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A TKEATISE ON ZOOLOGY

A TREATISE ON ZOOLOGY

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Part II. THE ECHINODERMA

BY F. A. BATHER, M.A.

Assistant in the Geological Department of the British Museum

ASSISTED BY

J. W. GREGORY, D.Sc.

Late Assistant in the Geological Department of the British Museum,
Professor of Geology in the University of Melbourne

AND

E. S. GOODRICH, M.A.
Aldrichian Demonstrator of Anatomy in the University of Oxford

Part III. THE PORIFERA & COELENTERA

BY

E. A. MINCHIN, M.A.

Professor of Zoology at University College, London

G. HERBERT FOWLER, B.A., Ph.D.

Late Assistant Professor of Zoology at University College, London

AND

GILBERT C. BOURNE, M.A.
Fellow and Tutor of New College, Oxford

AGENTS IN AMERICA

THE MACMILLAN COMPANY

66 FIFTH AVENUE, NEW YORK

A

TEEATISE ON ZOOLOGY

EDITED BY

E. EAY LANKESTER

M.A., LL.D., F.R.S.

HONORARY FELLOW OF EXETER COLLEGE, OXFORD ; CORRESPONDENT OF THE INSTITUTE

OF FRANCE ; DIRECTOR OF THE NATURAL HISTORY DEPARTMENTS

OF THE BRITISH MUSEUM

PART IV

THE PLATYHELMIA, MESOZOA, AND
NEMERTINI

BY

W. BLAXLAND BENHAM, D.Sc.(Lond.), M.A.(Oxon.)

PROFESSOR OF BIOLOGY IN THE UNIVERSITY OF OTAGO, NEW ZEALAND ; FORMERLY ALDRICHIAN
DEMONSTRATOR OF ANATOMY IN THE UNIVERSITY OF OXFORD

LONDON

ADAM & CHAELES BLACK
1901

V

EDITOR'S PEEFACE

THE present volume is the " Fourth Part " in order of a com-
prehensive treatise on Zoology, which has been for some time
in preparation under my editorship. In this treatise each
of the larger groups of the Animal Kingdom is to be described
by a separate author ; whilst, as far as possible, uniformity
in method and scope of treatment is aimed at. The authors
are, for the most part, graduates of the University of Oxford,
though it may not be possible to maintain this limitation in
future sections of the work.

The general aim of the treatise is to give a systematic
exposition of the characters of the classes and orders of the
Animal Kingdom, with a citation in due place of the families
and chief genera included in the groups discussed. The work
is addressed to the serious student of Zoology. To a large
extent the illustrations are original. A main purpose of the
Editor has been that the work shall be an independent and
trustworthy presentation, by means of the systematic survey,
or taxonomic method, of the main facts and conclusions of
Zoology, or, to speak more precisely, of Animal Morphography.

The treatise will be completed in ten parts of about the
same size as the present one. It will at once be apparent that
this limitation necessitates brevity in treatment which, however,
will not, it is believed, be found inconsistent with the fulfil-
ment of the scope proposed or with the utility of the work

vi PREFACE

to students. The immediate publication of the following
parts may be expected : —

Part I. Introduction and the Protozoa.

Part II. Enteroccela and the Ccelomocoela — The Pori-
fera — The Hydromedusae — The Scypho-
medusae — The Anthozoa — The Ctenophora
(published in September 1900).

Part III. The Echinoderma (published in March 1900).

Part IV. The Mesozoa — The Platyhelmia — The Nemer-
tini (the present volume).

These parts will be issued, without reference to logical
sequence, as soon as they are ready for the press. This pro-
cedure to some extent evades the injustice of making an
author, whose work is finished, wait for publication until other
more tardy writers have completed their tasks.

The following authors have undertaken portions of the
work : — Professor Weldon, F.E.S., M.A.Oxon. ; Professor Ben-
ham, D.Sc., M.A. Oxon. ; Mr. G. C. Bourne, M.A. Oxon. ; Mr.
G. H. Fowler, M.A. Oxon. ; Professor Minchin, M.A. Oxon. ;
Mr. F. A. Bather, M.A.Oxon. ; Professor J. W. Gregory, D.Sc. ;
Mr. E. S. Goodrich, M.A.Oxon.; Professor Hickson, F.RS.
of Manchester ; Mr. J. J. Lister, F.E.S., M.A. Cantab. ; Mr.
Arthur Willey, D.Sc. ; Professor Farmer, F.E.S., M.A. Oxon. ;
Mr. E. I. Pocock ; and Mr. Martin Woodward.

E. EAY LANKESTEE.

July 1901.

NOTE

IT is but just to the author to put on record the fact that the
MS. of the chapters on the Platyhelmia were written during
the years 1895-97; much of it was printed, and the proofs
corrected in 1897; and the whole of the Part was in proof,
and most of the figures were already prepared, early in 1898,
when the author left England for New Zealand. At the
same time the editor is satisfied that no important omissions
due to this fact occur in the hook, the proofs of which have
been revised and some additions made during the present year.

E. E. L.

CONTENTS

CHAPTER XVI

PAGE

THE PLATYHELMIA — TURBELLARIA ... 1

CHAPTER XVII
THE PLATYHELMIA — TEMNOCEPHALOIDEA . . .43

CHAPTER XVIII
THE PLATYHELMIA — TREMATODA . . . . .47

CHAPTER XIX

THE PLATYHELMIA — CESTOIDEA . . ._ .93

CHAPTER XX

APPENDICES TO THE PLATYHELMIA . . .148

CHAPTER XXI
THE NEMERTINI . . . . . .159

INDEX 197

CHAPTER XVI.

PLATYHELMIA — TURBELLARIA.

PHYLUM PLATYHELMIA.1

CLASS I. TURBELLARIA.

Order 1. Rhabdocoelida.
„ 2. Tricladida.
„ 3. Polycladida.

CLASS II. TEMNOCEPHALOIDEA.
Order Dactylifera.

CLASS III. TREMATODA.

Order 1. Heterocotylea.
„ 2. Aspidocotylea.
„ 3. Malacocotylea.

CLASS IV. CESTOIDEA.

GRADE A. CESTOIDEA MONOZOA.
Order 1. Amphilinacea.
,, 2. Gyrocotylacea.
,, 3. Caryophyllacea.

GRADE B. CESTOIDEA MEROZOA.
Branch a. DIBOTHRIDIATA.
Order 1. Pseudophyllidea.

Branch 1). TETRABOTHRIDIATA.
Order 1. Tetraphyllidea.
„ 2. Diphyllidea.
„ 3. Tetrarhyncha.
„ 4. Tetracotylea.

APPENDICES TO PHYLUM.

Rhombozoa, Orthonectida, Triclioplax, etc.

1 Phylum Platylielmia, Lankester, 1890 (Platydmia, Vogt, 1851 ; Platodes,
Leuckart, 1854 ; Platydmintlies, Gegenbaur, 1859 ; Plat/ielminthes, Minot, 1877).

THE PLATYHELMIA

THE group of " Flat worms " constitutes one of the phyla of
the Metazoa. Linnaeus associated Lumbricus with the various
worms which are now known as Flukes, Tapeworms, Nemertines,
Nematodes, and Leeches in the order " Intestina," which he
placed close to his heterogeneous group " Mollusca," in a class
" Vermes."

Lamarck separated the parasitic worms, for which he retained
the term " Vermes," as a class distinct from the Chaetopodous
worms, to which he gave the name " Annelides." Lamarck's
"Vermes" is thus essentially synonymous with the "Entozoa'r
of various subsequent writers. And in spite of the fact that
as long ago as 1850 Grube1 pointed out the affinities of the
Annelids with the Arthropoda, and insisted upon the unnatural
character of " Vermes " as a group, and although Lankester 2 was
one of the earliest of the more recent zoologists to give up the
term " Vermes," and the truth of this view has become more and
more evident in recent years, yet many writers still retain this
name almost in the sense of Linnaeus. Leuckart3 in 1848 broke
up the " entozoic worms," and associated the Cestodes with the
Acanthocephala as " anenterous worms," which he separated from
the " apodous worms " (Turbellarians, Trematodes, and Leeches) ;
while the other parasitic forms (Nematodes) were recognised a&
distinct from these and placed with the Annelids. Later on,
however, he4 put the Cestodes in a more natural position, in a
group " Platodes," which included the Trematodes, Turbellaria,
Nemertines, and Leeches.

But Vogt5 had already recognised in 1851 the affinity of these
various worms and invented the term Platydmia for the group, in
the sense in which it is usually understood at the present time.
The name was modified by Gegenbaur6 to Platyelminthes, and
adopted by Carus, Schneider, Haeckel, and others ; Haeckel in
1877 removed the Xemertines from the Platyelminthes (to which
group, however, he gave the name " Acoelomi ") and placed them
with the rest of the " Vermes " as " Coelomati." Lankester 7
modified Vogt's terminology and still retained in his " Platyhelmia "
the Nemertina and Hirudinea. But recent researches on the
anatomy and development of the latter class, and amongst others,
Biirger's work on the Nemertines, have shown conclusively the
necessity of removing them from the neighbourhood of the Flukes,

1 Grube, Die Fam. d. Anneliden, Arch. f. Naturgesch. 16. 1850, p. 249.

2 Lankester, Notes on Embryology and Classification, 1877.

3 Leuckart, Ub. Morphol. u. Verwandsch. d. Wirbellose Thiere, 1848.

4 Leuckart, Arch.f. Naturgesch. Jahrg. 20. 1854.

6 Vogt, Zoolog. Briefe, 1851, vol. i. p. 185.

0 Gegeubaur, Die Grundzuge d. Zoologie, 1859.

7 Lankester, The Advancement of Science, 1890 ; and Encyd. Brit. ix. edit., art,
"Zoology."

THE PLATYHELMIA

Tapeworms, and Turbellarians, which alone are now included
amongst the Platyhelmia, together with the probably degenerate
forms known as " Mesozoa."

The Characters of the Platyhelmia. — The animals belonging to
the three classes — Turbellaria, Trematoda, and Cestoidea — -while
exhibiting many differences in form, habits, and life-history yet
present certain fundamental points of agreement, so that it is
possible to picture a common ancestor from which the three groups
have been descended. Such an ideal Platyhelmirith would have
had a somewhat oval body, flattened from above downwards, and
with a distinct prostomium or region in front of the mouth and con-
taining the brain (Fig. II.). The surface of the body was probably
clothed with a ciliated epidermis similar to that of the Turbellaria
but of a simpler character, so that the animal was able to move
freely in the sea ; in this movement it was aided by the muscular
system which had developed below the epidermis with which it had
lost its connection and become arranged to form circular and
longitudinal sheets. No doubt the ancestral form was more or
less closely connected with the Coelentera by means of animals
of which we know nothing. (There are some features of
resemblance to the Ctenophora, as Lang has pointed out.1) But
in the Platyhelminth the endoderm had become separated from
the ectoderm by a great development of mesodermal tissue filling
up the blastocoele, and consisting of vertically arranged muscle
cells and of a packing of peculiar connective tissue cells ; in this
compact mass of cells or parenchyma distinct generative and
excretory organs had become differentiated, having each its own
independent communication with the exterior. Nevertheless, no
definite space, or coelom, existed in the substance of this inter-
mediate mass of cells. The archenteron of the coelenterate
ancestor had, however, become separated into a metenteron and
a coelom, which is represented by the cavity of the genital organs.

The excretory system consisted of a pair of laterally placed
canals, consisting of a series of perforated cells, some of which carry
cilia ; from each canal small lateral branches are given off which
branch and anastomose to form a network from which arise still
liner twigs, each of which terminates in a "flame cell" (Fig. I). This
flame cell (or pronephridiostome of Vejdovsky) is a comparatively
large, hollow cell from whose base, in which the nucleus is situated,
a bunch of long cilia projects into the cavity ; the flickering appear-
ance of a flame results from the synchronised movement of the cilia.
The cavity of this terminal cell communicates only with the excre-
tory tubule. It is possible that in the earliest ancestors a number of
isolated cells became hollowed out, and ciliated like this flame cell,

1 This is discussed by Mr. Bourne in Part II. " The Ctenophora," pp. 16 et seq.

THE PLATYHELMIA

and that each became elongated and effected a communication
with the exterior, and it has even been suggested that such cells
are derived from unicellular epidermal glands which have gradu-
ally sunk into the parenchyma, retaining their communication
with the exterior (on the other hand, similar flame cells have been
noted amongst the intestinal epithelium). As these isolated cells
became more numerous, with the increase in the size of the animal
there would be, as in other analogous instances, a tendency to form
a common collecting canal which would then replace the numerous

FIG. I.— Diagram of the Structure of the Platyhelminth Excretory System.

1.— A portion of the system of canals, a, the main canal or duct, receiving numerous
secondary canals (b) ; c, flame cells or terminal cells of the capillary vessels ; d, nucleus in the
wall of the canals ; e, tuft of cilia or "flame," arising from the side of the canal, in the neigh-
bourhood of a nucleus.

2.— A flame cell (somewhat diagrammatic), a, nucleus ; b, excretory globules in the cyto-
plasm; c, the "flame"; d, protoplasmic processes of the cell which extend amongst the
parenchymal cells, and are possibly in connection therewith ; e, the canaliculated portion of the
cell which communicates with the neighbouring excretory tubules.

isolated apertures. Nevertheless, in many existing forms, such
scattered or regularly arranged, isolated apertures exist either in
the absence of, or in addition to, the collecting canal and its pore.

The metenteron was a simple sac, having a single opening to
the exterior, which served both for inception of food and ejection
of faeces. This mouth was probably somewhere between the
centre and the anterior end of the oval body, as it is in many of
the Turbellaria. The surface in which the mouth is situated is
the ventral surface (Fig. II.).

The nervous system, like the muscular, had separated from the
epidermis and had taken on a much more definite form than in the

THE PLATYHELMIA

5

Coelentera, for the greater number of nerve cells became aggre-
gated near that end of the body which is directed forwards during
movement to form a bilobed cerebral ganglion, lying near the dorsal
surface, anterior to the mouth, i.e. in the prostomium. From it a
network of nerve fibres spread in all directions ; but certain of
these strands of fibres became more important than others ; a pair
of ventral, a pair of lateral, a pair of dorsal, as well as anteriorly
directed nerves were thus distinguishable (Fig. II. 2, 4). But

FIG. II. — The Anatomy of an Ideal Platyhelminth.

1. — The alimentary and excretory systems, a, mouth ; 5, pharynx ; c, intestine ; d, main
excretory canals ; e, excretory pore ; /, flame cells.

2. — The nervous system, ventral view, b, cerebral ganglion ; c, ventral nerve tract ; d,
marginal or lateral nerve tract ; e, dorso-lateral tract ; /, medio-dorsal tract ; g, male genital
pore ; h, female pore.

3. — The reproductive system. 6, testis ; c, sperm duct ; d, penis ; e, prostate glands opening
into the lower part of the sperm duct ; /, antrum masculinum, in which the penis lies ; g, male
pore ; h, female pore ; i, ovary ; j, oviduct ; k, spermatheca or dilatation at the junction of the
two oviducts ; I, shell gland opening into this dilatation ; m, antrum femininum.

4. — A transverse section through the body, a, epidermis, below which is seen the layer
of circular muscles, represented by the continuous line ; below this, the layer of longitudinal
muscles, by a series of dots ; b, vertical, dorso-ventral muscles ; c, ventral nerve tract ; d,
marginal tract ; e, latevo-dorsal nerve tract ; /, medio-dorsal tract ; g, intestine ; h, parenchyma
(mesenchyme) ; i, testis ; j, ovary ; k, main excretory canal or duct.

the nerve cells still retain a scattered arrangement, remaining at
various points of the general plexus, and do not give rise to ganglia
other than the brain. Sense organs were probably represented by
patches of pigment in the near neighbourhood of the brain, and
of widely distributed sensory cells.

THE TURBELLARIA

All existing Platyhelmia, with a very few exceptions, are
hermaphrodite, and we are justified in attributing to the ancestor
a similar character. The male organs consisted of a pair of
tubular testes and of ducts, which unite posteriorly to form a
muscular copulatory organ capable of being protruded from a
median pore behind the mouth. Probably this penis was used
for perforating the soft body of another animal at any point, so
that special female receptive ducts were not at first necessary.1
The female system consisted of masses of germ cells, derived from
the wall of the archenteron ; but very early in the history of
this group definite tubular ovaries, the walls of which are pro-
duced into special oviducts, were developed, for the liberation
of the fertilised ova ; these ducts then united to form, a special
sac for the reception 'of the penis (bursa copulatrix), while other
parts of the duct became dilated to form a spermatheca (Fig. II. 3).

Of the descendants of this ideal ancestral Platyhelminth, some
have retained the ciliated epidermis and the free mode of life ;
while others have taken to a parasitic habit, and lose this ciliated
covering in the course of their developmental history, and are
covered by a " cuticle " in the adult stage ; in connection with their
parasitism special organs of fixation, suckers and booklets, are
developed in various parts of the body. The line of descent of the
free-living forms includes the Turbellaria and the Temnocepha-
loidea. The parasitic forms embrace two classes — the Trematoda
and Cestoidea ; in the former the alimentary tract of the ancestor
is retained, while in the latter it has been entirely lost, and no
trace of it is presented at any period of the developmental history.

CLASS I. TURBELLARIA (EHRB.).

Order 1. Rhabcbcoelida.

Sub-Order 1. Rhabdocoela.
Fam. ]. Macrostomidae.
„ 2. Microstomidae.
., 3. Prorhynchidae.
,, 4. Mesostomidae.
,, 5. Proboscidae.
„ 6. Vorticidae.
„ 7. Solenopharyngidae.
Sub-Order 2. Alloiocoela.

Fam. 1. Plagiostomidae.
• ,, 2. Monotidae.
,, 3. Bothrioplanidae.

1 Cf. Whitman, Journ. Morph. iv. 1891, p. 386.

THE TURBELLARIA

Sub-Order 3. Acoela.

Fam. 1. Proporidae.
„ 2. Aphanostomidae.

Order 2. Tricladida.

Fam. 1. Otoplanidae.

„ 2. Procerotidae.

,, 3. Bdelluridae.

, 4. Planariidae.

„ 5. Leimacopsidae.

,, 6. Geoplanidae.

,, 7. Bipaliidae.

,, 8. Cotyloplanidae.

„ 9. Rhynchodemidae.

Order 3. Polycladida.

Fam. 1. Planoceridae.
„ 2. Leptoplanidae.
„ 3. Polypostiidae.
„ 4. Cestoplanidae.
„ 5. Anonymidae.
„ 6. Pseudoceridae.
,, 7. Euryleptidae.
„ 8. Enantiidae.
„ 9. Prosthiostomidae.

„ 10. Diplopharyngeatidae.

The Turbellaria are Platyhelmia, with a ciliated epidermis, in
which the body is nearly always flattened, oval, or leaf- shaped.
In the epidermis special cells occur, which may give rise either to
mucus, or to granular rod-like bodies, or to definite "rhabdites,"
which are discharged from the body on irritation.

Historical. — The name " Planaria " was given by 0. F. Miiller
in 1776 to certain worms living in fresh and salt water, and
characterised by a leaf-like form, which had previously been
confused with a Fluke and a Tapeworm under Linnaeus's name
" Fasciola " ; later, Miiller's genus Planaria (which included some
Nemertines) was split up into numerous genera, and the genus
Planaria restricted to certain fresh-water forms ; but it has also
been employed by several authorities as the name of the class.
The name "Turbellaria" was invented by Ehrenberg in 1831 to
include not only " Planarians," but also the elongated Nemertine
worms, which, by means of cilia borne by the epidermis, produce
the well-known movement of small particles coming within their
reach, giving rise to the appearance of a whirlpool.

Cuvier (1817) was the first to separate his genus Nemertes
(representing the Nemertines) from Planaria, and formed the

8 THE TURBELLARIA

orders " Yers cavitaires " and " Yers parenchymateux " for the
two groups.

To Ehrenberg, too, we owe the first definite attempt to classify
the Turbellaria in the restricted sense; and, indeed, he laid the
foundation for all the later systems of the class. He formed
two orders — the " Dendrocoela " and " Rhabdocoela " in reference
to the character of the intestine.

The next step in classification was made in 1844 by Oersted,
who divided the Dendrocoela into two families — (1) marine forms,
with short, folded pharynx and very much branched intestine ;
for them he used the term " Cryptocoela " ; and (2) fresh-water
forms, with long, tubular pharynx and feebly branched caeca;
for which he retained Ehrenberg's term " Dendrocoela."

A fourth group was erected by Uljanin (1870) for gutless
forms like Convoluta, for which he suggested the term " Acoela,"
as opposed to the remainder of the Turbellaria, for which he pro-
posed the name "Coelata" (58).

Our present classification is due partly to v. Graff (22), who
made a third group in the Rhabdocoela, viz. the Alloiocoela ; and
partly to Lang (42), who suggested the terms Polyclada for
marine, and Triclada for fresh-water and terrestrial Dendrocoeles.

Dreparnaud (1803) may be referred to for his peculiar views
on the relationship of the Turbellaria ; he regarded them as inter-
mediate between the Mollusca and Annelida ; and Oersted held
a similar view, that the " Cryptocoela " (Polyclads) or " Planaria
molluscina " form a passage to the opisthobranch mollusca. Girard
and v. Jhering held somewhat similar views.

Amongst the more important additions to our knowledge of
fauna, as well as of general anatomy, the following authors deserve
mention: — 0. F. Miiller (1773-83), who gives recognisable figures
and diagnoses of the many new forms discovered by him ; 0.
Fabricius (1820-26), Duge's (1828-32), Ehrenberg (1831-36),
Oersted (1844), 0. Schmidt (54), and in more recent times,
Jensen (35). Moseley's (1874) valuable account of terrestrial
Triclads, v. Graffs extensive series of papers and his great mono-
graph on Rhabdocoelida, and Lang's valuable monograph on
the Polyclads, form together the best general account of the
group. For an account of British marine forms, see Gamble (18).

The anatomy of these worms was first seriously studied by
v. Baer in 1827, who dealt with fresh-water Triclads; he was
followed by Duges (15) for Rhabdocoels ; by Mertens (1833) for
Polyclads; while Quatrefages (1845) gives an excellent account,
with very good figures, of the anatomy of various Polyclads.
These zoologists may be said to have laid the foundation of
our knowledge of the anatomy of the Turbellaria, more especially
of the generative organs, which are of so much importance in

THE TURBELLARIA

classification. Coming to nearer times, the works of Moseley (47),
Bohmig (5), Ijima (34), and Yejdovsky (59) will always be con-
spicuous for the elaborate and detailed account of the structure
of various members of the group.

As is frequently the case, the study of the habits — the Bionomics
— of the group was begun early, and the observations of some of
the older authors still retain considerable value, especially those of
0. F. Miiller, Bosc (1801), Dalyell (1814-53), J. K." Johnson
(36), M. Faraday (16), on the subject of regeneration and asexual
reproduction of Ehabdocoels ; while F. Schulze (53) and C. Darwin
(11) give accounts of general physiology and habits respectively.

Classification of the TurMlaria. — The class is divided into three
orders, primarily distinguished by the form of the intestine, viz.—
Ehabdocoelida, Tricladida, and Polycladida.

ORDER 1. Rhabdocoelida, v. Graff.

Turbellaria, in which the intestine is a simple, unbranched sac,
which may have ill -denned lobes, or the cells of the intestinal wall
may, in degenerate forms, give rise to a syncytium which blocks up the
cavity. The female gonads are compact, and generally a pair of germaria
and vitellaria. (For an account of this order, see especially 22 and 59.)

SUB-ORDER 1. KHABDOCOELA, Ehrb. Ehabdocoelida, in which the
intestine is a simple, straight sac ; variable pharynx ; testes compact ;
female gonads variable ; usually without otolith.

A. Without accessory female copulatory organs. FAMILY 1. MAC-
ROSTOMIDAE. Ed. v. Ben. The female gonad is an ovary ; the female
pore in front of the male pore. Macrostoma, E. v. B. (Fig. III. 2) ;
M. Lemanus, Dupl., is lacustrine ; Omalostoma, E. v. B. ; Mecynostoma,
E. v. B. FAMILY 2. MICROSTOMIDAE, 0. Schm. A pair of ovaries present ;
asexual reproduction as well as sexual. Microstoma, 0. Schm. (sexes said to
be distinct) ; Stenostoma, 0. Schmidt ; both have ciliated pits (see 49) ;
Alaurina, Busch. FAMILY 3. PRORHYNCHIDAE, Diesing. The male pore
opens in common with the pharynx ; female pore ventral. The female
gonad is a single germ-vitellarium. Prorhynchus, M. Schm. (see v.
Kennel, 39), (Fig. III. 4, 5). B. With accessory female copulatory
organs. FAMILY 4. MESOSTOMIDAE, Duges. Germarium usually distinct
from the vitellarium ; pharynx rosulate. a. Monogonoporous. Promeso-
stoma, v. Gr., M.1; Proxenetes, Jensen (Fig. III. 3), M. ; Mesostoma,
Dug. (Fig. III. 6), F. ; M. JEhrenbergii is the subject of a monographic
account by Leuckart (44) ; Castmda, 0. Schm., F. ; Otomesostoma, v.
Gr., F. /3. Digonoporous. Byrsophlebs, Jensen, male pore anterior to
female ; germarium single, M. FAMILY 5. PROBOSCIDAE, Cams. The
anterior end of the body is modified to form a retractile, tactile organ or
proboscis. Germaria usually paired, and vitellaria distinct; pharynx
rosulate; very complicated penis; usually monogonoporous. Pseudo-

1 The letter " M " indicates that the genus is Marine and " F " Fluviatile,

io THE TURBELLARIA

rhynchus, v. Gr., M. ; Acrorhynchus,. v. Gr.; Macrorhynchus, v. Gr., M. ;
Gyrator, Ehrb. ( = Prostomum, Oerst.), two genital pores, the female being
anterior to the male ; G. linearis, Oerst., F. ; Hyporhynchus, v. Gr., M. ;
Schizorhynchus, Hallez (30). FAMILY 6. VORTICIDAE, v. Gr., mono-
gonoporous ; mouth usually near the anterior end ; accessory female
copulatory organ present; pharynx barrel-shaped. SUB-FAMILY 1.
EUVORTICINAE, v. Gr., with brain and pharynx well developed ; germarium
small ; free living. SchuUzia, v. Gr. ; Provortex, v. Gr. ; Vortex, Ehrb. ;
V. viridis, with chlorophyll, F. ; Opistoma, O. Schm. (see 59) ; Jensenia,
v. Gr. ; Derostoma, Oerst., vitellarium reticulate. SUB - FAMILY 2.
PARASITICA, v. Gr., pharynx and brain feebly developed ; germarium
large. Graffilla, v. Jher. (see 4), Fig. III. 1 ; and Anoplodium,
Schneider ; occur parasitic in Gastropoda, and the latter genus in
Holothurians ; Syndemii*, Silliman, parasitic in Echinids, is stated to
contain haemoglobin in its parenchyma ; Fecampia, Giard (20), parasitic
in decapod Crustacea, which it leaves when mature. FAMILY 7.
SOLEXOPHARYNGIDAE, v. Gr. Monogonoporous ; single germarium ;
mouth posterior ; pharynx long and tubular ; Solenopharynx, v. Gr.

SUB-ORDER 2. ALLOIOCOELA, v. Gr. Rhabdocoelida, in which the
intestine may have irregular caeca ; testes numerous (follicular) ; no
conspicuous chitinous copulatory organ. (For an account of this sub-
order see 5 and 59.)

FAMILY 1. PLAGIOSTOMIDAE. Without an otolith ; usually a single
genital pore ; pharynx variabilis. SUB-FAMILY 1. PLAGIOSTOMIXAE, v. Gr.
Mouth anterior ; pharynx directed forwards ; genital pore posterior ;
germaria and vitellaria. Plagiostoma, 0. Schm. ; Vorticeros, 0. Schm.
(Fig. III. 7). SUB-FAMILY 2. ALLOSTOMIXAE, Bohrn. Pharynx directed back-
wards ; mouth posterior. Allostoma, P. J. van Ben (Fig. III. 9) ; Entero-
stoma, Clap. SUB-FAMILY 3. CYLIXDROSTOMIXAE, v. Gr. A ciliated circular
groove; a common enteric and genital pore; a germ-vitellarium. Cylindro-
stoma, Oerst. (Fig. III. 8); Monoophorum, Bohmig. SUB-FAMILY 4.
ACMOSTOMINAE, v. Gr. Genital pore posterior. Acmostoma ; commensal
in Cyprina islandica. FAMILY 2. MONOTIDAE. With a single otolith ;
pharynx plicatus directed backwards ; paired germaria and vitellaria ;
digonoporous, M. Monotus, Dies. ; M. hirudo is parasitic ; Automolos,
v. Gr. FAMILY 3. BOTHRIOPLANIDAE, Vejd. Mouth post-central ; mono-
gonoporous ; pair of ciliated pits, F. Bothrioplana, Vejd. (59).

SUB-ORDER 3. ACOELA, Uljanin. Rhabdocoelida, in which the cavity
of the enteron is obliterated by the concrescence of its walls ; the mouth
leads through a simple pharynx directly into the digestive syncytiuni ;
otocyst present ; a pair of ovaries (see 6, 24, and 50).

FAMILY 1. PROPORIDAE. Monogonoporous. Proporus, v. Gr. ( =
Schizoprora, Schm.); HaploJiscus, Weldon (62, for recent account see 52) ;
Monoporus, v. Gr. ( = Proporus, Schm.) FAMILY 2. APHAXOSTOMIDAE,
with female pore separate from and in front of male pore, with sperma-
theca. Aphanostoma, Oerst. ; Convoluta, Oerst. ; Amphichoerus, v. Gr. ;
PolychoeniSi Mark.

THE TURBELLARIA

FIG. III.— Rhabdocoelida.

l.—Graffilla muricola, \. Jher., parasitic in certain marine molluscs, ventral view, a, mouth ;
b, three of the four lobes around the body — the ventral lobe overlaps the genital pore (un-
lettered) ; the penis, which opens through the same pore as the female ducts, is indicated by
the shaded circle ; c, the left uterus ; d, the intestine.

2. — Mcicrostoma hystrix, Oerst. (modified after v. Graff), as an example of a " digonoporous "
Rhabdocoel. Sensory hairs are scattered over the body ; and the peculiar fish-like tail carries
a number of adhesive papillae, a, streaks of rhabdite cells ; b, mouth, leading into the
pharynx, immediately in front of which is the brain, on which lies a pair of eye-spots ; c, the
intestine ; d, the female genital pore ; e, the male pore ; /, the penis, which consists of a
glandular mass and a curved chitinous spine (black in the figure).

3. — Proxenetes roscweus, v. Gr. (modified from v. Graff), as an example of the " mpnogono-
porous " condition, a, streaks of rhabdite cells ; l>, brain ; c, eye ; e, ovary, which is here a
"germ-vitellarium," in which the upper part of the organ gives rise to yolk cells, and the lower
part to egg cells, /; g, the genital atrium ; h, genital pore ; i, bursa seminalis or spermatheca,
here an evagination of the atrium, but functionally is part of the female system ; j, seminal
vesicle, containing spermatozoa ; it is a dilatation of the conjoined sperm ducts ; k, chitinous
tube around the penis ; the glandular part of which is indicated by the dotted area ; I, sperm
duct ; ?)i, testis ; n, mouth, leading into the rosulate pharynx.

4. — Prorhynchus fontinalis, Vejd. (after Ve.jdovsky). «, terminal mou£h ; 5, lateral, ciliated
pit ; c, the pharyngeal sac ; d, the long tubular pharynx in a condition of rest ; e, its aperture
the functional mouth ; /, intestine.

5. — The anterior end of the same Turbellarian, showing the pharynx in the course of eversion
{letters as before). The pharyngeal introvert is acrecbolic.

6. — Mesostoma lingua, O. Schin. -(after v. Gr.), external view, a, mouth, leading into the
pharynx ; &, the common genital pore. The two black dots in front of the mouth are the eyes.

7. — Outline of Vorticeros (after v. Gr.). a, tentacular prolongations of the body.

8. — Cyllndrostoma quadriocidatum, Jens. A median -longitudinal section (after Bohmig)
•exhibiting a common oro-genital pore ; and the independent, dorsally situated spermatheca.
a, cephalic glands ; 5, brain ; c, testis ; d, yolk-producing region of the germ-vitellarium ; e,
intestine ; /, pore of spermatheca ; g, spermatheca filled with spermatozoa ; li, penis ; 7t', its
.opening into the atrium ; i, opening of the female duct into the atrium ; j, genital atrium ;
}:, tubular pharynx, lying in its pharyngeal sac, dorsal to the genital atrium ; m, common
pharyngo-genital chamber; n, oro-genital pore. Specialised epidermal unicellular glands are
shown opening near this pore, and others into the base of the pharynx.

9. — Allostoma. a, ciliated band behind the head (cf. the ciliated pits of Prorhynchus), which
carries four eyes ; fc, the intestine ; c, germarium ; d, pharynx, in its pharyngeal sac ; e, penis,
which opens into a genital atrium, communicating with a common " pharyngo-genital chamber";
/, the "oro-genital pore."

12 ' THE TURBELLARIA

Further Remarks on the PJiabdocoelida. — The Rhabdocoelid Tur-
bellaria contain forms which approach more nearly than do any
other of the orders to the ancestral Platyhelminth. The anteriorly
placed mouth, the comparatively simple " sucking pharynx," lead-
ing into a simple, straight intestine ; the symmetrical condition of
the excretory organs ; the " compact gonads," and the frequent
occurrence of " ovaries " — without differentiation into germ-pro-
ducing and yolk-producing regions — all agree with a generalised
flatworm. Nevertheless, the nervous system in the Rhabdocoela
is much more highly differentiated than in the Polycladida. Of
the three sub-orders included in the Rhabdocoelida it is amongst
the Ehabdocoela that we find these simple conditions, e.g. amongst
the Macrostomidae ; for the Acoela, which von Graff places at the
base of the Turbellarian tree, present every evidence, anatomically
as well as embryologically, of degeneration. The Alloiocoela,
through Bothrwplana, lead onwards to the Tricladida. Whilst
the Polycladida are descended from the Rhabdocoela along another
line.

The Rhabdocoela are represented abundantly in fresh water,
and in the sea ; some few genera even are ectoparasitic ; the
Acoela are marine, as also are the Alloiocoela, with the exception
of Plagiostoma lemani in the deep water of Swiss lakes (Duplessis),
and fiothrioplana, which occurs in springs. In form they are flat
or cylindrical, but with flat ventral surface ; ovoid, with frequently
the posterior end pointed.

The epidermis in Rhabdocoelida as in the rest of the Turbellaria
consists of a single layer of ciliated cells (discovered by Fabricius),
which are usually columnar or cubical in shape (Fig. IV.). Belong-
ing to this layer, though in Rhabdocoelida usually sinking below
it, are gland cells of two chief kinds : (a) cells producing unformed
secretion or " mucus " ; these are specially developed, though not
exclusively, on the ventral surface ; and (b) cells producing
" formed secretion " ; the products of these cells are either —

(A) Finely granular, block-like masses, with uneven surface,
pseudorhabdites, v. Gr. (schleimstabchen, Lang), (IV. 2, c), especially
in the Alloiocoela ; (B) spindle-shaped, homogeneous, refringent
rods, with smooth surface, " rhabdites " (discovered in Rhabdo-
coeles by 0. Schmidt ; and in Polyclads by Qua tref ages), (IV. 7) ;
(C) or each cell may produce a capsule or cyst (sagittocyst), (IV.
8, 9), in which is contained a single spindle-shaped needle (these
are rare in Rhabdocoela) ; or finally (D), in rare instances nemato-
cysts (Leuckart, 1848), (IV. 10), (Microstoma and Stenostoma). The
occurrence of nematocysts, quite similar to those of Hydra, in
several Turbellaria, and in certain Nudibranch Molluscs seems
to indicate the very close relationship of these two groups with
the Coelenterata.

THE TURBELLARIA

It is by no means certain that the " rod cells " of the Turbellaria
are the direct descendants of cnidoblasts of the ordinary Coelen-
terate ; more likely is it that they have a close affinity with the

._.-- -

*" ~°

'

FIG. IV.— The Microscopic Structure of the Body Wall in Turbellaria.

1. — A Triclad (after Woodworth). a, epidermal cell; b, rhabdites or rods, formed in sub-
epidermal cells, and passing upwards between the ciliated cells ; c, a sub-epidermal bacilliparous
or rod cell. In many Triclads these cells do not sink below the epidermis ; d, basement mem-
brane ; e, circular muscles ; /, longitudinal muscles ; g, vertical muscles ; h, nucleus of
parenchymal syncytium ; i, lacunae in the parenchyma.

2. — A Polyclad (combined from Lang's h'gares). a, epidermis ; b, rhabdite cell ; c, "pseudo-
rhabdites " in an epidermal cell ; j, parenchymal syncytium ; I; the nucleus of a muscle cell
{or myoblast) ; I, gland cell ; o, oblique or diagonal umsclefe ; d, e, /, g, i, as before.

3. — The Polyclad Anonymus (after Lang), o, b, rhabdite cells ; another in the middle is in
the act of discharging a rhabdite ; c, "needles" (striated rods) in their parent cell ; n, nemato-
cyst in its parent cell ; this is the uppermost of a tract of cells containing other nematocysts,
needle cells, and a sagittocyst ; such a tract constituting a u-a/cnstrasse is rare amongst
Polyclads, but common enough amongst Rhabdocoels, where it is formed, however, usually,
of rhabdites only ; S, a sagittocyst ; /, outer, and /', inner layers of longitudinal muscles ; other
letters as before.

4. — A Rhabdocoel (combined from Vejdovsky, etc.). b, rhabdite cell, in its primitive
position, as occurs in some forms; c, sub-epidermal rhabdite cell, such as occurs in other
forms ; c', an epidermal cell, in which rhabdites are commencing to be formed ; j, branched,
•central parenchymal cell ; /, peripheral parenchymal cells ; i, intercellular lacunae ; other
letters as before.

5, 6, 7.— Three stages in the development of rhabdites in epidermal cells of the Polyclad
Thysanozoon (from Lang), n, nucleus of cell ; x, refringent globules of secretion which develop
into the rhabdites (r).

8. — A sagittocyst from the acoelous genus Convoluta (from v. Gr.). s, the sagitta.

9. — The same, discharging its sagitta.

10. — A nematocyst from the Rhabdocoelid Microstoma lineare (after v. Gr.). The thread is
everted, but the cyst itself remains embedded in its parent cell or " cnidoblast. "

adhesive cells of Ctenophora. But the existence of true nematocysts
in several species does not forbid us deriving the group from a
more generalised Coelenterate.

14 THE TURBELLARIA

It appears that when discharged, the first two structures swell
up, or contribute to form the slimy material with which the animal
invests itself on irritation. It is still uncertain what is the chief
function of the rhabdites ; whereas Max Schultze regarded them
as serving to increase the sensitiveness of the skin, others believe
they give a firmness to the body. It should be mentioned that a
considerable number of Rhabdocoela have no rhabdites ; and that
these are frequently commensal or parasitic, viz. species of Proxenetest
Grqffilla, Fecampia, Acmostoma ; and amongst non-parasitic forms,
Cylindrostoma, Plagiostoma, Prorhynchus.

Below the epidermis is a distinct basement membrane, into-
which the muscles are attached (IV. d in all figs.). In the Khab-
docoelida the musculature consists of an outer layer of circular
fibres and a deeper layer of longitudinal ones, between which in
larger forms is a layer of diagonal fibres. In addition, dorso-
ventral muscle cells traverse the parenchyma in a more or less
definite way ; they are only feebly developed in the Acoela. The
muscle cells are all smooth, and those running dorso-ventrally are
branched at each end.

The characteristic connective tissue of the Platyhelmia occu-
pying the space between the dermal muscles and the viscera is
termed "parenchyma" (or mesenchyma, Bohmig). This meso-
blastic tissue gradually fills the blastocoele of the embryo. In
the adult Rhabdocoelida it appears to consist of branched cells,,
which may be vacuolated, and so give rise to intracellular spaces
(Fig. IV. 4) ; the .processes of the cells unite with their neighbours
and enclose intercellular spaces or lacunae, which may communicate
with one another and so form a sort of rudimentary lymphatic or
vascular system ; this seems to be a fairer comparison than to
regard these spaces as coelomic ; the true nature of this tissue is,
however, by no means agreed upon by the various authorities ; and,
indeed, it appears to differ in the different orders of Turbellaria.
In this connection reference may be made to the peculiar con-
nective tissue of the Mollusca, in the interpretation of which
precisely similar antagonistic views have been held by various
authorities. In the lacunae is a fluid which is frequently coloured ;:
and in Syndesmis (Cuenot) and Derostoma it is said to contain haemo-
globin. The parenchymal cells themselves are frequently loaded
with pigment granules, giving colour to the animal. In some
Alloiocoela this parenchyma is almost entirely confined to the
marginal region of the body, -and may even form a definite layer
immediately within the longitudinal muscles (59). In many of
the Acoela this peripheral parenchyma differs from that occupying
the greater part of the body (central parenchyma) which is of
much looser character, but it again gradually becomes more com-
pact as the axis of the body is approached (see Bohmig, 6); and in

THE TURBELLARIA 15

such forms as Convoluta and Haplodiscus there is occupying the central
region a compact mass of nucleated protoplasm, in which cell out-
lines are not distinguishable (Fig. V. 7, 8). In this axial syncytium
the remnants of prey are found ; it is the " digesting parenchyma,"
or more properly, the syncytial hypoblast ; in Proporus and others
this digesting parenchyma is represented by separate amoeboid
cells, which extend throughout the central parenchyma • in this
latter case, the hypoblast cells which in the embryo surround a
true enteron, have wandered in all directions ; in the former case,
the cells have fused to form a more concentrated syncytium.

In Convoluta Schultzii, Cortex viridis, and a few other species,
chlorophyll bodies or (in G. paradoxa) yellow cells occur in the peri-
pheral parenchyma ; it has been shown experimentally that these
bodies behave like the chlorophyll bodies of green plants, and they
appear to be of considerable importance to the animal, which then
presents the " holophytic " mode of nutrition. How far these
bodies, which are similar to those occurring in Anthozoa, to which
Brandt has given the name Zoochlorella, are part and parcel of the
animal, or whether they are symbiotic algae is still a matter of
dispute. Haberlandt (28) finds that they are nucleated, but with-
out a cell wall (Fig. V. 3, 4, 5) ; that when isolated they cannot
form a cell wall, and soon die, and in fact are unable to lead an
independent existence. They appear to be algae, or flagellata
(similar to Chlamydomonas), but so adapted are they to a symbiotic
existence, that they now form a definite and inseparable part of
the tissues of the worm and function as assimilating organs, at
the same time providing, by their disintegration, food for the
Planarian (Geddes, 19).

The nervous system in the primitive Turbellarian was no
doubt similar to that which occurs in the Polycladida, viz. a net-
work of nerve fibres and cells which had already sunk below the
dermal muscles, arising from or converging to a definite group of
ganglion cells forming a "brain" near the anterior end of the
body. The nervous system as presented by the majority of
Rhabdocoela has lost its ancestral character of a network ; there is
a pair of well-developed cerebral ganglia near the anterior end of
the body, whence four pairs of nerves arise, of which one pair
lying along the ventral surface is especially stout : other nerves go
forwards. In tmTAlloiocoela a few transverse commissures may
occur between these nerves ; whilst in Acoela, in which a network
occurs (Fig. V. 1), the nervous system, apart from the brain,
presents a comparatively primitive condition. There may also
be a nerve plexus in the wall of the pharynx. The brain was
first correctly interpreted as such by Ehrenberg, 1836. It had
previously been regarded as the "heart," while Duges held the
nerves for " blood-vessels."

i6

THE TURBELLARIA

As sense organs, the Turbellaria present eyes which are simple,
epidermic, pigment spots in Acoela, and in a few other cases, but
they usually sink below the epidermis and lie in the parenchyma ;

8

i'

FIG. V.— Anatomy of the Acoela.

1. — The nervous system (modified after Bohmig). a, brain ; b, marginal (lateral) nerve ;
c, dorso-lateral nerve ; d, dorsal nerve ; e, ventral nerve. The nervous network of the dorsal
surface is represented on the left ; that of the ventral surface on the right, where the dorso-
lateral nerve (c') is cut short. /, otocyst ; g, ventral nerve commissure connecting the two
ganglionic masses («) of the brain.

2. — Longitudinal section through the anterior end of the body, a, brain ; g, ventral com-
missure ; /, otocyst ; h, frontal gland.

3 and 4. — Chlorophyll bodies of Convolute (after Haberlandt). a, protoplasm of the cell ;
iloropl
mgh a
of the cell are starch granules ; b, the nucleus.

6, its nucleus ; c, chloroplast or envelope of chlorophyll ; d, pyrenoid.

5.— Section through a chlorophyll body (after Haberlaudt). The black dots in the centre

6.— Otocyst. a, the wall formed of two cells ; Z>, one of the two nuclei ; c, the otolith cell
with its nucleus.

7. — Half a transverse section across Convoluta in the region of the mouth (after v. Graff).
a, epidermis ; b, muscular coat, consisting of outer circular, and inner longitudinal fibres ;
c, gland cells opening on to the surface ; d, peripheral parenchymal cells ; e, nucleus of deeper
parenchyma cells ; /, lacunae in the parenchyma ; g, dorso- ventral muscles with their nuclei ;
h, ovum, in the ovary, which is not marked off in any way from the surrounding parenchyma ;
. i, mouth opening directly into the central mass of parenchyma ; fc, ventral nerve tract ; I,
marginal nerve ; m, dorso-lateral nerve ; n, dorsal nerve. The chlorophyll bodies are omitted.

8.— Half of a transverse section of Haplodiseus (after Bohmig), to show the differentiation
of the parenchymal tissue into (d) peripheral syncytium, with round nuclei forming a layer
underlying the muscular coat ; e, intermediate or general mass of amoeboid and star-shaped
cells ; and fc, a digesting, central syncytium ; other letters as in 7.

they then have a definite and peculiar structure. An otocyst,
discovered in Monocelis by Erey and Leuckart, occurs in the
Acoela (Fig. V. 6), the Monotidae, and Mecynostoma. Ciliated pits

THE TURBELLARIA 17

{originally observed by 0. Schmidt), sense organs of peculiar char-
acter similar to those which exist in many Annelida, also occur in
Microstomidae, Plagiostomidae, and a few others (III. 4 ; VII. 5) ;
the pit rests upon a group of ganglion cells, which is directly or
indirectly connected with the brain; these may, perhaps, be the
precursors of the elaborate " cerebral organs " of the Nemertines.

Another character of the Nemertines, the " proboscis " (as
Leuckart first pointed out), is foreshadowed in the family Probos-
•cidae (VI. 1-7). In all Turbellaria the anterior end of the body is
specially provided with tactile hairs ; and in several genera this
region is capable of a slight invagination. In this family the
simplest stage is represented by Pseudorhynehus, in which the
anterior end of the body is deprived of cilia, somewhat prolonged
.and capable of freer movement than usual by the action of numer-
ous short muscles. In the remainder of the family this "snout"
is permanently withdrawn into a pouch, which usually lies at the
tip of the body, but may be subterminal and ventral (Hyporhynchus,
Fig. VI. 5); the snout or proboscis now consists of a mass of muscles,
.and is capable of protrusion, while withdrawal is performed by four
long retractor muscles. The " frontal organ " of Acoela was at one
time thought to be a similar sense organ; but v. Graff (24) has
shown that it is entirely glandular (Fig. V. 2), containing neither
muscle nor sense cells.

The sub-order Ehabdocoela possess an intestine which retains
much of the ancestral character; it is a straight and simple
•elongated sac (Fig. III. 2, 4). The intestine may be constricted
by the ripe gonads, and by the development of dorso-ventral
muscles to form incomplete " septa " ; this leads to a lobing such
a,s occurs in Alloiocoela (Fig. VIII.), which reaches its highest phase
in Bothrioplana, where the lobes become long and regularly placed ;
the large pharynx of this genus, placed posteriorly, indents, as it
were, the gut, which now passes on each side of it, and has quite
the appearance of that of a Triclad.

The mouth retains its primitive position near the anterior end
in a considerable number of forms, though it may occupy any
position on the ventral surface ; this mouth leads directly into the
digestive parenchyma (hypoblastic syncytium) in Acoela, though
frequently the epidermis is slightly invaginated, and the muscular
coats are here thicker (Fig. V. 7, 8). This is ontogenetically what
happens in the other groups in which a distinct pharynx is formed.
This pharynx has various shapes within the group of Turbellaria,
which have received various names (Fig. VI. 8-13); the two chief
varieties distinguished are : (a) Ph. bulbosus, in which the muscles
of the pharyngeal wall are surrounded by a distinct sheath, separat-
ing them off from the parenchyma. This type of pharynx, which
is used for sucking and cannot be protruded far, occurs in the

1 8

THE TURDELLARIA

majority of the Rhabdocoelida under some form or another, (b}
Ph. plicatus, in which the sheath is absent, is characteristically
developed in the other two orders ; it is really an acrecbolic intro-
vert and occurs under two forms, which perhaps represent two
stages in development. In the Polycladida the pharyngeal sac is
of considerable diameter, with its axis at right angles to that of
the intestine ; the pharynx has the form of a freely projecting
muscular fold arising from the circumference of the sac, than
which it is frequently larger, and is, therefore, much folded when

at rest ; when brought into use this muscular organ is protruded
through the mouth, and is then spread out so as to envelop the
prey (Fig. VI. 9, 12). In a few of the Polyclads the axis of the
pharyngeal sac shifts so as to lie nearly parallel to that of the
intestine instead of at right angles to it ; and the entrance to the
intestine is no longer directly over the oral aperture ; the muscular
fold now loses its irregular shape, and its base becoming smaller it
forms a muscular cylindrical tube ; this is the form of pharynx
characteristic of the Tricladida (Fig. VI. 10, 13). Glands, more
or less abundant, exist in or around the pharynx, pouring their

THE TURBELLARIA 19

secretion into its lumen. As to the structure of the intestine, it
is chiefly interesting from the fact that some of the epithelial cells
can thrust out pseudopodia and directly take in food particles.
We have thus a starting-point for that syncytial condition of the
hypoblast which occurs in the Acoela.

The excretory system or " water- vascular system" was first
identified by Ehrenberg ; while 0. Schmidt added greatly to our

FIG. VI. — Figs. 1 to 7 illustrate the Structure of the " Proboscis" of the Proboscidae.

1. — The anterior end of Pseudorhynchus bifidiis, v. Gr. a, the introversible non-ciliatt<l tip
of the body ; b, the isolated strands of longitudinal muscles which act as retractors of this
proboscis.

2, 3, and 6 refer to Macrorhynchus (after v. Graff). «, the non-ciliated epidermis of the
proboscis ; b, the ciliated epidermis of the body, represented in all three diagrams by the
vertically shaded region ; c, the muscular coat of the body wall, which at x splits into two
sheets, forming (d') a sub-epidermal or outer sheath of the proboscis, and (d) the inner sheath.
The former (d') can be withdrawn from the epidermis which appears to slide over it, as in
3 and 6. Between these two sheaths and inserted into them at each end are the intrinsic
muscles (c) of the proboscis ; /, the retractor muscles (which are omitted in Figs. 3 and (i). The
points marked x, y, z deserve attention. In 2, z marks the apex of the everted proboscis ;
x, the point at which the muscular sheaths (ddf) separate ; y a point about half-way along
the side of the proboscis. In 3, the apex z and the upper half of the proboscis have been
entirely withdrawn by the active contraction of the intrinsic muscles of the proboscis, so that
the point y now marks the lip of a cup. The outer sheath has been pulled away from the
epidermis between x and y. In 6, the proboscis is entirely retracted, the side as marked by
the point y having followed the apex, and lies half-way down the cup. This further process is
partly due to the retractor muscles. As the inrolling of the sides takes place, the outer
sheath (d') resumes its normal position against the epidermis, and the gap m is reduced.

4 and 7. — The proboscis of Schizorhynchus (after Hallez). 4. The anterior end of the worm,
the proboscis being at rest, a, the aperture of the proboscis sac on the ventral surface of
the body ; b, the proboscis, consisting of two halves, leaving a channel between them, into
which open the ducts of glands (c), the duct on the right side is supposed to be cut away ;
these glands are probably poisonous and represent the scattered, diffuse glands on the pro-
boscis of Macrorhynchus and others; d, retractor muscles. 7. The proboscis of Scltizorhynchus
everted (the surrounding parts are omitted), e, the muscular sheath ; /, intrinsic muscles.

5. — side view of the anterior end of Hyporhynchus (after v. Graff), a, the entrance to the
proboscis sac ; b, glandular part of proboscis ; c, intrinsic muscles surrounded by the sheath ;
d, mouth ; e, pharynx.

8-13 illustrate the chief varieties of pharynx in the Turbellaria. a, mouth ; b, pharynx ;
&', prepharynx, or pharyngeal sac ; c, intrinsic muscles ; d, entrance to intestine. 8. Diagram-
matic section across the middle of a Rhabdocoel. a, mouth leading into a " pharynx simplex "
whose muscles (c) are not separated from the parenchyma ; d, the intestine, the dorsal wall of
which, as well as dorsal body wall, is represented in this, but is omitted from the subsequent
diagrams.

11.— A "pharynx bulbosus," in which the muscles of the pharynx are cut off from the
parenchyma by the sheath (e) ; the pharyngeal sac is better developed. This type of pharynx
is very frequent in Rhabdocoela, and is universal amongst the Trematoda.

9 and 12. — The "pharynx plicatus" typically developed in the Polyclads consists essen-
tially of a circular, horizontal fold (b) of the musoular wall of the pharyngeal sac. The muscles
spread outwards to be inserted in the body wall and act as retractors of the fold. On eversion
(12) the folded membrane spreads outwards and envelops more or less of the prey ; the pharynx
is thus turned inside out.

10 and 13.— The tubular pharynx, typically developed in Triclads, but occurring elsewhere.
10 at rest, 13 protruded. It is essentially an acrecbolic introvert, which can elongate and con-
tract by the action of its intrinsic muscles, and is withdrawn into the pharyngeal sac by the
retractors ; in these diagrams there is no attempt to represent the complex arrangement of
muscular fibres in the substance of the pharynx itself.

knowledge of the general plan of the system. Typically, there are
in the Ehabdocoela two main canals, each with a pore posteriorly
(Fig. VII. 1), or they may unite to form a short common duct
before opening by a median pore ; and the fusion may go so far as
to give rise to a single median canal (Stenostomd). In Mesostoma
each lateral canal opens into the peripharyngeal sac by means of a
transverse canal, or (Prorhynchidae) the twro canals open anteriorly
by a median pore. The course of this set of tubules has recently

20

THE TURBELLARIA

been carefully worked out by Vejdovsky for Bothrioplana (Fig.
VII. 5) ; the flame cells are in two series, one dorsal and another
ventral. In the Acoela it is doubtful whether an excretory system

FIG. VII. — The Chief Plans of Arrangement of the Main Canals of the Excretory System in
Rhabdocoels (Figs. 1-4), after v. Graff; Alloiocoel (Fig. 5), after Vejdovsky; and Triclad
(Fig. 6), after Ijima.

1. — Derostoma presents the most primitive arrangement ; each of the paired excretory pores
(c) leads into a main canal or duct (a), whence capillaries (b) are given off, terminating in
flame cells. By the approximation of the ducts posteriorly, and subsequent fusion of their
hinder ends, the condition represented in 2, for Plagiostoma, arises, where the median posterior
pore leads into a short common duct. A further step results in the total fusion of the two
ducts along their whole extent, as in 3, Stenostoma, and a specialisation of the terminal part
of the common duct gives rise to a contractile bladder (d).

4.—Mesostoma. Here the two excretory pores have become involved in the invagination
which forms the pharyngeal sac (g), in which lies the pharynx (/).

5. — In Bothrioplana there are two median excretory pores, one anterior (a), and one near the
centre of the body (g), both on the ventral surface. The latter appears to have been derived
from the condition seen in Mesostoma, by the approximation and fusion of the transverse
excretory ducts. The main canals on either side have the normal condition, being recurved
at the anterior end, and the four canals so formed appear to have effected a secondary com-
munication with the exterior, a, anterior pore leading into a duct (fo) with contractile wall ;
dorsal canal (d) entering the dorsal or recurrent limb (e) of the main lateral canal, ventral branch
(v) enters the main canal (c), which is connected with a plexus of capillaries along its whole
extent, the right and left canals being connected at the posterior end of the body by the
plexus in. The lateral plexus gives off at intervals short branches (xx) which pass towards
the surface of the body ; but no pore has been detected. From this lateral network there
arise mesially a definite number of branches, each terminating in a flame cell (h), of which
five lie in front of, and four behind the pore (gr). A second series of flame cells (i), seven in
number, are carried by branches from the dorsal stem ; the latter terminates in a plexus (j)
above the pharynx, n, the brain ; p, p' , the two pairs of ciliated pits. (The two median
plexuses are represented too strongly.)

6. — Plan of a Triclad. a, main canal opening at d, d to the exterior ; there are four or
five pores not strictly symmetrical in arrangement. Each main canal gives rise to a branch
(e) which gives origin to a plexus (/) in the substance of the pharynx (accordingxto Chichkoff).
g is the eye.

THE TURBELLARIA 21

exists. Geddes (-19) described certain structures under the name
" pulsatellae," which Yves Delage (12) regards as isolated flame
cells ; but these have not been described by more recent observers.

The generative organs of the Turbellaria, as in all Platyhelmia,
are very complicated ; but they present more variations in detail
in the Rhabdocoelida than in the other orders, and a given plan
does not hold even within the same family. The male organs
consist of a pair l of testes, from each of which a sperm duct passes
backwards to open into a seminal vesicle, whence a duct perforates
a glandular and muscular organ or penis, which is frequently
armed with chitinous spines or a chitinous sheath, the character
of which is of generic and specific value. The penis opens into
an epiblastic sac known .as the "atrium genitale," if it is common
to the male and female organs, or the duct of each sex may have
its own " antrum " and external pore. We have either a monogono-
porous (Fig. III. 3) or a digonoporous condition in the Rhabdo-
coelida, and the female pore may lie in front of the male pore
(Fig. III. 2). The genital pore was first recognised as suc^ by
Johnson (36) in Planaria torva ; previously it had been regarded
as the anus. The penis, appears to be used as much in catching
prey as in copulation / and in Macrorhynchus helgolandicus, in which
a poison gland traverses the organ, it appears to be entirely used
for this purpose ; and no doubt the arrangement in Prorhynchus,
where the penis opens at the same pore as the pharynx, and is
armed with a perforated spine, has come about by the employment
of this organ in catching prey (32 and 39).

In' the sub-order Rhabdocoela the testis of each side retains
the ancestral condition of a " compact," tubular organ (Fig. VIII.) ;
but in the Alloiocoela and Acoela this single testis becomes con-
stricted (? by dorso-ventral muscles) into a number of " follicles,"
which lie near the anterior end of the animal, each follicle of which
ontogenetically is derived from a single cell. Despite the most care-
ful recent research, the sperm duct has not been traced up to each
one of these follicles, and it is uncertain how the spermatozoa pass
from them to the seminal vesicle. One of two methods has been
suggested : (a) that by the enlargement of the follicles they come
to open into one another, and so communicate ultimately with
the sperm duct ; or (b) they burst into the parenchymal lacunae,
and their contents thus gain the duct. In some cases (Acoela)
the duct is not even continuous wTith the seminal vesicle.

With regard to the female organs, there can be little doubt
but that in the primitive gonad egg cells were formed and supplied
with yolk by their neighbours ; such an organ or " ovary " occurs
in Acoela (Fig. VIII.) and in many Rhabdocoela as a single or

1 Haswell (32) states that in - Prorhynchus sp. the male organs are only on the
right side, and the female only on the left side, impaired in each case.

22

THE TURBELLARIA

paired structure. Later, one part of this gland came to give rise
to germ cells, whilst the rest of it gives rise to cells similar in
origin, but loaded with yolk spherules. When the egg cells are
laid they are surrounded by these yolk or vitelline cells, upon
which the young embryo will feed ; such a gland, forming the
two kinds of cells in different parts, is sometimes called a "£erm-
vitellarium " (Fig. III. 3). We find one or a pair of such organs

FIG. VIII.

Plans of structure of Rhabdocoelids (from v. Graff). Left -hand figure is an Acoelous,
the middle is a Rhabdocoelous, and the right-hand is an Allpiocoelous Turbellarian. be, bursa
copulatrix ; en, cerebral ganglion ; e, eye ; g, germarium ; i, enteron ; In, ventral nerve cord ;
TO, mouth ; ot, otocyst ; ov, ovary ; p, digesting parenchyma ; ph, pharynx ; rs, spermatheca ;
s, salivary gland ; t, testis ; u, uterus, containing an egg ; v, vitellarium ; vs, seminal vesicle ;
<J , chitinous penis ; <J ? , genital pore;

amongst the Rhabdocoelida. Further, this differentiation of
function may become so complete that the yolk-forming part
becomes entirely separated from the germ-forming region, so that
a "vitellarium" becomes distinguishable from a "germarium"
(Fig. VIII.) ; each organ has its own duct, which may or may not
join before entering the female antrum. This differentiation of
the " ovary " into two parts was first understood by 0. Schmidt.
Amongst the Rhabdocoelida we have instances of a pair of germaria

THE TURBELLARIA 23

(more rarely a single one) and a pair of vitellaria, usually compact,
but the latter may branch and anastomose to form an apparently
single reticulated organ, but the two ducts indicate its double
nature. The accessory female organs are no less varied (Fig.
VIII.). A spermatheca, either as a swelling on the common duct,
or finally as an outgrowth of the atrium, may be present. A
bursa copulatrix (or vagina) may exist or not ; but there is
usually a sac in the Rhabdocoela in which the cocoon is retained ;
this function is originally performed by the atrium, but in most
cases a diverticulum of this chamber, provided with glandular
walls, receives the name "uterus."

Reproduction. — Our knowledge of the development of the Rhab-
docoelida is very scanty ; in most genera each egg cell becomes
enclosed together with numerous yolk cells within a hard capsule,
which is secreted by special gland cells. Sometimes the egg is
only set free by the death of the parent. This capsule, which has
characteristic shapes, is attached to water plants. Segmentation
results in the formation of micromeres and macromeres ; gastrula-
tion is effected by epibole, and when the embryo has attained a
stage with a distinct gut and pharynx it devours the surrounding
yolk cells.1 It is important to note that the animal is at first
nearly spherical, and the mouth central ; but by differentiation in
growth the mouth becomes carried forwards or backwards as the
case may be.

In some forms (Mesostoma) the winter and summer eggs differ ;
the summer ones, having a thin shell, undergo development
in the parent's body, as is the case in the Crustacean Daphnia.
But perhaps the most interesting fact is that amongst the
Microstomidae a mode of asexual reproduction takes place during
summer, and the genital organs only mature in the autumn.
The fact that Turbellaria can reproduce in this way seems to
have been observed first by Dreparnaud (1803); but in 1822
J. E. Johnson made further observation on the matter, and M.
Faraday (16) carried out some interesting systematic experiments
on this subject; both these authors were greatly in advance
of their contemporaries in this matter. This asexual process
resembles, in the main, that which occurs amongst the Naids
(Oligochaeta) and Syllids (Polychaeta), in that, after attaining
a certain size, the animal becomes partly constricted ; an active
production of cells takes place at the anterior end of this
young zooid, by which a new brain and a new pharynx are
formed. After this process has gone a certain length, a new
constriction and new budding take place near the end of each of
the two zooids ; in this way is formed a chain of four, eight, or

1 In the acoelous Polychoerus there is no trace of an enteron (see Gardiner, Journ.
Morph. xi. 1895, p. 155)..

THE TURBELLAR1A

sixteen
another

zooids (Fig. IX.), which will , ultimately separate from one
and proceed to live an independent life, reproducing in
the same way till some change in temperature or
food supply intervenes; then the genital organs
appear, and sexual reproduction takes place (see
61, 60, and 38) It is generally stated thatlftcro-
stoma differs from other Turbellaria in being
unisexual, but such is not the case ; it is a
protandrous hermaphrodite.

