, they measured
from 16 to 20y, but after liberation they measured from 18 to 23 in
diameter. Those present in the body-cavity about four hours after the
eggs were fed measured from 20 to 25u. Their form, however, constantly
changed. They did not remain fixed to the intestinal wall of the host by
means of their hooks but kept up almost constant motion. Since the
elongation and contraction of the body put the hooks in operation, the
action of the oncospheres resulted in the repeated extension and with-
drawal of their hooks.

After the oncosphere had gained the body-cavity of the Cyclops,
development proceeded very rapidly. Twenty-four hours after the eggs
had been fed, four oncospheres were liberated, these measured from 30
to 40u according to the stage of contraction. Figure 53 shows one as it
appeared within the abdomen of the Cyclops, while figures 44 and 45
represent their condition 5 to 10 minutes after being liberated. Clear spheri-
cal bodies (cells) surrounded by heavy granules were seen throughout the
body mass. When first liberated the oncospheres moved about with a
gliding movement. During this time the hooks were kept in almost con-
stant motion. Five or ten minutes after the larvae had been removed from
the Cyclops indications of degeneration were seen. Then a transparent
membrane was pushed out from the body of the oncosphere (Figs. 44, 45).
In the individual represented in figure 45 there was a secondary membrane
within the outer one from which the parenchyma had withdrawn. Thus it
appears that the larvae at this stage possess two membranes; the outer
may be considered cuticular while the inner may represent the basement
membrane.

Seventy-two hours after feeding, the larvae ranged from 25 to 70y in
diameter (Figs. 55, 48). They were capable of distinct contractions which
could be witnessed while they were still within the host. Upon removal,
which was accomplished by tearing the Cyclops open by means of two
sharply pointed needles, they appeared as a thin-walled sac containing
globular bodies representing the parenchymatous tissue, which resembled
an emulsion. Their movements were extremely feeble and continued for
only a few minutes, then a spherical form was assumed and degeneration
soon followed. The hooks, which were widely separated at one pole of the
body at this stage, were incapable of effective action.

Four days after feeding, 12 oncospheres, measuring from 25y in diameter
to 135y in length by 60u in width, were removed from the body-cavity of
one Cyclops. Figure 54 represents the most highly developed individual.
Its sac-like body showed considerable differentiation. A cuticular mem-

42 ILLINOIS BIOLOGICAL MONOGRAPHS [296

brane surrounded the body and beneath it the tissue had a striated appear-
ance, due to the development of the subcuticular musculature. Large cells
surrounded by more or less heavy granules were evident. A few small
calcareous bodies were to be seen scattered here and there throughout the
body mass.

On the fifth day a Cyclops was dissected and 14 larvae were present
in the body-cavity. These were from 0.06 to 0.24 mm in length. Except for
the increase in size, no marked difference between these and the four-day
individuals was noted.

One Cyclops observed on the sixth day had 16 larvae in the body-cavity
(Fig. 51). Some of these larvae showed an increase in size over those of the
fifth day, since they measured from 0.22 to 0.4 mm in length, according
to the state of contraction. Upon being liberated, they moved about more
vigorously for several minutes. The narrower end, which bore the hooks,
showed more activity than the broader portion. Further differentiation
had occurred, as the pole at which the hooks appeared presented a striking
contrast to the homogeneous structure of the remainder of the body. It
had become extremely transparent. The granules which appeared in the
remainder of the body were entirely absent in this portion. At the proximal
limit of this transparent region, or about 0.04 mm from the extreme body
limit, a slight constriction appeared. In some individuals the hooks were
attached to this portion, but in others they occurred just beyond the
constriction in the granular region of the body (Fig. 56). In a number of
cases some of the hooks were present on both regions (Fig. 57).

After six days no further increase in the length of the larvae took place,
but many changes in their structural aspects occurred in quick succession.
Thus on the seventh day there were evidences of differentiation at the pole
opposite that on which the hooks were found. On the eighth and ninth days
the larvae showed three distinct regions marked by two constrictions;
one delimited the transparent region, the other occurred about one-third
of the body length from the pole opposite that which bore the hooks
(Fig. 56). By the tenth day, outlines of the developing suckers could be
seen in this portion of the body, which was, therefore, the potential scolex.

Larvae studied on the eleventh day after the Cyclops were fed showed
the four suckers well developed and at the anterior extremity a distinct
end-organ. The large globular cells of the scolex region had disappeared.
In their place a reticulum of minute, rounded cells with an occasional
muscle fiber had appeared. The calcareous bodies, 5 or 6 in number, were
confined, with a very few exceptions, to the middle portion of the larva
The transparent region, more distinctly separated from the middle portion,
formed a bladder-like appendage or cercomer (Fig. 57).

297] STRUCTURE AND DEVELOPMENT OF CORALLOBOTHRIUM—ESSEX 43

The development on the twelfth and thirteenth days differed from that
on the eleventh in the following respects: The scolex, which had been
differentiated by the eleventh day, was invaginated; the number of cal-
careous bodies had increased; and the length, by reason of the invaginated
scolex, was somewhat reduced (Fig. 58).

Development in the Cyclops is completed by the fourteenth or fifteenth
day after the ingestion of the eggs. The best indication of this is the
invagination of the scolex and the loss of the bladder, or posterior ap-
pendage. Janicki and Rosen (1917) have given this larva the name of
procercoid. After this stage is reached the parasite must enter another host
before further development can be attained.

To indicate the extent of infection that may occur in such experimgnts,
it should be stated here that from one culture 50 specimens of C. bicuspi
daius were removed and 46 contained the larva of Corallobothrium fim-
briatum.

Development of Corallobothrium giganteum ix Cyclops

The development of this species corresponds closely with that of
Corallobothrium jfimbriatum. The oncospheres were observed in the body-
cavity of Cyclops serrulatus eight hours after the eggs had been placed in
the fingerbowls. Their presence was more difficult to detect because of
their smaller size and greater transparency (Fig. 52). The number of
larvae present in these species of Cyclops varied from 1 to 8. Therefore
the infection was less intense than that found in the previous species where
as many as 18 larvae were present.

No further observations on the progress of this species were recorded
until the eighth day after the eggs were fed. By that time the larvae had
attained a length of from 0.28 to 0.39 mm, which corresponded closely to
the size of the larvae of Corallobothrium fimbriatum at the end of an equal
period of time. However, the differentiation of various body regions had
progressed considerably more than was true of the C. fimbriatum larvae
in the same length of time. The suckers and end-organ were distinct and
the bladder, or posterior appendage, was almost completely separated
from the middle portion; and a larger number of calcareous bodies were
present in this species than occurred in C. fimbriatum at a much later
period. It was also noted that the globular cells, which were very prominent
in C. fimbriatum, were much less pronounced in these larvae. Aside from
the heavy granules scattered through the body, the structure was more
homogeneous than that of the other species (Fig. 70).

