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Columbia University Biological Series,

HENRY FAIRFIELD OSBORN.

1. FROM THE GREEKS TO DARWIN.
By Henry Fairfield Osborn, Sc.D. Princeton.

. AMPHIOXUS AND THE ANCESTRY OF THE VERTEBRATES.
By Arthur Willey, B.Sc, Lond. Univ.

3. FISHES, LIVING AND ‘FOSSIL. An Introductory Study.
By Bashford Dean, Ph.D. Columbia.

4. THE CELL IN DEVELOPMENT AND INHERITANCE
By Edmund B. Wilson, Ph.D. J. H.U.

Head of DINICHTHYS INTERMEDIUS, NEWBERRY, in front
From photograph of specimen collected by Dr. William

Frontispiece. —
and side views. X Yo.
Clark, in the Waverly (Lower Carboniferous) of Ohio, now in the collection of

Columbia College, New York. (V. p. 133-)

ee

COLUMBIA UNIVERSITY BIOLOGICAL SERIES. II.

FISHES, LIVING AND FOSSIL

AN OUTLINE OF THEIR FORMS. AND
PROBABLE RELATIONSHIPS

BY

BASHFORD DEAN, Pu.D.

InstRucTOR IN Biotocy, CotumspiA CoLLteGE, New York City

New Bork
MACMILLAN AND CO.

AND LONDON

1895

a aa

All rights reserved

a

_

LW, ; CoryriGu, 1895,

c By MACMILLAN AND CO.

* i.
—_——

Go ee 1895. Reprinted November,
1895.

> ©
‘ ‘ , Norfwood ress
J. 8. Cushing & Co. — Berwick & Smith.
Norwood Mass. U.S.A.

Ts
MY FRIEND AND TEACHER

JOHN STRONG NEWBERRY

LATE PROFESSOR OF GEOLOGY IN
COLUMBIA COLLEGE

*

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4

PREFACE

——+o0o——_

A KNOWLEDGE of Fishes, living and fossil, is not to be
included readily within the limits of an introductory study.
In preparing the present volume it has nevertheless been
my object to enable the reader to obtain a convenient
review of the most important forms of fishes, and of their
structural and developmental characters. I have also en-
deavoured to keep constantly in view the problems of their
evolution.

At the end of the book a series of tables affords more
definite contrasts of the anatomy and embryology of the
different groups of fishes. And as an aid to further study
has been added a summarized bibliography, including
especially the works of the more recent investigators. .

My sincere thanks are due to my friend and colleague,
Professor Henry Fairfield Osborn, for many suggestions
during the early preparation of the book, and for the care
with which he has later revised the proof. I must also
express my indebtedness to Mr. Arthur Smith Woodward
of the British Museum for his personal kindnesses in
aiding my studies. My thanks are also due to my father,
William Dean, for the preparation of the index.

The figures, unless otherwise stated, are from my
original pen drawings.

B. D.

BIOLoGIcAL LABORATORY OF COLUMBIA COLLEGE,
May, 1895.

CONTENTS

I

Introductory. The form and movement of Fishes. Their classifica-
tion; geological distribution; mode of evolution. The survival of
@omeraused forms 6 we se tk tk

II

The Evolution of Structures characteristic of Fishes; e.g. (1) gills,
(2) skin defences, teeth, (3) fins, and (4) sense organs . 2

III

The Lampreys and their Allies. Their structures and aie relation-
ships. The Ostracoderms and Paleospondylus . . Tae

IV

The Sharks. Their plan of structure; prominent ee ves and
extinct; their interrelationships. . . . ‘ ws

V

The Chimeroids. Their characteristic structures; their J esuoemanne

and relationships . .

VI

The Lung-fishes. Their structures. Extinct and recent forms. The
evolmson Of the group... 6 2. 6 s+ ee te te ht

xi

PAGE

14

57

72

116

xii CONTENTS

VII

The Teleostomes (7.¢. Ganoids and Teleosts). Typical members; their
structures and interrelationships; their probable descent . . .

Vill

The Groups of Fishes contrasted from the Standpoint of Embryology.
Their eggs and breeding habits. Outlines of the development of
Lamprey, Shark, apie: Ganoid, and Teleost. Their larval

development . . aie ee. Re ee

DERIVATION OF NAMES... .. .-. 2 ow een
WIPLIOGRAPHY. Gc 4: wks Sa no oe

EXPLANATORY TABLES:

I, Classification of Fishes. . . . . ‘ 3 3 ee
II. Distribution of Fishes in Geological Time ar 6 be Poe
III. Phylogeny of Sharks, Chimeroids, Dipnoans ... -«
IV. Phylogeny of Teleostomes .. . pos = fe
V. Characters of Vertebre, Fins, Skull (Figs. 310-31 5) ae
VI. Relations of Jaws and Branchial Arches (Figs. 310-315) .
VIL. Heart (Pigs. 316-328) 5. 5 we Se) ey
VIII. Gills, Spiracle, Gill rakers (Figs. 9-12, 326-331) . . .
IX. Digestive Tract (Figs. 326-331) . . .. +. « s
X. Swim-Bladder (Figs. 13-19). . . «. ». « « «
XI. Genital System (Figs. 331-337). . - ». - » 2 « +
XII. Plan of Circulation in Fishes (Fig. 338)
XIII. Excretory System (Figs. 331-337) - . «+ + + «© + +

XIV. Abdominal Pores (Figs. 331-337) - - + + «+=

XV. Central Nervous System (Figs. 339-344). .- + + +
XVI. Seuse.Orgams ope es, ew ee a te Se

XVIT. Integument; Laterdl'line . 2 6 6.6 6 he Ss
XVIII. Developmental Characters .. . 6.

XIX. Comparison of Phylogenetic Tables of aiahits eri

139

179

227

LIST OF FIGURES

ro

a Head of Dinichthys. | "6. PAGE
pace| 90. Pleuracanthus. . Pex
ay 2. Moving fishes, shark and go. Teeth of Miculachuthis - 84
eel . : . 2| 90B. HeadroofofPleuracanthus 84
} 3- Spanish mackeeel = , uerah we SB] OX. Cesteacion .. ‘se im» SS
4. Front view of Spanish g2. Chlamydoselache. . . . 87
: mackerel . . . 4| 93. Heptanchus .... . 88
f 5-8. Numerical lines of fishes - §| 94.Squalus. . .... . 89
- 9-12. Gills of fishes . . .17, 259] 95. Alopias. . . » . - - 89
13-19. Air-bladder . . . .22, 265) 96. lamna. .... + + 90
20-31. Teeth and scales . . . 24} 96A.Cetorhinus . . . . . 90
32-38. Finspines . . . . . 29| 96B. Lemargus ... . . QI
39-43. Unpaired fins . . . 32,33] 97- Squatina . . . . ~~ QI
44-48. Caudalfin . . . . . 37| 98,984. Pristis . . . - + 92
49-54. Pairedfins . . . 42| 99. Pristiophorus . . . . . 93
55-60. Barbels and sense organs 47| 100. Rhinobatis. . . . . - 93
61-68. Mucous camals . . . - 50/101. Raja. . . .. s+ + 94
69. General anatomy of ae 102. Torpedo. . . 95

stome. . - -+ 58| 102A. Dicerobatis (Cepbalop
69A. Skeleton of laniprey . « « 58 tera) . 96
70-72A-D. Bdellostoma, Myx- 103. Shark sbylopeey ai 98

ine, Petromyzon . . 60, 61| 104. General anatomy of Chtinsern 100
73. Paleospondylus. . . . - 65| 105. Skeleton of Chimera . . 102

74- Pteraspis. . - - - + + 66/1054. Ischyodus . . . . « 104
75- Paleaspis. . - - + 66] 106. Myriacanthus . . . . . 105
76, 77. Plates of Preraspis . - + 66) 106A. Squaloraja . . » 105
78,79. Cephalaspis. . . . . 66/1068, Cc. Derm plates of ‘Myria-

80-82. Pterichthys . . . - 68 canthus. . - 105
83. General anatomy of shack - 73| 107-112. Dental plates FP Chime.

84. Skeleton of shark . . «75, 255 a ae - 106
85. Vertebree of shark . . . . 76|113-116A. Spines and claspess

86, 86A. Cladoselache. . . . 79 of Chimzroids . . . . 107
868. Teeth of Cladoselache . . 80/117. Harriotta . . . . . . 108
87. Acanthodes . . . - « 81]118. Callorhynchus. . . . . 109
88. Acanthodes, giaareta: ee ie ee reef |
88a. Acanthodes, teeth . . . 82/120, Chimera, young . . . ut

89. Climatius . . . » » 82\| 121, General anatomy of lung-Gsh 117

xiv

FIG. PAGE
122. Skeleton of lung-fish . . 119
122A. Jaws and skull of Protop-
terus . . + 120
123. Dipterus. . . « « 822
124. Derm bones of head of Dip-
terus . ° . 22%
125, 125 A. Jaws of Dipterus . - 121
126. Phaneropleuron . 122
127. Ceratodus . ‘tee - 123
128. Skeleton of Ceratodus » 123
128A. Skull of Ceratodus . « 2a
129. Lepidosiren » 125
129A. Protopterus . - 126
130. Coccosteus . ‘ - 131
131. Coccosteus, dorsal view. . 132
132. Coccosteus, ventral « 132
133. Dinichthys. . . . « » 233

134-137. Dinichthys, dorsal view 134

138-144. Mandibles of Arthrodi-
rans . Par tS

General acatoniy of Teleost 140

145.

146. Skeleton of Teleost . . 142
147. Skeleton of Ganoid . - 144
148. Polypterus . "148
149. + 148

Polypterus, head of vont

150. Calamoichthys . - 150

151. Gyroptychius . - 151
152. Osteolepis . . 151
153- Holoptychius . » 15%
154. Eusthenopteron - 152
155. Coelacanthus . 153
156. Diplurus - 154
156A. Undina - 154
157. Lepidosteus + 155
158. Elonichthys - 156
159. Eurynotus . - 156
160, Cheirodus . . 157
161. Semionotus. - 157
162. Aspidorhynchus - 158
‘163. Microdon - 158
164. Palzeoniscus + 159
165. Acipenser . . ~ - 160
165 A. Chondrosteus . 161
166. Scaphirhynchus . 162

LIST OF FIGURES

FIG. PAGE
166A. Psephurus ... . 162
1668. Polyodon. . . . . . 163
167, Amia. . . o + « 56%
168. Amia, gular region - « ae
169, Caturus,. . 6 «is « =n
170. Leptolepis . . . . . . 165
171. Megalurus. . . . . « 165
171A. Phylogeny of the Teleo-
stomes + 368
172-174. Deep-sea. fishes . - « « 168
175. Fierasfer ‘ 169
176. Carassius. . 1 5 ss 890
177. Amiurus. . . « «+ « « MOE
178. Callichthys . 172
179. Mormyrus . cae 172
180, Anguilla. . . . + «© « 39%
181. Perca : : 173
182. Gadus A 174
183. Pseudopleuronectés ~ «th
184. Chilomycterus . . oe ke
184A. Lagocephalus . . . . 176
185. Hippocampus . . « 5 ae
185A. Syngnathus . . . . 178
186-199. Eggs of fishes 181
200-215. Development of lam-
prey. . . 189
216-230. Development ‘of shank 194
231-248. Development of lung-
Gen sy hse soe 199, 201
249-268. Development of Ganoid 203
269-283. Development of Teleost 208
284-289. Larval sharks . . . 216
290-295. Larval lung-fishes . 219
296-302. Larval sturgeons. . . 222
303-309. Larval Teleosts . . . 224
310-315. Skulls, jaws, and bran-
chial arches - 254
316-325. Heart and conus ates
riosus. . . 258
326-331. Digestive tracts ¢. . oats
332-337: Urinogenital ducts and
openings. . . - + 267
338. Blood-vessels of shark - 268
339-344. Brain . ... . + 292

= ee

I

FISHES IN GENERAL

INTRODUCTION

FisHEs, defined in a popular way, are back-boned ani-
mals, gill-breathing, cold-blooded, and provided with fins.
It is in their conditions of living that they have differed
widely from the remaining groups of vertebrates. Aquatic
life has stamped them in a common mould and has pre-
scribed the laws which direct and limit their evolution; it
has compressed their head, trunk, and tail into a spindle-
like form; it has given them an easy and rapid motion,
enabling them to cleave the water like a rounded wedge.
It has made their mode of movement one of undulation,
causing the sides of the fish to contract rhythmically,
thrusting the animal forward. A clear idea of this mode
of motion is to be obtained from a series of photographs of
a swimming fish (Figs. 1-2) taken at successive instants :
thus in the case of the shark (Fig. 1) the undulation of
the body may be traced from the head region backward,
passing along the sides of the body, and may be seen to
actually disappear at the tip of the tail. It is the press-
ure of the fish’s body against the water enclosed in these
_incurved places which causes the forward movement.

The density of the living medium of fishes exerts upon
them a mechanical influence ; they are, so to say, balanced

in water, free to proceed in all planes of direction, poised
B I

2 FISHES IN GENERAL

with the utmost accuracy, enabled to rise to the surface or
-sink readily into deep water. <A special organ, the ‘air-,’
or ‘swim-bladder,’ has even been acquired by the majority
of living fishes, which, whatever may have been its origin
or accessory functions (v. p. 21), has certainly to an extraor-

FIG. 1

Figs. 1 and 2.— Movement of fishes, — shark and eel. (After MAREY.)

dinary degree the power of rendering the specific gravity
of the fish the same as that of the surrounding water.
In an example of a swift-swimming fish some of the

most striking peculiarities of the aquatic form may be —

seen. The Spanish mackerel, Scomberomorus (Fig. 3),
shows admirably a stout spindle-like outline ; its entire sur-

——

i

FORM AND FINS

face is accurately rounded,
and there appear no irregu-
lar points which could re-
tard the forward motion of
the fish, Even in the
wedge-shaped head the
conical surface has been
made more perfect by the
tightly fitting rims of the
jaws, by the smoothly

. closed gill shields, and by

the eyes’ accurate adjust-
ment to the head’s curva-
ture. Viewed from in front
(Fig. 4) the fish’s outline
appears as a perfect ellipse,
and seems. surprisingly
small in size : the fins, which
appear so prominent a feat-
ure in profile, can now
be hardly distinguished ;
above and below they form
keels, sharp and thin. In
side view the vertical or
unpaired fins are seen sur-
rounding the hinder region
of the body: they resolve
themselves into dorsal (D),
anal (A), and caudal (C)
elements; the former are
low and stout, elastic in
their firm cutwater margin,
deeply notched and inter-

Fig. 3. — Type of swift swimming fish,
Spanish mackerel, Scomberomorus macula-
tus (Mitch.), J. &G. x 3. (After GOODE
in U.S. F.C.)

4 FISHES IN GENERAL

rupted posteriorly, where useless elements have been dis-
carded ; the caudal is broadly forked, stout in its support-
ing rays, strong in power of propulsion. At its sides a
remarkable ridge has been developed, functioning as a
horizontal keel (2) and preventing the stroke of the cau-
dal from varying from the vertical plane.
The lateral, or paired fins, pectoral and ven-
tral (P and V’), may rotate outward and
arrange themselves in the line of the fish’s
motion, so that in a somewhat horizontal

tion as keels. When thus erected, the
paired fins present a firm anterior margin
which serves as a cutwater. While thus
somewhat similar in function to the vertical

fins, the ventrals and especially the pecto-

Fig. 4. — Front ¥ oo
view of Spanish rals may acquire additional uses: they may
ee serve 4s delicate balancers, or may aid in
guiding or arresting the fish’s motions.

In further conformity to aquatic needs, the entire sur-
face of the fish is notably slime covered, and although
perfectly armoured by plates and scales, yet presents no
point of resistance to forward motion. An internal balance,
moreover, has been effected between the supporting, vis-
ceral and muscular parts: the firm vertebral axis acquires
its central position, and at its anterior end the head struct-
ures form a compact, wedge-like mass: the body muscles
which give the fish its form-contour thin away on the ven-
tral side, permitting in the region between the head and
the anal fin the space occupied by the closely compacted
viscera: respiratory organs occupy a restricted space on
either side of the gullet; the heart and its arterial trunk
are implanted closely in the throat in the median ventral

plane they may, like the unpaired fins, funec-

NUMERICAL LINES 5

line; the dorsal blood-vessel takes its position immediately
below the vertebral axis, and the air-bladder in the most
dorsal part of the abdominal cavity.

FIG. 5

a

‘Rigs. 5-8. — Numerical lines of fishes and cetaceans. The “entering angle”
! 0 Selly snout-tip at the right, and extends as far as the vertical dotted line
___ (36 %, about, of the entire length) ; the “run” then begins and is continued to the
body terminal. 5. Striped porpoise, Phocaena lineata, 6. Spanish mackerel
(Cuban), Scomberomorus cavalla. 7. Humpback whale, Megaptera longimana,
8. Striped bass, Zadrax /ineatus. (All figures after PARSONS.)

____ In acquiring this perfect outward symmetry it is inter-
_ esting to note that the forms of fishes may be said to have

| _ actually evolved the practical solution of the most theoretical
_ problems of curves and displacement in relation to sub-

6 FISHES IN GENERAL

marine motion. A study of the “lines” of typical fishes by
naval engineers * has led to some most interesting results
as to the uniformity of their mathematical “normals.” It
is found, for example, that the “entering angles” of many
and very different fishes are surprisingly similar (Figs. 6
and 8): they thus terminate regularly (at the plane of the
greatest cross-section of the body) at 36 per cent of the
fish’s total length; and the curves of the “run” (ze. of
the hinder part of the trunk, from the plane of the great-
est cross-section to the body terminal), similar for all, are
smooth hollow curves, which in the forward motion of the
fish permit the passage of the displaced water.

It would be unreasonable to doubt that the fish form is
adapted to the mechanical needs of its environment, even
if there existed no further evidence than that of the meta-
morphoses of aquatic mammals. Many of these have
shown so complete an adaptation to water-living that it is
scarcely remarkable that they were early included among
fishes. And it is of further interest that there exist
transitional forms between the land-living mammals on
the one hand and the cetaceans on the other. In the
Seal it is but the initial step in the transformation that
has taken place; the head and body have become bluntly
tapering, the hind legs displaced backward, the foot and
hand webbed, the hair adapted to submerged locomotion.
A further stage in the acquisition of the fish-like form is
shown in the Dugong and Manatee. And finally in the
Dolphin and Whale (Figs. 5 and 7) have been actually
attained the numerical lines of fishes (cf. Figs. 6 and 8).
In these cases, the mechanical conditions of aquatic living
have produced their result only at the greatest cost, —

*’88. Parsons, Displacement and Area Curves of Fishes, Trans. Am, Soc,
Mech. Engineers.

CLASSIFICATION 7

enormous structural and physiological changes had of
necessity to have been attained. The frame of the
head and trunk has become moulded as in the fish’s
form, contours have been elaborately filled out and
rounded, median dermal keels developed, vein valves lost,
and the legs transformed into fin-like appendages.

The form of the fish is accordingly to be looked upon as
cast in a more or less common mould by its environment.
Its internal structures, as in the cetacean, are also ob-
served to be modified in accordance with its external form.
This is a factor in the evolution of fishes which appears
in every group and sub-group. And it has ever stood in
the way of classifying them satisfactorily according to
their kinships.

“Fishes,” used as a popular term, may include Lam-
preys, Sharks, Chimzeroids, Lung-fishes, and “Modern
Fishes” (Teleostomes),—the major groups to be dis-
cussed in the present book. But the relative position of
each of these divisions must at present remain more or
less doubtful. The group of the Lampreys is certainly
widely removed from the remaining ones, standing mid-
way between the simplest chordate, Amphioxus, and the
true fishes: it is usually given a rank co-ordinate with
either of these, and, in fact, with all other groups
of vertebrates, taken collectively. Sharks, Chimezeroids,
Teleostomes, may be taken to represent true fishes ; and
each might be assigned co-ordinate rank, although geneti-
cally the Chimezroids are certainly far more closely allied
to the Sharks than are the Teleostomes. The Lung-fishes,
as a widely divergent group, appear, as W. N. Parker has
suggested, to be reasonably entitled to a rank equivalent
to that of the three groups of true fishes taken together.

