Full text of "A treatise on the common sole (Solea vulgaris), considered both as an organism and as a commodity"

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A TREATISE ON

THE COMMON SOLE

(SOLEA VULGARIS),
CONSIDERED BOTH AS AN ORGANISM AND AS A C0M3I0DITY..

PREPARED FOR THE

MAKIXE BIOLOGICAL ASSOCTATIOX OF THE UNITED KINGDOM

J. T. CUNNINGHAM, M.A., F.R.S.E.

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Lain Fellow of Vnircr-nty College, Oxford; Natural ixt to the Association. /

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TLrMOUTH

PUBLISHED BY THE ASSOCIATION.

1890.

LONDON :

UAmtlSOX AND SONS, PRINTEliS IN ORDINAnV TO nKi; MAJKSTV,

ST. MARI'IN's LAXK.

COIS^TENTS.

Page
Preface \-

PART I.

T A X N M 1 t A 1,.

Chapter 1, — Classification of the Flat-fishes 3

Chapter 2. — History of the Genus Solea 11

Chapter 3. — Solea vulgaris, Quensel 15

Chapter -l. — Solea lascaris, Bonaparte 20

Chapter 5. — Solea variegata, Fleming (Donovan) 25

Chapter 6. — Solea lutea, Bonaparte 29

Chapter 7. — Solea Greenii, Giinthei' 32

PART II,

iloKPHOLOGICAL.

Chaftek 1. — The Osseous Skeleton 35

The Skull 35

The Vertebral Coluum • . 38

The Jaws and Branchial Arches 41

Chapter 2. — The Fibrous Membranes and Musculature 45

The Fibrous Membranes 45

The Musculiitux-e 46

Chapter 3. — The Viscera, and Vascular System 64

The Viscera, female 54

Ditto, male 66

Minute Structure of the Reproductive Organs, and Develojiment of the

Reproductive Elements 69

The Vasjular System 64

A 2

Page

Chapter 4. — The Nervous Sj-stem t>G

The Brain GG

The Cranial Nerves G8

Chapter 5.— The Skin 73

Dermal Canals and Sense Organs 74

Minute Stracture of the Skin, Dermal Tubes, and Sense Organs .... 79

Chapter 6. — Embryology 84

Chapter 7. — Structni-e of Phylhmdla solece 93

PART III.

B 1 N M I C a L.

Chapter 1. — Geographical Distribntion 99

Chaiteb 2.— Habits, Food, &c 101

Food 105

Parasites 108

Enemies 109

Chapter 3.— Colour 110

Chapter 4. — Breeding 114

Chapter 5. — Development and Growth 119

PART IV.

E C N M I C A r,.

Chapter 1. — Artificial Propagation 129

Chaitkr 2.— The Sole Fishery 137

Chapter 3. — Pi-actical Measures 142

PREFACE.

The distinction between theory and practice is one that is generally recognised in all
departments of human affairs. By theory in this context is meant pure knowledge —
the knowledge of things as they are apart from any use which may be made of the
knowledge. This kind of knowledge — the result of the most careful investigation,
continually corrected by improved experiments and more widely extended observation,
and subjected to the most rigid criticism by successive generations of enquirers — is
pure science. Practice, on the other hand, or practical knowledge, is the knowledge
of the methods by which the material and the forces of nature can be made to
satisfy human needs and desires. Practice necessarily depends on some knowledge
of the properties and relations of natural objects and forces, though in many cases
it may simply consist in knowing that a certain desired result will generally be
produced by particular operations. This is the kind of knowledge possessed by
men trained and experienced in particular " trades " or crafts.

The distinction has existed since the very commencement of human civilisation.
The earliest representatives of humanity, like the most primitive savages now existing,
had some knowledge of their surroundings which was not directly useful to them, while
they understood very little the arts which they practised. To some extent the develop-
ment of pure science and that of practical science have proceeded independently, but to
a large extent they have influenced one another. Practical science has often received s
great impetus from the discoveries of abstract inquiry, and pure science has often made
enormous strides by the study of the results exhibited by industrial processes. On the
whole the tendency of the development of the two is towards a perfect harmony in
which the knowledge of the universal interaction of natural forces would completely

explain ;ill that takes place in iiuluslrial j)rocesses, and ou the other hand indusliial
processes would be perfected by the application of a complete knowledge of the
mechanism of nature.

Thus, although there is a great dialinction between science and practice, each is to a
large extent dependent on the aid of tlie other. Their influence upon each other
could be illustrated by the history of any branch of science : it is illustrated by the
history of biological arts and sciences. The discovery that the great depths of the
ocean were inhabited by living animals was directly due to the laying of the telegraph
cable from Europe to America. The medical sciences, anatomy and physiology, sprang
not solely from the desire for knowledge, but from the practice of the healing art,
and the desire to improve that art. Botany took its rise from the knowledge of
simples, the use of plants as remedies for diseases and disorders of the human body.
Zoology and comparative anatomy and physiology have been largely aided in their
development by the medical sciences. Marine zoology has ever been to a great degree
dependent on the assistance of fishermen and fishing engines. Science has received
definite additions from investigations carried out with the object of cultivating oysters.
The explanation of evolution is sought in the study of the variations of domesticated
animals and plants. Are there, on the other hand, any cases in which human arts and
industries have directly benefited by the biological sciences ? To answer this question
by even briefly enumerating the recent discoveries concerning animal and vegetable
parasites which have revolutionised the practice of agriculture would require a
volume. But it must be confessed that the fishing industry has hitherto, in tliis
country at least, not been greatly benefited by the scientific knowledge of fishes hitherto
available. Yet zoological science and the methods of that science have not been
entirely without efiect upon tlie supply of aquatic animals for the wants of man.
Oyster-culture based upon scientific knowledge has been very successful in Holland
and France. Knowledge of the conditions of life of the salmon has been apjjlied to
maintain and increase the abundance of that fish in this country, and of allied fishes
in America. The shad has been propagated with great success on tlie Atlantic coast
of the United States. It remains true that there exists a great deal of scienlific
knowledge of marine fishes which has hitherto not at all aflL'cted the sea-fishing
industry. But it is also true that no great endeavours have yet been made to
bring science and practice in this direction into relation with one another, and also
tliat our knowledge of the life of marine fishes is in many respects still extremel}-

Vll

limited. The structure of tliese fishes and their place in the general classification of
the animal kingdom has been to some extent ascertained, but of their conditions of life,
their food, rate of growth, the causes which favour or limit their abundance, we still
know very little. It was only in 1864, when Professor Sars identified the floating eggs
of the cod, that it was first discovered that the eggs of any marine fish passed through
their development while suspended in the surface waters of the sea. The know-
ledge of structure and classification is not entirely useless from the practical point
of view, for it is absolutely necessary as a basis from which to investigate the difl'erent
conditions of life of the different species. The species must be considered separately,
for their mutual relations are so complicated that it is impossible to deal witli them
together.

The object of the present work is to place side by side the results of a scientific
study of the common sole and an account of the present condition of the sole fishery,
and then to consider what are the possible practical applications of the former to the
purpose of maintaining or increasing the supply of soles available for the market.

The work was undertaken under instructions from the Council of tlie Marine
Biological Association, and the investigations described were carried out at the
Association's Laboratory at Plymouth. Nearly the whole of my time and energy since
November, 1888, have been devoted to the subject. The instructions of the Council
were quite general, but from Professor Lankester I have received much guidance
as to the scope of the investigations and the plan of the book. The responsibility,
however, for all the views and statements rests entirely upon myself. When studying
the taxonomical part of the subject in November, 1889, I visited the British Museum
of Natural History, and examined all the type specimens of European species of sole.
I have to thank Dr. Giinther for the courtesy and assistance I then received from
him. At that time I gathered from conversations with him that he still believed
in an English species, Solea aurantiaca, distinct from the Solea lascaris of either Risso
or Bonaparte. I was therefore surprised to see tliat in a communication to the
Zoological Society in January last lie abandoned this opinion, and adopted the
conclusion of most recent writers on the subject — that the English and the Mediter-
ranean form belong to the same species. My discussion of the question in the
present work was written in November, 1889, immediately after my visit to the
national collection.

I have nnich pleasiiro in thanking Mr. Dunn, of Mevagissey, and my iViend Eupert

vni

"Vallentin, Esq., of Falmouth, for the most important assistance they rendered me in
procuring specimens of tlie sole in the younger stages of growth. I am still more
deeply indebted to Miss Annie Willis for the skill and care \vluch she devoted to the
water-colour drawings reproduced in Plates I to IX. The beauty, minuteness of detail,
and artistic finish of her work are evident enough in the lithographic copies, and I need
only add that the drawings were executed from the actual objects under my direct
supervision, and that I can answer for their perfect faithfulness.

J. T. C.

PLyMOUTH,

March 13, 1890.

Part I.

TAXONOMICAL.

CHAPTER I.

CLASSIFICATION OF THE FLAT-FISHES.

It is a matter of general knowledge and experience that the various kinds of flat-
fishes resemble one another and differ from all other fishes in these conspicuous
features : that their form is very flat, that one side is coloured and the other of a pure
opaque white, and that there are two eyes on the coloured side and none on the white
side. It is further generally known, from the observation of such fishes in the living
state in aquaria, that when alive they are usually resting on the white side at the
bottom of the water, sometimes gliding gently over the ground, sometimes burying
themselves in the sand, which is the material on which they are accustomed to live,
and only occasionally rising up from the bottom and swimming in a horizontal position
through the water. The common sole is also as a rule recognised by everybody as a
particular kind of flat-fish, being readily distinguished by its gently curved outline,
especially by the regular, almost semicircular, shape of the snout, and by the dull
brown colour of its upper side after death.

But this is only true of the sole as it is usually seen by the majority of people, that
is in its adult condition. Ordinary habits of observation are not sufficient to dis-
tinguish the sole in its very young condition from other kinds of flat-fishes : only
naturalists are able to separate the kinds from one another among individuals from
one to three inches in length. Even fishermen, who might be supposed to have
unusual opportunities of comparing different kinds of fishes, but who, as a matter of
fact, have usually no leisure and no superfluous energy to devote to accurate and
minute observation, constantly mistake various kinds of flat-fishes in their young stages
for young soles. The reason of this is not that the young fishes between one and
three inches long differ in their characters from full-grown specimens, but simply that
the characteristic features are on a much smaller scale, and therefore are not seen
without attentive observation.

Untrained powers of observation are also unable to compare the degree of difference
between one kind of flat-fish and another. The plaice and flounder are named
independently ; but a fish which resembles the plaice and flounder far more closely
than it does the sole is sold under the name of merry-sole in Devonsliire and lemon-
sole in London. This may be partly due to an inclination to enhance its value in the

B 2

eyes of the consumer. Again, more than one kind of sole is sometimes sold under
that name.

It is evident, then, that before we commence the study of the common sole we must
make ourselves accurately acquainted with its special features, so that we may not
mistake other kinds for it, and may identify it with certainty at all stages of its
existence. In order to discover these special features we must compare all the kinds
of flat-fishes with other fishes and with one another and thus ascertain — 1st, what
features are common to all of them ; 2nd, what features are common to certain divi-
sions of them and especially to the division which includes the sole ; 3rd, what are the
differences between the several kinds or species included in this particular division.

In order to study the characters of the flat-fishes we must of course give names to
their various organs ; but all the bony fishes are made up of the same organs in
different shapes and sizes and in various proportions to one another. Thus we have
only to examine the sole and compare it with a fish of the more usual structure in
order to recognise the various organs which have long borne appropriate names.

In any fish of the ordinary type, for example, a salmon, lierring, cod, perch,
mackerel, &c., the two sides resemble one another in form, structure, and colour, and
correspond to one another in the position and direction of their component organs.
In other words, all the organs, with the exception of some of the internal, are in pairs,
the two members of each pair being situated on opposite sides of the middle plane of
the body, at the same level, and at equal distances from it. This plan of structure
occurs in the majority of fishes and nearly all the otlier vertebrates, and also in the
greater number of the lower animals, for instance in Crustacea and insects. To
obtain a distinct idea of it we may reflect that the body of any animal in which it
occurs, say a normal fish, a dog, or a man, has length, thickness, and breadth. The
length is measured from tlie head to the posterior end of the body, the thickness from
the back to the ventral surface, tlie breadth from side to side. Now the organs at
opposite ends of the line which measures length are utterly different in form and
structure, and those at the back are equally diflerent from those opposite to them at
the ventral surface. But, wherever we measure the breadth, the parts at one end of
the line along which we measure will be exactly similar in form and structure to
those at the other, but exactly reversed in horizontal direction, This structural
feature is called bilateral symniistry.

The greater number of fishes are bilaterally sj-mmetrical, and the line along the
surface which separates the two similar halves passes between the eyes at an equal
distance from each. If we look for the line which divides two similar halves in the
sole we shall not be able to find it. It is obvious that a line drawn between the eyes
does not divide the head into two equal and similar parts ; but if we look for the
paired organs of the ordinary fish in tlie sole we shall find in most cases that one of
each pair is on the coloured or upper side of the sole, and the other on the white or
lower side, but that in many cases the two members of each pair are not so exactly

similar as they are in the ordinary fish. Thus in the sole there is a gill-cover or
operculum on the upper side and another on the lower, and beneath each is a similar
gill-apparatus ; half tlie mouth is on the upper side and half on the lower ; there are
two nostrils on the upper side and two on the lower ; a pectoral fin and a pelvic fin on
the upper side and two corresponding fins on the lower ; scales on the upper side and
similar scales with a corresponding arrangement on the lower ; and finally a line of
peculiar scales, a lateral line, along the middle of the upper side and a similar line on
the lower. It follows, therefore, that the long continuous fins along the two edges of
the sole correspond to the median fins of the ordinary fish, and as we find the anus and
the junction of the gill arches on one edge of the sole, this edge corresponds to the
ventral median line of the ordinary fish, so that the elongated fringing fins of the
sole are the dorsal and ventral median fins respectively ; the ventral median fin is
generally called the anal fin. We thus find that the upper side of the sole is the right
side and the lower the left, and the edge on which the anus opens is the ventral edge,
the other the dorsal. But the two eyes, though in other respects similar to the two
eyes of an ordinarj" fish, are both on the right side, one nearer to the dorsal edge, the
other nearer to the ventral. We may distinguish these eyes as the dorsal and ventral
respectively, and even without further knowledge we might consider it probable that
the dorsal eye corresponds to the left eye of an ordinary fish and the ventral to the
right, and the idea would naturally occur to us that the left eye in the sole had been
somehow drawn out of its original position on the left side and carried round to the
right side.

The fins of the sole are all supported by flexible or soft rays ; none of the rays are
rigid pointed spines ; but this is a character which occurs in certain symmetrical
fishes, for example, the cod and whiting. The possession of a single elongated
median dorsal fin and a single similar ventral fin is also not peculiar to the sole : some
members of the cod family have but a single dorsal and ventral fin. But no
symmetrical fish has a dorsal fin extending so far forwards as the sole : in the latter
this fill is continued to a point on the edge of the body anterior to the eyes, and in
every flat-fish, except one species, it extends at least as far as a point above the dorsal
eye, while in all symmetrical fishes the limit is somewhat behind the eyes.

The lower or left side of the sole differs from the right side not only in being white
instead of coloured, but also in being flatter, and the fin-rays of the meiilian fins are
also more prominent on this side.

The examination of other flat fishes will show that they resemble the sole and difler
from symmetrical fishes in the features just mentioned, if we except the fact that in
some kinds it is the left side and not the right which is coloured and which bears the
eyes. Thus the turbot and brill have the eyes on the left side, while the plaice
flounder, dab, and halibut, like the sole, have them on the right side.

All the various kinds of flat fishes thus resemble one another and difler from
symmetrical fishes in the particulars now described, which may be thus summarised : —

Body much compressed bilaterally and extended dorso-ventrally : one side, on ■wliicli
the fish rests during life, opaque white, flatter than the other, which is more convex
and exhibits colour and markings : both ej^es on the coloured side of the head.
Pectoral and pelivc fins small, the former sometimes absent ; a single elongated dorsal
fin which extends forwards as far as or beyond the level of the dorsal eye, except in
one instance where it ends a little behind the eye ; a single elongated anal fin
extending fi-om the base of the tail to the anus, which is a short distance behind the
opercular apertures.

The fishes thus characterised form a single family — the Pleuronectidce ( = side-
swimmers, from Greek TrXevpd, the side ; vyjx^^^ I swim). The large number of kinds
or species which can be distinguished among them are divided into a number of groups
according to the degree of difierence between them, any two species of the same group
being much more closely similar to one another than to the members of any other
group. These groups are the genera. Thus the diflerence between a plaice and a
sole is much greater than the diflerence between a plaice and a flounder. The plaice
and the flounder resemble each other in the shape of the body, in the large prominent
eyes, and the small terminal mouth and pointed snout. Again, if we compare a turbot
and a brill we find that they resemble one another very closely : they both have a deep
straight mouth cleft, the anterior end of which is at the extreme aj)ex of the snout, and
both have a more or less rhomboidal shape.

The various kinds of sole are all distinguished from other flat fishes by the gradual
and regular curve formed by the outline of the body, which, excepting the tail, is
almost a perfect oval, the semicircular form of the snout being specially characteristic.
'J'he dorsal fin connnences on the snout, and is not continuous with the caudal fin ; the
cleft of the mouth on each side is curved downwards. The mouth is asymmetrical, the
jaws being stronger on the lower side, and only on this side containing teeth, which
are small and slender. The eyes are on the right side and small, the dorsal being in
advance of the ventral. The scales are small and fringed with small projecting spines,
that is, are of tbe kind called ctenoid. Tlie lateral line is straight from the head to the
tail, and runs along the middle of each side, but it also sends a curved branch forwards
on the head which runs parallel to the base of the dorsal fin towards the snout.

All the Pleuronectidce exliibiting the above features are called Solea, with a
distinguishing adjective to indicate the particular kind or species referred to. In
otlier words, the species which resemble one another in these particulars and differ
only in more minute details are classed together in a genus which bears the Latin
name Solea in the universal language of Zoology.

There are other kinds of sole besides the common sole, that is to say, there are other
kinds of flat-fishes which resemble the sole in all the features in which the sole difters
from the turbot or the flounder, but difier from it in more minute details. One kind
is sometimes sold tofjether with the common sole without bein" distinguished, and
sometimes is distinguished as the sand sole. It diflers from the common sole chiefly

in two characters : (1) it is somewhat lighter in colour after death, and instead of large
black blotches on the coloured side it has small black specks scattered almost
uniformly over the surface ; (2) the anterior nostril of the lower side is very large and
conspicuous, it is dilated and has folds radiating from its wall into its cavity. At
Plymouth and other places on the south coast of Devon and Cornwall another flat-
fish is commonly sold which is called the thick-back. This is evidently a kind of sole,
but is distinguished by its smaller size, and by its colour and marking, which consists
of black transverse stripes on a red ground.

Several kinds of flat-fishes are obtained from British seas, which are too small and
too scarce to be of any value as food, but which of course have been studied by
zoologists equally with the edible species.

After studying all the species of flat-fishes brought together in the British Museum
from all parts of the world, Dr. GUnther has classified them in thirty-four genera,
including Solea. But of these only seven include species which occur on the British
coasts. Zoologists often differ as to the limitations of genera, because it is in many
cases difficult to decide whether several species differ from one another to an equal
degree and ought therefore to be classed in a single genus, or whether they differ in
different degrees and ought to be separated into two or more genera. Eecent
authorities also recognise seven genera among British forms — namely, Hippoglossus,
Hippoglossoides, Rhombus, Zeugopterus, Arnoglossus, Pleuronecies, and Solea. The
external differences which distinguish the genera and species of British forms maj^ be
presented analytically thus : —

A. Eyes on the left side ; mouth terminal ; teeth on both sides ; ventral eye anterior
to the dorsal.

1 . Rhoinhus. Shape rhomboidal, middle of the body being very broad ;

mouth large ; lateral line with a semicircular curve anteriorly.

Rhombus maximiis, the Turbot. No ordinary scales, but pointed
tubercles uniformly scattered over skin.

Rhombus la'vis, the Brill. Small scales ; no tubercles.

2. Zeugopterus. Shape almost rectangular, anterior end obtuse ; lateral line

with a semicircular curve anteriorly ; scales ctenoid.

Zeugopterus unimaculatus, first dorsal ray elongated and undivided,
median fins not prolonged under the base of the tail ; a conspicuous
large dark spot towards the posterior end of the lateral line.

Zeugopterus punctatus, first dorsal ray not elongated, median fins
prolonged under the base of the tail.

3. Arnoglossus. Shape oval, rather narrow, with sharp snout; eyes large,

almost level, ventral slightly more advanced. Cleft of mouth deep.
Teeth small, one or two rows in bolh jaws ; present or absent from the
vomer ; none on the palatines. Gill- membranes somewhat broadl}' united

at the throat. Dorsal Gn commencing on the snout in front of the ej'cs,
and not continuous with caudal. Nearly all the rays of the dorsal and
anal simple and undivided. Scales somewhat large, easil}'- detached,
ctenoid. Lateral line with a rectangular bight above the pectoral.

Arnoglos-nis meijastoi/ia (Megrim at Plymouth). Teeth on the vomer.
Anterior dorsal rays united by membrane for half of their length. The
base of the dorsal fin not passing on to the lower side of the head
anteriorly. Anterior nostril of the lower side protected by a broad flap
of flexible membrane. Eyes very large. Scales not so deciduous as in
the following species. Snout pointed.

Arnofjlossus laterna (Scald-fish or Scald-back at Plymouth). No teeth
on the vomer. Anterior dorsal rays free and separate ; the membrane
of the rest of the fin very slight, the rays easily becoming separate.
The anterior rays of the dorsal fin arise from the lower surface of
the head. Eyes not very large. Snout somewhat blunt. The base of
the left pelvic fin extends from the throat to the anus, and behind it
are one or two prominent spines. The four anterior rays of the dorsal
fin are very thick and much elongated in the male, not in the female.
Arnoglosstis lophotes, GUnther, is the male.

JJ. Eyes on the right side.

I. Mouth terminal and large, teeth on both sides.

1. Ilippoglossus. Shape lanceolate ; dorsal fin commencing above the dorsal

eye ; scales cycloid. Lateral line with a slight curve anteriorly.
Hippoglossus vulgaris, the Halibut.

2. Ilippoglossoides. Anterior end not much narrowed; dorsal and ventral

ed<xes rather straight : scales ctenoid. Lateral line straight.
Hippoglossoides limandoides, the Long Hough Dab.

IL Mouth terminal and extremely small ; teeth most developed on the lower
side.

L Pleuroiiectes. Dorsal fin commencing above the dorsal eye ; eyes large
and prominent ; scales small or rudimentary.

Pleuronectes platessa, the Plaice. Bony tubercles on the interorbital
ridge. Bright red spots ; scales uniform. Lateral line nearly straight.

Pleuronectes microcephalus, the Merry-sole or Lemon-sole. Skin slimy.
Lateral line with a very small anterior curve. Colours mottled with a
good deal of yellow ; scales cycloid. Shape somewhat rectangular.

Pleuronectes cynoglossus, the Pole-flounder or Witch. Shape elongated;
dorsal and ventral edges very gradually curved. Lateral line straight.

Pleuronectes fiesus, tlie Common Flounder. Ossicles at base of dorsal
and anal fins. Scales rough along lateral line, elsewhere rudimentary.

Pleuronectes limanda. Shape rhomboidal; snout pointed. Lateral
line with a small semicircular curve anteriorly.

III. Mouth rather small, and not terminal, but curved down to the ventral
edge ; teeth present only on the lower side.

1. Solea. The shape oval, outline of tlie snout regularly semicircular. Scales
ctenoid. Lateral line straight, l)ut with an anterior dorsal curve on
the head. Tactile filaments on the lower side of tlie snout. Paired
fin^ may be rudimentary or absent. The dorsal eye anterior to tlie
lower.

Solea vulgaris, the Common Sole. Pectorals on both sides of con-
siderable size ; nostrils on the two sides similar ; filaments of the under
side of the snout closely crowded together not forming any pattern.
Markings of the upper side consisting of longitudinal series of black
blotches on a j-ellowisli-brown ground.

Solea lascaris, the French 'Sole or Sand Sole. Differs from tlie
preceding in two characters — viz., the anterior nostril on the lower side
is dilated and fringed internally ; each of the black blotches of the
preceding species is represented by a number of small black specks.

Solea varicgata, the Thick-back. Nostrils on both sides similar ;
pectcral and pelvic fins rudimentary ; filaments of the lower side of the
snout connected at their bases by membranes which surround square
depressions. Mouth more terminal and less curved than in tlie other
species. Markings consist of five transverse dark bands.

Solea lutea. Eesembles the preceding in other respects, but has the
mouth much curved, the dorsal fin commencing on tlie extreme
anterior end of the snout. The markings consist of dark blotches
arranged as in S. vulgaris, but there is in addition a thin black line
along every fifth or sixth ray in the dorsal and anal fins.

Solea Greenii, a new species just defined by Dr. Glinther, has tlie
scales, fin rays, and filaments of the left side of the head as in vulgaris,
but rudimentary pectorals.

Plates I to VII, which exhiljil with great accuracy the natural appearance of the
fish, will illustrate the distinguishing external features of the four commoner British
species of sole. But although the above-mentioned characters are those which
principally distinguish the species from one another, they do not exactly resemble one
another in every other respect. We may jiroceed to study their characters in greater

detail, in order to obtain a complete knowledge of their specific peculiarities. In
describing the characters of a fish, it is usual to commence by counting tho fin-rays in
each fin, the number of scales in the lateral line, wherever this is possible, the number
of vertebnc, and the number of rays whicli support the membrane covering the gills
beneath the operculum ; these are called the branchiostegal rays. These numbers
are all put down in succession with initial lettei's to indicate the organs they refer to,
so as to form a numerical foi'mula. Thus : —

B. := Branchiostegal.
D. = Dorsal fin.
A. = Anal fin.
L.l. = Lateral line.

Pt. = Pectoral fin.
Pv. = Pelvic fin.
C. = Caudal fin.
Vert. = Vertebras.

The proportions of the fish are expressed numerically by stating the number of
times a given length is contained in the total length : the reason of this is that the
measurements are made with a pair of compasses, which are first adjusted to the length
of a certain organ, and then used to mark olT successive lengths equal to this along the
body-length.

CHAPTER II.

HISTOEY OF THE GENUS SOLEA.

The flat-fislies liave been always placed together iu one group in all attempts to classify
fishes from the time of the ancient Greeks and Eomans up to the present. Thus
Aristotle called them »/;rjTT&jSei9. But in ancient times other fishes of a flat sl^ape,
but symmetrical, like tlie dorey and the skate, have often Ijeen united with them. Thus
Eondelet includes among the " poissons plats" the dorey and two other symmetrical,
fishes and all the skates and rays. In the ancient and pre-Linntean times ideas
of classification were somewhat vague ; the idea of genus and species existed, thouo-h
it was not accurately defined, but degrees of classification regularly subordinated to
one another could not be established by men who had little real knowledo-e of the
structure and physiology of animals. Eoudelet includes all marine animals among his
" Poissons," yet his arrangement of the true Pleuronectidas in genera and species is
more similar to that which is now accepted than the cltissification adopted by Artedi
and Linnasus. Eondelet describes the genus Rhombus with two species, one with
spines and the other without, the turbot and the brill ; the genus Ehomhoides ;
Citltarus with two species ; Passer with four species. Passer, the plaice. Passer qiiad-
ratuhis, Passer liraanda, and Passer fiesus (the flounder) ; the genus Solea, with six
species, Solea, the common sole, Solea oculata {la Petjouse), la Pole, Armoglossus, Solea
lingtda, and Hippoglossus.

Artedi arranged all the flat fishes into one genus — Pleuronectes, a name which he
introduced into zoology for the first time, and LinnsEus followed liis example. The
l'2th edition of the " Sj^stema Naturae" was published in 1766. Tlie successors of
Linnseus for some time continued to follow him and Artedi, merely dividiiig the genus
iu an arbitrary way into subgenera. Lacepede, in his '• Histoire Nat. des Poissons,"
published in 1798, defines four subgenera of Pleiironectes, but without o-ivino- them
distinguishing names : the first of them comprises only the halibut and the flounder,
united because their eyes are on the right side and they have a curve in tlie lateral
line. Similarly, Eisso, in his " Ichthyologie de Nice," 1810, arranges the species under
two subgenera, according to the side on which the eyes are situated.

Quensel in 1806 divided the senus into two, Avith the following definitions: —
Pleuronectes, having complete jaws not covered with scales ; the maxillary dilated

c 2

and free at its extremity ; tlie mandible with cutaneous folds between its limbs at the
chin. Gill-opening extending above the opercular angle or at least above the pectoral.
The lower eye more anterior than the upper one, and the nostrils distant from the
jaws, that of the blind side being near the dorsal edge.

Solea, in which the jaws are covered with scales, the superior one not fully
developed, and the scaly mandible not showing the usual folds at the chin. Gill-
openings wholly below the pectorals. The inferior eye farther back than the superior
one. Nostrils on both sides near the jaws. All the fui-rays divided, no spine in the
anal. (Richardson's Yarrell, Vol I., p. 608.)

In the " Rcgne Animal," first edition, 1817, Cuvier makes the Iinua?an genus into
a family, which he calls simply " poissons plats," and divides it into genera and species
as follows : —

Platessa, including the plaice, Platessa platessa ; the flounder, Platessa Jlesus ; the
dab, Platessa limanda.

Ilippoijlossus. including the PI. hippoglossus of Linnaeus, and several species of the
Mediterranean described by other authors.

Rhombus, including Rhombus maximus, the turbot and the brill, the PI. nwlus of
llisso (apparently an Arnaglossus), and other species in which the upper eye
is at a great distance above and behind the lower.

Solea, including tlie common sole, PI. solea, Lin., the Pole of Belon, the S 'lea
oculata of Hondelet, the Peyou.se of Eisso, and the lascaris and theophihis of
the same author. Also certain foreign species in which the vertical fins are
continuous, PL zebra, Bloch, PI. plagusia, Lin. (These species now form the
genus Plagusia.)

The Monochires, in which the right pectoral is very small, and the left minute
or altogether wanting, e.<i., Linguatula, Eondelet, and the Achires, which have
no pectorals at all, are mentioned apparently as subgenera. Those Achires in
which the vertical fins are continuous with the caudal are distinguished as
Pl'igK.'^ia.

The definition of Solea given by Cuvier is as follows : —

" Their peculiar character is that the month is twisted and as it were monstrous on
the side opposite to the eyes, and furnished on that side only with slender teeth closely
crowded together like the pile of velvet, while the side where the eyes are has no teeth.
Their ft)rm is oblong, their snout round and always projecting beyond the mouth; the
dorsal fin conunencing over the mouth, and extending like the anal up to the caudal.
Their lateral line is straight ; the side of the head opposite to the eyes is generally
furnished with a sort of villosity. Their intestine is long, with several convolutions,
and without creca."

It is evident that this definition of the genus admits of but liitle improvement.
Cuvier obviously meant the Monochires, Achires, and Plajusia to l)e mere subgenera

indicating the grouping of the various species. But subsequent authors iVequently
raised these divisions to the rank of distinct genera. Bonaparte, 1841, separated the
last subdivision of Cuvier only as a distinct genus, namely, Plagusia.

Dr. Glinther, in his important work, " The British Museum Catalogue of Fishes,"
gives a comprehensive classification of the Pleuronectida3, which includes all the
forms up to that time described in the literature or represented in the great national
collection. He distinguishes in all thirty-four genera, many of which are entirely
new, while the limits and definitions of tlie rest are revised. His definition of Solea
is as follows : —

Eyes on the right side, the upper being more or less in advance of the lower. Cleft
of the mouth narrow, twisted round to the left side. Teeth on the blind side only,
where they are villiform, forming bands ; no vomerine or palatine teeth. The dorsal
tin commences on the snout, and is not confluent with the caudal, Scales very small ;
ctenoid. Lateral line straight.

Thus the chief difference between this definition and Cuvier's is that it excludes all
the forms in which the longitudinal fins are continuous with the caudal. All the British
forms of sole described in the present work are included l^y Glinther in the genus Solea.
But almost every author defines the genera of Pleuronectid^e, even at the present day,
in some degree after his own fashion. There is a general agreement, together with
differences of opinion on certain points. In tlie Pleuronectidte, as in nearly all families
of animals, there are certain well-marked species which are recognised by all naturalists.
There are others, especially those founded upon a small number of specimens, which
are more difficult to separate, and concerning whicli differences of opinion exist. But
the question of the arrangement of the species into genera gives rise to much greater
differences of opinion. The arrangement of course depends on which of the characters
possessed by several species in common, are taken as characterising a genus. If one
character is taken, a certain number of species are united by it ; if another is taken
tlie same species are scattered among other genera. Thus the fish called in this work
Arnoglossus megastoina is variously placed. By Giinther it is placed in the genus
Rhombus, because it possesses teeth on the vomer. By Moreau, whose arrangement
seems to me more original than natural, it is placed in the genus PJeuronedes. The
characters in which the species agrees with Arnoglossus Interna seem to me to be more
numerous and important than the pi'esence or absence of vomerine teeth, and I liave
therefore followed those authors who include it in the genus Arnoglossus.

In describing tlie British species I shall give not merely the range of variation
of each numerical character, but the actual numbers observed in several individuals.
It must be pointed out that the number of scales in the lateral line is always
obtained not by counting the scales in the line itself, but the series of oblique trans-
verse rows of scales which cross the lateral line ; the scales are so arranged as to
form rows which run obliquely downwards somewhat from before backwards, other
rows which i-un more obliquely downwards and from behind forwards, and others,

vbich are not 8o distinct, wliicli run straight from before backwards; it is the rows of
the first kind which are counted. The number of these rows indicated by the letters
L.l. is not so absohitely certain as the number of fin-raj's in a fin, for the rows of scales
are counted from the commencement of the lateral line to the base of the tail, and as
the lateral line is actually continued to the very extremity of the tail, while the scales
diminish in size gradually at the base of the tail until they get so small that the rows
cannot be counted, there is, of course, no definite point where the counting ceases.

CHArTER III.

SOLEA VULGARIS, Quensel.

[Plates I to V.]

Synonymy.

Pui^lXwaaov, Athen. vii, p. 288.

" Lingnlaca," Varro and Plautus.

" Solea," Ovid, V. 124 ; Plin., ix, c. 16.

" Buglossus sive Solea," Rondeletius, xi, c. 11, p. 320, and other m'^diapval authors.

" La Sole," Rondelet, 1558, French edition, Lyons, p. 256.

" Plenronectes, sp.," Ai-tedi, 1734, Genera, p. 18, No. 6 ; Species, p. GO, No. 5 ; Synonymtn,

p. 82, No. 8.
" Plenronectes solea," Lin., Syst. Nat., 1, p. -157 ; Bloch, 1784, Fl^che Ben.tsr.hl., ii, p. 42,

taf. 45; Lacepede, iv, p. 023; Donovan, 1808, Brit. Fish., in, pi. 52; Risso, 1810,

Iclitli. Nice, p. 307.
" Sole," Pennant, Brit. Zool, iii, p. 203.
"La Sole," Duhamel, iii, sec. 9, p. 257, pi. 1.
"Solea vulgaris," Quensel, 1806, Vet. Akad. Handl., p. 230; Risso, 1826, Nat.

Hist. Eur. Mcr., iii, p. 247 ; Bonaparte, Fau7ia Ital., iii, 26 ; Giinther, 1862,

Brit. Mils. Catal., iv, p. 463; Morean, 1881, Poissons de la France, p. 304;

Francis Day, 1884, Fish. Gt. Brit, and Ire., p. 39, pi. cvi.

Males.

Females.

Total length |

16-9 cm.
= 6f in.

264 cm.
= 10| in.

33-2 cm.
= 13TVin.

17-6 cm.
= 6ffin.

19-4 cm.

35'6 cm.
= 14 in.

38 cm.
= 15 in.

Length 1^
height /

3tV

3ft

Length ]
head /

6tV

7 r. 8 1.

L.l

159

155

160

153

149

166

Vert

~~*

—

A COMPARISON of the above figures gives the following results. There are no
constant sexual differences in any of the ten characters given in the table, except

that the females reach the larger size, nor anj- constant differences depending on size,
although it is possible that a slight increase in the number of rows of scales takes
place in individuals which grow very large. The largest individuals in the above
table have the largest number of rows of scales. The number of pelvic fin-rays is
constant, that of the pectoral rays, and of the caudal, nearly so. The number of
vertebrae varies very slightly. The range of the numbers of tlie dorsal and anal
fin-rays is considerable, in the above specimens 83 to 90, and 66 to 74, respectively
The range for the lateral line scales is greater, namely, 149 to 166. In all these cases
examination of a greater number of specimens would duuljtless have extended the
range.

Fins. — The dorsal fin conuuences a little in front of the dorsal eye, but behind the
apex of the snout. The right pectoral is scarcely longer than the left and is contained
two and a half times in the length of the head.

Exjes. — Longitudinal diameter of e\-e one-.sixth the length of the head ; scaled skin
between the eyes equal in breadth to the longitudinal diameter of the eye ; distance of
dorsal eye from edge of the snout equal to the longitudinal diameter of the eye.
Posterior edge of dorsal eye on a level with the middle of the venti-al.

Nostrils. — On the right side both nostrils are close together inmiediately in front
of the ventral eye and close to the edge of the upper lip. Botli are tubulai-, the
posterior a little the wider, the anterior the longer. On the left side the two nostrils
are also thin walled tubes, the anterior being prominent and larger, the posterior quite
obscure; the latter is about half an inch (in adult) above and behind the former.

Mouth. — Extends backwards to beneath the middle of the ventral e3'e : the teeth
on the lower side are slender rods set close together in a broad curved patch in each
jaw. The villi on the under side of the snout are really connected at the base by
slight membranes which enclose depressions of the surface, l)Ut the latter are very
small and the villi are therefore closely crowded together.

Scales.— On the right side extend over the whole surface of the head up to its very
ed^es, on the lower side thev decrease in size in the neighbourhood of the villi and
disappear where these are full\- developed. The villous area is bounded posteriorly
by a straight transverse line running a short distance behind the angle of the mouth.
One of the largest scales from the middle region of the right side of the body (PI. XIV, 1 )
has sixteen radiating rows of spines, five spines in each of the middle rows.

The curved anterior portion of the lateral line is very distinct on the right side,
and can be traced running parallel to the edge of the body right to the apex of the
snout. On the lower side a similar curve exists, and in addition a line belonging to
the same system which runs straight forwards from the origin of the former above the
mouth, gi\'ing off transverse branches.

Colour. — The dead sole in the market generally appears to be of a uniform dull
dark brown on the upper side, but closer examination shows that there are black
blotches as well on the brown ground. During life the colours are much brighter.

and the markings much more conspicuous. Altliough the colours vary with the
ground on which the animal rests, this variation is only in depth of tint ; the
markings are constant for the same individual, and vary but little in different
individuals, they have therefore quite as much importance as a specific character as
any other feature in the animal.

The markings, then, in the living fish consist of large dark blotches and small white
spots on a yellowish-grey ground. The dark blotches, brown or black according
to their intensity, are ai-ranged sjonmetrically so as to form a definite pattern : the
largest blotches are in three rows, one along the lateral line, one near the base of
the dorsal, and one near that of the anal fin. Usually there are five or six of these
blotches in each row, but in some specimens there may be as many as eight in one or
more of the rows. The first blotch of the dorsal row is close behind the anterior
curve of the lateral line, and the last near the base of the tail ; the first of the central
row is just above the end of the pectoral fin, and the first of the ventral series is at
the base of the pelvic fin. The first and last in each series are alwaj's fainter and
smaller, while those in the centre of the series are larger and more conspicuous. In
each of the intervals between the blotches in each series is a lighter white spot,
smaller and with a more definite outline than the dark blotches. Other white spots
frequently appear around the dark blotches. Between the central row of blotches,
and each of the external rows is another row of similar blotches of smaller size ;
these are closer together, nine or ten of them can be usually counted in each series,
and in the intervals between them there are small white spots. These are the
principal markings, but there are in additioji narrow irregular branching streaks of a
lighter brown extending from the edges of the dark blotches over the spaces between
them ; these streaks usually contain dark or black specks, but under certain conditions
they are everywhere almost as dark as the blotches, and then the latter are connected
together by an irregular network of black streaks. Outside the external series of
blotches, between them and the bases of the dorsal and anal fins respectively, is a
band free from markings where the ground colour is uniform and lighter than
elsewhere. The dorsal and anal fins themselves exhibit three distinct longitudinal
bands of colour ; the basal third is dark, being densely sprinkled with minute black
specks on a yellow ground, the middle portion is yellow without the black specks,
while the extreme edge is colourless, the membrane between the rays being here
transparent, while the skin over the extremities of the rays themselves is opaque white.
The extreme dorsal and ventral edge of the tail fin are opaque white, the external
portion of the tail, including the terminal half, is yellow, this portion being continuous
with the light band vdiicli lies within the bases of the dorsal and anal fins ; the
internal and basal part of the tail is sprinkled with black like the l)asal jiart of the
dorsal and anal fins. The right side of the head is coloured like the parts of the
body-surface between the blotches, that is, with blacks specks connected by faint
brown lines on a yellowish ground.

The pectoral fin has usually a black spot on its outer half, but very often this spot is
only light brown, its intensity varying according to the action of light upon tli»?
animal.

When we examine still more minutely the elements of the coloration now described,
we find that each of them is compound, made up of still smaller markings which
have a definite relation to the scales. The scales are imbricated like the tiles ou a
roof, and the exposed portion of each, which projects backwards, has the shape
of the sector of a circle. Except in the white spots, where the whole sector is
opaque white, the basal angle of the sector is lightest in colour, and the colour
deepens in intensity to the extreme border which is darkest. Even in the lightest
part of the ground colour the border of each scale is distinctly defined by its
brownish colour, wliile in the darkest part of the blotches and black specks the curved
edge and the posterior half of the scale is black, while the anterior angle is light
brown or even yellow.

The scales do not extend right up to the edge of the transparent cornea of the eyes,
the skin bordering the cornea is smooth, and coloured green with brown specks, the
iris is vcllowish-grey marked with radiating brown lines. The pupil is black at its
edfres, but in the centre of it is a beautiful iridescent spot which dissection shows to
belong not to the surface of the cornea, but to that of the crystalline lens.

This species, being abundant on both the shores of the Mediterranean and the
Atlantic coasts of Europe, has been generally known since the earliest historical times.
It is mentioned by some of the ancient historical writers as ^SouyXwcrcros by the
Greeks, and llnr/nlaca or solea by the Romans. The former two names are taken from
its resemblance in shape to the tongue, the latter from its resemblance to the sole of
a shoe. Similar names are still in use in the various European languages : the
Germans call it zuncje, the tongue, and we call it the sole. In Italy it is called in
some places limjiia or Unguattula, in others sogliola. The name tongue is also used
sometimes for small soles at Billingsgate.

