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THE UNIVERSITY
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University of Illinois Library

L161—H 41

ILLINOIS BIOLOGICAL
MONOGRAPHS

VOLUME XV

PUBLISHED BY THE UNIVERSITY OF ILLINOIS

URBANA, ILLINOIS,

EDITORIAL COMMITTEE

JouHN THEODORE BUCHHOLZ
FRED WILBUR TANNER
HARLEY JONES VAN CLEAVE

No

No

No

TA BIE OL FCON TENTS

. 1. Experimental Studies on Echinostoma revolutum (Froelich), a
Fluke from Birds and Mammals. By PAuL CHESTER BEAVER.

. 2. A Generic Classification of the Nearctic Sawflies (Hymenoptera,

Symphyta). By Hersert H. Ross.

. 3. Studies on the Biology of the Crayfish Cambarus propinquus

Girard. By Wittiam Cart Van DEVENTER.

. 4. Taxonomic Studies on the Mouth Parts of Larval Anura.
Ray JANNEy NICHOLS.

+
3y

Digitized by the Internet Archive
in 2011 with funding from
University of Illinois Urbana-Champaign

http://www.archive.org/details/experimentalstud 15beav

ILLINOIS BIOLOGICAL MONOGRAPHS

Vol. XV No. l

PUBLISHED BY THE UNIVERSITY OF ILLINOTS
UNDER THE AUSPICES OF THE GRADUATE SCHOOL
URBANA, ILLINOIS
1937

EDITORIAL COMMITTEE

JoHN THEODORE BUCHHOLZ
FRED WILBUR TANNER
CHARLES ZELENY

NAT Eee a UNIVERSITY
1000—5-37—9900 OF ILLINOIS
st PRESS 1:

EXPERIMENTAL STUDIES ON
ECHINOSTOMA REVOLUTUM (FROELICH)
A FLUKE FROM BIRDS AND MAMMALS

WiITH-THREE “PLATES

BY

PAUL CHESTER BEAVER

CONTRIBUTION FROM THE ZOOLOGICAL LABORATORY OF THE
UNIVERSITY OF ILLINOIS
No. 491

CONTENTS

Introduction . :
Life History and Merahelbes :
Historical
Larval Stages
Es Miracidium.
a Redia
Cercaria
2 Adult. : :
Morphology _ Size erren :
Morphological Variation Induced by the re sles
Hosts and Geographical Distribution
Immunity Phenomena a Tar
Discussion of Related Species a ae :
Protocol of Experiments
On the Determination of ethos, Baie of Secs an ae
On the Transfer of Adult Worms from Host to Host
Conclusions
Summary .
Tables .
Charts.
Plates .
Bibliography .
Index .

ACKNOWLEDGMENT

The preliminary part of this work was done
under the direction of Professor Henry B. Ward.
It was concluded under Dr. L. J. Thomas, and
many valuable suggestions were received from
Dr. David H. Thompson. Whatever success has
been attained is in large part accredited to them.
I am indebted to Dr. Ward, Dr. W. E. Swales,
Dr Nw Ishi,’ Dr... Miller} cand rz E,W.
Price for numerous records and valuable assist-
ance gained from the study of specimens received
from them as loans or gifts.

INTRODUCTION

Studies on larval trematodes and life history researches have pro-
gressed rapidly during the last few years and it should now be possible to
take advantage of the accumulated facts in investigations of less familiar
related problems, particularly the still very perplexing problems regarding
the reproductive processes of the larval stages. In connection with
studies on another species a rough idea regarding the life history of an
echinostome species was obtained, and it was my original plan to study
some of the less familiar phenomena including the reproductive processes
within the snail host. There is at present much disagreement as to the
general type or types of reproduction in these stages; parthenogenesis,
polyembryony, and various other types of asexual and sexual reproduc-
tion each being proposed by various authors. Where studies have been
made with special attention to reproductive phenomena the method of
approach has been entirely cytological and the results contradictory. It
was thought that an analysis of the variation in pedigreed offspring
might serve as a favorable approach, and it appeared that the crown of
spines and the cuticular spination of an echinostome would provide ideal
material for a study of variation if the worms could be cultured in large
numbers; and since certain laboratory animals were easily infected, an
investigation of the above problems was attempted.

In order to take advantage of the researches already completed a
final determination of the species was soon attempted. This proved to be
a very considerable problem in itself, however, for so much contradiction
and confusion was found that it was not until after most of the studies
were completed that a final decision was reached regarding the species
studied. Long and tedious studies were necessary in order to elucidate
certain points regarding even the morphology of the very common adult
worm. Most of my earlier experiments were designed to discover suit-
able methods for culturing each of the stages in the life cycle and a
number of hosts were used with more or less success. It was noticed
that the worms from some hosts differed slightly from those of others
and two more problems were added by this observation. It was necessary
first to prove absolutely that only one species of parasite was being
studied, and secondly to determine the amount and nature of the variation
due to the type of host. During the experimentation to exclude the
possibility of mixed infections certain immunity phenomena were en-
countered. Only a very preliminary sort of study of these phenomena
was possible, but some of the data obtained are interesting enough to
report.

8 ILLINOIS BIOLOGICAL MONOGRAPHS

The whole of the present report is in many respects only preliminary.
The volume of data that had accumulated seemed to require analysis,
however, before further studies were made.

Special methods employed are described in the various sections where
the reader is most likely to be interested in them. Brief introductions
and discussions are also added to the various sections where they are
most pertinent. Some repetition is held to be preferred to profuse cross
reference and is therefore allowed for clarity.

LIFE HISTORY AND MORPHOLOGY
HISTORICAL

It is probable that the first experimental work on the life history of
Echinostoma revolutum was done by Pagenstecher in 1857. Although he
did not give a description of the encysted metacercaria or give sufficient
data on the morphology of the adult to exclude the possibility of misde-
termination, it seems fairly certain that he was working with Echinostoma
revolutum (D. echinatum). At any rate his was the first demonstration
of the so-called life history of an echinostome. He found that echino-
stome cysts which were present in great numbers in Paludina sp. when
fed to young ducks would develop into an echinostome species which he
identified as Distoma echinatum. He also found cysts in Lymnaea stag-
nalis and Planorbis corneus which he considered identical with those from
Paludina. Some of the other important observations which he made are
that unhealthy or starved ducks do not hold their parasites and that the
worms mature in about two weeks. He noticed too that although several
thousands of cysts were fed to the hosts only about a hundred mature
worms could be recovered from them. The gradual depopulation of the
gut was explained on the basis of two factors: first, as the worms become
mature the suckers become proportionally smaller and are thus less able
to overcome the natural flushing of the gut, and secondly, the crown
spines are gradually broken off until they are so reduced that the worms
are crippled and eventually passed out. The latter is of minor importance
if indeed it is a factor at all.

It has been observed many times that the cephalic or crown spines are
lost under certain conditions such as rough treatment after poor fixation
or death within the host so that fixation cannot be good, but it has not
been demonstrated that these spines are shed by a living animal. Johnson
(1920) reported that the cercariae have 43 spines while the adult has only
37, and stated that he believed this to be due to a natural shedding. A
suggestion from Tubangui (1932b) to which I subscribe is that Johnson
observed the spination of another species of cercaria (see page 15).

STUDIES ON ECHINOSTOMA—BEAVER )

Ercolani (1881, 1882) reported experiments on this species but his identi-
fication was incorrect and his work of no importance here excepting that
it has caused incorrect records to appear repeatedly in the literature.
This work in which he reported experimental infection in ducks and
mice and that of Generali (1881) in which he reported the same species
from the duodenum of the dog were accepted by Railliet (1895) and
Ercolani’s figures were copied into his “Traite de Zoologie Medicale et
Agricole.” These figures with summaries of Ercolani’s experiments have
since appeared in English (Neumann-Macqueen, 1905), and thus have
been fairly well distributed in Italian, French, German and English
literature. This, of course, has a rather important bearing upon the
present study because of the uncertainty attached to each of the reports
of host and distribution records that might be based upon this or similar
work. Wedl (1857) reported, described, and figured a species which he
incorrectly identified as D. echinatum. Perhaps it was Wedl’s description
and figure that Ercolani used in identifying his material. They are some-
what similar.

Johnson (1920) was the first to make observations on all or nearly all
stages in the life cycle of an echinostome. He was supposedly working on
Echinostoma revolutum. Whether or not this is true some of his observa-
tions are of interest here, for he again demonstrated the method of
infection and described some of the developmental stages. He took forty-
five eggs from adult worms which he found in a duck, Marila marila,
and when the miracidia hatched (in about three weeks) he exposed
laboratory raised Physa occidentalis to them. He learned by subsequent
studies that the miracidia develop directly into mother rediae, which after
about three months produce a generation of daughter rediae, and these in
turn produce the cercariae. As only forty-five eggs were collected it was
not possible to infect many snails and consequently the studies on lab-
oratory infections were not extensive. The morphology of the rediae and
cercariae was studied on material collected in the field. Metacercariae
were found encysted in Physa occidentalis, Lymnaea traski, and planarians,
but he (Johnson, 1920) was unsuccessful in an attempt to recover them
from laboratory exposed tadpoles of Hyla regilla Baird and Girard and
Notophthalamus torosus (Rathke). By feeding metacercariae in Physa
occidentalis he produced an infection in mongrel ducklings from which
he recovered eight “full grown” and sixty-five less mature adult worms.

Vevers (1923) fed a young duck some cysts of a form which he
identified as Cercaria echinata and after 12 days recovered fifteen imma-
ture specimens of Echinostoma revolutum. In the same year Miki (1923)
found the tadpoles of Rana esculenta heavily infected with echinostome
cysts and upon feeding these to rats and mice recovered worms identified

10 ILLINOIS BIOLOGICAL MONOGRAPHS

as E. cimetorchis (= E. revolutum). The following year Lutz (1924)
reported studies on this species. He obtained two infections in the duck
(Cairina moschata) by feeding it Physa rivalis which carried a laboratory
infection of metacercariae. The cercariae also came from Physa rivalis.
More recently Tubangui (1932b) reported observations on both the larval
stages and adult worms from experimentally infected pigeons; and Fallis
(1934) has infected goslings by feeding them infected tadpoles.

The various stages in the life cycle can now be fairly well described
and many of the details regarding the general biology of the species sum-
marized from the researches of others. The present studies were made
primarily as a basis for irrevocable identification, and the successful cul-
turing of cercariae and adult worms. For that reason the observations
were more or less confined to these stages. They will be discussed in the
following order: miracidium, mother-redia, daughter-redia, metacercariae
(agamodistome), and adult. The egg is considered a character of the
adult worm.

LARVAL STAGES

Miracidium

Eggs collected in feces, washed, and allowed to stand at room temper-
ature hatch in from 18 days to one month. Active miracidia may be
seen within the egg much earlier, however, as the flame cells and cilia
appear several days before the embryo assumes the elongate shape of the
fully developed individual. At about 6 days the young miracidium is
nearly spherical, is ciliated, and has two flame cells in the center of the
body. In diameter it is about one-half the length of the egg. During the
next few days it elongates, dark granules appear in the region where eye
spots are to be formed, cuticular plates become evident, and the right
flame cell becomes more anterior in position. After 10 or 12 days eye
spots are clearly defined, the body is as long as or slightly longer than
the egg, and it has, with the exception of size, the appearance of the
hatched miracidium (Fig. 11).

The following description of the fully developed miracidium is based
on individuals incubated from numerous hosts and from several stocks.
Very little variation was observed in the characters described. By invert-
ing a glass funnel in a beaker containing the washed feces, miracidia were
concentrated in the neck of the funnel and studied much the same as one
would study an infusion of protozoa. As soon as the miracidia hatch
they swim upwards, thus collecting in the narrow neck at the surface.
Intra-vitam stains were found to be useful in differentiating some struc-
tures, and others were more clearly shown in stained permanent mounts.
Many of the larvae were studied while still within the egg.

STUDIES ON ECHINOSTOMA—BEAVER 11

More often than not the larva is facing the operculum of the egg. The
body is longer than the egg but much less in diameter. This necessitates a
flexure which is at the posterior end and is in most cases dorsal, leaving
the entire ventral side in contact with the shell (Fig. 11). The space not
occupied by the larva is filled with two or three large clear globules
which appear to be attached to the miracidium between the first and
second row of plates.

The body is covered with large unicellular ciliated plates arranged in
alternate fashion in four circumferential rows (Figs. 7, 11). The cilia
are nearly uniform in length (10-14 ) over the entire body. The four
rows contain, respectively, from anterior to posterior 6, 6, 4, and 2 plates.
When stains are used a large elongate nucleus is clearly seen along the
posterior border of each plate.

The eye spots are clearly defined as dark crescents along the mesial
edge of the lobes of the brain. A few scattered granules are also some-
times present along the posterior border. There is one flame cell in the
anterior part of the body at the level of the second row of the cuticular
plates, and a posterior one at the level of the third row. The anterior one
is on the right side and ventral, the posterior one left and dorsal. The
somewhat coiled excretory ducts lead independently to the lateral excre-
tory pores at the triple junction of the posterior plates and those just
anterior to them. The “germ balls’’ lie loose in the posterior two-thirds
of the body and are variable in arrangement and number. Between the
proboscis or protrusible papilla and the eye spots is a sac-like structure
which in other species has been called an intestine. Lateral and ventral to
this structure are masses of cells which by their staining reaction seem to
be glandular.

The only echinostome miracidium sufficiently described to allow com-
parison is that of Echinoparyphium recurvatum which was recently de-
scribed by Rasin (1933). Both forms have the 6-6-4-2 arrangement of
the cuticular plates, two flame cells whose ducts empty between the third
and last rows of plates, eye spots in similar position, and, in general, a
very striking similarity is apparent. There is, however, one difference
according to the descriptions given. In E. revolutum the posterior plates
appear to be dorsal and ventral while in Echinop. recurvatum they are
lateral, one on either side of the body.

After hatching, the miracidia swim rapidly and almost constantly
until they find a host or finally die. Eighteen hours is the longest free-
swimming period observed but under natural conditions it may be some-
what longer. The exact method of penetration was not determined, but
they were often observed spinning vigorously with the proboscis-like
anterior end undergoing a rapid succession of expulsions and withdrawals

12 ILLINOIS BIOLOGICAL MONOGRAPHS

while in contact with the body of the snail. None of the individuals
observed were successful in breaking through.

Upon entering the snail, which may be almost any pulmonate, the
miracidia metamorphose either directly into a mother-redia or into a
sporocyst. Johnson (1920) believes that the sporocyst stage is omitted,
but Rasin’s studies on the closely related species Echinop. recurvatum and
Mathias’ (1925) observations upon Hypoderaeum conoideum indicate
that the sporocyst does occur.

In the present study sporocysts were not observed, but no special
effort was made to discover them. Snails were infected by the following
method: the feces from infected hosts were washed repeatedly by
decantation and the coarse material strained out, thus concentrating the
eggs and minimizing the bacterial growth. The sediment containing the
eggs was incubated at room temperature in 500 cc beakers or similar con-
tainers, and the water changed as often as was necessary to maintain
freshness. As the miracidia began to hatch they came to the surface
where they could be seen by looking through the glass container at right
angles to a beam of light. When it was known that miracidia were
present in the culture a few snails were placed in a coarse screen cage
and partially immersed for a day or two.

Thus far this method has not been as successful as is desirable.
Either because of improper conditions after exposure or because of too
heavy infections, practically all the snails died before mature cercariae
were produced. In the first of these experiments 96 snails were exposed
and only 3 lived to produce cercariae; 3 others lived to the end of the
experiment but were uninfected. As the snails died or were observed to
be dying they were opened and examined for developmental stages. Only
rediae were found in snails opened in less than six weeks after exposure,
and mature cercariae did not develop until the ninth or tenth week. The
snails were kept in a basement aquarium where the temperature ranged
between 50 and 60° F, and were fed regularly on lettuce. Later attempts
to infect snails were equally unsuccessful. Each snail was exposed to only
3 or 4 miracidia and kept in a green-house aquarium where the tempera-
ture was 80-110° F. Fewer snails died but none that lived were ever
found infected.

Redia

The rediae of E. revolutum are so variable in size and shape that
description of them is difficult. For that reason and for the reason that
there is a very close similarity between all of the species of the genus
none of the descriptions made thus far differentiate it from that of closely
related species. My own observations have not been detailed enough to

STUDIES ON ECHINOSTOMA—BEAVER 13

describe this stage adequately even when added to and compared with
other descriptions. Johnson’s description (1920) of it is rather detailed
but must be accepted with the reservation that it was made from studies
on questionable material.

In one instance mother-rediae were observed in a snail that had been
exposed to miracidia 62 days previously. These mother-rediae are large
and elongate, measuring about 2 mm in length and 0.3 mm in width when
extended. The pharynx is about 0.1 mm in diameter, which is relatively
larger than that of the largest daughter-rediae. The collar, which in the
daughter-rediae is fairly conspicuous, especially in the younger ones, is
barely distinguishable in the old mother-rediae and likewise the posterior
projections are not pronounced. Eighteen posterior and 9 anterior flame
cells were observed.

The very young daughter-rediae are colorless but gradually accumu-
late an orange-colored pigment as they become older, so that the largest
ones are always somewhat colored. This seems to be characteristic of all
echinostome rediae. The pharynx and gut change in relative size as the
rediae increase in total length. In small individuals they appear very
large, and in the largest ones very small and inconspicuous. For example,
a specimen which measures 0.28 mm in length has a pharynx which is
35 « wide and in one 0.85 mm long it is 40 » in diameter. Both specimens
are about equally extended. In these same specimens the gut measures
respectively 0.15 and 0.30 mm in length. A birth pore which seems to be
dorsal can be seen on some specimens, and a collar is evident on all con-
tracted ones. The pigment makes flame cell studies in the larger ones
difficult, and in the smaller ones the flame cells are themselves so small
that they are difficult to study. Although 36 flame cells were not seen in
any one specimen it seems probable that there are four groups of them, 2
posterior ones near the lateral projections and 2 about half-way to the
anterior end near the distal end of the gut, and that each of these groups
contains 9 flame cells. Johnson (1920) described them in two groups, 17
in the anterior and 18 in the posterior.

Cercaria

The cercariae of the genus Echinostoma exhibit but few specific
characters by which they may be distinguished. Tubangui (1932b) in
working with the two species Echinostoma revolutum and Euparyphium
(Echinostoma?) murinum, found that he could not distinguish one from
the other except by counting the spines on the cephalic crown. In some
forms it is difficult to study the cephalic spination, and accuracy in any
case is not easy to attain. It naturally follows that any of the earlier
descriptions which omitted the accurate notation of number and distribu-

14 ILLINOIS BIOLOGICAL MONOGRAPHS

tion of the spines must be considered as doubtful species save where other
circumstances such as feeding experiments confirm the identifications.

The several researches on the life histories of echinostome species
have demonstrated a relatively wide range of hosts for all of them, and
the practice of using the host as a diagnostic feature must be abandoned
in favor of more detailed morphological descriptions. For purposes of
identification there seems to be no morphological feature in the echino-
stome species as reliable and serviceable as the cephalic spination. Some
of the cercariae are alleged to be spineless, but none of these spineless
“echinostomes,” the “Agilis” group of Sewell (1922, p. 106), have, to
my knowledge, been definitely shown to develop spines in later stages.
The nature of the cephalic spines is perhaps no more characteristic of the
various species than any one of a number of other features, but most of
the other characters are either obscure or variable with the conditions
under which they are studied. After long and tedious studies on the
excretory system and the so-called “flame-cell formula” or “pattern” of
this and other species, I am inclined to agree with Wesenberg-Lund
(1934, p. 8) that while it is an admirable ambition it is also a practical
failure, and I must confess along with him and Tubangui (1932b) that I
cannot with absolute certainty determine the number of flame cells in
this species. The measurements and figures were for the most part made
on fixed specimens, since there is less variability due to methods of fixa-
tion than to the amount of pressure exerted on the living specimen.
Three different methods were used in studying the spination: (1) living
specimens were compressed and stained with the usual intra-vitam stains ;
(2) fixed specimens were cleared in glycerine to which a small amount
of methylene blue had been added; (3) fixed specimens were stained in
the usual manner and cleared in oil of wintergreen to which a few
crystals of picric acid had been added. All of these methods are good
but the second and third are best. For studying the cephalic spines I
have used the second method more than either of the other two, and the
third method is best for studying the cuticular spination.

The living cercariae are active swimmers and good creepers on a
smooth surface. With the use of the two suckers they are able to creep
fairly rapidly in the measuring-worm fashion, and even on relatively
large tadpoles they sometimes find their way into the cloaca in a few
minutes. They remain active and infective for 10-12 hours, then sink to
the bottom and die after 20-24 hours. The swimming movements seem
to be random. Numerous experiments were devised to determine whether
they are attracted by any of the secondary intermediate hosts, but no
action of this kind was discovered. However, after they have come into
contact with the body of the host they immediately begin the creeping

STUDIES ON ECHINOSTOMA—BEAVER 15

movements which seem to be in the majority of cases in the direction of
an entrance. This is particularly true on tadpoles. It was noticed that
they very rapidly find their way into the small opening of the cloaca, and
after a number of observations under magnification it was found that
they usually creep downward and posteriorly until they reach the mid-
ventral line of the tail, then turn anteriorly to follow this line into the
cloaca. Fig. 5 indicates the usual course followed.

The following measurements were taken on a typical fixed specimen:
length of body 0.323 mm, width 0.095 mm; length of tail 0.45 mm;
oral sucker 41 by 46 ».; diameter of acetabulum 58 p, pharynx 17 by 21 pn.
The acetabulum is in the posterior third of the body (Fig. 12). The
crown-spines over the head are identical in number and distribution with
those of the adult. Although there is less difference in the relative size
of the various spines there is a noticeable difference that corresponds
with the condition found in the adult worms (cf. Figs. 1, 2, 3, with Fig.
9 and Text-figs. 1-5, p. 24). Riech (1927) found the same condition in
Echinoparyphium aconiatum. Johnson (1920), on the other hand, re-
ported a greater number in the cercaria, 43 instead of 37, and Iwata
(1933, p. 1) implies the opposite in the statement that the head crown
usually has 37 spines but that the younger ones have only 35. Figs. 1, 2,
and 3 are camera lucida drawings of the crown seen from three views.
The important features of this region are that there are 5 spines on the
lappets, 6 unalternating lateral spines, and 15 dorsal ones in 2 alternating
rows. The spines of the oral row are very slightly smaller than those of
the aboral.

The cuticular spines are very inconspicuous, but when the specimens
are lightly stained with methylene blue and observed without pressure or
stained in picric acid after clearing they are distinctly evident over the
whole of the ventral surface and almost all of the dorsal. They are most
evident between the two suckers.