On the twelfth day an examination of infected Cyclops revealed that
the larvae had already become mature procercoids (Fig. 68). This was at
least two days earlier than the same stage was reached by C. fimbriatum.
The cuticula had increased greatly in thickness. The length of the larvae,

44 ILLINOIS BIOLOGICAL MONOGRAPHS [298

which was somewhat reduced by the invagination of the scolex, ranged from
0.2 to 0.25 mm according to the degree of contraction. As was true in the
case of the other species, the bladder or posterior appendage had been
shed and in addition a well-developed excretory vesicle had appeared in
the posterior portion of the body. This organ, which measured from 5 to 9u
in diameter, could be traced anteriorly for about 0.06 mm when it became
obscured by the surrounding structures. Efforts to detect smaller vessels,
which doubtless emptied into it, failed entirely. The vesicle terminated
posteriorly in a duct which emptied at the point where the bladder had
been attached. Pulsations which began at the anterior portion and passed
to the excretory pore, could be seen to proceed rhythmically along its
length. An attempt to discover the vesicle in individuals that still possessed
the bladder proved futile. There may be a relation between these two
structures, besides one of sequence in development, but any statement
further than this would be purely conjectural. Such a vesicle was not
observed in C. fimbriatum. If present, it was obscured by other structures.
It was easily seen in a later stage to be described presently.

Twelve-day larvae possessed a greater number of calcareous bodies,
from 15 to 25. These were not restricted as in C. fimbriatum almost ex-
clusively to the middle body region but were distributed everywhere along
the periphery. More of them, however, were present in the posterior
portion than elsewhere. The total number in this species is almost twice
that discovered in any of the larvae of C. fimbriatum of about the same age
(Figs. 58, 68).

The suckers and end-organ of the invaginated scolex could not be dis-
tinguished clearly in this species, as they were obscured by the overlying
tissues. Following their liberation from the Cyclops, the larvae moved
about actively for an hour or more. In one or two instances the scolex was
evaginated. Figure 64 (a to /) represents the successive movements and
shapes assumed by the larva before the evagination of the scolex. Figure 66
represents the appearance of one specimen with scolex everted after having
been fixed and mounted. Maturity in the Cyclops has been reached by this
species when the scolex has become invaginated, when the bladder appen-
dage has been shed, and when the excretory vesicle has appeared.

It is interesting to note the difference in the rate of development found
in these two species. Although Corallobothrium giganteum begins with a
much smaller oncosphere, it develops at a rate sufficient to attain maturity
in the Cyclops about two days before that point in development is reached
by C. fimbriatum. Furthermore, the size of the adults in the two species
would indicate that this difference manifests itself throughout the develop-
mental cycle of each.

An interesting observation, which was the cause of considerable concern
early in the course of these experiments, was made in connection with the

299] STRUCTURE AND DEVELOPMENT OF CORALLOBOTHRIUM—ESSEX 45

Cyclops that contained from 8 to 18 larvae. In such individuals several
stages of development were frequently represented. For example, fifteen
days after the eggs had been fed, mature procercoids and others, represent-
ing from three to ten days progress, were present in the same Cyclops.
These differences were first considered to be due to the variability in the
time at which the eggs had been ingested. The mature forms would thus
represent the ingestion of the first eggs, and the less mature individuals
the eggs eaten more recently. Further observation, however, indicated
that this explanation was incorrect, since it was noted, by examination
of the same Cyclops on successive days, that certain of the larvae increased
very little in size. Among six C. fimbriatum larvae present in one Cyclops
serrulatus, there were two fully mature, one represented the stage shown in
figure 57, and three showed a development of about 10 days. In another
Cyclops of the same species containing eight larvae of C. gigantewm, three
were mature (Fig. 68) and five were immature. Their movements after
liberation were very feeble and lasted for only five or six minutes. One
Cyclops bicuspidatus infected with 18 larvae of Corallobothrium fimbriatum
showed nearly all the stages from the oncosphere to that represented in
figure 56. This individual was examined just six days after the eggs were
fed (Fig. 51). Many of the Cyclops examined from 25 to 30 days after the
feeding of the eggs, showed this same condition of the larvae. This in-
hibition of growth among the larvae was probably due to the inability of
the Cyclops to furnish sufficient nourishment for the complete develop-
ment of more than three or four individuals.

In connection with the study of the development of C. giganteum an
observation was made that caused considerable perplexity. In the body-
cavity of several Cyclops, along with mature procercoids (Fig. 67), there
frequently occurred as many or more very transparent, weakly contractile
individuals devoid of hooks and calcareous bodies. They usually measured
about 0.10 mm by 0.05 mm (Fig. 63), though one individual measured
0.30 mm by 0.10 mm. This individual was constricted near the middle
and presented the appearance shown in figure 61. Kuczkowski (1925) in
his study of I. percae reports the observation of forms similar to those I
have encountered in connection with C. gigantewm. He offers the suggestion
that they represent the cast-off bladders (cercomers) of the mature pro-
cercoids. JI am inclined to the same conclusion since the size of these
transparent individuals is usually about the same as the bladder appendage.
Furthermore, the structure of the two is almost identical. In a few in-
stances, however, these peculiar forms were more than twice the size of
the attached bladder (Fig. 61). Consequently, if they are accepted as
being the bladders that have been separated from the mature procercoids,
there must be claimed for them a certain power of independent growth.

46 ILLINOIS BIOLOGICAL MONOGRAPHS [300

A shifting of polarity was noted in the course of the development of
the larvae of both species of Corallobothrium. During their early phases
(from the oncosphere to about ten days), when removed from the Cyclops
they moved slowly about with the end bearing the hooks directed an-
teriorly. Coincident with the differentiation of the scolex at the opposite
pole, their polarity was reversed and movements thereafter were made
with the scolex-end in advance. This phenomenon was noted also by
Janicki and Rosen (1917) in their study of Diphyllobothrium latum.