FIG. IX.

ORDER 2. Tricladida.

Turbellaria, in which the intestine consists of three
main branches : one median anteriorly directed, and a
pair of posteriorly directed lobes, each of which gives
off a series of caeca. The mouth is post- central ; the-
pharynx tubular ; there is a single genital pore common
to the two sexes (monogonoporous). For an account of
the anatomy see 7, 34, and 41.

There are nine families, which Hallez (31) arranges
in three tribes : —

TRIBE 1. MARICOLA. Marine Triclads, with in-
testinal caeca only slightly branched ; body depressed ;
uterus usually behind the genital pore.

FIG. IX.

Microstoma lineare, Oerst., undergoing division (from v. Graff). The
individual has first divided into two, near its middle, and each of these has
again divided. Each of the four zooids has again divided into two, and so-
on, till sixteen individuals are here marked out. TO, mouth of original
animal ; m', mouth of the hinder of the two individuals into which it-
divided ; in", the two mouths of the third generation ; m'", the four
mouths of the fourth generation ; the eight individuals of the fifth
generation have not yet acquired mouths, c, ciliated pits ; e, eye-spots ;
i, intestine.

FAMILY 1. OTOPLANIDAE, with a pair of ciliated pits and a median
otocyst. Otoplana, du Plessis. FAMILY 2. PROCEROTIDAE, with otocystr
but no ciliated pits. Cercyra, Schm. ; Fovia, Stimpson ; Gunda, 0.
Schm. (see Lang, 41) : Uteriporus, Bergendal ; Micropharynx, Jagersk.r
011 Earn batis. FAMILY 3. BDELLURIDAE, with a caudal fixing apparatusr
developed in relation to their parasitic habits. There are no rhabdites ;
two independent uteri or spermathecae, each with an independent pore,
Bdellura, Leidy ; Syncoelidium, Wheeler ; both occur fixed to gill hooks
of Limulus, on which they deposit their egg capsules (see 63).

TRIBE 2. PALUDICOLA. Fluviatile forms, in which the intestinal caeca
are usually much branched ; the uterus lies between pharynx and penis.

FAMILY 4. PLANARIIDAE. Planaria, 0. F. M. ; Dendrocoelum, Oerst. ;
Euplanaria, Hesse ; Dicotylus,-Griibe (27), (Fig. X. 5) ; Anocelis, Stimps. ;
Oligocelis, Stimps. ; Polycelis, Hemp, and Clap. ; Phagocata, Leidy (Fig,
XI. 2, see 65).

TRIBE 3. TERRICOLA. Terrestrial forms, in which the intestinal caeca
are merely lobed ; mouth variable in position; form of body variable ;

THE TURBELLARIA

uterus rudimentary; ventral body musculature well developed (see 13,.
26, 47).

FAMILY 5. LEIMACOPSIDAE. Dorsal surface very convex ; mouth pre-
central. Leimacopsis, Dies. FAMILY 6. GEOPLANIDAE, v. Gr. Land
Planarians without tentacles or suckers ; eyeless, or with many marginal
eyes. Geoplana, Stimpson (Fig. X. 3) ; Pelmatoplana, v. Gr. ; Choerado-
plana,, v. Gr. ; Polycladus, Blanch. ; Artio-
posthia, v. Gr. ; Geobia, Dies. FAMILY 7.
BIPALIIDAE. Anterior end is broadened out
to form a semicircular cephalic plate ; mar-
ginal eyes. Bipalium, Stimpson (Fig. X. 1) ;
Perocephalm, v. Gr. ; Placocephalus, v. Gr. ;
P. Jcewensis, Moseley. FAMILY 8. COTYLO-
PLANIDAE, v. Gr., with sucker on ventral
surface anteriorly, and with two spherical
eyes. Cotyloplana, Spencer (57, Fig. X. 4) ;
Artiocotylus, v. Gr. FAMILY 9. RHYXCHO-
DEMIDAE, v. Gr., with two spherical eyes
anteriorly. Platydemus, v. Gr. ; Dolicho-
plana, Mos. ; Rhynchodemus, Leidy ; Micro-
plana, Vejd. ; Amblyplana, v. Gr. ; Nema-
todemus, v. Gr. ; Othelosoma, Gray.

Further Remarks upon the Tridadida.
— The distribution of these forms on
land, sea and fresh water, is of great
interest, though it remains to be seen
how far Hallez's classification on this
basis is justified.

In general form they are flat and
leaf-like, though the terrestrial species
are usually elongated, some attain-
ing a length of nine or even fourteen -

in^ViPa "FWnecnp 1&4.1 srmpare to l.—fiipalium ceres, Moseley, show-

HlGlieb. reiUbbdt, 1O-±1, appeal b to ing tne characteristic head of the

have been the first to describe a land family, and the longitudinal colour-

-T... *»•!«• markings so common m terrestrial

rlananan trom Brazil. bmce that

time they have been found in nearly

all parts of the world (by Moseley, Dar- ^^oi^ceu!118^1*13*116™1

win, Dendy, etc.). The Triciads are 3.— Side view of the anterior «nd

, , rr-n . , . of G. Spcnceri, Dendy, showing nu-

CarniVOl'OUS and nocturnal. 1 heir dlS- merous eye-spots («) and the row of

tfibution seems to indicate that they C1 l^^^yiop&a whiteiega, Spencer;
are ancient forms ; nevertheless, they
have in many respects lost their primi- s'—ixcotyius putmnar,
tive characters, and present a greater
degree of complexity-' and differentia-
tion than do the Rhabdocoelida. The
majority are longer and narrower than in other orders ; the anterior
end is frequently eared (Planaria), or with tentacles (Leimacopsis),

26 THE TURBELLARIA

or extended to form a crescentic or hammer-shaped plate (Eipalium),
and may even bear suckers (Dicotylus, Cotyloplana).

The rod cells sink into the parenchyma, and are connected with
the epidermis by "rod tracts " (Fig. IV. 1). Peculiar Y-shaped
rods have been recorded in Placocephalus (Shipley). In a few
genera rhabdites are absent (Bdelluridae).

The parenchyma appears similar to that in Rhabdocoela.

The post- central position of the mouth, combined with the
great size of the tubular pharynx, appears to have led to the
modification of the originally central gut, so as to form three
lobes — one anterior lying above the brain and a posterior pair,
which lie at the sides of the pharyngeal pouch, and usually ex-
tend nearly to the hinder end of the body (Figs. XI., XII.) ; they
not unfrequently unite posteriorly (cf. Botlirioplami). The lateral
caeca may branch in the lower forms, but in the Terricola and
Maricola become larger and more regular in their arrangement ;
but they do not appear to be so strictly metameric with nerves and
gonads, as Lang (41) believed for Gunda segmentata and terrestrial
forms (Wheeler and Dendy).

The nervous system retains to a greater extent than in the
Rhabdocoelida a primitive condition, in that the brain gives
origin to a number of nerve strands, which form a subdermal
network all over the body; but a ventral pair of longitudinal
nerves are much more prominent than the others, arid connected
by transverse commissures in a fairly regular way, especially
in Gunda segmentata. But ganglion cells remain at the origin
•of the nerves and transverse commissures. The sense organs
may be (a) ciliated pits at the side of the head, receiving
nerves from the brain ; these are especially well developed, and
abundant in Bipalium and Geoplana, where they lie in a lateral
groove (Fig. X. 3) ; the former genus too has retractile papillae
round the margin of the head (Moseley). (b) Eyes are either
confined to the anterior end, or in many land Planarians along
the entire margin. Dendy has suggested that the unicellular eyes
(Fig. X. 2) of Geoplana, etc., are derived from modified rod cells ;
multicellular eyes occur in other terrestrial genera.

The excretory system (Fig. VII. 6) presents two laterally placed
main canals which give off numerous special branches, opening
dorsally on to the external surface. In Gunda there are two main
lateral canals on each side connected by short canals, and the
external pores exhibit the same repetition noticeable in other
systems of organs. The main trunks are sparsely ciliated. Lang
discovered in Gunda certain vacuolated cells with flames amongst
the intestinal epithelial cells, and therefore suggests that the flame
•cells generally have a hypoblastic origin. It is only within recent
years that the excretory system of Triclada has been described

-£

— c

FIG. XL

1. — Diagram of the anatomy of an elongated Triclad, Rhynchodermts (after Moseley), in
-order to show the repetition of gonads and the simple character and the almost symmetrical
.arrangement of the intestinal diverticula with which the genital organs alternate (which are
represented too symmetrical), a, group of eyes ; b, germ-producing follicle of the ovary ; c,
oviduct which receives duQtules from the yolk-forming follicles (rf) when these are ripe ; e,
testes ; /, sperm duct ; g, seminal vesicle into which the two sperm ducts open ; Ji, penis lying
in the antrura masculinum (i) ; j, common genital pore ; t, antrum femininum, into which the
two oviducts (germ-vitellarian ducts) open ; I, pharyngeal sac; m, mouth; n, pharynx; p,
Anterior of the three limbs of the intestine ; gr, right and left posteriorly directed limbs of the
intestine ; oo, simple, unbranched intestinal caeca, characteristic of the Terricola.

2.— Diagram of the alimentary system of Phagocata gracilis, Leidy (after Woochvorth).
.«, eye ; b, principal (normal) pharynx ; cc, several accessory pharynges lying in the large
pharyngeal sac (1), and each receiving a branch from the posterior limb (</?*) of the intestine ;
m, n, o, p, q, r, as in Fig. 1.

28

THE TURBELLARIA

(Lang, Francotte (17), and Chichkoff (7)), and the external pores

are known even now in only a few cases.

The male generative organs present further advance on that

follicular arrangement which is
just commencing in Alloiocoela.
In the female organs the differen-
tiation into germ -producing and
yolk'-producing organs, of which
every stage is presented by the
Khabdocoelida, has in the Tri-
cladida only reached half-way. In
fact, we have a branched "germ-
vitellarium," of which the most
4n anterior lobe or follicle produces
small egg cells, whilst the remain-
ing follicles give rise only to yolk
cells • but all these follicles open
into a common " oviduct " (Fig.
XII.). This organ thus differs
from the "germ-vitellarium " of
Rhabdocoelida, merely by being
" follicular " instead of " compact.'7
The two oviducts unite to form
a shorter or longer common duct,
into which numerous unicellular,
albuminiparous glands pour their
secretion. This region may be
muscular, and is termed " vagina.'7
In its turn it opens into the
atrium genitale, which is common
to both sexes. The "uterus"
(Fig. XIII.), probably originally a
dilatation of the lower part of the
. oviduct' becomes a diverticulum of

g, germ-producing follicle of the ovary; tj, the Vagina (XIII. 1), (GuncUt. Plan-
anterior branch ; i%, i^, the right and left . -ff, 7 7 rf 7 j?\ / e , i

posterior branches of the intestine; In, ven- ana, EhynckodemuS Scharfi), (cf. the

FIG. XII.

common genital pore.

i™/'; accessory sac of Polyclads) ; or it

i Ty Tn, incto,the atrium in-

dependently of the oviduct, as in
various species of Planaria and

Polycelis (XIII. 2) ; the process is carried further in Uteripoms,
where the organ opens outside the area of the atrium, and in the
parasitic Bdelluridae we find the same condition, but the uterus
is paired (XIII. 4).

In addition to the normal male and female copulatory organs
the genus Artioposthia possesses elaborate accessory copulatory

THE TURBELLARIA

29

organs, outgrowths of the atrial walls known as " adenodactyli "
or " adenocheiri," according to their shape.

The function of the uterus (see Bergendal) appears to vary ;
in some cases spermatozoa are found in it (it is a spermatheca,
Bdelluridae) ; in others, eggs have their cocoon deposited around
them ; in others, again, the cocoon is moulded in the atrium, or
even in the vagina (some land Planarians), but the uterus secretes
the substance which will harden to form the shell.

Development. — From four to twenty or even more egg cells
.are surrounded by several hundred amoeboid (v. Siebold, 1841)
yolk cells in each cocoon. Each egg cell undergoes development,

a---

FIG. XIII.— Plans of the Genital Atrium in Aquatic Triclads to illustrate the various
Relations of the Uterus.

1. — Gunda; the uterus is here a diverticulum of the egg duct, a, sperm duct; &, penis,
with ductus ejaculatorius ; c, atrium genitale ; c', antrum masculinum ; c", antrum femininum ;
d, atrial (genital) pore ; e, egg duct, with muscles around it, and frequently functioning as a
vagina ; the distal region receives gland cells, which appear to secrete the cocoon ; /, oviduct ;
{/, uterus ; h, its opening into the atrium, or to the exterior.

2. — In Planar ia, Polycdis, and many others the uterus opens into the atrium directly.

3. — In Uteriporus the uterus opens to the exterior by an independent pore at the side of
the genital pore.

4.—Syncoelidiuni presents a pair of independent uteri (</', g"\ each opening to the exterior.

but, as in some Gastropod Molluscs and Oligochaeta, they do not
.all survive.

The Triclads present a very peculiar phenomenon during
segmentation, in that the blastomeres resulting from the nearly
regular segmentation move apart from one another (Metschnikoff,
Ijima, and Hallez, 29), and lie in a fluid which appears to
result from this breaking down or fusion of the yolk cells (Fig.
XIV. 2, 3).

The exact details of the formation of the layers are imperfectly
known ; but the blastomeres become differentiated into flat epiblast
cells which surround and enclose the yolk material (Fig. XIV. 4) ;
into hypoblast cells which are arranged in two groups, while the
blastocoele is occupied by wandering cells, mesoblastic in appear-
ance, some of which give rise to additional epiblast, others to the
brain, and others apparently to additional hypoblast cells ; the
pharynx, which is at first "simple," is employed for engulfing

THE TURBELLARIA

yolk cells, and the embryo now becomes greatly swollen ; this
pharynx is, however, temporary, and disappears along with the
mouth. This, perhaps, is the remnant of some larval stage, for
the embryo is ciliated and moves within the cocoon. Later, a

FIG. XIV. — The Development of Planaria lactca. (After Hallez's figures and
description.)

1. — The egg cell (o) surrounded by some amoeboid vitelline cells (v).

2. — Segmentation ; stage with four blastomeres ; the vitelline cells are losing their
independence, and are forming a syncytium, represented by the small circles (y), in which
the blastomeres are embedded ; the blastomeres (bl) become completely separated from one
another ; n, nuclei of yolk syncytium.

3. — Later stage in segmentation ; one of the blastomeres is represented in division.

4. — A much later stage, showing the differentiation of the blastomeres into (ep) epiblast,
which comes to surround the yolk syncytium ; w, wandering cells moving in the syncytium ;
hy, a group of four hypoblast cells, destined to further subdivide and give rise to the wall of
the enteron ; and (ph) the provisional pharynx which marks the anterior end of the embryo.
A few vitelline cells still remain around the embryo.

5.— The cell differentiation has gone further and the epiblast (ep) completely surrounds tha
yolk syncytium (which in this figure is left plain). The four cells of the hypoblast (/< y) have
further subdivided, and now surround the enteron (ent). The pharyngeal cells have also
undergone similar changes, and enclose a cavity communicating with the exterior ; some
vitelline cells (v) have been taken through the mouth into the enteron, and are represented
by dotted circles (V) ; some of the wandering cells («/) have placed themselves round the
pharynx to form its outer layer, and no doubt give rise to its muscles.

6. — The embryo at a later stage changes its shape from a sphere to a flattened ovoid ; the-
definitive pharynx is being formed from the mass of cells, and the mouth is about to form by
the rupture of the lower boundary of the pharyngeal cavity. From the migratory cells (w) will
be formed the parenchymal tissue and generative organs.

new mouth and a new pharynx, said to be hypoblastic in origin,
replaces the temporary one. The enteron is at first rhabdocoelous,
the various caeca resulting from ingrowths of connective tissue
septa. Some species of Planaria multiply by fission, preceded in
some cases (P. albissima) by the formation of a new head.

THE TURBELLARIA 31

ORDER 3. Polycladida, Lang ( = Cryptocoela, Oerst).

Marine Turbellaria, in which the pharynx leads into a central enterori
which is produced laterally into a number of caeca that may branch and
extend nearly to the margin of the body. Typically this group is
digonoporous.

The families may be arranged in two sections according to the presence
or absence of a ventral sucker (for anatomy, etc., see Lang, 42).

SECTION A. Acotylea. Polycladida, without a sucker; with the mouth
central or post-central ; the genital pores being therefore near the hinder
end of the body. If tentacles are present, they are on the dorsal surface,
above the brain.

FAMILY 1. PLAXOCERIDAE, Lang, with tentacles, central mouth, small
stomach ; penis directed backwards. Planocera, Blv. (Fig. XV. 1),
several species are pelagic (v. Gr.) ; P. inquilina, Wh., inhabits the
branchial chamber of the mollusc, Sijcotypus canaliculatus (64) ; Conoceros,
Lang ; Planknoplana, v. Gr. ; Stylochus, Ehrb. ; Stylochoplana, Stimp. ;,
Alloioplana, Plehn. ; Plagioplana, Plehn. FAMILY 2. LEPTOPLAXIDAE,
Stimpson, without tentacles ; intestinal caeca numerous. Discocoelisr
Ehrb., male and female organs open by a common pore ; Cryptocoelis,
Lang ; Leptoplana, Ehrb. (Fig. XV. 2, 3) ; Trigonoporus, Lang ; Acelis,
Plehn. ; Semonia, Plehn. ; Polyporus, Plehn. FAMILY 3. POLYPOSTIIDAE,
Bergendal (3), with several male copulatory organs. Cryptocoelidts, Berg. ;
Polypostia, Berg. FAMILY 4. CESTOPLAXIDAE, Lang, elongate, without
tentacles ; copulatory apparatus directed forwards ; Cestoplana, Lang ;
LatocestuSj Plehn.

SECTION B. Cotylea. Polycladida, in which a sucker is developed
behind the genital pores ; mouth central or pre-central ; genital pores just
behind it. If tentacles are present, they are developed from the margin
of the body.

FAMILY 5. ANOXYJIIDAE, Lang, with numerous penes arranged in a
row along each side, but with only one female pore ; mouth central ;
Anonymus, Lang (Fig. XV. 9). FAMILY 6. PSEUDOCERIDAE, Lang,
tentacles in the form of folds of the anterior margin of the body ; mouth
pre-central. Thysanozoon, Grube (Fig. XVI.) ; Pseudoceros, Lang ; Yungia,
Lang ; Thysanoplana, Plehn. FAMILY 7. EURYLEPTIDAE, Lang, mouth
pre-central ; pharynx tubular, directed forwards. Prostheceraeus, Schmarda ;.
Cycloporus, Lang ; one species is commensal with Polyelinid Ascidians ;
Eurylepta, Ehrb. ; Oligodadus, Lang ; Stylostomum, Lang ; Aceros, Lang ;
Amlhjceraeus, Plehn. FAMILY 8. EXANTIIDAE, v. Graff. Enantia, v. Gr.
(23), agrees in nearly all essential features with the Cotylea, but is without
a sucker (Fig. XV. 4, 5). FAMILY 9. PROSTHIOSTOMIDAE, Lang, body
narrow, elongated ; mouth far forwards ; tubular pharynx. Prosthiostomnm,
Quatref. (Fig. XV. 8). FAMILY 10. DIPLOPHARYXGEATIDAE, Plehn. Diplo-
pharynx, Plehn.

Further Piemarks on the Polycladida. — The Polyclads are
entirely marine ; some attain a considerable size, viz. six inches
or more; they are flat, more or less ovoid or leaf -shaped,

THE TURBELLARIA

or more rarely elongated. They are frequently very brightly
coloured.

Lang regards members of this group as representing more

FIG. XV.— A Group of Polyclads. (All after Lang, but 4 and 5.)

1. — Planocera graffi, Lang ; one of the Acotylea, with dorsal tentacles, and eyes at their base.

2. — Leptoplana pallida, Lang ; an Acotylean without tentacles, with a group of eye-spots
above the brain.

3. — Leptoplana; ventral view, a, the nearly central mouth; b, the pharyngeal sac; c, the
pharynx folded in the sac ; <$ , male pore ; ? , female pore.

4. — Enantia spinifem, v. Gr. ; a peculiar Polyclad, bearing chitinous spines round the
margin of the body (after v. Graff), a, mouth; ^, antrum masculinum, receiving the right
and left sperm ducts, and opening to the exterior by the male pore ; ? , antrum femininum,
receiving the uterine duct, into which open the two uteri (c) ; it is continued backwards to form
an "accessory sac" (cZ) or bursa copulatrix ; e, the chitinous spines.

5. — A section through a spine of Enantia. a, ciliated epidermis ; b, epidermal syncytium
which secretes the great basal plate of the spine, which consists of solid columns of " chitinoid
substance " ; d, a projection of the epidermis consisting of a single cell which secretes the
denser part of the spine or hook ; e, the denser part of the spine.

6. — Leptoplana; section through an eye. a, pigmented cup; b, nucleus of pigment cell;
•c, rods, the modified ends of nerve cells ; d, the nerve cells, which are prolonged into nerve
fibres ; e, the optic nerve.

7. — Cydoporus papillosiis, Lang; horizontal section through the margin of the body, a,
a caecum giving off a couple of branches (b) which pass outwards to the epidermis ; here
each branch communicates by means of a perforated epidermal cell (c) with the exterior ; d,
a marginal pore. The intestinal epithelial cells are indicated only by means of the nuclei,
as dots ; /, the parenchyma ; g, groups of circular muscle fibres which constrict the caeca at
intervals and give rise to the moniliform appearance of these, so usual amongst the Polyclads.

8. — Prosthiostomum Dohrnii, Lang, a, the large everted pharynx, which is exceptional
in being tubular, issuing from the anteriorly situated mouth.

9. — Plan of the male organs of Anonymus virilis, Lang, a, marginal eyes, extending all round
the body ; bb, the numerous pear-shaped penes and seminal vesicles arranged in two lateral
rows ; the small male pore corresponding to each penis is indicated at <J at the point of the
penis ; the sperm duct (c) forms a ladder-like network, and communicates with each seminal
vesicle, m, mouth ; s, sucker ; ? , female pore receiving the uterus, right and left.

THE TURBELLARIA 33

nearly than any other the ancestor of the Turbellaria, and traces
the phylogeny of the Polyclads to the Ctenophora.1

In Lang's opinion all the constituent cells of the epidermis are
embedded in a nucleated interstitial tissue deprived of cell outlines.
,The rod cells retain their primitive position in the epidermis
(Fig. IV. 2), although in Anonymns rhabdites and sagittocysts are
grouped to form " batteries " on the dorsal surface, which project
downwards into the parenchyma (Fig. IV. 3) ; in this form and
in Stylochoplana tarda true nematocysts with coiled threads occur.

The chitinous spines of Enantia and Acanthozoon (8) are
specially worthy of mention. In the former they are marginal ;
in the latter on the dorsal surface. They suggest the chaetae
of Oligochaeta on the one hand, and the cuticle of Trematodes
on the other. Von Graff shows that each spine of Enantia (Fig.
XV. 5) commences as a cuticular secretion from a number of
epidermal cells raised up as a papilla ; around this spine, which
is hollow and golden -coloured, there are developed brownish
columns of chitin (?), each column being the product of a
single cell ; the whole group forms a broad base to the spine,,
causing it to resemble the prickle of a rose tree.

In accordance with the greater size of the Polycladida, the
dermal musculature becomes more complex, there being as many
as six layers of alternating circular, diagonal, and longitudinal
muscles, variously arranged ; these, as in other forms, are more
strongly developed on the ventral surface.

The parenchyma in Polycladida appears to differ from that v of
Rhabdocoela, in that the lacunae are intracellular, according to
Lang, who has traced their development.

The mouth and pharynx may either retain the anterior
position of the ancestral Platyhelminth, or by differential growth
be thrust backwards to a central position, which is the more usual
condition in the Polyclad • whilst in others it comes to lie near
the hinder end of the body. The pharyngeal sac is spacious and
the pharynx is almost universally a more or less folded, horizontal,
circular sheet of muscle, which arises from the circumference
of the sac (Fig. VI. 9, 12); only in the Euryleptidae and
Prosthiostomidae does it take on the form of a tubular pharynx
like that in Tricladida (Fig. XV. 8). The primitively simple
enteron which makes its appearance ontogenetically, becomes
at an early stage notched by the ingrowth of connective tissue
and dorso-ventral muscles, so that a greater or less number of
"caeca" are formed, and the varying extent to which this nipping
takes place leads to the persistence of a larger or smaller central

1 See Willey, Q. J. Mic. Sci. xl., who places Ileteroplana n.g. in a new order
Archiplanoidea, formed for the reception of Ctenoplana and Coeloplana. See Part II.
of this work, "The Ctenophora," p. 16.

3

34

THE TURBELLARIA

intestine or " stomach," from which more or less numerous caeca
which may be more or less branched pass outwards towards the
periphery. The caeca are arranged fairly symmetrically in pairs ;
and there is with a few specific exceptions always a median
unpaired caecum, which passes forwards above the brain.

cu

FIG. XVI.— Thysanozoon brochii, Grube (after Lang), as an Example of Cotylean Polyclad.

1.— Dorsal view, a, marginal tentacular fold. The body wall is produced into a number
of more or less conical papillae, each containing a caecal outgrowth of the intestine. The
number of these papillae increases with age.

2. — Ventral view of the anterior end. a, oculiferous tentacular lobes of the margin ; b,
mouth leading into the pharyngeal sac ; c, the folded pharynx ; $ , one of the pair of penes
carrying a male genital pore at apex ; $ , female pore ; s, sucker.

3. — The marginal tentacular fold of Yungia aurantiaca, seen from above. In addition to
the large pair of eyes resting on the brain, the fold is provided with numerous small eyes.

4. — Diagram of the anatomy. The gut is shown only on the left side, and on the right the
genital ducts, a, brain ; &, stomach or main gut ; c, network of intestinal caeca ; d, caeca
entering dorsal papillae ; h, uterus, from the network on each side a transverse branch goes to
the antrum femininum, which opens by the genital pore ($ ) ; e, sperm duct, forming a network,
which is connected from side to side by a few transverse branches in front of $ pore ; /, seminal
vesicle ; g, penis.

5. — Diagram of part of a transverse section showing the main intestine or stomach (b)
with lateral caeca (c) giving off the dorsal caeca (d) which enter the papillae (a) ; c, the muscular
coat of the stomach.

|

Naturally, in the elongated forms like Prosthiostomum or
Eurylepta the " stomach " becomes more tubular and the number
of caeca considerable. These caeca always bifurcate and branch,
and the branches may even anastomose so as to form a network
in some of the Cotylea. In Thysanozoon and Tliysanoplana branches
from this network enter the villi on the dorsal surface, but

THE TURBELLARIA 35

terminate blindly (Fig. XVI. 5) ; in Yungia some of these branches
open to the exterior ; while in Cycloporus such openings occur
close together around the entire margin of the body (Fig. XV.
7). This elaborate system of caeca is no ^oubt intimately related
to the great size of these Polycladida, for thereby nutriment is
conveyed throughout the body, so that the caeca function as a
lymphatic system. Nevertheless, there is but little structural
difference between the caeca and the stomach, either here or in the
Triclads, in which a similar process of extension, though to a less
degree, has taken place. Lang regards the enteric system as
homogenous with that of Ctenophora, from which he derives the
group; he therefore uses the term " gastrovascular " system to
indicate the stomach and its caeca. How far this is true morpho-
logically is an open question, but to some extent the comparison
is true physiologically.

The excretory system of the Polycladida is very insufficiently
known ; the pigmentation and large size of these forms are inimical
to study in the fresh state, in which alone the' excretory system
can be with certainty made out ; nothing, indeed, is known as to
the position of the main trunks and excretory pores ; all we know
is that the general features of the system are similar to those of
other Platyhelminths.

The nervous system appears to retain, to a great degree,
certain ancestral features ; it has, indeed, sunk below the epidermis
and dermal musculature ; but it retains the form of a close network,
in which cells and fibres take a share, extending all over the body.
This network, which is more strongly developed ventrally, in
relation to the more muscular character of this surface, radiates
from a brain which is more or less centrally situated, though in
longer forms it naturally occupies a more anterior position. Only
in Oligodadus is it behind the mouth. The nerve strands compris-
ing the network, however, are not all of a uniform size ; usually
three pairs of nerve tracts are stouter than the rest, viz. a pair
lying along each side of the median ventral line, a less conspicuous
strand along each lateral margin, and a pair of dorsal nerves.

The eyes in this order have the same structure as in some
Triclads (Fig. XV. 6), but are usually very numerous ; their
position and arrangement are variable, and serve as useful
diagnostic family and generic characters ; there is always a
group on the brain, usually on the tentacles ; or they may lie
along the margin of the body.

The genital organs attain, in the Polyclads, a more diffuse
character than in the preceding orders, both male and female
gonads being " follicular," and extending throughout the greater
part of the body. It seems that here too, as in the case of the
gut with which the organs are in close contact, this racemose

36 THE TURBELLARIA

condition is related to the size of the animal ; for in the smaller
forms of Rhabdocoelids these organs are compact.

The male and female organs are separate throughout their
entire course, there being two genital pores (the occurrence of two
genital pores in marine Planarians was first noted by Mertens),
the female pore being invariably behind the male (except in
Cryptocoelides). This appears to be an ancestral character ; and
we have seen that it frequently occurs in the Rhabdocoelida.
Though these two genital pores are usually some distance apart,
they come to lie very closely together in Stylochus, and the region
around them is slightly depressed; as this depression becomes
deeper a common genital atrium is formed in Stylochoplana agilis
and in Discocoelis.

The general arrangement of the male organs will be seen from
the diagram (Fig. XVII.) • there are one or two peculiarities in
regard to the copulatory organ which may be referred to. In
Stylostomum we have a repetition of the condition obtaining in
Prorhynchus and Cyliiidrostoma, viz. the penis and its sac open
externally in common with the pharynx and its sac.

The simplest case of duplication of penes is seen in some
species of Thysanozoon, in which there is a pair (first recognised
by Claparede) close behind the mouth (Fig. XVI. 2); whilst in
Anonymus virilis some twelve or more pairs form a row on each
side of the ventral surface ; nevertheless, there is no duplication
of the female apparatus (Fig. XV. 9). In Cryptocoelides there
may be two, four, or even six penes, which, however, lie one
behind the other in a common antrum. Lang has suggested
that the "penis," with its glands, is developed from a simple
group of glands, having originally no relations to the sperm
duct j Bergendal's observations on Polypostia (3) seem to confirm
this view. .Here there is a circle of some twenty penes around
the female pore, and each is traversed by a branch of the sperm
duct, but the more posteriorly placed structures which resemble
them in all other points are deprived of this duct ; they are merely
glandular. We have here, as it were, a passage from some
indifferent condition of glandular organ to a specialised condition
in which these glandular organs become related to sperm ducts,
and therewith take on a new function.1

The female gonad is an " ovary," there being no differentiation
to form a special yolk-producing region. The various lobes or
germ-producing follicles are no doubt connected with the oviduct
on each side, but such connection has not, in all cases, been traced.
The oviduct on each side, or uterus, as it is sometimes called,

1 Some interesting and suggestive facts concerning the use of the penis will be
found in Whitman's paper "Spermatophores as a Means of Hypodermic Impregna-
tion," Journ. Afurph. iv. 1891, p. 386.

THE TURBELLARIA

37

opens into a short median tube or "egg duct" with muscular walls.
This duct on its way towards the exterior receives the necks of
numerous glands, and this region is the "shell gland" (ootype), (Fig.

'i,

en

FIG. XVII.

Plan of the anatomy of a Polyclad (from v. Graff) ; ventral view, en, brain ; i, intestinal
caeca ; i\, anterior, median, supra-cerebral caecum ; In, ventral nerve ; m, mouth ; od, oviduct ;
ot', ovary ; ph, pharynx ; phi, pharyngeal sac ; st, stomach or midgut ; t, testis ; tt, uterus ; vd,
vas deferens ; <$, penis; 9> vagina.^

XVIII.) ; lower down the duct enters the " antrum femininum " ;
but in its course it, in many cases, becomes surrounded by a thick
muscular sheath and then forms a bursa copulatrix (Leptoplanidae,
Planocera, and others), and in these forms the penis is " armed."

THE TURBELLARIA

In a number of Acotylea the egg duct is continued backwards
as a blind sac beyond the point of entrance of the uterus (Fig.
XVIII.); and in Trigonoporus this "accessory sac" effects a com-
munication with the exterior behind the female pore (compare
" Laurer's canal " in the Trematoda).

It is worthy of note that both Lang (in Gunda) and von Graff
(in Planocera simrothi) have described the development of ova from
the lining of the intestinal epithelium ; this would go a long way in
support of the very close relations between the Turbellaria and
Coelentera, and of the view that there is no definite coelom in
the former group, it being represented by the intestinal caeca.

Reproduction. — The eggs of the Polycladida are not laid in
groups in capsules as in freshwater forms, but numbers are de-
posited in a jelly-like case, somewhat like the spawn of Nudibranch

FIG. XVIII.

1. — Diagrammatic longitudinal sec-
tion of the terminal parts of the genital
ducts of Leptoplana. a, male pore
leading into the antrum masculinum,
into which the penis (b) projects ; c,
vesicula granulorum ; rf, ductus ejacu-
latorius ; e, the seminal vesicle ; /,
sperm duct; g, female pore leading
into the antrum femininum ; h, ootype
surrounded by shell glands ; j, acces-
sory sac ; k, oviduct.

2. — Similar diagram of Trigono-
porus. Letters as before. Here the
accessory sac (j) has effected a com-
munication with the exterior (I), so
that there are three genital pores. The
region of the body wall between g and
I is folded, and acts as an organ of
fixation. (Both after Lang.)

Molluscs ; there is no yolk, but each egg has its own shell, which
may be operculated (Fig. XIX.). Some Polyclads undergo direct
development ; others pass through a free-swimming larval stage,
which was first noted by Joh. Miiller (48).

The development of Discocoelis and others has been carefully
worked out by Lang. Segmentation is holoblastic, but unequal,
giving rise to microineres and macromeres ; the mesoblast is very
early marked out as cells intermediate in size between the micro-
meres and the macromeres ; the latter do not directly become the
hypoblast, but cells free from yolk are budded off from them, which
gradually surround the centrally placed yolk masses. Meanwhile,
epibolic invagination has led to the formation of a definite embryo
writh ciliated epiblast ; the central yolk masses are now devoured
by the hypoblast cells, to which they stand in relation of parent to
children, and the enteron gradually acquires a lumen, and effects a
communication with the exterior by means of an anteriorly placed

THE TURBELLARIA

39

stomodaeum, which will give rise to the pharyngeal sac and
pharynx.

.a

>

5

FIG. XIX.

1. — Eggs of Yungia laid in a single sheet, embedded in jelly ; each egg is provided with an
operculum (a), which is represented in various positions, and entirely removed.

2. — An egg of Tkysanozoon. s, the egg membrane ; «, coarsely granular vitellus ; 6, fine
granular vitellus, containing the nucleus.

3, 4, 5. — Three stages in segmentation of Discocoelis. The result of the first two cleavages
is to produce four large cells, each of which then divides into a micromere (A;) and a macromere

(y). These first formed cells divide and the macromeres also divide, forming mesoblast
5 represents a later stage from the opposite (ventral) pole, anc"
derm (hypoblast) cells (e) derived from the four large yolk cells.

(ventral) pole, and shows the four primary endo-

(5, 7. — Diagrammatic transverse sections of later stages. 6 represents the same stage as 5.
The epiblast (k) is extending over the mesoblast, in. There is a small blastocoel, represented
black ; e, the primary hypoblast cells. 7 is a much later stage, after the epiblast has grown
right round the embryo, so as to enclose the cells, leaving however a small blastopore, &. In
addition to the primary, ventral, hypoblast cells, others (/) have been formed from the yolk
cells dorsally. By the subdivision of these hypoblast cells (e and /), the great yolk cells
will become enclosed ; the nucleus is no longer distinguishable, and the yolk spherules run
together to form a great homogeneous mass occupying the cavity of the gut, and serving as
food. The mesoblast in this stage has already extended downward for some distance.

8, 9 represent two stages in the development of the larva of Thysanozoon. a is the brain
with eye-spots ; 1 to 8 are the eight characteristic ciliated lobes which are so well marked in
Miiller's larva ; 1 is the median, supraoral, anterior lobe ; 2, 3, the paroral lobes ; 4, 5, great
lateral lobes ; 6, 7, pair of posterior lobes ; 8, median posterior lobe.

8 is a side view of a young larva. 9 is ventral view of an older layer, m, mouth, the light
area around which is the pharynx. (All after Lang.)

The embryo is now somewhat ovate ; as the yolk is absorbed
and the animal grows it becomes flattened, assumes the form of a
young Polyclad, and leaves the shell.

THE TURBELLARIA

In the case of metamorphic forms, the embryo, however, instead
of assuming the flattened character of a Polyclad before leaving
the shell, acquires eight processes of the body, arranged in a
definite way round the mouth (Lang has compared these lobes and
the bands of cilia upon them with the eight rows of swimming plates

of Ctenophora). They constitute a
preoral band, or more correctly, a
circumoral band (Fig. XIX. 8, 9).

This cephalotroch larva, or
"Miiller's larva," as it is termed
(Fig. XX.), after a free swimming
life, is transformed into a young
Polyclad by the gradual diminution
of the ciliated lobes.

The larva of Styloclius pilidium,
owing to the great development
of the dorsal surface, the unequal
development of the various ciliated
lobes, comes to resemble the typi-
cal Nemertine larva, "Pilidium";
and it is possible that this is more
nearly like the common ancestor of
Turbellaria and Nemertina, while
Miiller's larva has gone along a
special line in the former group.
Balfour showed that the trocho-
sphere and other larval forms were
readily derivable from these, which
can be easily derived from a coelen-
terate ; on this account he placed
these larvae near to the ancestor of the whole group of Coelomata.

FIG. XX.

Miiller's larva of Yiingia, seen from
the oral surface. (After Lang, from
v. Graft.)

LITERATURE OF THE TURBELLARIA.

1. Baer, v. Beit. z. Kemitn. d. nieder. Thier. Nova Acta, xiii. pt. 2, 1827,

p. 527.

2. Bergendal. (Uterus of Triclads.) Leuckart's Festschrift, 1892, p. 310.

3. Ibid. (Polypostiidae.) Rev. Biol. d. Nord. d. 1. France, v. 1893, pp. 237

and 366.

4. Bohmig. (Graffilla.) Zeit. f. Wiss. Zool. xliii. 1886, p. 290.

5. Ibid. (Alloiocoela.) Zeit. f. Wiss. Zool. li. 1891, p. 167.

6. Ibid. Die Tiirbell. Acoela d. Plankton Exped. 1895.

7. Ckichkoff. (Freshwater Triclads.) Arch. d. Biol. xii. 1892, p. 435.

8. Collingwood. (Acanthozoon.) Trans. Linn. Soc. Lond. (2), Zool. i. 1875,

9. Dalyell. Observ. on some interesting Phenomena in Animal Physiology,

exhibited by several sp. Planarians, 1814.
10. Ibid. The Powers of the Creator, etc., ii. 1853, p. 95.

LITERATURE OF THE TURBELLARIA 41

11. Darwin, Ch. Ann. Mag. Nat. Hist. xiv. 1844, p. 241.

12. Delage, Yves. (Convoluta.) Arch. Zool. Exp.etGen. (2), iv. 1886, p. 109.

13. Dendy. (Land Planarians.) Trans. Hoy. Soc. Victoria, I. pt. 2, 1889, p.

50 ; 1890, II. pt. 1, p. 65 ; and 1891, II. pt. 2, p. 25 ; also Tr. N.Z. Inst.
1894, 1895, and 1896.

14. Ibid. (Ciliated Pits in Land Planarians.) Proc. Roy. Soc. Victoria, IV.

(N.S.), 1892, p. 39.

15. Duges. Ann. Sci. Nat. xv. 1828, p. 139 ; xxi. 1830, p. 72.

16. Faraday, M. (On the Planariae.) Medical Gazette, ix. p. 723, 1832 ; and

Edinb. New Philosoph. Journ. xiv. 1833, p. 183.

17. Francotte. (Excretory System.) Arch. Biol. ii. 1881, p. 636.

18. Gamble. (British Marine Turbellaria. ) Quart. Journ. Mic. Sci. xxxiv. p.

433, 1893.

19. Geddes. (Convoluta.) Proc. Roy. Soc. xxviii. 1879, p. 449.

20. Giard. (Fecampia.) Comptes Rendus, cm. 1886, p. 499.

21. Goette. Untersuch. Entwick. der Wiirmer, 1882.

22. Graff, v. Monographic d. Turbellarien, i., Rhabdocoelida, 1882.

23. Ibid. (Enantia.) Mith. Natur. ver. f. Steinmark, 1889.

24. Ibid. Die Organisation d. Turbellarien (Acoela), 1892.

25. Ibid. (Pelagic Polyclads.) Zeit. f. Wiss. Zool. Iv. 1893, p. 189.

26. Ibid. (Land Planarians.) Verh. Deutsch. Zool. Gesell. 1896, p. 61 ; and

Boll. Mus. Torino, xii. 1897.
2Qa. Ibid. Monog. d. Turbellarien, ii., Tricladida Terricola, 1899.

27. Grube. (Dicotylus and other Planarians from the Baikal Lake.) Arch. f.

Naturgesch. 38, i. 1872, p. 273.

28. Haberlandt. (On Chlorophyll Bodies), in v. Graff, No. 24, p. 75.

29. Hdllez. (Development of Planaria.) Travaux. Instit. Lille, ii. 1879.

30. Ibid. (Schizorhynchus.) Rev. Biol. Nord. d. 1. France, vi. 1893, p. 315.

31. Ibid. (Classification of Triclads.) Bull. Soc. Zool. France, xvii. 1892,

p. 106.

32. Haswell. (Prorhynchus in Underground Waters.) Quart. Journ. Mic. Sc.

xl. 1898, p. 631.

33. Hesse. (Eyes.) Zeit. f. Wiss. Zool. Ixii. 1897, p. 527.

34. Ijinia. (Freshwater Triclads.) Zeit. f. Wiss. Zool. xl. 1884, p. 359.

35. Jensen. Turbell. ad lit. norveg. Occident, Bergen, 1878.

36. Johnson, J. R. (Observ. on Planaria.) Phil. Trans. 1822, p. 437 ; and

1825, p. 247.

37. Keferstcin. (Leptoplana. ) Abh. k. Gesell. Wiss. Gottingen, xiv. 1868, p. 1.

38. Keller. (Asexual Reproduction in Rhabdocoela and Tricladida.) Jen. Zeit.

xxviii. 1894, p. 370.

39. Kennel, v. (Prorhynchus.) Arb. Zool. Instit. Wurzburg, vi. 1883, p. 69.

40. Lang, A. (Nervous System of Triclads.) Mith. Zool. St. Neapel, iii. 1882,

p. 58.

41. Ibid. (Gunda segmentata. ) Mith. Zool. St. Neapel, iii. 1882, p. 187.

42. Ibid. Die Polycladen. Naples Monograph, xi. 1884.

43. Lehnert. (Bionomics of Bipalium.) Arch. f. Naturgesch. 57. 1891, p. 306.

44. Leuckart, R. (Mesostomum Ehrenbergii. ) Arch. f. Naturgesch. 18 Jahrg.

Bd. i. 1852, p. 234.

45. Mertens. Mem. Imper. Sci. Petersburg (ser. 6). Sci. Math. Phys. et Nat.

ii. 1833, p. 1.

46. Moseley. (Stylochus pelagicus.) Quart. Journ. Micr. Sci. xvii. 1887, p. 23.

42 LITERATURE OF THE TURBELLARIA

47. Moseley. (Land Planarians.) Phil. Trans, clxiv. 1874, p. 105.

48. Miiller, Joh. Arch. f. Anat. Physiol. 1850, p. 485 ; and 1854, p. 75.

49. Ott. (Stenostoma.) Journ. Morph. vii. 1892, p. 263.

50. Pereyaslawzewa. Monogr. Turbellar. mer noire, Odessa, 1892.

51. Quatrefages. Ann. Sci. Nat. iv. 1845, p. 129.

52. Sabussow. (Haplodiscus.) Mith. Zool. St. Neapel, xii. 1896, p. 353.

53. Schulze, Fr. (Inaug. Dissert.) De Planariarum vivendi ratione et structura

penitiori nommlla, 1836.

54. Schmidt, Osc. Die Rhabdocoelen Turbellarien des Siisswassers, 1848.

55. Ibid. Zeit. f. Wiss. Zool. xi. 1861, pp. 1 and 89.

56. SelenTca. Zool. Stud. (Entwick. d. Seeplan.), 1881.

57. Spencer. (Cotyloplana. ) Trans. Roy. Soc. Victoria, ii. pt. 2, p. 42.

58. Uljanin. (Die Turbell. d. Bucht v. Sebastopol. ) Ber. d. Vereins d. Freunde

d. Naturwiss. Moskau, 1870.

59. Vejdovsky. (Bothrioplana and other Rhabdocoelida.) Zeit. f. Wiss. Zool.

Ix. 1895, pp. 90, 163.

60. Voigt. (Asexual Reproduction summarised.) Biol. Centralbl. xiv. 1894,

pp. 745, 771.

61. Wagner. (Reproduction in Microstoma. ) Zool. Jahrbuch. (Anat.), iv. 1891,

p. 349.

62. Weldon. (Haplodiscus.) Quart. Journ. Micr. Sci. xxix. 1888, p. 1.

63. Wheeler. (Bdelluridae.) Journ. Morph. ix. 1894, p. 167.

64. Ibid. (Planocera inquilina.) Journ. Morph. ix. 1894, p. 195.

65. Woodworth. (Phagocata.) Bull. Mus. Comp. Zool. Harvard, xxi. 1891, p. 1.

CHAPTER XVII.

PLATYHELMIA — TEMNOCEPHALOIDEA.

CLASS II. TEMNOCEPHALOIDEA.

PLATYHELMIA, in which the flattened body is provided posteriorly
with a large ventral sucker. The epidermis is retained through-
out life as a nucleated syncytium, which secretes a thick cuticle,
but which may also carry cilia, and contain rhabdites.

ORDER Dactylifera.

The body is produced into finger-shaped tentacular processes along the
anterior margin or along the lateral margins as well ; the mouth is
situated anteriorly, and leads through a pharynx into a wide, nearly
rectangular intestine, which is without diverticula. A single genital pore
situated posteriorly is common both to the male and female apparatus.

FAMILY 1. TEMNOCEPHALIDAE. With four to twelve preoral tentacles.
The excretory system opens to the exterior by means of a pair of anteriorly
and dorsally situated contractile sacs ; the vitellarium is reticulate.
Temnocephala, Blanch. (Fig. I. 1, 6, 7) ; Craspedella, Hasw. ; C. Spenceri,
Hasw., sole species, in the branchial chamber of Astacopsis bicarinatus.
FAMILY 2. ACTINODACTYLELLIDAE. Tentacular processes along each side
of the body ; a second sucker is developed in front of the mouth ; no
contractile sacs at the excretory pore. Actinodactylella, Hasw. (orig.
Actinodactylus) ; A. Blanchardi, Hasw., on Engaeus fossor (Fig. I. 3).

Further Remarks on the Temnocephaloidea. — The members of this
class, so far as they are known at the present day, live on the
outer surface of fresh-water animals, to which they attach them-
selves by means of the sucker ; they do not, however, feed upon
the "host" but on small animals, such as Entomostraca, Rotifera,
Infusoria, etc. ; they can therefore scarcely be termed " ecto-
parasites " in the usual sense of the word. Most of the species
occur on the surface of fresh -water Crustacea; the Brazilian
T. Jlieringii, Hasw., in the pulmonary chamber of the mollusc
Ampullaria, and T. brevicornis, Montic., on the surface of Chel-
onians (Hydropsis and Hydro-medusa). The genus Temnocephala
was discovered in Chili by Blanchard, who regarded it as an

44

THE TEMNOCEPHALOIDEA

Annelid ; and later, Philippi placed it amongst the Leeches.
Thanks to the investigation of Max Weber and Haswell, we

FIG. I.— Temnocephaloidea. (After Haswell, and Figs. 6, 7 after Weber.)

1. — Temnocephala minor, Hasw., from the surface of Astaeopsis; ventral view, a, mouth ;

b, genital pore ; c, sucker ; d, tentacular prolongations of the body.

2. — Craspedella spenceri, Hasw., from the branchial chamber of Astaeopsis. e, eyes, resting
upon the brain ; /, excretory pore and contractile sac ; g, the three fringed lamellae on the
dorsal surface, behind which are four conical papillae ; c, dorsal edge of the sucker.

3. — Actinodactylella blanchardi, Hasw., from the surface of Engaeus fossor. a, mouth; 5,
pharynx ; c, intestine ; d, follicular vitellaria, arranged along the sides of the intestine ; e, the
left testis, deeply bilobed ; /, lateral, tentacular prolongations of the body ; g, dorsal edge of
the sucker.

4. — Actinodactylella, ventral view of the anterior end. or, most anterior tentacular pro-
longations of the body ; b, peculiar proboscis everted through the mouth and which exists in
addition to the pharynx, in which it lies when withdrawn into the body ; c, preoral sucker.

5. — A small portion of a section through the body Avail of Temnocephala. a, nucleus of
epidermal syncytium, which is vertically striated like the epidermal cells of Turbcllaria, and
here and there traversed by the necks of subepidermal gland cells. The artist has made these
too regular, so as to look like cell boundaries ; b, cuticle raised up into low papillae, some of
which bear tufts of sensory hairs (e), to which is seen going what appears to be a nerve fibre
(on the left of the figure) ; c, basement membrane ; d, circular muscles.

6. — Plan of the alimentary and excretory systems in T. semperi, M. Weber, as seen from
the dorsal surface, a, mouth leading into a small pharyngeal sac ; b, pharynx ; c, intestine ;
d, excretory pore ; e, contractile bladder, formed of a single perforated cell ; /, chief excretory
vessels ; g, the vessels entering the tentacle. The outline of the sucker is indicated by dotted
lines.

7.— Plan of the genital organs of T. semperi, M. Weber, as seen from below, a, mouth ;

c, genital pore leading into the genital atrium ; d, oviduct ; e, germarium ; /, receptaculum
seminis ; g, vitellarium in the form of a network covering the dorsal surface of the intestine ;
Ti, the testes ; j, sperm duct, which, after uniting with its fellow, gives rise to a seminal
reside ; fr, penis, with chitinous sheath.

8. — One of the excretory cells of T. fasciata, Hasw., which exists in addition to the ordinary
flame cells, a, tubule, branching in the substance of the cell to form a system of minute
capillaries ; b, large nucleus.

THE TEMNOCEPHALO1DEA 45

know that its true position is among the Platyhelmia. It occurs
in the Australian region, in New Zealand, in Celebes, Madagascar,
Chili, and Brazil. The other two genera are known only from
Australia.

The most interesting anatomical feature, and one which differen-
tiates the class from the Trematoda, is presented by the external
covering of the body, for the epidermis retains to a great degree
its original character of a cellular layer, but the cells are not dis-
tinct ; they form a syncytium, in which the round nuclei are disposed
regularly (Fig. I. 5). This epidermis has, however, so far lost
its original character as to be deprived of cilia in most species,
and gives rise to a cuticle, varying in thickness, traversed by " pore
canals " for the passage of the necks of subepidermal gland cells,
which may contain rhabdites similar to those of Turbellaria. In
this latter respect, then, the class resembles the Rhabdocoelida,
and this resemblance is increased by the fact that in at least two
species, T. minor, Hasw., and T. dendyi, Hasw., vibratile cilia have
been recognised over the general body surface. The subdermal
rhabdite glands form rod tracts (Stabchenstrasse), as in many
Ehabdocoels, and are arranged in definite groups.

The tentacular prolongations of the body are peculiar to the
group, though the Rhabdocoel Vorticeros presents two such pro-
cesses. The muscular system is specially developed and modified
at the posterior end to form a "sucker"; there are (a) fibres
which pass dorso-ventrally from the body wall to the centre of
the sucking disc ; (b) dorso- ventral fibres traversing the substance
of the sucker itself ; (c) circular fibres ; (d) radial fibres ; and (e)
certain longitudinal fibres from the ventral wall of the body into
the lateral part of the sucker peduncle. By the varying con-
traction and extension of the muscle fibres, this sucker is enabled
to attach itself firmly to any underlying surface. The possession
of the sucker naturally allies the forms with the Trematoda.

The pharynx retains a somewhat primitive character in being a
Ph. bulbosus, whose chief function is " sucking."

The excretory system of Adinodactylella is known only from
its flame cells ; but in the Temnocephalidae it presents certain
peculiarities, in that the number of component cells is very few,
and the nuclei of considerable size, recalling in both features the
Nematode excretory system ; for instance, each terminal contractile
sac is formed of a single cell. In addition to flame cells of a
normal structure, some of the branches of the system of capillaries
terminate in large cells, one to each such branch, riddled with a
number of very fine canalicules, giving rise to a structure recalling
very strongly the cells of the nephridium of Hirudo (Fig. I. 8).
The anterior position of the excretory pore, its contractile sac, and
the main course of the canal are features of resemblance with

46 THE TEMNOCEPHALO1DEA

the monogenetic (Heterocotylean) Trematodes, rather than with
the Turbellaria.

But in the nervous system the Temnocephaloidea retain a
much more primitive condition than that presented by the existing
Rhabdocoelida. The extensive network arising from the brain
presents three main tracts on each side of larger dimensions.

The genital organs (Fig. I. 7) are formed on the ordinary
Platyhelminth plan ; in their position posteriorly to the intestine,
and in the lateral position of the testes, the Temnocephaloidea re-
semble the Turbellaria. The testes retain the primitive, bilateral
symmetry ; but the testis of each side is so deeply constricted as
to form two oval, or it may be lobulated organs, connected together
by a narrow duct, so that there is here a commencement of that
process which results in the " follicular " arrangement of Tricladida,
and Polycladida. The penis presents a Rhabdocoelidan character
in being enveloped in a chitinous sheath, resembling that of many
tubificid Oligochaetes (such as Limnodrilus) ; while the terminal
region of the sperm duct is eversible, and provided with chitinous
spines.

The female gonad has undergone that same differentiation into
germarium and vitellarium which occurs in many Turbellaria. The
former is compact ; the latter presents a peculiar and characteristic
arrangement in its reticulate structure, covering the dorsal surface
of the sac-like intestine. The vagina is armed.

The whole anatomy, therefore, of the Temnocephaloidea
exhibits a remarkable intermediate condition between the
Rhabdocoelida and the Trematoda, while presenting certain
peculiarities of its own, which entitle the animals to a position
independent of these two classes. Nothing is known of the
development beyond the fact that the eggs are laid in capsules
(sometimes operculated), which are pyriform and stalked, except
in T. fasciata, where several oval eggs are embedded in a mass of
secretion.

1. Haswdl. Quart. Journ. Mic. Sci. xxviii. 1888, p. 279.

2. Ibid. (For all previous literature.) Macleay Memorial Volume 1893,

p. 93.

3. Ibid. (Actinodactylella.) Macleay Memorial Volume, p. 153.

4. Max Weber. Zool. Ergebnisse einer Reise in Niederl. Ost-Ind. 1890, vol.

i. p. 1.

5. Plate. SB. Akad. Wiss. Berlin, 1894, p. 527.

CHAPTER XVIII.

PLATYHELMIA — TREMATODA.

CLASS III. TREMATODA (RUDOLPHI).

Order 1. Heterocotylea.

Fam. 1. Monocotylidae.
,, 2. Tristomidae.
,, 3. Polystomidae.
„ 4. Microcotylidae.
„ 5. Gyrodactylidae.

Order 2. Aspidocotylea.
Fam. Aspidobothridae.

Order 3. Malacocotylea.

Fam. 1. Amphistomidae.

,, 2. Distomidae.

„ 3. Holostomidae.
„ 4. Monostomidae.
„ 5. Gasterostomidae.
„ 6. Didymozoonidae.

PARASITIC Platyhelmia which retain the mouth and alimentary
tract of the ancestor, but in which the epidermis not only loses its
cilia during embryogeny, but is apparently absent in the adult as a
distinct, continuous, cellular layer, having sunk into the mesoblastic
tissue, after secreting a thick, stratified, chitinous cuticle. Further,
in relation to their parasitic habits, suckers are developed at or
near the posterior end on the ventral surface, and also in the region
of the mouth.

Historical. — Our knowledge of Trematodes begins with Gabu-
cinus (1 547), who described the occurrence of the liver fluke in sheep,
which was, however, referred to by Jehan de Brie as early as 1379 ;
Leeuwenhoek (1695) added a form found in the herring; Swam-
merdam (1752) mentions a distome in the frog's lung; Roesel v.
Rosenhof (1758) gave a description and figure of a fluke (Poly-
stomum) which he discovered in the frog's bladder. Then came that

48 THE TREMATODA

wonderfully accurate observer, 0. F. Miiller (1777), who, in a series
of memoirs, described a number of species, and gave good pictures
of them. These earlier writers, naturally, were weak in the inter-
pretation of anatomical features, and it has taken nearly a century
since Miiller's time to obtain a proper knowledge of the anatomy,
while even at the present day one or two matters are open to
dispute.

After Miiller, the number of observers rapidly increased,
and it is impossible even to mention a hundredth part of those
who have aided in building up our knowledge of the anatomy and
variety of forms in Trematodes and Cestodes. Max Braun (11)
gives a complete list of works thereon, with a brief epitome of the
contents of each memoir. The most important amongst those who
have added to the number of genera and species are Rudolphi
(1808), v. Baer (1827), v. Nordmann (1832), Diesing, Wagener
(1858), P. J. van Beneden, Cobbold, v. Linstow, Willemoes-Suhm,
Taschenberg, and in more recent times Monticelli, Sonsino,
Parona, Perugia, and Stossich, as will be seen in the systematic
account.

Many of the above-named zoologists naturally added to our
knowledge of the anatomy and life-history of the members of the
group, and the various important advances are mentioned in
the text below. The following are conspicuous for the amount of
new knowledge which they contributed: — Bojanus (1818), Mehlis
(1825), Laurer (1830), v. Siebold (1835), Leuckart, Stieda (1867),
and Zeller. Carlisle (1794) deserves mention, as he appears to
have been the first to demonstrate, by means of injection, the
course of the canals of the excretory system which, however, he
regarded as the alimentary tract.

Certain stages in the life-history of the endoparasitic forms were
known in the last century, e.g. to Swammerdam, and some of the
more important contributions are due to Nitzsch (1807), Carus
(1835), Moulinie (1856), La Vallete St. George (1855), who con-
ducted experiments in feeding probable hosts with cercariae,
Pagenstecher (1857), Zeller, Schauinsland, and Thomas.

The limits of the class are very well defined, and consequently
we find but few animals wrongly included therein ; nevertheless,
some curious mistakes have been made ; for instance, Lacaze
Duthiers described " Phoenicurus " as a fluke, parasitic on Tethys ;
Spengel and Bergh have, however, pointed out that it is merely
a normal, readily detachable, appendage of that mollusc.
" Thysanosoma," from the caecum of Cervus dichotomus, was at
first described by Diesing as a fluke ; it is really a detached
proglottid of a Cestode ; van Beneden included Cydatdla, but
later recognised that it is a species of Loxosoma parasitic on
Clymene. Myzosloma was for a long time placed here, till Leuckart

THE TREMATODA 49

showed that it is an Annelid. While Kolliker pointed out that
Cuvier's " Hectocotyle " is not a fluke, but at the same time fell
into error in regarding it as a " pygmy male " of Argonauta and
Tremoctopus. Pentastoma was included, till P, J. van Benederi
(1849) discovered its embryo, and allocated it to the Arthropoda.

The first definite attempt to classify the parasitic worms or
" Helminths," as they were then called, was made by Zeder (1800),
who divided them into five families, to which he gave German
equivalents of (a) round worms, (b) hooked worms, (c) sucking
worms, (d) tape-worms, and (e) bladder-worms. Of the " sucking
worms " he recognised three genera, of which he gave diagnoses,
and divided the various species into groups. Eudolphi (1808), in
an epoch-making work on intestinal worms, invented the term
" Trematoda " : for Zeder's "sucking worms," which he raised to
the rank of an " Order."

Both these authors laid great and deserved stress on the
arrangement of the suckers, a character which, together with the
absence of " segmentation," is still a sufficient mark of distinction
of the Trematodes from the Cestodes.

The earlier authors were acquainted with endoparasitic forms
only, and the discovery of ectoparasitic Trematodes, and the
gradual increase in the number of genera and species, as well as a
more correct knowledge of anatomy, due to the researches of v.
Baer, Nordmann, Nitzsch, Diesing, and many others, led Leuckart
(1856) to propose a division of the Trematodes into the two
"families": (1) Distomea, for endoparasitic forms with a meta-
morphosis ; and (2) Polystomea, for ectoparasitic forms which have
no metamorphosis.

In the same year, Burmeister separated Aspidogaster from the
rest, and suggested a threefold division into (a) Malacobothrii (for
Distomids), (b) Pectobothrii (for Polystomids), and (c) Aspidobothrii
(for Aspidogaster).

This system has been generally overlooked and obscured by
P. J. van Beneden's great work (1858) on the group, embracing as
it did not only an account of several new species, but also an
experimental investigation into the life-history of the endoparasitic
and ectoparasitic forms respectively; these researches led to the
recognition of the importance of these two modes of reproduction :
the direct or " monogenetic," and the indirect or " digenetic." And
until quite recently this twofold division held the field, till Monti-
celli (1892) proposed the threefold division, which is essentially
the same as Burmeister's.

The class Trematoda is divided into the three orders, primarily
distinguished by the character of the suckers, viz. — Heterocotylea,
Aspidocotylea, and Malacocotylea.

5T]$ = pierced Avith holes.

5o THE TREMATODA

ORDER 1. Heterocotylea, Monticelli ( = Polystomea, Leuck. = Pecto-
bothrii, Burm. = Monogenea, v. Ben.).

Trematoda, in which there is a large posterior, ventral, terminal
adhesive organ in addition to a pair of anterior suckers in relation to the
mouth ; the latter may be absent. The posterior apparatus consists
either of a single sucker, usually of large size, which is generally divided
by radial ridges into a number of compartments ; or these ridges may be
so extensively developed as to give rise to a number of separate suckers
set upon a caudal disc or " cotylophore." This posterior apparatus is
very usually provided with chitinous booklets.

Eye-spots are not unfrequently present. The excretory system com-
municates with the exterior by a pair of pores laterally placed on the
dorsal surface, near the anterior end. The male and female ducts nearly
always open by a common pore. A third genital duct, known as the
vagina, is usually present, with an external aperture independent of the
uterine pore. The members of the group are nearly all ectoparasitic,
and development takes place without the intervention of an intermediate
host, and without any intercalated asexual reproduction (hence "mono-
genetic "), so that from each egg laid only one new fluke is produced.

For accounts of the anatomy of various genera, see van Beneden, 5 ;
Goto, 19 ; Cerfontaine, 14.