After the revival of learning in the sixteenth century, when the study of sj-stematic
natural history began to develop, the name Buglossus or Solea, borrowed from the
ancients, was used for this fish by all naturalists up to the time of Artedi, that is up
to the commencement of the eighteenth century.

Artedi, who died in 1 734, placed all the flat fishes which had previously been
usually grouped together by the mediaeval ichthyologists, in one genus, Plewonectes,
a name first introduced by himself.

Linnaeus, who edited Artedi's works, added little to the knowledge of fishes beyond
applying binomial terms to the species defined by the latter. He named the sole
Pleuronecies solea, in which he was followed by a number of his successors.

But it was soon found necessary to make the flat fishes not a single genus, but a
family, classifying the diverse foi-ms under various genera. This was in reality a
return to the practice of the pre-Linnasan naturalists, the results of Artedi's accurate

distinctions and Linnaeus' system of nomenclature being retained. The name Soleu
vulgaris was first used by Quensel, a Swedish zoologist, in 180(3, and it has been
generally employed since that time. The species has since then always formed the
type of the genus, the number of species included with it varying in the systems of
classification adopted by different ichthyologists.

D 2

CHAPTER IV.

SOLEA LASCARIS, Bonaparte

[Plate YI.]

Synony my.

' Plenroncctes lascaris," Ri.sso, 1810, Ichthyologie de Nice, p. 311.

' Solea lascai-is," Risso, 1826, Hist. Nat. de I'Eitr. Mer., t. iii, p. 249.

'Solea nasuta," Nordm, iu Bemid. Vmj. Russ. Merid. Zool., iii, Poissom, Tab. .31.

'Solea lascari.s," Bonaparte, 1841, Fauna Italica, t. iii, 27*, with 2 figures.

' Solea pegusa," Yarrell, 1829, Zuol. Journal, vol. iv, p. 4^37, pi. IG.

' Lemon Sole," Yarrell. 18:?6. Urif. Fishes, first edition, vol. ii, p. 2G0.

'Solea aurantiaca," Giinther, 1802, Cat. Brit. Mus., vol. iv, p. 407.

' Solea la.scaris," Moreau, 1881, Poissons de la France, t. iii, p. 307.

' Solea lascaris," Francis Day, 1884, Fishes, Gt. Brit, and Ire., vol. ii, p. 42, pi. 107

Total length |

Male.

Females.

17-2 cm.
(ji* in.

18-9 cm.
7tV in.

19-2 cm.
7-i in.

26-1 cm.
IOtV in.

Length \
height /

. n

Leneth 1
head J ' '

5; '

L.l

125

123

119

Vert

—

Of tills species I have only been able to make a detailed examination of the four
specimens whose numerical peculiarities are given in the above table.

Comparison of the above characters with those of Solea vuhjaris shows that the
presoit species is much broader in proportion to its length than the former, that the
proportion of the length of the head to the total length is abt)ut the same, that the
vertebras are fewer in number, and the scales larger iu proportion to the length of
the body.

Fins. — The doisal commeuces just a trifle farther forwards than in ,S. vuhjo.ris, the
base of the first ray being in line with the longitudinal diameter of the upper eye.
The two pectorals are equal in length, and the length is contained two and' a half
times in the length of the head.

Eyes. — Dorsal eye half of its longitudinal diameter in front of the ventral, and
more than its long diameter from the end of the snout; therefore not so near the edge
as in vulgaris.

Nostrils. — Both nostrils on the right side close together immediately in front of
the ventral eye, both tubular, but the anterior considerably the longer. On the
left side the anterior nostril is very broad and dilated, its edges being reflected
outwards. These edges are covered externally with the slender papillas of the under
surface of the snout. Internally there are a number of folds projecting from the
inner surface of the nostril radiallv towards its centre, the ventral of these folds beino-
thicker than the rest: the posterior nostril is tubular, narrow, and flaccid, and situated
a short distance behind the upper part of the rim of the anterior.

Mouth and Teeth as in vulgaris. The villi of the under side of the snout are finer
and even more closely crowded than in vulgaris ; they are especially long and
numerous round the edge of the dilated nostril. The villous area does not extend so
far backwards as in vulgaris. The scales cover the w^hole right side of the head, as in
vulgaris, but on the lower side they extend farther forwards above the nostrils, though
lines of villi are developed along the transverse branches of the cephalic portion of the
lateral line system. One of the scales from the middle region of the right side of the
body has seventeen radiating rows of spines, six spines in each of the middle rows.
(PI. XIV, 4.)

The curved portion of the lateral line on the head on the right side is almost as dis-
tinct as in vulgaris ; on the lower side the arrangement is the same as in that species.

Colour. — After death the colour is much lighter than that of vulgaris, being yellow-
brown instead of dull brown ; hence the name lemon sole by which the species is some-
times called. In life the ground colour. is a brownish- j-ellow, and the markings consist
of numerous small black specks scattered pretty uniformly over the whole surface.
Careful examination shows that among these black specks, groups can be recognised
which correspond in position with the black blotches of the common sole. In these
groups the specks are somewhat larger and closer together than elsewhere. Thus the
markings of the present species could be derived from those of vulgaris by taking
away so much of the black of the blotches in the latter as to leave only a group of
distinct specks. Among the specks are scattei-ed other small spots of a light blue
colour ; these correspond to the white spots of vulgaris, but I have never seen them
white. What was said of the relation of the colour to the scales in vtilgaris applies
here also ; many of the scales are bright yellow at their bases. The colour of the fins
resembles that in vulgaris ; there is a black spot on the outer half of the pectoral.
The eves are coloured as in vulgaris.

The British form of Solea, which is distinguif-hed from the others by the dilatation of
the left nostril, was first observed by Yarrell, who described and figured it in the
" Zoological Journal," \v\. IV, in 1829, under the name Solea pegusa. His description is
so bad that it would be impossible to identify the species by its means with certainty,
but his plate shows the distinguishing characters quite clearly. Yarrell considered
his specimens to belong to the species Plearonectes pegusa of Lacepede's " llistoire
Naturelle des Poissons," Vol IV, 1803, and with the Pleuronectes pegusa of Eisso's
" Ichthyologie de Nice," 1810, wliicli is called Monochirus f>egusa in the same author's
" Hist. Nat. de I'Europe Meridionale." In the third edition of Yarrell's " British Fishes,"
Sir John Richardson identified this species as the Pleuronectes nasutus of Pallas'
" Zoographia Rosso-Asiatica," 1811. 13ut the PL pegusa of Laccpede is the Solea
ocellata of Giinther's Catalogue, the Pleuronectes ocellaius of Linnanis, the Solea
ocidata of Eondelet, a well-marked species in which tlie nostril is not dilated ; and the
Monochirus pegusa of Risso is another species of the Mediterranean which has no
pectoral fin on the blind side, and in which also the left nostril is not dilated : it is the
Solea monochir of Giinther's Catalogue.

Yarrell's identification w^as therefore entirely incorrect, and Pallas' description of
PL nasutus is so extremely vague that it is difiicult to ascertain to what species it
referred. The specimens described by Pallas by the name n(t.sufus were taken in llic
Theodosian Gulf in llic Black Sea. The Solea ocellata and Solea munochir both occur
at Nice.

Dr. Giinther, in his "Catalogue of the Fishes in the British Museum," Vol. IV, 18G2,
distinguishes four species of Solea in which the left nostril is dilated and flattened.
The British form, called by Yarrell Solea pegusa, the lemon sole, or French sole, is
described as distinct from any other known species, and is named by Dr. Ciinther,
Solea aurantiaca. The second of the four species is the Solea lascaris of Risso, the
third Solea impar of Bennett, and the fourth Solea margaritifera of Giinther, another
new species. I have examined m3-self the specimens in the collections of the British
Museum, which Dr. Giinther thus described in his Catalogue, and in many respects I
cannot agree with him in his arrangement and identification of them.

Risso's original description of Solea lascaris is not very exact, and the small figure
he gives is quite worthless ; it would be impossible to identify the species from the
figure. The numbers of fin-rays he gives are as follows : —

D. 85, A. G8, P. 7, V. .5, C. 15.

He says that the colour is " fauve tigr(5 de noir, avec des reflets violets, parsem^s de
points grisatres sur la surface droite." He says that the upper jaw covers the inferior
in such a manner as to imitate the beak of a parroquet, and then continues: " Le
dessous de la tete est orne de petits cils soyeux, blanchatres, entourant un long tube
qui rc'^pand une humeur glaireuse." Now it is difiicult to understand how a naturalist
could describe the dilated nostril of Yarrell's lemon sole as " un long tube," but as

Risso makes no mention of any nostril on the nnder side of the head of any other
species of Pleui'onectes, it is pretty evident that he was struck with a peculiar
conspicuous nostril, such as exists in the English form we are considering.

Bonaparte gives a good description and two excellent coloured figures in his " Fauna
Italica," 1832-41, of a species which he calls Solea lascaris, and which he identifies
with the Solea lascaris of Eisso's " Hist. Natur. de I'Europe Mer.," the Pleuronectes
lascaris of the same author's " Ichthyologie de Nice." The fin formula given by
Bonaparte is —

D. 78, A. GO, P. 8,A^. 5, C. 19.

It will be seen that the formula given hj Eisso agrees perfectly with the numbers
observed by myself in British specimens, and that Bonaparte's differs so little from the
lowest numbers found by me that, considering the rest of his description and his figures,
there can be no doubt that the British specimens are of the same species as those
observed by him. I conclude, therefore, that Bonaparte was correct in his identifi-
cation, and that the British species of sole, described above, is the Solea lascaris of
Eisso, more completely described by Bonaparte under the same name.

Dr. GUnther identified the Solea irnpar of Bennett, of which he possessed only the
original type specimen described by Bennett himself, with the Solea lascaris of
Bonaparte. But, after carefully examining the specimen and the descriptions myself,
I am unable to accept Dr. Giinther's conclusion.

In the British Museum Catalogue a single specimen is identified as the Solea lascaris
of Eisso. The chief peculiarities in Dr. Giinther's definition of this species are : the
small size of the scales, the formula being LI. 150; the narrowness of the body, the
height being one-third of the total length ; and the prolongation of the upper jaw,
which is described as "produced into a longish lobe overhanging the lower." Of
these characters only the last corresponds to anything in Eisso's description ; but I
find that in my English specimens of the lemon sole, the upper jaw embraces the
apex of the lower somewhat more than in the common sole, and that in the
British Museum specimen the jaws do not differ to any appreciable extent in tliis
respect from the English form. What Eisso says on this point applies to the English
specimens. Eisso says nothing concerning the number of the scales nor of the
proportion of breadth to length in his lascaris.

The specimen which Giinther calls Solea lascaris came from Madeira ; the specimen
called Solea impar by Bennett came from the Atlantic coast of North Africa. Eisso's
Solea lascaris on the other hand, occurred at Nice, and Bonaparte's species is described
as common at Venice, at Nice, and on the Eoman shores. In the collections under
Dr. Giinther's charge there are specimens identified as Solea aitrantiaca from Lisbon
and from Nice. Thus specimens of the same species as the English specimens have
been found at Nice, while the l^ritish Museum possesses no specimen identified with
Eisso's lascaris, or with Bonaparte's lascaris from any pari of the Mediterranean.

I will now shortly consider the question of the identification of the actua- specimens
catalogued by Giinther. In the single specimen he calls lascaiis I could count only
133 rows of scales, a number not much larger than the maximum 125 found by
me in the English form. As for its narrowness, it had been forced into a bottle nmch
loo narrow for it, and had in consequence been much compressed in breadth, so ihat
I think it is scarcely possible to be certain about its proportions. I do not consider
it toTse specifically distinct from the Solea lascaris of Bonaparte.

Solea iiiipnr, Bennett, and Solea martjCiritifera, Giinther, must for tlie present be
considered distinct. They differ from English specimens of Solea lascaris in numerical
characters and also in colour. Both of them possess the marking characteristic of
vulgaris, that is to say, there are dark spots arranged as in vulgaris, not divided up
into small specks as in lascaris. Margaritifera is further distinguished by the con-
spicuousness of the small white spots in the type specimen in spirit. It may be found
in the future that Enghsli specimens of aS. lascaris exhibit a range of variation which
would include both these species.

Moreau, in his "Poissons de la France," 1881, also identifies the Solea aurantiaca of
Giinther with the Solea lascaris of Eisso and Bonaparte, but he further includes the Solea
impar, Bennett, in the same species, although it is not clear from his description
whether he actually discovered by his own observation that the range of variation of
lascaris included the characters of impar. Francis Day, in his "Fishes of Great Britain
and Ireland," 1880-84, gives ihe same synonymy as Moreau.

CHAPTER V.

SOLE A VARIEGATA, Fleming (Donovan).
[Plate VII, Figs. 1 and 2.]

Synonymy.

" Pleuronectes variegatus," Donovan, 1808, Nat. Eisf. Brit. FisJies, pi. 117
" Pleuronectes maugilli," Risso, 1810, Ichth. Nice, p. 310.
" Rbombns mangili," Risso, 1826, Hist. Nat. Em: Mer., p. 255.
" Variegated Sole," Yarrell, 1836, Brit. Fishes, first edition, p. 262.
" Monochirus variegatus," Thompson, 1839, Ann. Nat. Sist., vol. ii, p. 404.
" Solea mangilii," Bonaparte, 1841, Fauiia Italica, t. iii, 27**.
" Solea variegata," Fleming, Brit. Animals, p. 197 ; Giintlier, Cafal, iv, p. 469.
"Variegated Sole," Couch, Fish. Brit. Isles, iii, p. 203, pi. 177.
" Solea variegata," Giinther, 1862, Bnt. Mus. Catal., vol. iv, p. 469.
" Microchirus variegatus," Morean, 1821, Poissons de la France, t. iii, p. 317.
" Solea variegata," Francis Day, 1884, Fishes Gt. Brit, and Ire., vol. ii, p. 43, pi. 105,
fiff.l.

Total len

Length "1
height J
Length "I

gth{

heai
D.
A.
C.
Pt.
Pv.
L.l.
Vert.

i ■ ■

Males.

17-2 cm.
6f in.

68
63
18
4r. 11.
5
89

17-9 cm.
7 in.

5 r. 1 1.

5
93

18-3 cm.

68
62
18
4r. 21.
5
90

191cm.
7iin.

74
58
16
4r. 11.
6
92
40

Females.

19-7 cm.

19-9 cm.

20 cm.

21 cm.

7f in.

m in.

7|in.

8iin.

6ii

4r.21.

4r. 11.

6r. 31.

89 1

104

21 cm.

81 in.

54
. 18
4r. 11.
5

The above figures show that while the two preceding species cannot be separated
by the range of variation of the numbers of fin-rays in the dorsal and anal fins, the

present species can be so separated fioni those two. The range for the dorsal fin-rays
in the above specimens is 68-74. Dr. Giintlier in his Catalogue gives 63-73, Day's
"British Fishes" gives 65-74: the total ranrre recorded therefore is 63 to 74. Similarlv
for the anal fin-rays the rang? in the above table is 52-58; GUnther gives 53-57; Day
55-58, therefore the range in my table is the greatest recorded. Day gives the number
of caudal fin-rays as 15, evidently not counting the smaller external rays. GUnther
gives the scales of the lateral line as 85, Day as 85 to 90 ; the range in my specimens
is 87-104. The number of vertebrge is here again very constant, and forms a good
specific character, though it must be remembered that it is doubtful if it would serve
to distinguish this species from all other known species of Solea. The proportion of
breadth to length resembles that in vulgaris, and is therefore less than in lascaris,
while the proportion of head to length is izsually less than in the other two species, but
does not form a marked specific character.

Fins. — The dorsal commences slightly farther forwards than in the two preceding
species, the base of the first ray being actually nearer to the mouth than is the con-
tinuation of the longitudinal diameter of the dorsal eye. The right i)ectoral is much
larger than the left, but much smaller than the pectoral of the preceding species : its
length is contained 3| to 4| times in the length of the head. The left pectoral is a
mere insignificant filament, never more than ^ in. long, sometimes much smaller : it
may contain one, two, or even three rudimentary fin-rays.

Eyes. — The dorsal is only ^rd its own longitudinal diameter in front of the ventral,
and f rds of the same lengtli from the edge of the snout.

Xostrih.—T\ie two on the right side are in the same position as in the preceding
species, but the posterior is smaller, and the anterior a more elongated tube than in
tln'ni. Tlie two on the left side are situated as in «S. vulgaris, but are smaller and less
conspicuous.

Mouth, is much less curved downwards than in the two preceding species, the anterior
end of the cleft being slightly more dorsal than the angle of the cleft, while in the two
previous species it is considerably more ventral : the anterior end of the cleft is in fact
on the same longitudinal level as the lower border of the ventral eye, while in the
other two species it is considerably ventral to that level. The snout is more truncated
than in the other two species, the apex scarcely projecting beyond tlie anterior end of
the mouth-cleft. Two patches of rod-like teeth, as in the other species, cm the left side.
The villi of the under side of the snout form short fringes at the edge of somewhat
broad membranous folds of the skin, which have a reticulate arrangement enclosing
quadrangular depressions of considerable size. This conspicuous reticulate arrange-
inent of fringed membranes forms a distinct contrast to the closely crowded filaments
in tlie two previous species (PI. VII, 2).

The scales are absolutely broader than in any of the other British species, the
breadth being almost equal to the length : they are- also much larger in proportion to
the size of the body than in either of the two preceding species, as is evident from

tlie number of lateral line scales gis^en in the numerical table. A scale from the
middle of the body (PI. XIV, 3) has 26 rows of spines, the middle rows having 8 spines
each.

The posterior vertical portion of the curve of the lateral line oii the right side of the
head can be detected with difhculty, but the anterior part parallel to the base of the
dorsal fin is wanting altogether. The branches of the lateral line system on the left
side of the head in the previous species are also invisible in variegata.

Colour. — The general colour is much brighter than that of either of the preceding
species, being a distinctly reddish-brown with markings deepening to black. Of these
markings the principal are five broad dark transverse bands, each of which terminates
at either end in a large intensely black blotch situated partly on the side of the body,
parti)' on the longitudinal fin. The first of these bands passes across just behind the
pectoral fin, the others are at about equal distances, the last covering the ends of the
dorsal and anal fins and the base of the tail. The central part of each band is only slightly
darker than the neighbouring surface, but its anterior and posterior edges are usually
very sharply defined. The darkening of the bands is produced by the presence of a thin
black border at the edge of the scales, and the sudden extension of this black border
over the whole scale produces the black blotch at each end of the band. Between the
principal bands there are lighter areas which are again marked by one broad or two
uarrow secondary bands : these also terminate in black patches, which in this case are
usually situated on the outer part of the fin and extend to its edge : these patches are
smaller and less regular than those belonging to the principal bands. There is a
single secondary band not very well defined passing over the operculum : the rest of
the head is almost uniform in colour.

The anterior part of the tail, behind the last of the principal dark bands, is lighter
than any other part of the body, its tint being yellow, while the rest of the tail is dark
brown, the colour being here chiefly situated in the membrane between the rays. The
tips of the dorsal and anal fin-rays are, as in the preceding species, opaque white. The
Ijrightness of the red tint in the coloration fades considerably after death, approximating
more to grey.

What was said of the relation of the colour to the scales in the preceding species
applies to this species also, but to a less degree; the extreme edge of every scale in the
lighter parts is brown, but each scale is everywhere more uniform in colour than in
vulgaris or lascavis.

This species is well marked, and has generally been recognised by ichthyologists
since its first discovery. It was first distinguished in England by Donovan, who
obtained a single specimen from the London • market in 1807. He described and
fitTured it in his "British Fishes" under the name Pleuronectes variegatus as a nondescript
(new) species, although it has since been found that Duhamel had previously described
it in his " Poissons de la France " under the name Pole panachee. Donovan's coloured
figure is fairly good, but it represents the markings across the body as somewhat

E 2

irregular interrupted stripes, instead of regular dark bands. It is possible that in
Donovan's specimen the markings were as he figured them, but I have never seen such
a variety of colouring, and it is more probable that in the single dead specimen from
the market he did not perceive the markings accurately.

The species was independently described as new by Eisso in his "Ichth. de Nice": that
his species is the same is evident from his accurate description of the colour and
markings and some other characters. He gave it the name Pleuronectes mangilli, after
the surname of one of his contemporaries. In his later work, the " Hist. Nat. de I'Europe
Moridionale," he calls the species Rhombus mangili. He gives no figure.

Yarrell, in his first edition, gives a description and a woodcut from a specimen from
Cornwall, but his figure looks as if it had been copied from Donovan's plate. YarreU
incorrectly identified the species with the Solea lingida of Eondelet, the Linguatula of
Cuvier, a mistake which he afterwards corrected in his supplement.

Bonaparte gives an excellent description and a coloured figure of the species under
the name Solea iiiangilii, identifying it with Eisso's species. His figure beautifully
shows the dark transverse bands terminating at either end in black blotches which
extend on to the fins.

Gunther in his Catalogue gave a complete and correct account of the synonymy
of the species ; his list of synonyms .shows that the species has been described
independently at least four times, first as the Pole panachee by Duhamel, then as
PL variegatus by Donovan, as PL microchirus by Delaroche, and as PL mangilli
by Eisso.

Moreau and Day give good descriptions of the species. The former gives no figure;
the figure of the latter is not good, it gives the markings very incorrectly.

CHAPTER VI.

SOLEA LUTEA, Bonapaute.

[Plate VII, Figs. 3 and 4,]

Synonymy.

' Sulea parva sive lingula," Rondeletius, 1554, Be Fiscihus Marini!-, xi, c. 15, p. 31?,

with fig.
'La petite Sole," Rondelct, 1558, French edition.
' Pleuronectes luteus," Risso, 1810, Ichth. de Nice, p. 312.
'Rhombus lutens," Risso, 1826, Hist. Nat. Eur. Mer., t. iii, p. 257.
' Solea lutea," Bonaparte, 1841, Fauna Italica, t. iii, p. 28.

'Monochirus minutns," Parnell, 1837, Mag. Zool. and Bot., vol. i, p. 527, pi. 16, No. 2.
' The Solenettc," Yarrell, 1839, Brit. Fishes, first edit. Suppl., p. 36.
'Monochirus linguatulus," Thompson, 1839, Ann. Nat. Hist., vol. ii, p. 405.
■ Solea lutea," Giinther, 1862, Cat. Brit. Mus., vol. iv, p. 469.
' Solea miuuta," Giinther, 1862, ibid., p. 470.

Total length . |

Sex?

Male.

Female.

5-2 cm.

11'6 cm.
4Ain.

73 cm.

2iin.

Ill cm.
41 in.

Lengrth "[
height/

3t^

Length ■]
head J ' " '

5tV

2r. 1 1.

3 r. 11.

4 r. 11.

6 r. 3 1.

L.l

—

Vert

—

— -

The above table includes the characters of only a very small number of specimens, as
I have not had an ojjportunity of examining more. The measurements of the total
length show that this is the smallest species of the five. The head is longer in

proportion to the total len_<ftli than in any of the otlier sjiecies; the proportion of
greatest breadth to length is about the same as in vulgaris and variegnta. But the body
is considerably narrower towards the tail than in either of the other species. The range
for the dorsal fin-rays in the above specimens is 69-77 ; Day gives 65-72. The range
of number for the anal fin-rays in the above table is 53-63; Day gives 50 to 50.
Day gives the lateral line scales as 72 ; the range in my specimens was 62 to 68.

Fins. �� The dorsal fin commences nearer to the mouth than in any of the other
species ; the base of the first ray being on the very apex of the snout, on a level
longitudinally with the U2){)er border of the ventral eye. The jiectorals are as in
variegata rudimentary ; the right is contained al)Out 4^ times in llie length of the head ;
the left is extremely minute.

Eyes. — The dorsal is one-half its longitudinal diameter in front of the ventral and
less than its diameter from the edge of the snout ; they are very close together, the
distance between them eipial to half tlie longitudinal diameter of either.

Nostrils on the right side in their usual position, the posterior short and s:nall, the
anterior tubidar and long ; on the left side similar to those of variegata.

Mouth strongly curved downwards as in vulgaris; snout rounded as in tliat
species.

The villi on the lower side the snout are arranged in the same manner as in
variegata.

The scales absolutely are smaller than in either of the other species, though, as shown
by the number of scales in the lateral line, they are in proportion to the length of the
body lai-ger than in the other sj^ecies ; and they are not so broad in proportion to their
length as in variegata. One of the scales from the middle of the body has 21 rows of
spines, 4 spines in each of the middle rows (PI. XIV, 5).

No branches of the lateral line are visible externally on either side of the head.

Colour. — It is curious that, although in the character of its pectoral fins and of the
villi of the lower side of the snout, this species closely resembles viriegata, its markings
are almost the same as those of rnlg'tris. In other words, there is here no correlation
between the marking and other characters.

The ground colour of the right side during life is a dull reddish-brown. On this
ground there are dark brown spots arranged as in n/ljiaris ; there are three principal
longitudinal rows of these, of which the central row contains usually five spots, the
dorsal and ventral rows seven or eight. Alternating with the brown spots are light
blue ones representing the white spots of vulgaris. There are also two interniediate
longitudinal rows of dark spots, lint the markings of the dorsal and anal fins differ
considerably from those of vulgaris ; these fins show no longitudinal bands of (-olour,
but numerous narrow transverse stripes, each sixth or seventh ray being coloured a
deep black ; the rest of these fins has a yellowish colour which is deepest towards the
base of the fins. The anterior part of the head is free from spots, the tail has a little
black at its middle third.

This species was first recognised as disliuct in Britain Ijy raniell, wliu described it in
tlie "Magazine of Zoology and Botany," Vol. I, 1837, under the name Monochirus
rtdnutus. He believed that it had never been described before, and therefore "ave it
the name minutus. pLcing it in Cuvier's sub-genus JiJonochirus. He gives a figure of
it, and mentions as its specific character that every sixth or seventh ray of the dorsal
and ventral fin is black ; he obtained his specimens at Brixham from the travi^lers.
W. Thompson in the "Annals of Natural History," Vol. II, 1839, identified Parnell's
species minutus with that mentioned by Cuvier in the " Ivegne Animal," under the name
Linguatida, which is the Solea parva sine lingu/a of Eondelet. Cuvier defines the
Monochires as those specimens of Solea in which the pectorals are minute, the left
being either very minute or altogether wanting.

I have consulted a French translation of Ivondelet's original Latin work ; this trans-
lation is dated "Lion " (Lyons), 1558. The names here given are La petite Sole, and
Solea lingula, and though no characteristic specific features are mentioned in the
description, the figure given agrees very well in shape with specimens of the present
species ; this figure shows the left side of the fish.

Yarrell introduced a figure and description of Parnell's AlonochiruH minutus into his
supplement to the first edition of his " British Fishes," not having been acquainted with
the species when he published the book.

Parnell's species was described as distinct by Dr. Gunther in the British Museum
Catalogue, under the name Solea minuta from two specimens, one, a dried skin, from
Yarrell's collection, the other, stuffed and dried, from Brixham.

Moreau, in his " Poissons de la France," 1881, in describing Microchirus luteys, the
Solea lutea of Bqnaparte, suggests by means of a note of interrogation that Solea minuta
is a synonym of that species, and Francis Day, in his " Fishes of Gfeat Britain and
Ireland," states without reservation that the two species are identical.

Dr. Glinther in his Catalogue describes one specimen of Bonaparte's Solea lutea. He
has informed me that he now considers the two species to be identical, and after
examination of English specimens and Mediterranean specimens of lutea at tlie British
Museum, and comparing them with the various descriptions, I h^ve no doubt myself
that lutea and minuta are the same species.

This spepies was first described by Eissq, in his "Ichthyologie de Kice," under the name
PleuronerAes luteus, and his description is sufficiently accurate for its identification.
The same author, in his " Histoire Naturel de I'Europe Meridionale," placed the species in
the genus Rhoinhus, calling it Rhombus luteus. Bonaparte, in Ins " Faipa Italica," gives
an excellent description, and two very good coloured figures. He describes the colour
of the body, apart from the fins, as a uniform golden yellow without spots, Ijut in
Mediterranean specimens in the British Museum I found the markings which I have
described above in English specimens.

CHAITER VII.
SOLEA GREENII, Guntiier.

" Solea Greeuii," Giinther, 1889, Ann. Mag. Nat. Hist., vol. iv, No. 2-1.

Length Lennjtii

Sex, female. Total length, 19 cm. (/ Jj in.), ■y^^^-^ = over 3^. ^^^ = 6^.

D. 81. A. 67. C. 19. Pt. 4 r. 2 1. I'v. 5. LI. 138.

The above are the characters of a single specimen obtained by Mr. Bourne, Director of
the Plj-mouth Laboratory, by the trawl on board H.M.S. "Eesearch," on July 13, 1889,
in long. 49° 5' N., lat. 11° 14' W., at a depth of 217 fathoms.

The characters of the species are, as Dr. Giinther points out, intermediate between
those of vulgaris and variegata. The filaments on the under side of the head are
uniformly distributed as in vulgaris, but there is a series of transverse rows of such
fdameuts along the whole length of the lateral line on the lower side, a character I
have not seen in any other species. The pectorals are rudimentary as in variegata.
The cephalic curve of the lateral line runs backwards before turning forwards. In
colour the upper side is an almost uniform brownish-grey in spirit ; but there are
also dark blotches or large spots ; there are six of these along the dorsal edge of the
body and five along the ventral ; also two along the lateral line posteriorly ; these two
with two dorsal and two ventral spots form two almost continuous transverse bands ;
another interesting transition from vulgaris to variegata. The outer half of the
longitudinal fins has also a good deal of black pigment.

The ground where Mr. Bourne's specimen was taken was a fine grey sand containing
Foraminifera. Mr. Green also obtained only a single specimen from a depth ui
l.)0 fms. 47 miles west of Bull Eock off Balinskellys Bay.

Thus this species lives just beyond the 100-fathom line in llial \)a.vt of the Atlantic
which lies S.W. of Ireland.

Part II.

MORPHOLOGICAL

CHAPTER I.

THE OSSEOUS SKELETON.

The whole body of the sole is covered by the skin, which as everyone knows is so slightly
attached to the parts beneath it that it can be stripped off as a definite continuous
membrane. Beneath it is found the flesh, wliich consists of the muscles, by the
contraction of which all the movements of the fish are produced. The muscles are
attached to the bones which together form the skeleton. In the middle region of
the body on the ventral side is a cavity with smooth walls, within which are contained
the entrails, or viscera, consisting of the organs of digestion, excretion, and
reproduction. The principal organ of digestion is the digestive tube which leads from
the mouth and after various convolutions opens to the exterior again at the vent or
anus. The organs of respiration or gills are fringes supported on rods between which
are slits or clefts by which the cavity of the throat opens on each side into a gill
chamber. Each gill chamber again opens by a single aperture to the exterior. The
blood vessels ramify in the substance of aU the organs now mentioned, but the heart
which keeps the blood moving in circulation is contained in a special cavity which is
separate from that containing the viscera. The skin and the membrane lining the
digestive tube become continuous with one another at the mouth and anus, and at the
gill-clefts. The nerves also ramify in the substance of the muscles and other organs,
but, excepting the sympathetic system, they all radiate from the brain and spinal cord
which are contained in a chamber on the dorsal side of the skeleton, the brain being
contained in the cavity of the skull, the spinal cord being enclosed by a series of
arches formed by processes of the spine. Some of the nerves convey the impressions
received by the senses to the brain, and may be regarded as proceeding from the sense
organs to the brain ; the principal sense organs are the skin, the e3'es, the ears, and
the olfactory organs. The other nerves conduct impulses from the brain and spinal
cord to the muscles and other organs causing the former to contract and regulating
the functions of the latter.

The structure and relations of these various organs can be made most easily
intelligible by describing the skeleton first.

The Skull. — -The central part of the skeleton consists of tlie skull and the vertebral
column, the latter being composed of a longitudinal series of distinct bones, the

F 2

vertebras: the skull here meaus the bony structure which coiitaius the braii>, and
supports the eyes, ears, and olfactory organs, and which remains as a united whole
when the soft parts of the head of the fish are removed by boiling or otherwise. The
form of the skull is shown by four drawings of it on Plate XI (Figs. 5-8). It consists of
two main portiou.s. The posterior and larger portion has a somewhat cylindrical shape,
and encloses a cavity m which the brain lies in the entire fish, this is the cranial
portion ; the anterior or facial portion does not enclose a cavity, but may be said to
consist of three separate processes from the brain-case which unite together at their
anterior ends. One of these processes is (apparently) on the right side of the head of the
fish and separates the eyes from one another ; it may be called the interorbital septum,
the not very definite concavities on either side of it in which the eyes lie being the
orbits.

If the skuU is placed in the position it occupies when the entire fish is held vertically
upright on its ventral edge, that is in the same position in which a symmetrical fish
swims, the cranial portion of the skull will be seen to be almost perfectly symmetrical
while no symmetrj- is visible in the facial portion. Comjjaring the cranial portion
with the corresponding part of the skuU of a symmetrical fish, we can recognise in its
walls the same bones as in the latter, the walls being made up of these bones firmly
united at their edges. These edges are usually irregularly toothed so as to fit into
each other, and the lines of junction are called sutures. The sutures can be traced out
with care in the entire cranium, Init where they are obscure the exact limits of the
component bones can be found by boiling the skull and pulling the separate bones away
from one another. The outlines of these bones are indicated on the figures of the
skull. Tlie auditory organs in the entire fish are situated within the convex side walls
of the cranial portion, and the bones of this part have names with the suffix "otic,"
implying their relation to the ear.

The back of the cranial portion is called in all vertebrates the occiput and the bones
of this part occipital bones. In this wall of the cranium is a large circular aperture,
the occipital foramen, through which the spinal cord is continued forwards into the
brain. Below the occipital foramen is a solid bone witli a conical depression in its
posterior surface, this is the basi-occipital, and the depression marks the place where
the first vertebra is attached to the skull. At the sides of the occipital foramen
inferiorly are the two ex-occipital bones, ex.o., one on each side. Above these, reaching
to the upper edge of the foramen, are two large somewhat convex bones, the epiotics, ep.o.
On the dorsal surface of the skull there is in the centre a large median flat bone, the
supra-occipital, s.o., whicli in many vertebrate skulls extends to the edge of the occipital
foramen, but is here separated from it by the epiotics. On either side of the
supra-occipital is a parietal bone, pa. In either lateral wall of the cranium, adjoining
the edges of the ex-occipital, epiotic, and parietal, there is a somewhat large Ijone
having a rugged process projecting outwards ; this is the pterottc bone, pt.o. In front
of this is a shghtly smaller square bone, the sphenotic, sp.o. Between the pterotic

and (he basi-occipital is a small square bone, the ojjisthotic, op.o., and in front of this
below the sphenotic is the prootic, pr.o.

Adjoining the edges of both prootics and sphenotics, and attached behind to the
basi-occipital, is an elongated keeled bone which projects forwards to form the ventral
process of the facial portion of the skull : this is the jmrasphenoid, pa.s ; its posterior
portion forms the anterior part of the floor of the cranium. Attached to the ventral
surface of the parasphenoid is a bone which is elongated dorsally and projects
ventrally into a cylindrical knob ; this is the vomer, vo. The interorbital septum is
formed by the anterior processes of two bones whose flat posterior portions are nearly
symmetrical and form the anterior part of the roof of the cranium, attached behind to
the edges of the supra-occipital and parietals. These are the frontal bones, r.f., l.f.
These bones are, as compared with the corresponding bones of the skull of a
symmetrical fish, the most distorted of all the bones in the skull of the sole. In a
symmetrical fish the frontal bones are perfectly symmetrical, and their anterior parts
lie above and between the symmetrically placed eyes. In the sole also their anterior
processes are between the orbits, but have been twisted round through an angle of
90°, so that the middle line of the dorsal surface of the cranium when produced
forwards does not pass between the frontal bones, but a line drawn in a longitudinal
direction over the right surface of the cranium, across the pteroic aud sphenotic bones
does pass between their anterior processes. This shows that the dorsal eye of the sole
is really the left eye, and that the eyes and orbits with the interorbital septum have,
as compared with those of a symmetrical fish, been twisted round through an angle of
90° while the cranial portion of the skull remained stationary. Connecting the
inferior process formed by the parasphenoid and vomer with the interorbital septum
anteriorly is a single bone having a somewhat hooked process in front — the mesethmoid,
raes.e. Attached to the mesethmoid posteriorly on the left side, and joined also to the
parasphenoid, is a large flat bone concave towards the right, the left ectethmoid, ect.e.
A posterior process of this bone unites with an anterior process of the left sphenotic to
form the third process of the facial region of the skull. The right ectethmoid is a small
ring-shaped bone attached ventrally to the anterior end of the frontals and to the
mesethmoid.

Between the origins of the three facial processes the cranial cavity opens anteriorly
by a wide aperture. There is a large round foramen in the left ectethmoid, leading
from the left orbit to the external surface of the facial part of the skull. On the upper
surface of the cranial portion there is a small foramen in the flat posterior portion of
each frontal bone, the left foramen being larger than the right. At the anterior and
inferior edge of each sphenotic bone there is a considerable indentation, which, with a
corresponding indentation in the edge of the parasphenoid, forms a large foramen, the
sphenotic foramen. That of the left side is twice as large as that of the right, and in
front of the former are two small foramina which are absent on the right side.
Through each prootic bone is a smaller foramen, the prootic foramen ; the left of these

is a little larger than the riglit. In the posterior part of each opisthotic bone is a
minute opisthotic foramen. In each ex-occipital there is a considerable foramen
directed downwards, and behind this a minute foramen directed outwards.

It now remains to call attention to the form of the outer surface of the skull. The
pterotic process projecting outwards from the pterotic bone has already been
mentioned. A similar but longer and flatter process projects from the sphenotic
bone above the sphenotic foramen ; these processes serve for the attachment of muscles.
Below these two processes are two smooth depressions in which are articulated the two
heads of the hyomandibular, a bone which is connected with the jaws and branchial
apparatus. In the centre of the supra-occijiital bone is a somewhat elongated crest.
At each side of the dorsal surface of the skull posteriorly is another crest longitudinally
directed, formed partly from the pterotic, partly from the parietal bone : this may be
called the parietal crest ; the one on the right is larger than that on the left. These
crests also serve for the attachment of muscles. At the anterior part of the basi-
occipital bone are a pair of conical prominences with their broad bases downwards :
these are continuous with one another in the median plane. The left ectethmoid bone
sends ofl" a curved process towards the right side.

The Vertebral Column. — Any one of the vertebrse from the middle third of the spine
consists of a somewhat cylindrical central mass, the centrum, and two elongated
processes or spines, a dorsal and a ventral. The centrum has the form of two truncated
hollow cones placed with their narrower ends towards each other and united together
by a solid disc. The conical hollow at the anterior and posterior surfaces of each
centrum with the corresponding hollows of the adjacent vertebrae, enclose cavities
which are filled by an elastic gelatinous tissue. The lateral depressions at tlie right
and left sides of the centrum are each divided by a longitudinal ridge of bone. The
dorsal spine really consists of two hollow bony tubes which diverge at their bases,
where they are united with the centrum towards the anterior edge of its dorsal surface,
and which are united firmly together in the median plane of tlie fish's body for tlie
greater part of their length. The diverging legs of the spine form a pointed
arch, and through the series of these arches runs the spinal cord, wliicli is thus
protected from pressure by the bony arches. The leg of the spine on each side of the
vertebra is expanded longitudinally where it joins the centrum, and in this expanded
part are two foramina, through which the ventral and dorsal roots of a spinal nerve
pass. The ventral spine of the vertebra has a similar structure, but the arch between
its legs is larirer, and through the series of these arches run blood vessels. There are
50 vertebraj altogether, and the 11 ih to the 50th have tlie structure now described.
The dorsal and ventral processes in all these are very long, four to five times as long as
the centrum. In the first of these vertebnc the spines are almost at right angles to
the centrum, but towards the posterior end they slope more and more backwards.
The spines increase in length slightly towards the centre of this region, and again
decrease slightly at the posterior end. The centra become longer and narrower

towards the posterior end. "Behind the last of these vertebras are bones which
terminate the vertebral column : these consist of a central fan-shaped bone, the anterior
end of which is shaped like the anterior part of a vertebra, and is connected with the
posterior face of the last vertebra by membrane, and two other flat bones, dorsal and
ventral to the central one. The central bone expands posteriorly in the median plane
of the body into a triangular plate, which is partially divided by radiating furrows into
a number of rods. These rods are known from their development to represent the
ventral spines of a number of vertebrae fused together into the fan-shaped bone. The
flat bones dorsal and ventral to the fan-shaped bone are similarly divided, but are much
narrower : these are obviously also dorsal and ventral s})ines of the more anterior of
the vertebra3 represented by the fan -shaped bone. The rays of the caudal fin articulate
with the ends of these rods (PI. X).

The ten anterior veriebrte differ considerably from the posterior 40. All of them
have dorsal spines except the first : these spines resemble those of the vertebrae already
described, except that they become thicker and shorter and more inclined forwards
towards the anterior end. The dorsal spine of the second vertebra leans forward so
much that it is in contact with the posterior face of the skull. The fifth to the tenth
vertebra have ventral spines also, but these are of rapidly decreasing length from the
tenth to the fifth, and are also much inclined backwards. The first four vertebraj
have no ventral spines. The second to the eighth vertebraj, seven in all, bear very
slender short ribs which are not processes of the vertebrte, but separate bones which
articulate with the centra at the upper side of their lateral ridges. The first vertebra
is rudimentary : its centrum is very narrow antero-posteriorly, and it has two small
dorsal processes which lie along the front edge of the base of the dorsal processes of
the second vertebra, but do not unite to form a spine.

The centra of all these vertebrae are united together in the following way. The
posterior face of each vertebra has, as we have seen, a conical depression or cavity : the
rim of this cavity is united firmly to the corresponding rim on the anterior face of the
succeeding vertebra by strong tough membrane, which is continued over the surface of
the vertebras, which is in fact i)art of the periosteal membrane. The closed cavities
formed by the juxtaposition of the conical depressions are filled by a firm elastic
gelatinous tissue which forms so many elastic pads b9tween the centra. The connection
of the ex-occipital bone of the skull with the first vertebra is of the same kind as that
between adjacent vertebrae.

Closely connected with the vertebral column is the system of bones which forms the
framework and support of the median fins. Placed like the vertebral spines in the
median plane of the body and extending outwards from the ends of those spines are a
great number of bones shaped somewhat like paddles. These are the intcrspinovs hones.
Each consists of a long slender shaft and a broad head expanded in the median plane
They are placed with their shafts towards the vertebrte, their heads projecting
outwards. The ends of the shafts lie alongside the ends of the spines of the vertebra

in the intervals between the spines, hence the name of these bones. There are usually
two interspinous bones between two adjacent vertebral spines, never more than two,
but in many cases only one : one interspinous bone, in Fig. 1 on PI. X, has two shafts
to a single head, the end of a vertebral spine lying between the two shafts. In the
middle region of the body each interspinous bone has a small wing-like expansion on
each side of the shaft just below the head. On the dorsal side the interspinous bones
are perpendicular to the vertebral column at about one-fourth of the whole length
from the anterior end of the body : from this region to the tail they slope more and
more backwards ; from this region forwards they slope more and more forwards. In
front of the dorsal spine of the second vertebra there are three short stout interspinous
l:)ones whose inner ends lie close to the middle dorsal line of the cranial portion of the
skull. In front of these is a large curved spine-shaped bone pointed at its outer end,
stout and l)luiit at its inner, which curves forwards almost parallel to the axis of the
skull. To the dorsal side of this bone are attached two short interspinous bones.