8 FISHES IN GENERAL

The present writer has, however, retained in the main
the classification of Smith Woodward, in which Fishes
(Pisces) is looked upon as a class, and is made to include
as sub-classes, (I.) Sharks, (II.) Chimezeroids, (III.) Lung-
fishes, and (IV.) Teleostomes. A tabular grouping of the
fishes is shown below. And on the opposite page their
geological distribution is indicated.

TABLE I

A CLASSIFICATION OF FISHES

Type: CHORDATA (VERTEBRATES),
Class: Marsipobranchii, Lampreys, Paleospondylus, Hag, Lam-
prey, Ostracoderms.
Class: Pisces (True Fishes).
I. Sub-class: ELASMOBRANCHII, Sharks and Rays.
Order: Pleuropterygii (Dean), Cladoselachids (Dean).
os Ichthyotomt (Cope), Pleuracanthids.
= Selachii, Sharks and Rays.
II. Sub-class: HOLOCEPHALI, Chimeroids, Spook-fishes.
Order: Chimeroidei, Sgualoraiids, Myriacanthids,
Chimeerids.
III. Sub-class: Drpnot, Lung-fishes.
Order: Sirenoidei, Dipterids, Phaneropleurids, Cte-
nodonts, Lepidosirenids.
“ ? Arthrodira, Coccosteids, Mylostomids.
IV. Sub-class: TELEOsTOMI, Ganoids and Bony Fishes
(Teleosts).
Order: Crossopterygii, Holoptychiids, Osteolepids,
Onychodonts, Calacanthids.
= Actinopterygii, ;
Sub-order: Chondrostei (Ganoids), Paleoniscoids,
Sturgeons, Garpikes, Amioids.
a Teleocephali, recent Bony Fishes (Tel-
eosts).

NoTE. — The groups italicized are represented only in fossil forms.
The derivations of the scientific names are given on pp. 227-230.

EE Te ES ee a ee ae |

GEOLOGICAL DISTRIBUTION 9°

TABLE II
“a opengl OF FISHES IN GEOLOGICAL TIME

ical distribution of the prominent groups of fishes as here shown is in the main
as rod voy ittel (Palzontologie: Fische). The varying thickness of the lines denotes ap-
proximately increase or diminution in the number of existing genera.

; a itul ¢ 3 eB) 3 é oS)
= l'aa! §| 2 2]. 3g sig| 3s
gaia id iglal slé Sli 1 e
Marsipobranchii.
Cyclostomes . .
PPteraspids . . .
?Cephalaspids . . .
Palzospondylus . .
?Pterichthids

Elasmobranchii.
Cladoselache . . .
Acanthodians. . .
Pleuracanthids
Cestracionts °
Recent sharks (in-
cluding Notidanids)
Rhinobatus

te

:
|

Soue
i

Siluroids é
Gadoids and eiiet
Teleosts . .

10 FISHES IN GENERAL

Fishes hold an important place in the history of back-
boned animals: their group is the largest and most widely
distributed: its fossil members are by far the earliest
of known chordates; and among its living representa-
tives are forms which are believed to closely resemble
the ancestral vertebrate.

The different groups of fishes appear especially favour-
able for comparative study. Their recent forms are gen-
erally well understood, both structurally and developmen-
tally; while a vast number of extinct fishes has been
preserved to serve as a check, as well as an aid, to theoret-
ical investigation.

The remarkable permanence of the different types of
_ fishes seems a striking proof of how unchanging must
_ have ever been the conditions of aquatic living. From as
| early as the Devonian times there have been living mem-
bers of the four sub-classes of existing fishes, —Sharks, Chi-
mzroids, Dipnoans, and Teleostomes. Even their ancient
sub-groups (orders and sub-orders) usually present surviving
members; while, on the other hand, there is but a single
group of any structural importance that has been evolved
during the lapse of ages,—the sub-order of Bony Fishes.
There are many instances in which even the very types of
living fishes are known to be of remarkable antiquity:
thus the genus of the Port Jackson Shark, Cestvacion
(Fig. 91), is known to have been represented early in the
Mesozoic; the Australian Lung-fish, Ceratodus (Fig. 127),
dates back to Liassic times;* the Frilled Shark, Ch/amy-
doselache (Fig. 92), though not of a palzozoic genus, as
formerly supposed (Cope), must at least be regarded as
closely akin to the Sharks of the Silurian.

* Cf., however, Smith Woodward, Zhe Fossil Fishes of the Hawkesbury
Series at Gosford. Memoirs of the Geol. Surv. of N. S. W. Pal. No. 4, 1890.

MODE OF EVOLUTION 1

The evolution of groups of fishes must, accordingly,
have taken place during only the longest periods of time.
Their aquatic life has evidently been unfavourable to deep-

| seated structural changes, or at least has not permitted
these to be perpetuated. Recent fishes have diverged in
but minor regards from their ancestors of the Coal Meas-
ures. Within the same duration of time, on the other
hand, terrestrial vertebrates have not only arisen, but have
| been widely differentiated. Among land-living forms the
_amphibians, reptiles, birds, and mammals have been
evolved, and have given rise to more than sixty orders.

The evolution of fishes has been confined to a note-
worthy degree 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 more than of local im-
portance, 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. Aquatic life has built few
of the direct barriers to survival, within which the ter-
restrial forms appear to have been evolved by the keenest
competition.

It is not, accordingly, remarkable that in their descent
fishes are known to have retained their tribal features, and
to have varied from each other only in details of structure.
Their evolution is to be traced in diverging characters
that prove rarely more than of family value; one form,
as an example, may have become adapted for an active
and predatory life, evolving stronger organs of progression,
stouter armouring, and more trenchant teeth; another,
closely akin in general structures, may have acquired more

;

12 FISHES IN GENERAL

sluggish habits, larger or greatly diminished size, and degen-
erate characters in its dermal investiture, teeth, and organs
of sense or progression. The flowering out of a series of
fish families seems to have characterized every geological
age, leaving its clearest imprint on the forms which were
then most abundant. The variety that to-day maintains
among the families of Bony Fishes is thus known to
have been paralleled among the Carboniferous Sharks, the
Mesozoic Chimeeroids, and the Palzozoic Lung-fishes and
Teleostomes. Their environment has retained their gen-
eral characters, while modelling them anew into forms
armoured or scaleless, predatory or defenceless, great,
small, heavy, stout, sluggish, light, slender, blunt, taper-
ing, depressed.

When members of any group of fishes became extinct,
those appear to have been the first to perish which were
the possessors of the greatest number of widely modified
or specialized 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 characters —that is, those
whose structures were in every way least extreme — were
naturally the best fitted to survive. Thus generalized
fishes should be considered those of medium size, medium
defences, medium powers of progression, omnivorous feed-
ing habits, and wide distribution: and these might be re-
garded as having provided the staples of survival in every
branch of descent.

Aquatic living has not demanded wide divergence from
the ancestral stem, and the divergent forms which may
culminate in a profusion of families, genera, and species,

EVOLUTION 13

do not appear to be again: productive of more generalized
groups. In all lines of descent specialized forms do not
appear to regain by regression or degeneration the potential
characters of their ancestral condition. A generalized form
is like potter’s clay, plastic in the hands of nature, readily
to be converted into a needed kind of cup or vase; but
_ when thus specialized may never resume unaltered its
ancestral condition: the clay survives; the cup perishes.

II

THE EVOLUTION OF STRUCTURES CHAR-
ACTERISTIC OF FISHES

Ir will be the object of the present chapter to review
the gradations which occur in some of the characteristic
structures of fishes and to follow in some degree the
mode of their evolution. We may thus review the con-
ditions of the (1) gills, (2) skin defences (including teeth),
(3) fins, and (4) sense organs.

The structures of the immediate ancestor of the fishes
cannot be definitely inferred: the form, however, must
have been elongate and transversely jointed, for this con-
dition seems to have existed remotely before fishes — in
the broadest sense — had become evolved. This segmen-
tation, or metamerism, of the vertebrate body is best shown
among water-living forms, sometimes indeed in so perfect
a way as to suggest the jointed condition of an earth-worm.

The segmented body of the eel-shaped Lamprey, shown
in section in Fig. 69, illustrates an interesting condition
of vertebrate metamerism. Its entire body, from the
head region to the base of the tail, is composed of drum-”
like segments which closely correspond to one another
in size and in component structures. Each segment
thus resembles its neighbours in its equal portions of the
vertebral column, digestive tract, nerve tube, muscle >
plates and blood canal, and in the arrangement of these
parts with reference to bilateral symmetry. Motion in
this form requires no more of each segment than that its

14

Se aero

EVOLUTION OF STRUCTURES 15

sides contract alternately to produce a rhythmical wave
passing along the entire series of segments and giving the
trunk an undulatory movement. -

Should this elongate body now acquire a more fish-like
form, in attaining, for example, the power of more rapid
movement, it is obvious that this simple type of meta-
merism would undergo a series of changes. Every change
of outward form would be reflected on the parts not only
of each, but of all segments in their common relationships.
To perform more perfectly the functions of their location,
adjacent segments might become enlarged, folded, or
blended, and cause the most puzzling complications of
their component structures. One region of the body might
thus appear to develop at the expense of another, as in the
evolution of fin structures (cf. pp. 32-44), where a vertical
fin fold, representing the sum of the dorsal and ventral out-
growths of the hinder body segments, becomes reduced to
the lappet-like dorsal and ventral fins; the intervening
substance of the fin web becoming drawn to the points
where greater rigidity is required.

The simple metameral character of the lamprey acquires
an especial interest when the different groups of fishes are
examined; for it is found that all exhibit clearly body
segments and segmental structures in the most varied
stages of complexity. To trace metamerism seems, accord-
ingly, a mode of determining to what degree the differ-
ent groups have diverged from a common stem; and to
compare the sums of the archaic metameral characters in
the different types of fishes may perhaps be looked upon
as one of the safest aids in determining their genetic posi-
tion. From the conditions of segmentation the lampreys
must certainly be given a lowly rank; even with due allow-
ance for degeneration of structures they are clearly more

16 EVOLUTION OF STRUCTURES

primitive than the most archaic sharks: while, on the
other hand, to the metameral type of the sharks may the
structures of the remaining groups of fishes be best referred.

1. AQUATIC BREATHING

Respiration in fishes is developed on the primitive chor-
date plan of ejecting water through gill slits perforating
the throat wall. The water taken in by the mouth is rich
in absorbed air, and, as it passes out, is well calculated to
oxygenate the blood suffusing the sides of the gill slits.

Among the earliest chordates there seems evidence
that the gill openings of the gullet were arranged with
reference to some form of primitive segmentation. Per-
haps they occurred as well in the region of the mid-diges-
tive tract, before their location became restricted to the
gullet. There has been as yet, however, little satisfactory
evidence * as to the number or conditions of the gill slits
in very primitive forms. In Amphioxus the gill arrange-
ment seems clearly a most specialized one: its adult con-
dition presents an atrium and an elaborate branchial
basket,t which could hardly have occurred in the lowly
ancestral chordate. Its early larva, however, is known to
possess (but in a condition of assymmetry) but a few gill
slits (seven to nine) from which the many openings of the
adult branchial basket take their origin, —a developmental
stage which most closely and most interestingly suggests
the conditions of higher forms.

* It has generally been inferred that the immediate ancestors of fishes had
not many gill slits, probably not more than eight or nine. A Liassic shark, a
Cestraciont, 7yéodus (p. 85), is known to have had but five; a Permian Pleu-
racanthid, as in the recent Heptanchus, seven (p. 88); the Lower Carbonifer-
ous Cladoselache probably seven.

+ Cf Vol. II, of this series. Willey, Amphioxus and Other Ancestors of the
Chordates.

6 “314

wu

+

i) 1
we

\

YZ

Figs. 9-12. — Arrangement of gills of Bdellostoma (9), Myxine (10), Shark (11), and
Teleost (12). In each figure the surface of the head region is shown at the left.

B. Barbels. BD, Outer duct from gill chamber, 8S. BO, Common opening of outer
ducts from gill chambers. 4.5. Branchial sac, or gill chamber. 4S’, Branchial sac, sec-
tioned so as to show the folds of its lining membrane. G. Lining membrane of gullet.
GB. Gill bar, supporting vessels and filaments of gills. GC. Outer opening of gill cleft.
GF, Gill filament. GX. Gill rakers. GV. Vessels of gill. ¥, ¥'. Upper and lower jaw.
M. Mouth opening. NV, NV’. Anterior and posterior opening of nasal chamber. OP. Oper-
culum. SP. Spiracle. S7, Tendinous septum between anterior and posterior gill filaments,
* Denotes the inner branchial opening; —+, the direction of the water current.

c 17

18 AQUATIC BREATHING

In the singular group of lampreys and slime eels (Mar-
sipobranchs, v. p. 57), the segmental arrangement of the
gills seems of a primitive pattern. In the Californian
Myxinoid (p. 59) the slits are as numerous as thirteen and
fourteen on either side, each opening directly from the
gullet to the neck surface (Fig. 9, G, *, BS', BD). In the
lamprey the conditions are similar, but the number of gill
slits is reduced to seven. In Myxine (Fig. 10, G, BS', BD,
BO) the outer portions of the canals becoming produced
tail-ward have merged in a single pore (Fig. 71 *). In these
forms each gill canal has become dilated at one point of
its course, and in this sac-like portion the blood-suffused
tissues have grouped themselves into leaf-like plates (gill
filaments, or lamellz, AS') to increase their surface of
contact with the out-passing water. The dilating power
of this gill sac has then become specialized so that even
should the animal’s mouth be closed, water for respiration
could be drawn in through the canal’s outer opening:
from this acquired function the elaboration of bran-
chial muscles and a supporting framework of cartilage
(branchial basket, Fig. 69 A, B&B) may have taken its
origin. _

Among fishes proper many stages in the evolution of
gill organs are represented. They show altogether a
marked advance over the conditions of Fig. 9. There
has been a general tendency to press closely together the
gill pouches and to elaborate into thinner and larger
lamellz the blood-suffused tissue. In this process the
gill chamber has become slit-like, bearing gill lamellz only
on its front and rear margins; its supporting tissue has con-
solidated into stout vertical gill bars, the gill structures in
general, becoming more highly perfected, tending to recede
from the surface. These conditions may best be illustrated

eye

GILL CHARACTERS 19

——_ =. -,

by contrasting the highly modified gill apparatus of a bony
fish with the more archaic type of the shark.

In the sharks (p. 73) the gill slits pierce separately
the throat wall, as in the lamprey, and thus retain their
primitive segmental arrangement (Fig. 11). Their number
is usually five on either side, but in an archaic form (Hep-
tanchus, p. 88) may be increased to seven. Above and
in front of the line of gill slits occurs a small opening
leading into the gullet, the spzvacle (SP). This, though
at present possessing but few gill lamella, and therefore

ee SS ett

of little respiratory value, was doubtless quite like its
| neighbours before its gill-supporting tissue became of value
__~ in suspending the lower jaw. It may now aid the mouth

opening in admitting water to the gills. At the left of
; the figure (Fig. 11), the narrow slit-like openings of the
} gill clefts are seen at GC: at the right, where the upper
portion of the head has been removed, the gill lamellz
are shown at GF; the tissue intervening between the
gill pouches is reduced to a thin tendinous septum, S7,
at whose inner rim is the cartilaginous gill arch or bar,
GB, supporting the branchial vessels, GV.

In the gill region of a bony fish (Fig. 12) a number of
modified characters are now evident: the spiracle has
become obliterated; the number of gill bars reduced —
in one form but two on either side remaining. These
have become closely pressed together, and bent backward,
receding from the surface of the head: their gill lamellz
have become larger and more numerous, their intervening
septum, SZ, reduced in size. The gills no longer open|
separately at the surface, but into an outer branchial
chamber formed and protected by a large overlapping
scale, or opercle, OP. This shield-like organ is hinged
at its anterior margin and opens or shuts rhythmically as

———S
-

: —_

20 GILL CHARACTERS

the throat muscles draw in or eject the water used in
respiration. On the gullet wall, the gill bars, now seen
to be closely drawn together, have acquired marginal
outgrowths, or gill rakers, GR, which form an inter-
locking screen across the gill openings and prevent the
escape of food organisms. So perfect may this apparatus
become that the opening and closing gill bars may retain
even microscopic life.*

Between the conditions of Figs. 11 and 12 there occur
many transitional forms.

To protect the gill region, specialized devices are known
to have been evolved early in the history of fishes, —
the more early if, as Garman has supposed, the gill fila-
ments in primitive sharks protruded at the sides of the
head.t+ There are thus the gill-encasing derm frills of
the archaic sharks, Cladoselache, Chlamydoselache, and
Acanthodes (pp. 78-83), or of Chimzeroids (p. 100). These
protective structures, the writer believes, may well have
originated independently even within the limits of sub-
groups. They have certainly no direct relation to the
opercle of bony fishes.

Modes of respiration by gill filaments have been found
in endless variety among fishes, clearly dependent in the
majority of cases upon environment. Thus fishes that
require a temporary existence out of water will be found
to have specialized spongy gill filaments and a closely fit-
ting gill cover to keep moistened the respiratory organs
(e.g. Callichthys, p. 172). :

* Thus in many bony fishes, ¢,g. mullet or Brevoortia (menhaden), the
inner margins of the gill bars are fringed with what appears like the finest
gauze, each gill raker giving off primary, secondary, and tertiary branches. A
somewhat similar condition occurs in the shark, Selache (p. 90).

+ This condition appears to have been possessed by the Lower Carbo-
niferous Cladoselache. —

SWIM-BLADDER 21

To live a longer time out of water has been rendered
possible only by the appearance of a lung-like organ. Such
a structure, however, would have been of too great impor-
tance in the living economy of terrestrial vertebrates to
have had a sudden origin: it may most reasonably have
been derived from a similar structure occurring very gener-
ally among fishes. The lungs certainly resemble the swim-
: bladder of fishes in so many important characters that it
. seems difficult to regard these organs as morphologically

distinct. In itself the swim-bladder must be looked upon

as an ancient and essentially a generalized structure, for
within the groups of fishes it has already acquired a vari-
: ety of modified characters: appearing in a lowly condition
in sharks, it acquires a balancing function in the majority
of bony fishes ; in some forms (carp, siluroids) its function
connects it with the auditory organ, often by a highly
elaborated apparatus: while in other forms (Ama, Gar-
pike, Dipnoans), it is unquestionably of respiratory value.

_ The wide range in the characters of the air-bladder (cf.

Figs. 13-19, and Table, p. 264), even among recent fishes,

would naturally favour its homology with the lungs: it may

thus be paired or unpaired, attached by its duct to either
the dorsal, lateral, or ventral wall of the gullet: it. may
present the most varied characters in its lining membrane
or in its vascular supply. When, moreover, it becomes of |
respiratory value (e.g. Dipnoans, Polypterus), the gills are |
known to become in part degenerate. The larval history |
of amphibians, presenting so perfect a transition between |
-gill-breathing and terrestrial vertebrates, should alone seem |
to render more than probable the general homology of air- |
bladder and lung — an homology which a closer knowledge
of the conditions of the lungs of the lower urodeles (e.g.
Necturus may well be expected to establish definitely.

yy a ad FL a yaar ety ty Pe

ae,

FIG, 13

STURGEON
AND MANY
TELEOSTS

LEPIDOSTEUS
ann = «6AMIA

ERYTHRINUS

CERATODUS

POL YPTERUS
AND
CALAMOICHTHYS

LEPIDOSIREN ~
AND
PROTOPTERUS

Figs: 13-19. — Air-bladder of fishes, shown from the front and sides. Cf. p.
264. A. Air-or swim-bladder. AD. Air duct. D. Digestive tube. (After WILDER.)
13. Sturgeon and many Teleosts. 14. Amia and Lepidosteus, 15. Erythrinus, a
Cyprinoid Teleost. 16, Ceratodus. 17. Polypterus and Calamoichthys. 18. Lepi-
dosiren and Protopterus, 19. Reptiles, birds, and mammals. The diagrams illus-
trate the paired or unpaired character of the organ, its varied mode of attachment
to the digestive tube, and the smooth or convoluted condition of its lining mem-
brane.

22

SCALES AND TEETH 23

The mode of origin of the lungs as an unpaired divertic-
ulum of the gullet is in every sense similar to that of the
air-bladder.