FAMILY 1. MOXOCOTYLIDAE. Posterior sucker usually small ; anterior
suckers absent ; the common genital pore median. Pseudocotyle, v. Ben.
and Hesse, on skin of Selachians. Calicotyle, Dies. ; G. kroyeri, Dies.,
in cloaca of male Raia. Monocotyle, Tasch. (Fig. III. 2) ; M. mylio-
batis, Tasch., on Myliobatis aquila. FAMILY 2. TRISTOMIDAE, with one
large posterior sucker, with or without compartments ; with or without
booklets; a pair of anterior "lateral" suckers; male and female ducts
usually open by a common pore situated anteriorly, usually on the left
side ; vagina and its aperture single on the left side. Parasitic on gills
and skin of marine fish. Nitzschia, v. Baer ; N. elongata, Nitzsch, gill
cavity of Sturgeon. Epibdella, Blv. ; Phyllonella, v. Ben. and H. ; P.
soleae, v. Ben. and H. ; Tristomum, Cuv. (Fig. II. 1) ; Acanthocotyk,
Montic. ; A. lobianchii, Montic., on skin of Raia clavata. Encotyllabe,
Dies. ; E. nordmanni, Dies., on nostril of Bream. Udonella, Johnston
(Fig. II. 5), on parasitic Crustacea. Echinella, v. Ben. and H. ;
Ptefonella, v. Ben. and H. FAMILY 3. POLYSTOMIDAE. The posterior
adhesive organ is formed by six or eight suckers on a caudal disc or
" cotylophore " which is usually armed ; two anterior " buccal " suckers
communicating with the oral cavity are usually present ; vagina single
or paired ; common genital pore median. On gills of fishes, skin and
bladder of Amphibia and Reptiles (see Goto, 19). SUB-FAMILY 1.
OCTOCOTYLIXAE, with four to eight posterior suckers ; a pair of " buccal "
suckers ; genital booklets. A. Suckers, four on each side. Octobothrium,
Lkt. ; 0. alosae, v. Ben. and H., on gill of Shad. Diplozoon, v. Nordmann.
The genital ducts are so arranged that the male duct of each animal
becomes continuous with the vagina of the other (Zeller, 50), or with
vitelline duct (Goto, 1 8). D. paradoxum, v. Nordm., on the Minnow ;

THE TREMATODA

Europe (Fig. IV.). Diclidophora, Goto (non Diesing), (Fig. II. 4) ;
Dactylocotyk, v. Ben. and H. ; Cyclobothrium, Cerf. ; C. sessilis, Goto, oral

FIG. I. — Anatomy of a Schematic Heterocotylean.

1. — Dorsal view, showing the alimentary and nervous systems, a, mouth, on the ventral
surface, the outline being therefore dotted ; i>, pharynx ; c, bifurcate intestine ; d, branching,
intestinal caeca ; <?, post-genital union of the two intestinal limbs ; e', median portion of the
intestine, which is continued backwards, and gives origin to caeea in the posterior sucker (or
cotylophore, as the case may be) ; /, excretory pore, right and left, situated just dorsal to the
margin of the body ; g, the vaginal pore ; it is here represented as paired ; but frequently it is
unpaired ; h, anterior nerve, right and left, arising from the brain ; j, the cerebral ganglion,
which carries on each side a couple of eyes, represented by white spots ; A;, marginal or lateral
nerve ; I, dorsal nerve, which is frequently present ; m, ventral nerve. The nervous system
is shown in greater detail in Fig. XXI. ; n, the right anterior sucker ; it is unconnected with
the oral cavity, and is termed "lateral" ; o, posterior sucker; p, a hooklet projecting from the
posterior sucker ; r, the genito-intestinal (Laurer's) canal, entering the right limb of the in-
testine.

2. — Plan of the excretory system, seen from the ventral surface, o, mouth ; b, genital
pore and atrium, here represented as median, but it may lie on the left of the median line ; /,
excretory pore ; g, contractile excretory bladder, right and left ; h, large excretory duct,
passing backwards to the hinder end of the body ; k, the forwardly-directed (ascending) canal,
in continuity with the duct posteriorly, and running to the anterior end of the body, giving
off irregularly arranged branches, which subdivide to form capillaries ; i, capillaries terminating
in flame cells, which are indicated by the terminal thickenings ; j, transverse anastomotie
vessel, which is frequently present behind the genital organs ; n, the left anterior "lateral"
sucker ; o, the posterior sucker, which is here, as so frequently, subdivided into compartments
or "loculi" by radiating ridges; p, a hooklet; q, a lateral loculus ; q', the central loculus
which may, or may not, be present.

3. — Plan of the genital organs, seen from the ventral surface ; b, genital atrium ; c, uterus ; d,
germarium ; e, portion of the right limb of the intestine into which the genito-intestinal canal
opens ; /, longitudinal vitellarian duct, from each of which a transverse duct passes inwards to
enter the germ duct ; g, vitellarium ; h, testis, consisting of a number of follicles ; i, the sperm
duct ; j, ootype, surrounded by "shell glands " ; between it and the germarium is the germ duct ;
fc, vagina, right and left, connected internally with the median vitello-duct ; I, vaginal pore ;
111, the sperm duct ; n, o, p, as before ; r, genito-intestinal (Laurer's) canal, passing from the
oviduct to the intestine ; s, excretory pore ; t, penis.

cavity of Chaerops japonicus. Heterobothrium, Cerf. ; Vallisia, Per. Par. ;
V. striata, Per. Par., on gills of Lichia. Anthocotyle, v. Ben. and H.

THE TREMATODA

(Fig. II. 6) ; Onchocotijle, Dies., on gills of Elasmobranchs. B. Suckers
in a transverse row posteriorly. Hexacotyle, Blv. (Fig. II. 2); H.
thynni, de la Koche. Plectanocotyle, Dies., has only six suckers. SUB-
FAMILY 2. POLYSTOMINAE, with six posterior suckers ; without anterior
buccal suckers. Polystomum, Zeder ; P. integerrimum, Frol., bladder of
Frog and Toad (Fig. V. 1, 2 ; and for an account see 49). P. ocel-
latum, End., pharynx of Emys europaea. Erpocotyle, v. Ben. and Hesse ;
Diplobothrium, Leuckt. ; Sphyranura, Wright ; S. osleri, Wr., on skin of
Necturus lateralis (see 48). FAMILY 4. MICROCOTYLIDAE, with two "buccal"
suckers and numerous small posterior suckers carried on a variously

FIG. II.

shaped marginal cotylophore ; genital pore median ; vagina may open
on the left side (see 37). Microcotyle, v. Ben. and H. (Fig. III. 1) ;
Gastrocotyle, v. Ben. and H. ; G. trachuri, v. Ben. and H., on the gills of
Caranx trachurus. Axine, Abildgaard ; A. belones, Abild. ; A. triglae,
v. B. and H. FAMILY 5. GYRODACTYLiDAE.1 Elongated body with one or
two pairs of retractile cephalic lobes, carrying the openings of glands ;
anterior suckers may also be present ; the caudal disc does not carry
suckers, but is armed with peculiar hooks, central and marginal ;
eyes are usually present anteriorly ; genital pore median ; no vagina.

1 Dionchus, Goto (Joiirn. Sci. Coll. Imp. Univ., Tokyo, xii. 1899, p. 286),
combines several characters of this and the preceding family.

THE TREMATODA 53

Calceostoma, v. Ben. ; C. elegans, v. Ben., on gill of Sciaena agilis. Tetra-
onchus, Dies., various species on other fish. Dactylogyrus, Dies., numerous
species on fresh-water fish. Amphibdella, Chatin ; Diplectanum, Dies. (Fig.
III. 3) ; Gyrodactylus, v. Nordm. ; G. elegaiis, v. Nordm., on gills of various
fresh- water fish (see 22). The most interesting anatomical peculiarity of
Gyrodactylus is the absence of a vitellarium, so that, alone amongst the
Trematocles, the female gland is an " ovary " ; this is evidently related to
the peculiar mode of reproduction, the details of which are still somewhat

FIG. II. — A Group of Hetorocotyleans. 1

Letters common to all the figures except 3. b, anterior sticker, "lateral" or "buccal," as
the case may be ; e, excretory pore ; /, genital pore, or atrium, in 5 ; g, vaginal pore, single or
paired ; h, vitellarium, or its duct ; i, intestine ; p, pharynx ; r, germarium ; s, sperm duct ;
t, testis.

1. — Tristomum cocdneum, Cuv. ; ventral view (altered from Bronn's figure), a, mouth, lead-
ing into the pharynx ; c, the large posterior sucker, whose cavity is subdivided into a central
and seven peripheral "loculi," by a circular and seven radial muscular ridges ; a pair of small
booklets (scarcely visible in the figure) are carried by the pair of posterior radii. The intestine
consists of a subcircular main canal, bearing many much-branched caeca. The canal is only
represented in outline, and the caeca only partially indicated on the right of the figure. The
horseshoe-shaped vitcllarian duct and the branches therefrom follow the course of the corre-
sponding parts of the enteric canal. From the anterior end of each limb of the main duct a
transverse duct (represented only on the right of the figure) passes inwards to join the rest of
the female apparatus, which is not represented.

2. — Hexacotyle grossa, Goto, from the gill of Thynnus sp. (ventral view, after Goto). There is
a long oesophage«il region (o) passing back from the pharynx to the level of the genital pore,
behind which it bifurcates. Each limb gives rise to a series of anastomosing branches forming
a marginal network shown on the left of the figure, which is continued posteriorly into the
caudal disc ; and behind the testes a central network is similarly formed. The pore of the
vagina lies on the dorsal surface ; the vagina itself bifurcates posteriorly, indicating its true
double origin. 1, 2, 3, the three large suckers, and 4, the minute median sncker, represented
by a dot on the caudal disc. Between the latter are two small hooklets, represented by short
lines.

3.— The female organs of Sphyranura osleri, Wright, from Necturus lateralis, ventral view.
The genital atrium (/) receives the male duct (a) anteriorly and the female duct (&) pos-
teriorly ; d, uterus, dilated distally and containing an egg (o) which is provided with a
filament at one end ; g, vagina, right and left, here a blind sac, having lost its external pore and
functioning as a spermatheca ; h, right and left, transverse vitelline duct ; h', yolk reservoir
(? = ootype) ; i, portion of the intestine ; k, genito-intestinal canal ; q, germ duct ; r, germarium ;
x, the point of union of the various ducts.

4. — Diclidophora elongata, Goto, showing the alimentary system. The two limbs of the
intestine are united by several transverse branches, both in front of and behind the genital
organs (which are not represented). Caeca are also given off laterally, and one enters the stalk
of each posterior sucker. 1, 2, 3, 4, the four suckers at the left side, each is armed and pedun-
culated.

5. — Udonella callgorum, Jnstn., from Caligiis (after P. J. van Beneden). &, the anterior
sncker surrounds, as by a collar, the everted pharynx. The posterior sucker is a simple deep
cup. The uterus contains an egg anteriorly. The right and left lobes of the vitellarium are
tmited posteriorly by a median lobe. The transverse vitellarian ducts are seen passing to
the ootype, which receives also the germ duct from the germarium. The intestine, here, is a
simple bifurcated tube, without caeca.

6. — Anthocotyle imrlutii, v. Ben. and Hesse, from the gill of Mcrluchts mdgaris (after
Cerfontaine). Outline showiiig the ventral surface, pores, and suckers. 1, the large clasping
sucker of the posterior system, one valve algne, with its armature, is shown ; 2, 3, 4, the three
small suckers ; w, the terminal region of the disc (enlarged on the right), with its two pairs of
hooklets.

obscure. A single egg ripens at a time, and develops into an embryo while
in the uterus ; but within this embryo a second embryo becomes marked
out before the first leaves the mother (Fig. III. 6). There are thus three
generations, one within the other ; and Wagener (46) has suggested three
possibilities to explain what happens, but is unable to decide between them.
(a) The grand-daughter arises, like the daughter, by the ordinary sexual
process (which is very improbable). (6) Some of the blastomeres of the
original egg remain quiescent and take no share in the formation of the
daughter, but later undergo development within it to form the second

54

THE TREMATODA

embryo ; in this case the two are sisters, (c) The second embryo, or third
generation, is a " spore."

FIG. III. — Heterccotyleans.

l.—Microcotyle fusiformis, Goto, from the gill of Centronotus rululosiis (ventral view, after
Goto), a, buccal suckers opening into the oral cavity, behind which is the pharynx ; b,
common genital pore ; c, vaginal pore ; d, the lateral cotylophore with numerous small suckerlets,
each armed with chitinous skeleton.

2.—Monocotyle ijimae, Goto, from the oral cavity of Trygon postinaca (ventral view, after
Goto), a, mouth ; c, one of the eight compartments or loculi of the posterior sucker, which
is provided with a pair of small booklets Inserted in the hindmost pair of radii ; e, excretory
pore of the left side ; /, common genital pore ; g, vaginal pore, to the left of the middle line ; i,
intestine ; p, pharynx ; t, testis, here divided into three lobes ; y, the "sticky glands," which
functionally replace the anterior suckers.

S.—Diplectanum aequans, Dies, (side view after v. Beneden). a, the anterior end bilobed
and carrying a hook ; b, the left anterior, lateral sucker ; c, eye-spots ; d, great posterior sucker
armed with large hooks ; e, the rows of small spines in the wall of the sucker ; /, hooks.

4. — The same, anterior end, dorsal surface, c, eye-spot.

5. — The same, posterior end ; letters as before.

6. — Gyrodactylus elegans, v. Nordm., from gills of various fresh-water fish (after "Wagener) ;
ventral view, a, anterior lobe of the body which carries the pores of the " sticky glands " (b) ;
c, the mouth ; d, pharynx, lying in the pharyngeal sac ; the pharynx is eight-lobed, and each
lobe consists of an anterior clear portion and a posterior granular portion ; e, the intestine ; c',
mouth of first embryo ; d', the pharynx of first embryo ; /, uterus, with two embryos, one within
the other ; g1, the first embryo ; g", the second embryo within the first ; h, egg in oviduct ;
i, testis ; .;', ovary ; k, caudal disc, the margin of which is provided with a number of papillae,
each of which carries a booklet ; I, the great central hooks of the disc ; k', the caudal disc of
the first embryo ; k", the same of the second embryo.

7. — The same ; the everted pharynx seen from below, showing the eight tentacle-like
processes diverging through the oral aperture; the black centre is the entrance from the
pharynx to the cavity of the intestine ; the granular part of pharynx is not everted.

8.— The same ; one of the marginal hooks, a, the free end of the hook ; b, the plate to
which the handle e is inserted ; c, the hoop which serves for the attachment of muscles (d).

Metschnikoff (34) has made an interesting comparison with the normal
development of Monostomum mutabile and other Trematodes. The result

THE TREMATODA 55

of segmentation in these is a blastosphere in which the outer layer of
cells becomes ciliated while the central mass becomes the " sporocyst."
He suggests that the first embryo of Gyrodactylus or daughter may be
compared with the former, the grand -daughter with the latter, as they are
both formed from a mass of embryonic cells which separate in the same
way as in Monostomum ; whilst v. Linstow (1892) has suggested that Gyro-
dactylus is a larval form capable of reproducing by an asexual method.

Remarks upon the Order Heterocotylea. — The general anatomy of
the group is sufficiently evident from the figures, and will be
treated, together with that of the Malacocotylea, later (p. 77).

Reproduction. — The life-history forms an important distinctive
character of the order. The only observed instance of copulation
is that of Polystomum (Zeller, 49), which is temporary, and the
permanent copulation of two Diporpae (Dujardin), which was shown
by v. Siebold to form that anomalous animal Diplozoon.

From the fact that many of the Heterocotylea live isolated on
the gills of fishes, and that eggs are laid by them, it is probable
that self-fertilisation occurs ; this is borne out by observations on
Distomum, spp. by Looss (31), who finds spermatozoa within the
uterus before the external pore is formed. They could therefore
only have been derived from the ripe male organs ; and further, in
some species there is no penis, so that copulation could not have
taken place. If self-fertilisation may occur in Distomum, there is
every reason to expect its occurrence in the Heterocotylea.

Each egg, when laid, consists of a single germ cell, derived from
the germarium, embedded amongst a considerable number of vitelline
cells (yolk cells) derived from the vitellarium, as in Triclads, and sur-
rounded by a shell, which is secreted by the walls of the "ootype."
The form of the egg, which is frequently of systematic value,
depends upon the shape of the " ootype." The shell is provided
with an anterior operculum. The shell substance is produced into
a filament at one or both ends ; that arising from the body of the
shell — the " stalk " — is used for attaching the shell to the host.

Earely (Polystomum) the eggs are laid in the water. Practically
nothing is known of the segmentations and early stages in develop-
ment in the Order, though Zeller has described the course of events
in Polystomum. The egg cell becomes multinucleate before cell
division takes place ; ultimately a solid blastosphere is formed.
The yolk cells, meanwhile, become reduced in size ; and as
the growing embryo absorbs more and more of the yolk, the
yolk cells become broken down, and finally, when the embryo
acquires a mouth, the remains are swallowed. When hatched,
the larva swims freely in the water by means of -five incomplete
girdles of cilia, of which the three anterior are incomplete dorsally,
the two posterior incomplete ventrally (Fig. Y. 5, 6). Posteriorly
the body is produced into a caudal disc, armed with sixteen hook-

THE TREMATODA

lets, [but without suckers. The larva possess four eyes, an intestine,
and a well-developed excretory system. During its passage through
the water, the larva seeks for a young tadpole of the frog, and not

FIG. IV.

finding one within twenty-four hours, the cilia degenerate and the
animal dies. But having come across its future host, it swims and
creeps leech-like over the surface of the body till it arrives at the
branchial aperture; into which it darts with great suddenness.

THE TREMATODA 57

Arrived in the gill chamber, the larva undergoes a gradual meta-
morphosis, the cilia disappear, and the cells bearing them shrink
up ; suckers make their appearance in pairs on the caudal disc,
each being formed around a booklet, thus leaving ten booklets
outside the suckers. Meanwhile, the tadpole itself is undergoing
metamorphosis, and the young Polystomum makes its way into the
pharynx, and wanders along the alimentary tract to the rectum ;
on the formation of the cloacal bladder, the young Polystomum
enters it. It is not till the third year that the parasite
becomes sexually mature. But if, as sometimes happens,
the larva of the parasite has attacked a younger tadpole than
usual, one .in which the external gills are still present, it can

FIG. IV. — Diplozoon paradoxum, v. Nordia., from tlie Minnow. (Figs. 2-8 after Zeller.)

1.— The complete animal pair (altered from v. Xordmarm) seen from the ventral surface.
The individual A A1 is permanently copulating with BB1. The intestine is shown in each; it
consists of a single tube produced into caeca ; really on all sides, but appearing here only on
right and left. Beyond the point of union of AA ' with MB1, and in the region occupied by the
genital system, their lateral caeca are absent, but they reappear again behind the testes. In
I), nipponicinn the intestine bifurcates at the cross and surrounds the genital organs, behind
which the two limbs again unite, q, caudal disc, with four suckers upon it.

2. — A pair enlarged to show the genital organs. AA ' is seen from the ventral surface ;
BB1 is truncated, and seen from the dorsal surface, a, the mouth ; b, buccal sucker ; c,
pharynx ; d, intestine ; e, vitellarium of^4^4' ; /, vitelline duct ; /', its dilated region in the tail ;
it enters the germ duct just beyond the origin of the "vagina" ; g, testis of BB1; h, sperm
duct, which can be traced forwards into the anterior part of the animal, curves round and com-
municates with the vagina (i) of AA ', which is seen passing ventrally below the germarium.
k, the germarium, the hinder end of which is produced into the transversely disposed germ
duct which receives the vagina and vitelline duct, and is continued forwards to form the uterus
(I). The enlarged part (I1) of the uterus is lined by large cells ; the anterior part, which runs
transversely, is termed by Zeller "egg duct" ; it opens to the exterior at (m) the female pore
situated on a slight papillae and communicating with I by a narrow duct n. p, the caudal disc,
dorsal surface in B1, bearing below it (in A1) the four suckers (q), each of which is armed.

3. — An egg shell, a, operculum ; b, filament.

4. — Young ciliated larva, b, buccal sucker ; c, pharynx ; d, intestine'; q, the most anterior
sucker, the only one yet developed.

5. — Older larva, after the loss of cilia, and now known as Diporpa. On its ventral surface a
special sucker (e) has developed.

6. — Two Diporpae about to unite. The ventral sucker of A is seizing the dorsal papilla
(/) of B.

7. — The two Diporpae are twisting round, so that the ventral surfaces of the "tails" are
towards each other.

8. — The two Diporpae have arrived at the definitive position, forming a cross, and constitut-
ing a Diplozoon.

obtain so copious a supply of nutriment that it grows extremely
rapidly, and produces eggs in five weeks; it remains, however, in
the gill chamber when this is formed, and dies before the meta-
morphosis of its host. Thus " gill parasites " differ in several
points from the "cloacal form," notably in the absence of a vagina,
and consequently in the impossibility of copulation.

ORDER 2. Aspidocotylea, Monticelli ( = Aspidobothrii, Burm.).

Trematoda in which the adhesive apparatus has the form of a great
sucker occupying nearly the entire ventral surface of the body, from
which it is usually distinctly constricted off. This single sucker becomes,
during development, traversed by transverse (and usually also longitudinal)
ridges, and is thus in the adult subdivided into a number of more or less

THE TREMATODA

1

FIG. V.—Polystomum integerrimum, Frol., from the Cloacal Bladder of the Frog. (After
Zeller ; but 5, 6 partially original.)

1.— Dorsal view, showing the alimentary tract, a, mouth, b, pharynx ; between a and
b are the four eyes which are very small in the adult ; c, excretory pore of right side ;
d, vaginal pores on the " lateral swelling" of the right side ; e, the right limb of the intestine ;
/, the transverse anastomoses ; g, the prolongation of the median gut into the caudal disc ; h,
caudal disc or cotylophore.

2. — Ventral view, showing the reproductive system, b, penis ; e, common genital pore ; e,
sperm duct ; /, vaginal canal, dilated to form a spermatheca ; g, germarium ; h, the genito-
intestinal canal, passing from the oviduct to the left limb of the intestine, a small piece of
which is shown ; i, testis ; j, vitellarium, extending into the caudal disc ; fc, vitello-duct, the
index line passes to the point where the fore and aft longitudinal ducts unite to form the trans-
verse duct, from the middle of which a short nearly median duct passes to the oviduct ; I,
ootype, containing an egg cell, surrounded by vitelline cells ; the shell glands around the
ootype are not shown ; m, uterus, short and slightly undulating, containing a small number of
eggs ; n, the germ duct. On the caudal disc are the three suckers (1, 2, 3) on each side ; each
surrounding a small hooklet (cf. Figs. 6, 7). Six small booklets are visible between the
anterior pair of suckers, and four others, as well as two large hooks, lie between the posterior
pair of suckers.

3. — Two individuals copulating. The genital pore of each is placed in contact with the
right "lateral swelling "of the other; the left lateral swelling of each is indicated by a and
a' . By means of the suckers b, b' , each individual is attached to the wall of the cloacal
bladder, a portion of which is represented at c, and being transparent, allows the six suckers
of each animal to be seen through.

4. — An egg; a, the germ cell ; b, vitelline cells ; c, egg shell ; d, the "stalk."

5. — A larva, seen from the dorsal surface ; the eyes, ciliated bands, and apical tuft of
cilia are shown.

6. — A larva, from the ventral surface. The caudal disc at this stage is without suckers, but
is armed with sixteen booklets.

7. — A young Polystomum, in which the two hindmost suckers (2, 3) on each side have made
their appearance. The first to appear is No. 3 ; each is developed round a hooklet ; they are
here seen in optical section, as the young worm was much stretched ; e, the pair of great hooks
have made their appearance in the middle of the posterior region of the disc. The most
anterior sucker on each side will develop around the hooklet lying just behind that labelled*
d. The pharyngeal sac is everted (a) during the movement of the worm, and in its endeavours-
to find a resting-place ; b, pharynx ; c, sac-like intestine, beginning to exhibit central inter-
ruptions, which in the course of development are destined to increase in size, while the
transverse anastomoses will proportionately diminish. The circular marks represent large
cells which, during the course of metamorphosis, accumulate brown granules and concretions,
and then drop off into the gut.

THE TREMATODA

59

rectangular compartments (suckerlets). There is no anterior sucker
related to the mouth. The intestine is a simple sac like that of the
Rhabdocoele Turbellarians, and is entirely deprived of lateral caeca.

FIG. VI. — Aspidocotylea.

1.— Macraspis elegans, Olss., from the gall-bladder of Chimaera. (Altered from Monticelli.)

2. — Platyaspis lenoiri, Poir. (After Monticelli.) From the intestine of the Chelonian,
Tetrathyra vaillanti, from Africa.

S.—Catylogaster michaelis, Montic., from the fish Cantharus vulgaris. (Altered from
Monticelli.)

4. — Aspidogaster conchicola, v. Baer, from Anodon, etc. (After Monticelli.) g, the marginal
sense organs of the sucker.

5, 6, 7.— Three stages in the development of Aspidogaster. (After Voeltzkow.) In the
youngest freshly hatched embryo (5) the sucker is posterior and simple; the mouth is
provided with an oral sucker. In a later stage (6) the hinder end of the body has grown back-
wards, thrusting the posterior sucker on to the ventral surface ; the sucker itself has increased
in size, and a series of transverse muscular ridges has developed, dividing its cup into a
series of compartments ; the contractile sacs (j), which are at first apparent anterior to
the sucker, having during the process of growth been carried backwards beyond the hinder
margin of the sucker. In a later stage (7), of which only the posterior end is shown, the
process has gone still further ; a median ridge now divides each of the compartments into
two. By the appearance of a right and left lateral ridge the adult condition is brought about.

8. — Side view of an embryo at about the same stage as 5.

The following letters have the same signification throughout :— a, mouth ; b, genital pore ;
c, ventral sucker ; d, post-acetabular portion of the body in Aspidogaster; e, the curious tongue-
shaped prolongation of the sucker of the embryo, which ultimately disappears as the sucker
enlarges; /, pharynx; g, marginal sense organs in Aspidogaster; h, intestine; j, the pair of
contractile sacs, each with a concretion ; these sacs are the forerunners of the dilated portions
of the collecting tubes (b in Fig. VIII.) of the adult.

Development is direct ; there is no ciliated larva ; there is no inter-
mediate host (see 35, 41, 44).

FAMILY — ASPIDOBOTHRIDAE, Burmeister. The single family has the

60 THE TREMA TO DA

characters of the order. Aspidogaster, v. Baer, in Mollusca. Platyaspis,
Montic., in Chelonians. Cotylogaster, Montic., in Cantharus vulgaris.
Macraspis, Ols., in gall bladder of CJtimaera.1

Further Remarks on the Order Aspidocotylea. — The members of
this group agree in their life -history with the monogenetic
Heterocotylea, but structurally they are more closely related
to the Malacocotylea, especially in the arrangement of the ex-
cretory and the reproductive organs, as well as in their endo-
parasitic habit. In their young condition, with a small posterior,
ventral sucker and an anterior oral sucker, Aspidogaster very
closely resembles Distomum. The form of the alimentary canal
and details in the generative organs are, however, peculiar to the
order. It has been by some authors grouped with the Hetero-
cotylea (Monogenea), by others with the Malacocotylea (Digenea).

FIG. VI I.— Aspidogaster.

The upper figure represents a side view of
the animal, a, mouth ; b, pharynx; c, intes-
tine ; d, genital pore in the cervico-pedal pit
(of Stafford) ; /, foot carrying the sucker ; q,
ventro-lateral nerve ; r, cerebral ganglion ; t,
body ; x, excretory pore.

The :lower figure is a diagrammatic trans-
verse section, at about the level of the ger-
niarium. a, the horizontal muscular septum
dividing the body cavity — filled of course with
parenchyma— into an upper chamber, and a
lower, and extending from the genital pore to
the hinder end of the intestine ; b, the collect-
ing vessels of the excretory system ; c, intes-
tine ; d, excretory tubule ; /, uterus ; g, vitel-
lariuin ; fc, germarium ; p, penis ; q, longitudinal
nerve in the foot ; s, sucker showing the three
ridges and the margin.

But Burmeister first, Monticelli more recently, have erected a special
order for it and its allies.

Aspidogaster conchicola, v. Baer, is a small organism occurring
in various species of Unio and Anodon of Europe and North
America. According to Yoeltzkow it infests several organs, but
most frequently (66^/) Keber's red-brown organ; less frequently
(3 3^) the pericardium, and very rarely the organ of Bojanus ;
whilst in the young stages it is parasitic in the intestine. It also
occurs in some fresh-water Gastropods.

The general shape of the animal, with its neck, body, and
central sucking disc, recalls strongly that of some Gastropod
mollusc (Fig. VII.). The general anatomy will be gathered
from the diagrams (Fig. VIII.) ; it is a form comparatively easy
to obtain and to study.

1 It is probable that Stichocotyle, Cunningham, belongs to this family, rather
than to the Holostomidae (see 36). It is only known in an immature condition encysted
in the wall of the intestine of Homarus americanus and Nephrops norvegicus. Monti-
celli also includes Aspidocotyle in this order.

THE TR EM A TOD A

61

The simple and archaic character of the intestine appears to be
related to the exceptional dorso-ventral thickness of the body, for

FIG. VIII. — The Structure of Aspidocotylea, founded on that of Aspidogaster.

On the left, plan of the generative organs, seen from above. The alimentary canal is
indicated by dotted lines, in order to illustrate the dorsal position of the uterus throughout
the greater part of its extent, and its passage round the sides, to gain the ovary on the one hand
and the genital pore on the other, a, mouth ; b, pharynx ; c, the simple sac-like intestine ; d,
genital pore (really ventral in position) leading into the genital atrium ; e, the copulatory
region of the uterus surrounded by glandular tissue ; /, the uterus, long, undulating, as in a
Distome, and dorsal in position ; g, vitellaria, with a longitudinal duct on each side connected
by a transverse vitelline duct to open by a short common duct into the germ duct (h) ; i, ootype,
surrounded by the shell gland ; j, Laurer's canal (=recept. vitelli of Voeltzkow), arising from
the germ duct and passing backwards to terminate in a pyriform dilatation (/) just below the
skin of the dorsal surface, immediately behind the end of the intestine ; k, germarium ; I,
testis, here a single "compact" organ; in, sperm duct; n, seminal vesicle; p, penis, sur-
rounded by prostate gland ; s is the outline of the sucker which just projects beyond the
margin of the body ; t, outline of body.

On the right, plan of the excretory system, a, excretory pore (there are two, according to
Stafford) ; ft, the great collecting vessels or ducts dilated posteriorly to form a bladder ; c,
excretory tubule arising from its anterior end and passing into the neck ; d, the recurrent
limb ; from the point marked by the index line there are, in the whole course of the system,
bunches of cilia (flames) set close together along the mesial wall of the tubes. This main tube
gives off branches (e) which, according to Stafford, always came off in 3's, and the subsequent
branching is also in 3's ; after six such trifurcations the finest capillaries terminate in flame
cells. This figure was drawn before Stafford's paper appeared, and is schematised from
Voeltzkow's side view ; he, like Huxley, described the right and left canals as asymmetrical, as
here represented ; Stafford believes them to be symmetrical ; Ay, the branch from left canal to the
germarium; I', the branch to the testis; sf, the branch to the sucker; according to Stafford,
similar branches issue from the right canal as well.

the reproductive organs can attain their full size and development
without compressing the gut and interfering with its primitive
sac-like form. The wall of the intestine, as well as that of the

62 THE TREMATODA

wide collecting canals of the excretory organs, is provided with
distinct layers of circular and longitudinal muscles — an unusual
condition amongst the Trematoda.

The retractile sense organs arranged at definite intervals along
the margin of the ventral disc are extremely peculiar ; they are
supplied by a special nerve traversing this margin.

The body is divided into an upper and a lower portion by a
horizontal muscular partition (Fig. VII.), extending anteriorly
from the genital pore as far backwards as the end of the in-
testine ; in the dorsal portion are situated the intestine, the
terminal portions of the genital ducts, and the vitellaria ; whilst
in the ventral portion lie the gonads, the wide excretory canal,
and the lateral nerves.

With regard to the reproductive organs, the single globular
testis is exceptional, retaining the ancestral form. Certain parts
of the female apparatus are difficult of interpretation ; the recepta-
culum mtelli or receptaculum seminis is now regarded as homologous
with " Laurer's canal," which has lost its external opening (Looss,
Goto). It is stated to contain yolk spheres, and is developed
by proliferations of epiblast cells from the dorsal surface (44).
Self -copulation has been directly observed by Voeltzkow, and no
doubt constantly occurs, as frequently only a single parasite is
found.

The egg develops into a young embryo, which differs from the
adult, chiefly in the fact that the sucker is posteriorly placed
on the ventral surface, and is relatively small (Fig. VI. 5-8).
There is also an oral sucker. The posterior sucker gets carried
forwards by the growth of the hinder dorsal part of the body ;
and the gradual formation of the compartments has been observed.

The mode of infection is unknown, since the embryos have
only been hatched artificially, and it is unknown whether eggs or
embryos leave the body, and how they arrive in the organs in
which they are parasitic.

ORDER 3. Malacocotylea, Monticelli ( = Distomea, Leuck. = Mala-
cobothrii, Burm. = Digenea, v. Ben.).

Endoparasitic Trematoda in which the suckers are never more than
two in number, viz. a circumoral sucker, #nd a second, somewhere on the
ventral surface ; the latter may, however, be absent. In addition to
these two typical suckers, accessory organs are developed to aid in
fixation, in the form of glandular papillae, or scattered spines ; but there
are never any booklets or skeletal pieces on the chief ventral sucker.
The two forks of the intestine are usually without caeca. The excretory
system always opens to the exterior by a median posterior pore which
leads into a median contractile sac. In addition to the pores of the
sperm duct, and uterus, which normally open through a common atrium,

THE TREMATODA

there is usually a small aperture on the dorsal surface which leads into a
narrow canal, known as " Laurer's canal," opening into some part of the
female duct system. There is never a separate vagina in the sense in
which the word is used in the Heterocotylea.

FIG. IX.— The Structure of a Schematic Malacocotylean. (Founded on that of a Distomum.)

1. — Plan of the alimentary canal and the nervous system, supposed to be seen from the
dorsal surface, a, the ventrally placed mouth (represented by dotted outline) lying in the
centre of the anterior sucker, also indicated by dots ; b, pharynx ; c, median portion of the
intestine (this may be long or so short as to be practically absent) ; d, the bifurcate intestine
which typically is without caeca ; e, the brain ; /, anterior nerve ; g, marginal (lateral) nerve ;
7i, the ventral nerve ; i, the dorsal nerve stem (the commissures are not represented, see
Fig. XX.) ; j, the posterior, median excretory pore ; I, the dorsally placed aperture to which
Laurer's canal is seen passing upwards.

2. — Plan of the external anatomy of the ventral siirfaces and of the excretory system, c,
posterior or ventral sucker ; d, the genital pore ; j, the excretory pore leading into a median
contractile bladder (fc) which bifurcates anteriorly and receives on each side the duct or
collecting canal (I) ; this runs forward to a varying distance and then gives rise to two canals —
(m) the anterior and (n) the posterior canals ; eacli of which gives otf branches terminating in
flame cells.

3. — Plan of the genital organs supposed to be viewed from the ventral surface, c, margin
of the ventral sucker ; d, genkal pore leading into the genital atrium and receiving the male
and female ducts ; e, uterus, long and undulating ; /, ootype, surrounded by the shell gland ;
(7,*germarium. The region between /and g is the germ duct, and receives on one side Laurer's
canal (I), and on the other the median vitello-duct (m) ; n, the vitellarium, with longitudinal
vitello-duct connected by transverse ducts to the median duct ; p, cirrus in its sac ; r, seminal
vesicle ; s, sperm duct, formed posteriorly by the union of the two testicular ducts ; t, the
testes, here compact and nearly always double.

In the life-history of the Malacocotylea the fertilised egg gives rise to
a larva which, in order to complete the cycle, enters another ("inter-
mediate") host; here it usually gives rise asexually to numerous
individuals of a second form, and frequently these again to a third form,
from which the sexual worm is developed. So that from each egg
deposited by the adult a very large number of new flukes are developed.

64

THE TREMATODA

The adults live in Vertebrata, and nearly always in tlie enteron or its
outgrowths ; the intermediate host is usually a mollusc.

FAMILY 1. AMPHISTOMIDAE. Body more or less cylindrical ; oral

--a

7

FIG. X. — Some Malacocotyleans.

Letters common to all the figures, except Fig. 8. a, mouth and oral sucker ; b, genital
pore ; c, posterior ventral sucker.

1. — Amphistomum conicum, Zed., from the paunch of the cow; ventral view (after Laurer).
The genital pore is at the apex of a small papilla surrounded by a shallow groove (cf. Fig. A).

2. — Homologaster paloniae, Poir., from the caecum of Palonia (Bos) frontalis ; ventral view
(after Poirier). p, the adhesive papillae covering the ventral surface.

3. — Gastrothylax cobboldii, Poir., from the stomach of Palonia; lateral view (after Poirier).
The furrow surrounding the genital papilla has become deepened to form a sac (cf. Fig. B), the
entrance to which is labelled d. Figs. A and B are immediately below 2 and 4 respectively.

4. — Ogmogaster plicata, Crepl., from the caecum of Balaennptera sp. ; ventral surface (after
Jagerskiold). r, the longitudinal ridges constituting a secondary adhesive organ.

5. — Notocotyle serialis, Dies., from the colon of Anas penelope ; dorsal surface (after Diesing).
s, the dorsal suckers in three rows.

6. — Didymozoon thynni, Tschbg. (= Monostoimim bipartitum, Wedl.), from a cyst on the
gills of Thynnus vulgaris (after Wagener). The two individuals are closely wrapped round one
another, their "heads" projecting freely.

7. — Anterior sucker of Gasterostomum fimbriatum, v. Sieb., from the stomach of the pike
(after Wagener). ee', the tentacle-like processes from its margin.

8. — Gasterostomum armatum, Mol., from the intestine of Cottus scorpio ; ventral view (partly
after Molin, partly after Levinsen). b, genital pore ; e, anterior sucker ; /, vitellarium ; g,
simple sac-like intestine ; h, the left vitelline duct, which unites with its fellow, and opens
by a median duct into the germ duct ; i, uterus ; j, germarium ; k, mouth, which has a position
unique amongst the Trematoda, nearly in the middle of the ventral surface ; I, the right testis ;
m, seminal vesicle ; n, cirrns sac ; o, cirrus or penis ; u, excretory pore.

9. — The smaller of the two individuals of Didymozoon, probably the male. (After Wagener.)

10. — Monostominn mutabile, Zed., from the sub-orbital sinus and body cavity of various
aquatic birds. (After P. J. van Beneden.) •», excretory pore.

11. — Opisthotrema cochleare, Lkt., from the tympanic cavity and Eustachian tube of Halicore ;
ventral view (modified from Fischer). The genital pore (b) is posteriorly placed.

THE TREMATODA 65

sucker small ; posterior sucker terminal, usually large, and in front of it
fixing papillae may be developed on tlie ventral surface. Amphistomwn,
Hud. (Fig. X. 1) ; numerous species in various mammals. A. (Diplo-
discus) subclavatum, Goeze, in rectum of Ampliibia (see 30). Gastrothylax,
Poir. (Fig. X. 3) ; Homalogaster, Poir. (Fig. X. 2) ; Gastrodiscus, Cobb. ;
G. polymastos, Leuckt., in colon of horse. Aspidocotyle, Dies., intestine of
fish (Monticelli places the genus in the order Aspidocotylea). FAMILY 2.
DISTOMIDAE. The posterior sucker has shifted forwards along the ventral
surface, so as to come to lie in the middle of the body, or even in front
of this point ; no adhesive papillae, though spines are frequently developed
on the surface of the body ; the genital pore is almost always in front of
the ventral sucker, usually in the middle line, rarely shifting to the side
(see 32, 38, and Fig. XI.). Distomum, Retzius ( = Fasciola, L., in parte),
no retractile boring proboscis ; hermaphrodite. The genus has been
subdivided into eleven sub-genera. Sg. Cladocoelium, Duj. ; D. hepatic-urn,
L., occurs in the bile ducts of various mammals, especially common in sheep,
but also in man, kangaroo, ox, etc. The "Liver-fluke" is so commonly
taken as a " type " of the Trematoda, that a brief historical account of it
may be of interest.

Being the cause of a disease — " sheep-rot " — in a domesticated animal
it naturally claimed the attention of naturalists and others in early times ;
the first account of an epidemic of this disease being given by Gemma
(1575) as having occurred in 1552 in Holland. The earlier writers
believed the parasite to occur in the blood-vessels of the liver, till Faber
(1670) established the fact that it occurs not in the blood-vessels but in
the gall bladder and bile ducts and their capillaries (vermis e ductu
cystico et poro biliario). Ruysch (1691) gives the first (but extremely
poor) picture of the " fluke. " Redi, who was acquainted with quite a
number of parasites of birds, mammals, etc., referred to the fluke as
vermis vervecini hepatis, and gives a fairly good figure of it.

Faint inklings of its life-history occur in Gesner's work (1551), where
he mentions that in France it had been noticed that in the livers of
sheep, which had eaten certain plants growing by the water's side, and
termed " duva," small leech-like animals were found, causing a disease in
the sheep to which the name "duva" was given. These two uses of the
word still exist; douve in modern French is "spearwort," and douve de
foie is the liver-fluke. Leeuwenhoek, however, did not connect the fluke
with eating, but. believed that the flukes live freely in the water and
make their way into the gall bladder of the sheep, while the host is
drinking.

Romberg (1706), on the other hand, who discovered flukes in the calf,
regarded them as vermes cucurbitini (a term used at that time for
isolated proglottids of Cestodes). Pallas (1760) was the first to add man
to the list of hosts.

The correct name of the liver-fluke is even now a matter of discussion
amongst purists of nomenclature. Linnaeus (1746) used the word
Fasciola to include the "fluke," a fish Cestode (Schistoceplialus), and a
Triclad (Dendrocoetum), under the belief that they were all stages in
one life-history, starting with the Planarian ; and to this assemblage gave

66

THE TREMATODA

the name F. hepatica ovata. But Retzius (1776) invented the name
Distoma for the Trematodes, of which several were then known, retaining
Fasciola for something quite different (viz. Gordius) ; 0. F. Miiller
(1776) also separated Linne's Fasciola into two, retaining the name for
a Trematode and giving Planaria to the Turbellarian, and for some

FIG. XI.— A Group of Distomidae.

1.— Distomum variegatum, Rud. (after Looss), from the lung of Rana esculenta, to show the
general shape and disposition of the suckers. Its anatomy agrees closely with the generalised
"type "(see Fig. IX.).

2. — D. confusum, Looss, from the intestine of frog and toad. The genital pore has shifted
in this and some other species to the left margin of the animal. In this case the other organs
have undergone peculiar shiftings from the normal. The testes and vitellaria are anterior.
(After Looss.)

3. — D. acanthocephalum, Stoss. (after Stossich), from the rectum of Belone ams. t, hooklets.

4. — D. miescheri, Zsch. (after Zschokke), from the oesophagus of Trutta solar ; side view to
illustrate the fact that the male (<$) and female pores (9) may be separate.

5. — Koellikeria filieolle, Rud. (D. okenii, Kol.), from cysts in the branchial chamber of Brama
raji (partly after Kolliker).

6. — D. nodulosum, Zed. (after Looss), from the intestine of Acerina cernua, to show tentacles.

7. — Rhopalophorus horridus, Dies., from the duodenum of Didelphys myosurus ; ventral view
(after Diesing). r, armed tentacles.

8.— D. verrumsum, Poir., from stomach of Thynnus (after Poirier).

a, mouth and oral sucker ; 6, genital pore ; c, ventral sucker ; d, intestine ; /, vitellaria ;
e, testis ; g, cirrus ; h, vaginal region of uterus ; i, cirrus sac ; j, seminal vesicle ; fc, uterus ;
I, germarium ; m, spermatheca ; s, enlarged sac of 9 Koellikeria ; o, excretory pore.

time Fasciola hepatica was the name of the liver-fluke. Zeder and
Rudolphi, however, returned to Retzius's name Distoma, which Nitzsch
(1816) altered to Distomum; and since that time, with a few dissentients,
this modification of Retzius's name has been employed.

The anatomy of the liver-fluke may be found in nearly every text-
book, and has been the subject of much work by Leuckart in his well-

THE TREMATODA 67

known work on " Parasites " ; while Sommer (40) made a special study
of it, the illustrations to which are copied in nearly all accounts.
Eaillet has recently (1890) proved experimentally that it sucks the blood,
and does not feed upon the bile of its host.

Sg. Dicrocoelium, Duj. ; D. cylindraceum, Zed., lung of frog. D. reflexum,
Crepl., oesophagus of salmon. Sg. Podocotyle, Duj., only in the intestine of
fishes. Sg. Brachycoelium, Duj. ; D. claviformis, Brds., in rectum of Tringa
alpina,. D. rubellum, Olss., intestine of Labrus. D. heteroporum, Duj.,
intestine of bats. Sg. Brachylaimus, Duj. ; D. tereticolle, Hud., in pike. D.
variegatum, End., lung of frog (Fig. XI. 1). Sg. Apoblema, Duj., in fishes only.
D. appendiculatum, End., in Clupea alosa. Sg. Echinostoma, Duj. ; D. trigono-
cephalum, End., intestine of various carnivora ; other sp. in fishes, birds,
and mammals. Sg. Crossodera, Duj., in fishes only. D. nodulosum, Zed.,
intestine of perch (Fig. XI. 6). Sg. Cephalogonimus, Poir. ; D. lenoiri, Poir.,

FIG. XII.— Bilharzia haematobia, v. Sieb., from the Blood of Man. (After Fritsch.)

c5 , the male ; ? , the female. «, mouth ; 6, ventral sucker ; c, excretory pore ; d, gynae-
cophoral groove on the ventral surface of the male, in which lies the genital pore, and the sides
of which clasp the female.

in Chelonian. Sg. Urogonimus, Montic. ; D. macrostomum, End., in Fringilla,
etc. Sg. Mesogonimus, Montic. ; D. ivestermanni, Kerb., in lung of man, dog,
cat, tiger ; Europe and U.S.A.

The genus Rhopalophorus, Dies., has two retractile tentacles, armed
with booklets at the anterior end of the body. R coronatus, Eud.
(Fig. XI. 7) ; Bilharzia, Cobbold (Gynaecophorus, Dies.), the sexes are
separate and dimorphic (Fig. XII.) ; the male is smaller than the female,
which he carries in a ventral (gynaecophoral) groove, posterior to the
ventral sucker, and in which the genital pore lies ; the anterior part
of the body is cylindrical, the groove being formed by an inrolling
of the sides ; they live always in pairs in blood-vessels of mammals,
in hot climates (see 33). B. haematobia, Bilh., in the abdominal veins of
natives of Africa, in some parts of which nearly half the inhabitants are
infected. The eggs are laid in the blood, accumulate in the capillaries,
and cause inflammation and rupture of the vessels. According to Sonsino,

68

THE TREMATODA

FIG. XIII.— A Group of Holostomiclae.

1. — Diplostomiim longum, Brds., from intestine of Brazilian crocodile (after Brandes),
ventral view. The anterior region of the body (A) is well marked off from the tail-like genital
region (B\ which is cylindrical. The latero-posterior margin (/) of A is slightly prominent.
The new adhesive organ (e) consists of a pit ; from the bottom rise glandular papillae (cf.
Fig. 5).

2. — Hemistomum clalhratum, Dies., from intestine of Liitra Irasiliensis (after Brandes). The
margin (/) of the fore body is curved inwards and partially conceals the accessory adhesive
organ (e), which has the form of a long ridge (cf. Figs. 4 and 6), the edge of which overhangs the
base and hides the ventral sucker (d).

3. — Holost. variabile, Nitzsch. (modified from Molin and Brandes), from intestine of various,
carnivorous birds. The margin (/) of the fore body has now bent round and fused to form
a cup from which the elaborate " accessory organ " projects. At the posterior end is seen
the " bursa copulatrix" (/) — characteristic of the family — with the genital sucker (m) and
papilla (p) carrying the genital pore.

4. — Transverse section of Hemistomum. c, intestine ; the numerous small circles are sections,
of the excretory canals which invade the organ.

5. — Longitudinal section of the fore body of Diplostomum, Brds., to show the prominent
hinder margin (/).

6.— Hemistomum. Longitudinal section of the fore body to show the foot-like accessory
organ e.

7. — Holostomum (after Brandes). Diagrammatic transparent view of the fore body.

8. — " Tetracotyle " (partly original).

9. — Side view of Polycotyle ornata, Wilh. -Suhm., from the gut of Alligator lucius (partly
diagrammatic, after Poirier). x, the several dorsal suckers of hind body.

Letters common to all figures : A, fore body ; B, hind body or genital region, a, mouth and
buccal sucker ; fe, pharynx ; c, intestine ; d, ventral sucker ; e, accessory adhesive apparatus ;
e1, e2, its parts in Holostomum; f, the prominent and incurved margin of the fore body ; /', the-
cup produced ; g, uterus ; h, germarium ; i, testis ; j, sperm duct ; A;, prostate ; I, bursa
copulatrix ; m, genital (copulatory) sucker ; n, excretory pore and bladder ; p, genital papilla ;
s, glands in connection with accessory apparatus.

THE TREMATODA 69

the intermediate host is a small crustacean, into which Bilharzia, pene-
trates and encysts ; the host is swallowed, with the water, by man.
B. magna, Cobb., in the vena cava of Cercopithecus fuliginosus. B. bovis,
Sons., in domestic cow ; Egypt and Sicily. Koellikeria, Cobb., unisexual,
dimorphic; the male thread-like, the female swollen posteriorly (Fig,
XI. 5) ; they live coiled together in pairs, encysted in the oral and
branchial cavity of marine fish. FAMILY 3. HOLOSTOMIDAE. The
body is divided into two regions : in the hinder, cylindrical, tail-like
region the genital organs are developed, the copulatory aperture of which
is at the posterior end, where a sucker is developed. In addition to
the normal two suckers, which are both situated in the anterior region of
the body, there is developed here an adhesive apparatus by the inrolling
of the sides to a greater or less extent. The members of this family
present no " asexual " generation in their life-history ; each egg gives rise
to only one sexual worm, but passes through a larval stage, which,
when encysted in an intermediate host, is known as " Tetracotyle," and
resembles a cercaria ; 1 for an account of anatomy and development, see
10, 12). Diplostomum, v. Nordm., in birds and crocodiles (Fig. XIII.).
Hemistomum, Dies., numerous species in birds and mammals (Fig. XIII. 2).
H. excavatum, Nit, in Ciconia alba, has a larva living in Rana temporaria.
Holostomum, Nit., numerous species in intestine of birds. H. variegatum,
in Larus ridibundus and other birds, has as larva Tetracotyle ovata,
v. Linstow, which occurs encysted in the peritoneum, in the head and
elsewhere of Acerina cornua. H. variabile, Nitzsch (Fig. XIII. 3), has as
larva, Tetracotyle colubri, v. Linst. Ercolani was the first to prove by
feeding experiments that " Tetracotyle " or " Diplostomum " develops into
Holostomum. Polycotyle, W. Suhm. ; P. ornata, W. S., gut of Alligator
lucius. FAMILY 4. MONOSTOMIDAE. The characteristic posterior sucker
has disappeared, but the oral sucker (everted pharynx according to Monti-
celli) remains. The genital pore usually occupies the normal position ;
there is no Laurer's canal. Monostomum, Zed. (Fig. X. 10); many species
in all vertebrates (see 47). Opisthotrema, Lkt. (Fig. X. 11); Notocotyle,
Dies., in birds (Fig. X. 5). Ogmogaster, Jaeg., in Cetacea (Fig. X. 4).
FAMILY 5. GASTEROSTOMIDAE. Mouth ventral ; anterior terminal sucker
imperforate, surrounded by tentacular-^: e processes ; genital pore at the
hinder end of body ; intestine sac-like, unforked, short. Gasterostomum,
v. Sieb., in intestine of fish (Fig. X. 8). Gasterostomum fimbriatum,
v. Sieb., lives in Perca fluviatilis ; the egg gives rise to a larva which
makes its way into Unio or Anodon; a sporocyst is formed in the liver
or gonad ; and within this arises the peculiar cercaria known as Bucephalus,
v. Baer (1), from its resemblance to the head of an ox (Fig. XIV.).
When liberated they make their way out through the exhalant siphon
and live freely in the water for a few hours. This cercaria is destined
to be swallowed by the second intermediate host, Leuciscus erythroph-
thalmus, in which it encysts itself in the wall of the mouth, or on the
gills, and when Leuciscus is devoured by the perch, the cyst is dissolved,
and sets free Gasterostomum, into which Bucephalus (as Wagener showed,

1 In specimens of A mmocoetes great numbers of Tetracotyle sometimes occur in the
vascular membrane covering the brain (Brown, Qu. J. Mic. Sc. xli. p. 489, 1899).

THE TREMATODA

1858) has meanwhile changed. Gasterostomum, sp. of the shark, has
as first intermediate host Ostrea, Cardium, etc., whence issues Buceph.
haimeanus, which makes its way into a second host, the fish Belone.
The sporocysts castrate the mollusc which they attack. FAMILY 6.
DIDYMOZOONIDAE, Montic., live in pairs, encysted on the surface, oral
cavity, or branchial chamber of fishes; the anterior sucker alone is
present ; the genital pore is in front of the oral sucker. Didymozoon,
Taschb. (Fig. X. 6, 9) ; Nematobothrium, v. Ben.

A

B

FIG. XIV.

Bucephalus polymorphiis, v. Baer. The forked-tailed cercaria of Gasterostomum fimlmatum,
v. Sieb. The cercaria occurs in Anodon, etc., the adult in Leuciscus, sp. A, the body ; B, the
bifurcate tail ; a, the pharynx, behind which is the mouth, in the centre of the body ; b, the
pear-shaped glandular organ, which is replaced by the anterior sucker during its metamor-
phosis ; c, the ansatzstiick at the base of each limb of the bifurcate tail ; between them is seen
the base or median portion of the tail.

Further Remarks on the Order Malacocotylea. — Whereas the
general statement is true that sexual forms of this group occur
only in Yertebrata, there are at least two species of Distomum
which constitute exceptions : —

D. echiuri, Greef, is found in the nephridium of the male
gephyrean Ecliiurus pallasii. D. rhizophysae, Stud., occurs in
the siphonophorous hydrozoan, Ehizophysa conifera. An encysted
Distoma has been found in the tentacles of Synapta, and the
viscera of Ophiurids, by Cuenot (1892).

Further, several sexless, not encysted, cercariae have been
recorded from various marine non-molluscan animals : D. pelagiae,
Koll., in the gonads of Pelagia ; D. hippopodii, C. Yogt ; D. cesti-

THE TREMATODA

veneris, Vogt ; and others, from body cavity of Sagitta, Salpa,
F"elella, etc.

In addition to a number of anatomical peculiarities in the

FIG. XV. — Development of Embryo of Distomum tereticolle. (From Schauinsland.)

1. — The living egg with its gelatinous envelope (a) ; b, egg shell deposited in ootype ; cr
germ cell with large nucleus ; d, vitelline cells ; outlines not distinguishable in living egg, but
the seven nuclei indicate the number of cells.

2. — Segmentation of the germ cell has resulted in a solid blastosphere ; the yolk is greatly
reduced. One of the blastomeres (/) at the upper pore is larger than the rest.

3. — This cap cell has divided and given rise to three cells, two at one pole, one at the
other. The yolk is nearly absorbed and is not represented in this figure.

4. — The cap cells have flattened out and form a "yolk envelope," investing the embryo and
the remains of the yolk ; two nuclei are seen above, two below, and one on the left side.

5. — The embryo, after separation of the yolk envelope, has become differentiated into
an outer layer of flat cells or ectoderm (<?) and a central mass (e) ; four nuclei of the shell
membrane are seen ; ft', operculum.

6.— Longitudinal section of the larva or miracidium of Distomum hepaticiim. (From Coe in
Zool. Jahrb. ix. 189(3 (Anat.), p. 561.) g, flat epidermal ciliated cells, derived from g in Fig. 5 ; h,
the underlying cellular cutis ; i, head glands (Coe), one on each side of the body, each with a
narrow duct opening on the tip of the head papilla, which is represented partially retracted ; the
secretion is indicated by a row of dots ; j, the vestigial enteron ; fc, eyes, resting upon the
brain (t) ; in, flame cell, on each side, whence a fine duct (n) passes "backwards to open to the
exterior at (o) excretory pore ; p, general parenchyma ; q, a germ ball ; r, germ cells, posteriorly,
lying in a cavity which appears to represent the coelom.

7. — Transverse section of the embryo at the level of the eyes, g, ectoderm cell, with its
peculiar elongated filamentous nucleus cut longitudinally. In Fig. 6 the nuclei are cut trans-
versely, and appear in the hind end of each cell. Other letters as before. The nuclei outside
the eye are possibly part of a sensory apparatus. Coe was unable to see the retractor muscles
of Leuckart.

nervous and reproductive system, to which reference is made
below, the most striking and interesting differences between the
Heterocotylea and the Malacocotylea lie in the developmental
history, to illustrate which a concrete example may be described.

72 THE TREMATODA

The early stages of development up to the formation of a free-
swimming larva are best known for Dist. tereticblle, from the pike
(Schauinsland, 39). The egg cell is embedded near the anterior
end of the egg in a mass of yolk cells ; segmentation is total, and
nearly regular, giving rise to a solid blastosphere (Fig. XV.).
At the anterior pole one cell delays in its further segmentation,
whilst the rest continue to divide and give rise to smaller cells ;
this apical anterior cell flattens out and divides into two ; these
(after further subdivision) spread over the yolk cells, which have
in the meantime diminished in size and undergone a certain
amount of disintegration. Other flat cells make their appearance
posteriorly, and extend forwards ; in this way a " yolk envelope "
of flat cells is formed which lies immediately within the egg
shell, and is left behind within it when the larva escapes. This
envelopment of yolk by blastomeres is similar to what happens
in Triclads. Meanwhile, the other blastomeres have become
differentiated into a flat epibl-ast, which becomes ciliated, and a
central mass of cells in which, later, the enteron becomes marked
out (? by delamination) as a simple sac.

Between the enteron and the epiblast there is developed from
the central mass two layers of muscles, which are in many cases
separated from the gut by a distinct cavity, which is lined by a
layer of cells and may be regarded as coelom. The coelom may,
however, in other cases be more or less blocked up by cells of an
embryonic character, probably derived directly from blastomeres.

The egg, having passed out of the host's body with the faeces,
undergoes its development in the water. The young larva, or
" miracidium " (M. Braun), or " ciliated embryo " (audorum), now
leaves the egg, and the further history has been most fully studied
in the case of D. hepaikum (by Leuckart, 27; and Thomas, 43),
and in D. cygnoides (by Wagener, 45). The eggs of these flukes
pass out of the host with the faeces, as King was the first to show
for the liver-fluke (1836); and the miracidium escapes into the
water. It is to all intents and purposes a Ehabdocoelous Tur-
bellarian without gonads ; its shape and structure are shown in
Fig. -XV. 6, 7, and Fig. XVI. 1.

At the apex of the snout, which is moved by muscles, is
situated the mouth — armed with a stylet in the case of D.
lanceolatum and others — which leads into the short, sac-like enteron.
Locomotion is effected by the ciliated epiblast, aided by the
somatic muscles. Cilia are generally regularly developed all
over the surface, or in some species limited to definite areas, but
are never in bands ; a pair of eyes — recalling in their structure
those of adult Heterocotyleans — rests upon the brain ; a pair of
flame cells represents the excretory system, and are said to be
derived from the epiblast (Fig. XV. 6, m).

THE TREMATODA

73

The miracidium (Fig. XVI.), once set free, swims about seek-
ing for a definite mollusc, into which it will bore its way by
means of the snout. Wagener (1857) was the first to observe the

n

FIG. XVI.— The life-history of Distomum hepaticum. (After Thomas.)

1. — The free swimming larva, or "miracidium," showing external appearance.

2. — Sporocyst, containing germ balls and young rediae.

3. — A young redia, containing germ balls ; the enteron is shaded but unlettered.

4. — A fully formed redia, containing a daughter redia, two cercariae, and germ balls.

5.— A free cercaria.

a, head papilla ; ft, anterior ring of ectoderm cells ; c, eyes ; d, same, degenerating, in
sporocyst ; e, embryo, at gastrula phase, in sporocyst ; /, enteron of young redia ; g, pharynx ;
h, collar of redia ; i, lip ; j, oesophagus of cercaria ; k, " germs," at blastosphere stage ; I, paren-
chyma ; m, posterior, locomotive processes of redia ; n, germ cells, in wall of redia ; o, birth
opening ; p, young cercariae in redia ; q, daughter redia in redia ; r, circumoral sucker of
cercaria ; s, ventral sucker ; t, cystogenous cells.

entrance into a mollusc in the case of D. cygnoides. In the case
of D. hepaticum this " intermediate host " is Limnaeus truncatulus,
as was proved by Thomas (42). The animal makes its way into
the liver, and undergoes a degeneration — a result no doubt of its

74 THE TREMATODA

parasitism ; it loses its cilia and the cells that bear them. The
enteron, meanwhile, undergoes obliteration and degeneration.1

The organism is now known as a " sporocyst " (Filippi), and
the " germ cells " which occupy the cavity begin to divide up to
form " egg-balls " (Fig. XVI. 2). According to some authorities,
the "germ cells" are directly derived from undifferentiated
blastomeres (Leuckart, Schauinsland), whilst others have described
them as arising by division from the cells of the body wall
(Thomas, Biehringer, 7 ; Heckert, 20).

Anyhow, the germ balls consist of cells of different sizes, and
soon a flat epithelium is differentiated around a central mass, the
epithelial cells are said to lose their nuclei and become cuticularised .
(Leuckart), while from the central mass a new outer layer becomes
differentiated, and thereafter the history is very similar to that by
which the miracidium was produced. By a series of changes there is
developed from each germ ball another larval form, which is known
as "Redia" (Filippi), or "king's yellow worm" (Bojanus and Swam-
merdam were the first to observe this stage, 1737); within this a new
generation of " germ balls " is already formed (Fig. XVI. 2, 3).

The redia differs from the miracidium, in the absence of cilia
and of eyes, in the possession of a pharynx, and in the general
shape. The rediae escape from the sporocyst, the aperture closes,
and the wound heals. The rediae in their turn produce a new
generation, the " Cercaria " (0. F. Miiller), in the same way, no
doubt, as they themselves were produced. But one or more new
generations of rediae may be produced by rediae ere the cercariae
are formed.

The cercariae, several of which are produced in a redia, escape
one by one through a definite birth-pore (as was first noted by
Bojanus). The cercaria possesses all the organs of the young fluke
in a rudimentary condition, even the foundations of the genital
organs are present ; in addition, there are the tail, cystogenous
glands, and, in some cases, eyes, stylets, and rod cells, organs only
used during the brief larval life (Fig. XVI. 5).

This third generation now leaves the snail, swims freely in the
water by the movement of its tail, and having attached itself to
a blade of grass by means of its ventral sucker, secretes a "mucous"
substance around itself which soon hardens to form a cyst (this fact
was known to Nitzsch, 1807). This cyst is devoured with the
grass by a sheep, the final host of D. hepaticum; the cyst is dis-
solved in the host's stomach, and the tail having in the meantime
dropped off or undergone degeneration, a young fluke emerges, and
makes its way up the bile duct and into its finer branches, where
it grows into an adult fluke.

1 It appears that in Victoria the intermediate host of D. hepaticum is Bulimus
tenuistriatus, according to T. Cherry, Proc. Roy. Soc. Viet. viii. (n. s.), 1896, p. 183.

THE TREMATODA

75

This history is the best known, and is true only within
certain limits for the whole group ; for in some cases one genera-
tion— the redia — is omitted ; in other cases the sporocyst may
form by gemmation a second generation of sporocysts, within
which the cercariae arise.

