The story of fish life

UC-NRLF

531

Frontispiece.

THE STORY OF

FISH-LIFE

BY W. P. PYCRAFT
F.Z.S., A.L.S., &c.

AUTHOR OF "THE STORY OF BIRD
LIFE," "THE STORY OF REPTILE LIFE"

WITH EIGHTEEN
ILLUSTRATIONS

HODDER AND STOUGHTON
LONDON NEW YORK TORONTO

PREFACE.

EVERY reader who takes up this little volume
is certain to be more or less familiar with the
animal which we know as a fish. But this
familiarity will have been acquired through
many channels, varying with the individual.
One will have much to tell of angler's lore, of
knowledge gained by long hours of silent watch-
ing and waiting, ruminating on the mysteries of
Nature, and perfecting deep-laid plots to snare
her scaly children. He will talk with anima-
tion of a well-filled creel, and recount wondrous
tales of mighty fish lost when capture seemed a
certainty ; fish whose shades grow larger each time
the memory revives them, just as their solid selves
have doubtless been doing ever since, making
their capture less and less likely as they gain in
bulk. This must be so, for fish such as loom so
large in these stories never seem to be landed !
He will regale us with delicious word pictures of
stream and lake and sea, and curious facts of the
ways and customs of fish of all kinds, and of all
lands. Another will have much that is worth
knowing to tell, concerning fish as a food supply,
and of the industries connected therewith, of which
enough might be said to fill another book of the size
of this little volume. Yet others could add curious
facts gained in our various fish-hatcheries, or facts
encrusted but too often by painful memories of
days of peril and exposure encountered in that
great arena, where men war with Nature, and take
from her as by force — the deep sea-fisheries.
All these, in their respective spheres of know-

6 PREFACE.

ledge, will learn but little, probably, from this
little book. Its aim is quite other. Briefly, its pur-
pose is, as its title implies, to tell the Story of Fish
Life. Man's relations thereto is thereby excluded.
We are to take a peep into fish world, and see,
as far as may be, how they fight the battle of life,
how they "live and move and have their being."

Certain technicalities have been, here and there,
unavoidable, and will, I am sure, be patiently
tolerated by my readers. They are used only when
their omission would be at the expense of clearness.

In the preparation of this little volume I have
found much help from Dr A. S. Woodward's
" Vertebrate Paleontology"; Dr Bashford Deans'
"Fishes Living and Fossil"; Dr A. Giinther's
"Study of Fishes"; Dr E. H. Traquair's
Presidential Address at the Bradford meeting
of the British Association (1900), as well as his
numerous and valuable contributions to the
proceedings of various learned societies ; and to
Mr Lydekker's "Koyal Natural History." All
these works can profitably be consulted by those
of my readers who may be induced to pursue
this fascinating study further.

Finally, I have to record my grateful thanks
to many kind friends for much kind help in
seeing this little book through the press. And
especially am I indebted to Dr A. L. Giinther,
F.R.S., who has guided me through many dark
places, and in every way lightened my labours by
giving me the benefit of his own rich experience.

W. P. PYCRAFT.

CONTENTS.

CHAP . PAGK

I. INTRODUCTION 9

II. HOW FISHES BREATHE 19

III. HOW FISHES ARE CLOTHED .... 28

IV. TEETH AND SPINES ..... 37
V. HEADS AND TAILS 46

VI. FINS : THEIR USES AND WHAT THEY TEACH US 57

VII. FISH-LIVERIES, AND WHY THEY ARE WORN 69

VIII. HOW FISHES FEED 78

IX. COURTSHIP AND NURSERY DUTIES . . 99

X. LARVAL FISHES AND THEIR METAMORPHOSES 120

XI. MIGRATION AND HYBERNAT1ON . . . 138

XII. TRANSFORMATIONS 152

XIII. PEDIGREES 166

XIV. PUZZLES AND PATRIARCHS . , . .193

LIST OF ILLUSTRATIONS.

PAGE
Frontispiece.

FIG. 1 — A. Common Roach ; B. An. Outline figure

of the Burbot (Lota vulgaris) . . 12

,, 2 — Diagrammatic figure of an Eel . . 13

,, 3 — Head of a young Polypterus ... 26

„ 4— The Evolution of Teeth and Scales . 40

„ 5— Skull of Dog-fish . . . . 47

„ 6— The Evolution of the Fish's Tail . . 52

,, 7— The Evolution of Fins .... 66

,, 8 — Head of Gnathonemus elephas . . 90

,, 9 — Ohiasmodon niger ..... 95

,, 10— Sticklebacks and Nest .... 102

„ 11— A Larval Dog-fish 127

,, 12 — Fish Metamorphoses (three stages in the

life history of the Eel) . . .132

,, 13 — Three stages in the development of the

Sword-fish 135

., 14 — Outline figure of the American Mud-fish 151

,, 15 — Restoration of a Primitive Sturgeon . 178

,, 16 — Three extinct Ancestral Forms of Fishes 199

, 17— Three Primitive Sharks 203

THE STORY OF FISH LIFE.

CHAPTER I.

INTRODUCTION.

THE Story of Fish Life began ages and ages ago.
Of this we are assured, not by any written record,
but through the labours of those who spend their
lives in exploring the dried basins of ancient lakes
and seas, searching for the dead which may in-
cidentally have been preserved therein. The
accumulated results of these explorations have
provided us with a rich material for study in
the shape of the hard parts, at least, of fishes
of many kinds, the like of which, in many cases,
we shall never see again. But some of these may
be traced through a long series of geological forma-
tions, up to their living descendants ; and serve to
fill gaps otherwise incomprehensible. They enable
us to weave out of the whole of the collected
evidence a story, as plainly as though we had
transcribed it from the more familiar print.

But our story is even now by no means a con-
nected story : there are many gaps which we can
never hope to fill. For instance, the earliest of
the known fishes was most certainly preceded by

10 THE STGRY OF FISH LIFE.

still more primitive forms, whose structure did not
permit of preservation, lacking hard parts such
as bones or scales. The remains of certain other
early types leave us yet in doubt on very important
points, such as whether the mouth had jaws,
what was the position of the eyes, and so on.
Answers to many of these questions may, how-
ever, yet come to hand, for the examination of rock
systems of the world is by no means exhausted yet.

These remains, then, we know as fossils, and
the hardened mud in which they are embedded
we call rock. How these rocks came to be does
not concern us here. Those who would know
more on this head should read Prof. Seeley's little
book, the " Story of the Earth," published in
this series. Suffice it to say, that the various
kinds of mud with their peculiar fossils repre-
sent different periods of time of great duration.
These periods we shall refer to here under their
scientific names, as "Devonian," "Carboniferous "
or " Cretaceous," and so on as the case may be.
We shall find that as we proceed from the oldest
to the newest of these formations that the fossils
therein will increase in number, variety and
complexity of structure. This increased com-
plexity has resulted from the gradual modification
of simple types as they become more and more
perfectly adapted to their environment.

Those of us who can spell out more or less
connected portions of these riddles have gathered
one fact of prime interest. We cannot fail to be
impressed with the conviction that Nature has
pressed the plastic mystery which we call Life
into many moulds, and many creatures into the

INTRODUCTION. 1 1

same mould. Earth, air, and water are all
peopled, and the inhabitants of each of these
three worlds frequently bear very close resem-
blances one to another without being in the least
degree related. That is to say, there is evidence
of conformity to the mechanical needs of the
environment, resulting in a superficial conformity
in external appearance.

The fishes afford us an admirable object lesson.
They are creatures fashioned by a series of
gradual improvements to dwell in water. To
move freely in this comparatively dense medium
entails conformity to certain mechanical needs.
This conformity has resulted in the characteristic
" fish-like " form : the compressed head and
trunk, tapering gradually to the tail, giving the
whole the form of a rounded wedge ; to this
wedge-shaped body keels have been added along
the back and along the belly, as well as balancing
and steering organs projecting from the sides.
These keels and balancers we call the fins, and
because we shall have to make frequent reference
to these fins it would be well to pause here to
study their arrangement and distinctive names
in the accompanying picture (fig. 1). The fins,
which we have likened to keels, are known as the
median fins, whilst those which act as balancers
and for steering, are known as the paired fins.
These are never more than four in number, and
correspond with the arms and legs of terrestrial
animals. But the fish is, so to speak, balanced in
the water, and needs no support from the limbs,
which owe their peculiar form to adaptation to
their special requirements. The terrestrial limbs

12

THE STORY OF FISH LIFE.

have probably arisen by a modification of these
balancing organs. Poised in the water the fish
is free to move in all directions. To adapt the
fish still more perfectly to its environment a
very peculiar organ, known as the air-bladder,

has been developed,
at least in the
majority of living
forms, as well as in
the more modern
fossil types. This
air-bladder seems to
render the specific
gravity of the fish
the same as that
of the surrounding

FIG. 1.— A. Common Roach, showing Water. Modifications
arrangement of fins, and general which theair-bkdder
shape of body. D. dorsal fin ; C. .,, ,

caudal or tail fin ; A. anal fin ; PI. may Undergo Will be
Pelvic or ventral fin ; P. pectoral ^niin^ nn Q lof ATT\QO-O
fin ; O. gill cover; L. lateral line ; IOUn<

t. transverse line. The significance Further adapta-
of the transverse and latera 1 lines is . • , , •

explained further on. Only a few tlOH tO aquatic needs
scales have been indicated, in order V»aq rp^nlr.prl in a
that the transverse and lateral lines " ' jCSUlted
may be rendered more conspicuous. Complete investment
B. An outline figure of the Bur- f ~]jmp . howronionq
bot (Lota vulgaris), for comparison OI flime > noWCOplO

this Secretion may
-i n r -n

bream-tishers Will

testify ! This slimy
coat reduces friction to a minimum. Beneath
this slime we can generally descry a series of
overlapping plates — the scales ; these fit closely
one over the other so as to offer a perfectly
smooth surface.

The fish, as we have just remarked, being

with fig. ,4., note the difference in
the shape and position of the fins
and the absence of scales.-After

GUnther-

INTRODUCTION. 13

nicely balanced in the water, needs no support
from limbs as do terrestrial animals, neither are
the limbs needed to propel the body through
the water. Locomotion is effected in one of two
ways. Much elongated fishes, like sharks or eels,
for instance, move with great speed by rapid
undulations of the body. The forward motion is
effected by the pressure of the body against the
water, enclosed in the several incurved planes
arising from the un-
dulations. This un-
dulatory movement
is well expressed in

, ,. „ FiG.2.— Diagrammatic figure of an Eel,

the diagram, ng. A. showing the nature of the undulatory

Kelatively shorter movement of the body,
fishes progress by powerful side to side move-
ments of the tail ; and since the majority of
fishes seem to have shortened up the body, for
the sake of using the tail as a propeller, it
is probable that this is the more useful form
of movement of the two.

If any doubt the reasonableness or probability
of the characteristic "fish-like" form having
arisen as a result of adaptation to the mechani-
cal needs of the environment, let him pause and
consider what has happened to certain aquatic
mammalia — to wit, the whales and porpoises.
These animals are so peculiarly fish-like in form
that they are very commonly regarded as fish.
The authorities at the Natural History depart-
ments of the British Museum are being con-
stantly appealed to, to settle arguments such as
whether or no the whale is a fish. The same
spindle-shaped tapering form of body, the pre-

14 THE STORY OF FISH LIFE.

sence, in many cases, of a dorsal fin, and the
peculiarly fin-like fore-limbs render this mistake
a very natural and quite pardonable one. But
it is not a fish, because it suckles its young like
all the rest of the mammalia, consequently it is
with this group that we must place the whale
and its allies. But there are yet other reasons
which forbid us to regard the whale as a fish,
and compel us to recognise it as a mammal. If
we examine a skeleton of one of these creatures
we shall find it differs fundamentally from that
of the fish, and agrees closely with that of the
mammalia. The points wherein it differs from
the type all show undoubted adaptation to and
specialisation for particular mechanical needs.
Thus the fore-limb is obviously a mammalian
fore-limb, which has undergone certain changes,
converting it into a paddle for swimming pur-
poses. The whale, being poised in the water
like a fish, has ceased long since to need support
from its sometime functional legs. The fore-
limbs being useful have been transformed into
paddles, the hind-limbs not being required have
disappeared long ago, leaving only slight traces
of the hip-girdle imbedded in the muscles of the
body. The structure of the skull, backbone,
ribs, breastbone all tell the same tale ; so do the
brain, heart, lungs, and other viscera — all point
emphatically, beyond all possibility of doubt
whatsoever, to the irresistible conclusion that
the whale and its allies are not fish but mammals.
The seals point the way in which this peculiar
modification has come about, being half-way
stages between the typical walking mammal and

INTRODUCTION. 15

the highly specialised floating one. The seal is
amphibious, but the hind-limbs are already los-
ing much of their power of support on land, and
the fore-limbs are becoming more and more
paddle-shaped.

The old ichthyosaurus is but one of many
forms amongst the extinct reptiles which have
undergone a precisely similar modification to
that of the whale in the shape of the body and
limbs. Certain living snakes again, by adopting
an entirely aquatic existence, have become quite
eel-like in form, rendering it very difficult to
distinguish eel from snake. But there is no
need to go on multiplying instances of this kind.
The facts are beyond dispute. The fish, there
can be no doubt, owes its peculiar form to the
gradual adaptation to the needs of its environ-
ment.

Fishes hold, says Dr Bashford Dean, an im-
portant place in the history of vertebrate or
backboned animals ; their group is the largest
and most widely distributed ; its fossil members
are by far the earliest of known vertebrates ; and
amongst its living representatives are forms
which are believed to closely resemble the
ancestral vertebrate.

The origin of new groups of fishes yet remains
a mystery, but certain facts connected therewith
afford us food for reflection of extraordinary
interest. These facts have lately been set forth
with telling force by Dr A. Smith Woodward.
He points out that in tracing the history of the
evolution of any given group of animals, say of
fishes, we find that during different geological

16 THE STORY OF FISH LIFE.

epochs one particular type will have the ascend-
ency over all the others, this he calls the "domi-
nant" type. He then proceeds to show that
a dominant old race, at the beginning of its
greatest vigour, seems to give origin to a new
type, showing some fundamental change ; this
advanced form then seems to be driven from all
the areas where the dominant ancestral race
reigns supreme, and evolution in the latter be-
comes comparatively insignificant. Meanwhile
the banished type has acquired great develop-
mental energy, and finally it spreads over every
habitable region, replacing the more effete race
which originally produced it. The period of
greatest vigour of the " dominant old race "
represents the flowering out of new species
stimulated into being, by the occupation of
new territory, the new species developing as a
result of adaptation necessary to obtain a hold
on this or that particular area. Now, adaptation
spells specialisation, and the cessation of the
growth of the dominant race after this sudden
burst of activity points to inability to further
development, a balance being struck between
the organism and the environment. The banished
form which suddenly springs up in force replacing
the parent type is also the result of adaptation.
Born of members of the parent form, but possibly
far removed from the environment which was
slowly shaping the typical dominant forms, they
developed along the new lines demanded by the
new environment, which eventually appears to
have slowly replaced the old order of things and
the highly specialised forms dependent thereon.

INTRODUCTION. 17

Dr Woodward gives some striking examples of
this rise and fall of tribes of fishes, which may be
likened to the rise and fall of nations amongst
mankind. A certain type of fishes known as
the ray -finned fishes (p. 176) furnishes the first
of his examples. The earliest known members
of this type belong to a genus known as Cheiro-
lepis (p. 178). This appears as an isolated form
in the Lower Devonian fish fauna, where the
dominant fish are of two quite distincb types :
the one known as the fringe-finned (p. 176),
and the other as the lung-fishes (p. 25). When
these latter begin to decline, in the Lower Car-
boniferous (coal measures), " the sub-order to
which Cheirolepis belong suddenly appears in
overwhelming variety." From Cheirolepis we
derive our modern sturgeons. The period of
the Upper Permian witnesses another change. A
group of fishes, for the most part heavily
armoured, now first makes its appearance, "but
only a solitary genus is observed among the
hosts of the dominant race." In the Trias the
new type becomes supreme, and constitutes the
dominant fishes of the Jurassic period. From
thence onwards it gradually declined, leaving
but a solitary survivor in the mud-fish or bow-
fin of certain North American rivers (p. 183).
Out of the teeming hordes of the bow-fin type, of
the old Jurassic seas, new forms have silently
appeared to give battle to the old so soon as
they shall have gained a firm hold. These have
put off the old armour plate of enamelled scales,
and have adopted a peculiarly modern habit.
Many are scarcely distinguishable from the
B

18 THE STORY OF FISH LIFE.

living members of the herring tribe, which in-
deed trace their origin to this stock. With
these herring-like forms in the Cretaceous period
appeared numerous other familiar shapes, which
differ only in small points from their living
descendants of the seas and rivers of to-day.

"The evolution of fishes," says Dr Bashford
Dean, "has been confined to a noteworthy de-
gree within rigid and unshifting bounds; their
living medium, with its mechanical effects upon
fish-like forms and structures, has for ages been
almost constant in its conditions; its changes
of temperature and density and currents have
rarely been of more than local importance, and
have influenced but little the survival of genera
and species widely distributed ; its changes, more-
over, in the normal supply of food organisms
cannot be looked upon as noteworthy.

"When members of any group of fishes be-
came extinct, those appear to have been the
first to perish which were the possessors of the
greatest number of widely modified or specialised
structures. Those, for example, whose teeth
were adapted for a particular kind of food, or
whose motions were hampered by ponderous
size or weighty armouring, were the first to
perish in the struggle for existence. On the
other hand, the forms that most nearly retained
the ancestral or tribal character — that is, whose
structures were in every way least extreme —
were naturally the best fitted to survive. Thus
generalised fishes should be considered those of
medium size, medium defences, medium powers
of progression, omnivorous feeding habits, and

HOW FISHES BREATHE. 19

wide distribution ; these might be regarded as
having provided the staples of survival in every
branch of descent. ... A generalised form is
like potter's clay, plastic in the hands of nature,
readily to be converted into a needed cup or
vase ; but, when thus specialised, may never
resume unaltered its ancestral condition. The
clay survives ; the cup perishes.7'

CHAPTER II.

HOW FISHES BREATHE.

FRESH air is as necessary to a fish as to ourselves,
and this air is needed, just as with us, for the
sake of its oxygen. The taking in of this life-
sustaining gas is known as Kespiration. The
process of respiration, or breathing, in the fish is
performed by means of gills, not, as with us, by
means of lungs; and although the difference
between these two forms of respiration may seem
to be very considerable, we shall see that the
former is the more ancient practice, and gradually
gave place to the latter.

Yertebrated or backboned gill - breathing
animals are always aquatic, although the con-
verse— that luii g-breath ing vertebrates are always
terrestrial — is by no means true.

Breathing organs of whatever kind are always
intimately associated with the upper end of the
alimentary canal or food-pipe. Sometimes this
association remains throughout life ; as in the

20 THE STORY OF FISH LIFE.

fish, sometimes it is but a temporary phase, as in
the higher animals.

Fish, then, are gill-breathing animals, and these
gills are, it has just been hinted, in some way
connected with the tube into which the food
is taken. Let us now look closer into this
connection.

Everybody knows, of course, that a fish's gills
are to be found in its head. Many will be
further able to point out that they can readily
be seen by raising a bony flap or plate lying
on either side of this head, but that they have
anything to do with the food-pipe, or, as we
prefer to call it, the alimentary canal, is a fact
which doubtless will be new to many. Let us
make clear, then, the nature of this association
at once. Food is taken in at the mouth, and
thence, as everybody knows, passes down a tube
into a more or less extensive and sometimes com-
plicated bag called the stomach. This is true
equally of the fish, and of ourselves. But fish,
and some other lowly backboned animals, have
a series of slits in the wall of this tube, situated
at the back of the mouth, just before the region
where the tube suddenly narrows to become the
gullet, — the passage leading to the stomach. The
wall of the tube in the fish, between every slit,
becomes strengthened by a solid support, which
takes the form of a half-hoop, and from every
one of these half-hoops there arises a series of
slender rods, closely packed, so as to form a
kind of fringe to the hoop. These rods support
closely plaited folds of skin richly supplied with
.a series of fine blood-vessels, through which the

HOW FISHES BREATHE. 21

venous and impure blood of the body is forced.
The walls of these blood-vessels are of exceeding
thinness, so that the contained blood is brought
into very close contact with the water, which,
entering in at the mouth, is forced, as soon as
this is closed, through the slits in the wall
of the alimentary canal, and in thus escaping
bathes the vessels. The oxygen contained in the
air suspended in the water is seized upon by the
blood as the water flows past, and at the same
time the carbonic acid is given off and carried
away in the stream. And in this way, by the
passage of a stream of water over blood-vessels,
supported in the manner just described, is the
blood purified.

The form of gill arrangement just sketched is
such as is found in, say, a perch or cod-fish.
But in the sharks and dog-fish and rays, or
skates as they are often called, we find a yet
more primitive arrangement. Here each gill-slit
opens from the mouth into a kind of pouch ; and
the water which gains admission is forced out
through a slit in the outside of the animal.
Since there are a series of these slits, as in the
higher fish, so we get on the outside of the fish
a series of slits corresponding in number to those
on the inside — five to seven. These pouches are
formed by a double-walled partition or septum
extending outwards from, every one of the solid
arches or half-hoops already described, to the
outer wall of the body. The rays or rods of the
arches run up between the double walls of each
septum. The opposite walls of each pouch sup-
port closely plaited folds of skin supplied with

22 THE STORY OF FISH LIFE.

blood as in the higher fishes, and are divided by
the cavity through which a stream of water
is constantly passing for the aeration of the blood.
In the higher fish, as in the perch, for instance,
the septa or walls which constitute the pouches
have been dispensed with, and only a single slit
at the side of the head remains.

In the sea-horses and pipe-fish the typical
gills are replaced by curious rosette-shaped tufts.

The climbing perch (Anabas), serpent - heads
(Ophiocephalus), and some cat-fishes have curious
accessory structures enabling their owners to
quit the water for a more or less prolonged
sojourn on land. The accessory breathing-organs
of Anabas may serve as a type. If the outer
wall of the gill-chamber be removed, a cavity
will be exposed containing, below, the true gills,
and above a more or less rosette-like structure.
This rosette lies in a special air-chamber, and is
well supplied with blood-vessels for the aeration
of the blood whilst the fish is out of the water.

Breathing by gills may be aided by breathing
through the skin, or breathing through the in-
testine, or by structures that correspond to our
lungs.

Breathing through the skin or the intestine
may seem strange to many, but much of the
improbability that suggests itself at first will
disappear when we remember that " breathing "
is really the process of exchange of gases by the
blood. These gases can pass with the greatest
readiness through their membranes, such as the
skin, and so gain access to the blood almost as
easily as by the lungs. The common loach of

HOW FISHES BREATHE. 23

our streams is an instance of breathing by the
intestine. In this case air is swallowed by the
fish, which, frequently rising to the surface,
thrusts its mouth above the level of the stream
and gulps down a mouthful of the precious fluid.
This passes at once to the intestinal tube, when
the oxygen is quickly extracted by minute blood-
vessels. Certain cat-fishes and carps also trans-
form the intestine into an accessory breathing-
organ. Some fishes, it is contended, are more
easily drowned than such an essentially land
animal as the adult frog. For Milne Edwards,
the great French naturalist, assures us that a
frog, though immersed iu a wire cage in the
bed of a stream, will if it be supplied with food
thrive prodigiously, respiration being carried on
through the delicate skin; whilst the fish en-
closed in the same cage would speedily die.

The wonderful little walking-fish (Perioph-
ihalmus) passes the greater part of its life on
land, skipping about the mud-flats of mangrove
swamps. To render this amphibious existence
the more perfect, the gill-chamber has become
somewhat enlarged, and whilst the fish is out
of the water the chamber is kept filled with
air. Gill-breathing is said to be further sup-
plemented by respiration through the skin of
the tail.

Now let us take a peep at the lung-like struc-
tures. Before we can rightly understand these,
however, we must consider the organ to which
they themselves are due — the air-bladder or more
correctly perhaps the <7as-bladder. The air-bladder
must be familiar enough to many of my readers.

24 THE STORY OF FISH LIFE.

It is the long cylindrical body winch lies in the
body cavity, immediately below the vertebral
column or backbone. Puncture it, and see what
happens ! In a moment its once glistening and
silvery walls collapse, and nothing but a crumpled
mass of skin remains. That it contained air or
gas, there can no longer be any doubt. The
changes of form and other details which concern
the air-bladder are many, but too technical to
be discussed here. We must, however, pause a
moment to notice two very interesting and very
important points concerning this organ.

The first and most important of these points
which we will examine deals with the fact that
the air-bladder is intimately associated with the
gullet.

If we were to watch the course of develop-
ment of the fish within the egg we should see
that at one stage of this development the gullet
would send up a little bud, which, growing
larger and larger, at last would become the air-
bladder. As it grew more and more towards
perfection, so it would gradually separate off
from the gullet ; at last it would remain attached
only by a narrow tube. This tube in many
fishes remains open throughout life so that air
can pass from the gullet to the air-bladder; in
some it closes up, and in others it disappears
altogether. In cases where the connection be-
tween the bladder and the gullet is lost, it
becomes a nice question as to the means by
which the gaseous fluid gets into the bladder.
It is supposed that the difficulty is surmounted
by the bladder making its own gas.

HOW FISHES BREATHE. 25

In some bony fishes, and in sharks and rays,
the air-bladder is wanting altogether.

But what has all this to do with lungs and
lung-like structures 1

A great deal. In the first place the mode of
origin of both air-bladder and lung is precisely
-similar — as an outgrowth of the gullet. In the
second, we can follow by a series of gradations
the gradual evolution of the former from a simple
air-bag, as in the perch, for instance, to a true
lung such as is found in certain remarkable
fishes known as the lung-fishes. These fishes
are found in muddy rivers, whose waters are
often charged with foul gases. At such times
the lung fishes come from time to time to the
surface to breathe atmospheric air. When the
water is less impure they breathe by gills as
other fish. But the details of this matter belong
rather to text-books of comparative anatomy
than to a little work like the present.

One point more about gill-breathing before we
leave this subject. So far, the gills which we
have examined have been what are called in-
ternal gills. That is to say, they have been
concealed within, and protected by, either a
series of pouches or chambers communicating
with the outer world by slits, or by a single
large plate. In the young of many fishes, e.g. :
the young dog-fish, the gills are at first external,
and take the form of long delicate filaments pro-
truding through the outer gill-slit. In the young
bichir, or Polypterus, of the Nile, these gills are
retained for a somewhat longer period, and are
quite large (fig. 3) ; but in the adult, as in all

26 THE STORY OF FISH LIFE.

other fishes, they disappear, being exchanged for
the more easily protected internal gills. These
external gills become still more interesting when
we remember that the larval frogs and newts
also breathe by external gills, whilst in certain
aquatic salamanders (Necturus and Proteus) these
external gills are retained throughout life.

The breathing of fishes is attended by some
very characteristic movements of the mouth

rarely properly under-
stood by tiie lay
mind. " He drinks
like a fish" is a charge,
and a very serious
FIG. 3.— Headofayoungpofypterws one. often launched

(bichir). showing the external •*

giii. by one man against

another. Often it is

as false and unfounded as the comparison. To
begin with, fishes when they drink — if they
drink — drink water. But it is not the nature
of the draught but the frequency of its re-
petition to which allusion is made in this
quotation. It is apparently supposed that the
constant and rhythmical opening and closing of
the mouth is a proof of the act of drinking.
Nothing could be further from the truth.
This is the outward sign of the act of breath-
ing, and corresponds to the heaving sides and
the steaming nostrils of the galloping horse.
In opening the mouth water is drawn in ; in
closing it, it is forced out through the gill-slits
in the gullet, over the gills, that the oxygen may
be extracted by the blood, and out by the gill-
slits or slit, as the case may be. No water is

HOW FISHES BREATHE. 27

swallowed by this act, because the gullet, just
behind the hindmost slit which pierces its sides,
is able to contract itself so tightly as to prevent
the entrance of any water whatever. This con-
traction is performed by muscles, which bring
about the same result as the double string run-
ning round the mouth of a bag, the which it
closes by drawing the mouth smaller and smaller.
When the fish desires to swallow food this is
pressed against the centre of this closed-up gullet,
albeit ever so lightly. The touch signals to the
nerves controlling the muscles to relax their
hold somewhat, and at the same time to seize
upon the newly arrived solid refreshment. This
it does so perfectly that little or no water is
swallowed therewith. The gullet presses round
so tightly that the matter being swallowed
might be likened to a cork being thrust down
into a bottle with a flexible neck, which closed
up as the cork passed lower and lower down.

This chapter has surely left us in possession
of some very interesting facts. Thus we may
take it for granted that the gills of fishes were
originally formed by delicately waving branches
projecting on either side of the head, and that,
for protection's sake, they came to be withdrawn
into a series of little pockets, communicating
with the outer world by a series of slits. The
next stage in their history is that in which the
walls of these separate gill-pockets or pouches
become removed, so that the gills come to lie in
a single large cavity, opening by one slit be-
hind the head. Lastly, we must remark that
about the time when gill-pouches went out of

28 THE STORY OF FISH LIFE.

fashion, a new improvement was introduced—
the air-bladder. This in turn can be fol-
lowed through a series of transformations which
gradually change it into a lung, and so more or
less completely do away with the need of gills
at all. If we had the time we could go further
still, and follow these lungs into still greater
stages of perfection ; but this must be left for
another day.

CHAPTEE III.

HOW FISH ARE CLOTHED.

SOME fish, such as the lampreys, many eels, and
all fishes provided with well-developed electric
organs, have the skin entirely naked. These are,
however, exceptions, and there is good reason to
believe that this nakedness is, at least in most
cases, a degenerate character. That is to say,
scales were once present, but have now dis,
appeared. Thus, in many eels, if the skin be care-
fully (microscopically) examined, minute scales
will be found embedded therein. These, we infer,
are remnants of once much larger structures,
which served, at the heyday of their develop-
ment, to completely invest the body.

The typical scaly clothing of a fish may perhaps
best be studied in a roach or perch. In such a
fish we should notice that the whole body, save
the head and fins, was covered by a series of
horny plates overlapping one another like the
tiles on a roof. If we removed one of these

HOW FISH ARE CLOTHED. 29

plates we should find — if it was taken from a
roach — that it partook somewhat of the shape of
a human nail. Furthermore, we should probably
have noticed before removing it that its anterior
end was thrust deep down into a sort of pocket
in the skin, whilst its posterior, or hinder end,
was free, and could be easily raised by any
pointed or blade-shaped instrument. Such an
arrangement of horny plates or scales may be
taken as typical of the majority of living fishes.
Any variation of this arrangement may be re-
garded, roughly speaking, either in the direction
of further specialisation or of degeneration.

Instances of degeneration are numerous. Pro-
bably we should be correct in regarding the first
indication of degeneration to be the isolation of
the scales. In such cases the scales, instead of
overlapping, remain perfectly distinct from one
another. The African lung-fish (Protopterus), and
certain wrasses, are instances of this kind. In
some carp — known as " mirror-carp " — this isola-
tion of the scales is very marked. Those along the
sides of the body have assumed relatively enor-
mous proportions; those along the top of the
back are smaller, but all are widely separated
from their neighbours. In many eels, as we
have just remarked, the scales have become so
reduced in size that they must be sought for
with a microscope, and then are found to be
deeply embedded in the skin.

Of instances of specialisation we have a great
variety. Thus, to take a few of the most
striking. One of the cat-fishes of tropical South
America, known as Callichthys, has the scales

30 THE STORY OF FISH LIFE.

modified — probably by fusion of many to form
one — so as to form a complete coat of armour.
These fused scales take the form of broad bars,
or perhaps they had better be called shields.
They are arranged in a double series, an upper
or back shield, which extends downwards to the
middle of the body; and a lower shield, which
clothes the lower part of the body or abdomen,
the lower shield commencing at the point where
the back shield terminates. There are a great
number of these shields following one behind the
other, from the head backwards. They are what
is called metamerically arranged. That is to say,
if the body were cut into a number of pieces
corresponding to the number of the bones in the
vertebral column, there would be one pair of
shields — a dorsal and ventral — to every vertebra.
This metameric arrangement is a point of deep
significance.

In the coffer -fish (Ostracion) of the West
Indies, the scales have been modified into a
series of hexagonal plates, fitting closely together
like mosaic work. As a result, the fish is en-
closed in a kind of box, hence its name coffer-
fish. From this box only the fins and tail
project, or are capable of movement.

In a species of Diodon (Chilomyderus reticulatus),
of tropical seas, the scales are small, very dense,
and have broad tri-radiate bony roots, so that
the scales are widely separated one from another,
touching only at three points representing the
tip of each root. In another species of this same
genus (Diodon), called the porcupine fish, the
scale grows to a greater length, forming a bony

HOW FISH ARE CLOTHED. 31

rod resembling the quill of a porcupine — hence
its name.

In the sea-horse the scales are cruciform in
shape, and interlaced so as to form an outer
skeleton, which, when complete, may be com-
pared to filagree work.

In another very remarkable form, the tortoise-
fish (Amphisik), of the waters of the Indo-Pacific,
the scales have become completely replaced by a
bony cuirass, which is prolonged backwards into
a spine beyond the tail. This remarkable cuirass
has been shown by Dr Gunther to be formed
entirely by the bones of the skeleton, like the
carapace of the tortoise.

