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Marine Biological Laboratory Library

Woods Hole, Mass.

Dl

Presented by

In Memory of

Dr. Herbert W. Rand

1872 - I960

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3E

INTERNATIONAL SERIES OF MONOGRAPHS ON
PURE AND APPLIED BIOLOGY

Division: ZOOLOGY
General Editor: G. A. Kerkut

Volume 11

LEECHES (HIRUDINEA)

Their Structure, Physiology, Ecology
and Embryology

OTHER TITLES IN THE SERIES ON PURE AND
APPLIED BIOLOGY

ZOOLOGY DIVISION

Vol. 1 Raven — An Outline of Developmental Physiology

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Vol. 8 George — The Brain as a Computer

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Vol. 10 Raven — Oogenesis

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Vol. 1 Pitt-Rivers and Tata — The Thyroid Hormones

Vol. 2 Bush — The Chromatography of Steroids

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Vol. 1 BoR — Grasses of Burma, Ceylon, India and Pakistan

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MODERN TRENDS
IN PHYSIOLOGICAL SCIENCES DIVISION

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Vol. 1 1 Gross — Oncogenic Viruses

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Vol. 15 Rivera — Cilia, Ciliated Epithelium and Ciliary Activity

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Vol. 2 SiEGEL — The Plant Cell Wall

Vol. 3 Mayer and Poljakoff-Mayber — The Germination of Seeds

LEECHES (HIRUDINEA)^^;

Their Structure, Physiology,
Ecology and Embryology

by

K. H. MANN

DEPARTMENT OF ZOOLOGY

THE UNIVERSITY

READING

With an appettdix on the Systematics

of Marine Leeches

by Prof. E. W. Knight-Jones

PERGAMON PRESS

NEW YORK • OXFORD • LONDON • PARIS
1962

PERGAMON PRESS INC.

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Copyright © 1962
Pergamon Press Ltd.

Library of Congress Card Number 61-17953

Set in Imprint ll-on-12 pt. and printed in Great Britain by
THE BAY TREE PRESS, STEVENAGE, HERTS.

TO MY PARENTS

"Among the numerous tribes of lower animals distributed throughout
the universe, none has attracted equal notice perhaps as the Leech, and
that from the periods of the most remote antiquity. Its form, its motions,
its habits, are well adapted to excite the curiosity of the illiterate beholder,
and, above all, its utility in alleviating the afflictions of mankind have
gained a distinction for it which is denied to all the rest.

Though widely known of old, in general, the detailed investigation of
the history of the Leech has been reserved for the latest era of scientific
observers, and the most advanced state of science.

Doubtless the noted peculiarities of the Medicinal I^eech led to the
study of others, whether from the motives of mere curiosity or from the
hopes of finding them endowed with similar properties. Such expecta-
tions, however, have been disappointed; for among a genus, abounding
suflSciently in the variety of its species, I believe that no one is yet dis-
covered which can be so satisfactorily employed in relieving human
distress.

It is true that in this country there are leeches that will suck the blood,
and eat the flesh of animals ; and that in some distant regions others prove
a kind of pest to man, but none seem as yet habituated to the same office
wherein the medicinal leech is so useful at home.

Independently of the practical value of this animal, wherever it can
be found, certain singular facts are exposed by various species of the
genus Hirudo, which cannot but be interesting to the physiologist, and
assuredly deserve to be farther known and suitably appreciated."

Sir John Graham Dalyell,

" The Powers of the Creator
displayed in the Creation,"
1853, p. 1.

LIBRARY

MASS.

CONTENTS

'AGE

Preface ix

5

5
5
8

to

12
13
15
16

1

Introduction

2

The Medicinal Leech, Hirudo medicinalis

1.
2.
3.
4.
5.
6.
7.
8.

Occurrence
External characters
Alimentary canal
Reproductive system
Excretory system
Nervous system
Blood system
Histology

3

A Surv'ey of the Group

1.

2.
3.
4.

5.

Classification

Glossiphoniidae

Piscicolidae

Gnathobdellae

Pharyngobdellae

4

Nutrition

1.

2.

In Hirudidae

In Rhynchobdellae

22

22
23
29
32
34

36

36
42

5 Excretion and Water Balance 44

1 . Excretion 44

2. Water and salt balance 51

6 Circulation and Respiration 53

Muscle, Nerve and Locomotion

63

1 . The muscular system

2. The nervous system

3. Locomotion

4. Co-ordination

8024'1

63
69

73
75

Vm CONTENTS

8 Sense Organs and Behaviour 79

1. Sensory equipment 79

2. Reactions to light 83

3. Reactions to heat 92

4. Reactions to mechanical stimulus 94

5. Reactions to gravity 96

6. Reactions to chemical substances 97

9 Reproduction and Development 101

1. Introduction 101

2. Fertilization 104

3. Egg laying and brood care 110

4. Development of the eggs 116

5. Embryology of a glossiphoniid leech 121

6. Embryology of a gnathobdellid leech 127

7. Special features of piscicolid embryology 130

8. Phylogenetic considerations 133

9. Evolutionary history 134

10 Ecology 136

1. Relations with the inanimate environment 136

2. Relations with the animate environment 139

Appendix A. The Systematics of Freshwater and

Terrestrial Leeches. By K. H. Mann 147

Appendix B. The Systematics of Marine Leeches. 169
By Professor E. W. Knight-Jones

Bibliography 187

Index 197

PREFACE

In English speaking countries the leeches are a neglected group
of animals. Very few zoologists study them and apart from the
volume in the " Fauna of British India" series there is no book in
English devoted to them. In Germany and the central European
countries the Hirudinea are much better known. Antrum (1939)
lists over 2500 research papers, most of them in German, and
leech biology has been summarized in several extensive works.

The purpose of this volume is to present a fairly concise account
of the Hirudinea at a level appropriate to the honours student of
zoology at a university. It is hoped that a summary of present
knowledge, particularly in the realm of physiology, will also be of
value to more senior zoologists, so references to the original papers
have been given where appropriate. The guiding principle in
determining to what extent the text need be interrupted by
references has been that work summarized in the Hirudinea
volume of Bronns: Klassen und Ordnungen des Tierreichs (1936-9)
should be quoted without extensive references, while results
published since 1939 and here reviewed for the first time should
be fully documented.

The first three chapters are intended as an introduction to the
group for beginners. For this purpose it has been thought best
to give a fairly thorough description of Hirudo medicinalis as a type
species rather than an account of the group in general or compara-
tive terms. After this there follows a chapter in which the main
features of the various families are set out.

The reader whose prime interest is physiological may pass
straight to Chapter 4, using the previous chapters only as a source
of reference when unexplained morphological or taxonomic terms
are encountered.

ACKNOWLEDGEMENTS

Professor A. Graham, Professor G. P. Wells and Dr. R. B. Clark
have read various parts of the text and I am particularly grateful
to them for pointing out some of the mistakes resulting from my
ignorance of certain fields of physiology. Naturally they have no
responsibility for the errors that remain. I also wish to thank
my wife for her assistance in proof reading and Mrs. G. I. Smillie
for patiently typing and re-typing the script.

Professor Knight- Jones wishes to acknowledge the help given
towards the appendix on marine leeches by Dr. N. Tebble of the
British Museum (Nat. Hist.) and by Dr. P. H. D. H. de Silva
of the National Museum, Colombo.

CHAPTER 1

INTRODUCTION

Leeches are fascinating animals, full of strange zoological paradoxes.
In what other group of the animal kingdom do we find such
features as a gut with no digestive enzymes, haemoglobin circu-
lating in the coelomic fluid and fertilization carried out by intro-
ducing the sperms through the body wall of another animal? Yet
such things are quite normal among leeches and are only a few
of their peculiarities.

They belong to the phylum Annelida yet in many respects they
have advanced beyond the level of organization which we regard
as typical of annelids. When we compare the arthropods with the
annelids we notice that the arthropods usually have a smaller,
fixed number of segments and this has made possible a greater
mobility and agility. Leeches are the only major group of annelids
to have adopted a small, fixed number of segments for their basic
plan and they are certainly more agile than most other annelids.

In oligochaetes and polychaetes there is a spacious fluid-filled
coelom between the gut and the body wall which serves as a hydro-
static skeleton. In arthropods, which have an exoskeleton to
support the body, the coelomic spaces are very small and the blood
space or haemocoel has expanded to take their place. Leeches also
lack the spacious fluid-filled coelom for it has become almost filled
with mesenchymatous packing tissue, leaving only a system of
narrow channels in which there is a circulation of coelomic fluid.

The leech nervous system is built on the usual annelid pattern
of an anterior dorsal brain with connectives running to a paired
ventral nerve cord which expands in each segment to form ganglia.
It is characteristic of arthropods that they have more ganglia
crowded into the head region than have the annelids. Insects, for
instance, have six pairs of ganglia in the head region, of which three
lie dorsal to the oesophagus. Oligochaetes and polychaetes have

Z LEECHES

four or five, of which only one is dorsal to the pharynx and one is
on the circum-pharyngeal connectives, apparently in the process
of migrating dorsally. Leeches more closely resemble insects for
they have six pairs of ganglia in the head, usually with two placed
dorsally and one pair on the lateral connectives.

The group of annelids most closely related to the leeches is
undoubtedly the oligochaetes. There is in fact a connecting link in
Acanthohdella, a leech which has a number of clear oligochaete
features, such as chaetae and a spacious coelom. Both leeches and
oligochaetes have a clitellum which secretes a cocoon for the recep-
tion of the eggs. Both are hermaphrodite and have well defined
gonads with their own ducts to the exterior. There are many
peculiarities of the embryology of oligochaetes which are also seen
in leech development. In fact, it is reasonable to regard leeches as
oligochaetes which have become specialized for a blood-sucking
ecto-parasitic mode of life. In the process they have lost the
chaetae which earthworms use in locomotion and have developed
instead a ventral sucker at each end of the body, this arrangement
being better adapted to clinging to the host while sucking blood.
Their gut has been modified for the storage of large quantities of
blood and with the great reduction of the coelom the segmentation
of the body has become obscured.

The relationship of leeches to other annelid groups is expressed
in the following scheme ot classification :

Phylum ANNELIDA

Class POLYCHAETA Clitellum absent, chaetae borne

on parapodia.

Class ARCHIANNELIDA CiHated epidermis, simplified,

possibly degenerate organiza-
tion.

Class CLITELLATA Clitellum present, parapodia

absent.

Order OLIGOCHAETA Chaetae present, suckers absent,

number of body segments
variable.

Order HIRUDINEA Chaetae absent, suckers present,

number of body segments 33.

INTRODUCTION 6

The adaptation of the gut of leeches to blood sucking has taken
place in several ways. First there is the mechanism for piercing
the tissues of the host. In one major group this consists of three
muscular ridges each shaped like half a circular saw, which can be
everted from the mouth and used to make a Y-shaped incision in
the skin. In the other group of leeches there is a very muscular
proboscis which is forced out of a pore in the base of the anterior
sucker while this is held in contact with the host. This mechanism
is on the whole less efficient than the former, and few leeches
possessing it are able to pierce the skin of a mammal. The blood
is prevented from clotting by the secretion of numerous uni-
cellular salivary glands, and is sucked into the gut by the pumping
action of a muscular pharynx.

Although leeches resemble oligochaetes in being hermaphrodite,
they differ in having only a single male pore and a single female
pore. Moreover, while they have but a single pair of ovaries, they
normally have between ten and a hundred pairs of testes. The jawed
leeches transfer sperm to another leech by means of an eversible
penis, but those with a proboscis normally lack the penis and
implant a spermatophore containing sperms on the body surface of
another leech. After this the sperms migrate through the tissues
of the recipient and make their own way to the ovary.

Leeches with a proboscis (Rhynchobdellae) have a blood system
of the normal annelid plan with dorsal and ventral longitudinal
vessels, but the jawed leeches (Gnathobdellae) have completely
lost their blood vessels and have instead a system of coelomic
sinuses in which circulates coelomic fluid containing haemoglobin.

Before an accurate description of a leech can be given it is neces-
sary to determine the limits of the segments. The only external
evidence of segmentation in most leeches is in the arrangement of
the sensillae, minute whitish spots which are receptor organs for
tactile and light stimuli. Earlier workers adopted a convention
that the annulus on which these occurred should be regarded as
the first of its segment and this convention has been followed as
recently as 1941 (Bhatia) and 1945 (Miller). Castle (1900) and
Moore (1900) independently proposed that the nervous system
should be used as a basis for determining the limits of segments,
there being a general tendency for the parts of a segment to be
innervated from the ganglion of that segment and by no other

4 LEECHES

nerves. On critical examination (Mann, 1953a) it appears that the
method of Castle and Moore is the correct one, for the inter-
segmental boundaries then coincide with the intersegmental septa
which are present in the embryo but are lost in the adult leech.

The earlier method of delimiting segments led to disagreement
about the total number of segments present as well as about their
exact limits but analysis of the nervous system has led to the
conclusion that there are thirty-four pairs of ganglia in all, of
which the first is presumably homologous with the pre-oral
ganglion of other annelids and belongs to the prostomium. The
second ganglion pair is situated on the circum-oral commissures
or is fused with the first, the next four are fused into a post-oral
ganglionic mass, twenty-one (normally) are distributed along the
ventral nerve cords, and the last seven are fused into the ganglionic
mass of the posterior sucker. The descriptions of leeches which
follow are based on this analysis.

CHAPTER 2

THE MEDICINAL LEECH,
HIRUDO MEDICINALIS

He with a smile did then his words repeat:

And said that, gathering leeches, far and wide

He travelled ; stirring thus about his feet

The waters of the pools where they abide.

" Once I could meet with them on every side;

But they have dwindled long by slow decay;

Yet still I persevere, and find them where I may."

WORDSWORTH, Resolution and Independence ^ 1802.

1. Occurrence

The medicinal leech feeds by sucking the blood of mammals or
occasionally of frogs, tadpoles and small fish (Blair, 1927). It is a
native of Europe and south and east Asia (Lukin, 1957) and has
been introduced into North America. In Britain it was once plenti-
ful, but in the last two hundred years has declined markedly,
possibly as a result of its extensive collection for medical use. It
was once thought to be extinct in Britain (Harding, 1910) but is
now known to be present in various relatively undeveloped areas
such as the New Forest, the Lake District, South Wales, Anglesey,
and Islay, Scotland. Its opportunities for obtaining blood from
mammalian hosts have been greatly reduced now that fords have
been replaced by bridges and cattle are watered at troughs rather
than natural ponds.

2. External Characters

A large specimen measures about 12 cm X 1*5 cm when fully
extended, although it may contract to less than half this length.
The shape of the body varies according to the amount of blood

LEECHES

in the gut ; the specimen illustrated in Fig. 1 was preserved shortly
after gorging itself on the author! The colour pattern is very

-Anterior sucker

XXEZ:

Clitellum

-30

Male pore

-Female pore
• 40

■50
9th nephridiopore

-60

Segmentaf receptor

■90

I cm

-Posterior sucker

Fig. 1 . (a) dorsal view of Hirudo medicinalis ;

(b) diagrammatic ventral view of Hirudo medicinalis.
The segments are numbered in roman numerals and the annuli

in arabic.

THE MEDICINAL LEECH

variable, but in Britain usually consists of a greenish background
with a pair of longitudinal red stripes and a pattern of irregular
black markings nearer the lateral margins. The ventral surface is
usually black with white and grey markings.

The body of the leech, exclusive of the posterior sucker, is
divided by transverse furrows into 102 annuli. A typical mid-body
segment comprises five annuli but towards the extremities of the
body the number per segment progressively decreases. The distri-
bution of the annuli between the prostomium and body segments
is as follows:

P, I, II and XXVI . .

1 annulus . .

. . total 4

Ill, IV and XXV ..

2 annuli

. . total 6

V, VI and XXIV ..

3 annuli

. . total 9

VII and XXIII . .

. . 4 annuli

. . total 8

VIII to XXII . . . .

5 annuli

. . total 75

Grand total 102

The anterior sucker is a depression on the ventral surface of
segments I-IV, and at the base of the depression lies a small trira-
diate aperture, the mouth. The prostomium forms the anterior
border of the sucker and may be turned back ventrally, thus
partially closing the oral aperture. The posterior sucker is a
muscular disc, approximately circular in outline, which is a more
powerful organ of adhesion than the anterior sucker. It is clearly
marked off from the body and is made up of seven fused segments.
The anus is a very small aperture in the mid-dorsal line near the
junction of the body and the posterior sucker.

The male pore lies between annuli 31 and 32, while the female
pore lies five annuli further back between 36 and 37. The male
pore is the more conspicuous and may be used as a guide to the
position of the female pore. During the breeding season the
glandular clitellum is visible on annuli.26-40. The nephridiopores
are found in segment 7 between annuli 14 and 15, and between
the second and third annuli of the following 16 segments. They
are very small indeed, and the best way of finding them is to
squeeze gently a freshly narcotized specimen, when a little fluid
will be exuded from the nephridial bladders.

There are three principal kinds of sense organ on the surface

8

LEECHES

of the body. Every annulus has receptor organs which in a con-
tracted specimen may be seen to be raised on papillae. These are
the annular receptors which are thought to be tactile organs. On
every fifth annulus, the middle annulus of its segment, there are
also white circular areas which in a preserved specimen are not
raised on papillae. These contain cells which are thought to be
light-sensitive. They are a convenient outward indication of
internal segmentation, and are shown diagrammatically in Fig. 1.
They are known as the segmental receptors, or sensillae. Finally,
on segments I-V, there are five pairs of eyes which correspond in
position with segmental receptors. They have larger light-
sensitive cells, and are backed by a pigmented cup. They there-
fore appear as black dots on the head, but it may be necessary to
bleach the head in 5% caustic potash before they become visible.

3. Alimentary Canal

The cavity containing the jaws, the buccal cavity, is separated
from the cavity of the sucker by a low fold, the velum. When

Sub-oesophageal
ganglion

Salivary glands

Velum

Radial muscles

Jaw

Cut circum-

')S,^f^ oesophageal

connective

Longitudinal
muscles

Lining of pharynx

5 mm

Fig. 2. Ventral dissection of the head of Hirudo medicinalis
showing jaws protruded in biting position.

THE MEDICINAL LEECH

feeding, the velum is drawn back to allow the jaws to be pushed
forward into the cavity of the sucker and pressed onto the skin of
the host. Each jaw is a muscular ridge shaped like half a circular

Position of jaws-

Pharynx-
Radial muscles-

Crop -

Dorsal sinus-

Intestine-

Rectum-

xz

XX

100/

Broin

.Sub-oesophageoi
S ganglion

Bladder of
nephridium

^CL

^'

u

(f<o

Penis sac

Ovary
Vagina

Vas deferens

5 th testis

Ventral nerve cord

i6th nephridium

21 st free ganglion

(a) (b)

Fig. 3, (a) dissection of H. medicinalis to show gut. The body
wall has been opened by a median dorsal incision and pinned
back laterally, (b) dissection to show nephridia, reproductive
organs and central nervous system. The gut has been removed
and the body wall stretched laterally.

10 LEECHES

saw; one is median dorsal in position, the other two are ventro-
lateral. They have a covering of cuticle, and along the free edges
of the discs this is thickened to form a row of numerous minute
teeth. In making the incision, the muscles of the jaws rock them
so that the teeth move with a sawing action. The result is a
Y-shaped incision. Numerous unicellular salivary glands open
onto the jaws and secrete an anticoagulin which prevents the
clotting of the blood exuded from the wound. The blood is sucked
into the alimentary canal by the pumping action of the pharynx,
an oval sac about 5 mm long behind the buccal cavity. Its walls
are deeply folded when at rest, but unfold when the pharynx is
dilated by the action of the radial muscles which run out to the
body wall. The space between the radial muscles is almost
entirely occupied by salivary gland cells.

Immediately behind the pharynx is a short narrow tube, the
oesophagus, through which the blood is passed to the crop. The
crop is the largest part of the alimentary canal and is adapted for
the storage of a considerable volume of blood by the possession
of eleven pairs of diverticula, one pair in each of segments VIII-
XVIII. The last pair run back to the hind end of the body. In
segment XVIII the crop leads by a narrow pore to the intestine.
This is a thin-walled tube, slightly swollen into a heart-shaped
chamber in segment XIX, which runs straight back between the
last pair of crop diverticula to segment XXIII where it becomes
constricted and leads to the rectum. The latter, when full, is
distended to form a rectal bladder which opens to the exterior on
segment XXVI at the anus.

4. Reproductive System

The testes are contained in ten pairs of coelomic sacs situated
in segments XII to XXI. The number is not absolutely constant,
there may be one pair more or less. Short vasa efferentia connect
the testis sacs to the vasa deferentia of each side. These run
forward to segment XI where they become enlarged and coiled
to form storage organs known as epididymes or sperm vesicles.
Beyond these are thick-walled ejaculatory ducts which in turn lead
to a median organ, the atrium. The atrium consists of two parts,
a basal bulb covered with several layers of unicellular prostate

THE MEDICINAL LEECH

11

glands, and a penis sheath surrounding an eversible muscular
penis. Spermatogonia are budded off from the walls of the testis
sacs and develop into spermatozoa while floating freely in the
contained coelomic fluid. They pass via vasa efferentia and vasa
deferentia into the epididymes where they are stored at the begin-

Prostate gland —

Ejaculatory duct

Oviduct

Oviduca
gland

Vos deferens

Ventral nerve cord

Epididymis

Penis in
sheath

Ovary in
ovisac

Vagina

5 mm

Fig. 4. Details of reproductive organs. The penis sheath,

prostate bulb and female organs are shown with the dorsal wall

removed. After Leuckart & Brandes, 1886-1901.

ning of the breeding season. When required for use they pass
through the ejaculatory ducts to the prostate bulb where they are
cemented into spermatophores. The penis is used to transfer
them to the vagina of another leech at the time of copulation.

12

LEECHES

The ovaries are elongated cords with club-shaped terminations
which lie freely in a single pair of coelomic sacs in segment XL
Short ducts run from these to a common oviduct, which is closely
invested with a thick layer of unicellular albumen glands. The
oviduct leads to a U-shaped muscular vagina which in turn opens
to the exterior. Ova are budded off from the cords in the ovisacs,
are fertilized by sperm received from another leech, and finally
coated with albumen in the oviduct. After the cocoon has been
formed by the clitellum the fertilized eggs are passed from the
female pore into the cocoon, which the leech then slips over its
head.

5. Excretory System

There are seventeen pairs of nephridia opening on segments
VII to XXIII. The parts of a typical nephridium are shown in
Fig. 5. The outstanding feature of this nephridium compared
with those of most other annelids is the complete separation of the

Testis sac Vas deferens

Initial lobe

Inter -cellular duct

Main lobe

Intra -cellular
duct

Vesicle

Fig. 5. Details of a right nephridium as seen in situ when the
body wall has been pinned out as in Fig. 3(b). After Bhatia, 1938.

funnel from the rest of the nephridium. It has become modified
almost out of recognition and has become functionally a part of

THE MEDICINAL LEECH 13

the circulatory system rather than of the excretory system (Bhatia,
1938). It is totally enclosed within a blood-filled sinus which lies
on top of the testis sac and consists of a central capsule or reservoir
which is studded with many small ciliated funnels. The reservoir
is the site of formation of corpuscles of the coelomic circulatory
system (see p. 15) and the cilia of the funnels beat outwards,
wafting the corpuscles into the blood. The initial lobe of the
nephridium lies close to this ciliated organ, but has no connexion
with it. From the testis sac a winding intra-cellular canal may be
followed to the main body of the nephridium. Here it joins with
a network of intra-cellular canals, and these eventually lead to an
intercellular canal which loops several times round the nephridium
before running to the vesicle. All the glandular part of the nephri-
dium arises from a nephridioblast cut off early from ecto-mesoderm
but the vesicle and its duct to the exterior are ectodermal. The
whole nephridium is closely invested with branches of the blood
sinus system and excretory products are obtained from these rather
than from the ciliated organ.

The first six, and the last pair of nephridia are not associated
with testes. They do not have a ciliated organ, and the initial lobe
ends blindlv a little distance from the ventral nerve cord.

6. Nervous System

The central nervous system consists of a paired ventral nerve
cord connecting 34 paired ganglia. Of these, six are in the head
region, 21 are spaced along the ventral cord in the body and seven
are fused into a terminal mass in the posterior sucker. This
arrangement is shown in Fig. 3b. A typical ganglion of the ventral
chain consists of six capsules containing nerve cells, two median
ventral and the rest latero-dorsal in position, arranged round a
mass of nerve fibres. In the anterior and posterior ganglionic
masses there are also six capsules to each segmental ganglion and
these provide the basis for analyzing each mass.

In the head region there is a (paired) supra-pharyngeal ganglion
or brain lying dorsal to the pharynx at the level of segment VI
and a (paired) sub-pharyngeal ganglion connected to the brain by
peri-pharyngeal connectives. The distribution of cell capsules
in this mass was determined by Livanow (1904) and is shown in

14

LEECHES

Fig. 6. It is seen that the first ganglion pair consists of six capsules
dorsal to the gut, the second consists of three capsules on each side
of the gut, while the remaining four pairs of ganglia form the
ventral mass. There is an important difference between this

Supra-oesophagea
ganglion

Sub-oesophagea
ganglion

Nerve to prostomium
and first eye

Sympathetic
nerve ring

ve to eye 2

ve to eye 3

ve to eye 4

Nerye to sensilloe on EZ"

Nerve to eye 5

Ner\/e to sensilloe on 'SL

Fig. 6. Diagrammatic representation of the anterior ganglia

of Hirudo in dorsal view showing segmental numbering of the

ganglia, the capsules containing nerve cells and the roots of the

anterior segmental nerves. After Livanow, 1904.

arrangement and that found in the earthworms. In the latter the
cerebral ganglion is a single ganglion pair associated with the
prostomium and all the ganglia of the body segments are beneath
the oesophagus. In the leech one pair of segmental ganglia have
migrated round the pharynx and are closely associated with the
prostomial ganglia. This foreshadows the arrangement found in

THE MEDICINAL LEECH

15

the Arthropoda, where several segmental ganglia contribute to
the brain.

There are seven peripheral nerves in the head region, and the
sense organs with which each is associated are indicated in Fig. 6.
The sympathetic ( = stomatogastric) nervous system consists of a
nerve ring lying on the wall of the pharynx just in front of the main
nerve ring, and a plexus of nerve cells and fibres on the walls of
the gut (Terio, 1950). It links with the central nervous system at
two points on the circum-pharyngeal nerve ring.

7. Blood System

While more primitive leeches such as Glossiphonia have distinct
blood vessels lying within the coelomic sinuses (Fig. 16), Hirudo
has completely lost all traces of blood vessels and the blood circu-
lates in coelomic sinuses, some of which have secondarily acquired
muscular walls. There are four main longitudinal sinuses: a dorsal
sinus above the gut, a ventral sinus containing the ventral nerve
cord and anterior and posterior ganglionic masses, and two lateral
sinuses (Fig. 7). The lateral sinuses have the muscular walls and

Dorsal sinus

Lalera

nus

Latero- lateral sinus

o-ventral sinus

containing nerve cord

Fig. 7. Reconstruction of the coelomic sinus system of Hirudo
from one segment in the mid body region. Original.

are responsible for circulating the blood. They give off three main
pairs of branches in each segment which were named by Gratiolet

16 LEECHES

(1862): the latero-dorsals, latero-ventrals and latero-laterals.
These break up into capillaries in the botryoidal tissue and the
body wall, but the capillaries unite again to form tributaries of the
dorsal and ventral sinuses. The detailed course of the circulation
has not been worked out, but since blood is driven forward by the
contraction of the lateral sinuses, there is probably a compensatory
backward flow in the dorsal and ventral sinuses.

The blood consists of a plasma, coloured red by haemoglobin in
solution, and containing numerous amoeboid corpuscles together
with some chloragogenous cells.

8. Histology

Under this heading are described some of the details which may
be seen in transverse sections.

Epidermis

On the outer body surface is a very thin cuticle, secreted by the
epidermal cells and renewed at intervals of a few days. The epi-
dermal cells are columnar and widen at the outer ends to form
pentagonal heads which fit closely against the heads of neigh-
bouring cells. The inner ends are cylindrical and there are spaces
between the cells into which penetrate blood capillaries, nerve
endings, pigment cells and dermal fibres. Derived from the epi-
dermis are various kinds of unicellular glands. On the general body
surface there are two kinds of m-ucus glands : pear-shaped glands
with the body of the cell just under the epidermis and a narrow
neck opening at the surface, and elongated tubular glands which
penetrate down into the muscle layers (Fig. 9). In the anterior
head region all the available space between muscles is occupied by
densely packed pear-shaped glandular cells whose secretion is
poured on to the surface of the anterior sucker. The posterior
sucker is similarly equipped. The salivary glands, which lie
between the pharynx and the body wall, are modified epidermal
cells. They are unicellular pyriform glands with long ductules
leading to the jaws. Like the general body epidermis, the epidermis
of the jaws secretes a cuticle and bears the apertures of these
modified epidermal glands. In the clitellar region there are, in
addition to the mucus glands, two types of gland concerned with

THE MEDICINAL LEECH

17

E

to

3

Q)

3

C

O

^

m

'{/I

v_

O)

x:

o

>

Q.

i_

0)

CD

z

■*—

o

o

<D

2 ^

C c/}

o

■(-> +->

o S

bx)

?J G
*-' O

■M O

■t-> O

"is a

I ^

u

M

a;

O)

C/)

03

(U

a

2

(U

03

>

en

T3

2

■M

(U

CO

o

2i

bC.2

O .2

*■»->

• o

00 <u

CO

6 o

fo-5

18

LEECHES

Pigment cell Cuticle Epidermis Pearshaped gland

Dermis ^-—-^^z
Circular
muscles

Oblique
muscles

Botryoi
tissue

I m m

Blood
capi I lary

Tubular
gland

Longitudinal
muscles

Connective
tissue

Dorso - ventral
muscle

Fig. 9.

Details of the tissues found between the gut and the
cuticle in a transverse section of Hirudo.

the formation of the cocoon. The first are the chitogenous glands
which secrete the outer casing. These lie among the circular
muscles. The others are the albumen glands, which lie deeper,
among the longitudinal muscles. The sense organs of the epidermis
show several grades of complexity from simple nerve endings to
well differentiated eyes (Fig. 10). The details of these are discussed
in connexion with the physiology of the nervous system, p. 79.

Dermis

Between the epidermis and the muscle layers is a zone of fibrous
connective tissue. It consists of a ground-substance containing a
high concentration of acid muco-polysaccharide, and interlacing
connective tissue fibres. Bradbury (1958) has shown that the
fibres consist of a cortex which is probably collagenous and a
medulla which is an extension of the cell body of the fibrocyte.
He suggests that the collagen fibres are produced at the surface
of the fibrocytes. Pigment cells (brown, black, and green) are also
present in this zone. As has been mentioned above, the epidermal
gland cells penetrate into the dermis, and in highly glandular
regions may leave little room for connective tissue.

THE MEDICINAL LEECH

19

Muscles

The muscles of Hirudo are made up of elongated fusiform cells
having an outer contractile myoplasm and an inner sarcoplasm.
Immediately beneath the dermis lies a layer of circular muscle
fibres, and beneath this again is a layer of obUque muscles, the

Sense bud -

Blood cap

Nerve t

Epidermis

Optic cell

Pigment cup

Muscle

erve

0-2 mm

Fig. 10. Vertical section through an eye of Hirudo showing
also a group of epidermal sense cells. After Hesse, 1897.

cells of which run at about 45° to the longitudinal axis of the body,
right and left. Further towards the centre lies a thick layer of
longitudinal muscle cells. Finally there are dorso-ventral bundles

20

LEECHES

of fibres which are anchored beneath the epidermis and penetrate
all the previously mentioned layers of muscle. Prominent dorso-
ventral muscles are situated between the gut diverticula.

Botryoidal and vaso-fibroiis tissue

Between the gut and the muscles of the body wall is found a
tissue which is characteristic of jawed leeches and is called
botryoidal tissue, from a fancied resemblance in section to bunches
of grapes. It consists of a network of very fine capillary channels
of the coelomic blood sinus system, lined by swollen globular
cells which are heavily laden with brown pigment. The function
of these is not fully understood, but they correspond in origin and

Jaw

Muscle cells

Ducts of
salivary glands

Muscle cells
cut obllquel

sverse
e cells

Imm

Fig. 11. (a) plan of a transverse section through the jaws of
Hirudo, (b) details of one jaw in section.

THE MEDICINAL LEECH 21

probably in function with the chloragogen cells of oligochaetes.
The vaso-fibrous tissue consists of strands running in the con-
nective tissue which contain deposits of brown pigment. They
have a small lumen which was shown by Lankester (1880) to be
continuous with that of the botryoidal tissue. It is thought that
the vaso-fibrous tissue accumulates excretory products and is in
some way complementary to the botryoidal tissue (Bradbury, 1959).

The Gut

The buccal cavity and pharynx of Hirudo are of ectodermal
origin and are lined by cuticle. The pharynx has in its walls three
muscular ridges which are enlarged anteriorly to form the jaws.
In section each jaw is seen to have a core of closely packed salivary
gland ducts, then a layer of muscle cells, and finally an epidermis
surmounted by cuticle. On the cutting edge of the jaws the cuticle
is thickened to form the teeth and the openings of the salivary
ducts are between the teeth (Fig. 11).

The endodermal gut comprises the oesophagus, crop, intestine
and rectal bladder. The wall of the crop is composed of prismatic
cells having a striated border, and their cytoplasm contains
numerous fat droplets. There is a crop musculature composed of
interlacing muscle cells lying in connective tissue just outside the
epithelium. The wall of the intestine is also a single layer of
prismatic cells, but these are taller than those of the crop and lack
musculature. The epithelium of the rectal bladder is ciliated.
Only the tube from the rectal bladder to the anus is formed from
proctodaem and has a cuticular lining.

Nervous system

The fine structure of the nervous system is discussed in
Chapter 7. A transverse section of a leech usually passes through
the ventral nerve cord and shows two bundles of nerve fibres
together with a small median unpaired nerve known as Faivre's
nerve.

CHAPTER 3

A SURVEY OF THE GROUP

(a more detailed systematic survey is given in the appendixes)

1. Classification

The following is the scheme of classification adopted in this w^ork :
Order Hirudinea

Suborder Acanthobdellae
Suborder Rhynchobdellae
Family Glossiphoniidae
Family Piscicolidae (= Ichthyobdellidae)
Suborder Gnathobdellae (= Arhynchobdellae)
Family Hirudidae
Family Haemadipsidae
Suborder Pharyngobdellae
Family Erpobdellidae
Family Trematobdellidae
Family Semiscolecidae
The Acanthobdellae comprises the single genus Acanthobdella
which is in many ways intermediate between the Oligochaeta and
the Hirudinea. Chaetae are present in five anterior segments,
there is no anterior sucker, and the coelom is not entirely obliterated.
Acanthobdella is a small fish parasite from Lake Baikal (Fig. 12).
The Rhynchobdellae are jawless and are those leeches which
utilize a proboscis to penetrate the tissues of the host. There are
distinct blood vessels in the body and the blood is colourless. They
are marine and freshwater forms, none is terrestrial. The group
is divided into two families: the Glossiphoniidae which are
dorso-ventrally flattened leeches confined to freshwater and having
an anterior sucker which is continuous with the outline of the body,
and the Piscicolidae which are cylindrical mostly marine leeches,
having an anterior sucker which is bell shaped and clearly marked
off from the body.