The oral sucker and pharynx are joined by a fairly long prepharynx
which is rather indistinct. The esophagus and crura are also indistinct
in unstained specimens. Associated with the oral sucker is a group of
ducts which, as Brown (1926) and Wesenberg-Lund (1934) have already
noted for Cercaria echinata (?), are outlets to a group of gland cells
which are situated lateral to the esophagus (Fig. 12). There are 12 of
these ducts, but whether a single gland cell is attached to each could not
be determined. These cells and ducts are arranged in two groups. An
anterior one in contact with and lateral to the esophagus empties through
the three pairs of ducts which pass dorsally over the oral sucker and
terminate at its dorsal lip, and a second group is more posterior. The
three pairs of ducts from the posterior group are less easily demonstrated,

16 ILLINOIS BIOLOGICAL MONOGRAPHS

but by using only a small amount of neutral red they are shown to be
more coiled and much smaller. In fact, they do not look exactly like
ducts, being somewhat too irregular (Fig. 6). In about half of the toto
mounts of the adult worms these larval structures are still noticeable as
6 minute papilla-like structures along the anterior border of the oral
sucker (Fig. 9).

The excretory bladder is divided into a small anterior and a larger
posterior compartment, both contractile. A single duct runs posteriorly
into the tail and bifurcates abruptly into a right and left tributary with
an opening (?) to the outside in the region of the 40th-50th circular
muscle band, which is about 0.1 mm from the base of the tail. The two
main excretory trunks pass anteriorly, lateral and dorsal to the acetabu-
lum, where they enlarge somewhat and are filled with numerous (40-80)
refractive granules to about the level of the pharynx. Here they narrow
down and as they reach the level of the oral sucker turn back to form a
complete loop and extend almost to the posterior end of the body where
they again turn anteriad and extend to the region of the oral sucker. Fine
vibratile patches are numerous in the canal that extends from anterior
to posterior and are sometimes confused with flame cells. The total
number of flame cells is probably 36 although it is possible that some were
not found. The region between the two suckers is opaque and no flame
cells were found in that particular portion of the body. The flame cells
are arranged in 6 groups of three each, making a formula 2 [(3 + 3) +
(3 +3) + (3 + 3)]. Fig. 12 shows the distribution of the units found.
Sewell (1922) has used the excretory system as one of the characters for
separating the echinostome cercariae into the three groups “Echinatoides,”’
“Coronata,” and “Echinata.”’ On the basis of Johnson’s (1920) descrip-
tion of the cercaria of Echinostoma revolutum he placed it in the “Coro-
nata” instead of the “Echinata” group, although he had originally put it
in the latter and named the group after it. Sewell was correct in making
Cercaria Echinostomi-revoluti a member of his “Echinata” group, how-
ever, for the cercaria on which the present work was done seems to fit
this group in all respects excepting the tail. The presence of a tail fin is
one of the diagnostic characters of the ““Echinatoides,” but Sewell does
not definitely state that this character excludes a form from the “Echin-
ata” group. The tail of the cercaria of E. revolutum has a distinct fin
membrane, but as it is dorsal and vertical it is not seen in all prepara-
tions. At the tip of the tail the circular muscle bands do not continue
further than the tail fin membrane, which leaves the tip proportionately
more delicate than the rest of the tail (Figs. 4, 8, 10).

Discusston.—It is impossible to say how many times this species of
cercaria has been described or how many times other species have been

STUDIES ON ECHINOSTOMA—BEAVER Wa

mistaken for it. The original description is accredited to von Siebold
(1837). It was not possible to examine von Siebold’s description, and
many of the older descriptions have not been studied for the reason they
are too incomplete to be of use in this work.

In addition to the descriptions of the cercaria of FE. revolutum by
Johnson (1920), Tsuchimochi (1924), and Tubangui (1932b), there are
in the newer literature descriptions of eleven 37-spined cercariae. Some
of these are readily distinguished from Cercaria Echinostomi-revoluti by
the character of the cephalic spines and the absence of a tail fin mem-
brane, but the others do not allow a satisfactory systematic treatment.
Lithe (1909), Brown (1926), and Wesenberg-Lund (1934) have de-
scribed Cercaria echinata, which is generally accepted as the larva of
Echinostoma revolutum, as having no tail fin membrane, and as having
four corner spines larger than all the other cephalic spines. These
descriptions agree throughout with the cercaria of Echinoparyphium
aconiatum Dietz as described by Riech (1927) and Dubois (1928).
While it is not certain that they are all identical, it is certain that they
cannot be distinguished from each other and are all very different from
the cercaria of Echinostoma revolutum. Cercaria limbifera Seifert, 1926,
as originally described has 37 spines but differs from the cercaria of
E. revolutum in size, arrangement of the spines, and character of the
tail. According to the measurements given, it is a much larger form. The
tail has both a dorsal and a ventral fin fold, and the 6 lateral spines
of the collar are illustrated as being placed in two alternating rows
continuous with the dorsal ones, making the arrangement entirely differ-
ent from that of the cercaria of E. revolutum. The redia of Seifert’s
form has a much longer gut than the average mature redia of this species.
Brown (1931) described a form which he considered identical with
Seifert’s C. limbifera. There is at least one very important contradiction
in the observations of the two researchers, however. Brown’s cercaria has
only 35 spines, and the lateral ones are unalternating, as they are in the
cercaria of E. revolutum. Since they both have the peculiar tail fin over
the posterior two-thirds of the tail, both are larger than any of the others,
and the rediae are both of the long-gut type, it is probable that Brown
has corrected Seifert’s observations regarding the number and arrange-
ment of the cephalic spines. Rees (1931, Text-fig. a) who experimented
with C. limbifera has given the best illustration of its tail. Dubois (1928)
described 12 new species of larval echinostomes from Neuchatel, and
four of them are very similar to the cercaria of E. revolutum. One of
them is identical with it and the other three may also be. All four of
these cercariae are 37-spined forms with the spination formula (5) +
13 +1-+ 13 + (5), according to Dubois’s method of writing it. No
figures of them are given, and the descriptions of the spines are much too

18 ILLINOIS BIOLOGICAL MONOGRAPHS

brief to be of use in separating the 4 species. The description of C.
helvetica XxIv agrees throughout with the cercaria of FE. revolutum. The
rediae are also identical, and the two are doubtless identical species. The
only difference in the two forms Cercaria helvetica xx11 and xx1t and
the cercaria of E. revolutum is the absence of a tail fin in the two former.
C. helvetica xxi1 is a little larger than C. helvetica xxt11, but in other
respects they are very similar if not identical. The data given for C.
helvetica xxv hardly if at all constitute a description. The spination is
given as identical with C. helvetica xxl, xxi, and xxiv. A tail fin fold
is present, and the gut of the redia reaches almost to the lateral appen-
dages, being much longer than in any of the 3 other forms mentioned
above. I am doubtful, however, if the length of the gut in the redia is
reliable in separating species of the echinostome cercariae. Cercaria
trivolvis Cort, 1914, was found in the same host from the same general
region as the cercaria on which the present study was made (Cort, 1914,
1915). The cephalic spines were not described in detail and the tail fin
membrane was not mentioned in the description, making it necessary to
examine the type material in order to confirm the suspicion that the two
are identical. Very excellent preparations were made available to me by
Professor Henry B. Ward in whose collection the “type” specimens were
deposited. A dorsal fin is present in C. trivolvis, and the spination as well
as all other features are identical with my own specimens.

The relation of C. Echinostomi-revoluti (von Siebold, 1837) to the
most similar forms may be summarized as follows: Cercaria echinata as
described by Luhe (1909), Brown (1926), and Wesenberg-Lund (1934)
all differ from C. Echinostomi-revoluti in cephalic spination, the absence
of a dorsal fin on the tail, and the character of the rediae. They are all
probably identical with C. Echinoparyphii-aconiati as described by Riech
(1927) and Dubois (1928). Cercaria limbifera Seifert, 1926, differs in
the tail fin, which extends along the posterior two-thirds of the tail and
is both dorsal and ventral; and it probably has only 35 cephalic spines
instead of 37. Cercaria helvetica xx1t Dubois, 1928, differs from C.
Echinostomi-revoluti only in the length of the gut in the redia. The
cercaria of Echinost. revolutum described by Johnson (1920) is a 43-
spined form that is in all probability a misdetermination. Cercaria trivol-
vis Cort, 1914, and Cercaria helvetica xxiv Dubois, 1928, are synonyms
of Cercaria echinostomi-revoluti (von Siebold, 1837).

ADULT

Morphology and Size Variation

Three hundred stained permanent mounts are used as a basis for this
description. The worms vary from 0.3 to 21.4 mm in length, and,

STUDIES ON ECHINOSTOMA—BEAVER 19

except for an interval of about 4 mm between the lengths 13 and 17 mm,
the specimens used are fairly evenly distributed in size and almost reach
the maximum size given in previous descriptions. Leidy (1888) reported
specimens up to 25 mm, and Barker and C. A. Beaver (1915) give 22-30
mm as the length for Echinostoma coalitum, which is identical with E.
revolutum.

Echinostoma revolutum becomes mature, that is, it begins producing
ova, when it attains a length of 4 to 7 mm, differing considerably in
the various hosts. The range then for mature worms is from 4 to
30 mm in length. This size range is so great that a description of any
one size is grossly inadequate for an accurate diagnosis of all other sizes,
and a description by the ordinary methods is impractical when applied to
worms having so great a range in size. This would not be true, however,
if it were possible to give proportionate measurements applicable to all
sizes which, as is shown below, cannot be done. Practically every feature
has been measured and plotted; and in no instance is the proportion
between two organs or structures a constant throughout the series.

The worms used were all killed by dropping them from warm tap
water into Gilson’s fixative heated to 65° C. This method gave fairly
uniform results, leaving the worms well extended. Relaxing the worms
by shaking was avoided because of the possibility of injury to the cephalic
and cuticular spines. For very large worms it was necessary to raise the
temperature to 68-70° C in order to get straight specimens. As soon as
the specimens straightened out they were pipetted off and the fixation
completed in warm solution. No flattened specimens were used, for if
worms are even slightly flattened their body proportions are greatly
altered.

The greatest width of the body is at the acetabulum in immature
specimens, and in the region of the uterus in mature ones. Charts 1,
9, and 10 show the plotted measurements and the partially smoothed
curve which expresses the ratio between body length and width. In the
smallest specimens the length is three times the width, and it gradually
changes to about ten times the width in the largest ones. In worms that
have died without fixation the ratio of length to width is often as much
as 15:1. In like manner the acetabulum changes from one-fifth to less
than one-fifteenth of the body length (Charts 1, 11, and 12).

The position of the acetabulum and ovary is frequently used in
describing this and other species. Their position in FE. revolutum is
shown for all sizes up to 20 mm on Charts 4, 13-16. In the smallest indi-
viduals the ovary lies within the posterior fifth of the body, but when a
length of 5 mm is reached it becomes more anterior and remains near
the middle of the body for all larger sizes, being slightly nearer the

20 ILLINOIS BIOLOGICAL MONOGRAPHS

anterior end in individuals over 10 mm in length. The distance from
the acetabulum to the ovary or that part of the body occupied by the
uterus, shifts from about one-fifth of the body length to one-fourth of
it, varying considerably on either side of the line, but in no case is it as
much as one-third or as small as one-sixth of the length of the body.
The preacetabular region becomes less in proportionate length as the
animal increases in size. In the smallest individuals, less than 1 mm in
length, it is about one-half of the body length, and in the larger ones it
is only one-sixth to one-eighth of it.

The relative size of the suckers and the cephalic collar is shown in
Charts 2, 3, 17, and 18, where it may be seen that the acetabulum increases
in size at a greater rate than does either the oral sucker or collar. The
acetabulum and oral sucker are almost equal in the smallest individuals,
but in larger worms the latter has a diameter of less than one-third of
that of the acetabulum. The diameter of the collar is almost 2 times
that of the acetabulum in small individuals and in larger ones it is about
equal to it, while in the largest ones the collar is only three-fourths as
large as the acetabulum.

The transverse diameter of the pharynx is usually only slightly less
than its length. In all sizes of worms above 2 mm it is about equal in
length to the diameter of the oral sucker, and in very small worms it is
somewhat less, about two-thirds (Charts 19 and 20).

It is difficult to express the size of the testes and ovary because of
their variability in shape and the consequent inadequacy of length and
width measurements. An expression of the volume of each would of
course be ideal but impracticable. The average diameter (half the sum of
width and length) is used here as the most practical measurement of size
(Chart 5). The posterior testis is slightly larger than the anterior
one in most individuals but here the average of the two is used. After
sexual maturity is reached the average diameter of the testes is in all
sizes of worms about one-twentieth of the total length of the body, and
the ovary about one-thirtieth. These proportions, of course, do not hold
true for the youngest specimens, and there is a good deal of variability
in all sizes.

None of the structures or regions measured and plotted can be de-
scribed as having a constant proportion to any other part of the body in
all sizes of worms, although after maturity is reached some of the ratios
are fairly constant. The oral sucker is equal in diameter to the length of
the pharynx; the average diameter of the ovary is about one-thirtieth
of the body length; the average diameter of the testes is about one-
twentieth of the body length; and the ovary is near the middle of the

STUDIES ON ECHINOSTOMA—BEAVER Za

body. The length of the region between the acetabulum and ovary is also
fairly constant after the uterus is formed, regardless of the number of
eggs it contains.

Bopy Spines.—In addition to changes in body proportions there are
also structural changes caused by the growth and aging of the worms.
The cuticular spination is an example of this, as illustrated on Charts 7
and 8. Cuticular spination also varies in the different hosts. In young
individuals from all hosts the dorsal spines extend to the region of the
acetabulum, and in the very young individuals, less than two days old, the
whole of the dorsal side of the body bears minute spines. Ventrally they
reach to the posterior end in specimens up to about 3 mm. With increas-
ing age the dorsal rows diminish in number until they have entirely
disappeared in some individuals from bird hosts. Ventrally the spination
reduces much less in extent; and it also differs in the bird and mammal
hosts. The posterior limit of the spines moves forward more slowly in
mammals than in birds, sometimes reaching the ovary in bird hosts but
rarely going anterior to the anterior testis in those from mammals.
Anterior to the acetabulum the number of rows of ventral cuticular
spines is apparently not much altered by age or host. Counts made on all
sizes of worms vary between 28 and 42 rows from the genital pore to
the anterior end, but there seems to be no correlation between high or
low counts and the age or size of the worm. The mean is doubtless much
nearer the higher number, probably 36-38. The counts cannot be very
accurate since some of the posterior rows are usually folded under the
acetabulum. The rows on the dorsal and ventral sides are joined laterally,
and the spines of successive rows alternate, being arranged in oblique
rows as well as transverse.

The size of the cuticular spines cannot be determined very accurately
as it is rarely possible to get accurate measurements on both the length
and width of the same spine. However, the length of the lateral spines
and the width of the dorsal or ventral ones can be measured. Chart 7
gives the length of these spines in the tenth row measured at the lateral
margin of the worms. They become progressively smaller in proportion
to body length, and in worms from bird hosts they are relatively longer
than in those from mammals. The relation of width to length of the
spines also changes as the length of the worms increases. The width of
the ventral spines plotted against the length of the lateral ones of the
same row shows that the width changes from one-half to almost equal
the length in large specimens from bird hosts. In those from mammal
hosts the ratio of width to length is nearer 1:1.5 in the largest specimens.

A point that should be noted here is that this species is spiny on the
ventral side of the body in all individuals, but the larger specimens, 10

22 ILLINOIS BIOLOGICAL MONOGRAPHS

mm in length or more, may be without dorsal cuticular spines. Several
instances were observed in which the worms were entirely without spines
when taken by autopsy that had been delayed so long that the worms
were dead for several hours. This condition is not due to a loss of
spines alone, however, but to a loss of the entire cuticula. In some cases
portions of the cuticula may be seen adhering to the body in small patches.
It should be added also that this character, the distribution of the cuti-
cular spines, which has been used as an important character in both
specific and generic diagnosis of echinostomes, should be as thoroughly
investigated for other species, for just as it cannot be said that E.
revolutum is either with or without dorsal cuticular spines without reser-
vation, the same probably holds true for other species.

CoLLaR SPINES.—Except in cases where spines are lost or duplicated,
or where accessory spines appear, there are 37 cephalic spines in all of
the several hundreds of specimens examined. In other words, E. revo-
lutum is a 37-spined species but does not in all cases bear exactly 37
spines. In well fixed worms the spines are not often lost but are some-
times broken in handling. In fact they are so well attached in the living
worm that it is difficult to extract them at all. On the other hand, a
worm that has been dead a few hours in the gut of its host easily loses
both cephalic spines and cuticula and in some cases may be entirely with-
out either and still appear fairly normal in other respects.

The cephalic spination of 220 worms was observed minutely and
the condition of each spine carefully noted. Of this number, 173, or 79
per cent, were found to be entirely normal, i.e., they bear 37 typically
placed spines, all of which are normal in size and shape. The other 21
per cent fall into 3 general types of abnormalities. (1) Spines may be
missing either because of having been injured in life or improperly
handled after fixation. Usually these spines can be counted, however,
for a scar is often noticeable and even when a scar cannot be seen the
vacant space is evident. Thirty-one of the 220 worms were abnormal in
this respect. (2) A less common type 1s produced by accessory spines,
which are most common in the larger individuals, being added where
spines normally do not occur. They are smaller than the others in all
but one case observed and are easily distinguished from them. In a few
instances accessory spines were observed growing from the same position
as a normal one, a condition described here as a “duplication.” Accessory
spines were observed in 17 of the 220 individuals. (3) A third type was
observed in 11 of the 220. In these the position of the spines is normal
but one or more of them are much smaller, being in some instances very
minute. Their size and position suggest that they are being regenerated
to take the place of spines that have been lost by injury.

STUDIES ON ECHINOSTOMA—BEAVER 23

Due to the three types of abnormalities described above, particularly
the first, it is important to give special attention to the arrangement of
the spines of the collar. Fortunately this character is almost invariable
and for that reason is of greater value in diagnosis than spine number
or size. Even in specimens that have died in the host and lost most of
their spines an accurate determination may often be made if some region
including one of the lappets has retained most of the original spination.

Although the grouping of spines for description is somewhat a matter
of choice there is a more or less conventional terminology which has been
adopted here to facilitate comparison. There are 3 general groups, 2 of
which are paired: the 2 corner groups of 5 spines each, 2 lateral groups
of 6 each, and a dorsal group containing 15 alternating spines (Text-fig.
1, p. 24). When the specimen is seen in side view or when the lappets
are lifted, the position of the lateral and corner spines is seen most
clearly (Text-figs. 3, 4). The arrangement of the spines within the
various groups may be described as follows: 5 alternating corner spines,
3 of which are on the surface or oral, and 2 that are deeper or aboral ;
6 laterals in a single row; and 15 alternating dorsals, 8 of which are
anterior or oral to the other 7 which are aboral and continuous with the
6 laterals. The spines are symmetrically arranged; the saggital plane of
the animal passes through the median aboral spine.

The relative length of the collar spines to that of the body changes
very appreciably as the worm becomes larger (Chart 6). In 1-mm
worms the lateral aboral corner spine (LPV in Text-figs. 1, 3, 5) varies
slightly on either side of 28 », in 10-mm ones it is around 90 p, and in
the larger ones it is relatively much shorter, varying 15-20 » on either
side of 120. The relative length of each spine to each of the others
usually is not changed by age. In some instances, however, the median
dorsal spines become relatively smaller in the older worms, particularly
in the oral row in bird hosts. However, in the relative size of the various
spines there occurs a good deal of difference which cannot be correlated
with age. The lateral aboral one is, in all cases observed, the largest of
the 5 corner spines. The median aboral and the middle one of three orals
are about equal, the oral one usually being the larger. The lateral oral
corner spine is more often than not the smallest one on the collar, and
the median oral is about the same size (Text-fig. 5). The most ventral
one of the lateral spines is about equal in size to the middle oral
corner one or a little smaller than it, and each of the other laterals is
slightly larger in a dorsal progression (Text-fig. 4). The dorsal aborals
are about equal although the median ones are usually slightly longer
than the more lateral ones. The orals are each slightly smaller as a rule
than the aboral ones nearest them (Text-figs. 1, 2, 4).

24 ILLINOIS BIOLOGICAL MONOGRAPHS

A number of counts and measurements were made on the cephalic
spines of the cercaria and metacercaria in order to determine whether
spination is the same in both larval and adult stages. There is apparently

Text-Fics. 1-5.—Cephalic spines of the adult worm, showing the arrangement
and relative size of the individual spines. All are camera lucida drawings. All
scales are 100 u.

1—Ventral view. Notice that the oral spines of the dorsal side appear to be
much shorter than the aborals because they are seen more from end view. Spine
LPY is the lateral ventral aboral, the largest of the corner spines.

2.—Dorsal view. Aboral and oral spines almost equal in size when seen from
the same angle.

3—Ventral view of specimen killed with the lappets brushed up to show the
position of the ventral aboral spines. Corner spines all seen from end view.

4—Lateral view. Notice that the 6 unalternating lateral spines are continuous
with the aboral dorsals. In this specimen the orals are considerably smaller than
the aborals.

5.—Ventral view of the corner spines greatly enlarged.

STUDIES ON ECHINOSTOMA—BEAVER 25

no difference in the number of spines and only a slight difference in the
relative sizes. On the whole there is less size difference among the
various spines of a single individual in the larval stages than in the adult,
and the number is more constant. Careful examination of 25 cercariae
from each of 3 snail hosts, fixed and cleared in glycerine, gave the follow-
ing data: 72 with 37 spines, typically arranged; 2 with 1 of the dorsal
aborals missing; and 1 with a dorsal aboral spine duplicated—giving a
count of 38 for this individual. Accessory spines may have been over-
looked, as they would be very small if present.

GENITAL SystEM.—The genital system is apparently very similar to
that of all other species of the genus. The testes are usually regular in
outline in unflattened fixed specimens but frequently are divided into
3-5 shallow lobes (Figs. 13, 14). In worms that have died in the host
the inner parts of the testes pull away from the outer epithelium and
give the appearance of a lobed testis, and worms that have been killed
under pressure almost invariably have irregular testes. The vasa defer-
entia run into a large seminal vesicle which lies in the posterior part of
the muscular cirrus sac. The anterior part of the sac is occupied by the
pars prostatica, the voluminous prostate gland, and the well developed
cirrus. The cirrus opens through a common pore with the metraterm,
which runs along the right side of the cirrus sac in all specimens ex-
amined. Looss (1899, Figs. 5, 10) shows the uterus on the right side
in one and on the left in the other figure. The position of the cirrus sac
is usually anterior to the middle of the acetabulum and is often entirely
anterior to it in the younger worms; in some cases it is entirely dorsal
and reaches the posterior border of it (Fig. 14). The female system is
also typical of the genus, having, instead of a seminal receptacle, a more
or less voluminous receptaculum seminis uterinum. A fairly distinct
Laurer’s canal, a diffuse shell gland, vitellaria from acetabulum to the
posterior end, and a small vitelline reservoir are also characteristic struc-
tures. The uterus is long, regardless of the age or maturity of the worm,
and is coiled transversely into 7 or more loops. After it begins to fill
with ova it usually does not have less than 9 loops, and more are added
as the eggs increase in number. Barker (1916) has attempted to use the
number of eggs in the uterus as a character on which to key the muskrat
echinostomes. This is not a good character, however, for this species
may have from none at all to over 6,000 eggs. The uterus in a 21-mm
worm from a muskrat was teased out and the eggs counted. Each egg
was counted as it was drawn into a pipette and in this manner 6,200 were
counted and a hundred or more were probably left in the tissues. The
number of eggs produced in 24 hours was also determined for several
worms at different ages. In Transfer X (p. 64), a single immature worm

26 ILLINOIS BIOLOGICAL MONOGRAPHS

was taken from a rat and transferred to the cloaca of a pigeon. It ma-
tured and began producing eggs in 6 days, or when it was 18 days old.
After it had been producing eggs for 7 days, a 24-hour fecal sample was
taken, and by the dilution and direct count method the number of eggs
was determined to be 4,100. The following day the count was 3,800 and
the counts for the next 2 days were respectively 3,460 and 3,402. Similar
records were taken on other transferred worms and the highest number
for any one day was 4,600, which is more than 3 per minute. This count
was made by the Rivas method (1932, p. 479), which was finally adopted
as the most satisfactory for this type of work. Most of the worms pro-
duced 2,000-3,000 eggs daily to within a few days of death, and 700 per
day is the least any worm produced. The 700 per day count was made
on a worm 59 days old.