But the scales of a fish, like every other part
of its body, must have had a beginning, and if
we cannot exactly say what was the nature of
this beginning, we can, at least, with tolerable
certainty, point to the fish which bear to-day the
most primitive form of scales. Such fish we find
in the sharks and rays. With the sharks, of
course, we include also the dog-fish. Here, in
fishes of this type, we find the scales of the
higher forms represented by dense nodules,
varying greatly in size, embedded in the skin.
If one of these nodules be examined (fig. 4, -5.),
two distinct parts will be distinguishable — a
bone-like base, embedded in the skin, during life,
and a superficial more dense enamel - covered
portion, which is generally spine-like. If one of
these primitive scales be compared with a tooth
from the same fish, we shall be struck with the
very close resemblance between the two. On
account of this resemblance, these scales are

.32 THE STORY OF FISH LIFE.

known as "denticles" or " odontoids " — little
teeth (p. 34). We shall show in the next chapter,
furthermore, that there is more than a resem-
blance in the likeness between the teeth and
scales ; that the two, in short, are really to all
intents and purposes identical.

In some of the rays, or skates, as they are
more commonly called, and in the spinous shark
(Echinorhinus), these primitive scales 'are dis-
tributed unevenly over the body, sprinkled over,
we might almost say, and vary much in size.
But in the dog-fishes and sharks, where the
scales are very small, they are arranged more
definitely, generally running in oblique rows
from the middle of the back downwards and
backwards. It is this closely -packed mass of
tiny "scales" which furnishes us with what is
known as "shagreen."

In the Orkneys, Dr Giinther tells us, the
"larger" and "lesser spotted dog-fish" are
captured in large numbers. Their skins are
removed, spread on the rocks to dry, and used
for smoothing down cabinet-work — in place of
the more general sand-paper.

There is yet a third form of scale, which we
may regard as intermediate between the horny
somewhat disc-like plates which are noticed in
the roach, and the spine-bearing nodular scale
which we have just described in the sharks and
rays. The third form is found in certain very
ancient types of fishes once very numerous, but
now represented by only a very few living forms.
It can best be studied in the "gar-pike" of the
fresh waters of North America, or in the

HOW FISH ARE CLOTHED. 33

Polypierus or "bichir" of the Nile. In form, it
may be described as rhomboid. As in the
representative of the scale in the shark, so here
the main part of the scale is made up of dense
bony tissue. This is covered externally by a
hard glistening substance known as "ganoine,"
a substance which bears some resemblance to,
but differs from, the enamel coating which we
found in the shark.

These ganoine - covered plates are closely
packed, investing the body in a kind of mosaic,
and forming a most perfect armour. In many
of the old fossil fishes these scales were still more
perfectly united one to another by an arrange-
ment which constituted a peg and socket joint.

The gradual rise, perfection and decline of the
heavy armour plating, so conspicuous a feature
amongst the earlier fishes, is a matter of very
considerable interest. Of the condition which
fostered the development of such cumbrous
clothing we know nothing. In some cases, as in
fishes of the genus Mesodon, for instance, only the
head and forepart of the body were thus protected,
but in the majority, as in the surviving forms,
Polypterus (fig. 15, B.} and Lepidosteus the whole
body was completely invested. Amongst some
recent fishes we find armour-plating has once
more been adopted, as in Amphisik (tortoise-fish),
the coffer-fish and its allies, and the sea-horses, but
in all these cases the armour is of a quite different
type.

The ancient scale-mail, if we may so call it, re-
calls forcibly the ancient chain-mail and kindred
forms of armour adopted by our ancestors of the
C

34 THE STORY OF FISH LIFE.

middle ages, and likewise long since out of fashion,
or rather out of harmony with the times. The
need for such has not passed, but the end it was
intended to serve is now no longer attainable,
and hence its disappearance like all other useless
structures. What led to the disappearance in
the fish we cannot say.

It is interesting to note here that at one time
the character of the scale was an important
feature in the classification of fishes. Thus, the
horny, disc-like scale of the roach was known
as a cycloid scale. When scales of this type
possessed a number of fine tooth-like processes
along the free edge, they were known as
" ctenoid," or comb-like scales. When they took
the form of thick square plates with an enamel-
like surface, they wire described as ganoid; and
when they were of the form which we have seen
in the sharks and rays, they were called
"placoid." It was supposed that these various
forms could be regarded, more or less truthfully,
as representing at least three distinct types of
fishes. Thus the cycloid and ctenoid scales were
held to be typical of the higher fishes ; the ganoid
of an intermediate type ; and the placoid of the
lowest type of fishes. This is now known to be
an erroneous view. ^Etheolepis has been shown
by Dr Smith Woodward to possess cycloid scales.
Moreover these, by a gradual change of form,
pass from the cycloid to the characteristic rhombic
plate with peg and socket joints characteristic of
the "ganoids."

This study of the scales of fishes provides us
with an interesting lesson in evolution. Thus,

HOW FISH ARE CLOTHED. 35

in the sharks and rays, we meet with the earliest
and simplest form of skin-covering, in the shape
of small bony bodies provided with a projecting
spine on the outer surfaces. The projecting
spine is the first part to be developed, and arises
from the outermost layer of the skin ; the basal
bony portion is developed later by the deeper
layer of the skin in which it is embedded. This
basal portion serves for the support of the spine.
At first these separate "placoid" scales are dis-
tributed unevenly over the body. Later — in the
higher forms — they arrange themselves definitely
in oblique rows, closely packed. The culminating
point in the arrangement of this solid scale type
is met with in those fishes once known as the
" ganoid fishes," of which we took the gar-pike of
the American rivers as a type. Here the scales
from mutual pressure have assumed either a
lozenge or a rhomboid shape, and for further
completeness of connection have developed peg
and socket joints. In the higher fishes, such as
the roach, perch, cod, herring, and so on, the
development of enamel by the outer surface of
the skin is dispensed with, the bony portion
formed in the deepest layers of the skin is greatly
reduced in thickness and otherwise modified,
resulting in a thin flexible plate, deeply em-
bedded in the skin by its anterior end, and
projecting backwards and outwards to overlap
its fellows on either side and behind, so as to
form the characteristic tile-Kke arrangement
with which we started.

As birds renew their feathers by "moulting,"
so many fish — e.g. : salmon — renew their scales by

36 THE STORY OF FISH LIFE.

" shedding" them and replacing them by new
ones.

The number and arrangement of the scales are
important characters in the determination of
fishes. In most fishes they are arranged in
obliquely transverse series, and as the number of
scales, writes Dr Gunther, in the lateral line,
see below, "generally corresponds to the number
of transverse series, it is usual to count the
scales in that line. To ascertain the number of
longitudinal series of scales, the scales are
counted in one of the transverse series, generally
that running from the commencement of the
dorsal fin, or the middle of the back, to the
lateral line, and from the lateral line down to
the vent or ventral fin, or middle of the
abdomen."

No one who is observant can fail to have
noticed a peculiar and often well-defined line
extending from the head to the tail of a
fish. Sometimes this runs more or less down
the middle of the body, sometimes it is curved,
sometimes disconnected, the upper portion of
the line terminating abruptly, and the lower
portion commencing again below it, to terminate
as usual on the tail. This is known as the
" lateral line." This line is formed by a series
of perforations in the scales. When closely
examined these are seen to be filled with mucus,
and richly supplied with nerves. From this it is
generally held that the lateral line is to be regarded
as an organ for the reception of mechanical stimuli
transmitted through the surrounding water. In
the head this sensory organ is represented by

TEETH AND SPINES. 37

a series of interconnecting tubes, which open
along definite tracts, not always easily traced, on
to the surface. In the sharks the lateral line is
represented by a groove protected by overlapping
shagreen denticles. In the higher fishes the
organ communicates with the exterior through
apertures in the scales, apertures often tunnel-
shaped in form, and on this account rendering
the line more conspicuous.

CHAPTER IV.

TEETH AND SPINES.

IN the preceding chapter it was remarked that
there existed an intimate relationship between
the bony spine-bearing tubercles or "placoid-
scales " of the sharks and the teeth of these fish.
Let us now look at this statement a little more
closely.

This relationship is certainly not difficult to
follow, though it is as certainly one that would
not at first have seemed probable. In certain of
the shark tribe, the dog-fish, for instance, we
noticed that the skin was covered by innumer-
able closely set nodules of bone embedded in the
skin, and bearing each a small enamel spine. If
a young dog-fish be examined just before hatch-
ing, it will be seen that the skin with its closely
set spiny scales is continued actually into the
mouth and covers the jaws. As growth pro-
ceeds, and the lips develop, the original con-

38 THE STORY OF FISH LIFE.

tinuity of the skin surface is interrupted ; at the
same time the scales gradually assume the form
of teeth, eventually increasing greatly both in
size and solidity, whilst the scales on the outside
of the body remain unchanged.

This insight into the evolution of the teeth is
one of first- rate importancet It is very rarely
that we get so complete a chain illustrating the
development of one organ from another. As a
rule, we can only guess at origins. Thus, as we
shall see, in seeking for the origins of the fins
and limbs of vertebrated animals, we have not
yet got beyond the boundaries of hypothesis.
We cannot believe that they came into being at
once ; on the contrary, we feel sure they have
become what they are by a transformation of
some pre-existing structures. Teeth, then, are
highly specialised modifications of the scaly
armour covering the surface of the body, and are
to be found in their simplest condition in the
shark tribe.

The changes of form which the teeth of fishes
undergo are very remarkable. Even amongst the
sharks and rays there is a wealth of variation
that is quite wonderful. Often we meet with
several forms of teeth in the jaws of a single fish,
and the combinations of these different forms
are not seldom of real beauty.

To correctly interpret the meaning of these
forms is a difficult matter, for though some seem
obviously enough directly related to the nature
of the food, in one instance, at least, it would
seem that it is sex, and not food, which has
been responsible. Thus in the thorn-back skate

TEETH AND SPINES. 39

(Raja clavatci) the males have the jaws covered
with sharply-pointed teeth, whil-t in the females
they are tiny, rounded and flattened plates.

In the Port Jackson shark (Cestracion) of
Australia, and in the Rliynchobatis of the Indian
Ocean, we have instances of the combinations of
teeth resulting in patterns of undoubted beauty,
though we must remark that this beauty is
entirely an accidental feature (fig. 4).

In the first-mentioned of these two fishes — '
the Port Jackson shark — the teeth, when seen in
position on the jaws, present a wonderful grada-
tion, beginning with a series of small spines at
the anterior end of the jaw, and passing back-
wards into large, rounded, oval seed-like bodies,
forming a sort of raised mosaic work. A
reference to the figure, p. 40, F., should make
this clear. In one of the rays, known under
the scientific name of Rhynchobatus, the
tooth-covered jaws are of a most remarkable
shape. Here the upper jaw is alternately
hollowed and swollen, the lower presents a
corresponding swelling and depressions to fit
into upper jaw. The teeth are uniform in
size. In the sting-ray (Trygori) the teeth take
the form of a number of A-shaped bars fitting
closely together, and in the eagle-ray (Mylio-
batis), of a number of long hexagonal bars
bounded on either side by rows of small teeth
of hexagonal form. In the comb - toothed
shark (Notidanus) the teeth have many cusps
or tiny comb-toothed-like processes along the
cutting edge, hence its name. In the shark's
teeth, by the way, we meet with a great range

FIG. 4.— The Evolution of Teeth and Scales. A. Portion of skin
of a bhark showing symmetrically disposed shagreen denti-
cles. B.C. Shagreen denticles of varying form and size ;
showing how clusters of scales are formed : these may later
conjoin to form either (a) large bony plates investing the
sknll — skull bones; or (6) more or less complete teeth. D.
Two rows of shagreen denticles (teeth) from the jaws of a
shark (compare with A.). E. is a tooth of a shark (Noti-
danus), and shows the result of fusion of a row of separate
denticles such as in D. to form a single comb-like tooth. F.
The jaws of the Port Jackson shark (Cestracion), to show
the remarkably modified teeth for crushing purposes. G.
The jaws of an eagle-ray (Myliobatis), also showing teeth
modified for crushing purposes. In fig. B. note the spine
s. resting in the bony base of the isolated " odontoid.''

TEETH AND SPINES. 41

in size and form. In the Greenland shark, for
example, they are comparatively small. In the
larger sharks they are either spike-shaped or
triangular in form, and in some fossil sharks the
triangular type of tooth reached huge propor-
tions. They form terrible weapons in many
living sharks ; an instance is on record where
a man has been bitten in two at a single bite !

The origin of the curious comb-like teeth, and
of those teeth of sharks which have a large
middle cusp or point with a smaller one on
either side, is peculiar ; being due to the fusion
of three or more of the primitive single teeth
into one. How this came about we can see by a
study of the coarse " shagreen " of say the spiny
shark (Echinorhinus). Here it will be found
that little groups of these tubercles, which are
scattered irregularly over the surface, become
welded or fused together at their bases — here a
group of five, forming a long patch armed with
as many tooth-like spines, there a group of two
or three, and here and there a single tubercle
(fig. 4). On the jaw similar fusions have taken
place though they are always of denticles lying
side by side. As a result we get the " comb "
teeth of Notidanus, or the A-shaped teeth of other
sharks. The large plate-like crushing teeth of
many fossil and recent sharks, as well as of
fishes belonging to higher groups, have been
formed in this way.

Amongst the bony fishes, of which we may
take the perch, pike or cod-fish as examples,
the variations in the form of the teeth are quite
as numerous as in the shark tribe. In some

42 THE STORY OF FISH LIFE.

instances we find quite complex structures. In
the porcupine globe-fish (Diodori), for example,
the teeth are formed by the fusion of a series of
plates piled one above the other ; the lowermost
of this series, deep down in the jaw, are quite
separate, the uppermost touch one another, and
finally fuse into a solid mass. This form of
tooth is derived by modification of the order of
succession of which we shall speak presently on
p. 43.

So far all the teeth which we have passed in
review have been attached to the jaw. Bat,
amongst the fishes, teeth are by no means
confined to this region. Thus, in the lung-fish
(Cemtodus), large teeth are found in the roof of
the mouth. In the higher bony fishes, such as
the pike, the palate is crowded with teeth;
and not only the palate, but even the gill-bars
are thickly set with teeth. The gill-teeth of
the sun-fish, for instance, are of extraordinary
size.

Some fish, such as the roach and carp, have no
teeth in the jaws, but very large ones in the
throat.

The nature of the attachment of the teeth is
quite worth a hurried notice. We need, how-
ever, only institute a few comparisons. We
have already remarked that in the lowest fishes,,
such as the sharks and dog-fishes, the teeth
rest upon, but are not firmly attached to, the
jaws. In the higher fishes the teeth have
acquired an intimate connection with the jaws,
often as complete as in ourselves. In some,
as in the angler-fish (Lophius) and the pike, the

TEETH AND SPINES. 43

teeth are held in place by an elastic ligament,
which permits of their being bent backwards
into the mouth in swallowing food, but prevents
any escape thereof from the mouth most effectu-
ally. More frequently the teeth are immovably
fixed to the jaw, as in the eel, haddock and
mackerel. Only rarely are the teeth implanted
in sockets, as in the file-fish (Batistes).

Everybody must be familiar with the deadly-
looking weapon like a double-edged saw displayed
in the windows of the natural history and
curiosity dealers. These have been taken from
a kind of shark known as the saw-fish, an
inhabitant of tropical or sub-tropical seas.

The teeth forming this saw are set in sockets,
but are nob replaced by a regular succession of
new teeth; instead they grow continuously,
probably as long as the fish lives. This saw is
formed by an outgrowth from the head, and is a
very powerful and terrible weapon. By its aid
other fish are attacked and ripped open, and
pieces of jagged flesh, or protruding viscera, are
then nipped off and seized by the comparatively
feeble teeth borne by the mouth.

The growth and succession of the teeth has
already been hinted at ; we must now briefly
survey the main fact concerning these processes.

Of all the teeth - bearing animals except the
mammalia, we may say with tolerable certainty
that the teeth which we see at any given time
have not been long in use, and will soon be
replaced by others. That is to say, provision
is made for a constant supply of new teeth
to replace those in use, and this succes-

44 THE STORY OF FISH LIFE.

sion goes on throughout life. A most enviable
arrangement !

In the sharks, the young teeth will be found
adhering to the inner surface of the jaw, within
a cavity closed by membrane. Herein they lie,
closely packed, row upon row, with their points
downwards in the lower, upwards in the upper-
jaw. From this position they slowly erect them-
selves, as they approach the edge of the jaw, until
the last row of teeth are actually vertical. The
picture of a section through a jaw exposing one
of each of these several rows may help to make
this clear. In sharks only one row, in the
rays and skate several rows are in use at one
time.

In the Greenland shark (Lcemargus) the teeth
interlock one with another, and on this account
one complete row is shed at a time. But in
other sharks where this interlocking arrange-
ment does not obtain, every alternate tooth
is shed and replaced at once. So that two
rows continue to form one single functional
row.

With the higher fishes the succession of the
teeth presents yet other modifications.

In socketed teeth the succession is vertical,
somewhat as in ourselves, the new tooth being
formed immediately below the functional tooth,
and taking its place when this falls out. In the
majority of bony fishes, where the teeth are
numerous and closely packed together, the suc-
cession is irregular. When the teeth are less
closely packed the succession is alternate — there
is a young tooth placed between any two adult

TEETH AND SPINES. 45

teeth, and ready to replace them as soon as they
fall out.

To pursue this subject further would be to
overstep the aim of this little work. Those who
may have found the facts herein set down inter-
esting will find that interest increased twofold
by an examination of the actual specimens — such
as are displayed in the series of beautiful pre-
parations in the Natural History Museum of
London. To compare side by side the tooth
and the scale, and to trace the infinite grada-
tions leading from a tiny scale-like tooth to the
great triangular cutting tooth, as can be done
in many sharks, is a lesson in transforma-
tions that will not be soon forgotten. So great
is the difference between the two extremes that,
if they were examined apart from the inter-
mediate forms, they would be set down as teeth
of totally distinct species. This is a mistake
which has actually occurred in the identification
of the teeth of fossil fishes — and we can well
understand it !

Spines, like teeth, are for the most part
modified scales. It is believed that the spines
which occur immediately in front of the dorsal
fins, as in the dog-fish for instance, owe their
existence to the fusion of the shagreen, or scales,
covering the front of these balancing organs.
They begin by forming a dense " cut-water" for
the support of the fins, and ultimately acquired
an independent position in the body. Fin-spines
play an important part in the study of fossil
fishes. Indeed, the spines are often the only
record we have left. Some of these fossil fin-

46 THE STORY. OF FISH LIFE.

spines attained huge proportions. Thus the fin-
spine of an extinct shark, Oracanthus pustulosus,
from the carboniferous limestone of Bristol, was
three feet in length !

CHAPTER V.

HEADS AND TAILS.

THE heads and tails of fishes, if looked at from
the right point of view, will force upon us still
further the truth of the story of evolution.
Moreover, the history of the making of these
very essential parts will serve us for object
lessons of patience, as exhibited by Dame
Nature ; very profitable for contemplation. The
old adage, "Rome was not built in a day," is
equally true of the fish.

To get at the real inwardness, so to speak, of
the fish's head, we must start with an examina-
tion of this, as we find it in its most primitive
form. The dog-fish will serve us beautifully for
this purpose.

If we remove the skin and muscles from the
head of a dog-fish we shall find, in the first place,
not bones, as some might have expected, but a
much softer' material known as cartilage or
gristle. The skeleton of the dog-fish's head is,
therefore, not bony but cartilaginous. Further-
more, it is made up of several separate elements :
those which go to make the skull or cranium,
and those which constitute the upper and lower

HEADS AND TAILS.

47

A.C

jaws respectively, and form the arches or sup-
ports of the gills and tongue.

The true skull or cranium forms the receptacle
for the brain, and the organs of hearing, sight
and smell. It is box-
like in form, and
hollow. Within its
central cavity lies the
brain. O n the outsid e
of this box we shall
notice two pairs of
projections, one pair
<at its hinder, and one
,at its anterior end.
The form- r are the
capsules which lodge
the organ of hearing ;
the latter, which have
a, form something like
an inveited saucer,
lodge the organ of
smell. Between these
capsules for the organs
of hearing and smell
lies a cavern-like hollow for the lodgment of the
eye, and is called the orbit. At the extreme
hinder end of the skull is a small hole from
which the spinal cord emerges from the brain.
So much for the cranium.

We turn now to the series of arches which, as
we have air -ady seen, form the supports to the
anterior region of the mouth and the gullet.
These are arranged in pairs. The first pair
form what we know as the jaws. They differ

FIG. 5.— Skull of Dog-fish, showing
the separate cranium containing
the brain and organs of eight,
smell and hearing, and the dis-
tinct jaws and gill arches. S.
skull ; Ac. audifory capsule (hear-
ing); Oc. olfactory capsule (smell);
0. orbit; /.jaws ; A. gill arches.
The 1st pair are for the support of
the jaws, attacl ing them to tVe
skull, the 2nd pair, represent the
1st, pair of true pill an lies, the
solid supports in the wall of the
alimentary canal, p. 20.

48 THE STORY OF FISH LIFE.

from those of ourselves in several particulars,
but the differences are rather those of degree
than of kind. In the dog-fish we should find
the upper jaw quite distinct from the skull,
and connected therewith only by ligaments.
Attached to the hinder end of this jaw is the
lower jaw. In the very young dog-fish these
two formed one piece, and only later became
jointed to form separate jaws. In ourselves
the upper jaw is firmly fixed to the skull, not
separate as in the dog-fish. The next pair
of arches serve for the support of the tongue ;
the succeeding arches for the support of the gills.

This form of skull — a cranial box for the
lodgment of the brain and organs of hearing,
sight and smell, and a series of arches embedded
in the upper region of the mouth and gullet —
represents the simplest of all types, and is the
starting-point in the study of the skulls of all
other vertebrated animals. Let us now rapidly
sketch the outlines by which the complex com-
bination of bones, with which we are more or
less familiar, came into being.

An examination of the head of a sturgeon,
which has been carefully dissected, would show
that it differed in no important respects from
that of the dog-fish. But, if we turned to a
freshly killed sturgeon, we should meet with a
very great surprise. In the first place it would
be found that the head was not covered by a
" shagreen-like " skin as in the dog-fish, but by an
exceedingly dense bony armour. Secondly, this
armour, when closely examined, would be seen
to be made up of a number of separate and

HEADS AND TAILS. 49

symmetrical plates. These removed, as we have
already remarked, would reveal a skull differ-
ing only in some smaller particulars from that of
the dog-fish. In the cavity of the mouth we
should see, furthermore, thin plates of bone
investing the arches of the gills, and ensheathing
the floor of the cartilaginous brain-case. How
did this external armour plating come to be 1
We cannot say for certain. Possibly, even
probably, by the fusion or welding together of
numerous "placoid scales" or shagreen denticles.
The advent of these bones marks a very im-
portant epoch in the history of the development
of the skull. It is well, therefore, to make
careful note of their presence at this stage, and
of the relations which they bear; for from this
time onward the part which they play in the
protection of that all-important organ the brain,
and the perfection of what we may call the
machinery of mastication, becomes greater and
greater, ending only with ourselves.

Our next stage in the development of the
skull, then, we find in the lung-fishes, where
bony centres have established themselves in the
ear-capsules — till now cartilaginous, and there is
a slight advance in the bone-sheath of the mouth
parts. The skull of that remnant of an ancient
house, the biehir or polypterus, adds more links
to the chain. The quantity of bony matter has
now greatly increased, but the cranium is still
cartilaginous. As we work higher and higher,
however, this cartilage becomes less and less
conspicuous till, if we traced the development
of the skull into the higher vertebrated animals,
D

50 THE STORY OF FISH LIFE.

such as the reptiles or birds, or mammals, we
should find a skull made up entirely of the
bones whose arrival we have just been watch-
ing. They have slowly and quietly displaced
the cartilage, converting the soft cartilaginous
cranium into a strong bony box, and welding
with this, in greater and greater perfection, the
jaw apparatus ; till at labt the upper jaw be-
comes firmly and immovably fixed to the front
end of the cranium, and only the lower jaw,
now ensheathed in bone, remains movable,
Perhaps one of the most interesting features
in this transformation of the skull is that which
has resulted in the intimate relationship of the
plates which originally were only superficial —
being modifications of the skin — with the bony
portions of the skull which first appeared within
the cartilage forming the capsule of the ear, and
the hinder wall of the brain-case. These two
kinds of bone, of quite different modes of
origin, in all the higher vertebrates form a
complex whole, giving no trace of their original
very different derivation.

Those whose work it is to study the history
of the development of animals within the egg
tell us that much of the history of this
development of the skull which we have traced
"in time," as we may call it, is repeated in
the development of the individual. Thus the
bones which we found made their first ap-
pearance in cartilage, do so still, and slowly
replace it. Those, however, which made their
appearance as plates, developed as modifications
of the skin, are not preceded by cartilage, but

HEADS AND TAILS. 51

by thin membrane. They have not only thrust
themselves completely into the warp and woof of
the skull, but they have in some way strangled,
as it were, the development of the cartilage
altogether. In the lower jaw we have an
admirable object-lesson, showing how the carti-
lage is replaced by bone.

In the sharks, the lower jaw is cartilaginous,
and supports numerous specially modified scales
called teeth. In the higher fishes this cartilage
is invested, or surrounded, by bone, and the teeth
have not only undergone considerable change in
form, but have entered into complex relations
with the bone-sheathed jaw, as we have shown
in chapter iv., p. 37.

Now let us turn our attention to the tails of
fishes. The tails of adult fishes may assume one
of three forms, known respectively as the diphy-
cercal, heterocercal and homocercal forms. How
much of meaning there is behind this apparently
dry-as-dust information we will now proceed to
set forth.

To begin with, we will take the diphycercal
tail (fig. 6), this being undoubtedly the most
primitive form. A reference to the somewhat
diagrammatic figure will show that the diphy-
cercal represents that form of tail wherein that
portion of the vertebral column, which forms its
support, is continued straight backwards to its
farthest extent. Around it are arranged a series
of firm rods, which support, in turn, a mem-
brane, thus forming the fin.

The heterocercal tail can be well studied in a
dog-fish (fig. 5) or sturgeon. Herein the vertebral

52 THE STORY OF FISH LIFE.

column, instead of being continued straight
backwards, turns sharply upwards, and the
single fin becomes differentiated into two lobes,
an upper and larger — the dorsal lobe ; and lower

A

FIG. 6.— The Evolution of the Fish's Tail. A. B. C. Shows
how tail has passed from primitive elongated symmet-
rical form, through the unsymmetrical (.6), to the modern
falsely symmetrical form (C). The false symmetry being
due to the excessive development of the lower lobe
marked 'L I. in B. The upturned portion of the tail in B
has gradually disappeared, and isrepresented only by the
black portion marked N. in C. D. E. F. Stages through
which the tail of a modern fish successively passes dur-
ing its development, being practically a repetition of the
stages A. B. C.

and much smaller — the ventral lobe. The ven-
tral lobe, it will be noticed, takes its origin,
entirely from the lower side of the upturned
vertebral column.

The homocercal tail is found in the higher

HEADS AND TAILS. 5$

fishes, such as the flounder, the salmon (fig. 6, C.),
and the perch, for instance. In this we meet again,
apparently, with the same perfect symmetry that
characterised the diphycercal tail of Protopterus
and some primitive sharks. This apparent sym-
metry has been arrived at by some exceedingly
interesting stages, fraught with a deep significance
when we come to look below the surface. The
lessons which these stages have to teach we will
now proceed to discuss.

In our investigation we must begin with the
larval fish — that is to say, with a very young
fish, just before, or soon after, it has left the egg.
The tail of such a fish — that of a young flounder,
for instance — is, we shall find, truly diphycercal.
This we will call stage No. 1. In stage No. 2'
the axis of the tail — i.e. the end of the vertebral
column, begins, though ever so slightly, to turn
upwards, and from its lower surface numerous
rod-shaped processes are beginning to make their
appearance (fig. 6, D.). Our stage No. 3 ex-
hibits the tail in a bi-lobed form (fig. 6, E.).
The upper lobe is developed around the extreme
end of the axis of the tail, the lower from its
ventral surface. Passing to stage 4, we notice
the upper lobe has undergone a great decline,
whilst the lower has relatively increased in
size. In stage 5 the disproportion between the
two is enormous, the upper lobe having almost
entirely disappeared. In stage 6, our last,
the dorsal lobe is barely traceable, whilst the
ventral lobe has come to assume a superficially
perfect symmetry (fig. 6, F.). Thus, in the
life-history of a single fish, all three forms of tail

54 THE STORY OF FISH LIFE.

are represented, beginning with the diphycercal
— stage 1 — passing through the heterocercal —
stages, 2, 3, 4 — and ending in the homocercal—
stage 6. But our story must not end here. We
naturally ask : Is there any explanation for this
series of phases? Is any lesson to be derived
from these facts ? Well, in the first place, it
cannot be denied that we have, in studying these
phases, an admirable illustration of the evolution
of a tail. Here, in the flounder, we have watched
its gradual transformation from a perfectly sym-
metrical organ, through an asymmetrical, and
back to an apparently symmetrical form again.
We say apparently advisedly, for this last stage
is but a superficial symmetry, brought about by
the excessive development of one part at the
expense of the other. But what gain can the
result of this series of evolutional phases be to
the fish ? Or, rather, if these changes be for an
ultimate end, why cannot this be attained at
once, without the transformations 1

The gain to the fish is possibly a double one.
In the first place, in passing from the diphycercal
to the heterocercal tail, the vertebral column is
shortened, and hence there is effected at once a
saving of material, and a greater rigidity and
power added to the tail. So much for the gain.
But why, it may be asked, cannot this gain be
effected at once 1 Why this need for circum-
locution ? The answers to these questions are
not easily set down in a few words ; but, never-
theless, answers — most satisfactory answers — are
forthcoming. Moreover, they not only set at
rest these questions, but at the same time they

HEADS AND TAILS. 55

throw a flood of light upon questions of evolution
which confront us at every turn. They will bear
us back to the misty past and compel us to com-
pare afresh the revelations of the rocks with the
revelations of the microscope.

The fish of to-day, then, is " the heir of all the
ages," and the last of a long line, every member
of which was bound, albeit unconsciously, to
contribute something towards the greater per-
fection of his race. But there is no royal road
to perfection, and none may do more than bear
a share in its attainment. Furthermore, that
each may be perfect after his own kind, it is
necessary that each should proceed towards the
desired goal along definite lines. Thus it comes
to be that every animal, in the course of its
development, is obliged, as it has been said,
to climb its own ancestral tree. Thus it comes
to pass that what was the adult condition at one
period, is represented only as a passing phase
in later periods, and out of this phase a new
form is evolved. This rule is not, however,
absolute, for occasionally omissions are made,
and newer developments come into being without
recording the track along which they have come,
or without revealing the frame on which they
were modelled, so to speak. Generally speak-
ing, however, the forms of animals are reached
by a route along definite lines — by addition to
previously existing structures.

And so then with the fish's tail. If we turn
to the earliest known fossil fishes, we shall find
the tail diphy cereal in type. The heterocercal
type, however, soon made its appearance, as a

56 THE STORY OF FISH LIFE.

slight upward bend of the vertebral column, with
a large ventral and a smaller dorsal lobe. Such a
tail is seen in the ancient sturgeon-like forms, and
the sharks, and persists to this day in their living
representatives. The homocercal type was, how-
ever, well on the way towards perfection so far
back as that period of the world's history known
as the Lower Lias. Many of the fishes of the
ancient seas of that time, such as the Dapedius,
have acquired an almost perfect homocercal
tail. But we may confidently believe that the
homocercal tail of the ancient Dapedius acquired
its special characteristics in precisely the same
way as the flounder — by a gradual passage from
the primitive diphycercal to the ultimate homo-
cercal type, through heterocercy.

But one or two of the ancient fishes who
swam about in the ancient seas, whose dried and
hardened floors now form the rocks of what we
call the Triassic and Liassic formations, were blessed
with two tails apiece, or, to be quite correct, with
two tail-fins. The most interesting of these was
that of the Diplurus. In this fish the true tail
slowly dwindles in size, terminating in little more
than a filament, bearing a tiny tail-fin. But in
front of this we find what was probably the
functional tail-fin, and this fin appears to have
derived its origin in a rather curious way. It
will be remembered that the fins which project
from the middle of the back are known as the
dorsal fins, and may vary in number; whilst
the fins which project from the middle of the
abdomen are known as the anal fins. Now, in
Diplurus, the hindmost dorsal and anal fins in-

FINS : THEIR USES. 57

creased greatly in size, and apparently at the
expense of the caudal fin, which they gradually
superseded. Undina, whose remains occur in the
rocks of the Lower Lias, had similar false and
true tails, the false tail being functional.

CHAPTER VI.

FINS : THEIR USES, AND WHAT THEY TEACH US.

IT seems almost like presumption to think of
drawing attention to, or in any way describing,
the fins of fishes. They are such obvious, and we
think, at first, such inseparable appendages, that
no fish is complete without them. What fisher-
man is there who could not discourse upon fins 1"
If he be a fisherman of any experience, he will
have much to say concerning their offensive
possibilities, in some fish at any rate ; or he will
tell how useful, or sometimes undesirable, they
are in live bait fishing, how some are soft, some
hard, how there may be few or many, and so on.