22

A SURVEY OF THE GROUP
(a)

23

4 mm

Post. SU

Ovary

Fig. 12. (a) general appearance of Acanthobdella ;

(b) details of anterior region showing chaetae;

(c) diagram of anatomy of Acanthohdella.

All after Livanow, 1906. (c) reproduced from Grasse, 1959.

2. Glossiphoniidae
The characters of a typical glossiphoniid leech are illustrated
by Glossiphonia complanatay a common European, Asian and
American species which sucks the body fluids of aquatic snails.
A typical segment has three annuh, there being only 68 annuli in
front of the posterior sucker. There are three pairs of eyes
arranged in two parallel rows, and two lines of dark pigment,

24

LEECHES

regularly interrupted by papillae bearing sense organs. On the
ventral surface the posterior sucker is clearly marked off from the
rest of the body, but the anterior sucker is only a small depression

5mm

Fig. 13. Dorsal view oi Glossiphonia complanata.

on the under side of the head. The male pore is between annuli 25
and 26, and the female between 27 and 28. The general arrange-
ment of the internal organs is shown in Fig. 14. The proboscis
and proboscis sheath are of ectodermal origin, and are lined with
a fine cuticle. The endodermal gut begins with the crop, which has
six pairs of diverticula, the last pair being elongated and bent
posteriorly. The intestine, also endodermal in origin, has four
pairs of small lateral diverticula, and leads via the rectum (of ecto-
dermal origin) to the anus which is placed dorsally, at the junction
of the body with the posterior sucker.

The female reproductive system, which is the simpler, consists
of two ovisacs lying lengthwise in the body in ventral coelomic
lacunae. Each contains a single thread-like ovary, and the two
sacs have a common opening at the female pore. The male repro-
ductive system consists of ten pairs of spherical testes lying
between the gut diverticula. Short vasa efferentia join these to a

A SURVEY OF THE GROUP

25

Proboscis pore in
rior sucker

Proboscis exposed
in proboscis sheath

Male pore
Female pore

Salivary gland

Testis (2nd)

Last crop
diverticulum

Intestine

Tenth testis
Rectum

Anus dorsal to
posterior sucker

Fig. 14. Diagram of anatomy of Glossiphonia complanata.
After Harding, 1910.

24

LEECHES

regularly interrupted by papillae bearing sense organs. On the
ventral surface the posterior sucker is clearly marked off from the
rest of the body, but the anterior sucker is only a small depression

&:^,mm-:,^^i

5mm

Fig. 13. Dorsal view of Glossiphonia complanata.

on the under side of the head. The male pore is between annuli 25
and 26, and the female between 27 and 28. The general arrange-
ment of the internal organs is shown in Fig. 14. The proboscis
and proboscis sheath are of ectodermal origin, and are lined with
a fine cuticle. The endodermal gut begins with the crop, which has
six pairs of diverticula, the last pair being elongated and bent
posteriorly. The intestine, also endodermal in origin, has four
pairs of small lateral diverticula, and leads via the rectum (of ecto-
dermal origin) to the anus which is placed dorsally, at the junction
of the body with the posterior sucker.

The female reproductive system, which is the simpler, consists
of two ovisacs lying lengthwise in the body in ventral coelomic
lacunae. Each contains a single thread-like ovary, and the two
sacs have a common opening at the female pore. The male repro-
ductive system consists of ten pairs of spherical testes lying
between the gut diverticula. Short vasa efferentia join these to a

A SURVEY OF THE GROUP

27

in Fig. 16. There are longitudinal dorsal, ventral, and lateral
sinuses, transverse subcutaneous sinuses, and various intermediate
connecting sinuses. The dorsal sinus is almost completely filled

Dorsal connecting sinus

Intermediate sinus

Lateral sinus^

Subcutaneous sinus
Dorsal vessel
Dorsol sinus
Ventrol sinus

Ventral vessel

Ventral connecting sinus

Ventral nerve cord

Fig. 16. Reconstruction of part of the coelomic sinus system
of Glossiphonia cojnplanata. After Oka, 1894.

by the dorsal contractile blood vessel; the ventral contains the
ventral nerve cord, the ventral vessel, and the female genital organs,
as well as the funnels of the nephridia in certain segments. Chlora-
gogenous cells are present, adhering to the walls of the sinuses or
floating freely in the coelomic fluid. The parenchyma between
the coelom and the body wall contains many conspicuous adipose
cells and pigment cells.

The dorsal blood vessel is equipped with fifteen sets of valves
and by its contraction drives blood forward. A number of capil-
laries connects the dorsal and ventral vessels anteriorly, so that
blood is forced backwards through the ventral vessel. It then
travels through the capillaries of the posterior sucker, and up into
the dorsal vessel again. In the region of the intestine the dorsal
vessel has four pairs of lateral caeca which lie very close to the
intestinal caeca.

Other members of the Glossiphoniidae include parasites of fish,
water birds, reptiles and Amphibia. Hemiclepsis marginata (Fig. 17)
is chiefly a fish parasite, although it may also attack tadpoles and

Fig. 17. (a)-(g) various Glossiphoniidae. (h) a piscicolid
leech, (a) Helobdella stagnalis; (b) Hemiclepsis marginata;
(c) Glossiphonia heteroclita; (d) ventral view of Helobdella
carrying young; (e) Glossiphonia after rolling into a ball;
(f) Theromyzon tessulatwn starving; (g) T. tessulatiim after a
meal ; (h) Piscicola geometra.

A SURVEY OF THE GROUP 29

certain molluscs. It is found through most of Europe and Asia.
Theromyzon is a worldwide genus ; members of most species enter
the nostrils of wading and swimming birds and feed from the
mucous membrane. Placobdella (= Haementeria) is another widely
distributed genus and includes parasites of crocodiles, water
turtles, frogs and fishes. Helohdella, on the other hand sucks the
body fluids of invertebrates such as snails and insect larvae. It is
really a specialized predator rather than a parasite, as it normally
kills the host.

3. PiSCICOLIDAE

The characters of a typical piscicolid leech are illustrated
by Branchellion torpedinis. Both anterior and posterior suckers are
clearly marked off from the body, which is divided into two
distinct regions. These are the short, narrow anterior portion
which includes the clitellum and the genital pores, and the longer
and wider posterior portion which bears gills on the lateral margins.
As in Glossiphonia, a complete mid-body segment has three annuli
and the middle one bears, in addition to sensillae, a pair of lateral
pulsatile vesicles which help to circulate the coelomic fluid through
the gills. The anterior sucker bears six eyes arranged in an arc
across the dorsal surface of segment IV. In a mature specimen
segment XII is lifted into a fold which lies over the preceding two
segments and covers the genital pores. It has been likened to the
prepuce which covers the glans penis of a mammal and is often
given that name.

The arrangement of the internal organs is shown in Fig. 18. The
proboscis is followed by an oesophagus that bears a pair of oeso-
phageal diverticula. The crop has six pairs of diverticula, of which
all but the first pair are bilobed. The last pair of diverticula are
continued back to the hind end of the body. They lie ventral to
the intestine and so are almost completely hidden in dorsal view.
They anastomose at five points, as shown in Fig. 18c. The intes-
tine has four large pouches on either side and leads to the rectum
by way of a ciliated chamber bearing a pair of highly folded
diverticula.

There are five pairs of testes lying between the crop diverticula ;
the general arrangement of the reproductive organs is of the

30

LEECHES

Proboscis
\ ^^--Oesophageal gland

]„-- Male pore

Female pore

-Vas deferens

yvTT

Sffll

Folded orgon

Rectum

5mm

Fig. 18. Branchellion torpedinis: (a) dorsal view with gills
removed and segments labelled on left hand side ; (b) diagram
of gut and reproductive system ; (c) detail of the posterior crop
diverticula showing fusion in five places. After Sukatschoff, 1912.

typical leech pattern. The clitellar glands are particularly developed
in the Piscicolidae and in Branchellion take up all the space
between the gut and the body wall in segments X-XII.

A SURVEY OF THE GROUP

31

2 mm

2mm

Fig. 19. Various Piscicolidae. (a) Pontohdella miiricata in
characteristic resting position ; (b) P. muricata showing general
body form, with the posterior sucker much contracted; (c)
Pterobdella amara ; (d) Ozobranchiis hranchiatiis ; {e)Ozobranchiis
jantzeanus. ((a) after Harding, 1910; (c) after Kaburaki, 1921;
(d) after MacCallum and MacCallum,^1918; (e) after Oka, 1922).

32 LEECHES

Other Piscicolidae which may be mentioned are Piscicola
(Fig. 17) a parasite of freshwater fishes, Pontohdella (Fig. 19) which
attacks marine fishes, particularly elasmobranchs, and Ahranchus
which has been found on shore fishes round many parts of the
North Atlantic. Our knowledge of marine fish parasites is very
fragmentary, owing to the difficulty of obtaining material.

4. Gnathobdellae

Turning to the Gnathobdellae, the jawed leeches, there is little
to be said about the anatomy of members of the family Hirudidae,
since Hirudo, a typical and widespread form, has been fully
described. Although Hirudo has been introduced to North
America, the most common blood-sucking parasite of mammals
in that country is Macrohdella decora. In India and adjacent
countries Hirudidae abound in swamps, rice fields, etc., and
there are several abundant forms, including Hirudo and Hirudin-
aria, which pierce the skin of the body or limbs, and Limnatis
which enters the mouth of men and animals while drinking. Some
members of this family such as Haemopis have weak jaws and
blunt teeth and have abandoned the blood sucking habit in favour
of a carnivorous mode of life. Haemopis sanguisuga of Europe and
Haemopis marmoratis of North America are typical examples. They
spend a good deal of their time out of water and feed on earth-
worms, insects, molluscs, or decaying flesh of any kind. The crop
has lost most of its diverticula and Haemopis resembles in this the
members of the family Erpobdellidae.

The outstanding characteristic of the Haemadipsidae is that
they have become better adapted to terrestrial life than any other
kind of leech. They are blood-sucking forms which attack man
and animals, lurking on vegetation in damp places. They are
particularly abundant in South East Asia. One of the chief prob-
lems confronting leeches on land is the need to keep the sucker
sufficiently moist to enable it to function properly. The Haemadip-
sidae have achieved this by arranging that the first pair of nephridia
open onto the anterior sucker and the last pair open onto mem-
branous folds of the posterior body wall, the auricles, which are in

A SURVEY OF THE GROUP

33

2cm

(d)

2 mm

Fig. 20. Various Gnathobdellae and Pharyngobdellae (a) and
(b) Haemadipsa, from photographs of living specimens; (c)
Erpobdella octoculata; (d) Whitmania laevis; (e) Praobdella
biittneri. ((a) and (b) from photographs by Gert Heinrich re-
produced in Scriban and Autrum, 1934; (d) after Whitman,
1886; (e) after Blanchard, 1896.)

34

LEECHES

Mouth

Auricle

Anus

Buccal fri

2mm

Fig. 21 . (a) anterior end of Haemadipsa in ventral view to show
buccal frill; (b) posterior end of Haemadipsa in dorsal view

to show auricles.

contact with the posterior sucker (Fig. 21). The products of the
nephridia are used to moisten the suckers, and are conserved by
special frills and muscular rims on the suckers themselves.

5 . Pharyn gobdellae

The Erpobdellidae, sometimes knov^n as the v^orm-leeches,
are freshw^ater or amphibious leeches which have lost the power
of penetrating the tissues of a host and sucking blood. The pharynx
has muscular ridges homologous with those in the Hirudidae,
but no jaws or teeth. These leeches are carnivorous and worms,
insect larvae, etc., are swallowed whole. The gut is simple and
without diverticula. The plan of the reproductive system is fairly
typical, except that the testes are concentrated in the posterior
one third of the body and are very abundant. Erpohdella octoculata
is common in freshwater habitats of Europe and Asia, and is truly
aquatic. In North America the corresponding leech is Erpohdella
punctata. Erpohdella has five annuli per segment, but other mem-
bers of the family have one or more of these annuli subdivided.
Thus Dina, which is represented in both the Old and New Worlds
has the last annulus of each segment divided into two. This
tendency is carried furthest in Trocheta where the typical condition
is three wide and five narrow annuli per segment, but further sub-
division may lead to eleven annuli per segment. Trocheta spends a

A SURVEY OF THE GROUP 35

great deal of its time out of water, and in Europe is often dug up
in gardens where it feeds on the earthworms.

The Trematobdellidae and the Semiscolecidae merit only a
mention in passing. The former are similar to Erpobdellidae in
general structure, but have a duct from the mid gut to the body
wall. The latter are perhaps intermediate between the Hirudidae
and the Erpobdellidae, as they have only a single dorsal jaw rudi-
ment and very small crop caeca. The testes are frequently
subdivided. Opinions differ about whether they should be placed
in the Gnathobdellae or the Pharyngobdellae.

CHAPTER 4

NUTRITION

1. In Hirudidae

The nutrition of leeches is of interest for several reasons. One is
that typical leeches are blood-sucking ectoparasites and they are
remarkably adept at removing from the host a very considerable
quantity of blood without being noticed. This requires sharp,
precise cutting equipment and the assistance of a local anaesthetic.
Secondly, the blood must be prevented from clotting in the gut,
for during locomotion the leech becomes alternately short and
thick and long and thin and this would be impossible if the gut
contained a mass of clotted blood. Finally, a series of investigators
failed to identify any proteolytic enzymes in the gut of Hirudo and
it appears that the function of digestion has been taken over
entirely by symbiotic bacteria.

The jaws of Hirudo have been described in an earlier section
(p. 8). As soon as they begin to saw into the tissues of the host
a secretion from the salivary glands is poured into the wound.
It has long been known that an extract of the head of Hirudo con-
tains a powerful anticoagulin (Haycratt, 1884) which v/as given
the name of hirudin and the presence of this substance was thought
to account for the fact that a wound made by a leech bleeds freely
for a very long time. However, Lindemann (1939) collected some
blood from such a wound and found that its clotting time was
normal. He found that leech head extract also contains a histamine-
like substance capable of causing the dilatation of capillaries so he
postulated that this was the substance actually injected into the
wound and that the free flow of blood was due to the enlargement
of the blood vessels rather than the inhibition of clotting. He sug-
gested that the act of biting and the secretion of the salivary glands
is divisible into two phases (i) the biting phase, when the incision
is being made and the histamine-like compound is being injected

36

NUTRITION 37

and (ii) the sucking phase when the blood flowing past the jaws is
mixed with a secretion containing hirudin which prevents the
blood coagulating in the crop. On the other hand, Stammers (1950)
found that the blood flowing from a wound made by the land leech
Haemadipsa had an abnormal coagulation time for some 8 minutes
after the leech withdrew its jaws, so presumably a certain amount
of hirudin was injected into the wound. It therefore seems likely
that an anticoagulant is produced by all blood-sucking leeches but
that not all of them inject this substance into the wound on the
host. Some at least rely on a histamine to maintain a free flow of
blood and use the anticoagulant to prevent the meal of blood from
clotting during storage in the crop. Hirudin was prepared in pure
form and analysed by Yanagisawa and Yokoi (1938). They showed
that it is an hydrolysis product of protein with an empirical
formula C30H60O20N8 and a molecular weight of 852. It probably
acts by inhibiting the thrombokinase (Lenggenhager, 1936). Only
0-8 mg is required to prevent indefinitely the coagulation of 5 ml
of rabbit blood. Lenggenhager also pointed out that one may
apply tincture of iodine to a leech wound without feeling any pain,
indicating that the saliva also has a local anaesthetic eflPect, but the
substance responsible has not been identified.

It is a general character of blood-sucking leeches that they feed
infrequently but take large quantities of blood at one time. Hirudo
normally takes two to five times its own weight of blood and
Haemadipsa^ the land leech, may take ten times its own weight.
These large meals are digested slowly over a period of many
months. Putter (1907, 1908) drew up detailed balance sheets for
Hirudo. A typical example, quoted in dry weights, runs as follows :
a leech of 128 mg took in 640 mg during one meal. The digestion
of the meal took about 200 days and during that time there was
a loss in weight by excretion of 524 mg. The balance of 116 mg
had been incorporated into the tissues of the leech and as no further
meal was taken the leech lived on its reserves for another 100 days.
From this it is apparent that a leech will grow steadily if it obtains
a meal every six months and that it will not die of starvation if it
feeds only once per year. As one would expect. Putter found that the
leech derives most of its energy from protein breakdown so long
as it has blood in its crop ; he estimated the energy consumption

38

LEECHES

as 15 cal per day at 18°C. During starvation the leech utilized
the stored carbohydrates and fats and its energy consumption
dropped to about 7 cal per day.

When a meal of blood has been sucked into the crop it first
thickens, water being abstracted and passed out via the nephridia
together with considerable quantities of sodium chloride. Worth
(1951) reported that when land leeches are feeding they become
surrounded by a pool of clear fluid. This is presumably a nephridial
excretion. In Fig. 22 is shown that in Hirudo the weight of blood

100

10

20 30

Days after feeding

Fig. 22. Reduction in weight of Hirudo due to excretion of
water after feeding. Drawn from data in Busing et al.f 1953.

in the crop decreases by more than 40% in ten days. The haemo-
globin soon becomes deoxygenated but the erythrocytes remain
intact for a very long time. So remarkable is the freedom from
putrefaction that intact erythrocytes have been found 18 months
after ingestion and even white corpuscles and pathogens may be

NUTRITION

39

identified after many weeks in the crop. A digestive system which
produces such a slow, controlled haemolysis is clearly unusual and
several attempts have been made to identify the enzymes con-
cerned and to settle the question of whether digestion takes place

240

10 20 30 40 50 60 70

Days"

Fig, 23. Change in Rest-Nitrogen content of blood kept with
and without Pseudomonas hirudinis. From Busing et al., 1953.

in the crop or in the intestine. Diwany (1925) injected milk, egg-
proteins and peptones into the gut of starving Hirudo but found
that none was digested and the leeches continued to lose weight.

40 LEECHES

Graetz and x\utrum (1935) failed to find any proteolytic enzymes
in extracts of Hirudo gut wall. They suggested that digestion
depends on bacterial decomposition, but this is difficult to reconcile
with the observation that the corpuscles remain unchanged for
many months. A careful bacteriological examination was made by
Busing (1951) who found that only one kind of bacterium was
present, Pseudomonas hirudinis. Its properties were investigated
by Busing et al. (1953). They were first concerned to show that
it was capable of digesting blood protein, transforming it into
soluble nitrogenous comipounds. They therefore took two samples
of sterile defibrinated sheep's blood and inoculated one with
P. hirudinis. In subsamples taken at intervals the protein was
separated by coagulation and the nitrogen content of the residue
was determined. In the sterile blood the figure remained approxi-
mately constant at 25-28 mg% but in the inoculated samples the
figure rose to over 200 mg^() in 65 days (Fig. 23). This indicates
a progressive breakdown of protein during the whole period and
shows that the bacterium is capable of digesting blood at the slow
rate normally found in leeches. To complete the picture Busing
et al.y showed that P. hirudinis can also break down fats.

When an antibiotic, Chloromycetin, was injected into the crops
of leeches, further digestion was inhibited. When P. hirudinis was
added to a culture of Staphylococcus aureus in sheep's blood the
Staphylococcus was eliminated, suggesting that the Pseudomonas
has the ability to prevent the development of other bacteria. This
would account for the freedom from putrefaction of the blood in
the crop. Presumably the pseudomonads are well mixed with the
meal of blood when it comes into the crop, eliminate any organ-
isms which might cause putrefaction and slowly attack the red
blood cells one by one. The products of digestion are absorbed
by the leech as they are released and if the contents of the crop
are examined some time after ingestion only the corpuscles which
have not been attacked are seen.

It is Hkely that the problem of ensuring that pseudomonads are
present in the crop of every leech is met by arranging that during
the process of cocoon formation, when the leech is forming the
plugs of the cocoon with its mouth, it passes some of the pseudo-
monads into the nutritive fluid surrounding the eggs, for it is

NUTRITION 41

known that the young leeches have P. hirudinis in their guts before
they leave the cocoon. The extraordinary picture with which we
are presented of an animal handing over the whole of its digestive
processes to symbiotic bacteria has few if any parallels in the
animal kingdom (perhaps the nearest are those mammals and
insects which rely on micro-organisms for the digestion of
cellulose), yet it is an arrangement which enables the leech to store
a supply of food for a very long period and to receive a steady
supply of soluble nitrogenous compounds. It is capable of
evolving slowly from the more normal arrangement, the leech
producing progressively fewer enzymes and relying more and
more on the bacteria ; since it enables the leech to make its meals
last longer there is an obvious selective advantage.

The site of absorption may be the crop, the intestine, or both,
but the intestine is much more vascular and it w^ould be surprising
if it did not play some part in absorption. During digestion the
haemoglobin is split into its component parts globin and haematin
and the latter into proto-porphyrin and inorganic iron. It is the
globin which forms a major source of nutriment for the leech. It
has been reported that during assimilation there is an accumulation
of glycogen and fat in the gut epithelium and since there is little
glycogen in the meal of blood it is presumably synthesized from
the products of protein digestion.

Turning from Hirudo to Haemopis we find that the teeth of this
leech are blunt and food organisms such as earthworms and slugs
are devoured whole. Studies of the digestive enzymes present
(Antrum and Graetz, 1934; Graetz and Autrum_, 1935) showed
that enzymes for initiating protein digestion were absent, although
there were several enzymes for the later stages of the process. They
found a dipeptidase and a carboxypeptidase working optimally
at pH 7-8, an aminopeptidase (pH 8-05) and peptone splitting
factors (pH 7-6 and 8-2). Lipases were located in the intestinal
wall and the body tissues. They therefore postulated that the
initial stages of protein digestion were due to putrefaction, although
one difficulty about this theory is that boiled earthworms were
digested about as rapidly as fresh ones. All the evidence points to
the existence of symbiotic bacteria as yet not isolated, which have
taken over a part of the digestive process.

42 LEECHES

2. In Rhynchobdellae

Our knowledge of the nutrition of rhynchobdellid leeches is
very scanty indeed. Food is obtained by inserting a proboscis into
the tissues of the host. Many are fish parasites, but it is somewhat
surprising that a proboscis containing no hard skeletal parts can
be forced through the integument of a fish. A study of the forces
involved would prove interesting. Many rhynchobdellids have
a pair of diverticula between the base of the proboscis and the
beginning of the crop. In Placohdella costata according to
Reichenow (1922) the walls of the diverticula are made up of two
kinds of cells, tall columnar cells and broad ones. The latter con-
tain numerous thread-like micro-organisms and these organisms
are also found in the posterior part of the crop. This leech sucks
tortoise blood and in the neighbourhood of the micro-organisms
the blood corpuscles were haemolysed, while elsewhere they were
not. This might well be a case of digestion by symbiotic micro-
organisms. On the other hand, Reichenow also suggested that
symbiotic micro-organisms were responsible for digestion of
blood in certain mites and insects. These were subsequently
shown to have adequate gut enzymes and Wigglesworth (1953)
suggested that the micro-organisms supply vitamins or other
essential growth factors.

Jashke (1933) examined the oesophageal diverticula of various
other rhynchobdellids including Piscicola geometra, Cystohranchus
respirans and Branchellion torpedinis. He found that these diverti-
cula never contained blood but were filled instead with an
albuminous fluid in which were suspended large numbers of
bacteria. Once again these might well be micro-organisms respon-
sible for the digestion of blood, but their presence in the crop has
not so far been detected. A systematic survey of the crop flora of
leeches is much needed.

The food reserve of the rhynchobdellid leech Glossiphonia
complafiata appears to be mainly in the form of fat droplets.
Adipose cells are a very prominent feature of the connective tissue
and Bradbury (1956) has shown that ten weeks' starvation results
in a 95% reduction in the volume of the contained droplets.
Putter (1908) found that fat metabolism is comparatively

NUTRITION 43

unimportant in the physiology oi Hirudo and van Emden (1929)
thought that fat was actively excreted. The marked difference
between the two types of metabolism may be related to the differ-
ences in diet. While Hirudo is purely sanguivorous Glossiphonia
plunges its proboscis into the tissues of a freshwater snail and after
removing the liquids it may finally suck all the soft parts out of
the shell.

CHAPTER 5

EXCRETION AND WATER
BALANCE

1 . Excretion

The greater part of the food of leeches consists of proteins which
during digestion are converted to amino-acids and absorbed into
the body. A proportion of these amino-acids*"%fe synthesized
again into proteins for use in body building but most are deamin-
ated and used as a source of energy. Deamination results in the
production of ammonia, a substance which is poisonous and readily
diffusible, so it has to be excreted quickly or changed into some-
thing less toxic, such as urea or uric acid. Another source of
nitrogen in the food is nucleic acid which on digestion yields
purines such as adenine or guanine. These are likewise amino
compounds and on deamination give hypoxan thine or xanthine,
which in the presence of xanthine oxidase may be changed into
uric acid. In vertebrates most of these metabolic processes take
place in the liver and the end products, ammonia, urea or uric acid,
are then excreted by way of the kidneys. In annelids these pro-
cesses are particularly associated with the chloragogenous tissue,
while the organs of excretion are the nephridia.

Chloragogen cells are modified coelomic epithelial cells which
become loaded with yellow or brown material in their cytoplasm
and project freely into the coelom. When fully loaded they break
free and float about in the coelomic fluid. In oligochaetes and
polychaetes they are concentrated in the vicinity of blood vessels,
particularly those of the gut. In leeches, where blood vessels are
often lacking, they line the haemo-coelomic channels and may be
especially concentrated in a dense network of coelomic capillaries
known as the botryoidal and vaso-fibrous tissue (see p. 20).
Nitrogenous excretion has *^BbeQ^ most closely studied in

44

EXCRETION AND WATER BALANCE 45

earthworms and the results are worth recording as a guide to
what we may expect to happen in leeches.

Various workers have made physiological observations on
slices of earthworm intestine with chloragogenous tissue attached.
Cohen and Lewis (1949) showed that large quantities of ammonia
are found there and that arginase is present. Heidermanns (1937)
found that this tissue converts peptone to urea and called the
chloragogenous tissue '' the central organ of urea metabolism."
Bahl (1947) found, in addition to ammonia and urea, creatinine
which is presumably produced by muscular tissue. Florkin (1935)
showed the presence of xanthine-oxidase. These results clearly
indicate that ammonia is being converted to urea by the Krebs
cycle involving the production of arginine and its conversion to
urea and ornithine with the aid of arginase ; further, that uric acid
synthesis by the oxidation of xanthine or hypoxanthine is occurring
in the tissue slices. Semal-van Gansen (1956) also showed that the
chloragogen cells are the site of glycogen metabolism and fat
storage and contain abundant acid phosphatase. She drew atten-
tion to the similarity in function between chloragogenous tissue
and vertebrate liver.

It has long been known that chloragogen cells of earthworms
accumulate large numbers of yellowish refringent granules which
are insoluble in acids or alkalis (except ammonia) at ordinary
temperatures. Semal-van Gansen found that in Allolobophora
caliginosa these are made up of a purine, probably a heteroxanthine
such as 7-methyl xanthine, together with a chromolipid and a
small amount of mica. Roots (1960) working with Lumhricus
terrestris could find no purine. During starvation the chloragogen
cells retain their granules but give up glycogen and fat droplets
from the cytoplasm. It is now abundantly clear that earthworm
chloragogenous tissue is the main site of deamination and storage
of carbohydrates and fats. The waste products of metabolism are
ammonia and urea, which are presumably liberated into the
coelomic fluid, and possibly a purine which is accumulated in
granular form, to be liberated into the coelom at the breaking up
of the chloragogen cell. Particulate material in the coelomic fluid
may be ingested by coelomic corpuscles and disposed of in various
ways. It may be deposited in the body wall as pigment, deposited
as brown bodies in the posterior part of the worm or carried

46

LEECHES

through the epidermis to the outside (Stephenson, 1930). Cordier
(1934) estabUshed that the walls of the narrow, ciliated tubes of
the nephridia perform athrocytosis, i.e. the absorption of certain
colloidal and other finely dispersed particles. Bahl (1947) showed
how fluid passing along the nephridial tubes of Pheretima has its
chemical composition changed (Table 1). Glucose and amino-
acids are completely reabsorbed and PO4, CI, Na, K and creatinine

Table 1. Relative Concentrations of Various Substances

IN Blood, Coelomic Fluid and Urine of Earthworms,

AND Analysis of Urine

Constituent

Relative concentrations in:

Analysis of

Blood

Coelomic fluid

Urine

urine mg/100 ml.

Ammonia

1-5

1

2-7

Creatinine

7

5-5

0-5

Urea

0-8

1

3-2

Protein

121

16

30 *

Na

4

8

23-5

K

8

2-5

9-2

Ca

1-4

1-8

12

CI

13-5

22

3-7

Mg

1-4

7

5-4

PO4

16

1-8

M

SO4

2

1-4

1-6

* May have been derived from mucus contaminating urine.

From Bahl, 1947.

are absorbed to a considerable extent, along with water, leaving as
the chief organic elements of the urine urea, ammonia and
creatinine in the ratio 6-5 : 5-3 : 1. Ramsay (1949a and b) showed
that earthworm urine is strongly hypotonic to the body fluids
under normal conditions and that salt resorption takes place in the
distal rather than the proximal part of the nephridium.

Returning to leeches, we find that there is no single tissue
corresponding to the chloragogenous tissue of earthworms.
Cuenot (1931) found that when ammonium carminate is injected
into the coelomic fluid of rhynchobdellid leeches it is taken up by
certain cells lining the coelomic channels and when injected into
Hirudo it is taken up by the botryoidal tissue. In each case these

EXCRETION AND WATER BALANCE 47

cells normally accumulate pigmented granules and it is reasonable
to assume that they correspond in part with the chloragogenous
cells of other annelids. Cuenot further showed that when indigo
sulphate is introduced to the coelomic cavities it is taken up by the
vaso-fibrous tissue of Hirudo (p. 21) and by the large pigment cells
in the connective tissue of rhynchobdellids. Tilloy (1937) carried
the investigation further and concluded that in general the
botryoidal tissue of gnathobdellids and coelomic epithelial cells
of rhynchobdelUds take up particles of diameter greater than
10 A while the vaso-fibrous tissue of Hirudo and the pigment cells
of rhynchobdelUds take up those of diameter less than 10 A.

The only histochemical investigation of these excretory tissues
by modern methods is that of Bradbury (1957, 1959). He was
concerned primarily with the metabolism of iron, which is an
important constituent of the diet of blood-sucking leeches. The
haem probably breaks down to yield first a porphyrin and then
linear tetra-pyrrole compounds similar to vertebrate bile pigments.
These substances have been identified in the vaso-fibrous tissue
oi Hirudo and in the large pigment cells of Glossiphonia complanata.
Bradbury thinks that these are the sites of haem metabolism. In
the case of the pigment cells of Glossiphonia it appears that they
are derived from adipose cells which are such a conspicuous
feature of the parenchyma of this leech. Tetra-pyrroles accumulate
in the adipose cells until there comes a point when the cytoplasm
degenerates leaving an envelope containing a mass of pigmented
spheres. Previously it has been thought that these pigment cells
were derived from coelomic epithelial cells or from amoebocytes
but it now appears more likely that they are in fact derived from
adipose cells which function as kidneys of accumulation.

Bradbury failed to identify the pigment present in the botryoidal
tissue of Hirudo, but established that it is soluble in weak sodium
hydroxide and in glacial acetic acid. He found that iron was present
in the botryoidal tissue but not in the vaso-fibrous tissue. It there-
fore appears that during the metabolism of haem the pyrrholes
pass to the vaso-fibrous tissue while the iron is stored in the
botryoidal tissue. An investigation of the fate of the products of
protein metabolism in leeches along the lines of that of Semal-van
Gansen in earthworms, is much needed. Robin et al. (1957)
identified a new guanidine derivative in the muscles of Hirudo.

48 LEECHES

They gave it the name hirudonine and suggested that it probably
serves as a phosphate acceptor rather than an excretory material.

In leeches the act of phagocytosis by coelomic corpuscles has
frequently been observed but the route subsequently taken by the
corpuscles is less clear. Van Emden (1929) claimed that in
Erpohdella they pass into the lumen of the intestine. Others have
thought that they passed out of the epidermis or were laid down
as pigment, as in earthworms. A fourth possibility is that the
amoebocytes are swept up by the nephridial funnels and passed
into the nephridial capsule, there to break down their waste matter
and pass it into the nephridial tubules. When bacteria or carmine
particles are injected into the coelom of glossiphoniid leeches they
may subsequently be found concentrated in the nephridial
capsules, but in most leeches there is no opening from the capsule
to the rest of the nephridium, so it is difficult to see how the waste
products are eliminated.

In an attempt to understand the role of the nephridial capsule
we must pause to consider the structure and evolution of nephridia.
In both earthworms and leeches they are metanephridia (Goodrich,
1945) consisting basically of an inner ciliated funnel leading to a
coiled length of tube which opens to the exterior by way of a
terminal bladder. The special structure peculiar to leeches is a
capsule containing amoebocytes which is inserted between the
funnel and the tubular region. The capsule is small with a single
funnel in the primitive Glossiphoniidae but large with multiple
funnels in the Hirudidae. The Erpobdellidae have two capsules
and funnels per nephridium. Two functions have been ascribed
to the capsule. One is to receive coelomic corpuscles loaded with
excretory products, the other is to act as a site for the multiplication
of coelomic corpuscles. In primitive leeches such as Theromyzon
there is a communication between the cavity of the capsule and
that of the tubules (Fig. 24), so it is not difficult to see that
amoebocytes loaded with excretory products could break them
down and discharge them into the nephridium, but in most other
leeches there is a partition between the capsule and the rest of the
nephridium, and waste products must either diffuse through the
intervening tissue or travel via the coelomic circulation. Under
these conditions it seems that the capsule has changed its function
and become specialized for manufacturing coelomic corpuscles.

muscle fibre
cat in
transverse
section

moss of
fat drops

intermediate
zone

■pigmented

spheres

contents
of gut

Plate I

A, large pigment cell of Glossiphonia complanata, seen in a
section of the lateral coelomic sinus region ;

B, a similar section to that shown in A, but stained with iron
haematoxylin to show the slight basiphilia of the pigmented
spheres ;

C, an adipose cell containing numerous pigmented spheres. The
cell comprises a mass of fat drops, an intermediate zone and
pigmented spheres. From Bradbun*, 1957.