The sporocyst and redia are always parasitic in some mollusc ;
but the free-swimming cercaria chooses a great variety of hosts —
in fact, nearly any invertebrate may serve, though it is not neces-
sary for it to become parasitic at all ; the adult, however, is found
in members of all classes of Vertebrata, rarely in Carnivora, and
nearly absent in Pigeons and certain other birds ; Trematodes are
.especially common in fishes, aquatic birds, reptiles, insectivorous
birds and mammals, and marine mammals.

The cercariae are not all tailed, and this tail may present great
differences in size and structure. Many cercariae are known, some para-
sitic, others free-swimming, whose adult stage is unknown. And, as in the
case of the adult fluke, a species of cercaria may enter a variety of species of
host ; thus C. armata enters Paludina and Planorbis ; further, one host may
contain quite a number of different species of cercaria, e.g. L. stagnalis,
may harbour as many as eight species. Cercariae, with a well-developed
tail, are most numerous; the tail may be
provided with a fin-like membrane (G. lopho-
cerca\ or with bunches of " setae," regularly
arranged (G. setifera), (Fig. XVII.). It ac-
quires an enormous development in C.
macrocerca from Cyclas, and in C. elegant,
which occurs free in the sea. The tail is
retractile in G. mirabilis; it is bifurcated in
Bucephalus. The tail is quite rudiment-
ary in G. limacis and others, while the tail
is absent (" cercariaea ") in Leucochloridium
and others which live in terrestrial molluscs.

There is thus produced in the life-
history of the Malacocotylea a consider-
able number of flukes from each egg
cell by the intervention at one or more
stages of some form of non-sexual re-
production ; these asexual forms live in
a host different from that of the sexual
fluke ; hence van Beneden gave the
name Digenea to the group. But
amongst the Digenea were included As-
pidogaster and the Holostomidae, which
do not agree with this general history.
Aspidogaster has, owing to the possession of a number of anatomical
peculiarities, been removed from the group. The Holostomidae

1. —

FIG. XVII.

Cercaria setifera, Villot, in a
state of extension ; the long tail is
provided with a series of circles of
stiff bristles.

2.— C. fissicauda, Villot. Both oc-
cur in the marine lamellibranch
Scrobicularia tennis. (After Villot.)

76 THE TREMATODA

present this difference from the rest of the Malacocotylea ; the
young form, after entering the intermediate host, does not reproduce
asexually, but develops by a metamorphosis into the adult form,
when the intermediate host is swallowed by the final host ; Leuckart
has used the term " metastatic " in reference to this life-history.

This life-history of the common fluke is a favourite example
of "alternation of generations," or metagenesis, on the view that
the mode of reproduction in sporocyst and redia is an asexual one
(viz. budding) ; but Grobben first suggested that the cells which
give rise to "germ balls" are essentially ova, and that it is a case
of parthenogenesis — a view with which Leuckart essentially agrees.
In that case, the process is one of " heterogamy " (Leuckart) ; but
this term is more generally applied to cases in which two sexual
methods alternate, as in Bhabdonema nigrovenosum ; and Schwarze
has invented the term " alloiogenesis " to indicate alternation of
parthenogenesis with sexual reproduction. Glaus, regarding the
redia and sporocyst as larvae, sees in the history an example of
heterogamy with paedogenesis.

Leuckart, Balfour, and Looss regard the whole process as one
of a metamorphosis distributed over two or more stages (or gene-
rations), as a result of the appearance of vertebrates on earth ; for
before their appearance the flukes must have attained maturity in
an invertebrate, which, on the evolution of vertebrates, became
the intermediate host. Looss (30) has further shown that the sporo-
cyst, redia, and cercaria are all built upon a common plan, and
represent successive stages in development, the last being entirely
fluke-like, except for the full development of the generative organs.

The life-history of D. macrostomum is of interest in that the
redia and the free-living stage of the miracidium and cercaria are
omitted (see 20). The fluke inhabits the intestine of various sing-
ing birds, and its eggs pass out with the faeces of its host,- which,
falling on a leaf, may with it be eaten by the gastropod Succineaputris
(Fig. XVIIL). In the stomach of the snail the miracidium, of
peculiar form, is hatched out, and makes its way through the wall of
the intestine into the connective tissue. Here it becomes a sporo-
cyst; this grows very rapidly, absorbing the blood of the host, and
gives rise to numerous branches, one or two of which outrun the
rest, and push their way into the snail's tentacles. The branches
become banded with olive-green or brown, and the structure is now
known as Leucochloridium paradoxum (discovered by Carus, 1835).
Owing to its colouring and pulsations within the tentacle, it is
mistaken by birds for a dipterous larva, and is devoured. The
" cercariaea," which have in the meantime developed from the germ
balls inside the sporocyst, are without tails, which are evidently
not required, as the organism never leads an independent free
life ; they develop in the bird into a fluke.

THE TREMATODA

77

In D. ovocaudatum, from the oral cavity of Eana esculenta, the
miracidium is deprived of cilia, for the eggs are eaten by the inter-
mediate host (Planorbis).

Amphistomum subclavatum lives in the intestine of frog, etc. ;
the miracidium enters species of Planorbis ; the cercaria leaves this
first host, swims about for a few hours, falls to the bottom and
encysts. This happens throughout the summer ; and the cysts

FIG. XVIII.— The Life-history of D. macrostonfum, Rud. (After Heckert.)

' 1. — Outline of the adult fluke, parasitic in song-birds, a, mouth surrounded by the oral
sucker ; b, pharynx ; c, ventral sucker ; d, genital pore.

2. — The miracidium which is hatched in the stomach of the snail.

3. — The intermediate host, Succinea amphibia, crawling on a leaf (?u), (nat. size). «, the
cavity of the right tentacle is occupied by Leucochloridium. In some cases both tentacles will
be similarly occupied.

4. — The sporocyst, in various stages of growth, giving rise to a much-branched tube (D),
the ends of some of the branches becoming enlarged.

5.— A fully-grown Leucochloridium paradoxum — the elaborate sporocyst which occupies
the body cavity of the snail. One terminal branch is fully developed ; two others are
nearly so, and are banded with greens and browns.

are devoured by insect larvae, which in their turn are eaten by
the final host, the frog, during winter (Looss, 30). Or, according
to Lang, the encystment occurs on the skin of frogs and newts,
and the cysts are swallowed with the skin when moulting occurs.
In this way a gradual passage is formed between cases with and
without a second intermediate host.

Further Remarks upon the Class Trematoda. — The animals included
in this class are characteristically parasitic, and the two orders,

78 THE TREMATODA

Heterocotylea and Malacocotylea, exhibit two stages in this
parasitism. The former order are nearly exclusively ectoparasitic
on marine and fresh-water fish, attaching themselves to the outer
surface of the body, or to the wall of the branchial chamber, or
to the gills by means of the adhesive apparatus at the posterior
end of the body. Less frequently the worms make their way into
the canals or tubes formed by the invagination of the epiblast
— that is, into the nasal sacs, the oral cavity, and even into the
cloaca. The genus Polystomum is, as an exception, endoparasitic,
living in the urinary bladder of fish, amphibia, or reptiles.

On the other hand, the members of the Malacocotylea, as well
as the Aspidocotylea, are essentially endoparasitic, and must be
regarded as having passed through an ectoparasitic stage; and,
indeed, a few species of Distomum still retain this habit. These
digenetic Trematodes occur in the enteron and its outgrowths of
all groups of vertebrates ; the majority live, in the adult con-
dition, in warm-blooded members of the group, many in reptiles
and amphibia, and but few (Distomum sp.) in fishes. Every system
of organ, with the exception of the nervous system and skeleton,
is invaded by them, either in a free or encysted condition ; and
even the blood-vessels are affected by Bilharzia.

Although, as in other parasitic animals, it is a general rule
that each species attacks only one definite host, as the animal on
which the parasite lives is termed, or in hosts nearly related to
one another, yet there are instances, such as Distomum liepaticum
and D. lanceolatum, of the same species occurring in many widely
different hosts, such as man, rabbit, various ungulates, and even
the kangaroo. As in other groups, these parasites are only
injurious to the host, when they occur in large numbers, or in
certain delicate organs.1 It is well known that D. hepaticum, the
liver-fluke, produces " sheep-rot," especially in districts liable to
flooding, where the life-history can be readily completed.

The food of Trematodes consists in some cases of slime secreted
by the host; and this secretion is, no doubt, increased by the
irritation caused by the insertion of booklets into the host's skin.
But more usually nutriment is derived from the blood of the
host, which is sucked up by the parasite by means of the power-
ful pharynx, the intestine is consequently, in the fresh worm,
yellowish or red in colour ; and remains of blood corpuscles,
lymph cells, and epithelial cells have been noted in its contents.

In Polystomum peculiar crystals, reddish in colour, and octahedral
in form, suggest a derivative of haemoglobin (Zeller).

Some authorities (Taschenberg) describe intracellular digestion,
yet there is no doubt but that cavitary digestion also occurs.

1 It lias, however, recently been shown to be extremely probable that Nematodes,
Cestodes, and Trematodes excrete an active poison.

THE TREMATODA 79

The mouth was probably at first employed as a sucker for
adhesion to the host during the action of the pharynx, as it now is
in Monocotyle ; the next stage is exhibited by Onchocotyle, in which
special muscle fibres are developed around the mouth, so as to form
an indistinct " oral sucker," which has become much further
differentiated in the Malacocotylea. From this condition the
arrangement more usually met with in the Heterocotylea may
be derived where a pair of suckers are developed, one on each
side of the mouth, and communicating with the buccal cavity ;
these are known as " buccal suckers," and are met with in the
majority of the Polystomidae. By the removal of these from the
mouth, they lose the connection with the buccal cavity, and a pair
of independent " lateral suckers " are formed, as in Tristomum.

The posterior adhesive apparatus presents considerable variety.
No doubt the single sucker at the hinder end of the body represents
the primitive arrangement ; this sucker, which is always " simple,"
and never armed in the Malacocotylea, is usually "multiloculate" in
the Aspidocotylea and Heterocotylea, owing to the special develop-
ment of muscular ridges, giving rise in the former order to trans-
verse and longitudinal, and in the latter to radial ridges, starting
from a circular ridge surrounding the centre of the sucker.

It seems not improbable that the six or eight suckers of the
Polystomidae, arranged upon a caudal disc or " cotylophore," have
been derived phylogenetically by a further development of this
arrangement of muscle groups, till the loculi became entirely
independent. Finally, in the Microcotylidae, the presumed sub-
division of the sucker has gone very much further, resulting in a
considerable number of small suckerlets arranged on a membranous
cotylophore at the posterior lateral margins of the body ; this
apparatus must have been derived from the single sucker by the
cotylophore extending along each side, instead of remaining
terminal.

In the Malacocotylea the primitively posterior sucker has
moved forwards in the Distomidae, so as to lie quite far forwards
in the ventral surface. But accessory adhesive organs are developed
to a greater degree, and in more varied form, in the Malacocotylea
than in the Heterocotylea. The papillae covering the ventral
surface of Homalogaster (Fig. X.) and Gastrodiscus are provided with
retractile tips, and aid in fixation ; they appear, indeed, to be
replacing functionally the posterior sucker, which is small in the
former, and quite minute in the latter genus. In the Monostomidae
this posterior sucker has disappeared, and fixation is effected
partly by the oral sucker, but chiefly by the retractile warts along
the dorsal or ventral surface of the body (Fig. X.). An accessory
organ of quite another type is developed in the Holostomidae, the
sides of the fore body being folded over ventrally in various

80 THE TREMATODA

degrees, so that ultimately the original form of the body is lost
(Fig. XIIL).

The posterior sucker or the cotylophore in the Heterocotylea
is frequently armed with booklets or spines, aiding the worm in
fixation to its host; whereas booklets are never present in this
organ in the Malacocotylea, or in Aspidocotylea, a fact which
struck both Burmeister and Monticelli. Moreover, in the Poly-
stomidae the suckers are strengthened by a special development
of the cuticle to form a " chitinoid " skeleton (the substance is
soluble in 35 per cent KHO, according to Cerfontaine), (Fig. XIX.
5). In some forms the sucker, when in use, retains its cup shape,
when it may be termed " acetabulate," or it becomes folded
across its middle, like the two valves of a lamellibranch shell,
holding on to the host like a pair of forceps, when it may be
termed " valvate " (Fig. XIX. 4).

The muscles which constitute the sucker present some variety
in their arrangement (Goto). For instance, in Calicotyley three
sets of muscles are distinguishable : (a) radial along the ridges,
derived from the longitudinal muscles of the body ; (b) circular
muscles round the margin ; (c) dorso-ventral fibres traversing the
substance of the sucker from the dorsal body wall (Fig. XIX. 3).

On the other hand, the wall of the suckers in Polystomidae
consists of muscular fibres, arranged at right angles to the surface,
in between the chitinoid skeleton, and limited, bodywards, by a
distinct membrane; these may be considered" intrinsic"; while
muscle fibres from the general somatic musculature are attached
to the skeleton, and on their contraction the floor of the apparatus
is raised, and the sucking action produced (Fig. XIX. 6). In
valvate suckers other muscle fibres are attached to the various
pieces of the skeleton, serving as occlusor, divaricator, arid con-
strictor muscles.

It is an interesting fact that in Monocotyle (Goto) and in Diclido-
phora (Cerfontaine) the intrinsic muscles are transversely striated.

Apart from the existence of an elaborate adhesive apparatus,
which is foreshadowed by the sucker of some Polyclads and
Triclads, the Trematodes differ from the Turbellaria in only one
essential particular, and that is in the nature of the outer cover-
ing of the body ; for with the parasitic habit the cilia of the
ancestral Platyhelminth have gone, and the whole body is covered
by a thick, firm "cuticle," or "investing membrane" (Wright).
There can be little doubt but that this cuticle which occurs
also in Cestoidea and Nematoidea has been developed in rela-
+ 'on to the parasitic life, and serves as an efficient protection
against the action of digestive or other secretions of the host. In
the Heterocotylea and Aspidocotylea this cuticle is comparatively
simple ; in the Malacocotylea it is frequently armed with minute

THE TREMATODA

Si

3

FIG. XIX.

1. — Transverse section of the ventral sucker and neighbouring part of the body of
Distomum hepaticum (orig.). «, cuticle ; b, outer transverse muscles, which appear to become
continuous around the margin with the inner transverse muscle (h) ; c, radial muscles passing
through the whole depth of the sucker ; the bundles of muscle fibres are separated by con-
nective tissue represented by dots, in which the large myoblasts (d) are embedded, two of
which are shown in the section ; ee, circular muscle fibres, chiefly developed around the
margin of the sucker ; /, retractor muscles of the sucker, derived from the dorso-ventral body
muscles, which serve to move the sucker as a whole ; g, the internal limiting cuticular sheath
of the sucker ; h, the internal transverse muscles of the sucker.

2. — Diagrammatic transverse section through the body wall of a Trematode, composed
from descriptions and figures of various authors, and from my own observations, a, the cuticle,
vertically striped in its deeper portions ; b, spinelet, occurring in Malacocotylea ; c, sub-
cuticular protoplasmic layer joining the upper ends of the epidermal cells (c'), which have
been separated from one another by the upgrowth of the mesoblastic tissues. Below this layer
is the basement membrane (d) ; e, circular layer of muscles ; /, longitudinal layer of muscles ;
g, branched parenchymal cell, the processes of which subdivide and anastomose to form a net-
work^) of fine threads invading the muscular and epidermal layers; h, a "vesicular cell,"
such as occurs in various Trematodes, in greater or less abundance.

3.— Longitudinal section through the posterior sucker and the hinder end of the body
of Tristomum ovale (from Goto), a, sucker, not delimited internally from the tissues of the
body (6) ; c, longitudinal muscles of the body passing into the sucker and spreading out therein ;
d, radial or dorso-ventral muscles, between the bundles are groups of "sticking glands" not
indicated ; e, transverse muscles ; /, marginal membrane.

4. — Longitudinal section through one of the eight suckers of Dactylocotyle denticidatiim,
Olss. (from Cerfontaine), which is parasitic on the gill filaments of Gadus carbonarhis. The
sucker is " valvate " and armed ; the figure shows the armature, but not the muscular sucker ;
and three branchial filaments are clasped, a, b, chitinoid armature ; c, gill filaments ; d, divari-
cator muscles, serving to open the valves ; e, occlusor muscles.

5. — The chitinoid skeleton (armature) of a sucker of Dididophora elongata ; the skeleton
consists of three pairs of pieces (cde) set round the margin of the sucker, and two transven
unpaired pieces (ab).

C. — Longitudinal section through one of the eight suckers of Cycl. sessilis, Goto, from
the oral cavity of Chaerops japonicus. The sucker is limited internally (k), but the intrinsic
muscles are subdivided by the skeleton, ace (cf. Fig. 5), to which, as well as to the sucker
itself, retractor and other muscles (hj) are inserted for its movement ; g, the marginal membrane.

82 THE TREMATODA

spines scattered over the entire surface of the body (Fig. XIX.
2), or carried, in fihopalophorus, on two great tentacle -like
processes of the anterior end of the body (Fig. XI. 7), while in
Echinostoma the oral sucker is armed with spines (Fig. XI. 3).
These spines may be compared with those of Enantia, amongst
Turbellaria, and, like the cuticle, appear to be chitinous; they
aid in attachment, and perhaps in obtaining blood. The cuticle
presents two or three layers, differing in optical characters ; there
are no pore canals. Below the cuticle is a slight, granular
" subcuticula " ; below this come the circular muscle fibres of the
somatic musculature. Deeper still are gland cells, amongst the
longitudinal muscles, and parenchyma cells.

There are three chief views as to the nature of this " invest-
ing membrane " : (a) It is a metamorphosed, cellular epidermis
(Zeller, Ziegler, Biehringer, Braun, etc.) ; nuclei have been stated
to occur in it in various members of the group (Grosterostomum,
Amphistomum, Monostomum), and in cercariae the .nucleated epi-
dermis is stated to become a cuticle, (b) It represents a basement
membrane, the true epidermis and cuticle having been cast off
(Schneider, Kerbert); this view is founded on the fact that,
during the development of Malacocotylea, an external layer of
ciliated cells is shed, and in later stages a cuticle-like membrane
remains, (c) The investing membrane is a cuticle in the same
sense as that of a Chaetopod. But here again differences of
opinion as to its origin exist : (a) Some believe that the " sub-
cuticula" serves as its matrix, and represents an epidermis which
has lost its cellular character ; (/3) others regard this " inter-
muscular subcuticula" as the most external layer of the par-
enchymal tissue (Braun, etc.), and that the gland cells alone are
the representatives of the epidermis.

Recent studies by Blochmann (8, 9) and Kowalevski (23)
upon the structure of Cestodes and Trematodes go to show that
the investing membrane consists of two parts — the greater part
of it represents a true cuticle, while the lowest layer is a basement
membrane (Fig. XIX. 2). The epidermis which is more clearly
seen in some Cestodes (Ligida) than in Trematodes is represented
by deep-lying cells, some of which are glandular, with narrow
necks traversing the basement membrane ; the cells of the
epidermis have, however, become separated from one another by
the upward growth of the parenchymal tissue and muscles, just as
in Hir-udo (Lankester, 25) and in some Oligochaeta (Benham, 6)
the blood-vessels with connective tissue invade the epidermis
and, penetrating between the cells, break up -the layer ; in these
Annelids the cells remain attached to the cuticle by a broad external
end ; but in Trematodes the invasion of tissue has gone so far as
to leave only a very narrow part of each cell in connection

THE TREMATODA 83

with the cuticle ; and at the same time, the basement membrane
has been pushed upwards against the cuticle ; the cells have, so to
speak, slipped down through this membrane.

It is worthy of note that Max Braun has observed a definite
external layer of cylindrical cells in the lateral suckers of Nitzschia
and Epibdella ; they are not covered by a cuticle, which stops
abruptly against the cells.

The constitution of the parenchyma (or mesenchyma) also
presents difficulties of elucidation ; by most authorities it is
regarded as consisting of more or less highly vacuolated, granular,
nucleated cells, the extent of the vacuolation differing in different
genera, and in different parts of one and the same worm (see
Walters, 47). On the other hand, it has been more than once
suggested, and recently again by Blochmann, that these vacuoles
are intercellular, the cells themselves being extremely branched.

The musculature retains the same arrangement as in Tur-
bellaria, but the large " myoblasts " give rise not to one muscle
fibre, but to many.

In the Trematoda the necessity for fixation which is effected
primarily by the posterior sucker, appears to have led to a forward
movement of the generative pores in most forms, as well as of the
excretory pore in Heterocotylea, and in the former point the Class
contrasts with the Turbellaria. The peculiar secondary adhesive
apparatus of Holostomidae is clearly antagonistic to this forward
position, and we find the genital pore at the posterior end, which
must be regarded as secondarily acquired by them.

The mouth, however, retains its ancestral position at the
anterior end of the body. It leads into a buccal cavity, upon
which follows a pharynx bulbosus. The intestine has lost its
primitive, sac -like shape, owing to the forward and central
position of the generative organs. Coincidently with the great
development of these, the dorsal and ventral walls of the intestine
have coalesced as in many Turbellaria (cf. the origin of radial
and circular canals in Medusae), and in great part disappeared, so
that two main limbs, one on each side, remain. Nevertheless,
this obliteration of the central region has not occurred in the
Aspidocotylea or Gasterostomum, and only incompletely in many
Heterocotylea, where the two forks are united by transverse caeca
(as Polystomum). In this and other instances, too, the intestine
resumes its median position behind the gonads (Fig. II. 2, 4). The
reticular gut of the Polystomea is therefore more primitive than the
simple, bifurcated intestine of such forms as Calicotyle, Tristomum,
and most of the Malacocotylea. This view is supported to some
extent by the fact that in the young Polystomum the central intestine
is a simple sac which only exhibits its characteristic form during
the appearance of the gonads (Fig. Y. 7). In other forms, also,

84

THE TREMATODA

whose development has been followed, the intestine is at first sac-
like. The two main limbs may also carry lateral caeca, which
appear to have developed independently of those in Triclads and
Polyclads, and which ramify amongst the lobes of the laterally
placed vitellaria. It is necessary to point out that the intestine of
Distomum hepaticum, with its multitude of branching caeca, is quite
exceptional amongst the family Distomidae, and, indeed, amongst
the Malacocotylea ; for in this order the gut is characteristically
bifurcated, though the length of limbs may vary in different
species.

The excretory system presents little of the network character

seen in many Turbellaria; the ar-
rangement of the canals and the
position of the pores is seen in
the diagrams. Apparently, the
primitive position of these pores
is not posterior ; separate pores
exist in cercariae and rediae ;
the median pore of the adult
Malacocotylean and Aspidogaster
being due to a fusion of the
right and left ducts.

With regard to the nervous
system, which in its main lines
was first correctly recognised by
Ramdohr (1814), a comparison
of the figures will show that in
the Heterocotylea a more primi-
tive arrangement persists than
in the Malacocotylea, in which
there is a remarkable constancy
of longitudinal stems and cir-
cular commissures (Figs. XX,
and XXL).

Some of the ectoparasitic
forms, as well as the free larvae
of the endoparasitic forms,
possess " eyes " which, however,
no. xx. compared with those of Turbel-

Nervoussystemofz>.c2/Kttdraceim>asatype laria are in a degenerate condi-

of that of the Malacocotylea (from Looss). The fion Thp ran of rnVrnpnt i<*
animal is viewed from above, o, brain ; b, uon< [ P1^111'

dorsal longitudinal nerve stem ; c, lateral directed externally, and embraces

nerve ; d, ventral nerve. These three stems 1-1 * • ,11

are connected by the circular commissural a Spherical rciringent body Or

ouS.1"5' e'anterior^'ventralsuckersin "lens," which in its turn abuts-

upon a ganglion cell, a branch
of which runs to the brain. There is nothing which can be

THE TREMATODA

regarded as a retina, and Goto has suggested that they serve in
the Heterocotylea as " organs of temperature."

The generative system presents a somewhat greater com-
plication than in the most elaborate Turbellaria, but is built up
essentially on the same plan ; the female gonad being, except in
GfyrodactyluS) composed of germarium and vitellarium. The male
and female ducts, with rare exceptions, open together into an
" atrium genitale," and the penis is frequently armed with spines.
In the Malacocotylea the original pair of testes persists, and with
very few exceptions, such as D. hepaticum, each testis is a com-
pact, rounded body. In the Aspidocotylea and Heterocotylea one
of the original pair has disappeared, the remaining gland which is
provided with only one duct, may remain compact (Fig. IY. 2), or

FIG. XXI.

Nervous system of Tristomum
molae (after Lang), as type of that
of Heterocotylea, viewed from the
ventral surface, a, brain (on which
rest the four eyes indicated by
•white dots) ; b, dorsal nerve stem ;
c, lateral ; d, ventral. The ventral
steins are united by a series of com-
missures, which are continued on
to the lateral nerve, 13-15 in num-
ber (g). From the brain, on each
side, a nerve goes to " prostom-
ium," a second to the sucker.
These are joined by a ring-like com-
missure, arising from the stem
common to the posterior nerves.
The lateral and ventral nerves unite
in the posterior sucker and are
connected by a couple of semicir-
cular commissures, and give rise to
network in wall of sucker. Ji,
marginal network of body ; e, lateral
anterior sucker ; /, posterior sucker ;
/', radii.

become subdivided by ingrowths of connective tissue into a few
large lobes (Epibdella), or more generally into many small ones
(Fig. II. 2; V. 2), so as to assume the "follicular" condition
present in many Turbellaria.

The male copulatory apparatus varies considerably in details
of its structure, but these may all be reduced to two types : (1)
The word " cirrus " is used for the terminal, eversible part of the
sperm duct of Distomum and others which projects from the
bottom of the male antrum, and is enveloped in the " cirrus sac,"
containing glands ; booklets are borne along the wall of the duct,
and on eversion come to project outwards. A cirrus is rare
amongst the Heterocotylea, being met with in Tristomum and
Epibdella. (2) A "penis," such as occurs in the Holostomidae,
and in the majority of the Heterocotylea, and in Aspidocotylea, is
a specialisation of the terminal region of the sperm duct which

86 THE TREMATODA

traverses a papilla arising from the floor of the atrium. When in
use, this papilla is merely protruded through the genital pore.
The penis is formed of two parts : (a) a muscular, connective
tissue sheath, enveloped in a membrane ; and (b) distally a
chitinous armature, either in the form of a crown of booklets,
lying on the outer surface of the papilla, and projecting therefore
into the atrium and not into the sperm duct, or a tube. In a few
instances ( Udonella, Diplozoon, and some species of Distomum) there
is no penis or cirrus, and there is every reason to believe that
self-fertilisation occurs.

The germarium is single, the germ duct or oviduct is short,
extending as far as the special dilated region known as " ootype,"
into which the shell glands open ; into the oviduct there open the
vitelline ducts from the vitellarium, which is follicular or distinctly
lobed, except in Udonella and Cakeostoma, where it is compact.
In Diplozoon it is unpaired, in the rest paired ; it always lies dorsal
to intestine, against which it is closely placed. Beyond this point
the " oviduct " is known as " uterus," 1 and passes forwards, usually
in a more or less undulating course, to the atrium genitale, or in
rare instances to its own separate aperture.

But in addition to these organs there are certain ducts, the
homologies of which have been much discussed (Fig. XXIL).
(1) In the Heterocotylea there is typically a paired, or in other
cases a single vagina, the opening of which varies in position in
different genera (cf. Figs. I, II., III., V.). It is usually ventral, but
in Hexacotyle dorsal ; the single vagina appears, in some cases at
least, to be derived from the fusion of two, for in Axine heterocerca
the single (dorsal) pore leads into two ducts (Goto). In Poly-
stomum each vagina opens through twenty or thirty small pores
situated on the " lateral swelling." At its internal end the vagina
(XXIL 3, k) communicates with the transverse vitelline ducts, and
in its course is sometimes dilated to form a " spermatheca " ; the
vagina is the female copulatory organ for the reception of the
penis ; its pore is the " copulatory pore."

The uterine pore may, therefore, in opposition thereto, be
termed the " birth opening."

(2) In the Heterocotylea there is also a narrow duct passing
from the oviduct, opposite the entrance of the vitello-duct, to the
right limb of the intestine. This " genito-intestinal canal" (/)
whose true relations were discovered by Ijima, and since con-
firmed by Goto and all who have examined the matter, was
originally called the "internal vas def erens " by v. Siebold, and
believed to be connected with the testis, close to which it passes ;
it was then looked upon as a means for direct, internal self-fertilisa-

1 Goto finds cilia on the uterine epithelium of several genera of Heterocotylea
and in the vagina of Calicotyle.

THE TREMATODA

tion. It appears to serve for the conveyance of superfluous yolk
to the intestine, where it will serve as food.

(3) In the Malacocotylea and Aspidocotylea there is no vagina,
a fact that is associated with the much greater size of the uterus,

FIG. XXII. — Diagrammatic Transverse Sections to show the Relations of Various Parts of
the Female Ducts in the Three Orders of Trematoda.

1. — A Malacocotylean, showing Lanrer's canal (/).

2.— An Aspidocotylean. The "yolk receptacle" (/) arises from the oviduct in the same
position as does Laurer's canal.

3. — A Heterocotylean (the lowest figure). The canal (/) is here called "genito-
intestinal canal." The right and left vagina (fcfc) are represented as entering the median
vitelline duct (g). In some cases they join the transverse viteliine duct ; one or both may be
absent. In all the figures : — a, germarium, showing the distal syncytium and proximal germ
cells ; bb, germ duct or duct between the germarium and ootype ; c, shell glands set round (d)
the ootype, whence the duct is continued as uterus (c) ; g, median vitello-duct ; h, right and
left transverse vitello-ducts ; i, intestine, which in Fig. 2 is represented dotted; "Laurer's
canal " passes upwards behind it (see Fig. VIII. ./).

These organs do not lie in one plane, the figures represent "projections" in a vertical plane.

which contains a very much larger number of eggs than in the
Heterocotylea, and often comes to lie behind the testes. Nor is
there a connecting canal between the vitelline duct and the
intestine, but in place of it there is a narrow canal, first dis-

88 THE TREMATODA

covered by Laurer (1830), and- since known as "Laurer's canal"
(Stieda. 1867), which passes up from the oviduct, in the neigh-
bourhood of the ootype, to the dorsal surface, upon which it opens
by a minute pore (Fig. XXII. 1, /). It has been till recently
regarded as the homologue of the vagina of Heterocotylea ;
but it does not function as such ; it is much too small for the
insertion of the penis, and although spermatozoa have been
observed in it (Looss, 31), they are passing outwards, in which
they are aided by the current produced by the cilia lining the
canal; yolk granules also occur. Recently both Looss and
Goto independently have brought forward various arguments from
comparative anatomy tending to show that Laurer's canal of the
Malacocotylea is the homologue of the " genito-intestinal canal "
of the Heterocotylea, which has lost its connection with the
intestine and come to open to the exterior ; for it would be
manifestly less important for an endoparasite to make use of its
yolk as food than for an ectoparasite.

(4) In Aspidocotylea the duct leading to the " receptaculum
vitelli" agrees closely with Laurer's canal and the genito-intestinal
canal, except that it ends blindly below the dorsal integument
(Fig. XXII. 2) ; and there is little doubt that these three canals
are homologous.

The eggs of the Trematoda which are operculate, are of various
shapes and have a certain systematic value ; in the Malacocotylea
they are very numerous, much smaller than in Heterocotylea, and
rarely have the filament which is so usually present in the latter
order, since in the endoparasitic forms they are generally dis-
charged to the exterior and not attached to the host, as in ecto-
parasitic forms. In a few instances, however, one filament exists,
as in Bilharzia and species of Distomum, or less frequently two in
D. constrictum, Monostomum verrucosum, Opisthotrema cochleare.

Historical. — The earlier writers, who concerned themselves chiefly
with the liver-fluke, frequently confused the excretory canals with the
intestine ; thus Carlisle, having injected the former, described it as the
latter, the excretory pore being termed "poms ani." Even after the
true mouth and intestine had been correctly recognised by Ramdohr
(1814), and by Bojanus (1817), there was a general belief that the excre-
tory pore served as an anus, and that the excretory canals were in connec-
tion with the intestinal caeca, and acted as a kind of vascular system ;
indeed, Blanchard (1847) described the contractile bladder as a "heart,"
and went so far as to deny the existence of a posterior pore. Bojanus
(1821) was the first to establish the absence of an anus, though even v.
Baer (1827) mistook the excretory pore of Aspidogaster for the mouth.

The excretory system, even after it had been differentiated from the
enteric system by Bojanus, and by v. Siebold, who pointed out its true func-
tion, was variously regarded as (a) respiratory by Meckel (1846), who sug-

THE TREMATODA 89

gested that the canals absorbed water through the skin and passed it out
through the pore ; or (6) as lymphatic, or vascular, in part at least ; even
Villot, 1882, takes the view that it serves for excretion, absorption, respira-
tion, and circulation. The main course of the canals was known to Laurer
and to Mehlis (1831). The fact that the bladder and canals form part of
one system was first pointed out definitely by P. J. van Beneden (1852).
The movement of the contained fluid was caused, according to Ehrenberg
(1835), by valve-like folds, endowed with the power of oscillation ; but in
the next year v. Siebold rightly showed that it is due to the action of cilia.

The finer structure was investigated by Fraipont (16), who described
the " flame cells," but believed them to be in communication, not only
with the tubules, but also with the spaces in the parenchyma ; this has,
however, been shown to be erroneous.

The brain and the main nerves were first accurately localised by
Eamdolir ; but Otto, 1816, contended that the vitelline ducts, longitudinal
and transverse, were the true nervous system, and described ganglia at
their junction. Our knowledge of this system is due primarily to Lang
(24) and Gaffron (17).

The hermaphrodite nature of the Trematodes appears to have been
recognised by Miiller ; but for a long time the ventral sucker was inter-
preted as the "birth pore," till Nitzsch (1819) discovered that the sucker
is imperforate. The penis was known to Eudolphi, and the common
genital pore was held to belong only to the male ducts.

V. Siebold was the discoverer of the fact that the egg-producing organ
is distinct from the yolk-forming gland.

Relations of the Group — Parasitism. — It is almost an axiom that
parasitism leads to degeneration of the parasite, and this usually
in an extreme degree ; but in the Trematodes this degeneration
is scarcely recognisable ; for beyond the absence of the ancestral
locomotor organs, viz. the cilia of the outer surface, it is scarcely
possible to point to any sign of degeneration common to the group.
Degeneration of the sense organs is another characteristic of para-
sites, and although eyes are frequently present in the Heterocotylea,
they are less elaborate than in the majority of Turbellaria ; and in
Malacocotylea they are absent, except in the free-living miracidium
and cercaria. The nervous system shows no essential difference
from that of Turbellaria ; though in the Malacocotylea the peri-
pheral stems and commissures are more definitely arranged.

The generative organs, too, agree with those of many Rhab-
docoele Turbellarians, and the alimentary canal is well developed in
all members of the group.

The cuticle, as has been suggested, has been developed in
relation to the parasitic habit, and Temnocephala forms an interesting
link between the Turbellaria and Trematoda in this respect.

The suckers so frequently associated with parasitism, and so
eminently characteristic of the group, seem to be the cause rather
than the result of parasitism, for such relatively small animals as

90 THE TREMATODA

Dactylocotyle and other ectoparasitic forms would soon be carried
away by the current of water passing over the gills of the fish ;
and Amphistomwn, or other internal parasites, would be driven down
the alimentary tract of its host, by the passage of food, unless
they were able to adhere in some way to the host ; the modifica-
tion of the musculature of the body wall is the simplest method
of adhesion.

But suckers occur, though of a very simple kind, in many
Poly clad and several Triclad Turbellaria, and large ones in Temno-
cephala, so that even these characteristic organs are not in reality
novelties or peculiar to the class. It does not appear possible to
regard the suckers of Trematodes and Turbellaria as truly homo-
logous ; they are rather homoplastic, for they vary in position and
relation in both groups. Indeed, but for the absence of cilia, there
is no essential difference between a Trematode and a Turbellarian,
and there is little difficulty in deriving the former from some
Rhabdocoelous form of the Turbellaria, which had taken to the
habit of temporarily associating itself with a definite animal, as
the Triclad Bdelluridae do at the present day. As this habit
became fixed, the means of attachment became improved, resulting
in a single posteriorly placed sucker. The animal was thus able
to live permanently on its host, and having a ready supply of food
at hand, in the host's blood and mucus, took to sucking it, for
which purpose a second sucker in the neighbourhood of the mouth
would aid the parasite during the use of the "pharynx bulbosus,"
which acts as an aspirator. The two characteristic suckers having
been developed, each became modified in different directions. The
anterior sucker became double in the ectoparasitic forms ; the pos-
terior sucker became more elaborate, or hooklets were developed
to aid in adhesion.

It is customary to look on the Malacocotylea (Digenea) as more
highly developed than the Heterocotylea, and as probably derived
from them. This view, no doubt, depends on the endoparasitic
habit of the former order, and on the fact that the host is a
vertebrate, and that the life-history is a complicated one. But
Looss is of opinion that, on the contrary, the Heterocotylea are
the higher order. But if the anatomy of each order and of
Rhabdocoelida be compared, organ for organ, with one another,
we shall have to take a middle position and look upon the two
orders as diverging at a very early stage in phylogeny.

Very possibly some Temnocephala-like form was the ancestor
of the Trematoda — a form, as said above, with a posterior sucker,
but without the anterior ones ; the intestine was sac-like, and no
doubt the genital organs posterior to it.

The assumption of ectoparasitic and endoparasitic habits, with
the anterior suckers or sucker differently arranged, led to a diver-

LITERATURE OF THE TREMATODA 91

gence along two lines, in one of which a complicated life-history
gradually took place ; from this line the Aspidocotylea branched off,
and possibly the apparently primitive characters of the alimentary
canal is one of atavism.

The following " tree " represents the history of the group : —

Heterocotylea.

Malacocotylea.

spidocotylea.

TREMATODA.

Temnocephala.

RHABDOCOELA.

LITERATURE OF THE TREMATODA.

1. Boer, v. Nova Acta, xiii. (pt. 2), 1827, 2, p. 527.

2. Beneden, E. v. (Rech. s. 1. composition et la signification de 1'ceuf.) Mem.

Cour. Acad. Roy. Brux. (4to), xxxiv. 1870.

3. Bcneden, P. J. van. (Excretory System.) Bull. Acad. Roy. Belg. xix. (pt. 1),

1852, p. 573.

4. Ibid. Mem. sur les vers intestinaux, 1858.

5. Beneden, P. J. v., and Hesse. (Recherches s. 1. Bdellodes et les Trematodes

marines.) Mem. Acad. Roy. Belgique, xxxiv. 1864.

6. Benham. Quart. Journ. Mic. Sci. xxvii. 1886, p. 561.

7. Biehringer. (Cuticle : Germ-balls.) Arb. Zool. Inst. Wurzburg, vii. 1885,

p. 1.

8. Bloclimann. (Musculature, etc.). Biol. Centralbl. xv. 1895, p. 216.

9. Ibid. (Die Epithelfrage bei Cestod. u. Treinatod.) Vortrag. gehalt auf.

d. vi. Jahrs. d. Deutsch. Zool. Gesell. z. Bonn, 1896 ; also, Zool. Anz. xx.
1897, p. 460.

10. Brandes. (Holostomidae.) Zool. Jahrbuch (System.), v. 1891, p. 549.

11. Braun. Bronn's Thierreichs (Wiirmer), 1889, et seq.

12. Ibid. (Holostomidae.) Zool. Anzeig. xvii. 1894, p. 165.

13. Cerfontaine. (Striated Muscle.) Bull. Acad. Roy. Beige (ser. 3), xxvii. 1894,

p. 949.

14. Ibid. (Polystomidae). Arch. Biol. xiv. 1895, p. 497.

15. Diesing. Systema Helmintlmm, 1850.

16. Fraipont. (Excretory System.) Arch. Biol. i. 1880, p. 415 ; ii. 1881, p. 1.

17. Gaffron. (Nervous System.) Zoolog. Beit. hrsg. v. Ant. Schneider, i. 1884

p. 109.

92 LITERATURE OF THE TREMATODA

18. Goto. (Diplozoon nipponicum.) Journ. Coll. Sci. Imp. Univ. Japan, iv.

1891, p. 151.

19. Hid. (Ectoparasitic Forms. ) Ibid. viii. 1894.

20. HecTcert. (Leucochloridium.) Biblioth. Zool. (hrsg. v. Leuck. and Chun's),

Heft iv. 1889.

21. Ijima. Zool. Anzeig. vii. 1884, p. 635.

22. Katharina. (Gyrodactylus. ) Arb. Zool. Inst. Wurzburg, x. 1895, p. 127.

23. KowalevsM, M. (Epidermis.) Anzeig. Akad. Krakau, 1895, p. 78.

24. Lang. (Nervous System.) Mith. Zool. Stat. Neapel. ii. 1881, p. 28.

25. Larikester. (Epidermis of Leech.) Quart. Journ. Mic. Sci. xx. 1880, p.

303 ; Zool. Anzeiger, iii. 1880, p. 85.

26. Leuckart. Die Parasiten des Menschen, 1886-94, I. parts 3, 4, 5.

27. Ibid. (Development of Fluke.) Arch. f. Naturges. 48. 1882, i. p. 80.

28. Linstow, v. Compendium d. Helminthologie, 1878 ; and Appendix, 1889.

29. Looss. (Anatomy.) Z. W. Z. xli. 1885, p. 390.

30. Ibid. (Amphistomum.) Leuckart's Festschrift, 1892, p. 147.

31. Ibid. (Laurer's Canal.) Centralbl. f. Bakter. u. Parasiten -kunde, xiii.

1893, p. 808.

32. Ibid. (Distomum of Frogs, etc. ). Bibliotheca Zoologica (hrsgb. v. Leuck. and

Chun's), Heft xvi. 1894.

33. Ibid. (Bilharzia.) Arch. f. mikr. Anat. xlvi. 1895, p. 1.

34. Metschnikoff. (Gyrodactylus.) Bull, de 1'Acad. Imp. St. Petersbourg, xiv.

1870, p. 62.

35. Monticelli. (Cotylogaster, etc.). Leuckart's Festschrift, 1892, p. 168.

36. Nickerson. (Stichocotyle. ) Zool. Jahrbuch (Anat.), viii. 1895, p. 447.

37. Parana and Perugia. (Microcotyle. ) Ann. Mus. Civ. Storia Nat. Genova,

xxx. 1890-92, p. 173.

38. Poirier. (Anatomy of Distomids.) Arch. Zool. Expr. (2), iii. 1885, p. 465.

39. Schauinsland. (Dev. of D. tereticolle. ) Jen. Zeit. xvi. 1883, p. 465.

40. Sommer. (Dist. hepaticum.) Z. W. Z. xxxiv. 1880, p. 539.

41. Stafford. (Aspidogaster. ) Zool. Jahrbuch (Anat.), ix. 1896, p. 477.

42. Thomas. (L. truncatulus. ) J. Roy. Agricult. Soc. xvii. 1881, p. 1.

43. Ibid. (Dev. of Fluke.) Quart. Journ. Mic. Sci. xxiii. 1883, p. 99.

44. Voeltzkow. (Aspidogaster.) Arb. Zool. Inst. Wurzb. viii. 1888, p. 249.

45. Wagener. (Dev. of D. Cygnoides.) Beit. z. Entwick. d. Emgeweidewiirmer,

Haarlem, 1857 ; and Z. W. Z. ix. 1858, p. 73.

46. Ibid. (Gyrodactylus.) Arch. f. Anat. Physiol. 1860, p. 768.

47. Walters. (Monostomum.) Z. W. Z. Ivi. 1893, p. 189.

48. Wright and Macallum. (Sphyranura.) Journ. Morph. i. 1887, p. 1.

49. Zeller. (Polystomum.) Z. W. Z. xxii. 1872, p. 1 ; and xxvii. 1876, p. 238.

50. Ibid. (Diplozoon.) Z. W. Z. xxii. 1872, p. 168 ; and xlvi. 1888, p. 233.

51. Ziegler. (Cuticle, Bucephalus, etc.). Z. W. Z. xxxix. 1883, p. 537.

CHAPTEE XIX.

PLATYHELMIA — CESTOIDEA.

CLASS IV. CESTOIDEA.

GRADE A. CESTOIDEA MONOZOA.

Order 1. Amphilinacea.
„ 2. Gyrocotylacea.
„ 3. Caryophyllacea.

GRADE B. CESTOIDEA MEROZOA.
BRANCH A. DIBOTHRIDIATA.
Order 1. Pseudophyllidea.

Fam. 1. Bothriocephalidae.
,, 2. Solenophoridae.
„ 3. Bothriomonidae.
„ 4. Leuckartiidae.
,, 5. Triaenophoridae.

BRANCH B. TETRABOTHRIDIATA.
Order 1. Tetraphyllidea.

Fam. 1. Tetrabothridae.
„ 2. Gamobothridae.
Order 2. Diphyllidea.

Fam. Echinobothridae.
Order 3. Tetrarhyncha.

Fam. Tetrarhynchidae.
Order 4. Tetracotylea.

Fam. 1. Ichthyotaeniidae.
,, 2. Echinocotylidae.
,, 3. Taeniidae.
„ 4. Mesocestoididae.

THE class Cestoidea, as known at the present day, may be
denned as follows : — Platyhelminths in which an internal parasitic
habit has led to the disappearance of the alimentary canal from
every stage in the life-history. The ciliated covering, as well as

94 THE CESTOIDEA

definite organs of sense, are likewise absent in the adult. The
epidermis, which has sunk into the parenchyma, secretes a thick
cuticle, as in the Trematoda. In the parenchyma certain lime-
secreting cells are developed in greater or less number. Organs of
fixation are developed in a characteristic but varied form at one
extremity of the worm.

The egg gives rise to a six-hooked embryo or "onchosphere,"
which gains an intermediate host ; from it some form of " bladder-
worm " is usually developed, which has to reach a vertebrate as a
final host, in order to attain maturity.

Historical Account. — There can be little doubt but that tapeworms
have been known to mankind from very early times, for those
infesting domestic animals are sufficiently large to catch the least
observant eye; and even such "bladder- worms" as Cysticercus
cellulosae, C. tenuicollis, and Ecliinococcus must have been met with,
and recognised as foreign bodies, in the carcases of animals slain
for food or sacrifices. Moses probably was acquainted with them,
when the pig, rabbit, and hare were forbidden to the Jews. The
Greeks gave the expressive name x«'Wat ( = hailstones) to these
" hydatids," and some authors refer to the method, still employed, of
examining the tongue of the living pig in order to ascertain their
presence. The tapeworms were termed eA/ui/des -Xardai : and
Aristotle was aware that they were attached to the wall of the
intestine, whereas the nematodes or crr/ooyyvAcu were free therein.
At an early period (1592) at least two different cestodes were
distinguished as inhabiting man (Taenia and Bothriocephaltts), and in
the latter half of the seventeenth century the tapeworms and bladder-
worms of domestic animals, and later of wild animals killed for food,
etc., began to receive attention. But for a long time, even after a
considerable number of naturalists had been working on the subject,
the relation of these two stages was unknown, or only vaguely
guessed at, till Pallas and Goeze recognised that the head
contained in the bladder- worm is capable of evagination on
compression, and resembles the head of certain tapeworms. The
earlier systematists (Zeder, Rudolph!) separated the bladder-
worms, or " Cystica," from the tapeworms, or " Cestoidea," as dis-
tinct orders ; but Blainville and Dujardin united the two groups,
as being related to one another. P. J. van Beneden rightly
regarded the " Cystica " as some normally occurring stage in the
life-history of the " Cestoidea." Von Siebold, on the other hand, had
put forward the theory that the bladder-worm is some stage in the
history of a tapeworm which has gone astray in the wrong animal,
and, undergoing hydropic degeneration, is destined to die, unless this
animal is eaten by the proper host, when the bladder- worm will not
only live in the intestine of the host, but will give rise to a tape-
worm. This idea of von Siebold's received considerable support

THE CESTOIDEA 95

from Dujardin, Leuckart, and others ; but the matter remained one
of mere speculation till 1851, when Kiichenmeister, a medical man
of Zittau, commenced a series of experiments in feeding suitable
animals with bladder-worms. Thus, he mixed a known number of
Cyst, pisiformis from the rabbit's omentum with the food of dogs,
and he obtained after a time a number of specimens of Taenia
serrata from their intestines. Similarly, he demonstrated that
C. cellulosae from the muscles of the pig gives rise to Taenia solium
when swallowed by man ; and that the small heads removed from
Coenurus cerebralis, which lives in the brain of sheep, develop, when
fed to a dog, into Taenia coenurus. He then caused the ripe pro-
glottids of this worm to be swallowed by a sheep, which a month
later had an attack of " staggers." It was killed, and fifteen small
coenuri were found in its brain.

These and other experiments placed the relations of the " cystic
worm " to the " tapeworm " on a firm basis, and were soon followed
by others, undertaken by von Siebold (43), Leuckart, van Beneden,
whereby it was proved beyond doubt that the bladder-worm or hyda-
tid is an essential stage in the development of those tapeworms,
from the eggs of which they arise. Further, it became evident
that two different animals, or " hosts," are necessary for the com-
pletion of the life -cycle ; the bladder- worm occurring in some
definite intermediate host, which forms the prey or food of the final
host, in which the bladder-worm develops into the tapeworm.1 It
was recognised that " cystic worms " occur in the muscle, connective
tissue, and various viscera, other than the alimentary canal (of
herbivorous animals as a rule) ; and that the adult tapeworms
always live in the alimentary canal (of carnivorous animals as
a rule).

But still other problems remained for solution, especially that
which Steenstrup's famous theory of " alternation of generations "
had suggested, and this and other matters are dealt with at the
end of this chapter, as some of these details are still matters of
controversy.

Among the more important writers on the classification and descrip-
tion of new genera and species, the following may be mentioned : 2 — Redi
(1687-1705), Pallas (1781), Goeze (1782), Kudolphi, Zeder, Dujardin
(1845), E. Blanchard (1847), P. J. van Beneden (1849), Diesing, Krabbe,
Linton, Stiles, Raillet. The anatomy of various forms has received par-
ticular attention at the hands of Blanchard, Wagener, von Siebold, and

1 In a few instances there is, however, no change of hosts, but merely a change of
organs in one and the same host. The best known case is that, H. murina, elucidated
by Grassi, where the cysticercoid occurs in the villi of the intestinal wall, the strobila
in the cavity of the same intestine. Von Linstow has found the larvae of Tetra-
rhynchus longicollis in the same fish as the adult, and so for Triaenophorus nodulosus.

2 For a complete historical account and bibliography, see Bronn's Thierreichs,
Warmer, by Max Braun.

96 THE CESTOIDEA

especially van Beneden, whose work on Fish Tapeworms (2), like
Leuckart's great work on the Parasites of Man (22), is a storehouse rich
in facts. Among more recent writers mention may be made of Somnier
and Landois (44, 45), Zschokke (52), Pintner (32-34), Monticelli (30),
and others, to whom reference is made below.

The life-history of various genera has been gradually elucidated by
the researches and discoveries of von Siebold, Wagener (49), E. and P. J.
van Beneden, Leuckart (21), Kiichenmeister, Moniez (28), Schauinsland (40),
Grassi and Kovelli (1 3), Villot (48), and others. Among the more important
steps in anatomical discovery, which have led to our knowledge at the
present day, are the following : — The head or scolex of a dog tapeworm
was discovered for the first time by Tyson (1683), of T. saginata by Audry
(1700), of Bothriocephalus by Bonnet (1777), and of Cyst, cellulosae by
Malpighi. The suckers, at first regarded as "eyes and nose," were
correctly interpreted by Redi. The isolation and independent movement
of the proglottids or vermes cucurbitini were known to von Siebold. The
fact that eggs were laid by the proglottids was observed by Leeuwenhoek
(1722). Hermaphroditism of the joints appears to have been known to
Werner (1782), but the accurate determination of the constituent parts
has been very slow and gradual. On an isolated proglottid of Taenia, the
uterus, full of eggs, and the more or less prominent genital pore on its
margin, were the first to receive attention, and were, by many zoologists,
mistaken for intestine and mouth respectively (Linnaeus, Dubois). But
Goeze and Pallas, recognising the contents as eggs, concluded that the uterus
was an " ovary." This was set right by the discovery by von Siebold of a
"germarium" and a "vitellarium" in certain forms ; but to Leuckart belongs
the merit of tracing out the ducts connecting the various parts both of
the male and of the female system, though even some of his interpretations
were shown by Somnier to be erroneous (thus he mistook the vitellarium for
a germarium, and vice versa), and it was Somnier who has given us the best
descriptions and drawings of the structure of a proglottid in Taenia and
in Bothriocephalus, while Zschokke has extended this knowledge in other
forms. The testes were discovered by F. E. Schulze in 1820, and the
copulatory organs by Platner in 1859. The genitals of the Tetraphyllidea
were accurately described by van Beneden. The excretory system, origin-
ally identified by von Siebold (1838), was regarded by Blanchard as a part
of the alimentary system. It was followed out in its main course by
van Beneden in a number of fish tapeworms. Its histological structure
has been investigated by Fraipont, Pintner, Poirier (35), and Kohler
(18) amongst others.

The nervous system, which was first noted by J. Miiller (1836), has
been studied by Lang (20), Niemec (31), and recently by Tower and Liihe ;
the " brain " having been already recognised by WagenerT The structure
of the parenchyma, skin, etc., has received considerable attention in
recent years, the most modern writers on this subject being Zernecke
(51) and Blochmann.

In the majority of the Cestoidea the body is metamerically
segmented, the reproductive organs sharing in this segmentation ;

THE CESTOIDEA 97

but there are certain genera which consist of a single segment and
have only one set of genital organs. This group of forms only
differs materially from certain Trematodes in the absence of the
enteric cavity, and constitutes a lower grade, from which the
segmented Cestodes are derived.

This grade is the Monozoa, and the second grade may be termed
the Merowa.

GRADE A. CESTOIDEA MONOZOA, Lang ( = Cestodaria, Montic. ;

= Cestodes monogeneses, v. Ben.; = Atomiosoma, Montic.).

Cestoidea, in which the animal consists of a single segment, con-
taining a single set of reproductive organs. In addition to the
male pore and female (vaginal) pore, there is a third aperture,
that of the uterus (birth-pore). The apparatus by which fixation is
effected consists, usually, of a single sucker, but presents considerable
variation in form, as well as in disposition, with regard to the genital
pores.

ORDER 1. Amphilinacea.

FAMILY 1. AMPHILINIDAE. Oval or leaf-shaped, without a distinct
" head " ; with a single small acetabulate sucker at one end. Amphilina,
"Wagener ; A. foliacea, Rucl., in the sturgeon (see 39), (Fig. II. 1) ; A.
liguloidea, Dies., in fresh-water fish, Brazil ; Wagneria, Montic. ; W. pro-
glottis, Wagn., in the intestine of Scijmnus nicceensis.

ORDER 2. Gyrocotylacea.!

FAMILY 2. GYROCOTYLIDAE. Leaf-shaped, with crenate margins. At
the pointed extremity is a small but deep sucker ; at the opposite end is
a " rosette organ " carried by a cylindrical peduncle, traversed by a canal
opening at each end, from which a peculiar proboscis-like organ can be
everted. Gyrocotyle, Dies. ( = Amphiptyches, Wagn.), (see 46); in the
intestine of Chimaera and Callorhynchus (Fig. II. 4).

ORDER 3. Caryophyllacea.

FAMILY 3. CARYOPHYLLAEIDAE. Elongated, cylindrical worms, either
with a single sucker or without one, and then with one end capable of
considerable mobility. Monobothrium, Dies., with a single terminal sucker ;
M. tuba, Wagn., in the intestine of Tinea chrysitis ; Caryophyllaeus, Mull.,
without a sucker, but with a characteristic mobile organ, capable of being
thrown into undulatory folds, giving the appearance of a " clove-pink " ;
G. mutabilis, End. (Fig. I.), in the intestine of Cyprinoid fishes, and
(young) in the coelom of Tubifex, in segments 8 to 20 (see 50). The
worm described by Leuckart as Archigetes sieboldii, from the genital seg-
ments of Tubifex rivulorum (see 23), is in all probability only the
immature phase of Caryophyllaeus. The cylindrical body carries a tail
provided with three pairs of booklets, thus resembling the " caudal
vesicle " of such a Cestode as Taenia solium ; it has been suggested that
it is a permanent " cysticercus form " with the head everted. The head

98

THE CESTOIDEA

is known only from Leuckart's observations on preserved material. This
worm is stated to become sexually mature in the Oligochaete, and would
be remarkable, firstly, for being the only Cestode inhabiting a single
host, and secondly, in that host being an Invertebrate. The genital
organs (see 1 5) appear to be identical with those of Caryopliyllaeus, and it
is desirable to have further information about the character of the " head,"

FIG. I. — Caryophyllaeus mutabilis, Rud.

1. — Mature worm from the intestine of the roach, Leuciscus rutilus. (x7£, orig.). The
general disposition of the genital organs is shown, a, mobile organ ; c, cirrus ; g, germarium ;
t, testes ; v, vitellaria ; u, uterus, the coiling of which has been simplified ; v, vagina ; x, ex-
cretory pore. The male duct opens into the atrium (the outline of which is unfortunately
indistinct) opposite to the vagina, and the uterus opens also into the atrium, close to the latter.
The atrial pore is not lettered, but is seen in line with the letter u.

2. — Immature worm removed from the coelom of the genital segments of Tubifex rivul-
orum. (x!5, orig.). It still retains its "caudal vesicle," which is armed with six hooklets.
This specimen is a small one ; others occur in the Oligochaete of the same size as, or even
larger than some specimens found in the fish, and frequently have the genital organs fully
formed, but without eggs.

3, 4, 5. — Outline of the mobile organ in three stages of forward movement — 3, at the begin-
ning, and 5, at the terminal stage of the process. During this movement of the mobile organ r
a wave of contraction passes forwards along the body, so as to bring the whole animal forwards.

for in preserved specimens of the latter genus, an appearance, not unlike
that figured by Leuckart, is presented. It is, moreover, to be noted that
the genital organs of Caryophyllaeus are fully developed while it is still
provided with a " caudal vesicle " and inhabiting the body of Tubifex.

Remarks upon the Monozoa. — These unisegmental Cestodes
exhibit undoubted affinities with the Trematodes, and especially
with the Heterocotylea. A resume of the anatomy of the genera

THE CESTOIDEA 99

included will be found in (30). Of the various genera included in
the grade, it is Amphilina that appears to be the most primitive in
its anatomy, though Leuckart sees in " Archigetes " an archaic form ;
but in its general anatomy there is here a greater divergence from
the Trematodes than is seen in Amphilina.

It is usual to regard the single sucker of all these genera as
homologous throughout, and to place it anteriorly ; but if we have
regard to its position in relation to the genital pores, it is possible
to deny this homology. Spencer (46) and Lonnberg, though with-
out definitely expressing any general dissent from the usual view,
place the sucker of Gyrocotyle at the posterior end, whereas Wagener
and others place it anteriorly.

If we examine the genital organs and ducts in Amphttijia, on
the one hand, and any Heterocotylean Trematode on the other,
we shall see that the comparison is very much more easily appreci-
ated if the sucker of the former be placed posteriorly instead of
anteriorly as is customary.

In Amph. foliacea the sucker is at the pointed end (Fig. II. 1) ;
the male pore is at the opposite extremity ; the penis is armed
with ten booklets ; the vas deferens soon bifurcates, and its branches
are distributed to the marginal, follicular testes. The germarium
is single ; the short germ-duct opens into the ootype, which com-
municates with three canals : (a) the short, common vitello-duct ;
(/?) the egg-containing duct or " uterus," which is a long undulating
canal opening externally close to the sucker ; and (y) a short
" vagina " or copulatory canal, which opens near the male pore. In
A. liguloidea there is a fourth canal (8), which runs in the opposite
direction and ends blindly ; it is known usually as the " anterior
vagina."

Now in the Heterocotylean (see Fig. I. p. 51) the germ-
arium lies anteriorly to the testes ; the sperm -duct and the
uterus (or egg -containing duct) run forwards side by side to
open near the anterior end of the body, either close together
or into a common atrium. The vitellarium is identical in
Cestodes and Trematodes, the vitelline duct opening into the
oviduct opposite to the junction of the latter with the uterus.
Arising close to this point there is in the Heterocotylea the
vagina or copulatory duct, whose external pore is independent
of the uterine or birth-pore, and generally posterior to it. More-
over, the genito- intestinal canal (Laurer's canal) communicates
with the oviduct in the same region. Now, turning again to
Amphilina, the female copulatory duct or " vagina " has the same
topographical relation to the other parts of the apparatus as the
" uterus " or egg-containing duct of Trematodes ; and the " uterus "
of the Cestode corresponds with the " vagina " (when present) of
the Trematode. Further, the " anterior vagina " of A. liguloidea is

100

THE CESTOIDEA

comparable with the Laurer's canal of the Trematode, which has
lost its opening (cf. the receptaculum vitelli of Aspidog aster).

FIG. II. — Monozoa.

1.— Generative system of Amphilina foliacea, Rud. (combined from figures by Salensky and
Wagener), out of the sturgeon, a, sucker, with retractile muscles (?) or gland cells (?) ; b,
uterine or birth pore ; V, uterus ; c, vitellariuiii and vitellarian duct ; d, germarium ; its duct
'opens into the ootype ; e, the vaginal pore ; e', the vagina, dilated in its upper part ; /, sperma-
theca ; g, male pore ; h, cirrus ; i, sperm duct, which is represented as less convoluted than it
is in reality, the wide, convoluted region being the seminal vesicle ; .?', testes ; k, shell gland.

2.— The larva of Amphilina foliacea removed from the egg (after Salensky). The upper end
is ciliated ; the other end is slightly cupped and carries ten hooklets (5) ; o, gland cells opening
anteriorly.

3. — The same from behind, showing the ten hooklets, arranged round the terminal cup.
(Orig.)

4.—Gyrocotyle urna, Wagn. Outline of the ventral surface showing external apertures and
nervous system (after Spencer), a, peculiar frilled organ ; b, uterine pore ; c, terminal sucker ;
d, the left excretory pore ; the right one is not lettered ; e, vaginal pore ; g, male pore on the
margin ; n, lateral nerve ; o, anterior commissure ; p, posterior commissure.

5, 6, 7 represent the arrangement of the excretory system in Caryophyllaeus. 5. The mobile
organ, dorsal view. (Modified from Fraipont.) 6. A transverse section of the body. (After
Will.) 7. Dorsal view of body (orig.). a, b, c, d, e, the five descending canals of one side ;
these are connected by a network throughout their course, as is shown well in 5 and 7. At
the hinder end of the body the ten canals open into a contractile sac. /, g, the "ascending
canals " which, in the greater part of the body, lie superficially to the descending canals (6), but
in the neck sink into the "medullary region." [In 7 the canal marked "/" should be "</."]
These ascending canals are connected by a fine, superficial network (/i), which carries numerous
flame cells, which are indicated in 6 ; fc, the longitudinal, muscular layer separating the paren-
chyma into a cortical zone, in which the excretory canals lie, and a medullary region containing
the genital organs. I, m, n, o, p, the five longitudinal nerve cords of the left side ; n is the
stout lateral or marginal nerve corresponding to that in 4.

As was pointed out above (Trematoda, p. 87), the vagina or
copulatory duct of the Heterocotylea appears to have no homologue

THE CESTOIDEA 101

amongst the Malacocotylea ; it is a new structure ; l whilst the
uterus functions in both orders as an egg-containing duct, to which
is added in the latter order the function of a copulatory duct. In
the whole of the Cestoidea, however, both these ducts can be
recognised ; but the original uterus is now employed exclusively as
a copulatory organ or vagina, whilst the original copulatory organ
has lost its function, arid, becoming greatly enlarged, serves as an
egg-containing duct, which, as we shall see amongst some of the
Merozoa, loses its external opening, and becomes a mere blind sac.