But all are not fishermen of experience, and
there are doubtless many who have never realised
what an immense amount of interest is to be
found in tracing out the modifications which the
fins undergo in different fishes, or what may have
been their origin.

To these inexperienced our remarks are now
addressed, and for their benefit we will begin at the
beginning. The fins of fishes, then, are divisible
into two kinds : (1) The median fins — the fins.

58 THE STORY OF FISH LIFE.

which take their origin in the middle line of the
back and abdomen, and the tail or caudal fin ;
and (2) paired fins : these are four in number,
and correspond to our arms and legs — these fins
we know as the pectoral and pelvic fins. We
will accordingly discuss the median fins first, and
begin with those of the back, the dorsal fins, as
they are usually called.

In our typical fish, the perch or salmon, the
dorsal fins are two in number, called the first and
second dorsals respectively. If we raise, say the
first dorsal of a perch, we shall have an admirable
illustration of the constitution of a typical fin — a
thia sheet of membrane, supported by numerous
stiffened rods. On raising the second dorsal we
shall at once be struck with the fact that the rods
supporting these fins differ conspicuously. In the
first dorsal the rods were exceedingly hard and
sharp - pointed, in the second they are com-
paratively soft, and if we examine them further,
we shall find that towards the tip each rod breaks
up into a number of little branches, closely
pressed one against another. In some fishe^, as
in the cod-fish, for instance, both fins have these
"soft rays," as they are called. Sometimes, as
in the salmon, the second dorsal fin is very small
and composed entirely of fatty tissue, without
any supporting structures. This is known as an
" adipose " or fatty fio. In the mackerel, and the
tunny, and other allied forms, the second dorsal
is followed by a large number of smaller fins. In
the bichir (Polypterus) of the Nile, the dorsal fins
were represented by a large number of separate
fins, each consisting of a spine supporting a sail-

FINS : THEIR USES. 59

like flap of membrane (fig. 15, B., p. 178). la
many fishes only one dorsal fin is present, as in
the bream of our fresh waters. This single fin
sometimes attains hnge proportions. In an ex-
tinct fish of the Eocene age of the world's history,
named Semiophorus, the single dorsal fin was
longer than the whole body ! It is of enormous
size in one of the sword-fishes, Histiophorus (fig.
13, p. 135). The dorsal, like the ventral fins, as
we shall see presently, are sometimes modified to
form a sucker, as in the sucking-fish, Echeineis.
In this, the spiny rays of the dorsal fin are
composed of two halves, bent the one towards the
right, and the other towards the left, and forming
a support to a double series of transverse lamellas ;
the whole sucker is of an oval shape and surrounded
by a membranous fringe. By means of this
disc, writes Dr Giinther, the sucking-fishes "are
enabled to attach themselves to any flat surface,
a series of vacuums being created by the erection
of the usually recumbent lamellae. The adhesion
is so strong that the fish can only be dislodged
with difficulty, unless it is pushed forward by a
sliding motion. The c suckers ' attach themselves
to sharks, turtles, ships, or any other object
which serves their purpose. . . . Being bad
swimmers they allow themselves to be carried
about by other animals or vessels, endowed with
a greater power of locomotion." In the " fishing-
frog " (Lophius) the spines or rays of the dorsal fin
are separate, one from another, and bear flag-like
membranous appendages resembling short fronds
of sea-weed. By their means the fish comes to
harmonise so completely with its surroundings

60 THE STORY OF FISH LIFE.

that other fishes, upon which it preys, approach
near enough to be seized before they are aware of
its presence. Sometimes the fishing-frog will
bury itself in the mud, leaving only the "flags"
exposed. By skilfully waving these, fish are
attracted and suddenly engulfed.

The dorsal fin in the sea-horse (Hippocampus)
is quite peculiar, being used as a propeller, its
vigorous movement serving to drive the fish
through the water in its characteristic upright
(vertical) position. The tail or caudal fin is
absent. The tail itself is used as an organ of
prehension.

If we were to examine the skeleton of one of
the median fins, we should find that every one of
the supporting columns or fin-rays was attached
at its base to a second pointed rod or spike, which,
in turn, projecting downwards among the muscles
of the body, became attached to yet another
spine which grew upwards from the vertebral
column.

The caudal or tail-fin we have already studied
in discussing the tail proper. We need only
say here that, like the dorsal fins, it is made up
of stiff fin-rays supporting a thin membrane.
But there is one point which has not yet been
noticed, and that is, its position. In the fish
then it is vertical. There is nothing wonderful in
this someone will remark. But wait; compare
it with the caudal fin of the porpoise or the
whale. It will then be seen that its vertical
position after all has probably a lesson to teach.
In the whale or the porpoise the tail - fin is not
vertical but horizontal in position. Why is this I

FINS: THEIR USES. 61

Because the fish swims, generally, parallel with
the surface of the water. There is no need to
come to the surface for air periodically, since the
breathing is performed by gills. But the whale
and his kind swim by alternately rising and
diving in a sort of undulating course. This is
necessary, because the whale breathes by lungs,
and must accordingly rise frequently to the
surface. The vertical tail drives the fish
forwards; the horizontal drives the whale
upwards or downwards as the case may be.

The last of the median fins to be considered is
that which lies between the caudal and paired
pelvic fins. Like the dorsal, this may be divisible
into two or more portions. Sometimes the rays of
the first anal are spiny, whilst those of the second
anal are " soft," and branched like those of the
second dorsal. Spiny rays, then, associated with
" soft " rays, are always confined either to the
first anal, or the first few supports of the first
anal. But they are never preceded by "soft"
rays; in other words, soft rays always follow
spiny rays. Sometimes the anal fin is wanting
altogether.

So much for the median, we turn now to the
paired fins. These, as we have already remarked,
correspond to the arms and legs of the higher
animals. In our typical fish — the salmon or
perch — the pair which correspond to the arms,
the pectoral fins, as they are called, and will be
called here henceforth, are situated one on either
side of the body, just behind the gill opening.
The pair which correspond to the legs, the pelvic
fins — or ventral fins as they are sometimes called

62 THE STORY OF FISH LIFE.

— lie below and behind the pectorals ; and pro-
ject downwards from the ventral or under side
of the body. Bat the position of the pelvic or vent-
ral fins varies much. Thus, they may be seated
much further back than in the perch : as in the
salmon, for instance, where they lie in the middle
of the abdomen, behind the level of a line drawn
across the body from th e base of the dorsal fins. Th ey
are then said to be abdominal in position. In the
perch they are thoracic in position; that is to
say, they lie far forward in the region of the chest.
But in the burbot (Lota vulgaris) they actually
lie in front of the pectoral fins, and are then
said to be jugular in position (throat-fins) fig. 1, b.
But why this stress upon the jugular fins? A
moment's reflection will show. If the pelvic fins
really correspond to the hind-limbs in higher
animals, then the hind-limbs in such a fish as the
present lie in front of the arms !

If the question were asked — What is the
function or use of the fins ? probably the majority
would reply to swim with, as organs of locomotion
or rather propulsion. Well, this reply would be
partly, but only partly, true. The fins are
organs of locomotion ; but it is chiefly the tail
and caudal fin that serves this purpose : these
drive the fish forward by rapid and vigorous
strokes of the tail, which is lashed from side to
side alternately. When the fish is moving
slowly these movements can readily be seen. A
twist of the caudal fin alone is sufficient for gentle
forward movement, the fin working like the blade
of a screw. The pectoral fins serve, occasionally,
like the propellers of a ship when put fall speed

FINS: THEIR USES. 63

astern, to check further forward movement, or to
move actually backwards. The chief use of the
pectoral fins is to serve as steering agents. When
the fish wants to turn to the right, for instance,
he gives a sudden turn of the tail to the left,
the left pectoral fin acting at the same time,
whilst the right remains closely pressed against
the body. But the chief function of the paired
fins is that of balancers. Thus, when the pectoral,
or pectoral and pelvic of one side are removed,
the fish at once loses its balance and falls over to
the opposite side ; if both pectoral fins are lost,
it seems the fish's head sinks ; if the dorsal and
anal fins are lost, the course of the fish at once
becomes very erratic. The loss of all the fins
causes the fish to float belly upwards, like a dead
fish.

The forms which the fins take are very varied.
Let us begin our study of the variation of the
fins with the pectorals. These, by an enormous
increase in size, may serve as parachutes, en-
abling the fish to take long parachute-like flights
through the air as in the "flying herrings'7 and
41 flying-gurnards." Or some of the rays may be
modified to form finger-like organs for creeping
along the sea-floor as in the gurnards ; or some,
or all of the rays, may be enormously elongated to
form delicate organs of touch. Thus in Pentamerus
from the West Coast of Africa, and West Indies,
some five of the pectoral rays may be produced
into long hair-like filaments much longer than
the body. The South American cat-fish (Doras)
goes to the other extreme, and has the pectoral
modified into a sharp spine. In one of the

64 THE STORY OF FtSH LIFE.

fishing-frogs (Malthe) the pectoral and pelvic fins
are modified for walking on the sea-floor.

The pelvic fins, like the pectoral, sometimes
have the rays drawn out into filaments to serve
as organs of touch, as in the " gourami " (Ospliro-
menus olfax), and the dwarf cod-fish Bregmaceros
of the Indian Ocean. Sometimes, as in the
Monocentris of Japanese waters, the ventral fin is
represented by little more than a stout bony
spine. In the lump-suckers of our seas, the
ventral fins are modified to form a sucking-disc.
This sucking -disc is very powerful, it being
exceedingly difficult to remove a fish from any
object to which it may have attached itself. In
the " gobies " the ventral fins also serve as a
sucker, but they have not so completely lost
their fin-like appearance as have the lump-
suckers. In the little sucker-fishes of our coast
(Lepadogaster) the ventral fins form the rim
only of the sucker, the rest being formed by a
modification of the bones of the shoulder-girdle.
If these fishes be caught with the hand they at
once attach themselves thereto by this sucker.

We have now surveyed the principal facts
concerning the fins of fishes, and the modifica-
tions which they undergo to fit them to perform
new functions for which they were not originally
intended. The fact that these fins are capable
of modification is a very significant one, and
very naturally leads to the suggestion that this
adaptability may be traced in another direction,
and show us that the fins, normal fins, such as
we see in our type, the perch, or the salmon, may
themselves be but modifications of some earlier

FINS: THEIR USES. 65

structures. In other words, the facts disclosed in
this study of transformations lead us to hope that
we may get some insight into the origins of fins.
Scientific experts are generally agreed that
the earliest fishes possessed no true fins. Loco-
motion was performed by means of vigorous side
to side strokes of the tail, aided by undulatory
movements of the whole and probably much
elongated and cylindrical body. In other words
progression was eel-like. This mode of progres-
sion was soon followed by the appearance of the
first fin. An attempt to account for the origin
of this was the subject of an ingenious experi-
ment adopted by Mr J. T. Cunningham. He
took an ordinary penholder and coated it evenly
and thinly with wax. Then holding it by one
end, he moved it rapidly from side to side in a
basin of hot water. The pen being held in a
horizontal position, soon a vertical ridge made
its appearance above and below, and this gradu-
ally increased in size till, in about five minutes,
there was an upper and under ridge half-an-
inch in height, corresponding, as he points out, to
the median fins — the dorsal and anal and caudal
or tail-fins described on p. 12. The presence
of these median fins was a distinct gain to the
fish. A still further advance took place, when
the lower or undermost vertical fin, near the
middle of the abdomen, divided into two and ran
forwards on either side of the abdomen as a pair
of thin membranous folds terminating at the
head (fig. 7, A.}. The fish was now really well-
balanced, but improvement was yet possible.
Numerous rods or bars of cartilage now appeared
E

FIG. 7.— The Evolution of Fins. A. B. represent ideal shark-like
primitive fishes. In A. there are no separate fins, only continuous
folds of membranes. In B. separate fins have been derived by the
disappearance of certain portions of the once continuous membrane.
C. D. show how the paired fins gradually increased in complexity,
separate bars of cartilage in the earliest type of fin (T.) have gradu-
ally grafted themselves on to one simple bar which form an axis as
in D. E. F. show the difference between the fin which has three
distinct articular elements at its base (E.), an(* that which has but
one (F.). C. H. show the difference between the fringed fin (G.)
and the fan fin (#.)•

FINS : THEIR USES. 67

serving to stiffen these balancing membranes, and
obviously make them more effective. At about?
this time, however, there was a tendency to
diminish the extent of the lateral or side mem-
branes, and this tendency became more and more
pronounced till certain portions entirely dis-
appeared leaving four separate or detached folds
or lobes. In these four separate lobes we have the
origin of the paired fins, the two immediately
behind the head becoming the pectoral and the
two near the tail the pelvic fins (fig. 7, JB.).

We have seen already that the fins of modern
fishes act primarily as balancing organs ; in
addition they serve also as accessory steering
organs. For this purpose they have become
freely movable in various directions. In this
mobility we have one great distinction between
the fixed, newly isolated balancing organs, the
evolution of which we have just traced, and the
freely movable fin of the modern fish. How
did this mobility come about 1 To this question
we have at present no definite answer. We
may, however, endeavour to trace the improve-
ments which accompanied this mobility. One of
these improvements was the blending together of
certain of the supporting rods of cartilage to
form a central and definite axis, and the arrange-
ment of certain of the remaining rods on either
side of this in the form of rays, as shown in the
accompanying fig. 7, C. D. The size of the fin
became next enlarged by the addition of hair-
like fibres outside the rays, as in fig. 7, F. This
form of fin can be studied to-day in the lung-fish
Ceratodus.

68 THE STORY OF FISH LIFE.

But other modifications of the fin took place
at about this time, and the rays of the primitive
supporting rods grew stronger on one side of the
axis than the other, whilst the axis itself became
slowly transformed, ultimately resulting in a
series of flattened plates supporting jointed
cartilaginous rods, fringed by the hair-like rays
already described. Fins of this kind are present
in our modern sharks and dog-fishes (fig. 7, E.).
This form of fin in turn became modified into
that which we find in the typical bony fishes such
as the perch, pike or cod-fish ; and in the ancient
but still surviving " Bichir " or Polypterus of
the Nile.

In examining the fins of the perch, either the
median or paired fins, we should miss the
hair-like rays which fringe the border of the fin,
and we should find in the dorsal fin, for instance,
as we have already noticed (p. 60), that the fin
supports were solid and bony and rested upon
smaller spike-like bony supports which in turn
were connected with, and corresponded in
number with, the spines of separate vertebrae of
the vertebral column. It is generally believed
that these external bony fin-supports have been
formed by the fusion of clusters of the-e original
hair-like rays, the hair-like stage preceding the
osseous rod-stage.

Thus, by insensible gradations, we may trace
the origin and evolution of the fins of fishes.
Let us recapitulate these stages. First then to
arise are the vertical fins. These being profit-
able to the fish lead to a further extension of
the fin system by the addition of lateral folds.

FISH-LIVERIES, AND WHY THEY ARE WORN. 69

Next appears a discontinuity in these fins, gaps
appearing which isolate certain portions. The
cause of the gaps is unknown, but is probably in
some way connected with the undulating move-
ments of the fibh. From simple balancing — we
next proceed to movable balancing — organs
which take on the new duties of steering.
These become more and more perfect as we
work up the scale of fish life.

In the earlier part of this chapter we saw
how these fins, gradually, in response to new
demands, became transformed sometimes into
organs of touch, sometimes into weapons of
offence, and sometimes into organs of prehen-
sion, as in the suckers of the gobies, lump-fish
and remora.

CHAPTER VII.

FISH-LIVERIES, AND WHY THEY ARE WORN.

PROBABLY in thinking of birds we do so as often
as not in terms of their most conspicuous forms.
Thus we recall such birds as peacocks, pheasants,
parrots, canaries, and kingfishers at once ; a
further sifting of our memories brings up from
its darker recesses more sombre forms. Now in
dealing with the birds in this series of little
volumes, it was pointed out that this colouration
had a deep significance. Thus, we found that it
often happened that in the case of a brilliantly
coloured bird it is the male only which is
resplendent, whilst the female is quite dull.

70 THE STORY OF FISH LIFE.

The reason being, that the female by her incon-
spicuous colouration escaped the notice of prowl-
ing enemies, a great necessity when she is
performing the all-important task of incubating
the eggs. When this danger can be averted the
female may, and often does, assume the same
bright colours as her mate.

Sometimes in place of colour we met with
some other form of decoration, such as simply
elongated feathers or wattles ; sometimes, again,
certain tufts or ruffles of feathers, not necessarily
brilliantly coloured, were developed for a short
time only arid then discarded. Or, again, what
appeared at first sight to be cases of decora-
tion turned out, on closer examination, to be
instances of protective colouration.

So is it with the liveries worn by fishes.
Whether dull as the proverbial ditch-water, or
rivalling the hues of the rainbow, there is an
explanation behind it. The creatures of nature
reflect the tone of their surroundings.

Before all things it is necessary to observe
caution in formulating hypotheses to account for
the brilliant colouration of fishes ; or of any animal.
Let us take certain cases which illustrate the
necessity for this caution first.

It comes natural to assume that brilliant
colouration, — whether permanent, as in the case
of parrots (to take our illustration from the birds
again), or seasonal, as in many of the plover
tribe, e.g. : the golden plover, — is to be inter-
preted as due either, as in the last-mentioned
instance, to the exigencies of courtship ; or to
the need for protection. Thanks to the observa-

FISH-LIVERIES, AND WHY THEY ARE WORN. 71

tions of naturalists all over the world, we now
know that brilliant colouration is as often a form
of protective colouration as is the sober style
wherein the colours harmonise with rocks, or
mud, or reeds, and so forth, as the case may be.
Tnus birds often appear to be very conspicuously
coloured, because they are seen apart from their
surroundings. The hoopoe and the parrots are
admirable examples of this. The zebra, amongst
the mammals, is another wonderful illustration.

When we turn to the fishes we discover that
the same rules appear to obtain. This is con-
spicuously the case with fishes which inhabit the
neighbourhood of coral reefs. Here we meet
with the gaudily striped and barred scaly-finned
fishes, the Chcetodontidw, and the brilliant wrasses
or lip-fishes. These live in a world of colour,
for the coral animals themselves are also bril-
liantly coloured. The gurnards and mullets of
our own coasts are other instances of brightly
hued fishes.

It is significant in this connection to note that
those fish which pass most of their time in mid-
water, like the herring, for instance, have the
under parts silvery or white and the upper parts
darker. This, again, appears to be a form of
protective colouration, for the dark upper surface
tends to screen them from the view of enemies
above, whilst the light under part performs a
like service against enemies below, which look
upwards towards the light. Many young fishes,
as we shall see, are perfectly transparent, and
therefore invisible.

But the interpretation of colour is by no

72 THE STORY OF FISH LIFE.

means an easy matter, and contains many pit-
falls and puzzles, for many cases appear to be
capable of bearing more than one interpretation.
Amongst the most interesting cases of this
kind are the instances where the male and
female are both brightly or even gaily coloured,
but in different ways. Thus in the ornate coffer-
fish (Ostradon ornatus) the male has a ground
colour of grass-green, with spots and stripes of
brilliant blue, whilst the female, often mistaken
for a different species, is pale yellow or flesh
colour with brown markings. In one of the
parrot fishes again we have a similar twofold
form, or case of dimorphism; the male being
green and red, and the female blue and yellow.
Usually, of course, where the sexes differ, the
male is brightly and the female dull coloured.
One instance, at least, is on record where the
markings of the young are more ornamental than
in the adult stages ; this is the case in the young
of certain eagle-rays of the genus Myliobatis.

One of the most remarkable of all brilliantly
coloured fish is a small wrasse-like form, the
amphiprion. It is vividly coloured, being ver-
milion red banded with three cross-bands of
white. This seems about as conspicuous a coloura-
tion as possible, as if it had been adopted on this
account. At any rate, this fish plays the part of
a decoy for the mutual benefit of itself and a
gigantic sea anemone of some two feet in diameter,
which inhabits the coral reefs of Thursday Island.
It appears that this little monster resides within
the body of the anemone. When hungry he
emerges, swims about till he attracts the notice

FISH-LIVERIES, AND WHY THEY ARE WORN. 73

of some carnivorous species, and so soon as he
is chased rushes back and plunges headlong down
the mouth of his kindly host. This brings his
would-be captor within reach of the tentacles
and paralysing stinging threads of the anemone,
from which there is no escape. The fish and the
anemone apparently then share the spoil !

We have seen that the colours of fishes may
become more brilliant during the season of court-
ship ; and we may now turn to the consideration
of some cases in which the colouration may under-
go sudden changes in brilliancy during periods
of excitement; much as we ourselves turn colour
from a deathly white to scarlet when possessed
by some sudden emotion. But the methods in
which these changes are made differ very much
in ourselves and in the fish. With us the sudden
change to scarlet is due to an increased supply
of blood to the face ; its sudden or complete
withdrawal causes pallor. With the fish, change
of colour to begin with is not necessarily from
red to white, or vice versd, but varies as the
colour of the fish. Furthermore, as we have
already hinted, the change is not connected with
the blood-supply, but with the deeper layer of
the skin and the colouring matter contained
therein. And in this fact we have a point of
exceeding interest, for this colouring matter is
contained within certain little bag-like structures,
whose form can be suddenly changed from a
globe to a disc by means of the contraction of
numerous little strands of muscular fibres at-
tached to the outside of the bag. Now, when
these little bags of colour, which are scientifically

74 THE STORY OF FISH LIFE.

known as chromatophores, are at rest, they allow
the general ground colour to play a more or less
conspicuous part ; but so soon as the proper
stimulus is applied, the little strands or cords
contract on all sides and pull the bag flat, at
the same time, of course, causing its contained
colouring matter to be spread out in a thin layer
and cover the ground colour beneath. This
power of changing colour is of great use, for by
this means the animal is enabled to assume the
general tone of its immediate surroundings, and
so obtain a measure of protection against its
enemies.

Many animals have this power of changing
colour by means of contractile pigment cells or
chromatophores. Thus, a species of shrimp
(AtyMct) has been described, which is dark
green when among weeds, but changes to a pale
brown when resting in dark rocks; a dark
brown form placed in a tank containing numer-
ous greenish forms changed at once to this
colour. Frogs also change colour according to
the nature of the ground on which they rest.
The action of these chromatophores is, perhaps,
nowhere seen so well as in the Loligo, one of
the cuttle-fishes — not a fish, of course, but a
mollusc allied to the Nautilus. Here the ex-
pansion and contraction of these very active cells
goes on with great rapidity. All the blue or all
the yellow or all the red-containing cells may be
expanded and the others remain at rest, but so
quickly do the changes follow one upon another,
that a dazzling brilliancy is the result. Some-
times the contraction of these cells leaves a

FISH-LIVERIES, AND WHY THEY ARE WORN. 75

generally brilliantly coloured fish of a quite dull
hue, which remains for some time.

The colours in the scales of a fish depend
much on its surroundings, says a writer in the
'; En cyclopaedia of Sport/' "A trout taken off
a muddy, weedy bottom will often have a general
shade of rich yellow over its sides and belly;
while even in the same lake a trout taken from
the opposite shore which, let us say, is rocky and
sandy, will be of a steely blue colour. A trout
swimming in deep water over a peaty bottom
will have a dark back ; while fi»h which inhabit
shallow, bright, gravelly streams will have a
light brown back, in fact, almost gravel colour.
This is without doubt a provision of Nature to
disguise the fish as much as possible from the
keen eyes of herons and other fish-eating birds."

" In many bright-shining fishes," writes Dr
Giinther, " as mackerels, mullets, the colours
appear to be brightest in the time intervening
between the capture of the fish and its death ;
a phenomenon clearly due to the pressure of the
convulsively-contracted muscles on the chromato-
phores. External irritation readily excites the
chromatophores to expand — a fact unconsciously
utilised by fishermen, who, by scaling the red
mullet immediately before its death, produce the
desired intensity of the red colour of the skin
without which the fish would nob be saleable."

The red mullets have been esteemed for their
colour from time immemorial. So great was
the admiration it excited in the breasts of the
Eomans that the wealthy had it brought to table
alive that they might watch the brilliant display

76 THE STORY OF FISH LIFE.

of colour which it afforded daring its death
struggles.

Some colours are due to a combination of two
or more pigments. Thus the exquisite green
colour of the mackerel, so familiar to us all, is
due, not to a green pigment, but to a blending
of black and yellow chromatophores.

But the colours of fishes are not all due to
pigment. Some are what is called structural.
For instance, the silvery iridescent appearance
of many fishes is due to the presence of crystals
of a substance known as guanin, derived as a
waste product of the blood. These guanin
crystals figure very conspicuously in the colora-
tion of fishes.

We may gather then that the coloration of
fishes must be regarded as largely reflecting, and
determined by, their need for protection. It
may be either permanently dull or brilliant, or
more or less rapidly changed from one to the
other extreme.

Sometimes the coloration may be brilliant at
one season of the year and dull at another, and
then is generally connected with the niceties of
courtship. In such cases fleeting changes from
dull to brilliant or vice versa, due either to excite-
ment or sometimes fright, are common. These
changes are, we have seen, due to the action of
contractile cells containing colouring matter
called chromatophores.

But, it may be remarked, although it has been
shown that fishes undergo rapid and marked
changes of colour, of such a nature as to cause
them to resemble that of their immediate sur-

FISH-LIVERIES, AND WHY THEY ARE WORN. 77

roundings, no indication has as yet been given
which will explain why the change takes place
so soon as a lack of harmony is established.
That is to say, how the various colour cells of
the fish, or other animals which change rapidly,
are affected by the colour of the world outside.
Much has yet to be done by experiment before a
thoroughly complete answer can be formulated ;
but practically we may say these colour changes
are due to stimulations through the eye This
is shown by the fact that instances are on record
where fishes which did not correspond in colour
either with their fellows or their surroundings
were found to be blind.

Some colours may be what we might call acci-
dental. They represent waste products thrown
off from the blood, and the fact that they lend
their aid to more or less beautiful colour schemes
is an accidental result. Protective coloration
has probably resulted from the advantageous
disposition of this waste colouring matter, a
distribution determined by the needs of the
individual. Thus, to take a simple case, such
as that of a normally-coloured fish, one that is
white below and dark above, the silvery white
is due, we have seen, to the presence of crystals
of guanin. The dark coloration due to dark pig-
ments of various kinds, is derived, as some believe,
by decomposition of blood corpuscles. .Now, it
is possible that the distribution of these was
originally diffuse, that is to say, not definitely
confined to one region, as in the fishes of to-day.
If this were so, it is certain that there would
have been great variation amongst individuals,

78 THE STORY OF FISH LIFE.

some of which would tend to produce more dark
pigment above than below, and this would lay the
foundation for natural selection to work upon.
Natural selection would operate by render-
ing those fishes with darker backs and lighter
underparts less conspicuous than their fellows,
who would sooner fall a prey to other fish from
below, and fish-eating birds and mammals from
above.

We have done no more than touch upon the
fringe of this question in this chapter. It is one
that would well repay further study, for there
are many puzzles to be solved.

CHAPTEE VIII.

HOW FISHES FEED.

ALL living things must eat, and whether it be
dirt — the dust of the earth mingled with rain-
drops, such as forms the diet of an earthworm,
or whether it be of the dainty dishes set before
the king, that which we eat must contain some
nourishing properties. But what is good to eat
and what is hurtful is knowledge which comes of
experience. Knowledge bought sometimes at a
great price — even the death of the purchaser.
The pages of the history of mankind furnish
us with many lessons in the dangers as well as
the delights of Beating.

Sight, smell, taste and memory are the council
board which determine the menu for the higher

HOW FISHES FEED. 79

forms of living things. We ourselves, consciously
or unconsciously act upon the knowledge of this
fact, as we are told the serpent did of old to
beguile the unwary. One of the first queries we
make about any strange animal is : What does it
feed on ? Next : how does it procure its food 1
Often we have to depend largely, if not entirely,
upon our stock of knowledge of this kind for the
capture of other creatures, either for our personal
wants or to satisfy our deep-rooted love of killing
something. This is especially true of the capture
of fishes, and none will be more convinced of
this than the angler. A successful angler must
know much, not only of the nature of a fish's
food, but also of the faculties employed in its
discovery. He acts upon the old proverb : "The
belly hath no ears when hunger comes upon it."
It is difficult to say whether sight or smell
play the most important part in the capture
of food amongst the fishes. There seems to be
no doubt but that many fishes depend mainly,
though not entirely, upon sight for the capture
of their food. The success of the fly-fishers is a
sufficient proof of this. The salmon, for instance,
it is regarded as unsportsmanlike to take by any
other means than with the " fly," except under
special circumstances. This fly is cunningly
devised of feathers, so as to imitate as nearly as
possible some real fly well known and esteemed
by the fish. There can be no doubt that sight,
not smell, is the broken reed upon which the
poor victim trusted in cases where this deceit is
successful. But salmon apparently sometimes
hunt by smell as well as by sight. Thus, old

80 THE STORY OF FISH LIFE.

Isaac Walton relates an experience of his anent
a fellow- fisherman, "I have been a-fishing with
old Oliver Henley, now with God, a noted
fisher both for trout and salmon, and have
observed that he would usually take three or
four worms out of his bag, and put them into a
little box in his pocket, where he would usually
let them continue half-an-hour or more before
he would bait his hook with them. I have
asked him his reason, and he has replied : * He
did but pick -the best out to be in readiness
against he baited his hook the next time ' ; but
he has been observed, both by others and myself,
to catch more fish than I, or any other body
that has ever gone a-fishing with him, could do,
especially salmons. And I have been told lately,
by one of his most intimate and secret friends,
that the box in which he put these worms was
anointed with a drop, or two, or three, of the oil
of ivy-berries, made by expression or infusion;
and told that by the worms remaining in that
box an hour . . . they had incorporated a kind
of smell that is irresistibly attractive enough to
force any fish within the smell of them to bite."
Some two hundred and forty years after this was
written, actual and very careful experiments
were made by Mr Gregg Wilson in the Plymouth
Marine Biological Station, with a view to gaining
more definite information in this very interesting
and important matter. The more interesting of
his results may be briefly and profitably trans-
scribed here. He says: "So far as I could
determine, fish that are not very hungry habitually
smell food before taking it. The pollack seems

HOW FISHES FEED. 81

usually to be ready for a meal, and on almost
all occasions when anything eatable is thrown
into the tank in which it is swimming, it rushes
towards it and bolts it. It does not hesitate to
take stale food, or food that has been steeped
long in strong -smelling fluids ; and time after
time I have been amused to see its too late
repentance, after it had swallowed clams that
had been saturated with alcohol, chloroform,
turpentine, etc. It is only when it is satiated
with fresh food, or disgusted with what is
nauseous, that it takes the precaution to smell
before eating. On the other hand, various fish
that are equally keen -sigh ted, and habitually
recognise their food by the use of their eyes, are
more prudent. The whiting (Gadus merlangus),
for instance, appears to pay much more attention
to smell, and, as a rule, turns about and with-
draws on approaching within a few inches of
high-smelling objects that the pollack would take
without hesitation. Even whiting, however,
cease to be delicate if they are very hungry, and
if other fish are present to compete for the food
that is thrown to them. In such circumstances
bait that is very distasteful may be taken by
even the most cautious of sight-feeders; and
likewise, in such circumstances, a quite odourless
artificial bait may be successfully employed.
Where large shoals of fish are, there are likely
to be many that are very hungry, and the con-
sequent keen competition will lead to hasty
feeding by sight alone ; and hence it is, probably,
that lead-baits are successfully employed in cod-
fishing in the Moray Firth and off the northern
F

82 THE STORY OF FISH LIFE.

islands, while they are of no avail among the
scanty fish further south.

" It may be said that in these cases the fish
actually search for their food by sight alone, and
merely test the quality of what they have found
by smelling it. ... But more is possible : habitual
sight-feeders can be induced to hunt ly smell alone.
The pollack, which is such a pronounced sight-
feeder that it will take a hook baited with a
white feather or a little bit of flannel, and trolled
along the surface, is yet able, when blinded, to
get his food with great ease. Several blind
specimens in the Plymouth tanks were carefully
watched by me, and I had no difficulty in decid-
ing that it was by smell alone that they found
their food. Their conduct was exactly such as
was seen in the smell-feeders. ..."

The cod-fish is generally believed to feed more
by night than by day, hence we may conclude it
is a " smell-feeder."

Mr Gregg Wilson has also placed on record
the results on some of his experiments with
certain other fish, which throws yet more light
on this subject. Thus with the dabs (Pleuronectes
limanda}. "That they were sight-feeders," he
says, uwas evidenced by their behaviour when
I lowered a closed tube full of water, and with a
worm in the middle of it, into their tank ; time
after time they bumped their noses against the
glass at the very spot where the worm was
situated. That they could also recognise the
smell of food, apart from seeing it, was demon-
strated in various ways. First, if instead of a
closed tube . . . one open at the bottom was

HOW FISHES FEED. 83

used, after a short interval the ' nosing7 at the
part where the worm was seen ceased, and the
lower end of the tube, from which, doubtless, worm-
juice was diffusing, was vigorously nosed. If,
again, instead of putting worms into a tube, I
placed a number of them into a closed wooden
box with minute apertures to let the water pass
in and out, there was a similar excitement pro-
duced, and the dabs hunted eagerly in every
direction. When water in which many worms
had lain for some time was simply poured into
the tank through a tube that had been in position
for several days, and by a person who was out of
sight of the dabs, the results were most marked.
In a few seconds hunting began, and in their
excitement the dabs frequently leapt out of the
water, apparently at air-bubbles, and on one
occasion one even cleared the side of the tank,
which was about two inches above the water,
and fell on to the floor of the aquarium. Yet
there was nothing visible to stimulate the quest."