Egg size varies with the age of the worm and is possibly somewhat
altered by the host. The younger worms produce eggs with a very great
range in size, and the average length is much greater than in more
mature ones. The range in size for the eggs of the worms from all hosts
was found to be 91 to 145 yw by 66 to 83 pw. The largest were in the
first positive stools of Cat 4 and the smallest were found in Muskrat 261,
but those from some of the pigeons were almost as small as the ones
from the muskrat. Usually the eggs from bird hosts are darker in
color and appear to have a thicker shell but there are some exceptions
to the rule, for those from muskrat hosts are usually almost as dark as
the ones from the pigeon. Variability in the size and color is much too
great to allow the use of this character in distinguishing EF. revolutum
from other closely related species.

The transfer experiments also gave some interesting data regarding
the self-fertility of the species. On 10/24 Rat 26 was killed in order to
get some immature worms for transfer. These worms were 12 days old,
and so far as could be determined by means of microscopic examination
of the living worms, all were sexually immature, having no sperm in
either the seminal vesicle or receptaculum seminis uterinum. In fact the
latter organ was not yet formed. One worm was transferred into each of
4+ pigeons (T7, 8, 9, 10; see p. 64). Three of them gave positive stools
on the fifth day after the transfer was made, and T9 lost its worm before
it matured. About a week later 50-100 ova were collected from the
feces of each pigeon and incubated in tap water. Normal miracidia de-
veloped in the eggs from each of the worms and the rate of development
was the same as for those from hosts carrying an infection of several
worms, so that cross-fertilization would be possible. The question as to
whether trematodes are self- or cross-fertile is one that has received a
good deal of attention. The only data to be found on it are occasional

STUDIES ON ECHINOSTOMA—BEAVER 27

reports of observations on worms with the cirrus inserted into either
its own metraterm or into the genital pore of another individual (Looss,
1893). Where single individuals are found in the hosts it might be as-
sumed that they were self-fertile if viable eggs were produced, but one
could not be sure that a second individual had not been present earlier.

Morphological Variation Induced by the Host Species

In the preliminary experiments it was noticed that the worms from
the various hosts had slightly different appearances, but these differences
were in most cases so slight that they could not be described or figured.
It became especially noticeable when worms from avian and mammalian
hosts were compared, and since some confusion seems to be due to lack
of understanding of this variability it was thought worthwhile to study it
in more detail.

A fairly complete size series was obtained from both avian and
mammalian hosts, and in order to compare all sizes of worms the most
satisfactory method was found to be the graph system commonly used
in biometric studies. Three graphs were used for the comparison of each
character in most cases. One was used to show the number of individuals
used and their measurements from the bird hosts and a similar one for
those from the mammals. A third chart to show the partially smoothed
curves was taken from the other two. This method indicates the range
in all classes and the variability within the range; it gives the proportions
of the worms at all sizes, and the differences in the worms from the two
types of hosts. The significance of the differences can be judged directly
from the plotted data. About fifty such graphs were prepared, but only
twenty of the most illustrative have been included here.

Although there is a very marked difference in the size attained in the
various hosts used in these experiments, Echinostoma revolutum ap-
parently does not reach a definite size but continues to grow until it is
expelled. The maximum size indicated in the charts does not express
the absolute maximum size for the species but the actual size of the in-
dividuals studied. The curves were made by drawing straight lines
through the points obtained by averaging the points within arbitrary
limits of range. The worms from all hosts were fixed, stained, etc. in
exactly the same manner in so far as it was possible. None were killed
under pressure.

Various authors, notably Looss (1899), have suggested that much of
the variation in this parasite may be due to the host species, but no one
has to my knowledge attempted to measure or describe it.

One of the most conspicuous differences in worms from the two types
of hosts is the greater reduction in the dorsal cuticular spination in the

28 ILLINOIS BIOLOGICAL MONOGRAPHS

worms from birds. While there is also a variation in those from each of
the mammals and birds, the differences are less marked than when the
bird- and mammal-reared worms are compared collectively (Chart 8).
That the reduction in dorsal spines is not due to age alone is shown by
the fact that it is not so easily correlated with spine reduction as is the
body length. When the number of complete rows of dorsal cuticular
spines plotted against the length of the worms is averaged and a curve
drawn, a very pronounced contrast in the larger worms becomes apparent.
For example, an 8-10 mm worm from a duck may be completely spineless
on the dorsal side while on another of the same size from a rabbit or
muskrat there may be 10-15 complete rows of spines. This is particularly
important in the light of some of the definitions of the two genera Echin-
ostoma and Echinoparyphium. Sprehn (1930, 1932) considers one of the
differences in these genera to be the absence of dorsal cuticular spination
in the former and the presence of it in the latter. Following this defi-
nition would necessitate putting the worms of this species into both
genera.

The length of the cuticular spines was measured and plotted in Chart
7. Contrary to expectations, the spines are longer in comparison to body
length in bird-hosts, and the difference is considerable. In the smaller
worms the collar spines are longer in mammals, but in the larger worms
the variability is so great that although they are probably also longer in
mammals the data do not clearly indicate it.

Differences in body proportions are not very pronounced in most
cases, but since there seems to be a significant variation in the same
direction for all parts measured it is clear that some of the variation in
shape in this species can be attributed to the different types of hosts. As
a rule the worms develop more rapidly in birds (Table 7, p. 77), become
mature earlier and at a smaller size, and live a much shorter period.
The differences in proportion are shown in Charts 9-20. The worms from
birds progress toward mature proportions more rapidly than those from
mammals, making a rather pronounced difference in the younger indi-
viduals. There is less difference in those between 6 and 8 mm, but
between 8 mm and the upper limits the differences become progressively
greater, the worms from birds being generally wider and stouter than
those from mammals. There is apparently not much difference in the size
of the acetabulum (Charts 11, 12), but when the diameter of the oral
sucker is plotted against that of the acetabulum a significant difference is
observed (Chart 18). The larger worms from bird hosts have a relatively
larger oral sucker. Similarly the collar is larger as compared with the
acetabulum in the larger specimens from birds, and smaller in the shorter
ones (Chart 17). Coincident with this variation is the difference in

STUDIES ON ECHINOSTOMA—BEAVER 29

growth rate in the two types of hosts mentioned above. It should be
mentioned, however, that differences in body proportions are not great
enough to make them readily discoverable by inspection. It is only when
large numbers of individuals are compared biometrically that the differ-
ences become obvious. It is shown in Charts 9-14 that the variability
within each group is sufficient to give much overlapping.

In one instance the variation due to the host was very conspicuous.
The worms taken from the pig were barely mature after four weeks and
the size of the various parts as well as the whole were very strikingly dis-
similar to the average from the other hosts. The body is only 3.6-3.75
mm long and wider than normal. The acetabulum is large and the post-
testicular region is much reduced. The testes and ovary are nearly equal
in size and much too small, being slightly smaller than the pharynx. The
spination on the collar is normal in number and distribution of spines
but the length is greater than normal. The whole appearance of these
worms is so different from the normal that they could easily have been
described as a different species had their origin not been known.

It may be concluded that while there are very definite variations in-
duced by the conditions within the various hosts, they are comparatively
slight in most cases. However, they are conspicuous enough to account
for some of the confusion in the literature regarding this species. It is
particularly true of the cuticular spination and the total length attained,
there being a range of from less than 4 to about 30 mm in the length of
the worms producing eggs. The differences in proportion can be ex-
plained on the basis of differences in growth rate, but the differences in
the character of the cuticular spination are as yet unexplained.

Hosts and Geographical Distribution

Echinostoma revolutum is one of the most cosmopolitan of trematode
species, having been reported from every temperate region in the world
with the exception of South Africa and inland China. It is also found
near the equator but is apparently less common there. Tubangui (1932a,
b) records it as fairly common in the Philippine Islands (Luzon), and
Picard (1930) took an echinostome species from the pigeon in Java
which is probably E. revolutum. The regions where it is known to occur
are indicated in Tables 1, 2, and 3. Only the records that have been
published since Kowalewski (1895) and Looss (1899) redescribed the
species are used, and some of these reports are doubtful and have either
been excluded or indicated as questionable.

This species seems to be as cosmopolitan in its choice of hosts as it
is in geographical distribution. This lack of specificity in all of its
parasitic stages is of course the most important reason for its wide

30 ILLINOIS BIOLOGICAL MONOGRAPHS

distribution. The experiments of Tsuchimochi (1924) and Anazawa
(1929) in which they infected certain mammals suggested that this
species might also occur in mammals in nature. My own experiments
have confirmed those of Tsuchimochi and Anazawa and added many
new experimental hosts; a number of new records of natural infec-
tions in mammals and birds have also been obtained. Tables 1, 2,
and 3 give the hosts, distribution, and references for the incidence of the
cercaria, metacercaria, and adult, respectively.

Cercaria Echinostomi-revoluti is known to occur in at least four
genera and ten species of pulmonate snails. Although it may be found in
several species of a particular region it seems to be decidedly more preva-
lent in a single species. In the vicinity of Urbana, I have searched for it
in Physa gyrina for three years and have never found a single infection.
Miller (1936), who made more extensive collections in the same region,
has given but a single record of it from a stream where the incidence is
particularly high in Helisoma trivolvis. The percentage of infection in
P. gyrina in this region is probably much below 1 per cent while in the
same region it is as high as 60 per cent in Helisoma trivolvis during the
summer months.

The agamodistome may occur in any of a very great variety of hosts.
In this study a number of attempts were made to determine the most
“natural” hosts, and for this particular region it seems that they are
Physa gyrina, Helisoma trivolvis, and Rana pipiens, named in the order
of frequency of natural infection. Helisoma trivolvis, which also serves
as the primary intermediate host, carries a rather high percentage of
infection in nature, but not as high as it was at first thought; an er-
roneous idea regarding this is easily acquired if care is not taken to
insure against laboratory infections of the snails examined. By care-
fully drying each snail as it was collected in the field and isolating it in
the laboratory or by examining it immediately, I found that in the one
region which received most of my attention Physa is probably the most
natural host. Six adult Rana pipiens, 6 half-grown tadpoles of the same
species, 4 medium-sized Physa gyrina, and 6 small Helisoma trivolvis
were collected from the same bend of a stream, all on the same day, and
examined for cysts of E. revolutum. Each cyst from the frogs and most
of those from the snails were pressed under a coverslip and carefully ex-
amined. The results are shown in tabular form:

Number of hosts

Host Number of Cysts positive
Adult R. pipiens... cc. cc ccc cece cece ec eees 2to 27 4 out of 6
Larval FR: pipiens: <.o.s0ac be baron bee S00 oe. we ore 6to 41 4 out of 6
PURUSONOVVITE 53icon Cea ieeae Dae at eens oe aes 12 to 125 3 out of 3

Helisoma trivolvis.....ccccc ccc cccccceccees lto 18 6 out of 6

STUDIES ON ECHINOSTOMA—BEAVER 31

When tadpoles and the two species of snails, all laboratory raised,
were put into a small aquarium with active cercariae, the tadpoles seemed
to get the largest share of the parasites and the Helisoma the least. It
was found that it was necessary to govern carefully the infections in
the tadpoles and Physa for they would become so heavily infected in a
few hours that they would soon die. On the other hand the Helisoma
very rarely died because of heavy infection with metacercariae. Heavily
infected tadpoles became swollen and died with a sort of general edema.
Lutz (1924) made the same observation on tadpoles infected with
Echinostoma nephrocystis (?=E. revolutum). The following experi-
ments will serve to illustrate how readily the cercariae enter and encyst
in tadpoles. A laboratory raised tadpole (R. pipiens) about 25 mm in
length was put into a 200 cc container with 75 freshly emerged cercariae
and left for about one hour. They were observed from time to time,
and on one occasion 7 cercariae were seen creeping around within the
transparent cloaca. The following day the tadpole was dissected under
the binocular microscope and 53 cysts found in the kidneys and ad-
jacent ducts, and 7 cysts were found in the gill chamber. Many other
tadpoles were infected and used in the feeding experiments. A _half-
grown hairless rat (Rat 27), for example, was fed a 30 mm tadpole that
had been in a finger bowl with an infected snail (C6-9) for about 2 days,
and 431 worms were recovered from it. Two small Physa were also in-
fected from snail C6-9, and fed to Pigeon 15 from which 63 worms were
recovered (Tables 5 and 6). There can be no doubt that Tsuchimochi
(1926) and Fallis (1934) are correct in their statements that Echino-
stoma revolutum will use either a snail or a tadpole, depending upon which
is available. There is apparently very little difference in the two species
of tadpoles used in the experiments; the larvae of Rana catesbiana were
as easily infected as Rana pipiens. Pseudosuccinea columella and Fos-
saria modicella were also easily infected. It was also possible to get in-
fections in several more unusual hosts. Five Sphaerium sp. and 3
Pisidium sp. were exposed to heavy infusions of cercariae for 8 hours
and examined after 24 hours and 5 days, respectively. In one Sphaerium
14 cysts were found, but in the same individual 22 of the cercariae had
lost their tails and were still creeping around under the mantle; another
had 9 cysts and 18-20 unencysted cercariae; one had 6 creeping and none
encysted, and the other two, which were smaller individuals, had none.
Eight cysts were counted in a Pisidium five days after it had been ex-
posed for eight hours. Two others of the same lot were negative and
one had only two cysts. The cysts when present were in the flesh of the
clam near the hinge in both species. Several species of scaly fish were
exposed and examined but none were ever found positive. It is probable,
however, that the catfishes are sometimes natural hosts, for the two

32 ILLINOIS BIOLOGICAL MONOGRAPHS

experiments with the black bullhead, Ameiurus melas, indicate that the
cercariae react to it very much as they do to the tadpoles. A fish that
was about 8 cm long was put in a shallow dish with 250-300 cercariae
and left for eight hours. When it was dissected the next day 67 cysts
were found deep in the substance of the kidneys, 4 in the left mesone-
phric duct near the kidney, and 9 in the same duct near the cloaca—a
total of 80 cysts. They were all normal in appearance having well formed
walls, and the host did not appear to be suffering ill effects. A second
fish of the same species was left in a shallow dish in 1 liter of water with
an infected snail for 4 days. On the last day it was somewhat bloated
and very inactive and finally died. Several hundreds of cysts were found
in the kidneys and associated ducts.

In the experimental work done thus far on Echinostoma revolutum,
including the present study, it has been shown that 14 or 15 species of
snails may serve as secondary intermediate hosts, and none of the other
species of snails have been experimentally excluded as possible hosts.
Johnson (1920) has made the only unsuccessful attempt to infect tad-
poles. At least four species—R. pipiens, R. catesbiana, and the “tadpoles”
of Tsuchimochi (1926) and Fallis (1934, Bufo americana)—are known
to carry infections of this species. Miki (1923) found cysts in R. escu-
lenta, which he fed to rats and mice and recovered E. cinetorchis(= E.
revolutum). According to Ando and Ozaki (see Dollfus, 1925, p. 90)
the metacercariae of E. cinetorchis (= E. revolutum) were found in
Rana nigromaculata, R. rugosa, and R. japonica, which increases the
number to seven or eight known amphibian hosts if E. cinetorchis is ac-
cepted as a synonym of FE. revolutum (see p. 47). Ameiurus melas,
which is shown by this study to be a probable natural host, is the first
fish to be reported as a host for this species.

The adult worm apparently may be found in almost any bird or mam-
mal (Table 3). Natural infections are, of course, limited to those ani-
mals that feed upon aquatic animals, but many others may be experi-
mentally infected and act as “normal” hosts if not “natural” ones. In the
present study an effort was made to discover the host which would serve
as the most satisfactory one for routine culturing of this species, and
incidentally the pig was infected to determine the effects produced by
the larger host. These experiments are outlined in another section
(p. 56) and summarized in Table 6. For culturing the worms rapidly
the pigeon or guinea pig are the best adapted, but greater size is attained
in the duck or rabbit. The rats and mice used were found to be un-
dependable; and although the worms develop as well in the dog and cat,
these hosts require more space and attention and were for that reason
less often used. Although the worms develop slowly and attain a smaller
size in the domestic pig, in view of its habits it may be expected to harbor
natural infections of E. revolutum.

STUDIES ON ECHINOSTOMA—BEAVER 33

Immunity Phenomena

Although only a few experiments were designed specifically to test
the types or degree of immunity developed in the various hosts used,
the large number of infections and variety of hosts used has lead to
certain new conclusions and confirmations which are being reported even
though they must in most cases be repeated and extended before the
results are accepted.

Table 5 and 6 (pp. 72-76) indicate the number of hosts used in the
first series of experiments. The number of hosts from which no worms
were recovered or were at least not known to be infected are also given
here. In most of the hosts reported negative, it is certain that the worms
remained in the gut for a few days and in some cases were lost only
shortly before maturity was reached. Those hosts reported negative are,
then, those which contained no worms when autopsied or did not produce
stools which were found positive by fecal examination.

It may be seen from Table 6 that all attempts to infect cats, dogs,
chickens, hogs, and guinea pigs were successful. Very few of the
pigeons, ducks, or rabbits were negative, but the mice and rats could not
be relied upon to hold the worms. This is particularly true of the albino
and hooded rats, in which no infection was accomplished in 14 attempts.
On the other hand, large mature worms were taken repeatedly from
wild and hairless rats.

All of the rats were treated similarly. The diet after the experi-
ments began was the same for all and they were fed in all cases as much
food as they would eat. They were obtained from the “discards” at the
Animal Breeding Laboratories at the University of Llinois. Unfortu-
nately, the history of these rats was not obtained, as it was not thought
to be sufficiently important at that time. Accurate data on the diet and
the pedigree of each rat would, however, have made the experiments of
greater value since these factors probably account for some of the
“natural immunity” displayed. Ackert et al (193la, b) and others have
shown that vitamin deficiencies alter the natural course of infections, and
since other researchers (Tsuchimochi, 1924) have reported infecting
laboratory rats with E. revolutum, it seems even more likely that under
different conditions the rats used in these experiments would have been
more consistently positive. Tubangui (1932b) had similar experiences.
He was using pigeons and albino (?) rats in his experiments and fed cysts
of E. revolutum to both. While the pigeons were always positive the rats
were in each case negative. His rats may also have been maintained on a
diet which rendered them nonsusceptible.

The results obtained from the mice are not particularly significant in
this connection as it was not possible to determine whether the wild

34 ILLINOIS BIOLOGICAL MONOGRAPHS

ones actually ate infected snails or not; and all of the positive mice either
died in a few days after infection or were killed before the worms
matured.

In regard to natural immunity it may be concluded that among birds
it is practically nonexistent, and although the albino rats seem to demon-
strate some natural immunity none of the other mammals have been
experimentally excluded from the list of possible hosts for this species of
echinostome.

A few experiments were carried out to determine whether or not an
acquired immunity to reinfection could be demonstrated in pigeons. It
was demonstrated that pigeons usually lost their infections in about three
weeks. In one case (Pigeon 14) in which the infection was lost after
15 days (many eggs had been present in the feces for five days) and the
pigeon reinfected two weeks later, only one very immature worm was
recovered on the eighth day. An abundance of cysts (100-150) had been
fed both times, and the diet was not changed. These results indicated
that this pigeon had either acquired an immunity to reinfection or that
the diet used over the long period of time was unsuitable for the parasite.

The following is a summary of the experiments which followed this
observation.

Pigeon Im 1 had been used as T2 and T4 (p. 63). As T2 it had received
per anus 5 worms that had lived 18 days in Rabbit 7, and it carried this infection
for six days. As T4 it had likewise received 10 worms 14 days old from Pigeon 18.
It carried this infection for 12 days. Transfer 2 was made on 10/3/33, and the
other transfer was made just two days after all of the worms had been lost. On
11/2, or eight days after the last of the T4 worms had been lost, it was fed a
Physa carrying an abundance of one-day-old C7-1 cysts (see p. 63). No ova were
found in the feces, although careful daily examinations were made from 11/13 to
11/22. On 11/22 it was fed 35 of the C7-1 cysts that were twenty days old. These
were teased out from the Physa and administered in a small capsule. Daily fecal
examinations from 12/1 to 12/15 were made and no eggs were found. The host
was killed on 12/15 to determine whether the worms were present but retarded in
development. No worms were present.

Pigeon Im 2 had been used as 14 and T6. As 14 it had been fed C6-12
cysts on 10/15. Ova appeared in abundance on 10/15 but disappeared on the
fifteenth day (10/20). As T6 it had received per anus on 10/24 a single mature
worm that had been in Rat 24 for 39 days. This worm lived only six days in
Pigeon Im 2, and produced ova in fair abundance until it was expelled on 10/30.
On 11/2 it was fed two snails, each carrying about a hundred cysts that were 1-3
days old. No ova were discovered by daily fecal examinations from 11/12 to 11/23.
On 12/6 it was again fed about 125 cysts that had been in the snail host for 48
hours. Eight days later it was killed and a single very immature worm only 2.5
mm in length was recovered. This is about one-half of the length normally at-
tained in this time.

Pigeon Im 3 had been used as T3. As T3 it had received per anus on 10/8,
ten worms that had matured in Dog 3 (23 days). It carried these for 24 days, or
until 11/1. On 11/2 it was fed a snail with about a hundred cysts one day old.

STUDIES ON ECHINOSTOMA—BEAVER 35

Ova were first found on 11/12 or on the tenth day and continued to the sixteenth
day. No ova were found on 11/19 or thereafter. It was fed two snails each carry-
ing about 75 cysts two days old on 12/6. On 12/16 it was killed and three very im-
mature worms (1.6 to 1.7 mm in length) were recovered.

Pigeon Im 4 had been used as Tl. As T1 it had received per anus on 10/2, six
mature worms from Chicken 5. It carried these worms until 10/28, or 26 days.
On 11/2 it was given a snail with about a hundred cysts one day old. A few ova
were found in the feces on 11/18. This was the sixteenth day after feeding, which
is four to six days later than normal. The ova were present in very small numbers
until 12/5, or the 33rd day. On 12/6 it was again fed about one hundred cysts in
a Physa and killed nine days later. It was negative.