If the identification of these parts is correct, and they have the
same relative position in the Ampliilina as they have in the Trema-
toda, this becomes still clearer on the reversal of the ordinarily
assumed position of the sucker, and we may therefore conclude that
the sucker of Ampliilina is homologous with the posterior sucker of
Heterocotyleans, and not with the anterior, as is generally assumed.

G-yrocotyle also has a sucker at one end ; but in order to bring
the genital ducts and pores into agreement with those of AmpTiilina
and the Heterocotyleans, this sucker must be placed anteriorly when
that of Ampliilina is posterior. Hence, the suckers in the two
genera are not homologous, for that of Gyrocotyle corresponds with
the anterior sucker of the Trematodes, whilst the "rosette organ" and
its peculiar proboscis possibly represents the posterior caudal disc of
the latter class. In Gyrocotyle this position brings the paired excretory
pores anteriorly, as in the Heterocotyleans. We cannot at present
employ the nervous systems to aid us in comparison, for Spencer
and Wagener differ in their identifications of the " brain," which
leads to the difference in their mode of orientating the animal. It
is less easy to decide the point in Caryophyllaeus, for the male and
female ducts present quite peculiar relations (Fig. I. 1). The
male duct, instead of running alongside the vagina as in all
other | Cestoidea, runs towards it from the opposite end of the
body, and the three ducts open into a common atrium. If we
place the mobile organ posteriorly, and attempt to homologise it
with the rosette of Gyrocotyle, we shall have an anterior, median,
excretory pore, which position is unknown amongst the Trematodes,
though it exists in Eothrioplana. At the same time the relative posi-
tion of testis and germarium becomes that normal in the Trematoda.

This rotation of the axis would lead to the assumptions (1) that
the " caudal vesicle " or tail with its six hooks in Caryopliyllaeus, and
therefore in the rest of the Cestoidea, is morphologically anterior,
a view already adopted by Grassi, and by Perrier, Blanchard, etc.,
on quite other grounds ; and (2) that the suckers, etc., on the scolex

1 Looss, however, while taking the above view with regard to the uterus of
Trematodes, holds (with Monticelli, Pintner) that the uterus of Cestodes is homo-
logous, not with the vagina, but with the genito-intestinal or Laurer's canal of the
Trematodes. While adopting Goto's views it has been deemed advisable in this
article to retain the usual names for these various ducts in the Cestodes.

102 THE CESTOIDEA

or " head " of the Merozoa are posterior. There seems to be no
a priori reason why an organ of fixation, varied in character as it
is in the Monozoa, should not occupy different positions in the
different genera. But although we may conclude that in Amphilina
the sucker is morphologically posterior, that in Gyrocotyle it is anterior,
and that the mobile organ of Caryophyllaeus is also anterior, it has
been considered desirable, while drawing attention to this com-
parison between the " Archicestode " and the Trematode, to preserve
the usual terminology and mode of representation.

The excretory system of Caryophyllaeus consists of a super-
ficial network of capillary vessels (Fig. II. 5, 6, 7), bearing
numerous flame-cells, and communicating with certain larger canals
lying in a deeper plane — the " ascending canals " — of which there
are a dorsal and a ventral on each side ; they pass forwards into
the neck, where they unite to form a single lateral vessel on each
side, which enters an elaborate plexus in the mobile organ ; from
this plexus ten " descending canals " pass backwards, connected
here and there by transverse vessels, to open into a median con-
tractile sac at the posterior end of the body, which communicates by
a terminal pore, as in the Malacocotylea. This is essentially the
plan of this system throughout the class. In " Archigetes " it is
stated that there are only eight descending canals. We know
nothing of the system in Amphilina. In Gyrocotyle the system is repre-
sented by a network only, without main canals, opening by two pores
(as in Heterocotylea) ; and whereas in the Cestoid ea in general flame-
cells have been recognised in the outer layer of the parenchyma,
Spencer was unable to detect any in Gyrocotyle ; but many of the
larger canals of the excretory system are provided with a continuous
row of cilia on one side. -

The nervous system in Caryophyllaeus consists of a pair of deep
lateral nerves, with four dorsal and four ventral more superficial
nerves. All are connected anteriorly by a ring-shaped " cerebral
commissure," but without special accumulation of ganglion cells
here. Anteriorly, nerves go to the mobile organ ; and posteriorly
the lateral nerves unite around the excretory pore.

In Gyrocotyle and Amphilina (Lang, 20) a more or less laterally
placed pair of nerves runs along the body, united at each end of
their course.

Very little is known about the life -history of the Monozoa.
Caryophyllaeus passes the earlier part of its life in the coelom of
Tubifex (D'Udekem, 1855). Here, while retaining a "caudal
vesicle " with six booklets, it grows to a considerable size, and its
genital organs become fully developed, though we have no evi-
dence that eggs are fully formed while in this host, as those
of "Archigetes" are stated to do; the worm must be swallowed
by a carp, roach, etc., when the Caryophyllaeus becomes mature in

THE CESTOIDEA 103

the intestine of its new host. The eggs are operculate, as in
Bothrioceplialus latus, and do not undergo any development till they
are laid. The six -hooked embryo is not ciliated, and feeding
experiments have thrown no light on the question as to how
the parasite gets into Tubifcx. In Ampliilina (39) the non-
operculate eggs are provided with a filament at one end, as in some
Trematodes. After a development resembling that of a normal
Cestode, an oval embryo issues (Fig. II. 2, 3) ; one half is ciliated,
and at the opposite end it carries ten hooks, which, curiously, are
precisely like those of the penis in number and shape. There are
also in Gyrocotyle ten hooks in the embryo. A group of unicellular
glands opens at the ciliated extremity, which have been regarded
with little justification as a remnant of the enteron. It is even
doubtful whether they develop into the glands which open into the
sucker of the adult. The fate of the embryo is unknown, as is also
the intermediate host.

GRADE B. CESTOIDEA MEROZOA ( = Cestodes digen&ses, v. Ben. ;
= Cestoda polyzoa, Lang ; = Tomiosoma, Montic.).

Cestoidea, in which the adult worm or " strobila" consists of two
distinct- parts, viz. (1) a sterile head or " scolex," provided with
organs of fixation ; and (2) a genital region or " body," in which
the genital organs are metamerically repeated ; and in most cases
this repetition is expressed externally by definite constrictions
separating the worm into " proglottids," each of which contains
usually one set of genital organs. These proglottids in most
cases drop off from time to time when mature.

It will be convenient to describe a definite type, viz. Bothrio-
cephalus latus, in order to illustrate the anatomy of the Merozoa
in general. The "broad tapeworm" (Fig. III. 1) of man has a
wide area of distribution, but is limited to such peoples as employ
uncooked river fish as an article of diet, for in these fish, especially
the pike, the early stages of development are passed.

The adult worm or " strobila " 1 consists of head or " scolex," 1
and a large number of short but broad segments or " proglottids." l
These are much compressed dorso-ventrally, and broader from side
to side than they are long, so that the worm has the form of a band
or ribbon, to which fact the technical name for the class is due.
The number of proglottids in R latus may be as many as 3000, or
even more ; and the length of the worm reaches 20 or 30 feet.

The proglottids are not all of the same size or shape ; as the
proximal region (towards the scolex) is approached they become
narrower, and quite far forwards their dorso-ventral diameter or

1 These terms were introduced by P. J. van Beneden, but Dujardin had already
used the term "proglottis " for the free, isolated, mature segment of Taeniae. Van
Beneden, however, used the word in a slightly different sense.

104

THE CESTOIDEA

thickness approaches their lateral diameter or breadth. They
thus become sub-cylindrical, and at the same time the constrictions
between them become gradually less and less distinct, till finally

FIG. III.

l.—Bothriocephalus latus, L. The proximal part of a strobila, with successive portions from
the more distal region (reduced after Leuckart). a, the scolex, showing the ventral bothrium
h indicates the uterus, containing eggs ; i, terminal proglottid.

2. — The scolex of Bothriotaenia infundibuliformis, Rud. (=B. proboscideus, Rud.). From the
salmon. (Magn., orig.). a, one of the two deep bothria; b, c, its right and left lips.

3. — The scolex of Solenophorus (Bothridium) megalocephalus, Crepl., out of the intestine of
python. (Magn., orig.). It is seen from the side, so as to show the dorsal and ventral bothria,
each of which is a tube formed phylogenetically by the union, along part of their extent, of the
right and left lips (b, c) of the bothrium ; a, the cavity of the tube, the inner margin of the wall
being indicated on the right of the figure by dotted lines ; d, the small proximal opening ; e,
the wide, distal opening, which is provided with a couple of valve-like folds ; g, the commence-
ment of the strobila.

4. — Ventral surface of a proglottid, with portions of two neighbouring ones, of B. latus, L.
p, The atriopore— copulatory pore common to both male and female ducts ; in the lower pro-
glottid the cirrus (s) is represented as everted ; u, the uterine pore ; r, region of the proglottid
occupied by the testes and vitellaria.

5. — A ventral' view of a proglottid of Bothriotaenia, Disymphytobothriiim, and other genera,
in which the atriopore (p) is marginal.

6. — Scolex of Duthiersia elegans, Perr., out of VaroMus. (Magn., orig.). The lips (b, c) of
each bothrium are united proximally to form a funnel, the margins of the upper opening are
much folded ; d, proximal opening.

they disappear. This region is the " neck," and it is at this point
that new proglottids are being constantly formed.1

1 In a few instances, such as B. punctatus and a species from Japan, there are
apparently intercalated proglottids, as if a proglottid had budded off another one.
But this is not the case ; it is due to incomplete formation of a proglottid. In some
species each young proglottid contains 2-6 sets of genital organs one behind the
other, but the adult joint has only one set (Ijima).

THE CESTOIDEA

105

,,The neck bears the head or "scolex," which is usually regarded
as^the anterior end of the worm, but which is more probably the
morphological posterior end. It is here flattened in a plane at
right angles to that of the proglottids, viz. from side to side ; its
dorso-ventral diameter being greatest; the dorsal and ventral
surfaces are therefore narrow, along each there is a narrow but
deep sucking groove or " bothrium," elongated in the direction of
the scolex (Fig. III. 2). The wall of the bothrium consists of
bundles of muscles which are not limited internally from the paren-
chymal tissue (Fig. IV.).

In respect of the general microscopic structure, it is unnecessary
to confine ourselves to a type. The body of the Cestoidea is
covered by a cuticle (non-chitinous, according to Leuckart, and

FIG. IV.

B. microcephfilus, Rud. A trans-
verse section of the scolex. ( x 50,
orig.). D and V indicate the
dorsal and ventral sucking grooves
or bothria. The substance of the
scolex consists chiefly of muscle
fibres arranged in three main
lines, viz. dorso- ventral, trans-
verse, and oblique, the direction
of each of which is modified by
the outgrowth (a) to form the
sides of the sucking grooves ; b,
the main excretory canal, branches
of which are also shown in various
parts of the scolex ; c, the edge
of the ganglion and the uppermost
part of the main lateral nerve,
with accessory nerves passing
away.

containing CaCo3) which is of variable thickness. Probably in the
primitive Cestodes the cuticle bore small spinelets over the whole
surface of the body, as in Gyrocotyle; but in the majority these have
disappeared from the general surface of the body, and remain only
in the cirrus (or penis) of many genera, while in various parts of
the organs of fixation they have become greatly enlarged to form
booklets.

The cuticle consists of two to four layers (see Zernecke (51),
etc.), the outermost of which generally appears as if composed of
short, close-set " hairs," corresponding with the outermost layer of
Trematodes, and this appears to be shed periodically (Fig. V.).
The deepest layer is always distinguishable as a thin membrane
differing from the rest ; this is the basement membrane, produced
by the parenchymal cells (Blochmann, Trematode literature, 8) ; the
rest of the cuticle is produced by the " subcuticula," and is traversed
by fine canals (in Ligula, Taenia, and others) which contain either

io6

THE CESTOIDEA

FIG. V.

Diagram of a transverse section through the body wall of a young Ligula. (After Bloch-
mann.) a, cuticle ; ft, basal membrane ; c, outer circular muscles ; d, epidermal cells— only a
few are represented ; each is prolonged upwards through the basal membrane to the base of the
cuticle ; e, a gland cell (Korbchenzelle) ; J, a flame cell (the indo» lino unfortunately otopo afc a
th^amenreft4ies'a~rrttte-insiete-&. Another flame cell is shown between the index

lines g, o) ; g, bundle of outer longitudinal muscle fibres ; h, a calcareous corpuscle, "lime cell,"
with peripheral nucleus ; i, dorso-ventral muscle fibre, terminating above in branches amongst
the circular fibres ; j, much branched cell, which Blochmann calls "parenchyma" cell, but its
relations to muscle fibres recall a nerve cell ; k, nerve plexus ; I, excretory vessel giving off
capillaries, terminating in flame cells ; m, a sense cell, terminating below the cuticle above,
and connected below with the nerve plexus ; n, a myoblast ; o, the processes of myoblast ter-
minating in the circular muscles ; p, free end of sense cell ; q, a pore in the cuticle, above the
Korbchenzelle; r, a small part of the most superficial layer of cuticle.

THE CESTOIDEA 107

the necks of gland cells or a nerve fibre. There can be no doubt
that the " subcuticula," of which there have been various interpreta-
tions, as in the case of Trematodes, is a true epidermis, consisting
of spindle-shaped cells which send fine processes upwards through
the basement membrane, to cease at the cuticle. The epidermic
cells form a continuous "epithelium" in Triaenophorus, but this
continuous sheet is interrupted in Ligula, and still more in Taenia
and the majority of Cestoidea, by intrusive parenchyma, which may
also be accompanied by muscle fibres ; indeed, in Taenia the thin
layer of circular, and the longitudinal coat of the " dermal " muscu-
lature come to lie between the "subcuticula" and the basement
membrane.

The bulk of the musculature, however, lies below the " sub-
cuticula " ; the outer coat of the parenchymal musculature consists
of longitudinal fibres, which in the young part of the chain (or
throughout the worm in Ligula) are continuous from one proglottid
to another ; but as these become more and more deeply constricted,
the muscular coat becomes interrupted ; in the higher Cestodes this
longitudinal coat is often separated by parenchyma into outer and
inner layers. The inner muscular coat consists of a sheet of
transverse fibres on the dorsal and on the ventral surfaces, dis-
continuous at the right and left margins ; these transverse muscles
are also, at first, continuous from joint to joint ; they delimit a
central or medullary part of the parenchyma from a cortical part.
In the Cestoidea, as in the Trematoda, the same controversy has
raged as to the character of the parenchymal tissue ; the most recent
investigations, and the use of the most modern methods, tend to
show that the parenchyma consists of very greatly branched cells,
the processes from which, nutritive in function, extend in all
directions, and are extensively ramified (Blochmann). These cells
lie in a homogeneous matrix, containing vacuoles filled with a
coagulable fluid. This ground substance, which is not cellular, as
Leuckart and others believed, extends right up to the basement
membrane, interrupting the continuity of the epidermic layer of
cells. In this parenchyma, and chiefly in its cortical region, are the
characteristic " calcareous corpuscles." Each is structurally very
similar to a fat cell — that is, the concentrically marked spherical
concretion of lime is enveloped in a protoplasmic membrane, the
nucleus being on one side (Blochmann). These lime corpuscles con-
sist of about 21 per cent of lime, the rest being organic substance;
the lime is in the form of carbonate, partly of albuminate (Griesbach),
and perhaps even of a certain amount of urate. Originally
considered as an excretory product — and described as lying in the
excretory canals, which they do not — they are now usually regarded
as "skeletal" (Leuckart), or as counteracting the acidity of the
gastric juices. However, they do not disappear with age ; nor is it

loS

THE CESTOIDEA

likely that the gastric or other digestive juices can pass through
the thick cuticle. The lime corpuscles are, moreover, present in
Cysticerci, which cannot be affected by gastric juice. Monticelli
has found a red pigment associated with the lime corpuscles in
Scolex polymorphic.

The excretory system of the Merozoa (see Pintner, Fraipont)
consists typically of a superficial (cortical) network of fine capillaries,
into which the flame cells open, and a
system of collecting vessels in the medullary
region extending throughout the strobila
and entering the "scolex." Of these col-
lecting vessels there are normally two on
each side — a dorsal and a ventral — situated
near the margin of the proglottids. These
canals are at first equal, but during growth
generally become unequal in diameter, the
dorsal being the smaller, resulting in a com-
plete disappearance of this one in several
Taenia, spp., and in some Tetraphyllidea.1
The two canals of one side pass into one
another in the scolex, while at the hinder
end of the strobila, i.e. on the last proglottid,
a contractile bladder, and so
to the exterior. This is the condition in
the larval form, but various modifications
occur in this type — modifications which

The excretory system in a +>,„,, „„„„ ,'
proglottid of BothriocepMlus tne7 °Pen *
punctatus, v. Ben (after Frai-
pont). a, the largest longi-
tudinal ca,nal (= ventral), con-
nected to its fellow by several
irregularly arranged commis-

/' from 'the have ™ systematic importance (Fig. VI.).
single dorsal canal' of each In B. latus there are the deep longitudinal

side, connected together by , . , , i j i i

irregular anastomoses ("island canals, which nave a normal, dorsal, and
Central position; and further, the dorsal

OCCUr

This network communicates and the transverse canals are at irregular

with the dorsal canals at e ; d, • , -\ T> .L i AT_- *. i

foramina secundaria (Wagener) intervals. But whereas this segmental anas-

o?fpraorgiot™ged; /} limits tomosis occurs in these Dibothridiata, and

again in the Taeniidae, it is absent in most

of the Tetraphyllidea. The two canals of one side, however,
always pass into one another in the scolex ; but the transverse
cephalic anastomosis may be absent even here, as in most of the
Tetraphyllidea (Fig. VII.) ; in others it is represented by a simple
transverse canal, as it is also in Tetrarhyncha, whilst in the Taeniidae
its place is taken by a circular canal arising, according to Pintner,
by the splitting of this, in connection with the formation of a
retractile rostellum.

1 Blochmann identifies Sommer's " plasmatic canal " as the dorsal excretory canal
of Taenia solium and T. saginta (CentralU. f. Bakt. v. Parasitenkunde, xii. 1892,
p. 373).

THE CESTOIDEA

109

The posterior contractile bladder naturally persists only in those
genera which do not drop their proglottids, e.g. Ichthyotaenia, and
various Taenia, spp., which inhabit Teleostei ; in other cases, after
the separation of this terminal proglottid, the four collecting canals

a

FIG. VII. — Plans of excretory system (after Pintner).

l.—Acanthobothrium coronatum, Rud. Young. The two canals on each side pass into one
another in the scolex, but are not connected right and left. Posteriorly all four open into the
contractile bladder (e).

•2. — PhyUobnthrium gracile, Wedl. Scolex. The two canals of either side pass into the
phyllidia of this side ; i is an " island " formed by the local splitting of a canal and the reunion
at once of the two branches.

3. — Tetrarhynehus. Scolex. The frontal, transverse vessel (a) unites the right and left
canals at the point of recurrence.

4. — Scolex of Cysticerciis arionis (i.e. of Taenia multiformis). b, rostellum, which causes the
vessel (a) to form a circular loop, into which the four canals fall.

5. — Taenia. Scolex. The muscular sucker also causes the formation of a loop in each
of the longitudinal canals, a, the circular vessel ; b, position of the rostellum j c, the four
acetabular loops or islands.

6. — Tetrarhynchus and Tetracotylea. Proglottids. The ventral canal becomes'wicler than
dorsal, and there is a transverse canal (/) in each proglottid.

came to open independently ; or, in some cases, a median duct
develops from the last transverse connecting canal. But in a con-
siderable number of instances the main canals effect new lateral
communications in the scolex, neck, and proglottids; these "foramina
secundaria " appear in Schistocephalus to be segmentally repeated.

no

THE CESTOIDEA

The nervous system of Bothriocephalus (Fig. VIII.) consists of a

right and a left longitudinal
cord traversing the strobila
throughout its length, lying
nearer to the middle line than
to the margin. In the scolex
they are united by a " cerebral
commissure," containing gan-
glion cells, whence four nerves
pass back along each side of
the scolex. The nervous sys-
tem in the Merozoa generally
agrees with this simple type ;
there is always one, sometimes
two, marginal nerve cords,
which are, in several instances
at least amongst the higher
forms, united by a transverse
or circular commissure near
the hinder margin of each
FIG. VIIL proglottid (Tower (47), and

Bothrioceph. latus, L. Plan of the nervous Others). A Superficial net-
system of the scolex (altered, from Niemec). a, -iirrirlr nf nprvp fihrpc ic in r»rm
one lateral nerve which extends throughout worf °

the entire strobila ; &, the two lateral accessory nection with these main COl'ds

nerves of one side ; c, one dorsal and one ventral /-p, , >.

accessory nerve of one side; e, the incomplete (-DlOCnmannj.

circular commissure connecting the main nerve T f^ oPnW tliP pnrrlc QT-A

and the accessory nerves, c ; /, the anterior nerves ;

g, one bothrium- h, the transverse ganglionic always Connected by a tranS-
comnnssure (brain), in front of which is a small f

additional commissure. verse cerebral commissure, and

usually there are one or even

two accessory, circular connections, whence more or less numerous
nerves are given off (Fig. IX.). The degree of complexity of this
apparatus is connected with the development and needs of the
organs of the scolex, and appears to have no systematic value
(Niemec, 31).

The most important of the internal organs from the system-
atist's point of view are the genital organs ; these in B. latus are
fully developed in about the 600th proglottid, which is therefore
said to be " mature." On the ventral surface of such a proglottid
two pores lie in the median line ; the anterior pore is the opening
of the genital atrium into which open the male copulatory duct
or penis, and the female copulatory duct or vagina, the posterior
aperture is the " birth-pore " or opening of the uterus (Fig. III. 4).

In the youngest proglottids, immediately following the head,
no trace of the genital organs occur ; but as the proglottids grow
older, and become further removed from their point of origin, the
forecasts of the organs make their appearance, the male organs

THE CESTOIDEA

in

first, and further back the female system. As the proglottids
become mature they drop off in groups. The follicular testes are
scattered over the greater part of the dorsal surface (Fig. X.) ; the
numerous efferent canals unite to form a larger sperm-duct, which,
after an extremely undulating course, enters and traverses the
"cirrus pouch," to the muscular walls of which the duct is con-
nected by radiating reticular fibres. By the contraction of the
wall of the pouch, the sperm-duct is straightened out and the whole
cirrus is everted. The germarium is made up of a pair of groups of
acini, lying near the ventral surface, and it is noteworthy that, while
in the Trematoda the testis is posterior to the germarium, the reverse

FIG. IX.

1, 2. — Plan of the nervous system of the
scolex of Taenia (reconstructed from Niemec's
figures).

1. — View from the ventral (or dorsal) surface.
a, lateral nerve ; b, one of the two accessory
lateral nerves ; c, the ventral (or dorsal) nerves ;
d, the ganglionic enlargement of the lateral
nerve ; e, the transverse commissure ; /, nerve
ring round the rostellum giving off nerves for-
wards. Posteriorly it receives eight nerves : g,
two nerves to the lateral ganglion ; h, a pair
of ventral (and dorsal) nerves ; i, polygonal
commissure ; j, one of the two ventral (or
dorsal) ganglia situated on this polygonal com-
missure, and connected to the main transverse
commissure by the nerve (I).

2. — Plan of nervous system at the level of
the commissure, seen from above, after removal
of the "ring."

3. — Diagrammatic transverse section through
the hinder margin of a proglottid of Moniezia
(somewhat altered from Tower), a, lateral
nerve, here dilated to form a ganglion, which
is connected with its fellow by a ring-commis-
sure, m ; cc', the dorsal and ventral ganglionic
swellings at the junction of the dorsal and
ventral nerves, with this commissure ; n, a loop
round the ventral excretory canal (a;).

m'

holds in the Cestoidea on the assumption that the scolex is anterior.
The vitellarium consists of a vast number of follicles distributed
over the ventral, and partially along the dorsal surface at each side.
The uterus is a long tube, having a characteristic convoluted course,
and opens anteriorly. The vagina starting from the ootype is
straight (see 45).

The life-history of Botlmocephalus is incompletely known, though
the development of the egg as far as the six-hooked embryo 1 has
been carefully studied by Schauinsland (40). It is, on the whole,
similar to that of a Trematocle, in the character of its segmentation,
at the end of which a "yolk envelope" of flat cells is formed, which
is left behind in the egg-shell (Fig. XL). Within this envelope

1 The six-hooked embryo is also known as proscolex, onchosphere, and hexacanth
embryo.

112

THE CESTOIDEA

FIG. X.

Bothriocephalus latm, L. The genital organs (after Sommer and Landois). The upper figure
shows the female organs seen from below ; the lower figure, the male organs from aoove. In
each case only the central part of the proglottid is represented, so that only a small part of
the testes and vitellaria is shown (see Fig. III. 4) ; the anterior and posterior boundaries,
however, are shown, a, the prominent "cirrus sac"; b, the cirrus, partly everted, carrying
the aperture of the sperm duct at its end ; c, the genital atrium and pore ; d, the vaginal pore
opening into the atrium ; e, the large coiling uterus ; /, the uterine pore ; g, the vagina in the
middle line ; h, germarium ; i, shell gland ; j, vitello duct ; fc, lateral nerve ; I, vitellarium ; n,
cirrus canal traversing the muscular tissue of the cirrus sac in order to reach the male pore
(see upper figure) ; p, sperm duct ; q, seminal vesicle ; r and x, vasa eflerentia ; s, lateral ex-
cretory canal ; t, testicular follicles.

THE CESTOIDEA

there is developed from the superficial blastomeres of the embryo a
ciliated mantle or " embryophore " enclosing the solid six-hooked
embryo, which is developed from the central mass of blastomeres.

-\--S

FJG. XI. — Development of BothriocepJialus latus, L. (after Schauinsland).

"I. — Segmentation is completed ; some cells of the blastosphere have migrated through the
yolk, and have flattened out to form (c) a " yolk envelope." A second set of superficial cells of
the embryo have grown over the remainder, and have formed a layer (e) of flattened cells, the
embryophore (Schauinsland's " ectoblast "). The remainder (d) of the blastosphere will
develop into the six-hooked embryo.

2. — A later stage in which the embryophore (e) is becoming thicker.

3. — The larva has been artificially pressed out of the shell, the operculum (s') being
pushed off. The embryophore has developed cilia. The yolk envelope remains in the egg
shell, and HOAV the yolk (y) is seen to consist of separate cells.

4. — A free-swimming larva. The embryophore (e) is much swollen by the water. The six
hooks are developed.

This embryo leaves the thick operculated shell, still enclosed in the
embryophore in B. latus, though in other species it is not ciliated and
is left behind ; by means of it the onchosphere is enabled to swim
freely in the water for at least a week, rotating about an axis that

8

n4 THE CESTOIDEA

passes through one pair of booklets, which is always carried hind-
most. The fate of this onchosphere is unknown, as feeding ex-
periments with appropriate hosts have been unsuccessful. But if
we may judge from other histories, this embryo is swallowed by
some invertebrate or perhaps a small fish on which the pike preys,
for the tissues of this fish sometimes contain numerous encysted
young forms of Bothriocephalus — wormlike, with an invaginable
"scolex" or head at one end (Fig. XIL). Such a sexless, encysted
stage is known as a " metacestode " or " plerocestoid " (Braun). It
is by eating such infested fish that man
becomes the final host, in the Baltic pro-
vinces and elsewhere, where the pike is
a favourite diet, and is eaten in an im-
perfectly cooked condition.

We have, however, more definite in-
formation about the history of Ligula
and Schistocephalus ; the ciliated larva of
FIG. xn. these worms is swallowed by a fish, and

Metacestode of Bothriocephalus the six-hooked embryo makes its way
LneSaerdt).in * through the intestinal wall, by the action

of its booklets, and thus reaches the

body cavity. Here it develops directly, by growth and loss
of booklets, into the strobila, and in the case of Schistocephalus,
the body even becomes segmented ; indeed, the parasite only differs
from the adult condition in the imperfect development of the
genital organs. The great increase in size of the worm causes con-
siderable inconvenience to the fish. When the latter is devoured
by a bird, the tapeworm soon becomes mature in the intestine,
the warmth of the bird's body hastening the development of the
genitals. According to Leuckart, the strobila, after two and a
half days' sojourn in the final host, may leave it through the anus,
partially digested, it is true, and the eggs are thus scattered in the
water.

The meaning of the ciliated embryophore is variously inter-
preted as either (a) a primitive ectoderm, or (b) the remains of a
miracidium-like larva. The latter view commends itself at the pre-
sent day, and the free-swimming larva may be compared to that of
a Trematode, in which the " six-hooked embryo " may be regarded
as having developed simultaneously with its envelope (cf. Gyro-
dactylus, p. 53).

CLASSIFICATION OF THE CESTOIDEA MEROZOA.

In% the Merozoa the generative organs, more especially the
uterus, exhibit two well-marked types of structure. In the one
type, as in the Monozoa and Bothriocephalus, the uterus retains its

THE CESTOIDEA

communication with the exterior by a " birth-pore." In the second
type, this pore has been lost, so that the uterus is a closed sac
(Fig. XIII. ). In the former case, the eggs when ripe can pass out
from time to time without a necessary separation of the proglottids ;
whereas, in the second case, the ripe proglottids drop off from the
strobila, either singly or in groups, and the eggs are discharged
only by local dehiscence or decay of its walls.

Associated with the possession of a birth-pore is the existence
of only two adhesive organs of the scolex, whereas those Cestodes
without a birth -pore possess four such organs, except in a few
individual instances, where there is then evidence of fusion. These
characters serve to differentiate the grade Merozoa into two
branches — the Dibothridiata and the Tetrabothridiata.

These " organs of the scolex," comprehensively grouped as
" suckers," occur in the Merozoa under three well-marked forms :

FIG. XIII. — Diagrammatic longi-
tudinal median sections (or
rather projections) of a pro-
glottid.

1. Dibothridiata. 2. Tetraboth-
ridiata, showing the uterine pore
in the former; its absence in- the
latter, a, common genital (copu-
latory) pore ; b, cirrus ; c, vas de-
ferens and testes ; d, vitellaria ; e,
vitello - duct ; /, gerinariuin ; g,
ootype, surrounded by shell glands ;
h, vagina (with dilatation or sper-
matheca) opening into the genital
atrium ; i, the uterus, opening ex-
ternally at j, in the Dibothridiata,
but a blind sac in the Tetraboth-
ridiata.

A ff

(a) as sucking grooves or "bothria," which are narrow fissures or
widely open cuppings on the dorsal and ventral surfaces of the
head; their muscles are only slightly developed, and are not de-
limited internally from the parenchyma; they are characteristic
of the Dibothridiata ; (b) as " phyllidia " (or " bothridia," M.
Braun1), which are essentially outgrowths from the side of the
scolex, to the number of four. Each is more or less distinctly
concave distally ; this muscular cup is the " bothridium," the
margins of which, and indeed the entire structures, are extremely
mobile ; and Pintner has suggested that these are rather organs of
locomotion than of attachment. They present certain modifications
(see below), and are characteristic of the Tetraphyllidea, Diphyllidea,
and Tetrarhyncha. Finally, (c) as "acetabula," or suckers in the

1 Van Beneden used the term "bothridium " for all kinds of sucking organs in the
Cestoidea. Earlier writers used "bothrium." Braun uses "bothridia" for those
which are here termed " phyllidia," and I restrict the use of the term to the cup or
sucker carried by the phyllidimn.

ii6 THE CESTOIDEA

ordinary sense of the word. These are deep hemispherical cups or
excavations at the side of the scolex, without projecting lips. They
are not mobile, and their muscles are delimited internally. They
are characteristic of the Tetracotylea (Taeniidae).

BRANCH A. DIBOTHRIDIATA.

Cestoidea Merozoa, in which the scolex is provided with only two of
these organs or "bothria," situated respectively on the dorsal and ventral
aspect. The uterus retains its communication with the exterior.

ORDER 1. Pseudophyllidea, v. Ben. (Dibothridae, Dies. ;
Dicestoda, Perr.).

The scolex is usually unarmed, though hooklets occur in some genera.
The common copulatory pore is usually on the ventral surface, though in
a few forms it may move to the margin of the proglottid. The uterine
pore is ventral.

FAMILY 1. BOTHRIOCEPHALIDAE. Bothria more or less definite slit-
like furrows ; proglottids generally distinct, and drop off in groups.
Bothriocephalus, Hud. ; B. latus, Bremser, in the intestine of man, in
Russia, Switzerland, Southern France, North America. The embryos,
enclosed in a ciliated embryophore, swim freely in water. Pike and other
fresh-water fish are the intermediate hosts, but possibly they become
infected by devouring invertebrates containing the larvae. B. cordatus,
Lkt., in dog, Greenland. B. tetrapterus, v. Sieb., in Phoca. B. (Diplogono-
porus, Lonnb.) balaenopterae, Lonnb., with two copulatory pores in each
proglottid. B. (Krabbea, R. BL) grandis, Bl., Japan. B. (Anchistro-
cephalus, Montic.) microcephalus, Rud., in Orthagoriscus mola. Amphi-
tretus, R. Bl. B. (Diphyllobothrium, Cobb.) stemmacephalum, Cobb., in
Porpoise. Amphicotyle, Dies., with an accessory sucker to each bothrium.
Bothriotaenia, Raillet ; they occur mostly in fish. B. infundibuliformis,
Rud., in the salmon (Fig. III. 2), (see 38). B. rugdsa, Rud., lives in Gadus,
spp. ( = "Abothrium gadi" of van Beneden). Disymphytobothrium, Dies.,
with peculiarly modified head, in North American sturgeon. Schisto-
cephalus, Crepl. (see 17). S. solidus, Crepl., in aquatic birds; the young
form lives in the body cavity of Gasterosteus, in which it develops so far
as to become segmented ; the genital organs have already appeared.
Ligula, Block, body unsegmented externally ; final host is some aquatic
bird ; the intermediate host a Cyprinoid or other fish, in the coelom of
which the worm attains considerable development (see 8). L. mono-
gramma, Crepl., a single series of genitals. L. digramma, Crepl., two
alternating series. FAMILY 2. SOLENOPHORIDAE. The lips of each
bothrium meet to form a sucking tube, usually retaining a pore at each
end ; genital pores ventral. Solenophorus, Crepl. (Bothridium, Blv.), (see
7) ; S. megalocephalus, Crepl., intestine of boa and python (Fig. III. 3).
Duthiersia, Perr. ; D. expansa, Perr., intestine of Varanus (Fig. III. 6) ;
Diplocotyle, Kr. ; D. obrikii, Kr., in Salmo carpio ; Ptychobothrium, Lonn-
berg ; P. belones, Lonnb. FAMILY 3. BOTHRIOMONIDAE. The two bothria
are replaced by a terminal, unpaired cup, which has arisen either by

THE CESTOIDEA

117

fusion and modification of the bothria, or it may be a rostellar sucker.
Cyathocephalus, Kessl. ; C. truncatus, Pall., in fresh -water fish (Fig.
XIV.), (see 19). FAMILY 4. LEUCKARTIIDAE. Without apparent bothria.
Leuckartia, Moniez, in fish ; Blanchardella, Moniez. FAMILY 5. TRI-
AENOPHORIDAE. Body indistinctly segmented, copulatory pore marginal.
The bothria are very shallow, but wide ; each is armed distally with two
three-pronged hooklets. Triaenophorus, End. ; T. nodulosus, Rud., in
pike, and encysted in the tissues of Cyprinoid fishes (Fig. XV.).

FIG. XV.

Triaenophorus nodulosiis,
Rud., from the intestine of the
pike. The left-hand figure re-
presents the entire strobila.
( x 2, orig.). a, the scolex ; ft,
the series of uterine pores
which alone mark the repeti-
tion of parts, for there are no
distinct proglottids.

The right-hand upper figure
is the scolex. (x 17, orig.).
It is viewed rather obliquely,
so that a part of one of the
hooks of the dorsal surface is
shown in addition to the both-
rium (a) and the two character-
istic hooks of the ventral sur-
face.

Lower figure. The hinder
end of the strobila rendered
transparent, (x circa 20, orig.).
ft, uterine pores ; c, uteri filled
with eggs ; d, copulatory pores,
irregularly arranged right and
left ; e, cirrus ; /, excretory
bladder. The rest of the geni-
tal organs not presenting any
peculiarities are omitted.

FIG. XIV.

Cyathocephalus
truncatus, Pall.,
from the intes-
tine of Perca
fluviatilis. ( x
circa 20, after
Zschpkke.) a,
terminal "suck-
er " (see text) ;
ft, uterine pore ;
d, copulatory
pore ; both are
alternately dor-
sal and ventral.

FIG. XV.

Further Remarks on the Dibothridiata. — This branch of the
Merozoa is more nearly allied to the Monozoa than are the Tetra-
bothridiata. The majority of them are parasitic in fresh-water
fishes, though the genus Bothriotaenia occurs in birds, and Bothrio-
cephalus latus in man. The size of the strobila and the number of
proglottids varies considerably, as it does too in the other orders ;
the great Bothriocephalus latus, with its hundreds of proglottids, and
measuring some 20 feet or more, contrasts with Cyathocephalus, with
only some twenty segments, and a length of 20 mm.

The scolex, though always retaining the two bothria — one dorsal,
the other ventral — exhibits some interesting modifications of the
typical structure. The deep, narrow cleft of Bothriocephalus is repre-

H8 THE CESTOIDEA

sented by a slight pit in Ligula, and in Triaenophorus by a wide,
shallow depression. An accessory sucker, such as frequently occurs
in the Tetraphyllidea, is met with in Amphicotyle, above the limits of
the bothria. An extension of the bothria round the scolex, and their
fusion, may lead to the condition in Cyathocephalus, where a circular
disc is formed, capping or surrounding the scolex. Modification in
another direction, viz. by the union and coalescence of the lateral
lips of the bothrium, leads to the formation of a dorsal and a
ventral tube, as in the Solenophoridae ; by the closure of the
lower aperture in Diplocotyle, two " suckers " are simulated ; and in
Dutliiersia the upper opening is expanded, and the whole sides much
folded to form a very mobile organ recalling the "phyllidium" of
the Tetraphyllidea. Further, in a few cases, booklets are carried
by the scolex ; these aid very materially in fixing the parasite to
the wall of its host intestine. The scolex may be prolonged beyond
the bothria, to form a " rostellum," which in Ptychobothrium is long
and mobile ; and in Schistocephalus is provided with a small pit,
recalling the terminal sucker of other orders. Indeed, as will be
seen below, modifications and differences of the same character as
these occur again and again in different orders of the Merozoa,
The typical " proglottidisation " is not expressed externally in
Ligula and Triaenophorus, though the genital pores indicate tl\e
repetition of the genital organs (Fig. XV.) ; in other cases, also, the
demarcation of the proglottids is but feebly expressed (Cyatho-
cephalus and Diplocotyle}.

The copulatory pore, though typically ventral, may move out-
wards so as to become marginal (Fig. III. 5), and may even come to
lie on the dorsal surface in Ptychobothrium. But these differences in
position seem scarcely sufficient, by themselves, to justify new genera,
and far less new families; and it is a matter of speculation as to which
is the more primitive position. Throughout this order the penis
opens into the genital atrium in front of the vagina ; and as a rule
the birth-pore is behind the copulatory pore, but the reverse holds
in Bothriotaenia.

BRANCH B. TETRABOTHRIDIATA.

Cestoidea Merozoa, in which the scolex is provided with four organs
of adhesion (? or locomotion), and in which the uterus is a closed sac, so
that the eggs can escape only after the decomposition or rupture of the
proglottid.

The branch includes four orders (families of van Beneden) founded
chiefly on the character of the organs of the scolex : Tetraphyllidea,
Diphyllidea, Tetrarhyncha, Tetracotylea.

ORDER 1. Tetraphyllidea, v. Ben. ( = Tetrabothridae, Dies.).

Tetrabothridiate Cestoidea in -which, tlie organs of the scolex are
outgrowths from it; these "phyllidia" are more or less, but always

THE CESTOIDEA 119

slightly, cupped, their margins being extremely mobile and active. The
phyllidia may be pedimculated, their depressions (" bothridia ") may be
subdivided by ridges into loculi, and in a few cases carry booklets.
The copulatory pore is usually marginal; the vagina is anterior to
the penis. The proglottids are detached singly, even before the genital
organs are fully developed.

The members of this order are found almost exclusively in the spiral
intestine of Selachians (see v. Beneden, 2).

FAMILY 1. TETRABOTHRIDAE (Tetraphyllidea, v. Ben.) The phyllidia
are distinctly constricted at the base. SUB-FAMILY 1. TETRABOTHRINAE.
Phyllidia simple and attached by a broad base. Phyllobothrium, v.
Ben. (Fig. XVI. 3) ; Tetrabothrium, Olss. ; Calyptrobothrium, Montic. ;
Memory gma, Dies. ; Ceratobothrium, Montic. ; Orygmatobothrium, Dies. ;
Marsipocephalus, "Wedl. ; M. rectangulus, WedL, in Heterobranchus
anguillaris of the Nile ; Prosthecocotyle, Montic. ; P. forsteri, in dolphin ;
Dinobothrium, v. Ben. ; Diplobothrium, v. Ben. ; Zygobothrium, Dies. ;
Pelichnibothrium, Montic. ; Peltidocotyle, Dies., scolex globular, dilated,
with four " scutella " (? phyllidia), each with two accessory suckers. P.
rugosa, Dies., in Platystoma tigrinum from Brazil ; Ephedrocephalus, Dies.
Small tetragonal scolex, with phyllidia at the angles. The short neck is
dilated to form a flat, octagonal platform, with reflexed edges, from
which the scolex arises ; Brazil. Amphoteromorphus, Dies. ; Amphotero-
cotyle, Dies. SUB-FAMILY 2. PHYLLOBOTHRINAE, v. Ben. Phyllidia un-
armed, more or less complicated by subdivision into " loculi," each
phyllidium attached by a narrow base, which is frequently produced to
form a peduncle. Echeneibothrium, v. Ben. (Fig. XVI. 4) ; Rhinebothrium,
Lint. (Fig. XVI. 2) ; Spongiobothrium, Lint. ; Anthobothrium, v. Ben. (Fig.

XVI. 1) ; Crossobothrium, Lint., Anthocephalum, Lint. SUB-FAMILY 3.
PHYLLACANTHINAE, v. Ben. Phyllidia armed with booklets. Callio-
bothrium, v. Ben. (Fig. XVII. 1) ; C. (AcanthobotJirium^ v. Ben.) coronatum,
Rud. ; G. (Onchobothrium, Blv.) uncinatum, Rud. ; C. (Prosthecoboihrium,
Dies.) dujardini, Dies. ; Phoreiobothrium, Lint. ; Cylindrophorus, Dies. ;
TJiysanocephalum, Lint. (Fig. XVII. 2) ; Platybothrium, Lint. ; Pelyoncho-
bothrium, Dies. ; P. septicolle, Dies., in Polypterus bichir. FAMILY 2.
GAMOBOTHRIDAE, Lint. The four phyllidia united by their lateral
margins to form a single discoid or globular mass. Lecanicephalum,
Lint. (Fig. XVII. 3, 4). Tylocephalum, Lint., head formed of a globular
organ (? united phyllidia) with four accessory suckers, and beyond a large
rostellum. T. pingue, Lint., in Ehinopterus ; Discocephalum, Lint. (Fig.

XVII. 5).

fiemarks on the Tetraphyllidea. — The anatomy, as well as much
of what is known of the life-history of these forms, was investigated
by van Beneden, to whose valuable researches we owe so much of
our knowledge of parasitic Platyhelminths. These Tetraphyllidea
are almost exclusively found in the spiral intestine of Selachians,
and it appears that here they move about and are not permanently
attached as the more highly developed Taeniae are ; this locomotion
is effected partly, at least, by the movement of the " phyllidia."

120

THE CESTOIDEA

These " phyllidia " are outgrowths of the scolex, and contain a
part of the excretory network (Fig. VII. 2) ; they occur under
three chief varieties : (a) They retain their simple character with
a more or less marked, spoon-shaped depression or " bothridium "

FIG. XVI.— Scolex of various Tetraphyllkfea

1. — Anthobothrium cornucopia, v. Ben., out of Galeus canis (after v. Ben.). The four phyllidia
are typically developed, with long stalks, and a simple unarmed and undivided bothridium.

2. — Rhinebothrium flexile, Lint., out of Trygon centrum (after Linton). Each bothridium is
divided into numerous loculi by a median, longitudinal, and a series of transverse ridges.

3. — Phyllobothrium thridax, v. Ben., out of Squatina vulgaris (after Zschokke). Each both-
. ridium is provided with an accessory sucker (a).

4. — Echeiieibothrium variabile, v. Ben., in various species of Raia (after Linton). In addi-
tion to the usual four bothridia— here well developed— carried by the phyllidia, there is an
apical, rostellar sucker (x).

at the free end ; the point of attachment to the scolex is con-
stricted, and this narrow base may be prolonged to form a distinct
peduncle, or this simple depression in the Pliyllobothrinae (Fig.
XVI. 2) may be subdivided by transverse ridges into a small
number of " loculi," as in the posterior sucker of such a Trematode

THE CESTOIDEA

121

as Tristomum or Aspidogaster. This loculation no doubt aids in
attachment, (b) In the sub-family Phyllacanthime, (Fig. XVII. 1)
booklets may be added which convert the originally locomotor
organ into a more useful adhesive organ, (c) But both in the
simple and in the armed phyllidia an " accessory sucker " may be
present, either somewhere within the area of the cup (Tetrabothrium),
or frequently above it (Phyllobothrium) on the scolex; this accessory

FIG. XVII.— Scolex of various Tetraphyllidea.

l.—Calliobothriiimfilicolle, Zsch., out of Torpedo ocellata (after Zschokke). The phyllidia are
here short ; each bothridium is trilocular, and is armed, distally, with two bifurcate hooks.
Above each bothridium (e) is an accessory sucker (d).

2.—Thysanoeephalum crispum, Lint., out of Galeocerdo tigrinus (after Linton). The small
scolex (/) is, during life, partially concealed by the " pseudoscolex ' (g), which is formed by the
development of much-folded ridges from the neck. Each bothridium (/) is bilocular, and armed
with two simple spines.

3. — Lecanicephcdum peltatum, Lint. , out of Trygon centrum (after Linton). Viewed from above.

4. —The same from the side. The scolex is here flattened so as to form two horizontal plates,
the margins of which (a, 5) are membranous and folded, and separated by a slight furrow. The
lower plate carries four accessory suckers (c), two of which are indicated by the dark spots in
3, and one in 4, in which, however, the index line stops short.

5. — Discocephcdum pileatum, Lint., out of Carcharius obscuriis (after Linton). The scolex
is a flattened, mushroom-shaped disc ; below it is a swollen neck (g), the surface of which is
irregular ; it is separated by a groove from the scolex.

sucker differs in structure from the " bothridium " ; it is a pit in
the surface, with strong muscular walls, which are delimited from
the parenchyma ; in fact, these " suckers " have the structure of
the "acetabula" of the Tetracotylea, with which Pintner (1896)
homologises them, regarding the " bothridium " as something not
represented in the majority of the Tetracotylea.

But in addition to forms, in which the four organs are distinctly
separate, there are other forms in which the structure of the head

122 THE CESTOIDEA

is more or less modified by fusion of the phyllidia. In Dinobothrium
the phyllidia are arranged in two pairs, the members of a pair being
close together. In Diplobothrium, Zygdbothrium, and Platybothrium
the paired members are actually united, so that the head appears to
possess only two instead of four phyllidia ; but evidence of fusion
is provided by the existence of a slight ridge traversing each
apparent phyllidium. A step further, and the four phyllidia may
fuse to form a single structure, as in Gamobothridae, giving rise to a
plate-like or globular termination to the head (Fig. XVII. 3, 4).

In Thysanocephalum (see 25) the scolex is hidden by a great
swelling of the neck, which becomes folded and fringed so as to
give rise to a structure recalling the mobile organ of Gyrocotyle,
much exaggerated (Fig. XVII. 2). Here the " neck " is replacing,
functionally, the scolex, which is greatly reduced, and suggests that
possibly in " Phyllobothrium laduca" v. Ben., something of the same
sort has occurred.

The " rostellum " or apical region beyond the attachment of the
phyllidia may or may not be present ; it undergoes great modifica-
tions in some cases, and possibly in the Gamobothridae this organ
shares in the formation of the very peculiar "head" (see 25). It
may carry a terminal sucker (Echeneibothrium, Fig. XVI. 4), as in
some of the Tetracotylea.

The four phyllidia or other organs of the scolex in the Tetra-
bothridiata are normally arranged at equal distances around the
apex of the scolex, in such a way that, as the nervous and excretory
systems show, two correspond to the dorsal and two to the ventral
surfaces of the proglottids ; in other words, each bothrium of
Bothriocephalus is represented, topographically at least, by a pair of
organs in the Tetrabothridiata. It is not, however, probable that
the latter organs are descended from such a Dibothridiate form by
a process of duplication. We have no evidence from embryology
that this process takes place ; on the contrary, we have evidence
that the reverse process obtains in some of the Tetrabothridiata.
Nevertheless, the fact that, in the Dibothridiata, the generative
organs resemble those of the Cestoidea Monozoa and Heterocotylea,
forbids us taking the view that each of the two "bothria" in
this branch has arisen by fusion of a pair of ancestral organs.
We have, therefore, to fall back on the assumption that both
groups have been derived, along divergent lines, from a common
ancestor in which the organs of adhesion were not yet developed,
or possibly were in some such condition as that of Caryopliyllaeus.

The generative organs retain in some respects the arrange-
ment found in the Dibothridiata, viz. the vitellarium is marginal
and follicular, extending round the entire proglottid ; the vagina
is usually anterior to the penis ; the uterus is more or less tubular
and undulating, but has lost its pore. The genital pore is

THE CESTOIDEA 123

marginal ; but in Ephedrocepkalus the male organ opens here, the
vagina on the ventral surface. The eggs undergo little change so
long as they remain in the uterus ; but, as in the Dibothridiata,
develop outside the parent, from which they are discharged by the
decay of the joint. The proglottids are detached singly, and the
fringe of processes or lobes which frequently ornament the hinder
margin are used as locomotor organs ; after separation the pro-
glottid may grow, and the genital organs undergo further changes,
so that there is a close resemblance to an " individual " organism
leading its own independent life.

Very little is known about the life-history of the members of
the order. Van Beneden discovered isolated heads attached to
" sacs," or even enclosed in them, in various Selachians and other
fishes ; he noted the resemblance of these " scolices " to the heads
of various Tetraphyllidea, and rightly concluded that they represent
a stage in the life-history of the tapeworm. Such " metacestodes "
(which resemble Cysticercoids with everted head) occur free in the
intestine of various fish, and no doubt attain their adult state when
these are devoured as food by Selachians. One of the commonest
forms is Scolex polymorphus, which has been observed in a variety
of Teleosteans, in Sepia, and even in crabs. Monticelli (29) has
shown, by careful comparison with the head of adult Calliobothrium,
that it is the larva of C. filicolle, Zsch. In these metacestode
stages the organism consists of a sac and a head, invaginable
in some cases into the sac, the Avails of which are thin, mus-
cular, and provided with nerves and excretory canals, on the same
plan as in the adult ; the latter open by a contractile bladder
posteriorly, and are continued into the scolex anteriorly. By a
process of budding just behind the suckers, a series of segments
are formed, and it appears that the orginal sac or bladder — upon
which six hooks have in many cases been recognised — becomes the
most posterior, sterile proglottid.

ORDER 2. Diphyllidea, v. Ben.

The scolex is provided with a long " head stalk," which is armed
with several longitudinal rows of hooklets-; the "head" consists of a
retractile armed rostellum and four (apparently only two) phyllidia, with
projecting, slightly mobile margins. The strobila consists of few
proglottids. The generative organs are of the Tetraphyllidian type, but
the genital pore is on the ventral face.

SOLE FAMILY. ECHINOBOTHRIDAE. Echinobothrium, v. Ben., sole genus ;
in spiral gut of Selachians (Fig. XVIII.) ; E. musteli, Pintner, the meta-
cestode in the liver of Nassa reticulata. The rostellum has an elaborate
structure, consisting of a muscular mass lying dorsal ly and ventrally,
supporting two groups of " frontal hooks." Tins rostellum appears to be
homologous with that of the Taeniidae rather than with the proboscis

124

THE CESTOIDEA

of Tetrarhynchus (33). Each of the two phyllidia, which are dorsal and
ventral, consists really of two alae or flaps separated by the projecting
edge of the scolex. These four flaps are indeed the four phyllidia, united

FIG. XVIII.

1. — Echinobothrium affine, Dies., out of Raia, spp. (altered, after Pintner). View of scolex
from the side, with the commencement of the body, a, rostellum ; ft, rostellar or frontal
hooklets, situated in a dorsal and ventral group of eleven ; in each group there are two kinds —
six like &J,and five like 62 in this species ; at the sides of each group are three small accessory
hooklets; 6], fe2, the two kinds of frontal hooks of E. musteli, Pintner. The central muscular
mass of the rostellum is indicated by dotted lines, but in addition there is a group of retractor
muscles of the hooks on each side ; c, one of the ventral phyllidia ; d, e, the right and left dorsal
phyllidia, united below ; e, points to the inner face of the phyllidium, the dotted outline indi-
cates the lower limit of these organs ; c, d, are in reality separate from one another above, but
are represented as overlapping ; /, the long "head stalk" provided with eight rows of spines,
characteristic of the genus. In this species there are twenty to twenty-five spines in each row ;
/!, one of these spines ; it is quadriradiate, with its fourth spine directed inwards and slightly
curved ; g, the uppermost proglottid, which exhibits a notch at each side, indicating, probably,
a division into two ; h, the second proglottid.

2. — Transverse section of the scolex, a little above the level of c, in 1 (altered, after Pintner).
The parenchyma of the four phyllidia is not indicated ; the longitudinal muscles (as a row of
dots) below the cuticle, c, one of the ventral phyllidia ; d, e, the two dorsal phyllidia correspond-
ing to those in 1. It is now seen that d and e are in reality separate structures, the body wall
intervening between them, where the letter k is placed. The figure '"2" lies in the lateral
depressions between c and d • k, the retractor muscles of the dorsal frontal hooks ; I, the
central muscular mass of the rostellum, formed of transversely arranged fibrillae ; m, the four
excretory canals ; n, the great lateral ganglia of the nervous system ; below the rostellar mass
they are connected by a transverse commissure.

3. — Plan of the genital organs from below (composed from Pintner's description and figure
of E. musteli). In reality the testes would have undergone degeneration before the uterus
had attained the size represented, a, Vitellarium ; &, testes ; c, cirrus ; d, genital atrium, which
opens on the ventral surface of the proglottid ; e, germarium ; /, vagina dilated in its course
to form a receptaculum seminis ; g, uterus.

dorsally and ventrally (Fig. XVIII. 2). It is a noteworthy 'fact that
Pintner could find no calcareous corpuscles anywhere in the tissues of this
tapeworm.

THE CESTOIDEA 125

The systematic position of this isolated genus presents considerable
difficulty; it is evident that it is Tetrabothridiate both from the structure
of its suckers and from the absence of a distinct birth-pore. The fact that
the margins of the bothridia project freely and are slightly mobile points
to its affinity with the Tetraphyllidea rather than with the Taeniidae or
Tetrarhyncha, as also do the genital organs. Its long " head stalk " is a
point of resemblance to the latter group. This region is not one of
budding as is a " neck " in the rest of the Merozoa, for there is a sharp
demarcation between the region of budding and the armed region both
in Echinobotfvrium and the region which contains the proboscis sacs in
Tetrarhynchus. The fact that in both families there is a tendency for
the bothridia to fuse in couples must not be held to have great weight,
since in the Tetraphyllidea we find the same tendency in various genera.
The ventral genital pore too is not unknown amongst the Tetrarhyncha
nor the Tetracotylea, but at first recalls the Bothriocephalid arrangement.

Probably Echinobothrium came off from the Tetrabothridiate stem
at a very early period, and has remained thus isolated.

The genus Tetracampos, "Wedl., may possibly be allied to Echinobothrium.
The scolex possesses four round, flat, feebly expressed phyllidia ; the
rostellum carries four groups of booklets, but nothing is said as to its
retractility. The genital pores are on the ventral surface. The hexacanth
embryo is ciliated. T. ciliotheca, Wedl., in Heterobranchus anguillaris of
the Nile (Stzber. Akad. Wien. Math. Nat. Cl. I. xliv. 1861, p. 473).

ORDER 3. Tetrarhyncha, v. Ben. ( = Phyllorhyncha, v. Ben. ;
= Trypanorhyncha, Dies.).

The four phyllidia (bothridia) may be united in pairs, as in the
Diphyllidea. Each phyllidium is accompanied by a long spiniferous
proboscis (or " trypaiiorhynchus," Dies.) capable of retraction into a sac
occupying the " head stalk." The adults occur in Selachians. The
metacestode is encysted in various parts of Teleosteans. FAMILY —
TETRARHYXCHIDAE ( = Dibothriorhyncha + Tetrabothriorhyncha, Dies., etc.),
with characters of the order. Syndesmobothrium, Dies. ; Tetrarhynchus,
Rud. ( = Rhynchobothrium, v. Ben., Lkt., etc.). The genus contains a large
number of species. T. ruficollis, Eysenh., in Mustelus, Acanthias, etc. ; its
metacestode is Coenomorphus joyeuxii, Lonnb., which occurs in crabs (Vaul-
legeard, 1895). Rhynchobothrium, Rud. (incl. var. spp. of Tetrarhynchus,
auct.) ; Otobothrium, Lint. ; 0. crenaticolle, Lint., from Zygaena malleus.

Remarks on the Tetrarhyncha. — The numerous species occurring
in sharks have been, by various authors, referred to a variety of
genera distributed over two families founded on the character of the
bothridia, — whether they are two or four, independent or united.
Pintner in a recent work (34) would refer all species to one genus
Tetrarhynchus, for, as he points out, there is every gradation between
the various conditions of the phyllidia.

The scolex in this group is extremely elongated, and, as in the
Diphyllidea, is provided with a very long " head stalk," which is

126

THE CESTOIDEA

distinctly and markedly constricted from the "neck" (Fig. XIX.).
The head stalk carries the " head," which is nearly square ; the

1

FIG. XIX.

l.—Tetrarhynchus (RhynchobotJiriuiri) hispidus, Lint., out of Trygon centrum. Entire strobila
(X circa 45, after Linton). A, the long scolex; B, the "body" consisting of five proglottids,
the last of which is nearly mature, a, one of the two phyllidia, formed by the fusion of a pair ;
it bears a single bothridium ; b, one of the four spiniferous proboscides ; c, the membranous
proboscis sheath ; d, the muscular bulb ; e, the "head stalk" ; /, genital pore.

2. — T. (Syndesmobothriurii) gracilis, Wagn., out of a cyst in Orthagoriseus mola (x 4J, orig.,
from a specimen in the Oxford University Museum). The scolex had not separated from the
"bladder," a small portion of which is represented, a, one of the four independent and dis-
tinct bothridia ; b, one of the four proboscides.

3. — A portion of a proboscis of Tetrarhynchus, sp., out of the intestine of Carcharias(x 90,
orig.). The two kinds of hooks and their spiral arrangement are shown.

4. — Diagrammatic longitudinal section of a quadrant of a scolex, showing one bothridium,
and one proboscis which is partially everted, a, Bothridium ; b, proboscis ; c, proboscis sheath,
its cavity is shaded ; d, muscular bulb, with its cavity shaded ; g, retractor muscle ; /*, the
aperture in the scolex, through which the proboscis is everted, and to the margin of which the
membranous sheath is attached ; i, retractor muscles of the bothridium, inserted in the pro-
boscis sheath.

THE CESTOIDEA 127

four phyllidia — set in dorsal and ventral pairs — may be distinct,
terminal, and almost cup-shaped (Synde&mobothrwm), but more gener-
ally the pair of organs are adnate (Tetrarhynchus), or even more or
less closely united (Otobothrium), but there is frequently a ridge, or
other sign of fusion. However, in some cases this fusion is so
complete externally that there appears to be only two phyllidia, as
in Diphyllidea, but even then, the four structures are distinctly
recognisable in section by the distribution of the nerves and
excretory organs (lihyncJwbothnum).

The characteristic structures of the order, however, are the four
" proboscides " or trypanorhynchi (Fig. XIX. 4).

Each proboscis consists of three parts : (1) a longer or shorter
hollow tentacle, capable of eversion and introversion, and armed
with numerous booklets arranged in a definite way. This tentacle
can be withdrawn into (2) the tubular " membranous sheath," which
starts from the apex of 'the head where it opens and passes back-
wards iuto the head stalk, taking a straight or undulating course ;
it terminates in (3) the "muscular bulk" or cylinder, the walls of
which are formed of ten or more concentric sheaths of muscle
fibres, which are transversely striated. The wThole apparatus is
filled with a fluid, by the compression of which in the " bulb " the
tentacle is evaginated. Introversion is effected by a "retractor
muscle " attached at one end to the wall of the bulb, at the other
to the tip of the tentacle. The apparatus presents certain interest-
ing histological features, for instance, the sheath is lined by a
distinct epithelium. Each individual proboscis resembles in some
degree the single proboscis of Acanthocephala, in a less degree that
of Nemertines. It has been usual to homologise these " proboscides "
of Tetmrhynclius with the retractile rostellum of certain Taeniidae,
but apart from the difference in number, there are differences in
structure which militate against this view. It appears more
probable (Pintner) that each proboscis has been developed by the
deepening and modification of an " accessory sucker " of some
Tetraphyllidean, as its relation to the bothridia, and its mode of
development, closely agree with these structures. Functionally,
too, it is a perfection of the armature plus the accessory sucker of
three forms; whilst there is no doubt that the " phyllidia'' of the
two orders are identical. As will be shown below, the " acetabula "
of Tetracotylea are derived also from the "accessory sucker," so
that the proboscis of Tetmrhynchus is homologous with the sucker
of Taenia.

The excretory (Fig. VII. 3) and nervous systems, which
present nothing of any systematic value, have been worked out
by Lang, Pintner, etc. As to the generative organs, they are
constructed on the plan of the Tetraphyllidea, with marginal vitel-
laria, etc.

128 THE CESTOIDEA

The metacestode phase is a cysticercoid, the head Avith its
apparatus being enclosed in a bladder similar to that of Tetra-
phyllidea ; this occurs encysted in various tissues, especially the
wall of the gut, of Teleosteans, or with everted head, free in the
alimentary canal of sharks. The bladder may be a foot or more
in length, as T. elongatus, T. macrurus. The adults of some species
were observed by v. Beneden with this " bladder " attached at the
end of the strobila.

The scolex may after e version separate from the bladder, and
in this condition has been found in Sepia (as T. sepiae).

The cysticercoid, with the enclosed scolex, was known as Flori-
ceps (Cuv.), and as Anthocephalus (Rud.), and the term Tetrarliynclms
was applied to the stage with everted scolex ; van Beneden showed
that these are merely stages in the life-history of the strobila known
as Rhyncliobotlirium. It is still undecided amongst systematists
which of these two last names should be used.

ORDER 4. Tetracotylea, Dies. ( = Taeniidae, auct).