A very remarkable instance of sight-feeding is
that afforded by a fish known as the archer-fish
(Toxotes jaculator). This name has been bestowed
upon it on account of its remarkable habit of
squirting a drop of water at flies and other
insects perched on the water-plants above the
water. It is said to be able to strike down into
the water a fly as much as six feet distant. The
Malays dill it "Ikan surupit," says Dr Giinther,
" and keep it in a bowl, in order to witness
this singular habit, which it continues even in
captivity."

From the means by which fish aescry their

84 THE STORY OF FISH LIFE.

food we may well pass to the method of seizing
the same, and its disposition. And it will be
interesting to note, as we pass from one illustra-
tion to another, how numerous are these methods,
and the modifications of structure which have
often been induced thereby.

One of the sea-breams of the Mediterranean
(Chrysoplirys) or the gilt-head — which, by the way,
sometimes occurs on the south coast of Eng-
land— is said to stir up the sand with the tail
to discover the buried shell-fish. Its favourite
kinds are mussels, and it is said that its near
presence is ascertained by the fishermen by the
noise which it makes in crunching their shells
between its teeth.

The " fox-shark" or " thresher," one of the
commonest and largest of the shaiks which
periodically appear off our coasts, hunts in a
peculiar fashion : a fashion by the way first re-
corded by Dr Giinther. It preys upon the shoals
of herrings, pilchards and sprats, of which it de-
stroys incredible numbers. These shoals the fox-
shark follows on their migrations. Swimming
round and round the unlucky shoal with ever
decreasing circles, and accompanying its gyra-
tions with a violent beating of the water with its
enormous tail (hence its name of " thresher "),
the intended victims are swiftly huddled together
in a dense crowd, when they fall an easy prey.
This fashion of hunting recalls the " roumding up "
methods of the sheep-dog. The thresher attains
a length of some fifteen feet, about one-half of
which is represented by the tail.

The teeth of fishes are often profoundly modi-

HOW FISHES FEED. 85

fied for the purpose of crushing shell-fish.
Many of the brilliantly-coloured wrasses have
these modified teeth. Thus they have an inter-
maxillary tooth which is used for the purpose of
grinding shells against the lateral and front
teeth. One of the parrot-wrasses — a vegetable-
feeder- — reduces its food to pulp within the
mouth, by means of specially modified teeth.
The food is slowly worked backwards and for-
wards till thoroughly masticated. This has given
rise to the notion, says Dr Gunther, of its being
a ruminant. His further remarks on this fish
are well worth quoting here, though we may be
accused of making a digression in doing so.
"In the reign of Claudius, according to Pliny,
Optatus Elipentius brought it from the Troad,
and introduced it into the sea between Ostium
and Campagna. For five years all that were
caught in the nets were thrown into the sea
again, and from that time it was an abundant
fish in that locality. In the time of Pliny it was
considered to be the first of fishes (Nunc Scaro
datus prindpatus) ; and the expense incurred by
Elipentins was justified, in the opinion of the
Eoman gourmands, by the extreme delicacy of
the fish. It was a fish, said the poets, whose
very excrements the gods themselves were un-
willing to reject. Its flesh was tender, agreeable,
sweet, easy of digestion, and quickly assimilated;
yet if it happened to have eaten an aplysia (a
species of mollusc), it produced violent diarrhoea.
In short, there is no fish of which so much has
been said by ancient writers. In the present
day the Scarus of the Archipelago is considered

86 THE STORY OF FISH LIFE.

to be a fish of exquisite flavour ; and the Greeks
still name it Scaro, and eat it with a sauce made
of its liver and intestines."

The teeth have undergone innumerable modi-
fications in accordance with the nature of the
food to be ingested. The nature of these modi-
fications, and other features, such as the attach-
ment to the jaw and so on have been already
dealt with.

The point we wish to emphasise here is
the evolution of strange forms evidently adapted
to peculiar ends and purposes. Thus, for in-
stance, some of the shark-tribe, the eagle-rays
(Myliobatis), are remarkable for the possession of
a peculiar pair of processes projecting forwards
from the head, which are said to be used for
scooping food from the sea-floor and conveying
it to the mouth.

Another fish of this group, the " saw-fish "
(Pristis)) has developed a most remarkable and
most powerful weapon, by a modification of the
beak-like process of the front of the head. This
is produced forwards into a series of from three
to five hollow tubes placed side by side, tapering
towards the end, and covered by shagreen, the
nature of which we have already discussed. In
deep sockets along each side of this enormous
beak are implanted large conical flattened teeth,
thus forming a double-edged saw. This saw is
sometimes a foot broad at the base, and as much as
six feet long. It forms, it is needless to remark,
a very terrible and most effective weapon,
rendering its owner, as Dr Gunther justly re-
marks, most dangerous to all other large

HOW FISHES FEED. 87

inhabitants of the ocean. It is used in tearing
off pieces of flesh from its victim's body, or for
ripping open the abdomen. The detached
fragment, or protruding pieces of viscera, are
then seized by the mouth and swallowed. The
teeth of the jaws framing the mouth are, it
should be remarked, too feeble to inflict wounds,
or to be in any way useful as weapons of
offence.

Another large powerfully-armed and really
dangerous fish is the sword-fish (Xiphias). They
bear the name of sword-fish on account of
the great development of the upper jaw, which
forms a huge tapering sword-like weapon. It
might be noted here that this is of quite different
origin to the blade of the saw of the "saw-fish"
which we have just discussed. The sword of
the sword-fish is covered along its under surface
by numerous and small teeth ; and the weapon,
as a whole, is a very terrible and very powerful
one. They attack apparently, without provoca-
tion, whales and other large cetaceans, which
they invariably succeed in killing, by repeated
thrusts of the sword. Battles of this kind re-
mind one of the stories in " Gulliver's travels " —
this puny antagonist, of some twelve to fifteen feet
in length, ferociously assailing the giant whale of
sometimes seventy or eighty feet. It appears that
occasionally sword-fish make a mistake, and,
after the fashion of Don Quixote, tilts at wind-
mills in the shape of large vessels, under the
impression that they are whales. For this most
grave error of judgment it pays a heavy penalty;
in that having no power to make effective back-

88 THE STORY OF FISH LIFE.

ward movements, the sword remains fixed and is
eventually broken off in the struggle for freedom.
Frank Buckland reminds us that in the Museum
of the College of Surgeons is a section of the
bow of a whaler impaled by one of these swords.
That portion of the sword which remains is a
foot long and five inches in circumference. " At
one single blow," he writes, " the fish had plunged
his sword through, and completely transfixed
thirteen and a half inches of solid timber. The
sword had of course broken off and prevented a
dangerous leak in the ship. In the British
Museum is a second specimen of a ship's side
with the sword of a sword-fish fixed in it, and
which has penetrated no less than twenty-two
inches into the timber. When his Majesty's
ship Leopard was repairing in 1795, after her
return from the coast of Guinea, a sword of one
of these fishes was found to have gone through
the sheathing one inch, next through a three-inch
plank, and beyond that four and a half inches
into the firm timber ; and it was the opinion of
the mechanics that it would require nine strokes
of a twenty-five-pound hammer to drive a bolt of
similar size and form into the same depth into
the same hulk ; yet this was accomplished by a
single thrust of the fish." Mr Lydekker reminds
us that there are instances on record of bathers
having been transfixed by these fish, one such
instance occurring in the estuary of the Severn
about the year 1830. The normal use of this
sword is for the capture of food. Cod and other
fish being spitted thereon, but how they are
removed from the sword still remains a mystery.

HOW FISHES FEED. 89

The teeth of the sword-fish, it should be re-
marked, are either small or vestigial.

Those who have the good fortune to be within
easy reach of a museum, where a skeleton of the
sword-fish is exhibited — such as the Natural
History Museum, London — should make a pil-
grimage thereto for the purpose of inspecting
the wonderful vertebral column of the sword-fish.
It has undergone great and peculiar modifications
obviously designed to give strength and power to
resist the shocks of the violent and deadly charges
which the living fish is known to make.

Two fish bearing a superficial resemblance
to the sword-fish are worthy of mention here.
These are the gar-pike (Belone) and the half-beak
(Hemirhamphus). Both, however, differ from the
first-mentioned in that it is not the upper jaw
only .that is elongated but both jaws. In the
gar-pike the upper jaw is longer than the
lower. They capture their prey whilst skim-
ming along the surface of the water. In the
half-beaks the proportions in the length of the
jaws are the reverse of what obtains in the
gar-pike, the lower jaw being longer than the
upper.

It is interesting here to note that in all three
forms of these long-beaked fishes the jaws are of
equal length, and not elongated in the young.
In the young gar-pike, strangely enough, for a
short while after the increased length of the
jaws has begun, the lower is longer than the
upper jaw. Thus, during this stage it resembles
the half-beak (Hemirhamphus). As we have just
remarked, the resemblance between the sword-

90

THE STORY OF FISH LIFE.

fish and the gar-pike and half-beak is a superficial
In the former it is the upper jaw only

one.

which is elongated, and this is used as a spear ;
in the two latter both jaws are elongated, and
used as a pair of forceps, like a bird's beak. We
have now a third form of the elongation of the
jaws to examine. In this type the jaws are

FIG. 8. — A. Head of Gnathonemus elephas, one of the Mormyridse
from the Congo, to show the extraordinary modification of the
jaws (after Boulenger). B. Head of Ilistiopterus recurvirostris,
after Giinther, also showing modification of the jaws.

drawn out into a long and often curved tubular
beak or trunk, at the extreme tip of which is a
tiny cleft — the mouth. This beak resembles the
long drawn-out head of that curious mammal the
great ant-eater, even to the cleft-like terminal
mouth. This curious tubular beak is apparently
an adaptation enabling the fish to explore and drag
out from holes and crevices creatures which lie
hid therein. The "boar-fish" (Histiopterus) and
the chelmo of Australia, and some members of the
genus Mormyrus of the African rivers and lakes,
represent the most striking instances of this

HOW FISHES FEED. 91

curious bizarre type. One or two of the most
wonderful of these latter forms are sketched in
the accompanying figures (fig. 8). The mormyrus,
it should be remarked, was well-known to the
ancient Egyptians, and occurs not infrequently
in the hieroglyphic figures. It was regarded as
an object of veneration. The Egyptians, Dr
Gunther tells us, " abstained from eating it
because it was one of three different kinds of
fishes accused of having devoured a member of
the body of Osiris, which, therefore, Isis was
unable to recover when she collected the rest of
the scattered members of her husband." Since,
then, there has arisen a people who knew not
Osiris and his mournful history, and these eat
the mormyrus with great relish, pronouncing its
.flesh most excellent eating.

Some fish procure their food by stealth, and
the craft and cunning displayed in a study of
these instances is something diabolical, and
hardly to have been expected at first sight in
animals of this low grade. Take the cunning of
the skate, for example. The skate is a cousin of
the shark, but the shark is what we may call a
round fish, moving swiftly by virtue of a violent
side to side sculling action of the tail, whilst the
skate may properly be called a "flat" fish. Its
change of form has been brought about by the
enormous development of the pectoral fins, which
form huge fleshy lobes on each side of the body,
tapering off at their outer margins to a thin
edge. These great fins have superseded the tail,
and propel the body by a series of undulatory
movements, resembling those of the lateral fins

92 THE STORY OF FISH LIFE.

of the plaice or sole, for instance. Like the
shark, however, the skate is carnivorous, but is
unable to pursue and catch swiftly - mo ving
animals ; instead, it preys upon slow-moving or
stationary animals, such as shell-fish (mollusca)
and Crustacea (crabs and lobsters). It may be
that this modification is a result of adaptation,
fitting it for a new mode of life when competition
was less. But the craving for the flesh of
animals of its own class, or even species, has not
been lost, though it is one which could never be
gratified were it not for the fact that it is pro-
tectively coloured. That is to say, the colour of
its upper surface closely assimilates with that of
its surroundings. Taking advantage of this fact,
the skate lies quietly at the bottom, so quietly
that unwary fishes approach near enough to be
suddenly pounced upon. With a swift; sudden
spring the crafty ghost-like monster throws itself
upon its unsuspecting victim, so as, to quote
Dr Griinther, " to cover and hold it down with
its body, when it is conveyed by some rapid
motions to the mouth." Thus the poor victim is
both smothered and swallowed at the same time.
The position of the mouth on the under surface
of the flattened body, and the weak jaws and
teeth render this method of enveloping the prey
absolutely necessary.

But the death-traps of the sea are many.
Down in its silent depths we seem to see
" nature red in tooth and claw," urging her chil-
dren forward to deeds of blood as relentlessly as
on land. Or rather perhaps these should be
looked upon as the degenerate ones — those upon

HOW FISHES FEED. 93

whom the struggle for life has told adversely.
Keen competition and the consequent stimulus
of hunger have developed a certain low cunning
and deception, shared even by the "lord of
Creation," man himself. Some others of the
past-masters of this art of deception we will pass
in review now. One of the chief of these is the
"angler-fish" or " sea-devil," of which we may
take a very widely distributed form (Lophius
piscatorius] as an example. This species is found
all round the coasts of Europe, Western North
America, and the Cape of Good Hope. It has
an enormous flattened head, with a huge mouth,
and a tapering body. Around this head project
numerous short loose appendages resembling
little bits of sea-weed. From the middle of the
head there arise three or four slender stalk-like
and freely movable shafts, the foremost of
which bears a little flag-like blade. As this
monster lies close and quiet at the bottom the
flag-like pieces of sea-weed-like skin along the
head and sides of the trunk tend to divert
suspicion from the body, whilst the foremost
spine, with its attached "flag," is slowly waved
about. Little fishes in the neighbourhood gather
round this flag, and whilst busily engaged in
inspecting it, and speculating on its probable
palatability, are suddenly engulfed, being sucked
in by the mere opening of the huge mouth, till
now concealed. There are some anglers who
hold that fish have no curiosity ! It is interest-
ing, but puzzling, to note that in young angler-
fish all the elongated dorsal spines are beset with
lappets of skin, and that the fins are much longer

94 THE STORY OF FISH LIFE.

and their supporting rays are produced far out-
wards beyond the fin-membrane in the form of
long slender filaments. The cavern-like mouth
of this ugly and repulsive monster, it should be
noticed, is liberally beset with teeth ; they fringe
its jaws, and cover the roof of its mouth.
Moreover, they are hinged so as to move freely
backwards on pressure, allowing ready ingress
but no escape, for any backward wriggling of the
newly injected victim would impale him in their
inturned points.

The voracity of fishes varies much. Sea-fishes
would appear on the whole to be more voracious
than fresh-water species; since the latter may
survive without food for weeks or even months,
sea-fishes will succumb to a fast of a few days.
The capacity of the stomach of some marine
fishes is almost beyond belief. This is especially
the case with many deep-sea forms, where food
is but seldom to be come at, and as much as
possible must therefore be taken at a time. Our
illustration affords us a graphic example of this,
wherein the swallower, known as Chiasmodus
niger^ has succeeded in stowing away a fish more
than twice his own size (fig. 9). The stomach and
external skin in such species is remarkably dis-
tensible. Note the position of the displaced
pelvic (ventral) and anal fins. The action of
swallowing is performed, not as is usual with
fishes, by means of the muscles of the gullet,
but by the action of the jaws as in snakes.
These fishes, as Dr GKinther has remarked, can-
not be said to swallow their food, but rather to
draw themselves over their victim, in the fashion

HOW FISHES FEED.

95

of the star-fishes or sea-anemones. Another
deep-sea fish (Melanocetns\ mentioned by Dr
Giinther as occasionally taken at depths of from
360 to 1800 fathoms, is equally successful in
these feats of swallowing. From the stomach of
;a specimen not quite four inches in length,

FIG. 9. — Chiasmodus niger, a deep sea fish (1.500 fathoms) from
the N. Atlantic. It has swallowed another fish — a species
of Scopeius — much larger than itself, which can be seen
through the walls of the body, made transparent by disten-
tion. Note the displaced ventral fin of Chiasmodus (after
Giinther).

another fish seven and a half inches in length
and one inch in depth was taken. It was
spirally coiled into a ball. From the stomach
of the fishing-frog of our coasts other fish have
frequently been taken which equalled their de-
stroyer in size.

Another of these victims to an insatiable hunger
is the Plagyodus ferox. Some six feet in length,
he is a monster to be dreaded ; the nameless
terror of the mysterious dark shades and regions
of awful stillness and eternal night. From the

96 THE STORY OF FISH LIFE,

stomach of one of these fish were taken several
octopods, Crustacea and sea-squirts, a young bream,
twelve young boar-fishes, a horse-mackerel, and
one young of its own species !

The " skip-jack " (Tenmodern saltator), like some
carnivorous mammalia, seems to have developed
a thirst for killing for killing's sake. A voracious
feeder, destroying an immense number of other
shore fishes, yet it kills many more than it can
possibly eat.

The common stickle-back is likewise a voracious
feeder. Dr Gunther relates that a " small stickle-
back, kept in an aquarium, devoured in five
hours' time seventy-four young dace, which were
about a quarter of an inch long and of the thick-
ness of a horse-hair. Two days afterwards it
swallowed sixty-two, and would probably have
eaten as many every day could they have been
procured."

In some fishes, it is interesting to note, the
nature of the food actually influences the colour
of the flesh. The truth of this is particularly
well seen in the case of the salmon. These
fishes feed, at any rate at times, exclusively on
Crustacea, and the peculiar colouring substances
which pervade the system of these animals,
and to which they owe their characteristic red
colour when boiled, e.g. : lobster seems to under-
go similar chemical changes in the stomach,
and to pass from thence into the flesh of the
fish, imparting thereto its wonderful "salmon"
colour.

The evidence of these various modifications of,
and departures from, the typical fish, leads very

HOW FISHES FEED. 97

naturally to the query : Why have they come to
be 1 This is not easily answered.

What is undoubtedly a factor of prime im-
portance in the evolution of new forms and
types is the stimulus of hunger. We eat to live.
Food must be had at all costs. If the normal
food is scarce, an attempt will be made to find a
substitute. This will be more successfully done
with some individuals than with others ; because
of the fact that no two individuals of the same
group are exactly alike in all particulars. This
unlikeness, will be a positive advantage to some,
enabling them to seize upon new points of
vantage, from which their neighbours, by varying
unfavourably, will be excluded. Something of
the truth of this we may gather from the fact
that the further we trace back the history of any
group of animals, in time the more divergent
branches approach one another in form and
likeness.

The evolution of the prehensile organs of the
mouth is exceedingly instructive. We have seen
already that the teeth arose by gradual
modification of the scales, or rather denticles,
which make up the shagreen of the skin of the
most primitive fishes. These denticles on the
region of the skin covering the jaws gradually
changed their form, shape and method of
attachment, becoming more and more intimately
connected with the skeleton of the head, till
finally their primitive origin became obliterated.
This evolution of the teeth was brought about by
the modifications demanded to enable them to per-
form new duties. To-day we have the triangular
G

98 THE STORY OF FISH LIFE.

flesh-cutting tooth of the shark, the shell-crushing
mosaic of the skate, and the needle-like teeth of
the pike for holding prey, to take only a few
instances. On the other hand, by atrophy of the
outer teeth, we have evolution in a new direc-
tion, resulting in the toothless jaws of vegetable-
eating forms, and the development of fresh
teeth in a new position — the throat. That the
teeth have been lost in these, we gather from the
fact that they appear in the embryo.

We can imagine how these changes came
about. In the beginning, amongst the early and
very similar fishes, there would soon be great
competition for existence; the demand for food
tending to exceed the supply. If now certain
combinations of variations tended to permit of
some of thpse competing forms to supplement
their normal diet by the addition of, say, shell-
fish, and some of sea-weed, we can well imagine
that the progeny of these same would be still
better adapted in this new direction, and would in
time find a completely nourishing diet on the new
fare. The variation which favoured this change
would, of course, be now very marked, and in
course of time the annectant forms would die
out and leave these now specialised types. Thus
the vegetable feeding types would have become
toothless as to the jaws, and have developed new
teeth in the throat, as in the present-day vegetable-
feeders. The shell-fish feeding fishes would have
exchanged sharp-pointed teeth for broad flat
crushing teeth.

The course of ages has witnessed the gradual
evolution of countless variations of this kind;

COURTSHIP AND NURSERY DUTIES. 99

variations which have gone on increasing in
intensity in the new direction, till it becomes
more and more marked ; and this of necessity, as
each new generation became further and further
removed from the old method of feeding. As a
final result, we get the highly specialised struc-
tures delicately adjusted to the purposes they are
required to fulfil. This adaptation to require-
ments we call specialisation. As instances of
specialised structures, we have the crushing teeth
of various kinds, the beak of the saw-fish and
sword-fish, and the remarkable tube-mouth of the
sea-horse, mormyrus, the curious tactile barbules
of the siluroids, and a hundred more.

The importance of the part played by the
stimulus of hunger is shown by the fact that the
mouth parts of all animals vary most, and that
other modifications in the form of other parts of
the body are largely modifications connected with
the capture of the food.

CHAPTER IX.

COURTSHIP AND NURSERY DUTIES.

THE period of courting or mate-hunting with
many fishes, as with birds, is signalised by
special activity on the part of the males. Some-
times this is manifested by quite unusual
aggressiveness ; sometimes by the display of
brilliant colours, combined very often with
greatly elongated, or otherwise specially modified

100 THE STORY OF FISH LIFE.

and developed fins or membranes. If the
variations of these modifications are less notable
than the modifications of the epidermal structures
of birds, full compensation is found in the
marvellous range of brilliancy in the hues of the
skin which we have already discussed.

The difference in the size of the sexes of fishes
is a very noteworthy feature, and naturally one
of the first things which would attract our
attention in this connection. Thus, among what
are known as the "bony" fishes, e.g.: salmon,
perch, the females are larger than the males;
among some of the carp tribe the female is often
as much as six times as large as her mate ; some-
times, however, as in the cod, haddock, angler,
and cat-fish the males are larger, but only slightly
so. Occasionally, the female appears to be more
perfectly armed than the male ; thus, among
certain rays which are armed with bucklers or
pointed scales, it is the female on which they are
found, the male being almost or completely
smooth.

With the fishes as with the birds, the possession
of a mate seems to be accomplished in one of
two ways, conquest by battle, or conquest by
blandishment.

One of the best known and most interesting of
the instances of conquest by battle is afforded us
in the salmon of our rivers. The male salmon
fight ferociously amongst themselves, the strongest
driving away all rivals. So serious are these
engagements that Mr Darwin was informed, on
one occasion, as many as 300, all males with
one exception, were found dead in the Tyne

COURTSHIP A1SD NUH^R^ DtTTlfe. l'pl

during the month of June, killed by fighting.
The male salmon is further remarkable on account
of the fact that during this season of the year —
when he is fighting — the lower jaw becomes
elongated, and turns upward and backward into
the mouth, hook-fashion. When the mouth is
closed, this hook-like projection is received into
a special cavity in the upper jaw. The purpose
of this hook is not very clear, but it seems to be
that of stiffening the jaw to prevent dislocation,
which might otherwise follow one of the desperate
charges which they deliver, ram-fashion, upon
their opponent in fighting. An American species
of salmon develops large tusk-like teeth, which
inflict serious wounds. Besides this peculiar
hook to the jaw, the salmon also, at this time of
the year, becomes more brilliantly coloured.

The little stickle-back (Gasterosteus) of our
streams and ditches battles fiercely with his
fellows for the possession of his chosen.

By a natural sequence we pass from these
fierce battles or ecstatic cortortions, harlequin-
ades and displays, the tokens of what we may
call love-sickness, to a review of the more im-
portant facts concerning the deposition of the
eggs, and the often elaborate preparation for
their reception and safe-keeping. The range of
variation in the form, number and size of these
eggs is enormous. Much of this variation is
due to the fact that the egg of the fish differs
from what we may regard as the typical egg —
the hen's egg — in that it is never enveloped in
a hard limy shell, but, on the contrary, is gener-
ally quite unprotected. Such eggs are globular

10:2

OF FISH LIFE.

in form, and always relatively small, sometimes
minute. Instances of an outer covering are,
however, numerous, but in such cases the cover-
ing is of a horny character, and is, furthermore,
often produced into frills, thread-like processes,

FIG. 10.— Sticklebacks and Nest.

or other excrescences. The size of the egg
depends upon the number produced. This is
a quantity which may vary from several millions
to less than a dozen. When the number is
large the eggs, after they leave the parent, are
left more or less to chance ; when the number is
small they are often jealously guarded. How
and why this reduction of the eggs has come

COURTSHIP AND NURSERY DUTIES. 103

about, and the causes which have fostered de-
velopment of the parental instinct, are points
which may be more conveniently left till we
have digested the following instances.

We will begin with an account of those fishes
which have acquired the habit of nest-building.

The stickle-back of our ponds and streams will
afford us an admirable object lesson, illustrating
the perfection to which the parental instinct has
risen amongst the fishes. The stickle-back is
more than usually provident, for before he com-
mences his courting he provides the home, in the
shape of a very perfect nest, to which he proposes
to bring his bride (fig. 10). This nest he builds
entirely by his own efforts. The sides are raised
and finally a top is added, a small hole being left
at one side for an entrance. This is certainly
remarkable for a fish ; but, if possible, a still
stranger fact about this nest is the fact that the
materials of which it is constructed are held
together by a curious sticky secretion which
comes from the kidneys. In a similar way, the
nest materials of swifts and swallows are held
together by the secretion of the glands near the
mouth. The nest being complete, the new
householder casts about him for a mate. Having
sighted what he regards as one worthy of his
attentions, he conducts her, as it has been de-
scribed, with tender caresses to the nest, and
persuades her to enter through the doorway.
This done, she lays therein two or three eggs,
then bores a hole through the opposite side of
the nest and departs. This second doorway
proves useful, for it enables a continuous current

104 THE STORY OF FISH LIFE.

of fresh cool water to pass through and keep the
eggs constantly bathed. Next day he persuades
her, or a new mate, to repeat this ceremony.
This goes on till a large number of eggs have
been stored in the nest. Every time the female
enters, the male rubs his side against her and
passes over the eggs. When the nest is full he
mounts guard over the entrance, and stays at his
self-imposed sentry-duty for almost a month,
defending his treasures with great spirit against
all comers. Strange to say, the most dangerous
of these assailants are his own mates, his wives,
who would greedily devour every egg if they
could but get the chance. When the eggs hatch
out he watches for some considerable time over
the young, never leaving them till they can fend
for themselves. It seems that in order to ensure
a constant supply of fresh water to the develop-
ing eggs, he hovers over the nest driving the
water through by means of a fanning motion of
the pectoral fins and lashing of the tail. Frank
Buckland tells us that in a nest he watched this
vigilant little sentinel kept " constant watch over
the nest, every now and then shaking up the
materials and dragging out the eggs, and then
pushing them into their receptacles again, and
tucking them up with his snout, arranging the
whole to his mind, and again and again adjust-
ing it till he was satisfied."

But the stickle-back by no means relaxes his
care on the hatching out of the eggs. On the
contrary, his efforts for their protection are now
redoubled, and his vigilance is taxed to the ex-
treme. How hard the poor little fellow is worked

COURTSHIP AND NURSERY DUTIES. 105

has been graphically told by Mr Warrington,
who had the good fortune to watch the whole
sequence of events during this most critical
period of the fish's life. The nest he watched
was built in a large aquarium containing, besides
several others of his own species, two tench
and a gold-finch. " The other fish," he writes,
"three of them some twenty times larger than
himself, as soon as they perceived that the
young fry were in motion, used their utmost
endeavours, continuously, to pounce upon the
nest and snap them up. The courage of this
little creature was certainly now put to its
severest test, but nothing daunted he drove
them all off, seizing their fins, and striking with
all his strength at their heads and at their eyes
most furiously. . . . Another circumstance which
appeared to add greatly to the excitement that
he was constantly subjected to arose from the
second female fish . . . endeavouring most
pertinaciously to deposit her ova in the same
locality, and hence rushing frequently down
towards the spot; but the male fish was ever
on the alert, and although he did not strike at
her in the furious way he attacked the larger
ones, yet he kept continually under her, with the
formidable back spines all raised erect, so that
it was impossible for her to effect her apparent
object.

"The care of the young brood was very extra-
ordinary ... if they rose by the action of their
fins above a certain height from the shingle
bottom, or flitted beyond a certain distance from
the nest, they were immediately seized in his.

106 THE STORY OF FISH LIFE.

mouth, brought back, and gently puffed or jetted
into their place again. This was constantly
occurring, the other fish being continually on
the watch to devour these stragglers, and make
a savoury morsel of the lilliputian truants. In-
deed, the greater number of the whole brood
must have fallen a prey to their voracity, as it
was only some three or four that reached a size
to place them beyond the power of these de-
stroyers.

" As soon as the young fry could swim strongly
the parent fish gradually relinquished his duties,
though a constant watch appeared to be still
quietly maintained on their motions as they
swam about near the surface of the water. . . .
It is a curious circumstance that very soon after
these young stickle-back were left unmolested by
their companions, both the parent fish disap-
peared, and I presume have died in some hiding-
place among the rock-work; as though their
allotted functions, namely the propagation of
their species, having been completed, their period
of existence must terminate/'

Those crafty and subtle monsters, the skates,
furnish us with a striking instance of parental
affection. Thus one of the "devil-fishes'7 (Dicero-
batis) will defend its young with great ferocity.
Its capture, at all times attended with danger,
is especially perilous when it is accompanying its
offspring, at such times they have been known to
attack and capsize a boat.

The spotted goby or polewing (G. minutus),
which occurs in the Thames, is a nest-builder. Here,
however, an old cockle-shell is made to do duty

COURTSHIP AND NURSERY DUTIES. 107

for a nest. The shell is placed with its con-
cavity downwards, beneath which the soil is
removed, and cemented together by, it is said,
a special secretion of the skin. In the stickle-
back, it will be remembered, the kidneys fur-
nished the necessary cement. Access to this
nest is gained by a cylindrical tunnel, and the
whole structure covered by loose sand. The
eggs are fixed to the shell by the female, and
left to the care of the male, who mounts guard
over them and remains on duty till hatching,
which takes place from six to nine days.

CrenilabruSj one of the wrasses or lip-fishes,
builds a nest of sea-weed and shells, etc., in
which the eggs are deposited. But it is inter-
esting to note that in this instance at least both
male and female are engaged in its construction.

One of the angler-fishes (Antennarius) builds
in the floating " gulf-weed " off the Bermudas, a
very beautiful nest. This is suspended by deli-
cate silken fibres, quite strong enough to sup-
port the large grape-like clusters of eggs within.
"Each nest is made of one seaweed, the different
twigs being brought together and made fast to
each other by the fish by means of a pasty sort
of substance provided by the animal itself."

Perhaps one of the most remarkable of fish-
nests is that of one of the Chinese paradise fish
(Macropus). This is fashioned by the male, and
takes the form of a little disc of froth formed by
blowing air and mucus out of his mouth. The
nest made, he proceeds to collect the now fertil-
ised ova, dropped by the female, into his mouth,
and deposits them in his froth-like nest. This

108 THE STORY OF FISH LIFE.

done, he jealously watches over the eggs till
they hatch, renewing the froth from time to
time, and then, like the stickle-back, transfers
his affections to the young, guarding them with
great care.

One of the beaked fishes of tropical Africa,
Gymnarclius , builds a floating nest in about three
feet of water. Mr Budgett, who discovered this,
describes it as of about two feet long and a foot
wide ; the walls of the nest stood several inches
above the surface of the water, on two sides and
at one end. The opposite end was low, and at
this end was the entrance to the nest.

The males of some of the cat-fishes carry
the eggs about in the mouth, or in the gill-
chamber, thus ensuring both protection and
perfect aeration !

Amongst the fresh -water fishes known as
chromids, tropical of Africa and America, the
males of certain species build shallow nests, and
sit upon the eggs. This fact was discovered by
Lostert in one of the chromids of Lake Tiberias.
What is also unexpected in this connection is
the fact that although these males undertake
the duties of incubation, they do not adopt a
dull coloration as is so often done amongst
the birds. It is, of course, possible that the
brilliant coloration of the male may after all
prove to be not conspicuous, but protective.

Instances of the female taking care of her
offspring are, according to the high authority
of Dr Giinther, exceedingly rare in fishes. Only
a few examples appear to be known. One of
these is a cat-fish, one of the siluroids. In this

COURTSHIP AND NURSERY DUTIES. 109

fish (Aspredo batrachus), at about the time that
the eggs are ripe, the skin of the abdomen
becomes very swollen and tender, assuming a
soft spongy nature. As soon as the eggs are
laid, the aspredo presses them into the spongy
tissue by lying on them. When fixed she carries
them about with her, attached to the belly, till
they are hatched. As soon as this occurs the
skin shrinks to its former dimensions, and the
abdomen is once more perfectly smooth.