Pigeon Im 5 was used as T10. It had received per anus one immature worm
from Rat 26 on 10/24. The worm was expelled on 11/22, or 28 days later. This
worm had been in the rat host for twelve days. On 12/10 it was fed a snail with
78 cysts that had been encysted for two, three, and four days. It was positive
by fecal examination on the seventeenth day and was killed the next day (12/28).
Two small mature worms were recovered.

Pigeon Im 6 was used as T5. It received one mature worm from Pigeon
19 per anus on 10/18 and carried it until 11/28, or for forty days. This worm
had been in Pigeon 19 for 21 days. On 12/10 it was fed a small Physa with about
forty cysts two days old. It was positive by fecal examination on the twelfth day
and subsequently until it was killed on 12/31, the 21st day. Eleven mature worms
8 to 8.8 mm in length were recovered.

Pigeon Im 7 was used as T7. It had been given per anus one immature worm
from Rat 26 on 10/24. The worm was expelled on 11/14, or twenty days after the
transfer was made. On 12/10 it was fed a snail with 22 cysts one day old. Ova
were never discovered in the feces, and it was negative when killed on 12/27.

Pigeon Im 8 had been used as T9. It received per anus one immature worm
from Rat 26 on 10/24. The worm was expelled before it matured, probably im-
mediately. On 12/10 it was given a snail with 150-200 cysts. Ova were not found
in the stools until the nineteenth day. It was killed the same day (12/29), and a
single mature worm 6.95 mm long was recovered.

At the termination of the experiments the hosts had been in cap-
tivity, held in small cages 2’ x 2’ x 3’ for the following lengths of time:
Im 1, 8 weeks; Im 3 and 4, 10 weeks; and Im 2, 5, 6, 7, and 8, about
12 weeks each. These experiments are summarized in Table 4.

There is a good deal of variation in the behavior of the eight re-
infected pigeons. It seems to be generally true that the rate of develop-
ment is decidedly slower in the second and third infections. The aver-
age time for the appearance of positive stools in first infections is ten to
twelve days, but the time required in the second infection for Im 4 was
16 days; for Im 5 it was 17 days, and in Im 8 ova appeared in the stools
on the nineteenth day. However, in the case of Im 3 eggs were found
on the tenth day and in Im 6 on the twelfth, which would seem to con-
tradict the conclusion that the pigeons acquire a sort of immunity that
retards development. There is still a further contradiction offered by
Im 8 in which the one worm administered per anus in the first infection

36 ILLINOIS BIOLOGICAL MONOGRAPHS

did not remain long enough to be really considered as an infection, and
yet there is no essential difference between the second infection in it and
that of Im 5, whose first infection lasted for 28 days. In both cases the
rate of development was about equally retarded.

The number of worms present in the first infection is ruled out as a
factor influencing the second one by the fact that Im 1, which had only
a total of 17 worms for a period of 18 days, was refractory to both subse-
quent infections; while Im 3 had carried ten worms for 24 days and
several more for a second period of 16 days, and although the rate of
development was somewhat retarded in the third instance, an infection
was accomplished.

There is some possibility that the age and number of the cysts fed
are factors influencing the character of the infections, but they are prob-
ably minor ones, since in the first infections in these experiments and in
the infections used in other experiments no noticeable difference ap-
peared in cases where cysts ranging from one day to three weeks old
were used. The slight metamorphosis that occurs after the cercaria
encysts is accomplished very rapidly, and the metacercariae are infective
almost immediately after encystment. In Experiment 11, for example
(p. 61), Rat 27 was given cysts less than 36 hours old, and 431 worms
were recovered from it.

Because of such marked uniformity in the first infections in all of the
pigeons used, age immunity is considered to be of very little importance.
The pigeons were taken without regard for age.

While the data may be interpreted as indicating some immunity re-
actions it seems more probable that the diet of the hosts and the con-
ditions under which they were maintained in the laboratory more satis-
factorily explain the phenomena observed. In the case of the first and
single infections the pigeons were taken from a barn where they could
choose from a variety of foods, exercise freely, and follow a normal
daily program. When they were brought into the laboratory they were
held only long enough to determine by fecal examination whether in-
testinal parasites were present and to get them to feed. The diet used
was fairly uniform throughout the whole series of experiments, i.e., all
the hosts were given the same foods in nearly equal proportions. The
diet consisted of yellow corn, wheat, oats, and a little rice. Although
pronounced haemorrhagic enteritis was produced in a few cases (in the
experiments to determine the general nature of infection in the various
hosts), none of the pigeons used in the immunity experiments ever lost
weight noticeably but appeared to maintain excellent health throughout
the length of the experiments, which lasted for three months in some
cases. However, there was a decided change in the character of the

STUDIES ON ECHINOSTOMA—BEAVER 37

feces after a month or two in captivity, which indicates that there was a
change in the general condition of the host. During the first few weeks
the normal stool contained considerable greenish material regardless of
the type of grain fed. A few weeks later it became a pale green and
finally a greyish yellow with an occasional greenish tinge. This of course
varied greatly with the various individuals and in the case of Im 6 the
stools continued to be greenish during the whole period. It was also
noticed that some of the pigeons were considerably more restless than
others, thus introducing another variable, the amount of exercise. Im 6,
which was the most restless of all, was the most normal with respect
to the type of stools, and was the only one to carry what could be con-
sidered a normal infection after a long period of captivity.

I do not propose to attempt an explanation of these phenomena, but
in passing it is interesting to note again that the diet consisted largely
of yellow corn with some wheat, oats, and a little rice. The pigeons were
never in direct sunlight after they were captured and were not allowed to
exercise more than was possible in the small cages. The diet was not
made up with any regard for vitamins and must certainly have been
deficient in vitamins A and D, and as soon as the hosts’ reserves were
exhausted they would be deficient from that time on to the end of the
experiments. Ackert et al (193la) found that chickens maintained on a
vitamin A free diet developed more and larger Ascaridia lineata than
controls that were fed on balanced diets. This was interpreted as a result
of lowered resistance induced by the vitamin deficiency. The diet used
in those experiments differs considerably from that used in mine, and
the hosts in Ackert’s experiments were irradiated. In another series of
experiments (Ackert et al, 1931b) similar results were obtained with
vitamin B free diets. In the conclusions to the latter report it was sug-
gested that there may be a direct effect of the diet upon the parasite
rather than upon the resistance of the host. That the experiments of
Ackert differ greatly from mine both with respect to experimental ma-
terial and methods is, of course, recognized. However, since in both
cases vitamin deficient diets were involved and since they led to dia-
metrically opposed conclusions, it is worth while to point out again that
instead of the resistance of the pigeons being lowered or the parasites
being benefited by the diet and lack of sunlight or exercise, the opposite
was generally true in my experiments. The parasites either did not de-
velop at all or were decidedly retarded in their development.

The transfer experiments provide some interesting facts relative to
the topic of immunities in that there seems to be a definite increase
in the longevity of the worms by transferring them from one host to
another. These experiments have been described and summarized in

38 ILLINOIS BIOLOGICAL MONOGRAPHS

Table 9 (p. 77). The average duration for heavy and light infections
alike is about three weeks for the first infections in pigeons. In six
of the ten transfers the worms lived 20 days or longer in the second host,
and in Transfer 3 the one worm that was taken after it had lived its
expected limit in the first host, lived an additional forty days in the
second. In Transfer 4, in which the infection lasted only twelve days,
the pigeon which served as the second host had already been used in
Transfer 2, in which it had carried five worms for six days. This
would seem to show that the pigeon used in Transfers 2 and 4 had
more than the average resistance and should be compared with the
others on that basis.

Since no other transfers such as those described here have been made,
it is not possible to broaden the conclusions by comparisons, Un-
fortunately, they were few in number and for that reason merely indi-
cate rather than decide the above question as to whether or not there is
a sort of accumulative immunity developed which limits the length of
the parasite’s life.

In all the experiments which have a bearing upon the question of
immunity a good many factors have not yet come under consideration.
Taliaferro (1929, p. 247), in his extensive treatise on “Immunology of
Parasitic Infections,’ points out that age as a factor independent of all
others is often an important one and more especially in cases where the
host is an unnatural one. Since there are so many hosts for E. revolutum
and quite an extensive list of both birds and mammals from which it is
repeatedly taken in nature, it is hardly possible to decide whether the
pigeon should be considered a natural or incidental host. There have been
numerous reports of natural infections of echinostomes in pigeons
(Miller, 1897; Krause, 1925a; Bolle, 1925; Zunker, 1925; Heelsbergen,
1927; Sprehn, 1927, 1930; and Picard, 1930), and while most of them
were either determined only to genus, identified as new species, or species
closely related to E. revolutum, it is more than probable that in many
cases the worms dealt with are identical with EF. revolutum. This has
been discussed at length in another section (p. 51). Notwithstanding
these facts it must still be maintained that the pigeon is relatively inci-
dental as a host for this species or any other trematode parasite whose
occurrence in the pigeon’s gut is dependent upon its having fed upon
aquatic animals or vegetation. Furthermore, pigeons as a rule spend so
little time around bodies of water that it is most certainly true that the
snails from which the cercariae emerged to infect the second intermedi-
ate host, which the pigeons ate in order to become infected, probably
were not in the first place infected by miracidia which hatched from eggs
that were dropped by pigeons. If the pigeons may be considered to be

STUDIES ON ECHINOSTOMA—BEAVER 39

more or less incidental hosts, then they might also be expected to show
some age immunity. In a few cases it was possible to determine that the
pigeons used were scarcely more than “fledglings,”’ but in most cases it
could only be noted that they were relatively old or young. Some of the
lack of uniformity may then be due to this difference in age although it
is probably a relatively minor factor, since there was a very striking
uniformity in the pigeons that were used soon after they were captured.
Taking all of these factors into account there seems to be some evi-
dence that although the prolonged captivity and unsuitability of the diet
produce more obvious reactions which tend to obscure the immunity
phenomena, the pigeon does develop a slight immunity to Echinostoma
revolutum, as indicated by the transfer and reinfection experiments.

Discussion of Related Species and Synonyms

In the newer literature there are at least eighteen species which ac-
cording to the descriptions have about 37 cephalic spines. After having
made a detailed study of the diagnostic characters in a complete series
of worms from a variety of hosts, I had expected to be able to clear up
some of the confusion regarding these species. I am doubtful, however,
whether this single attempt will lessen the number of questions regarding
synonymy, for while it does reduce several of the described species to
synonymy it also shows that many others that might have been carried
along in the literature as valid species must now be considered doubtful
until they have been reinvestigated. This in itself would not be particu-
larly noteworthy if in all cases the type specimens were available, but this
is not so in many instances.

It was my original intention to restudy the descriptions of all closely
related species and possible synonyms, but after having worked at length
on the older literature I was convinced that it is indeed impossible to de-
termine from the figures and descriptions of most of the earlier authors
whether they had studied this or some other species. Furthermore, if
I were able to reach a conclusion regarding them I would merely add
another “opinion” to the already extensive list. There is even much doubt
in my mind that the laws of priority have been correctly followed in the
naming of Echinostoma revolutum. After examining Froelich’s descrip-
tion (Froelich, 1802) and figures of his “Fasciola revoluta” (see Fig. 26),
I am very much less convinced than Dietz (1910, pp. 293-296) that
Froelich actually studied this species. At least I cannot agree with him
that he was justified in changing the name “echinatum,”’ which had
already been in use for over a century. Dietz’s argument merely indi-
cates that Froelich’s worm could possibly have been the same as F.
echinatum and does not prove that it was beyond reasonable doubt

40 ILLINOIS BIOLOGICAL MONOGRAPHS

identical. “Echinostoma revolutum” has been accepted now and used as
the correct name for this species since 1910, and irrespective of opinion
regarding priority and propriety I would not propose further change in
the nomenclature for Echinostoma revolutum. Echinostoma echinatum
(Zeder, 1803) is then listed as the first synonym of Echinostoma revo-
lutum. Other synonyms which have been generally accepted, although
they have not and cannot be demonstrated as such, are Distomum oxy-
cephalum Rud. 1819, Distomum dilatatum Miram 1840, and Distomum
armatum Molin 1850 (see Hassall, 1896). I have examined the original
descriptions of each of these and agree that they could all be identical
with E. revolutum.

Only two of the eighteen forms which have been described as having
about 37 cephalic spines can be definitely distinguished from Echinostoma
revolutum. Eight of them are questionable species and the other eight
are probably synonyms. The two species which are easily distinguished
are Echinoparyphium aconiatum Dietz 1909 and Echinoparyphium con-
tiguum Barker and Bastron 1915. The very short uterus in these forms
readily separates them from all members of the genus Echinostoma, and
the relative size and arrangement of the cephalic spines further dis-
tinguishes them. It is doubtful whether they can be separated from each
other, however. Studies were made on numerous specimens of Echino-
paryphium sp. from the muskrat which is the host for Echinop. con-
tiguum, including two specimens identified as Echinop. contiguum (ac-
cessioned in the collection of the B. A. I. of the U. S. D. A. as #30851).
All of them have many more than 37 spines, having 45 in some and 47
in others.

I believe that it is unquestionably true that the number and above
all the arrangement of the collar spines serve as the most reliable charac-
ters for diagnosis of closely allied species. Kowalewski (1895), Dietz
(1910), Tubangui (1932a, b), Rasin (1933), and many others seem to
hold the same opinion. On the other hand some have argued, notably
Looss (1899), that there is too much variability in the spines to permit
diagnosis on this basis. Looss, however, did not consider the arrange-
ment of the spines in more detail than the alternating rows and grouping
of the spines of the ventral lappets. Other characters which have been
used are the extent of the vitellaria and the location of the worm in the
host. The character of the vitellaria is too variable with age to be of
value, and the position within the host although fairly constant for a
species is altered very considerably by the number of worms present and
the length of time elapsed between the host’s death and the autopsy. The
presence or absence of cuticular spines also depends upon the latter con-
dition since dead worms frequently slough off the whole cuticula. The

STUDIES ON ECHINOSTOMA—BEAVER 41

stoutness of the body and general shape depends too largely upon the
host, age, diet of the host(?), time of autopsy, and type of fixation to
be of very great value in diagnosis. The most constant characters have
already been described in another section (p. 18). As a result of the
present study the following characters have been adopted as of diagnostic
value: number of collar spines; relative size of the various spines; their
arrangement in the (2+3)+6+(8+7) +6+ (3+2) fashion;
the length of the uterus; and the relative size of the two suckers and the
pharynx. In my opinion the host species is not to be regarded as im-
portant in this parasite.

In studying the descriptions of closely allied forms, the above charac-
teristics have been used as a basis for conclusions regarding relationship.
Other characteristics such as size of the body, eggs, and gonads have also
been noted. The eight doubtful species mentioned above are those that
have been described as having 37 spines, but the data given is insufficient
to separate them from or identify them with Echinostoma revolutum; or,
as in the case of E. sudanense, the description and the figures do not agree
and one or the other seems identical with this species. In addition to E.
sudanense Odhner, 1911, the doubtful species are: E. acuticauda Nicoll,
1914; E. callawayensis Barker and Noll, 1915; E. erraticum Lutz, 1924;
E. neglectum Lutz, 1924; E. microrchis Lutz, 1924; and E. echinoce-
phalum (Rud., 1819). These species of dubious standing and those that
are shown by this study to be identical with E. revolutum will be dis-
cussed in detail.

Echinostomum sudanense, Odhner, 1911 (?=£. revolutum).—
Echinostomum sudanense, described by Odhner (1911, pp. 116-117, pl. 3,
figs. 12, 13), is based upon a single mature specimen from the rectum of a
“Sattelstorch,” Ephippiorhynchus senegalensis, and an immature speci-
men from the intestine of Scopus umbretta in North Africa. It is 6.5 mm
long, cuticula spiny on the ventral side only, uterus long and the eggs
numerous; length of pharynx equal to the diameter of the oral sucker;
oral sucker about one-third the diameter of the acetabulum. All of these
characters agree with specimens in my own collection taken from ducks.
The collar spines are described as “31 schlanke und spitz Kragenstacheln
sind vorhanden, von denen 4 in jeder der ventralen Ecken sitzen und
die ubrigen 23 in einer doppelten, ununterbrochenen Reihe angeordnet
sind.” His figure 13, which I have copied (Fig. 27), shows 33 instead of
31 spines and the arrangement is strikingly similar to that of E. revo-
lutum. The corner spines, which Odhner described as being four, are
distinctly five on the left side of the figure, and on the right side the most
lateral of the three oral corner spines is shown over on the adjacent one.
This specimen was flattened under a cover glass and the spines somewhat

42 ILLINOIS BIOLOGICAL MONOGRAPHS

displaced, but it still resembles E. revolutum so closely that I am of the
opinion that some of the spines were lost and that E. sudanense is really
E. revolutum, There are at least two points on the figure where spines
seem to be absent (cf. Fig. 27, 9; and Text-figs. 1-5). It is possible that
it is a distinct species, but since the description is based on a single
mature flattened specimen and the corner spines are so nearly identical
with £. revolutum as are also the others in the unalternating laterals and
alternating dorsals, it should be considered a probable synonym until more
information on it is obtained.

Echinostoma acuticauda Nicoll, 1914 (?—E£. revolutum).—This
species was described by Nicoll (1914, pp. 110-111, pl. 6, fig. 4) from the
straw-necked ibis, Carphibis spinicollis. It is a 37-spined form which
from the description alone cannot be differentiated from E. revolutum.
Nicoll states that E. revolutum is “altogether a much broader and
bulkier form.” It has already been pointed out that EF. revolutum is
bulkier and stouter in ducks than in other hosts and that it is quite deli-
cate and slender in some. As these specimens were taken from the ibis
they might be expected to differ from the ones seen in the duck. The
figure of Nicoll’s species resembles very much specimens which I have
taken from the guinea pig or specimens taken from any host after they
have been dead for some time. It is probably not as similar to EF. revo-
lutum as the description indicates, but since the cephalic spines are not
described it is not clearly a distinct species.

Echinostoma callawayensis Barker and Noll, 1915 (? = E. revolutum).
—-This species was described from a collection of parasites from the
muskrat, Ondatra zibethica, from Nebraska. It is described as having
37-41 cephalic spines; 31-33 on the rim and 2-5 on each flap. This
variability in number suggests at least one of the two following condi-
tions: either the material was in such poor condition that the spines were
lost on some of them, or more than a single species was used for the
description. I have not been able to examine Barker’s material, but the
figures and description lead me to the conclusion that small E. revolutum
and Echinoparyphium sp. were both used in describing EF. callawayensis.
There has been only one record of this species since it was described
(Law and Kennedy, 1932). Unfortunately the cephalic spines are not
included in the description, and no specimens could be procured. In the
figure given by Barker the posterior end is very much flattened so that
the testes appear to be very large and the post-testicular region much
shorter than normal for E. revolutum. The whole of the body looks more
like Echinoparyphium than Echinostoma. The figure given by Law and
Kennedy (1932, fig. 10) is, on the other hand, distinctly an Echinostoma
sp. If E. callawayensis is a valid species it must at present be separated

STUDIES ON ECHINOSTOMA—BEAVER 43

from E. revolutum on very unreliable characters, particularly since the
description is made from compressed specimens. I am not able to dis-
tinguish this species from related forms. In his key to the parasites of
the muskrat, Barker (1916, p. 183) separates it from the other species
on the compactness of the uterus. Since this character depends upon the
degree of maturity and extent of contraction it is not safe to use it for
diagnosis. Law and Kennedy (1932, p. 19) do not make any statement
regarding the distinguishing characters.

Echinostoma erraticum Lutz, 1924 (? = E. revolutum) .—Lutz, (1924)
described a number of new echinostomes from South America, several of
which are described as having 37 cephalic spines, and the collar of spines
is left entirely undescribed in one of them. Four of these species are
probably synonyms of E,. revolutum. FEchinostoma erraticum is so
named because of its showing so little choice in its hosts, which is very
definitely a characteristic of E. revolutum. Lutz found that Physa rivalis,
Planorbis sp., and Spirulina sp. serve as hosts for the metacercaria, and
if these are fed to pigeons, Gallinula galeata, Chamaepelia passerina, or
Aramides cayennensis, adult worms may be recovered from each of them.
He also found natural infections in Creciscus viridis, Nycticorax viola-
ceus, and Crotophaga ani. He found specimens up to 8 mm in length,
and his figure shows no characters not found in F. revolutum. The only
statement regarding the cephalic spines is that the number varies from
35 to 39, with 37 as the usual number. In this same paper Lutz reports
researches upon EF. revolutum but does not make any statement regard-
ing the specific characters by which he recognizes each of the several
37-spined species. I cannot find any characters to distinguish it from
other species. The redia is also similar to FE. revolutwm, having a
short gut and posterior appendages. According to the description,
the 37-spined cercaria is in every respect identical with Cercaria
Echinostomi revolutt.

Echinostoma neglectum Lutz, 1924 (? = E. revolutum ).—This species
looks very much like E. revolutum in the figures, but the description does
not include any of the important diagnostic features. It is stated (Lutz,
1924, p. 87) that it can be distinguished from FE. erraticum by the shape
of the testes. As the shapes figured for both species are common in F.
revolutum it is doubtful if E. neglectwm is a distinct species.

Echinostoma nephrocystis Lutz, 1924 (? = E. revolutum) ,—Echino-
stoma nephrocystis is a form with which Lutz was able to infect tadpoles.
He fed these to Aramides cayennensis and recovered the “new species”
with 37 spines. The description is too incomplete to allow a decision as
to the specific characters for it. Lutz seems to consider the host a dis-
tinguishing character. He says that it is most similar to Dietz’s Echin-

44 ILLINOIS BIOLOGICAL MONOGRAPHS

ostoma distinctum which is a form with 35 rather than 37 spines. There
is no question about its being a doubtful species and there is a very great
probability that it is identical with E. revolutum.

Echinostoma microrchis Lutz, 1924 (?=E. revolutum).—This is

another of Lutz’s 37-spined species. The description of it is based upon
several young specimens from Gallinula galeata and one mature one from
Creciscus viridis. It is characterized as follows:
Der ausgewachsene Wurm enthaelt zahlreiche Eier. Seine Laenge betraegt nur
5 mm bei einer Breite von 1 mm. Der Stachelkranz enthaelt 37 Stacheln in der
gewoehnlichen Anordnung; vom freien Ende aus gezeehlt, ist der fuenfte der
laengate. Stachelschuppen sind zahlreich und auffallend bis auf die Hoehe des
Ovariums, nachher werden sie seltener und undeutlicher.

This description fits exactly the average 5 mm £&. revolutum from

birds, particularly those that are contracted or slightly flattened. The
statement regarding the longest spine is especially characteristic of E.
revolutum, in fact in every one of several hundreds of specimens ex-
amined the most lateral one of the aboral corner spines is the longest
(Text-figs. 1, 3, 5). He says further:
.... die neue Art unterscheidet sich leicht von allen beschriebenen, da sie selbst
in erwachsenem Zustande sehr kleine Hoden besitzt. Dagegen ist das Ovarium
bedeutend grosser und voluminoeser, als bei verschiedenen ashnlichen Arten. Es
ist kugelig und liegt mit seinem Hintertande dem mittleren Querdurchmesser auf.
Die Hoden liegen ziemlich weit zurueck, aber nahe hintereinander. Die Vitellarien
sind lang und anastomosiren briet zwischen dem zweiten Hoden und den Enden
der Blinddaerme.