Tetrabothridiate Merozoa, in which the organs of the scolex have the
form of cup-shaped or hemispherical " acetabula " hollowed out in the sides
of the scolex, and without projecting or mobile margins.1 Booklets are
rarely present in these acetabula. There is usually a rostellum, which may
be armed with a crown of hooklets. Members of the order are mostly
parasitic in warm-blooded vertebrates. FAMILY 1. ICHTHYOTAENIIDAE,
Lonnberg. The sucking organs are acetabulate, but the generative organs
resemble those of the Tetraphyllidea.2 Ichthyotaenia, Lonnb. ( = Tetracotylus,
Montic.) ; several species in fresh-water fish (see 10 and 37). Corallobothrium,
Fritsch (Fig. XXII. 1). FAMILY 2. ECHINOCOTYLIDAE. The acetabula are
armed ; rostellum with one or two circlets of hooklets ; parasitic in birds.
Echinocotyle, Blanch., a single crown of hooklets, which are falciform.
E. rosseterij Blanch., in the duck ; " metacestode " in Cypris cinereus.
Davainea, Blanch, and Raillet (Fig. XXII. 7) ; D. proglottina, Dav., with
four proglottids ; fowl and slugs. D. contorta, Zscli., from Manis
pentadactyla. Cotugnia, Diam., with two sets of genital organs in each
proglottid. Idiogenes, Kr. ; Ophryocotyle, Friis. FAMILY 3. TAENIIDAE.
Scolex globular or pyriform ; suckers unarmed ; rostellum may or may
not be armed ; vagina elongated, posterior to the cirrus ; mostly parasitic
in mammals ; larval stage a "cysticerctis " or "cysticercoid." SUB-FAMILY 1.
HYMENOLEPINAE (= Cystoidea, Lkt). Strobila of moderate or small
size ; scolex with one, two, or several circles of hooklets ; eggs with
transparent, multiple envelopes ; larva, a cysticercoid in Arthropods and
Mollusca. Dipylidium, Lkt., rostellum armed with peculiar hooklets, like

1 In some avian tapeworms living in Apteryx the lower margin projects slightly
and may he mobile (Benham, Q. J. M. Sc. xliii. 1900, p. 83).

2 The gemis Sciadocephalus, Dies. (Fig. XXII.), is doubtfully placed here. It is by
some authorities put in the family Gamobothridae, among the Tetraphyllidea. The
family Ichthyotaeniidae, in fact is possibly a member of the latter order.

THE CESTOID E A 129

rose-thorns (Fig. XXIV.) ; genital organs and apertures double in each
proglottid (Fig. XXVI.). D. caninum, L. ( = T. cucumerina, Bloch. ; = T.
elliptica, Batsch), in the ileum of dog ; cysticereoid in Trichodectes canis and
in Pulex serraticeps. The strobila is 100 to 250 mm. long ; the scolex has
. four rows of hooklets ; the worm occasionally occurs in man. The larva
of D. echinorhynchoides, Sons., occurs in lizards. Hymenolepis, Weinl., the
proglottids much broader than long, with the posterior angles projecting like
saw-teeth ; genital pores all on the left side ; uterus transverse ; eggs with
three envelopes, far apart, the innermost having "horns" (Fig. XXVIII.).
H. nana, v. Sieb., in the intestine of man, was originally discovered in an
Abyssinian ; it is now known also from Italy, England, United States,
and the Argentine. It is about an inch in length ; the rostellum bears a
single row of hooklets ; the larva is unknown. H. murina, Duj., in rat
and mouse ; the larvae occur in the villi of the intestine, and the adult
in the lumen ; there is here, therefore, no change of host ; there is merely
a migration from one organ or part of an organ to another. Grassi has
suggested that these species are synonymous, but v. Linstow (1895) has
pointed out the various differences between them. Drepanidotaenia,
Raillet, in the gut of birds, especially aquatic birds ; cysticercoids in small
Crustacea. D. infundibuliformis, Goeze, in pigeon and house-fly;
Dicranotaenia, Kaill., D. coronula, Duj., duck and Cypris ; Chapmania,
Montic. SUB-FAMILY 2. TAENIINAE (= Cystotaenia, Lkt.). Strobila
usually of large size ; scolex with two or three circles of hooklets ;
uterus median, with lateral caeca ; genital pores, irregularly alternate ;
eggs with two envelopes ; the outer thin and deciduous, the inner one
thick, brownish, and immediately enveloping the six-hooked embryo.
The genus Taenia lias been subdivided into a number of sub-genera by
Weinland : Taenia, L. (s. str.), rostellum armed ; larva a cysticercus.
T. solium, Kud., intestine of man ; Cijsticercus cellulosae in muscle and
viscera of pig, rarely in man, rat, dog, etc. (Fig. XX. 3). Cosmopolitan
wherever the pig is a common article of diet, and eaten in an imperfectly
cooked condition. Scolex with two circles of hooklets ; strobila 2 to 3
metres long, with 850 proglottids, the 450th having fully-formed genital
organs. The uterus consists of a median sac, with eight to ten broad caeca,
which bear irregular wide lobes. T. serrata, Goeze, in small intestine of
dog, wolf, etc., with C. pisiformis in the rabbit and hare ; T. marginata,
Batsch, in wolf, butcher's clog, etc., is the largest dog tapeworm, measuring
1*5 to 3 metres. Its C. tenuicollis infests the peritoneum, liver, etc., of
pig and ruminants. Taeniarhynchus, Weinl., has neither rostellum nor
hooklets ; the larva is a cysticercus. T. saginata, Goeze (T. mediocan-
ellata, Kiich.), in the intestine of man ; its Cystic, bovis in the muscles of
ox (Fig. XX.). Originally from the East, now cosmopolitan, where im-
perfectly cooked beef is eaten freely. It measures 7 to 8 metres, and
is the largest tapeworm in man; there are about 1200 proglottids,
relatively broad, the genital organs being fully formed in the 600th ; the
worm appears to be the raiviai of the Greeks. Cystotaenia, Leuck., scolex
with two circlets of hooklets ; the larva is a " coenurus." C. coenurus,
Kiich., in the ileum of the dog and wolf; Coenurus cerebralis, in the brain
of sheep (or other domestic and wild herbivora), swells up to a great size,

130

THE CESTOIDEA

destroying more or less of the brain, causing the disease known as " gid "
or " staggers." G. serialis, RailL, of dog, with Coenurus in the connective

FIG. XX.

\.-Taeniarhynchus saginata, Goeze ( x £) ; entire strobila.

2. — Anterior part of the same ( x 8) as an example of unarmed tapeworms.

3.— The scolex of Taenia solium, Rud. ( x 22), showing the rostellum with double crown of
hooks.

4 — A genitally mature proglottid of T. saginata ( x 7). a, lateral nerve ; &, lateral excretory
canal ; c, testes ; d, genital papilla ; e, genital pore ; /, cirrus ; g, sperm duct ; h, testes ; i,
vagina ; j, germarium. The ootype and shell gland are unlettered. The vitellarium is the small
organ behind the germarium. n, uterus.

5. — The ootype and female ducts related to it (x 30). i, vagina ; Tc, ootype, the shell glands
not shown ; I, vitello-duct ; m, spermatheca ; n, uterus ; oo, germ ducts ; p, fertilising canal,
i.e. the lower end of the vagina.

6.— A detached ripe proglottid of T. saginata ( x 2), with fully formed uterus filled with eggs.

7. — Six-hooked embryo. (All after Leuckart.)

tissue of the wild rabbit and various rodents. Echinococcifer, WeinL,
scolex with two circles of hooklets. The metacestode is known as

THE CESTOIDEA

" echinococcus." E. echinococcus, v. Sieb., measure 5 mm., consists of only
four proglottids, the last of which, is ripe (Fig. XXI.). The strobila
lives in the intestine of dog, wolf, jackal, in immense numbers. The
" echinococcus " occurs in various tissue of ungulates,
carnivora, rodents, monkeys, and may even find its
way into man in countries such as Iceland and
Victoria, where he and the dog are very closely
associated, and where cleanliness is neglected ; in the
former country as many as two to three per cent
of the inhabitants are affected. SUB -FAMILY 3.
ANOPLOCEPHALINAE. Body lanceolate anteriorly;
scolex unarmed and without a rostellum ; proglottids
being much broader than long, the uterus is trans-
verse (Fig. XXV.) ; the eggs contain a " pyriform
apparatus" (see below). The adults occur in the
intestine of ungulates. Moniezia, R. Blanch., two
complete sets of generative organs and two genital
pores in each proglottid. M. expansa, End., in sheep
(Fig. XXV. 1). Thysanosoma, Dies., T. fimbriata,
Dies., in the small intestine and bile ducts of sheep,
etc. Stilesia, Raill., suckers of the scolex directed
forwards ; in sheep. Ctenotaenia, Raill., broad tape-
worm of rodents. Anoplocephala, E. Blanch., scolex
usually large (Fig. XXII. 6) ; proglottids much im-
bricated ; the proglottids are stated not to drop oif ;
pyriform apparatus very well developed ; in the
Equidae. Andnja, Raill., in rodents. Bertia, R.
Blanch. ; B. studieri, BL, in chimpanzee. Plagio-

taenia. Peters ; P. qiqantea in Rhinoceros africanus. E- echinococcus, v.

_;.. T,. ~, , ,.. .~. . Sieb.. out of the dog

Amabilia, Diam. ; A. lamelhgera, Diam., in flamingo, (after Perroncito). The

FAMILY 4. MESOCESTOIDIDAE, Raillet. Head un- strobila, and one of the

. -• i -i lostciiar nooKJ.6uS.

armed, with four terminal suckers ; genital pores

separate, on the ventral surface. Mesocestoides, Vaill. (Ptychophysa,
Hamann) ; M. lineatus, Goeze ( = T. lineata, Goeze ; = T. litterata, Batsch) ;
in dog, cat, especially in Iceland. The genital organs present some re-
semblance to those of the Tetraphyllidea \ the uterus presents a single
" ovarian capsule " (ovisac) ; the vaginal pore is anterior to the male pore,
near the anterior end of the proglottid. Ripe segments drop off separately.
According to Neumann, the worm develops from " Dithridium " of dog,
without an intermediate host.

Remarks on the Tetracotylea. — This order contains those Cestodes
which are parasitic in warm-blooded animals, as well as some few
parasitic in Teleostean fish, and in Amphibia. Since all the human
tapeworms, except Bothriocephalus, belong to it, the order has
received more attention than the others, and it is customary to
take one or other of the common species of Taenia (s. 1.) as a type
of the whole class. For an account of the anatomy and mode of
life of any human parasite reference should be made to Leuckart's

Fio. XXI.

132

THE CESTOIDEA

admirable text-book, while those infesting domestic animals are
described in Raillet's TraiU de Zoologie, medicale et agricole.

Certain fresh-water fish are inhabited by certain species of
Taenia (s. 1.), as well as by the genus Ichthyotaenia, and various
species of anurous Amphibia by T. dispar. Birds are attacked by
members of a special family, the Ecliinocotylidae, as well as by species of
Dr&panidotaenia, provided with a powerful armed rostellum, but the
majority of species occur in Mammalia. Although in higher forms
the parasite is confined to a single host, or to closely allied hosts, in

FIG. XXII. — Peculiar scolices of Tetracotylea. a, acetabulum ; b, rostellum, or its
representative ; c, expanded region.

1, 2. — Corallobothrium lobosum, Rigg., out of Pimelodus pati (after Riggenbach) ; side view ;
and viewed from above (compiled from Riggenbach's descriptions and figures). c, the
notched lobes rising up from below the scolex and hiding it ; d, groove between them.

3, 4. — Sciadocephalus megalodiscus, Dies., out of Cichla monoculus (after Diesing); side view
and top view ; c, disc-like expansion of the scolex.

5. — Parataenia medusia, Lint., out of Trygon centrum (probably synonymous with Polypo-
cephalus, Braun). b, the sixteen rostellar tentacles, capable of retraction, into a cavity in
the scolex.

6. — Anoplocephala perfoliata, Goeze, out of the caecum of horse (after Raillet). e, peculiar
ear-like flap, regarded as homologous with the phyllidium of Tetraphyllidea.

7. — Davainea echinobothrida, Megn., out of Gallus domesticus (after Megnin). The armed
rostellum is indicated in a retracted condition. A, rostellar hooklet ; B, acetabular hooklet.

those inhabiting fish, birds, the same parasite occurs in numerous
hosts, and vice versa, one host contains numerous species of Cestodes.

In this order of Cestodes the organs of the scolex are true
suckers (acetabula), the structure of which closely agrees with those
of Distomid Trematodes. Each is a deep, hemispherical, or sub-
spherical cup, hollowed out in the side of the scolex, with circular
(Taenia), oval, or even slit-like openings (Moniezia). No fusion of
these suckers occurs, and it is quite exceptional that they are
armed with booklets (Echinocotylidae).

A new light has recently been shed upon the homologies of
these organs by Pintner (34, b), who adduces evidence to show

THE CESTOIDEA

133

that it is with the " accessory suckers," and not with the bothridia
of the Tetraphyllidea, that they must be compared. They are,
therefore, homologous with the " proboscides " of Tetrarhyncha. In
a few cases, as Anopl. perfoliata (Fig. XXII. 6), vestiges of the
phyllidia are believed to be represented by the ear-like flaps at the
sides of the scolex, below the suckers.1

In the Anoplocephalinae the four suckers are at the apex of the
scolex, the apertures being directed forwards ; but more usually
they are laterally placed, and a rostellum is present, which may be
unarmed (as T. saginata) or armed, the armature consisting of from
one to four circles of hooks, which are generally of two sizes,

..C

FIG. XXIII.

Longitudinal section of the rostellum of
T. crassicollis. a, the muscular mass of the
rostellum, below which are seen concentric
coats of muscle ; b, hooklet , c, ganglion
and transverse commissure ; d, longitudinal
(retractor) muscles of the hooklets ; e,
lateral nerve ; /, excretory canal. (After
Leuckart.)

FIG. XXIV.

The rostellum of Dipylidium caninum,
L., out of the cat (orig.); in the upper
figure, retracted ; in the lower, everted.
a, one of the suckers ; &, the spiniferous
region of the rostellum ; B, one of the
spines ; c, the apical aperture on the
scolex, through which the rostellum is
everted ; d, the region of longitudinal
muscles ; e, the region of circular muscles.

arranged alternately (as in T. solium\ the shape, size, and number
of which afford valuable specific characters. In its simple form it
consists of a mass of muscles, acting on a cushion of connective
tissue, bearing hooklets (Fig. XXIII.) ; this muscular mass becomes
a hollow muscular sac, retractile into a pit (Fig. XXIV.). This
armed rostellum reaches its highest development in those species
of Taenia that inhabit birds, in which it consists of a muscular sac,

1 The peculiar form Polypocephalus, Braun ( ? = Parataenia, Lint.), resembles the
Tetracotylea in the arrangement of the acetabula ; but is quite unique in possessing
sixteen "tentacles," capable of being withdrawn into a sac in the centre of the scolex
(Fig. XXII. 5). They appear to represent a rostellum. The habitat, in Trygon and
Rhinobatus, is exceptional for a Tetracotyleau, and but little is known of the
anatomy (Braun, 1878, and Linton (25), 1887).

134

THE CESTOIDEA

bearing the booklets at its apex ; this rostellum is retractile into
a second muscular sac, or " receptaculum rostelli." In other cases
the rostellum carries a sucker. In any case the rostellum is retractile,
and the arrangement of its musculature presents certain differences
which appear to be characteristic of each sub-family (Liihe, 26).

In a few peculiar instances the scolex has been described as
being absent, as in T. malleus and Idiogenes otidis (both rare forms),
where the anterior proglottids become modified to form a " pseudo-
scolex" (cf. Thysanoceplialum). The size of the strobila, and the
number of proglottids, exhibit that same range of variation referred
to in the other groups ; for instance, in T. echinococcus there are but

FIG. XXV.

1. A proglottid of Moniezia expansa, Rud. (after Stiles and Hassall). 2. Mature proglottid
of Hymenolepis diminuta, Rud. (after Zschokke), out of the rat. 3. Ditto of Thysanosoma,
ovilla, Riv., out of sheep, a, uterus ; b, genital pore ; c, cirrus ; d, vagina e, germarium ;
/, vitellarium ; h, testis ; g, proglottidean glands ; x, excretory canal.

four proglottids; in T. saginata 1200 or more. The shape of the
proglottids, both before and after separation, is also a valuable
specific character ; but here the development of the free proglottids,
which, as a rule, drop off in groups,1 is but slight, since the eggs in
the uterus have already developed into hexacanth embryos before
the separation. The shape too of the uterus, filled with ripe eggs,
is employed as a specific character, while the egg coverings vary in
each of the sub-families of Taeniidae.

The genital pore is marginal, but Mesocestoides forms an excep-
tion, the male and female pores being separate, and on the ventral
surface. The genital pores, as in Tetraphyllidea, are either in the

1 In Anoplocephala and Drepanidotaenia spp. no proglottids drop off. The
strobila retains its entirety throughout life.

THE CESTO1DEA

135

same margin throughout the strobila, when they are " unilateral "
(on the left side in Hymenolepis), or in some proglottids they are on
the right margin, in others on the left margin, when they are said
to be " alternate " ; but it is only rarely that there is any approach
to a regular alternation. In opposition to what obtains in the
Tetraphyllidea, the penis generally lies anteriorly to the vagina,
except in Ichthyotaenia and Mesocestoides.

The female generative organs themselves present certain differ-
ences in structure and arrangement, as will be gathered from a
comparison of the typical proglottids figured ; but the most im-
portant difference is presented by the vitellarium, which, instead of
being an extensive follicular organ, is — except in Mesocestoides and
Ichthyotaenia, and some species of Taenia — a small acinous gland
situated behind the germarium. The uterus, as in all the Tetraboth-
ridiata, is a median sac, formed as an outgrowth of the germ duct ;
it is here more or less deeply notched, or even prolonged laterally
into branching " egg sacs," the shape of the whole organ forming a
specific character. In these forms, like Moniezia, with very short
but wide proglottids, the uterus becomes transverse (Fig. XXV.).

In some cases the wall of the
uterus disappears as the eggs
ripen, and these, either singly or
in groups, come to lie freely in
the parenchyma, the cells of
which form capsules around each
group (T. dispar, Davainea, etc.).
In a few instances it is stated
that the germarium actually be-
comes the uterus (D. struthionis).

A very interesting pheno-
menon is the duplication of the
genital organs (as in some species
of Bothriocephalus) ; thus in
Moniezia there are two complete
sets of organs in each proglottid
(Fig. XXV. 1); in Dipylidium
the uterus is single, but the
other organs are duplicated
(Fig. XXVI.) ; whilst in Ama-
bilia there is a single set of FIG. xxvi.

female Organs, but tWO penes in A mature proglottid of Dipylidium caninum,

Y ,,. -, L., out of the cat. (Orig. x35.) a, the uterus,

proglottid. here broken up on to a number of independent

TV/,* 7^'o^/v. TV. 4- sacs : b, one of the pair of genital pores; c, the

Life-history. Ihe Segmenta- cirT^s-' d> vagina; e, the ventral excretory

Of the egg and the develop- can^ J /» the transverse canal ; g, the lateral

ment of the hexacanth embryo

has been traced out by Leuckart, E. van Beneden, and Moniez,

136

THE CESTOIDEA

but their interpretations of certain phenomena do not agree
with one another, nor with those of Schauinsland for Bothrio-
cephalus. The best general account is that of van Beneden for
T. serrata. The egg, when it passes into the uterus, consists of the
thin egg-shell, deposited in the ootype, surrounding a transparent
non-cellular yolk, in which is embedded the egg-cell (Fig. XXVII. ).
The first segmentation gives rise to two blastomeres, one filled with
refringent spherules (b), and the other faintly granular ; the latter
continues to segment, and ultimately three large cells (c) and numer-
ous smaller ones are produced. The large cells increase in size and
give rise to a "yolk envelope " enclosing the "granular cell " (b) and
what remains of the original yolk (Fig. XXVII. 2). The whole egg
has greatly increased in size. The micromeres form a spherical

FIG. XXVII.— The early development of T. serrata (after v. Beneden).

1. The unsegmented egg. 2. Segmentation completed; the " chitinogenous layer" is
growing over the embryo. 3. The embryo exhibits an outer layer and central mass. 4. The
completed egg, with the six-hooked embryo within, c, egg cell, at first containing yolk
masses ; b, one of the two first blastomeres, loaded with refringent spherules (which are not fat) ;
c, the three macromeres, derived from the other blastomere, uniting to form the " albuminous
coat" or yolk envelope; c', their nuclei; d, embryonic mass, derived from the mieromeres ;
e, chitinogenous layer, derived from some of these, which overgrow the embryo, giving rise to
the striated coat in 4 ; /, outer layer (ectoderm) of the embryo, destined t^ give rise to the six
hooks ; gr, the central (mesodermal) mass ; s, shell, formed in the ootype ; y, yolk, formed by
vitellaria. 1, 3, 4 are equally magnified. 2 rather less.

mass, and two cells at one end flatten out to form a cap ; these cells
divide further, and gradually enclose the remainder ; the superficial
layer of cells thus produced gives rise to a chitinoid coat ; the central
mass becomes the hexacanth embryo (Fig. XXVII. 4). This chitinoid
coat, the homologue of the ciliated mantle of Bothrioc. latus, takes on
a characteristic structure in each of the sub-families of the Taeniidae
(Fig. XXVIII.). In the Taeniinae it is striated ; in the Hymenolepinae
it is homogeneous and refringent (1, 2); while in the Anoploceplialinae
it undergoes remarkable changes, becoming drawn out into two horns
on one side, which may even cross, scissor- wise, forming the peculiar
" pyriform apparatus " referred to above (Fig. XXVIII. 3, 4).

The development as far as this stage takes place in the uterus,
while the proglottid still forms part of the strobila ; and in the
Taeniidae, and probably in all the Tetracotylea, the eggs of different

THE CESTOIDEA

137

proglottids are in different stages of development, so that by
examining the proglottids from behind forwards, earlier and earlier
stages are met with independent of the time of the year, whereas
in the Dibothridiata all the eggs in a strobila, at the same time of the
year, are in the same stage of development. The general later history
of the onchosphere, or proscolex, is as follows : — Kipe proglottids drop
off from the strobila, and pass out of the host with its faeces ; the
proglottid either decays and sets free the eggs, which are then
swallowed by browsing animals, or the proglottids themselves are
devoured. But in order to attain maturity the egg of a given
tapeworm must be devoured by a definite intermediate host (only in

FIG. XXVIII.— Eggs of Tacniidae (modified from Moniez).

1. Dipylidium caninum, L. 2. Drepanidotaenia anatina, Kr., from duck. 3. Pyriform
apparatus of Andrya wimerosa, Moniez, out of rabbit. 4. Moniezia expansa, Rud., out of
ruminants, a, egg shell (vitelline membrane of Moniez) ; ft, albuminous coat, formed probably
in all cases from some of the earliest formed blastomeres ; two nuclei are represented in 4 ; the
cells undergo histolysis, and become nlled with refringent globules ; c, internal shell, formed,
according to Moniez, from modification of an outer layer of blastomeres, but possibly secreted
by this layer (-striated coat of Fig. XXVII.) ; c, is the pyriform apparatus in 3, 4 ; d, the hexa-
canth embryo ; c', a " delaminated " layer of cells formed before the internal shell (c), according
to Moniez ; /, peculiar modification of this mass.

a few cases do several different animals serve as hosts for one and
the same worm) which is, as a rule, an herbivorous vertebrate, and
in the majority a mammal, where the final host is a mammal ; but
in the case of bird and fish and amphibian tapeworms, the inter-
mediate host may be some invertebrate.

Arrived in the intestine of the intermediate host, the egg-
envelopes are softened and dissolved ; the proscolex is thus set free,
and by means of peristaltic movements, and by the movements of the
six hooks it bores its way into the intestinal wall, and arrives in a
blood-vessel (some constituent of the portal vein), in which it is
carried along till it reaches a capillary of less diameter than itself.
In this way it may be conveyed to the liver, peritoneum, mesentery,

138

THE CESTOIDEA

or even the brain and eye ; arrived here it may even burrow
through the tissues on its own account. In any case it causes
inflammation, and the tissues of the host give rise to a " cyst "
around it. In this position it will undergo further development,
resulting in a " metacestode " of one kind or another. This, when

FIG. XXIX. — Development of Dipylidium caninum (altered from Grassi and Rovelli).

1.— Proscolex, onchosphere or six-hooked embryo, at present solid.

2. — The embryo has elongated, and the " primitive lacuna " has arisen (a).

3.— The hinder part, bearing the hooks, narrows and elongates, so that a "head" and
"tail" are distinguishable; at the anterior end the foundations of the four suckers and the
rostellum are indicated — in reality at this stage they are mere solid heaps of cells.

4. — The organism is longer ; the body and tail are more distinct ; the rostellum, now armed
with spines, is cupped, as also are the suckers. The excretory system is developed (6, c).

5. — The fore body is being invaginated into the hind body ; the excretory bladder is provided
with a pore at the base of the tail, the surface of which is shown with the scattered hooklets.

6. — The tail has dropped off, a spherical " cysticercoid " remains, in which the " scolex" is
commencing to grow upwards into the sac formed by the fbre body, the outer wall consisting
of the hind body.

swallowed by the final host, will develop into a tapeworm in the
intestine of its new host.

One of the simplest metacestode conditions occurs in the case of
D. caninum (T. elliptica), whose history has been worked out by
Grassi and Eovelli (13). The eggs discharged with the faeces

THE CESTOIDEA

139

become scattered amongst the hair of the dog, and are swallowed
by its parasites, the flea (Pulex serraticeps) or the louse (Trichodedes
canis), in the tissues of which the proscolex elongates ; an excentric
cavity (" primitive lacuna ") arises by the liquefaction and de-
generation of the internal cells, and the proscolex becomes pear-
shaped, the hooks being at the narrow end (Fig. XXIX.). It is
possible now to distinguish a " body " and " tail " (the " cystozooid "
and " acanthozooid " of Villot). In the former a pair of excretory
tubules make their appearance, which open by a median bladder
and pore at the base of the tail. At the anterior end of the
" body " the forecasts of the rostellum and the four suckers suc-
cessively appear as cellular thickenings, followed by muscular differ-
entiation, in the wall of the body ; they mark out a " fore body "
from a " hind body " ; the tail, meanwhile, becomes constricted
from the latter. The rostellum becomes pitted,1 as also does each

FIG. XXX.

The cysticercoid of Hymenolepis
murina from the villi of the mouse's
intestine (after Grassi and Rovelli).
The tail is greatly reduced.

FIG. XXXI.

Cysticercoid of Dicranotaenia cu-
neata which occurs in the earthworm
Allolobophora faetida. The tail and
hind body have coalesced, the hook-
lets now appear on the wall of the
small bladder.

sucker rudiment, and the whole fore body now becomes invaginated
into the hind body. Meanwhile, the tail becomes larger and
bladder-like, and in this way the hooks become separated, one pair
remaining subterminal

The organism, before the invagination, resembles an immature
Caryophyllaeus, or even a Trematode cercaria, in which as here the
tail is a temporary larval organ.

The tail drops off when the intermediate host is swallowed by
the dog ; the " cystozooid," which is set free in the intestine of the
latter, is a more or less spherical sac containing the invaginated head
or " scolex," which nearly fills the cavity of the sac (Fig. XXIX. 6).
Such a metacestode is known as a " cysticercoid " or parenchymatous
bladder-worm. The head now evaginates, and its base commences
to elongate and to become segmented to give rise to the strobila.
The wall of the cysticercoid and of the following metacestodes is
muscular, and contains lime cells and ramifications of the excretory

- Grass! homologises this pit with the buccal cavity and pharynx of Trematoda.

1 40 THE CESTOIDEA

and nervous systems, which are absolutely continuous with the
systems in the scolex. In this instance it is evident that there is a
gradual metamorphosis of the proscolex into the scolex and neck
of the strobila.

In H. murina the tail of the onchosphere is so reduced as to form
part of the hind body, which envelopes the fore body or scolex,
and the aperture by which the latter has been invaginated closes
(Fig. XXX.).

A large number of other cases are known in which the in-
vaginated scolex occupies almost the entire cavity (Fig. XX XL).
In some other tapeworms this cavity is larger, but filled with a
loose tissue, as in the case of Tetrarhynchus, Calliobothrium, etc. But
in the tapeworms of most mammals, e.g. T. solium, this cavity
becomes very much more extensive, since the six-hooked embryo

PIG. XXXII.— The life-history of a Cysticercus (Bladder- worm, or hydatid). a, scolex ;
ft, fore body ; c, hind body-f tail, caudal vesicle, or bladder.

1.— The solid proscolex.

2.— The primitive lacuna has fonned as before, but the organism is greatly distended by the
accumulation of fluid in this cavity. The body and tail are no longer distinguished (cf. Fig.
XXIX.), and the booklets have become cattered. Excretory tubules have made their appear-
ance in the wall of the " bladder."

3.— A further stage of this hydropic distention. An imagination of the wall of the bladder
has arisen in the " fore body."

4. — The invagination proceeds ; the suckers and rostellum arise by evaginations at the
bottom of the tubular fore body, which hangs freely in the cavity of the cysticercus.

5. — The scolex is commencing to evaginate ; it rises up from the bottom of the " receptacu-
lum scolecis " (or fore body), and at the same time the sides of the latter commence to evaginate.

6. — E version is complete — the sides of the fore body folded together, fuse to form the neck.

7 to 10 refer to Taenia serrata (after Leuckart).

7. — The entire bladder-worm, Cysticercus pisiformis, from the rabbit, with scolex everted ;
the excretory network in the wall of the bladder or caudal vesicle is shown.

8.— The "bladder" (hind body+tail) has undergone digestion on reaching the stomach of
the dog.

9. — A further stage, in which the fore body is also destroyed, leaving only the " scolex."

10.--The scolex by elongation and "segmentation" of its neck has given rise to a young
strobila.

swells up by absorption of fluid l while encysted in the intermediate
host (Fig. XXXII. ). The hooks become scattered, and no " tail " is
differentiated. Here, as in H. murina, the acanthozooid is not dis-
tinguishable from the cystozooid. Then there arises at one end a
small tubular invagination ( = the " fore body "), at the bottom of
which the forecasts of the rostellum and suckers are formed. The
" fore body " is here known as the "receptacle of the head," which
in some cases, as C. pisiformis, may be very long. When this
" bladder-worm " or cysticercus is swallowed by the final host the
head (scolex) evaginates, and the original bladder ( = " hind body +
tail ") which is now known as the " caudal vesicle," is digested, and
the scolex gives rise to the strobila as before (Fig. XXXII.).

This cysticercus leads on to another form of metacestode, with
a still larger bladder, from the wall of which a great number of

1 The fluid contained in a cysticercus is a weak saline solution containing '2 to '3
per cent of albuminoids, possibly nutritive.

THE CESTOIDEA

141

9.

FIG. XXXII.

heads are produced. This is the " coenurus " which occurs in the
sheep's brain.

142 THE CESTOIDEA

Just as the development of the head is delayed in these last
forms, so apparently there is a delay in the differentiation of the
fore body, for in Monocercus we have a bladder which " buds "
off a secondary cyst within, from which the head is developed as
before (Fig. XXXIII. 1, 2, 3) ; while in Polycercus — occurring
in Lumbricids, and which is the metacestode of T. nilotica, etc. —
several such secondary cysts are formed, each with a head within it.

But this formation of secondary cysts reaches a maximum in
" Echinococcus," where the primary bladder attains an enormous
size, and from its walls numerous secondary bladders are formed,
which drop off into the primary cavity (XXXIII. 5) ; from each of
these secondary (and even tertiary) bladders a great number of heads
are formed, each of which, when the bladders are swallowed, will
develop into a strobila.

FIG. XXXIII. —Asexual reproduction by the Bladder-worm.

1 to 3. — Polycercus, from the coelom of an earthworm ; it is the bladder stage of Taenia
nilotica, out of Cursorius europaeus. (Altered from Metschnikoff).

1. — A cysticercus-like form, with five (or more) areas of proliferation on the wall of the
bladder.

2.— Bach of these becomes hollowed out to form a small sac, destined to drop into the central
cavity. Various stages of formation are shown (a, b, c).

3.— After becoming free in the central cavity, each sac gives rise to head, and so becomes a
cysticercoid as in previous cases.

4.— A Coenurus, from the brain of the sheep ; the numerous scolices, of various ages, arise
by invaginations of the wall of the bladder.

5. — Echinococcus , the secondary bladders arise at a, &, c, *n the same way as the scolices
in Fig. 2. Each then develops numerous heads by eversion of the wall of the bladder, into
which they may be secondarily withdrawn. At m is shown the ideal mode of origin, so as to
indicate the relation of head to daughter bladder, which is thus comparable to the "fore body"
of cysticercus.

6. — A Staphylocystis (S. glomeridis) as an example of external budding by a cysticercoid.
Each daughter cysticercoid develops a single scolex, the aperture of invagination of which is
shown.

In these latter cases — Coenurus, Polycercus, and Echinococcus —
there is a process of gemmation, so that from each egg, not one only,
but several tapeworms will arise. Another kind of asexual repro-
duction is met with in the case of a cysticercoid occurring in Glomeris,
where by successive branching, and by the external gemmation of
secondary cysticercoids, a complex organism, known as a " Staphy-
locystis," arises (comparable to the sporocyst of D. macrostomum),
(Fig. XJXXIII. 6).

In £nbse metacestodes called "Urocystis," the tail of the original
cystozooid drops off and becomes transformed into a second cysto-
zooid, which proceeds to form a second scolex.

But even now that the life-cycle of these tapeworms is understood,
and the relation of the "cystic" form, occurring in parenchymatous tissues,
to the " segmented worm " living in the alimentary canal, is perfectly satis-
factorily established, owing to the investigations of van Beneden, Kiichen-
meister, Leuckart, and others, there still remains a matter which is even
yet one of controversy, viz. to what degree does this history illustrate
Steenstrup's Theory of the Alternation of Generations. Up till recent times
the general opinion on the matter, founded as it was on an acquaintance

THE CESTOIDEA

143

with the life-cycle of T. solium and similar forms, was that there are at
least three different generations involved, viz. (1) the fertilised egg, which

5.

6.

FIG. XXXIII.

gives rise by the ordinary process of development to a six-hooked embryo,
or " proscolex," which becomes by modification the bladder-worm, Cysti-

144 THE CESTOIDEA

cercus or " hydatid." (2) From the wall of this hydatid, or " nurse "
(Steenstrup), the scolex is formed by internal gemmation. After being
swallowed by the final host the bladder is destroyed, and (3) the scolex
proceeds to produce by gemmation a series of sexual individuals — the
proglottids — which produce eggs.

Recent investigations, both anatomical and embryological, however,
tend to overthrow the view that the hydatid is a nurse, and that the
scolex is produced from it by gemmation. Belief in this view was, to a
great extent, fostered by the general custom of taking the life-history of
T. solium as typical, whereas there is little doubt but that the course of
events exhibited by various cysticercoid forms is to be regarded as more
archaic ; where, that is, the scolex is merely a part of the proscolex, and
becomes invaginated into the latter for the purpose of protection, in the
same kind of way that the Ainnion of the higher Vertebrates and of
certain Arthropods has been brought about by the sinking of the embryo
(Fig. XXIX.) ; and possibly, lower than the cysticercoids, will be found some
in which this invagination does not occur, as in Caryophyllaeus. It is,
moreover, to be noted that the greatly developed "bladder" occurs in
those tapeworms which inhabit the highest vertebrata, whereas in fish
tapeworms the cysticercoid, under one form or another, occurs.

Granted that the scolex does not arise by any asexual mode of repro-
duction from the proscolex, it remains to be decided whether this asexual
method can be allowed in the production of proglottids from the scolex —
in other words, is the strobila to be regarded as a metamerically segmented
individual comparable to an Annelid, or is it a linear colony, of which the
proglottids are the sexual individuals produced by budding from an asexual
scolex ? The former view is held by Burmeister, Gotte, Glaus, Perrier ;
the latter by von Siebold, van Beneden, Leuckart, and some of the older
authors. Up till P. J. van Beneden's time the strobila was almost
universally regarded as an individual, but his researches and his careful
comparison of a proglottid with a Trematode, followed as it was by the
observations of others, impressed naturalists with the idea that the strobila
is a colony — a view which has been adopted generally up till about ten
years ago, as it seemed to illustrate Steenstrup's theory so excellently. If
we regard the tapeworm as a colony, it is comparable to the " strobila "
of Aurelia and other Scyphomedusae, each ephyra, budded off from the
original hydro-polyp or scyphistoma, being comparable to a proglottid,
and the Scyphistoma itself, developed from the egg cell, being equivalent
to the scolex. If this be the case, the strobilation of Cestodes must be a
secondarily acquired phase in their life-history, which must have been
originally a metamorphosis ; but owing to the individualisation of certain
products of growth, it has given rise to alternation of generation (Glaus, 6).

But many anatomical facts appear to be against the " colony " theory ;
the continuity of the muscular, nervous, and excretory system, not only
throughout the entire adult worm and the scolex, but even in the cysti-
cercoid phase, where they are absolutely continuous in the bladder and
scolex. The excretory pore is at the posterior end of the proscolex, and
in many adults it is at the posterior end of the chain throughout life, viz.
in those forms which never drop proglottids, and though the development

THE CESTOIDEA 145

of these forms is not known in all its details, there can be no doubt but
that the pore and contractile excretory bladder are identical at both stages
of development. The permanency of the strobila in some worms, taken
in connection with the absence of external segmentation in Ligula and
Triaenophorus,1 and the easy transition from the latter to the uusegmented
Monozoa — these and sundry other facts seem to point most strongly to
the individuality of the adult tapeworm.

It is not difficult to see the advantage to the species gained by this
segmentation of the body as the genital organs ripen, for the continued
peristalsis of the intestine, and the passage of food, must tend to rupture
the attached worm. The scolex therefore regenerates this broken portion,
as in various Chaetopods ; and this power has been increased and per-
petuated, so that the process of regeneration has become premature and
resolved into one of " strobilation," or early production of segments, each
of which ripens in turn and ultimately separates (Lang). This process
is even more precocious in Ligula, where the repetition of the genital
organs occurs in the intermediate host.

If the tapeworm be regarded as a metamerically segmented animal,
the neck, as the point of formation of new segments, should be, in order
to be comparable with the corresponding point in Annelids, posterior, i.e.
antepenultimate, and the scolex or head must be the last segment or
telson. This, indeed, is the view taken by Perrier and Moniez, who
regard the " caudal vesicle " of T. solium and " tail " of Caryophyllaeus as
the anterior end of the worm ; though it is frequently assumed that the
"tail" was originally an organ of locomotion, which function it has
entirely lost, and has become in many cases part of the " bladder," and
aids in protecting the enclosed scolex.

A curious theory was in early times held by several naturalists (Linnaeus,
Dubois, Blumenbach) that the strobila is built up by the mutual attach-
ment in series of numerous free-living proglottids, or Vermes cucurbitini.

The probable phylogeny of the class may be indicated by the following

tree : —

Tetracotylea.

Tetrarhyncha.
Merozoa.

Tetrai

J>

hyllidea.

. Dibothridiata. Tetrabothridiafa.

Trematoda.

1 In the young Triaenophorus the proglottids are distinct ; obliteration of them
occurs as the worm matures.

10

146 LITERATURE OF THE CESTOIDEA

LITERATURE OF CESTOIDEA.

1. vanBeneden, E. Arch. Biol. ii. 1881, p. 183.

2. van Beneden, P. J. (Les vers Cestoides.) Nouv. Mem. Acad. Roy.

Belgique, xxv. 1850 ; and Mem. sur les vers Intestinaux, 1858.

3. Blanchard, E. Ann. Sci. Nat. 1847-49.

4. Blanchard, R. (Echinocotylidae.) Mem. Soc. Zool. France, iv. 1891,

p. 420.

5. Braun, Max. In Bronn's Thierreichs, "Wiirmer," 1893 (in progress),

p. 927, for complete literature.

6. Glaus. Ann. Mag. Nat. Hist. (ser. 6), v. 1890, p. 417.

7. Crety. (Solenophorus. ) Atti (Mem.) R. Accad. Lincei (ser. 4), vi. 1889,

p. 384.

8. Donnadieu. (Ligula.) Journ. de 1'Anat. et Physiol. xiii. 1877, pp. 321, 451.

9. Dujardin. Ann. Sci. Nat. (2), xx. 1843, p. 341.

10. Fuhrmann. (Ichthyotaenia, etc.) Zool. Jahrbuch. (Anat.), ix. 1895,

p. 207.

11 Ibid. (Taeniae of Birds.) Rev. Suisse. Zool. iii. 1895-96, p. 433 ; and iv.

1896, p. 111.

12. Gerinanos. (Bothriocephalidae.) Jen. Zeit. xxx. 1895, p. 1.

13. Grassi and Rovelli. Instit. Zool. Univ. Catania, 1892.

14. Griesbach. (Lime Corpuscles.) Arch. f. Mikr. Anat. xxii. 1883, p. 563.

15. Gruber. ( Archigetes. ) Zool. Anzeig. iv. 1881, p. 89.

16. Eamann. (Cysticercoids.) Jen. Zeit. xxv. 1891, p. 553.

17. Kiessling. (Schistocephalus. ) Arch. f. Naturg. (48), 1882, p. 241.

18. Kohler. Zeit. f. Wiss. Zool. Ivii. 1894, p. 385.

19. Kraemer. (Cyathocephalus. ) Zeit. f. Wiss. Zool. liii. 1892, p. 647.

20. Lang. Mitth. Zool. Sta. Neapel. ii. 1881, p. 372.

21. Leuckart. Die Blasenwiirmer u. ihre Entwickelung, 1856.

22. Ibid. Die Parasiten der Menschen, 1886-94; and English translation of

1st edition by W. E. Hoyle.

23. Ibid. (Archigetes.) Zeit. f. Wiss. Zool. xxx. (Suppl.), 1878, p. 593.

24. v. Linstow. (Tetr. longicollis. ) Jen. Zeit. xxv. 1891, p. 565.

25. Linton. Rept. U.S. Fish Commission, 1886, p. 453 ; 1887, p. 718 ; 1888,

p. 543.

26. Luhe. (Rostellum.) Zool. Anzeig. xvii. 1894, p. 279.

27. Ibid. (Nervous System.) Zool. Anzeig. xix. 1896, p. 383.

28. Moniez. Travaux Inst. Lille, iii. 1880-81.

29. Monticelli. (Scolex polymorphus.) Mitth. Zool. Sta. Neapel. viii. 1888,

p. 85.
30.' Ibid. (Cestodaria.) Atti Accad. Sci. fis. Napoli, v. (2), 1893, art. 6, and

various articles in Boll. Mus. Zool. Torino ; Boll. Soc. Nat. Napoli ;

Mem. Accad. Torino, 1890-92.
81. Niemec. Arb. Inst. Zool. Wien. vii. 1886, p. 1.

32. Pintner. (a) (Excretory System ; Tetrarhynchus Head.) Art. Inst. Zool,

Wien. iii. 1881, p. 163. (6) (Copulation, etc.) Art. Inst. Zool. Wien,
ix. 1891, p. 57.

33. Ibid. (Echinobothrium.) Art. Inst. Zool. Wien. viii. 1889, p. 371.

34. Ibid, (a) (Tetrarhynchus.) Stzb. Akad. Wiss. Wien. (Bot. Zool.), cii.

1893, p. 605. (b) (The Proboscis of T.) Biol. Centralbl. xvi. 1896r
p. 258.

LITERATURE OF THE CESTOIDEA 147

35. Poirier. (Excretory System.) C. R. Acad. Sci. cii. 1886, p. 700.

36. Raillet. Traite de Zool. Medicale et Agricole, 1895.

37. Riggenbach. (Ichthyotaenia.) Centralbl. f. Bakter. u. Parasitenkunde,

xviii. 1895, p. 609 ; and Rev. Suisse Zool. iv. 1896, p. 165.

38. Ibid. (Bothriotaenia.) Ibid. xx. 1896, p. 222.

39. Salensky. (Amphilina.) Zeit. f. Wiss. Zool. xxiv. 1874, p. 291.

40. Schauinsland. Jen. Zeit. xix. 1886, p. 520.

41. Schmidt. (Anatomy of T. anatina.) Arch. f. Naturges. (60), 1894, p. 65.

42. v. Siebold. Zeit. f. Wiss. Zool. ii. 1850, p. 198.

43. Ibid. (Ub. d. Band — und Blasenwiirmer, etc., 1854, Abstract in.) Ann.

Sci. Nat. (4), iv. 1855, pp. 48, 172.

44. Sommer. (Genitals.) Zeit. f. Wiss. Zool. xxiv. 1874, p. 499.

45. Sommer and Landois. (Genitals.) Zeit. f. Wiss. Zool. xxii. 1872, p. 40.

46. Spencer. (Gyrocotyle. ) Trans. Roy. Soc. Victoria, vol. i. pt. 2, 1889,

p. 136.

47. Tower. Zool. Anzeiger, xix. 1896, p. 324.

48. Villot. Ann. Sci. Nat. (6), xv. 1883.

49. Wagener. Nova Acta Acad. Leopold, xxiv. Suppl. 1851.

50. Will. (Caryophyllaeus.) Zeit. f. Wiss. Zool. Ivi. 1893, p. 1.

51. Zernecke. Zool. Jahrbuch (Anat.), ix. 1895, p. 92.

52. Zschokke. (Recherches sur la structure anat. et histol. des Cestodes.

Mem.- Instit. nation. Genevois, xvii. 1886-89.

(See also Nos. 9, 15, 16, 28 of Trematode bibliography.)

CHAPTER XX.

APPENDICES TO THE PLATYHELMIA.

APPENDIX I.
CLASS RHOMBOZOA, v. Ben.

THE forms included in this group are elongated, symmetrical organ-
isms parasitic in the renal sacs of Cephalopoda. The body consists of a
single layer of flat cells, which are usually ciliated, enclosing a central or
" axial cell," within which the genital cells or " germs " are produced. The
ectoderm cells are specialised at one end, to form either a " polar cap " or
terminal warts.

The individuals are of two kinds, producing different embryos — one,
known as the " nematogen," produces " vermiform embryos " ; the other,
the " rhombogen," produces " infusoriform embryos."

The class Rhombozoa contains two orders.

ORDER 1. Dicyemida, v. Ben.1

Adult forms worm-like and ciliated, with a polar cap formed of eight
or of nine cells arranged in two circles.

Dicyema, KolL, with eight polar cells, contains seven European
species (Fig. II.). Dicyemennea, Whitm.,2 with nine polar cells ; this
genus includes three species.

ORDER 2. Heterocyemida, v. Ben.3

The ectoderm of the adult is not ciliated ; there is no polar cap, but
at the anterior end the ectoderm cells contain refringent bodies and may
give rise to four large terminal wart-like papillae (Fig. I.).

Conocyema, v. Ben., in Octopus vulgaris. Microcyema, v. Ben., without
warts, in Sepia ojficinalis.

Remarks. — All the members of the Rhombozoa are parasitic in the
renal organs of various species of Cephalopods ; normally, the Dicyemids
are attached, as was first observed by Wagener, by means of the polar cap
to the renal cells which constitute the so-called "venous appendages."

1 Ed. v. Beneden, Bull. Acad. Roy. Beige; (2), xli. 1876, pp. 85, 116 ; and xlii.
p. 35 ; also in Q. J. Mic. Sci. (N.S.), xvii. 1877, p. 132.

2 Whitman, Mitth. Zool. Sta. Neapel. iv. 1883, p. 1.

3 E. v. Beneden, Arch. Biol. iii. 1882, p. 197.

THE RHOMBOZOA

149

They then have the appearance of small white threads ; but on the death
of the host the cells, with the parasite, drop off into the renal sac, where
they are to be found swimming freely, but they never enter the various
other cavities with which this renal sac communicates. The Hetero-
cyemids do not appear to be thus fixed.

FIG. I.

Heterocyemida (after van Beneden). A, Nematogen
of Conocyema polymorpha (van Ben.); «, the anterior
"verruciform cells" representing (?) the "polar cap"
of Dicyemida ; ft, their refringent contents; i, "cili-
ated " processes .(N.B. — The " cilia " are motionless and
retractile) ; b, ectoderm cells of body ; c, nucleus of
axial cell ; d, protoplasm of axial cell ; g, germs, in
outline, the largest being a fnlly formed vermiform em-
bryo. B, Nematogen of Microcyema vespa ; a, anterior
cells with refringent contents ; &, ectoderm of body ;
d, axial cell ; c, its nucleus ; g, germs. C, " Wagener's
embryo" of Microcyema; a, cell (or cells) containing
refringent bodies ; b body ectoderm (of which there
are only four cells in all) ; c, nucleus of axial cell (d).
(The embryo of Conocyema resembles this in general
structure, but is without refringent bodies ; the cell
(or cells) containing them being represented by four
cells ; there are also more ectoderm cells.)

Fio. II.

Dicyema typus, E. v. Ben. (after
Whitman). Surface view of a
young nematogen, from the left
side ; although cilia are indicated
only round the edges, it is to be
understood that the whole surface
is ciliated, a, polar cells in two
circlets of four ; c, parapolar cells,
followed by two dorsal and one ven-
tral cell ; t, terminal cells, which
in some species may contain refrin-
gent bodies, which are here con-
fined to the verruciform cells (v).

Leaving aside these aberrant and rare Heterocyemida, it is only
necessary to describe the structure of the Dicyemida.

The elongated cylindrical body is pointed at one end, which ia
regarded as the posterior, while the anterior end is thicker, owing to the
specialisation of certain of the ectoderm cells to form the " polar cap "
(" calotte " of Whitman). The ectoderm is everywhere one cell thick, the

THE RHOMBOZOA

cells are flat, lozenge-shaped, or rhomboidal, and all carry cilia, which, on
the " head," are shorter and denser than on the " trunk." The " polar
cap " consists of two circlets of cells. The apical circlet always consists of
four equal " propolar " cells (Whitman) ; the second circlet consists of
either four " metapolar " cells (Dicyema\ or of five cells (Dicyemennea).1
The polar cells are symmetrically arranged in the young when the head
is " orthotropous," but by the unequal growth of one, the dorsal, surface
the polar cap becomes pushed forwards on this side, so as to lie more or
less obliquely ; it is then " plagiotropous " (Fig. III.). The polar cells, when
eight, correspond in position, two of each circlet being dorsal and two ven-
tral. In Dicyemennea the extra metapolar cell is dorsal (Fig. IV.). The
whole organism recalls to some degree a Trematode "miracidium," and these

cap cells remind one of similarly placed
cells in such species as Dist. tereticolle.

FIG. III.

Dicyema macrocephalum, E. van Ben. (altered from
Whitman). A portion of a rhombogen seen from the
right side ; the plagiotropous cap is represented in
optical section, ad, av, dorsal and ventral propolar
cells ; bd, bv, dorsal and ventral metapolar cells ; c,
right parapolar cell ; dd, the two dorsal ; e, the ven-
tral body cell.

FIG. IV.

Dicyemennea eledones, Wagen. (after
Whitman). The cap seen from in
front, showing the five metapolars
(b), of which three are dorsal and
two ventral ; a, propolar cell ; D,
dorsal, V, ventral surfaces.

The first trunk cells lie one on each side, and as they differ somewhat
from the rest, have been termed " parapolar " cells. The next two are
dorsal and ventral, the next couple are lateral, and so on throughout the
body, though they are arranged somewhat spirally. The two terminal
cells differ slightly from the rest. There are only some twelve to twenty
trunk cells, exclusive of the parapolars.

The contents of the cells, at first finely granular, soon exhibit in
some cells coarser granules, and even crystalloid grains that may coalesce
to form balls, which collect in these cells, and as they accumulate they
form more or less pronounced swellings, or finally stalked sacs (Fig.
II. v) ; these " verruciform " cells never exceed six. The nature of their
contents is uncertain ; they are neither fat nor lime, and do not take
stains.

Within the ectoderm is a single "axial cell," from which, at an
early stage in the life-history, germ cells are produced in such a way
that they lie within the axial cell. The latter is derived from the larger
of the first two blastomeres, but remains inactive till it has been sur-

THE RHOMBOZOA

rounded by the products of the micromeres (Fig. V.) ; then the macromere

divides into two unequal cells ; the larger again divides in the same way ;

so that the central mass at this stage consists of an axial cell with two

small " primary germ cells," embedded in its cytoplasm one at each end.

These primary germ cells are comparable

to the "intermediate cells" of Ortho-

nectida, but have a different fate. Here,

in the Dicyemida, there is an early

setting aside of cells for reproduction, just

as there is in Ascaris and other higher

forms. The axial cell remains apparently

quiescent throughout life, but is possibly

engaged in elaborating nutritious juices

absorbed from the host by the ectoderm

cells ; it may be considered as an endo-

derm cell — the last representative of a

degenerate enteron. But the primary

germ cells soon divide, each into two, and

then into four ; so that there are eight

germ cells lying within the axial cell.

In some individuals (known as " ne-
matogens") each germ cell proceeds to
undergo segmentation, and develops into
a " vermiform embryo " of a comparatively
simple form — a miniature of the parent
(Fig. V.). But in other individuals,
known as " rhombogens " — differing, ac-
cording to Whitman, in no definite way
from the former — the germ cells pass
through a very peculiar series of stages,
and each produces a number of " infusori- Four stages in the development of

fnrm pmVirvns " Tlip<?p twn Vinrh nf a vermiform embryo of Dicyema typus

)rm embryos. >t (after E van Beneden). In j the re_

embryo were noted by Erdl, who regarded suit of segmentation^ is a solid biasto-
them as two different stages in the life-

FIG. V.

historv. Kolliker was the first to recog- ectoderm cells (a) ; from the macromere

J. ' a primary genii cell (g) has been given

nise that they are dimorphic torms ; off. In 2, 3, the embryo has elongated,

v "RpTiprlpTi and latpr Whitman the ectoderm is ciliated and already

v. ±>eneden, ana later, wmtman,

more accurately traced out their develop-
meat The vermiform embryos escape

from the nematogen and swim about with
°

differentiated into cap cells (d) and
body cells. The germ cell has divided

substance of the axial cell. In 4 the
vermiform embryo has put on all the
characteristics of a Dicyema; each of
their parents 111 the renal sac OI the host, the two germ cells has already sub-
wViiMi tliPV nPVPr Ipflirp • tliPv nrp inrlpprl divided to form four, of which one

which they never leave , they are, indeed, above and two below are proceeding to

killed by sea- water. They grow into develop into a second generation, c,

-i ,-, i • , f nucleus of axial cell,

nematogens, and repeat the history of

their parent.

But the infusoriform embryo is a more complicated organism (Fig. VI.).
It is nearly spherical, and built up of the following parts : — (1) Of an
hemispherical cup of ten ciliated cells ; (2) of two large cells containing
refringent bodies, and occupying the "anterior" part of the surface of the

1 52 THE RHOMBOZOA

embryo ; (3) of an " urn," which is partially enclosed in the preceding,
but conies to the surface antero-ventrally. This urn, in its turn, is made
up of (a) a " lid " or cover of four non-ciliated cells, which completes
the outer wall of the embryo ; (J3) an " urn- wall " formed of two curved
cells, laterally placed, underlying the ciliated cells ; and of (y) the
" urn-contents " — namely, four granular cells, arranged crosswise ; each
has at first a single nucleus, but later many nuclei. According to
van Beneden, these nuclei belong to minute cells provided with cilia, and
he suggests that they are spermatozoa. This elaborate organism, or
individual, arises in a very peculiar manner. Each germ cell divides,
first of all, unequally, the smaller cell taking no further share in
the process, but its nucleus enlarges, and lies freely in the axial cell ;
it is the " paranucleus " (Whitman), and is very suggestive of a polar
body of metazoa in general. The remaining cell proceeds to divide,
very much as in the case of the vermiform embryo — one large cell
becomes surrounded by a layer of smaller ones. This gastrula-like phase
is termed an " infusorigen " by Whitman, and the central cell is the

FIG. VI.

Infusoriform embryo (or the male) of Dicyema
(after van Beneden). A, from the right side ;
B, from the ventral surface ; r, the refringent
body ; u, the capsule or wall of the urn ; c, the
contents of the urn (granular bodies); I, the
lid ; b, ciliated cells of the body wall (ecto-
derm).

" germogen." But this germogen proceeds to divide, endogeuously, much
as the axial cell of a vermiform embryo does, so that its nucleus becomes
surrounded by a second generation of nuclei, each of which becomes
invested by protoplasm to form a cell. The " ectoderm " cells of the
infusorigen separate, and each develops into an infusoriform embryo,
which ultimately escapes from the rhombogen. The remaining cells
also separate, but develop into vermiform embryos, the central nucleus
(germogen) remaining behind — free in the axial cell of the parent as a
" residual nucleus " (Whitman).

The rhombogen, after the birth of the infusoriform embryos, becomes
a "secondary nematogen," containing vermiform embryos. Thus there
are monogenetic individuals (primary nematogens) and diphygenetic in-
dividuals which produce, firstly, infusoriform, and later, vermiform
embryos. The infusorigen is an embryo which gives origin to other
embryos, much as has been shown to occur in Gyrodactylus. The in-
fusoriform embryos escape from the parent, and, unlike the vermiform
embryos, can live in sea-water (Erdl, van Beneden) ; but no changes of
any kind have been observed in them, and their later fate is doubtful.
But van Beneden, influenced by Metschnikoff s discovery of sexual dimor-
phism in the Orthonectida, and by Julin's observation of the two forms
of females, suggested that the " infusoriform embryos " of Dicyemids are
males.1 Moreover, Whitman has occasionally observed in large specimens

1 This appears to be confirmed by Wheeler (Zool. Anzeig. xxii. p. 169, 1899),
who states that male dicyemids, i.e. infusoriform embryos are produced from

THE ORTHONECTIDA 153

of D. moschatum, one or even two somewhat deformed infusoriform
embryos, which he believes had penetrated into the nematogen. He is
therefore inclined towards van Beneden's view. In that case, the
nematogens will be females, and the germ cells true ova, which will be
fertilised by the infusoriform embryos. It is, further, probably of some
importance that in young Cephalopods nematogens predominate, while
rhombogens are in excess in older hosts. But this is entirely conjectural.
Nothing is accurately known about the fate of the infusoriform embryo,
nor as to how new hosts become infected.

The view held by van Beneden that each species of Cephalopod has
its own peculiar species of Dicyemid is not true. Whitman has noted
both that two or more species of the parasite may occur in one Cephalopod,
and that the same parasite may occur in different hosts ; for example —

Dicyema tiipus, \. Ben. 1 • /-> . i •

^ , , . • > in Octopus vulqams.

D. schulzwnum, v. Ben. J

D. moschatum, Whitm. } .

„. ' ,„ \\nEledonemoschata.

Dicyemennea eledones, Wagen.J

D, truncatum. Whitm. ^ . a . /,, . 7 .

., __ ' V in sepia omcmalis.

D. gracile, Wagen. /

( in Rossia macrosoma, Sepia elegans.
D. truncatum. Whitm. ~ „. . 7.

( 8. officinahs.

D. schulzianum, v. Ben., in S. biserialis, Oct. vulgaris.

CLASS ORTHONECTIDA, Giard.1

This group includes certain small ciliated organisms parasitic in some
low invertebrates. These parasites are built up of an outer layer of flat
ciliated cells, arranged in rings round the animal, and thus giving the
appearance of segmentation, and of a central mass of polyhedral cells,
which become ova or spermatozoa. Between the ectoderm and the central
mass are muscular fibrillae, having an obliquely longitudinal course.
The sexes are separate and dimorphic, the males being very much smaller
than the females, from which they differ structurally. The females may
themselves be dimorphic— one being cylindrical, the other flattened.

The group contains a single genus, Rhopalura, Giard, of which only
three species are accurately known ; R. giardii, Metschn. ( = R. ophiocomae,
Giard ; + Intoshia gigas, Giard), occurs in the peritoneal cavity of Amphiura
squamata. R. intoshii, Metschn. ( = Intoshia linei, Giard), in the body
cavity of Nemertes lacteus. R. pterocirri, St. J.,2 occurs in the Polychaete,
Pterocirrus macroceros. Further, a parasite was described by Keferstein
in Leptoplana tremellaris, which no doubt belongs to the group.3

fertilised eggs ; while females, i.e. vermiform embryos arise parthenogenetically.
Further, the same individual dicyemid may be at first a nematogen, and later a
rhombogen.

1 Giard, Journ. anat. et physiol. 1879, xv. p. 449; and Q. J. Mic. Sci. xx. 1880,
p. 225.

2 St. Joseph, Bull. Soc. Zool. France, xxi. 1896, p. 58.

3 Caullery and Mesnil have described a genus Staechartrum, from the Annelid
Scoloplos (O. R. Ac. So. Paris, cxxviii. pp. 457 and 516, 1899).

154

THE ORTHONECTIDA

R. giardii has been the subject of Julin's 1 researches, and is of more
frequent occurrence than R. intoshii. The present account chiefly refers
to the former species. The male is minute and spindle-shaped (Fig. VII.).
The ectodermal rings are six in number, including the anterior and
posterior terminal cones. The whole body, with the exception of the
second ring, is ciliated. The cilia borne by the anterior cone are
throughout the Orthonectida directed forwards, but elsewhere they point
backwards. The third ring is larger than the others, but the second ring
is noticeable for the refringent granular knobs borne by the cells. This
ciliated ectoderm encloses the " testis," a mass of cells enveloped in a
distinct membrane. In both sexes this central mass of cells, which give

FIG. VII.

Rhopalura, male (after
Julin).

FIG. VIII.

The cylindrical female of Rho-
palura (after Julin).

FIG. IX.

The flattened female of
Rhopalura (after Julin). x,
the peculiar subepidermic
cell.

rise either to spermatozoa or to ova, can be traced back, in the embryo,
to a single axial cell, which, as in the Dicyemida, is the larger of the first
two blastomeres into which the egg cell segments (Fig. X.). But whereas
in Dicyemida the genital cells are derived from a " primary germ cell "
at each end of the axial cell, here the axial cell itself subdivides to pro-
duce germ cells, which represent, in all probability, mesoblast, whilst the
last trace of " endoderm " has gone. Between the " testis " and the ecto-
derm a number of fine, obliquely directed streaks can be detected, forming
a continuous sheath (Julin), or limited to four bundles (Metschnikoff).
The ends of these fibrillae, which are regarded by Julin as muscular,
appear to be continuous with ectoderm cells at each end of the body.
Julin figures nuclei on them, superficial to the testis. Possibly they are
1 Julin, Arch. BioL iii. 1882, p. 1.

THE ORTHONECT1DA

155

derived from the " intermediate cells," which have been sometimes noted
in these positions. It has, however, been suggested that the " fibrillae "
are merely the expressions of a folding of the testis-membrane.

The female is not only larger than the male, but differs so greatly
from it that Giard referred it to a different genus, and described it under
the name Intoshia gigas. Further, Julin discovered that there are two
kinds of females — one flat, the other cylindrical. The cylindrical female
presents eight rings (or, according to Metschnikoff, nine), (Fig. VIII.). Of
these the second, as in the male, is not ciliated. The number of rows
of cells differs in the various rings.

The flattened female (Fig. IX.) is broader than the cylindrical form, and
presents no ectodermal rings. The ectoderm is formed of very flat cells,
and is ciliated over its entire surface. There is at one point a sub-
epidermal cell of considerable size, the meaning of which is obscure. It
has been suggested that it represents a degenerated, obliterated enteron — in

FIG. X.

Four stages in the development of the male of Rhopalura (after Julin). In A the maeromere
has become partially invested by the micromeres (a), and has already divided, giving rise to the
primary germ cell (6), and to an intermediate cell (c). In B the maeromere has again divided,
giving off an anterior intermediate cell (c'). In C the central cells have become entirely sur-
rounded by the ectoderm («), which is ciliated. The primary germ cell has subdivided and
now constitutes the testis. In D the ectoderm cells have become differentiated, in that the
cilia of the anterior cone are directed forwards, the rest backwards ; the testis is assuming the
condition of the adult, though the intermediate cells have not yet given rise to muscle fibres.

other words, it is hypoblast ; but there appears to be no evidence in support
of this view.

In both females the central mass consists of egg cells ; these are
free in the cylindrical form, and are discharged by dehiscence of the
ectoderm at the level of the non-ciliated ring. They are fertilised by
spermatozoa, and develop into males.

The eggs of the flattened form are embedded in a granular mass, and
develop parthenogenetically into females of either form.