On the ventral side the interspinous bone in front of the ventral spine of the eleventh
vertebra is almost perpendicular to the vertebral column: from this point to the tail
region the interspinous bones slope more and more towards the posterior end. In
front of the same interspinous bone there is one other free interspinous bone slightly
inclined forwards, and in front of this is a stout curved cylindrical boTie, which
terminates the series anteriorly and forms the posterior boundary in the median plane
of the main body-cavity of the fish. This cylindrical bone bears four shortened
interspinous bones which are inclined forwai'cls and are successively shorter and shorter,
the most anterior being merely a small head without a sliaft.

The fin-rays of the dorsal and ventral median fins, of the dorsal fin and anal fin as
they are usualh' termed, are not articulated directly with the outer ends or "heads "
of the interspinous bones : to these heads are attached a series of nodules of cartilage,
elongated from before backwards, and somewhat cylindrical in shape. Except in a
certain region each of these nodules is situated between two adjacent heads of
interspinous bones, attached to both of them. The region excepted is the anterior
part of the dorsal series, where one nodule is attached separately to each head.

The fin-rays have the following structure. Each ray is compound and constructed
somewhat in the same fashion as a vertebral spine. It consists of a right and left half,
which are separate and divergent at their inner ends, attached together in the median
plane of the fish for the outer seven-eighths of their length. The divergent ends embrace
one of the cartilaginous nodules previously described, Ijestriding it as a man bestrides a
saddle, and are attached to it by fibrous membrane in this position. One of the halves
of the fin-ray thus belongs to the riglit or coloured side of the fin, the other to the left
or white side. In consequence of the mode of attachment described, the fin-ray can
only move on the cartilaginous nodule backwards and forwards : as a matter of fact
its motion is limited between a jiosition in which it is perpendicular to the longitudinal
axis of the fish, and a position in whicli it lies inclined backwards from its attached

base, and almost parallel to the axis of the fish. The outer part of the fiii-ray formed
of the two united lateral halves bifurcates in an antero-posterior direction into two
divergent branches. Thus the outer half of the lin-ray consists of two diverging
branches both in the plane of the fin, one anterior and one posterior, but each of these
is made up of two lateral halves glued as it were together lengthwise. Thus if a lin-
ray is separated, and a knife passed between the diverging right and left legs of the ray,
the whole ray can be easily divided into a right half ray and a left half ray, and each
of these is forked at its outer half length into two branches. The basal portion of the
fin ray is solid, but the outer five-sixths, including the two forked branches, consist of
a series of short cylindrical bony pieces united by flexible membrane. Thus tlie ouler
part of the fin-ray resembles somewhat the series of vertebral centra on a small scale
and without the spines, if we suppose the series of centra after being single for a
certain length to branch into two series having the same structure.

The tail fin-rays resemble those of the dorsal and anal fins in general structure, but
are more branclied : in them each of the two original branches divides again into two,
and some of these again into two : the branching of the ray is always dichotomous,
that is, a branch when it divides splits only into two smaller branches, but of the four
secondary branches all do not always divide : thus the fin-ray terminates in seven or
eight branches spread out like a fan. The caudal fin-rays are not in connection with
either interspinous bones or cartilaginous nodules, but are articulated directly to the
terminal bones of the .vertebral column, and to the spines of the last vertebra.

The skeleton of the paired fins is closely related to that of the branchial region and
will be described in connection with it.

The Jaws and Branchial Arches.

We have now to consider the bones of the jaws and branchial arches, and other
bones connected with the skull. The more superficial of these bones are shown in
Figs. 1 and 2, PI. XI. The bones of the right side. Fig. 1, differ considerably in size
from those on the left, although in their relations the bones of the two sides correspond
to one another. The bones of the right side are as follows. The two sockets in the
side of the cranial portion of the skull, in the pterotic and sphenotic bones, contain
the two rounded heads of a flat elongated bone which extends downwards and
somewhat forwards. This is the hyomandibular, hm. To the lower end of this bone is
attached a system of flat bones which projects horizontally forwards into a smooth
knob with which the lower jaw is articulated, and sends off upwards and forwards a
flat band of bone, the end of which is again attached to the skuU at the side of the
vomerine projection. At the posterior border of the hyomandibular and the system
of bones just mentioned is a crescent-shaped bone, which is firmly attached to the
others and acts like a splint, binding them rigidly together. This is the jireopeiriilar, \)o.
The separate bones of the system connected with the lower end of the hyomandibular

are as follows. Directly attached to the end of the hyoinaudibular is seen the end of
a bone which passes downwards beneath the preoi^erculum out of sight, and is
connected with the system of branchial arches which occupy a deeper position. This
is the stylohyal. Anterior to this is a flat bone which projects into the quadrate in its
under surface, this is the si/mplectic, s. Dorsal to this is a flat somewhat concave bone
with a triangular outline, the metapterygind, mt. The triangular bone, which is at the
anterior end of the series, and which supplies the rounded head to which the lower
jaw or mandible, m., is articulated, is the quadrate, q. Running upwards from the
quadrate dorsally are a pair of splinter-like bones, the anterior of which is the
jHerygoid, pt., and the posterior the mesopterygnid, ms. Connecting these with the
skull at the side of the vomerine process is the palatine, pa. It will be seen that all
these bones are somewhat larger on the left side. Fig. 2, than on the right, Fig. 1.
The superiority is especially well marked in the pterygo-palatine bar, which is broad
and strong on the right, narrow and delicate on the left.

Attached to the posterior edge of the hyomandibular and preopercular is the oper-
culum, which is chiefly composed of the three bones,o.,io., so. : these are the opercular, o.,
which is articulated to a knob jjrojecting downwards on the posterior side of the
head of the hyomandibular, the intenqurcular, i.o., and the sub-ope rcular, s.o., which
are only held in their places by the fibrous tissue of the operculum. The lower jaw
is called the mandible, which consists of three bones, the articular, angidar, and dentary,
fltted and firmly united together : the upper jaw consists of two bones, the maxilla,x,
and the prema.villa, p x. All these bones are much smaller on the right or ujjjjer side
of the head than on the left or lower ; this is especially true of the maxilla and
premaxilla which, as the figures show, are almost rudimentary on the right side, and
very large on the left. On the left side the maxilla is entirely excluded from the edge
of the lip ; on the right side its posterior process forms part of that edge. The
mandible on the right side has the form of an elongated bar, on the left side it is a
broad triangular stout plate, the dorsal edge of which is strongly convex and bears a
patch of rod-like teeth, biting against a concave larger patch of similar teeth in the
premaxilla. On the left side the end of the premaxilla articulates with a knob on the
mandible, an arrangement which makes the bite much more effective ; on the right side
there is no such articulation. The two mandibles are firmly united together anteriorly
in what is called the symphysis of the mandibles. The anterior ends of the maxillie
and premaxilla:^ are all firmly united together and to the lower side of the mesethmuid
bone by fibrous membrane.

If we now dissect away all the bones above described except the hyomandibular,
we find the bones of the branchial a])paratus lying beneath them as shown in Plate XI,
Fig. 3, from the right side. The gills themselves are vascular fringes which project
outwards and backwards from a series of bars ; between these are the clefts by which
the water passes from the cavity of the throat to the gill chamber and so to the exterior.
These bars are called the branchial arches, from their curved shape, and each bar is

supported by a series of bones called a (bony) branchial arch. Tlie first of these arches
is different from the rest, and is called the hyoid arch. It is attached to the end of the
hyomandibular, and consists of, 1st, the small cylindrical bone, marked 2 in the figure,
and called stylo-hyal; next, two broad stout bones placed end to end, 3 and c.h. in the
figure, the epi-hyal and cerato-hyal ; and finally, two cubical bones placed side by side,
the hypo-hyals, h.h. Between the hypo-hyals of the opposite sides is inserted a bone
which is flattened in the median plane of the fish's body : this is usually called the 1st
basi'branchial, although in the sole it is connected only with the bones of the hyoid
arch. Above it is a cylindrical bone called the basi-hyal or entoglossal, b.h.

Attached to the lower edge of the epi- and cerato-hyals are a series of long bones like
curved spines, 3 to the epi-hyal, and 4 to the cerato-hyal. These are the hranchiostegal
rays, and they support a curved membrane which extends inwards from the inside of
the lower edge of the operculum, and in ordinary respiration closes the lower part of
the opercular aperture.

The 1st branchial arch is composed of a chain of bones of which the most dorsal
attached to the side of the keel of the parasphenoid bone is the pharyngo-hranchial, 8,
next to this is the ejn- branchial, 9 : these two are directed downwards and outwards, but
the cerato-branchial, c.b. 1, which succi^eds, passes inwards and forwards; it is followed by
the hypo-branchial, which is joined to the median 2nd basi-branchial, b.b. 2. The other
arches, four in number, exhibit a similar plan of structure, but the last is much reduced.
The pharyngo-branchials of the 2nd, 3rd, and 4th arches are not styliform, like that of
the first, but are broad and flat; the 3rd and 4th are fused together, the 2nd is united
to them, and all three bear teeth on their lower suifaces and form together the npper
pharyngeal bone. The second hypo-branchial is articulated with the third basi-
branchial, and the third hypo-branchial comes into slight connection with the posterior
end of the same median bone. The two hypo-branchials of the fourth pair of arches
are fused together to form a rhomboidal cartilage in the middle line behind the third
basi-branchial. The fifth arch is represented only by a cerato-branchial on each side,
which meets its fellow in the middle line ; these two bones bear teeth on their upper
surface, and being situated in the ventral wall of the throat they bite against the upper
pharyngeal teeth, forming a second masticatory apparatus ; these bones of the fifth
arch are usually called the lower pharyngeals. The relations of the hyoid and branchial
arches of the opposite sides are shown in Plate XI, Fig. 4 where they are seen spread
out with their internal surfaces upwards.

The pectoral and pelvic fins on each side are attached to the posterior border of a
bony arch which extends from the back of the skull downwards, curving first back-
wards and then forwards, and meeting its fellow of the opposite side at the ventral
edge of the body. This bony arch forms the posterior border of the opercular cleft. It
consists of the following bones : 2i. post-temporal, 25, Fig. 3, which is forked anteriorly and
attached by membrane to the posterior wall of the skull, the upper branch of the fork
being connected with the epiotic, the lower with the opisthotic ; a supra-clavicle, 26, an

G 2

elongated bone joined on to the lower end of the post-temporal, a clavicle, 27, which curves
forwards, and is shaped like a trough the cavity of which is posterior, the trough being
V-shaped in section. The clavicle is connected at its lower end, in the median ventral
line, with its fellow of the opposite side.

The pectoral fin is supported by a flat basal plate attaclied within the upper part of
the trough of the clavicle ; this plate consists of two bones united by cartilage ; the
upper of these, 29, is the scapula ; the lower, 30, the coracoid. The pectoral fin-rays
are articulated to the posterior cartilaginous edge of this basal plate directly as the
caudal fin-rays to the fan-shaped terminal bone of the vertebral column.

The pehic fin is similarly supported by a triangular single bone, 31, which is attached
to the lower end of the clavicle. It is usually called the pubic bone, thougli it is
probably homologous, not with any part of the pelvic arch of Elasmobranchs, but
with the basal cartilages of the pelvic fin in those forms.

A flat bone in the median plane extends forwards from the junction of the clavicles
to the lower edge of the first basi-branchial. This bone, marked 28 in Fig. 3, has been
called the urohyal by Huxley, basi-branchiostegal by Parker, but has really nothing
to do either with the hyoid arch or the branchiostegal membrane ; it is better to call
it simply the iwjuhir bone. Posteriorly it sends off a pointed ventral process, while
the anterior three-fourths of it form a band of uniform width.

CHAPTER II.

THE FIBROUS MEMBEANES AND MUSCUL.1TUEE.

The Fibrous Membranes,

All the bones of the skeleton now described are bound together by strong fibrous
membranes. . In the median plane a tough membrane of this kind extends from bone to
bone everywhere except in the median visceral cavity, so that the whole body of the fish,
excluding the region of this cavity and the ventral region of the head, is divided into
two lateral similar halves by a continuous partition consisting of a tougli membrane
supported by the bony framework. The structure of this partition in fact resembles
that of one of the screens often used in our rooms to keep off draughts, the bones
corresponding to the wooden framework, the membrane to the canvas stretched over
it. But there is in the organic structure a more intimate connection between the
fibrous membrane and the bony framework. Every bone is clothed externally by a
tough fibrous membrane, the periosteum, and this is actually continuous with the
membrane which connects the bones together. The whole structure is as it were a
continuous deposit in which certain parts have been differentiated by the deposition
of calcareous compounds and structural modification to form bone. Yet, tough and
strong as the fibrous membrane is in its natural state, firm as it is found to be when
the muscles are dissected away in the dead fish, if the fish is boiled for a short time it
dissolves, and the bones all fall asunder. The reason of this is that the basis of the
material of which the fibres consist is gelatine, and therefore though they retain their
strength and structure during life, or in cold water, when subjected to the action of
boiling water their structure is destroyed and they become simply a mass of soft liquid

jelly.

The median fibrous membrane is continuous laterally with other membranes which
are placed at right angles to it and connected with the vertebrae and interspinous
bones. These lateral membranes run between the various muscles, which are attached
to them, and externally become continuous with the derma, or deeper fibrous layer of
the skin. The principal of the lateral membranes on each side runs longitudinally
along the centre of the vertebraj from the skull to the tail, and extends outwards to
the skin, thus dividing the muscles of each side of the body into a dorsal and a ventral

half. Shorter membranes transverse to this divide the muscles again into a series of
oblique flakes which are seen separating from one another in a boiled fish brought to
table.

In a symmetrical fish the median skeletal partition formed by the vertebras and
their spines and the interspinous bones terminates at the back of the skull, but in the
sole it is extended still further anteriorly over the dorsal side of the skull to the
extremity of the snout. The attachment of the membrane to the skull runs at first
along the median dorsal line of the skull, that is, the morphological median line, but
anteriorly it runs to the left of this line. It crosses the base of the left frontal bone
and is continued alcng the edge of the larse left ectetlimoid and finally to the left edge
of the mesethmoid. '.riius, morphologically, the median skeletal partition is continued
forwards on the left side of the facial region ventral to the left eye, though actually
the anterior continuation is in the same plane as the main part of the partition. This
anterior continuation is of course due to the anterior development of the dorsal fin
Avhich is supported by it.

Mtisculaiure.

A general view of the muscles of the right side of the sole is given on Plate XII.

The white parts in that draAving represent the white tendinous membranes, excepting

some of the bones of the head which are smoothly shaded, and the fin-rays : the

shading of fine lines indicates the muscles, the lines being drawn in the direction of

the muscle-fibres. The principal muscles of the body are the great lateral muscles,

one dorsal and one ventral, separated from one another by the longitudinal fibrous

membrane already described as projecting from the centra of the vertebrae outwards

to the skin. Each lateral muscle consists of a longitudinal series of folded plates or

segments, separated from one another by the transverse membranes previously

mentioned. The fibres in the muscle-segments run in an antero-posterior direction

parallel to one another, and are attached at each end to the transverse membranes, or

to the bones and membrane in the median plane of the body. The transverse fibrous

membranes have a curious folded and twisted arrangement. The outer edge of each,

as can be seen from the illustration, has the form of the letter S. Starting from the

longitudinal lateral membrane it curves first anteriorly, tlien posteriorly, and finally

runs anteriorly again, tluis forming two curves in opposite directiims and a larger outer

portion running obliquely forwards. The membrane itself is deeply hollowed

forwards in the region of the first curve, backwards in that of the second, so

t' .at the inner edge of tlie membrane instead of being S shaped is Z-shaped. This

inner edge of the transverse membrane is attached to the median bones and membrane

in the following way : it runs first along a vertebral spine for a short distance, then

suddenly turns ofT at an angle and runs directly backwards till it reaches the next

spine behind, along which it runs outwards (dorsally or ventrally) for some distance,

and then again leaves that spine and runs obliquely forwards. Thus each transverse
membrane is attached by its inner edge to two adjacent vertebral spines at different
parts of its length, and along the rest of its length- is continuous with the median fibrous
membrane which extends between the spines and the interspinous bones.

The anterior segments of the dorsal lateral muscle are much elongated and bent
forwards, so that their separating membranes are attached to the dorsal surface of the
skull, the anterior interspinous bones and the membrane connecting the latter.

The anterior segments of the ventral muscle covering the visceral region are straighter
than the posterior, and the inner edges of the dividing membranes are not attached to
any firm skeletal structure, but simply to the fibrous membrane which encloses the body-
cavity, the peritoneal membrane. The ventral part of the ventral lateral muscle on
each side is also separated from the median skeletal partition by the posterior prolonga-
tion of the body-cavity.

The posterior muscle-segments, in correspondence with the greater backward slope
of the vertebral spines, are folded to a much greater extent than the anterior. The
terminal segments form a system of muscles which are attached to the bases of the
caudal fin-rays.

It follows from the description that in each lateral muscle there are as many muscle
segments as there are vertebrce, and that each dividing membrane corresponds to a
vertebra Thus the muscle segments themselves correspond to the junctions between the
vertebral centra, an arrangement which allows the vertebral column to be bent in all
directions by the action of the lateral muscles. It is clear that, although it is difiicult to
understand in detail the effect of the complicated attachments above described in the
contraction of the muscles, the general effect of the contraction of the lateral muscles of
one side is to bend the body powerfully towards that side, and it is by this alternate
bending of the body first to one side then to the other that the sole swims through the
water when it rises from the bottom, or swims along the bottom. The lateral muscles
form the bulk of the edible portion of the fish. The lateral muscles of the left or lower
side do not differ in any important respect from those of the right.

The other muscles of the sole are the muscles of the fins and the muscles of the
ventral retjion of the head, and the eve muscles.

The muscles of the longitudinal fins are well developed and important. The caudal
fin-rays are, as has been mentioned, moved by muscles which represent the terminal
muscle segments of the lateral muscles. The dorsal and anal fin-rays are moved by two
distinct systems of muscles. One system serves to erect the rays and to depress them
bv causing them to slope backwards till they are almost parallel to the edge of the
body. The other system moves the rays away from the median plane, either to the right
side or to the left (upwards or downwards in the natural position of the sole). The
muscles of the former system may be called the elevators and depressors of the fin-rays,
those of the other the right and left abductors. The abductors of the fin-rays are
superficial, lying innnediately beneath the skin ; there is a single muscle on each side

to each ray. These muscles take their origin from the fibrous tissue which covers the
lateral muscles and which is continuous with the fibrous layer of the skin. Each
muscle is inserted into the side of a fin-ray outside its articulation, but the end of
the muscle also has connections by means of fibrous tissue with the ends of the
iuterspinous bones.

The elevators and depressors lie beneath the abductors : there is one elevator and one
depressor on each side of the body to each fin-ray. In (he greater part of the fins the
heads of the iuterspinous bones are between the bases of the fin-rays, and each
elevator lies along the posterior half of the side of an iuterspinous bone, while each
depressor lies along the anterior half These muscles are considerably smaller than
the abductors. They are inserted into the bases of the fin-rays in front and behind and
take their origins from the surface of the iuterspinous bones and intermediate fibrous
membrane. Their inner ends extend beneath the outer edges of the lateral muscles,
which are free. The elevators and depressors of the fin-rays are shown in Plate XII.
along the whole of the ventral side of the body and the anterior part of the dorsal
side, while the abductors are shown along the posterior three-fourths of the dorsal side.

The muscles of the rays of the pectoral and pelvic fins are closely similar and require
no special description.

The muscles of the ventral region of the head may be classified according to their
functions into two divisions — the masticatory and the respiratory, the former moving
the jaw«, the latter the branchial arches.

The most powerful of the masticatory muscles is the common jaw muscle, which
partly corresponds to the temporal and masseter muscles in man. Its origin occupies
the outer surface of the " suspensorium," i.e., the system of bones to wliicli the
mandible.is articulated, and part of the surface of the skull. It consists of two portions,
a superficial and a deeper, the former arises from the hj-omandibular and the anterior
edge of the preoperculum, and from the anterior part of the sphenotic, and from the
basal portion of the right frontal ; the deeper portion is smaller and arises from the
metapterygoid, symplectic, and quadrate. Between the two portions runs a large nerve,
the mandibular branch of the fifth cranial nerve. Both portions of the muscle on the
right side of the head terminate in a tendinous structure which divides into two
tendons, the upper is longer and thinner and is inserted into the middle of the posterior
edge of the maxilla, the lower is shorter and broader and is inserted into the upper edge
of the mandible, chiefly into the articular bone, a little in front of the articulation of
the mandible with the quadrate. It is evident that the chief function of this muscle is to
bring the jaws together, which it does principally by powerfully pulling the mandible
upwards, while its upper tendon draws the upper jaw downwards and backwards. The
muscle on the left side of tlie head is somewhat larger than on the right, and is inserted
only into the mandible, the tendon passing to the maxilla being entirely absent.

The levator suspensorii is a muscle which arises from the sphenotic, especially from
the lateral process of that bone, and is inserted into the head of the hyomandibular.

"49

The depression of the lower jaw is effected by the paired geniohyoid muscles, each
of which arises from the external surface of the hypohyal and ceratohyal, and is
inserted into the inner surface of the symphysis of the lower jaw, that is to say, of the
junction between the two mandibles of opposite sides.

From the lateral surface of the parasphenoid passes on each side a broad band of
muscle outwards to the hyomandibular and pterygoid bones : these are the palatal
muscles wliich constrict the cavity of the mouth in swallowing.

Behind the last there are other transverse muscles passing from the side of the skull
to the inner surface of the hyomandibular and operculum.

A strong broad transverse muscle passes from the inner surface of one mandiljle
anteriorly to the inner surface of the other ; this is the muscidus transversus mancHbulce.
It lies immediately beneath the skin of the floor of the mouth, and assists considerably
in the biting action of the mandible of the left side.

Most of these muscles, although chiefly concerned in seizing and swallowin<T food, are
also used in inhaling water through the mouth for respiration. The followincr muscles
connected with the branchial arches are almost entirely respiratory.

The most supei-fici^il of them is the levator operculi, which rises from the ridcre and
process of the pterotic and is inserted into the head and upper edge of the ojjerculum :
it raises the gill-cover.

The gill-arches are raised in inspiration by the levatores arcuum branchialhmi, which
arise from the inner side of the articulation of the hyomandibular bone with the prootic
and opisthotic, and are inserted into the outer surfaces of the bony branchial arches
into the epi-branchial bones.

Internal to the last are other muscles which pass from the inferior conical process of
the basi-occipital to the pharyngobranchials of the 2nd, 3rd, and 4th branchial
arches, that is, to the superior pharyngeal bones. The first pharjaigobranchial bone,
which is small and slender, lies along the side of the posterior end of the parasphenoid,
to which it is connected only by connective tissue.

A powerful muscle posterior to the last passes from the lower surface of the anterior
vertebrai forwards to the dorsal surface of the superior pharyngeal bones : this muscle
retracts those bones, and is therefore inspiratory.

On each side two muscles arise from the anterior surface of the clavicle and pass
upwards and forwards to the posterior surface of the inferior pharyngeal bone. As
this latter bone is destitute of gills, and all the gill clefts lie in front of it, its retraction
assists to open these clefts : these muscles are therefore inspiratory.

Expiration is effected by all the muscles which constrict the cavity of the mouth and
throat, the jaws being shut first. In addition to some of those already mentioned the
following, which bring the branchial arches into contact with one anotlier, are expiratory.

Transverse muscles between the two inferior pharyngeal bones, and between the
cerato-l)ranchials of the 4th branchial arch.

Transverse muscles between the superior pharyngeal bones.

A strong flat muscle on eacli side which arises from the lower end of the clavicle
and is inserted into the sides of the jugular bone.

Small muscles between the upper and lower extremities of the branchial arches.

The eye muscles in tlie flat fishes are of special interest on account of the peculiar
distortion of the eyes which these fishes exhibit.

The eye muscles in the sole consist, as in symmetrical fishes, of four recti muscles
and two oblique. The recti pass obliquely forwards from the back of the orbit to the
outer surface of the eyeball, to which they are attached at equal distances ; in a
symmetrical fish, as in every other vertebrate, one is attached at the dorsal side, one at
the ventral, one to the anterior, and one to the posterior : these are respectively
named the superior aud inferior, internal and external, recti. In the sole the superior
rectus is uppermost in the natural position of the fish, having followed tlie torsion of
the orbits without altering its position in relation to the iuterorbital processes of
the frontal bones. Siinilarlj' the internal rectus of each eye is next to the interorbital
septum. The superior and inferior recti of each eye are much thicker than tlie
internal and external. All the recti of both eyes take their origin from the internal
surface of the parasphenoid bone, within the cavity of the skull, but below the anterior
part of the brain.

Of the two oblique muscles of each eye that wliich is nearest to the interorbital
septum is the superior, the other the inferior. Their direction is transverse to that of
the recti muscles. The superior passes outside the end of the internal rectus, and is
inserted into the eyeball between the insertion of that muscle and that of the superior
rectus. The inferior oblique passes outside the end of the inferior rectus, and is
inserted between the insertion of that muscle and that of tlie external rectus. The
orio^ins of the oblique muscles in the sole and their direction are extremely peculiar and
interesting. In a symmetrical fish the origins of these muscles are on the inner sides
of the orbits, that is, on the side towards the median plane of the head. The median
plane of the head in the sole is morphok)gically represented by the bony interorbital
septum ; the oblifjue muscles of the ventral eye in the sole do arise from the interorbital
septum, those of the dorsal or right eye do not. The superior oblique of the ventral
eye arises from the small left ectethmoid which is on the right edge of the interorbital
septum ; the inferior oblique arises from the external surface of the parasphenoid
below the right ectethmoid. But both oblique muscles of the left or doi-sal eye arise
from the inner surface of the left ectethmoid, which is not part of the interorbital
septum. The origin of the muscles is just outside the olfactory foramen. The surface
from which the muscles spring looks to the right side of the sole, or, in the natural
position of the sole, directly upwards. Thus the direction of the oblique muscles of
the dorsal (left) eye of the sole is at right angles to the direction of those of the ventral
(richt). In fact, though the right ectethmoid bone has been shifted from its original
position in the symmetrical fish to a very remarkable degree, the left ectethmoid is in
the fame position: it has been rotated but not shifted in position. The surface of the

left ectetlimoid, to which the oblique eye mxiscles are attached, originally looked
outwards to the left; now it looks upward, and it has become increased in size.
Moreover, the left ectethnioid is still on the left side of the head, where it was
originally before the distortion commenced. Another important fact is tliat the
oblique muscles of ihe left eye are somewhat larger and stronger than those of the
right.

These facts seem to me to have an important bearing on the question of the evolution
of the sole and other flat fishes, of the process by which the peculiar asymmetry which
characterises them was produced. All zoologists are evolutionists now, and it is
generally admitted that the flat fishes are descended from remote ancestors which
were symmetrical throughout their Yives. This is sufficiently evident from the fact
that all flat fishes when first hatched, and for some time afterwards, are at the
present day perfectly symmetrical. But two entirely opposite views are at present
held by different zoologists as to the process of evolution. One school of evolutionists
goes beyond Darwin in one direction, the other in another. The former school believe
that although the conditions of life and the habits of an individual animal do affect
its structure, modify it in various ways, these modifications are never inherited and
cannot therefore have anything to do with the process of evolution. All evolution
according to this view is due to the natural selection of variations which are an
advantage to the individuals in which they occur, and these variations are all due to
causes existing before the development of the individual. Such variations are called
congenital, and are inherited usually by the offspring of the ii'dividuals which
possess them, and usually develop to a still greater degree in the offspring of two
parents who both possessed them. These variations are entirely independent of
the habits or conditions or the use and disuse of organs. Such evolutionists explain
the distortion of the eyes in flat fishes in this way. A certain species of fish in remote
ages found it necessary to lie on the bottom ; among the individuals of this species
some had eyes which were very slightly asymmetrical, the lower eye being slightly
nearer the edge of the body than in the other individuals. Consequently these
individuals being able to see more than the others lived longest, escaped their
enemies, and left most offspring. As they bred together, and as variations again
occurred, some of these offspring had the lower eye still nearer to the edge of the
head, and these survived while the others perished, and so on, until in course of long
ages the present flat-fishes were produced.

The other school of evolutionists believe that acquired characters are inherited to some
degree. It is admitted that the use of an organ enlarges it and improves it. and they
believe there is plenty of evidence tliat when the use of an organ in a particular manner
is continued generation after generation the modification is partly inherited in eacli
generation, and at last is wholly inherited. They hold therefore that tlie adaptations
of ori:rans to particular purposes, which are so conspicuous in animals and in plants,
are due to the use of the organs for those purposes, and, though the modification

II 2

may be favoured and hastened by selection, it would take place without selection,
while selection could not produce adaptations without the inheritance of acquired
characters. They maintain, in fact, that there is no evidence of the occurrence of
such variations as would give rise to adaptations except under the influence of
stimuli and functional exercise.

Thus these evolutionists would explain the distortion of the eyes in flat fishes in
this way. A species of fish took to crouching flat on the ground on one side of the
body. But at first they did not lie perfectly flat, but slanting, lifting up their heads
so as to use the lower eye, and using the muscles of this eye so as to turn the pupil
into a horizontal direction, and look along the edge of the head. In consequence of
this, the lower eye pressed on the interorbital septum, and caused it to be flattened.
This pressure being continued for millions of generations the flattening and distortion
of the interorbital septum came to be inherited until at last the two eyes were on one
side of the head.

Now it is clear that no action of a given muscle of the eye could transport
that muscle from one part of the head to another, and evolutionists who had not
studied the anatomy of the head of flat fishes have made that objection to the above
explanation. But no such transjjortation has occurred as was shown in the description
given above. The attachment of the recti muscles of both eyes remains in the flat
fish exactl}' where it is in the symmetrical fish. The cranial region aiid branchial
rcjjion are unaltered. But the fishes which were the ancestors of the existing flat
fishes, in order to twist the lower eye till its optical axis was almost parallel to the
surface of the head, must have used the oblique muscles belonging to that eye. It is
a physiological necessity that such a constant and extreme exertion of those muscles
must in the individual have produced structural modifications, especially if it was
commenced at an early age. The eye must have pressed on the interorbital septum
in the sole oti the left side, and this pressure would not have been counteracted by
any pressure on the other side, for the right eye was required to look upwards and
ventrally. Such pressure must have caused absorption and distortion of the inter-
orbital septum, that is to say, the septum would by that alone have become thin and
flat and bent to the right side. The increased exercise of the left oblique muscles
must also have caused them to become larger and stronger, and also have resulted in
the enlargement of the bone to which they were attached ; for it is an established and
certain fact that the exercise of a muscle causes it to increase in size and causes an
increased development of bone at its attachment. But the direction of the strain of
the muscles must have caused a torsion of the bone to which they were attached,
so that the surface of attachment which originally looked outwards to the left came
to look upwards. These are exactly the changes which we find to have taken place
in the head of the sole. If the change had been due to the selection of variations
which were independent of the eflects of function, then we should expect that the
left ectethmoid would have remained symmetrical with the right, for the left eye could

have been worked in its present position just as well if tlie oblique muscles had been
attached to the side of the interorbital septum, as the right muscles are. But, on the
theory for which I contend, there must have been some fixed point or fulcrum which
remained fixed while the action of the muscles altered the position of neighbouring
parts in relation to this fixed structure. The left ectetmoid of the sole fulfils the
precise conditions required of such a fulcrum. A man cannot lift himself up in a
basket, and the eye muscles could not by physiological effects have removed themselves
bodily by their own action to a new position. But two muscles by straining on their
own attachment, when unresisted by other muscles could twist neighbouring structures
round that attachment, must in fact do so, the bone to which they were attached
remaining in the same position and becoming enlarged. This is exactly what we find
to have taken place in the sole. Thus the change which has taken place in evolution
in the eyes and orbits of the sole is exactly of the same kind and in the same direction
as, but much greater in degree than, the change which must have taken place in the
individual fish which lay on its side and looked out with its lower eye beyond the
edge of its head. Why, then, should we hesitate to conclude that the evolution has
been due to the accumulation, by inheritance, of the modifications due to known
physiological effects of functional activity? The only reason for hesitation is that
some zoologists say that acquired characters are not inherited, an assertion which
.seems to me to be contrary to the evidence on the subject. However, this is not the
place to enter upon a discussion of the question of the heredity of acquired characters.
My purpose has been merely to describe the relations of the eye muscles to the orbits
in the sole, relations which I believe are not accurately described in anj- existing
anatomical treatise, and to point out that these relations are such as would necessarily
have resulted if the distortion of the orbits and the migration of the left eye had been
due in the course of evolution to the constant action of the oblique muscles of the
left eye. It must be remembered that the other peculiarities in the structure of the
sole, namely, the extension of the dorsal fin to the snout and the asymmetrical
development of the jaws, are not in any sense consequences of the distortion of the
orbits. In many flat fishes both eyes are on one side, as in the sole, while the jaws of
the two sides are almost perfectly symmetrical, and the dorsal fin terminates behind
the eyes. I believe that both these peculiarities in the sole are modifications due to
physiological causes connected with the habit of lying on the left side; but it is certain,
I think, that these physiological causes have nothing to do with the action of the
oblique muscles of the left eye. In endeavouring to trace the evolution of the sole
from a symmetrical ancestor each modification must be explained separatelj- ; the
distortion of the eyes and orbits may be explained by the action of the oblique
muscles of the eyes, but this cause does not in the least explain the absence of colour
on the under side, nor the greater size of the jaws on the lower side, nor the anterior
extension of the dorsal fin.

CHAPTEE TTT.

THE YISCEEA, AXD VASCULAR SYSTE:\r.

Tlie Viscera.

In the female the body cavity consists of three parts: a main central cavity, and
two extensions or diverticula opening out of it. The central cavity is situated
immediately behind the gill region and beneath the ten anterior vertebrae, and extends
back to the anterior ventral interspinous bone. The tvro diverticula extend backwards
from the main cavity, one on each side of the median skeletal partition of the body
along the ventral edge. These lateral cavities extend from a liltle behind the anus
to yth the length of the body from the tail, getting narrower dorso-ventrally towards
the posterior end. The median anterior cavitj' contains the stomach and part of the
intestine, the liver, and the spleen {see Plate YIII, 1). The right lateral cavity is the
larger, and contains four parallel sections of the alimentary canal, also the right ovary.
The left cavity contains only the left ovary and a part of the left kidney, which projects
imo it.

The liver is shaped like a flat cake with one surface smooth and the other made
irregular by the entrance of blood vessels, &c. The greater j)art of this smooth
suiface is turned to the left, and occupies nearly the whole dorso-ventral extent of
the main body cavity ; it is the oidy thing seen in that body cavity on removing the
left body wall. But the liver is doubled on itself anteriorly so that a smaller portion
of the smooth surface lies beneath the body wall of the right side in the anterior
part of the body cavity.

Projecting from beyond this surface towards the dorsal boundary of the body cavity
on the right side is seen the gall bladder, which is spherical. The liver is attached to
the anterior wall of the body cavity by a short ligament, situated in the median line
towards the dorsal limit of the anterior wall, about 1 cm. long at its peritoneal
attachment, and 3 mm. at its hei)atic.

The oesophagus passes into the main body cavity at its dorso-anterior angle, dorsal
to the liver, then with a very slight dilatation to form the stomach it passes baekwards
enveloped between the two parts of the liver, then following the boundary of the

main body cavity in the median plane the stomach curves downwards, endino- at
the pylorus at the ventro-posterior angle of the body cavity. Then commences the
intestine, the first part of which may, as usual, be called the duodenum. At its
commencement this is but little narrower than the stomach, but it rapidly narrows,
and, passing forwards to the antero-ventral angle of the body cavity, bends at an acute
angle and runs backwards and upwards along the border of the right fold of the liver,
crossing the stomach on the right side to enter the right lateral body cavity alonw the
dorsal part of which it runs to a little distance from its posterior end. The duodenum,
like the stomach, is white, and has thick muscular walls, but towards the posterior
end of the right lateral cavity it commences to get thinner walled and wider, and also
darker from the contents seen through the walls. It now bends completely on itself,
becoming considerably wider, and so passes into what may be called the ileum, which has
extremely thin walls. This passes forwards along the ventral side of the right cavity
in contact ventrally with the right ovary till it reaches to about the middle of the
main body cavity where, lying on the right side of the duodenum, it again bends on
itself and passes into the next length, which may be called the colon. At the bend,
and about a centimetre on either side of it, the walls are again white, thick, and
muscular, and the diameter of the tube is much reduced at this portion, which forms
a kind of ileo-colonic valve, but internally there are no transverse folds of the wall,
only longitudinal folds. After the bend the tube again dilates, this time suddenly,
and the colon, with thin flaccid walls, passes back again into the right lateral
cavity dorsal to the ileum, to a point about 2 cm. anterior to the end of the
duodenum. At this point the colon, without any change of character, passes into the
rectum, which passes forwards again on the dorsal side of and partially covering
the colon, to the antero-ventral angle of the main body cavity, wliei'e it opens at the
anus.

The spleen lies anterior to the stomach, between it and the liver, and a portion of it
is sometimes visible on removing the right body wall, between the duodenum and the
rectum. There is no pancreas, and no pyloric cteca. All the parts of the intestine
and the liver and spleen are connected together by the branches of the splanchnic
artery and portal vein : these are especially conspicuous between the duodenum and
the liver, where they run from one to the other across the spleen.

The gall duct runs downwards from the gall bladder and opens into the duodenum
a little behind the pylorus on the anterior side. The hepatic duct leaves the liver iu
the anofle between the two folds and joins the gall duct about 1 cm. from the gall
bladder.

Cutting through the CEsophagus and the terminal part of the rectum we now
remove the whole of the intestine, liver, and spleen, and examine the kidne\-s auc?
ovaries.

The two ovaries extend, as has been said, along the ventral border of the right
and left body cavities respectively. They are both about the same length, but the

r^t

ht is thicker. The ovaries are not suspended by membranes (mesoaria) as in
symmetrical fishes, but lie like kidneys beneath the peritoneum which passes over
them. Morphologically the mesoarium may be considered to have fused with the
surface of tlie median i)artition which separates the lateral body cavities from one
another. Or, to regard the evolution in a dillerent way, it may be that the ovaries
have grow-n back post-anally beneath the peritoneum. Each ovary has a containing
wall which is independent of the peritoneum, though attached to it : the latter can be
separated from the former with facility. The ovarian artery and vein pass down together
on each side from the posterior end of the main body cavity, and run along the dorsal
side of each ovary. The walls of the two ovaries unite anteriorly on the ventral side
of the main body cavity to form a single wide tube whic-h opens to the exterior behind
the anus and conducts the ova to the exterior, ^\■ll^■u tlie o\;uy is cut open tlie
nerminal surface covered with projecting ovigerous lamellae having a gejieral
lontritudinal direction, is seen to extend all round the internal surface except along
the median ventral line, where the surface of the ovarian wall is quite smooth and
destitute of ovigerous lamellte : this probably represents the suture along which in
development the edges of the ovarian lamina joined together to form a tube.

On the dorsal wall of the main body cavity the renal organs form abroad reddish band,
placed in the centre and symmetrically, the two kidneys seem to be fused together in
the middle line. No part of the renal mass is continued into the right lateral body
cavity, but it is continued as a bulging thick mass into the dorsal part of the left
lateral cavity, where it is in contact ventrally with the left ovary. From the ventral
anterior corner of tliis mass there comes off a single short renal duct which opens out
into a large urinaiy vesicle. This vesicle sends a prolongation backwards between
the left ovary and tlie wall of the left lateral cavity, and it extends do^^^lwards behind
the common oviduct, between this and the wall of the main body cavity, to open to
the exterior on a small papilla on the right side. The opening of the oviduct,
although in the same depression of the skin as the anus, is separated from the
latter by a fold of membrane. Anteriorly the kidneys extend hivond the main body
cavity between the oesophagus and the muscles dorsal to it, as far as the posterior
surface of the skull.

Description of tlie Viscera of the male from a specimen Ifoot long (SI cm.).

Plate IX.

The intestines are arranged as in the female except that they do not reach quite so
far back in the right lateral body cavity, that is, they are slightly shorter. In front
of the bend which divides the colon from the ileum, is seen the urinary bladder,
distended. No part of the testes is seen without disturbing the organs in the body

cavity. Wlien the intestines are lifted up or removed, tlie riglit testis is seen, a
triangular flat solid mass about 8 mm. broad at its posterior end, and 1 3 mm. long,
lying at the anterior end of the right lateral body cavity, close to the front edge of tlie
skeletal partition to which its inner surface is attached.

On the left side there is no left lateral body cavity, but the posterior portion of the
fused renal organs extends backwards between the lateral muscle and the skeletal
partition : this part of the kidney is as large in proportion as in the female, and has the
same relations to the urinary bladder.

The left testis is only about half the size of the right. In this specimen it was 4 mm.
troad above, and 10 mm. in length. The right testis is somewhat flat, and its greatest
length is nearly antero-posterior in direction ; the left has the form of a triangular
pyramid with its point downwards, and its greatest length is dorso-ventral in direction.
The left testis is situated in the main body cavity attached to the peritoneum over the
surface of the kidney by a membrane, the mesorchium.

From the apex of each testis passes off the vas deferens or duct by which the milt
or semen is conveyed to the exterior. Each vas deferens contains not a single cavity
but several, and it is attached to the anterior surface of the urinary bladder. The
vasa deferentia being translucent are not conspicuous ; their external aperture is at
the end of a small papilla on the right side, which is pierced also by the terminal
part of the urinary duct. Thus in both sexes there is a papilla on the right side ; in
the female it is a urinary papilla, in the male it is urinogenital. In the figure the
wooden rod is inserted through the anus into the end of the rectum, while the black
bristle passes into the urinary bladder the walls of which are exceedingly transparent
and indistinct, especially when the bladder is empty and collapsed.