EXCRETION AND WATER BALANCE

49

Fig. 24. Diagram of nephridial capsule of Theromyzon.
Cy coelomic cavity of ampulla; cep, coelomic epithelium; cp^
cavity of capsule; ct connective tissue; ep, lining epithelium
of wall of capsule ; nb, nucleus of basal cell ; nc, nephridial canal
cell; nm, nucleus of marginal cell. From Goodrich, 1945.

From the work of Bradbury (1959) it seems possible that in Hirudo
particulate matter from the coelomic fluid is retained indefinitely
in the botryoidal tissue and not taken to the nephridia, as it is in
more primitive forms. In the Hirudidae, according to Bhatia
(1938) the cilia of the multiple funnels beat outwards and serve to
waft newly formed corpuscles into the coelomic circulation. This
being so, it follows that the urine passed out of the nephridia is
obtained entirely by filtration through the walls of the tubules and
that the material picked up by the coelomic corpuscles must either
be broken down to a soluble state or be carried to parts of the body
other than the nephridia.

The chemical composition of the urine of Hirudo has been
determined on a number of occasions (Heidermanns, 1937). Under
normal conditions about 72% of the nitrogen excreted is in the
form of ammonia while aminoacids, purines, urea and creatinine

50

LEECHES

each account for 5-10%. This is a much higher proportion of
ammonia than is produced by earthworms and is accounted for
by the presence in the nephridial capsule of bacteria which convert
more complex nitrogenous compounds into ammonia. Busing

anip.i.

amp. 3

Fig. 25. Longitudinal section of nephridial capsule of
Hirudinaria showing numerous funnels opening into a coelomic
ampulla (X ca. 180). ampy 1, 2 and 3, three coelomic ampullae;
h.c.y communications between ampullae and botryoidal tissues;
b.t.y botryoidal tissue; cr, coelomic corpuscles; d.c.y dividing
corpuscles; /, funnel of nephridial capsule; h.n.b.y nephridial
branch of coelomic sinus system; /./., initial lobe of nephridium ;
res, reservoir of nephridial capsule ; tr, trabeculae. After Bhatia,

1941.

et «/. (1953) showed that there are two species present, Corynebac-
terium vesiculare which forms a layer like the pile of a carpet on the
bladder wall (this has been mistaken for ciliation) and C. hirudinis
which floats freely in the fluid. When urine was removed from
the bladders and stored in sterile containers the ammonia content
progressively increased. When leeches were treated with antibiotic

Fig. 26. Symbiotic bacteria on the wall of the nephridial
bladder of Hiritdo. From Grasse, 1959; after Jaschke, 1933.

EXCRETION AND WATER BALANCE 51

to inhibit the bacteria there was a fall in the ammonia content of
the urine. Presumably the fluid entering the nephridial vesicles
contains a fair amount of urea and other complex nitrogenous
compounds which are acted on by the bacteria to give a urine
containing mostly ammonia.

2. Water and Salt Balance

The nephridia of leeches, in addition to their function of
excreting nitrogenous waste, perform the task of maintaining water
balance. There is no detailed study of this process in leeches but it
is certain that the osmotic pressure of the body fluids is consider-
ably higher than that of the water in which they live so that there
must be a constant inward flow of water through the integument.
The function of the nephridia is to remove the excess water while
retaining as many as possible of the inorganic ions other than
ammonia. It is unlikely that they are completely efficient, any
more than are the nephridia of earthworms (Table 1), so there is
a steady drain on the salt content of the coelomic fluid which must
be replaced. A certain amount of mineral salts will be taken in
with the food but Krogh (1939) showed that Haemopis has a salt
uptake mechanism in the epidermis. He first exposed the leeches
to a current of distilled water for two weeks during which time
there was no opportunity to replenish the stock of salts lost in the
urine. He then placed them in frog Ringer diluted to 1/100 and
found that they took up chloride ions at a rate of 048/xM/g/h. In
order to maintain electrostatic equilibrium these ions would have
to be accompanied by ions of opposite sign or exchanged against
ions of the same sign. When the experiment was repeated using
other salt solutions it was found that the leeches were able to take
up sodium ions from sodium bicarbonate solution and chloride
ions from ammonium chloride solution. Krogh therefore con-
cluded that the leeches had separate mechanisms for the active
uptake of sodium and chloride ions and that the two were
normally taken up together.

Although leeches frequently leave the water to feed or to breed,
they appear to have no very effective mechanism for controlling
water loss. When exposed to dry air they secrete abundant mucus

52 LEECHES

from the epidermis but it does not reduce water loss very appre-
ciably. Klekowski (1961) kept Hirudo and Haemopis in air of
80% relative humidity at 22°C and found that their water content
was reduced to 20% in 4-5 days, after which death ensued. If
returned to the water after about 4 days they were able to return
to full hydration within a few hours. A more drastic process of
desiccation was carried out by Hall (1922) on the rhynchobdellid
leech Placohdella parasitica. When a current of dry air was passed
over these leeches they lost 92% of the water in the body m 7 J hr,
but recovered when placed in water at 13°C.

CHAPTER 6

CIRCULATION AND RESPIRATION

In most annelids there is a well developed blood vascular system
consisting of longitudinal dorsal and ventral vessels, a plexus on
the wall of the gut and regular lateral segmental vessels supplying
the body wall, nephridia, etc. Leeches do not conform to this
pattern. The nearest approach is found in the rhynchobdellid

Pulsatile vesicle

Acanthobdella

Glossiphonia

Piscicola

Hirudo Erpobdella

Fig. 27. Comparative diagrams illustrating the progressive
loss of median dorsal and ventral blood vessels and their func-
tional replacement by lateral coelomic sinuses with muscular
walls in various leeches. Coelomic sinuses open circles; dorsal
and ventral vessels solid circles; thick-walled circles indicate
coelomic sinuses with muscular walls.

leeches which have small longitudinal vessels but no segmental
ones. These longitudinal vessels lie in coelomic sinuses (Fig. 27)
and it is the coelomic fluid which circulates to all parts of the body,
carrying out gaseous exchange and transporting food materials

53

54 LEECHES

and excreta. The blood in the longitudinal vessels is a clear fluid
in which no respiratory pigment has been identified. The coelomic
fluid is colourless in the rhynchobdellids but contains haemoglobin
in solution in the gnathobdellids. In the latter group there is
no trace of true blood vessels, not even in development. Their
circulatory system consists entirely of coelomic sinuses and
circulation is brought about mainly by the contraction of lateral
sinuses which have acquired muscular walls.

Oxygen uptake in most leeches takes place through the general
body surface, but the Piscicolidae have accessory respiratory
organs filled with coelomic fluid which may be large leaf-like gills,
as in Branchellion (Fig. 18) or small hemispherical vesicles which
pulsate rhythmically {Piscicola^ Fig. 17). When it is necessary to
increase the rate of oxygen uptake Piscicola increases the rate of
pulsation of its vesicles but other leeches ventilate the body surface
by means of dorso-ventral undulations which pass along the body
from head to tail. This movement is carried out while the posterior
sucker is held fast to the substratum, the head moving freely, and
it has been described as a swimming movement performed while
standing still. The rate of ventilation or of pulsation is related to
temperature in the manner shown in Fig. 28.

An alternative or supplementary method of increasing oxygen
uptake is to increase the rate of pumping of the coelomic fluid
round the body. Herter (1936) found that in Erpohdella^ where it is
sometimes possible to observe the lateral sinuses by transparency,
the rate of pumping varied from 3-7 per min at 17°C to 17-1 per
min at 27° C. The mechanism controlling pumping was studied
in Hirudo by Gaskell (1919). From each segmental gangHon two
nerves run out on each side and send branches to the walls of the
lateral sinus. The anterior segmental nerves accelerate the rate
of pumping while the posterior nerves cause a retardation.
Contractions continue for long periods after all nerves have been
severed, suggesting that the stimulus for contraction originates in
the muscles of the sinus wall. Such a mechanism is called myogenic
to distinguish it from one in which the stimulus originates in the
nervous system, which is neurogenic. The arrangement in Hirudo
may be compared with that in the mammalian heart, where the
beat is myogenic and is accelerated by secondary sympathetic
fibres but retarded by a branch of the vagus nerve. The parallel

CIRCULATION AND RESPIRATION

55

90

80

70

60

50

40

E

<D 30

20

Hirudo

Haemopis

• / G. complanata

■ • • Piscicola

J il

10 15 20 25 30 35

Temperature, °C

Fig. 28. Rate of making respiratory movements by various
leeches at various temperatures. Redrawn from Herter, 1936-9.

is even more striking if we consider the effects of drugs. In
Hirudo the accelerating effect of the anterior segmental nerve
is abolished by ergotoxin while the slowing effect of the posterior
nerve is abolished by curare. Injection of adrenalin increases the
rate of pumping, while muscarin decreases it. Schwab (1949)
found that adding acetylcholine to water surrounding Erpohdella
caused speeding up which was maintained for about half an hour,
after which there was a period of depression. Atropine, on the
other hand, slowed the contractions. These effects are very
similar to those found in mammals and indeed in many vertebrate
hearts, but are quite different from the state of affairs in any other
invertebrates. In most arthropods and annelids, for instance,

\m

DOS //,

LIBRARY

56 LEECHES

hearts are neurogenic and the principal accelerator is acetylcholine.
Gnathobdellid leeches are clearly exceptional in this respect, and
this is further evidence that their circulatory system is not homo-
logous with the blood system of other annelids. The source of the
adrenalin in leeches appears to be the ganglia of the ventral nerve
cord, for Gaskell (1919) demonstrated the chromaffin staining
reaction in certain cells of the ventral ganglia and identified
adrenalin in ganglion extract. Perez (1942) confirmed this result,
although he thought that the adrenalin was more localized in its
distribution than Gaskell had suggested.

Leeches are predominantly freshwater animals, but many fresh-
water habitats contain water which is only partially air-saturated.
There have been several investigations into the rate of oxygen up-
take by leeches at various oxygen concentrations of the water.
Early experiments with Hirudo (Lindeman, 1932, 1935) involved
placing the leeches in water in a closed container. Samples of
water were drawn off at intervals and from the rate of fall of
oxygen concentration the oxygen uptake of the leeches was calcu-
lated. It appeared that Hirudo was able to maintain a constant rate
of oxygen uptake independent of the oxygen concentration down
to about 10-20% air-saturation, the precise level depending on the
temperature. Similar experiments by Hiestand and Singer (1934)
and by Sgonina (quoted by Herter, 1936) gave rather diflFerent
results. These discrepancies were probably due to variation in the
state of nutrition, time of year and degree of acclimatization.

In more recent work (Mann, 1956) these variables have been
eliminated as far as possible. In Fig. 29 is shown the oxygen con-
sumption of five species of leech at various oxygen concentrations.
In these experiments the leeches were placed in a small container
with water of a known oxygen concentration and left for about
1 hr, during which time the oxygen concentration fell by a relatively
small amount. From the final oxygen concentration it was possible
to determine the oxygen consumption at the mean concentration
of the experiment. To build up the curves shown in Fig. 29 large
numbers of such experiments were carried out, each point on the
graph being the mean of at least five determinations. The highest
rate of oxygen uptake in air-saturated water is shown by Piscicola
geometra, the piscicolid fish parasite. This leech has to be
very active indeed when it is seeking a host and is provided with

CIRCULATION AND RESPIRATION

57

c
o

E

O

I 2 3 4 5'

Oxygen concentration, m' /L

I 2 3 4 5 6

Oxygen concentration, mL/l

^

5 -

1 ^

10

c
o
o 2

O

Erpobdella

testacea

/

<o

—

0 J
0 /

/o

-

0 /

o

o /

^S

- 9/
^C>J L.

I 1

I

Oxygen concentration, ml/L
6

I 2 3 4 5 6

Oxygen concentration, ml/L

2 3 4 5 6

Oxygen concentration, ml/L

Fig. 29. Oxygen consumption of various species of leech at
20°C at various oxygen concentrations. From Mann, 1956.

58

LEECHES

pulsatile vesicles so it is perhaps not surprising that its rate of
metabolism is high. In the two Erpohdella species as well as in
Piscicola the oxygen uptake was proportional to the oxygen
concentration of the water, suggesting that low oxygen concentra-
tions produced no special physiological response from the animals.
The curves for Glossiphonia complanata and Helohdella stagnalis
on the other hand are comparatively level over part of the range
of oxygen concentration, suggesting that there is some regulation
of oxygen uptake by the leeches.

Fig. 29a. Apparatus used in leech respiration studies, giving
the results illustrated in Fig. 32. The leeches were placed in
the chamber C and subjected to a constant stream of water
from reservoir A, driven by pressure from a gas or air cylinder.
The oxygen content of the outflow was determined by a drop-
ping mercury electrode in chamber F. From Mann, 1958.

The experiments described above were all repeated with leeches
which were allowed to become acclimatized overnight to the
oxygen concentration of the experiment. Only one leech responded
to this treatment, Erpohdella testacea, which began to regulate its
oxygen uptake at concentrations above J air-saturation (Fig. 30).
Further investigations showed that such acclimatization occurs in
summer but not in winter. This leech lives in ponds which are
relatively anaerobic in summer and the adaptive significance of
such a mechanism is clear. When the actual method of adaptation
was studied it was estabHshed that the leech did not make ventila-
tory movements so presumably it increased its rate of circulation.

CIRCULATION AND RESPIRATION

59

Erpobdella festacea

x>^ Erpobdella octoculafo

X

Oxygen concentration, ml/L

Fig. 30. The relation between oxygen consumption and

oxygen concentration in the two species of Erpobdella after

acclimatization overnight to the concentration of oxygen at

which the readings were taken. From Mann, 1956.

The low oxygen concentrations must have stimulated the adrener-
gic mechanism, thus accelerating the rate of contraction of the
lateral sinuses.

It is of interest to enquire into the function of haemoglobin in
leeches, for in many annelids such as Arenicola it is of value only
under conditions of extremely low oxygen concentrations in the
surrounding water. In Liimhricus it seems likely that the haemo-
globin transports between one-quarter and one-half of the oxygen
used by the worms. Johnson (1942) compared the oxygen con-
sumption of Lumhricus herculeus at various concentrations of
atmospheric oxygen, before and after the inactivation of the
haemoglobin with carbon monoxide, care being taken to ensure
that the respiratory enzymes were not affected. She concluded
that the haemoglobin of the blood was responsible for carrying
about 23% of the respired oxygen when the oxygen pressure was

60

LEECHES

152 mm, 35% at 76 mm and 40% at 38 mm (Fig. 31). When
similar experiments were carried out with the leech Erpohdella
testacea it was found that after carbon monoxide treatment the
oxygen consumption fell by 45% in air-saturated water and by
25% in J air-saturated water (Mann, 1958). This suggests

50

50 100

O2 tension, mmHg

50

0 1 2 3 4 5 6

O2 concentration, ml/L

Fig. 31. The percentage of oxygen carried by the haemoglobin
of an earthworm and a leech at various oxygen tensions. From
data in Johnson, 1942 and Mann, 1958.

that in Erpohdella as in LumbricuSj the haemoglobin functions in
oxygen transport at all normal oxygen concentrations of the
environment. Haemoglobin appears to play no essential part in
acclimatization to low oxygen concentrations, as it does in the
Cladocera for instance, for E. testacea was able to acclimatize even
after the haemoglobin had been inactivated (Fig. 32). Many
leeches have a considerable ability to withstand anaerobic condi-
tions. Numerous examples are quoted by von Brand (1946).
Hirudo medicinalis, Haemopis sanguisuga, Helohdella stagnalis and
Erpohdella octoculata survived for about 5 days at room temperature
while Glossiphonia complanata was able to survive for 16 days at
14-16°C without oxygen. Putter showed that Hirudo survived
only 3-5 days if it had been recently fed but over 10 days
when starving. This may well have been because the oxygen

CIRCULATION AND RESPIRATION

61

requirements of the recently fed leeches were higher. Hyman
(1929) showed that the oxygen uptake of planarians was high
shortly after feeding. The oxygen consumption of the leech
Erpohdella testacea rose fourfold soon after feeding (Mann, 1958).
Von Brand (1946) has reviewed the evidence for the occurrence

E
in

^

20

15

iO

t \

\

Air-sofurated wafer

>■ * T Air-sot. » < Air-sat. -»-*-^Air-sat.

Fed

CO treatment

Time, days

Fig. 32. Mean oxygen consumption of twenty-two Erpohdella
testacea of average weight 45 mg, subjected to various treat-
ments as indicated. Lines are drawn to represent twice the
standard error above and below each point. After feeding the
rate of oxygen uptake rose to a high level, but settled to about
7 /Lil/h/leech on the fourth to sixth days. On transfer to water
of low oxygen content this rate of oxygen uptake was maintained
but after treatment with carbon monoxide the leeches failed
to maintain a normal rate of respiration in water of low oxygen
content. From Mann, 1958.

of anaerobiosis in invertebrates and pointed out that when the
concentration of the oxygen in the environment falls many animals
have an increased consumption of carbohydrate, a greater produc-
tion of organic acids and a higher respiratory quotient, indicating
that anaerobic fermentation is taking place. He has further

62 LEECHES

suggested that the critical oxygen tension below which the
oxygen uptake of an animal falls rapidly is the tension at
which the metabolism changes from a mainly aerobic to a mainly
anaerobic type.

There is clear evidence from the work of Braconnier-Fayemendy
(1933) that Hirudo effects a transition to anaerobiosis, for in the
absence of oxygen there is a fourfold increase in the carbon content
of the urine. Moreover, there is no evidence of the repayment of
an oxygen debt after anaerobic metabolism (Hiestand and Singer,
1934) so the products of anaerobiosis must have been excreted.
In the other leeches whose oxygen uptake in relation to oxygen
tension has been studied it is probable that all are able to carry out
anaerobic metabolism, but those best adapted to life in low oxygen
concentrations are those which can maintain aerobic metabolism
to the lowest level of oxygen in the environment.

When leeches find themselves in water of low oxygen content
they tend to move to the surface. In extreme conditions they pro-
trude the anterior half of the body from the surface of the water,
thus in effect carrying out aerial respiration. During the nineteenth
century medicinal leeches were kept in jars and if the leeches were
restless or rose to the surface this was taken as a forecast of bad
weather. The explanation of this phenomenon is not clear,
presumably they responded to falling barometric pressure. It has
recently been shown that earthworms and many other organisms
show a correlation between respiratory rate and barometric pres-
sure (Brown, 1957) so the leeches may have responded directly
to pressure changes, but a fall in atmospheric pressure will also
lead to a small fall in the concentration of dissolved oxygen in the
water, so it is also possible that the leeches responded to this, and
only indirectly to the pressure changes.

CHAPTER 7

MUSCLE, NERVE AND
LOCOMOTION

1. The Muscular System

Locomotion in annelids in general is brought about by the
antagonistic action of two sets of muscles, the longitudinal muscles
whose fibres lie parallel to the longitudinal axis of the body and
the circular muscles whose fibres lie in a plane at right angles to
the longitudinal axis. The forces produced by one set of muscles
are used to stretch the others through the hydraulic action of the
fluid enclosed within the body wall. Thus an annelid may be com-
pared with a fluid filled cylinder which, when the circular muscles
contract, becomes long and thin and when the longitudinal
muscles contract becomes short and thick. In earthworms there
are internal septa which limit the movement of coelomic fluid and
help one part of the body to be longitudinally contracted while
another part is longitudinally extended, but in many polychaetes
the septa are reduced or absent so that several segments work as a
unit. In leeches the whole body works as a unit and all septa have
disappeared. Moreover the coelomic fluid has been replaced by
mesenchyme cells but these are sufficiently deformable to provide
the hydraulic mechansim described above.

Between the outer circular muscles and the inner longitudinals
leeches have a double layer of oblique muscles whose fibres run
at approximately 45° to right and left of the longitudinal axis
(Fig. 33). This condition is unique among annelids. In most
species they run spirally round the body in complete right and left
geodesic helices. The mode of action of these muscles has not
been investigated experimentally but Clark and Cowey (1958)
have considered the geometry of a geodesic system of inextensible
fibres in some nemertean w^orms and turbellarians and this gives

63

64

LEECHES

'.m.

b.t

cr. d.h.c. v.h.c.^-"-^- d.v.m.^''* l-m.

Fig. 33. Diagram of muscles of body wall of Hirudinaria.
Note oblique muscles, a.r.o^ annular receptor organ; b.t^
botryoidal tissue; cm, circular muscles; cr, crop; d.h.c, dorsal
haemocoelomic channel; d.v.m. dorso-ventral muscles; ep,
epidermis; l.h.c, lateral haemocoelomic channel; /.m, longi-
tudinal muscles; o.m, oblique muscles; s.r.o, segmental receptor
organs; v.h.c, ventral haemocoelomic channel; v.m, vertical
muscles ; v.n.c, ventral nerve cord ; 1-5, serial numbers of annuli.

FromBhatia, 1941.

US some idea of what is likely to happen with fibres that are
contractile.

Considering the nemertean as a fluid-filled cylinder in whose
walls runs a system of inextensible spiral fibres, we see that the
shape of the cylinder can be altered by changing the angle 6 which
the fibres make with the longitudinal axis (Fig. 34). The volume
contained by such a cylinder is maximal when the angle 6 is 54° 44'.
If the volume of the contained fluid were equal to the maximum
volume of the system there would be no possibility of changing
shape, so the volume of the fluid is something less than maximal
and the difference is taken up when necessary by the animal
becoming elliptical in cross section. In leeches the geometry is
comparable but the fibres are contractile. When the fibres are at
54° 44' to the longitudinal axis this is the position at which they

MUSCLE, NERVE AND LOCOMOTION

65

10 20 30 40 50 60 70

Angle between fibre and longitudinal axis,

(c)

90

e

Fig. 34. The relation between the volume of a cylindrical
system bounded by inextensible "fibres of length D and the
angle B which the fibres make with longitudinal axis, (a) the
course of a single fibre; (b) the cylinder slit lengthwise and
opened out ; (c) the relation between angle Q and volume of
the system, which is maximal when B = 54" 44' The horizontal
line represents the volume of an animal which is less than the
maximum permitted by the fibres. The limits of Q are at
F and G. From Clark and Cowey, 1958.

66

LEECHES

contract maximally for a given body volume. When the body is
long and thin the spiral fibres are clearly reinforcing the action of
the longitudinal muscles and causing the body to shorten (Fig. 35a).
When the leech is short and thick the spiral fibres reinforce the
action of the circular muscles and cause elongation (Fig. 35b).

(a)

Fig. 35. Diagram illustrating how spiral muscles may reinforce

the action of (a) the longitudinal muscles or (b) the circular

muscles. For explanation, see text.

There must be some intermediate position w^hen the spiral muscles
cause neither lengthening nor shortening, and this is when they
make an angle of 54° 44' w^ith the longitudinal axis. At this point
they serve only to increase internal hydrostatic pressure, imparting
rigidity to the body of the leech. This enables the leech to sit
upright on its posterior sucker, an activity vv^hich is characteristic
of certain leeches and important in their behaviour.

Leeches also have a v^ell developed set of dorso-ventral muscles.
These, on contraction, make the body flat and ribbon-like, thus
increasing the efficiency of the dorso-ventral undulations used in
swimming.

The longitudinal, circular and dorso-ventral muscle cells of
leeches are elongated unstriated cells with an inner axial sarco-
plasm and an outer rind of contractile myoplasm. In the longitu-
dinal and circular muscles they are usually simple spindle-shaped

MUSCLE, NERVE AND LOCOMOTION

67

Structures but in the dorso-ventral muscles they are frequently
branched at the ends, providing multiple insertions into the body
wall. The nucleus is usually in the central sarcoplasm but in a
few cases it is in a lateral protuberance of the sarcoplasm (Fig. 36c).
The myoplasm consists of large numbers of myofibrillae regularly
arranged and separated one from the other by thin lamellae of
sarcoplasm (Fig. 36a). In Haemopis longitudinal muscle cells are

(0)

(b)

(0

(d)

20/^

Tendon

Epidermal eel

Cuticle

Muscle cell

Fig. 36. (a) and (b) transverse and longitudinal sections of part

of a normal muscle fibre ; (c) and (d) sections showing how the

sarcoplasm may form a lateral protuberance ; (e) the attachment

of a muscle to the cuticle, after Sukatschoff, 1912.

5-15 mm long when moderately contracted (Schwab, 1949). In a
nerve-muscle preparation contraction may be initiated by electrical
stimulation of the nerve or muscle or by immersion in a dilute
solution of acetylcholine. The latter reaction has been used as a
test for the presence of acetylcholine (Minz, 1932) as contractions
are produced with concentrations as low as 1 X 10~^. Eserine
increases the response to a given stimulus, but curare inhibits it.
It has recently been found that morphine in the appropriate

68

LEECHES

concentration facilitates relaxation without affecting the sensitivity
to acetylcholine, so that the best method of preparing leech muscle
for assay of acetylcholine is to treat it with morphine and eserine
sulphate (Murnaghan, 1958). During electrical stimulation
acetylcholine is released into the surrounding fluid and it therefore
seems likely that it has been produced at the neuromuscular junc-
tion, and that this is the normal mechanism for inducing contrac-
tion (Bacq and Coppee, 1937). Cholinesterase is present in both
the muscles and the ventral nerve cord and presumably hydrolyses
the acetylcholine as soon as it has done its work. Eserine inhibits
cholinesterase, so this accounts for its effect of increasing the
response to stimulation.

The rate of action of leech longitudinal muscle is slow, con-
sidering that it is concerned with locomotion, escape reactions and
attachment to host. Schwab (1949) studied the time constants of
dorsal longitudinal muscle of Haemopis. Table 2 shows that it is

Table 2. Time Constants of Various Muscles

Contraction

Relaxation

Chronaxie

Conduction

time

time

(msec)

rate

(msec)

Haemopis

dorsal long

500

27 sec

68

49 cm/sec

Frog

sartorius

40

55 msec

3

2-4 m/sec

gastrocnemius

150

0-3

—

Crayfish

claw (fast)

200

1 sec

1-2

20 cm/sec

Helix

foot

200

"several" sec

20

—

Pecten

slow adductor

500

45 sec

—

—

Cat diaphragm

480

—

5-6

35 cm/sec

much slower than vertebrate limb muscle, e.g. frog sartorius, and
is more nearly comparable with such muscles as Pecten slow
adductor or cat diaphragm. Similar results were obtained with
the muscle of Hirudo by Lapicque and Veil (1925) who compared
them* with the muscles of the body wall of an earthworm. They

MUSCLE, NERVE AND LOCOMOTION 69

found that the chronaxies were 30 msec for Hirudo and 20 msec
for earthworm, while conduction rates were about 35 cm/sec.
The response of leech muscle to electrical stimulation is
decreased by immersion in hypotonic solutions of sodium chloride
or sugar (Winterstein and Ozer, 1949), but the same treatment
increases the amount of tonic contraction, suggesting that the
mechanism of contraction after stimulation is quite distinct from
the mechanism for maintaining tonus. Moreover, while increased
activity under electrical stimulation is associated with increased
oxygen consumption, there is no such relation between tonus and
oxygen consumption (Ozer and Winterstein, 1949). The oxygen
consumption is maximal when the muscle is immersed in 0-1 N
sodium chloride and at other concentrations the oxygen consump-
tion is lower irrespective of whether the tonus is increased or
decreased.

2. The Nervous System

The gross morphology of the central nervous system of Hirudo
has been described and the differences in other genera are mainly
ones of relative proportions. In this section we shall consider the
micro-anatomy of the nervous system of a typical segment in order
to provide a background for the understanding of its physiology.
As in most annelids the motor nerve cells are concentrated in the
ventral nerve cord while the sensory nerve cells lie peripherally,
in or near the sense organs. In earthworms the nerve cells are
widely distributed in the ventral half of the ventral cord with
special concentrations in the segmental ganglia, but in leeches the
motor cell bodies are found almost entirely in the ganglia, enclosed
within fibrous capsules so that they are sharply separated from the
mass of fibres which form the bulk of the nerve cord. There are,
however, certain cells in the fibrous mass. They are spindle shaped
when viewed from the side and star shaped in cross section. Miller
(1945) regards them as nerve cells but most authors, notably
Scriban and Antrum (1934) and Ito (1936) consider that they are
neuroglia, i.e. supporting cells whose processes bind together the
nerve fibres.

Each ganglion has six cell capsules, two antero-dorsal in position,
two postero-dorsal and two median ventrals. A typical transverse

70

LEECHES

section (Fig. 37) passes through two dorsal and one ventral capsule
and shows the nerve cells as pear-shaped structures with their
narrow ends directed towards the centre of the ganglion. They

Ventra

Transverse and
longitudinal fibres

Neuroglia cell

Nerve cell in
dorsal capsule

Neurilemma

Giant ceil in
ventral capsule

0-1 mm

Fig. 37. Transverse section through a ventral ganglion of

Haemopis.

give off processes which pass through the capsule wall and join the
fibrous mass. The course of the axons was studied by Retzius
(1891) and by Havet (1900) and their work has not been improved
upon. The main motor axons run from a given cell capsule into
the lateral segmental nerves of their own or the opposite side of
the body. Internuncial neurones form synaptic connexions with
both sensory and motor fibres, often running from one ganglion
to the next along the ventral cord. In addition to these there is
a giant cell in each ventral capsule and this has an axon which
forks, sending one process into the ventral cord and two into
lateral segmental nerves. There are no giant fibres of the type
seen in earthworms and polychaetes, but from the behaviour of
leeches it is clear that there is a fast conducting system (Miller,
1942). From Retzius' figures the axons of the ''giant nerve cells"
appear to be about twice the diameter of a normal nerve fibre.
It is doubtful whether these fibres would mediate the startle
reaction of leeches unless they were also myelinated. Wilson (1960)
studied the effect of stimulating an isolated segmental nerve of
Hirudo and found no evidence of a quick response in the peripheral
neuromuscular system. Horridge and Roberts (1960) reached the

MUSCLE, NERVE AND LOCOMOTION

71

Ventral nerve cord

Lateral segnnental
nerve

Posterior dorso- lateral
cell capsule

Fig. 38. Diagram illustrating the main routes taken by the
processes of the nerve cells lying in the ventral ganglion of a
leech. The four dorsal capsules are shown in firm outline, the
two median ventral ones in dotted outline. After Scriban, 1934,
based on the work of Retzius and Havet.

same conclusion regarding the segmental nerves of earthworms. This
is an interesting difference between annelids and arthropods, for in
the latter there is multiple innervation of muscle fibres, providing
for both quick and slow response. The ventral nerve cord of leeches
contains a large number of fibres mostly extending over no more than
one segment ; it is perhaps not surprising that the normal conduc-
tion rate in this cord is rather low, of the order of 18 cm/sec in
Haemopis according to Schwab (1949), and 40 cm/sec in Hirudo
according to Lapicque and Veil (1925). Schwab found substantial

72

LEECHES

quantities of both acetylcholine and cholinesterase in the ventral
nerve cord of Haemopis.

The general pattern of lateral nerves is that from each segmental
ganglion arise two pairs of nerves. The anterior ones run ventrally
at first and then turn outwards following the curvature of the body
wall while the posterior pair run to the dorsal half of the body,
serving primarily the dorsal body wall, but also sending a branch
to the organs in the postero-ventral part of the segment. Each of

Sensory
nerve eel

Sub-epidermal
ring

ventral

Gut

Posterior
segmental nerve

Epider

egmental
anglion

al muscle

Fig. 39. Diagram illustrating the lateral segmental nerves and
peripheral nerves of Erpohdella. After Bristol, 1898.

these lateral segmental nerves connects with an inter-muscular
nerve ring which circles the body between circular and longitu-
dinal muscles. There are two of these in each segment, corre-
sponding in position with the anterior and posterior pairs of lateral
nerves. There are nerve fibres running longitudinally between the
intermuscular rings and others which run to the nervous system
lying immediately below the epidermis. Bristol (1898) described

MUSCLE, NERVE AND LOCOMOTION 73

sub-epidermal nerve rings corresponding in number and position
with the inter-muscular rings, and it has been suggested (Miller,
1945) that there is also a network of nerve fibres just below the
epidermis comparable with that described for the earthworm by
Hess (1925). On the other hand Wilson (1960) studied the spread
of excitation over the body wall of Hirudo after stimulation of an
isolated segmental nerve and concluded that no nerve net was
present. Iwata (1940a, b) reached a similar conclusion regarding
a Japanese leech. The sense organs of the epidermis and the
proprioceptor organs in the body wall send neurones into the
peripheral network of fibres and from here they pass down the
segmental nerves to the ventral nerve cord.

3. Locomotion

Having discussed the structure and function of the nervous
and muscular systems we may now pass to the co-ordinated
activity of these systems as seen in locomotion. Broadly speaking,
leeches move in two ways: by swimming, which involves dorso-
ventral undulations of the body and by creeping, which involves
moving the anterior sucker forward and drawing the posterior one
up behind. Gray et al. (1938) resolved these activities into a
system of reflex responses. Stated rather simply, the sequence is
as follows : if Hirudo is freely suspended in water so that neither
the suckers nor the ventral body surface are able to make contact
with a solid object it will swim, the dorso-ventral muscles being
contracted and the circular muscles relaxed while dorso-ventral
undulations pass back along the body as a result of differential
contraction of the longitudinal muscles. If the anterior sucker is
now brought into contact with a solid object it attaches firmly and
the swimming stops ; the dorso-ventral and circular muscles relax
and the longitudinals contract, causing the body to become short
and thick. If now the posterior sticker is placed in contact with a
solid object it becomes attached and a wave of contraction passes
back over the circular muscles while the longitudinals are inhibited,
causing the body to become long and thin. Repetition of the last
two reflex actions results in crawling. Gray et al. therefore con-
cluded that if ventral peripheral stimulation is absent the leech
swims, if it is present it crawls ; and that the rhythm of crawling is

74

LEECHES

determined by a recurrent pattern of stimulation via the ventral
suckers. It should perhaps be added at this point that crawling is
not produced entirely by elongating and shortening the body.
In most species, when the posterior sucker is drawn forward the
body is flexed in a dorso-ventral plane, enabling the posterior
sucker to be placed immediately behind the anterior one (Fig. 40).

.^

^

Piscicola Erpobdella

Fig. 40. Successive stages in the creeping of Piscicola and
Erpobdella. After Herter, 1929, modified.

Chapman (1958) has pointed out that contraction of the dorso-
ventral muscles in the middle region of the body assists this
flexure. The movement is more marked in some species than in
others and in its extreme form is reminiscent of the movement of
a looper caterpillar.