The Surinam toad of tropical America,
strangely enough, adopts a precisely similar
method of guarding the eggs. But in this
case they are embedded in the swollen skin of
the back instead of the belly. They are placed
on the back by the male. Embedded in the
skin the egg then undergoes its full course of
development. That is to say, it does not com-
pel the young, at the tadpole stage, to turn out
and support themselves, but contains sufficient
food material to allow the tadpole stage to be
dispersed with, the young emerging as fully
formed though tiny toads.

Another instance of a female fish caring for
the eggs is that of an ally of the pipe-fish, the
Solenostoma cyanopterum, of the Indian Ocean.
These, according to Dr Giinther, are borne on a
pouch formed by the ventral fins, and for further
security the inside of this pouch is beset with
numerous long filamentous appendages. In a
third case the female shares with her mate the
anxieties of watching the eggs.

Amongst many species of true pipe-fish the
care of the offspring, as seems to be usual with

110 THE STORY OF FISH LIFE.

fishes, devolves upon the male. In some, as in
the common pipe-fish (Syngnathus acus), the eggs
are placed "by him in a pouch formed by a fold
of skin, which develops along each side of the
abdomen, arid finally meets in the middle line.
Here the eggs remain till they are hatched.
But the pouch is by no means done with on this
event, for the young continue to occupy it for
some considerable time, leaving it at once and
returning if danger threatens. Mr Yarrell relates
a very curious fact that he was told by some
fishermen. To wit, that if they take a pipe-fish,
open the pouch, and drop the young into the
sea, these will not disperse, but hover around
the spot, as if waiting for their parent. Then,
if they hold the newly-opened fish in the water,
the young immediately return to it and enter
the pouch. In the sea-horses (Hippocampus) this
is more completely closed than in the pipe-fishes,
only a small anterior aperture being present.
In some pipe-fish, e.g. the tropical Doryichthys,
the eggs are said to be " glued " to the skin of a
broad groove on the under surface of the males.
This groove would seem to indicate the begin-
ning from which the complete pouch has been
developed.

Some fishes, as in the viviparous wrasses,
many blennies and carps, the eggs are hatched
within the body of the parent, so that the young
are produced alive.

The roach-like bitterling (Ehoderis amarus), of
European waters, is remarkable on account of
the fact that the oviduct is produced into a long
tube, which serves the purpose of the ovipositor

COURTSHIP AND NURSERY DUTIES. Ill

of the insect. By this means the female is
enabled to deposit her eggs within the open
valves of fresh-water mussels, and thus the eggs
are placed out of the reach of enemies.

We may now turn our attention to that vast
majority of fishes which neither build nests nor,
in the majority of cases, show any sustained
regard for their progeny, save only a certain
caution in the selection of the site for the deposi-
tion of the eggs, which suggests but little more
than a kind of obedience to custom. That there
is something more than this at work we must,
however, feel convinced when we come to review
the facts which have been gathered together on
this subject. There seems to be ample proof
that the parental instinct is by no means slug-
gish, and that the deposition of the eggs is often
only accomplished after the severest obstacles
have been surmounted.

The eggs of the lamprey, which we distinguish
by the scientific name of Petromyzon marinus, are
very tiny, and enclosed in jelly-like membranes.
But the eggs of the allied forms, Bdettostoma and
Myxine, are quite different. In the first place,
they are very large and cocoon-shaped structures.
Furthermore, they are remarkable for the fact
that at each end of the egg there is a bundle of
thread-like processes terminating in little hooks.
These hooks are for the purpose of interlocking
with the corresponding processes of other eggs,
and with sea-weed at the bottom of the sea.

The eggs of the sharks, and rays or skates,
must be familiar to all, since those of the skate,
at least, are commonly to be seen strewn along

112 THE STORY OF FISH LIFE.

the beaches of our shores, and are known as
" mermaid's pinboxes." They may be likened to
padded stretchers, being oblong in form, with the
corners produced into four short handles. Some-
times these will, if opened, be found to contain a
young skate comfortably stowed away inside.
The eggs of the dog-fishes resemble those of the
skate, but the four handle-like processes are
much longer, and serve as anchors by twisting
round sea-weed. The egg of the Port Jackson
shark, Cestracion, is quite remarkable, being
cone-shaped, and encircled with a broad spirally-
twisted fold running the whole length of the egg.
The egg of the chimera (Callorliynchus), an ally
of the sharks, is perhaps the only egg with a
mimetic resemblance to foreign an object. It is
elliptical in form, and bordered by a fringe, so as
to give a close resemblance to a piece of sea- weed.

Amongst the more highly specialised bony
fishes, the dominant form .j of the present day,
the eggs may either be enclosed within a horny
capsule, as in the sharks — though the form and
size of the capsule differs — or are quite un-
protected.

The blennies afford us an instance where the
eggs are enclosed within a horny capsule. This
capsule is attached by its base to sea-weed or
other fixed object, till the young hatches out.
The eggs form little clusters of small, upright,
and somewhat pear-shaped bodies.

Sometimes, as in the case of the fresh-water
perch (Perca fluvialilis), the eggs are invested by
a gelatinous envelope of a viscid nature, causing
the eggs to stick together in masses. These

COURTSHIP AND NURSERY DUTIES. 113

masses take the form of long tube or net-shaped
bands, which are deposited on, and adhere to,
water-plants at the bottom of the stream. It is
interesting to remark that, rope-like masses of this
kind are also laid by the common toad. The
eggs of the fishing-frog (Lophius piscatorius) are
similarly invested by a gelatinous outer coat, and
form a floating sheet of from 60 to 100 square
feet. Floating masses such as this are rare
amongst fishes. The eggs of the herring are
laid comparatively near land, and in masses.
They are viscid externally, and adhere to any
object with which they may come in contact on
the sea-bottom.

In the plaice and cod-fish and the allied species,
the eggs are buoyant, and laid in enormous num-
bers at a variable distance from shore. They
float just below the surface, and drift accordingly
at the mercy of wind and tide.

The size of the egg depends probably upon the
number; and the number varies probably as
the risks to which they are exposed. How
variable the number may be we may gather from
the fact that in the closely allied members of the
lamprey tribe, Myxine and Lamprey, the former
lays probably not more than 30, the latter about
30,000. The sturgeon lays about 7,000,000 ; the
herring about 25,000 ; lump-fish, 155,000; hali-
but (which lays a relatively large egg), 3,500,000;
cod-fish, 9,344,000; ling, 150,000,000.

The number of the eggs deposited by each par-
ticular species of fish, it has just been remarked,
depends largely upon the risks from destruction
to which they are exposed. These risks are
H

114 THE STORY OF FISH LIFE.

greatest, obviously, in the case of pelagic eggs,
i.e. eggs deposited far out at sea, and which are
left, untended, to drift about at or near the
surface, at the mercy of wind and tide, or rather
current. Countless as may be the eggs of, say,
the cod or ling, thousands and thousands must
perish from one cause or another long before
hatching ; they will have served as food for other
fishes, or been borne away by adverse currents
and cast ashore ; change of temperature will
exterminate many more, and so on. Professor
G. 0. Sars has recorded cases in which myriads
of cod's eggs have been thrown up on to the
beach, forming a long glistening line at high-
water mark.

Many fishes have succeeded in escaping these
manifold dangers by fixing their eggs to seaweed,
or rocks at the bottom of the sea. Many of these
demersal, or deep sea eggs, are also, however,
subjected to a heavy tax. They are accordingly
produced in great numbers, for though the danger
of being carried away in adverse currents has
been insured against, there is still provision to
be made against the depredation of other fishes.
Thus the spawning herrings are followed by
countless shoals of haddocks, all greedily con-
testing for the newly-shed spawn. And to these
natural enemies must now be added man himself,
who, with the deadly trawl-net, sweeps away tons
of eggs yearly.

Those fishes, it will have been remarked, which
guard their eggs, either by placing them in a
nest, or carrying them on the body, lay but few
— comparatively few — for these have eliminated

COURTSHIP AND NURSERY DUTIES. 115

the dangers that threaten pelagic and demersal
eggs, and need only provide against accidents at
the hands, or rather mouths of carnivorous neigh-
bours in the immediate neighbourhood.

Many marine fishes leave the crowded sea, and
its innumerable dangers, to seek safety for their
offspring in rivers. Such, for the most part, retain
the old pelagic habit of leaving the eggs uncared
for, consequently they are produced in large
numbers to resist the inroads made upon their
numbers, and upon the young fry, by enemies of
all kinds. What these inroads are like we shall
show in the next chapter.

The salmon is one of the best known instances
of a marine fish which ascends rivers to deposit
the eggs. Considerable care is manifested in the
disposal of these. They are laid in a rough sort
of nest called a redd. This is trench-like in form,
and made by the female, in exactly what way
seems uncertain, but apparently by ploughing
out the gravel — the soil always chosen for this
purpose — with the under surface of her body.
The eggs, which are large, are deposited herein a
few at a time ; and after having been fertilised
by the male, become heavier, and sink to the
bottom of the trench. Being somewhat sticky
externally they adhere to the bottom, and are
then lightly covered over with gravel and left to
hatch. The loose gravel soil allows a complete
aeration, necessary for the development of the
egg. The burying of the egg is a precaution
against the raids of birds and other fishes, which
greedily devour these exceedingly delicate and
nutritious tit-bits.

116 THE STORY OF FISH LIFE.

The life-history of the salmon has been vividly
sketched by Mr Rooper, from whom we append
the following details : —

" Arrived on the spawning-ground the female,
then called a baggit, alone proceeds to form the
nest, or 'redd/ as it is termed. This she effects
by a sort of wriggling motion of the lower part of
her body working in the loose gravel. . . . The
redd, a deep trench, being formed, the female
proceeds, attended by the male fish — frequently
by two kippers, as they are then called — to
deposit her eggs. This she does, not all at once,
but in small quantities, at intervals, frequently
returning to the redd for the purpose. The eggs
are at once fecundated by the melt of the kipper,
this process going on for two or three days, the
fish sinking down occasionally into the pool below
to rest and recover their strength. The effect of
fertilisation of the ova is to add greatly to their
specific gravity; the eggs sink, and are at once
covered with gravel by a similar motion on the
part of the baggil to that used in the formation
of the redd. Here the process being completed,
the eggs remain during a period of from one
hundred and twenty to one hundred and forty
days, according to the temperature of the water.
At the expiration of that time the little fish come
into existence, and, after a few days, wriggle out
of their gravelly bed, and seek refuge under an
adjacent rock or stone, where they remain in
safety for some twelve or fourteen days longer.
. . . Buckland calculated that the number of
eggs laid by a salmon was about one thousand to
the pound weight, a fish of fifteen pounds, there-

COURTSHIP AND NURSERY DUTIES. 117

fore, producing fifteen thousand eggs. . . . After
spawning, the fish speedily recover their colour,
and to a great extent their condition ; the baggit
at once losing her dark complexion, and the
kipper discarding his hideous livery, his great
beak being rapidly absorbed, his sides becoming
silvery, and his back assuming a dark bluish
tinge."

Pelagic eggs, as we have already remarked, are
carried about by the drift of currents. In these
currents we may distinguish two kinds, acci-
dental and purposeful. By the former, eggs are
seized and borne away to ultimately perish ; by
tLe latter, they are gradually carried to a region
favourable to development, and to the require-
ments of the larval fish. The plaice affords us
an instance of the nature of pelagic eggs, and
their dependency upon favourable currents.
These fish lay their eggs far out at sea, whence
they slowly drift shore wards, meanwhile develop-
ing. By the time they have reached the shallow
water bordering the shore the young fish have
hatched-out and remain in this shallow water for
some considerable time, when they slowly move off-
shore into deep water. The precise movements
of pla'ce have been carefully studied, and some
very important facts have come to light. It has
been shown that the eggs of the plaice laid off
the east coast of Scotland drift southwards and
shorewards till hatching time. The larva then
slowly move northwards along the coast, and
then outwards to sea as they reach maturity, to
lay their eggs in turn. Thus the breeding area
is kept constantly stocked.

118 THE STORY OF FISH LIFE.

It is to this sojourn by the shore that most of
us owe our acquaintance with the living plaice,
sole and flounder. For it is not the lot of many
to " go down to the sea in ships and see the
wonders of the deep '' — at least, not the kind of
ship that goes wonder-catching. The young fry
which make their nursery off our coasts are
caught in hundreds in the "long-shore7' nets,
which are assiduously worked throughout the
summer months from favourable spots wherever
they occur. Who has not watched, arid with
something of infection too, the groups of excited,
bare-legged, holiday-making youngsters, as they
seize upon the poor little wriggling and flopping
victims, tossed contemptuously out of the nets as
" rubbish7' by the brawny and thoughtless grey-
beards, who earn their daily bread — and not much
more — by the continual effort to catch the bigger
fish in the sea than they ever succeed in getting
out of it 1 What reckless waste ! It is time
that some form of instruction, say by means of
simple lectures, was instituted to show these
same grey-beards — and youngsters too — who
do but transgress in ignorance, how tenderly
and speedily these young fry should be rescued
and restored to the sea : for our food supply is
being sorely tapped by the present wasteful
fashion of leaving them to die upon the beach.

As Mr Masterman remarks, in writing of the
cod's eggs : "It is evident that, for the successful
development of the young fish a concatenation
of favourable circumstances is necessary, which
depends in the main upon such essentially fickle
phenomena as wind and temperature. Let the

COURTSHIP AND NURSERY DUTIES. 119

wind blow shorewards with abnormal strength
and duration, and untold millions of unhatched
cod may perish, or let the temperature, for a few
weeks during the summer months, be abnormally
low, and the same fate may overtake hosts of
embryonic gurnards. Under such conditions it
is only by the selection of suitable spawning-
sites, a prolongation of the spawning-time (on
the principle of not putting all the eggs in one
basket), and other devices, that the pelagic spawn-
ing fishes have held their own."

The floating, or pelagic eggs, it is interesting
to note, are provided with an oil globule which
serves to diminish their specific gravity. But it
would seem that under certain conditions, as yet
unexplained, the specific gravity of pelagic eggs,
relative to sea-water, may undergo sudden changes
resulting in a sinking or rising. Thus eggs
which normally are found only floating at the
surface, may occur floating some distance below
this, in mid- water, or deeper, even on the bottom.
In the Baltic, according to Mr Masterman, " the
eggs of the plaice have been found far below the
surface, floating underneath the stratum of
brackish water." The eggs of the common eel
again, which are deposited in the deep sea in
250 fathoms of water, remain suspended in the
water at that depth, and there hatch (see
p. 129.)

One of the gobies (Latrunculus pellucidus),
common on the coasts of the British Islands,
is remarkable for the fact its whole life's course
is run in a single year. In June, July it deposits
its eggs, these hatch in August, by December the

120 THE STORY OF FISH LIFE.

young have attained their full development. At
this period both sexes are alike, having very
small teeth, and feeble jaws. In April, however,
the male loses his small teeth and replaces them
by very long and strong teeth, and with the
advent of these new teeth increases the size of
the jaws. The teeth of his mate remain un-
changed. July and August sees the death of all
the adults, so that in September only young fry
are to be found. Thus in this goby we have at
least one instance of an annual vertebrate. The
fifteen-s pined stickle-back (Gasterosteus spinachia)
is said likewise to run its life's race in the course
of a single year.

Some other fish appear to spawn but once and
then die, but these take more than one year to
come to maturity. The eels appear to belong to
this category.

CHAPTER X.

LARVAL FISHES AND THEIR METAMORPHOSES.

FISHES are born into the world in what is called
a larval condition, that is to say, in a condition
differing more or less from that of the adult,
which is only reached after a series, of frequently
well-marked, stages or transformations. Larval
vertebrates only occur amongst the fishes and
amphibia — the frogs and toads and their kindred :
but amongst the invertebrates we have quite a
large variety of larvae. The caterpillar is a
larval form with which every one must be

LARVAL FISHES : THEIR METAMORPHOSES. 121

familiar. Marine " worms," star - fishes, sea-
urchins, " shell-fish," and crustacea-crabs and
lobsters and their kind, furnish us with many
most curious and often wonderful and com-
plicated larval forms.

When we come to reflect upon this matter a
little, we remark that Iarva3 are characteristic of
those animals which lay small eggs, whilst those
which lay large eggs produce young which re-
semble the parents in all respects save size and
perhaps colour, or other minor details.

But what has the size of the egg to do with
the matter1? Just this. That which we know
as the egg, the hen's egg for example, contains
within the familiar shell two very important
parts — the germ which is to develop into the
chick, and a large store of food material, which
we call the yolk. The amount of this yolk in
the bird's egg is, relatively to the size of the
germ — enormous; quite sufficient, indeed, to
support the developing chick for a comparatively
long period. By the time this yolk is all absorbed
the development of the chick is almost complete,
little more than increase in size being now
necessary. The eggs of fishes, on the contrary,
never contain much yolk, only sufficient to sup-
port embryonic development — as opposed to
larval development — for a short time. So soon
then as this yolk is all absorbed embryonic de-
velopment ends, and the larval development
begins. The larval development often begins so
early that special or temporary feeding and loco-
motory apparatus have to be introduced to serve
whilst the permanent organs are being built up.

122 THE STORY OF FISH LIFE.

This is well seen amongst the invertebrates.
With the vertebrates changes of this kind also
occur, but not on quite so marked a scale. As
Prof. Miall has aptly put it, the choice between
embryonic or larval development depends " upon
the number of the family and the capital at
command. These are animals which are like
well-to-do people who provide their children
with food, clothes, schooling and pocket-money.
Their fortunate off-spring grow at ease, and are
not driven to premature exercise of their limbs
or wits. Others are like starving families,
which send the children, long before their
growth is completed, to hawk matches or news-
papers in the streets. "

The young fish then, being the product of a
small egg, ill- provided with nutritive yolk, comes
into the world in a larval condition. The precise
form of larva may be described as the tadpole-
larva, and it is interesting to note that this form
is common to larvss lower in the scale than the
fishes — to wit, those remarkable creatures which
lie in the borderland between the vertebrate and
invertebrate — the ascidians or sea-squirts; and
the larvae higher in the scale, the amphibia, such
as the frog and toad or the newt, for example.
The tadpole in its simplest form is a long-tailed
animal strengthened by a kind of fibrous rod
running down its body from the head to the tail,
immediately below the spinal cord. It breathes
by gills, and has a mouth in the form of a suck-
ing disc. "It is a cheap form of larva,77 says
Prof. Miall, " when reduced to its lowest terms,
requiring neither hard skeleton, nor limbs, nor

LARVAL FISHES : THEIR METAMORPHOSES. 123

neck, yet it can move fast in water by means of
its sculling tail."

In more than one instance these larvse have
been mistaken for adult species, their immature
condition being unsuspected.

A case in point illustrating this is afforded
by one of the lowest of the fishes — the fresh-
water lamprey (Petromyzon planeri). For a long
while the young of this was regarded as a dis-
tinct species, the ammocetes. Its true nature
was discovered by a German ichthyologist, Aug.
Miiller. The young ammocetes, like the typical
tadpole larva of our text, has a sucker-like mouth
devoid of teeth, and in many other respects
differs from the adult form. It is further re-
markable in that the full-grown larva may even
be larger than the adult ! Its larval life is a
very prolonged one, lasting often as long as five
years. Its transformation into the adult form
seems to be as sudden as it is radical. Amongst
the more important of these changes are the
introduction of conical horny teeth, and the de-
velopment of the eyes, which in the larval form
lie beneath the skin, like those of the young of
many of the higher vertebrates, e.g. : the cat, dog
and rabbit. Changes in the form of the skeleton,
of the gill-pouches, and of the alimentary canal
and kidneys also take place, and are changes of
great significance. We might mention here that
the adult life of the lamprey is very brief, and
terminates directly after the deposition of the
eggs or sperms, as the case may be.

The sucker-like mouth, or suctorial mouth, as
we may more conveniently call it, is a feature of

124 THE STORY OF FISH LIFE.

great importance, and occurs in a considerable
number of the larvse or embryos of the lower
vertebrates. When the mouth itself is not
directly suctorial, as in the lamprey which we
have just discussed, it is associated with a more
or less well-developed suctorial disc. For in-
stance, in the tadpoles of the frog, there is a disc
of this nature situated behind — tail wards — of
the mouth ; in the larval lepidosteous, or bony
pike of America, there is a similar disc in front
of the mouth. The larval ascidian, or sea-squirt,
has an adhesive disc, also situated in front of the
mouth. Traces of this disc appear in the young
sturgeon. It is believed, from these facts, that
the ancestral vertebrates probably all had the
mouth bounded by a suctorial disc, which is there-
fore a primitive organ of some importance. Of
this disc a part only is developed in modern
larvae or embryos, which may be either that part
bounding the front of the mouth, or that behind
— tail wards — of it. Furthermore, the mouth
itself was also probably suctorial in character,
like that of the young lamprey ; later, it became
further modified for biting purposes and de-
veloped jaws. The function of the disc is for
the purposes of attachment to weeds or other
object?, while the larva is at rest. The action of
these discs can be readily studied by anyone who
will take the trouble to collect a few young tad-
poles from the nearest pond during the spring
months. Artificially hatched, "bony-pike" all
attached themselves to the sides of the glass
vessel in which they were placed, by their discs.
The young sea-squirt soon after hatching attaches

LARVAL FISHES : THEIR METAMORPHOSES. 125

itself to a rock by this disc, and remains fixed
whilst it undergoes the very extraordinary and
remarkable changes which ultimately end in its
transformation into the shapeless mass from
which the adult form takes its name. The
curious tactile organs or barbels, described else-
where, are probably structures arising from the
modification of this disc. The larval sturgeon
shows how this has came about.

We may turn now from the mouth to a con-
sideration of the gills of the larval fish, since in
these we have again characters which are shared
in common with their allied but less humble
relatives, the amphibia. In the young shark,
and, to a certain extent, the sturgeon, and in the
young bony-pike (Lepidosteous) mud-fish (Pro-
topterus), and " bichir " (Polypterus) fig. 3, p. 26,
the breathing organs or gills, like those of the
larval frog or newt, take the form of more or
less branched or feather-like organs, the branches
springing from a common shaft, or of delicate
filaments projecting from the gill-slits.

It is to be noted, however, that it is the so-
called " ganoid-fish " and lung-fish larva which
most nearly resembles the amphibian : the deli-
cate filamentary gills of the shark, it is believed,
probably represent secondary and not primary
structures. These gills are in all cases but tem-
porary outgrowths, being replaced in the fishes
either by internal gills — which have already been
described (p. 20) — or by gills and lungs, e.g. :
lung-fishes, or by lungs only, e.g. : amphibia.
These permanent breathing organs, it appears,
require time for growth, hence the temporary

126 THE STORY OF FISH LIFE.

structures which gradually become absorbed in
proportion as the permanent structures assume
their duties. In the case of some of the
amphibia, e.g. : the axolotl of Central America, the
larval condition — and hence the external gills
also — is rarely exchanged for the adult form, all
the functions of life including the reproduction
of the species being fulfilled by the larva. The
young of the higher (Teleostean) fishes never
produce external gills.

Besides the suctorial mouth disc and the ex-
ternal gills, we have yet another larval character,
one which not only carries us back to, but
actually connects the larva with, the egg itself.
The larval condition, as we have already re-
marked, is consequent upon the fact that the egg
from which the young is produced contains only
a limited amount of food material insufficient to
enable the growing embryo or unhatched fish, to
complete its growth into a fully formed fish. For
this reason, as soon as the process of hatching
has become an accomplished fact, certain tempo-
rary structures have to be developed in order that
the processes of further development may be
completed. The nature of some of the more
important of these temporary structures we have
just discussed. Some of them undergo further
transformation and development into adult struc-
tures, and some are purely larval organs and are
put away with other childish things, if we may
be permitted the metaphor, when the adult stage
is reached. The newly-hatched young of the
shark tribe will best bring home the nature of
the relation between the larva and the egg.

LARVAL FISHES : THEIR METAMORPHOSES. 127

Fishes of this kind, often for several months
after they leave the egg-shell, bear about with
them a very considerable amount of the remains
of that portion of the egg which constitutes what
is called the food yolk, in a flask-shaped bag with
a long neck, attached to the under surface of the
body (fig. 11). The mouth of this flask opens into
the intestine, and thence the contents of the bag
pass up into the gut
as required. At least
this is the state of
things at first ; later
the connection with

the gut is CUt off, and FIG. ll.— A larval dog-fish.

the last remains of
the yolk are absorbed by the blood-vessels alone.
Why this curious method of absorbing the yolk
should be, depends upon the very extraordinary
fact that, the gullet or food-pipe, at first quite
tubular, later closes up and becomes quite solid,
so that all swallowing becomes absolutely im-
possible. During this period the advantage of
the pendant yolk-sack in open communication
with the gut is obvious. Its absorption later,
after the reopening of the proper food passage by
the blood-vessels, is as much a matter of con-
venience as for the sake of nourishment. The
explanation which has been given to account for
this curious closure of the gullet cannot be dis-
cussed here. In other larval fishes, such as luug-
fish, " ganoids," and the higher " teleostean "
forms, of which we may instance the salmon,
perch or cod-fish, the yolk-sack is relatively
smaller and packed away beneath the body, not

128 THE STORY OF FISH LIFE.

pendant as in the shark, but the same curious
history with regard to the closing of the gullet is
repeated here.

This matter of the relation between the larva
and the egg is somewhat of a digression, albeit
necessary. Besides the circular suctorial mouth
disc — which, however, as we have seen, may be
represented only in part, either by that portion
in front of, or behind the mouth, or more primi-
tively still, by a suctorial mouth — and the
external gills, our larval form is conspicuous
for the absence of limbs, and the presence of a
long tail fringed by a delicate membrane, the
tail-fin. This tail is the only organ of propul-
sion. Such a form is one of peculiar interest, and
of first-rate importance, since it is characteristic
of many very different, and only distantly related,
animals. Occurring as a phase in the life history
of the tunicates or sea-squirts, fishes and amphibia.
This fact is regarded by scientific experts as a
reasonable proof that these early stages, common,
to such different forms, represent the primitive
vertebrate model out of which all the vertebrata
have grown by gradual modifications, and
transformations. The nature of these trans-
formations we have already hinted at. Thus,
to take the breathing-organs. These are first
represented by external gills, which are gradually
replaced by internal gills, whose duties are in
great part transferred, in some fishes, to still
more internally removed respiratory organs,
which we call lungs. In the frog tadpole ex-
ternal and internal gills each in turn pass away,
.and are completely and slowly supplanted by

LARVAL FISHES : THEIR METAMORPHOSES. 129

lungs, whilst the internal gill supports become
modified to serve as supports for the tongue. In
the higher vertebrate, for many reasons into which
we cannot enter now, the gill-breathing stage is
entirely suppressed, but even in man himself the
gill-slits and arches still appear during the early
stages of his development. Out of these last
indeed, as in the frog, the supports for the tongue
are made. The nature of the transformations
and modifications which give rise in turn to
continuous fin-folds and fins, and the gradual
evolution of the latter into walking limbs, for
the support and carriage of the body on land, we
have already sketched in an earlier chapter.

So much for the typical and primitive larval
stages. Let us now turn to some of the more in-
teresting of the stages through which some larval
fish pass, on their way to the adult condition.
Perhaps one of the most remarkable of these is
that of the young of our common fresh-water
eel.

Until quite recently the early history — the
babyhood, so to speak — of the common eel was
enshrouded in mystery, and was regarded as a
zoological puzzle which would reveal itself in
due time. Some, anxious to hasten this longed
for time, allowed their imagination to carry
them beyond the sure grounds of fact into the
domains of romance ; or, at any rate, setting aside
all caution, they gave full vent to fancy, with the
result that fact and fiction were woven together
with dire results to truth. The outcome of this
unholy combination (in science) was a theory to
the effect that eels were developed from horse-
I

130 THE STORY OF FISH LIFE.

hair, which dropped into the water from the tails
of horses when they came to drink. After long
soaking they became endowed with life, and
turned into worms. These worms, almost hair-
like in thinness, were known as " hair-eels," and
they in course of time completed the wondrous
transformation by developing into true eels !

There never was a mystery but some one was
ready with an explanation. The above effort to
throw light in a dark place was regarded as
quite satisfactory by people of not so very long
ago. In that explanation we see now a sug-
gestion of that love of the fantastic, and the
wonderful, characteristic of the older generations.
A readiness to accept any hypothesis that pre-
sented itself without much question or demand
for credentials. But, as in so many other
instances, there is an element of truth per-
meating this untruth. This truth is represented
in so much as concerns the hair-eel. The
"hair-eel" belongs to a group of commonly
parasitic nematoid worms, the early stages
of existence of which are passed within the
bodies of aquatic insects, from which they
ultimately emerge to pass the adult condition as
free-swimming organisms. In this adult con-
dition the males at least bear a very remark-
able resemblance to horse-hair, being very
slender, hard, and shining black in colour.
Now, in the days when men believed that life
could be engendered from non-living matter,
given favourable conditions, there seemed no
reason to doubt but that horse-hair might
become, by sufficiently prolonged soaking,

LARVAL FISHES : THEIR METAMORPHOSES. 131

transmuted into its living prototype, the "hair-
eel," and this, by continuous growth, might in
turn become the true eel. When the belief that
non-living matter could, under certain con-
ditions, beget living organisms, was shown to
be untenable, the source of origin of the common
eel became more mysterions than before. And
a mystery it remained until the year of Grace
1864. In that year Mr Gill read to us the riddle
of all the ages, at least since Aristotle. He showed
us that some forms at least of certain curious, rare
and very delicately framed fishes, which had long
been a stumbling-frock to scientists, were none
other than the long-sought-for larval eels. They
had already received the name of Leptocephali,
but were regarded as monstrosities, the victims
of uncongenial surroundings. Thus Dr Giinther,
one of the most profound authorities of our time
on all matters pertaining to fishes, wrote of
them: "We must come to the conclusion that
the Leptocephalids are the offspring of various
kinds of marine fishes, representing not a normal
stage of development (larvae), but an arrest of
development at a very early period of their life ;
they continue to grow to a certain size without
corresponding development of their internal
organs, and perish without having attained the
characters of the perfect animal." A year after
this was written Dr Giinther himself was enabled
to add further confirmation of Mr Gill's discovery.
But it was not till 1896 that certain Italian
naturalists, by a very careful and exhaustive
study of a large series of Leptocephalids were
enabled to establish beyond fear of dispute, that

132 THE STORY OF FISH LIFE.

these remarkable and puzzling fish were larval eels
— not only of fresh water, but marine forms also.
These larvae, furthermore, brought to light some
very extraordinary facts, one of the most impor-
tant of which concerns the law of growth. Thus
they go on increasing in size and favour daily, up
to a certain point, when they actually begin to
grow backwards, that is to say, they decrease in

size from day

to da7uP *oa
certain point,

then growth
recommences;
with this new
growth they
assume the

FIG. 12.— Fish Transformations. A. B. C. Three i

stages in the life history of the Eel : showing Characteristic

the gradual decreasein size as the fish grows rnnnrl PP! li
older. With the decrease in size the eel-like Uj cc

shape is gradually acquired. At C. the mini- form, ascend

mum decrease has been reached. The young t flin OITT»

fish has now reached the "Elver" stage and L(J tllt3

ascends rivers to complete its growth into the face of the
adult eel. i

sea, and in

the case of the fresh- water species, make their
way with all speed up the rivers, in which
journey we shall follow them in the next
chapter (p. 144). The accompanying figures give
an indication of the delicacy and transparency
of these fish at this early stage, the internal
structures in the living larva being quite dis-
tinct (fig. 12). The curious changes in the rate
of growth and the small size of the head, very
striking features of the larvae at this stage, are
also well brought out in the figures. When a
Leptocephalas has completed the first stage of

LARVAL FISHES : THEIR METAMORPHOSES. 133

its growth it ceases to feed, and thereby loses
considerably in bulk. At the same time it
develops what has hitherto been lacking — pig-
ment or colouring matter, then it discards its
larval teeth, and replaces its soft membranous
backbone by a series of hard and complicated
bones. Much of what these Italian naturalists
have told us was the result of direct observa-
tions of living specimens kept in an aquarium .

The manner of capture of these Iiving4fish
is curious. The majority are procured from
the Straits of Messina by a series of fortu-
nate accidents, which are constantly repeated.
These " accidents" are due to the fact that
mighty currents every now and then boil up
in the narrow straits, bringing with them
the strange inhabitants of these unexplored
regions — eggs, larvae and fishes of many kinds,
besides other forms of animal life. But besides
this there is yet another source from which
Leptocephali are obtained ; one of these is,
curiously enough, from, the stomach of that
grotesque monster the sun -fish (Orthagoriscus
mola) ; another way is by dredging.

It is certain that there can be few fish with
which we are more familiar than those which we
know as "flat- fishes" — the sole, plaice, turbot,
halibut, and flounder tribe. Yet, probably few
people have any idea of the wonderful course of
events which leads to the characteristic "flat-
fish" shape. Into this shape then we must look
a little more closely. To begin with, the familiar
"dark "side and "white" side do not represent
the dorsal and ventral aspects of the animal.