Thus the male organs of reproduction in the sole are extraordinarily small in
proportion to the size of the body. In other flat fishes, e.g., the plaice, PL platessa, or
merry -sole, Fl. microcephalus, they are smaller than the ovaries, it is true, but many
times larger than those of the sole, and in the breeding season they become enlarged
and soft, and of a milk-white colour. In this condition they at once attract notice
when a male fish is cut open. In the sole, on the contrary, although the testes become
slightly enlarged during the spawning period, they become neither white, nor soft,
nor conspicuous. In fact they are not known to the fisliermen, who are unable to
recognise in the siuall yellow organs of the sole the male reproductive organs
which they usually find in other fishes as large, white, soft, and conspicuous
masses. The testes of the sole are, moreover, completely concealed beneath the
intestine. Until recently even ichthyologists were for the most part unacquainted
with the structure and relations of the male organs of the sole. In the
Fifth Annual Eeport of the Fishery Board for Scotland, p. 233, it is stated that " the
hatching of the sole, e.g., presents this one great difficulty, that males are rarely ever
captured, or, at least if captured, are seldom identified." As a matter of fact males

are captured in greater numbers than females, but fishermen are unable to distinguish
the males from unripe or immature females.

One part of the viscera, which has the same relations in both sexes, still remains
undescribed, namely, the anterior part of the intestine, and the gills which are con-
nected with it. The anterior part of the intestine itself needs no very elaborate
description : it consists simply of the mouth and throat, the walls of which differ oidy
from the stomach in the fact that they are almost everywhere continuous with the
surrounding muscles and otlier tissues, instead of being separated from them by part
of the body cavity. Beneath the throat there is a part of the body cavity entirely
separated from the rest, namely, the pericardium, whicli contains the heart, and wliich
will be described below. Tlie teeth previously mentioned as connected with or
embedded in tlie superior and inferior pharyngeal bones of course project through the
walls of the throat, and help to masticate or grasp the food. The series of basihyal
and basibranchial bones, clothed with raucous membrane, form a pointed conical tongue
in tlie floor of the mouth, which is used in swallowing.

At the sides of the throat is the important respiratory apparatus. Between the
branchial arches are a number of clefts by which the cavity of the throat opens to
the exterior. The bony arch is clothed with connective tissue, muscle, and mucous
membrane, and this mucous membrane becomes continuous through the cleft with the
outermost layer of the skin on the external surface of the body. The most anterior
cleft is between the hyomandibular bone and the iirst branchial arch : the cleft extends
upwards to the middle of the epibranchial bone, downwards to the end of the cerato-
branchial. The 2nd, 3rd, and 4tli clefts become gradually shorter, scarcely extending
upwards beyond tlie cerato-brauchials. The 5th cleft is very short, it is situated
between the 4th cerato -branchial bone and the 5th cerato-branchial or lower pharyn-
geal bone. The latter is continuously connected by muscle and connective tissue with
the pectoral arch ; there is no cleft behind it. On the outer face of each arch there is
a double series of long straight filaments, the branchial filaments. Each of these is
supported by a rod of fibnnis skeletal tissue which runs up its centre, and between
this rod and the epithelium, or layer of delicate cells which covers the surface of the
filament, there is a ricli plexus of capillary blood vessels. The blood coursing through
these gives out its carbonic acid to the sea water which passes through the gill clefts
and absorbs oxygen from the sea water, which oxygen is necessary for the oxidization
of the tissues that goes on throughout life.

In front of the first branchial cleft, running in an antero-posterior direction beneath
the dorsal part of the hyomandibular bone, is a rudimentary branchia, composed not
of long branchial filaments, but a few vascular folds of the mucous membrane : this
is called the pseudo-branchia and is found in the majority of bony fishes. The pseudo-
branchia represents part of tlie brancliia of the hyoid arch. On tlie inner surface of
the branchial arclies there are ?mall fleshy projections; in many fish these are long
projecting rods called the gill rakers. In the sole they are rudimentary.

The brancliiostegal rays support a membrane which is externally for the greater part
of its length contiiujous with the opercular flap, but is free at its edge, and extends
somewhat beyond the flap ; it forms a concavity which directs the water pressed out
in expiration upwards towards the base of the pectoral fin. The edge of the branclii-
ostegal membrane is, in ordinary respiration, kept pressed figainst the posterior wall
of the branchial cavity except opposite the base of the pectoral fin, where the membrane
forms a small aperture by which the water that has passed over the gills escapes. The
opercular flap supported by the opercular bones forms the external wall of the
branchial chamber, in which the branchise are contained and concealed, but the oper-
cular flap is morphologically nothing but a fold of skin projecting backwards from the
hyoid arch and supported by dermal bones. The branchiostegal rays represent the
branchial skeletal rods of the lower part of the hyoid arch : they have been much
enlarged, and the filaments they supported have lost their branchial function, and
coalesced to form the branchiostegal membrane.

Minute Structure of the Reproductive Organs and Development of the Reproductive

Elements.

It has already been mentioned that the ovary consists of a hollow tube from the inner
surface of the walls of which 23roject a number of longitudinal lamellas containing the
ova. A section of a j'oung ovary of the right side is represented in PL XIII, 1 , as
seen under a low magnifying power, namely Zeiss' objective A, ocular 2, The specimen
from which this ovary was taken was 7j in. long, and was immature. But the
structure of a mature ovary is similar in all respects except the size of the ova.
The wall of the ovary consists of laminated fibrous tissue, and the ovigerous lamellaj
are supported by projections of this tissue into the interior of the ovary. On the
dorsal side of the transverse section are seen two blood vessels, the ovarian arterj^ and
vein. Tlie ovigerous lameUas are absent from a small portion of the ventral wall of
the ovary, where the internal surface of the wall is smooth and barren. The surface
of the ovigerous lamellas is covered by a thin epithelium of cells too minute to be
distin<mished separately under a low power. Here and there in this epithelium young
ova are seen developing. The epithelium is called the germinal epithelium, and
from its cells all the ova are originally derived. The older ova are seen below the
epithelium in the substance of the ovigerous lamelliB. The lamellae contain in tlieir
centre a plate of somewhat dense fibrous tissue, from which a loose reticulum of
fibrous strands and bands extends to the germinal epithelium. The older ova sink
into this loose fibrous layer, and each ovum is surrounded and enveloped by strand.s
of the fibrous tissue. The spaces in the fibrous reticulum are doubtless in life filled
with lymph, while the tissue itself is richly supplied with capillary blood vessels. The

I 2

largest ova in the ovary at this stage are still verj' young, and each consists of a
protoplasmic mass containing a nucleus. The nucleus is a spherical vesicle bounded
by a membrane and containing protoplasmic strands and a number of nucleoli
which are all situated at the periphery of the nucleus. In a stained preparation the
nucleoli and the protoplasm of the ovum surrounding the nucleus are deeply stained,
but the rest of the nucleus, consisting chiefly of liquid contents, is scarcely stained at
all. Thus in each ovum the nucleus is seen as a clear central space containing several
deeply stained globules arranged within its external border. There is little doubt
that the fibrous connective tissue in the living state is more compact than I have
represented it to be. The ova contract in the process of preparation and leave open
spaces between them across which fibres are seen passing. But nevertheless it is
certain that the fibrous tissue is reticular, and that it is traversed bj* spaces containing
lympli.

When a portion of an ovigerous lamella from a young ovary is examined with a
high power it presents the appearance shown in PI. XIII, 2. The preparation from
which this figure is taken was made from the ovary of a sole 10^ inches long, killed
in January. This also was an ovary which had never produced ripe ova, an im-
mature ovary. It will be seen that the cells of the germinal epithelium are extremely
minute and their outlines undefined. The ova are evidently produced by the
enlargement of single cells of this epithelium, and as they increase in size they pass
downwards into the fibrous "stroma." Even round the largest ova in an ovary at
this stage no envelope can be detected except a fibrous membrane belonging to the
"stroma" of the ovary. The protoplasm of the ovum, although it has grown in
quantity, still exhibits no differentiation. The largest ovum represented in Fig. 2 is
•12 mm. in diameter.

But ova which are approaching maturity show a much more complicated structure.
Fig. 3 is drawn from a section prepared from an ovary in the spawning condition ;
in fact the ovary was almost spent, but a few immature ova remained in it, and a
section of one of these is represented in the figure. This ovum is seen to be enclosed
by a thick envelope, exhibiting in section close set radiating lines. This envelope is
not stained in the preparation. The radiating lines are really exceedingly fine tubules
passing through the substance of the envelope and through these the protoplasm of the
ovum communicates with the nutritive fluids outside. This envelope is the innnature
stage of the membrane surrounding the ripe ovum when it is shed, but at this stage it
is much thicker in proportion to the size of the ovum than in the state of maturity.
This envelope may be called the vitelline membrane ; in the eggs of some fishes it is
differentiated into two layers, but in the sole I can find no distinction except that the
exterior surface of the membrane forms a kind of thin cuticle. The ovum within the
membrane presents an appearance very different from that of tlie j-ounger ovum
previously described. Instead of a mass of granular protoplasm there are here a great
number of spherical vesicles crowded together. These vesicles contain a number of

granules scattered through a transparent substance. They are the yolk vesicles.
Attentive examination shows that the yolk vesicles are contained in the original
protoplasm of the ovum, which everywhere extends among them, forming a network.
In fact the yolk vesicles are developed by the protoplasm within itself. The protoplasm
takes up the nutritive liquid materials derived from the blood and alters these by its
living chemistry so as to form these yolk vesicles which grow as it were at all points
throughout the substance of the protoplasm. Tu the mature ovum these yolk vesicles
become homogeneous and transparent, and flow together, with the exception of a few
of them, which remain separate but transparent near the outer surface of the ovum.
In the ovum now under consideration the nucleus retains the structure described in
the younger stage, and is still near the centre of the ovum. When the yolk vesicles
fuse the nucleus passes to the exterior with the protoplasm, the whole of which forms
a superficial layer enclosing the central semifluid yolk as in a blalder.

We have now to consider the ovarian structures surrounding the egg at the stao-e
represented in Fig. 3. It is easy to recognise outside of all the thin membrane of
fibrous tissue connected with and belonging to the stroma of the ovary. This may be
called the follicular membrane, the ovarian capsule enclosing the ovum being usually
known as the follicle. The follicular membrane exhibits nuclei along the course of the
fibres composing it, and it contains a number of capillary blood vessels, communicating
with larger vessels in the stroma (b.v. in Fig. 3). But within the follicular membrane
is a regular epithelium which was not seen in the younger stage of the ovum. This is
composed of a single layer of cells possessing large distinct nuclei. These cells in the
preparation are separated from one another at their internal ends, but this is probably
due to the contraction caused by reagents. Such a follicular epithelium is found round
the ripening ova of all vertebrates. But it is still an open question whence it is
derived. It has been maintained by many great authorities that the follicular cells
are derived from the germinal epithelium ; that when on ovum separates from the
epithelium and sinks into the stroma it takes with it a few other cells of the epithelium,
Avhicli multiply by division and form the foUicular epithelium. This conclusion
has been drawn mainly from the study of the ovary in embryos, not from that of
developing ova in adult animals. As I have shown I have failed to trace any
connection between the follicular epithelium and the germinal epithelium. The former
seems to me to be entirely wanting for a considerable period after the young ovum has
separated from the germinal epithelium. The cells of the follicular epithelium become
visible about the same time as the commencement of the vitelline membrane. If these
cells are not derived from the germinal epithelium they must be derived either from
the egg itself or from the stroma of the ovary. There is no evidence of their derivation
from the egg itself at least in bony fishes, and it is inconsistent with what we know of
fibrous tissue to suppose that the nucleated fibres can produce cubical cells. The
follicular cells cannot be developed independently from nutritive material derived from
the blood, they must be descendants of previously existing cells, for we know of no

case in which nucleated cells arise, except as the progeny of other cells. Tliere is
thus only one source left to which we can attribute the origin of the follicular cells,
namely, the colourless aniccboid wandering lymph cells, which occur in the interstitial
l}nnph spaces of all connective tissue. These cells are usually small, and it is possible
that they might intrude themselves through the spaces between the fibres of the
follicular mem])rane and so take up a position between that membrane and the surface
of the vitelline meiubrane, and then growing in size form the follicular epithelium.
The question of the origin of the follicular cells cannot however be considered as
decided ; Professor Emery in his nionograph on Fierasfer, like myself, considers it
improbable that they are derived from the germinal epithelium, but expresses no
positive opinion as to their real origin.

As the egg in the ovary increases in size and approaches maturity its circumference
reaches again the surface of the ovigerous lamella, and ultimately when it is quite ripe
the germinal epithelium, the follicular membrane, and the follicular epithelium burst and
the ripe egg enveloped only by the vitelline membrane escapes into the cavity of the
ovary, whence it passes out through the external genital aperture to the exterior, >vhere
it is fertilised.

The structure of the testis of the sole is very different from that of the ov^ry, and
closely resembles that of the testis in other bony fishes. PI. XIII, 4, shows the structure
of the testis of a young male sole 9 in. long, killed February 4lh, 1889. The testis of
a full-grown male sole is similar, but I have represented the transverse section of
a small testis in order to include the whole of the section without making the
figure inconveniently large. The substance of the organ consists principally of
cylindrical tubes having walls of fibrous membrane and containing the spermatic cells.
These tubes are closed at the end which is most remote from the testicular duct leadins
to the exterior, and these closed ends are all situated immediately beneath the surface
of the organ. From the closed ends the tubes pass radialh^ inwards towards the
central region of the organ, except at the sides where their course is more longitudinal.
The tubes are sp numerous as to be in contact with one another along their sides. As
in the case of the ovary the " stroma " of the organ consists qf fibrous connective tissue
which fills up the interstices between the testicular tubes and forms a thin layer rouiul
the organ externally. In the central region of the organ the testicular tubes
conmuinicate with a number of longitudinal tubes much smaller in number than the
tubes themselves and of various sizes, some smaller, some larger, than the testicular
tubes. These longitudinal tubes convey the si)ermatozoa towards the efferent ducts,
and do not themselves produce spermatic cells : they are scattered with no regular
arrangement through the dense fibrous stroma. Infcriorly the fibrous stroma of the
testis is looser in texture and becomes contiiuious with the fibrous connective tissue of
the wall of the body cavity to M'hich the testis is attached. Thus, to use the terms
frequently employed in liuinan anatomy, the testis of the sole consists of a corlicid
portion and a central medulla, tlie cortical portion consisting of tubes placed

perpendicular to the surface, tlieir outer ends being closed, and the medulla of
longitudiual tubes separated from one another by fibrous connective tissue. This
medullary portion is prolonged beyond the organ itself in the form of a band which
passes down the surface of the urinary bladder to the genital opening. Sections of
this baud show that the longitudinal efferent tubes do not unite into a single duct or
vas deferens, but are only slightly reduced in number by coalescence, so that a large
number of tubes remain separate even to the external opening. Fig. 6 exhibits a
section of the cord or band connecting the testis with the exterior and containino- the
separate efierent tubes. This section is more highly magnified than that shown in
Fig. 4, and is taken from the testis of a full-grown male preserved while in full genera-
tive activity, in March, 1889. The spermatozoa are seen within the efferent tubes,
completely filling the cavity of some of them, and appearing under a low magnifyin<^
power as deeply stained granules : these granules are the heads of the spermatozoa,
the tails or vibratile appendages not being visible.

If the cortical tubes in the section shown in Fig. 4 are examined under a more
powerful objective, each of them presents the structure shown in Fig. 5. At the closed
end of the tube are a number of large polygonal cells forming an epithelium. Each
of these cells has a large nucleus with many nucleoli ; lower down the tube is filled
with smaller and smaller cells produced by the division of the large cells. The large
cells are evidently constantly being multiplied by division, and after reaching a certain
size each is pushed down into the cavity of the tube where it divides and subdivides,
forming a cluster of smaller cells. In some parts of the tube such clusters of small cells
produced from a single original cell can be distinguished, but they easily break up and
the cells of various clusters are confused together. In some of the voung clusters
near the closed end of the tube all the nuclei are seen in a state of division showing
that each cell is dividino; into two.

The large cells at the closed end of the tube correspond to the germinal epithelium
of the ovary ; they do not extend down the sides of the tube, but are confined to its
end : they are the male germinal cells and from them all the spermatozoa are
produced.

As the cells pass down the testicular tube they get smaller and smaller, and in the
lower ends and in sections of the deeper portions cut transversely they are seen to have
reached their limit of subdivision, for amongst them are seen deeply stained minute
spherical bodies which are the heads of spermatozoa. The minute cells produced
by continued subdivision are converted into spermatozoa and are called the
spermatoblasts. The details of the development of a spermatozoon from one of
these spermatoblasts can only be followed out by teasing up a portion of the testis on
a glass slide and examining it microscopically with the aid of reagents. The process
cannot be followed satisfactorily in sections because in these the elements are cut uj)
into pieces. I have not followed the process of development in the sole ; I will
therefore merely explain here that the protoplasm of the spermatoblast elongates

into a slender filament, while the nucleus alters in properties, imbibing stains such as
carmine more intensely, and forms what is called the head of the spermatozoon.
During the spawning period all the testicular cells, except the large cells of the
male germinal epithelium at the closed ends of the testicular tubes, are converted into
spermatozoa, which are conveyed to the exterior suspended in a litpiid similar to
lymph. Tliis li(piid is ])roduced within the testis, being probably exuded from
the blood vessels and lymph of the testicular stroma into the testicular tubes. The
liquid containing the spermatozoa is usually called the milt. When the spermatozoa
reach the sea water they swim about actively, and when one meets a ripe ovum it
enters its substance and fertilises it.

The Vascular System.

The blood vessels ramify through all the tissues, including the skin and nervous
system, which have not yet been particularly described. Ihit as the heart, which is the
central organ of the vascular system, is closely related to the body cavity and to the
branchiae, the system may be conveniently described here.

The heart, as was before mentioned, is enclosed in a special chamber of its own,
which is really a part of the body cavity, though it is entirely shut off from the visceral
cavity in which the organs of digestion, &c., are contained. This cavity containing the
heart, the pericardium, is situated between the posterior and internal walls of the two
branchial chambers ; the cavity is wedge-shaped, the edge of the wedge being anterior,
the base posterior. Posteriorly the pericardium is separated from the visceral
cavity by a thin membrane which lies in front of the liver and below the gullet or
oesphagus. Outside the pericardium on either side is the boiie called the clavicle.
The heart itself is conical in shape, the point being ventral and directed downwards
and slightly forwards, the broad base being dorsal. It is hollow and divided into two
portions connected by a valve. The dorsal portion has very thin walls, and is called
the auricle ; the ventral portion has thick muscular walls, and is called the ventricle.
Into the dorsal end of the auricle open three large veins by which the blood which has
passed through the various parts of the body is conducted into the cavity of the
auricle. These veins are the Juctus Cuvieri which pass one on either side of the
oesophagus from the kidneys, and the hepatic vein which passes forwards from the liver
below the oesophagus. The ductus Cuvieri of each side is formed by the union of two
veins, one ruiuiing forwards in the substance of the kidney and conveying the blood
from the trunk, the other running backwards from the head and conveying the blood
from the brain, skull, &c. ; these are called the anterior and posterior cardinal
veins.

The ventricle sends off a single main l)lood vessel, the ventral aorta. At the opening
of this vessel from the ventricle, there are three internal folds or valves which prevent

the blood returning to the ventricle. This vessel passes forwards along the dorsal
edge of the jugular bone, and beneath the basi-branchials it divides, giving off on each
side an artery to each of the first four branchial arches ; from the artery of the first
arch a branch passes to the pseudobranchia. The fifth arch, bearing no branchial
filament, does not receive a special branchial artery. The branchial arteries run along
the branchial arches giving off smaller vessels which break up into the capillaries of
the branchial filaments. These capillaries unite again into the efferent branchial
vessels which run in the branchial arches towards the dorsal side of the pharynx or
throat, where they unite together into a single median dorsal aorta. From the efferent
branchial vessels are given off arteries which supply the brain, skull, and other parts
of the head. From tlie dorsal aorta is given off at the anterior end of the body cavity
the coeliac artery which supplies the intestine spleen, and liver with arterial blood.
The dorsal aorta runs backwards in the canal formed by the series of divergent bases
of the ventral spines of the vertebrae, and is therefore in its anterior part dorsal to the
kidneys. It gives off special arteries which descend to supply the generative organs.
It also throughout its course gives off a pair of arteries to each segment of the lateral
muscles, fi-om which branches supply the skin, bones, and all parts of the body.

The return of the exhausted venous blood from the tissues to the heart takes place
by a somewhat curious route. The veins of the head unite into the two anterior
cardinals, already mentioned, one on each side. But nearly all the veins of the trunk
fall ultimately into the caudal vein which runs forwards in- the same bone-protected
canal as the aorta, as far as the interval between the ventral spines of the ninth and
tenth vertebra3, where it bends suddenly towards the ventral edge of the body and
enters the dorsal side of the renal mass. The veins of the trunk in front of the caudal
vein fall into the kidney by separate collecting veins. A number of the veins of the
ventral side of the trunk, behind the kidney, unite into a longitudinal vein, which runs
forwards along the left side of the median skeletal partition and enters the posterior
apex of the part of the kidney which extends backwards on the left side behind tlie
main body cavity. Thus nearly aU the venous blood in the trunk is conveyed into the
renal mass, where the urinary excretion is extracted from it, and whence it is passed
on by the posterior cardinal veins to the heart. The veins of the spleen and intestines on
the other hand unite into a single vein which enters the liver where it breaks up into
capillaries, and these unite again to form the hepatic vein which opens into the auricle.

CHAPTER TV.
THE NERVOUS SYSTEil

The Brain. — Tlie brain of the sole has no veiy special features which distinguish it
among those of other bony fishes. The position of the brain is almost entirely
unafTected by the change which has taken place in the normal jx>sition of the fish ; the
posterior part of the skull, as was previously pointed out, has neither twisted nor
become asymmetrical, and the corresponding part of the brain also retains its original
position and symmetry. But it seems still more remarkable that the anterior part of the
brain has not to any great degree followed the anterior part of the skull in the rotation
which the latter has performed. When the brain is exposed from the upper (right)
side of the fish, the right side of the organ is seen, the extreme anterior end being
alone very slightly turned round towards this side. This absence of change in the
position of the brain is not so paradoxical when we compare carefully the relation of
the organ to the skull. The anterior end of the biain lies beneath the posterior
portions of the frontal bones, and these retain their original position.

It might have been expected that the change in the position of the anterior cranial
nerves would have caused a greater twisting of the brain ; but we find that the trunks
of the nerves have moved while their roots have been very slightly affected.

Viewed from the dorsal side the brain exhibits the same series of ganglionic masses
which are seen in other bony fishes. At the posterior end is the single median globular
cerebellum which projects backwards above the anterior thickened continuation of the
spinal cord, called the medulla oblongata. In front of the cerebellum is the pair of
masses whence the optic nerves arise, the optic lobes, each of which is almost as large
as the cerebellum ; in front of thesa again is the pair of cerebral hemispheres which
are slightly smaller than the optic lobes, and immediately in front of the cerebral
hemispheres are the olfactory lobes. In some bony fishes the olfactory lobes are
removed to some distance from the brain and placed in proximitj- to the olfactory
capsules, being connected with the brain by long nervous peduncles or crura ; e.g., in
the cod and carp. But in the sole as in other flat-fishes, and in the perch, mackerel,
pike, gurnard, and others, the olfactory lobes form part of the brain and are at a
distance from the olfactory capsules ; witli which they are connected by the olfactory
nerves.

The under surface of tlie brain exhibits beneath the cerebellum the continuation
forwards of the medulla oblongata which forms as it were the stalk supporting the
dorsal lobes. Beneath the front part of the optic lobes, however, an inferior outgrowth
is seen ; this consists of a pair of lobes called the lolji inferiores between which is a
vascular organ called the pituitary body, or hypophysis cerebri, supported on a hollow
conical outgrowth called the iufundihulum.

The brain contains a central cavity which is the continuation of the central canal of
the spinal cord. This cavity terminates in the middle line between the cerebral
hemispheres, but laterally it sends off two diverging prolongations into the interior of
these hemispheres. The medulla oblongata and its continuation, the crura cerebri, are
situated below the ceiitral cavitj', while the cerebellum, the optic lobes, and the upper
part of the cerebral lobes are enlargements of the roof of the cavitj^ The infundibulum
and pituitary body form a downward diverticulum of the cavity beneath the point
where it bifurcates into the cavities of the cerebral lobes ; and a corresponding diver-
ticulum towards the dorsal side exists between the anterior part of the optic lobes, and
is called the pineal gland. The pineal gland, like the pituitary body, is a vascular
structure in fishes. In some reptiles it has been found to have a structure resembling
that of the vertebrate eye.

The olfactory lobes are continuous with the inferior portion of the cerebral hemi-
spheres. In the sole the left olfactory lobe is somewhat larger than the right, a dillerence
which is related to the great development of the left olfactory capsule. But there is no
inequality in the size of the optic lobes or optic nerves, such as that which according
to Owen occurs in the halibut and some other Pleuronectidce. In Owen's figure of
the halibut the right optic lobe and left optic nerve are the larger ; the eyes of this
species, as of the sole, are on the right side, so that the larger structures are those
belonging to the eye which has migrated.

It would naturally be inferred that the left eye was larger than the right in the
halibut, but I have not been able to find any allusion to an iricquality in the size of the
eyes themselves.

As in all bony fishes the brain of the sole is much smaller than the cavity in which
it lies. The widest part of the cavity within the skull is the posterior part : here the
brain passes forwards from i\i.e foramen magnum as an axis in the centre of the cavity,
the surrounding space being occupied by the auditory organs. The sacculi meeting
in the middle line below, occupy the space below the brain, while the semicircular
canals intervene between the latter and the skull-walls dorsally and laterally. A
transverse ridge on the inner surface of the skull-wall, forming part of the sphenotic
and prootic bones, limits anteriorly the cavity occupied by the saccuU. In front of
this ridge is another ventral depression occupied by the optic thalami and pituitary
body, while aljove the optic loljes and cerebral hemispheres there is a considerable
soace occupied only by spongy connective tissue containing fluid— tlie arachnoid
membrane. The internal hollow of the parasphenoid bone in front of the pituitary

K 1

body is occupied by the insertion of the muscles of the two eyes, these muscles bein<T
separated from the interior cavity of the skull by a tough membrane, continuous with
the dura mater posteriorly, and anteriorly with the membrane which completes the
septum between the orbits. This membrane is pierced for the exit of the optic,
olfactory, and other nerves, and on it rest the olfactory lobes.

The Cranial Nerves.

The olfactory nerves pass from the olfactory lobes to the olfactory capsules, termi-
nating in the olfactory epithelium of these organs. Owing to the rotation of the left
eye and orbit the position of these nerves in the sole is peculiar. Each olfactory nerve
in all fishes passes over the dorsal side of the recti muscles of the eye. Tlie relations
of the nerves to surrounding structures are not altered in the sole, but the rotation of
the eyes has brought the olfactory nerves into asymmetrical positions. Thus both of
these nerves are apparently on the upper (right) side of the head, though morphologi-
cally they are on opposite sides. Both of them, like other structures connected with
the orbits, are on the coloured side of the head, to the right of the anterior part of the
dorsal fin. The left nerve passes above the recti muscles of the left eye close to the
interorbital septum, and in front of these muscles bends downwards and passes through
the large foramen in the left ectethmoid bone (PI. XI, G, I) to reach the left olfactory
capsule on the lower side of the head.

The right nerve has a perfectly straight course along the ventral (right) siile of the
interorbital septum, dorsal to the recti muscles of the ventral (right) eye. It passes
through the foramen in the right ectethmoid without any bending, and then bends
slightly downwards to the olfactory capsule of the upper (right) side.

Each of these nerves, though spoken of in the singular, consists of a bundle of
separate nerves, whieli are separate tliroughotit their course, and not united into a
single cord.

The optic nerves, as usual in bony fishes, cross one another at their origin without
mingling. The dorsal (left) nerve is very slightly longer than the ventral (right). The
left arises from tlie lower side of the right optic lobe in front of the lobiis inferior or
optic thalanms, the right from a corresponding position on the left side. The optic
nerve passes between the internal and superior 7-ecins close to their origin into the
space enclosed by the recti muscles, and so reaches the eye-ball.

The third, fourth, and sixth pairs of cranial nerves are motor nerves all distributed to
the nmscles of the eyes. The third pair are called the motores oculorum and split up
into branches which enter ths superior, inferior, and internal recti, and the inferior
oblique nmscles. The fourth pair of nerves are called trochleares and supply the
superior obliciue muscles exclusively. The sixth pair are called nbduccntes, and enter
only the external recti maicles. These nerves arise from the sides of the lower part of

the brain behind tlie origins of the optic nerves, and pass from the slvull 1)y apertures
in the membrane wliich closes its anterior opening.

The fifth nerve or trigeminal arises by several roots from the side of the medulla
oblongata below the cerebellum : in its origin it is closely connected with the seventh
or facial nerve. In fact the two nerves arise from a number of roots common to both,
of which the dorsal are sensory, the ventral motor ; the fifth nerve is chiefly composed
of fibres from the sensory roots, with the addition of some from the motor, while the
facial consists chiefly of fibres from the motor roots, with the addition of some iiom
the sensorj'.

The fifth nerve consists of a large number of branches. It does not leave the skull
by a single trunk, but divides on the inner wall of the skull into several, the largest
and most important of which leaves the skull after a very short course by the large
trigeminal foramen in the lower part of the sphenotic bone. The other two branches
run for some distance on the inner wall of the skull before emerging ; one of them runs
directly forwards and emerges through the anterior membrane wliich separates the
skull from the orbits ; this forms the orbito-nasal nerve ; the other curves upwards arid
forwards and emerges by a small foramen in the frontal bone. As the corresponding
nerves difier on the two sides it will be necessary to describe them separately.

The course of both orbito-nasal nerves, like that of the two olfactory, is to be followed
by dissection of the upper side of the head ; for each orbito-nasal nerve lies in close
relation to the olfactory, lying in the ordinary fish dorsal to the olfactory and between
the eye muscles and the interorbital septum. Accordingly in the sole the orbito-nasal
nerves are found on the upper side of the head, one on either side of the interorbital
septum. But the dorsal (left) is much larger, and longer than the ventral (right). The
left nerve passes over the surface of the mesethmoid bone at the bottom of the rounded
notch between the left ectethmoid and the mesethmoid, and then enters the gelatinous
tissue of the end of the snout, sends branches to the skin of the upper side at this part
of the snout, but is chiefly distributed to the tactile filaments of the skin on the lower
side between the olfactory capsule and the edge of the snout. The right nerve just
behind the right ectethmoid passes into a canal between the right frontal bone and the
right ectethmoid, and thence emerges again on the right upper surface of the meseth-
moid, enters the gelatinous tissue of the snout, and supplies the small area of skin on
the upper side between the mouth and the apex of the snout.

The right dorsal branch of the fifth, after its upward course on the internal surface
of the skull, emerges by a small foramen in the flat proximal portion of the right frontal
bone, and thence passes forwards, at some depth from the surface, between the cephalic
portion of the lateral muscle and the membrane which forms the dorsal boundary
of the dorsal (left) orbit. It supplies the skin of the extreme anterior end of the
dorsal fin on the upper side. It seems at first sight that this nerve has changed its
morphological relations ; for since it belongs to the right side of the head we might
expect to find its anterior part on the ventral or right side of the interorbital septum,

with the right orbito-uasal ; whereas it actually runs on what is morphologically the
ventral side of the left eye, crossing in its course the left olfactory and orbito-nasal
nerves. But tlie explanation of this apparent anomaly is not difficult. The dorsal
branch of the fifth is a sensory nerve and was connected in the original symmetrical
fish with the skin of the extremity of the dorsal fin which was originally j)osterior to
the eyes. The fin remained behind the eyes during the rotation of the latter, and
after the left eye had travelled round to the right side, the dorsal fin with the neigh-
bouring muscles began to extend forwards. Jiut instead of extending forwards along
the now distorted median dorsal line, the fin grew forward along the edge of the left
ectethmoid bone, which supports the left eye in its new position, and which is mor-
])hologically ventral to the left eye. The nerve connected with the fin necessarily
accompanied the latter in its growth, and thus this nerve comes to be actually dorsal
and morphologically ventral to the left eye. The origin of the nerve remains in its
original position posterior to the eyes on the right side of the skull.

The corresponding nerve of the left side makes its exit from the skull fi-om a corres-
ponding foramen in the flat proximal portion of the left frontal bone, on the lower (left)
side of the dorsal fin ; it passes forwards on the left side of the fin to its apex.

On the ri'dit side the trunk of the fifth nerve, which emerges from the skull through
the sphenolic foramen, divides immediately after its exit into two large jjranches, the
maxillary and mandibular nerves. The maxillary branch supplies with sensory fibres
the skin of tlie upper jaw and also sends motor fibres to the palatal muscle. The
mandibular branch supplies with sensory fibres the skin of the lower jaw; the largest
division of it enters a canal in the nuindibular bone, whence it supplies the mucous
membrane of the floor of the mouth. The main trunk of these two branches, the
maxillary and nuuidibular, while still within the skull, gives oil" a snuUl nerve which
leaves the skull by the great anterior opening, and passes forwards below the recti
muscles of the eye ; it supplies the anterior jiart of the palate and is called the palato-

nasal.

On the left side these branches of the fifth are much enlarged, their sensory fibres
bein" multiplied in proportion to the great development of tactile filaments and
epidermic sense-organs on this side. The palato-nasal branch reaches this side of the
head partly through the gap between the ectetlnuoid and parasphenoid, partly through
a foramen in the sphenotic in front of the large sphenotic foramen. The latter foramen
is much larger than that on the right side, and the common trunk of tlie maxillary and
mandibular nerves which passes through it is proportionally large. These branches of
the fifth on the left side are represented in PI. XV, 2, where the maxillary is indicated
by V 2, the palato-nasal by V 2a, and the mandibular by V 3. The dorsal branch
of the fiftli, which accompanies the dorsal fin, is seen passing forwards just above the

palato-nasul.

The seventh cranial nerve is called the facial ; its distribution is the same on both
sides, as it belongs to a region of which the symmetry has not been disturbed. The

pi-iucipal trunk ol' the facial leaves the skull by a circular foramen in the pronticbone,
and then passes through a foramen in the head of the hyomandibular. But after this
it is still covered by the pi-eoperculura, which must be removed before the distribution
of the nerve can be obsi'r\ed : the facial runs for some distance between the
hyomandibular and the preoperculum. Soon after its exit from the hyomandibular
foramen the nerve trunk divides into two branches, the posterior of which is the
ramus opercularis, the anterior the ramus hyoideo-jnandibularis. The rawns operadaris
(VII 2a, PI. XV, 2) divides into branches which are distributed to the skin of the
operculum. The ramus hyoideo-mandibularis divides into two branches, one of which,
the ramus mandibularis, VII 1, runs along the anterior part of the surface of the
quadrate. It gives off branches to the jaw-muscle, and into the substance of the
c^uadrate, and passes through a foramen in the head of the quadrate to the inner side
of the mandibular bone, where it supplies the transverse mandibular muscle, the oenio-
hyoid muscle, and the mucous membrane of the floor of the mouth. The other branch,
the ramus hyoideus, VII 2, bends inwards to reach the iimer side of the stylohyal
bone, and is distributed to the inner surface of the hyoid arch.

The eighth cranial nerve is the auditory, which never leaves the interior of the skull,
but is exclusively distributed to the auditory organ : it is the auditory nerve.

The ninth cranial nerve is called the glosso-pharyngeal, a name taken from human
anatomy, but not at all appropriate to the anatomy of fishes. This nerve, like the
seventh, is distributed in the same way on each side. It makes its exit from the skull
by a special small foramen in the opisthotic bone, arising from the medulla oblongata
by an independent root. On the trunk of the nerve, a little beyond its exit from the
skull, there is a ganglion of considerable size, below which the nerve bifurcates into
two branches. The anterior branch goes to the posterior surface of the operculum
and hyoid arch, the posterior to the anterior surface of the first branchial arch.

The tenth cranial nerve, called nervus vagus, is more widely distributed than any
of the others, and represents a series of nerves united into a common trunk at their
origin. The single trunk passes out of the skull through a circular foramen in the
exoccipital bone, and then divides into several branches. The first branch, the most
anterior, bifurcates into two, and has a large ganglion at the jDoint of bifurcation ;
it forks over the second branchial cleft, the front branch going to the posterior face of
the first l)ranchial arch, the posterior branch to the anterior face of the second
branchial arch. Similarly the second branch of the vagus bifurcates over the third
branchial cleft, and has a ganglion at its point of bifurcation. The third branch has
no ganglion, but bifurcates in the same way over the fourth branchial cleft. The
fourth branch bifurcates over the fifth branchial cleft, its anterior branch going to the
posterior face of the fourth branchial arch, its posterior branch to the posterior wall of
the branchial chamber and the fifth branchial arch. A nerve from this branch goes
to the heart. The fifth branch of the vagus runs down the oesophagus to tlie stomach.
The sixth branch is the lateral nerve or nerve of the lateral line : it runs close above

the vertebral centra on the ventral side of the band of connective tissue which
separates the dorsal and ventral lateral muscles. From this position it sends off nerves
which supply the sense-organs of the dermal canal of the lateral line. At its origin
this nerve gives off on each side a branch which curves upwards and forwards and runs
immediately beneath the skin along the course of the supra-temporal dermal canal on
the right side, the series of supra-temporal superlicial sense-organs on tlie left side.
On the left side there is another nerve given off from the lateral nerve at its origin : this
nerve runs immediately beneath the skin straight forwards across the side of the lateral
ridge of the skull : it supplies the superficial sense organs of the epidermis which lie
alonfj this direction. The two nerves last mentioned are shown in PI. XV, 2, indicated
as X Ga and X 6b.

PI. XV, 2, exliibits the cutaneous brancli£s of the cranial nerves on the left side, and
is intended to show the great development of these branches which has taken place in
connection with the numerous tactile filaments and epidermic sense-organs which have
been developed on the skin of the left side of the head.

CHAPTER V.

THE SKIN.

The skin everywhere consists of two layers very diflereut from one another in structure.
The lower layer, which is much the thicker, consists of fibrous connective tissue,
forming a dense tough membrane. Tliis layer is about -^th of an inch thick (I mm.).
It is clothed externally by a thin layer of cells, the longer axis of which is perpen-
dicular to the surface of the body : this is the epidermis. The lower layer or derma
contains the scales, the ends of which project backwards through the epidermis, and
the pigment cells or chromatophores. On the lower side of the head anteriorly the
skin forms a number of flexible papillte, or filaments, which are delicate tactile organs.
The skin is continued over the CA'es, but the part which covers the eve is thin and
perfectly transparent. Scales are present in the skin everywhere, except over the eyes
and in the region of the tactile filaments. The scales can be detached from the skin
without difficulty, and when separated and examined with a low power of the
microscope present the appearance shown in Fig. 1, PL XIV. The largest scales are
in the central region of the surface of either side. The scales consist of plates of
fibrous tissue hardened by the deposition of lime-salts. Each has the form of a
rectangle at the posterior end of which is a portion bounded internally bj- two straight
lines meeting at an obtuse angle, outwardly by a semicircular curve, and covered with
sixteen rows of spines. In each row the outermost spine is the largest, the other.s
becoming gradually shorter : there are five spines in each row, and the rows radiate
from the angle at which the internal bounding lines of the spinous area meet. This
spinous area is the onlv portion of the scale which is expo.sed at the surface of the skin,
the remainder being imbedded in a socket and overlapped by adjacent scales ; they
are placed with their longer axes directed backwards, and each overlaps the one
behind it. They are arranged quincuncially, that is, each scale in any transverse row
lies over the line where the edges of two adjacent scales of the row behind meet one
another. In consequence of this quincuncial arrangement the transverse rows, which
are perpendicular to the longitudinal axis of the fish, are not easily recognised ; but two
series of oblique rows are visible, one series running downwards from right to left, the
other downwards from left to right. In the same way in the pattern of a wall paper
when there is a figure repealed at equal distances in lines crossing one another at right

angles, but arranged quiucuncially, the rectangular lines cannot easily be followed,
b\it two oblique or diagonal series become conspicuous. It is the oblique rows of
scales, either those from right to left or from left to right, which are counted in
descriling the specific characters of a fish.

Tlie iml)edded portion of a scale exhibits a numljer of parallel curved lines, the
edges of the lamince of which it is composed. The directions of these lines divide this
portion of the scale into three areas : a triangular area bounded by the anterior edge
of the scale and two lines which inaet at an acute angle near the anterior apes of the
spinous portion, and two similar areas on either side of this. The anterior portion is
divided up bv a number of radiating straight lines, into radiating strips, ea^h of which
is occupied by a series of short curved parallel lines. The two other areas are
occupied by lines parallel to the dorsal and ventral edges of the scale.

The scales of Solea lascaris, variegata, and bitea resemble those of S. mdgaris in
structure. The scale of lascaris. Fig. 4, PI. XIV, is the largest : it has the same
general shape as that of vtdgaris, but the spines are more pointed, and there are
seventeen rows of them, and six spines in each of the central rows. The scale of
variegata, Fig. 3, is shorter in proportion to its breadth than that of lascaris, it has 26
rows of spines, with eight spines in each central row : the spines, except the most
external, are short and blui^t. The scale of hitea. Fig. 5, is the smallest of the four :
in shape it resembles. that of mdgaris ; it has 21 rows of spines, four spines in each of
the central rows ; the spines are rather short and pointed.

The " lateral line " which runs down the centre of each side of the sole is formed by
a series of scales which are very different from the ordinary scales of the body. They
have no spines, and no portion of them projects beyond the surface of the skin. One
of those scales from Solea tmlgaris is represented in Fig. 2, PL XIV. Anteriorly its
structure resembles one of the ordinary scales, but posteriorly it is narrowed to a blunt
apex and the spinous portion is wanting. On its external surface, for a little more
than half its length posteriorly, there runs a kind of tunnel with rounded roof which,
with the scale below, forms a tube open at both ends : this tube or tunnel is broader in
front than behind. In the floor of the tunnel, not far from the posterior end of the
scale, is a larg(> oval aperture. These scales of the lateral line overlap one another in
such a way that the aperture in the floor of the tunnel of one is just in front of the
anterior aperture of the tunnel of the scale behind it.

Dermal Canals and !>ense-organs.