MUSCLE, NERVE AND LOCOMOTION

75

4. Co-ordination

Various experiments have been conducted on Hirudo and
Haemopis to elucidate the role of the nervous system in locomotion.
Rhythmical electrical activity is found in the ventral nerve cord
of a swimming leech, but this becomes irregular if the nerve cord
is isolated from peripheral stimulation by cutting all segmental
nerves. If the cord is isolated from the supra- and sub-oesophageal
ganglia by transection just behind the head the electrical activity
disappears. If the body of a leech is cut transversely leaving only
the ventral nerve cord intact the two halves will show co-ordinated
locomotory activity (Fig. 41), but if the nerve cord only is tran-

Posterior

Anterior

sec

Fig. 41 . Record, taken from a cinematograph film, showing
co-ordinated swimming movements of the anterior and posterior
regions of a leech which were connected by nerve cord only.
From Gvdiy etal, 1938.

sected the activity on either side of the cut is unco-ordinated.
Anterior to the cut the body becomes rounded in cross section as
for crawling, and there is an increase in tonus in the circular
muscles. Posterior to the cut the body becomes flattened and may
perform swimming movements, while there is a loss of tonus in
the circular muscles. It thus appears that the ventral nerve cord
plays a vital role in the co-ordination of locomotion but it only

76 LEECHES

does so when stimulated from the peripheral nervous system or
the ganglionic masses.

Clearly the reflex pattern described by Gray et al. is only part
of the mechanism of locomotion, for there are many exceptions to
the pattern they described. When a leech changes from crawling
to swimming it does so in spite of the ventral peripheral stimulation
which it is receiving. When it performs ventilatory movements it
in effect swims while retaining a hold with the ventral sucker
(Fig. 42). It is likely that the large ganglionic masses of the head

Fig. 42. Lateral view of Erpobdelia with ventilatory movements

in progress.

and anal regions play a part in determining locomotory behaviour.
Kaiser (1954) has considered in some detail the experimental
evidence for ganglionic activity. Decapitated leeches swim more
readily and for longer periods than intact ones. This is partly due,
no doubt, to the fact that the ventral nerve cord no longer receives
impulses from the anterior sucker, as these would normally
initiate crawling. The swimming movements of a suspended leech
may be stopped by stroking the ventral surface and conversely
they may be accentuated by gentle dorsal stimulation. However,
if the cerebral ganglion is removed while the suboesophaegeal is
left intact the leech is still abnormally active. It appears that one
of the functions of the cerebral ganglion is to inhibit locomotion
under certain circumstances. Another function, which we may
deduce from a study of the pathways of nerve fibres, is to receive
and sift information from the sense organs of the head.

Removal of the sub-oesophageal ganglion brings about a number
of changes at one time. It isolates the ventral nerve cord from the
influence of the brain, isolates it from peripheral stimulation
through the anterior sucker and removes the influence of the sub-
oesophageal ganglion. Leeches treated thus appear to be almost
incapable of crawling, remaining inert for long periods. Budden-
brock (1953) has pointed out that a number of experimental results

MUSCLE, NERVE AND LOCOMOTION 77

are explained by supposing that in response to peripheral stimula-
tion the sub-oesophageal ganglion excites the ventral nerve cord
to co-ordinate crawling activity. There are four situations in which
it might fail to do so: (i) when there is no ventral peripheral
stimulation, (ii) when inhibited by the brain, (iii) when the
ganglion has been removed and (iv) when the nerve cord has been
cut. Taken together these account for all the experimental and
behavioural observations quoted above.

According to Schluter (1933) removal of the anal ganglion
inhibits swimming so that leeches dropped into water fall passively
to the bottom. Removal of the brain of such leeches restores the
powers of swimming. It is thus possible that the division of labour
between the various ganglionic masses is as follows: the sub-
oesophageal ganglion is mainly responsible for initiating and
maintaining crawling movements, the anal ganglion for swimming
movements and the supra-oesophageal ganglion for inhibiting
locomotion under certain circumstances.

It is interesting and instructive to compare the locomotion
of leeches with that of earthworms. In the latter, the basic
mechanism is that a group of segments becomes elongated, obtains
a point of attachment anteriorly by protrusion of chaetae and then
shortens, drawing the posterior segments forward. Chaetae are
then protruded on the posterior segments before the next phase
of elongation begins. Normally, several waves of activity are
present in the body at one time, but the author has observed that
in certain circumstances one wave of activity may occupy almost
the whole body at least in certain species of earthworm. From this
condition it is only a short step to the arrangement found in leeches.
The anterior and posterior suckers replace the chaetae as means of
attachment and in crawling the whole body is involved in one wave
of activity.

It is no longer necessary for the body to be divided internally
into a number of distinct hydraulic units capable of independent
activity and this is probably the functional reason for the loss of
septa and the obliteration of the spacious coelom in leeches.
Earthworms are capable of co-ordinated movement after nerve
cord transection and even after the body has been completely
severed and joined again by stitches. Apparently a peripheral
mechanism for the transmission of locomotor reflexes is present in

78 LEECHES

earthworms but not in leeches. Ventral stimulation by contact
with the substratum is necessary for normal locomotion in both
earthworms and leeches. The ventral nerve cord is capable of
co-ordinating crawling without the assistance of the head ganglia
but does not normally do so in the absence of peripheral stimula-
tion. Swimming by leeches is an activity for which there is no
parallel in earthworms, and the anal ganglion appears to be neces-
sary for normal swimming. Although locomotion in both forms
can be reduced to a pattern of reflexes there is no doubt that the
brain exerts a modifying influence on the pattern in response to
the stimulation of external conditions or internal physiological
needs.

CHAPTER 8

SENSE ORGANS AND
BEHAVIOUR

1. Sensory Equipment

The basic sensory equipment of leeches corresponds almost
exactly with that of earthworms, but the sensory elements are
grouped into slightly more complex organs and the nervous
system appears to be capable of co-ordinating rather more complex
patterns of behaviour. This is not surprising when we remember
that many leeches rely for their nourishment on their ability to
make contact with vertebrate hosts capable of rapid movement.

There are three kinds of sensory equipment : free ending nerve
fibres in the epidermis, epidermal sense cells and light sensitive
cells. The free ending nerve fibres (Fig. 43a) are the terminations
of nerves arising either from the main segmental nerves or, more
often, from the sub-epidermal or inter-muscular nerve rings
described on p. 72. It is probable that they respond to changes
in temperature or to mechanical stimuli resulting from deformation
of the epidermis through contact with solid objects. The epidermal
sense cells (Fig. 43b) are tall spindle shaped cells occurring singly
or in groups among the other epidermal cells. Their outer ends
terminate in fine sensory hairs which pass through the cuticle and
project about 10/x beyond it, while their inner ends lead to sensory
nerve fibres. Groups of such cells are called sensillae and are
scattered over various parts of the body, being particularly numer-
ous on the head. In most leeches there are also sensillae which are
regularly arranged on the middle annulus of each segment and are
known as segmental receptors. In the diflFerent species the seg-
mental receptors attain varying degrees of complexity and may
include light sensitive cells, mucous glands and special muscle cells
which enable them to be protruded as papillae or retracted as cup

79

80

LEECHES

(a)

(b)

Fig. 43. (a) A free-ending nerve fibre in the epidermis of

Hirudo medicinalis.

(b) Epidermal sense cells grouped in a sensilla.

b.m, basement membrane; c, cuticle; c.t, connective tissue

sheath surrounding a nerve cell ; e, epidermal cell ; e.c. , epidermal

sense cell; w, nucleus of nerve cell; w./, nerve fibre; m.c, muscle

cell ; s.n, sensory nerve.

From Grasse, 1959, based on Apathy (a) and Autrum (b).

shaped organs. The functions of the sensillae are presumably
either tactile or chemoreceptive but it has not been possible to
distinguish one from the other in a particular organ. There is
some evidence that the chemoreceptors are confined to the head
region (Kaiser, 1954) and if this is so, the sensillae of the general
body surface are touch receptors.

Light sensitive cells (Fig. 44) are recognizable by the large
vacuole filled with hyaline, possibly albuminous fluid which acts
as a lens. Light is concentrated on to a neurofibrillar network
within the cytoplasm which makes contact with a sensory nerve
fibre. Such cells occur in small numbers in the sensillae or some-
times in the general epidermis but leeches, unlike earthworms.

SENSE ORGANS AND BEHAVIOUR 81

have distinct eyes formed from a number of light sensitive cells
backed by a pigmented cup. In some leeches, such as Piscicola,
the eyes are quite simple structures consisting of a small number
of photoreceptors in a shallow cup, but we may construct a series

Fig. 44. Light sensitive cell from Erpobdella octoculata.
From Grasse, 1959, based on Autrum.

showing a progressive increase in the number of photoreceptors
involved and in the depth of the pigmented cup until we reach the
condition described in Hirudo (p. 19) where there are very many
photoreceptors enclosed in a deep and narrow pigmented cup.
Such an eye has better directional properties than the simpler
kinds. It is also more superficial than the eyes of the glossiphoniids
so that it is less affected by the light scattering properties of the
tissues above it. Another improvement is in the disposition of the
nerve fibres. In Piscicola the fibres leaving the photoreceptors
pass out over the rim of the pigmented cup, thus interfering with
the passage of light to some extent. In Erpobdella the nerve fibres
may pass through the side of the pigmented cup and in Hirudo
they pass down the centre of the eye and out at the base of the
pigment cup, thus affording the minimum interference with
incident light. In its most advanced form a leech eye should be
capable of giving a highly directional response to light rays and

82

LEECHES

when, as in Hirudo, there are several eyes pointing in various direc-
tions it should be possible to obtain a crude impression of form
and movement. Boehm (1947) identified a red fluorescent
porphyrin in the pigment layer of the eyes of Hirudo. It is known
that the presence of certain porphyrins renders protoplasm light
sensitive but as this substance is in the pigment cup its physiolo-
gical function is not understood.

Fig. 45. Various leech eyes in vertical section, (a) Piscicola
geometra; (b) Glossiphonia complanata; (c) and (d) Erpobdella.
(a) after Maier 1892, (b), (c) and (d) after Hesse, 1897.

Apart from behaviour associated with reproduction, which is
complex and difficult to observe, the normal behaviour ot leeches
seems to be relatively simple and amenable to detailed analysis.
Broadly speaking the animals are either in a state of hunger and
respond to any stimulus which might indicate the presence of a
suitable food organism or they have food in the crop and rest in a

SENSE ORGANS AND BEHAVIOUR 83

position where they are reasonably safe from predators. In the
latter condition they appear to avoid light, to seek the contact
stimulus afforded by creeping under a stone or into a leaf axil and
to be relatively insensitive to chemical or vibration stimuli. In
the hungry condition they may come out into the light, change their
colour and be roused to activity by vibrations in the water, by
scents emanating from a food organism or by a passing shadow.
The foundations of our knowledge of leech behaviour were laid
by the careful descriptive work of Gee (1912) who studied the
American erpobdellid Dina microstoma and the glossiphoniid
Helohdella stagnalis. The study was carried much further by
Herter in a series of papers published between 1928 and 1942
on the behaviour of certain German freshwater leeches. These
papers are listed in the bibliography and will not be mentioned
individually in the account which follows.

2. Reactions to Light

In general leeches are strongly photonegative in their behaviour,
some species more so than others. Table 3 shows the result of a
series of observations in which leeches were given the choice of a
lighted or a shaded part of an aquarium. On each of 20 days the
position of each leech was noted and the shading was moved to
the opposite side. In the experiments where only one leech was
present in each experimental tank (columns 1 and 2) the majority
of leeches chose the shade every time. Those that did not were
Hirudo the medicinal leech, Theromyzon the duck leech, and
Hemiclepsis a parasite of fish and amphibia. Hungry Theromyzon
were much more frequently photopositive than satiated specimens,
suggesting that in these blood-sucking species it is the need to
obtain a meal which modifies their mormal light avoiding reactions.
Where there were several leeches in each experiment the percentage
of leeches taking up positions in the lighted zone was considerably
increased (columns 3-5).

Herter and later Denzer-Melbrandt (1935) gave leeches a choice
of four intensities of illumination which may be referred to as
lighted, lightly shaded, heavily shaded and dark. The percentage

84

LEECHES

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SENSE ORGANS AND BEHAVIOUR

85

of times that each leech settled in each zone is recorded graphically
in Fig. 46. This shows Glossiphonia heteroclita as the most strongly
photonegative in its behaviour. It also shows that blood-sucking
parasites of vertebrates settled more often in the lighted zone than
in either of the partially shaded ones. Apparently when these

90

80

70

60

50

40

30

20

10

H L

D

L

T

Fig. 46, The distribution of various species of leech between
(H) lighted, (L) lightly shaded, (T) heavily shaded and (D) dark
zones of an aquarium in a large number of trials, a, Piscicola
geometra; b, Hemiclepsis marginata; c, Theromyzon tessulatum;
dy Glossiphonia complanata; e, G. heteroclita ; /, Helobdella
stagnalis; g, Hirudo medicinalis; h, Haemopis sanguisuga; t,
Erpobdella. From Herter, 1936.

Species are seeking a host they are photopositive, not merely
indifferent to light. By contrast, the two species of Glossiphonia
were found in lighted or partially shaded zones with about equal
frequency.

Up to this point we have been concerned only with reactions to
diffuse lighting from above. Various people have also studied the
reactions of leeches to a beam of light from a single source.
Holmes (1905) gave a clear description of the behaviour of

86 LEECHES

Glossiphonia in such a situation. " In its progress the leech fre-
quently raises the extended anterior part of the body and waves it
from side to side as if feeling its way. If the animal turns it in the
direction of a strong light it is quickly withdrawn and extended
again, usually in another direction. If the light is less strong it
waves its head back and forth several times and sets it down away
from the light; then the caudal end is brought forward and the
anterior end extended and swayed about and set down still further
from the light than before. When the leech becomes negatively
oriented it may crawl away from the light, like the earthworm, in
a nearly straight line. The extension, withdrawal and swaying
about of the anterior end of the body enable the animal to locate
the direction of least stimulation and when that is found it begins
its regular movements of locomotion. Of a number of random
movements in all directions only those are followed up which
bring the animal out of the undesirable situation."

The swaying of the anterior end of the leech, which Herter calls
Suchhewegung, searching movement, is very characteristic of
leeches which are crawling, or are about to do so. Gee said "This
tendency to 'prove all things, hold fast to that which is good' is
perhaps the most striking single characteristic of the behaviour of
leeches . . .". Herter showed that when Hemiclepsis is moving
towards a source of light it makes many searching movements and
ultimately turns and moves away. It then makes fewer searching
movements. The circumstances under which the leech was in-
duced to move towards the light were perhaps a little unfair. A
typical experiment is illustrated in Fig. 47. The leech was placed
in the centre of a circular dish with a 40 W lamp at one side. It
moved away on a path which made an angle of 35° with the direc-
tion of the light and eventually reached the side of the dish. It
then turned and moved along the side of the dish and in doing so
was induced to move towards the light. It made searching move-
ments on five occasions before turning back from the light. While
moving away from the light it made searching movements on only
one occasion. When the light source was changed to 150 W it
turned and retraced its steps while at a much greater distance from
the light. The unsatisfactory element in this experiment is that
the leech was almost certainly responding to the contact stimulus

SENSE ORGANS AND BEHAVIOUR

B

87

Fig. 47. The track followed by Hemiclepsis when placed at M,
the centre of a circular dish which was illuminated by a single
light source at A. In experiment (a) the light source was a 40 W
lamp, in (b) a 150 W lamp. S indicates searching movements and
is followed by the time in minutes for which the movements
were carried out. From Herter, 1936.

88 LEECHES

from the side of the dish. It will be shown on p. 94 that leeches
are strongly thigmotactic. If it had not been for this complicating
factor the leech would probably never have moved towards the
light for any considerable distance.

Herter found that none of the leeches which he studied moved
directly away from the source of light when free to do so. Piscicola
moved along a path which was up to 48° from the line of the light
rays and Hemiclepsis up to 90°. On the other hand Gee found that
Helohdella frequently moved almost directly away from the light
source, pausing to make frequent searching movements as it did so.
Both these workers concluded that there is a very considerable
degree of random movement in the responses of leeches to light
and Herter found this surprising in view of the level of complexity
of the leech eye. Since he worked mainly with Glossiphoniidae,
which have the eyes rather far below the surface of the head, it
would be interesting to investigate the behaviour of leeches with
more superficial and more complex eyes, and to study the effects of
unilateral blinding and of varying the direction of the incident
light during the course of an experiment.

Leeches have no statocysts or other organs for orientation in
relation to gravity and it appears that when swimming they make
use of the fact that light normally falls on them from above and
exhibit a dorsal light reaction. If a swimming medicinal leech is
suddenly subjected to light from below and not from above it will
swim in a vertical arc until its dorsal side is directed towards the
light (Schluter, 1933). It does not maintain this position in-
definitely, however, but eventually returns to its normal orienta-
tion, presumably in response to the effect of gravity on the internal
organs. A similar dorsal light reaction is shown by leeches placed
between two glass plates and this response is shown even by
decapitated leeches, indicating that the eyes are not essential to
the reaction, the light sensitive cells of the dorsal body wall being
sufficient.

When a shadow passes over a leech in its natural habitat it is
likely that this is caused by the movement of a larger animal. The
blood-sucking parasites often react by making searching move-
ments, or even by swimming upwards through the water. The
non-parasitic forms react in other ways; they may flatten them-
selves against the substratum or abruptly cease making ventilatory

SENSE ORGANS AND BEHAVIOUR 89

movements. In this way they are less easily seen by a predator.
The reflex involving cessation of ventilatory movements is one
which is particularly suited to experimental study. Common
European freshwater leeches which exhibit it are Hirudo, Haemopis
and Erpohdella. It is not necessary to shade the whole of the
animal, for under favourable circumstances they will respond to a
decrease in light intensity on a small part of the posterior sucker
(Kaiser, 1954). Decapitated leeches respond just as well as intact
animals, so clearly it is the epidermal light sensitive cells which
mediate the response. There is no response to shading the ventral
surface.

If a leech is illuminated by two lights and one of them is switched
off, the fall in light intensity on the epidermis of a leech produces
the same effect as a shadow. By altering the intensities of the two
lamps it is possible to vary the percentage fall in light intensity.
Kaiser (1954) found that Haemopis responded to as little as 25%
decrease in light intensity. The suspension of activity did not last
indefinitely, ventilatory movements were resumed after 1 or 2 min.
If full illumination was then turned on, the experiment could be
repeated, and this time the period of inactivity was decidedly less.
With constant repetition of the experiment the period of inactivity
became shorter and shorter until eventually there was no response
at all to the stimulus. This habituation is illustrated in Fig. 48.
With 100% reduction in light intensity the first period of quies-
cence was 100 sec. It soon fell to about 10 sec, where it remained
for about 20 trials. After that the response quickly disappeared.
When the percentage reduction in light intensity w^as less the rate
of habituation was proportionately more rapid, so that at 30% drop
in light intensity the response disappeared after only three trials.

Another reaction to light exhibited by many leeches is that of
colour change. It is brought about by pigment cells in the tissues
which change their appearance according to circumstances. They
are much branched cells in which the pigment may be either
concentrated into a small sphere in the centre of the cell, in which
case the cell is very inconspicuous, or may be dispersed throughout
the branches of the cell, making it conspicuous and contributing to
the general colour pattern of the animal. It is the type of chromato-
phore found, for instance, in Crustacea and vertebrates. The

90

LEECHES

10 12 14 16
Number of trial

18 20 22 24

Fig. 48. Habituation in reaction to decrease in light intensity

(shadow reflex). The percentage drops in light intensity is

marked against each line. For further explanation see text.

Based on the data of Kaiser, 1954.

change from one state to the other is a relatively slow process,
usually taking about 1 hr, although the dark brown chromatophores
of Piscicola are exceptional and can expand in about 15 min. Most
of the leeches in which colour change has been observed are blood-
sucking parasites of vertebrates, for example Theroviyzon and
Hemiclepsis. These become positively phototactic when hungry
and so expose themselves to predators in daylight. Presumably
the change in colour makes them less conspicuous under these

SENSE ORGANS AND BEHAVIOUR 91

circumstances. Glossiphofiia complanata which is not of this habit
does possess variable chromatophores but they are so sparsely
scattered in the tissues that they make little difference to the
appearance of the animal (Wells, 1932).

Kowalewski (1900) claimed that Placohdella costata, a parasite
of the European water tortoise, was green when resting on vegeta-
tion but brown when on a tortoise. This suggests that the leech
possesses at least a rudimentary form of colour vision. Denzer-
Melbrandt (1935) studied the question of colour vision in leeches.
She prepared test containers in which the incident light passed
through various shades of coloured paper, and she observed in a
large number of trials which colours the leeches preferred. She
claimed that Helobdella and Hirudo showed a preference for colours
of longer wavelength, even when this involved moving into regions
of higher light intensity. The method used for determining the
light intensity involved making comparisons by the human eye.
If the leech eyes happened to be less sensitive than the human eyes
at the red end of the spectrum it is possible that they were in fact
showing a preference for the zones which appeared to them to be
illuminated at a lower intensity. We must therefore regard the case
for the existence of colour vision in leeches as not proven.

On the other hand. Smith (1942) showed clearly that the
chromatophores oi Placohdella parasitica respond to simple changes
in light intensity. This leech has three kinds of chromatophores,
yellow, green and reddish brown. Of these the green are most
active in colour change, expanding in light and contracting in
darkness. It appears that the chromatophores are under nervous
control, for electrical stimulation at either end of the body will
cause a pale leech to darken, but if the nerve cord is transected the
effect will not be produced beyond the cut. Decapitation causes
a pale leech to darken, but after it has recovered from the shock
of the operation it will still change colour slowly in response to
changes in light intensity. This shows that the eyes are not essen-
tial to the process and that the light sensitive cells of the epidermis
can mediate the response. In fact, if a decapitated leech is brought
from darkness into the light and one part of the body is shaded
that part will remain paler. Vavrouskova (1952) studied the colour
change mechanism of Theromyzon tessulatum and concluded that

92 LEECHES

V the chromatophores were themselves sensitive to Hght and could

respond to changes in light intensity without the mediation of the
central nervous system.

3. Reactions to Heat

Those leeches such as Hirudo and Theromyzon which sack the
blood of warm-blooded animals are stimulated to attach themselves
to an object warmed to 3 3-35° C. Placohdella costata is said to be
attracted to such an object from a distance of 15 cm (Mannsfeld,
1934). If the temperature is raised above 35°C Hirudo will
eventually release its hold and in a number of trials the average
temperature at which this occurred was 41-5°C. Theromyzon
releases its hold at a similar temperature but parasites of fish let go
at about 31°C while those which attack invertebrates release their
hold from the tube at under 30°C (Table 4 column 5). Land
leeches {Haemadipsa) when hungry will sit erect on their posterior
suckers. If they are then subjected to a current of warm, moist air
they will move towards the source of it (Stammers, 1950). A man's
breath or the wind moving past his hand (if this is held a few
inches from the leech) is sufficient to produce this reaction
(Matthews, 1954).

When placed in a temperature gradient Hirudo congregated in
water of 21°C and Kaiser (1954) concluded that it was capable of
distinguishing between temperatures differing by only 1-5°C.
When subjected to temperatures higher than those normally
occurring in the natural habitat leeches show a distinct series of
behaviour patterns. The first is a shock reaction, comparable
with that obtained with strong tactile stimulation, in which the
longitudinal muscles are strongly contracted. This occurs at
temperatures between 26° and 39° according to species. In the
next phase the leeches coil and uncoil vigorously, throwing them-
selves into a variety of contortions. At still higher temperatures
locomotion becomes impossible and finally paralysis sets in. The
temperatures at which the four stages were reached by various
German freshwater leeches are shown in Table 4 columns 1-4.
Piscicola showed the greatest sensitivity to rising temperatures
while the greatest tolerance of high temperatures was shown by
Hirudo and Theromyzon. Piscicola is closely related to marine

SENSE ORGANS AND BEHAVIOUR

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a ^ c 'r* to o ^

;S ^ J .§ ^ 2 ^

:::; ^ !lj a: O ti: fe^

94 LEECHES

leeches and is not normally found in small enclosed bodies of
water where the temperature may rise excessively. Hirudo and
Theromyzon on the other hand do inhabit such places and must be
able to survive contact with warm blooded hosts.

When the rate of locomotion of Hemiclepsis was measured at

20 1 ^

+

J 1 I ! ! 1 1 ] L

(0 12 14 16 18 20 22 24 26 28 30 32 34 36 38

Temperature, °C

Fig. 49. Rate of locomotion of Hemiclepsis in relation to
temperature. From Herter, 1932.

many temperatures it was found to increase in an almost linear
manner from 0 to 34°C after which it declined (Fig. 49). According
to Table 4 locomotion ceases at 36'5°C.

4. Reactions to Mechanical Stimulus

One of the most characteristic reactions of leeches is their
tendency to creep into crevices, i.e. their strong positive thigmo-
taxis. In nature freshwater leeches are most commonly found
under stones or in the leaf axils of plants. The reaction is not
entirely one of light avoidance as is shown by the experiment in
which leeches were given the choice of remaining in the open or of
creeping under a sheet of glass where there was little reduction
of Hght intensity. Table 5 shows that the majority preferred to
lie under the sheet of glass. Here again there is a distinction
between the predators of invertebrates, such as Glossiphonia and
Helobdella, and the blood-sucking parasites of mammals, for the

SENSE ORGANS AND BEHAVIOUR

Table 5. Observations on the Tendency of Leeches to
Take up Their Position in a Crevice under a Glass Plate

95

Number of

Number of
observa-
tions

Percentage

Percentage

leeches

free

under glass

Glossiphonia complanata

6

120

0-0

100-0

Helobdella stagnalis

6

96

1-0

99-0

Hemiclepsis marginata

6

90

2-2

97-8

Theromyzon tessulatum

1

16

6-2

93-7

(medium size)

Theromyzon tessulatuyn

5

80

57-5

42-5

(small)

Erpobdella sp.

6

84

45-2

54-8

Hiriido medicinalis

4

52

61-5

38-5

Piscicola geometra

6

54

100-0

0-0

former were much more positively thigmotactic. The way in
which hunger modifies this reaction is shown by Theromyzoriy
where the large animals with full gats were much more positively
thigmotactic than smaller specimens.

Leeches are very sensitive to touch. As far as can be judged
from experiments with paint brushes and needles they are most
sensitive on the front of the head and least sensitive posteriorly.
Large or well fed specimens are less responsive than small or
hungry ones. When a Glossiphonia is resting in a shallow dish of
water and a needle is brought towards it it responds long before
the needle touches it. First there is a response when the needle
touches the surface film ; if it is performing undulatory movements
these cease abruptly or if it is resting then it presses its body closer
to the substratum. If the needle is now brought towards the
margin of the body this will be withdrawn before the needle
actually makes contact (Gee, 1912). In these experiments the
leech is presumably reacting to vibrations in the water caused by
the movement of the needle. ErpobdeUids respond to vibration
by rapid longitudinal contraction and parasitic forms may respond
by making searching movements or even by swimming upwards
in the water.

Some leeches are able to locate the centre of a disturbance in

96

LEECHES

the water. Figure 50 illustrates an experiment in which Theromyzon
reacted to a disturbance created at three different points in succes-
sion by blowing down a tube on to the surface of the water. It is
obvious that it was able to direct its movements towards the
source of disturbance with a fair degree of accuracy. It is also

Fig. 50. The path taken by Theromyzon when a disturbance

was created successively at 1, 2, and 3 by blowing down a tube

on to the surface of the water. From Herter, 1929.

well known that Hirudo uses this method to locate its host, for
hungry leeches will converge on a centre of disturbance in a pond
in which they are living even if the disturbance is made by moving
a stick rather than by any part of an animal.

5. Reactions to Gravity

Leeches have no specific organs of gravity perception yet most
of them show a positive geotaxis as was shown by Herter's
observations on the distribution of various species in a tall glass
tube, precautions being taken to eliminate light influence. He
found that Helohdella stagnalis, Glossiphonia complanata, G. hetero-
clita and P. geometra were resting in the lower 10 cm of the tube
on more than 90% of the occasions while Hemiclepsis marginata
and Erpohdella sp. showed a greater tendency to wander upwards,
being found in the lowest 10 cm on just over 70% of occasions.
On the other hand, hungry specimens of Theromyzon tessulatum

SENSE ORGANS AND BEHAVIOUR 97

and Hirudo medicinalis congregated near the surface of the water.
Presumably the leeches detect the force of gravity from its effect
on the tissues of the body.

When light and gravity responses are in conflict it is the light
response that overrides the other on most occasions. When the
upper half of an aquarium was shaded while the lower half was
lighted specimens of Hirudo came to rest in the upper half on
89% of the occasions observed but when light and shade were
reversed they came to rest in the lower half on 76% of the occasions.
Another factor modifying geotaxis is oxygen lack, for many leeches
which would otherwise remain near the bottom rise to the surface
when oxygen is scarce.

6. Reactions to Chemical Substances

It is recorded that Hemiclepsis can with difficulty be persuaded
to suck blood from Raiia temporaria, that it will never suck the
blood of Rana esculenta but that it sucks readily on the larvae of
Pelohates. The basis of such discrimination may be partly tactile
but is almost certainly mainly chemical. Again, Hemiclepsis will
often ignore a glass rod brought into contact with its head but if
this glass rod has been rubbed on the skin of a fish it will attach
itself with alacrity and attempt to suck from it. There is therefore
no doubt that leeches have a well developed chemical sense.

Some authors have distinguished between taste and smell in
leeches. By this they have meant the distinction between a
response to chemical substances drifting in the water and a
response to close contact between the surface of the animal and a
particular substance. In fact there is no evidence at all that leeches
have more than one kind of chemoreceptor and it is perhaps best
to regard the two sensations as two aspects of the one activity.

Examples of response to substances drifting in the water are
afforded by the reactions of various leeches to extracts of their
normal host animals. In most cases the reaction is random and
undirected ; for example, if the juice of a pond snail is added to the
water in a dish containing Glossiphonia complanata the leeches may
respond by making searching movements, especially if their guts
are empty, but their movements do not bring them to rest at the

98

LEECHES

centre of the cloud of snail juice (Fig. 51). Hemiclepsis reacts to a
fish extract in a similar manner but Piscicola which is also a fish
parasite shows no such reaction. This is interesting in view of the
fact that Hemiclepsis normally lives in still water and Piscicola in

Fig. 51. Successive positions of three specimens (1, 2 and 3)
of Glossiphonia complanata after addition of snail extract to the
water (dotted area) at 16.55 hr. Arrows indicate direction of
light; times are in hours and minutes. Temperature, 16°C.
From Herter, 1936.

running water or the surf zones of lakes. It is unlikely that in its
natural surroundings chemical substances will stay in one place
long enough for Piscicola to react to them.

A detailed study of the substances which evoke a reaction in
Hirudo was made by Kaiser (1954). He placed five leeches in
200 ml of water in a dish and when they were at rest he added a
test substance drop by drop. With acids the leeches responded
by making characteristic jerking and quivering movements, while

SENSE ORGANS AND BEHAVIOUR 99

Table 6.
The Reactions of Hirudo to Substances added to the Water

Substance

Amount usee

(in solution where

(1 drop =

Reaction

appropriate)

0-04 ml)

Formic acid

1 drop

Quivering reaction, leave water.

Acetic acid

2 drops

Weaker reaction than above. After
5 min anterior sucker out of water.

Proprionic acid
Iso-butyric acid

2 drops ^
2 drops j

' As for acetic acid.

w-butyric acid

2 drops

Weaker reaction. Leave water after
30 sec.

Caprylic acid

Several
drops

React only to one undiluted drop.

Oxalic acid

2 drops

Malonic acid

5-10 drops

Succinic acid

5-10 drops y

Typical acid reaction (see text).

Citric acid

1 drop

Hydrochloric acid

1 drop

Phenol

1 drop

Shock reaction, leave the water.

Thymol

a crystal

No reaction.

Napthol

2 drops

Typical acid reaction. Soon leave
water.

/)-nitrophenol

a crystal

Leave water. Weak reaction.

Galactose

1

Sucrose

.

Glucose

No reaction.

Lactose

Methyl alcohol

<

Butyl alcohol

>

No reaction.

Glycerin

Quinine "1

<

Caffein

Swim about restlessly then come to

Atropine y

1 drop >

rest with anterior sucker out of the

Cocaine

water.

Morphia J

^

Ammonia

1 drop

Strong reaction, leave water.

Urea

a crystal

Clear reaction.

Indol

2 drops \
a crystal J

Skatol

Leave water hastily.

Pyridin

1 drop

React only to undiluted substance.

Camphor

1 drop

No reaction.

100 LEECHES

various other substances evoked normal locomotory exploratory
movements. Noxious substances caused the leeches to come to
rest with their anterior suckers out of the water but the rest of the
body still immersed. This suggests that the chemoreceptors are
confined to the head so that when this part of the body is out of
the water the leeches are no longer aware of the noxious stimulus.
In Table 6 is given a list of the substances tested and the reactions
they produced. Among the saturated fatty acids the most marked
effect was produced by formic acid. Sugars and alcohols produced
no effect in the concentrations used but alkaloids such as quinine
and caffeine gave rise to strong reactions. Substances which might
have been produced by a host animal, such as ammonia and urea,
gave rise to exploratory movements and substances which are
distasteful to man, such as indol and skatol, evoked a strong
reaction.

The case quoted above of Hemiclepsis reacting to a glass rod
previously rubbed on the skin of a fish is an example of contact
chemoreception. Practically all the European freshwater leeches
react to a suitably prepared glass rod, Hirudo to one which has
been held under a man's armpit, Theromyzon to one which has
been in contact with the preen gland of a duck, or Helohdella to
one smeared with the blood of a snail. As long ago as 1916 Lohner
studied the reactions of Hirudo to various substances mixed with
its food. He persuaded the leeches to take blood by sucking at a
piece of skin stretched across a glass tube. While the leeches were
feeding he mixed the test substances with the blood in the tube
and noticed whether they caused the leeches to stop sucking. With
sodium chloride they reacted to a concentration of 7%, with
sucrose at 5% but with quinine at only 0-1%. It is therefore clear
that leeches have chemoreceptors which provide information
about substances in the water, substances with which the anterior
sucker comes in contact and substances contained in the blood
which is passing through the buccal cavity.

CHAPTER 9

REPRODUCTION AND
DEVELOPMENT

1 . Introduction

The reproductive processes of leeches show interesting speciaHza-
tions when compared with those of earthworms and other anneUds.
Internal fertilization is general and in the glossiphoniids there is
a well developed pattern of brood care. The method by which
fertilization is achieved in most families is remarkable, for the
sperms are enclosed in a spermatophore which is then attached to
the body wall of another leech. The sperms make their way, by a
process not fully understood, through the body wall into the
coelomic sinuses and thence to the ovaries. Brood care often
involves the attachment of each of several dozens of embryos to
the ventral body wall of the parent by a curious ectodermal ball-
and-socket joint and the parent may hold the embryos under her
body for many weeks, passing a current of water over them by
gentle dorso-ventral undulations.