2. THE DERMAL DEFENCES OF FISHES

The dermal defences of fishes include scales, spines, fin -

rays, armour plates, and teeth, presenting in all a wide
range of calcified structures. They have usually an outer,
or surface layer of hard enamel-like texture and an inner
substance heavy, stout, and bone-like. The former is de-
rived from the outer layer of the skin (epidermis), the
latter from the derma. The relation of these structural
parts may be well seen in a section of shark skin which
passes through one of its minute limy cusps, or dermal
denticles (Fig. 20). The outer skin layer, £’', originally
covered the denticle, which grew outward, papilla-like,
beneath it ; its inner surface, in contact with the outgrow-
ing papilla, secreted the enamel, Z, and is known as the
enamel organ, ZO: at the cusp, however, the epidermis is
early worn away. The bone-like substance ofthe tooth is
clearly formed in the lower (dermal) layer of the skin, D’:
it is formed by the calcification of the outer layers of the
tip and base of the dermal papilla, leaving a vascular cavity,
PC, within. This limy substance, “dentine,” D, presents
microscopically a columnar “cancellated” structure; in

x this and in its lack of bone cells it differs structurally

from true (cartilage) bone.
The dermal denticle of the shark is certainly the sim-

_ Pplest form of a calcified skin defence: it appears to repre-

sent the ancestral condition of the various scales, teeth,
‘or bone plates which have been evolved in the groups of
fishes. It is usually of minute size, and studs closely the
entire surface of the skin, forming shagreen. In many

|

4
FIG. 20

Figs. 20-31. — Mode of evolu-
tion of (teeth and) dermal defences. —
20) Shagreen denticle of shark, x 30,+
“cross section, (After HOFER.) JD.
Dentine. DD’. Derma, £#. Enamel.
&'. Epidermis. £O.Enamelorgan, =
PC. Pulp cavity, showing nutritive
tubules passing into the dentine, —
(2p. Shagreen denticle (“placoid) —
scale") of Greenland shark,
gus, viewed from the side and (A),
top, enlarged. 22, Shagreen denti-.
cles of shark, Scy/dium, showing.
mode of arrangement. X 30, 23.
. Shagreen of sting-ray, Urogymnus,
nat.-size. (After SMITH WoopD-
WARD.) 24. Ganoid dermal plates of Lepidosteus. A. Inner face of ganoid plates,
showing tile-like device of interlocking. 25. Variation of ganoid plates in Aetheolepis,
(After SMITH WOODWARD.) Plates from different regions vary in outline from cir-
cular to lozenge shape. 26. Coalesced ganoid plates of the siluroid pares
(27. Jaw of Port Jackson shark, Cestracion, 28. Dental plate of extinct cestraciont (?),
“Sandalodus. 29. Dental plates of jaw of sting-ray, hte (?). 30, Dental plates
of eagle-ray, Myliobatis, 31. Scales of Teleost. A. A single scale enlarged.

24

EVOLUTION OF SCALES 25

members of the shark group the denticles are scattered
over the body without traces of metameral arrangement
(Fig. 23); in others they acquire a segmental position
(Fig. 22). Usually the denticles possess very definite
shapes and regional characters ; their basal portion, where
implanted in the skin, may thus become of enlarged size
and regular outline (Fig. 21 A), their projecting cusps
tapering, blunted (Fig. 23), or branched. Sometimes the
fusion of contiguous denticles may occur (as in the en-
larged blunted denticles of Fig. 23).

The evolution of the more perfect body armouring of
fishes from shagreen denticles has not been followed in
minor details. It appears, however, that the calcifica-
tion of the skin which occurs superficially in the dermal
papillae of the shark may in other fishes be traced oc-
curring in deeper and deeper layers of the derma: the
papilla at the surface accordingly lose their functional
importance, and tend to disappear, while the calcified
tissue of the derma—representing morphologically the
basal region of the denticles— is coming to occupy more
and more definite tracts. These processes have already
taken their origin within the group of sharks.

An interesting condition in the subsequent evolution of
the dermal armouring is illustrated in Fig. 25, and has
been described by Smith Woodward. The circular bone
plate of the figure is a calcified dermal tract which still
retains, scattered generally over its surface, traces of
shagreen tubercles: from this shark-like condition a
well-marked gradation in the form of the derm plates
may be traced in different body regions of the same
fish: according to metameral needs there are acquired
_ rectangular or lozenge-shaped outlines. In Fig. 24 these

_ bone or “ganoid” plates are seen to constitute a com-

26 EVOLUTION OF SCALES

plete but flexible body armouring, made additionally
strong by an interlocking articulation of its elements
(24 A).

In this form the enamel-like surface layer (“ganoine”)
of the ganoid plates is believed to be derived from the
dentine substance, and not deposited by the epidermis:
they bear numerous shagreen denticles during an early
period of life.

The most complete encasement of a fish’s body by
dermal plates is shown in Fig. 26, v. p. 172. The met-
ameral conditions have here permitted extended fusions,
a single dermal plate enclosing the upper, or lower
division of the muscle-plate of either side.

The thin horn-like scales of the majority of recent
fishes, ¢.g. carp or perch (Fig. 31 A) are probably
derived from a condition not widely different from that
of Fig. 24. They take their origin, however, in a deeper
layer of the derma, thence grow outward, arising as
if from deep and flattened pockets. Their substance
becomes horn-like, rather than limy, and they enlarge in
outline, rather than in thickness. Their hinder margins,
often crenulate, overlap widely the neighbouring scales ;
their arrangement is in direct relation to the underlying
metameres, and their surface is densely slime-coated.
The dermal armouring they thus constitute is both light,
tough, and flexible.

Degeneration of scales is shown to occur in many
types. In some forms their size may become micro-
scopic (eel), in others enormously enlarged (mirror carp).
In cases they may entirely disappear (leather carp).
The fusions of the dermal plates of the trunk-fish or
of the sea-horse (p. 177) are probably degenerate.

TEETH 27

Teeth

Teeth have long been known to represent the dermal
defences of the mouth rim. In this region they have
become of especial value in the living economy of verte-
brates —seizing, holding, cutting, or crushing the food-
material. They have here accordingly been retained and
specialized. In the sharks the dermal denticles of the
mouth rim are often identical in shape and pattern with
those of the entire body surface: they differ only in
their larger size. Their arrangement in many rows still
presents clearly their metameral character.

The forms of teeth acquired among the different groups
of fishes suggest closely the evolution of the more modi-
fied dermal defences. In general, they are found to vary
widely according to their function or location ; those near-
est the dermal margin of the mouth usually retaining
the cusp-like and more primitive features. Thus in the
jaw of Port Jackson shark (Fig. 27, v. p. 85), the teeth of
the symphysial region clearly represent shagreen denti-
cles ; while those deeper in the mouth, large and blunt,

serve as crushing or “pavement” teeth. These must evi- \.

dently be looked upon as standing in the same relation to
the anterior cusps, as do the bone plates of Fig. 25 to the
' derm denticles of Fig. 23 ; the fused crushing teeth have
still retained their metameral arrangement. The dental
plates (Fig. 30) of a ray, Myliobatis (p. 96) show more
perfect conditions for crushing; they are uniform in size,
tightly set, and present a smooth, mosaic-like surface. A
still more perfect fusion of the dental elements occurs in
a ray, closely akin to Myliobatis ; all lateral elements have
here been fused, but their metameral sequence has been re-
tained (Fig. 29). In Fig. 28 is shown a dental plate of a

A

28 TEETH AND SPINES

fossil shark (?), Sandalodus, which probably represents a
condition of complete fusion; it would accordingly cor-
respond to the sum of the dental elements of half of the
jaw of Fig. 27. ;

In more highly modified fishes the tooth-producing
region has become greatly extended ; teeth are present not
only on the jaw rims, but deep in the mouth cavity,
studding its floor and roof, and occurring even on the
tongue, gill bars, and pharynx.

Fin Spines

Primitive dermal defences appear to have played a
prominent part in the formation of fin spines. The clus-
tering of dermal cusps on the exposed margin of a fin
may have been an important initial step toward the for-
mation of a rigid cutwater. The anterior margin of the
fin of Fig. 49 is whitened with a fusion of dermal tuber-
cles which must have formed a firm encrusting support;
the extension of the calcification of the bases of the tu-
bercles would accordingly be the mode of origin of a fin
spine. In Fig. 32 is shown a spine that appears largely
of this origin. A similar spine (Fig. 33) shows its dermal
tubercles not only at its sides, but in a most marked
way at its hinder margins. In Fig. 34, representing the
“sting” of the sting ray, a series of dermal spines, bear-
ing rows of minute denticles are seen to arise in a meta- |
meral succession. A condition somewhat similar is known
in the Carboniferous shark, Edestus (Fig. 35), whose spine,
often of gigantic size, is of special interest, since it shows
how important a part in spine-formation may be taken by
the dermal defences of many successive metameres. The
spine is clearly segmented, and as its separate elements
(Fig. 37) are bilaterally symmetrical (Figs. 36 and 38), its

FIN SPINES 29

position was probably in the median line of the body.
The well-marked, backward curve of the spine suggests _

sl

—_————a. = =.

Figs. 32-38. — Fin spines. 32. Fin spine and pectoral fin of Acanthodian.
33. Hybodus (cestraciont shark). 34. Sting-ray, Zrygon. 35. Edestus heinrichsii
(Carboniferous shark, known only from its spine), side view of spine. X }. 36,
37, 38. Dorsal view, separated element and transverse section of Edestus spine.

that fin structures could not well have existed behind it.
Each separate element has an elongated basal portion,

rr

|
§

=< is ae

-

ny

30 EVOLUTION OF FINS

which ‘apparently was imbedded in the integument; its
gouge-like form (Figs. 37 and 38) permitted it to be firmly
apposed to its anterior and posterior neighbours. Each —
median enamelled cusp represents apparently the sum of
the shagreen papillz, occurring in the median-dorsal region
of each metamere, its gouge-like underlying portion the
metameral calcification of the bases of the denticles.

What has been the mode of origin of the primitive
derm cusps is a puzzling question. It is significant, per-
haps, that they occur in primitive forms (sharks) in con-
nection with the sense organs of the lateral line (p. 50),
and that they are in this region retained in a number
of archaic forms (Polypterus, p. 148, Callichthys, p. 172),
which have in all other body parts evolved protective derm
plates.* It is certain that for the sensory groove of the
lateral line, no more simple, protective devices could have
arisen than conical elevations of skin. Arising in this
region, they may have extended their protective functions
over the entire body surface.

3. THE EVOLUTION OF FINS

Fins are the organs of progression adapted to the
needs of aquatic living. A fish, balanced in its living
medium, acquires, as has been seen, a boat-like form,
enabling it to pierce the water in the least resisting
manner. Its appendages, when they come to arise, must
reasonably be looked to to fulfil the mechanical condi-
tions of aquatic motion in order to propel to the best
advantage the lightly balanced and boat-shaped mass.
Fins might thus be expected to arise as keel-like struct-

*In the sensory canals of the head of Chimera, the presence of scattered

bony plates, protective in function, v. p. 114, would suggest the concentration
of the marginal cusp elements for more perfect protection.

MEDIAN FINS 31

ures, z.¢. as ridges in the direction of the fish’s axis or
line of motion.

Fish fins have long been distinguished as vertical (me-
dian, or unpaired) or lateral (paired), the former function-
ing both as keel and means of propulsion, the latter as
accessory and specialized balancing organs.

Median Fins

Median fins are unquestionably the older. They exist
in the simplest condition in those fishes whose axis is long
and whose motion is undulating. Indeed, the sole swim-
ming requisite is here the continuous dermal keel which
passes down the back from the head to the body terminal,
and extends thence forward on the ventral side. The
undulatory motion of the body is well transmitted to the
surrounding medium by the exaggerated undulation of
this long, waving fin web. This condition was probably
the ancestral one in the evolution of fishes. It represents
the simplest metamerism ; it occurs as the adult condition
_ in the lampreys (p. 57), and as the embryonic or larval
stage in all fishes, appearing before any traces of paired
fins are known ; it is even adverse to their specialization :
should life habits require undulatory motion, paired fins
must inevitably tend to disappear (eel, p. 173; Cala-
moichthys, p. 150).

From this condition the further evolution of the un-
paired fins may thus be theoretically outlined.

The primitive continuous dermal fin could have been
of little value in active movement: its more rapid undu-
lations could not have greatly increased the rate of motion,
Since its web, lacking in supports, would not have retained
its rigidity. As the simplest means of strengthening the
fin fold, “ actinotrichia” (Ryder), appear to have been early

32

EVOLUTION OF FINS

evolved (Fig. 39, 7); these are slender, unjointed fin sup-
ports, passing from the body wall to the margin of the

fin, appearing to arise without relation
to the underlying body segments. The
more rapid undulations of the contin-
uous fin would next cause nodes to
arise ; and at other points the greatest
mechanical stress would occur. These
portions of the fin web would ‘accord-
ingly become prominent, while the in-
tervening or useless parts would dimin-
ish in width and tend to disappear. The
body terminal (tail, caudal fin) has now
become the seat of propulsion: dorsal
and ventral fins arise as lobate elements
of the fin fold, functioning as vertical
keels in the region of the body where
mechanical stress demands them (v. Fig.
40), increasing in size as the intervening
portions of the web gradually disappear.
Their rate of growth is doubtless af-
fected by the appearance of the paired
fins ; for even at.an early period .of de-
velopment these are known to have an
important function in balancing the fish.

The lappet-shaped fins (Fig. 40) next
acquire more rigid supports. Cartilagi- —
nous rod-like elements arise within the
fin web, arranged in metameral sequence,
representing, perhaps, fusions of actino-
trichia. As shown in Fig. 40, these car-

Fig. 39.— Hypothet- tilaginous “vadials,”’ R, appear to be

ical ancestral shark, Let
ters as on p. 33.

largest and stoutest in the widest por-

MEDIAN FINS 33

tions of the fin lobe, and thence to taper in size toward
the nodal points of the web. Each radial appears shortly
to segment off a proximal joint, or “ dasa/” cartilage, B, to
secure a more perfect attachment with the wall of the body.
_The subsequent evolution of the fins appears to have
been determined by two modifications of growth, —the
clustering of the radial and basal elements, and the
encroachment of newly formed marginal (distal) rays

40-43.— Evolution of unpaired fins. 40. Plan of reduction of vertical fin
web into its dorsal, anal, and caudal elements. 41. Arrangement of fin supports
in primitive fin (C/adoselache). 42, Plan of archaic unpaired fin in (larval) shark.
43- Unpaired fin of fossil Crossopterygian, Holoptychius. (After SMITH WoOoOD-
WARD.)

A, Anal fin. 2. Cartilaginous basal (fin support). C. Caudal fin. D. Dermal
margin of fin. D’. Anterior and D”. Posterior dorsal fin. . Cartilaginous radial
(fin support). 7. Actinotrichia,

upon the functions of the older fin supports. Three
stages in this metamorphosis will be seen in Figs. 41-43.

- The first illustrates the dorsal fin of an ancient shark

(Cladoselache, p. 79), and will at once be seen to present

_ most primitive conditions: it closely resembles the theo-
D

34 ANAL AND DORSAL FINS

retical dorsal fin, D' or D" of Fig. 40. The form of the
fin suggests the lobate constriction of the continuous fin
web ; its radial supports, #, extend from the body wall to
the margin of the fin, and between them traces of actino-
trichia are to be seen. The anterior margin of the fin
must now function as a strong cutwater, its supporting
elements, both radial and basal, tightly clustering. A fin
of this character could evidently have possessed a greater
freedom of lateral movement in its hinder than in its an-
terior part; and thus the clustering of the fin supports
becomes of especial significance. The region of move-
ment, restricting itself to the hinder part of the fin,
permits extensive fusions of the supporting cartilages
anteriorly, and leads ultimately to exceedingly complex
conditions. The dorsal fin of a Coal Measures fish (Ho-
loptychius, p. 151) has thus (Fig. 43) specialized the power
of lateral movement in the highest degree. The length
of the fin has, in the first place, become greatly compressed,
a process which seems to have resulted in implanting the
anterior basals, B, deeply into the integument and in
fusing them: the posterior basals then appear to have
been everted from the surface of the body. Here they
still retain their segmental arrangement, but are irregular —
in shape and reduce in size distally. :

An important part is taken by the dermal margin of
the fin in modifying the size of the older fin supports.
The simplest form of a dorsal fin of a recent shark (Fig.
42) has thus more than half of its functional area of a

dermal origin, although, in other regards it resembles — ¢

closely the conditions of Fig. 41. The dermal margin of
the fin has apparently increased to the detriment and
consequent reduction of the cartilaginous elements; it
produces in its secondary structures light flexible horn-

CAUDAL FIN 35

like rays, which prove stronger and more serviceable than
the heavier radials; it seems more capable of adapting
the fin for special uses.

Accordingly, in many forms of recent fishes, notably
bony fishes, the entire fin is found to become of dermal
origin; the radio-basals, greatly reduced in number and
size, extend no further outward than the base of the fin;
they are usually small and irregular, and are often deeply
sunken within the body wall.

After this glimpse at the mode of origin of the vertical
fins, z.e. dorsals and anals, the history of the final vertical
fin, the tail, and of the paired fins may next be reviewed.

The Caudal Fin

The tail, or caudal fin, is the main organ of aquatic
propulsion, and it is doubtless on this account that it
presents so wide a range in its structure and outward
form. From the earliest times there are found fishes of
all groups whose tail shapes are tapering (dphycercal, Fig.
47), unsymmetrical (heterocercal, Figs. 45, 46), or squarely
truncate (homocercal, Fig. 48), as the mechanical needs
in swimming may have demanded.

The following summary of the mode of evolution of
the caudal fin seems to be warranted by study of fossil
and embryonic forms. The vertical fin fold of the ances-
tral fish was probably carried around the body terminal
and strengthened by constant actinotrichia (Fig. 39 C), a
condition similar to that (Fig. 44) of an early larval
stage of living fishes (frotocercy). This caudal structure,
however, could have proven-of value only in sluggish
undulatory motion. The functional needs, which gave
rise to radials anteriorly, have in the tail region produced
firmer and stouter fin supports. These appear both on the

36 CAUDAL FIN

dorsal and ventral sides, but, unlike the radials of the anal
or dorsal fins, do not segment off basal elements. They
first occur in the region of the base of the caudal, as in
the embryonic stage (Fig. 44, 2), since, perhaps, it is in this
region that the greatest stress occurs in propulsion. It
is not until a later stage that their metameral sequence
is extended backward to the tip of the vertebral axis
(Fig. 40, C).

With the origin of cartilaginous supports there seems
‘to have arisen a mechanical need for enlarging the ventral
lobe of the caudal; it is here certainly that in the majority
of early forms the radials appear longer and stouter, giv-
ing rise to the condition of heterocercy of Figs. 45 and 46.
The greater functional importance of the radials of the
ventral region, R+H, is acquired contemporaneously with
the upturning of the end of the vertebral axis. In the
tail of a Lower Carboniferous shark (Fig. 46, v. p. 79), an
extreme degree of heterocercy has been acquired before
the radials of the lower lobe have extended themselves in
the hindmost region of the vertebral axis ; the ventral web
of the upper tail lobe, accordingly, is still strengthened
by minute (dermal) rays, which the writer believes homol-
ogous with actinotrichia; on the fin’s dorsal side the
radials have been abruptly upturned with the notochord,
and are fused into a compact Cutwater.

The plan of structure of the shark’s caudal fin (Fig. 45)
may in its most primitive form prove to be the ancestral
one of fishes; if this is the case it would give rise to the
types of caudal fins of Figs. 47 and 48. That it has given
rise to the latter form cannot be doubted, for even in the
adult condition of the fin the notochord, Vy, may be seen
passing to the upper lobe of the tail; the essential out-
ward form of this truncated, or homocercal, tail had already

<a

Figs. 44-48. — Evolution of caudal fin. 44. Embryonic caudal of Amia. 45. Hetero-
_cercal caudal of shark, Cestracion. 46. Heterocercal caudal of Cladoselache. 47. Diphy-
_ cercal caudal of Polypterus. (After L. AGASSIZ.) 48. Homocercal caudal of Teleost.
- (After RYDER.)
_ 2. Dermal fin supports. Z. Lateral line. 44. Spinal cord. A7C. Membranous caudal.
_ 4%. Notochord. N+, and R+N. Neural spines, including probably radial and basal
elements. #. Radials. R+-H. Hzemal arch and spine; includes as well, probably, radial
. aad basal elements.

i. 37

38 PRIMITIVE CAUDAL FIN

been acquired in ancient sharks (Fig. 46). The fin of Fig.
47, however, has not generally been looked upon as derived
from shark-like conditions ; it has, on the other hand, been
thought to be most nearly of the ancestral form. The
vertebral axis does not appear to be upturned, and the
ventral and dorsal lobes of the fin remain nearly sym-
metrical, or diphycercal. This form of the caudal fin, on
the other hand, has been noted to present many degener-
ate characters, ‘and to the writer* it seems more reasona-
ble to regard the diphycercal condition as in many cases
directly descended from the heterocercal. This might be
effected by the terminal portion of the vertebral rod abort-
ing (as in Fig. 47, VV), and the upper and lower lobes of the
tail becoming pressed backward until their hinder margins
appose in the axial line.t The form of diphycercy which .
is seen in Fig. 119 is unquestionably of little morphological
value ; it occurs commonly in deep-sea fishes of every group,
and must be looked upon as a degenerate condition result-
ing from impeded motion under the conditions of bathyb-
ial, or deep-sea living.