This system consists of a inimber of coimected tubular channels running in the
derma or in bones originally derived from the derma. The longest and most easily
observed of these tubes runs beneath the lateral line. It is lined by a cellular layer
somewhat similar to the superficial epidermis, aiul it runs through the series of bony
tubes just described as belon<>ing to the scales of the lateral line. Tracing the tube

from before backwards we find that the tube enters the anterior end of the tunnel on
each scale and passes through the aperture in the floor of the tunnel to enter the
tunnel of the next scale, and so on. But before passing through the aperture in the
floor of the tunnel the tube gives off a branch which continues to run through the
tunnel to its posterior aperture, and passes beyond the scale to open by a pore on the
surface of the skin. Thus corresponding to each scale of the lateral line there is a
pore in the skin which leads into the dermal tube of the lateral line. The course of
che tube and its relation to the scales are exhibited in Fig. 6, PI. XIV, which
represents an ideal longitudinal section of the skin along the lateral line : sc. indicates
the scales in section, d.t , the tube, p, the external pores. The left end of the section
is the anterior. On the inner wall of this lateral dermal tube are a number of sense-
organs supplied with branches of the nervus lateralis, which in the sole as in the
majority of fishes is a branch of the vagus. If Ave follow the lateral dermal tube
forwards we find that at the side of the back part of the skull, over the parietal crest,
it becomes separate from the skin and enters the hinder branch of a triradiate bony
tube : one branch of this bone passes straight forwards for a short distance and then
terminates, and the lateral tube then enters a tube in the pterotic boue. This tube
excavated beneath the surface of the bones of the skull is continued forwards, sometimes
opening into a groove on the lateral ridge of the skull : it passes just above the
posterior corner of the sphenotic bone, and then enters the outer edge of the posterior
half of the frontal ; then it is continued as an enclosed tube through the interorbital
process of the frontal, and emerging from this enters a separate tubular bone similar
to that which lies on the outer surface of the parietal crest. This bone bifurcates each
branch ending in the skin, probably by an opening to the exterior. Tliis last bone is
the nasal : the former ma}^ be called the supra-temporal bone. [See Fig. A on the
following page.)

It follows of course from the peculiar modification of the frontal Ijones that the
cephalic portion of the lateral tube on the left side, following the course of the left
frontal bone, passes from the apparent left side of the head to the right : morpho-
logically of course it retains its proper relations, but as it passed originally dorsal to
the left eye, it has been pushed over by the movement of that eye to the right side,
and so comes to lie to the right of the anterior part of the dorsal fin. But the left
nasal bone is on the left side, for the tube after leaving the left frontal bone bends
beneath the anterior dorsal interspinous bone, to the left side of the snout : thus the
left nasal bone is attached to the skin in front of the nasal capsule of the left side.
The right nasal bone lies in front of the nasal capsule of the right side.

The supra-temporal bone, besides its posterior and anterior openings, has two others,
a dorsal and a ventral. The dorsal opening is at the end of a short branch, and leads
into a tube in the derma surrounded by modified scales, and in all respects resembling
the tube of the lateral line : this supra-temporal dermal tube in fact lies under and is
the cause of the supra-temporal branch of the lateral line described with the external

leatures of the sole. Tlie ventral opening of the supra-temporal bone leads into a
membranous separate tube, which passes beneath the skin in a ventral direction, runs
through a tube which pierces the preopercular bone, and is continued forwards to the
mandible.

Kow the supra-temporal tubes are, as we have seen, dermal, and pass through
apertures in a series of scales similar to those of other parts of the skin in structure.
On the right side the supra-temporal tube retains this structure throughout up to its
termination at the extreme apes of tlie snout. But on the left side anteriorly the
scales disappear, and tlie supra-temporal tube opens out on to the surface, its sense
organs becoming quite superficial : they are situated between the bases of the tactile
iilaments of the lower surface of the snout.

In the cod [Gad us morr/ma) the lateral cephalic tube gives off another branch

Fig. A. A diagram to illustrate the distribution of the epidermic sense-orgnns and dermal tubes on
the head of the sole, a, the anterior continuation of the lateral tube; t, the supra-tempoi-al tube;
c, the preopercular tube; (l\ the suh-ocular organs of the left side; I, the lateral Hue tube;
r.n., right nasal bone ; l.n., left nasal bom; ; t, the supi-a-temporal boue.

besides those already mentioned, namely a sub-ocular tube, which is enclosed by a
series of scale-like bones, the sub-orbital bones. This sub-ocular branch is found in
the plaice [Pleuronectes platessa) on the right side as a canal in the derma beneath
the ventral eye ; while on the left side it exists as a dermal tube between the mouth
and tlie supra-temporal tube. In the sole I have been unable to find a trace of the
sub- ocular tube on the right side, but on the left side it is represented by superficial
epidermic sense-organs distributed all over the skin between the cleft of the mouth
and the sense-organs of the supra-temporal 11 lie. In the sole there are in addition a
number of superficial sense-organs along the line of the pre-opercular tube, forming a
single series along the upper part of that tube, and spreading out over the whole area
l)eliind the mouth- cleft below.

The lateral cephalic tube and the pre-opercular tuljc, which are to a large extent
enclosed in solid bone, nevertheless commuuicate at intervals with the exterior by

means of short tubes wliicli open on the surface of the skin ; the supra-temporal and
sub-ocular dermal tubes where they exist, are also connected by short tubes with
superficial pores, so that all the tubes of the sj'stem are related to the skin in almost
the same way as the tube of the lateral line. The cephalic tubes also in allprobability
contain sense-organs similar to those of the lateral tube. The tubes of the head are
innervated by branches of the cranial nerves. The supra-ocular part of the lateral
cephalic tube receives branches from the orbito-nasal nerve, the sub-ocular tube is
innervated by branches from tlie maxillary and palato-nasal nerves, the pre -opercular
tube is supplied from the seventh or facial nerve. There is little doubt that the
lateral and pre-opercular cephalic tubes, now enclosed in solid bone, were, like tlie rest,
originally dermal tubes enclosed by tubular scales. In fact, the bones through which
they pass represent dermal scales fused together. The tubes and the bones thus
produced have sunk beneath the skin, and the bones have become part of the skull.

Pig. B. A diagram to illustrate the distribution of the dermal tubes in the head of the cod. Letters
as in the diagi-am of the sole.

But all these dermal tubes at a still earlier period were part of the external surface of
the skin. The sense-organs of the tubes and their epithelium are really derived fi-om
the epidermis. In some cases the organs of the lateral line are superficial throughout
life, for example, in the gobies and tlie mullet, and in all cases they are developed in
the embryo or young fish in the external epidermis. The tubes are formed both in
evolution and development by the deepening and ultimate enclosure of grooves on the
surface which include the sense-organs.

In the cod, which may be taken as exliibiting pretty nearly the original condition
of the cephalic tubes of the sole and other flat-fishes, there are no superficial sense-
organs on the head, and the tubes of the two sides are symmetrically arranged.

The diagram, Fig. B, shows the position and the relations of the cephalic tubes in
that species. The supra-temporal tubes are short, and are surrounded by thin tubular
scale-like bones. The sub-ocular tube is also enclosed in a series of tubular bony
scales, the sub-orbital bones. Both these and the supra-temporal bones, though
homologous with the ordinary dermal scales, are not similar to them, having a much
larger size and deeper position.

In the sole the changes which have taken place in the course of evolution are as
follows : The supra-temporal tubes have become much elongated, having grown
forwards with the anterior extension of the dorsal fin till they reach the extremity of
the snout. On the right side the tube is no longer enclosed by peculiar scale-like
bones, but by tubular dermal scales, closely resembling the ordinary scales of the skin.
On the left side of the head, the scales having disappeared anteriorly, the supra-
temporal tube has opened out on to the surface, and the sense-organs which belong to
it have become superficial. The two supra-temporal tubes are symmetrical in relation
to the two sides of the dorsal fin, but entirely asymmetrical in relation to other parts
of the head; for in consequence of their relation to the fin they both lie morpho-
logically ventral to the left eye, between the left eye and the mouth.

The lateral cephalic tube of the left side has been distorted by the change of
position of the left orbit. Its posterior part retains its original position, but its
anterior or supra-ocular part lying in the inter-orbital process of the left frontal bone,
bends round towards the right side and runs close beside the right supra-ocular tube
between the two eyes.

The sub-ocular tube of the right side has disappeared; that of the left side is
represented by the immerous superficial sense-organs which lie above the mouth on
the lower side of the head.

The two pre-opercular tubes remain in their original position, but on the left side a
i\umber of superficial sense-organs have been developed over the region of the
j»re-opercular tube. This is, in some respects, one of the most remarkable of the
peculiar developments in the head of the sole. It is intelligible that a dermal tube
originally derived from a superficial groove should again become superficial ; but it is
surprising to find surperficial organs developing anew, outside a tube which contains
similar organs originally derived from the siiiface.

The supra-temporal tubes are innervated by a long branch from the lateral nerve
belonging to the vagus. On the left side a similar branch of the vagus passes
forwards towards the sub-ocular sense-organs. Along the proximal part of the course
of this nerve is a single series of superficial sense-organs, which lies over the proximal
pai-t of the lateral cephaUc tuljes. I have not been able to decide whether this series
really belongs to the sub-ocular series of the left side, or bears the same relation to the
proximal part of the lateral cephalic tube as the pre-opercular superficial organs to
the pre-opercular tube. In studying the relations of the mucous tubes and epidermic
sense-organs in the head of the sole, I have been very greatly assisted by a jjaper by

Dr. Eainsay H. Traquair, publialied in 18G5." The sole is not considered in this
paper, but the interpretation of the distribution of the orrraiis and canals in this
species is comparatively easy after Dr. Traquair's lucid explanation of the derivation
of the arrangements found in other flat-fishes from the original symmetrical condition.
The diagram of the arrangement in the cod which I have given is copied, with
slight modifications, from Dr. Traquair's ; and my diagram of the arrangement in the
sole is constructed on the same plan as his diagrams of the arrangements in the plaice
and other species.

Minute Structure of the Skin, Dermal Tubes, and Sense-orrjans.

When thin sections of the skin are prepared and examined under the microscope,
the derma is seen to be composed of a number of sheets and bands of felted fibres, as in
PI. XIV, 6. In my preparations no nuclei are visible in this tissue, Init the pieces of
skin were decalcified in weak nitric acid before they were cut, in order to remove the
lime from the scales, and the action of the acid may have somewhat altered the
condition of the fibrils. The scales, as seen in section, consist of thin lamince lying one
upon another ; the laminae are entirely homogeneous in structure, and seem to be
simply sheets of the fibrous tissue which have been consolidated and then impregnated
with calcareous salts. The scales are contained in cavities of the fibrous tissue. In the
preparations the fibrous tissue is separated slightly from the surface of the scales, but
this is doubtless due to the shrinking produced by the process of preparation, and in
life the fibrous tissue is in contact with the surface of the scale. Above the scales
there is a layer of delicate spongy fibrous tissue in which the fibres are short, and run
in a vertical as well as a longitudinal direction ; this reticular tissue contains
numerous nuclei. This tissue separates the external surface of the scale from the
dense fibrous laminated tissue, while the internal surface of the scale is in immediate
contact with the latter. The epidermis consists of several, six or seven, layers of cells.
At the base of the epidermis the cells are polygonal and as broad as they are high :
each cell contains a large nucleus, which becomes deeply stained under the action of
staining liquids. Towards the outer surface most of the cells become thin and flat,
as in the human epidermis, but in preparations a certain number of them are large
spherical vesicles. These are mucous cells. The surface of the sole as of most other
fishes is, during life, always covered with a certain amount of slimy mucus which is
derived from the epidermis. This mucus is produced by the discharge of the contents
of the globular mucous cells just mentioned. The cells at the base of the cpidermLs
are constantly multiplying and growing, and in consequence the outermost of them
are gradually pushed to the surface. The superficial layers are as constantly broken
down and, as it were, dissolved away, some of the cells becoming, before they reach
the surface, converted into capsules of mucus, and this mucus, together with the

* "On the Asymmetry of the Pleuronectidoe, as elucidated by an Examination of the Skeli'tou in
the Turbot. ILiIibnt, and Plaice." (-'Trans." Lin. Sue, vol. x.xv.)

8(.

debi-is of the other superficial cells, forms the slimy coating of the fish's skin. There
are no special glands connected with the skin of the sole.

In the outermost layers of the fibrous derma, immediately beneath the epidermis,
are situated the pigment cells or chromatophores. Some chromatophores are also
found in a deeper po.sition, in the fibrous tissue which lies between the deeper parts of
the scales, but no pigment is found below the level of the skin to which tlie anterior
edges of the scales reach. The epidermis and the thin subjacent layer of the derma,
which contains the chromatophores, are continued over the exposed portions of the
scales, with the exception of the longest most posterior spines of the scales : these pierce
through the skin and epidermis and project beyond the latter.

The appearance of a longitudinal section through the dermal tube of the lateral line,
magnified 40 times, is shown in Fig. 6, Plate XIV. In other parts of the skin muscles
are of course found below the derma, but the dermal tube of the lateral line lies
directly above the connective tissue partition between the dorsal and ventral lateral
muscles, and the connective tissue of this partition passes directly into the skin.
The fibrous tissue of this partition contains large spaces occupied by loose
reticular tissue the meshes of which are large and filled during life with lymph;'
this tissue is seen in the lowest part of the figure. The figure includes one whole scale
of the lateral line and parts of two others ; the three pores, p,p,p, corresponding to
these scales are seen leading into the dermal tu])e. The section passes longitudinally
through the centre of the dermal tube and therefore the roof of the tunnel formed by
each scale is seen above the dermal tube, and the floor below it. The dermal tube is
seen bending down to pass through the hole in one scale to enter the tunnel of the
scale behind it ; beyond the hole in the floor of the scale a branch of the dermal tube
passes backvvards to open on the surface at the external pore. The dermal tube is
lined by an epithelium which is only separated from the surface of the scales by
a very thin fibrous membrane. This epithelium is continuous with the epidermis at
the external pores, but diflers much from the epidermis in character. It is of verj-
slight thickness, consisting only of two or three layers of cells. The lowest layer
consists of small undifTerentiated cells which grow and multiply, continual!}'
replenishing tlie outer layers. Nearly all these outer cells are globular and vesicular;
that is they form hollow capsules, doubtless containing nuicus. During life the dermal
tube contains mucus, which is the product of this epithelium. But at certain places
this epithelium contains sense-organs, consisting of portions of the epitlielium which
have an entirely diflerent structure and function. The cells of the sense-organs are not
secretory but sensory, and they are connected with nerve fibrils. One of these sense-
organs, as seen in longitudinal section, is shown at s.o, in PI. XIV, G. It is situated on
the inner wall of the dermal tiil)e, and lies on the floor of the tunnel of a scale a little
in front of the hole through which the dermal tube passes to the next scale. At a point
near the anterior and deep border of the scale containing the sense-organ there is a
small aperture in the scale through which a nerve passes from the skin below the scale.

This nerve (n, Fig 6) runs posteriorly along the surface of the scale, beneath the
epithelium of the dermal tube, to the sense-organ. The sense-organ consists of a
number of thin elongated cells placed so that their length is almost perpendicular to the
wall of the dermal tube. Each of these cells contains in its lower portion a spindle-
shaped swelling which contains a nucleus. One end of each cell reaches the surface of the
sense-organ, and the other reaches its basement membrane : the cells are all in contact,
the nuclear swellings being so arranged that the cells are packed in the least possible
compass. Thus the nuclear swelling of one cell is at its base, that of the next some-
what higher up, so that the nuclei form two rows, and the nuclei of some of the cells
are even higher still, forming a third row. But it is only the nuclei wliicli are in two
or three layers, the cells are all in a single layer side by side. The nuclei, in spite of
the arrangement described, occupy more space than the cells, and consc^qnently the
base of the sense-organ is broader than its surface, so that only the central cells are
straight, the external cells curving at their upper ends towards the centre of the sense-
organ. The upper end of each cell ends in a delicate protoplasmic hair which projects
into the cavity of the dermal tube. The lower end of each cell is continuous with one
of the ultimate fibrils of the nerve previously mentioned. I have not made out this
connection in all the cells, but I have traced it in some, and l:)elieve that it exists in all.
In some preparations a kind of clot is seen on the surface of the sense organ, and
sometimes this seems to have separated from the surface of the organ, breakino- ofTthe
sensory hairs and taking them with it. This clot often present a laminated appearance,
as if formed of thin layers one over another. It has been seen in some fishes in an
organ examined in a perfectly fresh condition. Prof. Emery* concludes that the lamince
of the clot, which is generally called the cupula, are successive cuticles secreted by
the peripheral cells of the sense organ. I think it is difficult to accept this conclusion,
and am inclined to think the cupula is, during life, of a mucous nature, and therefore
semi- liquid. It seems certain that the sensory hairs are imbedded in the cupula. It
is difficult to understand how such cells as those of the sense-organ sliould secrete
mucus or form a cuticle : perhaps the cupula is nothing more than the ordinary mucus
of the dermal tube which keeps a constant position in preparations because it is retained
by the numerous sen.sory hairs.

There is not a sense-organ to every scale of the lateral line ; in the middle of the
body there is a sense organ on every third scale, that is to say, there are two scales
bearing no sense-organs between two scales which bear them. The position of the
sense-organ in relation to the scale on which it is situated is always the same.

The function of these sense organs is still entirely imknown. It has been suggested
that they convey to the fish a sense of its position in the water, and so enable it to
retain its vertical position, but the evidence for this is not very conclufive : if it were
true we should expect to find the organs atrophied in the flat fishes which have

* ■' Fauna nnrl Flora de.s Golfes von Xeapel." " Fierasfer."

abandoned the vertical position altogetlier. What stimulus afTects the organs it i.-*
difficult to imagine : and it is also difficult to understand how the sensory hairs act
immersed as they are in the substance, whether it be mucu.s or not, which forms the
so-called cupula. But that these organs are of great importance to aquatic vertebrates
there can be no doubt, since they occur not only in all kinds of fishes but in aquatic
Amphibia : they are even present in the tadpole and other larval batracliians so long
as they retain their aquatic respiration.

These sense-organs are in all cases first developed in the superficial epidermis ; the
development of the dermal tube in which they are enclosed takes place subsequently.
The dermal tube is formed from a superficial groove which appears on the surface of
the skin along the line where the sense-organs are situated. The groove becomes
deeper and its edges meet over it and coalesce everywhere except where the pores are
left by which the tube communicates with the exterior. In some fishes, e.g., Gobius,
the sense-organs remain superficial tluuvighout life, no lateral dermal tube being
developed.

As I have already mentioned (p. 7G) there are also a number of superficial sense-organs
on the under side of the head of tlie sole. These organs are situated in the depressions
between the villi or tactile filaments with which the skin in this region is provided.
The minute structure of this part of the skin is illustrated by Fig. I, Plate XV,
which is drawn from a section of the part of the skin above the posterior half of the
mouth cleft on the lower side of the body. Some of the filaments are long and slender,
others short and blunt. Eunning up the centre of each filament is a sausage- shaped
supporting rod which is composed of a tissue having the structure of fibro-cartilage.
In section this body exhibits fibres anastomosing with one another and running in a
direction transverse to the longer axis of the rod. These fibres contain nuclei, and
the interspaces between them are filled l)y a homogeneous solid substance of the
nature of cartilage. These supporting rods belong to the derma. The epidermis is
continued over the filament, l)econiing thinner at the apex, and between the supporting
rod or core and the ei)idcrmis is a continuation of the fibi'ous tissue of the derma.
Eunning up the sides of the supporting rod are several fine nerves. These nerves send
off fibrils which branch, and tlu-ir ultimate ramifications enter the epidermis. There
are no special sense-organs of any kind in connection with these nerve fibrils : the
ultimate termination of the fibrils I have not been able to trace : they penetrate between
the cells of the epidermis, and doubtless ultimately come into connection with some of
the epidermic cells. Nerve-fibrils are known to eiiter the epidermis in the same way in
the skin of the tip of the human finger, and in all probability help to give that skin its
delicate sense of touch. I have indicated the connection of the ultimate nerve-fibrils
with the epidermis on the right side of the figure. On the left side of the figure
are sections of four short blunt filaments which do not project far beyond the surface
of the skin. Around tlie cores of these, besides the black lines indicating parts of
nerves, is a coarse stippling which represents the appearance of a curious granular

tissue occurring iu lliis position in all llie lilanicuts. This tissue obscures the nerve
fibres and makes it somewhat difficult to follow out their course iu the sections. The
sections from which the present description is taken, and one of wliich is represented
slightly diagrammatically by the figure, were prepared from pieces of skin treated when
fresh with chloride of gold. This reagent stains the nerves black or violet, and aflects
the remaining tissues slightly or not at all. Thus the nerves can be traced through the
granular tissue just mentioiied. Tlie granular tis.sue is somewhat opaque, consisting of
irregularly branched cells the contents of which are coarsely granular. These cells
exactly resemble iu structure the chromatophores of the right or coloured side of the
body, but the}' are not coloured. In fact, to use a seeming paradox, these cells are
colourless chromatophores ; that is to say, they are chromato])hores of which the granules
instead of being black or orange ai-e white and opaque. 'J hus the white colour of the
under side of the sole is not due to the absence of chromatophores, but merely to the
absence of what is usually called colour in the chromatophores; the pigment cells are
not absent from the skin of the lower side, but are bleached. It is a very connnon
thing to find coloured blotches on the lower side of a sole, and from the above it is
evident that these coloured blotches are not due to the development of chromatophores
iu certain areas while they are absent elsewhere, but are due to the fact that the
chromatophores in these areas are coloured, while in the rest of the skin of the lower
surface the}' are white.

One of the superficial epidermic sense-organs of the under side of the head is
represented in section in the figure. It will be seen that they do not differ in structure
from the sense-organs of the dermal tube of the lateral line. The sensory hairs are
present in these organs, though not shown in the figure, as they are not well jireserved
by the chloride of gold method of preparation.

CHAPTEI! Vr.
EMBEYOLOGY.

The ripe ovum of Solea vuhjarU after it lias been removed from the bocly of the fish
and is floating in sea water, and wlu-n it has not been fertihsed, has tlie followinir
structure: The whole ovum is a spherical transpai'ent body measuring \\1 to 1'51
mm. ('05 to '06 inch) in diameter, the size of different eggs varying within these
limits. The ovum consists of a definite thin transparent membrane surrounding a
solid mass ; the former may be called the vitelline membrane, the latter the ovum in a
stricter sense of the word. The whole of the egg with its envelope corresponds only
to the yolk of a hen's egg, there is nothing about it which represents the " white " or
the shell of the latter. The yolk of a hen's egg is surrounded by a thin membrane of
its own which corresponds to the vitelline membrane of the sole's eg^. The ovum
])roper within the vitelline membrane consists of two different parts : a smaller
somewhat protuberant portion which is more granular and less transparent, and a
more transparent larger portion. Tlie former is the germ (blastodisc), and consists of
living organic matter known as protoplasm. Tiiis germ is actually alive, and it
exhibits spontaneous movements and changes which gradually lead to the formation of
the young fish, while the larger portion is the yolk, and is simply a supply of very
nutritious food on which the germ lives and by means of which it grows. TJie yolk is
in fact gradually aljsorbed by the embryo during its development. In consequence of
the protuberance of tlie germ, the vitelline membrane being stiff and spherical, tliere is
a space between the membrane and the surface of the ovum all round the junction of
the germ with the yolk : this is the perivitelline space. Immediately lieneath the germ
the yolk is divided up into large separate masses of a cubical sliajie : these masses
form a single layer, the rest of the yolk being undivided. The yolk is more or less
liquid, and it is confined within a delicate pellicle of protoplasm which extends from
the edge of the germ all round the yolk. Thus the yolk is really contained williiii the
protoplasmic germ. In fact the germ is the essential part of the ovum; some animals
produce ova without either membrane or yolk : the yolk is to be regarded as an
accumulation of food material within the protoi)lasm ol a reproductive "cell" or plastid.
On the surface of the yolk, immediatel}' beneath its protoplasmic pellicle, are several
groups of minute oil globules. On account of their refracting power these appear

8.')

opaque white by rellected light and durii. by traiisiuiLLed hghl. They represent an
excess of fatty matter belonging to the yolk.

I have not seen the ripe ovum of the sole immediately after its escape from the ovary.
But the ova of other flat-fishes have been studied by myself and others immediately
after extrusion, and it has been found, e.g., in the cod and the flounder, that at first
the germinal protoplasm is not aggregated into a protuberant mass, but is more
extended over the surface of tlie yolk, and that the vitelline membrane is everywhere
in direct contact with the ovum. The aggregation of the protoplasm into a distinct
germinal mass and the consequent formation of the perivitelline space take place after
the extrusion of the ovum, and take place in the same way whether the ovum is
fertilised or not.

I have not particularl}- studied the spermatozoon of the sole, but have observed it
sufficient^ to state that it does not differ in structure in any important respect from
that of other flat-fishes. The milt is very scanty in quantity and thin and transparent
in appearance, but its peculiarities will be considered in connection with the subject of
the artificial propagation of the species. I have given a figure of the spermatozoon of
the dab, Pleitronectes limanda, PL XIII, 7, having accidently omitted to make a drawing
of that of the sole. In all bony fishes (Teleostei) the head of the spermatozoon is pear-
shaped, the pointed end being directed forwards in motion. The long slender vibratile
filament or " tail " is attached to the broader end of the head. The spermatozoa are
exceedingly small, quite indistinguishable to the unaided eye, but when the fresh
milt is placed under the microsco]3e multitudes of them are seen actively lashing
themselves about in all directions. The total length of a spermatozoon of the sole is
about xo-Qotli'' of ^^ '\nc\x ("07 mm.).

Fertilisation of the ovum usualh' takes place immediately after extrusion, and
consists in the entrance of a single spermatozoon into the germinal protoplasm. I
have not studied the details of the process in the sole's ovum, but have done so in the
ova of the dab {Pleuronectes limanda) and another species [PI. ojnoglo.ssus). The
process in the sole is doubtless the same as in these species, and is as follows : Over
the centre of the germinal protoplasm there is a minute aperture in the vitelline
membrane which is called the microp}'le. Through this ajDerture a spermatozoon passes,
and penetrates into the germinal protoplasm. In the latter is the nucleus which, as
the ovum matures, becomes indistinct, and can only be made visible by coagulating
the protoplasm with acetic acid or some other chemical reagent. This nucleus can
also be stained, as it absorbs colouring fluids, such as solutions of carmine, to a greater
extent than the surrounding protoplasm. The nucleus before fertilisation is complete
passes to the surface of the germ and gives off in succession two small portions of itself,
the polar bodies, which are expelled from tlie ovum. The nucleus after this forms the
female pronucleus, and the head of the spermatozoon which has entered the germ
forms a similar minute body, the male pronucleus : these two unite into a single
nucleus, the segmentation nucleus

The fertilised ovum ol' llie sole, then, jjossesses the same stiucture as was above-
described in the unfertilised, aud also something not mentioned in the previous
description, namely, a nucleus in the germ formed by the coalescence of two pronuclei,
one derived from the nucleus of the unfertilised eg^:, the other from the head of a
spermatozoon.

The first visible change which takes place after fertilisation is the division of the
germinal mass into a number of small segments. The mass first divides into two
halves separated by a superficial furrow extending across its middle. Another furrow
then appears crossing the first, so thai the mass is divided into four portions. Each of
these divides again into two and then into four, so that there are now sixteen segments.
Then divisions take place in a direction parallel to the surface of the mass, so that it
comes to consist not of one layer of segments, but of several layers. As this process
of segmentation continues the segments continually become smaller, so that the
condition is reached which is seen in Plate XV, Fig. 3. During this time movement of
the protoplasm on the surface of the yolk and between the yolk segments has caused the
latter to extend somewhat beyond the edges of the germinal mass.

The mass of protoplasmic segments into which the original single large mass has
thus been converted now begins to become thinner and broader, extending itself
so as to envelop the yolk, us in Plate XV, Fig. 4. When lliis })rocess begins a cavity
is formed between the yolk and the central part of tlie germinal mass. The germinal
mass as it extends over tlie surface of the yolk soon becomes so thin that it must now
be called the germinai membrane (blastoderm). Fig. 5 shows the stage at which the
germinal membrane has enveloped more than half the yolk. The external part of the
irerminal membrane for some distance from the edue is thicker than the central
portion : this tliicker portion rests upon the yolk, while the central part is separated
from the yolk by the flat cavity already mentioned. This cavity is not exactly in the
centre of the membrane, the thicker external ring extending farther inwards (on the
right of Fig. 5) at one point than elsewhere : this broadest part of the germinal ring is
also the thickest part, and it forms the rudiment which will give rise to the upper or
dorsal })art of ilie body of the young lish. It nni.st Ije observed tliat tlie layer of yolk
segments extends jyari passu witli the germinal inenibrane, aud that llic patches ni oil
'dobules are alwavs at the edjjfe of the extendinsf membrajie.

As the germinal membrane continues to extend the circumference of the germinal
ring of course gets smaller ; the rudiment of the young fish above menticjned remains
with its internal extremity in the same position, continually increasing in length as the
edge of the nuMul)rane extends over the yolk, until when the yolk is completely
enclosed, the whole of the germinal ring has been taken uj) into this ludiment. The
dorsal rudiment by this time has become much thicker and forms an almost cylindrical
rod, from the sides of which the germiiuil membrane extends over the yolk. The oil
♦^lobules are now arranged beneath the sides of the dorsal rudiment, while the volk

segments fonn a layer exteudiug over the whole surface of the j'olk. The end of the
rudiment which was originally turned towards the centre of the germinal membrane
becomes enlarged and forms the head of tlie iish ; the point where the edges of the
membrane closed together forms the posterior end. After a short time two spherical
masses are seen defmed in the head of the embryo : these are the first rudiments of the
eyes. The centre of the dorsal rudiment begins to be divided by transverse divisions
into segments: these segments are blocks of tissue which will afterwards form the large
lateral muscles of the fish. At the tail end a small round cavity appears, which
afterwards becomes part of the cavity of tiie intestine. These various structures are
seen in Plate XV, Fig. 6, and Plate XVI, Fig. 1, one of which shows a profile, the other
a ventral, view of the embryo at the stage now described.

At this stage scattered black dots have appeared on the external surface of the dorsal
rudiment, extending out over the surface of the yolk some distance from the sides of
the latter. These are pigment cells, and are situated in the skin : they are usually
called chromatophores.

What I have called the dorsal rudiment is the solid dorsal portion of the young fish
containing the rudiments of the brain and spinal coi'd, of the backbone below these,
and of the lateral muscles at the sides. The yolk sac represents the abdomen of the
young fish. The intestine is formed as a simple tube beneath the dorsal rudiment
resting on the surface of the yolk. It is at first closed at each end, neither mouth nor
anus being yet formed

After this stage a cavity appears at the anterior end of the embryo between the
germinal membrane and the yolk. The segmentation cavity previously described
ceased to be visible after the envelopment of the yolk by the germinal membrane, the
latter having come into contact with the former. The cavity which now appears has
exactly the same position as the segmentation cavity. The embryo grows out
posteriorly, forming a tail which is independent of the yolk sac. The black chromato-
phores increase in number and extend over the whole surface of the yolk sac, al the
same time they become branched, sending out short branches in all directions so as to
assume a stellate fornr. Other chromatophores also appear in addition which are of a
yellow colour, appearing darker when seen by reflected light. These changes are seen
in Plate XVI, Fig. 2.

As the tail increases in length a fold of the skin is formed in the middle line alongf
its dorsal and ventral edge ; the dorsal fold extending to the head of the embryo. The
other changes which have taken place by the time the young fish is hatched will be
understood by reference to Plate XVI, Fig. 3, which shows the fish immediately after
hatching. The yolk is now considerably diminished and the intestinal tube opens
behind it by the anus. The tail measui'ed from the anus is as long as the distance
from the anus to the front of the head. The wide membranous fold is seen extending
along the middle ventral line of the tail and along the median dorsal line of the fish to
the back of the head: this is the primordial median fin. There is still no n;outh.

Behind the eye is a small oval cavity containing two specks. This is the primitive ear,
the black specks being small particles of carbonate of lime formed within the auditory
cavity. Beneath the throat is seen a small tubular structure, which in the living young
lish pulsates regularly : this is the heart. From the line where the wall of the yolk sac,
or abdomen, joins the body there projects a semicircular membranous fold, which is
the beginning of the pectoral fin. No indication of the pelvic fins is yet present. The
trunk of the young fish is seen to be divided by a series of curved transverse lines :
these are the divisions between the muscular masses of which the trunk muscles are
composed. A kind of tube runs down the centre of the body, the contents of which
show a recticulate structure. This tube is the notochord, which contains gelatinous
material in a number of cavities divided from one another by thin partitions like the
cavities of a sponge. No bone is yet formed, but the vqrteljraj when they develop
arise as a series of bony rings formed round the notochord. Tlie chroma tophores are
now much more abundant than in the embryo before hatching ; there are still only
two kinds, the black and yellow, and both are much branched ; the two kinds are
evervwhere mingled together. The pigment is abundant in the primordial median fin,
except at its posterior e.Ktremity.

Fig. 4 is a drawing from another recently^hatched sole, a few hours older than that
.shown in Fig. 3. It will be observed that this figure shows the left side of the fish,
while Fig. 3 shows the right side, and that the two sides correspond in all respects.
The newly-hatched sole, or larva of the sole as it may be called, exhibits perfect
bilateral symmetry and therein resembles the adults of the greater number of marine
fishes. In Fig. 4 the olfactor}- organ is seen in front of the eye : it is on each side a
simple rounded cavity opening by a small aperture to the exterior.

It may be explained here, though it is not evident in the figures, that tlie cavity
surrounding the yulk in the larval sole contains primitive l)lood; this ])rimitive blood
contains minute colourless corpuscles, but no red corpuscles, which are not formed till a
later stage. The posterior end of the heart is open to this cavity, and the blood is
propelled from the cavity along the vessels at the side of the throat into the aorta
which runs beneath the notochord, and from the aorta to the cavity again.

The newly-hatched larva is from 3"o5 to 3'7.5 mm. in length (•14'2 to '15 inches), or
Ijetween one-seventh and one-sixlh of an inch, and al)out two and-a-half tiiiies as long
as the di.ameter of the ovum.

Up to this point the stages t)f development have been descril)ed as they are seen in
the living egg or newly-hatched fish, and all the figures referred to are fiom drawings
made by the aid of the camera lucida with a low power of the microscope. But,
although I have not studied the subject especially in the egg of the sole, it will be con-
venient here to give a brief description of the internal processes of development so far
as they are known to occur in the eggs of fishes.

The germinal ring when examined by means of prepared thin sections is found to
consist of three lavers of cells. The outermost, which is two cells thick, is called the

epiblast, and gives rise to the epidermis and otlaer organs, tlie innermost, which is only
one cell thick, is called the hypoblast, and gives rise to the intestine, the middle layer is
called the mesoblast, and gives rise to the bones, muscles, and blood vessels. In the
dorsal rudiment the same three layers are found, but the epiblast is here thickened into
a great keel which extends inwards and causes the projection of the rudiment; the
greater part of this keel ultimately separates from the extreme outer layer and forms
the brain and spinal cord. In the centre of the rudiment beneath the keel is a
cylindrical rod of cells which become converted into an elastic supporting structure,
the notochord. Eound the yolk, when it has been completely enveloped, there is a
layer of protoplasm containing nuclei, but not divided up into cells. The hypoblast
rests on this layer which is called the periblast. In the ventral region of the developing
embryo there is nothing but epiblast separated from the periblast by the flattened
cavity previously mentioned and called the segmentation cavity. The hypoblast bends
round and forms a straight tulje which lies in a depression in the periblast. This tube
is the intestine, and when first formed has neither anterior nor posterior opening,
neither mouth nor anus. The swelling of the anterior part of the epiblastic keel forms
the brain and causes the protuberance of the head. The sense organs are formed by
thickenings of the epiblast: these thickenings become hollow and globular and, sinking
into the interior part of the head (except the nasal organs), become connected with the
brain by the sensory nerves. The nasal organs become cup-shaped, their cavities
being open to the exterior by a single aperture each, which is ultimately divided
into two, the two nostrils of each organ. The heart is formed from mesoblast which
extends below the front part of the intestinal tube ; it opens posteriorly at first from
the segmentation cavity, but when the yolk is absorbed becomes connected with
veins. The inner part of the mesoblast forms the muscles and skeleton, the outer part
forms the fibrous layer of the skin in which the scales are produced. Eings of bone
formed round the notochord give rise to the vertebrae, while the bones of the skull
are formed from the mesoblast round the brain. The formation of the mouth and gills
takes place after hatching by the development of rods of cartilage between which clefts
appear placing the anterior part of the intestine in communication with the exterior.
The mesoblast on each side splits horizontally, its inner thinner layer remaining
attached to the intestine to form the muscles and fibrous tissue of the gut, while the
outer part forms the body muscles. The cavity thus formed is the body cavity, and at
the dorsal part of it are formed the kidneys and reproductive organs. The liver is
formed as an outgrowth from the intestine. The fins are merely folds of the skin, the
mesoblast of which gives rise to their muscles and bony rays.

I have not succeeded in obtaining any specimens of the young sole in process of
metamorphosis ; the next stage in which I have met with it is that of a small fish
having in almost all i-espects the same structure as the adult. The smallest specimens
of this kind which I obtained were from ^ in. to f in. in length (12 to If) mm.).
One of them is represented in Plate XVI, Fig. 5, magnified 8^ times. The great

similarity of the young sole at this minute size to the full-grown adult is evident from
the figure. The chief difference is in the relations of the intestine. The right lateral
diverticulum of the body cavity is scarcely at all developed, and the four lengths of
intestine which occupy that diverticulum in the adult are absent. The intestine
extends backwards only very slightly beyond the anterior ventral interspinous bone.
The dorsal eye is slightly nearer to the edge of the head than in the adult, otherwise
the metamorphosis is complete. The colour has disappeared from the lower side, the
markings of the species are completely developed on the upper side. The pigmentation
of the upper side is not nearly so dense as in the adult, and the whole body is some-
what translucent, but nevertheless when the young fish is seen in the living state by
reflected light, whether resting on the bottom or swimming horizontally in the water,
its upper side shows the same colour as the adult, and undergoes the same changes of
colour on different materials in consequence of the action of light. The identification of
the young sole, Solea vulgaris, at this stage is neither doubtful nor diflJicult, for, although
some of the characters of the adult are not discernible, others can be perceived easily-
enough. The large number of anal fin rays distinguishes it from either S. varieijata
or minuta, while the tubular form of the anterior left nostril distinguishes it from
lascaris. I obtained specimens of this stage on three occasions within a short time, in
1889, from the shore at low water at spring tides. On the third occasion I received
only one specimen which was nearly three-quarters of an inch long (18 mm.).

I could not trace the further development of these young soles, for they disappeared
from the shore. But no important changes of structure were required to produce the
adult, further development consisted almost entirely in the increase of size. For the
discussion of the later growth reference must be made to the next part of this
memoir.

The only other species of Solea whose development I have been able to study is
S. variegata. The eggs of this species are smaller than those of vulgaris, measuring
1-28 to 1-36 mm. in diameter. The egg, Plate XVI, Fig. 6, is easily recognised and
distinguished from that of S. vulgaris by the peculiarity of its oil globules, which, instead
of being very minute and numerous and aggregated in a number of distinct groups,
are of considerable size and scattered singly and separatel}'' all over the surface of the
yolk. The external layer of segmented yolk is present as in *S. vulgaris. The develop-
ment of course takes place in the same way as in the latter. When the chromatophores
appear they form another distinguishing feature ; there are both yellow and black
chromatophores as in vulgaris, but the former are much lighter in this sjjecies, inclining
to lemon colour, while those of vulgaris are darker.

Figs. 1 and 2 on Plate X"VT!I show two stages of the hatched larva of the " thick-
back." The younger. Fig. 1, inuuediately after hatching, has of course the largest
yolk-sac and the shortest length of body ; it is 2*42 mm. in length. The heart
is just visible, but is compressed between the yolk and the under side of the throat,
the pericardium being but slightly developed and scarcely visible. The stage shown

in Fig. 2 is that of a larva two days after liatcliinp ; the larva from which the figure
was taken was 2'52 mm. in length.

The eggs of the other species of Solea I have not yet seen, but for the sake of
comparison I have illustrated the development of several species of flat-fish. Figs.
3, 4, 5, Plate X^II, and Fig. 1, Plate XVIII, represent a series of stages in the
development of the common flounder, Pleuronectes Jlesiis, from the time of hatching
till the completion of the metamorphosis. Fig. 3, Plate XVII, is from a larva hatched
under artificial conditions on February 18, 1889, and drawn two days afterwards:
its length was 3-5G mm. The chromatophores are arranged in such a way as to form
two transverse bands, one at the level of the anus, the other some distance behind it ;
two dark bands in these positions are more or less conspicuous in several species of
Pleuronectes in the adult condition. Fig. 4 shows the same larva when the yolk has
been entire!}' absorbed and the mouth and gill-slits have been developed : its length was
3' 94 mm. The pectoral fin is relatively very large at this stage. This condition was
reached in confinement on February 24, by larvae hatched on February 18. The next
stage was observed in young fish found in the harbour at Mevagissey at low tide on
April 2, and is represented in Fig. 5. The length of the fish from which this
figure was drawn was 10 "5 mm., or a little over three-eighths of an inch. This stage
is the beginning of the metamorphosis. The left eye has travelled upwards so as to
project al)Ove the edge of the head, but it is still on the left side. The little fish in
this condition swims on its edge, but slightly inclined to the left side. It is still
extremely transparent, so that when alive it is only rendered visible by the metallic
brilliancy of the choroid coat of the eyes, which shine through the transparent tissues
in the sun like two metal beads. The yellow spot in the visceral cavity in the figure
is the gall bladder. Fig. 1, Plate XVIII, shows a later stage in which the left eye
has reached the edge of the head, so that its lens and cornea are visible on the right
side. The fish from which this figure was taken was actually smaller than that
represented in Fig. 5, Plate XVII, probably because its metamorphosis had begun
somewhat earlier. It seems that in some individuals the metamorpliosis is completed
while they are smaller in size than others at an earlier stage of development. The
fish represented in Fig. 1, Plate XVIII, was exactly 1 cm. in length. It was much
more opaque and more pigmented than the stage previously described ; in fact, though
slightly translucent when seen under the microscope by transmitted light, to the
unaided eye it appeared quite opaque. It wiU be noticed that the interval of time
between the stage of Fig. 4, and that of Fig. 5, Plate XVTI, was about five weeks, and
that in that time nearly all the organs had reached their final form. The muscles
and skeleton have developed very greatly. The part of the body behind the anus
has increased v&vy much in dorso-ventral breadth, and in it the vertebra; with their
spines, the interspinous bones, and the fin rays have been completely formed.

Fiw. 2, Plate XVIII, represents the larva of tlie dab (Pleuronectes limanda) imme-
diatelv after hatching. The larva from which this figure was taken was hatched in

the Laboratory from an egg artificially fertilised on March 1, 1889. The length
of the larva was 2"87 mm. The development of chromatophores in the median
fin fold does not take place in this species at so early a stage as in P. flesus.

Fig. 3 of the same Plate represents a stage in the development of P. microcephalus,
the merry sole of the Plymouth fishermen, the lemon sole of Scotland and most parts
of England. The larva from which this figure was drawn was also hatched in the
Laboratory, and was four days old ; a small quantity of yolk still remained in the
body cavity. The chromatophores at this stage form five well-marked interrupted
transverse bands.

Fig. 4 of the same Plate represents a larva of the plaice {P. pi atessn), just after the
complete absorption of the yolk. This larva was also hatched in confinement : it was
drawn on February 27, five days after hatching. The larva of the plaice is much
larger than that of any of the other species here mentioned : at the stage figured it was
6'5 mm. in length.