Lutz’s figure of this species shows the one mature worm which he
collected, and it is clear that the specimen is somewhat flattened and com-
parisons of relative sizes of the parts are therefore uncertain. In spite of
this, however, it is clear that the specimen is indeed different from the
average E. revolutum. I have never seen a specimen whose ovary is one
and one-half times larger than the testes, but a number of the barely
mature specimens have all three of the gonads about equal in size. The
testes of Lutz’s worm are considerably larger than the pharynx, and the
uterus contains about 150 eggs. I have specimens of E. revolutum which
also have small testes and consider them as slightly more abnormal than
Lutz’s worm. The testes in one of these specimens are slightly smaller
than the pharynx and the uterus contains fifteen eggs. The ovary in this
specimen is only slightly smaller than the testes. Since Lutz found but one
mature specimen of this type and such abnormalities in the gonads are
known to occur, I believe that the similarities in his specimen and E.
revolutum are striking enough to almost, if not actually, establish their
identity. If it is shown that a form exists in which the testes are con-
sistently smaller than the ovary, then it may be distinguished from E.
revolutum on the basis of that character.

STUDIES ON ECHINOSTOMA—BEAVER 45

Echinostoma echinocephalum (Rud., 1819) (?==£. revolutum) .—
Echinostoma echinocephalum is also a 37-spined species. It was origi-
nally described by Rudolphi (1819) and redescribed from the type ma-
terial by Dietz (1910, p. 303, Pl. X, fig. 4, text fig. C). The specimens
are immature, only 2.7 to 3.3 mm in length. The width of the head crown
is 0.23-0.27 mm and body width at the level of the acetabulum is 0.47-0.60
mm. The head crown contains 37 spines described by Dietz as follows:

Davon liegen wie bei Echinost. revolutum 27 Stacheln in einer doppelten Reihe
am Rande des Kragens; dieselben sind gleichgross, 0.0544-0.0720 mm lang und
0.012-0.0144 mm briet. An den beiden Enden dieser Stachelreihen befinden sich
beiderseits in den ventralen Ecklappen noch je eine Gruppe von 5 Stacheln, von
denen je 2 paarweise itbereinander gelagert und ein finfter einzelner Stachel
median neben dem innern Stachel der vordern Reihe dieser Gruppe gelegen ist.
Diese Eckstacheln sind im Gegensatz zu Echinost. revolutum (bei denen sie die
gleiche Grdsse besitzen wie die Randstacheln) kleiner als die Randstacheln; ihre
Lange betragt 0.048-0.060 mm, ihre Dicke 0.01-0.012 mm. Eine Hautbestachelung
konnte ich bei keinem Exemplar nachweisen.

The contrast which Dietz describes in the spines of E. revolutum and
E. echinocephalum is very slight when actually compared. That the
corner spines are slightly smaller (54-72 », by 12-14 » as compared with
48-60 » by 10-12 ) than the others is really no contrast, for contrary
to Dietz’s statement it is the usual condition in FE. revolutum. Dietz’s
figure “A” (see Pl. III, fig. 18) shows a very considerable addition to the
difference given in his text. The measurements given in the text overlap
both in length and width, and they are very near the mean length for
the spines of E. revolutum at the same body size (Chart 6). If the
distribution of the spines is as inaccurately figured as the size of the
corner spines it can be assumed that no difference is shown in the cephalic
spination in the two species. The figure shows a character that would dis-
tinguish E. echinocephalum but Dietz does not mention it. He has shown
a distinct alternate arrangement in the lateral spines, a condition that
does not occur in E. revolutum. If the figure could be accepted as re-
liable there would be no reason to discuss this species further for it could
be distinguished from all of the other 37-spined forms of the genus by
the character of these lateral spines. Since, however, as was shown
above, the figure does not support the text and practically none of the
written description actually disagrees with my own observations on
specimens of FE. revolutum, and furthermore, since only seven immature
specimens were used for the description, and no one has since reported
finding this species, it is very probable that FE. echinocephalum is identi-
cal with E. revolutum. The measurements given by Dietz are added
here since they do not agree in every detail with E. revolutum: oral
sucker 90-120 p in diameter ; pharynx 100-120 » by 80-110 »; acetabulum

46 ILLINOIS BIOLOGICAL MONOGRAPHS

0.37-0.44 mm in diameter. These measurements agree with correspond-
ing ones for E. revolutum with the exception of the acetabulum, which
is slightly larger than the same organ in unflattened specimens of E.
revolutum. The figure given by Dietz (1910, Pl. X, fig. 4) appears
slightly flattened although it is not so designated. Zunker (1925) re-
examined the type material and confirmed Dietz’s observations. His only
significant remarks are that he could see no cuticular spination and that
the acetabulum is large. Although I am not convinced that E. echino-
cephalum is distinct from E. revolutum, it is possible that it differs in the
following characters: smooth cuticula, acetabulum four times larger than
oral sucker while in EF. revolutum it is only two to three times larger
than the oral sucker in immature specimens. The six lateral spines are
alternating instead of being unalternating, and the corner spines may be
somewhat smaller in relation to the other cephalic spines.

Echinostoma miyagawai Ishii, 1932 (= £E. revolutum).—This is a
37-spined form which Ishii (1932, pp. 91-100, PI. 2, figs. 10, 11; PI. 1,
fig. 1) described from the domestic fowl and wild and domestic ducks in
Japan. It is described as being 21-26 mm long by 2-3.5 mm wide. The
head crown is 0.89-1.10 mm in diameter, and the 37 spines are arranged
exactly as in £. revolutum in the figure. In the text, however, it is stated
that six spines lie on each ventral side of the crown and the other 25 are
arranged around the crown in two rows. It is clearly shown in the figure
that only five spines occur on the ventral corners, the six laterals do not
alternate, the fifteen remaining spines alternate across the dorsal side
of the head, and the median spine is aboral as it is in E. revolutum
(Figs. 22, 23). The figure also shows that the relative size of the spines
is identical with E. revolutum. They are 84-108 p» in length and 26-28
in width, which also checks with E. revolutum. The oral sucker is 0.221-
0.476 mm in diameter, the acetabulum is 0.714-1.088 mm and is 2.0-2.3
mm posterior to the oral sucker. The cuticular spines are closely set in
the anterior part of the body but more scattered posteriorly. The
diameter of the acetabulum is slightly less than the average for E. revolu-
tum but is just within the range. The relative size of the two suckers is
the same for the two forms and the diameter of the collar is also the
same. The length of the pharynx is equal to the diameter of the oral
sucker in both forms, and the internal organs of the two are identical
throughout. Ishii says that his species resembles Echinostoma cine-
torchis in body size and number of crown spines but differs from it in
the character of the testes. Ishii’s figures show the testes distinctly lobate
while his figure of FE. revolutum shows more rounded testes. It has al-
ready been pointed out that under some conditions the testes of FE.
revolutum are also lobate, more so than is shown in the figure for E.

STUDIES ON ECHINOSTOMA—BEAVER 47

miyagawai. Since there are no other characters, with the possible excep-
tion of the size of the acetabulum, by which to separate the two forms it
seems very probable that they are identical. Ishii’s E. miyagawai is
merely a description of the very large specimens of E. revolutum. It is
important to note that Ishii does not describe the individuals of his
species that are less than 21 mm in length, and I am sure that a 10 mm
specimen of “E. miyagawai” could not be distinguished from a 10 mm
specimen of E. revolutum.*

Echinostoma cinetorchis Ando and Ozaki, 1923 (= E. revolutum).—
Echinostoma cinetorchis is a 37-spined form which Ando and Ozaki
found in the intestine of wild rats in Japan (Dollfus 1925, pp. 85-91,
text figs. 1-3). It is a form that reaches a length of 21 mm and a cor-
responding width of 3.7 mm in flattened specimens. The oral sucker has
a diameter of 0.26-0.30 mm in average specimens and 0.31-0.38 mm in the
larger ones. The distance between the two suckers is 1.75-2.18 mm
(about one-sixth of the body length) in average specimens and 2.29-2.95
mm (about one-ninth of the body length) in larger specimens. The
acetabulum is 0.72-0.73 mm in diameter in average specimens and 1.01-
1.18 mm in larger ones. Cuticular spination reaches the region of the
posterior testis. The cephalic crown is 0.44-0.53 mm wide. The arrange-

*Two specimens and a communication from Ishii have been received since the
above was written. The following notes are based on a study of them. Specimens
12.8 mm and 15 mm in length. Cuticula entirely lacking on both. On the smaller
one there are thirty-seven cephalic spines arranged exactly as in E. revolutum; the
relative size is typical and the actual size is near the average for specimens taken
at delayed autopsy where they usually are shorter with points more blunt than the
normal ones. The actual and relative size of the suckers, pharynx, and collar agree
with E. revolutum. Vitellaria, uterus, ova, ovary, and cirrus also agree in general
character, size and position. The testes, however, are more deeply lobed than
any I have previously seen in this species, being constricted into four very definite
lobes. The larger specimen has been fixed under considerable pressure and appears
to have been dead in the host longer than does the smaller one. The cephalic
spination does not differ from that in E. revolutum and as far as can be determined
all other organs are identical with it. The testes are less deeply lobed than those
in the smaller specimen but more so than is usually seen in E. revolutum. I have,
however, several specimens in my collection with more deeply lobed testes, and I
do not separate them from “sister” individuals on the basis of this character. In
view of the fact that the cuticula is lacking on both specimens and the cephalic
spines are rather blunt it seems evident that post-mortem changes must be taken
into account here. The tissue’s reaction to the stains support this view.

Through a personal communication Ishii has pointed out that he believes that
E. miyagawai has a very long neck, longer esophagus, greater head crown, and
longer crown spines than F. revolutum.

It is possible that a study of specimens that were fixed while still active would
alter my conclusion, which is at present that the two are identical.

48 ILLINOIS BIOLOGICAL MONOGRAPHS

ment of the cephalic spines is the same as in E. revolutum. In average
specimens the dorsal spines are 55-59 w long by 11-13 » wide. Those
of the end groups are slightly smaller, 36-38 » by 10-11 y. The figure
(see Fig. 15) of the crown shows that the relative size of the various
spines is the same as for EF. revolutum. The internal organs are ap-
parently identical also. The egg size is 96-100 » by 61-70 p, which is
about the same as for the largest specimens of E. revolutum. The
testes are smooth or slightly lobed and are somewhat variable in po-
sition, the anterior testis being in some cases on the level with the ovary
or even anterior to it. I have not observed any such extreme anomolies
in my specimens of E. revolutum. Ando and Ozaki do not compare this
form with E. revolutum or any of the other very numerous 37-spined
species of the genus. Very extensive tabular comparisons of the de-
scriptions and comparisons of every detail indicated in the figures fail to
show a single difference in E. cinetorchis and E. revolutum. It is in-
teresting and important to observe that both Ishii (1932) and Kurisu
(1932) reported finding both species in the same region. The only as-
sumption necessary to account for this, however, is that they have been
misled by the very pronounced changes in body proportions that always
occur in FE. revolutum as its length increases over 12 mm.

Echinostoma armigerum Barker and Irvine, 1915 ( = E. revolutum).
—This is one of the four species of muskrat echinostomes described by
Barker et al as having about 37 cephalic spines. Two of these species,
Echinoparyphium contiguum and Echinost. callawayensis, have already
been discussed. Echinostoma armigerum has been reported recently from
the muskrat in Canada, and a brief description of it given by Law and
Kennedy (1932, p. 24, fig. 15). Although both authors report it as
common I have not been fortunate enough to obtain specimens for com-
parison with specimens in my own collection which seem to be identical
with E. armigerum and are at the same time identical with E. revolutum.
This form according to the original description (Barker, 1915, p. 189,
text-fig. A) is 9.4 to 12.4 mm long by 1.2 to 1.8 mm wide. Cephalic spines
37 in number, 27 on the rim, and 5 on each ventral point of the collar.
Collar spines 61 to 94 » in length, and the ventral corner ones are the
smaller. The anterior third of the body spiny. Uterine coils fairly com-
pact in transverse coils. Eggs 84 to 105 » by 57 to 66 ». All other parts
of the description would apply to almost any species of the genus. The
figure (Barker’s text-fig. A) so closely resembles a large number of the
specimens in my own collection that I am convinced that they are identi-
cal and that Barker’s E. armigerum is E. revolutum after it has reached a
length of 9.4 to 12.4 mm. Comparison of the measurements for E.

STUDIES ON ECHINOSTOMA—BEAVER 49

revolutum and all points of description fail to show any difference in the
two forms. E. armigerum is doubtless a synonym for £. revolutum.
Echinostoma coalitum Barker and C. A. Beaver, 1915 (= E. revo-
lutum).—The fourth species of muskrat echinostome described by Barker
is E. coalitum. It is also identical with E. revolutum and the same as E.
armigerum but described from only the older and larger individuals. It
is difficult to take muskrats alive and in most cases autopsies are made
several hours post-mortem. The large specimens of E. revolutum die
much sooner than the smaller ones and consequently most of the largest
specimens in my collection were taken after the worms had died. I have,
however, several specimens over 20 mm in length with firm bodies and
good spination. The original description of E. coalitum was based upon
“22 specimens of an unusually large trematode .... found among
several hundred specimens of different species of trematodes in the in-
testine of 46 muskrats.” The body is described as “very flabby,” which
suggests that the specimens were dead when collected. They are 22 to
30 mm long by 1.5 to 2.3 mm wide at the level of the ovary. The an-
terior part of the body is covered with minute spines. The collar bears
“35 spines arranged in a single or slightly alternate rows, 25 large spines
on the rim and 5 smaller spines on each lappet.” Oral sucker 0.37 to 0.46
mm in diameter. Acetabulum at the level of the second anterior sixth of
the body, 1.12 to 1.32 mm in diameter. Uterus with dense transverse
coils. Eggs numerous, 104 to 108 » by 67 to 70 ». When this form 1s
compared with E. revolutum there is but one significant difference in the
two. That is in the number of spines in the collar, there being only 35
instead of 37. There are, however, five on each corner lappet, and since
most of the specimens studied were in all probability dead before fixation,
there is a very strong probability that the 22 specimens studied did not
show typical spination. Through the kindness of E. W. Price of the
B. A. I. of the U.S. D.A., I have been able to study a slide (#30850)
containing three specimens which were accessioned in the Washington
collection under the name of E. coalitum. These specimens are 16 to 20
mm in length and identical with specimens which I have collected from
the muskrat and have identified as E. revolutum. Although none of the
three specimens on slide #30850 have a complete set of cephalic spines
and all have lost the cuticular spination, it is evident from the pattern
of the spines still present that they are the 37-spined E. revolutum. Law
and Kennedy (1932, p. 16, fig. 9) report E. coalitum from the muskrat
in Ontario, Canada. The description and figure given by them are
about the same as Barker’s. Leidy (1888, p. 126) also reported on an
Echinostoma sp. from the muskrat. He had two collections, and in the

50 ILLINOIS BIOLOGICAL MONOGRAPHS

first one he says “there are 25 worms, and in their present condition they
are pale brown bordered by dark brown, and measure from 12 to 18 mm
long by 1 to 1.5 mm broad. If not identical, they are closely allied to
Distomum echinatum, which in the mature state lives in ducks and other
water birds and in the larval state in fresh-water snails. The muskrat
eats the latter so that it may likewise become infested in the same manner
as the ducks and this would also seem to make it probable that the para-
site is the same.’ Leidy characterizes them as follows: 36 straight
spines on the collar. Acetabulum much larger than the head, “situated at
the base of the neck.” The oral sucker is small and the pharynx oval.
Body nearly the same width throughout. Testes almost midway between
acetabulum and posterior end. Head 0.5 to 0.6 mm broad, spines about
100 by 20 », oral sucker 0.25 mm in diameter, pharynx 0.30 by 0.225 mm,
and acetabulum 0.875 to 1.25 mm. Ova 100 by 72 p». Regarding the
second collection Leidy states: ‘Since the above communication a col-
lection of worms, from the small intestine of a muskrat, has been re-
ceived. Eighteen of the worms pertain to the supposed Distomum
echinatum, and range from 18 to 25 mm long. In all, the fore part of the
body a short distance behind the acetabulum is finely echinate, while
the rest is smooth.” Leidy did not report any observations on the
cephalic spination of the second collection, but it is very probable that
37 instead of 36 spines could have been counted on these since they were,
judging from the fact that the cuticular spination was intact, in a much
better state of preservation than the first lot. Assuming that the spines
on the first lot were atypical, the worms reported by Leidy can be con-
sidered correctly diagnosed by him as Distomum echinatum ( = Echino-
stoma revolutum). It is perhaps important to note too that Distomum
echinatum was at the time Leidy made this report sometimes character-
ized as having 36 rather than 37 cephalic spines.*

Echinostoma mendax Dietz, 1909 ( = E. revolutum).—Echinostoma
mendax is a 37-spined form that is so similar to E. revolutum that it has
already been considered a doubtful species (Lutz, 1924, p. 81). Sprehn
(1932, p. 306) lists it as a synonym of E. revolutum but does not indicate
whether he has himself re-examined the types or not. It is obvious from
the original description that it cannot be distinguished from E. revolutum.
The only differences noted by Dietz himself are expressed in the follow-
ing statements:

*Krull (1935) has recently made a brief report on a form which he has called
E. coalitum. Since the morphology of the worm is not discussed, no confirmation
of the above conclusion is given, although certain host records have been confirmed
and certain others added (Tables 1, 2, and 3).

STUDIES ON ECHINOSTOMA—BEAVER 51

In der vordern Korperpartie ist die Cuticula sowohl auf der Dorsal—wie auf der
Ventralseite mit feinen Hautstacheln besetzt, die sich jedoch im Gegensatz zu
Echinost. revolutum auch in den Seitenrandern nicht tiber den Bauchsaugnapf
nach hinten verfolgen lassen.... Der Bauchsaugnapf ist in Verhaltnis zu
Echinost. revolutum nur schwach entwickelt, kugelig (0.60-0.64 mm) oder ein
wenig nach hinten verlangert (0.65-0.72 : 0.60-0.62 mm).

It has been shown that the cuticular spination varies with both the age
of the worm and the type of host, and differences in it are unreliable for
diagnosis (Chart 8). That there is a difference in the development of
the acetabulum in the two forms is doubtful, for the measurements given
by Dietz fall very near the average for E. revolutum. The figures given
by Dietz (1910, text fig. A, Pl. 10, fig. 2) are identical in all the im-
portant diagnostic features with E. revolutum. In fact text figure A
(see Pl. III, Fig. 16) shows very distinctly both the typical arrangement
of the spines and the typical order in the relative lengths of the various
spines. Echinostoma mendax Dietz 1909 is without question identical
with Echinostoma revolutum.

Echinostoma paraulum Dietz, 1909 ( = E. revolutum), and Echino-
stoma columbae Zunker, 1925 (= E. revolutum).—Echinostoma par-
aulum was desecribed by Dietz (1909, p. 300, Pl. 10, fig. 3, text-fig. B)
from Colymbus cristatus and several species of ducks from middle
Europe. Several authors (Baylis, 1929, p. 40; Iwata and Tamura, 1933,
p. 2) have expressed strong doubts as to its legitimacy, while others
(Skrjabin, 1915, p. 399; Sprehn, 1927, p. 454, 1930, p. 767, 1932, p. 314;
Wetzel, 1933, p. 772) report its occurrence and consider it a valid species.
Sprehn (1927, 1930, 1932) considers E. columbae Zunker 1925 a synonym
of E. paraulum, and in 1930 he put it into the genus Echinoparyphium, al-
though I am doubtful if this can be justified. The situation is made still
more complex by the fact that E. columbae Zunker is variously described
by Zunker (1925), Bolle (1925), Krause (1925a, b), Otte (1926), and
Sprehn (1927, 1930, 1932). According to Dietz’s original description
FE. paraulum is a form that ranges in length from 4 to 7 mm. Its other
measurements are: greatest width 0.94 to 1.66 mm, width of head crown
0.43 to 0.54 mm, diameter of oral sucker and acetabulum, respectively
0.21 to 0.26 mm and 0.54 to 0.83 mm, pharynx 0.21 to 0.22 mm by 0.14
to 0.20 mm. The body is spiny as far posterior as the acetabulum on the
dorsal side and to the testes on the ventral side. The 37 spines of the
cephalic collar are arranged exactly as in E. revolutum and the relative
size of the various spines is also identical with E. revolutum (Fig. 17).
His figure of the entire worm is in all respects identical with a slightly
contracted 6-7 mm specimen of F. revolutum. The middle constriction
in the testes occurs not uncommonly in this species, particularly if the

52 ILLINOIS BIOLOGICAL MONOGRAPHS

specimen is either under pressure or fixed in the contracted condition.
There is positively not a single character by which FE. paraulum can be
separated from E. revolutum.

Echinostoma columbae has been restudied by Sprehn and shown to
be a synonym of E. paraulum, which probably is sufficient evidence that
both E. paraulum and E. columbae are identical with E. revolutum.
Since, however, the several descriptions of E. columbae differ, and
especially since Sprehn (1930) has put this form into the genus Echino-
paryphium a more complete study of the descriptions is necessary.

Krause (1925a) made a preliminary report on a number of pigeons
infected with echinostomes of two species, a 37-spined form and one
with forty-two spines. Then Zunker (1925) published a description of
a 37-spined echinostome from the pigeon, which he considered closely
related to E. echinocephalum but distinct from it. He called it Echino-
stoma columbae spec. nov. Then Krause (1925b) followed Zunker
with a second report on his material. He described his specimens in
good detail and considered it similar to E. revolutum, which it is
indeed. Krause’s description leaves no doubt in my mind that both
his and Zunker’s worms are E. revolutum. Zunker could find no cuticular
spines on his worms, but Sprehn (1927) re-examined Zunker’s worms
and found them identical with a collection which he himself described
as having a distinct cuticular spination over nearly all of the ventral
side and the dorsal side of the anterior end. Bolle (1925) also corrected
Zunker’s observation regarding the cuticular spination. It was Bolle
who first compared the pigeon echinostomes with E. paraulum, but he
decided against their identity on the basis of differences in size of the
crown spines and the position of the cirrus sac. Bolle described the
dorsal spines of the head crown as being larger in the aboral row than in
the oral. This feature prompted him to compare it with members of
the genus Echinoparyphium. He could distinguish it from all members
of that genus and decided that it was indeed a distinct species which
should be designated as Echinostoma columbae. There is very little dis-
agreement among the various authors that cannot be readily explained
on the basis of differences in degree of maturity in the specimens
studied by them. Zunker and Bolle both used smaller specimens while
Krause and Sprehn had about average specimens. Sprehn emphasized
the size difference in the spines of the two dorsal rows and observed
(1927, p. 452) that “eine deutliche pars prostatica lasst sich in Schnitten
nachweisen.” He compared his specimens with the types for E. paraulum
and found that they were identical. On the basis of these studies he
declared all of the pigeon echinostomes with 37 cephalic spines to be

STUDIES ON ECHINOSTOMA—BEAVER 33

E. paraulum (= E. columbae). Krause, however, argued that these
worms were most similar to E. revolutum. In spite of the fact that he
had in a former communication declared that a pars prostatica was dis-
tinctly present in the worms studied by him, Sprehn (1930) offered the
following reason for transferring them to the genus Echinoparyphium:
.... bei ihm die Pars prostatica fehlt, die Hautbewaffnung die ganze Bauch-
seite iiberzieht und sich auch noch auf die Riickenseite ausdehnt und ausserdem
ein doppelter Stachelkranz vorhander ist. Bei den Arten der Gattung Echinostoma
s. str. ist die Bestachelung dagegen nur auf die Bauchflache des Vorderkorpers
beschrankt und ausserdem eine Pars prostatica vorhanden.