The leeches about which we have most information, the fresh-
water leeches of temperate climates, usually begin to breed in
spring or early summer. Breeding condition is indicated by the
differentiation of the clitellum or by the fact that stores of eggs or
sperm are visible through the ventral body wall. In Britain
Glossiphonia complanata, Helohdella stagnalis and Erpobdella
testacea first come into breeding condition in March, E. octoculata
in May and Theromyzon tessulatum in lune (Mann, 1951; 1953b;
1957a; 1957b; 1961). There has been no experimental study of
the factors controlling the reproductive cycle but from field
observations it is fairly clear that there is a correlation between the
environmental temperature and the onset of breeding. Not only
is the breeding time of a particular species later in more northerly

101

102

LEECHES

latitudes, a fact which might also be accounted for by differences
in day length, but it is later in higher altitudes and can be advanced
or retarded in the laboratory by appropriate changes of tempera-
ture (Leopoldseder, 1931). In a detailed study of the life history
of Glossiphonia complanata (Mann, 1957a) it appeared that the
onset of breeding was governed by three factors : temperature, the
density of the population and the age of the leeches. The popula-
tion was living in a network of streams which ran through water-
cress beds and carried water from a spring at the foot of chalk hills
in Berkshire, England. Owing to the fact that some streams were

:A

April

7

\

- 1 \j'\

Moy

.^^^^£2^

•-•■• Leeches without

ciitellum
CKM3 Leeches with

ciitellum

M!!!m

Aug.

•••-• Leeches without

ciitellum
o-oo Leeches with

ciitellum

6
c^3So 1

Sept.

July

200 300

Weight, mg

Fig. 52. The life history of Erpobdella octoculata. Smoothed
frequency polygons representing the distribution of weights of
leeches in 6 monthly samples of about 100, between April and
September, 1952. The weights are arranged in 10 mg classes.
Each point represents the mean value of its own class, the one
above and the one below. A, B and C indicate the same three
populations in successive samples, and in May represent 1 , 2 and
3-year age groups. Those emerging from the cocoon in 1952 are
first seen in the samples in September. Note that 2-year-olds
breed before 1 -year-olds. From Mann, 1953.

REPRODUCTION AND DEVELOPMENT

103

heavily shaded while others v^^ere not, the diurnal rise of tempera-
ture was more marked in some streams than in others. The
breeding activity was most advanced in the warmer waters. Within
a given section of the stream breeding was more advanced in
places where the leeches were densely aggregated, presumably
because the opportunity for fertilization was greater, or because
there was some physiological response to the presence of numbers
of other leeches. Moreover, 2-year-old leeches began breeding
about one month earlier than 1 -year-olds.

Erpohdella testacea is an annual species, breeding at 1 year of

Fig. 53. Diagram of the life history of Helobdella stagnalis in a
calcareous artificial lake. The width of the line is roughly-
proportional to the density of the population. Dotted areas
indicate breeding leeches ; arrows indicate the release of young
by the parents. From Mann, 1957.

104 LEECHES

age and dying soon afterwards, but Erpohdella octoculata and
Glossiphonia complanata are longer lived. Most of the leeches of
these two species breed at 1 year of age, they all breed at 2 years and
after that most of them die. Those that survive beyond this time
are probably the ones that failed to reach maturity in the first year
of life. Helohdella stagnalis has a life history which is different
again, some ofthe leeches passing through two generations in lyear.
Overwintering leeches breed in spring and die soon afterwards;
some of the spring brood grow to maturity that summer, breed and
die, but the remainder overwinter to breed the following spring.
The proportion reaching maturity in less than 1 year seems to
depend on the weather (Mann, 1957b).

2. Fertilization

Leeches are protandrous hermaphrodites and cross fertilization
is the general rule. The Hirudidae have an eversible penis and
at copulation this is inserted into the vagina of another leech. If
the animals take up a head-to-tail position reciprocal fertilization
is possible, but this is by no means general and unilateral action is

Fig. 54. Hirudinaria granulosa copulating. From Bhatia, 1941.

probably more usual. Leslie (1951) described a simple courtship
display by the land leech Haemadipsa. It involved tapping (with
their anterior suckers) the leaf on which they were sitting and
entwining the anterior ends of their bodies in various ways before
copulating. Leeches of the families Erpobdellidae, Glossiphoniidae
and Piscicolidae lack the eversible penis and transfer the sperm

REPRODUCTION AND DEVELOPMENT

105

by means of spermatophores secreted in the terminal portion of
the male duct, the atrium. The only known exception among the
Glossiphoniidae is Theromyzon tessulatum in which the atrium can
be everted in the form of a low cone which functions as a penis.
Typical spermatophores are illustrated in Fig. 55. Although the

(b)

Fig. 55. Various spermatophores. (a) from Erpobdella;
(b) from Trachelobdella punctata; (c) from Placobdella para-
sitica, b.p., basal plate; p.s.y proteolytic substance; 5, sperms;
zo, wall of spermatophore. From Grasse, 1959 after Brumpt
(a) and (b) and Whitman (c).

shape varies greatly from one species to another they all consist of
a median chamber from which originate two horns. The median
chamber may be enlarged at the expense of the horns, or vice versa,
and the horns may be widely separated as in Erpobdella or closely
bound together as in Glossiphonia. The upper part of a spermato-
phore is packed with sperms but the lower one third usually

106

LEECHES

contains a granular secretion which is thought to have proteolytic
properties. The wall of the spermatophore is secreted by glands
in the wall of the atrium and the sperms are pumped into it by the
ejaculatory ducts. There is a base plate, perforated to allow for
the passage of sperm, and when the spermatophore is expelled by
the action of the muscles of the atrium walls the base plate adheres
to the body of another leech.

Exchange of spermatophores is often accompanied by a close
intertwining of the bodies of the leeches (Fig. 56). The clitellar

Fig. 56. Piscicola copulating, sp, spermatophore being
deposited on the copulatory area. From Grasse, 1959, after

Brumpt.

region is the most usual site of deposition but spermatophores are
not infrequently found as far away as the dorsal region of the
posterior half of the body. The most detailed study of the process
of fertilization is that of Brumpt (1900). He showed that in

REPRODUCTION AND DEVELOPMENT

107

Fig. 57. Successive positions during copulation by Erpohdella.

From Nagao, 1957.

Fig. 58. Section through two specimens, A and B, oi Erpohdella
octoculata during implantation of the spermatophore. m, mass of
spermatozoa in ovary; o, ovarian strand; o.s., ovarian sac; sph,
spermatophore; spz, spermatozoa. From Grasse, 1959,

after Brumpt.

108

LEECHES

Glossiphoniidae and Erpobdellidae the sperms pass through the
epidermis into the dermal connective tissue and from there to the
coelomic spaces in which the ovaries he (Fig. 58). He favoured
the view^ that there was no proteolytic action at the point of entry,
suggesting rather that the tissues were parted by the mechanical
pressure of the injected fluids. The presence of a base plate would
appear to be an obstacle to such action, and it therefore seems
more likely that, as other authors have suggested, the granular
contents of the lower end of the spermatophore have proteolytic
properties. Once attached to the body of another leech, the
spermatophore empties its contents into the tissues. The force
required to effect the transfer is probably obtained from the walls
of the spermatophore which shrink on contact with water.

In many Piscicolidae there is a special area for the reception of
the spermatophore, called the copulatory area. In Piscicola for
instance (Fig. 59) it lies behind the genital pores. Immediately

Copulatory
area

Fig. 59. Ventral view of part of body wall of Piscicola, showing
genital pores and copulatory area. After Brumpt, 1900.

beneath it there is a pad of fibrous connective tissue with two
strands running to the ovarian sacs. It is called conducting tissue.
The spermatophores are normally deposited on the copulatory
area and the sperms travel most readily through the underlying
fibrous connective tissue, and are conducted direct to the ovaries.
In other Piscicolidae, such as Callobdella lophti, there are

REPRODUCTION AND DEVELOPMENT

109

Strands of conducting tissue running from the male genital
aperture to the ovaries, so that cross fertilization can be achieved
by introduction of a spermatophore into the male genital aperture
of another leech (Fig. 61).

o.s

c.t,

cl.g,

Fig. 60

Fig. 61

Fig. 60. Reproductive organs of Piscicola geometra, dorsal
view, c.t., conducting tissue; ej.d., ejaculatory duct; gl, glands
secreting wall of spermatophore; o.s., ovarian sac; t, testis sac;
v.n.c, ventral nerve cord. From Dawydoff, 1959, after Brumpt.

Fig. 61. Sagittal section through Cystobranchus mammillatus
to show conducting tissue, a, male genital atrium; c.a., copu-
latory area; c.t., conducting tissue; cl.g., clitellar glands; g, gut;
m, muscular wall of atrium; o, ovarian sac; sp, spermatophore.
From Grasse, 1959, after Brumpt.

110 LEECHES

3. Egg Laying and Brood Care

Once fertilization has been achieved the eggs are ready to be
deposited in a cocoon. There is often a considerable delay between
copulation and cocoon deposition. In the case of the Hirudidae,

Table 7. Time which may Elapse between
Copulation and Cocoon Deposition

Species

Time

Erpohdella sp.
Glossiphonia complanata
Haementeria officinalis
Haemopis sanguisuga
Hirudo medicinalis

2-20 days
8-21 days
10 days
li months
1-9 months

where sperms have been introduced into the vagina directly, we
must presume that the sperms are stored and fertilization is
delayed, for there is no evidence that the eggs are at an advanced
stage in development when they are placed in the cocoon. In other
families the delay is only a matter of days and this is presumably
the time taken for the sperms to migrate through the tissues after
the implantation of the spermatophore.

There are two kinds of glands contributing material for the
formation of the cocoon, those which secrete the outer wall
material and those which secrete the albuminous fluid in which the
eggs are suspended inside the cocoon. The normal arrangement
is for these glands to be distributed over the whole of the body wall
in the clitellar region but in a few cases which have been investi-
gated, such as Hemiclepsis marginata and Glossiphonia lata the
clitellar glands are restricted to a small area round the genital pores
on the ventral side of the body. As a result, the method of cocoon
formation is considerably modified. Before dealing with it let us
consider the more normal method.

Erpobdellid leeches first prepare a position for cocoon deposition
by applying a secretion to the substratum with a ** lapping" move-
ment of the anterior sucker. They then place the clitellum over
this position and begin to secrete the cocoon. During this process

REPRODUCTION AND DEVELOPMENT

111

the anterior and posterior ends of the cKtellum are greatly con-
stricted so that the cocoon is formed in a lemon shape. The inner
surface is smoothed by turning the body of the leech about its

Fig. 62. Erpobdella lineata in process of cocoon formation.

(a) rotating the body to shape the inner wall of the cocoon;

(b) withdrawing the body by pulling backwards; (c) the cocoon.

From Nagao, 1957.

longitudinal axis and when this is done the whole of the anterior
part of the body is made as long and thin as possible by contraction
of circular muscles. Into the space left between the body of the
leech and the wall of the cocoon is passed an albuminous nutritive
fluid and a number of fertilized eggs. The anterior part of the
body is then slowly worked backwards out of the cocoon. As the
head passes the anterior and posterior apertures of the cocoon
these are sealed off by means of a plug produced by the glands of
the anterior sucker. At this stage the cocoon is a soft, translucent
and colourless bag. The leech now proceeds to flatten it into an
elliptical sac of the form shown in Fig. 63 and in a few days it
becomes dark brown, hard and almost opaque. The parent takes no
further interest.

In the Piscicolidae, Hirudidae and Haemadipsidae the process
of cocoon formation is very similar except that the cocoon is not
pressed flat but is allowed to retain its rounded shape. Moreover,

112

LEECHES

(a)
(b)

(d)

5 mm

Fig. 63. Details of cocoons of Erpobdella. (a) and (b) schematic
longitudinal sections of the cocoon of E. testacea before and after
the young have emerged ; (c) and (d) the same for E. octoculata
showing a different method of forming the terminal plugs;
(e) cocoon of E. octoculata with one plug removed ready for the
young to leave; ( f ) a cocoon emptied by a snail. From Bennike,

1943.

Fig. 64. Three stages in cocoon formation by Cystobranchus
respirans. The upper figure represents the latest stage. From

Hoffmann, 1956.

REPRODUCTION AND- DEVELOPMENT

113

the wall is usually differentiated into an outer ornamented or
spongy layer and an inner smooth layer (Fig. 65). In the case of
the Hirudidae and Haemadipsidae it is thought that one function
of the spongy layer is to reduce water loss, for members of these

mm

v^i^'

^'

'^^Hf,^

Fig. 65. Cocoons of Cystobranchus. 1, complete; 2, with
spongy layer removed from upper surface. From Hoffmann,

1955.

families lay their cocoons on land. Zick (1933) analysed the wall
of the cocoon of Hirudo and found that it was a scleroprotein
closely related to fibroin, a constituent of insect silk. He proposed
for it the name hirudoin.

The Glossiphoniidae are interesting for the degree of parental
care which they exhibit. They produce a very thin-walled cocoon
and immediately after deposition they place their bodies over it
and assume a protective role. Most glossiphoniids produce the
cocoon in the same manner as other leeches, secreting it as a girdle
round the body and fastening it to the substratum before backing
out of it, but in those species mentioned earlier where the clitellar
glands are confined to an area round the genital pores the cocoon
forms like a bubble over the genital pores and the eggs are dis-
charged into it. The process has recently been described and
illustrated for the Japanese leech Glossiphonia lata by Nagao (1958)
(Fig. 66).

At an early stage in development, while still enclosed within the
egg membrane, the young glossiphoniid leeches develop an
embryonic attachment organ. It takes the form of a knob of

114

LEECHES

elongated ectodermal cells placed near the anterior end of the
body in the mid-ventral line. The embryos, which at this stage
break free of the thin-walled cocoon, become arranged in a single
layer with their attachment organs directed upwards and each of
these then becomes interlocked with elongated epidermal cells

(j)

Fig. 66. Egg laying by Glossiphonia lata, (a), (b) formation of
a cavity on the ventral side of the body; (c) to (g), secretion of a
saclike cocoon by a ring of clitellar glands round the genital
pore and extrusion of the eggs into the cocoon ; (h), (i), cocoon
moved to a posterior position for brooding; (j), appearance of
cocoon. From Nagao, 1958.

which form a kind of socket on the parent's ventral body wall.
It has been suggested that a transfer of nutriment takes place at
this stage but on the whole this seems unlikely as the embryo is
well provided with yolk and the egg membrane is interposed
between embryo and parent.

REPRODUCTION AND DEVELOPMENT 115

While in this position the young leeches develop until anterior
and posterior suckers are well formed and there is a nervous system
capable of co-ordinating their activity. They then hatch from the
egg, lose their attachment by the larval organ and hold on to the
parent by their posterior suckers. In this position they may be
carried about by the parent for several weeks or months, according

Fig. 67. Young Glossiphonia complanata taking their first meal
of blood from an Erpobdella:- From Pawlowski, 1955.

to the species. Glossiphonia complanata holds the eggs in the
cocoon for 5-6 days, holds them by the embryonic attachment
organ for 4-5 days and then shelters the young leeches which are
holding by their posterior suckers for up to 14 days so that the
whole process occupies about 24 days (Mann, 1957a). Theromyzon
tessulatum on the other hand may hold the eggs in the capsules for

116 LEECHES

8-10 days, but then hold them under her body for nearly four
months (Mann, 1951). The parent not only provides shelter but
by undulating movements of her body provides the young leeches
with a fresh supply of water for respiratory purposes. It has often
been noticed that young leeches prematurely removed from the
parent fail to survive. Since it is unlikely that they had been
receiving nutriment it may well be that the ventilatory movements
of the parent's body were essential to the young leeches.

The time when the young leave the shelter of the parent is
probably determined mainly by the size of the store of yolk in the
crop. When all this has been utilized the young leeches are ready
to take their first meal. Pawlowski (1955) records what happened
when the young of a Glossiphonia complanata took their first meal.
They deserted the parent and attached themselves en masse to the
body of a specimen of Erpohdella octoculata. They forced their
proboscides as deeply as possible into the body wall of the
Erpohdella and proceeded to fill their crops with its red blood. The
attacked animal swam, lashed about and almost tied itself in knots
in an eff^ort to dislodge the parasites but to no avail. Their
posterior suckers were free and their bodies waving freely but they
retained their hold by virtue of having their proboscides embedded
to the maximum depth. An Erpohdella may survive the attack of a
small number of Glossiphonia but the attack of a large number is
fatal.

When the young of Theromyzon tessulatum leave the parent,
often on account of the death of the latter, they tend to remain
densely aggregated until the opportunity arises to enter the nostril
of a water bird. There is at least one case on record (Mann, 1951) of
ducklings being killed in considerable numbers by the attacks
of young Theromyzon. When dozens of leeches enter the nostril
of a bird and there gorge on blood from the mucous membrane of
the nose and throat there is danger of asphyxiation or of death
from loss of blood.

4. Development of the Eggs

The cleavage of leech eggs is basically of the spiral type. Other
groups in which this method of cleavage is found include platy-
helminths, nemerteans, molluscs other than cephalopods, poly-

REPRODUCTION AND DEVELOPMENT

117

chaetes and oligochaetes. While there is great individual variation
in both the method of cleavage and the type of larva formed, it is
possible to discern a general pattern of development which runs
somewhat as follows. Two divisions in a vertical plane separate

Fig. 68. Diagram illustrating spiral cleavage. From Waddington,

1956.

the fertilized egg into four blastomeres, usually of unequal size.
These are conventionally known as the macromeres A, B, C and D.
Each macromere then cuts off a small cell, a micromere, at one end
of the egg (the animal pole) and these are named la, lb, Ic and Id,
Instead of lying immediately above the macromeres which gave
rise to them the micromeres lie a little to one side owing to tilting
of the cleavage spindle during division. A second set of micro-
meres 2<2, 2b, 2c and 2d are now formed but when the first set are
displaced clockwise the second set are displaced anticlockwise, and
vice versa. A third set is formed and a fourth, each being offset in
the opposite direction from its predecessor. While this is going on
the earlier sets of micromeres themselves divide, still with their
spindles tilted. In this way a hollow blastula stage is formed with
a cap of micromeres surmounting four macromeres. If the latter

118

LEECHES

have little yolk, gastrulation may be possible by invagination, the
macromeres forming the endoderm and the micromeres the ecto-
derm and mesoderm but if the macromeres are large and yolky
the micromeres multiply and spread down around the outside of
the macromeres bringing about gastrulation by epiboly (Fig. 69).

Ectoderm

Mesoderm

Anus

Fig. 69. Gastrulation and formation of the trochophore larva
in polychaetes. (a) section through a late cleavage stage ; (b) the
micromeres spread over the macromeres ; (c) early trochophore
with mesoderm stem-cells budding off a row of mesoderm cells
between the ectoderm and endoderm; (d) elongating trocho-
phore with mesoderm cells taking up a vertical position. From

Waddington, 1956.

The fate of each individual blastomere can be predicted accur-
ately and isolated blastomeres tend to develop only into those
organs which they would have formed if left undisturbed. It has
therefore become usual to regard the egg as a mosaic of localized,
organ-forming areas but it is a concept which must not be pushed
too far, for many spirally cleaving eggs possess a limited ability
to regulate the fate of the blastomeres according to circumstances.

In polychaetes the blastomere D is particularly important for
most of the ectoderm and mesoderm of the adult worm are derived
from its descendants 2d and 4d. 2d is known as the somatoblast ;

REPRODUCTION AND DEVELOPMENT

119

it divides many times to form the somatic plate, an area of irregu-
larly arranged cells which is first seen dorsally but spreads over the
surface of the embryo until its edges meet ventrally (Fig. 70).

Micromeres

Mesoblast

Micromere
2d derivatives

Endoderm

Macromere

(a)

Somatic
plate

iVIesobiast

Apical organ

Endoderm

(c)

Nerve cord rudimen't
(d)

(e)

Somatic
plate

Fig. 70. Development of polychaetes. (a) blastula, showing
beginnings of subdivision of 2d to form somatic plate tissue;
(b) section through slightly later stage ; (c) to (e) diagrams illus-
trating the spread of the somatic plate tissue from dorsal to
ventral side of the embryo, (a) after Child, 1900; (b) after
Wilson, 1932; (c) to (e) after Dawydoff, 1959.

From the somatic plate are formed the ventral nerve cord and most
of the trunk ectoderm. 4d is known as the mesoblast and at the
time of gastrulation it sinks below the surface of the embryo. It
divides once and its descendants then bud off long chains of cells
which eventually form the segmented mesoderm. It is usual for
polychaetes to pass through a free-swimming trochophore larva
stage, the organization of which is basically that of a triploblastic
acoelomate.

The oligochaetes, many of which are terrestrial and which
deposit their eggs in a nutritive fluid enclosed within a cocoon,
have lost the free swimming larval stage. Moreover, the pattern
of cleavage is often so much modified that it is difficult to detect

120 LEECHES

any resemblance to the polychaete pattern of spiral cleavage. The
aquatic forms are the least modified and in Tubifex four quartettes
of micromeres are formed in a fairly typical manner. Instead of 2d
giving rise to a plate of irregularly arranged cells it divides in a
regular manner to give four mother cells on each side of the
embryo. These then proceed to bud off four rows of cells on each
side, forming prominent longitudinal bands often called the
germinal bands. Beneath these superficial rows of cells are rows
of mesodermal cells budded off from the descendants of 4d, much
as in polychaetes. The germinal bands are at first situated fairly
near to the dorsal side and are separated one from the other only
by a small cap of micromeres (Fig. 71) but when the micromeres

M i cromere

Germinal
band

acromere

Fig. 71 . Lateral view of embryo of Tubifex to show one of the
two germinal bands. After Penners, 1923.

begin to multiply the germinal bands are pushed before them
towards the ventral surface of the embryo and at the time of closure
of the blastopore the germinal bands meet one another along the
mid-ventral line. The inner row of cells from each side gives rise
to the ventral nerve cord and the other rows form first the circular
musculature and later the ectoderm of the adult worm, replacing
the embryonic ectoderm formed from the micromere cap. The
presence of these regularly arranged longitudinal rows of cells
budded off from four mother cells on each side is a feature which
distinguishes oligochaete embryos from those of polychaetes and

REPRODUCTION AND DEVELOPMENT 121

we shall see that in this feature as in many others the Hirudinea
resemble the oligochaetes.

In terrestrial oligochaetes the formation of the germinal bands
proceeds much as in Tuhifex but the formation of quartettes of
micromeres and of the endoderm is frequently modified by the
failure of two of the four original blastomeres to take any part in
development. In Bimastus for instance blastomeres A and B form
no micromeres. B divides once, A not at all and these cells lie at
the animal pole for a considerable period before finally degenerating.

Against this background of annelid embryology we may turn to
the embryology of leeches. In general the Glossiphoniidae have
the least modified type of spiral cleavage and have relatively large
amounts of yolk, while the eggs of other families show greater
deviations from the typical pattern of spiral cleavage and have less
yolk, relying more on the supply of albuminous fluid contained
within the cocoon.

5. Embryology of a Glossiphoniid Leech

The egg of a glossiphoniid is about 0-5-1 -0 mm in diameter and
is often coloured green or yellowish by the yolk. First and second
polar bodies are cut oflF in the first hour or two after the eggs have

Fig. 72. Egg of Theromyzon tessulatwn at 2-ceIl stage showing
pole plasm. From Dawydoff, 1959, after Schmidt.

been laid and soon afterwards two masses of clear cytoplasm, the
pole plasms, become differentiated at the animal and vegetable
poles. The animal pole plasm has a ring formation and the
vegetative pole plasm is disc-shaped. The first cleavage is into

122

LEECHES

two unequal blastomeres, AB being smaller than CD and subse-
quent divisions in CD precede those in AB. Blastomere D is
larger than C and contains most of the pole plasm. The first set
of micromeres is offset in a clockwise direction when viewed from
the animal pole (Fig. 73) and the second set in an anticlockwise
direction. The cleavage of the egg of Theromyzon is particularly
interesting because the pattern of spiral cleavage is so like that of

(a) (b)

Fig. 73. (a) early stage in the spiral cleavage of an egg of

Glossiphonia complanata viewed from animal pole ; (b) later stage,

showing cap of micromeres, mother cells of germinal bands

(dotted) and mesoblast (hatched). After Muller, 1932.

polychaetes that Schmidt (1917) was able to recognize the cells
of the " apical rosette " and the " annehd cross ". This is unusual
because the formation of such a regular pattern is normally
prevented by the precocious cleavage of the D blastomere but it is
usually possible in the eggs of Glossiphoniidae to follow the
formation of four complete sets of micromeres much as in Tubifex.
The micromere 2d stands out from the others because it is usually
as large as the macromere 2D. 2d divides several times, cutting off
a number of small cells destined to join the micromere cap, and
then forms eight equal sized cells. These are the mother cells of
eight rows which are budded off to form germinal bands (Fig. 74).

Germinal band

Fig. 74. Late cleavage stage of Glossiphonia showing germinal
bands. After Whitman, 1878, modified.

REPRODUCTION AND DEVELOPMENT

123

As in oligochaetes these rows of cells grow forward from a postero-
dorsal position forming prominent ridges at the junction of the
micromere cap and the macromeres. At the same time two rows
of mesoderm cells are formed beneath them. They are developed
from a pair of mesoblasts which in this instance result from the
division of 3D and are therefore 4D and 4d. This state of affairs
is different from anything found in either polychaetes or oligo-
chaetes, for in these groups it is 4d which gives rise to the right
and left mesoblasts, while 4D contributes to the endoderm. In the
Glossiphoniidae there is no contribution to the endoderm from
any cell of the D quadrant.

At this stage we have a blastula which consists of a mass of
micromeres at the animal pole, three macromeres at the vegetative
pole and between them on each side a ridge, comprising four
superficial and one deep row of cells, the germinal band and its
underlying mesoderm. The micromeres of the fourth quartette
sink in and join the macromeres, which are destined to form the
endoderm, but the micromeres of the first three quartettes begin

Pharynx

Mocromere A
under covering
of micromeres

Germinal band

Fig. 75. Gastrulation in Glossiphonia. (a) the micromere cap
is beginning to spread towards the vegetative pole while the
germinal bands move before it; (b) a more advanced stage;
(c) the two germinal bands have almost met ventrally. All viewed
from the anterior end. After Whitman, 1878, modified.

124

LEECHES

to proliferate and spread from the animal pole towards the
vegetative pole. The germinal bands move before them. At this
stage they are seen as two arcs arising from a group of eight cells
at the posterior end of the embryo and running on each side to
meet anteriorly. As the micromere cap grows and spreads the two
germinal bands move towards the vegetative pole. Their anterior
and posterior points of union remain almost stationary and the two
semi-circular germinal bands rotate about these points and are
brought together in the mid-ventral line like the jaws of a trap. The
micromeres continue to grow ventrally, finally moving over the top
of the germinal bands to meet at the vegetative pole and thus effect
the closure of the blastopore. As in the oligochaetes, the two
median ventral rows of cells of the germinal bands form the ventral

Ectodermal
micromeres

Mesoderm

Cells of
germinal
band

Fig. 76. Transverse section through ventral part of a Glossi-

phonia embryo after the micromeres have covered the germinal

bands; a, b, c macromeres. After Burger, 1902.

nerve cord while the others form the circular musculature. The
deeper row of mesodermal cells forms the somites. In the Glossi-
phoniidae, but not in other families, the micromeres which have
spread over the surface of the gastrula form the definitive epi-
dermis, the descendants of the first quartette covering the head,
those of the second and third the trunk.

During the next phase of development the main organs of the
body are differentiated. The ventral nerve cord, as we have seen,
originates from the ventral edges of the germinal bands, but
opinions differ about the origin of the cerebral ganglia. Dav^doff

REPRODUCTION AND DEVELOPMENT

125

(1959) favours the view that in Glossiphoniidae they are formed
from the head ectoderm quite separately from the ventral nerve
cord. If this is so, the situation is comparable with that found in

(c)

Fig. 77. Later stages in the development of Glossiphonia.
(a) dorsal view of an embryo a little older than that shown in
75c ; (b), (c) and (d) stages in the appearance of somites and ganglia
in lateral view ; (e) dorsal view of a young leech ready to leave
the parent ; c, crop diverticulum ; e, eye ; ^1-^3, endodermal macro-
meres seen through ectoderm ; gi-gs, three outer rows of cells of
germinal bands ; h, head ; n, inner row of cells of germinal band
which forms nerve cord ; p, proboscis ; ph, pharynx ; /).^., posterior
sucker. After Whitman, 1878.

polychaetes where the brain and prostomial organs are derived
from the apical organ of the trochophore larva and not from the
ventral plate.

The gut is formed from macromeres 4A, 4B, 4C and the fourth
quartette of micromeres. At first the endoderm is a syncytium,
the nuclei dividing faster than the cytoplasm. Later the nuclei
become arranged around the periphery of the yolky mass. The

126

LEECHES

yolk is slowly withdrawn from the centre to form a lumen sur-
rounded by a gut epithelium and an opening to the outside world
is acquired when ectodermal cells sink in to form a stomodaeum.
The proctodaeum is formed last of all.

While this is in progress the mesodermal tissue beneath the
germinal bands is dividing up into segmental blocks, beginning at
the anterior end. The blocks hollow out to form the coelom and
spread laterally round the gut, giving rise to gut musculature and
longitudinal muscles of the body wall, but in addition many mesen-
chyme cells are budded off both inwards and outwards from the
walls of the coelomic sacs and septa break down to bring the
coelomic cavities into communication one with the other. Eventu-
ally the coelom becomes almost obliterated and is represented only
by four longitudinal channels, two lateral, one dorsal and one
ventral, together with a complex system of transverse channels.
In Glossiphoniidae blood vessels are formed mid-dorsally and
mid-ventrally but they do not develop a full set of segmental
branches, remaining instead as rather small longitudinal vessels
totally enclosed within the dorsal and ventral coelomic channels.

Nephridia are formed in two parts: the funnels and glandular
parts are formed from nephridioblasts which are intersegmental
in position (Figs. 78 and 79) while the end sacs and ducts to the

Rudiment of nephridial tubules

Nephridioblast
Fig. 78

Nephridioblast
Fig. 79

Fig. 78. Longitudinal section showing the coelom, rudimentary
septa and nephridioblasts of Glossiphonia. After Bychowsky,

1921.

Fig. 79. Nephridial rudiment in Erpohdella. From Burger,

1891.

REPRODUCTION AND DEVELOPMENT 127

exterior are formed from ectodermal tissue. The question of
whether the nephridioblast is ectodermal or mesodermal in origin
has not been finally settled. It may well be cut off very early
from ectomesoderm.

Testes differentiate from the inner walls of the coelomic sacs
while these are still intact in such a way that each testis sac en-
closes a small part of the coelom. At a later stage the vasa efferentia
arise as evaginations of the testis sacs. They join together to form
the vas deferens of each side and these in turn unite with the
genital atrium which has differentiated from the somatopleure
anteriorly. A pair of ovarian sacs forms just behind the genital
atrium. They are first seen as a pair of gonoblasts cut off from the
walls of coelomic sacs and looking very like nephridioblasts.
Each gonoblast divides once and one of the cells thus formed
divides many times to form a group of cells which are organized
into a capsule surrounding the other cell. By elongation of the
capsule and subdivisions of the internal cell an ovarian sac is
formed with an ovarian strand inside it and a duct to the exterior.

The segmentation of the mesoderm imposes a pattern of annula-
tion on the epidermis and circular muscles. At first there is only
one annulus per segment but soon a second annulus is cut off
from the posterior border of each original one. Then another is
cut off on the anterior border, giving the triannulate condition
characteristic of the majority of Glossiphoniidae.

6. Embryology of a Gnathobdellid Leech

The gnathobdellid leech which has been most often studied is
Erpohdella. The eggs are small and contain little yolk. The
cleavage follows the normal annelid pattern up to the formation
of the first quartette of micromeres. After this the blastomeres lA
and IB become passive and produce no more micromeres. IC
divides to form 2C and 2c and then it too becomes inactive.
2c passes into the blastocoel and only ID continues to divide. Its
next cleavage produces two cells of about equal size, 2d and 2D.
The latter cuts off two more micromeres, 3d and 4d and these join
2c in the blastocoel. At this stage the first quartette of micromeres
occupies the animal pole, macromere 4D is at the vegetative pole
and around the equator lA^ IB and 2C occupy left, anterior and

128

LEECHES

right sides respectively, while the large micromere 2d lies pos-
teriorly (Fig. 80). 2d divides three times to form eight cells, four
on each side in the postero-dorsal position, and these are the
mother cells destined to bud off the longitudinal rows of cells

(c)

Fig. so. Segmentation in the egg of Erpobdella. The mother
cells of the germinal bands are dotted, the mesoblasts hatched.
The arrow points to the animal pole, (a) 9-cell stage viewed
from the animal pole; (b) 16-cell stage from the D-quadrant;
(c) 23 -cell stage in dorsal view, (a) after Sukatschoff, 1903;
(b) and (c) after Dimpker, 1917.

comprising the germinal bands. 4d divides once to form a pair
of mesoblasts and these eventually bud off rows of cells for the
segmental mesoderm.

Thus in a gnathobdellid, as in a glossiphoniid leech, the germ
bands are derived from 2d and the mesoblasts are derived from a
macromere of the D quadrant. The peculiar feature of the
development of a gnathobdellid leech is that the macromeres A^ B
and C become inactive after cutting off one or two micromeres.
They do not form the endoderm for this is derived from the
micromeres 2c^ 3d and 4d which pass into the blastocoel at an early
stage. Almost the whole of the rest of the adult leech is derived
from the cells 2d and 4D, so that with the exception of the
micromere 2c in the endoderm, the whole of the adult animal is
derived from the D quadrant.

Another difference between gnathobdellids and glossiphoniids
is that whereas the glossiphoniids completely lack a larval stage,
the gnathobdellids form larval organs which are discarded at

REPRODUCTION AND DEVELOPMENT

129

metamorphosis. The larva (Fig. 81) never has a free swimming
existence but it is adapted to living in a pool of albuminous fluid
within the cocoon and absorbing nutriment from it. The larval
organs are formed during gastrulation. The micromeres of the

Pharyngeal muscle
cells

Larval
ectoderm

Blastocoe

Thoracic
portion
germina
band

Protoneph-
r i d i u m 2

Mouth

Pharynx
Gland cells

Head portion
germinal
and

Protoneph-
ridium I

Endoderm
cells

Degenerating
mocromeres

Fig. 81. Crypto-larval stage oi Erpobdella. From Grasse, 1959,

based on Bergh.

first quartette proliferate and spread from the animal pole down
to the vegetative pole covering the germinal bands and closing oflF
the blastopore. These cells form a delicate larval ectoderm,
ciliated in the mid-ventral line, and a lining to the larval pharynx.
The larva is also equipped with temporary pharyngeal musculature
and with two to four pairs of protonephridia. It has no anus and
the central nervous system is still rudimentary, but albumen is
wafted into the gut by ciliary action and is used for growth in size
and complexity.