The effects of infection on the Cyclops deserve brief consideration.
Infection with a large number of oncospheres (20 to 50) appeared to cause
the Cyclops no discomfort. Individuals so infected were quite as active
as those unparasitized. Cyclops whose body-cavities contained from 1 to
6 larvae in advanced stages of development disclosed little evidence of any
serious effects. When the infection went beyond this point, however, the
Cyclops showed evidences of being greatly inconvenienced by the presence
of the larvae. An infection as intense as is shown in figure 51 almost totally
incapacitated the Cyclops. Such individuals no longer attempted to swim
about but settled to the bottom of the fingerbowls and only moved when
stimulated with the point of a needle or by vigorous stirring of the water.
Then only a few strokes were made with the antennae and abdomen, after
which they again settled to the bottom where they remained, apparently
dispossessed of every desire for food or action. As has been pointed out by
Meggitt (1914) and Janicki and Rosen (1917), such individuals fall an
easy prey to the fish which feed on them. However, according to my ob-
servations no Cyclops that had been infected in nature contained more than
a single procercoid. When it is considered that the chances of a multiple
infection are rather slight in a large lake or river, the effect of the parasites
on the Cyclops is of relatively little significance.

THE SECOND INTERMEDIATE HOST

The experiments in this line were carried on from August 24 to Sep-
tember 9, 1926. Studies on the food of Ictalurus punctatus, Ameturus melas
and Leptops olivaris had shown that minnows and occasionally other
species of fish constituted a part of their diet. Copepods were never found
in the food examinations of any of the foregoing species. Therefore it
seemed improbable that such a high percentage of infection (nearly 70%
in the case of J. punctatus) could have resulted from the accidental ingestion
of infected Cyclops. Consequently no experiments were made on the
direct infection of J. punctatus through the agency of the Cyclops. I in-
clined to the belief that infection of the catfish very likely occurred through
the ingestion of forms that fed largely on the Entomostraca of the river.
Since the Entamostraca were known to comprise a high percentage of the
food of minnows, it was evident that some species of minnow might act

301] STRUCTURE AND DEVELOPMENT OF CORALLOBOTHRIUM—ESSEX 47

as a second intermediate host for the species of Corallobothrium. One of
the most widely distributed minnows (Notropis blennius) was selected as
the first subject. These fish could not be obtained except from the open
waters of the streams in the vicinity of the laboratory. About 100 were
taken from Rock River on August 24 and placed in the laboratory aquaria,
where they remained 12 days before infection experiments were begun.
During that time the weaker individuals were eliminated by death and the
stronger were left for the experiments. No food was given them except
bits of bread and cracker crumbs, on which they seemed to thrive very
well.

From among these fish 8 individuals were examined but no larval
cestodes were found. Although the findings which resulted from the
examination of eight minnows are not considered as final evidence on the
presence or absence of larvae in the remainder of the group, they may be
taken as a fair index of the degree of infection in that particular school of
minnows.

From a culture containing Cyclops bicuspidatus 30 to 40 specimens in-
fected with procercoids were removed. These were placed in an aquarium
(2’ long, 10” wide, 12” deep) containing water about three inches deep.
Three of the smaller minnows were selected and placed in the same aquar-
ium on September fourth. Three days later one minnow was examined
and three cestode larvae were discovered on the mesentery along the outer
wall of the intestine. Very probably there were others that escaped detec-
tion because of their extremely small size as they were only 0.2 to 0.4 mm
in length, according to the exact degree of contraction (Fig. 60). The two
remaining minnows were killed September ninth and preserved in formol
for study by the section method.

Another group of three minnows was infected in the manner just de-
scribed on September second. On the day of my departure from Rockford,
September ninth, these minnows were placed in a quart jar containing
3 inches of water in which they remained for about 12 days. One of them
died while I was enroute to Urbana. Of the two that remained one was
killed October first, but there were no free larvae observed in the body-
cavity. Any that may have been present had probably migrated to the
musculature of the body-wall. The third individuei was placed in an
aquarium with a small uninfected Ameiurus melas. The aquarium over-
flowed shortly afterwards, and this gave the minnow an opportunity to
escape. An examination of the catfish on April twenty-ninth gave negative
results.

Sections prepared from a minnow killed three days after infection
showed two larvae in the intestine, one outside of the intestine in the body-
cavity, one in the ovary and three in the musculature. These larvae were
not encysted (Figs. 65, 69). Since the larvae were found alive in the body-

48 ILLINOIS BIOLOGICAL MONOGRAPHS [302

cavity of the minnows and since a sectioned minnow showed their presence
in the lumen of the intestine, in the coelomic cavity near the intestine and
in the ovary and musculature of the body-wall, it is concluded that this
minnow (Notropis blennius), and probably others, may serve as a second
intermediate host for Corallobothrium fimbriatum. No experiments other
than those already described were made on the life-cycle of C. giganteum.
However, it is very probable that the developmental cycle of this species
closely approximates that of C. fimbriatum.

After the conclusion of the experiments just described, I had an oppor-
tunity to secure additional data on the life-cycle of Corallobothrium jfim-
briatum. By the use of a specially devised trawl, Dr. David H. Thompson
has been able to take small fish which are rarely obtained by the use of
ordinary apparatus. In the early part of September, 1927, he secured 32
Ictalurus punctatus and shipped them to me alive. These fish measured
from 2 to 3 inches in length. Six individuals out of the shipment harbored
from 1 to 3 sexually mature Corallobothrium fimbriatum. The food of the
young I. punctatus consists of plankton, insects, and various kinds of debris.
It is quite improbable that infection with this cestode occurred in any other
way than by the ingestion of copepods that harbored the procercoids.
Therefore it was evident from my studies that the infection of catfish
with Corallobothrium fibriatum might result either by feeding on minnows
which harbored the larvae, or by the ingestion of infected copepods. The
evidence for the latter contention seemed quite substantial but further
experimentation was necessary to establish the former statement.

To determine whether or not infection with Corallobothrium fimbriatum
might take place through the agency of a minnow, the following experiment
was carried out. From the cestodes obtained from the small Jctalurus
punctatus a large number of eggs were collected. These eggs were fed
October third and fourth to uninfected Cyclops prasinus, and the pro-
cercoids developed in about 2 weeks. On October nineteenth the Cyclops
were placed in an aquarium with two minnows (Hybopsis storerianus)* and
I witnessed the ingestion of the Cyclops by the minnows. Two Ameiurus
melas which had been kept in a laboratory aquarium since November 5,
1926, were used for the next phase of the experiment. No food had been
given to these fish from June to September, 1927. Any parasites that they
may have had when brought into the laboratory, it seemed reasonable to
suppose had disappeared during their confinement. One of them was
examined in September and no parasites of any kind were found. On
October twenty-sixth the two minnows that had been fed the infected
Cyclops were placed in the aquarium with the other A. melas. Both
minnows were eaten. An examination of the catfish was made November
eleventh and 6 larvae were recovered from the intestinal tract. They

* Identified by Dr. G. K. Noble, American Museum of Natural History.