Fig. 5 represents the appearance and natural size of a living larva of the brill
{Rhombus Icevis). The young of the turbot and brill remain pelagic until after the
completion of the metamorphosis, that is, they swim about near the surface of the
water, ai\d are commonly met with in the still waters of inlets and liarbours at the
proper time of year, namely, in June and July. The one here represented was taken
in Sutton Pool, Plymouth, on June 1. Their pelagic habit is correlated with the
development of a relatively large air bladder, an organ which is entirely wanting
in the adult. Although they swim freely in the surface waters they do not swim
vertically when the right eye has migrated to the left side, but horizontally ; during
metamorphosis their inclination from the vertical in swimming is proportional to the
degree of asymmetry of their eyes.

CHAPTER VTT.

STRUCTURE OP PHYLLONELLA SOLE.E, VAN BENEDEN AND HESSE,
A PARASITE OP THE COMMON SOLE.

On the lower side of the sole are usually found specimens of a small parasitic flat
worm which lives on the surface of the skin. This creature was first named and
described by two Belgian zoologists, Van Beneden and Hesse, who called it Phyllonella
solece. It is of flattened shape, the dorsal surface being slightly more convex than

Fig. C.

Fig. C— Egg of Phyllonella solece, seen under microscope in the fresh condition. Magnified 100 times.
Yig. B.— Phyllonella solew,, the ventral side uppermost, magnified 17 times; p.s., posterior sucker;
a.g., anterior glandular patches ; p., aperture of penis-sheath ; u., aperture of tlic uterua,

the ventral, ami the outhne of the body is an oval with projecting ends, so that its
sliape resembles that of a small leaf. The animal, when adult, is usually about one-
fourth of an inch in length (6 or 7 mm.), and one-eighth of an inch (3 mm.), in
greatest breadth, but young individuals are smaller, and larger specimens are often
seen. The structure of this parasite is shown in the accompanying woodcut, Fig. D,
which represents the appearance of a living specimen under the microscope. At the
posterior end of the body is a large muscular sucker, p.s., almost circular in shape :
the concavity of this sucker is ventral, and it is attached to the body by a peduncle
at about the middle of its dorsal surface. On the ventral side of the sucker are two
pairs of hooks imbedded in the skin, with their recur\cd points protruding. One
])air of these hooks are long and directed backwaixls, their points being near the
posterior edge of the sucker, the other pair are short, and their points near the centre
of the sucker. At the anterior end of the body there is a semicircular projection, the
ventral edges of wliich are provided with a pair of glands, a.(j., for adhesion Behind
this projection is the small mouth, and at the left hand side of the projection are the
two genital apertures, /i., ?<., close together. The worm crawls about on the skin of
the lower side of the sole, anchoring itself to the spines of the fish's scales by means
of its sucker and its hooks, and using the anterior glands for adhering by that end
when it moves its posterior sucker from one position to another.

The most extensive and conspicuous organs are the generative, male and female,
for the animal is hermaphrodite, and each individual jiroduces both spermatozoa and
ova. The digestive organs are small, consisting only of a sac-like organ into which
the mouth opens, and which is lined by very large cells with enormous nuclei. This
organ may be called the alimentary sac, since it presents no distinction of parts. In
front of the alimentary sac dorsally are two simple nerve ganglia, giving off a main
lateral nerve cord on each side, which passes backwards. In the skin above these
ganglia, ihe cerebral ganglia, are two pairs of eyes, or rather pigment spots which
are doubtless organs sensitive to light. The renal organs consist of a system of minute
ramified ciliated tubes communicating with two main lateral tubes, which probably
open by a single dorsal opening at the posterior end. The rest of the body consists
of the generative organs, and a dense parenchyma of cells filling up the interspaces
between the various organs.

Uniformly scattered throughout the parenchyma of the body are a large number of
globular organs consisting of aggregations of peculiar cells : these are the yolk-glands.
They are situated at the ends of the ultimate ramifications of a ramified sj-stem of tubes
which are the yolk-ducts, and which are completely filled with granular globules similar
to the contents of the cells of the yolk-glands. The yolk-ducts on each side of the body
ultimately unite into a single large duct which opens into a sac situated a little to the
left of the middle line, about one-third of the length of the body from the anterior
end. This is the j-olk-reservoir : it is elliptical in shape and transversely placed. The
volk-reservoir is filled with the same material as the volk-diicts ; tlie terminal volk-ducts

wliich open into it on each side are ventral in position. The ovary is a flattened sac
with a circular outline situated immediately behind the yolk-reservoir. It is filled with
small spherical ova, each containing a large nucleus or germinal vesicle. In front of
the ovary, dorsal to the right main yolk-duct, is a sac with the shape of a pyramid.
Into this sac or vestibule open a short oviduct from the ovary, a short duct from the
yolk-reservoir, and two minute short ducts from two spherical capsules containing
spermatozoa. Here the egg is fertilised. From the vestibule the oviduct is continued
for some distance as a narrow convoluted tube, which then suddenly expands into a
thick-waUed sac shaped like a club, the thick end being internal, and the thin end
opening to the exterior on the edge of the body to the left of the anterior apex. This
thick-walled sac may be called the uterus. The fertilised ovum in the vestibule is
surrounded by a quantity of j'olk, and the compound mass thus formed passes down the
oviduct to the uterus, where it is surrounded by a chitiuous hard shell produced from
the wall of the uterus The shell has the shape of a triangular pyramid, and its apex
is prolonged into a long thin filament, swelling at intervals into bead-like globules.
This filament is doubtless adhesive, and by it the egg when laid, Fig. C, is attached to
the skin of the sole, there to develop into a young Phyllonella.

The primary male organs are a pair of globular testes situated a short distance
behind the ovary, one on each side of the middle line. These testes are simple sacs,
the walls of which are lined b}' cells which give rise to the spermatozoa. Some of
these cells become free in the cavity of the testis, and undergo subdivision, each of
them forming a spherical cluster of small cells, the spermatoblasts, each of which is
converted into a spermatozoon. From the anterior surface of each testis passes off a
tube or duct, the vas deferens ; the two ducts unite just behind the ovary, and the
single vas deferens passes round the left side of the ovarj^ and the left side of the yolk-
reservoir, dorsal to the left main yolk-duct. In the part of its course which lies in
contact with the j'olk-reservoir the vas deferens is connected with a coiled sac closed
at its farther end. This is a reservoir for the ripe spermatozoa, and must be called the
vesicula seminalis. After a tortuous course the vas deferens opens into an intromittent
organ, the penis. The mechanism of this organ I have not been able completely
to elucidate. It consists principally of a club-shaped structure lying between the
uterus and the alimentary sac. Along its outer half this structure contains a canal,
which is at the side of it, not in the centre : into this canal the vas deferens opens,
and by it the spermatic fluid is conveyed to the exterior. The inner half of the
structure contains granular matter, but, as far as I can make it out, is not a gland.
At the base of the penis is a pear-shaped structure with radiating bands in its interior,
which converge into a band apparently of muscle, which seems to run into and become
merged in the substance of the penis. I am inclined to think that these structures
have something to do with the protrusion and retraction of the penis, but I am unable
to understand how they act.

In the chief features of its structure riiyllonella solece resembles a number of other

external parasites of fishes -ivhich are classed in a family called the Tristomidfe.
Most of these forms possess a small sucker on either side of the anterior end of the
body as well as one large posterior sucker, hence the name of the family. The
glandular areas described on the anterior end of PhyUonella represent the anterior
suckers. The Trislomidcc belong to the order Trematoda.

r.,„

Part III.

BIOJSIOMICAL.

CHAPTER I.

GEOGRAPHICAL DISTEIBUTION.

The common sole is a somewhat southern species. In the neighbourhood of the
British Islands it is found, in considerable abundance all over the southern part of
the North Sea, south of a line drawn from Flamborough Head in Yorkshire to the
north-west coast of Denmark. North of this line it is scarce. It is occasionally taken
off the mouth of the Firth of Forth, but very rarely. It is said to have been taken in
the Moray Firth, and off the Orkney and Shetland. Islands. On the east side of the
North Sea it enters the Baltic, being occasionally taken on the north and east coasts of
Denmark and the coasts of Schleswig-Holstein and Mecklenburg. Further east in the
Baltic it has not been observed. Occasional examples have been taken on the west
coast of Norway up to the sixtj'-fourth degree of north latitude — the neighbourhood of
Trondhjem. It occurs in some abundance all round the shores of Ireland, and on the
west coast of Britain from the mouth of the Firth of Clyde southwards, becoming
more abundant towards the south. It is abundant in the Bristol Channel and
throughout the English Channel, in the Bay of Biscay and southward along the west
coast of Portugal. It extends throughout the Mediterranean and probably into the
Black Sea. How far south the s^^ecies extends along the coast of Africa I have not been
able to ascertain : it is not mentioned in Lowe's " Synopsis of the Fishes of Madeira,"
1837.

The other three species, lascaris, variegata, and luiea, are conunon to the south-west
coast of England and the shores of Italy. In all probability they occur also along all
the intermediate coast-line. Lascaris occurs also at Madeira, if the specimen called
lascaris by GUnther is to be considered as of the same species as the English form.
Solea impar, Bennett, and probably S. niargariii/era, Giinther, both closely allied to
lascaris, come from the Atlantic coast of northern Africa.

There are a large number of other species of Solm as here defined besides those
which occur in Britain. There are several which exist in the Mediterranean, namely,
Solea Kleinii, Solea ocellata, Solea monochir. One species is known from the west
coast of Africa, viz., Solea senegalensis. On the west side of the Atlantic the genus
is but slightly represented. One of the few things in which the citizens of the United

o 2

100

States of America confess that their country is inferior to Europe is that they have
neitlier the sole nor the turbot in their seas. The only species of Solea on the
northern part of the Atlantic coast of tlie United States is Solea achirus, Linnaeus, a
species with no pectoral fins, which grows to the length of only six inches, and is
quite useless as food. Solea inscripta, Gosse, occurs at Jamaica. Other similar species,
with pectorals rudimentary or absent, occur at the Keys of Florida. Solea reticulata,
Gronovii, maculipinnis, mentalis, Jenynsii, in Dr. Giinther's catalogue, are all forms
witli rudimentary pectorals occurring on the Atlantic coasts of the West Indies
and South America. In tlie Indian Ocean, according to Dr. Glinther, there is one
species, Solea Indica, from Madras, also belonging to the subgenus Achirus. In the
East Indian seas there are several species known: Solea heterorhina, from Celebes
and Amboyna, and Solea humilis, from the Malacca Straits and Java, with well
developed pectorals ; Solea trichodactylus and S. Thepassii, with rudimentary
pectorals. Solea microcephala lives on the coast of New South Wales in Australia;
further north on the west side of the Pacific we have S. Japonica, from Japan,
S. ovata, from Chinese seas. On the east side of the Pacific, on the coast of Central
America, there are Solea scutum, S. Fonsecensis and *S'. fimbriata. Thus the genus is
well represented in all the tropical seas, extending into the temperate zones both to
the north and south. But no species is of any importance as human food except the
Solea vidgaris of Europe.

K)l

CHAPTER II.

HABITS, FOOD, ETC.

The habits of the adult sole in its natural state cannot be directly observed : we can
only ascertain the means by which it is captured, the character of the sea-bottom
whence it is taken, the animals which are taken with it, and the food which is found
in its stomach. By supplementing the knowledge thus gained with observations on
the living fish kept in large aquarium tanks we can obtain a tolerably complete
knowledge of the sole's mode of life.

The sole is rarely, if ever, captured by any other instrument than the trawl. The
great majority of the soles brought to market are obtained by the large beam trawl,
worked by the large deep-sea trawlers, but it is also frequently captured by the
otter-trawl used chiefly by amateurs, and also by the small trawls used for catching
shrimps and prawns. The usual depth at which soles are found is from 20 to
40 fathoms, but it may exist at greater depths ; it probably does not extend beyond
loo fathoms.

Adult soles may occur at any depth less than 20 fathoms, but usually in shallow
water, less than ten fathoms deep, only young individuals are found. However,
exceptions to this rule occur not infrequently ; the fisherman of tlie Plymouth
Laboratory has several times caught an adult sole in Plymouth Sound within the
Breakwater. Once he caught a full-grown specimen of large size in the Catwater,
which is the estuary of the Eiver Plym, opening into the north-east corner of the
Sound. On May 9, 1889, he took a specimen 13f in. (35 cm.) long, a short dist.ance
from the mouth of the same estuary, and a third specimen he captured a little later
in another part of the Sound. Small specimens six and a half to nine and a lialf
inches (17 to 23 cm.) in length are not unconnnon in the Sound, half a dozen being
frequently taken in two or three hours' work with the shrimp trawl. These immature
soles in fact, according to ray experience, are more abundant within the Sound than on
the neighbouring open shores outside it.

Off Plymouth soles are comparatively scarce at the present time : it is rare to take
more than four or five in a single haul of the trawl, and sometimes only one or none
at all are obtained. At a considerable distance south of the Eddystone they become

102

somewhat nidie plentiful. They are much more abundant on a rough area of ground
to the west of the Eddystone, off Dodman Point in Cornwall. In this neighljourhood
I saw about fifteen soles in a single haul of the trawl in April, 1889. This ground
is often called the " California " ground, a name which was given to it when it was
first worked at the time of the rush to the gold-diggings in California. On the area
calhid by the Plymouth fishermen the Mount's Bay ground, soles are fairly abundant.
This ground lies off the entrance of Mount's Baj' to the south of the Wolf Rock.
When I was on a trawler woiking there in April, 1889, the catches of soles numbered
six, seventeen, and fifty-seven, in three did'erent hauls. The species is still more
abundant on the fishing grounds off the north coast of Cornwall, and in 1889 large
numbers of trawlers from Ijowestoft, Grimsl)y, and other ports on the east coast
worked over these grounds for several months in the earlier part of the year ; but
I have i^ever been there myself. In 1889 the Newlyn fishermen, who are usually
exclusively engaged in drift-net fishing, found that large soles were abundant inside
Mount's Bay on the west of the Land's End promontory. They obtained small
trawls about twenty feet long which they worked over this area from their small
luggers in the month of Marcli, when no mackerel or other surface fish were to be
caught. One boat in which I went out obtained eleven, seventeen, and eleven soles
in three separate hauls, many of the fish being very fine specimens.

None of the grounds mentioned are at a much greater depth than forty fathoms ;
over the ground last mentioned the ground varies from twenty to thirty-five fathoms.
All these areas are more or less sandy, the sand being in all cases of a very fine
texture and of didl grey colour. Trawls cannot be worked over a hard and rugged
bottom formed of rocks, but some of the grounds above mentioned where trawling is
carried on are by no means smooth. From the California ground the trawl brings
up numbers of the large nmssel-like bivalve. Pinna nohilis, called caperlonga at
Plymouth, numbers of Pectens, called at Plymouth queens, at other places scallops or
clams, and large rugged stones. But we may conclude from the habits of the sole in
the aquarium that such ground contains patches of loose sand or gravel, and that
the soles live on these ; for in the a([uarium the sole invariably when alarmed, like
all otlier flat-fish, buiies itself in sand or gravel by rapidly shaking its longitudinal
iins. If a live sole in caijtivity is placed in sea water on a smooth solid surface, such
as the bottom of a flat porcelain dish, or the bare wooden or slate bottom of a tub
or tank it instinctively shakes its fin in the peculiar way by which it shakes the sand
or gravel over its "back." when there is any sand or gravel beneath it. This rapid
movement of the fins is therefore a characteristic of its habits of life, and it is extremely
effective. The fish on a layer of sand, when alarmed, disappears in an instant, the
agitation of the sand renders the water around it turbid so that it is diflicult to
locate the exact spot where the fish has buried itself. Usually when resting undisturbed
beneath the sand or gravel it leaves its eyes uncovered, and these can be detected by
careful search : but not easily for they do not differ greatly in appearance from small

103

bright pebbles or fragments of ttoue. When the material the fish rests ou is fine, like
sand, or contains an admixture of tine particles, a thin layer of the finer material
remains on the back of the fish when it emerges and moves about ; the fine particle
are retained on the skin partly by the adhesive property of the viscid mucus which
exists on the skin of all fishes, and partly by the minute spines of the scales The
sole thus moving gently about with its upper side covered with sand is partially
concealed, often only its actual movement betrays its existence.

Solea lascaris is a rare fish in the neighbourhood of Plymouth. For a long time 1
never met with a single specimen. The fishermen did not seem to know it by any of
the vernacular names given in books. The first specimen I obtained was discovered
by the Laboratory fisherman among a number of common soles exposed on the fisli
quay for auction. He selected it on account of its peculiar appearance, after I had
described the species to him and requested him to search for specimens. The
fisherman to whom it belonged when asked its name said it was a " sand-sole." I
could not ascertain accurately where this specimen was taken, but it probably was
caught a long distance from land towards the central region of the channel. On
June 17, 1889,1 trawled at night in Whitsand Bay for the purpose of obtaining if
possible young specimens of the common sole. In the products of this trawling I
discovered on my return three small specimens of Solea lascaris measuring 7^, 7^,
6f inches (19 cm., 19 cm., 17 cm.), respectively. The depth of water where these
were taken was three to five fatlioms, the bottom a fine clean sand of liii-ht vellow,
almost silvery, colour.

Solea variegata, the thickback, is very common off' Plymouth, but only in deep
water. I have never met with a specimen in or near the Sound, either young or
adult. On April 19, 1889, when I was on board a trawler fifteen or sixteen miles
S.W. of the Eddystone, 213 thickbacks were taken in a single haul of the trawl. On
the Mount's Bay ground the}- are much less plentiful.

Half-grown specimens of Solea lutea are fairly common in Plymouth Sound, but I have
never found adults there. The only adults I have seen were obtained from deep
water by a larger trawl, and the exact locality was not recorded. In the Sound the
young sjjecimens, one to two inches in length, are especially abundant in Cawsaud Bay,
in three to five fathoms of water on a bottom of fine sand of a dull grey colour. I have
frequently taken half a dozen there in a single haul of the shrimp trawl, together witli
young scald-backs [Arnoglossus laterna). The shrimp trawlers believe i)oth these fish to
be the young of the common sole.

I have not been able to keep thickbacks alive in the acpiarium, but there are living
specimens of the lascaris and lutea in our tanks, and they do not differ in their habits
from the common sole.

There is no doubt, then, that the common sole lives naturally on ground consisting of
sand or gravel or other loose material, and that it has the instinct of seeking
concealment bv burvinrr itself beiieatli the surface of the ground by a rapid shaking of

1()4

its fins, an instinct which is exercised at tlie least cause of alarm, as the fish is
exceedingly shy and timid. All the other flat-fishes have the same habit, but of those
observed in our aquaria, namely, the plaice, dab, flounder, and turbot, none remain
concealed so persistently as the sole, at least in the daytime. In the night soles
behave quite differently, they then emerge from beneath the ground and move actively
about in search of food. In the daytime it is extremely difficult to discover how
many soles there are in a given tank even by driving them out of the gravel with a
stick : but on going to the same tank iu the dark with a lighted taper one may count
twenty or thirty where only five or six were expected. But they soon disappear if the
light is held over the surface of the water.

The sole then is a nocturnal fish in the aquarium, and therefore doubtless also at the
bottom of the sea. This agrees with the belief of the majority of trawlermen that
more soles are caught in the trawl by night than by day. I have met one or two
fishermen who deny this and assert that they have sometimes taken a good number of
soles in a daylight haul and scarcely any in the following night. But of course
exceptional cases may well occur, and are probably to be explained by the fact that
soles were abundant in the track passed over by the trawl in the daytime, and very
scarce in the ground swept at night. Of course some soles are taken in daylight, and
it will be easily luiderstood when the mode in which the trawl works is considered,
that it depends on the position and behaviour of oarh individual sole whether it passes
over the foot-rope into the net or not. If the foot-rope is heav}' and the trawl going
at a moderate speed it may disturb the ground deep enough to cause naost of the soles
in its i)ath to rise from the bottom, in which case they will most likely pass over the
foot-rope and be swept into the net : if on the other hand the foot-rope 2)asses more
lightly over the surface, or if the soles bury themselves more deeply instead of rising
in alarm the rope will pass above them and they will escape capture.

There can be no doubt that at 30 to 40 fathoms depth beneath the surface of the
sea there is in the da3'time a good deal of light, but still much less than at the surface
or in an aquarium tank. It has been ascertained that light disapjiears altogether at
200 fathoms, and if we assume that the absorption is proportional to the depth there
must be at 50 fathoms three-quarters of the quantity of light that exists at the surface.
Now the quantity of light in our aquarium is a great deal less tiiaii the quantity
outside, as a great part of the windows are obscured. It follows, therefore, that the
tanks in the aquarium are not very much more illuminated than the sea bottom at a
de})th of thirty fathoms, ai\d it may justly be concluded that soles in their natural
condition at that depth will for the most part remain buried during the day and emerge
from the sand to seek food at night : the sole therefore is a nocturnal fish in its natural
state.

105

The Food of the Sole, and its Method of Feeding.

Although the sole is more active by night than by day, it can often be seen feedin.
m our tanks nx the daytnne : there is not a constant supply of food in the tanks, anS
when food xs thrown .n the fishes are usually so hungry that they begin to fe^d at
once. The food snpphed to the soles and other flat-fishes consists principally of marine
worms chxefly Nere^s Dumerilii), shrimps, and fish cut up into small pieces, usually
pilchard, mackerel, or gurnard. Of these the soles prefer the worms. In seeking their
food the soles are guided first of all by the sense of smell : by this they perceive the
presence of food in thexr neighbourhood, and the sense of sight is not employed
for this piirpose. But in hunting for their food, and in localising its position before
bitmg at It, they rely entirely on the specialised tactile filaments of the skin on the
under side of the head. A sole when searching for food moves slowly about <.ently
tapping every part of the sandy bottom with the lower surface of its head While
the sole is thus engaged its back is very frequently covered with a thin layer of
sand, so that scarcely any part of it is visible except the eyes and mouth and some
of the filaments below the snout when the latter is raised : it is only noticeable on
account of Its movements, and because its form can be traced out and distin<nii.hed
from tlie flat surface of the sand around it, When in the course of this defiberate
exploration the lower side of the head feels a worm or other morsel of food the sole
immediately seizes it with a vigorous and sudden snap of the lower half of'the jaws
where the teeth are situated, and then swallows it with the sand which adheres to it
I have often placed a worm on the upper side of a sole thus engaged in hunting its
prey. When this is done it makes not the shghtest diff^erence to the sole's behaviour •
the fish goes on tapping as before, evidently unconscious that it is carryin^r a palatable
morsel about with it. When the sole feels a worm or other piece of food with its
tactile filaments it cannot see it, and it never snaps at any food which it has not first
felt in this way. It is in fact unable to localise the position of its food and so to
direct the motion of its jaws to the object to be seized unless it has felt this object with
these tactile filaments. In other words the afferent sensory impulse produced by the
contact of the food with the sensitive filaments is necessary for the co-ordination of the
movements of the head and jaws by which the food is seized.

I have examined the intestines of a large number of soles in order to discover what
they had been feeding on before they were caught. It is the custom of trawlers to gut
their soles on board before they put them away in the hold of the vessel. They also
gut turbot, brill, dorey, and haddock, though of the latter they do not usually 'catch
many ofi" Plymouth ; sometimes they take a considerable number ofi' Mount's Bay and
the north coast of Cornwall. I obtained the intestines of soles sometimes by puttincr
tliem into a jar of spirit when I was out with a trawler myself, more frequently by
sending jars of spirit on board a boat and paying tlie men to bring back in them the

106

intestines of all the soles they caught. It is very seldom that anything is found in the
stomach or intestine of a sole which can be satisfactorily identified. The stomach is
very slightly differentiated, it is only distinguished by the somewhat greater thickness
of its walls from the intestine, and is only marked off from the latter by a slight
pyloric constriction situated beneath the middle of the liver. The stomach after death
is almost invariably found empty. In the course of the intestine in a small percentage
of specimens small masses of the indigestible remnants of food occur. These masses
are usually black and enveloped in mucus. Usually they contain fragments of shells
with bristles of marine (Clia3topod) worms and other debris, and rarely something is
found in them whose specific origin can be recognised. The following is the record of
the intestines I have examined : —

December 22 and 23, 1887, 9 miles W. by S. of Eddystone, 40 fms. A number of
specimens : six contained food.
(1.) Proboscis of Gasteropod, one small Ophiurid, pieces of Lamellibranch shells.
(2.) Pieces of Lamellibranch shells, and remains of the contained animals.
(3.) Fragments of Lamellibranch shells.
(4.) Ditto.
(5.) Ditto, and a long specimen of errant Polychaste worm, genus and species

unrecognizable.
(G.) Fragments of Lamellibranch shells.

January 23, 1888. Nine miles S.W. of Eddystone, nine specimens, two containing
food.
(1.) i\'ika edulis, Risso (a Decapod Crustacean) a single specimen; also a Holo-

thurian, sp. ?
(2.) llemains of Chaetopoda.

Same date. Six miles S. of Eddystone, sixteen specimens, all empty except one.
(1.) A piece of Serhdai'ella (Hydroid).

January 30, 1888. Kine miles S.E. of Eddystone; bottom sand. Fourteen
specimens, three containing food : —
(1.) Two Synapta digitata.
(2.) Several OjdiiiKjhipka albida.
(3.) Two Ophioglt/pha albida.

February 7, 1888. Seven or eight miles W. by S. of Eddystone; "queen ground,"
i.e., Pecten opercidaris abundant on the bottom ; nine specimens, four con-
taining food.
(1.) Nine Ophioglypha albida; one Chtetopod unrecognizable.
(2.) One Chajtopod.

(3.) Two Ophiogh/p/ut albida, one Amphipod.
(4.) Four Oj'liioglgp/ta albida, one Amphipod.

107

February 17, 1888. Twenty-five miles off the Lizard, 40 fms., sand. A great
number of specimens, eight containing food.
(1.) Eemains of Ophioghjpha alhicla, and fragments of Lamellibranch shells.
(2.) Fragments of Lamellibranch shells.
(3.) A few fragments of shells, small pieces of membrane, and a large number of

large Chtetopod bristles, Aphrodite or Hermione.
(4.) Small Lamellibranch shells and fragments. One of these close to the anus

was entire, the colour unaltered and the animal undigested.
(5.) SmaU LamelUbranch shells and bristles oi Aphrodite or Hermione.
(6.) Fragments of shells ; one small Lamellibranch Donax shell entire near

anus, animal absent.
(7.) Chastopod bristles.

March 24. Off Mount's Bay. Thirty-seven specimens, ten containing food.
(1.) Pieces of Sertularian Hydroid, and remains of Chfetopod tube.
(2.) Anterior part of large Chsetopod of fam. Terebellidse. Fragments of shells.

Piece of CcUaria fistulosa.
(3.) Fragments of shells. Piece of Chastopod tube.
(4.) Large Chsetopod bristles, probably of Hermione.
(5.) Piece of Chastopod tube. Fragments of shells
(6.) Large bristles, probably of Hermione.
(7.) Piece of Chastopod tube. Fragments of shells.
(8.) Fragments of shells.
f9.) Large bristles, probably of Hermione.
(10.) Tail of Decapod Crustacean, probably shrimp.

April, 1889. Off Mount's Bay. A large number of specimens.
(1.) Bristles of CliEetopoda.
(2.) Bristles of Chsetopoda, among them the dorsal hook of Melinna cristata,

Malmgren.
(3.) Cuticle of a long specimen oi Linnbrinereis sp.
(4.) A long, much-digested specimen of a Gephyrean, Sipvnculus (?)

Also in several the aciculi of Hermione or Aphrodite and, in several,
cyhndrical masses of debris containing small shells, e.g., Pecten tigrinus and
fragments of shells, entangled fibres, and pieces of membrane from the tubes
of tubicolous Chsetopoda ; also fragment of calcareous Polyzoon.

I believe that the fragments of shells and pieces of tough membrane which occur so
frequently in the sole's intestines are the remains of the tubes of Thelepus circiumita,
Malmgren, a Chsetopod belonging to the family TerebcllidiB, which inhabits a mem-
branous tube attached by its whole length to stones or shells, and covered externally
with calcareous fragments of all kinds, such as fragments of shells, or entire small

p 2

108

shells, small stones, pieces of calcareous Polj'zoa, &c. If this is so, this species and
others possessing a similar tube must form a large portion of the sole's food. The
total number of specimens the contents of whose stomachs are recorded in the above
list is thirty-six. Of these eighteen, or 50 per cent., contained remains of marine
annelids (Chajtopods). If we add to these the number of specimens which contained
no remains of Cha;topods but fragments of shells, probably derived from the tubes
of annelids, the number becomes twenty-eight or 77 per cent. Seven specimens
contained Ojihiogli/pha albida or other Ophiurid, or 19 per cent. One specimen
contained Synapta difjitata, and one another Holothurian. Crustacea were present in
four specimens, or 1 1 per cent. In tliree specimens there were Mollusca probably
not derived from the tubes of Chietopods, or over 8 per cent. Thus it is evident
that soles in their natural state feed chiefly on Chietopods, and it is probable that the
bodies of these are rapidly digested, so that it is very diflicult to identify the species to
which their remains belonged.

Parasites.

The common sole is remarkably free from parasites, which in many fishes occur
constantly in great number and variety. I have seen no internal parasites in the sole
except an occasional Nematode, or small thread-worm. Of external parasites the only
form I have observed is the Trematode, PhjlloneUa solece, whose structure has been
described at length in the preceding Section. This creature appears to do no harm to
the fish. I have never seen any signs of irritation or inflammation of the skin on which
numbers of the parasite were hving. Sometimes as many as twenty or thirty specimens
of the parasite occur on a single sole. Phyllonella is, as I have described it previously,
hermaphrodite, but it does not fertilise its own eggs. I have not seen it in copula-
tion, but it may be inferred from the structure of the generative organs that two indi-
viduals copulate reciprocall}% the penis of each being inserted into the uterus of the
other, and the seminal fluid received by each uterus passing up the oviduct to be
stored up in the spermathecas. Fertilisation of the ova then takes place after copu-
lation, and is efiected by the spermatozoa which are expelled from the spermatheca3
into the vestibule into which the ova pass from the ovary. The fertilised ovum,
together with a quantity of yolk, is surrounded by its peculiar shell in the uterus and
then the deposited ovum adheres by its filament to the skin of tlie sole. I have not
traced the development of the parasite, but have no doubt that it is direct, that the
young is hatched in a form closely resembling the adult, and immediately adhei'es by
its posterior sucker to the sole's skin. The parasite doubtless is nourished by the
mucus of the skin on which it lives, but how far its nutrition is efiected by digestion of
the mucus within the small alimentary sac, and how far by direct absorption through
the surface of the body, it is impossible to say. The parasites spread from one sole to
another in all probability when the fish accidentally come into contact with one
another.

109

Enemies.

I am inclined to think that the principal and most deadly enemy of the sole is man.
But my evidence on this subject is by no means extensive. I have never seen an adult
sole in the stomach of any fish except the angler, but on the other hand, I have not
devoted much time to recording the contents of the stomachs of the larger predatory
fishes. Considering the great timidity of the sole it is difficult to avoid the inference
that it has many enemies to fear. Probably young soles aud other flat-fishes living in
the conditions in which I found them in Mevagissey harbour are largely devoured by
gulls and shore birds when left by the receding tide in the shallow pools of the shore,
but I cannot assert this from direct observation. I have once or twice seen larse
conger seize and devour flounders in a large tank of our aquarium ; there were no
soles in the same tank, but it may be inferred that conger would devour soles when
they had the opportunity, and that they do devour them in the open sea. But it
must be mentioned that our captive conger have by no means eaten all the flounders
in their tank ; probably they are never so hungry when fed regularly in captivity as
when they have to seek their own living in the wild state, and therefore conger may
reasonably be reckoned, ou the south coast, among the enemies of the sole. I have
never teeii the common spotted dog-fish [ScyUium canicula and So. caiulus) eat flat-
fishes in the tanks, though they are kept together in the same tank, but I think
cod and hake probably eat soles and other flat-fishes sometimes. One of the
commonest and most destructive enemies of ground fishes is the angler {Lophius
piscatorius) which grows to an enormous size and consists almost entirely of a huge
mouth and a small conical tail. I have frequently seen several large specimens of
this fish in a single haul of the trawl, and it constantly swallows other fish, including
flat-fish, even after it is in the trawl, its voracity being so great that it devours its
fellow captives. I have often seen soles taken from its stomach on the deck of a
trawler, and when extracted thej' are usually quite uninjured and are packed away
with the rest for market ; so that when we eat a sole we cannot be certain that it has
not been swallowed before. The angler is very inactive, its powers of locomotion
being limited. It partly buries itself in the sand on which it lives, and its colour and
appendages are such that in this condition its true character is perfectly concealed.
Over the head are long flexible filaments which are sxipposed to serve as a lure to
attract other fishes, but which probably have little eflect on soles because they do
not hunt by sight. The angler thus forms a living and deadly pitfall. Any fish
coming unconsciously near its terrible gape is seized and engulphed in the great
cavity of its mouth, and soles of the largest size are swallowed by it with ease.

110

CHAPTER in.

COLOUE.

The colour and markings of the upper side of the common sole, so far as they are
permanent and characteristic of the species, have already been described. But, as was
mentioned in connection with that description, the skin of the fish is capable during life of
exhibiting considerable changes in the intensity and to some extent in the quality of its
colours. It is exceedingly difficult to study these changes of colour in a living fish if the
material on which it is placed consists of fine particles, like sand or mud. For the fish
will persist in burying itself, and it is impossible to keep the skin free from particles of
ihe material, so that an accurate estimation of the colour under particular conditions
can scarcely be made. It is not difficult to keep a sole alive and in a healthy condition
for several days or even weeks in a shallow vessel supplied with a current of sea water.
In order to study the colour-changes carefully I kept specimens in this way, allowing
them to rest either on a solid surface or on a material of coarse texture without fine
particles, namely, coarse gravel or broken coal thoroughly washed in running water.

It is generally believed that the colour and marking of the sole's skin assimilates
itself to the colour and texture of the ground on which it rests. The following
observations were made in order to obtain definite results as to the extent and
character of this assimilation : I found that the contrast between the markings and
the ground-colour of the skin was most conspicuous when the fish was lying on a coarse
bright clean gravel. The gravel which I used had a general orange tint, but it
contained, besides yellow and orange coloured pebbles, a considerable number of black
and white. The appearance of the fish when resting on this gravel is shown in Plate I.
The ground colour is a greenish grey, and on this ground all the spots and markings
ever present in a sole are well marked. The principal dark blotches are very
conspicuous and well defined ; the irregular lighter bands which connect them ramify
in the spaces between them. The blotches are in places quite black, the black being
always confined to the outer part of the scales, the anterior part of these being always
somewhat lighter. The small white spots alternating with the blotches are also fully
expressed. The dark spot at the outer end of the pectoral is pronounced. It is
evident from the drawing that there is no exact similarity between the colour and
markings of the fish and the appearance of the surrounding gravel ; but it is also

Ill

evident that the sole in this condition has, like the gravel, a variegated colouring
which at some distance from the eye renders it less conspicuous. The black spots and
the small white spots resemble the black and white pebbles of the gravel ; but on the
other hand, the continuous streak of opaque white along the edge of the fins is
distinctly conspicuous. A sole on gravel of this kind in a tank of some size is usually
either completely or partially buried under the gravel, and when the fins are thus
concealed and only part of the body exposed the sole may easily escape notice from a
human observer. On the other hand, it is also very easy to discover a sole in such a
condition when one looks for it. I believe that soles are seldom on gravel in their
natural state ; for I have found that on gravel or sharp sand they nearly always sooner
or later injure their fins or skin, and that abrasions so produced usually lead to
inflammation which causes death.

I placed another sole in a large shallow dish of white porcelain of the kind used in
photographic manipulation. No material of any kind was placed in the dish, the fish
rested on the smooth white surface of the porcelain, and it was exposed to the full
daylight of the south windows of the Laboratory. Plate III is a reproduction of the
water colour drawing made from the sole in this condition. The paleness of the
colouring is extraordinary. The darkest tint in the blotches is a straw colour,
scarcely darker than the yellow of the fin-membranes. The ground-colour is a pale
grej' with a slight tinge of blue in places. The white spots have disappeared entirely,
a result which would not have been expected : the spots whei'e they existed are
somewhat blue. The dark spot on the fin is the darkest colour in the whole surface,
and has still streaks of dark brown between the fin raj^s. The sole used in this
experiment was a male 10^ inches (26"7 cm.) long ; but I found that the sole from
which Plate I was drawn became as pale as this when placed under the same
conditions.

The drawing of the sole just described was finished on June 8, 1889. This sole
died shortly afterwards and its appearance the day after death is represented on PI. IV.
Another sole was taken for the drawing given in PL I. I found when this latter
specimen was placed on the white porcelain that it became in a few minutes as light
as the figure on PI. Ill, but after it had been left all night in the same condition, on
the following morning the small spots which on gravel were opaque white had become
quite a dark grey and formed a marked contrast to the surrounding yellow.

To ascertain the maximum darkening of colour possible I used the same sole from
which PI. I was taken. At first I found it difficult to produce any colouring much
darker than that of PI. I. I lined the porcelain dish with black paper and placed the
fish on that, but it showed much the same colours. Then I varnished the dish with
black varnish of a deeper black than the paper, but got no better result. It then
occurred to me that the maximum of darkness could not be obtauied until the quantity
of light was reduced ; accordingly 1 placed some washed coal at the bottom of a tub
about nine inches deep, and placed the sole on this ; then I placed the tub on the

112

north side of the Laboratory at some distance from the windows in a position where it
was partly shaded. Then the result shown in I'hite 11 was produced. But the
drawing for this plate had to be finished from the sole in the position I have described.
When the sole in the tub at its maximum darkness was carried to a table in front of
the window, the colours immediately began to get lighter. I found that the white
spots were exceedingly curious in their behaviour. As I have mentioned, on white
])orcelain with plenty of light the white spots disappear as such and are changed into
bluish spots which sometimes become quite dark and conspicuous. The white spots
also disappeared in the sole which was kept on coal with very little light, reappearing
in a few seconds when more light was admitted. Thus the white spots are generally
visible except on white ground with a great deal of light, or black ground with very
little.

As to the rate of change it is usually quite rapid. A sole placed on the white dish
begins to get lighter almost immediately ; when it is disturbed with the hand the colours
become darker again, but when left alone it continues to grow paler, However, the
full effect is not seen till the fish has been some hours on the white ground.

A sole kept on coarse yellow gravel in front of a window is very inconstant in its
colouring : it sometimes exhibits its markings quite distinctly for some hours, and then
begins to grow pale, its black blotches almost vanishing.

On May 22, I took a sole in Avhich the markings were well expressed and the
colour moderately dark, and placed it on the white porcelain dish ; in a short time the
colours had become pale, and the dark blotches had become yellow. Then I ])laced
some fine shingle in the dish, intending to bring the niarkings out again, but to my
surprise the black blotches had not returned when I examined the fish the next
morning, and did not return completely when I placed it in an oaken tub nine inches
high, although the ground colour became somewhat darker.

All the changes are evidently due to the action of light and depend on the quantity
of light acting on the sole, not on the tint or texture of the ground on which it rests.
The behaviour of the whjte spots I cannot 'yet explain, but all the rest seems to me
easily intelligible when regarded in this way. The colour and markings of the skin are
due to a vast number of chromatophores situated in the skin beneath the epidermis:
these are of two colqurs, the black and the yellow, and in some places there are others
containing a somewhat iridescent pigment. The last are particularly abundant in the
white spots, the black especially abundant in the dark markings. Light causes these
chromatophores to contract. Whpn expanded the chromatophores or pigment-cells
are stellate, giving out ramified processes on all sides. When they are contracted all
these processes are withdrawn and each cell becomes a mere minute speck of pigment
The position of these chromatophores is fixed, and therefore when they are expanded,
in the absence of light, the markings always reappear in exactly the same positions, in
fact the markings never entirely disappear. When a very strong light falls upon the
sole all the chromatophores are contracted, and all the parts become proportionally

113

lighter; when the light is diminished the chromatophores expand and the colours
become darker. It is evident that with the same amount of illumination the alteration
of the colour and composition of the ground on which the sole rests alters the quantity
of light acting un the fish. For if the ground is black all the light whicli falls upon
that ground is absorbed, and the sole is only affected by the rays which fall directly
upon it, while if the ground is light-coloured nearly all the light which falls upon it is
reflected, and the diffused light which falls upon the sole is therefore greatly increased.
Just as a room is n\uch lighter with the same windows if its walls are white than if
they are black.

The sole does not become uniformly coloured on a uniformly coloured ground. In
some of the laboratory tanks we have at the bottom a dark grey fine sand brought
from a part of the sea shore. This sand is extremely uniform in colour, and is exactly
of the same kind as the sand brought up by the trawl from the trawling grounds ofl'
Plymouth and off Mount's Baj^. In the tanks the soles usually have some of this sand
on their skins, and are therefore by no means conspicuous, but whenever their skins
are visible it is seen that the black markings are pronounced. The ground colour of
the soles in this condition approximates closely to that of the sand, but the presence of
the black spots does not seem to me to aid in the resemblance at all. I placed a large
sole in a shallow tub on some of this sand in order to make a careful observation.
After three davs the colouring of this sole was as follows : The intermediate black spots
were almost invisible ; of the dorsal series the second was faint, the third, fourth, and
fifth well marked and black ; of the median series only the third and fourth were
well marked, but not black. The ventral spots were all visible but faint ; termination
of the pectoral reddish-brown, white spots alternating with black quite distinct.

114

CHAPTER IV.

BEEEDIXG.

The egg of any particular species of fish is derived from a female individual of that
species, and after a process of development becomes another individual of that species,
presenting the characteristic specific characters. As the eggs of nearly all marine fishes
are left to themselves after being shed from the body of the female, the parents taking
no care of them, there are only two possible methods of ascertaining the species to
which a particular kind of egg belongs, or of tracing the development of any particular
species of fish. One method is to observe the deposition of the eggs by the female, or
to detain them by artificial fertilisation, then to examine these eggs and study their
development. The other is to examine all kinds of eggs that can be obtained, and to
trace their development up to the stage when the young fish presents specific charac-
ters by which it can be identified. The latter method presents more difficulties and
uncertainties than the former.