134 THE STORY OF FISH LIFE.

That is to say, they do not represent the back
and the belly, but the right and left sides. In
some fish it is the right side which is upper-
most, in some the left. When the fish swims it
does so by an undulatory motion of the body ;
that is to say, progressing by means of wave-like
movements passing from head to tail. But it
does not swim vertically, but retains the position
which it holds when at rest — the dark side being
kept uppermost. Another point about the adult,
which we shall appreciate now, is the fact that
the eyes are not on opposite sides of the head,
but lie side by side on the upper surface. How
this comes to be, and how it is that the fish comes
to lie always on one side or the other, we may
discover from a study of the larval fish. This,
when it emerges from the egg, is perfectly sym-
metrical, and gives all promise of developing into
the typical fish-like form. Soon, however, a
change becomes obvious, for there is a marked
tendency to lie at rest on one side, right or left,
which becomes more and more pronounced daily.
Simultaneously with this new position, the left
or right eye begins to migrate from what is now
fast becoming the under to the upper sicle, and
the attainment of this end is accomplished at the
expense of the symmetry of the skull, which
eventually, with the complete migration of the eye
to the upper surface, becomes quite asymmetrical.
The reason for the really wonderful transforma-
tion exhibited by the young flat-fish is one of
nature's mysteries which no one has yet succeeded
in solving.

But eels and flat fish do not exhaust the list of

LARVAL FISHES : THEIR METAMORPHOSES. 135

transformations to be found amongst the fishes,
though in these two particular instances we have

FIG. 13.— Three stages in the development of the Sword fish
(after Giinther).

the most interesting of them all. The signifi-
cance of transformations is in some cases more
or less obvious and intelligible ; but as often as

136 THE STORY OF FISH LIFE.

not we have to rely mainly on conjecture in
endeavouring to find an explanation of their
meaning. In some cases it would indeed seem
as if the now almost discarded recapitulation
theory received some support. That many of
the phases of these transformations have a
direct relation with the past there can be no
doubt ; on the other hand, many are as certainly
special adaptations belonging to, and necessary to,
the particular phase in which they appear. An
exceedingly instructive series of stages in develop-
ment is shown in the life history of the sword-
fishes. The young of Histiophorus, of the Pacific
and Indian Oceans, has been beautifully illustrated
by Dr Giinther, and these figures, by his kind
permission, have been reproduced here (fig. 13).
In the first stage, a fish of 9 mill, long, it is to
be noted that the jaws are of equal length and
both bear teeth ; above the eye is a series of short
bristles ; from the back of the head project, above
and below, long pointed spines. The dorsal fin
is long and low, the pectoral fin large and trun-
cated, whilst the ventral fins are represented
only by tiny buds. In the next stage, a fish of 14
mill, long, the dorsal fin has increased enor-
mously in size, whilst the spines projecting from
the back of the head are relatively shorter ; the
bristles above the eye have vanished ; the upper
jaw has grown slightly longer than the lower ;
the ventral fins, represented previously by buds,
have now increased to long slender filaments ; the
pectoral fin has changed its shape, and the pre-
operculum or gill-cover has increased greatly in
size. In the third stage, a fish of 14 mill, long, the

LARVAL FISHES : THEIR METAMORPHOSES. 137

dorsal fin has developed unequally, dividing the
whole into two distinct parts, an anterior of great
size and a smaller posterior ; the upper jaw has in-
creased so as to project considerably beyond the
lower, whilst the teeth have disappeared ; the
long spines from the back of the head have
almost vanished, whilst the ventral filamentous
fins have become reduced in size. In the eye
there is a conspicuous relative decrease in size
from the earliest stage onward. The great size
of the eye is a feature of all vertebrated animals,
during the embryonic stages of their growth at
any rate.

The young of the sun-fishes again present
some very remarkable features — of which there is
no indication in the adult forms — so much so that
these young have been described as of distinct
genera. The main features which characterise
them at this period is a series of sharp spines
projecting in all directions all over the body.
The adults are either smooth-skinned or covered
with minute prickles, according to the species.
Similarly, the young of one of the flying-fishes
(Dadylopterus), of the sea-perch (Serranus), the
" rockling " (Motella\ and some others have passed
unrecognised, and have also been described as
distinct genera, their identity being so completely
masked.

The young of the ribbon-fish (Trachypterus) are
remarkable for the very extraordinary develop-
ment of the fin-rays, exceeding that of any other
known fishes ; sometimes their fin-rays are many
times longer than the body ; moreover, these fin-
rays are provided with curious lappet or flange-

138 THE STORY OF FISH LIFE.

like dilatations. The great length of these
fin-rays shows that these fish are hatched far
down in the depths of the sea, where absolute
stillness prevails, the currents such as prevail at
the surface would wreak ruin on such fragile
structures at once.

A most remarkable trait in the life history of
larval fishes is that exhibited by the young of the
sand-smelts (Atkerina), which, for some time after
hatching, cling together in dense masses and in
enormous numbers. It is said, by the way, that
that peculiarly larval and archaic type, the
Amphioxus, occasionally forms a swimming chain
by uniting one with another by their mouths.
This is the only other instance I can recall com-
parable to the masses of young fry of the
sand-smelt.

CHAPTER XL

MIGRATION AND HYBERNATION

THE migratory impulse seems to be as strongly
developed in the fishes as in the birds. In no
other vertebrates, indeed, save these two classes,
do we find these periodic movements so well
marked. This is probably due to the peculiar
facilities oifered either by air or water for ex-
tensive journeys under fairly uniform conditions.
Barriers such as confront non-flying terrestrial
animals being absent.

Migration with both bird and fish is generally
associated with the provision for the next genera-

MIGRATION AND HYBERNATION. 130

tion, but whilst in the former it seems to be due
to the need of securing a certain and suitable
food supply, in the latter it appears to be rather
the need of securing a larger amount of protec-
tion for the offspring. In this solicitude, if we
may call it so, for the preservation of the species,
many fishes have succeeded in passing what
proves an insuperable barrier to most — to wit,
the passage from salt water to fresh, and vice
versa. Surface temperature, however, and climate
present an additional barrier to many fresh water
fishes, preventing their further movement even
if they could survive the transition into salt
water. That is to say, a fish which might sur-
vive this exchange of medium, would succumb
to the effects of changed temperature. Salt
water fishes do not appear to be so deeply
affected in this matter.

In addition to this orderly and periodic migra-
tion, in which shoals of countless millions are in-
volved, we have a form of what we may call sporadic
migration — many marine fishes individually as-
cending rivers for hundreds of miles of their
course, whilst many fresh water fishes similarly
descend into the sea, though these are fewer in
number. This passage from fresh to salt water is
often very gradual, broken by a longer or shorter
sojourn in brackish water, but in some cases (as
in the common stickle-back) the transition may
be quite sudden without producing any injurious
results. Migration of this kind is not associated
with any known cause. The exchange from a
salt to a fresh water habitat may have been
to avoid competition in the more crowded sea ;

140 THE STORY OF FISH LIFE.

to this exchange we owe the preservation of
some very interesting and archaic forms, such
as the bony-pike (Lepidosteus), bichir (Polyptents),
and barramunda (Ceratodus), for instance.

There can be no doubt but that fish life
originally commenced in the sea, and spread
thence to the brackish and fresh water by a
series of sporadic migrations such as we have
just instanced. Possibly this migration was due
to pressure and competition amongst the species
involved in this migration, just as amongst our-
selves, overcrowded populations seek relief by
emigration.

The causes of the migration of the mackerel
seems to be an exception to the rule suggested —
that migration in fishes is probably due to the
desire to secure a safe harbourage for the young
fry. Mackerel swim in shoals, and spawn in
the open sea. Periodically, however, they ap-
pear off shore, apparently, as Dr Gunther sug-
gests, in pursuit of other fishes on which they
feed. They prey upon the young and adults of
the herring-tribe, the pilchard and sprat. These
guide the movements of the mackerel.

The perils of the migrating adults of such
species as the herring or sprat, for instance, are
many, for not only are they subjected to an
unceasing attack from hordes of their predaceous
relatives, but toll is taken by numberless others
besides, such as "schools" of porpoises, and
countless flocks of birds, who seize them from
above. Besides these we have to reckon the
millions captured annually by our fishing-fleets.
In spite of all this persecution, wonderful though

MIGRATION AND HYBERNATION. 141

it be, the herring, for instance, still holds its
own.

In studying migratory movements many facts
have to be kept in sight, and a close watch has
to be placed on the migrants in order that we
may discover, if possible, whether, there is
any return of those fishes which move to some
distant spot for the purpose of depositing their
eggs, and what, if any, changes are under-
gone in the appearance of the pilgrims during
their journeys to and fro. Some of the more
interesting of the details of this aspect of the life
history of fishes will be discussed now.

The migration of the salmon may fittingly
come first under consideration, and illustrates the
migration from salt into fresh water, of which
we have already hinted. The efforts which the
salmon makes to gain the upper waters of the
rivers they ascend may often be truly described
as Herculean. Kapids, even of six feet high,
they surmount by leaping, trying again and again
until successful (see frontispiece). In some of
the Scotch rivers artificial stairs have been con-
structed in order to enable them to overcome
some of the otherwise unsurmountable barriers.
" Excelsior" seems to be the salmon motto. So
violent are their exertions that they have per-
force often to rest for days in some quiet pool,
from whence they continue their struggle up-
wards. At last the Mecca of the pilgrimage is
reached ; but the journey and the nature of its
termination tells sadly upon both males and
females. "To such," writes Mr Eooper, "as
have only seen the salmon in prime condition,

142 THE STORY OF FISH LIFE.

the appearance of the fish when on the eve of
spawning would come as a surprise. The female
is then dark in colour, almost black, and her
shape sadly altered for the worse from that
which she presented when in condition. As for
the male, he is about as hideous as can well be
imagined, his general colour being a dirty red,
blotched with orange and dark spots. His jaws
are elongated, and the lower one furnished with
a huge beak, as thick and nearly as long as a
man's middle finger; while his teeth are sharp
and numerous, and his head, from the shrinking
of his shoulders, appears disproportionately
large. His skin also is slimy and disagreeable
to handle, and, in fact, scarcely a more repulsive
creature in appearance exists. . . . After spawn-
ing, the fish speedily recover their colour, and,
to a great extent, their condition ; the baggit
(as the female is called) at once losing her dark
complexion, and the kipper discarding his hideous
livery, his great beak being rapidly absorbed, his
sides becoming silvery, and his back assuming a
dark bluish tinge."

Salmon return year by year to the river in
which they were hatched, just as swallows and
many other birds return each spring to their
own particular nesting-places. At least this is
generally the case, but it would seem that some
on leaving the river stray so far away that they
are unable to find their way back. There seems,
however, to be a yet deeper, may we say "in-
stinctive," impulse behind these apparent tender
associations and regard for the ancestral waters.
Since year by year fish hover longingly at the

MIGRATION AND HYBERNATION. 143

mouths of the Thames and the Liffey, for in-
stance, yet, at least in the former river, are
compelled to relinquish their attempts to make
their way up on account, to our discredit be it
said, of the foulness of its waters. When these
shall be once more free from pollution — and they
are slowly approaching this blessed state, thanks
to modern sanitation — we shall once more restore
to these debarred ones their ancient home and
shelter in Father Thames. With the Liffey it
would appear things are not quite so bad, and,
remarkable as it may seem, the fish apparently
know that the polluted water is but local and of
a limited area, for they have been remarked to
charge this befouled region at full speed, and
successfully emerging in pure water, to lie quiet
for a few hours to recover from their exertions.
How is it, we may ask here, that since no fish
have been hatched in the Thames for many
generations, an effort is still made, or at least
contemplated, to gain the paradise of the quiet
upper reaches which lay far from the busy tur-
moil at the river's mouth ? Is there a tradition
of golden days within the sanctuary of this
grand old stream ? or is this yearning to ascend
to be regarded as a transmitted impulse *?

The sturgeon is another denizen of the sea —
though there are some fresh water species —
that annually ascends the rivers to spawn. " In
summer, " writes Mr Lydekker, " regular fishing
stations are established on the Russian rivers,
where the approach of a shoal is heralded by a
watchman. Upwards of fifteen thousand have
been taken in a day at some of these stations ;

144 THE STORY OF FISH LIFE.

and when the fishing is suspended for a short
time, a river of nearly four hundred feet in width
and five-and-twenty in depth has been known to
be completely blocked by a solid mass of fish."
Sturgeon fishing is prosecuted for the sake of the
flesh, the ova, from which caviare is made, and
the air-bladder, from the inner lining of which
isinglass is prepared.

The sturgeon and the salmon afford us
instances of a universal migration of adults
from the sea into the rivers for the purposes
of making provision for the future generation.
But besides these armies of adults, the rivers are
also invaded by hosts of young fishes hatched in
the sea, but which complete their growth in the
rivers. The common eel is one of the most
interesting of these hosts. " In the course of the
summer," writes Dr Giinther, " young individuals
from three to five inches long ascend rivers in
incredible numbers, overcoming all obstacles,
ascending vertical walls or flood-gates, enter-
ing every larger and smaller tributary, and
making their way even ov^r terra firma to waters
shut off from all communication with rivers.
Such immigrations have been long known by the
name of Eel-fairs. The numbers participating in
these migrations are so vast as to be almost
incredible. Upwards of three tons of " elvers "
— as these young eels are called — were de-
spatched in one day from the Gloucester district
in the spring of 1886, and it has been estimated
that over fourteen thousand of these elvers go to
make a pound weight. " In the previous year,"
writes Mr Lydekker, " the annual consumption

MIGRATION AND HYBERNATION. 145

of eels was estimated at a minimum of 1650
tons, with a total value of £130,000." It is
believed that the adult eel does not return to
the river, but dies soon after having deposited
its eggs, or their equivalent.

The young salmon on their way down to the
sea are equally subjected to persecution, though
only from their natural enemies. These young
fish, it should be remarked, for the first year of
their existence, at least, are known as " parr."
At the end of this first year they take on the
brilliant silvery ness and characteristic marking
of the adult form, and are known as " smolt."
" Perhaps," says Mr Eooper, " with a wish to
exhibit himself in his new and beautiful apparel,
[he] evinces a daily increasing restlessness and
desire to quit his home. With the first floods
in May myriads of these lovely little fishes start
on their downward journey toward the sea. It
is a beautiful sight to watch their movements
when descending ; and for many days the river
teems with them, not a square foot of water
being without one where the stream is at all
rapid. As fry the smolts were exposed to many
dangers, but they were nothing to those which
beset them as parrs, on their journey towards
the sea. Their enemies are legion. Trout and
pike devour them, gulls swoop down and swallow
them wholesale, herons standing mid-leg deep in
the water pick them out as they pass, and even
their own kindred devour them without scruple.
Unluckily, too, for them, a certain number of
great hungry kelts (as the fish are called after
spawning) having recovered to a great extent
K

146 THE STORY OF FISH LIFE.

their condition, accompanying them on their
seaward journey, and prey upon their young
companions as they travel ; and I believe that a
hungry kelt will devour upwards of forty or fifty
smolts in a day. Arrived at the sea, the little
fish are met by a fresh array of enemies. The
army of gulls is always with them, and these are
reinforced by cormorants, divers, and other sea-
birds, besides which shoals of ravenous fish
await their arrival, and assist in thinning their
ranks. It is wonderful that any should escape,
and but for the extraordinary fecundity of
the salmon they would speedily be annihilated ;
but such is their prolific nature that a remnant
always survives to return to the spawning-
beds and keep up the supply. . . . The food
of the smolt during his sojourn in the sea is
abundant, consisting chiefly of sand-eels, molluscs
and marine insects. The smolts increase accord-
ingly very rapidly in size, and in three or four
months the fish that came down five or six
ounces in weight returns to the river from
whence he came, a grilse of from four to six
pounds : the grilse being the fifth stage of the
salmon's existence. Unless accidentally pre-
vented, the grilse always returns to the river
from whence it came, and after spending the
autumn and winter at home, and providing for
the continuance of the family by spawning, as
already described, returns as a kelt to the sea in
the following year, reappearing the next as a
salmon of at least ten or twelve pounds' weight."
Oar common stickle-back affords us an instance
of that mysterious sporadic migration by vast

MIGRATION AND HYBERNATION. 147

numbers which occurs amongst all groups of
animals not usually regarded as migration
species. Thus Dr Giinther records, on the
authority of Pennant, " that at Spalding in
Lincolnshire, there was once in seven years
amazing shoals, which appear in the Willand,
coming up the river in the form of a vast
column. The quantity may, perhaps, be con-
ceived from the fact that a man employed in
collecting them, gained, for a considerable time,
four shillings a-day by selling them at the rate of
a halfpenny a bushel."

Similarly, the horse - mackerel sometimes
appears off our coasts in incredible numbers.
On one occasion, it is on record, as many as ten
thousand were taken in Cornwall. In 1834 one
of Yarrell's correspondents informed him huge
shoals were seen on the Glamorganshire coast.
" They were first observed in the evening, and
the whole sea, as far as we could command it
with the eye, seemed in a state of fermentation
with their numbers. Those who stood on some
projecting rock had only to dip their hand into
the water, and with a sudden jerk they might
throw up three or four. The bathers felt them
come against their bodies, and the sea looked on
from above, appeared one dark mass of fish.
Every net was put in requisition ; and those
which did not give way from the weight, were
drawn on shore laden with spoil. One of the
party who had a herring-seive with a two-inch
mesh was the most successful ; every mesh held
its fish, and formed a wall that swept on the
beach all before it. The quantity is very in-

148 THE STORY OF FISH LIFE.

adequately expressed by numbers, they were
caught by cart-loads. As these shoals were
passing us for a week, with their heads directed
up channel, we had the opportunity of noticing
that feeding-time was morning and evening.
They were pursuing the fry of the herring, and
I found their stomachs constantly full of them."

Another form of sporadic migration, and less
mysterious, is that of some of the South American
cat-fishes, which appear to possess a remarkable
power of anticipating disasters. For they have
a " habit of travelling during the dry season,
from a piece of water about to dry up, in quest
of a pond of greater capacity. These journeys
are occasionally of such length that the fish
spends whole nights on the way, and the bands
of scaly travellers are sometimes so large that
the Indians who happen to meet them, fill many
baskets of the prey thus placed in their hands.
The Indians supposed that the fish carry a supply
of water with them, but they have no special
organs, and can only do so by closing the gill
openings, or by retaining a little water between
the plates of their bodies."

The Indian serpent-head (Ophiocephalus) can
travel considerable distances over moist ground,
progressing in a serpentine manner, by means of
their pectoral and tail fins.

It sometimes happens that fish are forcibly trans-
lated from one place to another by floods, for in-
stance, and manage to establish themselves in their
new conditions and thrive. In this way many
isolated pools and lakes may have been peopled ;
often with forms not naturally to have been expected

MIGRATION AND HIBERNATION. 149

to obtain there. The writer well remembers an
extraordinarily high tide on the river Yare in
Norfolk, which flooded the marshes some seven
or eight miles from the sea. Some four months
later, at about Easter-tide, codlings and whitings
were being daily captured in the ditches which
bounded the various marshes. The water here
was almost fresh, yet these salt-water forms when
captured were in fine condition, apparently having
suffered neither from change of water nor their
narrow surroundings.

The disappearance of an animal from its
familiar haunts does not necessarily imply
migration to some distant region. Indeed the
older naturalists, both lay and professional, com-
monly overlooked the phenomena of migration
altogether, and believed the sudden disappear-
ance of this or that particular animal to be
explained by its retirement to some sheltered
nook or cranny. This disappearance was more
particularly associated with the approach of
winter. Many believed that the swallows, for
instance, sought shelter from the rigours of this
season in sheltered caves or other hiding-places,
or even in the mud at the bottom of pools and
streams ; and there are most circumstantial
accounts extant of eye-witnesses to this strange
disappearance, which, needless to say, never
happened. In justice, however, to these older
observers, it must be remarked that many
animals actually do seek retirement at the fall
of the year, as witness the bat, squirrel, dor-
mouse, bears, snakes, lizards, frogs, fish, and, in
short, quite a host of animals. This periodical

150 THE STORY OF FISH LIFE.

retirement we know as "hybernation." Ex-
tended observation has shown that extremes of
heat are followed by a similar retirement on the
part of many animals, so that we may discuss
the facts herein concerned under two heads : (1)
winter sleep and (2) summer sleep.

The winter sleep seems to be gradually in-
duced by the reduction of the temperature, and
to be sustained so long as the low temperature
continues. The desire to sleep felt by ourselves
on exposure to extreme cold is well known, as
are the fatal effects which follow any yielding to
this desire.

The carp amongst the fishes is one of the most
familiar instances of winter-sleepers. In winter
great numbers bury themselves .in the mud
amongst the roots of plants, where they remain
torpid for many months. So, too, does the
tench.

The facts concerning summer sleep are much
less familiar. The drowsiness that overcomes us
on a hot summer's day will naturally be recalled
in this connection, and we may even proceed to
connect this with the similar inclination to sleep
under the influence of extreme cold. To suppose
that in either case the temperature alone is the
cause of this deep sleep — chill-coma and heat-
coma — would be to fall into an error. This deep
sleep is rather a way provided by Nature as an
escape from famine. Excessive cold arid exces-
sive drought alike cut off the food supplies, and
drought, in the case of many fishes even the
element in which they live. The African mud-fish
(Protopterus) will afford a case in point, illustrating

MIGRATION AND HIBERNATION. 151

the effects of prolonged drought (fig. 14). The
rivers in which these fishes live for many weeks
or months are absolutely drained, and their beds
become baked by the burning sun. To escape
an otherwise certain death the mud-fish burrows
down into the mud, and there tarries till the
clouds come again bringing the grateful rain.
In burrowing, as soon as the fish has reached
a sufficient depth it coils itself up into a half-
circle, covering its mouth with its tail. The
skin then secretes a quantity of slime, which
forms a sort of inner coat-
ing to the mud-chamber
in which it is now en-
closed, and which serves
to keep the walls moist.
This chamber is known as FlG. i4._0utiine figure of the

a " COCOOn " from its re- African Mud-fish (Protop-

, , , , terus annecteus).

semblance to the cocoons

of beetles and moths, which, it will be re-
membered, are constructed variously of siik,
wood-pulp, or earth. While enclosed in their
self-made prison numbers are dug out and sent
to this country. The writer well remembers
assisting Dr H. O. Forbes to release a number of
these fishes from their cocoons, at one of the
evening conversaziones held during the last meet-
ing of the British Association at Oxford. The
clods of earth containing each fish, or some-
times two, were then more than six months old,
and had to be broken up with a saw and chisels.
When the bulk of the earth around the slimy
case had been removed, the cocoon was placed in
a tank of tepid water. This rapidly dissolved

152 THE STORY OF FISH LIFE.

the mud and set free the captives, who were soon
swimming about as if in their native rivers.
Some of these fish were kept alive for many
months.

The Indian serpent-head (OpJiiocephalus) like-
wise passes prolonged seasons of drought en-
closed in mud, emerging therefrom only after
the rains have filled the bed of the stream.

The climbing-perch (Anabas) of Ceylon also
withdraws to a mud retreat, and is habitually
unearthed with the shovel by natives.

A trout-like species of fish (Neochanna) of New
Zealand is so far known only by specimens which
have been obtained from mud-burrows at a dis-
tance from water. These burrows are excavated
by the fish, but how, or under what conditions,
appears yet to be a mystery !

CHAPTER XII.

TRANSFORMATIONS

THE stock-in-trade with which fishes start in life
is a comparatively limited one, being no more,
in fact, than is sufficient to complete the outfit
necessary to meet immediate needs. Evolution,
progressive or otherwise, is possible only by
modifications of, and additions to, the original
structures represented in the person of the founder
of the house. Other chapters in this little book
bear witness to the magnitude of the changes which
have taken place during the development of the

TRANSFORMATIONS. 1 5 $

various organs of the body. The present will
indicate a few of the changes of another kind, of
which evidence is to be found in a study of the
anatomy of fishes. These well show how the
already elaborated structures and secretions may
combine to form yet other structures. Often
these arise in parts of the body which have been
relieved of their original functions, and are there-
fore free to undertake such new duties as may be
beneficial for the continuance of the species.
This replacement of one organ by another is
known as the substitution of organs. Instances of
such substitutes we shall discuss here, together
with cases wherein organs of long standing have
become further adapted to perform new duties
without undergoing any great changes in external
appearance.

A simple instance of the substitution of organs
is illustrated by certain members of the skate
tribe. The skates are nothing more than highly
specialised sharks. They have become skates,
we may put it, by virtue of the fact that they
have transferred the seat of locomotion from the
tail to the pectoral fins. These have become
enormously developed in consequence — a de-
velopment accomplished at the expense of the
tail, which has become greatly reduced in size,
and functions only as a rudder. The changes in
the general form of the body, consequent on this
substitution of the pectoral fins for the tail, have
become so marked that naturalists once separated
all the animals so affected into a group by them-
selves— the skates. The release of the tail from its
original function of propelling has been followed

154 THE STORY OF FISH LIFE.

in some cases by its degeneration, and in others
by its transformation into an organ of prehension
and weapon of offence. Thus in some of the
eagle-rays of the genus jElobates, it has assumed
the form of a long trailing and very slender
whip-lash armed with spines, the whole forming
a very formidable weapon indeed, as will be seen
presently. In the genus Urolophus the tail is
short, and armed with but a single spine. Eagle-
rays appear occasionally off the coast of Scotland.
" They frequently arrive suddenly in oyster-beds,
to the dismay of the owners, where they remain
so long as any of the molluscs are obtainable."
Mr Day, in describing the spine-tailed rays, says
" they lie concealed in the sand, and are reputed
to be able to suddenly encircle fish, or other prey
swimming above them, with their long whip-like
tails, and wound them with their serrated tail
spines."

The possession 01 spines is common to many
fishes. Their earliest appearance is in the form
of supports to the fins. But, as we have just
seen, their original function may be lost, and the
spine by a very natural transition becomes a
weapon of offence. In its new role, however,
the spine undergoes further modification, and
adds to its dread powers the sting of poison.
The evolution of this poison organ is, we shall
see, as gradual as is the rise and development of
all other organs

The spines in the tail of Violates may be
five in number, and are seated on the upper
surface of the tail ; all are barbed, and in con-
sequence inflict a very dangerous wound. " Al-

TRANSFORMATIONS. 155

though," says Dr Gunther, "they lack a special
organ secreting poison, or a canal in or on the
spine by which the venomous fluid is conducted,
the symptoms caused by a wound from the spine
of a sting-ray are such as cannot be accounted
for merely by the mechanical laceration, the
pain being intense, and the subsequent inflamma-
tion and swelling of the wounded part terminating
not rarely in gangrene. The mucus secreted
from the surface of the fish, and inoculated by
the jagged spine, evidently possesses venomous
properties." The common weaver-fish (Tmchinus)
will be a familiar form to many of my readers,
for it is so frequently shaken out of the nets of
"long-shore" fishermen at the seaside during
the summer months. In this fish the spine of
the dorsal fin, and of the plate covering the gills
on either side of the head, are very venomous.
Unlike those of the sting-ray just described, the
spines of the weaver are deeply grooved, for the
passage of a violently poisonous mucus. The
genus Synanceia, of the In do-Pacific, is repre-
sented by two species, justly feared on account
of their poisonous properties. They are as
hideous in appearance as they are dangerous in
fact. The poison organ is more perfectly de-
veloped than in the weavers, each dorsal spine
having its terminal half provided with a deep
groove on each side, at the lower end of which
lies a pear-shaped bag containing a milky poison.
This bag is prolonged into a duct lying in the
groove of the spine, and open at the point of
this. The native fishermen, knowing the danger-
ous properties of these fish, give them a wide

156 THE STORY OF FISH LIFE.

berth ; out people walking in the sea with bare
feet often step upon this fish, and the poison is
injected into the wound by the pressure of the
foot on the poison bags. So virulent is the
action of this poison that death is not infrequently
the result.

But the most perfect poison organs yet dis-
covered are those of a genus of frog-fishes
(Thalassqphryne) of Central America. Here, as
in the weaver of our own shores, the poison
spines are those of the operculum or gill-plate,
and of the dorsal fin. These spines are hollow,
and resemble the poison fangs of the snake.
They are perforated at the base and tip. The
base of the spine is embedded in a poison sac
filled by the secretion of a fluid from its inner
walls. As these sacs are not provided with
muscular tissue, it is supposed that they must
discharge their contents down the hollow spine
as a result of the pressure of the spine when it
enters the body of the victim.

In many cat-fishes there is found a very re-
markable apparatus, which it is believed repre-
sents a poison organ. "Some of these fishes,"
observes Dr Giinther, " are armed with powerful
pectoral spines, and justly feared on account of
the dangerous wounds they inflict ; not a few of
them possess, in addition to the pectoral spines,
a sac with a more or less wide opening in the
axil of the pectoral fin, and it does not seern
improbable that it contains a fluid which may
be introduced into a wound by means of the
pectoral spine, which would be covered with it,
like the barbed arrow-head of an Indian. How-

TRANSFORMATIONS. 157

ever, whether this secretion is equally poisonous
in all the species provided with that axillary sac,
or whether it has poisonous qualities at all, is a
question which can be decided by experiments
only made with the living fishes."

With some fishes, by the way, it would seem
the flesh is more or less permeated with poison,
either at certain seasons or at all times of the
year. "When eaten," says Dr Gunther, "it
causes symptoms of more or less intense irritation
of the stomach and intestines, inflammation of
the mucous membranes, and not rarely death.
The fishes, the flesh of which appears always to
have poisonous properties, are Clupea thrissa,
Clupea venenosa (West Indian herrings), and some
species of Scarus (parrot- wrasses), Tetrodon and
Dioclon (globe-fishes). There are many others
which have occasionally or frequently caused
symptoms of poisoning. Poey enumerates not
less than seventy-two different kinds from Cuba ;
and various species of Spliyrwna (barracuda),
Batistes (file-fish), Ostracion (coffer-fish), Caranax
(horse-mackerel) . . . have been found to be
poisonous in all seas between the tropics. All
or nearly all these fishes acquire their poisonous
properties from their food, which consists of
poisonous medusae, corals, or decomposing sub-
stances. Frequently the fishes are found to be
eatable if the head and intestines be removed
immediately after their capture. In the West
Indies it has been ascertained that all the fishes
living and feeding on certain coral banks are
poisonous. In other fishes the poisonous pro-
perties are developed at certain seasons of the

158 THE STORY OF FISH LIFE.

year only, especially the season of propagation,
as the barbel, pike and burbot, whose roe causes
violent diarrhoeas when eaten during the season
of spawning."

It is probable, however, that the presence of
poison in the cases just related is an accidental
character, and such fishes are, therefore, to be
distinguished from those which secrete poison at
certain restricted areas of the body and in con-
nection with spines, for the purpose of causing
punctures for the admission of the venom.

More remarkable than the poisonous are the
electrical properties of fishes. No less than fifty
species of electrical fishes are known to science,
though only a few, some five or six, species have
been carefully studied. These are Gymnotus, the
electric eel of the rivers and lagoons of Brazil
and the Guianas ; Malapterurus, the raash or
thunderer fish of the Arabs, found in the Nile,
Niger, and other African rivers ; the torpedo or
electric skate of the Mediterranean and Adriatic,
and various species of British skates.

It will be noticed from the above list that the
electrical fishes are by no means always closely
related, neither are they confined either to fresh
or salt water.

The electrical powers are most strongly de-
veloped in gymnotus, the South American eel;
next in order of strength comes the malapterurus ;
then the torpedo. The electric organs, or bat-
teries, are seated in different parts of the body in
these three fish. In the torpedo they form a
broad mass lying on either side of the head, and
extending backwards on either side to terminate

TRANSFORMATIONS. 1 59

at the level, and to the outer side of the hindmost
gill-slit. In the gymnotus they lie in the ventral
region of the tail, which is enormously elongated,
displacing the ventral postures of the powerful
lateral muscles. In the malapterurus the electric
organ invests the body like a mantle, lying be-
tween the skin and the muscles of the body.

In the British species of -skate, various species
of Mormyrus and Gymnarchus (African beaked-fish),
the electric organs lie on either side of the end
of the tail. These fishes were formerly described
as pseudo-electric, the shock which they give
being comparatively feeble. Recently, however,
the possession of an electric organ has been fully
demonstrated, lying, as we have indicated, in the
tail.

The electrical organ is to be regarded as
modified muscle-tissue. Dr Giinther has thus
graphically described those of the torpedo.
" The electric organs with which these fishes are
armed are large, flat, uniform bodies, lying one
on each side of the head, bounded behind by the
scapular arch, and laterally by the anterior cres-
centric tips of the pectoral fins. They consist of
an assemblage of vertical hexagonal prisms, whose
ends are in contact with the integuments above
and below ; each prism is sub-divided by delicate
transverse septa, forming cells, filled with a clear,
trembling jelly-like fluid, and lined within by an
epithelium of nucleated corpuscles. Between
this epithelium and the transverse septa and
walls of the prism there is a layer of tissue in
which the terminations of the nerves and vessels
ramify. Hunter counted 470 prisms in each

160 THE STORY OF FISH LIFE.

battery of Torpedo marmorata. . . . The fish gives
the electric shock voluntarily when it is excited
to do so in self-defence, or intends to stun or kill
its prey ; but to receive the shock the object
must complete the galvanic circuit by communi-
cating with the fish at two distinct points, either
directly or through the medium of some conduct-
ing body. ... It is said that a painful sensation
may be produced by a discharge conveyed through
the medium of a stream of water. The electric
currents created in these fishes exercise all the
other known powers of electricity ; they render
the needle magnetic, decompose chemical com-
pounds, and emit the spark. The dorsal surface
of the electric organ is positive, the ventral
surface is negative." A correspondent in Land
and Water, in reply to Frank Buckland, con-
tributes some very interesting information con-
cerning two torpedos taken in the estuary of the
Tees. He says : "I was curious enough to see
what those I caught were living upon, so I pufc
my knife into one and took from him an eel
2 Ibs. in weight, and a flounder nearly 1 Ib.
The next one I opened also, and was more as-
tonished to find in him a salmon between 4 and
5 Ibs. in weight; and what I was more astonished
at was that none of the fish had a blemish of any
description, showing that your idea of the fish
killing his prey with his electrical force is quite
correct."