The cartilaginous supports of the caudal, like those of
other unpaired fins, become greatly reduced in size by the
encroachment of dermal rays. In the tail of the fossil
shark (Fig. 46) the cartilaginous supports, X, extend to the
very margin of the fin: in the modern shark (Fig. 45) a
large part of the functional fin area has become of second-
ary, or dermal origin, D. In the caudals of Figs. 47 and
48, distinct dermal rays, D, are seen, extending from the
body wall to the fin margin, splitting and segmenting dis-
tally in becoming more perfectly specialized in function.
The cartilaginous supports, R+/V and Rk +H, must now be

* Fournal of Morphology, 1X, 1, 1894.
¢ Gephyrocercy of Ryder.

PAIRED FINS 39

* looked upon as including the elements of both the radials
and the hzemal or neural processes and spines.

The Paired Fins

The paired fins of fishes claim an especial interest as
the precursors of the limbs of the land-living vertebrates.
In this light they have been widely studied, and many
schemes have been devised for the comparison of the parts
of the five-fingered extremity, or chetropterygium, of the
amphibian with the fin structures of many fishes. The un-
satisfactory character of these homologies, however, is felt
at the present time more generally than ever, and many
morphologists believe with Dr. Mollier * that the ancestral
form of the terrestrial limb cannot be found in any of the
known types of paired fins.

Among fishes, on the other hand, there appears to be a
well-marked unity of plan in the varied forms of the
paired fins; and there exists so perfect a gradation in
structural characters in the different forms that it seems
impossible to doubt their genetic kinship. Which fin,
however, must be looked upon as the ancestral type is still
disputed. Professor Gegenbaur has long maintained that
the fin of Fig. 54 (or, better, the pectoral fin of Fig. 147)
is to be looked upon as the most primitive form, or Archip-
terygium. It is a leaf-shaped fin, whose principal carti-
laginous supports are arranged in a row from base to tip
in the position of a mid-rib: and whose minor fin supports
are grouped more or less symmetrically on either side of
this axis (cf. Figs. 53, 54, 121, 123, 126). The archipteryg-
~ ium is believed by Gegenbaur to have had a centrifugal

origin: it arose behind the gill region, representing in its

* SB. Gesell. f. Morph. Miinchen, 1894, p. 17.
+ Gegenbaur, Das Flossenshelet der Crossopterygier. Cf. Morph. FB, 1894.

40 : LATERAL FOLD FINS

supporting substance the fusion of the cartilages of the
hindmost gill bars ; in its outward growth the median axis of
the fin was first produced, the minor supports then arrang-
ing themselves on both anterior and posterior margins.
The fin of Fig. 52 was believed to represent a specially
evolved (or “monoserial’’) form of the archipterygium: the ©
hindmost of its elements, 2, was homologized with the
primitive fin stem, along whose posterior (post-axial) mar-
gin the elements, 2, no longer occurred. The structures
of Fig. 53 were adduced as a transitional stage in the dif-
ferentiation of the biserial archipterygium (Fig. 54) into the
monoserial form of Fig. 52.

The theory of Gegenbaur as to the origin and evolution
of the paired fins cannot be said to be in any way generally
supported at the present time. The opposing view, that
of their derivation from a continuous lateral dermal fin
fold, based on the work of Thacher, Balfour, Mivart, —
Dohrn, Wiedersheim, and others, is widely accepted, and
continues to gain supporting evidence on the sides both
of embryology and palzontology.

In the following discussion of the paired fins the
writer has mainly followed the recent studies of Wieders-
heim.*

The paired fins are believed to have arisen as balancing
organs, accessory in function to the vertical fins. They
probably occurred early in the line of descent as a response
to a need for balancing the fish’s body, at the time when
the vertical fin was separated into caudal, dorsal, and anal
elements. There can be little doubt that they first arose
in the line of the fish’s motion, and are known primitively
(Figs. 49, 50), as a pair of keel-like lateral lappets arising
somewhat ventrally, and directed outward and downward.

* Das Gliedmassenshelet der Wirbelthiere, 1893.

PAIRED FINS 41

The foremost pair appears anteriorly not far behind the
gill region: from its position it has certainly the more im-
portant mechanical function in balancing the fish’s length
—on this account becoming more widely modified in form
and function as the pectoral fins. The hinder pair, or ven-
tral fins, though in the plane of the pectorals, has a more
ventral position, the hinder borders converging in the
region of the anus. The ventral fins are certainly placed
in the most motionless region of the fish: they are little
affected by either the lateral or upward movements of the
body ; and. remain accordingly smaller in size and simpler
in structure than the pectoral fins. That there may have
existed in primitive fishes a third (post-ventral) pair of fins
is by no means improbable (cf. T. J. Parker, Ref. p. 244),
although its presence has not as yet been satisfactorily
demonstrated.

The paired fins thus appear to have been derived from a
continuous dermal fold, similar in every way to that giving
rise to the vertical fins. They appear, moreover, to have
undergone the same mode of evolution in their structures
as have the dorsal or anal fins. The unpaired fin fold as it
passed forward on the ventral side of the body may primi-
tively have forked in the anal region, and given rise on
either side to a lateral fold. In these might next appear
an anterior and posterior pair of lappets, — pectoral and
ventral fins,— whose positions would be determined by
mechanical needs, and whose size would increase as the
intervening and useless portion of the dermal féld disap-
peared. In the subsequent history of pectoral and ventral
fins, supporting elements, actinotrichia, radials, and basals,
would arise in the same way as in the unpaired fins, and a
similar metamorphosis of the fin form would take place,
owing to the concrescence of these elements and to the

ASN Nat
PASAY
WSO

»

Figs. . — Evolution of paired fins. 49-50. Pectoral and ventral fins of Cladose-
lache. X }. 51. Pectoral fin of Acanthodian, Parexus, (After SMITH WOODWARD.) 52.
Pectoral fin of Heptanchus. (After GEGENBAUR.) 53. Pectoral fin of Xenacanthus
(Pleuracanthus.) (After A. FRITSCH.) 54. “Archipterygial” pectoral fin of Ceratodus,
(After HOWEs.

B. Basal. D. Dermal. 2. Radial.

42

ES =_

PAIRED FINS 43

subsequent encroachment of the dermal fin margin. These
conditions may be briefly illustrated. The paired fins of a
primitive shark (Figs. 49, 50, v. p. 79) appear as the actual
lappet-shaped remnants of a continuous dermal fold. The
ventral fins (Fig. 50) have clearly retained even the out-
ward shape of the fin fold; the supporting elements are
arranged in metameral order ; the radials, X, are unjointed,
extending from body wall to fin margin; the basals, agree-
ing in number with the radials, are uniform in size, and as
yet unfused. The pectorals, acquiring more special func-
tions (Fig. 49), are enlarged in size, their basals, B, becom-
ing compressed and obscure. In these fins the effect of
concrescence is admirably marked ; the anterior fin margins,
pressed tail-ward in their plane of growth, become firm and
rigid, their elements stout and compact; the basals, re-

_ Sponding to this outward need, cluster more firmly together,

are compressed and fused, their anterior elements, largest
and stoutest, become inturned, their posterior elements,
slightest and most clearly metameral.*

The next stage in the evolution of the paired fins is
clearly comparable to that already noted as occurring in
the dorsal fin of Holoptychius (Fig. 43), where the line of
basals, fusing compactly into a plate-like mass, had in-
turned its anterior, and protruded its posterior tip; a
change apparently slight, but great in functional impor- ~
tance. Up to this stage the fin has been firmly implanted
in the body wall; its motion, probably slight upward or

_ downward, served but to balance the fish, its fin rays,
__ tending to concentrate anteriorly, functioned as an efficient
_ cutwater. This process of concentration in the anterior

- fin margin may have resulted, the writer believes, in the

* The effect of the enlarged and clustering dermal denticles in strengthen-
ing the cutwater margin of the fin has already been noted (p. 28).

44 PAIRED FINS

formation of fin spine, as in Acanthodian * (Figs. 32, 51,
and p, 81). But the protrusion of the line of the basals
must have brought with it a new use in the economy of
fish motion. The plane of the fin could now be directed
upward or downward; the fin would become a direct aid
in propulsion ; it would acquire a paddle-like function ; it
could also be extended sideways as a check to motion.
Under these circumstances it is not unnatural that the
region of the concrescence of the fin rays should now be
transferred from the fin’s anterior to the more useful pos-
terior (now distal) margin, and that the fin rays, as well as
the line of basals, should acquire a more jointed structure,
suited to flexible motions. The course of the differentia-
tion of fin structures may be traced from this point on-
ward, as Wiedersheim has shown, by means of a series of
gradational stages: from the conditions of Fig. 49 we may

in the present figures pass to those of Fig. 52, thence to _

those of Figs. 53 and 54. In the pectoral fin of a modern
shark (Fig. 52) the basal cartilages, 2, may still be com-
pared with those in the older form (Fig. 49 2) ; their distal
element (2, at the right of the figure), however, protrudes ~
from the body wall and is becoming surrounded by clus- _
tered radials, R; the cartilaginous elements, it is here —
noted, have been placed in competition with the dermal
elements, and have already yielded them over half of the
fin area. In the next stage of the evolution, as in the
pectoral fin of a Permian shark (Pleuracanthus, p. 83, Fig.

53), the line of the basals is seen to boldly protrude from — x

the body wall and to have become distinctly jointed; the
radials have surrounded its distal end, and taken a position

* This homology proposed by the writer has not been accepted by Smith
Woodward; the spine is unquestionably encased outwardly by dermal den-
ticles.

PAIRED FINS 45

along the outer half of the hinder margin of the fin stem ;
the dermal region of the fin, D, has notably increased.
Indeed, the fin area in the modern bony fishes (Fig 145,
PF) may become entirely dermal, and the basal supports
greatly reduced and metamorphosed. In a final type of
fin (Fig. 54) the line of the basals has become widely spe-
cialized, and the characters of the archipterygium have
been attained: the fin stem is long, tapering, jointed; the
radials occur as clearly along the hinder as along the ante-
rior margin; and, as in Figs. 52, 53, dermal rays contrib-
ute largely to the fin area. This form of fin may be noted
as most closely approximating in function the limb type of
land-living vertebrates.

It has recently been urged that the lateral fold origin of
the paired fins as thus described is not confirmed by devel-
_ opmental studies,—the especial ground for this belief
being that in sharks these fins appear, even in very early
stages, as paired lappet-like outgrowths, destitute of inter-
vening fin membrane. The perfected fin fold is therefore
claimed to represent nothing more than a specialization to
bottom-living, since this condition is known to maintain in
earlier stages and in more primitive metamerism in the
development of skates: and as skates (p. 93) are well known
to represent a comparatively recent offshoot from the stem
of the sharks, it is accordingly inferred that the chief proof
of the lateral fold doctrine is destroyed.

Since these objections, however, were raised, the struct-
ural conditions of the ancient shark of Figs. 49 and 50
have been described, and may be looked upon as the

_ weightiest evidence of the origin of paired fins from lat-

eral folds. Nor does it seem to the present writer that
the early character of the fin-fold metamerism of skates
is to be looked upon as an unexpected condition. Their

46 SENSE ORGANS OF FISHES

broad longitudinal fins, specialized to bottom-living, become
fashioned in an ancestral mould; and it seems not unnatu-
ral that they tend to reacquire their latent primitive form
at an early period. On the other hand, the fin-fold condi-
tion of the shark might be less perfectly shown on account
of processes of accelerated development.

4. THE CHARACTERS OF THE SENSE ORGANS OF FISHES

It has already been seen that the conditions of aquatic
living have caused fishes to evolve adaptive structural char-
acters, such as body form, specialized metamerism, organs
of progression, and dermal investiture. It is not, accord-
ingly, unnatural to expect that, from the same causes, the
condition of the sense organs may have been strikingly
modified.

The sense of “feeling”? — using the word in its general _

meaning — has been of especial value in fishes, and tactile
organs appear to be independently developed in all fish
groups whose living habits demand them. In the form of
barbels they thus occur in members of the various divis-
ions of bony fishes, as cod (cusk, Ophidium) (Fig. 55),
drum-fish, Pogonias (Fig. 56), or, sculpin, Hemitripterus
(Fig. 57). Their form may be lobate, thread-like, or villose ;
they are often surprisingly similar in size, position, and
innervation; they usually appear on the inferior head
surface, most often in the anterior throat region, in the
position most exposed to tactile impressions. The thread-
like barbels of the catfishes (Fig. 58, p. 171) are arranged
in pairs about the margin of the mouth; the longest lat-
eral pair is connected with the marginal bone (maxillary)
of the upper jaw and directed at will. In other mud-living
forms, sturgeons (Fig. 160), the barbels have arisen on the
under side of the shovel-like snout, directly in advance of

{ > ne
j 4 ee
_— ai ei =
— ae Oe a ee a

Pye

$S
a

eS
~ ar

a
fe
We:
p
|
NS
sll
2

av
Co

Ze

a
<5
aa

——<

.. 6 . — Barbels and tactile sense organs, (After GOODE in U.S. F.C.)
55. Cusk, Ophidium. 56. Drum-fish, Pogonias. 57. Sea-raven, Hemitripterus,

58. Catfish, Amiurus. 59. Spoon-bill sturgeon, Polyodon (ventral view of snout).
_ 60, Sea-robin (Gurnard), Prionotus.

47

48 BARBELS AND LATERAL LINE

the protractile sucking mouth. There can be little doubt
that the most aberrant tactile organ in fishes is the long
spatulate rostrum of the paddle-fish (Polyodon) of the Mis-
sissippi (Fig. 59): the sense organs are here known to be
most highly specialized, although their intimate structure
is as yet not understood. Tactile organs are often to be
found upon fin structures, especially those of the anterior
body region. In the sea-robin, Prionotus (Fig. 60), the sen-
sory structures are borne by three anterior fin rays; these
are greatly enlarged, lose their connecting fin web, and
can be moved at will in a variety of ways. In all cases
the barbels appear. to be true and highly specialized
organs of touch, and the end organs are comparable ap-
parently with the touch papillz of higher forms. Of their
extreme sensitivity there can be no doubt, and as far as
can be judged from their innervation, it would appear that
their function is tactile rather than gustatory, as has been
suggested. The limits of these processes, however, are
no doubt poorly defined in aquatic living.

The Lateral Line

The sense organs, generally known &s the /ateral line,
or mucous canal system, are looked upon as essentially
peculiar to fishes. In the form of a ‘lateral line,’ they
are arranged more or less segmentally along the median
line of either side of the body and form a conspicuous
feature in the outward appearance of the fish (Figs. 87,
104, LL, 121, LL, 145, LL). Often by striking colora-
tion, the lateral line is rendered even more prominent,
passing from the. head to the tail as a pale or brightly
coloured band, against the dusky side of the fish. In the
region of the head, however, this sensory structure is, as
a rule, no longer conspicuous: it dips below the skin sur-

LATERAL LINE ORGANS 49

face and becomes a series of interconnecting tubes, which

pass along the most exposed ridges of forehead, cheek,

cy orbit, and jaw rim. Here in different regions, these sen-
sory mucous tubes may become dilated, constricted, or
ramose, and may communicate with the surface by occa-
sional or numerous pores.

The mucous canal system has long been a subject of
study and investigation. It is looked upon generally as a
sensory organ, adapted to the conditions of aquatic living,
but its function has not been definitely established. How
it was acquired, or how its ancestral conditions have been
modified in the present groups of fishes, must at present
be looked upon as in many ways doubtful.

The simplest conditions of the mucous canal system
appear to exist in primitive sharks: and to these the
writer believes that the modified sense canals in other
fishes may best be referred.

The ancestral condition of the lateral line of sharks
appears to have been represented in an open continuous
groove,* lined with ciliated sense cells, and protected
only by an overcropping margin of shagreen denticles

_ (Fig. 61). In this condition it at least exists in the
ancient sharks of Figs. 86, 87, 92, and in the Chimera

(Fig. 104). That the canals of the head region were also
primitively of this character appears exceedingly prob-

_ able: they are thus retained in the adult Chimera (Fig.

— 104, W.C).+

_ In the modern forms of sharks the condition of the

___-* It is to be noted that this condition occurs in deep-sea fishes: it here is
4 evidently an adaptation to their peculiar environment, which causes an early
_ ontogenetic stage to be permanently retained.

___ ¢ In Callorhynchus this condition has been largely lost: the outer margins
of the sensory groove have sealed over.

wwe

eS Oe gs Q aes ‘¢
a NS ABORT

64

shesetys
ge EAE
soot J

7 So efe, ve
Ss Ss 7

Figs. 61-68. — Mucous canals (lateral-line organs). 61. Chlamydoselache, groove-like
lateral line. (After GARMAN.) 62. Plan of lateral line of sharks, longitudinal section,
63. Plan of sensory end buds (lateral line). 64, Sensory tracts of head of larval Amia. —
65. Surface openings of tubules of sensory tracts of head of adult Amia, 66. Ramification —
of sensory tubules in dermal plate of Amia. Se Cycloid scales of Amia, showing the ©
openings of the tubules of the lateral line. 68. Cycloid scale of the lateral line of Amia, —
ee course of the sensory tubule. (Figs. 64-68 after ALLIS.) bs

N. Nerve supply. S. Sensory tissue. * Denotes an outer opening; -» the direction
of an incoming stimulus,

50

LATERAL LINE ORGANS 51

sensory canals suggests the modifications to which the
open sensory groove has been subjected. There are thus
forms in which the canal becomes more and more deeply
sunken in the integument, and acquires a tubular char-
acter by the fusing together of its outer margins. The
section of the lateral line of the Greenland shark, Ze-
margus (Fig. 62, v. p. 90), shows the tube-like sensory
canal well sunken from the surface, but retaining met-
ameral openings at the points. The sensory cells, S,
are no longer, as in Fig. 61, scattered evenly along the
floor of the canal; they now occur in metameral masses
supplied with a distinct nerve branch, J, located in the
region immediately below the external tubules. When
sunken in the integument, the sensory canal is known to
have acquired supporting structures to enable its tubular
character to be maintained; in the Cretaceous shark,
Mesiteia, an elaborate series of surrounding calcified rings *
were thus evolved.

Further changes in the mucous canal are often accom-
panied by the subdivision of the external apertures ; each
of the openings of Fig. 62 might by this process give rise
to a series of minute surface pores, as at S in Fig. 65, or
enlarged, showing the collecting mucous canals in Fig. 66.
This ramose mode of termination of the external tubules
has been admirably described by Allis f in the ontogeny of
a ganoid ; in a larval stage (Fig. 64, S, S, S), the condi-
tion of the sensory canals is seen to differ little from
those shown in section in Fig. 62; although imbedded
in the integument, occasional pores are seen, 5S, S, to
open to the surface; these subsequently by repeated sub-
division give rise to the great number of minute open-

* A condition somewhat similar has been noted (Leydig) in Chimera.
+ On the Lateral Line System of Amia calva. F. of Morph., 1889.

s :

52 LATERAL LINE

ings already noted in Fig. 65. A process of this kind
is carried to great lengths among the fishes which
develop horn-like scales, as Amia, herring, or cod: in the
scales of the lateral line region the distal tubules appear
at the surface as a cluster of pores, as shown in Fig. 67,
or in the detached scale of Fig. 66.

The organs of the lateral line (of a bony fish) shown
in section in Fig. 63 are regarded by the writer as of
a highly modified character. They appear to have been
derived from the conditions of Fig. 62; the end organ,
S, corresponds with that, S, of the preceding figure; its
size, however, has greatly increased, and the, intervening
sensory tube has been lost; its metameral opening at
the surface corresponds with that of Fig. 62; the nerve
supply, 1, is now seen to have secured a more perfect
relation to the end organs.