303] STRUCTURE AND DEVELOPMENT OF CORALLOBOTHRIUM—ESSEX 49

measured about 0.3 mm in length. When the scolex was evaginated they
resembled very closely the larva shown in figure 64m, but when the scolex
was invaginated they resembled in every respect the procercoid of Corallo-
bothrium fimbriatum; so much so that I have no doubt whatever as to their
identity. The results of this investigation make possible an explanation
of how adult catfish, which do not feed on plankton to any appreciable
extent, become infected with Corallobothrium.

Plerocercoid Larvae

As has already been stated, the completion of the growth of the larvae
in the Cyclops has been designated as the procercoid stage. Upon entering
the next host transformation into the plerocercoid stage is begun. In
Corallobothrium the first step in this process is the evagination of the
scolex. Should the Cyclops infected with the procercoid be ingested by a
catfish, development into the plerocercoid begins at once. However,
should the procercoid be taken into another fish such as a minnow, which
might be considered an accommodation host, the larva migrates from the
intestine and takes refuge in the body-cavity or some organ of the second
host where it remains until ingested by the definitive host. Little develop-
ment occurs before it reaches the proper fish. There was close similarity
between the larvae recovered from the minnow and the procercoid of
Corallobothrium fimbriatum taken from the Cyclops. The only differences
noted were the appearance of a larger number of calcareous bodies and an
excretory bladder which was not observed in any of the procercoids when
removed from the Cyclops (Fig. 60). The smallest plerocercoid found in
the intestine of the catfish measured about 0.2 mm in length. In this in-
dividual, as in all the young plerocercoids, the scolex is the most prominent
feature. The body is only a small cone-shaped projection in which no in-
ternal organs can be distinguished. Not until the larvae reach a length
of about 1 mm is there a distinct resemblance to the adult individual
(Fig. 62).

As has already been shown by Table I, no adult parasites belonging to
the genus Corallobothrium were present among the fish examined from
October to April. This was taken as decisive evidence that the adults do
not appear before late spring or early summer and disappear entirely in
the late fall or early winter. While this study was in progiess it was dis-
covered that the fate of the larvae was entirely different. Because of the
difficulty of determining accurately the species of the smaller plerocercoids
(Fig. 59), no attempt was made to record them according to species. It
was found, however, that larvae of both species of Corallobothrium were
present throughout the year. Therefore in the data recorded below, the
total number of larvae present in each fish is recorded without regard to
the species. In the examination of 130 Ictalurus punctatus, cestodes belong-

50 ILLINOIS BIOLOGICAL MONOGRAPHS [304

ing to any other genus than Corallobothrium were encountered only four
times. In those instances the parasite belonged to the genus Proteo-
cephalus. Since the larval stages of this form would be exceedingly rare,
they should not affect very materially the data on the plerocercoids of
Corallobothrium.

Taste II

SEASONAL OCCURRENCE OF CORALLOBOTHRIUM PLEROCERCOIDS
Data from Ictalurus punctatus taken in Rock River

Number Number Average
Date Examined Plerocercoids per fish
April, 1926 14 6 0.43
June, ¢ 10 53 Byes)
July, 46 150 one,
August, « 25 18 0.72
September, “ 6 2 0233
November, “ 11 23 2-0
December, “ 18 49 3.3
Total 130 301 2:3

These data indicate that the larvae which enter the fish host in the fall
remain in the intestine through the winter. Since those found during
December and April measured only from 0.5 to 0.8 mm in length, it is
evident that little growth takes place during the winter and early spring.
This cessation of growth may be due to temperature conditions or to the
absence of sufficient nourishment for further development. Unpublished
data collected by the Hlinois Natural History Survey indicate that [ctalurus
punctatus feeds very little during the winter. Doubtless both temperature
and the lack of food are responsible for the inhibition of growth during this
season.

305] STRUCTURE AND DEVELOPMENT OF CORALLOBOTHRIUM—ESSEX 51

COMPARISON OF PROTEOCEPHALUS AND
CORALLOBOTHRIUM

With the exception of the work of Rosen, all of the experimental work
on life-histories of fish cestodes has been on species of Proteocephalus
(=Ichthyotaenia). Megitt’s description of the development of Proteo-
cephalus filicollis in Cyclops varius is incomplete in some respects. Briefly
stated, he made the following observations: After the ingestion of eggs the
oncosphere attaches itself to the wall of the alimentary canal where it
remains about a week before breaking through into the body-cavity. After
gaining the coelom it takes up a position near the anterior end of the
carapace or in the head above the eye. The embryonic hooks gradually
disappear. The body becomes covered with highly refractive bodies. The
procercoid reached maturity at the end of three weeks. He states that the
procercoid is an elongate gray body of variable size, without scolex or neck.
The larva is devoid of divisions. Four suckers occur at the anterior end but.
an apical sucker is absent. The end bearing the suckers is never invaginated
during development. No signs of excretory organs were seen.

The development of Proteocephalus torulosus in Cyclops strenuus and
Diaptomus castor as described by Wagner is as follows: The oncospheres
were observed in the coelom 24 hours after the eggs had been placed in
with the copepods. At the end of 48 to 72 hours the larvae measured 20
to 30u. They had settled themselves on or near the intestine. After a short
time the larvae began to elongate. At one pole the first trace of the suckers
appeared. Circular and longitudinal muscle fibers appeared along with
excretory ducts and large calcareous bodies. An invagination occurred
at the posterior end which was eventually taken over by the excretory
bladder. The procercoid attained a length of 0.5 to 1 mm. It possessed
four suckers whose radial muscles were distinct. The scolex possessed
neither hooks nor rostellum. It was not set off from the rest of the body.
The body was extremely contractile. The cuticula is broken up in a cover
of fine hairs and bristles. In some individuals the embryonic hooks were
strewn over the posterior half of the body. The excretory system was
plainly visible in its entirety and consisted of an excretory bladder and
a dorsal and ventral vessel on each side. Wagner makes no mention of a
bladder appendage or cercomer.

Kuczkowski’s description of the development of Proteocephalus percae
in Cyclops strenuus may next be summarized. In the course of a few
days after the infection, the spherical larvae of a diameter of 35u, were
observed in the coelom of the Cyclops. This larva soon began to grow

52 ILLINOIS BIOLOGICAL MONOGRAPHS [306

and lose its spherical form. A vaculated region appeared within the
body mass which the author interpreted as the “lacuna primitiva”’ of
Grassi and Rovelli. At this stage the larva was 41 to 55u in diameter.
There was a decided growth in length and an increased contractility.
A cercomer appeared from 14 to 21 days after the infection, then the length
of the larva was from 138 to 3274 and the length of the bladder from
13 to 42u. The bladder was without hooks. These were found on the pos-
terior portion of the larval body. The procercoid possessed four elliptical
suckers. No apical sucker was present but a bladder-like protrusion was
noted at the apex of the scolex. The figures indicate that the cuticula
was smooth. A well developed excretory system was present, also cir-
cular and longitudinal muscle fibers. The larva showed the typical cal-
careous bodies.