The nerves of the electric organ in the torpedo
arise from the brain ; in all the other electric
fishes from the spinal cord. In gymnotus over
two hundred of these nerves pass to the electric

TRANSFORMATIONS. 161

organ. Malapterurus is remarkable in that the
electric nerves arise from a single, enormous
lens-shaped nerve-cell, lying in the neighbour-
hood of the head, to wit, near the origin of the
second spinal nerve ; it is continued into a large
primitive fibre, which passes backwards, giving
off branches as it goes, to the end of the tail.

The use to which these organs are put is pro-
bably chiefly for the capture of food. The shock
given by Gymnotus is very considerable, quite
sufficient to kill other fish, or small mammalia.
Humboldt related a story to the effect that the
Indians, who wished to procure these eels, drove
horses into the water, which caused the eels to
discharge so much electricity into the water as to
exhaust themselves by their efforts, when they
fell an easy prey. The poor horses, it was said,
were often killed by the violence of these dis-
charges. There is, however, no confirmation of
this story by recent travellers. Bates, in his
" Naturalist on the Amazons," tells how he amused
the Indians, with whom he was travelling, " by
showing them how the electric shock from the
eels could pass from one person to another. We
joined hands in a line, whilst I touched the
biggest and freshest of the animals on the head
with the point of my hunting-knife. We found
that this experiment did not succeed more than
three times with the same eel when out of the
water, for the fourth time the shock was barely
perceptible." This experiment was made upon
fishes which had just been taken out of the water.
They had been captured, it is interesting to note,
from " little ponds " made by the eels in which
L

162 THE STORY OF FISH LIFE.

to pass the season of drought. These ponds, it
seems, abound with other fishes. It would be
interesting to know if these live in peace and
amity with the eels, or are gradually devoured
when other food supplies fail.

We have yet a third very remarkable trans-
formation. This concerns the change which
certain gland-cells of the body in fishes undergo,
converting them into phosphorescent organs. It
is a well known fact that the slime secreted by
the skin glands of certain sharks is highly phos-
phorescent, and in this we have the foundation
for natural selection to work upon. If we pass
in review all the known species of phosphorescent
fishes, we shall find numerous gradations of in-
creasing perfection, leading up to exceedingly
complicated and powerful light-producing organs.

Two kinds of phosphorescent organs are dis-
tinguishable. One of these takes the form of
peculiar eye-like, or lens-like bodies, arranged in
one or more rows down the sides of the fish's
body, forming, as Professor Hickson remarks, " a
series of miniature bull's-eye lanterns to illuminate
the surrounding sea " ; the other, to quote the
same authority, is constituted by a series of
"glandular organs, that may be situated at the
extremity of the barbels (the filamentous organs
of touch round the mouth), or in broad patches
behind the eyes, or in other prominent places in
the head and shoulders." The light given off by
these organs, in some species, is said to shine
with a reddish lustre.

These phosphorescent organs, it should be
noticed, are found either in fishes which inhabit

TRANSFORMATIONS. 163

the open sea, but which come to the surface only
by night, passing the day in depths so great that
light is almost excluded : or in fishes which live
at still greater depths, from which there is no
escape save by death ; so deep that absolute
darkness always prevails — it is the region of
eternal night. In consequence we find that the
eyes of the fishy prisoners of these dark water-
ways are either of enormous size, very small,
or wanting. But as the eyes decrease so the
luminous organs increase, till in some of the
totally blind fish those of the head have reached
a size which has been described as colossal.
Thus the eyes become replaced by lantern-like
phosphorescent organs. The reason for this re-
markable luminosity is at first sight not quite
clear. Keflection suggests, however, that being
blind, or nearly so, the capture of food becomes
impossible, unless the food can be induced to
come to the fish. A sort of realisation of the
very obdurate mountain being induced to go to
Mahomet at last. In the luminous organs we
have, strangely enough, the necessary wonder-
working charm. These, it would seem, are used
as a lure to draw the more fortunate sight-pos-
sessing brethren to destruction. Just as salmon
poachers decoy salmon within spear-reach by
means of a lantern whilst the world sleeps. But
it may be objected that this same lure will serve
equally well as a beacon to draw down upon itself
larger and equally hungry fish, as pirates might
be guided by the light of a ship riding at anchor !
So that this specious benefactor standing in dark
places diffusing light and gobbling up all who

164 THE STORY OF FISH LIFE.

attempt to profit thereby, is in hourly danger of
being hoist by his own petard ! Possibly this
occasionally does happen. As a rule, however,
it is probable a catastrophe of this kind is
avoided by the fact that together with these
luminous organs has grown up a wonderfully
delicate sense of touch and approaching danger.
This new safeguard has been formed, either
by exceedingly long and delicate filaments pro-
duced by the excessive development of the
fin-rays, and which act like the vibrissse of the
cat: or as "beards" and "barbules" developed
round the mouth. In addition it is not improb-
able that these fishes have developed a sense of
size by which they may judge the measure of
approaching animals, just as we ourselves can
tell when in the dark that we are approaching
some larger body before we actually touch it.
Should danger be at hand the lights would be
dulled, or even extinguished, and in a few
moments escape would have been effected.

This replacement of the eye by luminous
organs is another instance of the " Substitu-
tion of Organs."

The enormous eyes of the fishes which see are
the result of selection and adaptation to the
requirements of the new light — the light given
off by the numerous phosphorescent animals.
A large proportion of the worms, polyps and
star-fish, for instance, are also phosphorescent,
some of them highly so. Thus Professor
Wyville Thomson remarks of a phosphorescent
brittle-star (one of the Echinoderma), that the
light was of a brilliant green, corruscating from

TRANSFORMATIONS. 1 65

the centre of the disc, now along one arm, now
along another, and sometimes vividly illuminat-
ing the whole outline.

Mention may fittingly be made in this chapter
of transformations in the shape of the body as a
whole, selecting from the very numerous in-
stances two of the most striking.

Of these the most familiar will be that of
the sea-horse (Hippocampus). The change in
shape here is not perhaps very considerable,
but it is quite unique. The fish in swimming
moves in a vertical position, and is driven along
by rapid vibrations of the dorsal fin. The tail-
fin has disappeared, and the tail has become
transformed into an organ of prehension. The
external scaly armour has developed exceedingly,
and at the expense of the internal skeleton. It
forms a delicate bony framework, which may be
likened to filagree work. Further modifications
which the fishes of this genus may undergo may
be studied in the " Story of Life in the Seas,"
where a picture will be found showing the extra-
ordinary mimetic resemblance to seaweed, which
some species develop for protective purposes.

Our second example of transformation of the
external form is furnished by the wonderful
sun-fish (Orthagoriscus). This fish has the appear-
ance of having undergone the amputation of the
hinder end of the body, just behind the dorsal
fins. One is naturally puzzled to account for
such an extraordinary modification, but it seems
to be associated with, and has, perhaps, resulted
from its peculiar diving habits. It is the ogre
which haunts the night of the deep seas, and

166 THE STORY OF FISH LIFE.

preys upon the larval eels, Leptocephali (p. 132),
which at certain seasons abound there. This
we know, because large numbers of these once
mysterious fish have been taken from the
stomachs of stranded sun-fish. When at the
surface the sun-fish swims by vibratile motions
of the curiously shortened tail-fin, which acts
precisely like the dorsal fin of the sea-horse
described above. On diving the dorsal-fin is
brought into requisition, and apparently by a
sort of sculling motion affects the desired
descent, and perhaps the ascent.

These two modifications are sufficient to call
attention to the importance of a careful study of
the external form as a whole, as well as of the
individual parts, of fishes.

CHAPTER XIII.

PEDIGREES.

THE pedigrees of most of us are like our worldly
possessions, small in compass. The proverbial
"mists of antiquity" — the limbo to which all
obscure things are assigned — begin with them at
about the third generation, if they carry us back
so far. Occasionally some one or other of us,
for various reasons, desires to know more of his
descent, and in such cases calls in the aid of the
trained specialist, who, like some other specialists,
fills in from his imagination the "missing links,"
arid in the end furnishes the desired and much
treasured " genealogical trees."

PEDIGREES. 167

The interest to the world at large attached to
the pedigree of an individual of our own species,
however distinguished or popular he may be at
any particular moment, is never very deep or
widespread, and but rarely of any very great
importance or value save to the individual con-
cerned. But with the lower animals this is not
so. Whatever we can gather of the life history
of an animal, of its ancestors and its relations to
other forms, is knowledge of universal interest
and profit received with gladness by men of all
tongues. Indeed the piecing together of the
pedigrees of animals is now one of the most
important considerations of men of science.

The present and succeeding chapters of this
little book will be devoted to a brief presentation
of the main facts which have been discovered
concerning the ancestry of that very ancient
house of cold-blooded vertebrates — the fishes,
and the nature of the consequent grouping
together of the various forms which has re-
sulted therefrom.

For the sake of clearness we shall begin not
with the most primitive of all known fishes, nor
with forms undoubtedly primitive and of great
antiquity, but concerning whose affinities there is
much dispute. For concerning these last some
hold that they bear the stamp of so lowly a char-
acter .that they are probably to be regarded as
forms yet lower in the scale than the fishes them-
selves. Eather we shall choose as a starting-point
the more specialised descendants of these which re-
present some of the most lowly of the living fishes,
and about the primitive nature of which all are

168 THE STORY OF FISH LIFE.

agreed. These constitute the sharks, dog-fishes
and rays of the present day. But how do we
know, some one may ask, that these fishes are
more primitive than, say, the salmon tribe ?
Because, we should answer : comparison of the
anatomy of these two types (shark and salmon)
shows that the shark in every respect is simpler
in structure than the salmon. What is the
evidence for this ? Well, in the first place, it is
an established fact that the earliest vertebrates
have the skeleton or supporting framework of
the body made up not of bony but of fibrous and
cartilaginous tissue. The skeleton of the shark
is cartilaginous. Again, in the shark, the upper
and lower jaws are made up of simple bars of
cartilage; in the salmon they are formed of
numerous separate bony elements. In the shark
the teeth differ but little in form and structure
from the scales covering the body, from which
we know they have been derived, whilst in the
salmon the difference between teeth and scales
is so great that it seems impossible that the one
could ever be associated with the other. The
adult shark does not differ very much struc-
turally from the young one — the adult salmon
differs greatly, the young having a cartilaginous
and the adult a bony skeleton. And so we
might go on, each new character bringing out the
fact that the salmon in the course of its develop-
ment from young to adult increases in complexity,
whilst the adult shark differs but little from its
early stages. There is abundant evidence, in
short, that the adult salmon has made a distinct
advance in the direction of complexity and per-

PEDIGREES. 169

fection, whilst the adult shark has not far out-
stretched the condition of its babyhood. This
advance from the simple to the complex, which
takes place in the course of the life history of the
salmon, is illustrated again in the life history of
the development of the race of fishes, the simpler
forms, such as the shark tribe, appearing earlier
in the world's history than the more complex
bony fishes, of which we have taken the salmon
as a type. The gradual advance in complexity
of structure and variety of form which has taken
place since the appearance of the early fishes, we
call their evolution.

One word more; we shall discuss fossil and
recent forms indiscriminately, both in the fol-
lowing and all other orders of fishes, for, as Dr
Traquair pertinently remarks, "Does an animal
cease to be an animal because it is preserved in
stone instead of spirits ? Is a skeleton any the
less a skeleton because it has been excavated
from the rock instead of prepared in a macerating
trough ? And I may now add, Do animals, be-
cause they have been extinct for it may be
millions of years, thereby give up their place in
the great chain of organic beings, or do they
cease to be of any importance to the evolutionist
because their soft tissues, now no longer existing,
cannot be embedded in parafin and cut with a
Cambridge microtome."

The sharks and rays, though belonging to
an ancient and lowly organised group, are of
that group exceedingly specialised forms. The
evidence of specialisation here is found in the
changes which have taken place in different

170 THE STORY OF FISH LIFE.

regions of the body, changes which show, a
gradual advance in structure, as a consequence
of more perfect adaptation to their environment.
The structure of the pectoral fins, the equivalent
of the fore-limbs of higher animals, is much more
complex, for instance, than is the case with the
similar fins in the older sharks, about which we
shall speak in the next chapter. So too with
the main axis of the body, which we call in our-
selves the backbone or vertebral column. In the
sharks this is made up of a series of separate
hard bodies or vertebrae, each of them shaped
roughly, like a dice-box, when seen in section.
In the living animal they are joined one to
another by their ends to form a long jointed
support — the vertebral column. Immediately
above this column runs a tube, formed by a
series of A-shaped arches, one to each separate
vertebra. Through this tube runs the spinal
marrow. Besides, the vertebrae also bear pro-
cesses for the support of ribs and for the protec-
tion of blood-vessels, details of which must be
sought for in more technical works. This verte-
bral column we call a specialised structure,
because in the very young or embryo dog-shark it
was preceded by a much simpler structure, in-
herited from its ancient and more lowly forbears.
The transformation of this into the complex
vertebral column then is another piece of evidence
of specialisation. This simpler type of vertebral
column took the form of a continuous, or as we
say, unsegmented, gelatinous rod, called the
notochord. Such a notochord always precedes
the more complex types of vertebral column or

PEDIGREES. 171

backbone. In many living fishes, and a large
number of fossil forms, the " backbone" is repre-
sented only by this unsegmented gelatinous rod,
around which are arranged the A-shaped " neural
arches" for the spinal marrow, and the elements
for the support of ribs and protection of blood-
vessels. In many fossils we find these separate
elements preserved and arranged evenly around
a space. This indicates that the space was filled
by the very perishable gelatinous "notochord,"
and tells us that the vertebial column retained
permanently the unsegmented and unhardened
condition such as we find in the embryos of
to-day.

The modern type of shark made its first
definite appearance so far back in the world's
history as the period known as the Lias. We may
distinguish two groups of sharks, the one embrac-
ing the sharks and dog-fish which have an "anal
fin" (pp. 12, 61), the other certain dog-fish and
the rays in which the anal fin is wanting. If my
readers will forgive the introduction of apparently
long-winded names, he will find it useful to
remember that these two groups are known
respectively as the Asterospondyli and Tecto-
spondyli, in allusion to the characters of the
vertebra. In the Tectospondyli (covered verte-
brae) the vertebra are strengthened by con-
centric layers of hardened tissue : in the Astero-
spondyli the strengthening tissue is mainly
arranged in the form of lines radiating from a
common centre, hence the name Asterospondyli
(star-vertebrae). The sub-order Asterospondyli,
or sharks and dog-fishes with an anal fin, con-

172 THE STORY OF FISH LIFE.

tains several forms of considerable interest. One
of the most remarkable of these is the formidable
hammer-headed shark and the curious angel or
monk-fish, very closely approaching the form of
the rays in consequence of its similar habits.
These are the two most profoundly modified in
external form. The largest member of the sub-
order is the Charcharodon, and is at the same
time the most dreaded, attaining a length of
some forty feet. Teeth of a gigantic species,
only recently extinct, are occasionally dredged
up between Polynesia and the West Coast of
America, some of these teeth being as large as
those of a fossil species found in the Crag, and mea-
suring five inches in length and four iaches wide
at the base. The seven-gilled shark of the genus
Nokidanus and the Port Jackson shark (Cestracion)
are of great interest, on account of certain very
primitive characters of the skeleton and the
teeth. These last bear a close resemblance to
certain fossil forms. Those of the seven-gilled
shark are interesting on account of the fact that
they are provided with numerous cusps, giving
the free edge of the tooth a saw-like appearance
resembling similar teeth found in the Eed Crag
of Suffolk, and as far back in time as the Jurassic
period. Whole skeletons of Notidanus occur in
the Solenlufen slates of Bavaria, The Port
Jackson shark of to-day, occurring from Australia
to Japan, the Galapagos Islands and California,
carries us back into the remote past to the
Carboniferous period ; teeth differing but little
from those of the living Cestracion occurring in
the rocks of this age. These teeth it will be

PEDIGREES. 173

remembered we discussed on p. 39. They are
remarkable as well for their beauty — seen in situ —
as for the evidence of adaptation to function
which they have undergone, resulting in crush-
ing teeth of a very perfect description. The
Cestracionts reached the hey-day of their de-
velopment during the Mesozoic period. The
living species is but an isolated member of his
kind. Another very remarkable and ancient
type of shark, living at the present day in the
sea around Japan, is the Japanese frill-gilled
shark (Chlamydoselaclie). Amongst its most
striking features are its teeth, resembling those
of the living Notidanus, to which it is related,
and certain fossil forms occurring as far back as
the Jurassic epoch.

The Tectospondyli contains those dog-fishes
which have no anal fin, arid the rays and devil-
fishes. Earlier naturalists, impressed by the
superficial characters only, grouped all the shark-
like fishes together, leaving the ray-like forms
together to form a separate sub-order. Eecent
investigation has shown how dangerous are con-
clusions based on external appearances. We
now realise that adaptation to similar physical
conditions may result in the transformation of
animals not nearly related to an extraordinary
external likeness. This is exemplified in the
case just mentioned. More deep-seated char-
acters show that the spiny dog-fishes agree rather
with the rays than the sharks. It is significant
that many of the very oldest known rays
apparently differ but little from species now
living.

174 THE STORY OF FISH LIFE

So much for the shark-tribe, the Elaemo-
branchii of the scientific text-books (p. 192).
We will turn now, not to a consideration of
the still higher groups of fishes descended from
the sharks, but to some other shark-like forms —
the chimeras. In spite of their superficial re-
semblance to the sharks, they are held to be
distinct therefrom. Their points of resemblance
are probably derived from an ancestor common to
both. One species of chimera, Chimcera monstrosa,
is found occasionally in the Atlantic and Medi-
terranean. It occurs sporadically. Another,
Chimcera affinis, is occasionally to be seen, ac-
cording to Mr Bashford Dean, in Lisbon market,
''where, from its low price, it evidently ranks
with the sharks as a food-fish." Another species,
Chimcera antardica, is common in the Straits of
Magellan. Yet another is abundant in the
shallow waters of Vancouver, where it is known
as the " rat-fish," and "may often be seen in the
neighbourhood of the docks swimming slowly at
the surface." The last of the chimeras to be
discovered has been placed in separate genus,
Harrotia. It is the most primitive and most
shark-like of all.

The chimeras are divided into four families,
three of which are now extinct. The family to
which the living chimeras belong attained the
zenith of its development in the Cretaceous and
Eocene periods. The surviving members are to
be regarded as the degenerate descendants of those
days, for they never exceed five feet in length,
whilst Edapiwdon, one of the fossil members
of the family, attained gigantic proportions.

PEDIGREES. 175

There is nothing very exciting to relate about
Chimseroids. They are very ugly fish. Their
claim, however, to attention is a strong one, for
there seems to be no doubt that they form a
connecting link with the dipnoi. The backbone
is not divided into separate bony segments, but
is represented by that more primitive structure,
the forerunner of the typical backbone, known
as the notochord (p. 170). There is but a
single £ill opening, as in the dipnoi (lung-fishes).
But there are two particulars which lift the
chimeras out of the, ranks of the commonplace.
The first of these concerns the teeth. These are
somewhat plate-like structures, bearing hard-
ended areas known as "tritors." There are two
pairs of these in the upper jaw, and they bear a
resemblance, on the one hand, to the teeth of
the lung-fishes, and on the other to those of
certain extinct sharks known as Cochliodonts.
The resemblance to these latter is significant,
suggesting that they may have had a similar
origin — the fusion of separate smaller teeth.
The second of the chimeras7 notable characters
is represented in a remarkable movable spine
in the head, of unknown function, the free end
of which is covered with recurved spines, and is
received into a pit in the forehead. In some of
the fossil members of this group this spine was
represented by a sword or spike-like structure.

About the life history of Chimaeroids we know
next to nothing, about the embryology and
larval development nothing at all.

We must turn now to the discussion of that
higher group of fishes, the descendants of the

176 THE STORY OF FISH LIFE.

ancient sharks. These are represented bj the
modern bony fishes — the Teleostomi of science.
By many of the older naturalists this group was
sub-divided into two portions, known respectively
as the Ganoid and Teleostean groups. This
division is not followed now.

The Teleostomi are distinguished from the
sharks, their ancestral kindred, by the fact that
both the upper and lower jaws are ensheathed
in bone, which in turn supports the teeth ; that
the skeleton is more or less well ossified ; and
that the gill-clefts open into a large chamber
with a single aperture. The outer covering of
this gill-chamber is constituted by a bony shield
known as the operculum. The outer covering
of the body, instead of the placoid scales of the
Elasmobranchii (shark-tribe), is made up of
a bony mosaic or of delicate horny lamellae,
which form the characteristic "fish - scales."
These are the principal characters of the sub-
class Teleostomi.

The Teleostomi are divided by modern natural-
ists into two groups or "orders": (1) the
Crossopterygii or fringe-fmned fishes, and (2)
the Actinopterygii or ray-finned fishes. The
differences between these two and the more inter-
esting members contained in each order we will
now proceed to discuss.

The fringe-finned fishes are regarded as the
more ancient type. Their oldest fossil remains
are extremely ancient, carrying us back to the
Devonian period. The epithet "fringe-finned"
is bestowed on account of the fact that in the
paired fins there may be distinguished two

PEDIGREES. 177

distinct parts, a lobe-shaped central and basal
portion, surrounded by a marginal or fringed
portion. The former is constituted by the
muscles covering the axial portion of the
skeleton, and the latter by delicate fin-rays
connected with the central or axial portion.

Of the fringe-finned fishes, as Dr Smith
Woodward points out, there are two distinct
types, distinguishable by the form of the pectoral
fins (fore-limbs). In all the extinct members
these fins are attached to what corresponds with
the shoulder girdles of the higher vertebrate by
a single support, whilst in the other type these
fins are attached to the girdle by means of three
separate elements placed side by side. A refer-
ence to the accompanying figures (fig. 7, p. 66),
should make this clear. The latter type of fin is
called a tribasal, the former a unibasal fin. The
tribasal fin is found only in living forms.

In some respects these fringe-finned fishes
resemble the lung-fishes, but whether this re-
semblance is due to adaptation to similar physical
conditions or to actual affinity, is a matter for
debate. The evolution of the group is accom-
panied by specialisation in many directions,
details of which will be found in more profound
works.

The remains of these fishes, which we dig up
to-day as fossils, are but samples of the denizens
of the ancient lakes and inland seas, whose dried
basins form the rocks known as the old red
sandstone. The most characteristic feature of
these remains is the nature of the form of the
scales. These, in the majority of the fossils
M

178

THE STORY OF FISH LIFE.

preserved to us, take the form of very large and
thick overlapping scales, coated externally with
an enamel-like substance known as "ganoine"

FIG. 15.— A. Restoration of a primitive Sturgeon— Cheirolepis, after
Traquair. B. The African "bichir," Polypterus bichir, living
in the Nile at the present day. Note the heavy armour of rhom-
boid scales. C. Restoration of the extinct lung-fish, Holoptychius,
after Traquair.

(hence the old name " ganoid " fishes). In addi-
tion these scales were also more or less elaborately
sculptured. The head was encased in hard,
closely-fitting plates.

Other forms of this period have rhomboid

PEDIGREES. 179

scales, very thick and closely set, forming a
kind of pavement or mosaic ; that is to say, they
did not overlap.

The accompanying beautiful restoration, by
Dr E. H. Traquair, of the form known as
Holoptychius, shows the nature of the overlap-
ping scales. The mosaic arrangement can be
studied (fig. 15 E).

Coelacanthus, Diplurus, Undina and Macropoma
are four noteworthy genera, for they are all
highly specialised forms, having arrived at this
distinction chiefly by degeneration. Further-
more, "these have," says Dr Smith Woodward,
" perhaps the most remarkable range of all
known extinct fishes, occurring almost un-
changed throughout the whole series of forma-
tions from the lower Carboniferous to the upper
Chalk." Amongst other things, they are remark-
able for the fact that the air-bladder was ossified.

Diplurus seems to have threatened to forestall
the Cheshire cat, for its body has become exces-
sively shortened, so that the head is relatively
enormous in size. It is further remarkable for
the fact that it, together with its cousin Undina,
was blessed with two tails, one behind the other
(see p. 56).

Strangely enough, a few of these crossop-
terygian or fringe-finned fishes have survived to
the present day, in the "bichir," Polypterus bichir of
the Nile (fig. 15 E), the reed-fish (Calamoichthys
malabaricus) of Old Calabar. These are, further-
more, remarkable in that they differ from the
fossil forms described above in the form of
the skeletal elements of the pectoral fin, which

180 THE STORY OF FISH LIFE.

have the tribasal arrangement which we referred
to on p. 177, fig. 7, p. 66. This tribasal form of fin
presents a close resemblance to the basal carti-
lages of the modern sharks, a fact of great
interest and significance. The scales of these
fishes are very thick and dense ; quadrangular in
form, therefore not overlapping, and coated with
" ganoine." Very little is known of the breed-
ing habits of these wonderful mail-clad fishes.
The young have very large and well-developed
external gills (fig. 3).

The " ray-finned fishes," the Adinopkrygii,
embrace the whole of the remaining forms to
be discussed in this chapter. For the fishes
belonging to this order we may adopt Mr
Lydekker's name of "fan-finned," since the rays
or bony supports of the fin spring from a common
base, fan-wise, instead of being distributed so as
to form a fringe to a more or less extensive
scale-covered lobe. There are, of course, other
additional characters peculiar to the fan-finned
fishes, but these need not concern us here.

It is a remarkable fact, but nevertheless true,
that the fan-finned are as old as the oldest of
the fringe-finned fishes, occurring as far back as
the Devonian period. And, furthermore, it
seems to be equally true that we have in the
modern sturgeons the highly specialised descen-
dants of the earliest forms of the fan-finned
group. For this we have the authority, so often
quoted here, of Dr Smith Woodward.

These ancestral sturgeons differ much from
their modern descendants. The latter have in
the course of ages undergone great specialisation,

PEDIGREES. 181

accompanied by degeneration. The oldest of the
ancestral forms belongs to the genus Cheirolepis,
and occurs in the Old Red Sandstone (fig. 15 A).
One of the most striking features of this fish was
its covering of scales. These were exceedingly
small, and closely fitting, but they did not over-
lap. The head was enveloped in bony plates,
and the mouth was large, at the front of the head,
instead of on the under surface after the fashion
of modern sharks, and armed with teeth. These
characters stand in strong contrast with the
typical modern sturgeon, wherein the body is
covered, not with closely-fitting scales, but with
rows of isolated bony bosses arranged, one along
the back, one along each side, and one along
each side of the under surface. Again, in the
living sturgeon the mouth has shifted to the
under surface of the head, and the jaws have
lost the teeth, the mouth now being suctorial.
But it is interesting to note that in the embryo
sturgeon the jaws bear teeth.

But there are other sturgeons which serve as
links in the chain which we hope will one day
be complete enough to carry us back by easy
transitions from the toothless and curiously
armoured form, which we have just discussed,
to the toothed and scaly members of the genus
Cheirolepis. These links are, however, it must
be admitted, somewhat slender.

The most interesting are the living shovel-
beaked sturgeons of the genus Polyodon. In
many respects they are, like their more familiar
cousins, the sturgeons of the genus Acipenser,
both highly specialised and degenerate. They

182 THE STORY OF FISH LIFE.

are highly specialised in that the anterior end
of the head is produced forward into a broad
shovel-like process, used, it is supposed, as an
organ of touch : and degenerate in that, the
eyes are so extremely small as to render them of
but little use. This degeneration of the eyes,
and the compensatory organ of touch, seems to
have been induced by the turbidity of the rivers
in which they lived, which is so great as to
render eyes almost useless. Another degenerate
feature is seen in the scales, which are very
minute and star-shaped. Teeth are retained
throughout life. From the living Polyodon we
are carried geologically back to the fossil genus
Chondrosteus of the Lias formation, which, like
Polyodon, had, amongst other things, developed a
tactile paddle.

In studying the animal life of the globe, from
its earliest dawn till to-day, we shall find evidence
of a gradually increasing complexity therein.
Furthermore, if we select any particular group
of animals for review, we shall not fail to be
struck with the fact that that group exhibits a
series of characteristic forms, the rising, waxing,
and waning of which may extend through one
or more geological periods, and then suddenly
die out ; or it may persist under greatly modified
aspects till to-day, either in the form of an isolated
survivor of an ancient race, or as a congeries of
forms in the hey-day of development.

In the history of the house from which the
sturgeons derive their origin, we may find some
instructive instances of this rise and decline.
The earliest representatives of this house, we

PEDIGREES. 183

have already remarked, were armoured fishes,
which increased in wealth of form till they
reached the climax of their evolution in the
Carboniferous and Permian periods. By this
time they had flowered out into a very numerous
company, in which we may distinguish two types
— an elongated, and a deep-bodied. Above the
Permian, remains of the deep -bodied form
gradually dies out, finally disappearing towards
the end of the Jurassic period. Although these
deep-bodied fishes held their own for an enor-
mous period of time, they yet have a shorter
record than the parent stock. This, during the
lower Carboniferous period, produced a very re-
markable scaleless form, known as Phanerosteon ;
and during the Jurassic an equally remarkable
type, characterised by deeply overlapping scales,
ornamented with tubercles of the glistening
ganoine. Finally, as we have already remarked,
we may reckon as descendants of the earliest
forms our modern sturgeons, which again afford
us valuable material for our evolutionary studies
in the highly specialised shovel-beaked, and the
more typical sturgeon, which we can trace back
to the Lias, in the form of Chondrosteus.

From the sturgeons we must pass to the con-
sideration of a fish which, until recently, was a
stumbling-block to many. This is an American
fish (Amia calva)9 commonly known as the bow-
fin, but also as the mud-fish, lawyer-fish, and
Joseph Grindle. For a long while this fish was
believed to be closely allied to the herrings, it
was only after a closer acquaintance of its
anatomy was made that its real affinities became

184 THE STORY OF FISH LIFE.

known, and with this knowledge came a revela-
tion as to its great importance from a pedigree-
making point of view. The bow-fin is a carni-
vorous fish. The streams in which it lives
frequently become very foul ; on such occasions
it comes to the surface to breathe air, taking in
large mouthfuls at the surface without making a
single bubble. It is said that when near to the
surface the bow-fin often gives vent to a bell-like
note, which is explained as probably due to the
passage of air from the air-bladder. This last
is cellular in structure, and hence adapted for
breathing purposes.

Once upon a time the distribution of the bow-
fin over the earth's surface was much wider than
at present, for its fossil remains have been found
in the Upper Eocene of Hampshire and the Isle
of Wight, and of Paris. But we can trace it
much further back than this, for under another
generic name — Megalurus — it occurs as far back
as the Kimmeridgian formations of Bavaria, that
is to say, it is a Jurassic fish, and that is a long
while ago ! But we can trace them yet further
back, for the Amiidce, the family to which the
bow-fin belongs, were preceded by, and descended
from, a group of fishes known scientifically as the
Eugnathidce, occurring in the Lias formations at
the bottom of the Jurassic series. One of the
chief points of difference between these and the
modern bow-fin was the possession of a coat of
armour in the shape of a heavy pavement -like
scale.

A branch of the bow-fin family, which ranges
throughout the Jurassic and Cretaceous periods,

PEDIGREES. 185

is distinguished by the remarkable resemblance
which it bears to the modern sword-fish, with
which it cannot possibly be related. In Proto-
sphyrcenea of the upper Cretaceous period, the
sword — which has been gradually increasing in
length in different genera, beginning with a
form known as Pachycormus (thick hide) of the
Upper Lias, and passing through Hypsocormus
of the Kimmeridgian — was as formidable a
weapon as in the living sword-fish. This curious
resemblance is another instance of parallelism
(pp. 13, 173).

It will be sufficient to show the importance
of the bow-fin family to remark that this is
regarded as probably the group from which the
majority of the modern fishes may be traced.

Of uncertain relationships are the American
bony-pikes, or gar-pikes, Lepidosteus, and their
fossil kindred. The living Lepidosteus — of
which genus there are three species — like the
bow-fin, is at present confined to the fresh waters
of North America; but, like the bow-fin, once
enjoyed a much wider distribution, its remains
occurring with great frequency in Europe — in
the Eocene and Lower Miocene periods. The
living gar-pike in many respects resemble the
fringe-finned Polypterus (p. 178), being similarly
clad in heavy armour. Polypterus, Amia and
Lepidosteus are each alike interesting as the
isolated survivors of different branches of extinct
groups. The living gar-pike, or bony-pike, some-
times attains a length of six feet. They are
carnivorous. In South Carolina Mr Bashford
Dean tells us he has known it to occur in such

186 THE STORY OF FISH LIFE.

numbers as to fill the shad-nets, and thus render
that fishery impracticable for many days. In
the formation of the vertebral column Lepi-
dosteus is unique, being the only fish in which
the vertebrae are connected by cup and ball
articulations.