The original significance of the lateral line system as
yet remains undetermined. As far as can be judged from

its development, it appears intimately, if not genetically
related to the sense organs of the head and gill region of |

the ancestral fish: in response to special aquatic needs, it
may thence have extended further and further backward
along the median line of the trunk, and in its later differ-
entiation acquired its metameral characters.

A significant feature of its development is its peculiar
innervation. Its lateral tract is innervated by a specially
evolved root of the vago-glossopharyngeal group, but its
head region is supplied by a similar root of the facial
nerve (perhaps also by the trigeminus; cf. Collinge, Ref
p. 248).

In view of this innervation, the precise function of this en-
tire system of end organs becomes especially difficult to de-
termine. Feeling, in its broadest sense, has safely been

PINEAL EYE ‘ 53

admitted as its possible use. Its close genetic relationship
with the hearing organ suggests the kindred function of
determining waves of vibration. These are transmitted in
so favourable a way in the aquatic living medium, that from
the side of theory a system of hyper-sensitive end organs
may well have been specialized. The sensory tracts along
the sides of the body are certainly well situated to deter-
mine the direction of the approach of friend, enemy or

prey.
The Pineal Eye

_ The presence or absence in fishes of the pzneal end organ,
the “unpaired median eye of chordates,” may finally be
noted, since the condition of the epzphysis and its associ-
ated structures in fishes has an important bearing on
general vertebrate morphology.
It is well known that in many forms of reptiles there
_ exists, at the distal end of the epiphysis, a well-defined
sensory capsule, whose structure shows unquestionably its
optic function. It has seemed to many, therefore, that
throughout the chordates the epiphysis has been primi-
tively associated with a median eye, which has degenerated
as the paired eyes became better evolved. That it has
been retained in an almost perfect condition in reptiles
has accordingly been looked upon as an outcome of a
life habit which concealed the animal in sand or mud,
and allowed the forehead surface alone to protrude: —
the median eye thus preserving its ancestral value in
enabling the animal to look directly upward and backward.
If this view as to the presence of a parietal eye in the -
ancestral vertebrate is to be generally accepted, one would
_ fhaturally suggest that the organ should be present, at all
_ €vents to a recognizable degree, in some of the varied forms

54 PINEAL EYE

of the lowest vertebrates extant, —fishes and amphibia. If
there are no suggestions of its visual nature among these
forms, one would be inclined to believe with O. Hertwig,

that the epiphysis was originally of a different function |

and that its connection with a median eye may have been
altogether of a secondary character.

The evidence as to the presence, primitively, of a median
eye in fishes is certainly far from satisfactory :* in all the
forms of recent fishes, no structure has been found associ-
ated with the epiphysis which, by the broadest interpreta-
tion,’ could be looked upon as suggesting a visual function.
It is possible that fishes and amphibia may, in their extant
forms, have lost all definite traces of this ancestral organ on
account of some peculiar condition of their aquatic living.
On this supposition, evidence of its presence might be
sought in the pineal structures of the earliest Palaeozoic
fishes — whose terrestrial kindred, and probable descend-
ants, may alone have retained the living conditions which
fostered its functional survival.

It is accordingly of interest to find that in a number
of fossil fishes the pineal region retains an outward median
opening, whose shape and position suggest that it may have
enclosed an optic capsule. If the median eye existed in
these forms, it may well have been passed along in the line
of descent through the early amphibia (where substantial
traces of a parietal foramen occur, e.g. as in Cricotus) to
the ancestral reptiles. This view is greatly strengthened,
as Beard has shown, by the presence in the lamprey of a
pineal end organ (optic ?).

The evidence, however, that the median opening in the
head shields of ancient fishes actually enclosed a pineal

* Hertwig (Mark), Handbook of Embryology of Vertebrates, and Cattie, v.
Ref. p. 250.

.
5
’
4
4
2
fl
5
Z

PINEAL EYE 55

eye, is now felt by the present writer to be more than ques-
tionable. The remarkable pineal funnel of the Devonian
Dinichthys (Fig. 134) is evidently to be compared with
_the median foramen of Ctenodus and Paledaphus (=Sire-
noids, p. 122); but this can no longer be looked upon as
having possessed an optic function, and thus practically
renders worthless all the evidence of a median eye pre-
sented by fossil fishes. It certainly appeared that in the
characters of the pineal foramen of Dinichthys there ex-
isted strong grounds for believing that a median visual
organ was present: its opening was in the pineal plate,
midway between the orbits (PJ, Fig. 134). _ At the surface
it was of minute size (X, Fig. 136), but below (Fig. 137)
it flared out into a funnel-like form, shown in longitudinal
section in Fig. 137 A. The peculiar character of this
opening seemed to render it especially fitted for a visual
function; the minute external opening forms an image
near the plane of the visceral opening of the funnel, with-
out the specialization of a lens, — an image so perfect that
it might readily be photographed. It is evident, accord-
ingly, that if an optic capsule were enclosed by this fora-
men, it would have enabled its possessor to have looked
directly upward and backward; and, without the need of
developing lens-like and focussing structures, it could have
readily received the images of all outer objects near or
remote.

But the function of this pineal foramen, unfortunately
for speculation, could not have been optical. It occurs in
a fish (7itanichthys) closely related to Dinichthys, and,

J ___ as the writer * has recently found, is of a distinctly paired

* He is obliged by accumulating evidence to abandon his former view that
the pineal foramen of Dinichthys contained a specialized optic capsule (WV. Y.
Rep. of Fisheries, 1891, pp. 310-314).

56 PINEAL EYE

character, its visceral and outer openings bearing grooves
and ridges which demonstrate that the pineal structures
must not only have been paired, but must have entered
the opening in a way which precludes the admission of
the epiphysis. It is now, therefore, that the pineal fora-
men which has been described in Siluroids * becomes
of especial interest, since its contained structures are ap-
parently connected with the lateral line system of paired
nerves.
It must for the present be concluded, accordingly, that
the pineal structures of the true fishes do not tend to con-
firm the theory that the epiphysis of the ancestral verte-
brates was connected with a median unpaired eye ; it would
appear, on the other hand, that both in their recent and
fossil forms, the epiphysis was connected in its median
opening with the innervation of the sensory canals of
the head. This view, it is now interesting to note, seems
essentially confirmed by ontogeny. The fact that three
successive pairs of epiphysial’outgrowths have been noted —
in the roof of the thalamencephalon, appears distinctly
adverse to the theory of a median eye.

*Dean, V. Y. Rep. of Fisheries, 1891, and Klinckowstrém, Anat. Anz.,
1893, viii, p. 561.

-
** Ome ons eo ee **

III

THE LAMPREYS AND THEIR ALLIES

Tue relations of the more primitive chordates to the
true fishes have not been considered in the present dis-
cussion. A brief account, however, must be given of the
Cyclostomes, or Marsipobranchii, which are represented in
the recent lampreys and hags.

The three prominent forms.of Cyclostomes are figured
on a following page (Figs. 70-72, A—D). They are eel-
like in shape, but are lacking both in paired fins and in
an under jaw. Their mouth is of a rounded form, and
is suctorial; when closing, its lateral margins draw to-
gether. Their skeleton is of-the simplest character, mem-
branous rather than cartilaginous; its elements are never
more highly differentiated than those shown in the ac-
companying figure (Fig. 69, A).

Bdellostoma is shown in surface view in Figs. 70 and
72 A, and in sagittal section in Fig. 69. It is looked
upon as the most archaic form of the living Cyclostomes.
Barbel-like structures surround its mouth region; its nasal
canal (Fig. 69, VV and C) has a forward opening at the
snout, and a hinder one piercing the roof of the pharynx,
—a very exceptional character in fishes; its tongue, stud-
ded with rows of rasp-like teeth,* may be greatly everted,

* The teeth of Myxinoids are cuticular structures, and may well have been
evolved within the limits of the group. Beard has homologized them with the
teeth of sharks, but his determination of the presence of true enamel has not
been confirmed (Ayers).

57

‘aSepnies pene,

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58

THE LAMPREYS 59

as in Fig. 72, A, and then drawn in by stout tongue
muscles, 7 (Fig. 69) ; its digestive tube is almost straight,
terminating at the base of the tail region at A; the
region of the gullet, OZ, is pierced by a number of
branchial openings, varying from seven to fifteen, often
assymmetrical. The body cavity is an extremely large
one for the size of the contained viscera. An unpaired
fin, supported by delicate, unbranched (dermal) rays is
restricted to the hindmost part of the body. Passing
down the side is a row of mucous pouches by which a
‘remarkable supply of slime is secreted. The living animal
is enabled, by the peculiar character of this slimy secre-
tion, to render a pailful of water jelly-like in consistency.
Bdellostoma occurs plentifully in the bays of the Pacific
coast of America, notably at Monterey, California. It is
active in its movements, is carnivorous, and is well known
to take a baited hook. Its numbers make it an enemy of
the fishermen, entangling and sliming their set lines, and
destroying the captured fish. It is said to feed at night,
although little is yet known of its general habits of living.
None but adult specimens have thus far been observed.
The Hagfish, Wyxine glutinosa (Fig. 71, and 72, 8), is in
many regards similar to Bdellostoma; it differs mainly in
the character of its unpaired fin and in its branchial struct-
ures (Figs. 9, 10). As already noted, the outer ducts of the
gills, instead of opening separately at the surface as in
Fig. 70, are drawn together tail-ward, and terminate on
either side in a common ventral opening (Fig. 71, at the
point*). The unpaired fin is almost lacking in supports ;
its ventral origin is even as far forward as the branchial
openings; the anus, as a slit-like opening, pierces it in
the tail region. Asin Bdellostoma, the nasal canal begins
at the snout, and at its hinder opening pierces the roof of

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SSS

<7 fo

LAMPREYS AND HAGS 61

the pharynx; this, with other related conditions, has caused
Myxine and Bdellostoma to be included in a sub-group
of Cyclostomes, as Myxinoids, or Hyperotretes.* In each
genus there is possibly no more than a single valid species.
Myxine is a well-known form: it occurs along the Atlan-
tic coast at moderate depths. It is exclusively carnivorous,

Fig. 72.— A-D. Ventral aspects of headg of (A) p
Bdellostoma (after AYERS); (2) Myxine (after GUN-
THER); (C) Ammocetes (after GUNTHER) ; (D) Pe-
_fromyzon (after GUNTHER).

often boring its way into the abdominal
cavity of (diseased or injured) fishes, and
with them is brought to market; it is
also taken not infrequently by line fisher-
men. The smallest example that has
thus far been described is 6 cm. in length; it was
recorded by Beard. (V. Réf. p. 239).

The Lamprey, Petromyzon, is the most perfectly studied
member of the Cyclostomes. Its species are common
to the continents of the northern hemisphere; and in
South America and Australia there occur very closely
allied genera, as Mordacia and Geotria. The largest
lamprey, P. marinus (Fig. 72, and C, D), is known to
attain a length of nearly four feet ; it occurs in the coast
* v. Glossary, p. 228.

62 THE LAMPREYS

rivers, ascending them in numbers in the springtime
(April) on the way to the spawning grounds (v. p. 182).
During its adult life it is supposed to be exclusively car-
nivorous, to some degree, perhaps, parasitic, although many
doubt that it is truly parasitic in the sense of entering the
body cavities of healthy fishes. It certainly is often taken
attached to other fishes, as shark, sturgeon, or salmon.

Immature lampreys differ so strikingly from the adults
that they were formerly regarded as species of a separate
genus, Ammocetes (v. p. 215). In feeding habits the am-
moccete is widely unlike the mature form ; it is toothless
(Fig. 72, C), and in part mud-eating, z.e. vegetivorous.

Petromyzon must be regarded as the most highly organ-
ized of Cyclostomes. Its mouth has no longer the fring-
ing barbels of Myxinoids, — which suggest, according to
Pollard, the buccal cirrhi of Amphioxus, — it has acquired
stout supporting cartilages and a funnel-shaped form,
studded with a series of conical teeth, as shown in Fig.
72, C. The teeth of the hinder mouth region now appear
almost as though they were supported by a mandibular
cartilage ; the tongue, as in other Cyclostomes, bears the
teeth which are probably of the greatest functional impor-
tance. The nasal canal of Petromyzon has its outer opening
on the dorsal surface of the head ; its inner end, however,
does not perforate the roof of the mouth, although produced
backward as a blind sac, closely apposed to the pharynx.
Petromyzonts are, accordingly, arranged as the sub-group —
Hyperoartia, in contrast to the Myxinoids,

Further structural characters, which the lamprey seems
to have derived from simpler conditions, may be noted in
its unpaired fin, gill chamber, nervous system, and skele-
ton. The unpaired fin has subdivided into dorsal and
caudal elements, and is now supported by well-marked

AFFINITIES OF LAMPREYS 63 .

rays, which (sometimes) bifurcate. The branchial region of
the adult lamprey’s gullet is restricted to a pouch-like
diverticulum (v. p. 263 and Fig. 326). A ‘sympathetic’
nervous system, and a ‘lateral line’ has appeared: the
latter passes down the side in two branches, one above
and one below the median lateral plane: its end organs
are the pouches of nervous epithelium which in Myxi-
noids are scattered generally over the body surface. The
skeletal structures of the lamprey (Fig. 69, A) indicate
well-marked advances: a stouter supporting tissue of car-
tilage-like character has appeared ; the brain case is partly
roofed over; neural processes, VP, a branchial basket,
BB, and a series of mouth cartilages are especially note-
worthy.

Affinities of the Cyclostomes

The relations of the group, Cyclostomi, to the earlier
chordates, and, on the other hand, to fishes, have been by
no means definitely established. Dohrn and others have
suggested that the Cyclostomes are greatly degenerate, and
are even closely akin to the recent bony fishes, as perch
or cod. Their views have been based upon several struct-
ural characters, notably vestigial organs, such as the ap-
pendages at the sides of the cloacal opening of Petromyzon
which were believed to represent pelvic fins ; and there was
further taken into consideration the belief that the entire
group was one of degenerate life habits. The views of these
writers, however, do not appear to be confirmed by later
studies, and the belief is becoming more and more general
that Cyclostomes represent a very ancient chordate stem
whose ancestral form is most nearly exemplified by Bdel-
lostoma. Parasitism has been acquired to a limited degree,
but does not appear to have affected the general characters

64 KINSHIPS OF CYCLOSTOMES

of the group. Among its primitive features are to be in-
cluded: skeleton and muscles, continuous vertical fin, gill
characters (p. 260), viscera (p. 263), urino-genital organs
(pp. 266, 270), nervous and circulatory systems (pp. 260,
269, and 274). With these must be taken into account:
absence of mandible* and of paired fins and girdles; and in
addition the remarkable conditions of metamerism (p. 14).

Little more that a vague kinship between lampreys and
fishes has been established by the study of living forms.
And, on the other hand, it would appear equally impracti-
cable to obtain evidence bearing upon this problem from
the side of palzontology. All that is known of the recent
Cyclostomes more than suggests that their soft body struct-
ures would prove most unfavourable to fossilization. It
would be only, therefore, in the event of some of their
ancient members possessing calcified structures that palae-
ontology would be able to offer a clue as to their ancient
affinities.

Upon the problem of their descent the evolution of
fishes has, however, an undoubted bearing, in suggesting
the lines and effects of aquatic evolution and the perma-
nence of generalized types. It certainly tells of the ex-—
treme slowness of the evolution of aquatic forms and con-
vinces us that the ancestral Cyclostome could only have
occurred in a time stratum exceedingly remote. Palzon-
tology cannot perhaps hope to obtain more than sugges-
tions of the ancestral forms, although these, from their
generalized characters, may well have survived during geo- |

* The cartilages of the mouth region of Cyclostomes have been homologized
with the structures of gnathostomes; Pollard recently (Amat. Ams. ix, pp. —
349-359) ascribes a cirrhostomial origin to the mouth parts of a Teleostome
(catfish), which the writer cannot believe has been demonstrated; variations
in the number, shape, and function of the cartilages of the mouth rim of
Cyclostomes might well have occurred within the limits of this ancient group.

A FOSSIL LAMPREY 65

logical ages. It can, however, show that Cyclostomes are
_ not the degenerate descendants of shark-like forms; and
— if only by analogies in the evolution of fishes — it may
still be able to demonstrate with fair probability their
genetic kinships. It may, for example,
prove that in the most ancient time there
existed undoubted Cyclostomes, and that
these in many and most specialized forms
were even then branching-off twigs of a
great descent tree. In such an event an
inference would certainly be the more
reasonable which derived the advancing
line of fish descent from the genealogical
tree of the more primitive Cyclostomes,
than that vice versa.

It is now accordingly of especial inter-
est that the fossil remains of what seems
undoubtedly a lamprey (Fig. 73) have been
discovered in the Devonian ; and this, to-
gether with a better knowledge of the
ancient and curious chordate group, Os-
tracoderms, may, it is hoped, lead to some
solution of the Cyclostome puzzle.

Fig. '73. — The De-

vonian Cyclostome,

The Ostracoderms Paleospondylus gunni,

T. xX 4. (After TRA-

Ostracoderms, as they are called from Quai.) Achanarras

their shell-like, dorsal and ventral derm 7” ee
plates, are certainly the oldest known remains of verte-
brates.* In their simpler forms they occur in the Upper.
Silurian ; they flower out in a variety of types in the De-
vonian, and shortly become extinct. In the present con-
* The earlier (Ordovician) vertebrate remains described by Walcott are as

yet uninterpretable.
F

FIG. 74

75

“ -
as on ¢
thet deteiedl a

Figs. 74-79. — Pteraspis (restored). 4. (After LANKESTER.) Lower Old Red
‘Sandstone, Herefordshire. 75. Paleaspis americana, Claypole. X 3. (Restoration after
CLAYPOLE, somewhat modified by the writer.) 76. Pteraspis, dorsal shield, slightly
restored, (After LANKESTER.) 77. Pteraspis, ventral shield (‘‘ Scaphaspis"), showing
mucous canals. (After SMITH WOODWARD.) 78. Cephalaspis lyelli, side view. (Re-
stored by LANKESTER.) 79. Cephalaspis lyelli, dorsal aspect. X }. (After L. AGASSIZ.)
Specimen from Old Red Sandstone, Forfarshire. A C. Rhomboidal scales from different
body regions. 2. Tessera from middle layer of head shield.

66

OSTRACODERMS 67

nection they may be described, if only to indicate that
they are in no way closely connected with the ancient
shark types (p. 78), and that they are accordingly of but
indirect interest in the descent of jaw-bearing vertebrates.
Ostracoderms may readily be reduced to three general
types, Pteraspid, Cephalaspid, and Pterichthid. The first,
oldest, and probably simplest occurs in the Lower Old
Red Sandstone of Herefordshire. It was provided with
arched back and breastplate (Figs. 74, 76, 77), from whose
anterior lateral notches a pair of eyes protruded ; the sur-
face of these plates (Fig. 77) appears to have been grooved
for sensory canals. Pteraspis, as seen in the restoration;
had a snout plate, a dorsal spine, and a body casing of
rhomboidal scales ; its mouth was probably in the region
immediately below the eyes, in front of the margin of the
well-rounded ventral plate; this was generally regarded as
the dorsal plate of a kindred genus, “ Scaphasfis.” Closely
related is the American Pteraspid, Palegaspis (Claypole),
from the Upper Silurian of Pennsylvania (Fig. 75); this
form lacks the dorsal spine of the English species; it has a
well-marked lateral plate intervening between those of the
back and ventral side, and, according to its discoverer,
Professor Claypole, possessed pectoral fins similar to those
seen in Fig. 123. Its hinder trunk region is unknown.
Cephalaspis, the second type of Ostracoderm, is from
the Old Red Sandstone of Scotland (Figs. 78, 79). It was
curiously suggestive of a trilobite, and with little doubt
mimicked this ancient crustacean in its life habits. Its
most prominent feature is a crescent-shaped head, with
sharp rounded margin like a saddler’s knife. This is
protected dorsally by but a single plate, arching upward
and backward; at its summit was a pair of closely apposed
eyes, and near its flattened rim were pouch-like sensory

CTs

689 rH
HORA

S

<) i |
me ; AIR a

‘

as

Figs. 80-82. — Pterichthys testudinarius, Ag.; restored by R. H. TRAQUAIR, from the
dorsal aspect (80), ventral aspect (81), and lateral aspect (82). The double dotted lines
indicate the grooves of the sensory canal system; and in the trunk, the thick lines repre-
sent the exposed borders of the plate, the thin line showing the extent of the overlap,

ADL, Anterior dorso-lateral. AMD. Anterior median dorsal. AVL. Anterior ventro-
lateral. JZ. Extra-lateral (or operculum), JZ. Labial. M/OCC, Median occipital. PAZ
Premedian, PDL, Posterior dorso-lateral. PMD, Posterior median dorsal. PVL, Pos-
terior ventro-lateral, SZ. Semilunar. (Figure from SMITH WOODWARD.)