A comparison of the developmental phases of the species of Pro-
teocephalus just described with those of Corallobothrium brings out
some rather significant differences. In Proteocephalus the bladder ap-
pendage or cercomer is entirely wanting in two species according to the
descriptions given and rather rudimentary in the third. In Coralloboth-
rium the cercomer is a decidedly prominent structure whose length equals
one-third that of the body, 40 to 60u, and is never rudimentary. In
Proteocephalus percae where the bladder has been observed, it shows
signs of being rudimentary since in some cases it measures only 13y in
length. According to Kuczkowski the cercomer of P. percae never bears ©
the embryonic hooks. These hooks are always found on the posterior
portion of the body. This condition is likewise true of the other species
of Proteocephalus which have been described. In Corallobothrium, how-
ever, they may be confined to the cercomer, divided between the cercomer
and the body, or all on the body. In Proteocephalus the suckers are
differentiated near the anterior end of the larval body without the scolex
being set off. The scolex is never completely invaginated. In Corallo-
bothrium the scolex is set off early from the the rest of the body (Figs.
57, 70) and soon afterward is completely invaginated. The Proteoceph-
alus procercoid bears a close resemblance to the plerocercoid found in
the intestine of the final host. This is not true of the procercoids of Cor-
allobothrium, in which a decided transformation takes place in the pro-
cercoid before the plerocercoid stage is attained (Figs. 58, 59, 68). In
every case the Proteocephalus procercoid has a greater length than that
of the Corallobothrium procercoid. In the three species of Proteocephalus
whose life-cycles have been studied, only one intermediate host is re-
quired. The evidence is fairly substantial that at least one species of Cor-
allobothrium, C. fimbriatum, may use two intermediate hosts for its
development. The striking differences in the development of these ces-
todes, combined with the differences in adult morphology, should be, in

307] STRUCTURE AND DEVELOPMENT OF CORALLOBOTHRIUM—ESSEX 53

my opinion, sufficient evidence to satisfy the most critical worker that
Corallobothrium should remain a separate genus.

COMPARISON WITH DIPHYLLOBOTHRIUM LATUM

The species of Proteocephalus have been compared with those of
Corallobothrium from the point of view of their development. A similar
comparison between Diphyllobothrium latum and the species of Corallo-
bothrium is of interest. As described by Janicki and Rosen, D. latum
develops in the following manner: The ciliated larva is ingested by
Cyclops strenuus. Within a few hours the oncosphere has gained the body-
cavity of the Cyclops. The larva remains attached by its hooks to the wall
of the intestine 10 to 15 days, during which time it loses its contractility.
It becomes elongated and at the end of 6 to 8 days development measures
0.10 to 0.15 mm. At the end of from 8 to 12 days the larva shows cal-
careous bodies, longitudinal and transverse musculature and a strongly
developed cuticular covering. On the twelfth day after beginning de-
velopment the opposite poles of the body show differentiation. By
the twelfth to fifteenth day a special bladder appendage with the em-
bryonic hooks upon it is formed. Now the larva measures from 0.35 to
0.40 mm. At the end of 15 to 20 days the larva has attained a length of
from 0.5 to 0.6 mm. Then the bladder gradually degenerates and dis-
appears. At the time of the formation of the bladder an evagination
occurs at the opposite end. Later this structure is capable of being in-
vaginated. At the end of development in the Cyclops the larva is covered,
especially its anterior portion, with bristle-like processes. At this stage
the body is highly contractile. The scolex and excretory vesicle are not
formed by the larva while in the Cyclops. These two organs make their
appearance in the second intermediate host.

The behavior of the oncosphere of Corallobothrium in some particulars
is decidedly different from that of D. latuwm. In the former the oncosphere
does not remain attached to the intestine of the Cyclops by its hooks.
The hooks may be seen in action at any time after the oncosphere has
gained the body-cavity. Neither does the larva lose its contractility.
The development of Corallobothrium larvae is much more rapid, as they
attain their greatest length at the end of from 6 to 8 days. In D. latum
the bladder bears the embryonic hooks; but in Corallobothrium the bladder
may or may not possess the hooks. The scolex and excretory vesicle
are not formed in D. Jatuwm until the larva has developed in the second
intermediate host. In Corallobothrium the scolex is formed early, by
the tenth or twelfth day. The species of the last-named genus do not pos-
sess the covering of bristle-like processess noted for D. latum. The Corallo-
bothrium procercoid is never more than two-thirds the length of the
procercoid of D. Jatum. Another interesting difference is found in the

54 ILLINOIS BIOLOGICAL MONOGRAPHS (308

appearance of the excretory vesicle. In D. latum this organ does not
occur until the plerocercoid stage, but in Corallobothrium giganteum it
arises during the development in the Cyclops. It was not observed in
Corallobothrium fimbriatum until the plerocercoid stage. This might be
expected since the procercoid development of C. giganteum covering 10 to
12 days is more rapid than that of C. fimbriatum which takes 14 to 15 days.

Janicki and Rosen never found more than one mature procercoid in
the same Cyclops. I have observed as many as three mature procercoids
and three individuals representing 10 days development in the same host.
The largest number of larvae reported for D. Jatum in a single Cyclops
was from 8 to 10. As many as 18 were found in a single host infected with
the eggs of Corallobothrium fimbriatum.

This comparative study of the Bothriocephalid, Proteocephalus, and
Corallobothrium procercoid furnishes evidence indicating an intermediate
postition for Corallobothrium between the Bothriocephalids and _ the
genus Proteocephalus. First, in the Bothriocephalids the cercomer is
always present and nearly always bears the embryonic hooks, but in
Proteocephalus it may be wanting entirely. When present, however, it
never bears the embryonic hooks. In Corallobothrium the cercomer is
always present and it may or may not possess the hooks. Second, the
procercoid of the Bothriocephalids bears little resemblance to the plero-
cercoid, whereas the Proteocephalus procercoid is almost identical to the
plerocercoid while the procercoid of Corallobothrium does not bear a close
resemblance to the plerocercoid stage. The Bothriocephalids usually
require two intermediate hosts, the Proteocephalids only one, while
Corallobothrium may or may not use two intermediate hosts.