Concerning the actual descent of the more
modern fishes, we have much yet to learn. But
the general model upon which the most familiar
of our existing forms was shaped appears as far
back in time as the Upper Triassic formations.
Some of the fishes of this period, Dr Woodward
tells us, differ only from such groups as the her-
ring tribe in the more primitive form of the
backbone, which was only imperfectly ossified,
in the presence of peculiarly shaped scales at the
base of the fins, known as " fulcra," characteristic
of the older so-called "ganoids" such as the
sturgeons, and in the possession of the thick
enamel-coated scales known as "ganoid." These
are the models which time and evolution have
changed into the herrings, salmon, pike and
perch, and so on, of to-day.

The tropical and sub-tropical Elops is one of
the most ancient of living fishes of the modern
type. Like the sharks, and many other primitive
forms, its intestine is provided with a spiral
valve — to be quite correct, in elops there is a
vestige of this valve. Furthermore, it bears
another badge of lowly origin in the shape of a
bony plate beneath its jaws — the gular plate;
in this respect it resembles the bow-fin and its
allies.

The herrings form another group of ancient

PEDIGREES. 187

lineage. They may be traced back as far as the
Cretaceous period. Other relatives of the her-
rings— the sardine tribe — are also to be traced
back to the cretaceous. The sardines are a
numerous family. In addition to our familiar
little friend of the breakfast table, there are
numerous deep sea phosphorescent forms, with
which we cannot deal here for lack of space.
The herring-like elops, the true herrings and
sardines, are the living representatives of a much
larger and ancestral stock. The extinct forms
all bear a very striking resemblance to modern
herrings. To discuss these in cold print were
profitless ; but those who have the good fortune
to live near great collections of fossil-fishes, such
as that of the British Museum, can glean for
themselves some very striking lessons in the
pedigree of the herring and its kindred. All
these forms are grouped together to form one
family, the Isospondyli.

As allies of the herrings, we turn now to the eels
— a tribe with which we are all more or less familiar,
at least with some members. Three well-marked
forms are included in this group — the common
fresh water and conger eel, the mursenas, and
the electric eel. The muraenas are probably but
little known to most people. They differ from
all the other forms with which they are asso-
ciated in their remarkable colouration, which is
very brilliant and generally mottled in pattern.
The feature which makes the electric eel cele-
brated we have already discussed (p. 158). The
eels serve as admirable object lessons in the effect
of adaptation to a peculiar mode of life burrowing

188 THE STORY OF FISH LIFE.

in the mud for the purposes of concealment. To
this adaptation is due the peculiar and familiar
elongated form. This change in shape has been
followed by the loss of the pelvic fin in all, and
both the pectoral and pelvic fins in the mursenas,
whilst the scales have been reduced to mere
vestiges embedded in the skin. Moreover, the
primitive condition of a continuous median fin
fold, from the middle of the back to the middle
of the belly, has once again been introduced,
or secondarily acquired, as it is scientifically
expressed. Eeasoning from experience, some
scientific specialists in the natural history of
fishes, have been led to suspect that the supposed
common descent of these three forms of eels may
prove to have no foundation in fact. In other
words, that originally unlike and unrelated forms
have become moulded by adaptation into a
common resemblance.

Fossil eels occur in the upper cretaceous rocks
of Mount Lebanon. The eels form a sub-order
by themselves at present — the Apodes.

Near here we encounter a host of familiar
forms, constituting the sub-order, Plectospondyli,
of Dr Smith Woodward. This sub-order em-
braces the carps, breams, roach, chubb, barbel,
gudgeon, tench and loaches.

These are forms with which we are all more
or less familiar: a comparatively modern group
of fishes, carrying us back but ^ very little way
into the past, geologically speaking.

So it is with the cat-fishes, which are generally
regarded as a tribe which may claim kinship
with the above. In the record of the rocks we

PEDIGREES. 189

do not find them until comparatively near the
end.

Similarly, it is not till we get to the closing
chapters, so to speak, of the ancient history of
the world that we find any record of the pikes
and toothed-carps, the flat-fish — such as the sole,
turbot, and so on — and the cod-fish and haddock
tribe. Of the ancestral forms of these, as yet we
know absolutely nothing.

The pedigree of the perch tribe, which em-
braces the blennies, gobies, millers-thumbs, angler-
fishes, mackerels, sea-breams, coral-fishes, and
perches, is of more interest. Not so much, how-
ever, on account of what it reveals concerning
remote ancestors, which show us the lines along
which the living forms have gradually developed,
as on account of records of troublous times and
days of horror, with which the chapters of the
past are occasionally punctuated.

In the collection of fossil fishes in the British
Museum of Natural History, there can be seen a
slab of rock containing the fossil remains of a
shoal of fishes of the genus Bolopteryx, a near
ally of the living perches. These remains are in
the most extraordinary state of preservation, and
seem to show that this shoal wras suddenly over-
whelmed in some great catastrophe. And this
because the fishes are lying one upon another in
all kinds of contorted positions, with gaping
mouths and gills and erected fins, suggesting
suffocation by the escape of volcanic gases at the
bottom of the sea. And further, they must have
been rapidly interred by the settling of vast
quantities of suddenly raised sediment before

190 THE STORY OF FISH LIFE.

decomposition could set in, or before they could
fall a prey to the scavengers of the sea, in the
shape of other fishes of vulture-like habits, or
of Crustacea, and other carrion-feeding animals
of the lower orders. Such a catastrophe recalls
the great earthquake of Lisbon, or the over-
whelming of Pompeii by Vesuvius, whereby
hundreds of people were as suddenly en-
tombed as these fishes. But the fate which
l>efel these ancient perches was by no means an
isolated case. Far back in the world's history —
as far back as the time when the old red sand-
stone was accumulating — there is proof of just
such another calamity, as is shown by a portion
of a slab containing the remains of some of the
ancient fringe-finned fishes (Holoptychius}. Yet
again we have a third instance, this time in-
delibly stamped upon a slab of cretaceous rock
from Mount Lebanon, in which are embedded
the bodies of hundreds upon hundreds of young
herrings. These, however, all lie flat, suggesting
less violence in the manner of their death.

Of fishes whose origin remains at present a
mystery are the pipe-fishes and sea-horses, and
the bizarre globe-fishes, coffer-fishes, and sun-
fishes. Of the last mentioned species, a dis-
tinguished professor of comparative anatomy at
Oxford once remarked, that they should be
called cherub-fishes, "because they are cut off
behind " ! Connecting links, or " annectant
forms," as Professor Huxley called them, in
the chain of evolution through which these
have passed, would be valuable indeed. Hip-
pocampus, the sea-horse, comes nearest to the

PEDIGREES. 191

realisation of this, inasmuch as a fossil species
from the Eocene of Monte Bolea possesses a
caudal fin, which may be said to have since gone
•out of fashion.

The present chapter may be summarised
briefly as follows : —

The fishes of the present day may be divided
into two great groups according to the -structure
of the skeleton of the head. In one group we
have the ancient sharks and rays, and the
modern bony fishes represented by the salmon,
perch, and cod-fish, for instance. In the other
we have the curious chimeras, which will be
described presently, and the lung-fishes, which
we have discussed from some aspects (pp. 25, 67).

The shark-tribe and the modern bony-fishes
are bracketed together because the upper jaw is
but loosely attached to the skull — a type of
skull known as the hyostylic — whilst in the
chimeras and lung-fishes the upper jaw is indis-
tinguishably welded to form one piece with the
skull, and on this account forms a second type of
skull, the autostylic.

The hyostylic group of fishes are divided into
two sub-classes — the Elasmobranchii and the Teleo-
stomi.

The sharks and rays constitute the Elasmo-
branchii— a name given in allusion to the strap
or band-like bars that divide the gill-slits. They
are distinguished from the Teleostomi by the
fact that the body is covered with "placoid"
scales (p. 34), and that the gill openings are
numerous and exposed.

The modern bony fishes form the Teleostomi,

192 THE STORY OF FISH LIFE.

or fishes with the mouth parts composed of
separate bony elements. The Teleostomi have the
body clothed with symmetrical plates or scales,
and a single gill opening covered with a shield-
shaped plate.

The autostylic group of fishes are similarly
divided into two sub-classes — the holocephali, or
whole-headed, in allusion to the autostylic skull
and the dipnoi, or lung-fishes.

The holocephali are represented by the chim-
eras. These bear a great resemblance to the
sharks, having the body covered with placoid
scales. But there is but a single gill-opening
covered by a fold of skin.

The dipnoi are the lung-fishes. Herein the
body is covered with overlapping scales, resemb-
ling those of the Teleostomi, and the gill-opening
is protected by a bony shield.

We may express these relationships briefly as
follows : —

CLASS PISCES.
Branch A.

Hyostylic.

Sub-class I. Elasmobranchii.
,, II. Teleostomi.

Branch B.

Autostylic.

Sub-class III. Holocephali
„ IV. Dipnoi.

This is the classification of Dr A. S. Wood-
ward, one of our greatest authorities on this
subject.

PUZZLES AND PATRIARCHS. 193

This sub-division of the fishes is the result of
a careful analysis of all the characteristics of the
class, and has brought us not only somewhere
near the extreme base of the piscine branch of
the great vertebrate tribe, but it has also marked
out the lines along which our investigation into
the descent of the various smaller groups must
proceed, if we would know more of the evolution
of fishes.

CHAPTER XIY.

PUZZLES AND PATRIARCHS.

MOST of Nature's children are, so to speak, " ear-
marked," so that those who will take the trouble
to learn the nature of these marks may tell
thereby to what great branch of the animal
kingdom any particular individual belongs.
Those who are skilled in the interpretation of
these marks can go further, they can tell not
only to what tribe it belongs, but what position
it holds in that tribe.

Sometimes just one mark alone is of sufficient
importance to enable us to dispense with all
others. Birds afford us an admirable instance of
this. We can distinguish a bird at once from
all other known animals by the fact that it pos-
sesses feathers. Feathers form the external
covering of the bird, and are absolutely unique
structures, being produced by no other animal
under the sun. Now fishes are by no means
so distinctly and decidedly marked. Generally

194 THE STORY OF FISH LIFE.

speaking we are right in our determination that
this or that particular creature is a fish. But
there are many pitfalls, for not a few animals,
not even remotely related, are from their general
contour classed by the uninitiated as "fish."
Those who are on their guard and are familiar
with the credentials of fishhood, when suspicion
is aroused look for the characteristic scales, fins
and gill-openings. Generally all these will be
found, but scales may be wanting, so also may
the paired fins, but the median fins and gills,
never. And so it would seem then that it is
easy after all to determine what is a fish. By
no means, for the early tadpole stages of the
common frog are practically fish, whilst the
greatest experts of the year of grace 1901 differ
among themselves as to the claims to fishhood
which have been put forward on behalf of certain
living and fossil forms which we shall now
describe.

Let us take the living forms first. These are
represented by the somewhat unfamiliar eel-like
lampreys and hag-fishes. In a number of char-
acters these differ markedly from the forms
hitherto discussed. There are no movable
jaws ; there is but a single nostril placed in the
middle of the snout ; the mouth is a circular
cup-shaped cavity armed with numerous horny
teeth ; there are no limbs, no ribs, no gill-arches.
The skeleton of the head is cartilaginous ; the
vertebral column is represented by an elastic and
fibrous rod. The gills are of a quite peculiar
pouch-like form, hence the scientific name of the
group — Marsipobranchii. The skin in the region

PUZZLES AND PATRIARCHS. 195

of the gills is supported by a delicate cartila-
ginous basket-work called the branchical basket,
and representing the jointed, cartilaginous
gulars of the sharks and the similar bony
bars of the higher fishes. The body is naked,
and eel-like in form.

Lampreys are marine inhabitants which ascend
the rivers to spawn. Years ago they ascended
English rivers in vast hordes, nearly four thou-
sand having been taken at Newark in a single
night; they were captured as bait for cod and
similar fish. More fish were caught in the
Severn than in any other of our rivers.

Lampreys are carnivorous in their habits, and
are, on this account, the more interesting, for
whilst other fishes have become, so to speak,
quickened by their carnivorous desires, the
lampreys have become degraded. The sharks
and the mackerel, for instance, to select familiar
examples, have developed extraordinary activity
and general physical perfection to enable them
to overtake and destroy their prey. The lam-
preys, on the other hand, have degenerated, as
we have just remarked. How far this degrada-
tion has gone is a moot point, to which we will
return presently. But it is significant that the
species of Petromyzon fasten themselves by their
sucker-like mouths to other fishes, and scrape off
the flesh therefrom with their teeth. "Whilst
thus engaged," Dr Giinther tells us, t{they are
carried about by their victim. Salmon have
been captured in the middle course of the Rhine
with the marine lamprey attached to them."
This apparent doggedness of purpose is really

196 THE STORY OF FISH LIFE.

their undoing. For the members of another
genus, Myxine, have acquired the habit of boring
into the victim's body and feeding thereon till
death puts an end to the long-drawn tragedy.
On account of this ghoulish practice this species
has been christened the hag-fish. Now the
lampreys are, as we have already hinted, re-
garded by some as degenerate, a contention
which the living forms amply support. For we
can see how, by a very natural transition, a pre-
datory form has become degenerate by adopting
the method of the leech instead of the vigorous
attack of the shark, and how this leech-like
method has led to further degradation, ending
in the parasitism of the hag-fish. The evidence
for degeneration lies mainly in the absence of
jaws and paired fins. These may well have been
lost in consequence of the habit above described.
The loss of hardened scales or skin armour of
any kind, and the absence of bony matter in
the skeleton, may be further consequences of
their evil ways. There is certainly much to be
said for the degenerate theory, for dissection of
the lamprey in its early stages of development
reveals traces of a hardened skeleton. By way
of additional evidence in favour of this hypothesis
that the skeleton of the modern lamprey is de-
generate we may adduce the fact, that in the most
ancient known members of this tribe, the remains
of which occur in the old red sandstone of Caith-
ness, there was a well-defined vertebral column or
backbone, made up of calcified or hardened bone-
like vertebrae. This fossil was discovered and
has been described by I)r Traquair, and named

PUZZLES AND PATRIARCHS. 19T

by hirn Palceospondylus gunni. It is a very small
fish and, it should be noted, shows no trace
either of jaws or limbs, so that if these have been
lost it must have been at some infinitely remote
period. But there is another side to this question,
for many and very eminent authorities hold that
the evidence of degeneration is more imaginary
than real, and that we are to regard the lamprey
as an exceedingly primitive type.

This indecision as to the true nature of the
lamprey necessarily leaves the question of the
pedigree still a matter for debate. Many of
those who hold the lamprey to be a degenerate
fish consider that it is possibly closely akin to
the recent bony fishes. Whilst those who deny
its claim to rank as a fish at all, regard it as the
representative of the ancestral stock from which
the fishes took their origin.

With the fossil forms, to which attention must
now be turned, there is the same indecision, the
same interpretation of facts, so as to demonstrate
opposite conclusions. The forms in dispute are
relics of a past exceedingly remote, dating back
in fact to the old Silurian epoch, and representing
the earliest record we have of vertebrate life on
the earth. Whether they are closely related or
not is uncertain. The feature that would im-
press the observer most on seeing one of these
fossils for the first time, would be the remarkable
development of the external skeleton, which
formed a more or less complete coat of mail.
Further examination would lead to the discovery
that in some there were no paired fins or limbs ;
whilst in others only the front pair were present,

198 THE STORY OF FISH LIFE.

and these differed fundamentally from those of
all other vertebrates. Traces of eyes, nostrils
and gill apertures would only be discoverable
after careful search. There is reason to believe
that there were numerous gill-slits, but that they
opened, not directly on to the surface, but into a
common chamber below the head shield, and
that the water escaped from thence by a pair of
openings at the hinder end of this shield.

There are three well marked types of these
ancient creatures distinguished by the structure
arid form of the j^reat shield enveloping the head
and upper part of the back, and hence called the
dorsal shield. All three types are generally in-
cluded in one common group, or sub-class, known
as the Ostracodermi, or shell - skinned animals,
but this grouping together is rather for the pur-
poses of convenience than to suggest any close
relationship.

Those who would study these remains for
themselves in museum collections would find
these three groups arranged under three heads :
the Heterostraci (anomalous shells), Osteostraci
(bony shells), and the Antiarcha.

The Heterostraci represent the simplest and
possibly the oldest of these groups. The head
shield, which may be seen in our illustration
(fig. 16 A), is made up of no less than seven
pieces marked by numerous concentric lines.
Each of the separate plates are believed to have
been caused by fusion of minute shagreen
tubercles. A section through the shield shows
it to consist of three layers — an inner, called the
" nacreous " layer, on account of its resemblance

PUZZLES AND PATRIARCHS.

199

to the pearly layer of the oyster and other
similar shells; an outer very dense layer, in
structure resembling teeth, and a middle layer
of polygonal chambers. The dorsal spine seen
in the figure doubtless served the purpose of a

FIG. 16. — Three extinct ancestral forms of fishes. A. Pteraspis
rostrate, one of the Heterostraci. B. Cephalaspis lyelli.
C. Pterichthys, after Traquair.

dorsal fin, as a balancing organ. The tail was
covered with a closely-fitting armature of scales.
About the structure of the fin we know very
little. The typical representatives of this order
belong to the genus Pteraspis, of which one species,
Pteraspis rostrata, is figured here (fig. 16 A).

The Osteostraci are practically confined to the
Upper Silurian and Lower Devonian rocks. The
characteristic genus is Cephalaspis, the finest

200 THE STORY OF FISH LIFE.

known specimens of which have been found in
Forfarshire and Herefordshire. This fossil
presents many features of peculiar interest.
One of the most important concerns its general
form, which is curiously like that of the old
trilobites, the ancient Crustacea amongst which
it lived, arid which for some inexplicable reason
it seems to have mimicked. As will be seen in
fig. 16 B, the head-shield is of considerable size,
and in some species was produced backwards into-
two bony spines, and these again bore spines,
which it is surmised were used in progression.
The body was ensheathed in numerous hard plates,
disposed in bands round the body. Some of
these plates rise up in the middle line of the
back to form a dorsal fin. By the way, the need
for a dorsal fin seems to be a very real one,
judging by the totally different structures which
have been made to serve this purpose. The
spine in Pteraspis, the arched scales of Cepha-
laspis, cartilaginous, horny and bony rays in the
higher fishes, and fatty tissue in the aquatic
mammals — the whales, the porpoises, and the
dolphins. A further interesting feature of
Cephalaspis is the possession of a pair of flap-like
structures behind the head-shield, which it has
been suggested, represent not fins but gills.

The Antiarcha represent the most highly
specialised of these ancient puzzles. The genus
Pterichthys contains the typical species. The
armour-plating of the head and trunk was very
complex and perfect, the separate plates over-
lapped one another (fig. 16 (7). Another feature
of these plates is the series of shallow grooves.

PUZZLES AND PATRIARCHS. 201

by which they are traversed. These it is sup-
posed represent sense-organs. Behind the head,
it will be noted, are a pair of jointed append-
ages, whose origin is problematical. They pro-
bably served the purpose of fins, but they do not
seem to have been derived in the same way.
These fin-like structures are further remarkable
on account of the fact that they were hollow,
thus recalling the tubular limbs of invertebrates,
with which, however, they of course have nothing
to do.

How long these forms will remain "bones of
contention " we of course cannot say, but there
are signs that the veil is lifting. Dr Traquair is
of opinion that both the Heterostraci and Osteo-
straci are rightly to be regarded as forming one
sub-class — Ostracodermi. Furthermore, recent
researches of his have succeeded in establishing
a connection between these and certain exceed-
ingly interesting and puzzling forms known as
the Ccdolepidce.

The Coelolepidse are extremely ancient shark-
like fishes of the Devonian age. The name they
bear is bestowed on account of the fact the scales
are hollow. These hollow scales or rather spines,
were shagreen-like in general form, but were open
below, and without the basal plate seen in the
typical shagreen-forming scale. The form of
the tail was shark-like. Bat as yet no traces
of jaws, teeth, eyes, gill-slits or internal skele-
ton have been discovered. The peculiar nature
of the external covering leads Dr Traquair to
believe that these curious and ancient creatures
derive their origin from the same stock as

202 THE STORY OF FISH LIFE.

that which gave rise to the sharks. The
study of the Coelolepidae has thrown a flood of
light upon some otherwise unintelligible fish
remains found in the old red sandstone, in the
form of skin-plates. These skin-plates prove to
be made up by the fusion of shagreen denticles
resembling those of the Coelacanths. This dis-
covery is one of great importance, for it establishes
a connecting-link between the creatures who wore
this ancient armour-plate, and who have been
christened by the generic name of Psammosteus,
and the Coelolepidse on the one hand, and the
enigmatical Heterostraci, on the other. For by a
precisely similar fusion of denticles the head-
armour of these curious forms was probably
derived. Indeed it is believed that traces of
this fusion are obvious in the concentric lines
which mark the separate elements making up
the armour, which we have already described
(p. 198).

The Ccelolepidse may be included both as
puzzles and patriarchs. So also may the re-
markable fossil-forms known as the Arthrodira.
The fishes of this group attained enormous size.
The head and anterior end of the body were
heavily armoured with bony plates. Between
the head-shield and the dorsal-shield of the trunk
immediately behind, a very perfect and elaborate
joint was formed — hence the name Arthrodira —
joint-necked. This is a feature unique among
fishes. One of the largest of the group was the
Dinichihys of the Upper Devonian, Ohio, U.S.A.
The Arthrodira are generally held to be ancient
lung-fish. No trace has yet been found of

PUZZLES AND PATRIARCHS.

203

pectoral fins, but there are vestiges of the
pelvic series.

The goodly fellowship of the patriarchs in-
cludes several forms of deep interest and
importance. One of the oldest of these is

FIG. 17. —Three primitive sharks. A. Cladoselache tyleri. B.
Acanthodes. C. Pleuracanthus.

known under the name of Cladoselache and lived
during the Devonian period, in the seas of that
far away age, which have long ceased to be ;
where they swirled and foamed now stands the
flourishing State of Ohio.

The name Cladoselache, being interpreted,
means the branch-toothed shark, from the saw-

204 THE STORY OF "FISH LIFE.

like or comb-like shape of its teeth. The ancient
creature upon whom this name has been im-
posed is one of the very ancient and primitive
sharks. Its discovery has done much to enlighten
us on the vexed question of the evolution of
paired limbs. These appendages in this early
type are little more than triangular folds of skin
strengthened from within by supports in the
shape of rods of cartilage (fig. 17 A). How
these rods, by fusion and other modifications,
probably formed the foundation of the modern
fin we have already discussed (chap, vi., p. 67),

Of a somewhat more advanced type, and of a
somewhat later date — the Carboniferous and lower
Permian — is the form known as Pleuracanthus
(fig. 17 C). The fins are now much more ad-
vanced in type, but like those of Cladoselache,
have formed the subject of much speculation.
From its general form and the structure of its
fins, this fish looks as though it might, as Dr
Smith Woodward points out, with very little
modification, become either a shark, lung-fish, or
one of the fringe-finned fishes.

No less remarkable are some small shark-like
fish, also of the Carboniferous period, known as
Acanthodii — the spiny ones (fig. 17, B.). Their
claim to special notice is a strong one, inasmuch
as the fins are of a type that is quite unique. They
appear to have been derived by specialisation of the
type seen in Cladoselache, which has resulted in a
fusion of certain of the cartilaginous rays to form
a single support at the front of the fin, the rest of
the fin was formed by skin only stretched between
this support and the body. As in Pleuracanthus,

PUZZLES AND PATRIARCHS. 205

the shagreen denticles of the head had become
fused so as to form a number of separate bony
plates for the protection of the skull. The
denticles of the body had become modified to
form a closely fitting mosaic of diamond-shaped
pavement-like scales. The teeth were few in
number and degenerate in type. The peculiar
type of fin, not only as a whole, but also on
account of the disappearance of distinct support-
ing rays, must also be regarded as degenerate
in form. This early specialisation led to their
speedy extinction, without leaving direct des-
cendants.

INDEX.

A.

Acanthodes, affinities of, 200.

, , structure of, 204.

^fflobates, spines of, 154.
^Etheolepisy scales of, 34.
Air-bladder, 12, 24.
Amia, affinities of, 183.
Amphiprion and anemone, 72.
Amphisile, armour plating of,

31, 33.
Angler-fish, teeth of, 42.

„ feeding of, 93.

. , sexual differences,
100.

, , nest, 107.
Antiarcha, affinities of, 200.
Archer-fish^ feeding of, 83.
Arthrodira, armour of, 202.
Aspredo, eggs of, 109.

B.

Bafistes, poison of, 157.
Barbel, poison of, 158.

,, affinities of, 188.
Barracuda, poison of, 157.
Barramunda, survival of, 140.
Beaked-fish, eggs of, 109.
Bichir, gills of, 25, 125.

,, scales of, 33.

, , fins of, 58.

,, archaic nature of, 140,

185.

Bitterling, oviduct of, 110.
Blennies, eggs of, 112.
Bream, affinities of, 188.

Breathing, nature of, 19.
Boar-fish, jaws of, 90.
Bow-fin, affinities of, 183.
Burbot, fins of, 12-62.
,, poison of, 158.

C.

Caranax, poison of, 157.
Carp, breathing of, 23.

,, sexual differences in,

100.

,, hibernation of, 150.
,, viviparous, 110.
,, affinities of, 188.
Cat-fishes, breathing of, 23.
,, scales of, 29.
,, sexual differences

of, 100.

,, poison organ of, 156.
Cepkalaspis, structure of, 199.
Ceratodus, teeth of, 42.
Chiasmodus, voracity of, 94.
Chimera, eggs of, 112.

, , classification of , 1 74.
,, structure of, 175.
, , teeth of, 175.
Chromatophores, nature of ,73.
, , changes in, 75.

Chubb, affinities of, 188.
Cladoselacht, affinities of, 202.
„ structure of, 203, 204.
Climbing-perch, breathing of,

22.
Climbing-perch, summer sleep

of, 152.
Cod-fish, scales of, 35.

INDEX.

207

Cod-fish, teeth of, 41.

,, (dwarf) fins of, 64.
„ feeding of, 81.

sexual difference in,

100.

eggs of, 113, 118.
€offer-fish, scales of, 30.
,, colours of, 72.

•Colouration of fishes, bril-
liance of, 73.
,, change of, 73, 75

Colour, change of, 173.
,, of dying fishes, 75
, , nature of, 73, 76, 77.
,, need of, 76.
,, variation of, 72, 75.
•Crenildbrus, nest of, 107.

D.

Dabs, feeding of, 82.
JJapedius, tail of, 56.
Devil-fish, defence of young

of, 106.

Diodon, scales of, 30.
Dinichthys, armour of, 202.

,, ' affinities of , 202.
Diphirus, tail of, 56, 179.
Dog-fish, gills of, 25.

, , scales of, 37.

,, eggs of, 112.

E.

Eagle -ray, teeth of, 39.

,, feeding of, 86.
Echeineis, suckers of, 59.
Eels, naked skin of, 28.

„ scales of, 28.

,, lava of, 129.

,, electric, 158.

,, fossil, 188.
Eggs, numbers of, 113.
Eggs, floating, 119.

Electrical fishes, 158.

JKlops, ancient nature of, 186.

F.

Fan-finned, fishes, 176, 180.
> ceding, methods of, 79.
File-fish, teeth of, 43.
,, poison of, 157.
, , locomotion of, 13.
Fins, nature of, 11, 17.
uses of, 57.
origin of, 65, 68.

Fi

i, form of, 11.

transparent, 71.

voracity of, 94.

armour of, 100.

classification of, 191.

tadpole stage of, 194.

evolution of, 18, 97.

origin , new groups of, 1 5.

liveries of, 69.
Fishing-frog, eggs of, 113.
Flying-fishes, flight of, 63.

, , young of, 137.

Food, influence in colour, 96.
Fox-shark, feeding of, 84.
Frog-fish , poison organs of , 1 56.

G.

Gar-pike, beak of, 89.

,, affinities of, 185.
Gills, function of, 19.

,, forms of, 21, 22, 25, 27,

57.

Gilt-head, feeding of, 84.
Globe-fish, teeth of, 42.
,, poison of, 157.
Goby, nest of, 106.

,, duration of life of,

119.

Gourami, organs of touch of,
64.

.208

THE STORY OF FISH LIFE.

Gurnards, colours of, 71.

, , flying, fins of, 62.

H.

Haddock, sexual difference

in, 100.
Hag-fish, affinities of, 194.

,, parasitism of, 196.
Halibut, number eggs of, 113.
„ origin, flat shape of,

133.

Half -beak, jaws of, 89.
Head, skeleton of, 46.
Herring, colour of, 71.
„ eggs of, 113.
j, poisonous, 157.
,, fossil fry of, 190.
Hippocampus (sea-horse).
Histiophorus (sword-fish).
Holoptychius, scales of, 179.
Holopteryx, preservation of,

189.
Horse-mackerel, migration of,

147.
Hypsocormus, sword of, 185.

Lamprey, skin of, 28.
„ eggs of, 111.
young of, 123.
affinities of, 194,

197.

,, fossil, 196.
Larval fishes, 120.
Lateral line, 36.
Lepidosteus, gills of, 125.

,, affinities of, 185.
Leptocephali, nature of, 131.
Ling, eggs of, 113.
Loaches, affinities of, 188
Lump-fish, eggs of, 113.
Lung-fish, scales of, 29.

Lung-fish, teeth of, 42.
,, larva of, 125.

M.

Mackerel, fins of, 58.
Melanocetus, voracity of, 95,
Mormyrus, jaws of, 91.
Mullets, colours of, 71, 75.

NeocJianna, burrows of, 152.
Nesting of stickle-back, 103.

crenilabrus, 107.

angler-fish, 107.

paradise fish, 107.

beaked-fish, 108.

cat-fish, 108.

chromids, 108.

aspredo, 109.

pipe-fish, 109.
uS) teeth of, 39.

primitive character
of, 172.

0.

Orthagoriscus, food of, 133.

,, young of, 137.

,, diving habits of,
167
Ostracion, poison of, 157.

P.

of,

Pachycornnus, affinities

185.

Paradise fish, nest of, 107.
Parrot- wrasse, feeding of, 85.
, , poison of, 157.

Pentamerus, fins of, 63.

INDEX

209

Perch, teeth of, 41.

,, sexual difference in,

100.

„ eggs of, 112.
Phosphorescent organs, 162.
Pike, teeth of, 42.

,, poison of, 158.
Pipe-fish, eggs of, 109.
Plagyodus, 95.
Plaice, eggs of, 113.
Poison organs, 154.
Pollack, feeding of, 81, 82.
Polyodon, ancient character

of, 182.
Polypterus, external gill of,

26.

,, fins of, 58, 179.
,, affinities of, 185.
Porcupine-fish, scales of, 30.
Protopterus, scales of, 29.

, , summer sleep of,

150.

Psammosteus, affinities of, 202.
Ptemspis, affinities of, 199.
Pterichthys, affinities of, 200.

a

Kays, teeth of, 39.
Reed-fish, ancient character

of, 179.

Remora (see Echeineis).
Ribbon-fish, young of, 137.
Roach, scales of, 35.

„ teeth of, 42.

,, affinities of, 188.

S.

Salmon, colour, flesh of, 96.
, , sexual differences,

100.

,, fighting, 100.
,, nest of, 115.

Sand-smelts, masses of larvae

of, 138.

Saw-fish, weapon of, 43.

feeding of, 86.

Scales, forms of, 29, 33.

,, method of counting,

36.
Scams, delicate flavour of,

85.

Sea-horse, swimming of, 60.
,, mouth of, 99.
,, eggs of, 110.
,, form of body, 165.
Serpent-head, overland jour-
neys of, 148.

,, summer sleep of,

152.

Shark, Port Jackson, teeth of,
39, 173.

,, scales of, 31.
,, comb-toothed teeth of,

41.
,, Greenland, teeth of,

41.

5, spiny shagreen of, 41.
,, phosphorescent, 162.
,, primitive nature of, 168.
,, first appearance of, 171.
,, classification of, 171.
Skate, feeding of, 91.
„ eggs of, 111.
,, poison organs of, 153.
,, capture of food in, 94.
Skin, respiration by, 22.
Skip-jack, voracity of, 96.
Sole, transformation of, 133.

,, affinities of, 189.
Spines, origin of, 45.
Stickle-back, voracity of, 96.
fighting of, 100.
nest of, 103.
care of young,

105.

short life of, 120.
migration of, 146.
Sting-ray, teeth of, 39.

O

210

THE STORY OF FISH LIFE.

Sturgeons, origin of, 17.
skull of, 48.

„ eggs of, 113.

,, ancestral, 180.
Sucker-fishes, fins of, 64.
Sun-fish, food of, 133.

,, young of, 137.

,, form of, 165.
Sword-fish, feeding of, 87.

,, transformations, 135.

T.

Tail, forms of, 53.

,, position of, 60.
Teeth, evolution of, 38.

,, forms of, 42.
Teleostomi, meaning of, 176.
Tench, winter sleep of, 150.
Thallassophryne, poison of,

156.
Thresher, feeding of, 84.

Toothed-carp, affinities of,

189.
Tortoise -fish, armour of, 31.

Undina, tail of, 57, 179.
Urolophus, poisonous tail-
spines of, 154.

V.

Vertebral column, structure
of, 170.

Walking-fish, breathing of, 23.
Weaver-fish, poisonous, 155.
Whiting, feeding of, 31.
Wrasses, colours of, 71.

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