The females occur in a peculiar vacuolated mass of granular material
in which no cellular structure is to be detected. This " plasmodial tube "
(Metschnikoff, or " sporocyst " of Giard) fills up the body cavity of the
host, but is enveloped in a nucleated layer, which appears to be part of
the tissues of the host. Metschnikoff believed that both sexes passed
their entire life in these " plasmodial tubes," but Julin has never detected
males or embryos of males in them. These only occur free in the fluid of
the body cavity.

156 THE ORTHONECT1DA

These plasmodial tubes appear to be formed in this way : — The flattened
females fragment ; each piece, containing a number of eggs, rotates for a
time in the cavity of the host, but later becomes attached to the wall of
this cavity; the ectoderm cells now drop off, swell up, and undergo various
changes resulting in the formation of the plasmodium. On the other
hand, it is suggested by Max Braun that the latter arises by degeneration
of the gonads of Amphiura, owing to the attacks of the parasite.

The development of the fertilised egg leads to a blastosphere consist-
ing of a central macromere surrounded by ectoderm cells (Fig. X.) ; the
former divides, twice, unequally producing a small cell at each end, whence
the " intermediate cells " arise (cf. the primary germ cells of Dicyemida),
the macromere now divides up into numerous germ cells. There thus
appears to be no remains of an endoderm in this history ; the macromere
is mesoblastic, giving rise to muscular cells, and genital cells. In the
history of the parthenogenetic eggs, the homologue of the terminal
"intermediate cells" appears to be a continuous layer between the
ectoderm and the axial cell, so that the two forms of females can be
recognised at a very early stage.

[Caullery and Mesnil in the last three years (1898-1900) have described
four new species of Orthonectids : (1) Ehopalura metschnikovi, parasitic
both in a Chaetopod (Spio martinensis, Mes.), and a Nemertine (Tetra-
stemma flavidum). (2) Eh. julini, parasitic in a Chaetopod (Scotelepis
fuliginosa, Clpde.). (3) Eh. pelseneeri, parasitic in Tetrastemma flavidum.
(4) Staechar thrum giardi, parasitic in a Chaetopod (Scotoplos muelleri,
Rathke). The two first-named species present distinct males and females
as do the previously known species of Ehopalura. On the other hand,
Eh. pelseneeri is hermaphrodite, as is also Staecharthrum giardi, which
differs from all other Orthonectids by the great length of its filiform body.
According to the observations of these authors (Comptes rendus Acad.
Sciences, 20 fevrier 1899, and later results privately communicated),
which have extended to Eh. ophiocomae, Giard, as well as the species above
named, the plasmodium is a true protoplasmic nucleated structure,
capable of amoeboid movement. It is under this form that the Ortho-
nectid makes its first appearance in the infected host. By segregation of
certain of the nuclei and portions of surrounding protoplasm of the
plasmodium, germ-cells are produced, and from these develop ciliated
embryos which finally become adult males and females. The same
plasmodium can give rise to both males and females. The sexual
products of these ciliated offspring of the plasmodium are not discharged
within the host, but only after the escape of the males and females into the
sea-water. The sexually fertilised egg-cell and the resultant embryo are
unknown, but it is this embryo which effects an entry into a new host
and becomes a nucleated plasmodium which in turn again produces
ciliated males and females. Thus there is an alternation of genera-
tions, sexual and asexual. The comparison of the plasmodium to the
sporocysts of Malacotylous Trematoda by Giard appears to be justified,
in so far that both are the first forms assumed by the sexually produced
individual on entering upon parasitic life ; and both give rise asexually

THE ORTHONECTIDA 157

to numerous individuals which in some Malacotyla as in Orthonectida
are destined to become sexually mature. Caullery and Mesnil consider
that the plasmodium of the Orthonectida corresponds to the axial cell
of the Dicyemida; the one as the other giving origin by endogenous
germ-formation to sexual ciliated forms. According to Wheeler, the same
axial cell of a Dicyemid produces successively females and males. There is
therefore close agreement with the facts observed as to the "plasmodium"
of the Orthonectida. Wheeler, however, suggests, but has not actually
observed, that the males (so-called infusoriform embryos) of Dicyemids
proceed from fertilised germ-cells only (see note, p. 152). — E. R. L.]

The Orthonectida and Dicyemida have been grouped together to
form a grade Mesozoa by v. Beneden — a grade intermediate between the
Protozoa and Metazoa, and characterised as containing multicellular
organisms consisting of ectoderm and endoderm, the latter not being in
the form of a layer surrounding an enteric cavity.

But Giard, Whitman, and others have shown that the groups do not
require the formation of this new grade to contain them ; they are in
reality Metazoa, for there can be no doubt but that the " intermediate
cells " of Orthonectida and, at any rate, the " primary germ cells " of
Dicyemida are mesodermic ; possibly the axial cell of the latter
represents an endoderm, reduced by parasitism to its last remnant — a
single cell. In the Orthonectida, since the central cell of the embryo
gives rise to genital cells, it may be regarded as mesoderm, so that in
this group all trace of endoderm has disappeared. Nor is this fact
unique amongst parasites, for both in Cestoidea and in some Nematoidea
the gut is entirely absent.

The simplicity of these organisms is not primitive, but secondary ;
they are degenerate Platyhelminths, but whether descended from
Turbellaria or from Trematoda is uncertain ; the resemblance to the
ciliated embryos of the latter class is more apparent than real, for they
are really much simpler than these.

Owing to the gap between these two groups and the rest of the
Platyhelminths, Pagenstecher suggested the term " Mionelminthes " in
place of " Mesozoa." *

APPENDIX II.

Trichoplax adhaerens, F. E. Schulze,2 occurs in the marine aquarium
at Graz, and is known nowhere else. It is a small, circular disc, moving
partly by means of cilia, partly by thrusting out simple pseudopodia-like
processes. The organism consists of an outer layer of ciliated cells, but
those on the lower surface, by which the animal creeps over the glass,
etc., are columnar ; those of the upper surface are flat. The central mass
of the body is composed of spindle-shaped and slightly branched cells,
leaving spaces filled with fluid between them. Nothing is known of
the process of reproduction beyond the fact that in autumn Schulze
observed (1) that the individuals were drawn out into long threads, and

1 Bronn's Thierreichs, Wiirmer. 2 Zool. Anzeig. vi. 1883, p. 92.

158 SALINELLA

(2) there were numerous small circular discs in the water ; he concludes
that multiplication is effected by fission or fragmentation.

The homologies of the cell layers is uncertain ; whereas some authors
regard the columnar cells as endoderm, and look on the organism as a
flattened-out gastrula, Butschli regards it as a " placula." There appears
to be no reason to believe that the whole external layer is not ectoderm,
but whether the internal tissue is mesoderm or endoderm, there is no
evidence to show. Possibly Trichoplax is a degenerate, acoelous Turbel-
larian, deprived of rod cells.

Treptoplax, Korotneff, is somewhat similar, and has been seen in the
Naples Aquarium.1

APPENDIX III.

Pemmatodiscus socialis, Montic.,2 is essentially a gastrula, with cili-
ated ectoderm, containing rhabdites. One surface is flat, with a small
central mouth leading into a distinct enteron. It occurs in cysts in the
tissues of Rhizostoma pulmo, and appears to multiply by fission within
the cyst ; nothing is known of any " organs."

APPENDIX IV.

What was termed Salinella salve by Frenzel, was stated by him to
occur in a 2 per cent solution of salt at Cordova, in the Argentine. He
describes it as an oval sac, with a wall formed of a single layer of cells,
and containing a cavity communicating with the exterior at each end.
The " ventral " cells are ciliated ; the dorsal are not ciliated but carry
" setae," and all the cells are ciliated at their internal ends. Reproduction
is said to take place by fission, and also by multiple fission after encyst-
ment and conjugation. The "larvae" are declared to be unicellular
likenesses of the "adult" and closely resemble hypotrichous ciliated
Protozoa.3

If Salinella has a real existence, it forms, as Apathy 4 has argued, an
intermediate form between Protozoa and Metazoa, and the term Mesozoa
has been resuscitated in this new sense. But there is not sufficient
ground for accepting Frenzel's interpretation of his observations.

So little is known about the anatomy or life-history of Trichoplax,
Pemmatodiscus, and Salinella that it is impossible to make any definite
statement as to their affinities. Moreover, with the exception of Pem-
matodiscus, they have only been met with in a " domesticated " condition
in aquaria, and it has been suggested that they are in reality imperfectly
developed animals — embryos which cannot attain full development owing
to these conditions.

1 See Monticelli, Mitth. Zool. Sta. Neapel. xii. 1896, p. 432.

2 Monticelli, loc. cit.

3 Arch.f. Naturges. Iviii. 1892, p. 71 ; and Ann. Mag. Nat. Hist. (6), ix. 1892,
p. 79.

4 Annals Mag. Nat. Hist. (6), ix. 1892, p. '465.

CHAPTEK XXL

NEMERTINI.

PHYLUM EHYNCHOCOELA, MAX SCHULTZE.

CLASS. NEMERTINI (von Siebold and Stannius).

BRANCH A. DIMYARIA.

Order 1. Protonemertini.
Fam. 1. Carinellidae.
„ 2. Hubrechtiidae.

Order 2. Mesonemertini.
Fam. Cephalothricidae.

Order 3. Metanemertini.

Fam. 1. Eunemertidae.

„ 2. Ototyphlonemertidae.

„ 3. Prosorhocmidae.

- ,,4. Amphiporidae.

„ 5. Tetrastemmatidae.

„ 6. Nectonemertidae.

„ 7. Pelagonemertidae.

„ 8. Malacobdellidae.

BRANCH B. TRIMYARIA.

Order 4. Heteronemertini.
Fam. 1. Eupoliidae.
,, 2. Lineidae.

THE Nemertine worms constitute a compact group of animals
distinguished alike from the lower Platyhelmia and from the more
highly organised class of Chaetopoda by certain definite structural
peculiarities.

Historical Survey. — The first account and figure of a Nemertine worm
is given by Borlase in 1758. The early zoologists, such as 0. F. Muller,
Johnston, Bosc, considered them as Turbellarians, and included them in

160 THE NEMERTINI

the genera Planaria, or Fasciola, or Gordius. And even when the anatomy
of the group was better understood, they were retained as members of
that class, though various positions were assigned to them within it.
Thus, Ehrenberg placed them in his order Rhabdocoela ; Quatrefages
created an order Miocoela, which he placed side by side with the Rhabdo-
coela and Dendrocoela ; Max Schultze divided the Turbellaria into («)
Proctucha, to include the Nemertines, which he termed Rhynchocoela ;
and (6) Aprocta, for the Turbellaria, s.s. And even in recent times
this position has not been entirely given up, for Hatschek, in his Text-
book, places the Nemertines in his group Autoscolecida, with the Platy-
helmia, Rotifera, Nematoda, etc., all agreeing in the structure of the
excretory organs.

On the other hand, some zoologists have exaggerated the resemblances
to the Annelids which the Nemertines undoubtedly bear, and place them
in this class (v. Siebold, Leuckart, M'Intosh). Lang includes them
in his "Vermes," by which he understands the Annelids, Gephyrea,
Polyzoa, Brachiopoda, Nematoda. The more recent authorities who
have worked upon the group (Hubrecht, Burger) raise the Nemertines
to an independent position between the Platyhelmia and the Annelida :
a view that was first taken by Cuvier, who formed the groups "Vers
cavitaires" for the Nemertines, in opposition to the "Vers parenchy-
inateux " (Platyhelmia) ; later, Blanchard invented the term Aplocoela,
and Oersted followed in the same line. The interesting speculations
of Hubrecht may here be referred to, viz. the suggestion that in the
Nemertine various organs of the Chordata are represented, or are even
anticipated in a humble fashion.

Amongst those who have added materially to our knowledge of
genera and species reference may be made to the following : — 0. F.
Miiller, Oersted (34), Johnston, Keferstein (23), Stimpson, M'Intosh,
Hubrecht, Joubin, and Burger; while Duplessis (13) and Guerne
worked upon fluviatile species ; Semper and Dendy (10) on terrestrial
forms.

As contributors to our knowledge of the general anatomy of the class,
the following deserve mention : — Quatrefages (36), Frey and Leuckart (14),
Max Schultze (39), Keferstein. But all earlier writers are eclipsed by
the brilliant monograph by M'Intosh (27), wherein he gives a critical
account of all the earlier work on the subject. Since that time Hubrecht
and Burger have, by more modern methods of research, built up on this
foundation a magnificent superstructure, culminating in the elaborate
memoir by Burger, published in the series of monographs of the Fauna
and Flora of the Bay of Naples.

With regard to special points of anatomy, it is interesting to note
that the eversibility of the proboscis was first noted by Da vies (1815) on
the addition of alcohol to water in which a Nemertine was living.
Johnston was the first to recognise that in some Nemertines the proboscis
is provided with a stylet, which is absent in others. But it was a long
time before this proboscis and its sheath were properly understood ; for
by most of the earlier writers it was regarded as the intestine (Duges,
Ehrenberg, Quatrefages), while Oersted described it as a male copulatory

THE NEMERTINI 161

or excitant organ. Its true nature, and the fact that it is quite distinct
from the gut, was first recognised by Frey and Leuckart in their account
of Linens gesserensis (1847), where, too, the real character of the mouth,
hitherto regarded as the genital pore, was established.

The vascular system was recognised as a closed system of canals by
Quatrefages (36) ; and our present knowledge of the comparative anatomy
of the system is due to Oudemans (35), who in the same memoir gave an
account of the excretory system in a variety of genera. This excretory
system was originally described by Max Schultze in 1851 as a branched,
ciliated canal ; but it remained for Burger (7) to make the valuable dis-
covery that these canals terminate blindly in a multicellular swelling,
containing a flame, which had, however, already been seen by Silliman
in 1885 in Tetrastemma aquarum dulcium, and was figured by Dendy in
1890 for Geon. australiensis (10).

The genital sacs were already known to Oersted, and the fact that
the worms are dioecious was recognised by Quatrefages, and was a reason
for separating the Nemertines from the Turbellaria. The nervous
system was correctly described by Duges (1828), who fell into the curious
error of regarding the brain as a " heart," and the lateral nerves as
" blood-vessels," owing to the fact that the system is tinged with red in
the larger forms. Our present knowledge of this system is due to
M'Intosh and to Hubrecht (17), while the finer histology of the system
has been studied by Haller (16), and by Burger (6).

The cephalic fissures of the larger genera, such as Linens and Cere-
bratulus, early attracted notice, but the function of the peculiar cerebral
organs associated with them has been variously interpreted. Both Delle
Chiaje and Hubrecht maintained that they were respiratory, while van
Beneden took them to be excretory. The detailed account of these organs
which we are now able to give rests upon the work of Dewoletzky (11) and
of Burger (5).

But although the study of anatomy and histology has made much progress
in these recent years, the embryology of the class still presents a wide field
for future investigation. The Pilidium larva, originally described in 1847
by Joh. Muller (33), has been studied by several zoologists of note, especially
by Metschnikoff (28), and by Butschli/ and by Burger. The larva of
Desor has been the subject of research by Barrois (1), and by Hubrecht
(19), while the direct development of Cephalothrix has been studied by
Dieck (12), and that of various other genera, quite recently, by Lebedinsky
(26).

With regard to the taxonomy of the Xemertines, reference need only
be made to three zoologists : Max Schultze (1853) divided them into two
orders — the Anopla and Enopla. This classification was generally adopted,
till Hubrecht put forward his threefold division into Palaeonemertini,
Schizonemertini, and Hoplonemertini, depending on the superficial position
and diffuse condition of the nervous system in the first, on the cephalic
slits in the second, and the armed proboscis in the third order. More
recently Biirger (8), laying stress on the relative depth of the nervous
system, and on the structure of the body wall, proposed the four-fold
division adopted in the present article.

ii

162

THE NEMERTIN1

-4U'

e-

The General Characters of the
Nemertines. — These worms are, with
a few exceptions, elongated, and sub-
cylindrical in form, and marine in
habitat. As in the Turbellaria, the
epidermis is ciliated and the body
is devoid of external segmentation.
But unlike the Platyhelmia, the gut
is provided with an anus, situated at
the posterior end of the body (Figs.
L, II., III.). The mouth, always
anterior and subterminal, leads into
stomodaeum, which is, in the
majority, a short, simple, cylindrical
tube, leading to the enteron. The
latter is a straight canal, usually
provided with regularly arranged,
paired, lateral diverticula. The most
characteristic organ of the Phylum
is the proboscis, which is a muscular
pleurecbolic introvert, capable of
eversion through an anterior terminal
pore — the rhynchostome. This tubu-
lar proboscis is invested in an epi-
thelium similar to the epidermis,
containing rhabdites and nemato-
cysts • and in one group calcareous
stylets are carried on its wall in
such a position that they lie at
the apex when the proboscis is
everted. In a state of introversion,
the proboscis is contained in a closed
tubular cavity, with a muscular
wall — the rhynchocoel — lying above
the enteron, extending for a vari-

FlG. I.

Diagrammatic view of Cerebratulus, as seen from
above when the dorsal wall of the body has been re-
moved, to show the proboscis and its sheath, the
enteric and nervous systems ; in the middle region
the gut has been omitted, a, rhynchostome ; ft,
rhynchodaeum ; c, proboscis, the tubular, eversible
region ; c', the posterior, solid, non-eversible region,
which serves as the retractor muscle ; d, rhyncho-
coel ; e, dorsal ganglion, or lobe of the brain ; the
dorsal commissure has been removed, to show the
continuity of proboscis and rhynchodaeum ; /, ventral
ganglion, or lobe of the brain ; g, horizontal cephalic
cleft, the depth of which is indicated ; h, cerebral
organ ; the canal of which opens externally into the
hinder end of g ; i, lateral nerve trunk ; j, stomo-
daeum ; k', intestinal caeca ; z, anus.

THE NEMERTIN2 163

able distance along the body, and containing a corpusculated
fluid.

The nervous system consists of a pair of lateral nerve cords run-
ning the entire length of the animal, and connected with one another
at the hinder end, above the intestine (Fig. I.). At the anterior
end each cord is enlarged to form a more or less complex cerebral
ganglion, which is connected to its fellow by a dorsal and a ventral
commissure embracing the proboscis. There is usually in addition
a median dorsal nerve. The peripheral system is formed of a
diffuse plexus, or of a more regular series of commissural nerv.es
connecting the longitudinal nerves. On each side of the head
there is, with few exceptions, a ciliated pit of simple or complex
character — the cerebral organ — in close relation to the hinder part
of the brain.

The excretory system (Fig. II.) consists of a longitudinal canal
on each side of the stomodaeum, opening to the exterior by one or
more short ducts, and at "its inner end gives rise to a greater or
less number of short, simple, or slightly branched tubules, each of
which terminates in a multicellular swelling containing a bunch of
cilia similar to the " flame " of the terminal cell of the Platy helminth
system (Fig. XXVIII.).

There is in the Nemertines another system of tubes entirely
shut off from every other cavity, and containing a corpusculated
fluid, sometimes red in colour. This " vascular system " (Fig. III.)
which is not present in the Platyhelmia, consists fundamentally of a
pair of contractile lateral vessels extending the whole length of the
animal, and connected with each other by a preoral and a supra-
anal anastomosis. To this system there is usually added a median
dorsal vessel, lying between the intestine and the wall of the
rhynchocoel. In the majority of Nemertines these three longi-
tudinal vessels are connected by transverse vessels more or less
regularly arranged.

Between the muscular coat of the body wall and the wall of
the gut is a loose connective tissue or " parenchyma," in which the
excretory canals and the lateral blood-vessels are embedded. In
it too the genital organs are developed. The sexes of the
Nemertines are, as a rule, separate, and each genital organ is a
simple sac, surrounded by a thin cellular membrane, which, at the
breeding season, is prolonged outwards as a duct, to open
externally above the lateral nerve. These genital sacs appear to
be the only representatives of a coelom ; and are repeated, more or
less regularly, usually alternating with the intestinal pouches,
throughout the body (Fig. II. m).

The development of the Nemertine is either direct or in-
direct ; the larva is of a characteristic form, known as a Pilidium
(or in a modified condition, as Desor's larva). In this larva

THE NEMERTINI

s-t-

FIG. II.

Deeper dissection of the anterior end of
Cerebratulus, after removal of the proboscis, and
of the greater part of the dorsal blood-vessel. The
lateral nerve trunks are omitted, a, rhyncho-
stome ; &, rhynchodaeum ; e, dorsal ganglion,
or superior lobe of the brain, with dorsal com-
missure intact ; h, cerebral organ ; j, stomo-
daeum ; k, intestine ; k', caeca ; I, excretory pore,
leading into the excretory duct, and thence to
the. branching canal, alongside the lateral blood-
vessel ; m, gonad (perigonadial coelom) ; m',
genital pore ; n, dorsal blood - vessel ; o, trans-
verse vessel ; p, lateral blood-vessel ; r, s, an-
terior anastomoses.

t- -\-

FIG. III.

Plan of the vascular system of Cerebra-
tulus, from above, n, dorsal blood-vessel ;
o, transverse vessels ; p, lateral vessels ;
p (above), anterior, apical anastomosis ; q,
parastomodaeal sinus and network ; q',
the median vessel giving origin to these ;
s, preoral anastomosis in region of brain ;
t, supra-anal anastomosis ; m, mouth.

THE NEMERTINI

165

the body of the Nemertine is formed, and the larval skin is
cast off.

The result of the total and nearly equal segmentation of the
egg is a blastula with a capacious blastocoel ; the cells on one side
are rather larger than the rest, and by their invagination the
larva becomes a gastrula, which is at first uniformly ciliated.

A special tuft of long sensory hairs is developed in a pit at the
aboral pole (Fig. IV.), and by the downgrowth of the sides of the
body two or four great lappets are formed ; the organism gradually
becomes helmet-shaped (Fig. IV. (7). The margins of these lappets

FIG. IV.

Development of the Pilidium larva (after Metschnikoff), from Joubin. A, blastula, already
ciliated and moving within the vitelline membrane ; a few mesoblast cells have been given off
by the blastoderm ; B, the young gastrula ; C, the larva. The blastocoel is filled with jelly, in
which mesoblast cells are embedded ; the side walls have grown down into the right and left
lappets ; s, the anterior ; s', the posterior invaginations of the ventral surface which give rise
to the "imaginal discs."

bear long cilia, which are continued round the whole of the ventral
edge of the Pilidium, so as to form a circumoral band. Balfour
has pointed out the phylogenetic significance of this larva, from
which the Trochosphere of Annelids may have been derived. The
Pilidium consists of epiblast, of hypoblast, and of mesoblast which
gives rise to a jelly-like connective tissue between them. The
greater part of the body wall of the future Nemertine is formed
out of four invaginations of the ventral surface of the Pilidium
— a pair of anterior or cephalic, and a pair of posterior or somatic
pits (first recognised by Krohn and by Miiller), (Fig. VI.). The
wall of each pit soon becomes divisible into two regions — the

1 66

THE NEMERTINI

bottom is formed of columnar cells, and constitutes the "germ
disc " or imaginal disc (cf. those of some insects). The outer walls
consist of a flat epithelium. The aperture of invagination closes,
and the pit becomes a sac, the thin wall of which is the "amnion"
(cf. vertebrates and insects). These four flattened sacs sink in-
wards and extend laterally in all directions till they finally meet,

FIG. V.

The fully developed Pilidium, bearing the young Nemertine within its amniotic sac (after
Korschelt and Heider). Am, amnion ; D, enteron of Pilidium and Nemertine ; EC, ectoderm
of Nemertine ; M, mouth of Pilidium ; JV, nervous system of Nemertine ; E, proboscis ; So,
excretory organ.

thus embracing the larval enteron and a certain amount of meso-
blast, and giving rise to the body wall of the young Nemertine
(Figs. V, VI.).

From the inner surface of the imaginal discs new mesoblast arises,
thus a new body wall is formed within the larval skin. A fifth pit has
meanwhile made its appearance at the anterior end of the larva, above
the ciliated band ; instead of flattening out as the others do, it elongates
backwards to form a tube ; it is the forecast of the proboscis (Ret). The

THE NEMERTINi

167

FIG. VI.

Three figures to illustrate the formation of the young Nemertine within the Pilidium (from
Burger). They are diagrammatic sections (or projections) across the larva, just above the origin
of the lappets. 1 shows the origin of the two pairs of imaginal discs, the pair of excretory pits
(from the stomodaeum), and the median proboscis pit. In each of the imaginal discs the bottom
becomes thickened and the sides thin. In 2 the imaginal discs are closed sacs (amniotic sacs) ; '
each is flattening and extending round the enteron of the larva, the cerebral organ is making its
appearance. 3, the imaginal discs have reached their fullest development ; the new mesoblast
has been given off, and the body wall of the Nemertine established. The dorsal and ventral
ganglia are denned (the cephalic "plates" are left unshaded to show these), and the excretory
organ is branched. Am, arnnion ; Amh, amniotic cavity ; C, cerebral organ ; D, enteron ; Dg,
dorsal ganglion ; Ep, definitive epidermis of young Nemertine ; Kp, cephalic plate, the thickened
floor of the cephalic pit ; Ks, cephalic pit, or imaginal disc ; N, nephridium, or its foundation ;
Oe, larval stomodaeum ; R, proboscis ; Ro,, invagination to form proboscis ; Re, the foundation of
the rhynchocoel, its muscular wall, and the muscular coat of the proboscis ; Rp, somatic plate,
the thickened floor of the somatic pit ; Rs, somatic pit or imaginal disc ; S, lateral nerve stem
of Nemertine ; Vg, ventral ganglion.

1 68 THE NEMERTINI

mesoblast formed from its wall splits, giving rise to the rhynchocoel ; tlie
inner layer becoming the musculature of the proboscis ; the outer layer
the wall of the rhynchocoel or proboscis sheath.

The nervous system originates in two independent thickenings of the
epiblast on each side ; the dorsal lobe of the brain arises from the hinder
part of the cephalic disc ; the ventral lobe and the lateral nerve from the
somatic disc. The cerebral organ arises as a secondary pitting at the
anterior end of this latter disc (C).

The excretory system is epiblastic in origin, arising as a pit on the
ventral surface of the larva, on either side of the stomodaeum (Figs. V., VI.).
This undoubted epiblastic origin of the excretory system is of considerable
general interest, since it confirms the view of Lang and others that the
system in Platyhelmia is epiblastic, and provides some confirmation of
Goodrich's distinction between a "nephridium" and a " coelomoduct."
The blood-vessels arise as a liquefaction of the mesoblastic jelly.

The Classification of the Nemertines. — Although the presence or
absence of an armature on the proboscis is no longer regarded as
of taxonomic value, yet the terms Anopla and Enopla may be used
as descriptive, and contrasting epithets, in the same kind of way
as " Invertebrata " and " Vertebrata," are
used. Since Burger's classification is
founded on the relation of the nervous
system to certain tissues in the body wall,
it is necessary^ to describe a transverse
section of a ^Nemertine in this place,
and Carinella is chosen as an example.

The epidermis consists of a single
layer of cells, of four kinds — ciliated cells,
goblet cells, club-shaped gland cells, and
- -i^r ••-^b'T^sr grouped gland cells (Fig. VII.) ; below it
iiiPil^^^ is a basement tissue or cutis, then an
dm f) outer layer of circularly disposed muscle

FIG. vn. fibres, followed by a deeper layer of longi-

Epidermis of Carimiia poly- tudinal muscles (Fig. VIII.). The paren-

morpha, Ren. (from Perrier, after . . \ f>

Burger), b, basement tissue ; d, cnyma is thin in this genus, and below it

ducts of eland cells (p) ; dm, • u ,-> -\ _c • i ~\ /

diagonal muscles (present only in is another layer of circular muscles (con-
ttg£$USJ8S£&3> sidered by Hubrecht as somatic, but by
filaments; m, circular coat of Burger as splanchnic), closely investing

muscles ; n, nerve layer IP,,-, •, -, , , -, T

grouped gland cells ; r, radiating the enteroii and the rhynchocoel. In
the middle line, dorsally and ventrally,

& S0me muscle fibres Pass from tnis Ia7er

to the cutis. The wall of the rhyncho-
coel consists of deeper circular muscles, to which longitudinal
muscles are added.

In this transverse section the lateral and dorsal nerves (e, j) will
be seen lying outside the circular somatic muscles, immediately

THE NEMERTIN1

169

below the cutis. These nerves are connected by a nerve tunic, or
plexus in this position, extending all round the animal. The
brain likewise occupies the same relative position.

The characters upon which Biirger chiefly founds his classifica-
tion are (a) the somatic musculature, and (b) the relative position
of the lateral cords. The dermal musculature consists either of
two layers, as in Carinella, or of three layers, in which case a
second coat of longitudinal muscles is developed in the cutis,
external to the circular coat (Fig. X.). In these "trimyaric"
Nemertines the lateral nerves lie between this secondary coat of
longitudinal muscles and the circular muscles — that is, in the same

FIG. VIII.

Transverse section of Carinella, (somewhat schematised, after Burger), a, epidermis ; 6,
basement tissue (cutis) ; c, circular muscles ; c', inner (splanchnic) coat of circular muscles ;
d, longitudinal muscles ; e, lateral nerve stem ; /, portion of nerve network ; i, enteron ; j (super-
ficial) dorsal nerve ; k, proboscidial sheath nerve ; o, portion of excretory canal ; p, lateral blood-
vessel ; r1, longitudinal muscular coat of the proboscis ; r", circular coat ; r'", epithelium of
proboscis ; between these two last coats lies a, nerve, above and below ; s, the proboscis sheath,
or muscular wall of the rhynchocoel (w) ; v, parenchyma.*

position, with regard to the latter, as in Carinella. But in. the
" dimyaric " forms the nervous system may either (a) lie outside
the circular coat, or (b) in the substance of the somatic muscula-
ture, or (c) below it, in the parenchyma.

There can be no doubt but that the first of these three condi-
tions is the most primitive, and the last the most recent ; and the
trimyaric arrangement has been derived from the dimyaric in
another direction.

Using, then, the terms Anopla and Enopla as descriptive rather
than as taxonomic terms, the Nemertines may be divided into two
branches — the Dimyaria and the Trimyaria ; and the former may
be anoplous or enoplous, as follows : —

i;o THE NEMERTIN1

CLASS NEMERTINI, SIEBOLD AND STANNIUS, 1848

( = Nemertina, Ehrenb. ; =Nemertea, Quatref. ; =Nemertinea) Dies. ;
= Aplocoela, E. Blan chard ; = Rhynchocoela, Max Schultze).

BRANCH A. DIMYARIA. Nemertines in which the dermal muscula-
ture consists of an external coat of circular muscles and an internal coat
of longitudinal muscles.

SECTION 1. ANOPLA, Max Schultze ( = Palaeonemertini minus Eupo-
liidae, Hubr.). Dimyaric Nemertines in which the proboscis is not pro-
vided with a calcareous stylet ; the mouth is behind the brain, and there
is no anterior caecum to the intestine.

ORDER l. Protonemertini, Burger.

Dimyaric anoplous Nemertines in which the brain and lateral nerve
cords lie outside the musculature.

FAMILY 1. CARINELLIDAE, M'Intosh. The cerebral organ is in
the form of a shallow vertical furrow, without any relation to the lateral
blood-vessel ; there is no dorsal blood-vessel. The intestinal pouches are
short and ill-defined. Carinina, Hubr. ; CarmeUa, Johnst. FAMILY 2,
HUBRECHTIIDAE, Burg. The cerebral organs are spherical and impinge
upon the lateral blood-vessel. A dorsal vessel is present ; the intestinal
pouches are deep. Hubrechtia, Burg.

ORDER 2. Mesonemertini, Burger.

Dimyaric anoplous Nemertines in which the lateral nerves have sunk
into the somatic musculature.

FAMILY — CEPHALOTHRICIDAE, M'Intosh. There is no cerebral organ
nor cephalic furrow. Carinoma, Oudem. ; Cephalothrix, Oersted.

SECTION 2. ENOPLA, Max Schultze. Dimyaric Nemertines in which
the proboscis is armed with calcareous stylets, except in certain modified
genera. The mouth is in front of the brain, and may be coincident with
the rhynchostoine. The stomodaeum is complex, and there is usually an
anterior, median, and ventral caecum to the midgut.

ORDER 3. Metanemertini, Burger ( = Hoplonemertini, Hubr.).

The brain and lateral nerves have sunk through the somatic muscu-
lature and lie in the parenchyma. The mouth is in front of the brain.

TRIBE A. PRORYNCHOCOELA. Metanemertines with a long, thin body
which can coil into a ball ; they creep with eel-like undulations and never
swim. The rhynchocoel never extends into the hinder half of the body,
and the proboscis is much shorter than the worm.

FAMILY 1. EUNEMERTIDAE, M'Intosh. Eyes present. Eunemertes,
Vaill. ( = Nemertes, M'Intosh nee Guv.) ; Nemertopsis, Burger. FAMILY
2. OTOTYPHLONEMERTIDAE, Burger. No eyes, a pair of otocysts. Oto~
typhlonemertes, Dies.

TRIBE B. HOLORHYNCHOCOELA. Metanemertines with usually a short
body, which does not coil into a ball ; they creep without undulations.

THE NEMERTINI

171

The proboscis is as long as the body. The rhynchocoel extending into
the hinder third, and even to the end of the body.

FAMILY 3. PROSORHOCMIDAE, Biirger. With four eyes, cerebral
organs are rudimentary. Cephalic gland large. Mouth and rhynchocoel
coincident. Usually hermaphrodite. Prosorhocmus, Keferst. ; head
notched anteriorly (Fig. IX.). Prosadenoporus, Burg. ; Geonemertes, Semper,
is terrestrial (10). FAMILY 4. AMPHIPORIDAE, M'Intosh. Eyes numerous.
Cerebral organ large ; the intestinal pouches
are branched, and the gonads do not alter-
nate regularly with them. The anterior
caecum has long lateral diverticula. Amphi-
porus, Ehrenb. ; Drepanophorus, Hubr. ; with
unique armature to proboscis ; the rhyncho-
coel is provided with inetameric diverticula.
Zygonemertes, Hontg. ; Proneurotes, Montg.
FAMILY 5. TETRASTEMMATIDAE, Hubr.
Small, flattish worms, with four eyes in a
rectangle. Tetrastemma, Ehr. ; several fluvi-
atile as well as marine species. SticJio-
stemma, Montgomery ; fresh water. Oerstedia,
Quatref. FAMILY 6. NECTONEMERTIDAE,
Verrill. Short, broad body, with " cirri " ;
tail with horizontal fin ; apparently without
stylets on the proboscis (see 41). Necto-
nemertes, Verr., 636 to 1735 fms. Hyalo-
nemertes, Verr., 826 to 1641 fms. Atlantic.
FAMILY 7. PELAGONEMERTIDAE, Moseley.
Pelagic, deep sea, transparent, leaf-like body ;
proboscis unarmed ; no dorsal blood-vessel.
Pelagonemertes, Moseley ; P. rollestoni, M. ;
South Sea, 1800 fms. (Fig. XL). P. moseleyi,
Biirg.; S.E.Japan, 755 fms. Pterosoma, Lesson
(see 20). FAMILY 8. MALACOBDELLIDAE,
v. Kennel. Parasitic ; short, compact body,
with a posterior, ventral, glandular "sucker."
The intestine is undulating, without pouches
or anterior caecum, the proboscis is unarmed.
Malacobdella, Blv. ; without eyes or cerebral
organs. The proboscis opens into the fore-
gut. M. grossa, 0. F. M. (Fig. XIII.) ; in the mantle chamber of various
lamellibranch molluscs (see 24).

BRANCH B. TRIMYARIA. Anoplous Nemertines in which a secondary
coat of longitudinal muscles is developed outside the circular coat (Fig. X.).

ORDER 4. Heteronemertini, Biirger ( = Schizonemertini, Hubr.
+ Eu2wliidae, Hubr.).

The lateral nerve stems lie between this secondary coat and the
circular coat. The mouth is behind the brain ; there is no anterior
enteric caecum.

FIG. IX.

Prosorhocmus claparedii, Kefer-
stein. A viviparous Nemertine,
(After M'Intosh, from

172

THE NEMERTINI

FAMILY 1. EUPOLIIDAE, Hubrecht. There are no lateral, horizontal,
cephalic fissures. Eupolia, Hubr. ; the head is sharply marked off
from the trunk, into which it can be retracted. Poliopsis, Joubin ;
with a dorsal and a ventral median cephalic furrow, and a circular
furrow between head and trunk. Valencinia, Quatref. ; head awl-
shaped ; rhynchostome ventral. FAMILY 2. LINEIDAE, M'Intosh. A
deep, horizontal fissure on each side of the head, into the hinder end of
which the cerebral organ opens. GROUP A. Amicrurae. Without a small,
filamentous tail. Linens, Sowerby ; unusually long, thread-like body;

Transverse section of Cerebratulus marginatus, Renier (modified, after Burger)
b, connective tissue or cutis, into which the epidermal glands dip, and which is occupied by
the outer coat of longitudinal muscles, characteristic of the Heteronemertines ; c, circular coat ;
d, longitudinal coat of muscle ; e, lateral nerve stem ; /, outer ring of nerve fibres ; g, blood-
vessel passing from lateral trunk to the parastomodaeal plexus (h) ; i, stomodaeum ; j, dorsal
nerve; k, proboscidial sheath nerve; I, deep nerve ring; m, vessel of proboscis sheath; n,'
aperture of excretory organ ; o, excretory tube, receiving below one of the finer canals ; p,
lateral blood-vessel ; q, parastomodseal vessel ; r, proboscis ; s, proboscis sheath ; the rhyncho-
coel is unlettered ; t, dorsal blood-vessel ; v, parenchyma.

head broad and spathulate. The animals cannot swim, but creep at the
bottom or on the surface of the water, and can coil into clumps and
balls. Euborlasia, Vaill. ; body short, thick ; contracts like a snail.
GROUP B. Micrurae. With a small filamentous tail. Micrura, Ehrenb. ; small,
thin worms, unable to swim, but creep, coil into balls, and are contractile.
Mouth small and circular. Cerebratulus, Renier ; broad, strong worms, roll-
ing up spirally and not coiling ; they swim well, with eel-like undulations.
The lateral margin of the body projects as a distinct ridge. Mouth
long and slit-like. Langia, Hubr. ; lateral margins curved upwards pro-
duce a deep dorsal groove ; the margins are folded and lobed.

THE NEMERTIN1 173

Remarks upon the Class. — The Nemertine worms usually live
under stones, or amongst sea-weed, or in empty mollusc shells and
similar places ; some even burrow in the mud or sand, and a few
secrete a tube of mucous material to which foreign substances
adhere (e.g. Carinella linearis, C. rubicunda, Valencinia longirostris).
The majority occur in shallow water, down to about 100 fathoms ;
only a few have been obtained from a greater depth, viz. Pela-
gonemertes, Nectonemertes, Hyalonemertes, and Carinina grata, at 1340
fathoms. These pelagic species, as well as Cerebi'atulus, spp., and
Drepanophorus, are characteristically Arctic. Eupolia is tropical.
The non-marine forms are exclusively Metanemertines, some
occur in fresh water, viz. Tetrastemma, sp. (13, 40), and Sticho-
stemma (31); others live on land, viz. Geonemertes, of which five
species have been described from various islands. A few live in
association with other animals, arid these again are Metanemertines,
with the exception of Cephalothrix galatheae, which is endoparasitic
in the ovaries of Galathea strigosa (12) ; others are ectoparasitic (3),
or perhaps only commensals, viz. Eunemertes carcinophila, Tetra-
stemma, spp., on Ascidians ; Malacobdella, in lamellibranchs (24).
The Nemertines are generally cylindrical worms of consider-
able length, but of small diameter, exhibiting a great degree of
contractibility ; some indeed attain an enormous length, e.g.
Linens longissima reaches a length of 8 or even 27 metres.
On the other hand, a few species of Tetrastemma, Oerstedia, and
Ototyphlonemertes are quite small. Euborlasia is an exception to
the designation "long," as it is short and sausage-shape, like a
Holothurian or Echiurid. Drepanophorus is relatively broad and
flat as is Malacobdella. Pelagonemertes (Fig. XL) is quite leaf -like
(32). The colouring is often bright and of various tints; patterns
are rare, either in the form of longitudinal stripes (Micrura), or
combined with circular rings of lighter tone or different colour
(Carinella). As a rule, the body presents no definite external
regions, nor is it segmented ; the hinder end is, however, generally
narrower than the rest of the body, and more pointed than the
anterior end which is truncated. In some of the Heteronemer-
tines (Cerebratulus, Micrura) there is a distinct " tail," having the
same structure as the body wall, but without gonads, and carrying
the anus at its apex. Only in a few cases (Carinella, Eupolia) is the
head definitely marked off from the trunk by a furrow (Fig. XXV.).
The mouth in the anoplous forms is some little distance from
the anterior end of the body, and is situated behind the brain ;
but in the Metanemertines it shifts forwards so as to lie in
front of this organ, and comes to lie close to the rhynchostome —
in fact, in some species of Amphiporus, Malacobdella, and the Proso-
rhochmidae the two pores are coincident. The mouth leads into
a " foregut " or stomodaeum, which in the Anopla is a tube of

174

THE NEMERTINI

relatively short extent ; it has only a feebly developed muscular
coat, and differs histologically from the enteron, which is directly
continuous with it. In the Metanemertini, however, this foregut
is much longer and divisible into the following regions : — (1) A
narrow, buccal tube passing from the mouth as far as, or beyond
the brain ; (2) a dilated " stomach" ; and (3) a narrow " pylorus

N

Pelagonemertes rollestoni, Moseley, dorsal view (from Perrier, after Moseley). A, anus; C,
cerebral ganglion ; D, intestinal caecum ; G, rhynchocoel ; I, intestine ; m, longitudinal
muscles ; N, lateral nerve trunk ; 0, ovaries ; P, proboscis, partially everted ; t, circular
muscles ; V, lateral blood-vessel.

tube " ; both lined by gland cells (Fig. XII.). This last region opens
into the enteron on its dorsal surface, so that there is a longer or
shorter ventral " caecum " (m) differing in no way from the midgut
itself. This caecum may, like the latter, be produced on each side
into a series of diverticula. This caecum originally communicates
with the exterior by means of the blastopore ; when this closes, the
stomodaeum, having arisen some little way in front of it (Lebe-
dinsky), joins the enteron on its dorsal surface; whereas, in other

THE NEMERTINI

175

cases, the stomodaeum is formed in the blastoporal region.
The enteron is in Carinella a simple cylindrical tube, which be-
comes slightly constricted, at intervals, by the developing gonads ;

71 --

a---

FIG. XII.

Diagrammatic sagittal section of Amphiporus, to show the median, anterior, intestinal
diverticulum (m) of the Metanemertines. a, rhynchostome ; b, rhynchodaeum ; c, cavity of the
proboscis ; d, muscular wall of proboscis ; e, rhyuchocoel ; /, dorsal cerebral commissure ;
g, ventral cerebral commissure; h, mouth; i, buccal tube ; j, "stomach"; k, pylorus tube;
I, intestine ; m, anterior caecum ; s, muscular wall of rhynchocoel.

in Carinina and Cephalothrix these constrictions are more definite ;
while in the rest of the class longer or shorter pouches or
diverticula are formed, which in some cases may even branch;
they are separated from one another by dorso-ventral muscles
forming more or less complete septa. There thus comes about a
kind of metameric segmentation not only of the enteron itself but
also of other organs, such as the gonads, which alternate with

FIG. XIII.

MalctcoMella grossa O. F. Mullet (after von Kennel, Oudemans, and Burger), a, the
mouth (dorsally situated), which is common also to the proboscis ; b, the great "foregut"
or "stomach" ; c, the pylorus tube ; d, the intestine ; e, rhynchostome, opening into the roof
of the stomodaeum ; /, proboscis ; g, gonads ; h, sucker ; i, excretory pore ; j, dorsal blood-
vessel ; k, lateral blood-vessel. The figure on the left is seen from the ventral surface ; the
middle one from the dorsal ; it illustrates the vascular and the excretory systems — the latter
is indicated on the right side only, — and here a part of the lateral blood-vessel has been
omitted ; the left excretory duct and pore are shown.

these pouches. Only in Malacobdella is the intestine a simple tube,
unconstricted by the gonads, and taking an undulating course from
mouth to anus (Fig. XIII.). The anus is always small and terminal.

1 76 THE NEMERTIN1

The integument of Nemertines consists of an epidermis resting
upon a basement connective tissue, which is usually thin, but in
Heteronemertini acquires a great thickness, and is then usually
invaded by the outer longitudinal muscles. The epidermis con-
sists of filamentous ciliated cells and gland cells of different kinds,
of these the most peculiar are " grouped gland cells " (see Figs.
VII. and XIV.), which are absent in Metanemertini.

That characteristic Nemertine organ, the proboscis, occurs in
one of two conditions, as Johnston was the first to note ; it may
be unarmed, or it may be provided with calcareous stylets. In
the anoplous forms (viz. the Proto-, the Meso-, and Hetero-
nemertini) it is a cylindrical, muscular tube, closed at its hinder

1 FIG. XIV. 2

1, Epidermis of Drepanophorus crassus Quatrefages (from Perrier, after Burger). 6, basement
tissue ; e, epidermal filament cells ; si, goblet cells with mucous contents ; st, cells with
refringent, rod -like contents. 2, the integument of Eupolia delineata, D.Ch. (from Perrier, after
Burger). J), basement membrane ; c, cilia ; e, epidermal (filamentous) cells ; /, goblet cell ; g,
connective tissue forming the cutis (in most Heteronemertines this cutis is invaded by the
outer longitudinal muscles) ; j, interstitial nuclei ; fc, partitions between the groups of gland
cells ; I, subepidermal layer of longitudinal muscles ; m, subepidermal layer of circular muscles ;
p, packets of gland cells, sunk in the cutis ; r, radial muscle fibrils.

end but open anteriorly ; its wall becomes continuous with the
body wall at about the level of the brain. This precerebral
region is termed the " rhynchodaeum," and opens at the apex of
the head by a small round pore, the " rhynchostome." Behind the
brain the invaginated proboscis lies in a closed tubular cavity, the
" rhynchocoel," with muscular walls, to which it is attached, some-
where near the hinder end, by the retractor muscle (Fig. I. c, c'). A
transverse section of the proboscis shows the 'following layers of
tissue : — internally (at rest) it is lined by tall columnar and gland-
ular cells, similar to those of the epidermis, from which, indeed,
this epithelium is derived during embryogeny ; these columnar
cells are arranged in groups and clusters, forming wart-like papillae
of various shapes and character, diagnostic of species. In most
genera these cells contain " rods " similar to the " rhabdites " of

THE NEMERTINI

177

Turbellaria ; to these are added, in Cerebr. urticans, nematocysts
like those of Coelenterates, except that several are contained in
each cell. Below this is a basement membrane, then follows the
musculature, which in general repeats that of the body wall, only
reversed, being " dimyaric " in the Proto- and Meso-nemertini, and
" trimyaric " in the Heteronemertini. Outside, again, comes the
flat rhynchocoel epithelium. Behind this tubular, eversible region
the circular muscles cease ; but the longitudinal muscles are con-
tinued backwards to form a " retractor muscle." In Eupolia this

FIG. XV.

Proboscis of Metanemertine.
Longitudinal section in the
"middle" region in a state of
retraction (from Joubin). A, the
cavity of the anterior region,
capable of eversion ; U, cavity of
posterior, retractor region. The
cavity of the middle region is un-
lettered ; it consists of a dilated
"•reservoir" communicating by a
"duct" with the anterior region. J
The plane in which the nerve rings
lie is the " diaphragm." Ep, epi-
thelium of rhynchocoel ; gl, gland
cells, whose ducts pass to the
"acanthophore," which they prob-
ably secrete ; Mce, layer of circu-
lar muscles, which are external on
evagination ; Mel, layer of internal
circular muscles ; Mle, layer of .
longitudinal muscles, wttefHal on j/YvV-^
evagination ; Mli, internal longi-
tudinal muscles ; N, nerve layer in
proboscis ; it is continued down to
the diaphragm, when it forms two
rings round the "duct." P, the
epidermal papillae ; S, the median
(functional, or chief) stylet, sup-
ported on its acanthophore, which
is unlettered ; Sa, right and left
"acanthocysts" containing lateral,
reserve or accessory stylets.

.Ml?

retractor muscle is hollow, the narrow tubular cavity being con-
tinuous with the wider cavity of the proboscis proper ; there are
thus in this genus two tubular regions to be distinguished in the
proboscis — an anterior eversible region, and a posterior non-
eversible region. This leads on to the more complicated apparatus
of the Metanemertines (Fig. XV.). Here the two regions are quite
definite, and are separated by a third, middle region in which the
calcareous stylets are developed. The wall of this middle region
is much thickened, owing to the development of special muscles
and of gland cells ; the canal which puts the anterior and posterior
cavities into communication is differentiated into three parts : (1)

12

i;8 THE NEMERTINI

the posterior part is termed the " canal " ; this dilates to form (2)
a "reservoir" or bladder, which communicates with the anterior
chamber by means of (3) the "ductus ejaculatorius," which traverses
the " diaphragm " or anterior part of the middle region. On the
anterior face of this diaphragm are set the " stylets " ; these are
solid, calcareous spines (containing organic matter), generally
shaped like a tin-tack ; of these, one is median and fixed at
the bottom of a funnel-shaped depression, by a somewhat conical,
granular mass, formed by the secretion of gland cells in the
diaphragm ; this is the " basis " or " acanthophore." On each side
of this median stylet (Begriffstilet, of Burger) is a small sac contain-
ing two or more lateral stylets, differing from the median one in the
absence of the acanthophore, and somewhat also in size (Fig. XVI.).
In AmpliiporuSy alone, are there more than two
sacs of lateral or accessory stylets ; in this genus
five, or seven, or even twenty-two sacs may be
present. Each sac of lateral stylets opens into
the anterior proboscis cavity by a short duct.
According to Burger, each of these sacs is an
enormous cell, in which one or more calcareous
stylets arise in vacuoles — each commencing as a
small spicule and soon attaining its full size.
These cells (or sacs) may be termed "acantho-
cysts," and each is comparable to a "rhabdite
cell " or " sagittocyst," from which they may pos-
. sibly be descended. It is supposed that these

Stylets oi Amphi- » •• •

poms (from Joubin, lateral or reserve stylets are destined to take the
^ iateraim6sly- place of the median one when (and if) this be

let; B, a median
stylet.

This arrangement of stylets obtains in all the
armed Metanemertines with the solitary exception of Drepano-
phorus (Fig. XVIL). Here the " acanthophore " is a long, narrow,
curved plate bearing as many as twenty short, conical stylets
arranged in a row, so that the apparatus appears to be used
rather as a rasp than as a dart or spearhead. On each side
is a number of acanthocysts, each with several accessory stylets.

The length of the proboscis is of no systematic importance,
for in some of the longer forms, such as Carinella, Lineus, Eupolia,
Eunemertes, it is very short ; whereas, in other cases, either
longer or shorter worms like Cerebmtulus and Amphiporus, it may
be actually longer than the body. The exact use of this pro-

1 According to Montgomery (30), who follows Keferstein, they are complemental ;
he argues against the possibility of their transference and fixation in the funnel ;
his account of the structure of the sacs differs considerably from Burger's, for he
describes an epithelium round each sac, which is a pouching of the wall of the pro-
boscis cavity.

THE NEMERTINI 179

boscis of the Nemertines is uncertain. It appears probable that
a poisonous fluid is discharged into the wound made by > the
armed proboscis — a fluid secreted by the epithelium of the hinder
region of the proboscis. While in the Anopla the rods and
nematocysts possibly have some
stinging or numbing function.1

Eversion of the proboscis is
effected by the contraction of the
wall of the rhynchocoel, acting
upon the contained fluid.

The rhynchocoel, which is de-
veloped as a cleft in the meso-
blast that forms around the in-
vaginating proboscis, is a closed,2
cylindrical tube lying above the
intestine ; in Drepanopliorus, alone, FlG- XVIL

it o-ivpcj ri«P tn a «PriA« nf Inner The armature of the proboscis of

u g1 V 68 Ong, phorug crassus (after Burger). 1, the curved

naiTOW, non-muscular diverticula, »iedian aeanthopfcore, with several stylets

' ' fixed upon it. 2, a transverse section of it ;

right and lett, Which Correspond a, basis or acanthophore ; b, stylet. 3, one

in position with the intestinal °

diverticula (Fig. XXI. w). The wall of the rhynchocoel (or pro-
boscis sheath) consists usually of an internal coat of longitudinal
muscle, and an outer coat of circular muscles, some of which in
Carinella are continued round the intestine. It is lined by a flat
epithelium, which is replaced by goblet cells over the dorsal vessel,
where this passes along its floor. The rhynchocoelic fluid contains
flat, ellipsoid, amoeboid corpuscles, frequently coloured by red or
yellow granules, possibly haemoglobin ; as a rule, the cells are
larger than the blood corpuscles, but vary in shape and size in
different genera. It is noteworthy that even in a "resting con-
dition," an attraction sphere is readily visible in them.

This characteristic apparatus has no exact counterpart in the
Platyhelmia, although it resembles in its general anatomy and
mode of action each one of the four " proboscides " of Tetrarhynchus,
and still more, the complex rostellum of Drepanidotaenia. But
with these it can have no genetic relation ; the Nemertines have
probably been descended from some Turbellarian-like ancestor, and
among these the family Proboscidae appear to furnish a starting-

1 It is worth noting that M'Intosh doubts both the fact that poison is secreted,
and the fact that the organ is one of aggression. There are curiously few actual
observations on the eversion of the proboscis. The matter requires investigation, as
also does the mode of action of the muscles of the organ. C. B. Wilson gives an
account of the employment of the proboscis in burrowing and locomotion ; see
"Habits, etc., of Cerebratulus lactens " (in Q. J. M. Sci. xliii. 1900, p. 97), for many
interesting facts concerning the habits of this species.

2 Biirger speaks, with considerable hesitation, of communications with the vascular
system in Cerebratulus.

i8o THE NEMERTINI

point for this proboscis (see p. 17). Nevertheless, it is a very
long step from the one to the other, and no intermediate stages are
known ; for in the Proboscidae there is nothing comparable to a
rhynchocoel, which must have been developed pari passu with the
elongation of the eversible organ — as the only means of everting
the proboscis — probably in the same way in which it is developed
ontogenetically. Burger has suggested that it represents the
pharynx of the Turbellaria, and sees in those genera in which the
rhynchostome is coincident with the mouth the original condition.
But apart from the difficulty of comparing structurally the pro-
boscis with the tubular pharynx, it is extremely improbable that
the Metanemertini — in which alone this condition is realised —
should have retained a primitive condition in this respect, whilst
in the remainder of their anatomy they are so evidently much
less primitive than the Proto- or Meso-nemertini, in which there is
no sort of connection between the two organs.

The nervous system of the Nemertines (see 6, 16, 17) is primi-
tively in the form of a network, as in Turbellaria; but in the
lower orders this network retains a more superficial, and phylo-
genetically, more archaic position than in that Class ; for in the
Protonemertini it lies among the bases of the epidermal cells
(Carinina), as in the Coelentera (Fig. XVIII. 1, e) ; in Carinella and
Hubrechtia it sinks through the basement membrane so as to lie
immediately below it ; in the Mesonemertini this process continues,
so that in Carinoma the nerves lie outside the circular muscles, in
the region of the foregut, but come to occupy a deeper position,
viz. in the longitudinal coat, in the posterior region of the body —
a position which they occupy throughout the body in Cephalothrix
(Fig. XVIII. 2). Finally, in the Metanemertini the nervous
system has sunk into the parenchyma, and occupies the same
position as in the Turbellaria (Fig. XVIII. 3). The case of the
Heteronemertini must be considered apart, for although the nerve
cords lie between the muscular coats, this position is not so much
the result of sinking inwards, as of being thrust downwards by
the development of a new muscular layer outside the circular
coat (Fig. X.) ; indeed, with regard to the latter, the nerves
occupy the same position as in Carinella.

The nervous network, even in the lowest Nemertines, presents
^i differentiation into a central and peripheral system, though it
is impossible to draw a hard-and-fast line between them ; for
certain tracts have, as in the Turbellaria, become larger and more
definite than others, giving rise to longitudinal nerve stems ; but
of these only three are recognisable, namely, a pair of stout lateral
stems, and a smaller median dorsal nerve. These traverse the
whole length of the body, and are connected at each end by a trans-
verse, supra-enteric commissure or anastomosis. The elongated

THE NEMERTINI

181

ring, thus formed, consists of nerve fibres wrapped round by gang-
lion cells. As in the case of all the Coelomocoela, except Echino-

FIG. XVIII.

Portions of transverse sections to illustrate the position of the lateral nerve stem in relation
to the muscular coats (after Biirger, more or less altered). 1, Carinina, a Protonemertine; 2,
Cephalothrix, a Mesonemertine ; 3, Amphiporus, a Metanemertine. a, epidermis ; b, basement
tissue ; c, circular muscles ; d, longitudinal muscles ; e, lateral nerve stem ; /, peripheral nerve
sheet ; i, enteron ; j, dorsal nerve ; p, lateral blood-vessel ; s, proboscis sheath or wall of the
rhynchocoel ; the proboscis is omitted ; t, dorsal blood-vessel ; v, parenchyma ; w, rhynchocoel ;
y, gonad ; y1, position of genital pore.

derms, the anterior end of the system has come to be of greater
importance than the rest ; here each lateral stem thickens to form
a ganglion, to which is added a dorsal ganglion, closely connected

182

THE NEMERTINI

with it (Fig. XIX.). The two ganglia are developed from different
"rudiments," — the dorsal possibly represents the prostomial "cere-
bral ganglia " of the Annelids ; the ventral probably represents the
suboesophageal ganglion of an Annelid. But here in the Nemer-
tines there is no repetition of ganglia ; these two ganglia constitute

the " brain," and are so closely
united in the lower forms that
in Hubrechtia there is no ex-
ternal demarcation between
them. But usually they are
distinct as a dorsal and ventral
lobe of the brain. The dorsal
lobe is usually the larger, and
is connected with its fellow by
a delicate, supra - proboscidial
commissure; the ventral lobes
are connected by a broader
commissure below the proboscis
tube. The "cerebral organ"

Brain of Eupolia giardii, Hubr. (from Perrier, frequently becomes Very closely

associated with the hinder part
of the dorsal ganglion (Fig.
XIX. P), or a special ganglion
may separate from it, to be-
come connected with the organ (Fig. XX. L). The dorsal lobe
is essentially sensory ; the ventral motor.

The third longitudinal cord is thin, and arises from the supra-
proboscidial commissure; it always retains its superficial sub-
epidermic position, even when the rest of the system has sunk
into the parenchyma (Metanemertines). In all but these it gives
off a branch which passes below the circular muscles, and runs
back as a second dorsal nerve (see Figs. VIII., X. Ic). Hubrecht, its
discoverer, called it the " proboscidial-sheath nerve." l These three
longitudinal nerves — specialisations as they are of a primitive net-
work of cells and fibres — are connected by this network, or tunic,
in the Protonemertini and Heteronemertini, in some of which,
especially Hubrechtia, it attains a considerable thickness. Even in
Carinella this primitive nerve plexus exhibits a tendency to form
circular, commissural nerves, for the circular strands are more pro-
nounced than the rest. In the Metanemertines this nerve tunic has
become specialised, in connection no doubt with the sinking of the
whole system, for it is represented by a ladder-like series of ventral
commissures connecting the lateral stems (Fig. XX.), and by a series

1 For a suggestion as to the importance of the dorsal nerve, as well as of the
proboscis and its sheath of Nemertines, in the evolution of Vertebrata, see Hubrecht
(18).

FIG. XIX.

after Hubrecht). c, aperture of cerebral organ
cd, dorsal commissure ; cv, ventral commissure ;
L, lateral nerve trunk ; M, middle lobe of the
dorsal ganglion ; P, posterior lobe (cerebral
organ) ; S, dorsal ganglion.

THE NEMERTINI

183

of nerves, passing dorsally from the latter, which subdivide and
enter the muscular body wall. In the Mesonemertini nothing is
known of a nerve tunic or its representative. In Drepatwphorus
the lateral stems appear to lie nearer the ventral mid-line than
usual (Fig. XXI.) ; this is due rather to the great development of
the lateral margins of the body than to a real movement of the

Nervous system of Drepanophorus lankesteri, Hubr. (from Perrier, after Hubrecht). C,
dorsal ganglionic lobe ; fc, transverse commissures between the lateral stems ; L, hinder lobe of
brain or cerebral organ ; n, peripheral nerves ; o, aperture of cerebral organ ; ce, nerves to
stomodaeum ; s, sensory nerves to snout ; 2', lateral nerve trunk ; t, nerves to proboscis ; v,
transverse_commissures.

nerves, for they occupy the same position, relatively to the
rhynchocoel and midgut, as in other forms. On the other hand,
in Langia (Fig. XXII.), the upward growth of the lateral margins
has evidently carried the lateral nerves upward, for they lie on
the same horizontal plane as the rhynchocoel.

The nervous system of Heteronemertines is tinged by haemo-
globin ; the muscular tissue of Euborlasia is reddish, but whether
this is due to the same pigment is unknown.

1 84

THE NEMERTINI

The most interesting and characteristic sense organ is the
ciliated, neuro -glandular pit at the side of the head (see 5, 11).

FIG. XXI.

Transverse section of Drepanophorus albolineatiis, Biirg. (after Burger), to show the
apparent ventral shifting of the lateral nerve cord (e) due to the great development of the
intestinal caeca (i') and of the diverticula of the rhynchocoel (ir') ; i, intestine ; p, lateral
blood-vessel ; t, dorsal vessel ; w, rhynchocoel; y, gonad ; y" genital pore.

It presents various stages of elaboration, and is only absent in the
Mesonemertini, and in such exceptional genera as Malacobdella and

FIG. XXII.

Transverse (slightly oblique)
section of Lanqiaformosa, Hu-
brecht (after Burger), a, epi-
dermis ; b, longitudinal muscle
of cutis ; c, circular muscles ;
d, longitudinal muscles (inner
coat) ; e, lateral nerve cord ap-
parently shifted dorsal wards ;
i, intestine with caecum on left
side ; p, lateral blood - vessel,
here shifted ventrally ; w,
rhynchocoel ; x, dorso-ventral
muscles forming a septum be-
tween successive intestinal
caeca.

Pelagonemertes. This organ, which is no doubt phylogenetically
derived from the simple pit of some Turbellaria, becomes closely

FIG. XXIII.

Cerebral organ of Cerebratulus
in schematic, longitudinal sec-
tion (from Perrier, after Burger).
AI, ^2> nerve fibres in upper
and lower part of dorsal gang-
lion ; C, cerebral canal ; E, epi-
dermis ; Gl, Gl, glands open-
ing into the lateral canal (the
posterior bunch is probably re-
presented in Drepanophorus by
the " glandular canal ") ; N, ner-
vous tissue of the cerebral
organ ; OE, aperture of canal
into the posterior end of the
horizontal cephalic cleft.

O.E

connected with a special ganglion, or in Heteronemertines penetrates
the hinder part of the dorsal ganglion, of which it forms a definite

THE NEMERTINI

185

O.E

Gl

lobe ; hence the organ receives the name " cerebral organ." In its
simplest form, in the Protonemertini, it is a mere groove in the epi-
dermis not extending deeper than the basement membrane ; it is
lined by ciliated cells, and at the bottom are large gland cells ;
the organ is supplied by nerves from the brain. In Carinella
rabicunda and others the groove becomes an oblique canal, the
blind end of which is surrounded by a mass of ganglion cells, lying
outside the cutis. In the higher forms the canal penetrates deeper
into the body as far as the brain (Fig. XXIII. ). The gland cells and
the nerve tissue associate with it, increase in amount, and the canal
becomes differentiated into two regions — an extra - ganglionic
" lateral canal," and an intra-ganglionic " cerebral canal " (C), which
frequently terminates in an en-
larged sac. In Drepanopliorus the
cerebral canal is quite exceptional,
in that it bifurcates — one branch
terminating in a sac with sensory
epithelium (Fig. XXIV. (7), the
other being glandular (GT) ;
this, in D. crassus, extends back- c
wards beyond the brain as a free
tube. In several genera of this
order the cerebral organ lies in
front of the brain, e.g. Tetra-
stemma, sp. of Eunemertes and of
Ampliiporus ; in others it lies at
the side ; and in still others, be-
hind the brain — in which case it
attains a great size. In all cases
the organ is separate from the^
brain, from which it receives
nerves.