EARLY DEVELOPMENT IN BOTHRIOCEPHALIDS AND PROTEOCEPHALIDS

Observations on the early development of the Proteocephalids are in
close agreement with those on Diphyllobothrium latum, Triaenophorus
nodulosus, Abothrium infundibuliforme and Ligula simplicissima. There
are, however, a number of differences that should be considered. The
egg of the Proteocephalids when extruded from the uterus, possesses a
gelatinous outer covering which enables it to float about for a time before
sinking to the bottom of the stream or lake. Within this gelatinous material
is found a second membrane (shell) which contains a quantity of granular
material and the fully-formed oncosphere which may or may not be in-
vested with a third membrane. The oncosphere of the Proteocephalids
is held a prisoner within its membranes until liberated through the agency
of the first intermediate host. The egg of each of the Bothriocephalids
mentioned above, closely resembles that of the trematodes. A gelatinous
covering is absent. The oncosphere may be fully developed before the egg

309] STRUCTURE AND DEVELOPMENT OF CORALLOBOTHRIUM—ESSEX 55

is extruded from the uterus, as in Abothrium infundibuliforme; or an
incubation period of varying length may be necessary after the egg is
extruded, as in Diphyllobothrium latum. When the egg is mature it is
composed of an outer shell, which I consider to be homologous with the
second membrane of the Proteocephalid egg, and a layer of cells which
envelops the oncosphere. This layer of cells is probably homologous
with the innermost membrane reported in most Proteocephalid eggs.
Contrary to what occurs in the Proteocephalids, the egg of the Bothrio-
cephalid hatches, thus liberating the oncosphere. The layer of cells envelop-
ing the oncosphere may be provided with cilia, as in D. datum, or the cilia
may be wanting, as in A. infundibuliforme.

A comparison of the size of the oncospheres of certain Bothriocephalids
and Proteocephalids is given in the following parallel columns.

Bothriocephalids Sizein Authority Proteocephalids Sizein Authority
micra micra
Diphyllobothrium latum 22to30 8 Janickiand Proteocephalus
Rosen filicollis 27(estd) Meggitt
Triaenophorus nodulosus 22to24 Rosen P. torulosus 20 to30 Wagner
Abothrium infundibuliforme 50to60 Rosen P. percae 28 to35 Kuczkowski

Corallobothrium
fimbriatum 20 Essex
C. giganteum 13to16 86“

It is of interest to note that the first intermediate hosts of the Pro-
teocephalids and Bothriocephalids considered in this paper are found
exclusively among the copepods. The species recorded in the following
columns have been studied experimentally.

PROTEOCEPHALIDS

Parasite

Proteocephalus filicollis

P. torulosus

P. percae

P. longicollis

Corallobothrium fimbriatum

C. giganteum

First Intermediate Authority

Host
Cyclops varius Meggitt
Diaptomus castor

Cyclops strenuus Wagner

Cyclops strenuus
C. serrulatus

C. oithonoides Kuczkowski

Cyclops strenuus

C. serrulatus Kuczkowski

Cyclops bicuspidatus
C. serrulatus

C. prasinus Essex

Cyclops serrulatus

C. prasinus Essex

56 ILLINOIS BIOLOGICAL MONOGRAPHS

[310

BoTHRIOCEPHALIDS

Parasite
Diphyllobothrium latum

Diphyllobothrium latum
Triaenophorus nodulosus

Abothrium infundibuliforme

Ligula simplicissima

First Intermediate

Host Authority
Cyclops strenuus
Diaptomus gracilis Janicki and

Rosen

Diaptomus oregonensis Essex
Cyclops strenuus
C. fimbriatus Rosen
Cyclops strenuus
C. serrulatus Rosen
Cyclops strenwus
Diaptomus gracilis Rosen

There may be some significance attached to the fact that Cyclops
strenuus acts as the first intermediate host of all the Bothriocephalids
and three of the Proteocephalids; that Cyclops serrulatus is found among
the first intermediate hosts of both groups.

311] STRUCTURE AND DEVELOPMENT OF CORALLOBOTHRIUM—ESSEX 57

AFFINITIES OF THE PROTEOCEPHALIDS

A study of the life-cycle of organisms has long been used as a guide
to their true affinities. Adult morphology alone is not always a reliable
criterion of true relationship. Certain forms, the barnacles and ostracods
for example, which were thought to be widely separated phylogenetically
on the basis of the adult structure, have been brought close together
through the discovery of their developmental cycles. The lack of com-
plete knowledge on the life-cycles of the vast majority of the Cestoda
has necessitated a grouping based almost entirely on adult morphology.
In recent years sufficient data have been gathered on the development of
the fish cestodes to justify pointing out certain apparent affinities.

By the discovery of the life-history of Diphyllobothrium latum Janicki
and Rosen (1917) were able to indicate more fully the relationship between
the Digenea and the Bothriocephalids which was first suggested by
Leuckart (1886). This is shown by the following points:

1. Similarity of the eggs

2. Existence of a uterine pore

3. Structure of the larvae

4. Two intermediate hosts

5. Resemblance between the miracidium and coracidium
6. Resemblance between the cercaria and the procercoid

On the basis of the points just enumerated, Diphyllobothrium latum,
Triaenophorus nodulosus and Ligula simplicissima show a clear affinity
to the Digenea. The development of Abothrium infundibuliforme as
described by Rosen (1918) differs from the three Bothriocephalids just
mentioned in respect to the fifth point. Although the egg of A. in-
fundibuliforme goes through the process of hatching, it does not give
rise to a ciliated larva or coracidium. In this respect it is further removed
from the Digenea than the other Bothriocephalids whose life-cycles are
known.

Using the points enumerated above as criteria of the relationship
between Bothriocephalids and Proteocephalids, the first variation from
the usual Bothriocephalid condition if found in Abothrium infundibuli-
forme; the eggs of which show an intermediate position. Since the eggs
of the last-named species contain a fully formed oncosphere when extruded
from the uterus, they resemble the eggs of the Proteocephalids; but
since the eggs of A. infundibuliforme give rise to unciliated larvae, they
differ from the usual Bothriocephalid condition. Except for the first and

58 ILLINOIS BIOLOGICAL MONOGRAPHS {312

Afth points there is substantial agreement between Corallobothrium jim-
briatum and the Bothriocephalids. Proteocephalus percae agrees on the
second, third, and sixth points, but P. filicollis and P. torulosus differ in
all points except the second and third. Therefore, starting with a typical
Bothriocephalid such as Diphyliobothrium latum, there is a striking series
of transitions in arriving at the typical Proteocephalid condition.