68 :

PTERICHTHYS AND CEPHALASPIS 69

organs. The angles of the head plate are in some genera
produced most acutely, and bear spines which served prob-
ably in progression, The body walls were encased in
metameral derm plates, which became arched in the
median line to serve as a dorsal fin. <A heterocercal tail
and an anal fin were also present. Problematical opercu-
lar flaps protruded at the sides of the head plate, and
represented (as is now known) a continuation of the elastic
middle layer of the head plate.

Pterichthys must be looked upon as the culminating
type of these anomalous forms (Figs. 80-82). As in some
Cephalaspids, there are two body regions that are cui-
rassed,—head and thorax. The tail portion is encased
in dermal plates; it bears a dorsal fin and a clumsy
heterocercal tail. In the consolidation of its armoured
parts the elements are usually clearly indicated. The
curious arm-like jointed appendages at the lateral head
angle were formerly regarded as homologous with the
opercular flaps of Cephalaspid, but are now known to be
nothing more than the lateral head angles produced and
specialized (¢.e. jointed for locomotion). The strengthen-
ing spine of the dorsal fin is also but a primitive speciali-
zation of the body integument ; it is formed by a pair of
the bent scales of the dorsal ridge, and is not, therefore,
homologous with the radial fin cartilages of fishes.

' In Cephalaspids and Pterichthids there occurs a pineal
plate (or its equivalent) which may have been either
movable or fixed. In this are to be found the paired eyes
and the socket of a median unpaired eye (?). In all of
these singular forms mouth parts* are wanting. In

* Smith Woodward has since described a pair of inturned labial plates in
the mouth of Pterichthys. Their position suggests that the sides of the mouth
tim might become apposed, as in the Cyclostomes.

70 KINSHIPS OF OSTRACODERMS

no instance has a trace of endoskeletal parts been ob-
served.

The more that is determined of the structural characters _

of Ostracoderms, the less is it possible to accept the
views as to their affinities with forms other than “ fishes,”
either (Cope) as to their permanent larval-ascidian char-
acters, or (Patten) as to their relationships with arachnids.
Their general kinship is certainly to the fishes. Accord-
ing to Smith Woodward, the markings appearing on the
visceral surface of head tests indicate the presence of
gill pouches; in some forms clearly marked furrows sug-
gest the possession of vertical semicircular canals; fish-like
sense organs occur (Fig. 77); and their derm plates, in
their cancellated and bone-like characters, cannot well be
likened to the exoskeletal parts of invertebrates.

The lamprey-like form, Pa/gospondylus gunni, Traquair
(Fig. 73), in the Lower Devonian is by many looked upon
as the actual solution of the Cyclostome, and even of the
Ostracoderm puzzle. This interesting fossil was discov-
ered by Dr. Marcus Gunn, in the Lower Old Red Sand-
stone of Caithness, and was described in several papers by

Traquair (Zvans. Edin. Soc., 1892-1894). It is of very —

small size, commonly of about an inch in length, but is
admirably preserved (Fig. 73). There can be no doubt
that Palzeospondylus possessed a ring-like mouth sur-
rounded by barbels like those of a Myxinoid, and that it
lacked paired fins. But as a Cyclostome it must have

highly specialized, having the same relation to the more ~

primitive Cyclostomes of its day, as had the minute Acan-
thodians (p. 81) to the existing sharks.- It had thus a
remarkably large caudal fin with elaborately bifurcating
supports; it had evolved stout, ring-like vertebrae, even in
the caudal region, which had developed stout neural proc-

™

PALAOSPOND YLUS 71

esses. Its skull was highly evolved: in its anterior part
were represented, according to Traquair, the palatine car-
tilages; the brain case was complete, and the auditory
capsules were of relatively enormous size. The lateral
plates of the neck region are as yet uninterpretable.

From the evidence of Palzeospondylus, accordingly, it
may reasonably be inferred that lamprey-like forms existed
in highly specialized conditions, even at the beginning of
Devonian times. If they then existed, it is of course not
impossible, and perhaps even not improbable, that their
offshoots may have culminated in the Ostracoderms, as
Smith Woodward has suggested. These can certainly
belong to no gnathostome stem. Their organs, though
often highly specialized, were yet of the most primitive
order, —lack of paired appendages,* softaess of axial parts,
lowly sense organs; even the dermal plates, elaborate in
their subdivision or ornamentation, or in the special uses,
as “‘opercula,” “ pectoral fins,” or “fin rays,” T are yet but
primitive specializations of the exoskeleton.

* The presence of paired fins in Palzeaspis, as determined by Claypole, has
not been confirmed. The present writer, to whom the type specimens were
kindly shown by their describer, must regard these structures as elasmo-
branchian (Chimzroid?) spines, in crushed condition, accidentally associated
with the head region of the fossil.

¢ It is obvious that these structures are but analogous to the opercular and
fin structures of fishes, and would tend to separate, rather than closen, the
ties of kinship of these groups.

1V
THE SHARKS

ALL true fishes may conveniently be grouped into the -
four sub-classes that have been noted (p. 8) in the introduc-
tory chapter. These are now in turn to be considered, and
in this review the principal forms, fossil and recent, of each
group must be exemplified. From the standpoint of their
structural and developmental characters, a general idea of
the mutual relationships of the fishes may finally be
deduced. ;

The sub-class Elasmobranchii, which includes the sharks
and rays, is usually regarded as representing most nearly
the persistent ancestral condition of fishes, and, indeed, of
all other jaw-bearing vertebrates. As a group it should
certainly be taken first in the present discussion, as a con-
venient basis of comparison. |

Sharks and rays should be looked upon at the beginning
as the representatives of the oldest, most widely diffused, |

and possibly largest group of fishes. In their living — q
forms they suggest but faintly the number and variety of

their fossil kindred. It is generally thought that the his-
tory of this group, when more perfectly determined, is to
furnish the most important evidence as to the general
lines of descent of the fishes.

72

‘uy enuea ‘4 ‘np AreunQ ‘GQ ‘apendg gs ‘yorwmojg ‘g ‘seipey ‘y ‘eSerpseo
ajeipenbowwleg “Od “uyyeiopeg ‘yg *(ONp ueuayN) MNpIAO ‘GAO ‘A1eAQ YO ‘ouldsyeinaN “s~y ‘ssed0id yeunan “yAy ‘ada
jO ouBIquiaU SuNeINOIN YWAY “PIOYOOION ‘DAV ‘oanjiode yeseu JOLIa}sod jo Ay pue JOLajUe Jo uONIsOg “Ay *(aZe[Nseo soyoayy)
aqpuryl ‘yy “uy peiyey 77 ‘wary “7 ‘Aoupry ty ‘ayejd (jemousojur) Areyeosajuy “97 «= *aayea yestds Surmoys ‘auysayuy *7
‘reinqipuewody ‘yyy *syioddns ;erpes pue ‘jeseq ‘eway “yg “SIISIIID ‘SO “shvruyl[eWieg “7 ‘uylYsIog ‘g ‘uy [eNuaA jo
odepuadde Surdse[D *,79 ‘winjoe1 pure ‘onprao “Jajain Jo aouvsjUa Surmoys ‘voVO[D “7 “wNtueID snouLSe|NIeD *9.9 « “saayea Surmoys
‘snsOMeye snuOD "PD “UNHUaD *.D “Uy [epneD + ‘s[eIpes pue sjeseg “yg ‘sjoddns uy snourfenieo jeseg ‘g ‘uy [euy ‘"¥

*(4) yaeys Jo Awojyeur jersuey — “fg “31g

74 STRUCTURES OF SHARKS

Structural Characters

The definition of a shark emvphnatiee its cartilagitibn
skeleton, investiture of shagreen, uneven (heterocercal) tail,
and its separate and slit-like gill openings. Its more defi-
nite characters may well be summarized in the accompany-
ing figure (Fig. 83).

I. The sKELETON is cartilaginous (cf. Fig. 83, 84, and
p. 252), sometimes calcified generally, but always (in recent
forms) lacking in dermal bones. Behind the simple, trough-
like brain case the vertebral rod, beginning at the occip-
ital condyles, is clearly segmented ; the notochord is often
retained, especially in the tail region, VC, but is encroached
upon by the cartilaginous rings, centra, C, arising metamer-
ally in its sheath (Fig 85). The vertical supports of each
centrum include a well-marked ventral plate, the hemal
arch and spine, HBR,—which in the tail region probably
represents as well the cartilaginous elements of the fin
support,—and a pair of small dorsal plates, the neurals
and interneurals, VP, /C, each capped by a neural spine, —
NS. The fin supports compare closely in structure with
the vertebral processes; they form a large part of the
functional fin, and preserve clearly, both in basal and
radial parts, their metameral character. This segmental
arrangement is also characteristic of the supporting ele-
ments of the cavity of the mouth and throat. These con- —
stitute the “visceral arches” (cf. p. 256) which pass — 4
backward from the rim of the mouth to the region of the —
pectoral fin. The first visceral arch strengthens the rim of
the mouth; it is margined with teeth and functions as jaws,*

* The writer believes that the upper element of the mandibular arch is to
be regarded as the palatoquadrate cartilage, rather than the ee
ligament. H

a i ei i i i ee = -— = 7

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sopinoys ‘OS “ary Ly ‘Tepea ‘ay ‘arerpenboyyjeg ‘Od = ‘23plt [NqGIOISOd “DOd “Od Jo ssaooad jws10q] "Dd “aps ole
‘Og ‘“perpouviqoSudsreyg “gg “Uy ye10yed ‘J ‘38219 [BUGIO DAO ‘a{puoo jeHdi09 90 ‘NqIO ‘CO ‘ansdeo jwseN DAV
‘ssanoid einen ‘Ay ‘ayeld yemmourajuy vy “1e[nqypuewody WH ‘eryouniqodsyy ‘gy ‘ourds uly ‘sy = ‘yergouriqidy “gz
‘uy jo skerpeuuag “gq ‘“suyyesiog ‘q ‘siedsviD “79 *(jeXyoyesao ay} St JoL9;Ue ATayeIpowUy yuoUI[a Yor [113 ay}) perqourlsq
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*(avud atonuy Aq Suimviq: "dav “V ‘H jo uoneredeid worq) *() SnzvazvF uorrvajsaD ‘yxVYS JO U0W]9AS — “bg ‘31g

AY .
SOU

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4 GF
SMA RARER MD Ae Re

75

064
¢ g f

tee y: Ata Ar A A 4 WVYV VV YY YY YY
Sc

76 STRUCTURES OF SHARKS

Pand M. The second arch serves as the principal support
of the jaw hinge, 1, while holding in position, ventrally,
the hinder arches; it also supports the tongue, and forms
the hinder border of the spiracle (p. 19). The succeeding
arches, usually five in number, are the bearers of the func-
tional gills, their jointed structure permitting the dilating
and contracting movements of breathing.

As a further skeletal element of the Elasmobranchs the
sub-notochordal rod is to be mentioned. It is present in
the larval stages of sharks, and appears to persist in the
adult Cladoselache (p. 79). It is a prominent structure
of the hinder body region, passing along, like a second
notochord, immediately below the
vertebral axis. “Its significance is
unknown. :

II. The INTEGUMENT of the
sharks, as has been noted (p. 23),
is studded with shagreen denticles,

Fig. 85.— Vertebre of often in metameral arrangement.
shark (Sguatina), longitudinal

section. (After ZITTEL.) These have been shown to corre- ©
ch, Notochord. d. Calcified *

rim and anterior surface of SP0nd clearly with the teeth.

centrum. iv, Intervertebral The soft structures characteristic

space. w. Centrum. .
of the Elasmobranchs include :—

III. Gitvs, arranged metamerally (p. 19); the most
anterior one partly functional in the spiracle, SP.

IV. SENSE ORGANS OF THE LATERAL LINE, in some
forms in an open sensory groove, in others sunken and
constricted in metameral pouches.

V. Brain, simple in its segmental characters and
cranial nerves (v. p. 274). \

VI. NASAL ORGAN, EYE AND EAR, as shown on p. 276.

VII. RENAL AND REPRODUCTIVE SYSTEMS (p. 270), ab-
dominal pores (p. 271).

FOSSIL SHARKS 77

VIII. Dicestive TuBE with a single bend, S, J, the
intestine provided with a spiral valve (p. 263), terminat-
ing, together with the ducts of the renal and reproduc-
tive organs, in a common cloaca, CL (p. 266). Liver, Z,
spleen, and pancreas large ; mesenteries simple but greatly
fenestrated ; air bladder absent.

IX. Heart with a contractile arterial cone, CA, con--
taining several rows of valves (p. 260) ; circulatory system
in general as described on p. 269.

X. “Caspers” developed at the hinder margin of
the ventral fins as the intromittent organ of the male.
They are rudimentary in the female, CZ’. Each clasper
is the trough-like hinder rim of the fin, which becomes
transformed into the compact, elongated, tube-like sperm
canal. Its tip is often studded with elongated shagreen
denticles whose recurved cusps retain it 2 copulo.

Fossil Sharks

Of all fishes, sharks certainly suggest most closely in
their general structures the metameral conditions of the
Cyclostome: it should also be noted that they possess the
greatest number of body segments, in some instances
over three hundred, known among vertebrates. Little is
known, however, of the primitive stem of the sharks, and
even the lines of descent of the different members of the
group can only be generally suggested. The development
of the recent forms has yielded few results of undoubted
value to the phylogenist: it would appear as if palaon-
tology alone could solve the puzzles of their descent.

The history of fossil sharks has as yet been but imper-
fectly outlined. The remains of the more ancient forms
have usually proven so imperfectly preserved that little
could be determined of their structural characters. Spines,

78 PALAOZOIC SHARKS

teeth, shagreen denticles, have proven the antiquity of the
shark stem and the wealth and variety of its fossil forms ;
they have provided the evidence that even in Silurian
times there lived sharks whose exoskeletal specializa-
tions had progressed further than in their recent kindred :
that in the Carbon there occurred the culminating-point
in their differentiation, when specialized sharks existed
whose varied structures are paralleled only by those of
existing bony fishes, — sharks fitted to the most special
environment; some minute and delicate ; others enormous,
heavy, and sluggish, with er hi and fin spines, and
elaborate types of dentition.

But the detached fragments of the fossil sharks can give
little satisfactory knowledge of their general structures.
The simpler the form of the shark, indeed, the less liable
is it to become fossilized. The more generalized of the
ancient sharks must thus remain structurally unknown
until more perfect fossils come to be found. To this event
the discoveries of the past few years have certainly yielded
most encouraging aid. Several forms of sharks of the
Lower Carbon and Permian have been obtained in a con-
dition of admirable preservation, and have already con-
tributed materially to the morphology of Elasmobranchs.
Other early forms may be forthcoming which will be found
to have retained sufficient of the characters of their an-
cestors to warrant more definite views as to the general
relationships of fishes.

Of the three primitive forms of fossil sharks lately
described: the earliest, from the Ohio Waverly (Lower
Carbon) is Cladoselache; Dean; a later and puzzling form,
from the Carboniferous, is Chondrenchelys, Traquair; the
latest from the Permian and Coal Measures, is P/euracan-
thus, Agassiz. The only early shark type that had previ-

CLADOSELACHE . 79

ously been structurally known was that of the aberrant
and highly specialized Acanthodian of the Coal Measures.
Cladoselache is the most primitive, as well as the oldest,
of these ancient sharks. It is relatively of small size,
varying in the length of its species from two to six feet.
Its outward form, as restored by the writer, is seen in Fig.
86, and in ventral view in Fig. 86 A. The shape is clearly

Fig. 86.— Cladoselache fyleri, Newb. X }. Restoration by writer. After speci-
men in the museum of Columbia College from Cleveland shales, Ohio.
Fig. 86 A. — Cladoselache fyleri ; ventral aspect.

that of a modern shark; the fins, too, in their size and
position, have somewhat of a modern look; and at the
base of the tail occurs the small horizontal keel of many
living forms. But in spite of these peculiarities, Cladose-
lache must be looked upon as the most archaic, and, in
many ways, the most generalized of known sharks; its
paired fins are but the remnants of the lateral fold (p. 43),
serving alone as balancers; the tail, curiously specialized,
is widely heterocercal, its hinder web lacking supports in
the upper lobe (p. 36); the vertebral axis is notochordal ;

‘

80 CLADOSELACHIAN SHARKS

and the writer now finds that an exceedingly simple con-
dition existed in the neural and hzmal arches ; they prove
to be of moderate size and thickness, each a tapering rod
of cartilage, forked at its base; each body segment con-
tains a single neural and hzemal spine, closely alike in size.
Unlike modern sharks, Cladoselache was without claspers :
its eggs must have been fertilized after their deposition, as in
the majority of fishes other than Elasmosbranchs. The gill
openings, at least seven (probably nine) in number, appear
as in the restoration, to have been shielded anteriorly by
a dilated dermal flap. A spiracle was probably present.
The jaws were slender, and apparently hyostylic (p. 257) ; *
the teeth are of the pattern of shagreen denticles, but occur

Fig. 86 B.— Teeth of (“Cladodus”) Cladoselache:=3%-4. The above forms
occur in different regions of the mouth.
in clusters (“ Cladodus,” Fig. 86, B). The mouth was ter-
minal in its position. The nasal capsule was apparently
not connected with the mouth by a dermal flap. The eye
was protected by several rings of rectangular plates, clearly
shagreen-like in character. The integument was finely
studded with minute lozenge-shaped denticles, and was
everywhere lacking in membrane bones. The lateral line
retained its groove-like character.

The shark, Acanthodes (Fig. 87), of the Coal Measures
is now to be regarded (Smith Woodward) as a member of
a highly specialized Palaeozoic group. And its many spe-
cialized structures —added to its greatly reduced size —

* As Claypole’s recent figure seems to demonstrate. Am. Geol., Jan. 1895.

ACANTHODES 81

may, perhaps, have been the cause of its extinction.
The present writer believes that Cladoselache may well
have represented the ancestral form of the Acanthodian.
The generalized structures of the former have given place
to a perfected dermal armouring, and a completed series

Fig. 87. — Acanthodes wardi, Egert. X about}. (Restoration slightly modified
after SMITH WOODWARD.) Coal Measures, England.

of balancing fins. In Acanthodes the shagreen denticles
have thus become greatly enlarged and thickened, their
flattened and enamelled surfaces wedging closely to-
gether (Fig. 88); and on the roof of the head and
mouth traces of membrane bones have appeared. Around

Fig. 88.— Acanthodes gracilis, Beyr. Shagreen. x-aboutyts. (After ZITTEL.)
a. Outer face. 4, Inner face. c. Isolated denticle.

the eyes the many shagreen plates of Cladoselache have
fused into a group of four. Supporting the dermal gill
frills, there have also appeared rows of minute sculptured
plates (corresponding, perhaps, to those, BR, of Fig.

145), homologous, apparently, with shagreen denticles.
G

82 ACANTHODIAN SHARKS

Further resemblances to Cladoselache are to be traced in
the position of the fins, gill slits, eyes, mouth, nasal cap-
sule, and in the structures of the caudal fin (Kner), and of
the lateral line. The teeth, however, are no longer of the
derm-denticle pattern; they have become few in number,

_large, and “degenerate” in their fibrous structure (Fig.

88, A). The fins are clearly more per-
fect balancing organs than those of
the older shark ; their anterior rim is
Fig. 88 A.—Teeth of formed by a stout spine, representing,
Acanthodopsis wardi. Xt the present writer believes, the con-
From_sketeh-after~speci- Rates |
men in-British Museum. | Crescence of the radial fin supports ;
it is heavily crusted over with the
calcifications of shagreen denticles. The functional fin
area has thus become dermal, and is lacking in supports,
excepting in the pectoral fin. This, as the most highly
specialized of all the body fins (p. 41), appears in some
cases to have evolved ‘strengthening (dermal) rays in its
proximal portion (as in Figs. 87 and 32).