The greater number of marine fishes shed eggs or spawn at one particular period of
the year, a period extending over one or a few months. During the rest of the year
the development of ova in the ovaries proceeds gradually until the next annual breeding
season, when the annual crop of mature ova is again shed. As the ova develop in the
ovary they increase greatly in size and number, and thus the ovary itself becomes
much enlarged, and finally attains a very considerable size in proportion to the rest of
the body of the female. This enlargement of the ovary produces a corresponding
enlargement of the visceral region of the female. The small testes do not exhibit any
corresponding increase in size in the sole. In most fishes the testes in the male enlarge
at the breeding season in some degree, and in some they become very nearly as large
as the ovaries in the female. In the herring, for instance, it is not possible to distinguish
the males from the females among ripe specimens taken from the net when captured,
except by squeezing them and observing whether eggs or milt escape from tlie genital
aperture. But in the sole the ripe females can be easily distinguished by the enlarge-
ment of the ovarian region. It is not so easy to distinguish the smaller males from
small immature females, but among larger specimens the males can usually be identi-
fied by holding the fish up against the light, when in the male the posterior part of the
ventral region behind the intestines is seen to be translucent ; while in the female even

115

if the ovary Le not mucli enlarged it usuall}' j^roduces an oi)acity extending back far
behind the intestines near to the base of the taih

The enlargement of the ovaries in the female sole becomes noticeable in January and
February, and ripe actively moving spermatozoa ai-e found at this season by examining
under the microscope a portion of the testis of the male. I have not succeeded in
observing the natural deposition of the ova by living soles in captivity. I attempted
to do this in the spring of the present year (1889). At my request living soles were
brought to the aquarium during the previous vrinter months from the deep sea
trawlers and from the shrimp trawls worked in Plymouth Sound. But the specimens
obtained from the latter were all small, and although they lived well were too young
to breed ; while the larger ones from the large trawlers although living when brought
in invariably died after a. few days in the tanks. The reason of this was that the large
soles were always more or less injured by the trawl or by subsequent handling. The
large trawls are towed usually for a long time, six to twelve hours or more, and the
captured soles and other fish during this time are injured by their struggles and by the
pressure and weight of the whole contents of the trawl. After the soles are placed in
tubs of water on board the vessel the voyage back to harbour occupies a long time
during which they are knocked about by the motion of the vessel. In consequence of
this mechanical violence the skins of soles brought to me from the deep sea were
always more or less abraded, and the scales torn off at one or more places. The
injured parts of the skin in a few days always underwent inflammation and sloughing,
and the diseased condition spread over the surface till the fish died. I have found
that the sole is tenacious of life and will bear a great deal of handling so long as the
skin is uninjured and the scales not removed, but that very slight injury to the skin
and scales leads to inflammation and death. In other fish, for instance, the conger and
grey muUet {Mugil chelo), considerable wounds on the skin are healed up in a very
short time without any inflammation ; the muUet will reproduce nearly aU its scales m
a week or two.

I was unable therefore to study the breeding of the sole in specimens living in
captivity, and my investigations of the reproduction of this species, as of many others,
have been carried on at sea on board of trawhng smacks by examination of the fish
when brought up by the trawl.

With very few exceptions the eggs of all deep sea food-fishes have been found to be
small in size, spherical in shape, transparent, and buoyant in sea water, and after being
extruded by the parent fish to undergo development while suspended, separate and
independent of one another, in the surface waters of the sea. All the flat-fishes
investigated have been found to shed eggs of this kind, and the sole proves to agree in
this respect with its allies, the plaice, flounder, turbot, &c. As in other fishes, gentle
pressure by the fingers and thumb applied to the ovarian region of the ripe female
sole causes the ripe ova to escape from the aperture bj^ which the ovaries open to the
exterior. The ovaries lie entirely behind the aperture, and therefore the pressure must

Q 2

IIG

be exerted from behind forwards. To examine the eggs and keep them alive they must
be received when pressed from the fish into a bottle of clean sea water. By squeezing
a number of captured soles in this way in March, when the ovaries are found to be
much enlarged and soft to the touch, some are found from which transparent eggs can
be pressed out. When a considerable pressure is exerted part of the contents of the
ovary can be squeezed out of any sole in which the ovaries are large, but when the
ripe transparent ova have once been obtained it is easy to distinguish them from the
.smaller unripe ova w^hich escape when too much pressure is applied. These unripe ova
are yellowish-wliite and quite opaque : they do not separate from one another when
they fall into sea water, and membranes containing blood, derived from the tissues of
the ovary, are usually seen connected with them. In March a number of soles taken
at one haul of the trawl include, besides somewhat small immature specimens and males,
some large females which yield no ripe eggs, whose eggs have not yet reached maturity,
and only one or two from which ripe eggs can be obtained. Very often only a small
number of ripe eggs can be obtained when the fish is first squeezed, afterwards unripe
eggs escaping. This proves that the eggs in the ovary are not matured all at once,
but in gradual succession. But the process of ripening seems to become more rapid
towards the end of the spawning period in a given fish than at the beginning, and the
eggs are evidently extruded immediately after they are ripe ; for although I have
examined large numbers of female soles which yielded a few dozen ripe ova, and whose
ovaries al^er the extrusion of these remained distended with unripe ova, I have only
once found a specimen whose ovaries contained ripe ova only. Tliis specimen was
captured in a small-sized trawl worked from a Newlyn drift-net boat, on the morning
of March 23, 1889. I squeezed several thousand ripe ova from it, and the ovaries
were then completely empty. When uU the ova of one season are shed the ovaries
are left as flaccid sacs which soon shrink considerably in size. Fish in this condition are
usually said to be " spent " or " shotten": the latter is the Scottish expression. The
specimen just referred to was of very large size. It measured 20^ inches in length, 9i in
breadth. The boat by which it Was taken was trawling at a depth of about 30 fathoms
on the north-west side of Mount's Bay, off the coast of the Land's End pi-onioutory.
At the same haul, and in others previously made, shotten females, partially ripe and
unripe females were taken. The only conclusion to be drawn fi'om these facts is that
only a few ova are ripened at a time in a given female at the earlier stages of the
spawning process; while at the later stages though a large number of ova are ripened
at one time they are very soon shed, and therefore the capture of a female at the par-
ticular moment when she contains a large number of ripe ova is a rare occurrence.

As stated above the spent condition of the female is easily recognised, ami when
only spent females are captured the end of the spawning period for the species is
determined. I investigated the duration of the period during the two successive
seasons of 1888 and 1889, and found that it ended some weeks earlier in the latter
year than in the former, a fact which can only be explained by the warmer weather

117

and consequently higher temperature of the sea in the spring of 1889. In the latter
year, when on board a trawler south of the Wolf Eock which lies to the west of the
Land's End, on April 11 and 12 I found nearly all the female soles completely
spent, a few containing nothing but a small number of ripe ova. The surface tempera-
ture of the sea at that time and place was 48°-5 F. (9°-2 C). In 1888 the fisherman in
the service of the Plymouth Laboratory obtained ripe soles on April 26 and 27 at a
distance of 40 miles north of the Land's End where the surface temperature was 46°-0 F.
(7°-7 C.) and the bottom temperature at 50 fms. was 45°-0 F. (7°-2 C). The temperature
on April 6, 1888, to the south of the Wolf Eock was 46°-0 F. (7°-7 C). The following
temperatures of the surface of the sea wiU show the difference of the two seasons : —

18 8 8.

18 8 9.

March 6.
April 4.
May 10.

S. of Wolf Rock ....
)j >i ....

M .) ....

March 1.
April 9.

S. of Wolf Eock ....

»1 » ....

45° -8
45° -5
50° -1

7° -6

7° -5

10° -0

48° -0
48° -5

8° -8
9° -2

March 26.

„ 29.

April 9.

Mav 31.

S. of Plymouth Breakwater

» )> >»
Plymouth Sound ....
S. of Plymouth Breakwater

43°
43° -5
44° -0
49°

6°-l
G°-3
6" -6
9° -4

April 3.

Mav 15.

„" 21.

S. of Plymouth Brealiwater

46° -0
54° -0
56° -5

7° -7
12" -2
13° -6

I have not determined so exactly the commencement of the spawning period in the
two seasons. In 1888 I examined several soles taken nine or ten miles W. by S.
of the Eddystone, on February 6. Only one yielded a few ripe ova, about a dozen ;
the rest were all unripe.

It is thus evident that the spawning period of the sole extends from the middle of
February to the end of April ; but that the greater number of individuals shed their
spawn in March, and the eai'ly part of April ; and that in warm seasons the spawning
is completed by the end of the second week in April ; while in colder seasons some
individuals are found still spawning up till the end of April, and a few eggs may not
be shed till the middle of May.

Little has yet been said about the males. Necessarily the male reproductive
elements consisting of the fluid milt, which contains the innumerable spermatozoa,
are discharged at the same period as the ova. But the testes and the milt of the sole
differ remarkably from those of any other marine fish I have examined. In other
fishes the testes in the spawning season are much enlarged, and very soft, so that
when the fish is opened very slight handling tears or ruptures the testes, causing the
escape of a thick viscous opaque white fluid, the milt. When the ripe male fish i.s
gently squeezed the milt escapes from the genital aperture in large white drops
having the appearance of milk, which when allowed to fall in sea water mix with it
and render it turbid. But when a male sole is opened in the breeding season the testes

118

are neither much enlarged nor soft : they present much the same appearance as at any
other time of the year, though spermatozoa may be seen in a portion examined
under the microscope. And when the male is squeezed in the region of the testes, no
milk-white fluid is seen to escape ; some fluid may, and does, escape, but it is small
in quantity and ihin and transparent, so that it is almost impossible when handling
soles on board a trawler to distinguish milt thus squeezed out from the sea water,
urinary fluid, or mucus from the skin, which also drijj from the fish.

119

CHAPTER V

DEVELOPMEXT AND GROWTH.

The eggs of fishes do not develop unless acted upon by the milt of the male. In all
species of marine bony fishes, with very few exceptions, the eggs do not come into
contact with the milt until after they have been discharged from the body ot the
female; the whole process of development takes place outside the body of the parent in
the water of the sea. Wlien the egg of a bird is laid it requires only to be kept at a
certain constant temperature to develop into a chick. When the egg of a snake or lizard
is laid it develops at the natural temperature of the air without any additional warmth
derived from the mother's body, and after a certain time a young snake or lizard is
hatched from it. When the egg, or "purse," of the skate is laid, or taken from the
body of the mother, it develops into a young skate as it lies at the bottoiii of the sea,
or in an aquarium tank. In the spiny dog-fish {Acanthias vulgaris), the eggs develop
within the oviducts of the female, and do not escape tiU they have reached the
condition of actively moving young dog-fish, in all respects except size resembling
their parents. But in all these cases the egg has been acted upon by the milt of the
male while still within the body of the female. When ripe eggs are pressed
from the ovary of the female sole into clean sea water they do not develop into
young fishes, but after floating for a few days in the condition previously described as
that of the unfertilised ovum they die, sink to the bottom, and decompose. This
proves that the eggs of the sole are not fertilised or acted upon by the male repro-
ductive elements within the body of the mother, but only after extrusion.

I have not been able hitherto to observe the natural process of shedding and
fertilising the eggs of the sole in living specimens in our tanks, and it is of course
impossible to observe the process in living soles in the sea. It is kno^vn that in
pelagic fish, like the herring, the fish spawn while collected in crowded shoals,
males and females being mingled together, and that the females simply shed their eggs,
and the males their milt into the water near the bottom simultaneously. The water
into which the eggs pass is thus teeming with spermatozoa, and none of them
can escape fertilisation. But in the herring the testes are as large as the ovaries,
and the ([uantity of milt produced by a single fish is very large. In most flat-fishes

120

the testes are smaller than the ovaries, but still they are of considerable size,
and a considerable quantity of milt is produced. When we consider the small size of
the testes in the sole, and the small quantity of milt produced by a single male, it
seems difficult to understand how the large number of eggs produced by a single
female get fertilised at all. It seems to me that the only way to explain the facts is
to suppose that soles pair together like birds, or at least that the males do not like
some other fish shed their milt into the water at random, but shed it in the immediate
neitrhbourhood of a female at the moment when she discharges some ova. Some of
the wrasses pair and shed their milt in tliis way : I remember watching the process
once in one of the tanks of the Naples aquarium, but I do not remember to what
species the fish I saw belonged.

After I had drawn the inference that some kind of direct fertilisation took place in
soles, I found my opiiiion supported in a curious way by a statement of Nordmaii in
his description of the fishes of the Black Sea, published in 1840 (see DemidofTs " Voy.
Euss. Merid. Zool., Ill, Poissons," Solea nasuta). The statement I refer to is that the
male and female of the species called by Nordman Solea nasuta, which is, as far as I
can see, the same as the Solea lascaris of the English coast, during copulation
adhere together by means of a glutinous liquid, and are sometimes taken in the nets
in this condition.

The ripe ova pressed from female soles during the spawning period, when i)lac('d in
a bottle containing sea water taken from the surface of the sea at the place where the
fish are caught, float at the surface of this water. That ova so obtained are perfectly
ripe and uninjured by the artificial method by which they are taken from the fish is
proved by the fact that when milt is added to the water the eggs are fertilised, and
when taken on shore and kept in proper conditions will go on developing until they
hatch into normal young fisli. Tliis is tlie process of artificial fertilisation which will
be more fully considered in the next section. The observation of artificially fertilised
ova kept in aquaria shows the rate at which the development proceeds at a given
fenq:)orature, for it must be noted that the rate of development of all fishes' ova varies
considerably according to the temperature of the water in which they are contained.
The ft)llo\ving are the details of my observations on artificially fertilised ova kept in
aquaria : —

May If), 1888. — Two or three soles' ova fertilised south of the Wolf Eock at
4 p.m. Temperature of surface of tlie sea, 50° F. (10° C).

May 19. — One of the above ova still alive: the blastoderm had completely
enveloped the yolk, and the dorsal rudiment with Kupher's vesicle was
completely formed. Temperature in hatching jar, 5;^»'^0 F. (11"''7 C).

March 23, 1889. — Several thousand soles' ova fertilised off" the Land's End promon-
tory at 7 a.m. Temperature of the sea water at surface, 48°'2 F. (t)°-0 C).
Eggs placed in hatching jar at the Laboratory the same evening.

121

March 24. — Examined the eggs ; found segmentation completed, the blastoderm
commencing to spread over the j-olk. Temperature of water in tlie hatching
jar, 50°-l P. (10"-1 C).

March 25. — Blastoderm covering three-fourths of the yolk. Temperature the
same.

March 26.— The yolk completely enveloped by the blastoderm, stage shown in
PI. XV, Fig. 4.

March 27.— Eggs all dead.

March 29. — Six soles' ova obtained from surface of the sea in stage just after the
closing of the blastopoi-e, that is, after the envelopment of the yolk by the
blastoderm. Placed in a small jar with water at 50°-3 P. to 53°-6 P. (10°-2 to
12° C).

April 5 and 6. — Three of the above eggs hatched.

The eggs last mentioned were at about the same staeje when first obtained as the
previous lot when they died. It may be inferred therefore that at the temperature
above given, about 50° to 53° P. (10° to 12° C), soles' eggs would hatch ten or
eleven days after fertilisation. The following experiment is more complete : —

April 11. — 12.5 a.m. Several hundred ripe eggs obtained from soles trawled

south of the \Yolf Rock : artificial fertilisation attempted with testes taken from

the males and crushed in the water. Temperature of surface water of the sea,

48°-5 P. (9°-2 C).
April 13. — Eight of the above eggs found to be fertilised and developing;

temperature of the water in the bottle in which they were carried, 9'5 C.

These were transferred to a small jar in the Laboratory ; temperature, 10°'0 C.

Density of the water brought from south of Wolf Eock, 1'0271. Density of

aquarium water, 1'028.

April 16. — Two of the eggs killed for investigation; one died. Temperature in
aquarium, 9°'0 .C,

April 17. — Temperature in aquarium, 9°"2 0.

April 18. — Temperature in aquarium, 9°' 7 C.

April 20. — Two of the eggs hatched out.

Thus two of these eggs hatched on the tenth day after fertilisation in water at a
temperature of 48°-0 P. to 50°0 P. (9° to 10° C). Now, as I have shown, the spawning
period of the sole terminates sooner or later according to the temperature of the sea,
and scarcely any ova are shed after the temperature lias risen to 50°-0 P. At the
beginning of the spawning period, in the latter half of Psbruary, the temperature is

122

from 43° to 45° F. (6°1 C. to 7°-2 C), and at this temperature the ova would probably
take between two and three weeks to hatch.

It is certain that the eggs of the sole do undergo the same development at about
the same rate in their natural condition as they do in experimental conditions. For
the characteristics of the sole's ovum having been observed, nanieh', the size, the layer
of segments in the yolk, and the groups of minute oil globules, it is possible to identify
ova found in the sea possessing these characteristics as those of the sole. The surface
waters of the sea ofi" the coasts of Devon and Cornwall contain nearly all the year round
vast numbers of buoyant fishes' eggs. These can very easily be collected by slowly
towing through the water from a boat a conical net made of muslin or silk bolting
cloth. Anion" the ejisrs so collected those of the sole are found in small numbers in
March and April, sometimes at the end of February or beginning of May, but at no
other time of the year.

The development of the sole within the egg is rather slow compared to that of
some other flat-fishes. The eggs of Pleuronedes Jlesus, the flounder, hatched in my
hatching jars in six days at a temperature of 50° F. (10°'O C.) ; the eggs of the plaice
{Pleuronedes ^j/ato5«) hatched in 10 days at the same temperature; those of
Pleuronedes mici-ocephalus, the merry-sole, hatched in eight days at a temperature of
about 49°-l F. (9°-5 C).

I have never found the ova of the common sole very numerous among the pelagic
ova collected by means of the tow net. The largest number I have obtained at one
time is six : these were taken a little to the south-west of the Mewstone.

The density of the water in which soles' ova are found suspended at sea varies
slightly in difl'erent places. Examples of water from the sea to the south of the Wolf
Eock I have found to be 1*027 (distilled water being 1*0), while samples from the sea
ofl" Plymouth, inside the Eddystone, have a density of 1-0267 or r0268. I found in
my experiments that the sole's ova frequently sank in the aquarium water towards the
close of their development, that is shortly before they hatched, and that the larvse
lay on the bottom of the jar after hatching : yet the density of this water was 1'027.
This shows that the eggs become heavier as development advances, though the
sinking of the eggs is probably hastened in the hatching apparatus by the accumu-
lation of particles of sediment upon them. The eggs themselves certainly float in the
sea until they are hatched, for they are frequently taken in the tow net when just
ready to hatch.

I have not been able to keep the larvaj alive more than a day or two after hatching.
In fact, owing to the difficulties of artificial fertilisation I have never had a sufficient
number to experiment with. I have been equally unsuccessful in procuring the larvse
from the sea: it is probable that soon after hatching the larvas sink towards the
bottom. Some of the stages given in the illustrations to this book of the larva; of
other species of ffat-lishes show that at first one of the most obvious changes which
takes place after hatching is the absorption of the yolk. Nourished by the yolk thus

123

absorbed the larva developes in all its organs. The pectoral fin grows into a large
semicircular paddle, the length increases, the black pigment of the eyes (in the
choroid) is developed, and the jaws acquire their definite structure. When the sole is
first hatched it has no mouth, and takes no food : the mouth is developed before the
3-olk is absorbed, but not until the absorption is completed does the young fish begin
to feed. The newly hatched sole is 3'55 to 3"75 mm. long, between |^th and v^ths of
an inch. It is perfectly symmetrical, having an eye on each side of its head, and
swimming vertically in the water, but it swims with its ventral edge uppermost,
because the yolk is lighter than the back of the fish.

The next stage in which I have discovered the young sole is immediately after the
completion of its metamorphosis, that is, after it has ceased to be symmetrical and to
swim vertically in the water, and has taken to lying flat on the sand, and has both
eyes on the right side of its head. I had searched everywhere for larval soles at the
bottom of the sea, after the eggs had disappeared from the surface, and had had a
special trawl with very small meshes made to capture them with, but could not
discover any. At last I obtained some through the assistance of Mr. Matthias Dunn,
of Mevagissey, who has been for years the friend and counsellor of all naturalists
engaged in the study of British fishes. On April 3, Mr. l)unn sent up to the Plymouth
Laboratorj' a number of young living flat-fishes. I found on examination that these
were all Pleuronectes flesus, the flounder. Some of these were very transparent and
only partially metamorphosed, the left eye being still on the lower side, but near the
edge of the head ; in others the eye was actually in the edge of the head, looking
horizontally outwards. Mr. Dunn said nothing about soles, in fact at this time there
were no young soles in process of metamorphosis. Having failed to obtain young
soles by trawling, I wrote to Mr. Dunn, and arranged with him to meet him at
Mevagissey and examine the place where he caught his young flounders. I went to
Mevagissey on May 15, and found that the young flounders were found in thousands,
if not millions, in the pools and runlets left at low water during spring tides on the
bottom of the harbour. The old harbour at Mevagissey (a new additional outer
harbour was then being built) is completely emptied of water at the ebb during
springs, and the bottom consists of sandy mud. I went over the harbour with ilr.
Dunn, and caught numbers of the young flounders with an ordinary cup. The little
fish are in constant motion, some of them continually rising to the surface of the
shallow pools in the sand and then sinking again to the bottom. We found a few
soles along with the innumerable flounders. Many of the flounders were still
transparent and only partially or scarcely at all metamorphosed, but in all the soles
the metamorphosis was complete. On this day I only caught three young soles, but
the following day Mr. Dunn sent to me at Plymouth fifteen more. These young soles
were from 12 to 15 mm. long: their characters are represented in PL XVI, 3,
which is 83 times the natural size. They possess nearly all the characters of the
adult, the chief exception being that the intestine is simpler and shorter, its coils only

124

extending back a little behind tlie anterior end of the ventral fin. The eyes are both
on the right side as in the adult. The skin and body are more transparent than in
full-grown soles, but the pigment of the upper side exhibits perfectly the arrangement
of spots which characterises Solea vulgaris.

On May 17, I examined at low water the shores of Sutton Pool and the mouth of
the Cattewater in order to find out whether young flounders or soles were to be seen
in the tidal pools there, as in the harbour at Mevagissey. I could not find a single
specimen, but the next day some boys brought me two specimens of young flounders
{PL Jlesus) taken at low tide on the shore of Sutton I'ool.

Tliese young soles, 12 mm. long, from Mevagissey could not have been more than
two months and a half to three months old, if the eggs from which they grew were
shed at the middle of February or the beginning of March, tliat is at the commence-
ment of the spawning period of the sole ; and it is very probable that they were only two
months old or even less. As the larvae are not hatched until a fortnight after
fertilisation, we may conclude that the metamorphosis occurs within about six weeks
after hatching.

At the next spring tides, namely, on May 31, Mr. Dunn sent me up some more
young flat-fishes from Mevagissey harbour: among these was one young sole, the only
one he could find, it measured | in. (18 mm.) in length. After this he could find no
more young soles in the tidal pools : they all disappeared, having either left the shore
for deeper water, or having become strong enough and active enough to swim away
with the retreating tide and avoid being left between tide marks. During the
fi)llowing months I perseveringly endeavoured to capture young soles in their later
stages. I trawled with my specially constructed trawl in Whitsand Bay frequently
both by night and day, and also in Cawsand Bay and other sandy parts of Plymouth
Sound, but I never got any young soles. In Whitsand Bay at night I got a large
numl:)er of young plaice, pouting {Gadus hiscus), and other young fishes, but not a
single sole.

Mr. Dunn having told me that he believed there were large numbers of young soles
in the estuaries of the Fal and Ilelford rivers, I asked my friend Mr. Eupert Vallentin,
of Falmouth, to make investigations and see if he could find any specimens. Mr.
Vallentin accordingly made a most careful and complete examination of the two
estuaries ^^ith the following results. He went to Malpas, a place about two miles
below Trurt), and there found one man, the innkeeper, who possessed a seine which
he used for taking flat-fish. On the 27th July Mr. Vallentin had a series of hauls
made with this seine, the meshes of which were so small as only to admit the tip of
tile little finoer. After several hauls the total catch of flat fishes was:
Four Flounders from 8 to 12 inches long,
Four Soles, 5jj inches, 5| inches, G inches, 7| inches in length.

The two smallest of the soles were sent to me, and I was able therefore to make
certain that they were really Solea vulgaris.

125

Mr. Vallentiu next on July 29, had a large seine sixty fathoms long and two
fathoms deep hauled in the Helford Eiver ; two hauls were taken, and a number of red
mullet and flounders were taken, but only one sole, which was sent to me. It was
4-j^e- inches in length.

Now it is obviously impossiljle to believe that young soles which were f inch in
length on May 31, ct)uld have grown to 5 inches in length by the end of July. Tlie
growth of flat-fishes is not so rapid as that. The spawning of the jilaice at Plymouth
takes place in February, and is completed early in March. On June 17, 1889, I
obtained a large number of young plaice by trawling at night in Whitsand Bay ; these
measured If to 2-^-g inches (3'4 to 59 cm.) in leogth ; another specmien which I got
from Sutton Pool on September 28, measured 2-j^ inches (62 cm.). On May 16,
1889, I obtained a large number of small plaice from the Cattewater, where I saw
them caught in a small seine : these measured 4| to nearly 7 inches in length. It is
evident therefore that these last specimens were more than a year old, namely, fifteen
months, and it is obvious that the soles caught by Mr. Vallentin were sixteen months
old, reckoning from the end of March as the spawning time. They were soles in the
second year of their growth. I have in my collection another small sole, measuring
4| inches (12-5 cm.) which was caught either in Plymouth Sound or on the trawling
ground off" Plymouth, at the end of February, 1888. Tliis must have been just a year old.

Why I have failed to obtain soles in the first year of their growth, after the stage
of those found at Mevagissey in May, I cannot understand. It may be owing to some
peculiarity of habit, that though I obtained young plaice and other species of flat-
fishes by trawling in shallow water in Whitsand Bay, I caught no soles. Of course
soles in the neighbourhood of Plymouth are much less numerous than plaice, flounders,
dabs, or merry-soles (PL microcephahis), and this doubtless adds to the difiiculty of
finding them. However, the problem will, I hope, be solved next year.

It has been shown that the young soles spawned in March have completed their
metamorphosis by the middle of May, when they are ^ to -^ inch in length (12 to
15 mm.); that on May 31 they are about f inch long (18 mm.); and that in one
year they grow to about 5 inches in length. We have now to consider their subsequent
growth.

Soles of small size but larger than any of those just mentioned are taken in
Plymouth Sound in considerable numbers by the small shrimps trawls, which have a
beam of 12 to 15 feet in length. Such trawls are regularly worked in the Sound for
shrimps and prawns, and one of them is regularly used for the collecting work of our
Laboratory. On May 10, 1889, the Laboratory fisherman took with the shrimp
trawl in the Cattewater, six soles measuring 6| to 7f inches in length (17-1 cm. to
19-G cm.). Another caught on May 6, measured 9-^ inches (23-3 cm.). I consider
these soles to be just over two years old. Soles from this size upwards are almost
always to be caught in the Sound, but the larger are less plentiful. They are never
very abundant, but usually about half-a-dozen can be caught in a day's work.

12G

Adult soles, as sold in the market, vary from about 12 to 16 inelies in length (30
to 40 cm.). If we take the medium size, 14 inches (or 35 cm.), it is evident that this
size cannot be reached in one year more by soles which at two years are only 6f to
9 inches in length. In all probability the length of 1 4 inches is not reached until
after the fish is four years old, and at three years it is only about 1 1 inches long.

The difficulty of distinguishing the ages of soles after the first year is due to the
fact that at a given time a series of sizes may be found from those which are probably
two years old to those which are three. The explanation of this is, first, that the
spawning time lasts altogether at least two months, and that the rate of growth
doubtless varies in different individuals according to the amount of food they have
been able to obtain.

The largest sole I have ever seen was one I obtained when trawling off the Land's
End in March, 1889. It was a ripe female, and measured 20^ inches in length, 9^
in breadth (52 cm. by 24 cm.). But still larger specimens have been recorded.
According to Day a Mr. Grove, of Charing Cross, received one from Torbay in 1882,
which was 24 inches (61 cm.) long, and weighed 6^ lbs. Yarrell mentions one taken
to the Totness market in 1826 which was 26 inches (66 cm.) long, 11^ inches
(29-2 cm.) broad, and weighed 9 lbs. Probably the sole, like most fishes, goes on
crrowing as long as it lives, and taking the growth as 3 inches a year after the first
year, when it grows 5 inches, the fish I saw, which was 20^ inches long, must have
been six years old.

Part IV.

ECONOMICAL.

129

CHAPTER T.

ARTIFICIAL PROPAGATION.

The commonest and most obvious method of attempting to increase the supply of a
valuable fish is to hatch its eggs. The young when hatched may be disposed of in one
of two ways. They may be kept in captivity and regularly supplied with food until
large enough to be valuable, or they may be set free in the natural haunts of the
species so as to replenish its numbers. The question of the best way to increase the
supply of soles will be fully discussed subsequenth'. At present I shall describe my
own experiments on the artificial pi'opagation of the species.

In the case of a number of species of valuable marine food-fishes there is no great
difficulty in obtaining large numbers of eggs from the fish, fertilising and hatching
them. The eggs become ripe at the spawning period, and it is perfectly easy to tell
whether the eggs of a given species are ripe or not. The number of eggs which ripen
at one time varies in different species. In some, as the herring, nearly all the eggs
become ripe simultaneously. When the eggs are ripe they can be squeezed out of the
ovary by gently stpieezing the abdomen of the fish with the fingers and thumb. They
run out in a continuous stream, and no blood or membranes escape with them : if the
eggs are not ripe no eggs escape unless considerable pressure is applied, and when they
are forced out they are accompanied by blood and by membranes containing blood
vessels. When the eggs in the ovary all ripen simultaneously, or nearly so, as in the
herring, the ovaries can be entirely emptied by gentle jDressure. In all fishes that I
have examined, the number of eggs ripe at the same time increases after the spawning
has commenced, so that the ovaries after a certain number of eggs have been shed
contain ripe eggs only and can be entirely emptied. In the cod family the ripening of
the eggs goes on very gradually, so that only a portion of the eggs in the ovaries of a
female can be pressed out at one time. The eggs of the sole ripen gradually at first,
but after spawning has commenced and some of the eggs have been shed the rest all
ripen simultaneously. The eggs also seem to be shed as soon as they are ripe. These
are the conclusions I form from my experience, which is that I have usually met with
soles whose ovaries were either full of unripe eggs and yielded very lew which were
ripe, or else were quite empty, all tlie eggs having been shed.

I commenced my experiments on the st)le in 1888. At my first attempt, which was

130

on a trawler to llie west of tlie EtUl3'stone on February G, I cot a few, verj- few,
ripe ova, and could get no milt by squeezing any of the fish. I did not then know that
the testes were small and the milt small in quantity in ihe sole. Only two or three of
the ova then obtained were found to be floating in my bottles when I returned to shore,
and none of these were fertilised. My next attempt was on ^larch and 7, when
I was on a trawler to the S.E. of the Wolf Eock. Only two or three females out of
nearly a hundred were then found to yield ripe ova, and as I could squeeze no milt
from the males, I cut out the testes, cut them into two or three pieces and placed them
in the bottles with the ova. On my return to Pl3niioutli on March 8, I found only
about a dozen ova floating, and of these onlj' two or three were fertilised and showing
the commencement of development. I made another attempt on the same fishing
ground between April 3 and 7, but on my return found that not a single ovum
was fertilised. On this occasion I got a considerable number of rij)e eggs altogether,
but onlj' a few from each fish. From May 1.5 to 18, when I was in a trawler on
the same ground, we had verj' bad weather : nearly all the soles were spent, but some
ripe ova were obtained from one specimen, and three or four of these were found to
be fertilised by the pieces of testis.

It seemed therefore from these experiments made in 1888 that the artificial fertilisa-
tion of soles' ova was a matter of the greatest difiiculty. T had succeeded in ascertaining
the characters of healthy fertilised ova from the few I had been able to procure, and
was therefore able to identify the sole's ovum when it occurred in the produce of the
tow-net, and I had also observed and made drawings of some stages of the development,
but this, though valuable knowledge, brought me very little nearer to the practical
object of my experiments.

In the season of 1889 I continued the experiments. I had found that soles were
scarce on the Plymouth trawling ground, which extends from the Dodman Point in
Cornwall, to the neighbourhood of Bolt Head in Devon, both inside and outside the
Eddystone. On this ground very often no soles at all are found in a haul of the traAvl,
and when there are some very often all are immature, or when a ripe female is taken
there are no males. On February 12, 1889, I was on a trawler which towed her trawl
from ofl' Eooe to a ])oint south of the Plymouth Breakwater lighthouse : four soles
were taken in this haul of which only one was adult, and that not ripe. On March 14,
I went out again, and this time the trawl was worked about 10 miles south of the
I'ddystone. Two hauls were made : in the first there was one sole, in the second none,
although the first haul was made in the night. After this I heard that some of the
Xewl3Ti mackerel boats were working small trawls in Mount's Baj" in order to earn
something while waiting for the commencement of the mackerel season. I therefore
went down to Penzance by rail, taking with me a number of collecting bottles to bring
back soles' ova. I went out in one of the boats on March 22. On this occasion I
examined tlie testes very carefully. I tried a large number of males, and could not
squeeze from an}- of them the thick milk-white milt which is so characteristic of the

131

ripe males of other fishes I have exaiuiued. Licjuid came from them of course, and in
some cases it had a slightlj^ milky appearance, but it was never possible to distinguish
the milt derived from the testes from the urine coming from the urinary bladder. It
was therefore useless to squeeze a male sole over a bottle containing ova in order to
fertilise them, for it was impossible to know whether any milt entered tlie bottle or
not. I dissected out the testes themselves from several specimens, and cut them iu
half and crushed them between my fingers, and found that all the liquid that came
from them was thin and almost clear, only very slightly turbid. It is evident, therefore,
seeing that these testes came from ripe males, that the sole does not produce any milk-
white thick secretion such as constitutes the milt of other fishes. The milt of the sole
is not only very limited in quantity, but is a thin liquid only slightly turbid, which is
difficult to distinguish when the male is squeezed. A considerable number of soles
were taken on this excursion. Some of the females were spent, some unripe, some
yielded only about a dozen ripe ova. But one female, the largest specimen I ever saw
{see page 126) yielded several thousand ripe ova. The ovaries of this specimen con-
tained ripe ova only : she was at the last stage of spawning, and probably these ripe
eggs were nearly half the entire number produced that season, the rest having already
been shed. Having fully investigated the males I concluded that the only method
likely to ensure fertilisation was to extract testes from the male soles, and crush these
up into a pulp between my fingers in the water into which the ova were to be allowed
to fall. In this way the whole of the milt contained in the male organs was sure to be
set free in the water containing the ova. I found this method perfectly successful.

At the Laboratory there was now a constant circulation of sea-water, and apparatus
for hatching floating ova which had been found to work admirably. The year before
the Aquarium was unfinished and there was no constant supply of sea-water. I landed
at Penzance with fertilised soles' eggs on the morning of March 23. The eggs were
contained in short wide glass jars such as are used foi- conveying sweets : over the
mouth of each was tied silk bolting cloth to prevent the eggs escaping, and this, to
some extent, prevented the water splashing over. I placed the bottles, held in a
divided basket, in the break-van of a train, and took them to Plj'mouth, where I arrived
the same evening. The eggs were at once placed in the hatching jars ; they seemed
quite health}-, and microscopic examination showed that they were all fertilised.

The apparatus and method I adopted last spring for hatching floating eggs were as
follows : — The apparatus is a modification of that recommended by II. C. Chester, of the
United States Fish Commission.""' The arrangement of Chester's apparatus is represented
in Fig. £" (p. 132) : it consists of a tall glass jar, j, which has an open narrow neck
above and is widely open below. This is placed in a tank having a constant supply of
sea-water, the overflow of which takes place through a siphon tube, s, having a diameter
greater than that of the inflow. The water in the jar is of course always at the same

Vide '• Devel. Osseuus l-"islics," by J. A. Racier, Rep. U. S. Fisli Coniuiissiou for 1885, p. 400.

13-2

level as the water in the tank. When the siphon of the outflow tube is empty the
water in the tank and jar rises until the level of its surface reaches the bend of the
siphon. Then the siphon fills and commences to act and the level of the water sinks
gradually until it falls below the short leg of the siphon, when the latter empties and the
outflow stops. The wide opening at the bottom of the jar is covered with a single
thickness of coarse cheese cloth to prevent the escape of the eggs which are introduced
into the jars through the narrow opening of the neck above. The rise and fall of the
water is only five inches vertically. Eyder says that cod eggs were hatched in this way
with a loss of only five per cent. I tried this apparatus with a large number of eggs
of the flounder and plaice {Pleuronectes fiesiis and P. platessa).

Fig. £. Fig. F.

Fig. E. DiagraTD of a transverse section of an apparatus for hatching buoyant fish eggs, arranged

according to the method devised by Captain Chester, of the United States Fish Commission.
Fig. F exhibits the modification of the apparatus adopted in the Laboratory of the Marine Biological
Association.
j, The glass hutching jar, resting on two bricks in a small tank containing si?a-\vater ; o, the overflow
tube; s, si])lion in the overflow tube; /, an iudiarubber tube conducting the inflowing water
into the interior of the hatching jar. The dots represent the eggs.

On February 12 I placed a large number of ova of the flounder, artificially
fertilised the same day, in two glass jars of the form described. The jars were 8 inches
wide and 17 inches high. The bottom of each jar was covered with silk bolting cloth.
Each jar was supported on two bricks resting on the bottom of a shallow aquarium tank
made of slate and glass. The water escaped from the tank by a stand pipe into which
I fitted a glass siphon so that the level of the water in the tank oscillated between limits
about 4 inches apart. The water in.side the jar was of course perfectly stiU : its
gradual rising and sinking caused no disturbance in it, in fact I found that the upper
part of the water in the jar was scarcely changed or affected by the rise and fall.
This will readily be understood. The total height of water in the jar was about 10
inches : .at the top of this floated the eggs which formed a layer about | inch thick.
As the level of the water in the tank sank, the water at the bottom of the jar escaj^ed
through the bolting cloth. \\'hen the tank was at its lowest level the height of the
water within the jar was still (> iiichos. When the water rose again all this water
was bodily lifted up with the Liver of eggs at its surface, while 4 inches of new water

133

entered the bottom of the jar. Thus the G inches of water simply rose and fell
gradually without being renewed or circulated : the only change effected in it was that
which took place at the bottom layers by contact with the new water which entered
the jar every time the level of the water rose. The upper layer of water containing
the ova was practically stagnant. The fall and rise of the water occupied each three
quarters of an hour.

On February 16 I found that about half the ova in each jar were dead, lying on the
bolting cloth at the bottom and contaminating all the water that entered the jar. I
therefore removed these dead ova by means of a siphon, and changed the arrangement
in one jar. I left the jars in the same position, but removed the siphon from the
overflow pipe of one tank and introduced into the jar (Fig. F) an indiarubber
tube, t, leading from a jet supplying clean sea-water. I regulated the force of the water
discharged by the indiarubber tube. The tube reached just below the lowest level to
which the water in the jar sank, and the force of the water escaping from it kept the
ova in constant but very gentle motion. Thus clean water was constantly entering the
jar and escaping through the bolting cloth at the bottom, and the eggs were separate
in the water, not in contact with one another in a dense layer.

On Februarj' 17, I found that all the ova in the unaltered jar, except a dozen or
two, were dead, while in the jar provided with the new arrangement, only a dozen
or two out of several thousand had died. But I found that the new arrangement was
not perfect. The water when its surface fell in the jar left a number of ova adhering
to the sides of the jar, which were thus for a considerable time out of water. These
eggs so stranded died. I therefore placed the jar in another tank in which there was
no siphon in the overflow pipe, so that the water in the tank and jar was at a constant
level. I made the indiarubber tube delivering inside the jar longer so that the
water escaping at its end threw it into a regular gentle rhythmical motion which
served to keep the ova uniformly distributed throughout the water in the jar. I found
this method answered perfectly. The water in the jar was constantly renewed, and,
a very important point, no sediment settled on the ova. In fact, the eggs thus treated
were as clean and transparent as eggs taken by the tow-net from the sea, a result I
never before obtained with e<i<?s artificially treated.

On February 18, I found all the ova in the new apparatus had hatched ; in the
jar left with the original arrangement a few eggs were still alive and some of these
were hatched, but not all. It seems therefore that the motion of the eggs facilitates
hatching, as it enables the larva to get rid of its egg shell more easily than it can in
still water. The number of larva; hatched in the vinaltered jar was quite insignificant,
not more than a dozen altogether, while in the altered arrangement I had between
one and two thousand healthy l;irva\ The two jars originally contained about the
same number of eggs. In a tliird jui- I had placed, on February 12, a large
number of fertilised ova of the plaice. This jar was arranged on the American plan,
and was left in this condition without change. On February 10, only about twentv

1.S4

of these eggs remained; the rest had all died, notwithstanding that I took care to
remove all dead eggs every day.

The arrangement which I adopted and found perfectly satisfactory is shown in the
dia"ram, Fig. F. It may of course be carried out on any scale, and does not require
a great deal of space. It is better to increase the capacity of the apparatus by
increasing the number of the jars ratlier than by increasing the size. Jars larger than
those I have described become unwieldy.

I found the method suited the hatched flounder larvae extremely well : they lived
in the jars in perfect health until the yolk was entirely absorbed. I did not succeed
in feeding them after that period. It would probably be necessary when the yolk
was absorbed to turn then out into a larger tank, as feeding in a confined space
contaminates the water. A few of tlie plaice eggs hatched on February 22, and
one or two of them lived till the yolk was absorbed in the apparatus arranged on thu
American method ; but this was the total result out of several thousand ova.

To return to the eggs of the sole which I obtained in Mount's Bay on March 23.
I placed tliem in two hatching jars arranged in the way I have described. There
were several thousand of the eggs, but I did not count them. As I have said, they
were all fertilised and had commenced to develop when placed in the hatching jars.
On March 21, when I examined them, I found to my surprise that nearly half in
each jar were dead. The blastoderm in the dead ones was formed, but some abnormal
appearances were seen round its edge. I removed the dead eggs, and hoped the
mortality was over and that the rest would live. But the next day I found again
half of those left had died. In the living ones the germinal membrane had enveloped
more than half the yolk : nuiny of them seemed unhealthy. On March 26, only about
six eggs in each jar were left alive, and these were dying, although in them the
embryo was already formed. As I had succeeded in keeping eggs of the sole,
artificially fertilised, ahve for a considerable time with only the roughest apparatus,
and as I afterwards hatched eggs taken by the tow-net from the sea, the cause of
death in the above experiment clearly could not be attributed to the water of the
a(juarium or any of the conditions under which the eggs were kept after they were
brought to the Laboratory. I could only attribute it to the railway journey which
had shaken and jolted the eggs and so injured them mechanically. It might be
su^o-ested that there was too great a dillerence of temperature between the water in
which the eggs were carried from Penzance and the water of the hatching jars, but
other experiments showed that eggs taken from the sea lived well in the sea water of
the Laboratory, and the weather during the railway journey was neither hot
enouo-h to heat the water in the jars containing the eggs nor cold enough to cool it
to any extent.