The first variation is found in Abothrium infundibuliforme; whose
larva is unciliated. Next comes Corallobothrium fimbriatum, which varies
from the former only in the type of egg. Then Proteocephalus percae
follows, varying from C. fimbriatum in the rather rudimentary condition
of the cercomer. Finally, in Proteocepalus filicollis and P. torulosus a condi-
tion is reached which differs from P. percae in that no cercomer is re-
ported and thereby the resemblance of its procercoid to the cercaria is
lost.

On the basis of the scolex, Fritsch (1886) suggested that Corallo-
bothrium solidum represented a connecting link between the Bothrio-
cephalids and the Taenias. In the light of the knowledge of the develop-
ment of the two groups there is much to support his suggestion. La Rue
(1914), after a thorough study of the species of the Proteocephalidae,
found them closely related morphologically to the Tetraphyllidea. How-
ever, in their development the Proteocephalids show a close affinity to
the Pseudophyllidea.

SUMMARY

1. An intensive study has been made of two new species of Corallo-
bothrium. Both species are parasitic in /ctalurus punctatus, Ameturus
melas, and Leptops olivaris. Woodland’s proposal (1925) to delete the
genus Corallobothrium has not been accepted. The genus has been re-
tained and the two new species have been designated as Corallobothrium
giganteum and C. fimbriatum. A description is given of the adult anatomy
of each parasite. The scolex of C. giganteum is subject to wide variation.
Amphitypy occurs in the arrangement of the interovarial organs of both
species. A new role has been suggested for the excretory system.

2. Particular attention has been paid to the degree of infection and
seasonal occurrence of these cestodes in Ictalurus punctatus. Among
130 adults of this species nearly 70 per cent harbored one or the other of
these cestodes or both. The adult parasites occurred only from spring
to fall but the plerocercoid stage was present in the final host through-
out the year.

3. The life-cycle of each cestode was studied experimentally. In-
fection was produced in Cyclops serrulatus and C. prasinus by feeding
eggs of Corallobothrium giganteum. Positive results were obtained by
feeding the eggs of C. fimbriatum to Cyclops bicuspidatus, C. serrulatus

313] STRUCTURE AND DEVELOPMENT OF CORALLOBOTHRIUM—ESSEX 59

and C. prasinus. The complete development of both parasites in the first
intermediate host has been described. The procercoid of Corallobothrium
giganteum reached maturity in the Cyclops by the twelfth day after the
Cyclops had been exposed to the eggs. The development of the pro-
cercoid of Corallobothrium fimbriatum required from 12 to 14 days.

4. Observations on the feeding habits of Cyclops reveal that organic
debris and cercaria are eaten and that protozoa are consumed in large
numbers.

5. Cyclops infected with mature procercoids of Corallobothrium
fimbriatum were fed to minnows (WNotropis blennius). Larvae were re-
covered from the body-cavity of the minnows 3 days after feeding. Sec-
tions of an infected minnow showed the presence of the larvae in the
intestine, within the coelom, and in the musculature.

6. Ictalurus punctatus measuring from 2 to 3 inches in length were
found to harbor adult Corallobothrium fimbriatum.

7. Cyclops infected with the procercoids of Corallobothrium fim-
briatum were fed to minnows. The minnows were fed to Ameiurus melas
and the larvae of Corallobothrium fimbriatum were recovered from the
intestine of A. melas.

8. The evidence indicates that catfish may be infected with Corallo-
bothrium fimbriatum either by ingesting infected Cyclops or by feeding
on infected minnows.

9. A comparison of Bothriocephalid and Proteocephalid develop-
ment indicates a close relationship between the two groups.

60 ILLINOIS BIOLOGICAL MONOGRAPHS (314

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are used:

cip
dj
def
exd
exv
fs
ml
mr
nl
nr
od
oot
ov

ILLINOIS BIOLOGICAL MONOGRAPHS

[318

EXPLANATION OF PLATES

All figures, except 39 and 41, were drawn with the aid of the camera lucida. The value
of the scale projected is indicated in the explanation of each plate. The following abbreviations

cirrus-pouch

ductus ejaculatorius
vas deferens

excretory vessel, dorsal
excretory vessel, ventral
foramina secondaria
longitudinal muscles
muscle rhomboid
lateral nerve

nerve ring

oviduct

ootype

ovary

00c
rs
sm
tt

ut
ull
utp
utop
va
val
vt
vid
vide
vir

oocapt

receptaculum seminis
sphincter muscle
testes

uterus

lateral uterine pouches
uterine passage
ventral uterine pore
vagina

lower vagina

vitellaria

vitelline ducts
vitelline duct, common
vitelline reservoir

319] STRUCTURE AND DEVELOPMENT OF CORALLOBOTHRIUM—ESSEX 65

PLATE I

66

_ILLINOIS BIOLOGICAL MONOGRAPHS

EXPLANATION OF PLATE I

The value of the scale projected on each figure equals 0.3 mm.

Fic. 1. Corallobothrium fimbriatum, scolex of adult, toto.
Fic. 2. C. giganteum, apical view of scolex.

Fic. 3. C. fimbriatum, organs of interovarial space, toto-mount.

Fic.
Fic.
Fic.
Fic.
Fic.
Fic.
Fic.
FIG.
Fic.
Fic.
Fic.
Fic.

shown,

C. fimbriatum, scolex of adult, toto, more expanded than fig. 1.

C. giganteum scolex, showing apical prominence.

C. giganteum, fully extended proglottid from near posterior end.

C. gigantewm, protruded cirrus, cirrus-pouch, vagina and vas deferens, toto.
C. fimbriatum, ovary of immature proglottid, toto.

C. fimbriatum, ovary of mature proglottid in same chain as fig. 8.

. C. giganteum, dorsal view of the scolex, much contracted, toto.

. C. giganteum, apical view of the same scolex as in fig. 10.

. C. fimbriatum, ovary of immature proglottid, toto.

. C. fimbriatum, ovary of mature proglottid in same chain as fig. 12.
. C. fimbriatum, frontal section of immature segment.

. C. giganteum, expanded scolex, toto.

[320

Vitelline ducts are not

ILLINOIS BIOLOGICAL MONOGRAPHS VOLUME XI

15

ESSEX CORALLOBOTHRIUM PLATE I

321] STRUCTURE AND DEVELOPMENT OF CORALLOBOTHRIUM—ESSEX 67

PAE it

68

ILLINOIS BIOLOGICAL MONOGRAPHS (322

EXPLANATION OF PLATE IT

The value of the scale projected on each figure equals 0.3 mm. except
fig. 24, on which it equals 0.1 mm.