That the two genera Echinostoma and Echinoparyphium cannot be
separated on the basis of the cuticular spines is evident since all of the
most recent researches on EF. revolutum have shown that at least some
dorsal cuticular spination is present. It is furthermore evident that
Sprehn is in error in considering the crown spines of the pigeon echino-
stomes as more typical of the genus Echinoparyphium, for all of the
figures given by himself (1927, fig. 1), Zunker (1925, fig. 2), and Bolle
(1925, fig. 1) picture the head crown as being typical of Echinostoma,
not Echinoparyphium (Figs. 19, 20, 21). They show a very slight size
difference in the two rows, a condition characteristic of E. revolutum
(Text-figs. 1, 2, 4, p. 24). The figures of both Bolle and Sprehn are
drawn in a manner that emphasizes this difference, since the oral row is
more vertical than the aboral, and spines thus seen in end view appear
to be shorter. Were it not for the question of the pars prostatica, all of
the pigeon echinostomes described by the above authors could be readily
put into the genus Echinostoma s. str. and considered as unquestionable
synonyms of E. revolutum. In 1927 Sprehn declared that in Echinostoma
paraulum ( = E. columbae) the pars prostatica is distinctly seen in sec-
tions. Three years later he contradicted his earlier statement and stated
that “die Pars prostatica fehlt.’”” The only figure of an entire specimen of
one of these disputed forms is given by Zunker (1925, fig. 1). The
length of the uterus alone prohibits putting it into the genus Echinopary-
phium (Fig. 24). If this form can be distinguished from FE. revolutum
at all it is on the basis of Sprehn’s later statement that the pars prostatica
is absent.

Van Heelsbergen (1927) and Picard (1930) have also reported finding
echinostomes in pigeons, but neither has made a final identification of his
material. The figures and data given by them suggest that each found
both E. revolutum and Echinop. recurvatum.

MIsDETERMINATIONS.—In addition to the large number of doubtful
species and synonyms there are a few obvious misdeterminations that
should be mentioned. Looss (1899, p. 681) has already called attention

54+ ILLINOIS BIOLOGICAL MONOGRAPHS

to the misdetermination by Wedl (1857, pp. 245-246, Pl. 1, figs. 5-6).
Wedl’s form which was taken from Phalocrocorax carbo is not even
closely related to Echinostoma revolutum. A form which Ercolani (1881,
1882) determined as E. echinatum obviously does not belong to the
genus Echinostoma s. str. His figures (1881, Pl. 1, figs. 50-58, Pl. 2,
figs. 1-5; 1882, Pl. 3, figs. 19-21) were copied by Railliet (1895, fig. 244)
and designated as D. hérissé (D. echinatum Zeder). Neumann (Neu-
mann-Macqueen, 1905, fig. 237) also copied these figures and put them
under the name Echinostomum echinatum.

Johnson (1920, p. 368) has doubted Looss’ determination of a form
which he found in Machetes pugnax (1899, pp. 683-684, PI. 24, figs.
6, 7). Looss described it as a variation of Echinostoma revolutum.
Several of the crown spines had been lost but the exact point where some
of them had been could be located, so that a total of 34 spines was ac-
counted for. Since this form did not differ in other respects from the
FE. revolutum of other hosts Looss did not make a new species of it.
Johnson was of the opinion that the host in this case was so different
from the “normal” that it might be expected to be a new species of worm.
He argued also that the spination in the two forms (those from ducks
and those from M. pugnasx) is very different, a point on which I cannot
agree with him. The fact that only 34 spines are shown does not mean
that the form is a 34-spined species. Looss made it clear in the text
that the spines were not all present and that only 29 were actually ob-
served. The difference in the size range in the eggs was also a point in
Johnson’s argument, but this is not, in my opinion, significant, since the
measurements given by Looss (101 to 110 p» by 59 to 63 yp) are easily
within the range for E. revolutum. Taking all of these facts into con-
sideration there can be little doubt that Looss has correctly identified his
material and that Echinostoma limicoli, the name which Johnson sug-
gested for Looss’ worm, is a synonym of E. revolutum (cf. Figs. 28, 29).

Looss’ figure of the metacercaria of E. echinatum (1894, PI. 9, fig.
192) is, on the other hand, a misdetermination. Sewell (1922, p. 122)
has suggested that Looss’ figure (1894, fig. 191) of the cercaria is also a
misdetermination because of the difference in the excretory system of it
and the young adult. Judging solely on the basis of the cephalic spination
there can be no doubt that the figure of the metacercaria is not that of
E. revolutum. It is instead very similar to Echinoparyphium aconiatum
Dietz, a form which also has 37 spines. The corner spines in Looss’
figures are four in number, all nearly equal and very much larger than
the other crown spines. These characters are present in Echinop. aconia-
tum but not in Echinost. revolutum.

STUDIES ON ECHINOSTOMA—BEAVER 55

SumMary OF Forms Discussep.—The present status of the forms
discussed and the conclusions the present study has led to may be sum-
marized as follows: Echinostoma revolutum can be distinguished from
all other described forms by the following characters: (1) 37 cephalic
spines arranged in the manner indicated by (3-++2) +6-+ (7+8) +
6+ (3+ 2), which means that there are 5 on each ventral lappet, 3 of
which are on the surface or oral in position and 2 deeper in the flesh
or aboral, 6 unalternating laterals, 15 dorsals arranged in alternating
fashion with 8 orals and 7 aborals. The median spine is in the aboral
row which is continuous with the row containing the six lateral spines.
(2) The ventral side of the body is spiny as far back as the anterior
testis or farther, and the dorsal side bears spines in most specimens but
may be without them in older worms from bird hosts. (3) The uterus
is long, containing eight or more coils even in the smallest mature worms.
(4) The proportions of the body change with age as indicated in
Charts 1-7.

Echinoparyphium aconiatum and Echinoparyphium contiguum are
distinguished from Echinostoma revolutum by the very short uterus and
the different arrangement of the cephalic spines, Echinop. acomatum
having an arrangement that is different in all parts of the crown. Echino-
paryphium contiguum must be redescribed before it can be definitely
separated from Echinop. aconiatum. None of the other species discussed
can be positively separated from Echinostoma revolutum. It may seem
almost incredible that all sixteen of the species discussed here must
be either reduced to synonymy or considered as doubtful species. It may
also seem that too much emphasis has been placed on the similarity of
the cephalic spination, and too little attention given to other structures.
In most cases the character of the cephalic spination has borne more
weight in my decisions than any other one factor. It must be conceded,
however, that it is highly improbable that any two species could be
identical in number, arrangement, and relative size of these 37 structures
and at the same time be sufficiently dissimilar in other respects to be
recognized as separate species. Echinostoma miyagawat, cinetorchis,
armigerum, mendax, paraulum, and columbae are all unquestionably
identical in this respect, and more than sufficient evidence is at hand to
prove beyond reasonable doubt that the other two species which have
been declared synonyms are indeed identical. Insufficient information
regarding variations due to the age and the host as well as the question
of host specificity account in part at least for the rather long list of
synonyms. The procedure recommended by Kowalewski (1897) for
designating synonyms is followed in the summary below:

56 ILLINOIS BIOLOGICAL MONOGRAPHS

Echinostoma revolutum (Froelich, 1802)
Syn. dem.

(Dietz, 1910) Distomum echinatum Zeder, 1803

(P. Beaver, present paper) Echinostoma miyagawai Ishii, 1932

(Idem) Echinostoma cinetorchis Ando and Ozaki, 1923

(Idem) Echinostoma armigerum Barker and Irvine, 1915

(Idem) Echinostoma coalitum Barker and C. A. Beaver, 1915

(Lutz, 1924; Sprehn, 1932; P. Beaver, present paper) Echinostoma mendax
Dietz, 1909.

(Baylis, 1929; Iwata and Tamura, 1933; P. Beaver, present paper) Echinostoma
paraulum Dietz, 1909.

(Krause, 1925a, b; P. Beaver, present paper) Echinostoma columbae Zunker,
1925.

(P. Beaver, present paper) Echinostoma limicoli Johnson, 1920.

Syn. ing.

Echinostoma sudanense Odhner, 1911

Echinostoma acuticauda Nicoll, 1914

Echinostoma callawayensis Barker and Noll, 1915

Echinostoma erraticum Lutz, 1924

Echinostoma neglectum Lutz, 1924

Echinostoma nephrocystis Lutz, 1924

Echinostoma microrchis Lutz, 1924

Echinostoma echinocephalum (Rud., 1819)

Echinostoma oxycephalum (Rud., 1819)

Echinostoma dilatatum (Miram, 1840)

Echinostoma armatum (Molin, 1850)

PROTOCOL OF EXPERIMENTS

ON THE DETERMINATION OF METHODS, PURITY OF
STOCKS, AND Hosts

Preliminary experiments had shown that by feeding the cysts of the
37-spined echinostome cercariae to various birds and mammals, 37-spined
adults could be recovered from them. This was not always true, however,
as sometimes a negative was obtained even though it was definitely
known that an abundance of cysts had been fed. This was particularly
true with rats; and in one case a negative was obtained from a pigeon
although it is probable that the snail fed did not contain cysts. With
these experiences unexplained and Tubangui’s (1932b) somewhat similar
experience with pigeons and rats in mind it seemed possible that more
than a single species or at least two varieties of the same species were
being handled. Careful examination of the cercariae from each of the
infected snails collected in various localities failed to disclose, however,
what could be considered more than one species with 37 spines. Since
several echinostome species have been described as having 37 cephalic
spines, it was thought imperative to check the purity of the material
employed.

STUDIES ON ECHINOSTOMA—BEAVER 57

The experiments to check on the above question are as follows: in-
fected snails (H. trivolvis) were collected from three different localities
(Table 8, p. 77), which represent three different streams and two entirely
separate drainage systems, although only about thirty miles separate the
headwaters of one from the other at the nearest point. The snails were
wiped dry as they were collected in the field so that no cercariae could
emerge and become mixed. Then as soon as they were brought into the
laboratory each of them was cleaned, marked with india ink, and
registered before they were isolated in various clear glass containers,
usually eight-dram vials. Special care was employed to guarantee that
no cercariae escaping from one snail might be allowed to mix with those
of another. At no time during the experiments were any two infected
snails in the same container. As soon as cercariae emerged they were
examined to check on the various morphological characters used in diag-
nosis of species, especially the number, distribution, and relative size of
the cephalic spines; body spination; character of the tail fin; number of
cephalic ducts; and the main ducts of the excretory system. Size was
also checked. In every case the characters exhibited were apparently
identical. After the cercariae were checked the snail was given an ad-
ditional number and again registered, so that complete records were kept
on each infected snail. Various secondary intermediate hosts of labora-
tory origin were employed: Physa gyrina, Helisoma trivolvis, and tad-
poles. Usually Physa were used. No careful check was kept on the
number of cysts fed as this was thought to consume too much time to
be worth while in this particular series of experiments. The following is
a brief outline of the separate feedings and results. The experiments
carry the same designation as the registered number of the snails which
produced the cercariae, in addition to “1, 2, 3,” etc. A single snail pro-
duced all of the cercariae used in each experiment. For example, in
experiment 1, snail C3-A was used; in experiment 2, C4-28; etc.

EXPERIMENT 1(C3-A)

On 7/28/33 Pigeon 7 was fed two small Physa carrying many C3-A cysts, 1 day
to 2 weeks old. Ten days later this pigeon developed a severe bloody diarrhea
which continued into the next day. No ova were present yet in the stools when it
was killed and examined on 8/8. The examination was made immediately, and
621 worms were recovered, none of which were really mature although about 30%
of them had 5-20 ova in the lower uterus. These worms were scattered along the
gut from anus to proventriculus. There were 44 worms in the gizzard but over half
of these were dead. Most of the worms were in the lower duodenum and upper
ileum. It is also of interest to note that two active worms were taken from above
the gall bladder in the liver and nine were in the oviduct (upper). Death appeared
to be imminent at the time the host was killed.

58 ILLINOIS BIOLOGICAL MONOGRAPHS

On 8/13/33 a half-grown albino rabbit (Rabbit 2) was fed three small Physa
carrying many C3-A cysts, 1-14 days old. This animal died on 8/17. The autopsy
was made 6-8 hours post-mortem and 284 specimens were recovered from about
the middle of the ileum. Whether the worms were responsible for the death of
this host is uncertain. It developed a rather severe diarrhea 36 hours before death,
which may have been due to a change from a dry to a green diet. As all the other
rabbits procured at the same time were fed infective cysts and as they too died,
there was no control animal.

EXPERIMENT 2(C4-28)

Pigeon 10 was fed one small Physa with cysts on 8/13/33. Ova appeared in the
feces on 8/22 and were more numerous each day until 8/26 when it was killed and
18 mature worms were taken from the middle ileum.

Rabbit 4, a half-grown albino, was fed 2 Physa with numerous cysts on
8/13/33. It died on 8/20 and was autopsied 3-4 hours post-mortem. One hundred
twenty-two immature worms were taken from the ileum, for the most part from
the second and third twelve inches above the cecum. It is uncertain as to whether
or not the worms caused the host’s death.

EXPERIMENT 3((C4-16)

Rabbit 5 was fed 2 Physa, each with about 100 cysts, on 8/31/33. Ova ap-
peared in the feces on 9/12 and became more numerous daily until 9/17 when the
host was killed and 28 mature worms taken from the lower and middle ileum.

Rabbit 6 was supposedly fed 1 Physa on 8/31. It fought violently, however,
and it was thought doubtful at the time that any part of the snail was actually
swallowed. It was not surprising then that its feces were negative, and no worms
were found when it was killed on 9/18.

Pigeon 11 was fed 2 small Physa on 8/31/33. Ova appeared in the feces on
9/12 but were not numerous. They were easily found, however, by direct exami-
nation for five days, but none were found on the sixth. The pigeon was then
killed and no worms were found.

EXPERIMENT 4(C5-A)

Pigeon 9, Rabbit 3, and Dog 1 were used in this experiment.

Pigeon 9 was fed 2 Physa with many C5-A cysts one to seven days old on
8/13/33. A few ova appeared in the feces on 8/22, were fairly numerous the next
day, and very numerous on 8/24 when the pigeon was killed and 580 worms re-
covered. Some of those from the upper ileum were immature.

Rabbit 3 was fed C5-A cysts in one medium-sized Physa on 8/13/33. This
rabbit died on 8/21/33 before the worms matured. The autopsy was made 12-14
hours post-mortem and 540 worms were recovered from the ileum, most of them
about half-way between the duodenum and cecum. Many of those near the upper
and lower ends were dead.

Dog 1 was fed C5-A cysts in 3 small Physa on 8/31/33. It was killed on
9/18 and 7 slightly immature worms were taken from the cecum and just above it in
the lower ileum.

EXPERIMENT 5(C6-2)

Chicken 5, Dog 3, Cat 5, and Rats 30 and 31 were given cysts of C6-2.
Chicken 5 was fed a small Helisoma containing relatively few cysts on

STUDIES ON ECHINOSTOMA—BEAVER 59

9/19/33. On 10/1 the feces became positive for ova and on the next day the ova
were abundant. The host was killed on 10/2 and 46 worms were taken from the
middle ileum.

Dog 3, a setter bitch pup, was given 3 small Physa each harboring about 25
cysts and a tadpole with an unknown number of cysts on 9/15/33. This dog was
anesthetized on 9/26 and devocalized, a procedure which caused an illness of about
one week. Afterwards, however, it maintained good health and was found by
fecal examination on 10/8 to be infected. It was then killed and 64 mature worms
recovered from the second and third twelve inches of the ileum above the cecum.

Cat 5 was fed about 200 cysts in 6 very small Physa on 9/24/33. This cat was
only about one-fourth grown and in rather poor health when given the cysts.
It ate a normal meal of bread and milk at the time the cysts were given but re-
fused to eat afterwards. It was passing a little blood in frequent stools the next
day and soon developed a severe bloody diarrhea and died just 48 hours after it
had eaten the cysts. Autopsy was delayed 12-14 hours, and was not thoroughly
done. Only three specimens were discovered and these were badly disintegrated.

Rats 30 and 31 were fed 7 crushed Physa containing many metacercariae on
9/27/33. No ova were discovered in the feces, and when they were killed on 10/18
no worms were found.

EXPERIMENT 6(C6-3)

Chicken 6, Cat 2, and Pigeon 19 were fed the metacercariae of C6-3.

Chicken 6 was given 4 small Physa, each with a few cysts, on 9/19/33. Ova
were found in the feces on 10/1 but were never numerous. Only two specimens
were present when the host was examined on 10/5 and these were both in the
cloaca.

Cat 2 was fed numerous metacercariae in a tadpole and one Helisoma. It
became ill soon afterwards and on 10/2 looked as though it soon would die. The
next day it was found in a state of coma. It was then killed and 39 immature
worms taken from the lower ileum, 13 of which were dead. As the autopsy was
made immediately it is certain that the worms were dead even before the host was
killed.

Pigeon 19 was fed metacercariae on 9/27/33 in 4 small Physa. Ova appeared
in the feces on 10/9 and nine days later the animal was killed. There were 93
worms in the middle ileum. This pigeon was also heavily parasitized with an
internal mite.

EXPERIMENT 7((C6-5)

Rabbit 8, Pigeon 16, and Mice 14, 15, 16, and 17 were fed metacercariae of
C6-5. They developed in the rabbit and pigeon but the mice were negative.

Rabbit 8 was fed metacercariae in a tadpole (R. pipiens) and 2 small Physa
on 9/15/33. Ova were found in the feces on 9/27 and increased daily until the
animal was killed (10/2). There were five mature worms in the middle ileum.

The four mice were fed five small Physa with metacercariae on 9/14/33. They
were all negative when examined on 9/29.

Pigeon 16 was fed metacercariae in four small Physa on 9/28/33. The cysts
were 1-7 days old. Ova did not appear until 10/12, several days later than was ex-
pected. It was killed on 10/13 and found heavily parasitized. There were 291 of
the worms and about 1000 internal mites in addition. This may account for the
delayed appearance of the ova. The 291 worms were scattered from lower ileum
to duodenum, but most of them were in the middle section.

60 ILLINOIS BIOLOGICAL MONOGRAPHS

EXPERIMENT 8((C6-6)

Chicken 7, Guinea pig 1, and Rats 25 and 26 were fed metacercariae of C6-6.
The chicken, guinea pig, and Rat 26 were positive but no worms were found in
Rat 25.

Chicken 7 was fed metacercariae in 2 Physa on 9/19/33. It was killed on
9/30 in order to get some immature worms for another experiment. Only one
worm was present, however. It was located in the lower ileum about ten inches
above the ceca.

Guinea pig 1 was given a medium-sized Helisoma on 9/20/33 which had been
in a finger bowl with the snail for about one week. It ate well and maintained
good health until 9/30 when it became restless and refused food. The next morn-
ing it was dead. Autopsy was made about six hours post-mortem and the immedi-
ate cause of its death was found to be a large perforated duodenal ulcer. As there
were 354 worms recovered from this host and nearly half of them were almost
mature it seems very probable that they were in part at least responsible for the
host’s death. They were rather unevenly distributed between the middle colon
and the stomach.

Rat 25 had been fed metacercariae from another snail (C6-10) on 9/15/33 but
as it was never positive by fecal examination it was not killed. Then on 10/15 it
was given a medium sized Physa carrying about 100 C6-6 metacercariae. The
stools were never positive but as the feces were always solid it was thought that
worms were possibly present even though no ova could be found. No worms were
found, however, when it was killed on 11/4.

Rat 26 had been fed C6-11 metacercariae on 9/15/33 and although they must
have been present no ova had been found in the feces up to 10/12. The pellets
were always dry enough to collapse the ova and thus render the examination very
difficult. A soft pellet was examined on 10/24, only twelve days after it had been
fed C6-6 metacercariae and ova were easily found. This rat had been fed 26 or
more metacercariae teased out of the kidneys of a tadpole (FR. pipiens). These
cysts were administered by mixing them into a bit of cornmeal and water. On
10/24 there were 33 worms in the middle ileum, three of which were much larger
than the others and had the uterus well distended with ova. These were doubtless
Co-11, which were fed on 9/15, and the other 30 were the C6-6. As was noted
above, 26 metacercariae were counted in the kidney tissue, but several others could
have been present but obscured from view.

EXPERIMENT 9(C6-7)

Rabbit 7, Chicken 3, and Pigeon 17 were used in this experiment. Worms
developed in all three.

Rabbit 7 was fed 4 small Physa on 9/15 which carried metacercariae less than
four days old. It was found positive by fecal examination on 9/27 and was killed
six days later. There were 29 worms recovered, mostly from the middle ileum.

Chicken 3 was fed metacercariae in 3 small Physa on 9/19. A few ova were
found in the feces on 10/1, and they were somewhat more numerous the next
day when the animal was killed. Autopsy was made three hours post-mortem and
22 worms recovered. Most of them were in the middle ileum.

Pigeon 17 was given metacercariae in 7 small Physa on 9/28/33. A few ova
were found on 10/9 and 10/11. It was killed on 10/11 and only two specimens
were present, one of them not quite mature. They were in the middle ileum.

STUDIES ON ECHINOSTOMA—BEAVER 61

EXPERIMENT 10(C6-8)

Duck 3, Cat 4, and Pigeon 18 were fed metacercariae from C6-8. The cat
and pigeon were positive; the duck was negative.

Duck 3 was fed 3 Physa carrying very many metacercariae on 9/15. No fecal
examinations were made and when it was killed on 9/23 no worms were present.
Although two or more explanations may be made for this the most probable is
that the host was allowed to go without food for about a week. This occurred
by accident, not as a part of the experiment.

Cat 4 was fed a Helisoma and 7 small Physa, each carrying a few metacer-
cariae, on 9/23/33. Ova appeared in the feces on 10/13/33 and were found in
abundance the following day. On 10/14 the host was killed and 352 worms taken
from the caudal three feet of the ileum; 297 of these were concentrated into the
second foot above the cecum.

Pigeon 18 was fed metacercariae on 9/28/33 in 2 small Physa. The feces
becarne positive for ova on 10/9 and three days later the host was killed. The
autopsy was delayed three hours. There were 80 worms entangled in the feathers
around the anus, 74 in the cloaca and rectum, and 41 in the caudal four inches of
the ileum.

EXPERIMENT 11(C6-9)

Pigeon 15 and Rat 27 were fed metacercariae of C6-9 and worms developed in
both of them.