130 LEECHES

At metamorphosis the larval ectoderm together with some under-
lying muscular and connective tissues and the protonephridia
degenerate and are replaced by tissues derived from the germinal
bands. The adult gnathobdellid is thus formed almost entirely
from germinal band and mesodermal tissue. In the larval stage
the bands are divided on each side into an anterior cephalic portion
and a posterior trunk portion (Fig. 81). The latter gives rise to
the ventral nerve cord in the normal manner but the brain is
formed from the cephalic portion of the germinal bands and not
from the larval head ectoderm as in the glossiphoniids.

The endoderm, at first represented by a number of large discrete
cells, soon takes on the form of a syncytial gut epithelium by the
fusion of the cells and the subdivision of the nuclei. It does not
become divided into separate epithelial cells until a iew days after
the leeches have left the cocoon, and up to this time the gut lumen
is filled with albuminous fluid. The formation of the proctodaeum
takes place after the shedding of the larval organs. The passive
macromeres A, B and C come to lie between the gut wall and the
ectoderm in the posterior part of the embryo, where they gradually
degenerate and are absorbed.

Schoumkine (1953) has shown that in all important respects the
embryology of Hirudo corresponds with that of Erpohdella.

7. Special Features of Piscicolid Embryology

Eggs of piscicolid leeches cleave normally until after the
formation of the second quartette of micromeres but subsequent
development is complicated by precocious gastrulation. The events
which occur during development are basically similar to those
occurring in other groups but the timing is quite different. At the
stage when two quartettes have been formed all micromeres except
2d begin to multiply and their descendants spread rapidly over the
other cells providing a complete covering of very flat ectodermal
cells (Fig. 82). Within this outer covering the macromeres and 2d
continue to divide, 2d giving rise to the mother cells of a pair of
germinal bands and 4d forming a pair of mesoblasts. As the
original egg contained very little yolk the macromeres are quite
small. They organize themselves into a solid mass, multiply and
then form a hollow organ which is the gut rudiment (Fig. 83). At

REPRODUCTION AND DEVELOPMENT

IB lA

131

Endoderm

Fig. 82. (a) segmentation of egg of Piscicola. (b) vertical section

illustrating precocious gastrulation in Piscicola. From Dawydoff,

1959, after Schmidt.

Mese

Germinal
band

Mother cell
of germinal -
band

Larval ectode

Mother cell
f germinal
and

oblast

Fig. 83 . Dorsal view of embryo of Piscicola showing endodermal

gut rudiment and formation of germinal bands after precocious

gastrulation. From Grasse, 1959, after Schmidt,

132

LEECHES

this Stage there is a large fluid-filled space within the covering of
ectodermal cells and the gut rudiment is small, occupying only
a fraction of the available space. However, it soon acquires an
opening to the exterior and begins to absorb nutriment from the
fluid in the cocoon. This enables the endodermal cells to grow
and divide until the gut occupies the greater part of the embryo
(Fig. 84).

Mesobia

Mesode

Germ

Fig. 84. Sagittal section of advanced embryo of Piscicola,

showing the germinal bands and developing gut. From

Dav^^ydoff, 1959, after Schmidt.

While this has been going on the germinal bands have become
well developed and the embryo possesses essentially the same
structures as are present in the embryos of other groups after
gastrulation : a gut with a stomodaeum but not a proctodaeum ; a
pair of germinal bands destined to give rise to the nervous system.

REPRODUCTION AND DEVELOPMENT 133

the circular muscles and the definitive epidermis; two rows of
mesodermal cells destined to form the somites ; an endodermal sac
which will eventually form the crop and intestine of the adult leech.
Subsequent development is by way of a larva equipped with a
ciliated larval ectoderm, a temporary larval pharynx and proton-
ephridia. At metamorphosis these are lost, just as in the
gnathobdellids.

The Piscicolidae occupy in respect of their development a
position intermediate between the Glossiphoniidae and the
Gnathobdellae. They share with the former an unspecialized
pattern of cleavage in which all four quadrants contribute to the
final animal but resemble the latter in possessing a larval stage with
larval organs which are shed at metamorphosis. In the Glossi-
phoniidae the eggs carry a large store of yolk which enables them
to complete their development without absorbing nutriment from
the fluid in the cocoon, while in the Piscicolidae and
Gnathobdellae there is little yolk and there is a larval stage
adapted to the absorption of nutriment from the fluid in the cocoon.

8. Phylogenetic Considerations

Whereas in polychaetes external fertilization and a free swim-
ming larva is normal, most earthworms and leeches have evolved
a habit of enclosing the fertilized eggs in a thick-walled cocoon
filled with nutritive fluid. This frees the parent from the necessity
of providing the eggs with a large supply of yolk, for nutriment
can be absorbed as development proceeds. Schmidt (1944) con-
siders that the habit has arisen by parallel evolution in the
terrestrial oligochaetes, the gnathobdellid and the piscicolid
leeches. In each case this method of rearing the eggs has resulted
in a number of embryonic adaptations, particularly in the forma-
tion of a larval pharynx, an ectodermal ciliary apparatus for
passing nutriment into the gut rudiment and larval nephridia.
The fact that the adaptations are arrived at in a different way in
each group points to an independent origin in each. The glossi-
phoniid leeches lack these adaptations and we may consider
whether this state has been achieved by simplification or is
primitive. In favour of the first view is the presence of a ciliated
larva in the polychaetes. This might suggest that while the other

134

LEECHES

annelids have retained a simplified form of ciliated larva the
glossiphoniids have progressed further and suppressed it entirely.
On the other hand it is among the Glossiphoniidae that we find
a pattern of cleavage most closely resembling that of the poly-
chaetes and Schmidt (1944) takes this to mean that the Glossi-
phoniidae are a primitive group of leeches and that they never
evolved the thick-walled cocoon and its attendant larval adapta-
tions. The peculiarities of the cleavage process in Gnathobdellae
and Piscicolidae are seen by Schmidt as preliminary stages
in the development of special larval organs.

9. Evolutionary History of Leeches

While we are on the subject of phylogeny it is worth while to
draw together the various lines of evidence for the relationships of
the various groups of leeches. Wendrowsky (1928) determined
the chromosome number in various species. These are listed in
Table 8. They suggest that the primitive diploid number is 16

Table 8

Species

Diploid number

of chromosomes

Acanthohdella peledina

16

Theromyzon tessulatum

16

Glossiphonia heteroclita

16

Glossiphonia complanata

26

Hemiclepsis marginata

32

Piscicola geometra

32

Erpohdella octoculata

16

Dina lineata

18

Haemopis sanguisuga

26

and that Theromyzon^ which has a primitive pattern of develop-
ment is also primitive in its chromosome number while Piscicola
which has a specialized mode of development appears to be a
tetraploid.

Another line of evidence is from the number of annuli per

REPRODUCTION AND DEVELOPMENT

135

segment. Oligochaetes have one annulus per segment and leeches
pass through the uniannulate condition during development so it
is reasonable to infer that a small number of annuli is a primitive
feature. Once again it is the Glossiphoniidae with three annuli per
segment which appear to be the primitive group. Next come the
Gnathobdellae with five as the typical number and lastly the
Piscicolidae where more than five is common {Piscicola has
fourteen).

It seems unlikely that the Hirudinea as a whole are polyphyletic
for it would be difficult to explain how more than one line of
evolution arrived at 33 segments as the optimum number. If we
therefore assume a common ancestral stock it is obvious that there
was an early and fundamental divergence between the Rhynchob-
dellae and the Gnathobdellae according to whether the method
of sucking blood was by a proboscis or by jaws. Within the
Rhynchobdellae there is abundant evidence for regarding the

Piscicolidae

Glossiphoniidae

Erpobdellidae

Hoemadipsidae
Hirudidae

Rhynchobdellae

Gnathobdellae
Acanthobdeilae

Ancestral oligochaete stock

Fig. 85. Diagram illustrating the evolution of the main
families of leeches from the ancestral oligochaete stock.

Glossiphoniidae as primitive and the Piscicolidae as special-
ized. In the Gnathobdellae it is likely that those forms with well
developed jaws are primitive and that those which have become
carnivorous have done so secondarily. Using this evidence it is
possible to construct the evolutionary tree illustrated in Fig. 85.

CHAPTER 10

ECOLOGY

1. Relations with the Inanimate Environment

In this chapter we shall consider the ways in which the distribution
and abundance of leeches is affected by factors of the environment,
both living and non-living. We may begin by considering the
inanimate environment, the characteristics of which have the
advantage of being more easily measurable. With few exceptions
leeches live in aquatic habitats. The exceptions fall into two
groups, the land leeches which live in damp situations like tropical
jungle and feed from time to time on passing terrestrial animals
(Haemadipsidae, p. 32), and amphibious leeches which leave the
water for part of the year to live in soil or under stones, feeding on
worms or slugs which they swallow whole (e.g. Trocheta and
Haemopis). The remainder, the truly aquatic leeches, show a
pattern of distribution which may be correlated with the physical
and chemical characteristics of the water. There have been four
main studies of the ecology of leeches in Europe. Pawlowski (1936)
and Sandner (1951) worked in Poland, Bennike (1943) in Denmark
and Mann (1955) in Britain. Ten species of leech were common to
all three areas so there is a good body of knowledge on the ecology of
European leeches. For descriptive purposes it is convenient to divide
freshwater lakes and ponds into hard, intermediate and soft waters
with dividing lines at calcium concentrations of about 24 mg/1 and
8 mg/1. These calcium figures give a fair indication of the total
amounts of dissolved solids in the water and at the levels mentioned
it has been shown that there are marked changes in the composition
of the fauna of fresh waters (Ohle, 1934; Boycott, 1936). In hard
waters the most abundant leech is almost always Helobdella
stagnalis and the same is true in the intermediate group, provided
that the body of water is a reasonably large one. Small ponds have

136

ECOLOGY

137

a different fauna (see below). Accompanying Helohdella, but in
smaller numbers, one finds Erpohdella octoculata, Glossiphonia
complanata and G, heteroclita, Hemiclepsis marginata and Thero-
myzon tessulatum. The most abundant leech in soft waters is
normally Erpohdella octoculata, alone or accompanied by small
numbers of Helobdella, Glossiphonia complanata or Theromyzon.
The change from a leech fauna dominated by Helohdella to one
dominated by Erpohdella is illustrated in Fig. 86.

Water

Soft

Intermediate

Hard

Productivity

Dystrophic
0 r

Oligotrophia

Transitional

Eutrophic

\

w

I \
I \

\ Ponds
\
\
\
\

\ /

Lakes and tarn

I 17 i 19 I

3033 35 38i40! 2 45'47l49'52l53i 7 I 9l II I I3'l5ll71 I9I2I
32 34 36 39 43 44 3 48 50 6 54 8 10 12 14 16 18 20

Station nunnbers

Fig. 86. The relative numbers of Erpohdella octoculata and
Helobdella stagnalis in different types of standing water. Collec-
ting stations are arranged in order of total alkalinity. The
dotted line connects stations of a surface area less than 5000
square yards. From Mann, 1955.

As was stated above small bodies of water tend to have a different
fauna from large ones having the same calcium content. One
feature in which they differ is in the amount of rooted vegetation
relative to the volume of water. Small ponds have a large proportion
of rooted plants and the products of their decay lead to a high
concentration of " humic acids " in the water (Tucker, 1958). The
effect of this accumulation, either directly or indirectly, is to

138

LEECHES

prevent Helohdella thriving in bodies of water which otherwise
appear favourable. In soft waters the same process leads to acid,
dystrophic conditions which may exclude all species of leech.

The distribution of certain leeches may also be correlated with
the dissolved oxygen content of the water. This factor fluctuates
diurnally and annually, but it is obvious that on average the
oxygen concentration is higher in unpolluted running water and
on the wave-washed shores of lakes than it is in sheltered ponds
having accumulations of decaying organic matter. It has been
shown (p. 59) that Erpobdella testacea is better able to maintain
aerobic metabolism in poorly oxygenated water than is E. octoculata
and it is probable that this factor determines which of the two

Erpobdella octoculata Erpobdella testacea Glossiphonia complanota Glossiphonia heteroclito

7o 50

LiL kl Li

ABCDE ABCDE ABCDE ABODE

Helobdella stagnolis Theromyzon tessulatum Hemiclepsis marginata Piscicola geometra

100

% 50

yi UL LiL

"ABODE ABODE ABODE ABODE

Fig. 87. The frequency of occurrence of various leeches in the
diff"erent types of habitat. A, soft standing water; B, inter-
mediate; C, hard standing water; D, slowly running water;
E, fast running water; ordinates, percentage of stations within
each group which contains the leech in question. From Mann,

1955.

species is the more abundant in a particular type of habitat.
E. testacea builds up dense populations in shallow, swampy situa-
tions having a rich accumulation of decaying plant material (Mann,
1959, 1960). In all probability dissolved oxygen plays a part in
determining which of the two fish parasitic leeches is present in a
given habitat. Piscicola geometra has a relatively high rate of
oxygen uptake which is depressed by low oxygen concentration in
the water (p. 57) and it occurs mainly in fast flowing streams and

ECOLOGY 139

on the wave- washed shores of lakes. Hemiclepsis on the other hand
is found chiefly in standing water or in slowly running rivers.

Some species of leech are better adapted to life in a strong
current of water than others. All are equipped with suckers and
so are hardly likely to be washed away in the normal course of
events, but during the breeding season some species are better
equipped to protect the eggs and young from being washed away
and lost. Erpohdella octoculata produces a low, smooth cocoon,
firmly fastened to a stone or plant and this species is always to be
found in running water. Glossiphonia complanata produces a soft,
gelatinous cocoon, but this is cemented down and the leech pro-
tects it with its body. This works well, and G. complanata is some-
times the most abundant species, especially in chalk streams.
G. heteroclita on the other hand does not cement its cocoon to the
substratum, but holds it loosely under its body. This may be the
reason why flourishing populations of this species are never found
in situations exposed to a current of any strength.

2. Relations with the Animate Environment

It seems that only in Europe have leeches been studied inten-
sively so that conclusions can be reached about their habitat
preferences. For the rest of the leech fauna of the world our.
information is mainly confined to brief notes about the food
organisms with which the leech is associated, with perhaps some
information about the habitats in which occasional specimens have
been found. A comprehensive list of the leeches of the world with
their hosts or food organisms is beyond the scope of this book, but
in Table 9 this information is given for a number of better known
genera. Here again the information from European sources is the
more reliable since many doubts have been resolved by the careful
serological, chemical and haemocytometric studies of the gut
contents of leeches by Jung (1955).

Only a few leeches are restricted to one kind of host. Hemibdella
soleae is restricted to Solea spp. and Callohdella lophii feeds only
on the angler fish, Lophius piscatorius, but the majority of leeches,
while disposed to attack a particular kind of host, such as birds or
bony fish, will take a meal where they can find one. Hirudo, for
example, while predominantly an ectoparasite of mammals, is

140

LEECHES

Table 9.

Species

Blood sucking on :

o

•2 J3 '-'
5« -Q .22 '5

u

Devouring :

CO

o

W CO

3 ■"

y «« c

2 g .2

- - I o ^

^ ^ O ^ U

Hirudidae

Hirudo

Macrohdella

Philobdella

Hirudinaria

Haemopis

Erpobdellidae

Erpobdella
Trocheta
Nephelopsis
Dina

Haemadipsidae

Haemadipsa

Glossiphoniidae

Glossiphonia

Batracohdella

Hemiclepsis

Theromyzon

Helobdella

Haementeria

Piscicolidae

Piscicola

Cystobranchus

Pontobdella

Branchellion

Abranchus

X X X X X
X XX

X
X

X

X

X X

X X X X

7 ?

X X X X

X
X

X
X X
X

X X X X X

X X X X X

X X X X

X X X X

X X X X

ECOLOGY 141

reported as sucking blood from snakes, tortoises, frogs and even
fish, especially when young. The very young may even swallow
small worms. It is thus very difficult to draw a sharp distinction
between parasites and predators among the leeches. Not only do
their habits vary during the life history of an individual, but their
effect on the host may vary according to its size. Thus the
Glossiphoniidae which have a proboscis and are equipped for
sucking blood may suck the entire body fluids from a small snail
and even finish the job by sucking up all the soft parts of the
animal. This is clearly predation, but young specimens of the
same species may live for long periods inside the mantle cavity of a
large snail taking only occasional meals of blood, a mode of life
which may reasonably be called parasitism.

Compared with the blood-sucking leeches the macrophagous
forms take an even wider variety of food. Most of them will take
any kind of proteinaceous material that is offered, including
carrion or young of their own species. In fact Jung (1955) con-
cluded that the only consideration is particle size. In practice the
habits of the leech determine the food available to it, so that
Trocheta suhviridis which burrows in moist soil will most often
encounter earthworms and slugs, while Nephelopsis which remains
in water is particularly attracted to the corpses of fish and frogs.
Similarly the American species Macrohdella decora will attack fish
or swallow the eggs of frogs or salamanders in spite of its clear
adaptations to piercing the skin of mammals (Cargo, 1960). When
comparing the distribution of sanguivorous and carnivorous
leeches we find that while the former have patterns of distribution
related to those of their normal host organisms, the latter, which
are more catholic in their tastes, have distribution patterns which
are more closely related to physical and chemical features of the
environment.

Feeding relationships are not the only ones which we should
consider when dealing with the relations between leeches and the
animate environment. Leeches also act as hosts to other parasitic
forms and as vectors in the life cycles of parasites of other animals.
In common with most other invertebrates leeches have their quota
of endoparasitic Protozoa. Of these, some, such as Entamoeba
aulastomi from the gut of Haemopis or Orcheohius herpohdellae
from the testes of Erpohdella are specific to the leeches but others

142

LEECHES

Fig. 88. See legend on p. 143.

ECOLOGY 143

such as Entamoeba ranarum occur in a variety of aquatic animals.
Possibly of greater interest are the parasites for which leeches are
the intermediate host by reason of their blood-sucking habits.
Many species of Trypanosoma from the blood of freshwater fishes
are transmitted by Piscicola and Hemiclepsis, and a similar role is
played by Pontohdella and Trachelohdella in respect of marine fish.
In these cases reinfection of the fish occurs during blood sucking,
the infective stages migrating to the proboscis. Barrow (1953,
1958) in an intensive study of the biology of Trypanosoma diemyctyli,
which has the newt Triturus as its primary host and the leech
Batracobdella picta as its secondary host, showed that the passage
of the infection from mother to offspring in the leech takes place
via the vertebrate host. When the young leave the mother to take
their first meal of vertebrate blood they may stay on the newt for
7-14 days. During this time the newt becomes infected by the
mother and the trypanosomes are picked up by the offspring
during feeding. Haemogregarines may also be carried by leeches,
Haemogregarina stepanowi of the pond tortoise Emys orbicularis
being transmitted by Placobdella costata.

When handling Erpobdella octoculata it is often possible to see
numerous clear cysts in the mesenchyme or body wall. These
were called tetracotyles, one kind being given the name Tetracotyle
typica. Subsequently it was shown that they were metacercariae
of strigeid trematodes, and Szidat (1930) showed that they develop,
when the leeches are eaten by birds, into Cotylurus cornutus and
Apatemon gracilis. Other cysts which occur in Erpobdella clearly
show a ring of hooks characteristic of cestodes. One such cyst
has been shown to be the cysticercoid of Hymenolepis parvula, a
small cestode found in the intestine of ducks.

Fig. 88. The life cycle of Haemogregarina stepanowi. a-h,
from the turtle Emys orbicularis; i-n, from the leech Placobdella
costata; a, schizont with fully formed merozoites, from bone
marrow; b, entry of merozoite into blood corpuscle; c, d, e,
further merozoite formation; /, formation of gamonts; ^i,
macrogametocyte ; hz, microgametocyte ; i, maturing of macro-
gametes ; k, fusion of gametes ; /, oocyst ; m, sporozoite forma-
tion; n, free sporozoite in proboscis blood vessel of leech.
From Herter, 1937, after Reichenow.

144

LEECHES

The existence of parasites with this type of Ufe history provides
evidence that water birds and fish are predators of leeches. Other
evidence is scanty since leeches seldom leave indigestible remains
so that they may be identified from stomach contents. From direct
observation of the feeding habits of various water birds and fish
and from occasional records from stomachs it is possible to say
that erpobdellids in particular are preyed upon by herons, swans,

FiG.'^89. (a) diagram showing cysticercoid stages of the cestode
Hymenolepis parvula distributed in the tissues of a specimen
of the leech Erpobdella octoculata (drawn from a whole mount) ;
(b) a drawing of one cysticercoid, showing the ten characteristic
hooks; (c) details of one hook. Original.

ducks, bitterns, trout, perch, tench, sticklebacks and eels. There
is no reason to suppose that they are rejected by aquatic amphibia
and mammals, and are no doubt taken by carnivorous inverte-
brates such as Hemiptera and Odonata. The mortality rates in
natural populations of Erpobdella octoculata^ Glossiphonia compla-
nata and Helohdella stagnalis have been roughly estimated for
certain habitats in Britain (Mann, 1953b, 1957a, b). In each case
there was a heavy mortality in the first three months of life, more

ECOLOGY 145

than 95% of the offspring being lost. In Erpohdella and Glossi-
phonia, where most individuals lived for 2 years, there v^as subse-
quently a mortality at the rate of one third to tvv^o thirds of the
population per annum (Table 10). In Helohdella, where there are

lOOOx

500

100

0 3 6 9 12 15 18 21 24 27

Months after hatctiing (calculated from 1st May)

Fig. 90. Survival curve for 1000 newly hatched young of
Glossiphonia complanata. From Mann, 1957.

two generations a year, the rate of mortality is correspondingly
higher.

Looking over our very incomplete knowledge of the ecology of
leeches, it appears that for the blood-sucking ectoparasites the
most important single factor influencing distribution and abun-
dance is the presence or absence of an appropriate host organism.
In temperate climates, however, the predatory macrophagous

146

LEECHES

Table 10. Comparison of the Life Histories of
Glossiphonia complanata and Erpohdella octoculata

Glossiphonia

Erpohdella

complanata

octoculata

Breeding period

March-May

June-Aug.

Average number of young per parent

26

23-5

Mortality in the first 6-9 months of life

97%

91%

Proportion of year-group breeding at

70%

87%

1 year old

or less

Mortality from 6 to 18 months

33%

49%

Proportion of year group breeding at

2 years old

100%

100%

Mortality from 18 to 30 months

84-88%

69%

Proportion of total population surviving

to 3 years

5-6%

4%

forms greatly outnumber the sanguivorous parasites and these
tend to feed on a wider variety of animals, so that almost any
aquatic habitat will contain some suitable food organisms. For
these the chemical and physical characters of the environment
sway the balance in their competition with other organisms, the
oxygen and calcium content of the water and the rate of water
movement being particularly important.

BRITISH FRESHWATER LEECHES

1. Hiriido mediciualis. la, a few annuli in lateral view. 2. Ghssiphonia
heteroclito. 3. Piscicola geonietra. 4. Erpobdella octoculata. 4a and 4b,
a few annuli in dorsal view, enlarged to show variation in the amount ot black
pigment present. 5. Hemiclepsis mariyinato. 6. Helohdella stagnalis.
1. Haemopis sanguisuga. 7a, a few annuli in lateral view. 8. Glossiphonia
complanata. 9. Erpobdella testacea. 10. Therornyzon tessulatum.
The vertical line beside each leech represents its actual length.

From a water-colour painting made by Dr. E. V. Watson. Reproduced from
Scientific Publication No. 14 of the Freshwater Biological Association, by kind

permission of the Council.

APPENDIX A

THE SYSTEMATICS OF FRESHWATER
AND TERRESTRIAL LEECHES

By K. H. Mann

To give a full and accurate account of the leeches of the world as
far as they are known is beyond the scope of this book, even if it
were not an impossible task on account of the number of genera
and species that have been named without providing an adequate
description. To assess the validity of these names and the proper
relationships of the leeches which bear them would require many
years of work in many parts of the world.

This appendix and the one following are attempts to present a
summary of the present position as far as it can be gleaned from
the literature without study of the original specimens. Nearly
three quarters of the world's genera are found in fresh water or
terrestrial habitats and these form the subject of Appendix A. The
genera are reviewed, with indications of their geographical distri-
bution, and a key is given for the identification to species of the
freshwater leeches of Central Europe, Britain and North America.

The marine genera have been treated separately by Professor
E. W. Knight-Jones in Appendix B. He has given a key to the genera
of the world and followed this with an account of the main characters
of each genus and of the species occurring in the North Atlantic.

Synopsis of the Hirudinea

Order Hirudinea

Suborder Acanthobdellae
Family Acanthobdellidae

one Genus Acanthohdella Grube 1850

A parasite of salmonid fishes of Lake Baikal and other parts of
Russia and Finland.

147

148 LEECHES

Suborder Rhynchobdellae

Family Glossiphoniidae Vaillant 1890

Autrum (1939) divided the family into the subfamilies Glossi-
phoniinae in which the mouth is within the cup of the anterior
sucker and the Haementeriinae in which the mouth is a small pore
on the rim of the anterior sucker. Since 1939 several genera have
been set up with insufficient description for a decision to be made
as to which subfamily should hold them. Caballero (1956) and
Moore (1959) amended the scheme in various ways and the
arrangement given below is an attempt to incorporate the valid
points of each scheme.

Subfamily Glossiphoniinae Autrum 1939
Genera: Glossiphonia Johnson 1816, a world-wide freshwater
genus comprising mainly mollusc feeders which roll into a ball
when handled; Batracohdella Viguier 1879, resembling Glossi-
phonia in appearance and habits but differing in internal anatomy ;
world-wide distribution; Helohdella Blanchard 1876, also world-
wide with many species; small, attacking mainly freshwater
invertebrates; Theromyzon Filippi 1867, a parasite of buccal and
nasal cavities of water fowl ; cosmopolitan ; Hemiclepsis Vedjowsky
1883, sometimes grouped with Theromyzon; sucks blood of fish
and amphibians; Europe and Asia; Aticyrobdella Oka 1917, Japan;
Oligoclepsis Oka 1935, Japan; Marsupiohdella Goddard and Malan
1912, parasite of African freshwater crabs; has an internal brood
pouch opening ventrally.

Subfamily Haementeriinae Autrum 1939
Genera: Haementeria PhiHppi 1849, many S. American species,
including H. officinalis the medicinal leech of Mexico ; Placobdella
Blanchard 1893, of S. Europe, America, Asia and Africa; some-
times made a subgenus of Haementeria; includes parasites of man,
other mammals and reptiles; Paraclepsis Harding 1924, India, and
Parahdella Autrum 1936, India and Ceylon, Africa and N. America
are often also united under Haementeria or Placobdella; Oculobdella
Autrum 1936, N. and S. America; Anoculobdella Weber 1915,
S. America; Granelia Harant and Vernieres 1935, Central Africa;
Desmobdella Oka 1930, S. America; Oligobdella Moore, 1918,
N. and S. America, Japan, Korea and New Zealand; attacks

APPENDIX A 149

Amphibia; Torix R. Blanchard 1893, of China should perhaps be
united with Oligohdella; Actinohdella Moore 1901, of N. America,
sucks blood of vertebrates.

Genera of Uncertain Subfamily

Archaeohdella Grimm 1876 Dartevellida Sciacchitano 1939

Dermohdella Philippi 1867 Dundjibdella Sciacchitano 1939

Lobina Moquin-Tandon 1846 Matadibdella Sciacchitano 1939

Semilageneta Goddard 1908 Trigonobdella Sciacchitano 1939.

Family Piscicolidae Johnston 1865
(= Ichthyobdellidae Apathy 1888)

The majority of the members of this family are marine leeches
but a few are found in fresh water. The marine forms are reviewed
separately in Appendix B.

Freshwater genera: Piscicola Blainville 1818, a fish parasite, in all
parts of the world except Australasia and Polynesia ; Cystobranchus
Diesing 1859, also a fish parasite, S. Europe, Asia, N. America,
Mexico; Ozobranchiis Quatrefages 1832, attacks tortoises, croco-
diles and pelicans of Africa, S. America, Asia; Phyllobdella Moore,
1939, Africa, on Barbus; Illinobdella Meyer 1940, fish parasite
of Alaska; Piscicolaria Whitman 1889, N. America.

Suborder Gnathobdellae
Family Hirudidae

In this family are many important blood-sucking parasites of man
and domestic animals:

Hirudo Linnaeus 1758, Europe, Asia, Africa, introduced into
N. America; used in medicine; Limnatis Moquin-Tandon 1827,
enters the nostrils of horses and men when drinking, S. Europe,
Africa, Asia.; Poecilobdella Blanchard 1S9?> (=HirudinariaWhitma.n
1886 preoccupied) cattle leech of India and S.E. Asia; Dinobdella
Moore 1927, enters the air passages of mammals, may remain for
very long periods; India, Burma, Ceylon; Hirudobdella Goddard
1910, Australasia; Macrobdella Verrill 1872, important mammalian
parasite of N. America; Oxyptychus Grube 1850 occupies the same
niche in S. America; Aetheobdella Moore 1935, New South Wales;
Limnobdella Blanchard 1893, Australia and New Zealand.

150 LEECHES

There is a tendency in some genera for the jaws to be reduced
and the leech to become macrophagous :

Haemopis Savigny 1820, widespread in the N. Hemisphere;
Philohdella Verrill 1874, N. America; Myxohdella Oka 1917, India,
China, Africa; Whitmania Blanchard 1887, India, China, Japan;
Americohdella Caballero 1956 { = Cardea Blanchard 1917 pre-
occupied) is an aberrant burrowing form from S. America, placed
by some authorities in a separate family.

Other genera include: Democedes Kinberg 1866; Hararhdella
Sciacchitano 1941; Hexahdella Verril 1872; Hylacohdella
Sciacchitano 1935 ; Monghwaluhdella Sciacchitano 1939 ; Paraobdella
Blanchard 1896; Pintohdella Caballero 1937; Praobdella Blanchard
1896; Typhlohdella Diesing 1850.

Family Haemadipsidae Blanchard 1893

In this family we have the sanguivorous land leeches found most
abundantly in S.E. Asia and Indonesia.

Genera: Haemadipsa Tennent 1861; S.E. Asia from India to
China, Japan, Philippines, Borneo, New Guinea, Madagascar,
Seychelles; Mesohdella Blanchard 1893, Chili; Nesophilaemon
NybeHn 1943, Juan Fernandez; Phytobdella Blanchard 1894,
Philippines, New Guinea, Malaya; Planohdella Blanchard 1894,
Borneo, Celebes; Tritetrabdella Moore, 1938, Malaya.

The following genera are distinguished by the loss of the median
dorsal jaw: Philaemon Blanchard 1897, Madagascar, Australia,
Samoa, S. America, Juan Fernandez; Chtonobdella Grube 1866,
Australia and New Guinea; Idiobdella Harding 1913, Seychelles.

Xerobdella Frauenfeld 1868 from Yugoslavia and Diestecostoma
Vaillant 1890 from Mexico and Guatemala are land leeches of
aberrant form. Ringuelet (1954) separated them into a new
family Xerobdellidae.

Family Semiscolecidae Scriban and Autrum 1934
Central and South American amphibious leeches, related to the
Hirudidae, in which the jaws are reduced to a single median dorsal
rudiment, the crop has only rudimentary caeca and there is
usually more than one pair of testes per segment.
Genera: Semiscolex Kinberg 1866; Semiscolecides Augener 1930;
Orchibdella Ringuelet 1945; Potamobdella Caballero 1931.

APPENDIX A 151

Suborder Pharyngobdellae
Family Erpobdellidae
These are the leeches with the most extreme modifications for a
predaceous life. Some are aquatic, devouring freshwater inverte-
brates, while others take up a burrowing existence at the edges of
lakes or streams, or occasionally become fully terrestrial, devouring
earthworms.

Genera: Erpobdella Blainville 1818, widespread in the northern
hemisphere; Dina E. Blanchard 1892, with a similar distribution,
is sometimes regarded as a subgenus of Erpobdella; Trocheta
Dutrochet 1817, Europe and Asia; Salifa Blanchard 1897, Africa,
Asia; Barhronia Johansson 1918, Africa, India, Malaya, Indo-
nesia; Odontobdella Oka 1923, China, Japan, Formosa; Orobdella
Oka 1895, Japan; Mimobdella Blanchard 1897, Sumatra, Borneo;
Dineta Goddard 1909, Australia; Ornithobdella Benham 1909,
New Zealand; Nephelopsis Verrill 1872, N. America. There is a
group of S. American genera: Bibula Blanchard 1917; Cylicobdella
Grube 1871; Hypsobdella Weber 1913; Lumbricobdella Kennel
1886.

Family Trematobdellidae Johansson 1913
Leeches closely resembling the Erpobdellidae but having a pore
from the gut to the body wall (on segment XIII), either mid-
dorsally or mid-ventrally.

Genera: Trematobdella Johansson 1913, Africa; Acrabdella
Harding 1931, Sumatra; Foraminobdella Kaburaki 1921, India;
Gastrostomobdella Moore 1929, Malaya, Sarawak, Borneo, Hawaii.

The Collection^ Preservation and Identification of Leeches

Most leeches avoid light and should be looked for under stones
or in the crevices of aquatic plants. Blood sucking ectoparasites
are sometimes collected with their hosts, but most freshwater
species drop off after taking a meal.

The identification of leeches is rendered difficult or even im-
possible by unsuitable preservation. If dropped alive into
preservatives such as 70% alcohol or 4% formaldehyde they
contract strongly and such features as the eyes and the genital
pores are difficult to discern. They should therefore be narcotized

152 LEECHES

in weak alcohol, chloroform, chloretone, magnesium sulphate or
soda water. Excessive relaxation leads to the annuli being difficult
to make out and practice is needed before the right degree of
narcotization is achieved. The method favoured by the author is
to add 70% alcohol to the water containing living leeches, gradu-
ally increasing the concentration over a period of about 30 min
until movement ceases. The leeches are then removed, passed
rapidly between the fingers to straighten them and remove excess
mucus, and then laid out and kept flat while the fixative is poured
on. Alcohol or formaldehyde is suitable for simple morphological
work, but Bouin's or Flemming's fixative should be used for
histological studies.

The characters which are fundamental in leech identification
are the annulation, the number and arrangement of eyes and the
positions of the male and female genital pores. To determine the
number of annuli per segment look for segmentally repeated
features such as colour pattern and sensillae (see Chapter 2). To
see the eyes, flatten the head of a narcotized leech between two
glass slides. If the leech has been fixed and the eyes are hidden
by pigment, decolorize the head by immersion in 5% caustic
potash. The genital pores are in the mid- ventral line about one-
third of the distance from anterior to posterior suckers. The male
pore is normally anterior and the more prominent. The female
pore is often small and difficult to see. It is seen most easily
immediately after narcotization, its position often being revealed
by some colour diflFerence which is lost during fixation.