Fic. 16. Corallobothrium giganteum, frontal section of contracted scolex showing excretory
vessels much reduced in apex.

Fic.
Fic.

Fic.
Fic.
Fic.

Fic.
Fic.
FIc.
Fic.
Fic.
Fig.
Fic.

uli
18.

C. giganteum, cirrus fully protruded, drawn from living specimen.
C. gigantewm, cross-section near apices of suckers, showing sphincter about suckers

and muscle fibers connecting each pair of suckers.

19.
20.
21.

C. fimbriatum, sagittal section of much contracted scolex.
C. giganteum, cross-section at level of cirrus-pouch.
C. giganteum, frontal section of expanded scolex showing distended excretory vessel

in apex.

22.
23.
24,
20
26.
27.
28.

star.

C. fimbriatum, frontal section of expanded scolex.

C. giganteum, fully expanded ovary and associated organs, toto.

C. giganteum, procercoid showing scolex partially protruded.

C. fimbriatum, ripe proglottid, toto.

C. giganteum, mature proglottid.

C. fimbriatum, cross-section.

C. giganteum, cross-section near posterior limit of suckers showing part of muscle

ILLINOIS BIOLOGICAL MONOGRAPHS VOLUME XI

De th,
US

XY,
bit

ESSEX CORALLOBOTHRIUM PLATE II

323] STRUCTURE AND DEVELOPMENT OF CORALLOBOTHRIUM—ESSEX 69

PLATE III

70 ILLINOIS BIOLOGICAL MONOGRAPHS (324

EXPLANATION OF PLATE III

The value of the scale projected on each figure equals 0.3 mm. except on
figs. 39, 40 and 41, on which it equals 0.03 mm.
Fic. 29. Corallobothrium fimbriatum, frontal section of mature proglottid.
Fic. 30. C. gigantewm, frontal section of scolex contracted as in fig. 10.
Fic. 31. C. fimbriatum, cross-section showing extent of uterus.
Fic. 32. C. fimbriatum, frontal section of dorsal region of mature proglottid.
Fic. 33. C. giganteum, frontal section of an expanded scolex showing the sphincter muscle
of the suckers as a knob-like structure.
Fic. 34. C. giganteum, drawing made from three frontal sections. The proglottids shown
here are three segments posterior to those shown in fig. 38.
Fic. 35. C. gigantewm, cross-section through scolex near apices of suckers.
Fic. 36. C. fimbriatum, frontal section of vagina and protruded cirrus and cirrus-pouch.
Fic. 37. C. giganteum, frontal section of contracted scolex, sphincter of sucker shaded.
Fic. 38. C. gigantewm, drawn from three frontal sections. The excretory vessels are much
less distended than those shown in fig. 34.
Fic. 39. C. giganteum, reconstruction of interovarial organs.
Fic. 40. C. giganteum, cross-section of dorsal excretory vessel.
Fic. 41. C. fimbriatunt, reconstruction of interovarial organs.

ILLINOIS BIOLOGICAL MONOGRAPHS VOLUME XI

ESSEX CORALLOBOTHRIUM PLATE III

325] STRUCTURE AND DEVELOPMENT OF CORALLOBOTHRIUM—ESSEX 71

PLATE IV

72 ILLINOIS BIOLOGICAL MONOGRAPHS {326

EXPLANATION OF PLATE IV

The value of the scale projected on each figure equals 0.03 mm. except on
figs. 47 and 51, on which it equals 0.3 mm.
Fic. 42. Corallobothrium fimbriatum, mature egg. The funnel-like cavities at each pole are
indicated.
Fics. 43 and 46. C. fimbriatwm, mature eggs in which the middle membrane is ruptured.
Fics. 44 and 45. C. fimbriatum, oncosphere 10 minutes after being removed from the body-
cavity of the Cyclops.
Fic. 47. Cyclops bicuspidatus, containing 8 C. fimbriatum larvae 3 days after feeding of eggs.
Fic. 48. C. fimbriatum, larva removed from Cyclops 3 days after feeding of -eggs.
Fics. 49 and 50. C. giganteum, mature eggs.
Fic. 51. Cyclops bicuspidatus, which contained 18 C. fimbriatum larvae 6 days after feeding
of eggs.
Fic. 52. C. gigantewm, tracing of oncosphere seen in the body-cavity of Cyclops 8 hours after
feeding of eggs.
Fic. 53. C. fimbriatum, larva seen in abdomen of Cyclops 24 hours after feeding of eggs.
Fic. 54. C. fimbriatum, 4-day old larva.
Fic. 55. C. fimbriatum, 36-hour larva as seen through body wall of Cyclops.
Fic. 56. C. fimbriatum, larva about 10 days old.
Fic. 57. C. fimbriatum, larva from 10-11 days old.

VOLUME XI

ILLINOIS BIOLOGICAL MONOGRAPHS

CORALLOBOTHRIUM PLATE IV

ESSEX

327] STRUCTURE AND DEVELOPMENT OF CORALLOBOTHRIUM—ESSEX = 73

PLATE V

74 ILLINOIS BIOLOGICAL MONOGRAPHS [328

EXPLANATION OF PLATE V

The value of the scale projected on each figure equals 0.05 mm. except on
figs. 62, 66, 67 and 69, on which it equals 0.2 mm.
Fic. 58. Corallobothrium fimbriatum, procercoid 12-13 days old with the bladder appendage
still attached.
Fic. 59. Plerocercoid taken from intestine of 7. punctatus.
Fic. 60. C. fimbriatum, larva somewhat contracted taken from body-cavity of Notropis
blennius to which infected Cyclops had been fed.
Fics. 61 and 63. C. gigantewm, forms found in Cyclops which also contained procercoids as
shown in fig. 68.
Fic. 62. C. fimbriatum, very young plerocercoid.
Fic. 64a, b, c, etc. C. gigantewm, procercoid, outlines indicate shapes assumed before evagina-
tion of scolex.
Fic. 65. C. fimbriatum, cross-section of NV. blennius intestine with larva outside of intestinal
wall.
Fic. 66. C. giganteum, procercoid with scolex evaginated, from preserved material.
Fic. 67. Cyclops serrulatus, containing 3 procercoids of C. giganteum.
Fic. 68. C. gigantewm, mature procercoid.
Fic. 69. C. fimbriatum, a much enlarged drawing of larva shown in fig. 65.
Fic. 70. C. giganteum, larva from 8-10 days old.

ILLINOIS BIOLOGICAL MONOGRAPHS VOLUME XI

CORALLOBOTHRIUM PLATE V

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