Pigeon 15 was fed the metacercariae in 2 small Physa on 9/15/33. Positive
stools were passed on 9/27. Two days later it was killed and 63 worms taken from
the middle ileum.

Rat 27 was fed a single tadpole (R. pipiens) that had been in four ounces of
water with snail C6-9 during the 36 hours which immediately preceded the feeding
on 9/15/33. Thus the cysts were 1-36 hours old. This host was killed by another
rat on 9/29. The autopsy was made about ten hours post-mortem. There were
431 worms in the ileum, most of them near the middle. It is important to note
that these 431 worms all developed from the metacercariae in one frog larva. It
is also of importance to note that none of the cysts were over 36 hours old when
administered.

EXPERIMENT 12(C6-11)

Hog 2, Pigeon 13, and Rat 26 were fed metacercariae of C6-11. The worms
developed in all three.

Hog 2 was fed the cysts in 4 small Physa on 9/14/33. On 9/26 it was slaugh-
tered and the autopsy made fourteen hours post-mortem. There were 32 worms
recovered from the caudal eight feet of the ileum. Ten of these worms were dead
and all were immature.

Pigeon 13 was given metacercariae in 2 small Physa on 9/15/33. Ova were
found in the feces on 9/27, but may have been present earlier as no examination
was made previous to that date. It was killed and 31 worms recovered on 9/30.
Most of them were in the middle ileum.

Rat 26 was fed metacercariae in one tadpole on 9/15/33. It was killed on
10/24 and 3 large worms recovered from the middle ileum,

EXPERIMENT 13(C6-12)

Hog 3 and Pigeon 14 were fed metacercariae of C6-12. Both were positive.
Hog 3 was given the metacercariae in 5 small Physa on 9/14/33. No fecal

62 ILLINOIS BIOLOGICAL MONOGRAPHS

examinations were made. On 10/16 the animal was slaughtered and eight mature
worms were recovered from the caudal one-fifth of the ileum, the most posterior
one being about eighteen inches above the cecum. The autopsy was made about
three hours post-mortem.

Pigeon 14 was given the metacercariae in 2 small Physa on 10/5/33. Ova ap-
peared in the feces on 10/15 and were numerous for four days, then suddenly
decreased and no more were found after the fifth day. The host was not killed.

EXPERIMENT 14(C6-17)

Rat 28 and Chicken 4 were fed metacercariae of C6-17 and worms developed
in both of them.

Rat 28 was fed the metacercariae on 9/18/33 in one small tadpole (R. pipiens)
that had been dead about eighteen hours. This rat seemed normal in every way
until 10/2 when it was noticed that it had not eaten on that day. The next day it
was obviously very ill. It was killed and an autopsy performed immediately.
Ninety-five worms were taken from the middle and upper ileum. Some of them
had ova in the uterus.

Chicken 4 was fed metacercariae in 2 small Physa on 9/19/33. Ova appeared
in the feces on 10/1, and increased in abundance daily. On 10/4 the host was
killed and 30 mature worms taken from the cloaca, rectum, ceca, and ileum. The
autopsy was made about one hour post-mortem.

A summary of the above experimental feedings is given in Table 5.
In all fourteen of the experimental feedings in which both birds and
mammals were fed encysted cercariae from the same snail host, there is
no instance of failure to infect at least one of each. Some of the hosts
were entirely negative and others lost their infection before they were
killed. Results with the rats were particularly inconsistent and somewhat
confusing. Several races of rats were used, however, and there is a very
great difference in the way each serves as a host for this species of worm
(Table 6). Mature worms of each of the stocks were not always pro-
cured from more than one host, but there are, it seems, more than enough
cases, nine in all, in which mature worms were recovered in considerable
numbers from both birds and mammals to show that only one species was
used in infecting both types of hosts. As was indicated above, there are
not enough morphological differences in any of the cercariae used even
to suggest a mixture of species, and the morphological variation in the
adults is interpreted as being induced by the different host species
(see p. 27).

ON THE TRANSFER OF ADULT WorMS FROM Host to Host

In order to test further the possibility of physiologic differences in
the worms from the different hosts a number of experiments were under-
taken in which identical worms rather than worms of common parentage
were used. Worms taken from mammals and introduced into the cloaca
of pigeons were able to adjust themselves to the higher temperature, more

STUDIES ON ECHINOSTOMA—BEAVER 63

active gut, etc., and generate large numbers of ova for from several days
to several weeks (Tables 7 and 9, p. 77). The individual transfers
were made as described below. Some of them were bird-to-bird trans-
fers which gave data on questions other than the one mentioned above.

TRANSFER I

Six mature worms (13 days old) were transferred from the lower ileum of
Chicken 5 into the cloaca of Pigeon T1 at 9 a.m., 10/2/33. This pigeon like most
of the others was put in a cage over a shallow pan of water for a day or two in
order to check whether the worms were immediately expelled. None had been
expelled after 24 hours. Ova appeared immediately in the feces and were very
numerous the next day. There was no apparent reduction in the numbers until
after twelve days (10/16) when there was a rather sharp decline. During the
next ten days there was no further decline. On 10/27 the eggs were scarce and
none were found after 10/28. At least one of the original six worms lived 26 days
in the new host.

TRANSFER II

Six mature worms, 18 days old, were taken from the middle ileum of Rabbit 7
and transferred to the cloaca of Pigeon T2 on 10/3. Two hours later one of the
worms was discovered in the pan under the cage. None others were found 24
hours later, however, so it was considered that five worms were successfully in-
troduced. Ova appeared immediately and were numerous for five days. None were
found after the sixth day (10/9).

TRANSFER III

Ten mature worms, 23 days old, were taken from the lower ileum of Dog 3
and transferred to the cloaca of Pigeon T3 on 10/8. Seven were expelled as soon
as the pigeon was released but when they were reintroduced they established them-
selves successfully. Ova were found in very great abundance until 10/27 when
there was a noticeable decline. A gradual decrease followed and none were found
after 11/2.

TRANSFER IV

The pigeon used in Transfer IJ was also used in this one. It was given ten
mature worms from the upper ileum of Pigeon 18 on 10/12. The worms were 14
days old. Ova were found daily until 10/25. They were never very numerous,
however. It is important to note that this pigeon had only three days previous to
this transfer lost the last of the worms from Transfer IT.

TRANSFER V

This transfer was made from the upper ileum of Pigeon 19 to the cloaca of
Pigeon T5 on 10/18. Only one robust worm was transferred. It was then 21 days
old. Ova were found in very great abundance, 3,000 per 24 hours on 10/22. On
11/26 this worm was producing only 700 per 24 hours, and on 11/28 none could be
found.

TRANSFER VI

A transfer was made from the middle ileum of Rat 26 to Pigeon T6. A single
mature worm 39 days old was used. The pigeon had been used as Pigeon 14,

64 ILLINOIS BIOLOGICAL MONOGRAPHS

which had been infected from stock C6-12 and has lost its infection after fifteen
days (10/20). The transfer was made on 10/24. Ova appeared in the feces im-
mediately and continued for six days only.

TRANSFER VII

A single specimen, age 12 days, was taken from the middle ileum of Rat 26
and introduced into Pigeon T7. This pigeon had never been infected before. Ova
lid not appear until the fifth day after the transfer and continued for about two
weeks. The last positive stool was found on 11/14.

TRANSFER VIII

Same as Transfer VII. Pigeon T8 had never been used in previous experi-
ments. Ova appeared in the feces on the fifth day and continued three days longer
than in T7. The last positive stool was found on 11/17.

TRANSFER IX

Like the above. Pigeon T9 lost its worm, however, before it matured.

TRANSFER X

Similar to VII, VIII, and IX. Pigeon T10 had never been infected before.
The ova appeared on the fifth day and continued five days longer than in T8 and
eight days longer than in T7. The last positive stool was found on 11/22, on the
28th day after the transfer.

A summary of these experiments is given in Table 9.

From the above experiments in which metacercariae of common par-
entage were fed to several hosts including in most cases both birds and
mammals, and in the experiments in which worms were transferred from
one host to another, the conclusions that may be reached are: (1) that
the experimental worms constitute but a single species which (2) demon-
strates a very high degree of adaptability, being able even after maturity
is reached, to adjust itself to a new host that is very different from the
original, thus (3) inter-class transfers are easily made, and (4) it is also
probable that the life of the worms is prolonged somewhat by the trans-
fer, which suggests that (5) there is probably a slight immunity de-
veloped which is of an accumulative nature. These points are discussed
at length in the text (pp. 18-33).

CONCLUSIONS

When the previous studies on the life history and individual stages
of the cycle were restudied it was found that relatively few of the older
researches could be definitely shown to pertain to Echinostoma revolutum.

The eggs of this species hatch in about three weeks into miracidia
which penetrate any one of a great variety of pulmonate snails and prob-

STUDIES ON ECHINOSTOMA—BEAVER 65

ably metamorphose into sporocysts which produce mother rediae which
in turn produce a second generation of rediae. These daughter rediae
produce cercariae which begin to emerge in about three months.

The cercaria resembles the adult so closely in cephalic spination that
positive identifications can be made from this character alone. Other
features by which it can be recognized are the tail-fin membrane and the
twelve cephalic ducts and gland cells arranged in two groups. The
arrangement of the units of the excretory system may also aid in
identification.

In addition to the descriptions of cercariae that have been identified
as Cercaria Echinostomi-revoluti by feeding experiments there are eleven
other descriptions of 37-spined cercariae in the more recent literature.
These cercariae are easily separated into two types and perhaps only two
species. At least only two species of the 37-spined cercariae can be posi-
tively recognized.

Cercaria helvetica xx1v Dubois and Cercaria trivolvis Cort are syno-
nyms of Cercaria Echinostomi-revolutt.

-It is shown by this study that the cephalic spination is the most re-
liable character for diagnosis of the adult worm. The arrangement and
relative size of the cephalic spines distinguish it from the other 37-
spined echinostomes.

The morphology of the adult worm is best described by the use of
graphs which describe any given size from the entire range of from 2 to
over 20 mm in length.

The only character that is not variable with age is the number, ar-
rangement, and relative size of the cephalic spines.

By transferring single individuals from one host to another it was
found that individuals of this species produce as many as 4,600 ova per
day. The same experiments have shown that self-fertilization is possible
and that it does occur when the possibility of cross-fertilization is
precluded.

A study of the original and other earlier descriptions of E. revolutum
have shown that none of these records and descriptions can be accepted
without so much reservation as to render them almost valueless.

Eighteen species of adult echinostomes have been described more
recently as having about 37 cephalic spines. Two of them belong to the
genus Echinoparyphium and are easily distinguished from Echinostoma
revolutum. None of the other forms can be positively distinguished from
one another or from E. revolutum. In addition to Echinostoma echina-
tum, which has already been reduced to synonymy, eight others are shown
to be synonyms and eight are shown to be probable synonyms or species
of dubious standing.

66 ILLINOIS BIOLOGICAL MONOGRAPHS

Echinostoma revolutum has been found in the temperate zone of all
parts of the world excepting South Africa and the interior of Asia. The
cercaria is recorded from eleven species of pulmonate snails in diverse
geographical regions. The metacercaria may be found in molluscs, am-
phibia, fish, and (?) planaria. It is recorded from sixteen molluscs, pri-
marily pulmonate gastropods; probably eight species of amphibia; and
one scaleless fish, Ameirus melas. The adult worm is recorded from 32
species of birds and nine species of mammals, including man. The
present study has contributed ten new records for the metacercaria and
seventeen for the adult.

It is shown that experimental and “incidental” hosts are “normal”’ if
not natural hosts for this species of parasite and that natural infection
would probably occur in almost any bird or mammal whose feeding
habits are similar to the so-called “natural’’ hosts.

By repeatedly infecting both tadpoles and snails from the same stock
of cercariae and feeding these to both birds and mammals it was shown
that only one species of parasite was being studied rather than two or
more indistinguishable forms, and that there is relatively no specificity
shown in the metacercaria and adult stages.

Experiments in which worms were transferred from mammals to
birds support the above conclusions.

The same transfer experiments indicate that the life of the parasite
is prolonged by introduction into a new host.

Transfer and reinfection experiments have demonstrated that although
prolonged captivity of the host and unsuitable diet produce more obvious
reactions which tend to obscure immunity phenomena, the pigeon does
develop a slight immunity to EF. revolutum.

A total of 42 different measurements on each of about 300 worms
were made and the worms from birds compared by biometric methods
with those from mammals. While the differences are in most respects
slight they are nevertheless in many instances significant, and may ac-
count for a good deal of the confusion regarding the morphology of the
adult worm. The most obvious differences were found in the character
of the cuticular spination. Differences in proportions are probably due to
the very pronounced difference in growth rate in the two types of hosts.

STUDIES ON ECHINOSTOMA—BEAVER 67

SUMMARY

The life history of the trematode parasite Echinostoma revolutum has
been experimentally determined and the morphology of the various
stages described.

The adult worm has been described by biometric methods, which was
found to be the only adequate means of description for a worm whose
size range in adult life is so great as to allow much confusion in
diagnosis.

Extensive studies have been made on normal variation, especially the
variation induced by the different types of hosts.

Related species have been reviewed and eight species reduced to
synonymy,

All of the more reliable records of hosts and distribution have been
reviewed and summarized.

For the first time adult worms have been successfully transferred
from mammal- to bird-hosts.

Certain immunity phenomena have been observed and discussed.

TABLE 1.—Cercaria Echinostomi revoluti
(e = experimental infection only)

Host Locality Reference
Helisoma trivolvis........0.0.0.0.00.00.4. Illinois Cort, 1914, 1915
Illinois Faust, 1918
Illinois Beaver (this paper)
Ontario Fallis, 1934
Lymnaea peregra...............4-. Philippine Islands Tubangui, 1932b
Lymnaea pervia........ 0.00... eee Taiwan Tsuchimochi, 1924
Taiwan Morishita, 1929
Lymnaea radix.... 0.00. ee Taiwan Tsuchimochi, 1924, 1926
Lymnaea stagnalis..............4.. Italy Vevers, 1923
Switzerland Dubois, 1928
Lymnaea swinhoe.................. Taiwan Tsuchimochi, 1924
TERY SQ STUNG reais at a) delete 6a + ae Illinois E. L. Miller, 1936
Ontario Fallis, 1934
Physa occidentalis (?).............. California Johnson, 1920
IPUYS@ T10GS ors piece view cee eae ws Brazil Lutz, 1924
IPIGHOL USSD tanacs 5 res hiss blue ee Taiwan Tsuchimochi, 1924, 1926
Pseudosuccinea columella........... Maryland Krull, 1935 (e)

Stagnicola palustris..........00000% Ontario Fallis, 1934

68 ILLINOIS BIOLOGICAL MONOGRAPHS

TABLE 2.—Metacercaria Echinostomi revoluti
(e = experimental infection only)

Host Locality Reference

Corbicula producta..........-0.005s Taiwan Anazawa, 1929

Fossariad Qbrussd.. oe eee Ontario Fallis, 1934

Fossaria modicella.... 0.0.0... ce eee Illinois Beaver (this paper) (e)
Ontario Fallis, 1934

Helisoma trivolvis..........0.00 00 Illinois Beaver (this paper)
Ontario Fallis, 1934
Maryland Krull, 1935 (e)

Lymnaea peregra.... 2.2.0.0. eee eee

Philippine Islands

Tubangui, 1932b

LYMNGED PerUId... oo. oe siweeeceeeess Taiwan Tsuchimochi, 1926

LYMNGEG TOM16 6 s.cccaw cia e wena Taiwan Tsuchimochi, 1926

LYMNGCW SIAENOIES: 6 io5 on ox once 8s Italy Vevers, 1923

Lymuaes Waskt (2). 5.24.08 es biases California Johnson, 1920

Musculium partumetum............ Maryland Krull, 1935 (e)

PU YSOREVIANG ss eee cee nae Illinois Beaver (this paper)
Ontario Fallis, 1934

PUYSO NGC ae re eee ee ee Maryland Krull, 1935 (e)

Physa occidentalis (?)...........40. California Johnson, 1920

PHYSAPWGUS. 5 PIRES BAe Oe Brazil Lutz, 1924

PIGHOVOUS SPs fo ee ace ee Brazil Lutz, 1924

Pseudosuccinea columella............ Illinois Beaver (this paper) (e)
Maryland Krull, 1935 (e)

Vavtparus SPosivnrc¢ Oeste «ese Taiwan Tsuchimochi, 1926

PESUGIID: BD. 5.555. a0 wich aod Oe we aoe Illinois Beaver (this paper) (e)

SOPAGCNIUNE SIN oa ahd 4: Sales nd Ba ioe ad Illinois Beaver (this paper) (e)
Ontario Fallis, 1934

Stagnicola palustris... 0.0.0.0. 000. Ontario Fallis, 1934

PIGHAPIG BOE) iielos:% ane 8S as ae California Johnson, 1920

IKGHG CSCULGHIE: Fin sa pies an be sw Oe Japan Miki, 1923

RONG JAPONICA. 0.6 ces Japan Dollfus, 1925

Rana pipiens (larva)............... Illinois Beaver (this paper)

Rana pipiens (adult).............. Illinois Beaver (this paper)

RONG VUGOSES 4.12 OAR 2St8 ba2 28 Se Japan Dollfus, 1925

Rana catesbiana (larva)............ Japan Dollfus, 1925 (e)

Rana nigromaculata.............04% Japan Dollfus, 1925

TAA POLES 3 i..5, 5 sac a8toans a hoe acct ale Sake Taiwan Tsuchimochi, 1926

“Tadpoles” (Bufo americana)....... Ontario Fallis, 1934

AMOI US MELOS P88 Sows Wake eos ee Illinois Beaver (this paper) (e)

STUDIES ON ECHINOSTOMA—BEAVER 69

TABLE 3.—Echinostoma revolutum, ADULT

(e = experimental infection only)

Host

Anas brasiliense... 0.0.0... eee
Anas platyrhynchos (domestic)......

Anas P. platyrhynchos (wild).......

Anas superciliosd.......... 0c eee

Anser anser (domestic).............

ANSE? CINETUUS 0 0 eee
Anseranas semipalmata.............
Bueteo lagopus-s. johannis..........
Catrina moschata...........0..0055

Cheniscus pulchellus...........445.
Chenopsis atrala.........-2..0 000s
Coloeus monedula............0.2445
Columba domestica.............0055

COlyMoUS CYUSIAIUS ~h.80s 3 cose 88s

CORDCIDS BOTT UID=. oo6 one bene ne es
COPUUS COPNIM:. 6. cee wi cs eee es

Locality

Brazil

Poland

Taiwan

Taiwan

Taiwan

Japan

Japan

Philippine Islands

England

England

Turkestan

Middle-Europe

Illinois

Illinois

Japan

Middle-Europe

Illinois

Queensland,
Australia

Queensland

Taiwan

Middle-Europe

Ontario

Ontario
Queensland
Illinois

Brazil
Brazil

Queensland
Queensland
Poland

Philippine Islands
Germany

Germany

Germany
Germany

Illinois
Middle-Europe

Egypt
Poland
Brazil
Ontario
Turkestan
Taiwan
Taiwan
Japan
Japan

Reference

Dietz, 1910

Kowalewski, 1895, 1897
Anazawa, 1929 (e)
Iwata and Tamura, 1933
Tsuchimochi, 1924
Yamaguti, 1933

Ishii, 1932

Tubangui, 1932a
Vevers, 1923 (e)
Brown, 1926 (e)
Skrjabin, 1913

Dietz, 1910

Beaver (this paper) (e)
Miller, 1936 (e)

Ishii, 1932

Dietz, 1910

Beaver (this paper)

Johnston, 1913, 1916

Nicoll, 1914

Iwata and Tamura, 1933
Dietz, 1910

Fallis, 1934 (e)

Swales, 1933a
Nicoll, 1914
Beaver (this paper)
Lutz, 1924 (e)
Dietz, 1910

Nicoll, 1914
Nicoll, 1914
Markowski, 1933

Tubangui, 1932b (e)
Krause, 1925a

(Echinostoma sp.)
Zunker, 1925

(E. columbae)
Bolle, 1925 (E. columbae)
Sprehn, 1927

(E. paraulum)
Beaver (this paper) (e)
Dietz, 1910

(E. paraulum)

Looss, 1899

Markowski, 1933

Dietz, 1910 (EZ. mendax)
Swales, 1933b (corrected)

Skrjabin, 1913
Tsuchimochi, 1924
Anazawa, 1929 (e)
Ishii, 1932
Kurisu, 1932

70)

ILLINOIS BIOLOGICAL MONOGRAPHS

TABLE 3.—Concluded

Host

Gallus gallus (domestic fowl) cont’d..

Mareca americana

Mareca penelope

Marila marila...

Neochen jubata...
Nyroca fuligula. .
Nyroca maria...
Oidemia nigra....
Pernis apivorus. .

ee

Philomachus pugnax...............

Scolopax rusticola

Cavia porcellus. ..

Epimys norvegicus

Felis domestica...
Homo sapiens....
Mus musculus...

Rabbit (domestic)

DUS SCVOPO ci S3aca es no aa aan hae

Slim) wy iene ce Wee ‘ef ie! e! 6) @ 8c ea 18

*Collected by W. E. Swales.
{Records obtained from a study of specimens in the collection of Henry B. Ward.

Locality

Japan

Poland
Middle-Europe
Illinois

Alberta, Canada
Middle-Europe
California
Ekaterinburg,
U.S.S.R.
Brazil
Japan
California
Middle-Europe
Egypt
Egypt

Ekaterinburg,
ULS.S.R:

Taiwan
Middle-Europe

Taiwan
Taiwan
Illinois

Illinois
Maryland
Japan
Taiwan
Illinois
Illinois
Taiwan

Taiwan
Illinois

Pennsylvania
Nebraska

Ontario

Quebec
Alberta
Pennsylvania
Illinois
Colorado
Maryland

Illinois
Maryland

Illinois

Reference

Iwata and Tamura, 1933
Kowalewski, 1895, 1897
Dietz, 1910

Beaver (this paper) (e)
Beaver (this paper)*
Dietz, 1910

Johnson, 1920

Skrjabin, 1915

Dietz, 1910 (E. mendax)
Yamaguti, 1933
Johnson, 1920

Dietz, 1910

Looss, 1899

Looss, 1899

Skrjabin, 1915

Iwata and Tamura, 1933
Dietz, 1910

Tsuchimochi, 1924 (e)
Anazawa, 1929 (e)
Beaver (this paper) (e)
Beaver (this paper) (e)
Krull, 1935 (e)
Dollfus, 1925

(E. cinetorchis)
Tsuchimochi, 1924 (e)
Beaver (this paper) (e)

Beaver (this paper) (e)
Anazawa, 1929

Anazawa, 1929 (e)
Beaver (this paper) (e)

Leidy, 1888
Barker, 1915
(E. armigerum and
E. coalitum)
Law and Kennedy, 1932
(E. armigerum and
E. coalitum)
Beaver (this paper)*
Beaver (this paper)*
Beaver (this paper) t
Beaver (this paper)
Beaver (this paper)
Krull, 1935 (£. coalitum)

Beaver (this paper) (e)
Krull, 1935 (e)

Beaver (this paper) (e)

STUDIES ON ECHINOSTOMA—BEAVER 71

TABLE 4.—SUMMARY OF REINFECTION EXPERIMENTS

Days Dates of
Host infected infections Remarks
ich 6 10/3 —10/9 5 worms administered per anus
12 10/12—10/24 12 worms administered per anus
? 11/2 — Negative by fecal examinations
? 11/22— Negative by fecal examinations
and autospy 12/15
ee A ne 15 10/5 —-10/20 Positive by fecal examination
from 10/15 to 10/20
6 10/24—10/30 1 worm administered per anus
? 11/2 — Negative by fecal examination
8 12/6 —12/14 1 immature worm recovered
Poor tute eons 24 10/8 —11/1 10 worms administered per anus
16 11/2 —11/18 Positive by fecal examination
from 11/2 to 11/18
10 11/6 —12/16 3 immature worms recovered
FL eee aPS BARS oe 26 10/2 —10/28 6 worms administered per anus
32 11/2 —12/4 Positive by fecal examination
from 11/18 to 12/5
? 12/6 — Negative by autospy on 12/15
ee Ore rere 28 10/24—11/22 1 worm administered per anus
18 12/10—12/28 2 mature worms recovered
RESP eer 40 10/18—11/28 1 worm administered per anus
21 12/10—12/31 11 mature worms recovered
Macc ee eee 20 10/24—11/14 1 worm administered per anus
? 12/10— Negative by fecal examination
and autospy on 12/27
NAMES saa debra etn ecu ? 10/24— 1 worm administered per anus;
probably expelled immediately
19 12/10—12/29 1 worm recovered, mature

We

ILLINOIS BIOLOGICAL MONOGRAPHS

TABLE 5.—EXPERIMENTS IN WHICH CERCARIAE OF COMMON PARENTAGE WERE
FED To BIRDS AND MAMMALS

Exp.
no.