A Key to the Freshwater Leeches of Central Europe,
THE British Isles, and North America north of the

Rio Grande

The species to which this key refers are those included in the
following works:

AuTRUM, H. 1958. Die Tierwelt Mitteleuropas. I, 7b. Hirudinea.
Mann, K. H. 1954. A key to the British Freshwater Leeches, with

Notes on their Ecology. Freshwater Biological Association

Scientific Publication 14.

APPENDIX A

153

Moore, J. P. 1959. Hirudinea in Freshwater Biology (2nd ed.)

Edited by W. T. Edmondson.
Meyer, M. C. and Moore, J. P. 1954. Notes on Canadian Leeches

(Hirudinea) with the Description of a New Species. Wassman.

J. Biol 12, 63-96.
References to full descriptions will be found in these.

As the various geographical areas have many species in common
a combined key to the freshwater species has been produced.

Section 1. Key to Families

1. Mouth a small pore on the oral sucker from which a
proboscis may be protruded; no jaws present; blood
colourless.

Suborder Rhynchobdellae

— Mouth large, occupying entire cavity of the oral
sucker ; no proboscis ; blood red

Fig. 1

Fig. 2

Fig. 3

Fig. 4

Fig. 5

Fig. 1-3 and 5. Dorsal views of the heads of various leeches
to illustrate the arrangement of the eyes: 1, a gnathobdellid ;
2, a pharyngobdellid ; 3, Xerobdella; 5, Theromyzon.

Fig. 4. Ventral view of the head of Placobdella to show mouth
on rim of anterior sucker.

154 LEECHES

2. Eyes, 5 pairs forming lateral crescents as in Fig. 1 ;
5 annuli per segment in the mid body region ; pharynx
short, less than quarter-length of body ; mouth armed
with toothed jaws; testes in large sacs arranged
segmentally in pairs.

Suborder Gnathobdellae 4

— Eyes, 3 or 4 pairs arranged in two transverse rows as in
Fig. 2; 5 annuli per segment or number increased by
sub-division of annuli; pharynx long, about one-
third length of body ; mouth with muscular ridges but
no jaws; testes in small, numerous bunched sacs.

Suborder Pharyngobdellae

Family Erpobdellidae 53

3. Body at rest depressed, not divided into distinct
anterior and posterior regions; head usually much
narrower than the body with anterior sucker not, or
only slightly distinct from the body; usually 3 annuli
per segment in the mid body region; eyes confined to
the head except in Placohdella hollensis.

Family Glossiphoniidae 5

— Body at rest cylindrical and (especially when con-
tracted) usually divided at segment XIII into distinct
anterior and posterior regions; head sucker usually
distinctly marked off from the body; usually more
than 3 annuli per segment ; simple eyes may be present
on head, neck and posterior sucker.

Family FiscicoLiDAE ( = Ichthyobdellidae) .. 31

4. Eyes, 5 pairs, the third and fourth separated by

1 annulus (Fig. 1).

Family Hirudidae . . 40

— Eyes, 4 pairs, the third and fourth separated by

2 annuli (Fig. 3).

Family Haemadipsidae 52

Section 2. Key to the Family Glossiphoniidae
5. Mouth within the anterior sucker cavity, on segments

APPENDIX A 155

II-IV; body only moderately flattened; salivary glands
diffuse ; no oesophageal pouches 6

— Mouth on anterior rim of sucker (Fig. 4) body often
excessively flattened ; salivary glands usually compact;
oesophageal pouches often present 20

6. Eyes, 4 pairs arranged as in Fig. 5 ; body (except when
distended with eggs) soft and translucent; small,
hungry leeches strap shaped with dilated head, but
mature recently fed leeches almost globular.

Theromyzon Philippi 1884 7

— Eyes fewer than 4 pairs; body usually opaque and firm 10

7. Gonopores separated by 2 annuli 8

— Gonopores separated by more than 2 annuli . . . . 9

8. From Central Europe.

Theromyzon maculosum (Rathke 1862).

— From North America.

Theromyzon m^jym (Livanow 1902).

9. Gonopores separated by 3 annuli.

Theromyzon rude (Baird 1863).

— Gonopores separated by 4 annuli.

Theromyzon tessulatum (O. F. Miiller 1774).

10. Head and anterior sucker when at rest rather broader
than the body segments just behind them (Fig. 6);
eyes, 2 pairs on annuli 3-5 ; colour green or pale yellow
with 7 longitudinal rows of lemon yellow spots; size
at rest about 17 X 5 mm.

Hemiclepsis marginata (O. F. Muller 1774)

— Head and anterior sucker not wider than the body
segments just behind (Fig. 7); eyes not arranged as

in Fig. 6 ^ 11

11. Eyes, 1 pair, simple, well separated ; small leeches at rest
about 10 mm long. Helohdella E. Blanchard 12

— Eyes more than 1 pair, or if 1 pair these are lobed
showing that they have been formed by the fusion of
several eyes (Fig. 8) 15

156

LEECHES

Fig. 8

Fig. 6-8. Dorsal views of the heads of various leeches to

illustrate eye arrangement: 6, HemiclepsiSy 7, Helohdella

showing chitinous scute; 8(a)-(d) variations in the eyes of

Glossiphonia complanata.

12. A horny scute present dorsally about one-sixth of the
distance from the anterior to the posterior sucker.

H. stagnalis (L.)

— No dorsal scute present 13

13. Body cylindrical, very slender, translucent, colourless;
only one pair of crop caeca. H. elongata (Castle 1899)

— Body moderately flattened, wider posteriorly ; normally
6 pairs of crop caeca but some may collapse when
empty 14

14. Tubercles absent or limited to mid-dorsal line of
posterior segments; colour coffee brown with 6 or 7
white spots on every third annulus.

H. fusca (Castle 1900)

— Tubercles absent or nearly so; with prominent longi-
tudinal brown stripes and transverse rows of white
spots. H. punctata-lineata Moore 1939.

— Tubercles small, smooth and conical, deeply pigmented
and often double ; many fine longitudinal light and dark
lines, no large white spots. H. lineata (Verrill, 1874)

[G. fusca (Castle) part]

APPENDIX A 157

— Tubercles prominent, numerous (5-9 longitudinal
rows), smooth, conical, black or dark brown; general
colour dark yellowish brown. H. papillata Moore 1 906

[G. fusca (Castle) part]

15. Body of firm consistency; crop with 6 pairs of lateral
diverticula (the anterior ones may collapse when
empty); eyes normally 3 pairs but some fusion may
take place. Glossiphonia Johnson 1816 16

— Body of soft consistency; crop with 7 pairs of lateral
diverticula; eyes, 3, 2 or 1 pairs.

Batracohdella Viguier 1879 17

16. Adults at rest more than 15 mm long; prominent dorsal
tubercles usually present; eyes in 2 longitudinal rows
but variable in number and extent of fusion (Fig. 8) ;
gonopores separated by 2 annuli; 10 pairs of testes;
patterned with brown, yellow or green.

Glossiphonia complanata (L.)

Fig. 9. Head of Glossiphonia heteroclita.

— Adults at rest less than 1 5 mm long ; no dorsal tubercles ;
first pair of eyes closer together than the others (Fig. 9) ;
gonopores united; 6 pairs of testes; colour uniform
amber or whitish with median dorsal brown pigment.

Glossiphonia heteroclita (L.)

17. European species 18

— American species 19

18. Large and distinct tubercles present dorsally (Fig. 10);

isl

^

Fig. 10. Part of the dorsal surface of Batracohdella verrucata

showing tubercles.

158 LEECHES

at the level of the genital pores, but on the dorsal sur-
face, 2 large irregular blotches of colour ; eyes, 3 pairs,
in two close parallel rows, often with the first pair
smaller than the others or almost touching in the mid-
dorsal line; colour, dark green, spotted with yellow,
with 2 longitudinal regularly interrupted dark lines
dorsally; about 25 mm X 10 mm.

Batracohdella verrucata (Fr. MuUer 1884)

— No conspicuous tubercles or dorsal blotches; eyes, 2
pairs, often fused in various ways; colour similar to
above species; smaller, about 10 mm X 4mm.

Batracohdella paludosa (Carena 1824)

19. Eyes, 2 pairs, first pair close together or fused.

Batracohdella paludosa (Carena 1824)

— Eyes, 1 pair, close together or fused; no white bar on
segment VI. Batracohdella picta (Verrill 1872)

— Eyes, 1 pair, usually fused, surrounded by a white area ;
a dense white bar on segment VI.

Batracohdella phaler a Graf 1899

20. Mid-body segments with 3 annuli of which the first and
third may be faintly subdivided; body at rest very
broad and flat; salivary glands compact; epididymis a
tight mass. Placohdella Blanchard 1896 21

— Mid-body segments with 2-6 annuli; body at rest less
broad and flat; salivary glands diffuse; epididymis
loosely coiled 28

21. European species.

Placohdella [= Haementerta] costata (Fr. Miiller 1846)

— American species 22

22. Head distinctly wider than the segments just behind it;
3 prominent dorsal ridges bearing tubercles ; eyes clearly
separated. Placohdella montifera Moore 1912.

— Without widened head and dorsal ridges 23

23. Anus separated from posterior sucker by a slender,
tapering peduncle comprising about 16 annuli -

Placohdella pediculata Heminway 1912

APPENDIX A 159

— Anus close to posterior sucker, no peduncle 25

25. Minute simple supplementary eyes near mid-dorsal
line of head; every third annulus deeply pigmented
green and brown ; length 25-40 mm

Placobdella hollensis (Whitman 1872)

— No supplementary eyes; length 50-100 mm; very

flat 26

26. Dorsal tubercles inconspicuous or absent; brown,
green and yellow pigment dorsally, about 12 bluish
stripes ventrally. Placobdella parasitica {S3.y \S24)

— Dorsal tubercles prominent 27

27. With large, rough dorsal tubercles and many smaller
ones; body translucent; colouring a fine mixture.

Placobdella ornata (Verrill 1872)
[=P. rugosa (Verrill)]

— With smaller, more uniform tubercles ; colour, mottled
on surface, about 30 dark brown lines beneath and these
remain after preservation.

Placobdella multilineata Moore 1953

— With small but conspicuous tubercles in 5 longitudinal
rows, appearing as whitish spots on coffee brown
stripes; ground colour pale, brownish, with white or
yellow spots. Placobdella papillifera (Verrill 1872)

28. 2 annuli per segment; 7 pairs of crop caeca; 5 pairs of
testis sacs. Oligobdella Moore 1918

Oligobdella biannulata (Moore 1900)

— More than 2 annuli per segment 29

29. Posterior sucker with marginal circle of glands and
retractile papillae. Actinobdella Moore 1901 30

— Posterior sucker without marginal retractile papillae;
3 annuli per segment; gonopores united; 5 or 6 pairs
of crop caeca. Oculobdella Antrum 1936

Oculobdella lucida Meyer and Moore 1954

30. 3 annuli per segment; about 30 conical papillae on
posterior sucker; dorsal tubercles prominent, in 5
longitudinal rows.

Actinobdella triannulata Moore 1924.

160 LEECHES

— 6 equal annuli per segment; about 60 sucker papillae;
dorsal tubercles in 5 longitudinal rows.

Actinohdella annectens Moore 1906

— 6 unequal annuli per segment ; about 30 sucker papillae ;
tubercles confined to mid-dorsal row.

Actinobdella inequiannulata Moore 1901

Section 3. Key to the Family Piscicolidae
31. Pulsatile vesicles on margins of body (Fig. 11) . .

32

(a) (b)

Fig. 11. Outlines of (a) Piscicola geometra and (b) Cysto-
branchus fasciatus showing lateral pulsatile vesicles.

— Pulsatile vesicles absent 38

32. Pulsatile vesicles small, difficult to see on preserved
leeches ; 14 annuli per segment; body not clearly divided
into anterior and posterior regions.

Piscicola Blainville 1818 33

— Pulsatile vesicles large, clearly seen after preservation ;
7 annuli per segment ; body clearly divided into anterior
and posterior regions. Cystobranchus Diesing 1859 35

33. OcelU present on posterior sucker 34

— OcelU absent from posterior sucker ; eyes, 2 (or 1) pairs ;
gonopores separated by 3 annuli.

Piscicola punctata (Verrill 1871)

APPENDIX A 161

34. 8-10 crescent-shaped ocelli on posterior sucker; gono-
pores separated by 2 annuli; sperm duct convoluted.

Piscicola salmositica Meyer 1946

— 10-12 punctiform ocelli on posterior sucker; 2 annuli
between gonopores; sperm duct simply looped.

Piscicola milneri (Verrill 1871)

— 12-14 punctiform ocelli on posterior sucker; 3 annuli
between gonopores; sperm duct simply looped.

Piscicola geometra (L.)

35. American species. Cystohranchus verrilli Meyer 1940

— European species 36

36. Eyes absent from anterior and posterior suckers; no
distinct copulatory area.

Cystohranchus mammillatus (Malm 1863)

— 4 eyes on anterior sucker and 10 ocelli on posterior
sucker; a well marked copulatory area (Fig. 12) . . . . 37

Fig. 12. Anterior portion of Cystohranchus fasciatus, ventral
view, to show copulatory area (shaded). After Autrum.

37. Diameter of anterior sucker nearly twice the greatest
width of anterior body region.

Cystohranchus fasciatus (Kollar 1842)

— Diameter of anterior sucker about the same as the
greatest width of the anterior body region.

Cystohranchus respirans (Troschel 1859)

38. 3 annuli per segment; no clear division between
anterior and posterior body regions.

Piscicolaria Whitman 1889
One species, P. reducta Meyer 1940

162

LEECHES

• — 14 annuli per segment; contracted specimens reveal
distinction between anterior and posterior body regions.

Illinobdella Meyer 1940
39. Gonopores separated by 8 annuli (apparently 4 annuli
faintly subdivided) ; distinct seminal vesicle present.

Illinohdella moorei Meyer 1940

— Gonopores separated by 4 annuli (2 faintly subdivided) ;

no seminal vesicle. Illinohdella alba Meyer 1940

39

40.

41.

42.

Section 4. Key to the Family Hirudidae

Jaw^s well developed, with 1 row of sharp teeth ; pharynx
short and very muscular; crop with many large, lobed
caeca 41

Jaws reduced, with 2 rows of blunt teeth; pharynx
longer and less muscular; crop of adults with only the
posterior pair of caeca well developed 45

Copulatory glands present behind gonopores (Fig. 13).

Macrobdella Verrill 1872 43

00

XGz:

(b) ' (c)

Fig. 13. Diagrams of the arrangement of copulatory gland
pores of Macrobdella; (a) M. decora; (b) M. sestertia; (c) M.
ditetra. After Moore.

Copulatory glands absent 42

Jaws with salivary gland papillae (Fig. 14); upper Up
with median ventral groove (Fig. 15); diameter of
caudal sucker about same as maximum width of body.

Limnatis Moquin-Tandon

One species L. nilotica Savigny 1822

Jaws lacking salivary gland papillae; upper Hp lacking

median ventral groove ; diameter of caudal sucker about

J maximum width of body.

Hirudo L.

One species H. medicinalis L.

APPENDIX A

163

Fig. 15

Jaw of Limnatis to show salivary papillae.
After Autrum.

Fig. 15. Ventral view of anterior sucker of Limnatis showing
groove on ventral surface of upper lip and jaws protruding
through velar pore. After Autrum.

43. About 21 bright red spots in mid dorsal line 44

— Red spots absent; 2 annuli between genital pores;
8 copulatory gland pores as in Fig. 13c; about 50 teeth
per jaw. Macrohdella ditetra Moore 1953

44. 5 annuli between gonopores; 4 copulatory gland pores
as in Fig. 13a; about 65 teeth per jaw.

Macrobdella decora (Say 1824)

— 2| annuli between gonopores; 24 copulatory gland
pores as in Fig. 13b; about 40 teeth on each jaw.

Macrohdella sestertia Whitman 1884

45. 5 annuli between gonopores; copulatory glands absent;
jaws low and rounded, rarely absent; teeth large, blunt
and in 2 distinct rows. Haemopis Savigny 1820 46

— 3 or 4 annuli between gonopores but in mature leeches
gonopores obscured by numerous gland pores (Fig. 16);
jaws high and narrow ; teeth small and in rows which are
not entirely separated. Philobdella Verrill 1874 51

46. European leech; segment VI with 3 annuli, VII with
4 annuli (Fig. 17a); colour varies from dark grey-green
to pale yellow-green, paler ventrally, with variable
amounts of black flecking; 11-19 pairs of teeth per jaw.

Haemopis sanguisuga (L.)

164

LEECHES

47.

XIIL

Fig. 16. Ventral view of segments XII and XIII of Philobdella
gracilis showing genital pores in glandular area.

American leech 47

Segment VI with 3 annuli, VII with 4 annuli (Fig. 17a) 48
Segment VI with third annulus subdivided making 4
in the segment; VII having first annulus subdivided
making 5 in the segment (Fig. 17b) 49

vm

(a) (b)

Fig. 17. Diagrams illustrating the subdivision of annuli of
segments VI and VII in certain species of Haemopis. The 2
annuli shaded in (a) are subdivided to form 4 annuli in (b).
{a) H. sanguisuga; (b) H. lateralis.

48. Colour variable but usually blotched with black, brown
and yellowish grey; 12-16 pairs of teeth per jaw.

Haemopis marmorata (Say 1824)

— With a median dorsal black stripe; 9-12 pairs of teeth
per jaw. Haemopis kingi Mather 1954

49. Jaws present, bearing 20-25 teeth; dorsal surface
usually with a median black stripe and orange marginal
stripes. Haemopis lateralis (Say 1824)

APPENDIX A 165

— Jaws absent or vestigial ; median dorsal stripe absent . . 50

50. Genital pores in furrows between annuli ; ground colour
of ventral surface lighter than that of dorsal.

Haemopis grandis (Verrill 1874)

— Genital pores in middle of annuli; ground colour of
ventral surface not lighter, usually darker than that of
dorsal. Haemopis plumbea Moore 1912

51. With a dark brown median dorsal stripe, no spots;
about 20 teeth per jaw.

Philohdella floridana Verrill 1874

— With a light yellow median dorsal stripe and dorso-
lateral brown spots ; about 40 teeth per jaw.

Philohdella gracilis Moore 1901

Section 5. Key to the Family Haemadipsidae

Only one genus in the area, Xerohdella v. Frauenfeld
1868 (Fig. 18).

Fig. 18. Dorsal view of the head of Xerohdella annulata.

From Autrum.

52. 3-3 J annuli between gonopores.

Xerohdella lecomtei v. Frauenfeld 1868
— A\ annuli between gonopores.

Xerohdella annulata Autrum 1958

Section 6. Key to the Family Erpobdellidae

53. European leeches (can be identified on external features) 54

— American leeches (require dissection for further

identification) 59

54. All annuli of the body of about the same width . . . . 55

166

LEECHES

55.

56.

57.

In any group 6 consecutive annuli at least 1 is different
from the rest, being either much narrower or wider

and subdivided 56

Genital pores separated by 2-3^ annuli; typical forms
with a broken network of black pigment on the dorsal
surface. Erpobdella octoculata L.

Genital pores separated by 3|-5 annuli; typical forms
lack black pigment dorsally, less common varieties may
have a median dark line or a transparent body revealing
deep lying black pigment.

Erpobdella testacea (Savigny 1820)
A group of 5 consecutive annuli consists of 4 of equal
width and 1 which is wider but divided by a faint trans-
verse furrow (Fig. 19); genital pores separated by 2-3
(or 3 1) annuH. Dina E. Blanchard 1892 57

Fig. 19

Fig. 20

Fig. 19. Ventral view of segment XII of Dina lineata to
show genital pores and annulation.

Fig. 20. Ventral view of segment XII of Trocheta bykowskii
to show genital pores and annulation.

The most common arrangement of annuli is 3 broad
and 5 narrow (Fig. 20) but the narrow annuli may be
associated in pairs forming broad annuli faintly sub-
divided or each broad annulus may be divided to form
2 narrow ones; there are many arrangements, all of
which differ from those found in the other Erpobdellidae.

Trocheta Dutrochet 1817
Eyes present, number and position variable.

Dina lineata (O. F. Muller 1774)

58

APPENDIX A

167

— Eyes absent. Dina ahsoloni (Johansson 1913)

58. Gonopores separated by 4^10 annuli depending on
the degree of subdivision of the annuli.

Trocheta suhviridis Dutrochet 1817

— Gonopores separated by 2-4 annuli.

Trocheta bykowskii Gedroyc 1913

59. Vas deferens with a pre-atrial loop reaching to ganglion

XI (Fig. 21) 61

Fig. 21

Fig. 22

Fig. 21 and 22. Dissection of reproductive systems in region

of genital pores, ventral view; 21, Trocheta; 22, Mooreobdella,

after Moore, g.a., genital atrium; g. XII, twelfth ganglion;

O.S., ovarian sac; p.l. preatrial loop of male duct.

— Vas deferens without preatrial loop (Fig. 22); every
fifth annulus subdivided as in 56 above.

Mooreobdella Pawlowski 1955 60

60. Atrium ellipsoidal, wider than long, with horns shorter
than diameter of median atrium; 3 annuli between
gonopores Mooreobdella microstoma (Moore 1901)

— Atrium globular with prominent horns longer than its
diameter; gonopores separated by 2 annuli and nor-
mally on the rings, not in the furrows; eyes 4 (or 3)
pairs; length 5 cm.

Mooreobdella fervida (Verrill 1874)

— Atrium globular as above; gonopores separated by

2 annuli and lying in the furrows ; eyes, 3 pairs ; length

3 cm. Mooreobdella bucera (Moore 1947)

168

LEECHES

Fig. 23. Dorsal and lateral views of the male genital atrium
of Nephelopsis obscura, after Moore.

61. Atrial cornua spirally coiled, like ram's horn (Fig. 23);

Nephelopsis Verrill 1872
One species Nephelopsis obscura Verrill 1872

— Atrial cornua not spirally coiled 62

62. All annuli of approximately the same width.

Erpohdella puctata (Leidy 1870)

— Every fifth annulus subdivided as in 56 above (occa-
sionally 2 out of every 5 are subdivided) 63

63. Eyes absent. Dina anoculata Moore 1898

— Eyes present 64

64. Eyes, 3 pairs; 2 annuli between gonopores.

Dina lateralis (Verrill 1871)

— Eyes 4 pairs; 3-3 J annuli between gonopores . . . . 65

65. Length about 2 cm; a few dark spots or no pigment.

Dina parva Moore 1912

— Length about 4-5 cm; with a dark median stripe and
blotches. Dina dubia Moore and Meyer 1951

APPENDIX B

THE SYSTEMATICS OF
MARINE LEECHES

By Professor E. W. Knight-Jones
Department of Zoology^ University College of Swansea

The marine leeches constitute the greater part of the family
Piscicolidae. They are even less well known than the freshwater
and terrestrial forms, and it is not unusual to find undescribed
species. The last synopsis was that of Herter (1935) but new
forms have been described since. In this appendix a tentative
key to the marine genera of the world is followed by a list of
genera in alphabetical order, giving their characters and most of
their North Atlantic species.

Marine leeches can seldom be collected to order but are often
found at sea or on dead fish and have to be fixed by whatever
method happens to be available. The technique of study is rather
different from that used with freshwater forms. Internal anatomy
is important and this can be observed by clearing in cedar wood
oil but better by sectioning. The intersegmental testes are a useful
guide to the limits of segments and make it possible to determine
the number of annuli per segment in a cleared specimen. Clearing
also reveals eyes, which may otherwise not be visible after death.
Good sections are obtained after narcotizing with menthol and
fixing in sea water Bouin.

The following terms and abbreviations are used in the key and
descriptions :

abdomen, body behind clitellum, often flattened dorso-ventrally ;
annuli, number of annuli per mid-body segment, the convention
3 (6) meaning that each of three annuli is faintly divided into two ;
coelom, refers to the coelom of the mid-body (testicular) region;
coelom typical, as in Piscicola, with dorsal, ventral, lateral and

169

170 LEECHES

transverse lacunae linked to a row of pulsatile vesicles on each side
(Fig. 27, p. 53); diverticula^ the elongated posterior pair of crop
diverticula which may be more or less fused together; eyes, eyes
on head; ganglia, number of ganglia in the ventral chain, not
including the suboesophageal and caudal masses; ocelli, simple
eyes on posterior sucker; pulsatile vesicles, externally visible
respiratory vesicles like those found in Piscicola (Fig. 17, p. 28);
trachelosome, anterior part of body including clitellum.

Key to the Genera of the World

1. Body with many conspicuous branchiae or tubercles . . 2

— Body smooth or with a single fin or row of vesicles on
each side 6

2. Body with lateral branchiae 3

— Body with numerous tubercles 4

3. Branchiae finger-shaped and branching

Ozobranchus (Fig. 19, p. 31)

— Branchiae leaf-shaped and unbranched

Branchellion (Fig. 18, p. 30)

4. One annulus of each somite bears large tubercles, most
of the other annuli bear small tubercles; 4-6 very dis-
tinct annuli per somite 5

— All tubercles small and arranged longitudinally in 6
rows dorsally and in 6 rows or absent ventrally; 12-14
annuli per somite Oxytonostoma

5. Body rounded with regions ill-defined

Pontohdella (Fig. 19, p. 31)

— Body sharply divided into slender trachelosome and
broad flattened abdomen Pontohdellina

6. Body with a flattened, fin-like expansion extending
along each side 7

— Body without lateral fins 8

7. Fins confined to anterior 2/3 of body ; genital ducts with

a common opening Pterohdella (Fig. 19, p. 31)

— Fins extending whole length of body; separate genital
openings Pterobdellina

APPENDIX B 171

8. Eyes 9 pairs; oral sucker bears small papillae; from
Southern Ocean 9

— Eyes 0-3 pairs; oral sucker generally without papillae 10

9. Body with narrow trachelosome and broad flattened
abdomen Trulliohdella

— Body not clearly divided into regions . . . . Cryohdellina

10. Mouth at about the centre of oral sucker 11

— Mouth in anterior border of oral sucker 30

11. Posterior sucker small, little or no wider than the
posterior end of the body 12

— Posterior sucker considerably wider than the posterior
end of the body 15

12. With a row of at least 8 pulsatile vesicles on each side

of abdomen 16

— Pulsatile vesicles absent or no more than three on each
side 13

13. Anterior sucker relatively huge, nearly as wide as the
short flattened abdomen Ganymedehdella

— Both suckers very small 14

14. No eyes Hemibdella

— Eyes 1 pair on about tenth annulus; suckers almost
covered by annuli Myzohdelld

15. With a row of pulsatile vesicles on each side 16

— Pulsatile vesicles absent or indistinguishable . . . . 18

16. With about 8 pulsatile vesicles on each side . . Cyrillohdella

— With 11-13 pulsatile vesicles on each side 17

17. Abdomen broad, somewhat flattened and very distinct
from narrow trachelosome; suckers rather small,
narrower than abdomen Trachelohdella

— Abdomen more or less rounded and not very dis-
tinct from trachelosome; posterior sucker wider than
body Calliobdella*

♦The New Zealand genus Makarahdella, Richardson 1959 (Trans, roy.
Soc. N.Z. 87,283) resembles Calliobdella in having 3 (6) annuli per somite
but differs in that the bursa lacks an accessory muscular organ. Possession
of 7 (14) annuli per somite in a leech of this kind would indicate a marine
species of Piscicola or Cystobranchus.

172 LEECHES

18. Annuli 12-14 per mid-body somite 19

— Annuli 2-6 per mid-body somite 23

19. Eyes absent 20

— Eyes 2 or 3 pairs 22

20. Median spermatheca lying between ovaries; from
California Marsipohdella

— Spermatheca absent 21

21. Posterior crop diverticula absent; from New Zealand

Bdellamaris

— Posterior crop diverticula fused, with 5 fenestra;
coelomic system typical, but pulsatile vesicles are
hidden in skin Johanssonia

22. Annuli 12 per somite; testes 5 pairs . . Crangonohdella

— Annuli 14 per somite; testes 6 pairs . . Carcinobdella

23. Annuli 2 per mid-body somite; with 2 pairs eyes, each
made up of several black pigment spots . . Janusion

— Annuli 3 (6) per mid-body somite ; if eyes are present,
each is a simple, rounded or crescent-shaped spot of
pigment 24

24. Posterior sucker somewhat compressed laterally, typic-
ally folded round a fin-ray but also capable of adhering

to flat surfaces Sanguinothus

— Posterior sucker more or less circular in outline . . . . 25

25. Coelom fairly spacious, not divided into lacunae

Arctobdella

— Coelom restricted to narrow lacunae 26

26. Dorsal and ventral lacunae both communicating seg-
mentally with a contractile lateral lacuna lying in the
dermis on each side Austrohdella

— Ventral lacuna lacking segmental communications with
other lacunae 27

27. Dorsal lacuna communicating segmentally with lateral
lacunae 28

— Dorsal lacuna lacking segmental communications with
other lacunae 29

APPENDIX B 173

28. Abdomen rounded and not very distinct from trachelo-
some ; skin opaque Ottoniohdella

— Abdomen broad, flattened and distinct from trachelo-
some ; skin transparent Oceanohdella

29. Testes 4 pairs; posterior sucker tends to face postero-
dorsally Cryohdella

— Testes 5 pairs ; posterior sucker faces postero-ventrally

Platyhdella

30. Annuli 14 per somite Carcinohdella

— Annuli 16 per somite Notostomohdella

Genera of Marine Leeches
WITH Some of the Species from the North Atlantic
AND Neighbouring Seas

Particularly distinctive characters are given in italics. The
treatment is not exhaustive and only a selection of references is
cited. Species reliably recorded from Britain are marked by
asterisks.

ARCTOBDELLA de Silva and Kabata 1961. Oral sucker
small, eyes 0, posterior sucker discoid, abdomen flattened and
smooth, annuli 3(6) but obscure, coelom fairly spacious and not
divided into lacunae, diverticula separate, ganglia 18+1 fused
anteriorly, testes 4 pairs.

Arctohdella hranchiarum de Silva and Kabata. 10 mm long.
Gills of Drepanopsetta platessoides. Iceland.

AUSTROBDELLA Badham 1916 (Ingram, 1957). Suckers
discoid, eyes 0-1 pair, abdomen flattened, smooth and forming
"shoulders" behind clitellum v^hich is not more constricted than
rest of trachelosome, annuli 3 (6), a contractile lacuna in dermis
throughout length of abdomen on each side and w^ithout separate
pulsatile vesicles or subdermal lateral lacunae but coelom other-
wise fairly typical, ganglia 21, testes 5 pairs. Two spp. from
Australia and Tasmania.

Austrobdella anoculata Moore (1940). 5 mm long. Greenland.

174 LEECHES

BDELLAMARIS Richardson 1953. Like Calliohdella or
Trachelohdella except annuli 12, diverticula absent. One sp. from
New Zealand.

BRANCHELLION Savigny 1822 (Harding, 1910; Sukatschoff,
1912; Ingram, 1957). Suckers large, eyes 0-3 pairs, posterior
sucker containing many minute subsidiary suckers, constricted
clitellum partly covered by preputial fold of abdomen, abdomen
flattened with 31-33 pairs of lateral foliaceous branchiae (3 per
somite), annuli 3 (6), pulsatile vesicles 11 pairs, coelom typical,
diverticula fused, testes 5-6 pairs. At least 6 spp. mostly on
elasmobranchs.

*Branchellion borealis Leigh- Sharpe (1933). 30 mm long,
31 pairs branchiae, no eyes, 4 tubercles dorsally on each of 4
anterior somites of trachelosome. Dorsally on Raja clavata.
English Channel.

Branchellion ravenelii (Girard) (Meyer, 1941). 15 mm long,
31 pairs branchiae, 1 pair branching eye-spots. Ventrally on
Dasyatis hastatus, Amphotistius sabinus, Aetobatus freminvillii.
Florida and Carolina.

Branchellion torpedinis Savigny. 50 mm long, 33 pairs branchiae.
On Rhinobatis thouin, Raja clavata^ Torpedo, Trygon pastinaca,
Labrus, Rhombus maximus. Mediterranean, North Sea, Ireland,
Senegal.

CALLIOBDELLA Beneden and Hesse 1863 (Johansson, 1896;
Oka, 1910; Selensky, 1915; Leigh-Sharpe, 1914 and 1916).
Suckers discoid, eyes 0-2 pairs, posterior sucker broader than body,
abdomen more or less rounded, annuli 3 (6), pulsatile vesicles 11-13
pairs, coelom typical, diverticula more or less fused, testes 6 pairs,
rounded muscular organ connected with bursa. Several spp.

*Calliobdella lophii Beneden and Hesse. 50 mm long, eyes 0,
posterior sucker 3^ X breadth of oral sucker, abdomen some-
what flattened and trachelosome well defined. On Lophius pisca-
torius. W. Europe.

*Calliobdella nodulifera (Malm). 30 mm long, eyes 0, posterior
sucker 2 X breadth of oral sucker, abdomen rounded and
trachelosome ill defined. Externally on a variety of fish, especially
gadoids. W. Europe, Faroes, Iceland.

Calliobdella punctata Beneden and Hesse. 20 mm long, eyes

APPENDIX B 175

2 pairs. On Cottus huhalis and Blennius pholis. Common at Roscoff
(Brumpt, 1900).

CARCINOBDELLA Oka 1910 (1927; 1933). Suckers discoid
(type species has mouth situated as in Notostomohdella and
clitellum swollen), eyes 0-3 pairs, abdomen rounded, annuli 14,
diverticula fused, testes 6 pairs. Three spp. off Japan.

CRANGONOBDELLA Selensky 1914; 1915 (Borovitzkaia,
1949). Resembling Platyhdella but with annuli 12 and copulatory
zone with vector tissue. Several spp. from Russian seas.

Crangonohdella murmanica Selensky. 20 mm long, eyes 3 pairs.
On Sclerocrangon horeas. White Sea, E. Greenland.

CRYOBDELLA Harding 1922 (Brinkmann, 1948). Like
Platyhdella (Moore, 1938) except posterior sucker has finely
serrated margin and is often bent dorsally, testes 4 pairs. One
sp. from Antarctic.

CRYOBDELLINA Brinkmann 1948. Like Platyhdella but
eyes 9 pairs, ganglia 18, testes 4 pairs. One sp. from Antarctic.

C YMA TOBRANCHUS. The promised description (Selensky,
1931) appears to have been forestalled by the author's death.
The species referred to seems never to have been adequately
described.

CYRILLOBDELLA Leigh-Sharpe 1933. Like Trachelohdella
but 8 pairs of pulsatile vesicles. Single specimen incompletely
described.