.

Fig. 89. — Climatius scutiger, Egert. X1. (From ZITTEL, after. POWRIE.)
Old Red Sandstone, Forfarshire.

In connection with these fin structures the remarkable
Acanthodian, Climatius (Fig. 89), should finally be men-
tioned. In this form the paired fins are represented by a
series of fin spines whose size grades backward from the
pectoral region; a series of paired fins appear, therefore,

PLEURACANTHUS ,

f. 6%
w

to have been present,
and suggest strongly
continuous fin-fold char-
acters. (V. p. 40.)

Pleuracanthus (Fig.
90), the third of the
well-known Palzozoic
sharks, is widely differ-
ent from the Acantho-
dian: it suggests a tran-
sitional form between
the generalized Cladose-
lachian, on the one hand,
and the Dipnoan on the
other; or, more accu-
rately, it demonstrates
that the stems of shark
and lung-fish were at one
time drawn very closely
together. It has thus
far occurred only in the
Carbon and Permian,
but may reasonably be
expected in lower hori-
zons as a contemporary
of the earliest lung-
fishes.

Pleuracanthus is in
many ways the most in-
teresting and suggestive
member of the shark
group; for it destroys -
many of our conventional ideas as to the general characters

HM. Hyo-

HA, Heemal arches.

N. Notochord. MA, Neural process and spine.

R'. Rib. SG, Shoulder girdle.

DS. Dermal head spine.

MC. Mandible (Meckel’s cartilage).

(Restoration slightly modified after A. FRITSCH.) From the

xX about }.
FR. Radial fin cartilages.

PPS ee
erdenu es ote
A

PQ. Palatoquadrate,

MARS
Meade cr,

MAD aI

4, Basal fin cartilages. D. Dermal margin of fin.

/C. Interneural plates.

LLL fy tp PP,

pita
SIP yy
<LS72

Fig. 90.— Pleuracanthus decheni (Goldf.), 2.

Permian of Bohemia.
A’. Anal fin,

mandibular.
Pelvic cartilage (girdle),

84 PLEURACANTHID SHARKS

essential to sharks. That it was actually a shark cannot
be doubted; its gills, six or seven in number, opened
separately to the surface; its teeth (Fig. 90 A) were
typically shark-like, arranged in many rows on Meckelian”
and palatoquadrate cartilages ; a tuberculated dorsal spine
was present ; claspers occurred in the male; the vertebral
column, although notecherdal, NV, presented intercalary

plates, /C, and the

jaw was essentially
JS & a a hyostylic, HZ. On
the other hand,

Fig. 90A.— Teeth of Pleuracanthus. *%# many of its struct-
(After DAVIS.)
ures are clearly tran-

sitional to the Dip-
noan : the pelvic fins
are shark-like, with -
the radial supports,
R, arising from but
one side of the line
of basals, B; but the
pectoral fin is typi-
cally archipterygial,
and the caudal diphy-

cercal, as inthelung- |

Fig. 90 B. — Dermal bones of the head roof of fishes. In this r
Pleuracanthus, X 4. (After DAVIS.) pin eb

gard the continuous
dorsal fin, with its separate basals and radials, B and R, is
again noteworthy. But most singular of all the features
of this lung-fish-like shark were its integumentary charac-
ters ; shagreen tubercles had disappeared on the body sur-
face, and derm bones had appeared roofing the head : their
arrangement (Fig. 90 &) is strikingly similar to that of the
lung-fish of Fig. 124.

CHONDRENCHELYS 85

The final form of Palzeozoic shark whose structural char-
acters have in any way been described is Chondrenchelys.
It appears to have somewhat resembled the Pleuracanthid

in its elongate form and tapering tail; but as yet the

details of its structure have not been discovered. In its
vertebral characters it had certainly made a marked ad-
vance; the notochord had become greatly constricted ;
and well-marked centra and arches were present. These
appear to have been highly calcified, and show a peculiar

Fig. 91. — Port Jackson shark, Cestracion philippi (2). X Ys. (After GARMAN.)
Australia. A, Ventral. &. Anterior, and C. Dorsal aspect of head.

beaded or fretted structure which in this form is appar-
ently unique.

Other ancient sharks, as far as can be inferred from
fragmental structures, appear to have closely resembled
forms that are still extant.

Such unquestionably were the Cestracionts, a group
of sharks especially abundant in the early Palzozoic
seas, judging from the numbers of their fin spines and

86 PORT JACKSON SHARKS

pavement teeth that have been preserved. Their bygone
réle was certainly a long and important one. In some
of their forms they could have differed but little from
their single survivor, the Port Jackson shark, Cestracion
(Heterodontus) (Fig. 91, A, B, C). In others, the denti-
tion and dermal defences suggest a wide range in evo-
lution. Their general character appears to have been
primitive, but in structural details they were certainly
specialized ; thus their dentition had become adapted to a
shellfish diet, and they had evolved defensive spines at
the fin margins, sometimes even at the sides of the head.
In some cases the teeth remain as primitive shagreen
cusps on the rim of the mouth, but become heavy and
blunted behind; in other forms the fusion of tooth clus-
ters may present the widest range in their adaptations for
crushing ; and the curves and twistings of the tritoral sur-
faces may have resulted in the most specialized forms of
dentition (e.g. Janassas, Petalodonts, Cochliodonts, and Psam-
modonts of the Coal Measures) which are known to occur
not merely in sharks but among all vertebrates. Equally
interesting may prove the evolutional details of other
cestraciont structures when they come to be known.
Ray-like proportions may well have been evolved even
among the earliest Palaeozoic forms.

The surviving member of this group, Cestracion, sug-
gests in itself the adaptations of a bottom-living form in
its greatly enlarged pectorals. Its genus, however, has
not been traced earlier than the Mesozoic, although its
comparatively generalized dentition (Fig. 27) suggests a
far more remote descent.

It is of interest to note that Cladoselache approaches in
its dentition the characters of the primitive Cestracionts
(e.g. Synechodus).

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88 PRIMITIVE LIVING SHARKS

Recent Sharks

The fornis of Sharks and Rays
common at the present time are
generally looked upon as closely
related genetically, although
their lineage cannot be defi-
nitely traced. As far as pale-
ontological evidence goes, they
may well have been derived
from a single Palzozoic an-
vestor. .

Perhaps of all recent forms,
Chlamydoselache (Fig. 92), and
Notidanus (Heptanchus, or Hep-
tabranchias) (Fig. 93), which are
universally regarded as. “ primi-
tive,’ have inherited most di-
rectly the features of this gen-
eralized Paleozoic form. But
which of these two sharks must
be regarded as resembling its re-
mote ancestor the more closely
seems to the writer a very doubt-
ful matter. Chlamydoselache
derives its great interest from
its late discovery (1884, Gar-
man), rareness, and Pleuracan-
thid type of teeth. (Fig. 92, A) ;
but now that it has been taken
in numbers — comparatively —
in deep water, one is inclined
to believe that many of its

Fig. 93.— Heptanchus, Heptabranchias maculatus. 2. X 4, From specimen loaned by Smithsonian Institution. Collected

in Pacific,

N’, NW”. Anterior and posterior nares. SP. Spiracle.

RECENT SHARKS 89

“primitive” eeatures, like its eel-like shape, may partly be
due to its environment: its resemblance, moreover, to the
Pleuracanth has since been found to be of a superficial
character. Notidanus, on the other hand, adds to its
primitive characters the presence of no less than seven

Fig. 94. — The horned dog-fish, Sgualus acanthias,L. 3. X%. (After GOODE:
in U.S. F.C.) Atlantic,

gill slits, a feature which morphologists generally are
inclined to regard as of great significance.

The many forms of recent sharks have certainly not
diverged widely from the stem of descent which Notidanus
may well represent: they retain the sub-cylindrical body
form, specializing more or less to environment; in deep-
sea genera the body length appears proportionally in-

Pig. 95. — The thrasher shark, Alopias vulpes (Gmel.), Bonap. 2. x Ys. Atlantic.

creased : predatory forms, such as Squalus, Alopias, Lamna
(Figs. 94, 95, 96), acquire great size and strength, travel
great distances, and are enabled to become cosmopolitan.
Among the minor details to which their evolution has
been carried, may be noted: the pattern, size, and arrange-

go RECENT SHARKS

ment of teeth and shagreen denticles ; the calcification of
the vertebra (great differences sometimes occurring in the
same genus, e.g. Scyl/ium), the size, disposition, and num-

Fig.96.— The mackerel shark, Lamna cornubica (Gmel.), Fleming. X %.
North Atlantic,

ber of the fins, the more or less pouch-like character of
the sensory canals. .

In the basking shark, Cetorhinus (Selache) (Fig. 96 A),
widely specialized conditions occur in the gill rakers,
which enable the throat to retain the smallest food organ-

Fig. 96 A.— The basking shark, Ceforhinus maximus, (L.) Bainville. ¢.
X go. (After GOODE in U. S. F. C.)

isms. In another shark, Lemargus (Fig. 96 B), the eggs
are probably fertilized after being deposited, — a condition
unique among recent Elasmobranchs.

SQUATINA AND PRISTIS gI

The different families of the existing sharks appear to
to have been already differentiated during the early Meso-
_ zoic times. The ancient shark-like form had then given
_- place to the flattened and rostrated types, adapted to the

Fig. 96 B. — The Greenland shark, Lemargus borealis,L. X ds. (After GUNTHER.)

conditions of bottom living and to the special ‘character of
their shell-fish or crustacean diet.

One of the earliest offshoots from the main selachian
stem appears to have been Sgwatina (Fig. 97), popularly
known as the monk-fish, or angel-fish. As early as the
Mesozoic times it was existing, differing but little from the
recent species. Its general shape is shark-like, although its

eh te

_ Fig. 97.-—The monk-, or angel-fish, Rhina squatina, &. x Atlantic,
Mediterranean, Pacific.

head and trunk are clearly depressed. This, together with
its enlarged pectoral fins, enables it to take a position
closer to the bottom.

The recent saw-fish, Pristis (Figs. 98, 98 A), is next to

92 SA W-FISHES

be mentioned as a form somewhat transitional from shark
to ray. Its body, as may be seen in the figure, has been
strikingly flattened, the gill openings changing their posi-
tion from the lateral to the ventral side, but the fins re-
taining in general the selachian characters. Its singular
rostrum with lateral spike-like teeth is unquestionably a

“Fig. 98.—The saw-fish. Pristis pectinatus, Latham. @%. X as. Tropical
seas. (After GOODE in U.S. F. C.)

highly specialized organ. Pristis is thus far known not
earlier than the Eocene, but its close connection genetically
with the ancient and more generalized Pristiophorus is
usually conceded.

Pristiophorus (Fig. ‘99) is certainly more closely allied
to the sharks: its gill slits have not as yet acquired their
ventral position, and its rostrum suggests the ancestral

Fig. 98 A. — Saw-fish, ventral view.

conditions of that of Pristis. Its barbel-like structures,
however, distinguish this form clearly from all other
Elasmobranchs. It is known to have occurred as early
as the Jura.

The Skates or Rays are well known to represent the
most highly modified survivors of the ancient stem of the

SKATES 93

sharks ; they appear comparatively late in time, and may
well be regarded as the culminating forms of the specializ-
ing bottom-living sharks of the Mesozoic. Whether they
are directly descended from forms like Squatina or Pristio-

Fig. 99. — Pristiophorus (cirratus). 2. (After JAEKEL.) Australia.

phorus must be looked upon as exceedingly doubtful, as
the depressed body form may possibly have arisen
independently in these different families. The most
nearly ancestral form of the skates appears to have sur-
survived in Rhznobatus (Fig. 100). The shark-like body
form is here most nearly retained, and its fin structures

Fig. 100.— Rhinobatus planiceps. 2. XX}. (After GARMAN.) (The lower
portion of the figure showing ventral side.) S. Spiracle. GO. Gill slits.

are the least specialized ; these transitional characters of
Rhinobatus become more prominent in view of its ancient

occurrence: its genus was clearly defined as éarly as the
Odlite.

94 FLATTENED SHARKS

The body form of the Skate (Fig. 101) has become ~~
admirably adapted to bottom living; it is exceedingly
flattened anteriorly, its head and trunk and paired fins 3
fusing so perfectly that from the surface view one could —
not define their limits; the tail region, on the other hand, —
has dwindled away to rod-like or whip-like proporieaaay

Fig. 101. — The barn-door skate, Raja levis, Mitch, g. X }. (After GOODE
in U.S. F.C.)
In the process of flattening, the gill openings take their
appearance early in the ventral side of the body, and the
pectoral fins, enlarging rapidly, press closely forward at —
the side of the flattened head, fusing with its tissues.
Motion is now accomplished by the gentle undulation
of the long horizontal fin margin: and the enlarged |

AFFINITIES OF THE ELASMOBRANCHS 95

anterior element of the fin stem, by being raised or de-
pressed, comes to direct the upward or downward motion
of the fish. In this mode of movement seems to have
__ been paralleled the undulation of the ancestral fin fold.
On the fish’s dorsal side colour adaptations have become
marked, the ventral |
aspect becoming de-
ficient or wanting in
pigment. In its hab-
its the skate mimics
the colour of the
bottom and glides
along inconspicuous-
ly, apparently with-
out movement; when
alarmed, it will press
its enlarged and flat-
__tened fins so closely
to the bottom that it
appears to adhere,
and is to be dislodged
only with the great-
est efforts.
_ -Two of the aber-
“ _ rant forms of Tays are Fig. 102.— The torpedo, Torpedv occidenta-
z. loeen in Figs. 102 o% "ae dg. X44. (After GOODE in U. S.
and 102 A. The for- —
P ; _ mer, the Zorpedo, is remarkable on account of its electric
. organs; the latter, Dicerobatis, on account of the great
i breadth of its pectorals, and its enormous size.

96 KINSHIPS OF SHARKS

Affinities

In concluding the present chapter, the probable affini-
ties and interrelationships of the Elasmobranchs may be
summarized as follows (v. Fig. 103) :—

1. Of all known stems that of the shark is most: nearly
ancestral in the line of jaw-bearing vertebrates.

2. A generalized form not unlike Cladoselache might
well represent the ancestor of Pleuracanthid, as well as ,
of the primitive Cestraciont, of Acanthodes, and of the
modern sharks and rays.

Fig. 102 A. — The mantis, or devil ray, Cephaloptera (Dicerobatis) draco. X te. —
(After GUNTHER.) Tropical seas.

3. On the evidence of the Permian Pleuracanthids,
lung-fishes (Dipnoans) and the earliest bony fishes
(Crossopterygians) are to be derived from an advancing —
shark type. ‘

4. From the ancestral stem of the recent sharks
Cestracionts were the most early differentiated: it is one
of their more generalized forms, Cestracion, that has alone

KINSHIPS OF SHARKS 97

survived among the widely evolved genera and families of
Palzeozoic times.

_ §. The more primitive types of modern sharks, Chlamy-
doselache, Notidanus, represent in an almost differentiated
condition the Palaeozoic phylum. .
6. The modern rays are derived in early Mesozoic times
__ from the main shark stem, not (in the opinion of the
_ writer) descended from Cestracionts, Pristids, Pristiopho-
rids, or even (?) Rhinids. |

_ 7. Chimezeroids, next to be discussed, represent the most
ancient of known offshoots from the (Pre-Silurian ?) sharks :
they are not degenerate in their essential structures, nor
are they connected with the ancestral phylum of the lung-
fishes, save through a common descent from early shark-
like ancestors.

These results the writer has expressed in the diagram
on the following page. The diverging phyla are indicated
as they are represented historically ; their primitive con-
currence with the main line of descent is suggested by
dotted lines.

H

—--— Cladoselache.

SBe6bSn66

__— — Acanthodian.

(TABLE III)

\---—— Pleuracanthid,

ce6- 24666 068588.

Squaloraja.

Amphibian,

ae cere ee Pate

ze
¢ fyi.
S$ &@ .€8 2 é@

Fig. 103. — Scheme suggesting the interrelationships of Sharks, Chimeeroids, “a

and Lung-fishes.
98

V

THE CHIMAROIDS

CHIMZROIDs are shark-like in their general characters,
but cannot be looked upon as in any strict sense closely
_ associated with the Elasmobranchs. They constitute the
second of the more important groups of fishes. Their
typical representative is the Chimezera, spook-fish, or sea-
cat (Fig. 119).

Structural Characters

The typical structures of Chimera are shown in the dis-
section given in Fig. 104. Its thick, round, and blunted
head tapers away gradually to the tip of a diphycercal tail,
C. The body surface is generally smooth. The paired fins
are somewhat shark-like, but their dermal margins have be-
come greatly enlarged, tapering distally to an acute point ;
the foremost dorsal fin provided with an anterior spine folds
like a fan and may be depressed into a sheath, SH, in the
__ body wall; this fin and the hinder ones are largely dermal,
D’, basal and radial supports existing only at B’, RX’. The
"gill arches, BA, may be seen to be closely drawn together;
_ their outer openings are now reduced to the slit-like aper-
_ ture beneath the dermal flap, OP. Teeth exist in the
_ form of dental plates, closely fused with the jaws; as
_ shown in the figure, D, three of these occur in each side,
_ asingle one on the mandible, an anterior and posterior on
99

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STRUCTURES OF CHIMAEROIDS IOI

the upper jaw (‘“premaxillary”’ and “ palatine’’) ; they are
studded with hardened points, or “tritors”’ (Figs. 109-112).
The sense organs are similar to those of sharks ; the nasal
- capsule, VAS, has both an anterior and a posterior open-
ing, O, O', the latter within the cavity of the mouth.

The visceral parts are decidedly shark-like; the diges-
tive tube is straight (p. 263) ; the intestine, /, with a spiral
valve of three turns; the liver, Z, is prominent; the
kidney, A, reproductive organs, 7, and their ducts, VD,
SS, VS, and abdominal pores are as in sharks; the intes-
tine, however, opens directly to the surface, A, separating
an anal from a urogenital aperture, VG. The mesenteries
are string-like.

The male fish is provided with a highly specialized intro-
mittent organ, CZ; it has a supplemental clasping organ,
VC, at the front margin of each ventral fin, V (cf. also Fig.
116 and Fig. 1162), and a retractile spine in the region of
the forehead, 17SP (cf. Figs. 113 and 115).

The skeleton of a Chimezeroid is shown in the following
figure (Fig. 105). Its structure is cartilaginous. The ver-
tebral axis is notochordal; its sheath, lacking in definite
centra, is strengthened anteriorly by a series of calcified
rings. In the anterior region of the trunk, neural proc-
esses, interneurals, and neural spines, VP, JN, WS, to-
gether with hzmal processes, occur as in sharks; toward
the tail region they fade away, and before joining with
the head at the occipital condyles, OC, they fuse into a
compact mass, joining with the basa] supports of the
dorsal fin.

The cranium is of a highly compacted structure ; its
vertical height has been greatly produced ; the orbits, OR,
are of great size and are separated from each other by a
membranous septum. The snout region is greatly meta-

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102

STRUCTURES OF CHIMAZROIDS 103

morphosed ; the mandible appears to be azfostylic, or artic-
ulated directly with the skull cartilage, PQ. The gill
arches are shark-like, but the hyoid arch appears far less
modified than in sharks; its upper element, /7JZ, is thus
unconnected with either the skull or the joint of the jaw;
its distal element, C//, has, however, developed a series of
specialized supports for the dermal gill shield, OP. The
study of the fin supports shows the dorsal elements, 2+ XR,
representing probably the radial and basal elements to-
gether, arranged in a single row margined distally by the
longitudinal ligament, ZZ, supporting the dermal func-
tional fin, D. The paired fins are readily reduced to the
plan of those of Fig. 84; their girdles, however, seem to
have acquired more modified characters, their ventral and
dorsal elements greatly increasing in size.

Chimeeroids as a group have received but a small share
of the attention paid to the other fishes; their living
forms are few and comparatively rare; their embryology
and larval history are unknown; and their life habits have
been suggested only in the work of Dr. Giinther (Cha/-
lenger Report). His record of the taking of immature
specimens of Chimera at great depths seems thus far the
most important clue as to the conditions of their living
and breeding.*

Fosstl Chimerotds

Fossil Chimzeroids have left behind them very imperfect
records of the history of their group. Like the sharks,
little more than their dental plates and fin spines have
usually been preserved. The structures of some of their
ancient members appear to have differed little from those
just described in the recent Chimera. In Ischyodus,

* Cf. also Goode and Bean, on Harriotia, P. U.S. Nat. Mus., XVII. 471-473.