1

2

Cer-
caria
used

C3-A

C4-28

C4-16

C5-A

C6-2

C6-3

C6-5

C6-6

Host

Pigeon 7
Rabbit 2

Pigeon 10
Rabbit 4

Rabbit 5
Rabbit 6
Pigeon 11

Rabbit 3
Pigeon 9
Dog 1

Chicken 5
Dog 3
Cat 5
Rat 30
Rat 31

Chicken 6
Cat 2
Pigeon 19

Rabbit 8
Pigeon 16
Mice 14-17

Chicken 7
Guinea pig 1
Rat 25

Rat 26

Rabbit 7
Chicken 3
Pigeon 17

Duck 3
Cat 4
Pigeon 18

Pigeon 15
Rat 27
Hog 2
Pigeon 13
Rat 26
Hog 3
Pigeon 14

Rat 28
Chicken 4

Position in host

Anus to proventriculus
Cecum to duodenum

Middle ileum
Lower and middle ileum

Lower and middle ileum

?

Cecum to duodenum
Anus to duodenum
Cecum and lower ileum

Middle and lower ileum
Lower part of middle ileum
Lower ileum

Cloaca
Lower ileum
Middle and upper ileum

Middle ileum
Middle and upper ileum

Lower ileum
Upper colon to stomach

Middle ileum

Middle ileum
Cloaca, lower and middle ileum
Middle ileum

Lower and middle ileum
Cloaca, rectum, and lower ileum

Lower, middle, and upper ileum
Lower, middle, and upper ileum

Lower ileum
Lower, middle, and upper ileum
Middle ileum

Lower ileum
Host not killed

Middle and upper ileum
Cloaca, lower and middle ileum

a3

STUDIES ON ECHINOSTOMA—BEAVER

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ILLINOIS BIOLOGICAL MONOGRAPHS

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STUDIES ON ECHINOSTOMA—BEAVER 77

TABLE 7.—RATE OF DEVELOPMENT IN THE EXPERIMENTAL Hosts

Days required to

Body temperature reach maturity
Host (Approximate)
Range Average

ea te ee hones wade’ uke sven ae 100 17-19 18
IMGUSCLI ere oe scre ese seeeeen 6 Sites ae

| 2eyzi| bY Te Ais SA Sai cre ee 102 iy 12
MD Opera taye eae ie cous one use Deuonss. soca eye ei 101.5 22 ZZ
Oe ies Ser eee we 102 16?-18 18
Pe iowa fo oe Aa he es 102 32 32
(Guinn (G2) 2 nn. eae 101.7 11 11?
WD Cae aisha oi eedd cities she enaks Oveie as 110 10-11 10.2
TOW ibe tee ss ote retedsis st eter ee sa ats esarcern 107-109 12-14 12.5
ARCOM S car 5 she Ans ah dw om Su ain y's vel 106-108 9-123 11
Mlimaminals: scaaecsscsecc ees en| acnwce es 11-32 19
JN]\Noytigfe (ean gna Oe ee eg (ae 9-14 11

1No mature worms taken.
2Worms almost mature, eggs in uterus but none in host’s feces.
8Pigeons with reinfection required longer than 12 days.

TABLE 8.—COLLECTIONS OF Helisoma trivolvis IN THE VICINITY OF URBANA, ILLINOIS

Collection Number Number

number Date Source collected | infected

Gl kien cs 6/ 9/33 Camp Creek, Seymour 14 1
(Crs E 6/20/33 Drainage ditch at Crystal Lake

Park 35 0
CSF ne 7/ 8/33 First north tributary of Salt Fork,

West of Homer Park 14 2
Oe 8/1/33 Camp Creek, Seymour 100 43
(Cheah 8/ 5/33 Leverette, Illinois, Drainage Ditch 41 1
C65. ie: 9/11/33 Camp Creek 72 38
Oy eer 10/28/33 Camp Creek 9 1
CShrnne.:. 3/10/34 Camp Creek 12 1

TABLE 9.—TRANSFER EXPERIMENTS
Transferred Transferred Number | Days in Days in | Total age
from to of worms | original second in days

Chicken $<. «wie. Pigeon T1 6 13 26 39
Rapbit 7 cs: dacces «s Pigeon T2 5 18 6 24
DO gS ee tuccc esses Pigeon T3 10 23 24 47
Pigeon 1 8:03.66 2 5 Pigeon T4 (T2) 10 14 12 26
Pigeon 19.......... Pigeon T5 1 21 40 61
BR LO Seat te lcs 5 asus Pigeon T6 (14) 1 39 6 45
Rati 202. cugecad ins Pigeon T 1 12 20 32
ae 0 eae Pigeon T8 1 12 23 35
RAGE LOM aciindn sta. Pigeon T9 1 12 ? ?
MAL LO te ewe ware Pigeon T10 i 12 28 40

78 ILLINOIS BIOLOGICAL MONOGRAPHS

EXPLANATION OF CHARTS

The charts serve three separate purposes. Charts 1, 2, 3, 4, 5, 6, 7, 19, and 20
give the average measurements for specimens of any given size under 20 mm. The
range of variability that is due to factors other than host is best shown on Charts
8, 9, 10, 11, 12, 13, 14, 19, and 20, where measurements of individual worms are
plotted separately. Charts 7, 8, 9 and 10, 11 and 12, 13 and 14, 15, 16, 17, 18, 19 and
20, and especially 8, serve to show the differences and similarities to be found in
specimens taken from the two types of hosts in which they commonly occur in
the adult stage.

The curves are made from lines drawn through points obtained by averaging
all of the individual points within arbitrary limits. The lines radiating from zero
are drawn through points of equal proportion and this proportion is indicated in
each case on the line as 1:2, 1:3, etc.

Chart 1 shows the diameter of the acetabulum and the width of the body in
relation to the total length of the body. The former shifts from one-fifth in very
small worms to about one-sixteenth the body length in specimens over 13 mm in
length. Similarly the body width shifts from one-third to nearly one-tenth.

Chart 2 shows the size relationship between the acetabulum and the collar.
The acetabulum is the larger in worms over 4 mm in length.

Chart 3 shows the size relationship between the acetabulum, oral sucker, and
collar. The body length may be determined from Chart 1, and the relative size of
the pharynx may be seen in Charts 19 and 20.

Chart 4 shows the relative lengths of the three regions of the body limited by
the acetabulum and the ovary.

Chart 5 shows the relative size of the gonads in relation to the body length.

Chart 6 shows the relative length of the lateral posterior ventral collar spine
(see Text-figs. 3 and 5) in relation to the body length.

_Chart 7 shows the relationship between the body length and the length of the
cuticular spines in specimens from the two types of hosts.

Chart 8 shows the relationship between the body length and the number of
complete rows of dorsal cuticular spines (see Text-fig. 2) in specimens from the
two types of hosts. In this chart the lengths of the individuals having the same
number of complete rows have been averaged and the total number within the
class indicated by a number near each point.

Charts 9 and 10 show the relationship between the body length and the great-
est width of the body in specimens from the two types of hosts, The larger worms
are slightly stouter in bird hosts.

Charts 11 and 12 show the size relationship between the body length and the
acetabulum in specimens from the two types of hosts. The acetabulum is slightly
smaller in the smaller specimens from mammals.

Charts 13 and 14 show the length relationship between the whole body and
the pre-acetabular region in specimens from the two types of hosts. Differences
here appear to be insignificant.

Chart 15 shows the length relationship between the body and the region of the
uterus. It appears here that there is no significant difference in the length of this
region in the specimens from the two types of hosts.

Chart 16 shows the length relationship between the body and the post-ovarian
region in specimens from the two types of hosts. The greater length of this
region in larger specimens from bird hosts is probably significant.

Chart 17 shows the difference in the size relationship between the acetabulum
and the collar in specimens from the two types of hosts.

Chart 18 shows the size relationship between the acetabulum and the oral
sucker in specimens from the two types of hosts. The oral sucker is relatively
larger in the larger specimens from birds.

Charts 19 and 20 show the size relationship between the pharynx and the oral
sucker. The variation in this character in the specimens from the two types of
hosts is probably not significant.

STUDIES ON ECHINOSTOMA—BEAVER 79

Ss
|
diameter of acetabulum in mm.

length of body in mun

ee ALL HOSTS |
millimeters fo diemeter of collar in mm.
|

| | \ |
12 1.6

Cuart 1 CuHart 2

Os
mn.

a3
s
as

acevab

ar a ee
diameter of

diameter in mm.

04 | ole

CuHart 3 CHART 4

80

length of body (in mm.

ILLINOIS BIOLOGICAL MONOGRAPHS

|
length of body in mm

ALLHOSTS
length of spin€ Lev ih Mmyerons
'

|
do to _' ido |

CuHart 5

O——BIRD HOSTS
om===MAMMAL HOSTS

Ta A

complete rows of dorsal cuticular spines

s

a

PPLE ACTH

body length in me. O e

f ow t fy
{ed ced, PRR |

o

| |
16 24 28 5:

length of tenth lateral cuticular spine in la
co \
2

CuHartT 7 CHART 8

ioe)
—

STUDIES ON ECHINOSTOMA—BEAVER

B/RD HOSTS
greakst width of body in mine.

I le be ky
1.2 1.6 20

MAMMAL HOSTS
gredest width of body ia mere

[eet Set ® vl
1.2 16 2.0 B j : 0.8

CuHartT 9 Cuart 10

|

N
S
<
3
_—
Ss
=
SS
nd

_ MAMMAL HOSTS) ye BIRD HOSTS
diameter of acetabulum in mm. ‘ aameter of acetabulum in mm.
| | | | | | | | ! | | | | | | |
0.6 0.8 10 : a4 0.8 10

CuHart 11 Cuart 12

82 ILLINOIS BIOLOGICAL MONOGRAPHS

BIRD HOSTS :
min. From acetabulum to anterior end

re ame feert
Le: 18

S. MAMMAL HOSTS
mim. from acetabulum to anterior end

|
0.8 tp 1.6

Cuart 13

=
Ss
i}

R
NS
s
=
*
~
=
Ss

length of body in nm.

mm. from ovary to posterior end
hs a ae ea

min frame acetobulum to ovary
l
10

3 4

!
5

CuHart 15 CHart 16

STUDIES ON ECHINOSTOMA—BEAVER 83

NN
IS
06-8
IS
S
=
=~

diameter of acetabulum in mm.
£
diameter of aceta

diameter ot ord sucker in raicrons
do | sh | 20 ' abo

diameter of colar in mam.

trert rrtda
d's Ai ates srt

eS

CuHartT 17 Cuart 18

MWUCtONS

8

n
v

B
!

‘S
N
N

N

“
iS

SS

S

MAMMAL HOSTS BIRD HOSTS

iar af aid slche ie Hiitrens ds dhameler of oral sucker /a microns
| | 1 | ! | ! | i}
20 | 180 R10 240 : 300 360 180 240 300 360

CuHart 19 Cuart 20

ILLINOIS BIOLOGICAL MONOGRAPHS

fore)
me

PLATE 1

Fics. 1, 2, 3—Head of cercaria, showing cephalic spination in lateral, ventral,
and dorsal views, respectively. (Camera lucida drawings).

Fic. 4—Camera lucida drawing of a fixed specimen of the cercaria.

Fic. 5—Diagram of tadpole showing the usual course followed by creeping
cercariae.

Fic. 6.—Diagram showing the cephalic ducts as seen in the unflattened speci-
men (cercaria).

Fic. 7—Diagram of the cuticular plates of the miracidium in dorsal view.

Fic. 8—Camera lucida drawing of the partially contracted tail of the cercaria.
Lateral view.

Fic. 9—Camera lucida drawing of the head of an 8.55 mm adult from a
chicken.

Fic. 10.—Camera lucida drawing of the tip of the tail of a fixed cercaria, show-
ing the extent of the circular muscles and the fin fold membrane.

Fic. 11—The miracidium, almost mature within the egg. Outlines made with
the camera lucida, details free-hand.

85

STUDIES ON ECHINOSTOMA—BEAVER

ATE I

PL

86 ILLINOIS BIOLOGICAL MONOGRAPHS

PLATE, 11

Fic. 12—Camera lucida drawing of a fixed specimen of the cercaria, ventral
view. Excretory system added free-hand from drawings made from living speci-
mens.

Fic. 13—Camera lucida drawing of a 20 mm specimen from a muskrat. Ven-
tral view.

Fic. 14—Camera lucida drawing of an 8.8 mm specimen from a chicken, ex-
perimentally infected. Ventral view.

87

STUDIES ON ECHINOSTOMA—BEAVER

ww l'o

PLATE II

88 ILLINOIS BIOLOGICAL MONOGRAPHS

PLATE III

Fic. 15——Cephalic spines of Echinostoma cinetorchis. Text-fig. 1, Ando and
Ozaki, 1923. (From Dollfus, 1925, text-fig. 2.)

Fic. 16—Cephalic spines of E. mendax. (From Dietz, 1910, text-fig. A.)

Fic. 17.—Cephalic spines of FE. paraulum. (From Dietz, 1910, text-fig. B.)

Fic. 18—Cephalic spines of E. echinocephalum. (From Dietz, 1910, text-fig. C.)

Fic. 19—Cephalic spines of FE. columbae. (From Bolle, 1925, text-fig. 1.)

Fic. 20.—Cephalic spines of E. columbae. (From Zunker, 1925, text-fig. 2.
Scale is 0.1 mm.)

Fic. 21—Cephalic spines of Echinoparyphium (?Echinostoma) paraulum.
(From Sprehn, 1932, text-fig. 8.)

Fic. 22.—Echinostoma miyagawat. (From Ishii, 1932, Plate II, fig. 10.)

Fic. 23.—Cephalic spines of E. miyagawai. (From Ishii, 1932, Pl. IT, fig. 11.)

Fic. 24—Echinostoma columbae. (From Zunker, 1925, text-fig. 1. Scale is
about 1 mm.)

Fic. 25.—Cephalic spines of E. echinatum (= revolutum). (From Kowalewski,
1895, Plate 8, fig. 1.)

Fic. 26.—“Fasciola revoluta’ (= Echinostoma revolutum) as figured in the
original description. (From Froelich, 1802, Plate II, fig. 7.)

Fic. 27.—Cephalic spines of E. sudanense. (From Odhner, 1911, Plate III,
fig. 13.)

Fic. 28.—Cephalic spines of E. echinatum (= revolutum) from a goose. (From
Looss, 1899, Plate XXIV, fig. 7.)

Fic. 29.—Cephalic spines of E. echinatum (?syn. limicoli) from Machetes
pugnax. (From Looss, 1899, Plate XXIV, fig. 6.)

STUDIES ON ECHINOSTOMA—BEAVER 89

PLATE Iti

90 ILLINOIS BIOLOGICAL MONOGRAPHS

BIBLIOGRAPHY
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STUDIES ON ECHINOSTOMA—BEAVER 95

INDEX

Ameiurus melas, 32, 66, 68
Anas brasiliense, 69
platyrhynchos, 69
superciliosa, 69
Anser anser, 69
cinerius, 69
Anseranas semipalmata, 69
Aramides cayennensis, 43
Ascaridia lineata, 37
Bueteo lagopus-s. johannis, 69
Bufo americana, 32, 68
Cairina moschata, 10, 69
Canis familiaris (See Dog)
Carphibis spinicollis, 42
Gat. 32, 33, 70, 76, 77
Catfish (See Ameiurus melas)
Cavia porcellus (See Guinea pig)
Cercaria, Agilis group, 14
Coronata group, 16
Echinata group, 16
Echinatoides group, 16
Cercaria echinata, 9, 15, 17, 18
Echinoparyphii-aconiati, 17, 18
Echinostomi-revoluti, 13, 17, 65, 67
helvetica xxtt, 18
xxi, 18
xxiv, 18, 65
xxv, 18
limbifera, 17, 18
trivolvis, 18, 65
Chamaepelia passerina, 43
Chemiscus pulchellus, 69
Chenopsis atrata, 69
Chicken (See Domestic fowl)
Coloeus monedula, 69
Columba domestica (See Pigeon)
Colymbus cristatus, 51, 69
Coracias garrula, 69
Corbicula producta, 68
Corvus cornix, 69
Creciscus viridis, 43, 44
Crotophaga ani, 43
Dendrocygna viduata, 69
Distomum armatum, 40
dilatatum, 40
echinatum, 8, 9, 50, 56
hérissé, 54
oxycephalum, 40
Dog, 9 32,.39,./0, 77
Domestic fowl, 33, 46, 69, 70, 73, 74, 77
Duck, 8, 9, 32, 33, 46, 50, 51, 69, 74, 77
Echinoparyphium, 28, 51, 52, 53, 65
aconiatum, 15, 17, 40, 54, 55
cercaria, 17

contiguum, 40, 48, 55
recurvatum, 11, 12, 53
sp., 40, 42

Echinostoma, 28

acuticauda, 41, 42, 56
armatum, 56
armigerum, 49, 55, 56
callawayensis, 41, 42, 48, 56
cinetorchis, 10, 32, 46, 47, 48, 55, 56, 88
coalitum, 19, 49, 50, 56
columbae, 51, 52, 53, 55, 56, 88
dilatatum, 56
distinctum, 44
echinatum, 40, 54, 65, 88
echinocephalum, 41, 45, 46, 52, 56, 88
erraticum, 41, 43, 56
limicoli, 54, 56
mendax, 50, 51, 55, 56, 88
microrchis, 41, 44, 56
miyagawai, 46, 47, 55, 56, 88
neglectum, 41, 43, 56
oxycephalum, 56
paraulum, 51, 52, 53, 55, 56, 88
revolutum, acetabulum, 19, 20
body spines, 21
cercaria, 13, 67
description, 14, 15, 16, 24, 25
geographical distribution, 29, 67
hosts, 30, 67
related species, 17, 18
synonyms, 17, 18
collar, 20
spines, 22
diagnosis, 55
genital system, 25
geographical distribution, 29, 69, 70
hosts, 29, 32, 56, 62, 69, 70, 72
immunity against, 33, 71
life history, 8
metacercaria, 30, 31, 32, 68
methods used, 10, 12, 14, 18, 19, 26,
56;57
miracidium, 10
misdeterminations, 53
morphology, 18, 78
mother-redia, 13
oral sucker, 20
ova, 25, 26
ovary, 19, 20
pathology, 31, 57, 58, 59, 60
pharynx, 20
rate of maturity, 28, 77
redia, 12
self-fertility, 26

96 ILLINOIS BIOLOGICAL MONOGRAPHS

Echinostoma revolutum (continued)
size and form, 19, 20
spination of body, 21
crown, 22, 23, 24
synonyms, 39, 55, 56
testes, 20

transfer to pigeons, 26, 37, 62, 64, 77

uterus, 20
variation, induced, 27, 56, 62, 78
natural, 18, 56, 78
sp. (Leidy), 49
(Heelsbergen), 53
(Picard), 53
sudanense, 41, 42, 56, 88
Ephippiorhynchus senegalensis, 41
Epimys norvegicus (See Rat)

Euparyphium (Echinostoma?) murinum

13
Fasciola revoluta, 88
Felis domestica (See Cat)
Fossaria abrussa, 68
modicella, 31, 68
Gallinula galeata, 43, 44
Gallus gallus (See Domestic fowl)
Gosling, 10
Guinea pig, 32, 33, 70, 76, 77
Helisoma trivolvis, 30, 57, 67, 68, 77
Hog (See Pig)
Homo sapiens, 70
FHyla regilla, 9
Hypoderaeum conoideum, 12
Lymnaea peregra, 67, 68
pervia, 67, 68
radix, 67, 68
stagnalis, 67, 68
stagnicolis, 8
swinhoe, 67
traski, 9, 68
Machetes pugnax, 54
Mareca americana, 70
penelope, 70
Marila marila, 9, 70
Meleagris gallopavo, 70
Mouse, 9, 32, 33, 70, 75, 77

Mus musculus (See Mouse)

Musculium partumeium, 68
Muskrat, 25, 40, 42, 48, 49, 50, 70
Neochen jubata, 70
Notophthalamus torosus, 9
Nycticorax violaceus, 43
Nyroca marila, 70
fuligula, 70
Oidemia nigra, 70
Ondatra zibethica (See Muskrat)
Paludina sp., 8
Pernis apivorus, 70
Phalocrocorax carbo, 54
Philomachus pugnax, 70
Physa halei, 68
gyrina, 30, 57, 67
occidentalis, 9, 67, 68
rivalis, 43, 67, 68
Pig, 32, 33, 70,.76, 77
Pigeon, 10, 32, 33, 34, 53, 69, 77
Pisidium sp., 31, 68
Planaria, 9, 68
Planorbis corneus, 8
sp., 43, 67, 68
Pseudosuccinea columella, 31, 67, 68
Rabbit, 32, 33, 70, 76, 77
Rana esculenta, 9, 32, 68
catesbiana, 31, 32, 68
japonica, 32, 68
nigromaculata, 32, 68
pipiens, 30, 31, 32, 57, 68
rugosa, 32, 68
Rat, 9,32, 33,70, 742.77
Scolopax rusticola, 70
Scopus umbretta, 41
Sphaerium sp., 31, 68
Spirulina sp., 43
Stagnicola palustris, 67, 68
Sus scrofa (See Pig)
Swan, 70
Tadorna tadorna, 70

Tadpole, 10, 15, 31, 32, 68 (See also,
Bufo, Hyla, Notophthalamus, and

Rana)
Viviparus sp., 68

Tm