Cyrillohdella alcihiades Leigh-Sharpe. 8 mm long. From Sargus
annularis. Mediterranean.

GANYMEDEBDELLA Leigh-Sharpe 1915. Anterior sucker
huge, eyes 0, posterior sucker small, abdomen flattened and very
broad, annuli 1, pulsatile vesicles 3 pairs, diverticula separate,
testes 6 pairs.

*Ganymedehdella cratere Leigh-Sharpe. 8 mm long. From
cloacal papilla of Callionymus. North of Scotland.

HEMIBDELLA Selensky 1931. Suckers small, eyes 0, abdomen
rounded, annuli 12, coelom typical but without vesicles, diverticula
fused, testes 5 pairs, copulatory zone.

176 LEECHES

^Hemihdella soleae (Beneden and Hesse). 5-10 mm long.
Attached to scales on pigmented side of Solea vulgaris, Solea impar
and Solea monochir. W. Europe, Greenland and Mediterranean.

ICHTHYOBDELLA BlainviUe 1827. Not a defined genus
today but one to which several smooth-skinned leeches without
pulsatile vesicles have been referred provisionally (Oka, 1910,
1931; Ingram, 1957).

JANUSION Leigh-Sharpe 1933. Suckers cup-shaped, eyes
2 pairs consisting of clusters of black spots, abdomen flattened,
clitellum narrow, annuli 2, imperfectly described.

^Janusion scorpii (Malm). 15 mm long. On Cottus scorpius.
Plymouth, U.K.

JOHANSSONIA Selensky 1914. Suckers discoid, eyes 0,
abdomen rounded and ill defined, annuli 14 (16), coelom typical
but pulsatile vesicles small, embedded in skin and indistinguishable
after death except by sectioning, diverticula fused with 5 fenestrae,
testes 5-6 pairs.

Johanssonia kolaensis Selensky. 20 mm long, posterior sucker
broader than abdomen. On Anarrhichas lupus. Arctic seas.

Johanssonia pantopodum Selensky, 1914. 20 mm long, posterior
sucker not as broad as abdomen. On Nymphon stromii. Arctic
and perhaps W. Europe.

MARSIPOBDELLA Moore 1952. Suckers discoid, eyes 0,
trachelosome somewhat constricted, annuli 12-14, diverticula
fused with 5 fenestrae, testes 5 pairs, median spermatheca lying
between ovaries. One sp. California.

MYSIDOBDELLA Selensky 1927. Eyes 0, annuli 13, coelom
as in Hemibdella, diverticula fused with 5 fenestrae, copulatory
area poorly defined with no conducting tissue.

Mysidobdella oculata Selensky. Uniform olive green. On
Mysis oculata. White Sea.

MYZOBDELLA Leidy 1851 (Moore, 1946). Like Hemibdella
but eyes 1 pair, coelom reduced to ventral lacuna, testes 4-5 pairs.
At least one fresh water species (Meyer and Moore, 1954).

Myzobdella lugubris Leidy. On the crab Callinectes sapidus in
brackish coastal waters. New Jersey to North Carolina.

APPENDIX B 177

NOTOBDELLA Benham 1909. Suckers discoid, eyes 1 pair,
abdomen rounded but distinct from trachelosome. One im-
perfectly described sp. from Antarctic.

NOTOSTOMOBDELLA Moore and Meyer 1951
(=Notostomum Johansson 1898). Suckers equally large and cup-
shaped, mouth in anterior edge of oral sucker, eyes 0, abdomen
rounded and ill-defined, annuli 14-16, coelom reduced to dorsal
and ventral lacunae, diverticula fused with 5 fenestrae, testes
6 pairs.

Notostomobdella laeve (Levinsen, 1882). 100-150 mm long.
On Hippoglossus pingvis, Somniosus microcephalus and Platyso-
matichtys hippoglossoides. Greenland.

OCEANOBDELLA Caballero 1956 {=Abranchus Johansson,
1929). Anterior sucker very small, eyes 3 pairs, posterior sucker
discoid and usually with ring of ocelli, skin transparent, clitellum
constricted, abdomen flattened, annuli 3 (6), coelom somewhat
reduced so that segmental transverse communications link lateral
and dorsal lacunae only, diverticula separate or partially fused,
testes 4-6 pairs.

^Oceanobdella microstoma (Johansson, 1896). 25 mm long,
unpigmented, ventrally on Cottus scorpius. W. Europe, Iceland,
Greenland, Spitzbergen.

*Oceanobdella blennii (Knight-Jones, 1940). 12 mm long, trans-
versely banded with brown and capable of extreme abdominal
flattening, posterior sucker less broad than abdomen and with
few or no ocelli, attached behind pectoral fin of Blennius pholis.
Anglesey and Swansea, U.K.

Oceanobdella sexoculata (Malm, 1863). 11 mm long, banded
with brown, posterior sucker somewhat broader than abdomen
and with complete ring of ocelli round margin. On Zoarces
viviparus, Gadus callarias, Cyclopterus lumpus. W. Sweden.

OPHIBDELLA Beneden and Hesse 1863. Young of Pontob-
della (Apathy, 1888)?

OSTREOBDELLA Oka 1927. Suckers discoid and equally
large, eyes 1 pair, abdomen rounded and ill-defined, annuli 14,
internal anatomy undescribed. One sp. Japan.

178 LEECHES

OTTONIOBDELLA Moore andMeyer 1951 (= OttoniaM2\m)
(Johansson, 1929). Like Oceanohdella except anterior sucker
discoid, skin opaque and pigmented, abdomen rounded and ill
defined.

Ottoniohdella hrunnea (Johansson, 1896). 25 mm long, uniformly
brown, posterior sucker ringed by 10 ocelli and not much broader
than anterior sucker and abdomen. Dorsally on Cottus scorpius.
W. Sweden, Greenland.

Ottoniohdella scorpii (Malm, 1863; Moore andMeyer, 1951).
30 mm long, with longitudinally elongated markings on body,
posterior sucker ringed by 12-14 ocelli and twice as broad as
anterior sucker and abdomen. On Cottus scorpius. Faroes,
Iceland, Greenland, Spitzbergen, Bering Sea.

OXYTONOSTOMA Malm 1863 (Johansson, 1898; Selensky,
1914 and 1915; Moore and Meyer, 1951). Suckers discoid, eyes 0,
numerous small tubercles arranged longitudinally in 6 rows dorsally
and 6 rows or none ventrally, abdomen rounded and ill-defined
with 11 pairs pulsatile vesicles, annuli 12-14, coelom typical,
diverticula fused with 5 fenestrae, testes 6 pairs.

Oxytonostoma arctica Johansson. 25 mm long, tubercles present
ventrally. Greenland, White Sea, Kara Sea, Alaska.

Oxytonostoma typica Malm. 20-30 mm long, tubercles absent
ventrally. On Raia radiata. W. Sweden, Iceland, Greenland,
Alaska.

OZOBRANCHUS de Quatrefages 1832 (Selensky, 1915;
McCallum, 1918; Oka, 1927; Sanjeeva Raj, 1954). Anterior
sucker small, posterior sucker discoid, trachelosome narrow,
abdomen broad with a pair of finger-shaped branching branchiae
on each somite, annuli 2-3, pulsatile vesicles 0, coelom fairly
spacious and not divided into lacunae, diverticula separate,
testes 4 pairs. On chelonians and crocodiles.

Ozobranchus margoi de Quatrefages. On Thalassochelys corticata.
Naples.

PARAPONTOBDELLA Harant (1929). Not clearly distin-
guished from Pontobdella.

APPENDIX B 179

PISCICOLA de Blainville 1818 (Harding, 1910; Meyer,
1940). Like Calliohdella except eyes 2 pairs, annuli 14, bursa
simple.

*Piscicola geometra (L.). 20-50 mm long, with ocelli and
radiating marks on posterior sucker. Brackish as well as fresh
water, e.g. on Coitus scorpius and Pleiironectes flesus in Baltic
(Herter, 1935).

Piscicola zebra Moore (1898). On lips of Petromyzon marinus.
Nova Scotia.

''Piscicola''' rectangulata Levinsen. 20^0 mm long from gills
and body of Gadus in Arctic seas. Has been removed from this
genus (Moore and Meyer, 1951) but not yet assigned to a new one.

PLATYBDELLA Malm 1863 (Johansson, 1898; Leigh-
Sharpe, 1916). Suckers discoid, eyes 0-3 pairs, abdomen rounded
and ill-defined, annuli 3 (6), coelom reduced without pulsatile
vesicles, dorsal, lateral or segmental lacunae, diverticula fused
with 5 fenestrae, testes 5 pairs. Only the first sp. listed below
has been fully described but about 7 others have been placed
tentatively in this inappropriately named genus.

*Platybdella anarrhichae (Diesing). 20-30 mm long, eyes 0.
Gills and body of Anarrhichas lupus and A. minor. W. Sweden,
North Sea, Bergen, Iceland, Greenland.

Platyhdella quadrioculata Malm (1863). Eyes 2, posterior
sucker not much broader than oral sucker. Labrus. W. Sweden,
Greenland.

Platybdella buccalis Nigrelli (1946). Eyes 2, posterior sucker
twice as broad as oral sucker. Within mouth of Macrozoarces
americanus. E. coast U.S.

Platybdella fabricii Malm. Eyes 3, posterior sucker twice as
broad as oral sucker, row of 12 protuberances on each side of
abdomen. Cottus scorpius. Greenland, Spitzbergen.

Platybdella olriki Malm. Eyes 3, posterior sucker not much
broader than oral sucker. Hippoglossus vulgaris, Sclerocrangon,
Hyas.

PODOBDELLA Diesing (1858). Imperfectly described. Like
a Trulliobdella reversed antero-posteriorly.

180 LEECHES

PONTOBDELLA Leach 1815 (Harding, 1910; Hickman,
1941; Ingram, 1957). Suckers cup-shaped, trachelosome ill-
defined, body rounded and studded with numerous large and small
tubercles, annuli very distinct 3, 4 or 5, pulsatile vesicles very
inconspicuous, coelom typical, diverticula fused, testes 6 pairs,
copulatory area with vector tissue. Several spp.

*Pontobdella muricata (L.) 100-200 mm long, anterior sucker
much wider than trachelosome. Various sp. of Raia, Torpedo
and Pleuronectes. W. Europe, Mediterranean, Iceland, Greenland,
Spitzbergen.

Pontobdella vosmaeri Apathy (1888). Anterior sucker not much
wider than trachelosome. Mediterranean and Roscoff.

PONTOBDELLINA Harding and Moore 1927. Like Ponto-
bdella except that body is sharply divided into slender trachelosome
and broad flattened abdomen.

PTEROBDELLA Kaburaki 1921 (Harding and Moore, 1927;
Scriban and Antrum, 1928-34). Oral sucker small and deeply
cupped, eyes 0, posterior sucker large, anterior two-thirds of body
bears on each side a longitudinally running fin which is indented
opposite the clitellum, annuli 14, diverticula absent, testes 5 pairs,
genital openings emerge into a common pore. One sp. from
Trygon in brackish waters of Chilka Lake.

PTEROBDELLINA Bennike and Bruun 1939. Like Ptero-
bdella except oral sucker bears 4-6 papillae on each side, fins run
whole length of body, genital openings are separate.

Pterobdellina jenseni Bennike and Bruun. 20-40 mm long. On
Raia. Off Faeroes at depths of more than 400 m.

SANGUINOTHUS de Silva and Burdon-Jones 1961. Suckers
well developed, eyes 3 pairs, posterior sucker capable of folding
round each side of a fin ray and bearing a ring of ocelli, clitellum
constricted, abdomen flattened, annuli 3 (6), coelom reduced as in
Platybdella, diverticula separate, ganglia 18+1 fused anteriorly,
testes 5 pairs.

^ Sanguinothus pinnarum de Silva and Burdon-Jones. 10 mm
long, uniformly reddish brown. On fins of Cottus bubalis. Anglesey
and Isle of Man, U.K.

APPENDIX B 181

STIBAROBDELLA Leigh-Sharpe 1925 (Harant 1929). Like
Pontobdella, with which this should perhaps be united. One sp.
from Pacific.

TRACHELOBDELLA Diesing 1850 { = Scorpaenobdella Saint-
Loup, 1886; Apathy, 1888; Blanchard, 1894; Oka, 1910 and 1927,
Selensky, 1915; Dogiel and Bychowsky, 1934; Ingram, 1957).
Like Calliobdella except posterior sucker fairly small, deeply
cupped and facing posteriorly, abdomen more flattened and so
more distinct from trachelosome, bursa without muscular organ.
About 12 spp.

Trachelobdella lubrica (Grube). 20-30 mm long, yellow or
olive-green with white spots, abdomen 1 -5 X breadth of posterior
sucker which has radiating markings, trachelosome with 4 pairs
of lateral vesicles which are non-pulsatile. From a variety of
teleosts. Mediterranean and perhaps Atlantic coasts of Europe.

Trachelobdella nigra (Apathy). Black, contracted abdomen
2-3 X breadth of posterior sucker. Naples.

TRULLIOBDELLA Brinkman 1948. Suckers small but strong,
eyes 9 pairs, posterior sucker with ring of ocelli, abdomen flattened
and trachelosome narrow like blade and handle of a paddle, annuli 3
(6), pulsatile vesicles and diverticula absent, testes 5 pairs. One sp.
from South Georgia.

Host List

This can serve only as a preliminary guide. It is divided
regionally to help when leeches are found apart from hosts. The
aim has been no more than to cover the North Atlantic forms, but
a few records from elsewhere have been included. Many of the
invertebrates may serve merely as substrata for cocoons, but some
are truly parasitized (Meyer and Barden 1955).

Arctic Seas

Autrum 1936; Borovitzkaia 1949; Bruun 1938; Johansson 1898;
Levinsen 1882; Malm 1863; Meyer and Barden 1955; Moore
1940; Moore and Meyer 1951; Remy 1928; Selensky 1914, 1915,
1927; de Silva and Kabata 1961; Wesenberg-Lund 1926.

182

LEECHES

Hosts

INVERTEBRATES

Colossendeis sp.
Crangon horealis
Hyas araneus
My sis oculata
Nymphon str'Cmii
Paralithodes camtschaticus
Sclerocrangon boreas
Sclerocrangon boreas

VERTEBRATES

Anarrhichas lupus

Anarrhichas lupus gills

Anarrhichas minor

Cottus scorpius ventrally

Cottus scorpius dorsally

Cottus scorpius

Cottus scorpius

Cottus scorpius

Gadus macrocephalus gills

Gymnacanthus tricuspis

Drepanopsetta platessoides gills

Hippoglossus hippoglossoides

Hippoglossus vulgaris

Hippoglossus pingvis

Ly codes pallidus

Myoxocephalus polyacanthocephalus

Pla tysoma tichtys hippoglossoides

Raia radiata

Somniosus microcephalus

Leeches

Johanssonia pantopodum
Platybdella olriki
Platybdella olriki
Mysidobdella oculata
Johanssonia pantopodum
cocoons of Notostomobdella cyclostoma
Crangonob delta murmanica
Platybdella fabricii

Johanssonia kolaensis
Platybdella anarrhichae
Calliobdella nodulifera
Oceanobdella microstoma
Ottoniobdella brunnea
Ottoniobdella scorpii
Platybdella fabricii
Platybdella olriki
^'Piscicola^' rectangulata
Platybdella affinis
Arctobdella branchiarum
Platybdella hippoglossi
Platybdella olriki
Notostomobdella laeve
Platybdella anarrhichae
''Piscicola^' rectangulata
Notostomobdella laeve
Oxytonostoma typica
Notostomobdella laeve

Temperate North Atlantic

Beneden and Hesse 1863 ; Bennike and Bruun 1939; Brumpt 1900;
Bruun 1938; Herter 1935; Johansson 1898; Knight-Jones 1940;
Leigh-Sharpe 1914, 1915, 1916, 1933; Malm 1863; Meyer 1940,
1941; Moore 1898, 1946; Nigrelli 1946; Scott 1901; de Silva
and Burdon-Jones 1961.

APPENDIX B

183

Hosts

INVERTEBRATES

Callinectes sapidus

VERTEBRATES

Aetobatus freminvillii

Amphotistius sahinus

Anarrhichas lupus gills

Anarrhichas lupus externally

Blennius pholis

Blejinius pholis behind pectoral fin

Callionynius lyra cloaca

Chimaera monstrosa

Cottus hubalis fin rays

Cottus hubalis body

Cottus scorpius

Cottus scorpius

Cottus scorpius

Cottus scorpius (in Baltic)

Cyclopterus liimpus

Dasyatis ha status

Gadus aeglefiniis

Gadus callarias

Gadus callarias

Gadus carbonarius

Gadus merlangus

Gadus virens

Hippoglossus hippoglossoides

Hippoglossus vulgaris

Labrus bergylta

Lophius piscatorius

Macrozoarces americanus mouth

Merluccius merluccius externally

Petromyzon marinus

Platichthys flesus {in Baltic)

Pleuronectes sp.

Raia batis

Raia batis

Leeches

Myzobdella lugubris

Branchellion ravenelii
Branchellion ravenelii
Platybdella anarrhichae
Calliobdella nodtdifera
Calliobdella punctata
Oceanobdella blennii
Ganymedebdella cratere
Calliobdella nodidifera
Sanguinothus pinnarum
Calliobdella punctata
Janusion scorpii
Oceanobdella microstoma
Ottoniobdella brimnea
Piscicola geofnetra
Oceanobdella sexoculata
Branchellion ravenelii
Calliobdella nodulifera
Calliobdella nodulifera
Oceanobdella sexoculata
Calliobdella nodulifera
Calliobdella nodulifera
Calliobdella nodulifera
Platybdella hippoglossi
Calliostoma nodulifera
Platybdella quadrioculata
Calliobdella lophii
Platybdella buccalis
Calliobdella nodulifera
Piscicola zebra
Piscicola geometra
Pontobdella muricata
Calliobdella nodulifera
Pontobdella muricata

184

LEECHES

Raia batis

Rata clavata

Raia clavata

Raia clavata

Raia fullonica

Raia lintea

Raia radiata

Scophthalmus maximus

Squatina squatina

Sebastes norvegicus

Solea solea on scales

Squaliis acanthias

Torpedo torpedo

Torpedo torpedo

Trigla giirnardus

Lepidorhombus whijf-iagonis

Zoarces viviparus

Pterobdellina jenseni
Branchellion borealis
Branchellion torpedinis
Pontobdella miiricata
Calliobdella nodulifera
Pterobdellina jenseni
Oxytonostoma typica
Branchellion torpedinis
Branchellion torpedinis
Calliobdella nodulifera
Hemibdella soleae
Calliobdella nodulifera
Branchellion torpedinis
Pontobdella muricata
Calliostoma nodulifera
Calliobdella nodulifera
Oceanobdella sexoculata

Mediterranean

Apathy 1888, 1890; Leigh-Sharpe 1933; Selensky 1931; Sukat-
schoff 1914.

Hosts

VERTEBRATES
Arnoglossus laterna

Blennius pholis
Coris giofredi
Corvina nigra
Cottus bubalis
Diplodus annularis
Diplodiis annularis
Gobius niger
Labrus sp.
Lophius piscatorius
Lophius piscatorius
Raia batis

Leeches

Ichthyobdella bioculata
= Cymatobranchus q.v.
Trachelobdella lubrica
Trachelobdella lubrica
Trachelobdella lubrica
Trachelobdella lubrica
Cyrillobdella alcibiades
Trachelobdella lubrica
Trachelobdella lubrica
Branchellion torpedinis
Calliobdella lophii
Trachelobdella lubrica
Pontobdella muricata

APPENDIX B 185

Raia clavata Branchellion torpedinis

Rata clavata Pontobdella muricata

Rhinohatis thouin Branchellion torpedinis

Rhomhoidichthys podas Ichthyohdella bioculata

Rhombus maximus Branchellion torpedinis

Scophthalmus maximus Branchellion torpedinis
Scorpaena porcus gills or ventrally Trachelobdella lubrica
Scorpaena porcus gills or ventrally Trachelobdella nigra

Scorpaena scrofa Trachelobdella lubrica

Solea impar Hemibdella soleae

Solea hispida Hemibdella soleae

Solea vulgaris Hemibdella soleae

Solea vulgaris Trachelobdella lubrica

Squatina sp. gills Ichthyobdella bioculata

Thalassochelys corticata Ozobranchus margoi

Torpedo marmorata Branchellion torpedinis

Torpedo marmorata Pontobdella muricata

Torpedo ocellata Pontobdella muricata

Trachurus trachurus Trachelobdella lubrica

Trigla sp. Ichthyobdella semicoeca

Trygon pastinaca Branchellion torpedinis

Umbrina cirrosa Trachelobdella lubrica

Uranoscopus scaber Trachelobdella lubrica

Southern Ocean and Temperate Pacific

Badham 1916; Benham 1909; Brinkman 1948; Harding 1922;
Hickman 1941; Ingram 1957; Leigh-Sharpe 1916, 1925; Meyer
and Barden 1955; Moore 1938, 1952; Murphy 1914; Oka 1910,
1927, 1931, 1933; Richardson 1949, 1950, 1953.

Hosts Leeches

INVERTEBRATES

Crassostrea gigas Ostreobdella kakibir

Chionecoetes opilio Carcinobdella kanibir

VERTEBRATES

Callorhynchus milii Branchellion parkeri

Dasyatis sp. Branchellion parkeri

186

LEECHES

Eptatretus cirrhatus externally
Leptocephalus conger
Mustelus antarcticus
Parachaenichtys georgianus mouth
Parachaenichtys georgianus head
Platycephalus bassensis
Pristiophorus sp.
Raia sp.
Raia sp.
Raia lemprieri
Raia lemprieri
Raia nasuta

Rhombosolea tapirina dorsally
Sillago ciliata fins

Tetraodon hispidus
Trematomus hansoni gills

Bdellamaris eptatreti
Trachelohdella leptocephali
Branchellion parkeri
Cryohdellina bacilliformis
Trulliobdella capitis
''Ichthyobdella'' platycephali
Branchellion parkeri
Pontobdella benhami
Pontobdella tasmanica
Branchellion australis
Branchellion parkeri
Branchellion parkeri
Aiistrobdella bilobata
Austrobdella translucens
Johanssonia abditovesiculata
Cryobdella levigata

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INDEX

(Italics indicate illustrations)

As the Appendixes A and B are arranged for easy reference they are not covered by the index

Abranchus, 140
Absorption (of food), 41
Acanthobdella, 2, 22, 23, 134
Acclimatization, 58-60
Acetylcholine, 55, 56, 67, 68, 72
Adipose cells, 42, 47
Adrenalin, 55, 56
Aerial respiration, 62
Albumen glands, 12
Alimentary canal, 8
Allolobophora caliginosa, 45
Amoebocytes, 48
Anaerobiosis, 61, 62
Annular receptors, 8
Annuli, 6, 7, 127, 135
Anticoagulant, 10, 36, 37
Anus, 7, 10, 25
Apatemon gracilis, 143
Arenicola, 59
Arhynchobdellae, 22
Atrium, 10, 105, 106, 109, 127

Batracobdella, 140, 143
Behaviour, 79, 82-100
Bimastus, 121
Blood, 46, 53
Blood system, 15, 53
Blood vessels, 27, 53, 126
Botryoidal tissue, 17, 18, 20, 21,

44, 47, 49
Brain, 1, 76-78, 130
Branchellion, 29, 30, 42, 54, 140
Breeding, 101-116, 139
Brood care, 101,110

Callobdella lophii, 108,139

Chaetae, 2

Chemical substances, reaction to,

97-100
Chemoreceptors, 80, 97, 100
Chloragogen tissue, 44, 45
Chromatophore, 89-92
Chromosome number, 134
Circulation, 53-56
Classification, 2, 22, {see appendix)
Cleavage (of eggs), 116, 117, 119-

122, 127, 128, 131, 133, 134
Clitellum, 2, 5, 7, 110
Cocoon, nO-114, 119, 133, 134,

139
Coelom, 1, 53, 77, 126, 111
Coelomic corpuscle, 45, 48, 49
Coelomic fluid, 1 , 3, 44-46, 53, 54
Coelomic sinuses, 3, 15, 27 y 53,

54, 101, 108
Colour change, 89
Colour vision, 91
Conducting tissue, 108, 109
Connective tissue, 18
Co-ordination, 75
Copulation, 104, 107
Copulatory area, 108, 109
Corynebacterium, 50
Cotylurus cornutus, 143
Courtship, 104
Creeping, 73, 74
Crop, 9, 10, 21, 24, 25, 29, 30, 39,

125, 133
Cuticle, \6-18
Cystobranchus, 42, 109, 112, 113,

140

197

198

LEECHES

Deamination, 44
Dermis, 18

Development, 101, 116-133
Digestion, 37-43
Dina, 34, 83, 134, 140
Dorsal light reaction, 88

Ecology, 136-146

Ectoderm, 118-120, 125, 126,

129-133
Egg, 110, 111, ii4, 115, 119, 121,

127, 133, 139
Ejaculatory ducts, 10, 11, 109
Embryology, 121-133
Endoderm, 118, 119, 121, 123,

125, 128-133
Entamoeba, 141, 142
Enzymes, 39, 40
Epidermis, 16-18
Epididymes, 10, 11
Erpobdella

appearance, 33

behaviour, 84, 85, 89, 93, 95, 96

breeding, 101, 110-112

chromosomes, 1 34

circulation, 53, 54, 55

copulation, 107

description, 34

ecology, 115, 116, 137-lAl,
143, 144

embryology, 126-130

eyes, 81, 82

excretion, 48

locomotion, 74

mortality, 145, 146

oxygen consumption, 57-61

parasites, 143, 144

spermatophore, 105
Erpobdellidae, 22, 34, 48, 104,

108
Evolutionary history, 134
Excretion, 44—51
Excretory organs, Hirudo, 12
Eye, 19, 81, 82, 91

Faivre's nerve, 21
Female pore, 6, 7, 25, 30

Fertilization, 104-109, 110, 133
Fibrocytes, 18

Ganglia, 13, 69

anal, 77, 78

segmental, 15, 72

sub-oesophageal, 14, 75-77

supra-oesophageal ( = cerebral),
14, 75, 77, 124

ventral, 70, 71
Gastrulation, 118, 123, 130
Genital pore, 108
Geotaxis, 96, 97
Germinal band, 120, 122-132
Gills, 29, 30
Glossiphonia

anaerobiosis, 60

anatomy, 25

behaviour, 84-86, 93-98

breeding, 101, 110, 113, 114

chromatophores, 91

chromosomes, 134

description, 23-28

ecology, 137-140

embryology, 122, 123-126

eyes, 82

feeding, 43, ii5, 116

food reserve, 42

mortality, 144, 145, 146

nephridium, 26

oxygen consumption, 57, 58

pigment cells, 47

spermatophore, 105
Glossiphoniidae, 22, 23, 48, 88,
104, 108, 113, 121-127, 133,
135, 141
Glycogen metabolism, 45
Gnathobdellae, 3, 22, 32, 127,

133-135
Gonads, 2, 11, 25, 30, 101
Gravity perception, 96
Gravity reaction, 96-97
Gut, 3, 8, 9, 17, 25, 30, 36-43

Habituation, 89, 90
Haemadipsa, 33, 34, 37, 92, 104,
140

INDEX

199

Haemadipsidae, 22, 32, 111, 113,

136
Haem enter ia {see also Placobdella),

29, 110, 140
Haemoglobin, 54, 59, 60
Haemogregarina, 1 43
Haemopis

anaerobiosis, 60

behaviour, 85, 89

breeding, 110

chromosomes, 1 34

co-ordination, 75

feeding, 41, 136, 140

habits, 32

muscle, 67, 68

nerve, 70-72

parasites, 141

salt uptake, 51

water relations, 52
Heat, reaction to, 92
Helobdella

anaerobiosis, 60

appearance, 28

behaviour, 83-55, 88, 91, 93-
96, 100

breeding, 101

ecology, U6-138, 140, 144, 145

oxygen consumption, 57, 58
Hemibdella soleae, 139
Hemiclepsis

appearance, 28

behaviour, 83-88, 90, 93-98,
100

breeding, 110

chromosomes, 1 34

ecology, 137-140

food, 27

locomotion, 94

parasites, 143
Hirudidae, 22, 32, 48, 104, 110,

111, 113
Hirudin, 36, 137
Hiriidinaria, 32, 50, 64, 104, 140
Hirudo

anaerobiosis, 60, 62

behaviour, 83-55, 89, 92-98,
100

blood system, 15

breeding, 110

circulation, 5J-56

cocoon, 113

colour vision, 91

digestion, 38-41

embryology, 130

excretion, 46, 47

excretory system, 12, 49, 50

external characters, 5, 6

eye, 19, 81, 82

feeding, 36, 37, 139, 140

gut, 8,9

habits, 32

histology, 16, i 7

locomotion, 73, 75

metabolism, 43

muscle, 68

nervous system, 13, 14, 69-71

reproductive system, 9, 10, 11

sense organs, 80, 81

water relations, 52
Hirudoin, 113
Hirudonine, 48
Histamine, 37
Hosts (of leeches), 139
Hosts (leeches as), 141
Hymenolepis parvida, 143, 144
Hypoxanthine, 44

Ichthyobdellidae, 22

Intestine, P, 10, 21, 24, 25, JO, 39,

133
Iron metabolism, 47

Jaw, 8, 9, 20, 21

l^arva, 129, 133
Life history

Erpobdella octoculata, 102, 146
Erpobdella testacea, 103
Glossiphonia complanata, 102,

146
Helobdella stagnalis, 103, 104,
146

200

LEECHES

Light reaction, 83
Light sensitive cells, 79-81
Locomotion, 73-78, 94
Lophiiis piscatorius, 139
Lumbricus heradeus, 59
Lumbricus terrestris^ 45

Macrobdella, 32, 140, 141
Macromere, 117-120, 122, 123,

125, 127, 129, 130
Male pore, 6, 7, 25, 26, 30
Mesoblast, UO-132
Mesoderm, 119, 120, 123, 126,

128, 130-133
Metamorphosis, 129, 130, 133
Micromere, 117-130
Mortality, 145, 146
Mosaic egg, 118
Mucus glands, 16, 18
Muscle, 19, 63-69

circular, 17, 18, 63, 66, 111,
120, 124, 127, 133

dorso-ventral, 18, 66

longitudinal, 17,18,63,66,68,
126

oblique, 63

tonus, 69

Nephelopsis, 141

Nephridia, 9, 12, 26, 44, 46, 48,

49, 51, 126
Nephridioblast, 13, 126
Nephridiopore, 7
Nerve cells, 69

Nerve cord, see ventral nerve cord
Nerve fibres, 70, 72, 79, 80
Nerve ring, 72, 79
Nervous system, 9, 13, 14, 69-73
Neuroglia, 69
Nutrition, 36-43

Oesophagus, 10, 21

Optic cell, 19

Optic nerve, 19

Orcheobis herpobdellae, 141

Ovary, 3, 11, 12, 24, 25, 30, 101, Pole plasm, 121

108, 109 Pontobdella, 31, 140, 143

Oviducal gland, 11

Oviduct, ii, 12

Oxygen consumption, 56, 57, 59,

61
Oxygen (as ecological factor), 1 38,

146
Ozobranchus, 31

Parasites (leeches as), 141
Parasites (of leeches), 142, 143,

144
Parental care, 113, 114
Pelobates, 97
Penis, 3, 11, 105
Penis sheath, 11
Phagocytosis, 48
Pharyngobdellae, 22, 34
Pharynx, 3, 8-10, 34, 129
Pheretima, 46
Philobdella, 140
Photoreceptor, 81
Phototaxis, 90
Pigment cell {see also chromato-

phore), 18, 89
Piscicola

appearance, 28

behaviour, 84, 85, 88, 92, 93,
95, 98

breeding, 108, 109

chromatophores, 90

chromosomes, 134

digestion, 42

ecology, 138

embryology, 131, 132

eye, 81,82

food, 140

locomotion, 74

oxygen uptake, 56, 57

parasites, 143

pulsatile vesicles, 53, 54
Piscicolidae, 22, 29, 104, 108, 111,

133, 134, 135
Placobdella, 29, 42, 52, 91, 92,

105, 143
Polar body, 121

INDEX

201

Predators (leeches as), 141
Predators (of leeches), 144
Prepuce, 29
Proboscis, 3, 24, 25, 30
Proctodaeum, 1 26
Prostate glands, 10, 77
Prostomium, 4, 7
Protonephridium, 129, 130, 133
Pseudomonas hirudinis, 40
Pterobdella amaray 31
Pulsatile vesicles, 29, 30, 53
Purines, 44

Rana esculenta, 97

Rana temporaria, 97

Reactions (to light, heat, gravity,

etc.) see under subheadings
Rectal bladder, 10, 21
Rectum, 9, 10, 24, 25, 29, 30
Reproduction, 101-116
Reproductive organs, 9-11, 25,

30, 107, 109
Respiration, 53, 56-62
Respiratory movements, 55
Respiratory organs, 54
Rhynchobdellae, 3, 22, 135

Salivary glands, 3, 10, 16, 25, 36
Searching movement, 86, 95
Segment, 1, 7
Segmental nerves, 54, 55, 72, 73,

79
Segmental receptors, 8, 79
Segmentation (of body), 3
Segmentation (of eggs) see cleavage
Semiscolecidae, 22, 35
Sense bud, 19
Sense cells, 79, 80
Sense organs, 73, 79-83
Sensillae, 3, S, 79, 80
Skeleton, 1
Solea, 139
Somite, 133
Sperm, 101, 108
Sperm vesicles, 10
Spermatophore, 3, 26, 101, 105-

110

Staphylococcus aureus, 40

Starvation, 38

Swimming, 66, 73, 75, 78, 88, 95

Tactile organs, 80

Testis, 3, 10, 24, 25, 29, 30, 34,

109, 127
Tetracotyles, 143
Theromyzon

appearance, 28

behaviour, 83-55, 90-95, 100

breeding, 101, 115, 116

chromosomes, 134

copulation, 105

ecology, 137, 138

embryology, 1 22

food, 140

nephridium, 48, 49
Thigmotaxis, 87, 94, 95
Tooth, 20

Trachelobdella, 105, 143
Trematobdellidae, 22, 35
Triturus, 143
Trocheta, 34, 136, 140, 141
Trypanosoma, 143
Tubifex, 120-122

Urea, 44, 51
Uric acid, 44, 45
Urine, 46, 49-51

Vagina, 11, 12, 110

Vas deferens, 11, 25, 26, 30, 127

Vasa efferentia, 10, 24, 127

Vaso-fibrous tissue, 20, 21, 44, 47

Velum, 8

Ventilatory movements, 55, 89,

116
Ventral nerve cord, 9, 11, 13, 27,

56, 69, 71, 75, 78, 109, 119,

120, 124, 125, 130

Water balance, 44,51,52
Whitmania laevis, 33

Xanthine, 44