Believing it useless to carry fertili-sed eggs by rail, I went out on April the 8th, on
board a trawler which was going to fish on the Mount's Bay ground. On April 11,
12.5 a.m., the trawl was hauled with seventeen soles in it. Of these I examined

.).)

eleven, the rest were not found till afterwards when the decks were cleared up. (Jf
these eleven, three were temales almost spent but still containing some ripe ova ; one
was a female still unripe, four were spent females, and three were males. I got 300
or 400 eggs altogether which I tried to fertilise as before by crushing testes in the
water. At 4.80 p.m. the same day from six soles taken I got about a dozen more ova.
On April 12, at 8 a.m., after a good night's haul, fifty-seven soles were brought on
deck. Of these fifteen were small, under nine inches in length, and not sexually
mature ; eighteen were males ; nineteen large females entirely spent ; five large females,
which yielded a few ripe ova.

I may conveniently refer to the eggs obtained from the different hauls of this cruise
as lot 1, lot 2, and lot 3. On April 12, while still at sea, I observed that a large
proportion of the eggs of lot 1, fertilised the previous day, had died and sunk. These
were probablj' not fertilised, but I do not know why the fertilisation had failed ; it
may have been because the males were either immature or spent. I found when I
returned to the Laboratory, on April 13, that only eight eggs in lot 1 were alive and
developing ; in lot 2 some were floating but none fertilised ; in lot 3 two or three ova
were alive and developing.

On April 15, there were altogether nine eggs left alive: of these I preserved two
for microscopic examination and left the other seven in a small glass jar provided
with a circulation, not in one of the hatching jars above described, but an ordinaiy
jar, the only difference in the arrangement being that the overflow of the water took
place through a protected siphon, the jar standing in the air, not in the water of a
tank. On April 16, I again went to sea, and returned on April 20, when I found
of the seven eggs I left in the Laboratory two were hatched, two alive but unhatched,
and the rest dead. The circulation had almost stopped, the supply tube having got
choked. On April 21 the two larvte were dead, and one of the eggs: the last egg
hatched on April 22, but died the same day.

The above results prove that it is possible to artificially fertilise the eggs of the
sole and to hatch the eggs so fertilised in a hatching jar provided with a circulation.
The}' prove also that the cause of the death of the large number of eggs brought from
Penzance was not in any of the conditions to which they were exposed in the
Laboratory. The reason that I did not place the seven eggs just mentioned in a large
hatching jar was that it is difficult to find such a small number in such a jai-, or
extract them for closer examination.

PosTSCHiPT (May 3, 1890). While these pages have been passing through the
press the spawning period of the sole has again arrived, and I have renewed ray
endeavours to perfect a method of artificial propagation. Li consequence of
previous experience my success has been greater than in former seasons. During
a week I spent on a Lowestoft trawler in the Bristol Channel from April 9 to
April 16, I obtained a large numl)er — hundreds of thousands — of ripe soles' eggs.

I tried to fertilise these in the usual iiiaiiiier by extracting the male organs and
crushing them in the water containinpr the ejrgs. On mv return. I found less than
half the eggs taken were floating, but only about half of these last proved to be
fertilised. However, those which were fertilised were hatched in the hatching jars
without ditricully, and I obtained thousands of larvae. Some of the eggs were lost
before hatching because they ceased to float, and many larvse were lost for a similar
reason, as they began to sink two or three daj's after hatching. However, a large
number of the larvas were successfully kept alive until the mouth had developed,
the yolk was almost entirely absorbed, and feeding had commenced. Then they
all died. Thus when the eo"s are once fertilised thev can be hatched without
difficulty.

137

CHAPTER II.

THE SOLE FISHEEY.

We have next to consider tlie present condition of the sole fishery and to ascertain
whether the supply of soles in British waters has decreased in recent times. The
materials available for this enquiry are extremely scanty. Fishery statistics have been
systematically recorded for manj' years past in Scotland, but as there are no soles,
except as occasional rarities, in Scottish waters, these statistics are of no use for our
present purpose. The statistics of Irish fisheries on the otlier hand have only been
collected at all comprehensively since 1887, and the quantity of soles and other fish
landed at a certain number of Irish ports is recorded for only two years up to the
present time, namely, 1888 and 1889. For England and Wales analytical statistics
have been published in the " Statistical Tables and Memorandum relating to the Sea
Fisheries, &c." compiled by the Fisheries Sub-department of the Board of Trade, since
the year 1886. The figures in these tables of the total quantities of soles and otlier
prime fish landed on the English and Welsh coasts in successive j^ears are given in the
following table :—

Soles.

Turbot.

Prime Fish not separated.

Quantity. \ Value.
Cwts. ! £

Average

price
per cwt.

Quantity.

Cwts.

Value. ! -^"^g"
£ 1 price

per cwt.

Quantity.
Cwts.

Value.
£

Average

price
per cwt.

1 . & s. d.

1886 . . 98,078 ; 427,452 4 7 2

1887 . . 85,316 | 389,414 4 U 3 J

1888 . . 72,522 379,382 5 4 74

1889 . .; 74,143 431,269 . 5 16 4

59,850
63,166
55,041
53,576

£ «. d.
182,665 3 1 Oi ,

184,662 2 18 5J

171,967 3 2 5J

180,841 13 7 6

370,014

115,850

113,415

35,982

£ s. d.
369,089 19 Hi

368,674 3 3 7i*

316,966 2 15 lOJ

126,924 3 10 6i

m . , « T, • T-.- i II Totals of all Fish except
Totals of Prime Fish. |1 Shell-fish.

Quantity.
Cwts.

Value.
£

^'■•^.'"S^ Quantity.

P"<-\ Cwts.
per cwt.

Value. A^^™g«
„ pnce

per. cwt.

1886 .... 527,942

1887 .... 264,332

1888 .... 240,978

1889 ... 163,701

979,206
942,750
868,315
739,034

£ «. d.

1 17 1 6,412,433

3 11 4 6,029,481

3 12 Of , 6,348,072

4 10 3 6,464,564

£ .!. d.
3,688,079 U 6

3,778,953 12 6i

3,948,013 12 5i

3,862,389 11 US

138

All the above figures, according to the explanation given by the officials who
publiyh the statistics, refer to the fish as landed ; the prices are the " wholesale values
at the places of landing," by which I believe is meant the prices actually paid to the
auctioneers who sell the fish for the fishermen and smackowners. The classification
is made according to the way in which the fish are packed when brought ashore.
The best and the largest quantity of the soles and turbots are placed in boxes by
themselves not mixed with any other fish, while if there are not suflicient soles or
turbots in a catcli to make it worth while to pack them separately they are put
together with other kinds of " best " or " prime " fish. Therefore the figures under
tlie heading " soles " do not rei^resent the total quantity of soles landed. There are tons
of soles and turbot included under the heading of " prime fish not separated." Now,
if we look at the figures referring to soles only, we find that in the three years 1886,
1887, 1888, there was an annual decrease of 13,000 cwt., a very startling result. But
in 1889 there was an increase of nearly 2,000 over 1888. 15ut this latter increase
is much more than balanced by the enormous decrease in the quantity of miscellaneous
prime fi.sh in 1889, a decrease of 77,433 cwt. In no year was the decrease in
the quantity of separated soles balanced by an increase in the quantity of mis-
cellaneous prime fish ; on the contrary, there was a steady decrease in the latter
in 1887, 1888, and 1889. The figure of this item in 1886 must be kept apart, for
in five months of that year haddock were included under it at Billingsgate when
packed with prime fish, while since then haddock have been estimated separately.
This alteration also affects the totals of prime fish; but neglecting 1886 there was a
great annual decrease in the total quantity of prime fish landed. There is no doubt
therefore on the whole that since statistics have been kept, since the year 1886, there
has been a steady decrease in the (jnantity of soles landed on the coast of England
and Wales. I think it is very probable that the slight increase in the quantity of soles
landed separately in 1889 is due to the fact that in the eai'lier half of this year a large
number of North Sea trawling smacks left their own grounds and went to work off the
north coast of Cornwall, on a trawling ground which had previously been almost
entirely neglected, and on which soles were found in great abundance. This ground
was first tried bj' some Brixliam trawlers in 1887.

Another .sure indication of the increasing scarcity of soles is the steady rise in price.
Tlie price of soles sold separately has risen 45. to 13s. per cwt. every year. Tlie
price of turbot has not increased so steadily, though there is indication of increasing
scarcity of this fish also. The price of mixed prime fi.sh is somewhat irregular : that
of the year 188() is of no value to our iiuiuiiy for the reason Ijefoie nu-ntioned, and
the prices in other years may and probably do vary with the jiroportion of soles in (lie
boxes. The average price of prime fish taken altogether has increased steadily. In
1889 it was 18s. 3c/. per cwt. greater than in 1888. The Board of Trade tables give
the average price of soles per lb. for each year, and it is interesting to compare the.se
with the prices for the ten years 1856 to 1865. In the report of tlie Sea Fisheries

139

Commission of 1S6G 1 find a table giving the price of various kinds of fisli during tliose
years both in tlie Manchester Fish Market and that of Newcastle-ou-Tvne. The figures
are as follows : —

Manchester. f 1856. 1857. 1858. 1859. 1860. 1861.

I 3d. to -id. 6d. to 8d. 5d. to 8d. Gd. to lOd. M. to (id. (id. to 8d.
Soles per Hi. .-\

I 1862. 1863. 1865.

(. 6(/. to 8d. 8d. to lOJ. Gd. to 8d.

Newcastle. f 1856. 1857. 1858. 1859. 1860. 1861.

9rf. to 1/3. 1/- to 1/G. 1/- to 1/6. 1/3 to 1/9. 1/3 to 1/9. 1/3 to 1/&.

Soles per pair

1862. 1863. 1864. 1865.

1/6 to 2/.. 1/6 to 2/-. 1/9 to 2/-. 1/9 to 2/-.

Thus the price in both places was about doubled in the ten years. The average
prices of soles per lb. in the past four years according to the Board of Trade returns
are : — ■

1886. 1887. 1888. 1889.

9-Ud. 9-78d. ll-21tZ. l-2-iiJd.

To compare these with the Manchester prices given above it must be remembered
that the latter prices are retail, or very nearly so : that is, they are the prices of the
fish after they had been carried from the landing place to Manchester, and therefore
include the cost of carriage and the profits of the merchants and salesmen. Thus the
rise in the price of soles since 1856 is at least from Sd. to Is. per lb., or fouifold : and
this is not due to any decrease in the value of money, for almost everything else has
become cheaper.

It may be urged that the total quantity of all fish landed has not decreased but
only slightly fluctuated. But this is no compensation for the scarcity and dearness of
soles. It may be partly due to the greater value of second rate fish caused by the
diminution in the supply of prime fish, and it may be partly due to the fact that manj^
kinds of fish such as herrings, mackerel, and pilchard vary considerably in abundance
in difierent years from causes which are apparently not connected with fishing
operations. But soles are stationary fish : they do not move in shoals, nor as far as we
know move about at all to any great distance, and the only cause to which we can
attribute the decrease in the supply is constant fishing. The decrease is certainly not
due to any decrease in the numbers of trawlers, for the trawling fleets grow larger
almost every year.

The statistics I have discussed are as far as I can discover all that are available. As

a nation we ought to be thoroughly ashamed that no statistics worth the name were

kept either in England or Ireland before the year 1886. Before that time there were

periodical agitations about some particular kind of fishing which was said by those not

engaged in it to be injuring the fisheries. These agitations usuallj' arose out of jealousies

between diflTerent classes of fishermen, and were founded chiefly on prejudice and

T 2

ignorance. The Government of the day appointed Royal Commissions to inquire into
the questions in dispute. These Commissions proceeded to investigate the matter not
by considering the facts, for tliere were usually none establislied either of a statistical
or biological character, but by taking down carefully and printing the statements of
the disputing lishernien themselves and weighing the assertions of one set against those
of the other. Of course the Ctmuiissions collected together those facts bearing on the
matter which were known, and their reports contain a certain amount of grain
amongst a great deal of cliafT. They also constantly reported that the only satisfactory
method of investigating problems concerning the fisheries was to study the natural
history of the fishes and to record fishery statistics. Probably the various Commissions
cost quite as much as a proper fisheries department, including a scientific as well as a
statistical staflT, would have cost, but it was the traditional British method to appoint
Commissions. The public authorities have now commenced to collect and record
statistics, but they are yet far from the organisation of a satisfactory and convenient
system. In order to find information about the English sea-fisheries now we have to
search three distinct publications; the statistics of fish landed are given in the
" Statistical Tables and Memorandum," the number of boata and men are to be found in
the Annual Statement of Navigation and Shipping, the preparation of which is entirely
out of the control of the Fisheries Sub-department, and finally a certain amount of
miscellaneous information is given in the Annual Reports of the Inspector of Sea
Fisheries.

But apart from this inconvenience a great deal of improvement might be effected in
the system of recording the statistics. The difficulty of finding the total quantity of
soles landed has been sufliciently obvious from the above discussion. It might at first
be supposed that all the soles landed were included under the heading " soles," but we
find on careful examination that some soles are also included in the item of " prime
fish not separately distinguished." Of course this inconvenience is due to the customs
of the trade : sometimes soles are sold in trunks unmixed with other fish, while boxes
of mixed fish, including soles and small turbot, are also sold entire. But at least some
effort might be made to ascertain and inform the public what proportion the soles sold
separately bear to the total amount, whether the proportion is approximately constant
or not. If it has been found possible to separate the haddocks wliicli are sent to
Billingsgate packed with prime fish, it ought to be possible to separate the soles.
Another peculiarity in the tables which must shock the mind of anyone engaged in the
fish trade on the east coast or in London, is that beside the item soles in the figures for
England and Wales is placed an item in the figures for Scotland which a foot-note
explains to refer to lemon-soles. Now lemon-soles are no more soles than plaice are,
and their value is scarcely greater than that of plaice. Besides, quantities of lemon-soles
are sold in the London market and other English markets, but we are not told where
they are placed in the English statistics. We do not even know whether they are classed
as " prime fish not separately distinguished " or not. However, it is very satisfactory

141

that complete statistics are now aunually recorded, and it ought to be possible in future
to find at once whether the supply of a given fish has decreased or increased : the
importance of this possibility in relation to the trial of any measures, legislative or
otherwise, intended to maintain or increase the abundance of particular kinds of ILsh,
cannot be over estimated.

142

CHAPTER III.

PRACTICAL MEASURES.

The question we have here to consider is : Can soles be made more plentiful by measures
which are not only possible but practicable, that is, which are sufficiently easy to be
carried out, when they are understood and have become familiar, without a degree
of exertion and expense too great in comparison with the results gained? In
examining into this problem we must distinguish the (wo ways in which human action
can be applied to a valuable wild animal. One way is to keep the animal under entire
control by taking it into captivity : this may be called domesticating the animal, the
word domestication being used with a wide signification, and not necessarily implying
the taming of the animal. The other way is to leave the animal in perfect freedom, and
to increase its numbers Ijy protecting it and promoting its reproduction. With regard
to the sole we will consider the latter metliod first.

At present our knowledge is much too scanty to allow us at once to reach definite
conclusions and calculate with certainty the efiects of measures which suggest them-
selves. We do not know exactly what proportion of soles are usually destroyed in
nature at different stages of their existence: the proportion which reach adult age
from a given number of eggs must, we know, be very small.

We know that the " prosperity," if I may use the word, of a species depends on a
chain of extremely delicate relations between it and the other species of the fauna and
flora of its habitat : and we have reason to infer tliat in some cases these relations and
the species themselves are affected to an enormous extent by i)hysical, i.e., meteoro-
kxrical conditions over which man has no control. In order to know how man's action
can increase or maintain the abundance of a species we require to know how his
action in the past has decreased its numbers. Professor Huxley, in the case of the
herrinw, for instance, has argued that enormous as is the number of herrings captured
annually on the coasts of Britain, the evidence leads to the conclusion that the
number destroyed by man is quite insignificant in comparison with the numbers
destroyed by the natural enemies of the herring — by the cod and sea-birds and other
animals which prey upon it. 7\.nd this conchision seems to be supported by a
comparison of the abundance of herrings in different years. The number of herring
fishermen, the effifiency of their boats and nets, and the extent of their operations has

In llie

year

1870

»j

1874

5»

1871)

1880

1881

1884
1888

143

increased steadily and largely during the past twenty years. IJut although herrings
have been somewhat scarcer in some years than others, there is absolutely no evidence
that the supply has gradually decreased. On the contrary, the following figures will
show that the supply has on the whole increased as the number, efficiency, and size
of boats and nets increased, but has not increased continuously in proportion to the
increase in the apparatus of capture, nor decreased after a certain maximum in
consequence of the great number annually captured. In fact as far as we can see at
present the abundance of herrings in different years fluctuates in consequence of
conditions not only beyond human control, but at present unknown. The number ol
barrels of herrings cured in Scotland was : —

833,160

1,000,5G1

841,796

1,473,600

1,111,155

1,697,952

.. 1,118,872

But, on the other hand, we know that human rapacity and recklessness have entirely
or nearly exterminated certain species of animals which were at one time very
abundant in certain regions. The Dodo and the Ehytina were exterminated by man,
and the Greenland whale and the American bison seem to be rapidh^ approaching the
same end. The Dodo was confmed to the island of Mauritius, and seems to have
been more persecuted by the domestic animals introduced by the Dutch discoverers of
the island than by the Dutch themselves : it could only have been saved by being
domesticated, and apparently it was not sufficiently valuable to be worth keeping.
The Rhytina was a kind of Manatee which lived on Behring's Island and Copper
Island in the Xorth Pacific, and was extremely numerous on the former in 1741, when
the island was first discovered. It was exterminated in less than fifty yeai's by Russian
hunters and traders who lived upon its flesh. The Ehytina was of enormous size, and
quite harmless, and its extinction was doubtless largely due to these circumstances,
which made its slaughter easy, and to its slow rate of multiplication.

The history of the northern fur seal of the Bebring Sea is less mournful, and at the
same time most interesting and instructive. This species, Callorhinus ursimis, breeds
only on two islands of the Bribylov group off the coast of Alaska, on the ■Connnander
Islands in Behring Sea, and one other in the same region. The seals arrive at these islands
late in spring, and remain on shore until the beginning of November. The females bring
forth their pups soon after landing, and before the mothers leave the islands these pups
are weaned, and able to tmvel with them. During the winter months the seals seem to
disperse and live in the sea, but I have found no account of their mode of life during this
period. In 1870 the Alaska Commercial Company of San Francisco received a lease

144

of the Pribylov Islands from the United Slates Government at a rent of §55,000 or
£11,000 a year, and afterwards rented the other seal islands from the Eussian
Government. This company since that time has slau^ditered 100,000 seals annually
on the Pribylov Islands alone, for the sake of their skins, and yet has not diminished
in the least the abundance of the animals, but rather increased it. Yet it is practically
certain that if the seal islands had been open to hunters of all nations, considering
the great value of the skins, the numbers of the species would by this time have
been seriously diminished, and probably the species would ultimately have been exter-
minated. Wliat is the reason of the different results obtained by the Company? It
is tlie story of the goose with the golden eggs. The old male seals are polygamous
and very pugnacious, and do not allow the young males to possess any wives at all.
The young bachelors live in a herd by themselves, and only these are killed ; no
females are destroyed. The check on the number of males is an advantage to the
species, for when there are too many, the amount of fighting that goes on in the
" rookeries " destroys a number of cubs.

In the case of this fur seal a whole species has been practically made private
property without being in any sense of the word domesticated. It is evidently
impossible for a company to acquire exclusive possession of the whole of any species
of marine fish. But our marine fisheries are the property of the nation, and the
fishermen can be controlled by legislation, if measures can be found which have such
a relation to the conditions of life and reproduction of the various species as to result
in benefits both to the fishermen and the whole nation.

Legal measures have fri^m time to time been taken to prevent the reduction of the
numbers of valuable marine animals by prohibiting the capture of the young individuals
below a certain size. Such measures doubtless have a good effect when carried out,
for, in the first place, small individuals have generally a very small value, while the same
individuals when full grown are worth many times as much ; and, in the second place,
if the young individuals are destroyed there will be no parents to succeed those from
which they were derived. But these measures, however effectively carried out, will not
prevent the scarcity of a species if the adults are constantly destroyed in such
numbers tliat there are not enough left to produce sufficient eggs to give rise to rhe
next generation. The latter has been the case with species of fish which ascend rivers
and estuaries in order to breed. A measure applied to prevent the too great
destruction of adults in this case is that of prohibiting the capture of any individuals
whether young or adult during the breeding period, the institution of " close seasons."
Now if the regulations concerning close seasons were carried out in regard to the
salmon in such a way that no adult salmon in a river in a given winter were killed
until after it had spawned, and all were killed after spawning, and at the same
time no immature fish were killed, it is clear that the result would be that each
fish that arrived at maturity would certainly breed once, and only once. And
there seems no reason why this should not be sufficient to maintain the abundance

145

of the species ; for the number of eggs produced by a female sahnon at one spawning
season is very large. But as a matter of fact the regulations are not enforced
in this way : the salmon ascend rivers throughout the summer, and do not spawn
till autumn, and the fish that have recently spawned are of no value. Those that
are sought are those that have just entered the river. The annual close season
is limited to the actual spawning period. In consequence it is only those adults
which escape the net, the hook, and the trap which survive to deposit their eggs and
milt. However, even thus the close season has a good effect, for it ensures that the
adults who do escape shall shed their reproductive products in peace and security, and
the eggs are therefore all fertilised and placed in conditions proper for development,
while if the fish were disturbed, a greater number would be destroyed, and the eggs
of those that were left would not be so properly deposited.

But another method which has been applied to anadromous fish is tliat of artificial
propagation. This has been successful chiefly in the case of Salmonidaj and of the
American shad, Alosa sapiclissima. It seems to me that the application of this measure
deserves to be considered carefully. Let us suppose a river visited regularly by salmon
for the purpose of spawning. If during the close season pisciculturists are permitted
to catch a number of the spawning salmon in the river, strip them of their eggs and
milt and hatch them in the most perfectly arranged hatchery, and then turn the fry at
a certain stage again into the river, what wiU be the result ? If a greater percentage
of eggs can be hatched under artificial conditions than under the natural, then of
course the result will be to increase the number of fry produced in the river.

This may be the case supposing that the eggs are preyed upon by other fishes or
animals in the natural state, from which they are of course protected in the hatchery.
But it would be equally effective to leave the eggs in the natural state and destroy
their enemies. The artificially hatched fry are returned to the river soon after
hatching, so that they are protected for a very short time, which, however, may be an
advantage if in the natural state they are devoured in numbers when first hatched. Of
course all this only applies to the case supposed. When artificially fertilised eggs or
hatched fry, derived from other places, are put into a river, they will of course add to
the sahnon population of the river if the conditions necessary for their life prevail iit
that river.

Considering now the case of the American shad, we find the problem different. The
estuaries, when the American Fish Commission commenced operations, were over fished,
and some had been entirely depopulated. There was no close season for shad, in fact it
was scarcely possible to institute one, for the shad unlike the salmon enters the river
only a very short time before it actually spawns, and the immense majority of
individuals captured are, like the herrings taken in Britain, either actually rij^e or
very nearly so. Hence a close season would have meant prohibiting the fishing
altogether. Such numbers of shad were taken for many years, that the number of
eggs deposited was not nearly sufficient to keep up the numbers of the species. Kearly

146

all tlie ripe eggs and milt -which ought to have developed into the next generation were
actually devoured by the people who ate the shad. The pisciculturists, under the
direction of the Fish Commissioner, therefore first invented methods and apparatus by
which the eggs of the shad could be artificially fertilised and hatched, and then they
organised a system under which every year a large number of the ripe fish captured
were stripped of their eggs and milt which were returned either to the same river or
others in the form of healthy fry. The consequence is that now the estuaries on the
Atlantic side of the United States yield annually a rich harvest of adult shad, and this
valuable fishery is absolutely dependent on the piscicultural operations of the National
Fish Commission.

Let us now consider the case of the sole. Soles are captured without- intermission
the whole year round, and their habitat is practically only coextensive with the
trawling grounds. Soles do not, our knowledge enables us to infer with some
certainty, migrate or travel about to any great extent. There may be of course
distant areas where soles are abundant, but the existence of these is not sufficient to
maintain the sole population of the extensive areas where they are constantly captured.
Now I have shown that the artificial fertilisation and hatching of soles' eggs, though
presenting unusual difficulties, is by no means impossible. It is almost impossible to
interfere with trawling. Suppose that by further experiments it were shown that
millions of soles' eggs could be artificially fertilised, hatched, and returned to the sea.
It is evident that this would necessarily have the effect of increasing the supply of
soles. For all these eggs would be procured from soles captured for the market, and
would, if not artificially hatched, be devoured along with the soles themseh-es. Of
course the expense of providing properly equipped hatcheries and mamtammg a staff
of men who would collect the eggs and take care of them during development would
be very large. But if this expense were provided from the public funds, some return
for it would be received by the public in the form of more abundant and cheaper soles.
Whether the national account on this item would result in an annual profit or an
annual loss I am not yet prepared to say.

On the other hand, it seems to me at least possible that the artificial fertilisation
of the eggs would alone be sufficient, and that the artificial hatching in expensive
hatcheries would be unnecessary. We have at present little reason to assume that,
given a certain number of fertilised eggs more fry would be produced from them by
hatching them in artificial apparatus than by placing them in the sea to develop under
natural conditions. It is conceivable that the ripe females and males captured by the
trawl during the spawning season should be stripped by a man on board a trawler,
and the fertilised eggs so obtained should be simply thrown overboard. This would
be a direct gain to the sole population of our seas, for every one of those eggs would,
if not artificially fertilised, be sent to market inside the female soles and cooked. In
fact ripe eggs are now cooked in the ovaries of soles in enormous numbers everj'
spawning season.

147

Of course much greater results would be effected by simplj- prohibiting the capture
of soles at all from the middle of Februarj^ to the end of April ; but this could only be
done by prohibiting trawling during those months, for in my opinion soles once
captured in the trawl are usually too much injured to survive if again returned to the
sea. I have shown that they do not survive when placed in our aquarium tanks {see
p. 115). If trawling were prohibited who would compensate the fishermen and capitalists
engaged in the business ? That would be more expensive than maintaining a national
staff of pisciculturists to hatch soles' eggs. On the other hand, we must consider if it
is possible under any imaginary system that there should be a mail on board every
trawler capable of artificially fertilising the eggs of soles during the spawning period.
It would scarcely be practicable to send out a trained pisciculturist in every trawler.
It is possible, however, in imagination at least, that the skipper of every trawler should
carry out the necessary operations, though it would probably be a long time before
trawling skippers would possess the necessary knowledge or care sufficiently for the
future. If such operations were expected of them they would have to be trained in
practical pisciculture, and pass an examination in that subject as they are now
required to pass in seamanship.

I make no claim to originality in this idea. Years ago Professor Ewart, of the
University of Edinburgh, who has identified himself with the piscicultural work of the
Scottish Fishery Board, published the suggestion of a similar scheme to be applied to
herrings. I believe it has never been carried out, and I doubt at present if such
measures for maintaining the supph* of herrings are required. It has occurred to me to
consider whether the same scheme might be applied to soles, and I think it quite pos-
sible that Professor Ewart's suggestion may in the future lead to very important results.

The only other possible methods of increasing the numbers of soles are to increase
the supply of food or to diminish the numbers of the natural enemies of the sole. No
practical means can be suggested by which the supply of food could be increased, but
it might well be worth while to rigoi'ously destroy useless predatory fish which have no
value themselves and which live entirely on valuable food fishes. At present trawlers
constantly throw back anglers and dog-fishes into the sea alive after they have brought
them on deck. I think it would be advisable that these fishes should be systematically
killed before being returned to the sea, for if valuable fishes can be diminished in
numbers the abundance of their enemies could be reduced also.

There is not much to be said about the domestication of soles. It is certain that
soles will live in captivity and grow to a large size. The Association is now making
arrangements to keep young soles in a large piece of enclosed sea-water at Sheerness.
But it is evident that the capture of young soles to be merely retained in captivitj- and
killed when mature will not prevent the diminution of the numbers in the sea. If the
adults were kept in captivity and their eggs taken and reared a new industry of sole-
raising might be started, but it is doubtful whether this would compensate for the
extermination of soles from the great trawling grounds.

PLATES.

Pl^AIE I.

Drawing of a living Sole, lying on coarse bright-coloured gravel, in a shallow porcelain
distil full of sea-uatei', and exposed to dajlight from a south window.

Plate II.

Dravying of the same specimen as that represented in Plate I lying on washed coal in
a deep wooden luij and shaded from the light.

<
o

D
>

LU
_l

Plate III.

Drawing of a living Sole, not the same specimen as represented in I'late I, lying in a
shallow dish of while porcelain full of sea-water and exposed to strong day-
light from a south wiudcw.

"CO

■X.

Li,

Plate IV.

Drawing of the specimen represented in Plate III on the day after its death.

-J

D
>

O
CD

Plate V.

The lower (left) side of the Common Sole. Two specimens of the parasite Phyllonella
sulece are shown on the skin beliind the liead jusL below the lateral line.

•

D
>

_l
O
CO

f\\

Platk VI.

Fig. 1. The Lemon or Sand Sole {Solea lascaris), natural size.

Fig. 2. Lower side of tlie head of llie same, showing the dilated anterior nostril.

Plate VII.

Fig. 1. The Thickback {Solea variegata), natural size.

Fig. 2. Lower side of tlie head of the same.

Fig. 3. The Solenette {Solea lutea), natural size.

Fig. 4. Lower side of the same,

-I—

.'-. I.

''. ,'+/

■ ,"«

.-/^^f

^^-.^.

"■(?'•

mj '

V-*.-

V^-

klii'ik'

Q::

..I

-1

(f)

•^

CNJ

•9

tf)

t—

-OO

-o/)

Plate VIII.

Fiw. 1. The viscera of the female Common Sole in situ, natural size.

Fiff. 2. The body cavity of the female Common Sole after all the viscera have been
removed except the ovary and kidneys, which are left in situ. The wooden
rod passes through the anus, the blue probe passes through the external
aperture of the common oviduct up into the left ovary, the black bristle
passes into the urinary bladder which lies beneath the oviduct.

.11

■*^

.-a

■CO

o
'o

Plate IX.

Fi2- 1. Tlie viscera of the male Common Sole in situ, natural size.

Fig. 2. The body cavity of the male Common Sole after all the viscera have been
removed except the testes and kidneys, which are left in situ, natural size.
The wooden rod passes through llie anus, the black bristle passes into the
urinary bladder, which lies beneath the cords containing the testicular
ducts.

•00

Plate X.

Fig. 1. The skeleton of the Common Sole; the branchial arches, jaws, and bones of
the paired fins have been removed, all the other bones are in their natural
position in relation to one another.

Fig. 2. One of the dorsal fin-rays : a. from the side ; b. from the front.

n
3

o
CO

Pj^ati: X

Fig. 1. The superficial bones of the right or iqiper side of the head of the Comiuon
Sole.

Fig. 2, The superficial bones of the left or lower side.

Reference letters : —

hm.

hyomandibuliii

mx,

niesoptt'iT','oi<l

int.

metapterygoid

mandible.

pterysroid.

pa,

palatine.

«.

syniplectic.

px,

po,
to,
so.

quadrate.

maxilla.

premaxilla.

opercular.

])reopercular.

interopercular.

snbopercular.

Fig. 3. The bones of the branchial arches and paired fins, lateral view.
Fig. 4. The bony branchial arches spread out and seen from the dorsal side.

Reference letters and numbers

14, 2ud epibraiichial.

16, 2nd hypobranciiial.

17, 3rd pliarynfTobrancliial.

18, iJrd epibrauchial.

19, 3rd ceratobraiichial.
'20, 3rd hypobraiK-liial.
21, 4th epibrancliial.

25, post-temporal.

26, supra-clavicular.

27, clavicle.

28, jugular.

29, scapula.

30, coracoid.

31, pubic.

Fig. 5. The skull, showing the separate bones and their sutures, from the right side.
Fig. 6. The same from the left side.
Fig. 7. The same from the dorsal side.

hbl.

1st basibranchial.

U2,

2ud ditto.

hb3,

3rd ditto.

hh.

basihyal.

hh,

hypohyals.

ch.

ceratohyal.

cbl.

1st cerato-branchial.

cb2,

2nd ditto.

IP^

lower pharyngeal.

np,

upper pharyngeal.

•>

styluhyal.

epihyal.

1st pliarj-ngobranchial.

1st epibrancliial.

11,

1st hypobranchial.

Fig. 8. The posterior surface.
Reference letters : —

h.o.

basioccipifal.

s.o.

supraoccipital

e.x.o.

exoccipital.

ep.o.

epiotic.

pt.o.

pt erotic.

op.o.

opisthotic.

pr.o.

prootic.

sp.o.

sphenotic.

jia. parietal.

l.f. left frontal

r.f. right fiontf.l.

pa.s. parasphenoid.

vo. vomer.

■tnes.e, mesethmoid.

r.ect.e. right cctethiuoid

l.ect.e. left ditto.

iilll

Plate X

Firr. 1. The superficial bones of tlie riglit or upper side of the head of the Common
Sole.

Fig. 2, The superficial bones of the left or lower side.

Eeference letters : —

A III .

hjoniandibular.

}rut.

mcsopterygoid.

ml.

metapterj-goift.

in.

mandible

pt.

ptciyaroid.

pa,

palatine.

»'•

syraplectic.

(luadratc.

,c,

maxilla.

px,

prcma.xilla.

opercular.

po,

10,

so.

prcopercular.

interopcrcular

snbopercular.

Fic 3. The bones of the branchial arches and
Fig. 4. The bony branchial arches spread out
Eeference letters and numbers : —

paired fins, lateral view.

and seen from the dorsal side.

14, 2nd cpibrancliial.

16, 2nd hypobrancliial.

17, 8rd pliaryngoliraiicliial.

18, 3rd cpibrancliial.

19, 3rd ccratobrancliial.

20, 3rd hypobrancliial.

21, 4tli epibrancliial.

25, po.st-temporal.

26, supra-clavicular.

27, clavicle.

28, jugular.

29, scapula.

30, coracoid.

31, pubic.

Fig. 5. The skull, showing the separate bones and their suiures, from the right side.
Fig. 6. The same from the left side.
Fig. 7. The same from the dorsal side.
Fig. 8. The posterior surface.

661,

1st basibranchial.

66 2,

2nd ditto.

66 3,

3rd ditto.

bh,
hh,
ch.

basihyal.

liypob}-aIs.

ceratoliyal.

chl.

1st cerato-branchial.

cb2,

2nd ditto.

Ip,

lower pharyngeal.

up,
•2,

upper pharyngeal.

stylobyal.

■\

epihyal.

1st pliaryngobranchial

!»,

1st e[iibrancliial.

ll,

Ist hypobrancliial.

Eeference letters : —

6.0. basioccipital.

s.o. supi-aoccipital.

e.x.o. exoccipital.

ep.o. epiotic.

pl.o. pterotic.

op.o. opisthotic.

pr.o. prootic.

sp.o. spbenotic.

jia. parietal.

l.f. left frontal.

r.f. right fi-ontf.l.

pa.s. paraspbcnoid.

vo. vomer.

men.e. uiesethmoid.

r.ect.c. right cctethnioid.

l.cct.c. left ditto.

Plate XI

jjr o.

pro

J.T. Curainghamdil

Solea vulgaris

L]th£>Inip CBmb Sci !•

Plate XII.

General view of the niusculaturs of the Coimuou Sole seen from the right side, after
removal of the skin. The superficial abductors of the ventral fm have been
removed, to expose the elevators and depressors of the ventral fin-rays which
lie beneath tliem ; the same dissection has been made along the anterior
fourth of the dorsal fin.

sssg^..

<u
■q
en

rhAiF. XIII.

Fig. 1. Transverse section of the right ovary of a young Common Sole, 7^ inches long,
killed May 2, 1889 ; magnified 45 times, linear.

f.e. fibrous tissues forming the wall of the ovary.
o.g. ovigerous lamellie.
hx. blood-vessels, ovarian artery and vein.

Fig. 2. Portion of an ovigerous lamella from transverse section of an ovarv of a Sole
10^ inches long, killed January 26, 1889 ; magnified 450 times.

ff.e. germinal epithehuni.
(). ova.

Fig. 3. Section of an ovum approaching maturity, from the ovary of a Sole killed
when spawning was almost finished, on April 1 1, 1889 ; magnified 70 times.

h.v. blood-vessels.
f.e. follicular epithelium.
f.m. follicular membrane.
v.m. vitelline membrane.

Fig. 4. Transverse section of the right testis of a Sole 9 inches long, immature ;

magnified 45 times.

f.e. fibrous envelope.

r.t. radial testicular tubes.

Li. longitudinal testicular tubes.

Fijf. 5. Closed end oi one of the radial testicular tubes shown in Fig. 4 : magnified 450

times.

f.e. fibrous envelope.

ij.c. male germinal epithelium.

Fig. ha. Longitudinal portion of a testicular tube from the same section cut
transversely, containing spermatoblasts and ripe spermatozoa ; magnified
450 times.

Fig. 6. Transverse section of the cord containing the testicular ducts from an adult
male Sole killed in the breeding season, March 28, 1889; magnified 70
times.

f.t. fibrous tissue.

l.t. the testicular ducts.

u.h. urinary bladder lined by an epithelium.

Fig. 7. Spermatozoon of Dab [Tleuronectes limandoC) ; magnified 500 times.

;»■_

'■^^-f

Plate Xlll

f'U--'

/e.

^
•^^.

.fr>

■■<£i &

;.«.

f.e..

4:.

ae ti.!T

^^■^-

,..ajb~

^:--^

t^^

5a.

J T '.lunninghiTT; del

3oiea vulgaris

Lithiimp Camb ScilnttCo

Plate XIV.

Fig, 1. Scale of Common Sole from middle of body ; magnified.

Fig. 2. One of the lateral line scales of the same.

Fig. 3. Scale of Thickback.

Fig. 4. Scale of Lemon or Sand Sole.

Fig. 5. Scale of Solenette.

Fig. G. PhyJIonella solece, the parasite from the skin of the Common Sole ; magnified.

l^s. i)osterior sucker.

p. aperture for the penis.

u. aperture of the uterus.
n.g. anterior glandular areas.

Fig 6a. Egg of same, magnified 100 times.

Fig. 7. Ideal longitudinal section of the skin along the lateral line of the Common Sole ;
magnified 70 times.

ep. epidermis.

c. chromatophores.
d.t. dermal tube.
s.c. scale in section.

/. fibrous tissue of the derma with areolar tissue in spaces.

J), external pores.
s.o. sense organ.

11. nerve.

Plate XIV

ti "'

:^"

'i-..

' — r

9..

■'3£--^:.

J T. Cunningham. del

Solea vulgaris

: i^.L'amb.Sc: InstC'c

Plate XV.

Fig. 1. Sectiun of a portion of the skin of the lower side of head of the Common
Sole ; magnified 70 times. Reference letters as in Fig. 7, PI. XIV, with
the addition of /"/, tactile filaments.

Fig. 2. Lower side of the head of the Sole dissected to sliow the cutaneous nerves :
natural size,

V 2. Maxillary branch of the 5th.
V 2 a. palato-nasal branch of 5th.

V 2. mandibular branch of 5th.
VII 1. mandibular branch of 7th.
VII 2. hyoidean branch of 7th.

VII 2 a. opercular branch of 7th.
X 6 a. supra-temporal branch of vagus.
X 6 Z*. another anterior branch of the vagus.

Fig, 3. Egg of Cominon Sole taken in tow-net in Mount's Bay, March 1, 1SS9.
Magnified 45 times, hi. blastoderm, y.s. yolk segments, o.(j. oil globules.

Fig. 4. An egg of the same, artificially fertilised, March 23, 7 a.m. ; drawn March 24,
5 p.m.; same magnification.

Fig. 5. An egg of the same, artificially fertilised, March 23, 7 a.m. ; drawn March 25,
12 noon ; same magnification.

Fig. ti. An egg, fertilised artificially. April 12, 188'J ; dranw April 15, 4 p.m.
Both black and coloured pigment cells present, the latter green by reflected
light; e. eye, m.s. mesoblastic somites.

Plate XV

J r Cunnjngham.del

SoJea vulgaris

Plate XVI.

Fig. 1. Egg of Common Sole, artificially fertilised, April 12,1889, 10 a.m.; drawn
April 15, 4 p.m. Magnified 45 times; same stage as that shown iu PI. XV,
Fig 6, in profile, o.g. oil globules.

Fig. 2. An egg of same taken in tow-net off Plj-month (near the Mewstoue), March 29,
1889; drawn March 30 ; same magnification, e. eye. _?/L yolk.

Fig. 3. Larva of same taken 4 m. south of the Mewstone, March 30, 1889; right
side ; magnified 35 times, yk. yolk. cm. auditory organ, na. nasal capsule.

Fig. 4. Larva of same, hatched March 28, from egg taken off Penlee Point, March 27,
left side ; magnified 35 times, ht. heart, pt. pectoral fin. int. intestine.

Ficr. 5. Young Common Sole | inch long, taken in Mevagissey Harbour, May 15,
1889 ; magnified S| times.

Fig. 6, Egg of I he Thickback {Solea vanegata), taken in tow net S. of the Eddystone ;
drawn April 21, 1889; magnified 45 tunes.

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Tlate XVII.

Fig. 1. Larva of Thickback newly hatched, April 24, 1889; magnilied 35 times.
Pigment as seen by reflected light, yk. yolk.

Fig. 2, Larva of same two days after hatching, April 23, 1889. Same magnification
2^. pectoral fin. Jd. heart.

Fig. 3. Larva of Flounder {Pleibronectes flesus), two days after hatching, February 20,
1889, from egg artificially fertihsed ; magnified 35 times.

Fig. 4. Larva of same six days after hatching, February 24, 1889, from the same
lot as the preceding ; same magnification.

Fig. 5. Young Flounder taken in Mevagissey Harbour, April 2, 1889 ; drawn K])v\\ 5 ;
nuignified about IS times.

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PLEURONF.CTES FLESUS

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PLEURON'ECTES

Fio. 1.2. SOLEA VARIECATA. Fi,.|. 3 5. PLEURONECTES FLESUS

Plate XVIIL

Fi". 1. Young 'Floundev {Pleuro7iectcs fesus) taken h\ Mevagissey Harbour, April 2,
1889 ; magnified about 14i times, pv. pelvic fin.

Fig. 2. Larva of Dab {Pleuronectes limanda) newly hatched, from artificially fertilised
egg, March 11, 1889 ; magnified 35 times, pt. pectoral fin. yk. yolk.

Fig. 3. Larva of Merry Sole {Pleuronectes viicrocephalm), March 25, 1889, four days
after hatching, from artificially fertilised egg ; same magnification. /. liver.
ht. heart.

Fig. 4. Larva of Plaice {Pleuronectes platessa), February 27, 1889, five days after
hatching, from artificially fertilised egg; same magnification, a. anus.
nch. notochord.

Fig. 5. Young Brill {JUinnihits Icinns) taken at surface of water in Sutton Pool, June 1,
1889 ; natural size.

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PRINTERS IN ORDINARV TO HEK MAJESTY,

ST. martin's lani:, London.

SMITHSONIAN INSTITUTION LIBRARIES

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