The lateral canal of the cere-
bral organ opens to the exterior
in relation to a furrow or groove

FIG. XXIV.

Cerebral organ of Drepanophoruscrassus (from
place Perrier, after Burger). Schematic horizontal

class. '

section ; A, hinder end of dorsal ganglion ; B,
ProtO- nerve to cerebral organ ; C, cerebral sac—
the dilated outer limb of the original canal
— embedded in a mass of nerve tissue ; E,

on the head, which is somewhat
variously disposed in tl
It is simplest in the
nemertini, being a shallow,
vertical furrow — the " cephalic
furrow," — marking the head

.__ <~7 . Utl'VUUa \J\JL U1U1I Ul UllU Ul^ctll , L/JJ/J oj-n--* U^AV, VM.

from the trunk (Fig. XXV.), and lateral canal of the organ; P, pigment; R,

in most of these the cerebral L

organ is little else than a deeper part of the furrowT, but in C. ruU-
cunda opens independently of the latter. In Metanemertini and
in the genus Eupolia this furrow becomes crescentic with its con-

1 86

THE NEMERTINI

vexity backwards, and the dorsal and ventral horns nearly meeting
their fellows of the other side (XXV. C) ; the bottom of this furrow
is subdivided into pits by tranverse ridges ; the " lateral canal "
opens at the hindmost part of the curve.

But in the Heteronemertini (Fig. XXV. C, D, E) this vertical

FIG. XXV.

Heads of Nemertines (after Burger). A, ventral, and B, lateral views of Carinella; C, ventral
view of Drepanophorus ; D, ventral view of Valencinla,; E, lateral view of Cerebratulus ; a,
mouth ; 5, rhynchostome ; c, groove in side of head, vertical or horizontal, in connection with
the cerebral organ.

furrow is replaced by a horizontal " cleft " — deeper or shallower,
longer or shorter — especially well developed in Cerebratulus (Fig. I.
g), where it starts at the apex of the snout on each side, and is so
deep as to touch the brain ; at its hindmost point the " lateral
canal " opens. The haemoglobin ous nerve tissue is thus brought
close to the surrounding medium, and on this account Hubrecht

suggested that the cere-

J

organ is respiratory
in function. Probably
both the " cephalic fur-
row " (or cleft) and the
cerebral organ together
are derived from the
" ciliated pit " of Turbel-
laria.

Eyes are present in
many Nemertines, and
have the structure of
Polyclad eyes. An oto-

Brain of OtotypMorwiMrte* (from Joubin, after Biirger). . npmira nnlv ;„

dc, dorsal commissure ; vc, ventral commissure ; dg, dorsal LJ bl OOOUI S only
|obe or ganglion ; vg, ventral ; ot, otocyst ; sst, lateral nerve Qtotyphlonemertes, resting

against the ventral gan-
glion, and resembles the molluscan otocyst (Fig. XXVI.).

At the anterior extremity of the snout, above the rhynchostome,

FIG. XXVI.

THE NEMERTINI 187

is a " frontal organ " — a single retractile papilla in Metanemertini
and in Eupolia ; or a group of three papillae in Cerebratulus and
Micrura. In all cases the papilla consists of ciliated cells, between
which there open the ducts of the "frontal gland" (cf. Acoela).

Finally, in Carinella, there is present a " lateral organ " in the
form of a retractile papilla, close to the excretory pore on each
side, and recalling that of Capitellids.

The vascular system (35) consists primarily of a pair of
lateral vessels (in Proto- and Meso-nemertini) extending along the
entire length of the worm, lying in the parenchyma, just above the
level of the lateral nerve. Anteriorly these vessels pass through
the nerve ring (Figs. II. p., XXVII. c) and unite at the tip of the
snout — and in Carinella are also joined at the level of the brain —
at the posterior end they are united by a supra-enteric commissure.
The anterior part of the lateral vessel in Carinella is dilated (b), and
a series of short vessels are given off to a longitudinal, lateral,
proboscis-sheath vessel. In the Metanemertini (Fig. XXVII. 2, m)
a median dorsal vessel arises from this intra-neural commissure
and passes backwards above the gut, to fall into the supra-anal
commissure. For a part of its course the dorsal vessel runs just
within the rhynchocoel, the epithelial lining of which is here
modified. Moreover, a series of transverse vessels unite these three
longitudinal ones, but no branches are given off by the system —
no blindly ending vessels — except in Malacobdella (Fig. XIII.).

The Heteronemertini (and Hubrechtia) combine the three
longitudinal and transverse vessels of the Metanemertini with the
anterior dilated regions of the Protonemertini, from which several
pharyngeal vessels arise (Figs. III., XXVII. 3, 4).

This system of vessels is entirely closed, and contains a
colourless fluid in which there float nucleated cells of fixed outline,
usually oval and flattened. In the majority these corpuscles
are colourless, but in a few (Amphiporus) they are red or yellow ;
in others yellowish with a green tinge ; and in Eiiborlasia they are
yellow, spotted with red, so that the blood appears red. The
yellow tint is due to haemoglobin.

Details are wanting as to the way in which this "blood" or
" haemal fluid " (?) circulates in those forms in which only the
lateral vessels are present. According to Burger, the blood, in
Metanemertines, flows out of the dorsal, through the circular
vessels, into the lateral ones, returning to the dorsal vessel at each
end of the worm. But this is very unsatisfactory and uncertain.
As to the morphological nature of this vascular system, it seems
certain that it is not "coelom" as we understand the term
in the case of Annelids, etc.; it has none of the characters which
we associate with this cavity. It arises in the young worm
during the formation of the " imaginal discs," as a space or spaces

i88

THE NEMERTINI

in the mesoblastic jelly ("mesenchyme"). Although Salensky
terms this space " coelom," it is more probable that, if there is a
coelom at this stage, it is represented by the narrow cleft between
the somatic and splanchnic mesoblast, such as exists in some cases

FIG. XXVII.

Plan of the vascular and excretory systems (from Perrier, after Oudemans). 1, Carinella ;
2, Drepanophorus ; 3, 4, Eupolia; 5, Valenti.nia, (mid body), c, preoral anastomosis of lateral
vessel (the intraneural anastomosis is not represented in 1) ; d (in 4), supra-anal anastomosis,
(in 5) dorsal vessel ; b, parastomodseal sinus ; g, vessel of proboscis sheath ; fc, lateral vessel
of proboscis sheath ; I, lateral blood-vessel (in Fig. 3 the index line is carried to the dorsal
vessel, and in 5 to the proboscidial- vessel) ; TO, dorsal vessel ; n, nephridium ; p, p', p", ne-
phridial pore or pores ; s, preoral dilatation ; s', parastomodaeal sinus ; t, transverse vessels,
from dorsal to lateral vessels ; v, lateral vessel.

according to Lebedinsky (26). The spaces run together to form
a large sinus, which becomes divided into a right and left channel
by the developing proboscis ; these channels become the lateral
vessels, and decrease in relative size. Probably this vascular

THE NEMERTINI 189

system is represented in the Turbellaria by the intercellular
lacunae of the parenchyma.

It is by no means certain what function the system performs
in Nemertines. It is so far removed from the surface of the
body and the surrounding medium, except in those cases in which
the cerebral organ impinges upon the lateral vessel, that respira-
tion seems out of the question. Even in the head, where the
vessels are dilated into capacious sinuses, these are below the
musculature of the body wall, except in the region of the mouth
(Cerebratulus, etc.), where they come up to the basement tissue;
but in this case it has no respiratory pigment as far as we
know. Even if there is a certain amount of gaseous interchange
in this region it seems more probable that the " vascular system "
in the Nemertines serves rather as a " nutritive " (lymphatic)
system, for the vessels are placed close to the wall of the enteron,
and dissolved food material can readily diffuse into them. Further,
the excretory system is always in contact with the lateral vessel,
from which the excretory products are, no doubt, removed. It is
probable that the distension of the dilated vessels at the anterior
end serve also to give firmness to the head during burrowing.

The excretory system, which was originally observed by Max
Schultze and figured by him,1 is always paired, and usually of
limited extent, being confined to the region of the foregut (Fig.
XXVII. n)t extending backwards in short species at the side of
the enteron ; and, in Linens lacteus, forwards beyond the mouth.2
The system (see 35) consists essentially of a
longitudinal, horizontal canal, which opens ex-
ternally below the lateral nerve, through a short,
transverse duct (p). This is usually single, but
in Amphiporus, Valendnia longirostris, and Eupolia
curta (Fig. XXVII. 3) there is a number of ducts,
one behind the other, each opening by a pore.
The canal which is lined by a ciliated epithelium
runs alongside the lateral vessel, and gives origin
to a number of branches, generally of the same
diameter as itself. These are short in Proto-
nemertini, or longer in other cases, and may even
be branched in Metanemertini, where they are
wrapped round the blood-vessel. Each branch FlG- xxvin.
terminates in a multicellular dilatation, contain- A " flaaf™er «el1 " Ot
ing a "flame" (Fig. XXVIIL). These "end
bulbs " push the wall of the blood-vessel inwards ; but there is no

1 Max Schultze, Beit. z. Naturgesch. d. Turbellarien, 1851.

2 Montgomery has recently described a series of nephridia extending throughout
the length of the body in Stichostemma, each with from one to five ducts, — Zool.
Jahrb. (Anat.\ x. 1897, p. 265.

190 THE NEMERTINI

communication between the two systems, as Oudemann believed.
There is never any anastomosis between the branches, nor any
communication between the right and left organ.

The restriction of the system to a limited region of the body,
and the absence of a network, such as occurs in Platyhelmia, is
no doubt connected with the existence in the Nemertines of a
" vascular or lymphatic system," which brings to the excretory
system the material for its activity. There can be no doubt but
that the system, though differing in details and in plan from that
of Platyhelmia, is descended from it, and belongs to the same
category as the " head kidney " of Annelids, which it resembles in
its limitation to the stomodseal region of the gut.

The reproductive organs contrast as much as is possible with
those of the Platyhelmia, for in the Nemertines there is nothing
resembling the copulatory organs of the former phylum; there are
no glands set aside for the formation of egg-cases, no differentia-
tion of the ovary into " germarium " and " vitellarium." We have
to do with mere sacs (Fig. XVIII. y) containing the products of
the proliferation and modification of the epithelial cells which line
these sacs, and in due time, when these products are ripe, these
sacs push their way outwards through the body wall to form genital
ducts, which will ultimately open to the exterior. In a few
Metanemertini ovaries and testes occur together and ripen simul-
taneously (Prosadenoporus, two sp., Tetrastemma, two sp., Geonemertes
spp., and Prosorochmus), while " Borlasia " Kefersteini, Stichostemma
Eilhardi are protandric hermaphrodites.

The genital sacs are coextensive with the midgut, and as a rule
are repeated in a regular series, one sac between every two suc-
cessive enteric pouches. This regularity is, however, concealed in
Amphiporus, in that only some of them ripen at a time, so that in
A. pulcher there are only five, at irregular distances. In Carinella
and Malacobdella, in which the intestinal pouches are not found, the
genital sacs are closely packed together. The pores, as a rule,
form a simple linear series above the lateral nerve, but in the two
genera just named, and in G. australiensis they form a broad band
extending nearly to the mid-dorsal line. In Drepanophorus, owing
probably to the great development of the dorsal organs of the
body, e.g. the rhynchocoel, the genital organs, like the lateral
vessels, seem to be ventral (Fig. XXI.).

The genital sacs arise either (a) simultaneously with the de-
veloping genital cells (as Carinella, Malacobdella, Prosadenoporus, and
others) from a group of parenchymal cells which gradually become
differentiated into a central mass of " germ cells " and a peripheral
membrane of flat wall cells ; or (b) the sacs develop first, and then
from some of the epithelial cells the germ cells arise (as in Cere-
bratulus, Drepanophorus) by the accumulation of yolk spherules

THE NEMERTINI 191

around the nucleus, etc. ; in these cases the sac seems empty when
the worm is mature, for the ripe egg cells push the wall outwards,
and come to lie in independent follicles in the parenchyma (Fig.

XXL).

It has been pointed out by Hatschek and by Mayer that each genital
sac presents all the usual relations and characters of a coelom, and these
sacs are the only organs which can be regarded as such. The excretory
system, at one time identified as coelom, is now known to be epiblastic
in origin (as in other worms) and to appear after the mesoblast has
formed, nor has the vascular system any claim, from developmental con-
siderations, to the title. The fact that the genital sacs appear late, and in
the simplest forms arise contemporaneously with the genital cells (as they
do also in Platyhelmia), cannot be regarded as a solid argument against
the view. It is, indeed, rather remarkable that in both these groups,
the lowest of the Coelomocoela, the coelom is an inconspicuous cavity. We
are so generally led to think that the coelom is a constant accompani-
ment of the mesoblast, that we forget that possibly the chamber is later,
phylogenetically, than its wall. Here, in Nemertines, when the gonads
are mature, there is a remarkable resemblance, in their repetition, in
their relations to other structures, to the coelomic segments of Annelids.

The matter of " metamerism " is closely bound up with that of the
coelom. In the Annelids it is the mesoblast and its cavity that first
present repetition during embryogeny ; the internal segmentation
which exists in the Nemertines — the repetition of the gonads, of the in-
testinal pouches, of the blood-vessels and nerves, and in Drepanopliorus of
the rhynchocoelic diverticula — is essentially the same as in Annelids.
But in the Nemertines it is never accompanied by external marks of
metamerism, with the interesting and important exception of the genital
pores. There is no constriction of the body, no interruption in the
musculature of the body wall.

It is a remarkable fact that the nephridia are not metamerically re-
peated ; it is true that in Ampliiporus and in Valencinia the nephridial
ducts and pores are numerous, but this repetition is quite irregular, asym-
metrical, and not coincident with that of other organs. This may perhaps
be explained by regarding the nephridia of Nemertines as homologous
with the "head kidneys" of Annelids, which appear early in ontogeny
and differ in structure from the metameric nephridia. We must believe
that these have not yet made their appearance, phylogenetically, in the
Nemertines. This fact is strongly opposed to Perrier's view that this
group is a degenerate descendant from Annelids, for we should then
expect to find traces of nephridia in the " trunk," where the gonads, etc.,
are situated. The more usual view, that they are descended from the
Turbellarian stock, and have in some respects, and in some degree,
followed the Annelid line of evolution, is the more plausible view. The
condition of the nervous system fits in with this view — specialisation of two
lateral tracts, which in the higher Annelids are destined to come together
and even to fuse on the ventral surface.

The statement of Lebedinsky, too, that the mesoblast arises from two

1 92 THE NEMERTINI

pairs of cells, each of which gives rise to a " mesoblastic streak," destined
to split into a somatic and splanchnic coat, with a small coelom between,
is a further support for this view.

Reproduction and Regeneration. — The best known ontogeny is
that of the Pilidium (see above) of the Heteronemertines, and of
the larva of Desor, which occurs in the life-history of Linens
gesserensis (1, 19).

Internal fertilisation has been definitely observed by Dendy
in Geon. australiensis (10). It occurs also in the viviparous forms,
such as Prosorhocmus daparedii, etc.

The Metanemertini have been most studied ; they undergo no
metamorphosis, their development is direct, and has recently been
studied in several genera by Lebedinsky (26). Nothing is known
about the history in Protonemertini, nor Eupolia, and very little
in Mesonemertines, but so far as we know it is direct (9).
But in addition to this sexual generation, a kind of asexual
reproduction exists in the larger species, which, as is well known,
break in pieces when attacked, or possibly automatically. Dalyell
was the first to recognise that Linens was able to regenerate a
new posterior end. M'Intosh found that the hinder pieces could
reproduce a new "head" and proboscis as well as a new tail.
Brown (4) has recently made a study of the same species. Biirger
has investigated the regeneration of the proboscis in Drepanophorus,
and Benham (2) has traced some of the histological conditions of
a " fragmenting " Carinella, and has suggested that fragmentation
may take place, apparently, without any stimulus other than the
ripening of the gonads, which are present in this case, only in the
" segmented " hinder region of the worm. Hubrecht saw in this
power of fragmentation a precursor of metamerism, and there can
be little doubt but that this power of separating into pieces, even
automatically, is of considerable value to the worm, for the part,
overburdened with genital products, must be less able to help in
the movement of the worm, and thus hinder its escape from
enemies, or search for food. If each piece had the power of repro-
ducing a head, after expulsion of the genital cells, there would be
a close analogy with the asexual reproduction of Syllids and other
Annelids.

LITERATURE OF THE NEMERTINI.

1. Barrois. (Embryology of Lineus.) Ann. Sci. Nat. (6), vi. 1877.

2. Beriham. (Fission.) Quart. Journ. Micr. Sci. xxxix. 1896, p. 19.

3. Braun. (Parasitic Forms.) Centralbl. Bakt. Parasitenk. iii. 1888, pp. 16,

56.

4. Brown. (Fragmentation.) Proc. Roy. Soc. Ixi. 1897, p. 28.

5. Burger. (Anatomy and Histology.) Zeit. f. Wiss. Zool. 1. 1890, p. 1.

LITERATURE OF THE NEMERTINI 193

6. Burger. (Histology of Nervous System.) Mitth. Zool. St. Neapel, x. 1891,

p. 206.

7. Ibid. (Excretory System.) Zeit. f. Wiss. Zool. liii. 1892, p. 322.

8. Ibid. (Systematic.) Verh. Deutsch. Zool. Gesellsch. 1893.

9. Ibid. Monograph, 22. Fauna v. Flora d. Golfe d. Neapel, 1895.

10. Dendy. (Geonemertes.) Proc. Roy. Soc. Victoria, iv. p. 85 ; v. p. 127,

1891-92.

11. Dewoletzky. (Cerebral Organ.) Arb. Zool. Inst. Wien. vii. 1886, p. 233.

12. Dieck. (Cephalothrix galatheae.) Jen. Zeit. (2), viii. 1874, p. 500.

13. Duplessis. (Fluviatile forms.) Rev. Suisse Zool. i. 1893, p. 329.

14. Frey and Leuckart. (Anatomy of Linens.) Beit. z. Kenntniss wirbelloser

Thiere, 1847, pp. 71.

15. Graff, v. (Geon. chalicophora.) Morph. Jahrb. v. 1879, p. 430.

16. Holler. (Nervous System. ) Arb. Zool. Inst. Wien. viii. 1889, p. 276.

17. Hubrecht. (Nervous System.) Quart. Journ. Mic. Sci. xx. 1880, pp. 274,

431.

18. Ibid. (On the Ancestral Form of the Chordata.) Quart. Journ. Mic. Sci.

xxiii. 1883, p. 349.

19. Ibid. (Embryology.) Zool. Anzeig. viii. 1885, p. 470.

20. Ibid. Challenger Reports, xix. 1887.

21. Joubin. Arch. Zool. Exper. (2), viii. 1890, p. 461.

22. Ibid. "Nemertines" in Blanchard's Traite de Zoologie, 1894.

23. Keferstein. Zeit. f. Wiss. Zool. xii. 1862, p. 51.

24. Kennel, v. (Malacobdella.) Arb. Zool. Inst. Wurzb. iv. 1878, p. 305.

25. Krolm. (Pilidium.) Miiller's Arch. Anat. Physiol. 1858, p. 289.

26. LebedinsJcy. (Embryology.) Arch. Mikr. Anat. xlix. 1897, p. 503.

27. M'Intosh. Monog. Brit. Annelids, Part I. Nemerteans. Ray Society,

1873.

28. Mctschniko/. (Development.) Mem. Acad. Sci. Petersbourg (7), xiv. 1869.

29. Ibid. Zeit. f. Wiss. Zool. xxxvii. 1882, p. 286.

30. Montgomery. (Stylet Apparatus.) Zool. Anzeig. xvii. 1894, pp. 298, 301.

31. Ibid. (Stichostemma.) Zeit. f. Wiss. Zool. lix. 1895, p. 83.
31«. Ibid. (Connective Tissue.) Zool. Jahrb. (Anat.), x. 1897, p. 1.

32. Moselcy. (Pelagonemertes.) Ann. Mag. Nat. Hist. (4), xv. 1875, p. 165 ;

and xvi. p. 377.

33. MUller, Joh. (Pilidium.) Arch. Anat. Physiol. 1847, p. 157.

34. Oersted. Entwtirf e. system. Eintheil. u. spec. Beschreib. d. Platt-

wiirmer, etc., 1844, p. 76.

35. Oudemans. (Excretory and Circulatory Systems.) Quart. Journ. Mic.

Sci. xxv. (Supplement), 1885, p. 1.

36. Quatrefages. Ann. Sci. Nat. (3), vi. 1846, p. 173.

37. Salensky. (Development.) Arch. Biol. v. 1884, p. 517.

38. Ibid. Zeit. f. Wiss. Zool. xliii. 1886, p. 481.

39. Schultze. Zeit. f. Wiss. Zool. iv. 1853, p. 178.

40. Silliman. (Fluviatile forms.) Zeit. f. Wiss. Zool. xli. 1885, p. 70.

41. Verrill. Trans. Connecticut Acad. New Haven, viii. 1892, p. 382.

42. Willemoes-Suhm, v. (Tetra. agricola.) Ann. Mag. Nat. Hist. (4), xiii.

1874, p. 409.

ADDENDA AND COERIGENDA TO THE
NEMEETINI

THE following notes have kindly been furnished by Mr. E. C. Punnett of
St. Andrews. In a rapidly growing study like that of important groups
of marine organisms, it is impossible for an author who has removed to
so distant a colony as New Zealand, where Dr.* Benham now is, to give
the final touches to his work, if it is to be up to date. The editor has
gladly availed himself of Mr. Punnett's knowledge of the Nemertin.es to
complete this chapter. E. E. L.

9th July 1901.

Within the last few years considerable attention has been paid to this group
of worms, resulting in the discovery of certain points in the anatomy of the
group, and also in the addition of a number of new forms to those already known.
This has led to the establishment of the following new genera : — CARINELLIDAE,
Callinera, Bergendal ; Carinesta, Punnett ; (FAM. ?) Gononemertes, Bergendal.
EUNEMERTIDAE, Paranemertes, Coe ; EUPOLIIDAE, Parapolia, Coe ; Zygeupolia,
Thompson ; Oxypolia, Punnett ; LIXEIDAE, Micrella, Punnett ; Lineopsis, Staub.
Of these the two genera Zygeupolia and Micrella are of especial interest on
account of certain primitive features which they exhibit, and which render them
of importance in the question of the derivation of the two great Heteronemertean
families. Among the more interesting points which have been recently noted
in the anatomy of the group may be mentioned the following : —

Montgomery (vi) has carefully described and classified the various connective
tissues in the group. In the same paper he has come to the conclusion that a body
cavity is sometimes represented by spaces between the alimentary canal and inner
longitudinal muscle layer of the Heteronemerteans. Montgomery has also pointed
out that whilst the posterior nerve commissure is almost always above the anus
in the Metanemerteans, in. the genus Proneurotcs it is sub-anal. It has also
been shown (vii) that this commissure in the genus Eupolia may be either above
or below the anus, or may be altogether absent. The excretory system has been
worked out in numerous forms ((iii), (iv), (vii), (viii), (ix), (xi)), and in one
species of Eupolia it has been shown to possess both ducts opening to the exterior,
and also ducts opening into the alimentary canal (vii). It may be further noted
that the caudal appendage of the Lineidae, upon which much stress is laid in
classification, shows differences of structure which may ultimately necessitate a

NEMERTINI— ADDENDA AND CORRIGENDA 195

revision of the family in which it is found (ix). Contributions to the develop-
ment have been made by Coe (ii) and Wilson (xii).

(i) Bergendal. (Callinera and Gononemertes.) Zool. Anz. 1900.
(ii) Coe. Early Development. Zool. Jahr. 12 Bd. 1899.
(iii) Coe. (Anatomy and Parapolia.) Trans. Connect. Acad. 1895
(iv) Coe. (Paranemertes.} Proc. Wash. Acad. 1901.
(v) Montgomery. (Nervous System.) Journ. Morph. vol. xiii. 1897.
(vi) Ibid. (Connect. Tiss.) Zool. Jahr. Abh. Anat. 10 Bd. 1897.
(vii) Punnett. (Anatomy.) Quart. Journ. Mic. Sc. vol. xliv. 1900.
(viii) Ibid. (Carinesta.) Willey's Zool. Results, pt. v. 1900.
(ix) Ibid. (Micrella and Oxypolia.) Quart. Journ. Mic. Sc. vol. xliv. 1901.
(x) Staub. (Lineopsis.) Semon's Forschungsreisen, 5 Bd. 1900.
(xi) Thompson. (Zygeupolia.) Zool. Anz. 1900.
(xii) Wilson. (Habits and Development.) Quart. Journ. Mic. Sc. vol. xliii. 1900.

P. 163 (a). Mention should be made of the oesophageal (or buccal) nerves which
occur throughout the group.

(j3). In spite of what has been often written to the contrary it is exceed-
ingly probable that in most cases, if not all, the blood-vessels are
destitute of muscle fibrils ; and that the blood is kept in circulation
by the waves of contraction passing over the body wall.

(7). The transverse connections are always dorsal to the gut.

(r5). The gonads may open on the ventral surface within the area between
the lateral nerve cords.

P. 168 (a). Hubrecht states that in Linens gesserensis the excretory system arises
as an out-pouching from the endodermal portion of the alimentary
canal.

P. 173 (a). Drepanophorus is characteristically tropical and sub-tropical. Cere-
bratulus is just as much tropical and temperate as arctic.

P. 173 (a). The "tail" differs in structure. The alimentary canal does not
necessarily extend into it.

P. 176 (a). The "retractor" end of the proboscis is not always attached.

P. 178 (a). The largest number of stylet sacs yet met with in an Amphiporus is
twelve.

P. 182 (a). The median dorsal nerve cord in the Heteronemerteans is situated
below the cutis and outer longitudinal muscle layer.

P. 187 (a). "Head gland" is the term more frequently used here ( = Germ.
Kopf druse],

P. 189. The great majority of the species of Ampliiporus possess only one pair
of excretory ducts.

INDEX

To names of Classes, Orders, Sub-Orders, Families, and Genera ; to technical
terms ; and to the names of Authors discussed in the text.

Abothrium, 116
Acanthobothrium, 119
Acanthocotyle, 50
acanthocyst, 178
acanthophore, 178
acauthozooid, 139
Acanthozoon, 33
accessory sucker, 121, 127,
133

— female organs, 23, 38
Acelis, 31

Aceros, 31

acetabulate sucker, 80
acetabulum, 115, 121, 127,

132

Acmostoma, 10, 14
Acmostominae, diagnosis,

10
Acoela, 7, 8, 12, 14

— diagnosis and classifica-
tion, 10

Acoelomi, 2
Acotylea, diagnosis, 31
Acrorhynchus, 10
Actinodactyletta, 43, 45
A ctinodactylellidae, diagno-
sis, 43

Actinodactylus, 43
adenocheiri, 29
adenodactyli, 29
Alaurina, 9

albuminiparous glands, 28
Alloiocoela, 6, 8, 12, 14

— diagnosis and classifica-
tion, 10

alloiogenesis, 76
Alloioplana, 31
Allostoma, 10
Allostominae, diagnosis, 10
alterations of generations
in Trematodes, 76

— in Cestodes, 142
Amabilia, 131, 135

Amblyceraeus, 31
Amblyplana, 25
Amicrurae, 172
amnion, 166
Amphibdella, 53
Amphichoerus, 10
Amphicotyle, 116, 118
Amphilina, 97, 99, 102
Amphilinacea, 1, 93
— - diagnosis and classifica-
tion, 97

Amphilinidae, diagnosis, 97
Amphiporidae, 159

— diagnosis, 171
Amphiporus, 171, 173, 178,

185, 187, 189, 190, 195
Amphiptyches, 97
Amphistomidae, 47

— diagnosis, 64
Amphistomum, 65, 77, 82,

90

Amphitretus, 116
AmpJwterocotyle, 119
Amphoteromorphus, 119
A nchistrocephcdus, 116
Andrya, 131
anenterous Avorms, 2
Anocelis, 24
Anonymidae, 7

— diagnosis, 31
Anonymus, 31, 33, 36
Anopla, 161, 168, 169,

173

— diagnosis and classifica-
tion, 170

Anoplocephala, 131, 134

(footnote)
A noplocephalinae, diagno -

sis, 131

Anoplodium, 10
Anthobothrium, 119
Anthocephalum, 119
Anthocephalus, 128

Anthocotyle, 51
aatrum, 21
Apathy, 158
Aphanostoma, 10
Aphanostomidae, 7

— diagnosis, 10
Aplocoela, 160, 170
Apoblema, 67
apodous worms, 2
Aprocta, 160
Archigetes, 97, 99, 102
Archiplanoidea, 33 (foot-
note)

Aristotle, 94
Artiocotylus, 25
Artioposthia, 25, 28
asexual reproduction, 23,

30
Aspidobothridae, 47

— diagnosis, 59
Aspidobothrii, 49, 57
Aspidocotyle, 60 (footnote),

65

Aspidocotylea, 1, 47, 49,
78, 83, 85, 87, 91

— anatomy, 60-62

— diagnosis and classifica-
tion, 57

Aspidogaster, 49, 60, 75,

84

Atomiosoma, 97
atrium genitale, 21
Audry, 96
Automolos, 10
Autoscolecida, 160
axial cell (Dicyemid) 150

— syncytium, 15
Axine, 52, 86

Baer, v., 8, 48, 69, 88
Balfour, 40, 76
Barrois, 161
batteries, 33

198

INDEX

Bdellura, 24

caecum, ventral, 174

Cestoidea monozoa, 1, 93,

Bdelluridae, 7, 26, 28

calcareous corpuscle, 107

145

— diagnosis, 24

Calceostoma, 53, 86

— anatomy, 98-103

Beneden, E. v., 96, 136,

Calicotyle, 50, 80, 83, 86

— diagnosis and classifica-

151

(footnote)

tion, 97

— P. J., 48, 49, 89, 94, 95,

Callinera, 194

Cestoplana, 31

96, 119, 144

Calliobothrium, 119, 123

Cestoplanidae, 7

Beneden, v., 161

calotte (Dicyemid), 149

— diagnosis, 31

Benham, 128 (footnote),

Calyptrobothrium, 119

Chapmannia, 129

192-

Carinella, 168, 170, 173,

Cherry, 74 (footnote)

Bergendal, 29, 36, 194

175, 178, 180, 182, 185,

Chichkoff, 28

Bertia, 131

187, 190, 192

chlorophyll (Turbellaria)

Biehringer, 74, 82

Carindlidae, 159, 194

Choeradoplana, 25

Bilharzia, 67, 78, 88

— diagnosis, 170

ciliated embryo, 72

Bipaliidae, 7

Carinesta, 194

- pit, 16

— diagnosis, 25

Carinina, 170, 173, 175,

cirrus, 85

Bipalium, 25, 26

180

— pouch, 111

birth-pore, 74, 86, 110,

Carinoma, 170, 180

Cladocoelium, 65

115

Carlisle, 48, 88

Claparede, 36

bladder- worm, 94, 95, 140

Carus, 2, 48, 76

Claus, 76, 144

Blanchard, 43, 88, 95, 96,

Caryophyllacea, 1, 93

Cobbold, 48

101, 160

— diagnosis, 97

Coe, 194, 195

Blanchardella, 117

Oaryophyllaeidae, 97

Coelata, 8

Blochmann, 82, 83, 96, 105,

Caryophyllaeus, 97, 101,

coelom, 191

107

102, 145

Coelomati, 2

Blumenbach, 145

Castrada, 9

Goeloplana, 33 (footnote)

Bohmig, 9, 14

caudal disc, 79

coelum in Platyhelmia, 3

Bojanus, 48, 74, 88

— vesicle, 97, 101, 140,

Coenomorphus, 125

Bonnet, 96

145

coenurus, 95, 129, 141, 142

Borlase, 159

cephajic fissure or cleft,

colony, Cestode, 144

Borlasia, 190

186

Conoceros, 31

Bosc, 9, 159

— furrow, 185

Conocyema, 148

Bothridium, 116

Cephalogonimus, 67

contractile sac (Temno-

bothridiura, 115, 120

Cephalothricidae, 159

cephala), 45

Bothriocephalidae, 93

— diagnosis, 170

Convoluta, 10, 15

— diagnosis, 116

Cephalothrix, 170, 173, 175,

copulatory pore, 86, 118

Bothriocephalus, 94, 96, 116,

180

Corallobothrium, 128

117, 122

cephalotroch larva, 40

Cotugnia, 128

— anatomy of, 103-111

Ce ratobothrium, 119

Cotylea, diagnosis, 31

— life-history of, 111

cercaria, 48, 74

Cotylogaster, 60

Bothriomonidae, 93

cercariaea, 75, 76

cotylophore, 79

— diagnosis, 116

Cercyra, 24

Cotyloplana, 25, 26

Bothrioplana, 10, 12, 17,

cerebral organ, 163, 182,

Cotyloplanidae, 7

20, 26

184

— diagnosis, 25

Bothrioplanidae, 6

Cerebratulus, 172, 173, 179

Craspedella, 43

— diagnosis, 10

(footnote), 178, 186, 187,

Crossobothrium, 119

Bothriotaenia, 11 6, 11 7, 118

195

Crossodera, 67

bothrium, 105, 115, 122

— anatomy of, 162

Cryptocoela, 8, 31

Brachycoelium, 67

Cerfoutaine, 80

Cryptocoelides, 31, 36

Brachylaimus, 67

Cestoda polyzoa, 103

Cryptocoelis, 31

Braun, Max, 48, 82, 156

Cestodaria, 97 -

Ctenophora, 3, 33, 35, 40

Brie, Jehan de, 47

Cestodes digeneses, 103

Ctenoplana, 33 (footnote)

Brown, 69 (footnote), 192

— monogeneses, 97

Ctenotaenia, 131

buccal nerves, 195

Cestoidea, 1, 6

Cuenot, 70

— sucker, 79

— diagnosis and classifica-

cuticle (Cestode), 105

Bucephalus, 69

tion, 93

— (Trematode), 80

Biirger, 160, 161, 168, 178,

Cestoidea merozoa, 1, 93,

Cuvier, 7, 160

180, 187, 192

145

Gyathoceplialus, 117, 118

Burmeister, 49, 144

— anatomy, 103-111

Cydatella, 48

bursa copulatrix, 23

— classification, 116

Cyclobothrium, 51

Byrsophlebs, 9

— diagnosis, 115

Cydoporus, 31, 35

INDEX 199

Cylindrophorus, 119

dimyaric, 169

Ehrenberg, 7, 8, 15, 89,

Cylindrostama, 10, 14

Dinobothrium, 119, 122

160

Cylin drostominae, 1 0

Diphyllidea, 1, 93, 115,

embryophore, 113, 114

cystic worms, 95

145

Knantia, 31, 33

Cystica, 94

— diagnosis and classifica-

Enantiidae, 7

cysticercoid, 139

tion, 123

— diagnosis, 31

cysticercus, 94, 95, 140

Diphyllobothrium, 116

Encotyllabe, 50

Cystoidea, 128

Diplectamim, 53

endoparasite, 78

Cystotaenia, 129

Diplobothrium (Trematode),

Enopla, 161, 168, 169

Cystotaenia, 129

52

— diagnosis and classifica-

cystozooid, 139

- (Cestode), 119, 122

tion, 170

Diplocotyle, 116, 118

Enterostoma, 10

Dactylifera, 1, 43

Diplodiscus, 65

Entozoa, 2

Dactylocotyle, 51, 90

Diplogonoporus, 116

Ephedrocephalus, 119, 123

Dactylogyrus, 53

Diplopharyngeatidae, 7

Epibdella, 50, 83, 85

Daly ell, 9, 192

— diagnosis, 31

epidermis, of Cestoidea,

Darwin, 9, 25

Diplopharynx, 31

107

Davainea, 128, 135

Diplostomum, 69

— of Temnocephala, 45

Davies, 160

Diplozoon, 50, 55, 86

— of Trematoda, 82

Delage, Yves, 21

diporpa, 55

— of Turbellaria, 12

Delle Chiaje, 161

Dipylidium, 128, 135, 138

Erdl, 151

Dendrocoela, 8, 160

Discocephalum, 119

Erpocotyle, 52

Dendrocoehtm, 24, 65

Discocoelis, 31, 36

Euborlasia, 172, 173, 183,

Dendy, 25, 26, 160, 161,

— development of, 38

187

192

Distoma, 66

Eunemertes, 170, 173, 178,

Derostoma, 10, 14

Distomea, 49, 62

185

Desor's larva, 161, 192

Distomidae, 47

Eunemertidae, 159, 194

development, Distomum, 72

— diagnosis, 65

— diagnosis, 170

— Bothriocephalus, 111

Distomum, 65, 78, 84, 85,

Euplanaria, 24

— Polyclads, 38

86, 88

Eupolia, 172, 177, 185,

— Taenia, 135

— life-history of, 72

187, 189, 192, 194

— Trematodes, 76

Disymphytobothrium, 116

Eupoliidae, 159, 194

— Triclads, 29

dithridium, 131

— diagnosis, 172

Dewoletzky, 161

Dolichoplana, 25

Eurylepta, 31, 34

diaphragm, 178

Drepanidotaenia, 129, 132,

Euryleptidae, 7, 33

Dibothridae, 116

134 (footnote)

— diagnosis, 31

Dibothridiata, 1, 93, 115,

Drepanophorns, 171, 173,

Euvorticinae, 10

117, 137, 145

178, 179, 183, 185, 190,

excretory system, in Ces-

— diagnosis and classifica-

195

toidea, 108

tion, 116

Dreparnaud, 8, 23

— in Eupolia, 194

Dibotliriorhyncha, 125

Dubois, 96, 145

— in Platyhelmia, 3

Dicestoda, 116 ,^^J^

Duges, 8, 15, 161

— in Polycladida, 35

Diclidophora, Sl/wP*^-

Dujardin, 55, 95

— in Rhabdocoelida, 19

Dicotyhis, 24, 1§//

Duplessis, 12, 160

— in Temnocephaloidea,

Dicranotaenia, 129

Duthiersia, 116, 118

45

Dicrocoelium, 67

— in Trematoda, 84

Dicyema, 148

Echeneibothrium, 119, 122

— in Tricladida, 26

Dicyemennea, 148

Echinella, 50

— of Caryophyllaeus, 102

Dicyemida, diagnosis and

Echinobothridae, 93

eyes, in Polyclads, 35

classification, 148

— diagnosis, 123

— in Triclads, 26

Didymozoon, 70

Echinobothrium, 123

Didymozoonidae, 47

Echinococcifer, 130

Faber, 65

— diagnosis, 70

echinococcus, 2, 94, 131,

Fabricius, 8, 12

Dieck, 161

142

Faraday, 9, 23

Diesing, 48, 95

Echinocotyle, 128

Fasciola, 7, 65, 66, 160

Digenea, 62, 75

Echinocotylidae, 93

Fecampia, 10, 14

digenetic Trematodes, 49

— diagnosis, 128, 132

Ferussac, 25

digonoporous, 21

Echinostoma, 67, 82

Filippi, 74

Dimyaria, 159, 169

ectoparasite, 78

flame - cell, 3, 89, 1 63,

— diagnosis and classifica-

egg- balls, 74

189

tion, 170

— duct, 37

Flat -worms, 2

2OO

INDEX

Floriceps, 128

Gunda, 24, 26, 28, 38

host, intermediate, 73

foramina secundaria, 109

^ynaecophoral canal, 67

Hubrecht, 160, 161, 168,

Fovia, 24

Gynaecophorus, 67

192

fragmentation, 192

Gyrator, 10

Hubrechtia, 170, 180, 182,

Fraipont, 89, 96

Gyrocotylacea, 1, 93

187

Francotte, 28

— diagnosis and classifica-

Hubrechtiidae, 159

Frey, 160

tion, 97

— diagnosis, 170

frontal organ, 187

Gyrocotyle, 97, 99, 100, 101,

Hycdonemertes, 171, 173

— (Acoela), 17

102

hydatid, 94, 144

— hooks, 123

Gyrocotylidae, 97

Hymenolepinae, 128

Gyrodactylidae, 52

Hymenolepis, 129, 135

Gabucinus, 47

Gyrodactylus, 53, 85, 152

hypoblastic syncytium, 17

Gaffron, 89

hypodermic impregnation,

Gamble, 8

Haberlandt, 15

36 (footnote)

Gamobothridae, 93, 122

Haeckel, 2, 160

ffyporhynchus, 10, 17

— diagnosis, 119

Haller, 161

Gasterostomidae, 47

Hallez, 25, 29

Ichthyotaenia, 109, 128,

— diagnosis, 69

Haplodiscus, 10, 15

132, 135

Gasterostomum, 69, 82, 83

Haswell, 21 (footnote), 44

Ichthyotaeniidae, 93

Qastrocotyle, 52

Hatschek, 160

— diagnosis, 128

Gastrodiscus, 65, 79

"head gland," 195

ideal Platyhelminth an-

Gastrothylax, 65

head-stalk, 125

cestor, 3

Geddes, 15, 21

Heckert, 74

Idiogenes, 128, 134

Gegenbaur, 2

Hectocotyle, 49

Ijima, 9, 29, 86

Gemma, 65

Helminths, 49

imaginal discs, 166, 187

generative organs, in Ces-

Jfemistomum, 69

individuality of Cestode,

toidea, 110, 122, 134

hermaphrodite Nemertiues,

144

— in Polycladida, 35

190

infusoriform embryo, 151

— in Khabdocoela, 21

Heterobothrium, 51

iiifusorigen, 152

— in Trematoda, 85

Heterocotylea, 1, 47, 91, 99

internal vas deferens, 86

— in Tricladida, 28

— diagnosis and classifica-

Intestina, 2

genito-intestinal canal, 86,

tion, 50

intestine of Polyclads, 33

88

— reproduction in, 55

— of Rhabdocoels, 17

Geobia, 25

Heterocyemida, diagnosis ; — of Trematodes, 83

Geonemertes, 161, 171, 173,

and classification, 148 ' — of Triclads, 26

190, 192

heterogamy, 76 | Intoshia, 153, 155

Geoplana, 25, 26

Heteronemerteans, 194

investing membrane, 80, 82

Geoplanidae, 7

Heteronemertiui, 159

— diagnosis, 25

— diagnosis and classifica-

Jensen, 8

germarium, 22

tion, 171

Jensenia, 10

germ-balls, 74

Heteroplana, 33 (footnote)

Johnson, J. K, 9, 21, 23

— cells (Dicyeinid), 151

hexacanth embryo, 111

Johnston, 159, 160

— disc, 166

(footnote), 136

Joubin, 160

germogeu (Dicyemid), 152

ffexacotyle, 52, 86

Julin, 154

germ-vitellarium, 22, 28

historical account of Ces-

Gesner, 65

toidea, 94

Keferstein, 160

Giard, 157

— of Distomum, 88

Kerbert, 82

gid (in sheep), 130

— of Trematoda, 47

King, 72

Goeze, 94, 96

— of Turbellaria, 7

King's yellow-worm, 74

Gononemertes, 194

historical survey of Nemer-

Koellikeria, 69

Gcrrdius, 66, 160

tines, 159

Kohler, 96

Goto, 62, 80, 85, 86, 88

Holorhynchocoela, 170

Kolliker, 49, 151

Gotte, 144

Holostomidae, 47, 75, 79,

Kowalevski, 82

Graff, v., 8, 12, 17, 33

83, 85

Krabbe, 95

Graffito, 10, 14

— diagnosis, 69

Krabbea, 116

Grassi, 95 (footnote), 96,

Holostomum, 69

Krohn, 165

101, 139 (footnote)

Homalogaster, 65, 79

Kiichenmeister, 95, 96

Griesbach, 107

booklets on sucker, 80

Grobben, 76

Hoplonemertini, 161, 170

Lamarck, 2

Grube, 2

host, 78, 95

Landois, 96

Guerne, 160

— final, 74

land-planarians, 25

INDEX

201

Lang, 3, 8, 12, 26, 32, 33,

Macrostomidae, diagnosis, 9

Mionelmiutlies, 157

36, 40, 89, 96, 102, 145,

Malacobdella, 171, 173,

miracidium, 72

160

175, 184, 187, 190

Moniez, 96, 145

Langia, 172, 183

Malacobdellidae, 175

Moniezia, 131, 132, 135

Laiikester, 2

— diagnosis, 171

Monobothrium, 97

lateral organ, 187

Malacobothrii, 49, 62

monocercus, 142

— sucker, 79

Malacocotylea, 1, 47, 70,

Monocotyle, 50, 79, 80

— swelling (Polystomum,

87, 89, 91

Monocotylidae, 47

86

— development in, 72-77

— diagnosis, 50

Latocestus, 31

— diagnosis and classifica-

Monogenea, 50

Laurer, 48, 89

tion, 62

monogeiietic Trematodes, 49

Laurer's canal, 38, 62, 88

Malpighi, 96

monogonoporous, 21

La Valette St. George, 48

Maricola, 26

Monoophorum, 10

Lebedinsky, 161, 188, 192

— diagnosis and classifica-

Monoporus, 10

Lecanicephalum, 119

tion, 24

Monorygma,' 119

Leeuwenhoek, 47, 65

Marsipocephalus, 119

Monostomidae, 47, 79

Leimacopsidae, 7

Meckel, 88

— diagnosis, 69

— diagnosis, 25

Mecynostoma, 9, 16

Monostomum, 54, 69, 82,

Leimacopsis, 25

Mehlis, 48, 89

88

Leptoplana, 31

Merozoa (Cestoidea), 1, 93,

Monotidae, 6, 16

Leptoplanidae, 7, 37

97

— diagnosis, 10

— diagnosis, 31

— diagnosis and classifica-

Monotus, 10

Leuckart, F. S., 2, 12, 48,

tion, 114

Mouozoa, Cestoidea, 1, 93,

66, 72, 76, 95, 96, 107,

Mertens, 8, 36

97

114, 144, 160

mesenchyma, 14

Montgomery, 178 (foot-

Leuckartia, 117

Mesocestoides, 131,134, 135

note), 189 (footnote), 194

Leuckartiidae, 93

Mesocestoididae, 93

Monticelli, 48, 49, 60 (foot-

— diagnosis, 117

— diagnosis, 131

note), 96, 101 (footnote),

Leucochloridium, 76

Mesogonimus, 67

123

life - history of Bothrio-

Mesonemertini, 159

Moseley, 8, 9, 25

cephalus, 111

— diagnosis and classifica-

Moses, 94

— Carophyllaeiis, 102

tion, 170

Moulinie, 48

— Dipylidium, 138

Mesostoma, 9, 19, 23

Muller, Job., 96, 161, 165

— Taenia, 135

Mesostomidae, 6

— 0. F., 7, 8, 9, 48, 66,

— Tetraphyllidea, 123

— diagnosis, 9

74, 89, 159, 160

— Trematodes, 72, 76

Mesozoa, 3, 157, 158

Muller's larva, 40

Ligula, 82, 107, 114, 116,

metacestode, 114, 138

multiloculate sucker, 79

118, 145

metagenesis, 76

Myzostoma, 48

lime -corpuscles, 107

metamerism, 191, 192

Lineidae, 159, 194

Metanemertcans, 194

neck of tapeworm, 104

— diagnosis, 172

Metauemertini, 159

Nectonemertes, 171, 173

Lineopsis, 194

— diagnosis and classifica-

Nectonemertidae, 159

Linens, 161, 172, 173, 178,

tion, 170

— diagnosis, 171

189, 192

metapolar cells, 150

Nematobothrium, 70

Linnaeus, 2, 65, 96, 145

metastatic, 76

nematocyst, 12, 33, 162,

Linstow, v., 48, 55, 95

Metschnikoff, 29, 54, 152,

177

(footnote)

154, 161

Nematodemus, 25

Liuton, 95

Micrella, 194

nematogen, 151

liver-fluke, 47, 65

Microcotyle, 52

Nemertea, 170

loculi in sucker, 79, 120

Microcotylidae, 47, 79

Nemertes, 7, 170

Lonnberg, 99

— diagnosis, 52

Nemertina, 170

Looss, 55, 62, 76, 88, 101

Microcyema, 148

Nemertinea, 170

(footnote)

Micropharynx, 24

Nemertini, classification,

Liihe, 96

Microplana, 25

159, 168, 170

Microstoma, 9, 12

— anatomy, 162

M'Intosh, 160, 161, 179

Microstomidae, 6, 17, 23

Nemertopsis, 170

(footnote), 192

— diagnosis, 9

nervous system of Caryo-

Macraspis, 60

Micrura, 172, 173, 187

pliyllaeus, 102

Macrorhynchus, 10, 21

Micrurae, 172

— Cestodes, 110

Macrostoma, 9

Minot, 1 (footnote)

— Polyclads, 35

Macrostomidae, 6, 12

Miocoela, 160

— Rliabdocoels, 15

202

INDEX

nervous system of Trema-
todes, 84

— Triclads, 26
Neumann, 131
neuro-glandular pit, 184
Niemec, 96, 110
Nitzsch, 48, 74, 89
Nitzschia, 50, 83
Nordmann, v., 48
Notocotyle, 69

Octobothrium, 50
Octocotylinae, 50
Oersted, 8, 160, 161
Oerstedia, 171, 173
cesophageal nerves, 195
Ogmogaster, 69
Oligocdis, 24
Oligodadus, 31, 35
Omalostoma, 9
Onchobothrium, 119
Onchocotyle, 52, 79
onchosphere, 111 (footnote),

113, 137

ootype, 37, 55, 86, 99
Ophryocotyle, 128
Opisthotrema, 69, 88
Opistoma, 10
oral sucker, 79
Orthonectida, 153
Orthotropous calotte, 150
Orygmatobothrium, 119
Othelosoma, 25
Otobothrium, 125
otocyst, 16
Otomesostoma, 9
Otoplana, 24
Otoplanidae, 7

— diagnosis, 24
Ototyphlonemertes, 170, 186
Ototyphlonemertidae, 159,

173

— diagnosis, 170
Otto, 89
Oudemans, 161

ovary in Gyrodactylus, 53

— in Turbellaria, 21
Oxypolia, 194

paedogenesis, 76
Pagenstecher, 48, 157
Palaeonemertini, 161, 170
Pallas, 65, 94, 96
Paludicola, 24
papillae, adhesive, 79
Paranemertes, 194
paranucleus (Dicyemid),

152
parapolar cells (Dicyemid),

150
Parapolia, 194

Parasitica, 10

parasitic Nemertines, 173

— Turbellarians, 14

— worms, 49
parasitism, 77, 89
Parataenia, 133 (footnote)
parenchyma in Cestodes,

107

— in Polyclads, 33

— in Khabdocoels, 14

— in Trematodes, 83

— in Triclads, 26

— digestive, in Acoela,
15

Parona, 48
parthenogenesis, 76
Pectobothrii, 49, 50
Pelagonemertes, 171, 173,

184
Pelagonemertidae, 159

— diagnosis, 171
Pelichnibothrium, 119
Pelmatoplana, 25
Pdtidocotyle, 119
Pelyonchobothrium, 119
Peminatodiscus, 158
penis, 36, 85
Perocephalus, 25
Perrier, 101, 144, 145
Perugia, 48
Phagocata, 24
pharynx bulbosus, 17

— plicatus, 18
pharynx, in Polyclads, 33

— in Khabdocoels, 17

— in Trematodes, 83
- in Triclads, 18, 26
Philippi, 44
Phoeuicurus, 48
Phoreiobothrium, 119
Phyllacanthinae, 119
phyllidium, 115, 120, 127
Phyllobothrinae, 119
Phyllobothrium, 119, 121,

122

Phyllonella, 50
Phyllorhyncha, 125
pilidium, 161, 163
Pintner, 96, 101 (footnote),

108, 115, 121, 127, 132
Placocephalus, 25, 26
Plagioplana, 31
Plagiostoma, 10, 12, 14
Plagiostomidae, 6, 17

— diagnosis, 10
Plagiostominae, 10
Plagiotaenia, 131
plagiotropous calotte, 150
Planaria, 7, 21, 24, 25,

28, 30, 66, 160
Planariidae, 7

Planariidae, diagnosis, 24
Planknoplana, 3.1
Planocera, 31, 37, 38
Planoceridae, 7

— diagnosis, 31
plasmatic canal, Sommer's,

108 (footnote)
plasinodial tubes, 155
Platyelmia, 2
Platyelminthes, 2
Platyhelmia, 2

— characters of, 3
Plathelminthes, 1 (footnote)
Platner, 96

Platodes, 2

Platyaspis, 60

Platybothrium, 119, 122

Platydemus, 25

Platyhelmiuth, ideal ances-
tral, 3

Plectanocotyle, 52

plerocestoid, 114

Podocotyle, 67

Poirier, 96

polar cap, 149

Poliopsis, 172

Polycelis, 24, 28

polycercus, 142

Polychaerus, 10, 23 (foot-
note)

Polyclada, 8

Polycladida, 1, 7, 12,
90

— anatomy, 31-38

— development, 38

— diagnosis and classifica-
tion, 31

Polycladus, 25
Polycotyle, 69
Polypocephalus, 133 (foot-
note)

Polyporus, 31
Polypostia, 31, 36
Polypostiidae, 7

— diagnosis, 31
Polystomea, 49, 50
Polystomidae, 47, 80

— diagnosis, 50
Polystominae, 52
Polystomum, 47, 52, 55, 78,

83, 86
Proboscidae, 6, 17

— diagnosis, 9
proboscis, 162, 176, 178,

195

— sheath, 179

— Turbellariurn, 17

— Tetrarhynchus, 127, 133

— use of, 179
Procerotidae, 7

— diagnosis, 24

INDEX

20'

Proctucha, 160

Redi, 65, 95, 96

Schizonemertini, 161, 171

proglottid, 103

redia, 74

Schizoprora, 10

proglottidisation, 1 1 8

regeneration, 192

Schizorhynchus, 10

Promesostoma, 9

reproduction of Caryophyl-

Schmidt, 0., 8, 12, 17, 22

pronephridiostome, 3

laeus, 102

Schneider, 2, 82

Proneurotes, 171, 194

— Cestodes, 111, 135

Schnltze, Max, 14,160, 161,

propolar cells, 150

— Heterocotylea, 55

189

Proporidae, 7

— Malacocotylea, 72, 76

Schulze, F. E., 9, 96

— diagnosis, 10

— Polyclads, 38

Schultzia, 10

Proporus, 10, 15

— Rhabdocoels, 23

Schwarze, 76

Prorhynckidae, 6, 19

— Triclads, 29

Sciadocephalus, 128 (foot-

— diagnosis, 9

reservoir (in proboscis), 178

note)

Prorhynchocoela, diagnosis

residual nucleus (Dicy-

scolex, 103

and classification, 170

emid), 152

Scolex polymorphus, 108,

Prorhynchus, 9, 14, 21

retractor, 195

123

Prosadenoporus, 171, 190

— muscle, 177

self- fertilisation, 55, 62, 86

proscolex, 111 (footnote),

Retzins, 66

Semonia, 31

137

rliabdites, 7, 12, 14, 26, 33,

Semper, 160

Prosorhocmidae, 159

45, 162, 176

sheep-rot, 65, 78

— diagnosis, 171

Rhabdocoela, 6, 8, 12, 17,

shell -gland, 37

Prosorhocmus, 171, 190,

19, 91

Siebold, v., 29, 48, 86, 88,

192

— diagnosis and classifica-

89, 94, 95, 96, 144, 160

Prostheceraeus, 31

tion, 9

Silliman, 161

Prosthecobothrium, 119

Rhabdocoelida, 1, 6, 46

six-hooked embryo, 111

Prosthecocotyle, 119

— anatomy of, 12-23

skeleton of sucker, 80

Prosthiostomidae, 7, 33

— diagnosis and classifica-

Solenopharyngidae, 6

— diagnosis, 31

tion, 9

— diagnosis, 10

Prosthiostamum, 31, 34

— reproduction of, 23

Solenopharynx, 10*

Prostomum, 10

Rhin ebothrium, 119

Solenophoridae, 93

Protonemertini, 159

rhombogen, 151

— diagnosis, 116

— diagnosis and classifica-

Rhombozoa, 148

Solenophorus, 116

tion, 170

RhopalophoruSi 67, 82

Sommer, 67, 96

Provortex, 10

Rhopalura, 153

Sonsino, 48, 67

Proxenetes, 9, 14

Rhyn chobothriitm, 125

Spencer, 99, 101

Pseudoceridae, 7

rhynchocoel, 162, 176, 179

Sphyranura, 52

— diagnosis, 31

Rhynchocoela, 160, 170

spines, chitinous, 32, 33,

Pseudoceros, 31

— classification, 159

80

Pseudocotyle, 50

rhynchodaeum, 176

Spongiobothriuin, 119

Pseudophyllidea, 1, 93,

Rhynchodemidae, 7

sporocyst (Distomum), 74

145

— diagnosis and classifica-

— (Orthonectid), 155

— diagnosis and classifica-

tion, 25

staggers in sheep, 95, 130

tion, 116

Rhynchodemus, 25, 28

staphylocYstis, 142

psendorhabdite, 12

rhynchostome, 162, 176

Staub, 194

pseudoscolex, 134

rod cells, 13, 26, 33, 176

Steenstrup, 142

Pseudorhynchus, 9, 17

— tracts, 26, 45

Stenostoma, 9, 12, 19

Pteronella, 50

Romberg, 65

Stichocotyle, 60 (footnote)

Pterosoma, 171

Rosenhof, 47

Stichostemma, 171, 173, 189

Ptychobothrium, 116, 118

rosette organ, 101

(footnote), 190

Ptychophysa, 131

rostellum, 118, 122, 133

Stieda, 48, 88

pulsatellae, 21

Rovelli, 96

Stiles, 95

pylorus tube, 174

Rudolphi, 48, 49, 66, 89,

Stilesia, 131

pyriform apparatus, 136

95

Stimpson, 160

Ruysch, 65

stomach, 34, 174

stomodaeum 173

Qnatrefages, 8, 12, 160,

sa.dttocyst, 12, 33

Stossich, 48

.

Salensky, 188

strobila, 103

Salinella, 158

strobilation, 145

Raillet, 67, 95

Schauinsland, 48, 74, 96,

stylets, 176, 178, 195

Ramdohr, 84, 88, 89

111, 136

Stylochoplana, 31, 33, 36

receptaculum seminis, 62

Schistocephalus, 65, 109,

Stylochus, 31, 36, 40

— vitelli, 62, 88

114, 116, 118

Stylostmmim, 31, 36

204

INDEX

subcuticula of Trematoda,

Tetraphyllidea, diagnosis

Udonella, 50, 86

82

and classification, 118

Uljanin, 8

— of Cestoidea, 105

Tetrarhyncha, 1, 93, 108,

urn (Dicyemid), 152

sucker, accessory, 118, 121

115, 133, 145

urocystis, 142

— of Cest. merozoa, 105,

— anatomy, 125-128

Urogonimus, 67

115, 121, 122, 127, 132

— diagnosis and classifica-

Uteriporus, 24, 28

— of Cest. monozoa, 99

tion, 125

uterus in Cestoidea, 99

— of Temnocephaloidea, 45 Tetrarhynchidae, 93

— in Trematoda, 86

— of Trematoda, 79, 89 — diagnosis and classifica-

— in Triclads, 28

Swammerdam, 47, 48, 74

tiou, 125

symbiotic algae, 15

Tetrarhynchus, 95 (foot-

vagina in Heterocotylea, 86

Syncoelidium, 24

note), 125

— in Cestoidea, 89

syncytial hypoblast, 15, 17

Tetrastemma, 161, 171, 173,

Valencinia, 172, 173, 189,

syncytium, axial, 15

185, 190

191

Syndesmis, 10, 14

Tetrastemmatidae, 159

Vallisia, 51

Syndesmobothrium, 125

— - diagnosis, 171

valvate sucker, 80

Thomas, 48, 73

Vejdovsky, 3, 9, 20

Taenia, 94, 96, 107, 108,

Thompson, 194

Vermes, 2

129, 132, 135

Thysanoceijhalum, 119, 122,

vermes cucurbitini, 65

— life-history of, 136, 140

134

vermiform embryo, 151

Taeniarhynchus, 129

Thysanoplana, 31, 34

verruciform cells, 150

Taeniidae, 93, 108

Thysanosoma, 48, 131

vers cavitaires, 8

— diagnosis and classifica-

Thysanozoon, 31, 34, 36

— parenchymateux, 8

tion, 128

Tomiosoma, 103

Villot, 89, 96, 139

Taeniinae, 129

Tower, 96, 110

vitellarium, 22

tape-worm, 94, 103

Trematoda, 1, 6, 49, 145

viviparous Nemertines, 192

Taschenberg, 48, 78

— anatomy, 77-81

Voeltzkow, 62

Temnocepkala, 43, 89, 90

— diagnosis and classifica-

Vogt, 2

TemnocepJialidae, 43

tion, 47

Vortex, 10, 15

Temuocephaloidea, 1, 6

Treptoplax, 158

Vorticeros, 10

— anatomy, 43-46

Triaenophoridae, 93

Vorticidae, 6

— diagnosis and classifica- ! — diagnosis and classifica-

— diagnosis, 10

tion, 43
Terricola, 26

tion, 117
Triaenophorus, 95 (foot-

Wagener, 48, 53, 69, 73.

A r r\£* QQ im 1 A Q.

— diagnosis and classifica-
tion, 24
Tetrabothridae, 93, 118

note), 107, 117, 118, 145
Trichoplax, 157
Triclada, 8

yo, yo, yy. lui, i*±o
Wagneria, 97
Weber, Max, 44

— diagnosis and classifica-
tion, 119
Tetrabothridiata, 1, 93,

Tricladida, 1, 7, 12, 18, 90
— anatomy, 25-29
— development, 29

Warner, 96
Wheeler, 26, 152 (footnote)
Whitman, 36 (footnote),

115, 122
— diagnosis and classifica-
tion, 118
Tetrabothrinae, 119

— diagnosis and classifica-
tion, 24
Trigonoporus, 31, 38
Trimyaria, 159, 169

Willemoes-Suhm, 48
Willey, 33 (footnote)
Wilson, 179 (footnote), 195

ITT • VJ. Q(\

Tetrabothriorhynchus, 1 25

— diagnosis and classifica-

vvrignt, ou

Tetrabothrium, 119, 121
Tetracampos, 125

tion, 171
trimyaric, 169

yolk envelope, 72, 111, 136
Yunnict 31 35

Tetracotyle, 69

Tristomidae, 47

Tetracotylea, 1, 93, 116, 145

— diagnosis, 50

Zeder, 49, 66, 95

— anatomy, 131-135

Tristomum, 50, 83

Zeller, 48, 55, 82

— development, 135-142

Trypanorhyncha, 125

Zernecke, 96, 105

— diagnosis and classifica-

trypauorhynchus, 127

Ziegler, 82

tion, 128

Turbellaria, 1, 3

zooids, 23

Tetracotylus, 1 28

— classification, 6

Zschokke, 96

Tetraonchus, 53

— diagnosis, 7

Zygeupolia, 194

Tetraphyllidea, 1, 93, 108,

Tylocephalum, 119

Zijgobothrium, 119, 122

119-123, 133, 145

Tyson, 96

Zygonemertes, 171

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