104 FOSSIL CHIMAEROIDS

a Jurassic form (Fig. 105 A), the skeletal structures are
readily comparable to those of Fig. 105. In the case of
two of the Mesozoic genera, however, the evolution of
the Chimezeroids had evidently attained a high degree
of specialization: Myriacanthus and Sgualoraja, whose par-
tial restoration has been attempted in Figs. 106 and
106 A, must be both looked upon as highly modified forms ;
their snouts and frontal spines are greatly enlarged, and
their dental plates (Figs. 107 and 108) widely divergent
from the general Chimzeroid type: in Myriacanthus a series
of membrane bones occurs in the head region (Fig. 106,
B,C). In Squaloraja a horizontally flattened body shape
parallels the development of the ray-like form of sharks.

Fig. 105 A. — The Mesozoic Chimeeroid /schyodus. Xx 4. (After ZITTEL.)

Living Chimeroids

The Chimzeroids of to-day must be looked upon as the
survivors of a group comparatively numerous in Mesozoic
times: the few existing forms accordingly, from the palz-
ontological standpoint, acquire an exceptional interest.
They have been grouped under three genera, — Harriotta,
Callorhynchus, and Chimera. The first of these (Fig.
117, A, B, C) has been only recently discovered, and but
a few examples have been taken ; it merits especial atten-
tion, since it is unquestionably the most shark-like of
known Chimezeroids. In the male it lacks entirely the
frontal spine and has its claspers in an exceedingly un-

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105

is represented by but

The eggs are evidently fertilized

FOSSIL CHIMAZROIDS

The second genus, Callorhynchus,

differentiated condition.
after they have been extruded.

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106

f

_ Figs. 113-116 A. — Spines and clasping organs of Chimeeroids. 113. Clasping spine
‘of the forehead of male Chimera collici. Xx 6, 114. Myriacanthus dorsal spine. (After
‘L. AGAssiz.) 115. Frontal spine of male Sgualoraja, (From SMITH WOODWARD.)
116. Ventral fin and clasping organs of male Chimera colliei, xX 1. 116A. View of tip
hinder clasper (intromittent organ), when the three tips are drawn together.

_ A. Anus. AV. Anterior rim of ventral fin, specialized as a clasping organ. 5C. Body
- ‘the posterior clasper (intromittent organ). D. Dermal denticles. DS. Dermal spine-
like DT, Dermal tubercles, GD. Urinogenital aperture. ¥. Jointed base of
‘inner ventral element of intromittent organ. 47C. Mucous canal. S, Sheath of frontal
SC. Sperm groove of inner face of clasper. V. Ventral fin.

107

Fig. 117.— Harriotta raleighana, Goode and Bean, ¢. X}. Anew genus
of Chimzeroid —a bathybial form. A. Ventral view, showing rudimentary claspers.
B, C, Immature specimens.

108

CALLORHYNCHUS 109

a single species, C. antarcticus. It is said to be common in
the Straits of Magellan, and is popularly known as the
Bottle-nosed Chimera (Fig. 118, A, B). Its remarkable
snout is well supplied with sense organs, and its pad-like
dilation in front of the mouth is evidently of barbel-like
function ; it illustrates closely, no doubt, the remarkable
snout process of Myriacanthus. Callorhynchus is shark-
like in its general shape; and its caudal, dorsal and ventral

Fig. 118. — The bottle-nose Chisieare. Callorhynchus antarcticus, 2. X 4. From
% Mageion Straits. A. Dorsal aspect. 2B. Ventral view of head. (After GARMAN.)

fins correspond closely in appearance and structure with
_ those of certain sharks; the greatly enlarged pectoral fins
have, however, a more highly specialized character; they
stand boldly out from the sides of the body, and their
_ bases are rounded and muscular. The mucous canals
_ (Garman) have paralleled the saccular or tubular struct-
ures of the majority of sharks. The mandible (Fig. 110)
__ shows but a single broad tritoral area.

+ fe) RECENT CHIMAROIDS

Chimeera, the third genus of the recent forms, is well —
represented in the commoner form, C. monstrosa (Fig. 119,
A, B). This species is widely distributed in the Mediter-
ranean and Atlantic, taken usually in deep water; it is the
largest of the living species, often attaining a yard in
length. Its occurrence is usually erratic: in a favourable
locality, as at Messina, months often elapse before one is
taken; at other times many will be brought in in the
course of a few days. The Portuguese species, C. affints,

Fig. 119.— The sea-cat, Chimera monstrosa, g. XX}. A. Ventral view of
snout. 8, Front view of head. (After GARMAN.)

is said to be numerous in the deep fishing grounds; the
writer has seen it in the Lisbon market, where from its
low price it evidently ranks with the sharks as a food fish.
The smaller Pacific C. colliei (Fig. 104), rarely half a yard
in length, differs sharply from the other species, and is
therefore often given rank as a distinct genus, Hydro-
lagus, Gill. The writer learns from his friend Dr. Bean

AFFINITIES OF CHIMAZROIDS III

that it occurs abundantly in the shallow waters of Van-
couver; it is there well known as the “rat fish,” and may
often be seen in the neighbourhood of the docks, swim-
ming slowly at the surface.

The shape of the body of Chimzra seems in some re-
gards to have diverged from the more shark-like form of
Callorhynchus. Its organs have become concentrated in
the pectoral region, and ‘the disturbance in the curve
normals of the fish seems to have caused the shortening of
the snout, and the sudden dwindling of the hinder trunk
region; the tail, with its thread-like terminal, the opis-
thure (Fig. 120), is accordingly to be looked upon as de-

Fig. 120.— Chimera monstrosa, 3. Juv. X about 3. (After L. AGassiZ.)
The anterior ventral clasper is noted at X; the tail terminates in a thread-like

opisthure,

generate. In the anterior region, however, a number of
what seem to be primitive characters have been retained;
_ the mucous canals are groove-like ; and the dental plates
_ (Figs. 109, 109 A) exhibit a series of tritoral areas.

Affinities

_ All that is known of Chimzeroids, living or fossil, gives
_ but little definite knowledge of the kinships or evolution
of the group. Their shark-like structures cannot be shown
to have taken their origin from shark-like conditions.
_ Thus the dental plates even of the most ancient forms
_ do not suggest their derivation from shagreen cusps; the

112 CHIMAEROIDS

beak-like jaws of the Devonian Rhynchodus (Fig. 111),
of the Devonian Ptyctodus, or of the Mesozoic genera,
e.g. Ischyodus (Fig. 112), differ little in their structures
from those of their living kindred (Figs. 109, 109 A, 110).
The tritors accordingly are only doubtfully to be derived
from the fusion of the primitive basal substance of the teeth
with the tissue of the jaws. But the history of Chime-
roids tells of their ancient importance and of the diversity
of their forms, and demonstrates that they cannot be con-
nected with other existing forms of fishes. In Liassic
times their specialized members bore the same relation to
Chimera as did the aberrant Cestracionts of the Coal
Measures to the simpler sharks. In their dental evolution
they had even reached a more specialized condition than
the Cochliodonts (Cestracionts?). Thus in Myriacanthus
and Squaloraja, ‘all anterior prehensile teeth have disap-
peared, and the growth of the dental plates, instead of
taking place exclusively at the inner border, seems to have
gradually extended to the whole of the attached surface.
The Chimeeridz exhibit an advance in the circumstance
that all the dental plates are thickened, while the hinder

upper pair are both closely apposed in the median line and _

much extended backward” (Smith Woodward).* Squaloraja
had certainly attained a high degree of evolution in the
calcified vertebral rings, and in its specialized girdles, fins,
and clasping organs. Myriacanthus, on the other hand,

while retaining its ancient vertebral characters, had evolved —

a well-marked series of membrane bones. .

One cannot deny that the study of Chimzroids as a

group emphasizes many of their structural affinities to

the sharks. They resemble them in their cartilaginous

skeleton, fins and girdles, “claspers,” integument, and
* Cat. Fossil Fishes Il, xvi.

KINSHIPS OF CHIMAEROIDS 113

sense organs: they present similar visceral characters,
spiral intestine, heart, gills, abdominal pores, renal and
reproductive organs.

Their more important divergences from the plan of
elasmobranchian structure may thus be summarized : —

I. SKULL AND MANDIBLE (Vv. pp. 252, 256). The mandi-
ble articulates directly with what appears to be the carti-
lage of the cranium, ze. without the hyoid-arch element
serving as the suspensorium (Awfostylic, p. 257).

II. Fins, paired (Wiedersheim) and unpaired (Ryder),
and fin defences. The first dorsal, armed with an anterior
spine, is so specialized that it folds like a fan, and may be
depressed into a receptive sheath. The tail is (second-
arily) diphycercal.

III. SKIN DEFENCES AND TEETH. Shagreen tubercles
occur in Chimeroids and are in every way shark-like.
They are scattered thickly over the entire dorsal region
in Menaspis,* sparsely in Squaloraja. They occur in the
head region and on the spines in Myriacanthus (Figs. 106
C, 114); and on the head, spine, and clasper tips of recent
forms (Figs. 113 D,116 D). But dermal bones also occur,

4 asin Myriacanthus (Fig. 106 4), which do not outwardly
_ resemble the structures of ancient sharks shown, e.g. in
_ Fig. 90 B. The dermal plates protecting the suborbital
sensory canal of Chimera (Fig. 104, DP) must be looked

upon as specialized defences, not as degenerate remnants
of a complete dermal armouring (Pollard). And the dental
plates, as already noted (p. 99), are altogether unshark-like ;

their tritors are few in number and constant in position,
| Suggesting an origin from more superficial tooth centres,
_ but these in turn, like the toothplates of Cestracionts, may
have been evolved from shagreen denticles.

* Jackel, SB. d. Gesell. nat. Freunde, Berlin, 1891, Nr. 7.

114 CHIMA2ROIDS

IV. Gitt arcuHeEs. The gills have become drawn
closely together as in the more highly evolved types of
fishes (e.g. bony fishes), and are enclosed by a protective
dermal flap which fringes the sides of the head. The con-
centration of the arches and the appearance of the dermal |
shield suggest, however, the conditions we have seen in
ancient sharks (Cladoselache, Chlamydoselache, Acantho-
des), and cannot be given significance as the ancestral
form of the opercular apparatus of Teleostome. Even
the similar conditions of the Chimzroid and ancient
shark may well have been evolved independently. It is
interesting to note that in Chimzroids the spiracle is
absent.

V. Brain. The brain structure is archaic. Its gen-
eral plan is, however, more shark-like than Dipnoan
(Wilder, Ref. p. 244).

VI. LaTERAL Ling. The sensory canals possess many
distinctive features ; they retain their groove-like charac-
ter, but become widely sacculated and dilated, especially
in the snout region.

VII. Craspinc spine. The forehead clasper of the
male has been a well-marked character of Chimeeroids
from Liassic time. It folds anteriorly into a receptive
groove; its distal end, studded with recurved spines,
serves in the recent forms for strongest retention. It
seems to represent morphologically the anterior spine of
a dorsal fin (cf. Pleuracanthus, p. 83). |

In spite of these differences, however, the kinships of
the Chimzeroids seem unquestionably nearer the stem of
the sharks than that of other fishes. On existing evi-
dence the Chimzroid could not have been derived from
either Teleostome or lung-fish; nor, on the other hand,
could any of the larger groups of fishes be reasonably

AFFINITIES OF CHIM/EROIDS 115

derived from its conditions as ancestral. The dentition
of Chimeeroids alone is so remarkable that no direct proc-
ess of differentiation could convert it into the structures of
lung-fish or Ganoid. A number of archaic features draw
fishes together in the lines of their descent, but they can-
not be interpreted as linking the Chimzroids with the
Dipnoans, or the Dipnoans with the Chimzroids. Auto-
stylism, often adduced to ally these groups, differs widely
in its characters in each (p. 254): and the apparent similar-
ities in dental plates and membrane bones are closely
paralleled by the sharks. The diphycercal tail of the
Chimezeroid can be made no standard of comparison, since
it is evidently a secondary structure, arising within the
limits of the group, as it may well have done among
’ sharks (Pleuracanthus) or Teleostomes (Polypterus, eel).
If the sum of the general characters of Chimzroids be
considered, their affinities would clearly be to the most
ancient sharks. Their structures are not so widely at vari-
_ance with those of Elasmobranchs that they cannot rea-
sonably be derived from their more generalized conditions
in vertebral characters, cranium, mandible, girdles, fins,
membrane bones, gills. Absence of swim-bladder is again
strikingly shark-like. Like the ancient sharks, they have
been well adapted for survival by evolving but few special-
ized structures (e.g. dentition, gills). Their ventral clasp-
ing organs separate them clearly from the Dipnoans.
Until the discovery of Harriotta the frontal clasping spine
_ remained as one of the most distinctive features of Chi-
_ meeroids ; its high degree of specialization in Liassic times
is alone significant of the antiquity of their descent.

VI
THE LUNG-FISHES

LUNG-FISHES, or Dipnoans, have long been looked upon
as the linking type between amphibians and fishes. In
some regards of structure they approach the primitive
sharks ; in others, they resemble so closely the salamanders
that they were recently regarded by W. N. Parker as worthy
of a class by themselves, intermediate between fishes and
amphibians. As with the Chimzeroids, their few surviving
members give but a mere suggestion of the former size
and importance of thé group.

—

Structural Characters

The general structural plan of a Dipnoan is shown in
the adjoining figure (Fig. 121), taken from a dissection of
the African form, Protopterus. Its thick, spindle-shaped
body, enclosed in rounded, horn-like scales, CS, terminates
in a diphycercal tail, C/ The head is salamander-like
both in shape and in slimy integument. The paired fins
(schematized in the figure, P¥, VF) are archipterygial.

The head region is characterized by a cartilaginous brain
case, roofed by dermal bones, HR; a mandible, JA,
directly articulated with the skull (autostylic); an anterior
and posterior nares, VO,— the former opening under the
lip, the latter within the mouth ; a row of small, compressed

(unsegmented) gill arches, GA, whose single outer aperture
116

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TRANON “SA ‘seivu sojajsod puv JoajUy ‘OA’ “PIOYOO}ON “QW ‘AV ‘UOHYINONIe (oyAjsoyne) sreinqipuey “yy ‘syuaWas aposnyy
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SP “Uy [epney wz *(purjs yeyoor) wow jwovo[D +99 *SNSOHIB SNUOD "PD “BdVOID DQ ‘ood jeulmopqy ‘yr ‘snuy ‘"y
“pezpewmayos oie suy pasted ayy, *(scazdogosgy yO ain3y SMaMAVd “N*M Joye ure aq} uy) = “ysy-Suny Jo Awojyeur pesrouar) —‘1e1 ‘Bia

117

118 LUNG-FISHES

is guarded by an operculum, OP. The stunted external
gills which here protude, £2, are sometimes looked upon
as significant of an ancestral condition (Garman, Wieders-
heim).

The viscera are somewhat shark-like in their features.
They include a short digestive tract, with well-marked
spiral intestinal valve, S7/V; a fenestrated dorsal mesen-
tery, DM; a large, elongate liver, Z; a heart whose
arterial cone, CA, contains transverse rows of valves; a
cloaca, abdominal pores (or pore), A; and a rectal caecum,
CC (v. p. 263). The elongate kidney, K, the ovary, OV,
with its many small eggs, and the long, paired, sacculated
air-bladder (lung) may be named as among the least shark-
like of its visceral characters.

The skeleton of a Dipnoan (Fig. 122) is almost entirely
cartilaginous. A stout notochord, encased in a heavy
sheath, VCH, passes from the skull to the tip of the tail:
vertebral centra encroach upon it only in the caudal region,
C. Dorsal and ventral processes, arranged in metameral
sequence, extend from the notochordal sheath outward and
become distally the cartilaginous supports of the dermal

unpaired fin. The proximal elements might thus be re- a
garded as neural, JV, VS, or hemal processes and spines, —

the distal elements as equivalent to the basal and radial fin
supports, B+ R. <A stout, longitudinal ligament, ZZ,
serves to connect the outer ends of the cartilaginous
processes, as well as the proximal ends of the dermal fin —
rays. The ribs are probably the homologues of the haemal _
processes ; the most anterior pair, greatly enlarged, extends
downward on either side as the occipital ribs, OR, special-
ized in the function of the air-bladder. ]

The structure of the paired fin is normally of the
archipterygial form of Fig. 54. In Protopterus, however, 4

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Tesiog “OS ‘spud sepnoys ‘Ng ‘swuowsj uy [eulep pue jeIpey.g+y ‘eIpey ‘y “yeIpend ‘O “prosfsajdoywyeq Yr
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-owolg ‘dy ‘onoidg ‘oy “Arewaq ‘wg ‘sher uy eueq ‘gq ‘uoldor uy esiog ‘G ‘TekyoyelaD ‘HD ‘JepneD + ‘suod
-dns jeipes puv yeseg “y+ ‘sywoddns uy snoursenivo jeseg “g ‘ajnsdeo A1oypny ‘QP ‘Iensuy ‘DY ‘uorser uy jeuy ‘PY ©
(avu5 GIONUy “iq Aq uMVIp foray JouoHesedeid Woy) ‘sunp2auuv snaapdojo4sg ‘YSY-BUN| JO UOjajaxg — “CCI “BL

Il,
*,
D

d

SNA

SSSI

°

119

120 LUNG-FISHES

(Fig. 122), this plan of structure is somewhat obscured by
the rudimentary character of the radial and basal elements,
R+D, although the fin stem presents a well-marked
jointed character, B. The pelvic girdle, a solid plate of
cartilage, is produced anteriorly into a narrow median out-
growth, PG, and laterally into a pair of dorsal spurs, PG’.
The shoulder girdle is composed on either side of a large
ventral element, SG, which meets its fellow in the median
ventral line, and of a short dorsal element, SG’, which

connects it with the skull. |

aspects, showing pair
M. Dental plates of (dentary) mandible; P. of palatopterygoid; V. of vomer.

In the head region (v. pp. 252, 254), the brain case is
cartilaginous, with, however, a few true bone centres (e.g.
epiotic) appearing; the roofs of the skull and mouth, —
together with the mandible, are well sheathed by dermal
bones, as HP, N, PP, DN, AG. Paired dental plates
fringe the rim of the mandible (Fig. 122 A, J/), the
vomerine region (V), and the anterior end of the palato- |

pterygoids (P).
Fossil Lung-fishes

The structures of the recent Dipnoans can as yet be but
imperfectly compared with those of fossil forms. Their
ancestral conditions can only be determined when more

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—

oa

te

SF.
= of

122 LUNG-FISHES

perfect evidence is discovered as to their kinship and the
lines of their descent.
In the history of fishes, Dipnoans are known to have been
early a dominant group. In some regards, one of their
ancient forms bore many resemblances to the Pleura-
canthid shark, which, although known at present only in
a later period, may well have been its contemporary. But
the range in the forms of Dipnoans occurring in the early
Palaeozoic indicates the remote antiquity of their origin.
They had even then evolved exoskeletal characters which
are scarcely less specialized than those of existing forms.

'
\
Worst

7

ations
ieee!
SCC

Fig. 126. —A restoration of the Devonian lung-fish, Phaneropleuron. X }.

Dipterus, of the Old Red Sandstone (Fig. 123), had a
complete body armouring of cycloidal scales, a head roofing
of dermal plates (Fig. 124), and well-calcified jaw rims —
(Figs. 124, 125, 125A). Its fin rays were dermal in —
structure, its paired fins were archipterygial, its tail and
its dorsal fins separate and lobate. Its mucous canals had
become elaborately adapted to the body scales (lateral line,
Fig. 123) and head plates, piercing the latter with minute
pores, as in Figs. 65,66. Anterior and posterior nares are — 3 .
indicated under the rim of the upper jaw (Fig. 125, 1-2).
Marginal teeth have disappeared; a pair of elaborate dental
plates on the mouth roof (palatine) are apposed by a simi-
lar pair in the hinder part of the mandible (splenial).

The Carboniferous Ctenodus was a nearly allied form.

Another Devonian lung-fish, Phaneropleuron (Fig. 126),

(After GUNTHER.)

Fig. 127. — The Australian lung-fish, Ceratodus miolepis. X }.

123

Fig. 128. —Skeleton of Ceratodus. (After GUNTHER.) The vertebral structure of the tail region is shown in detail immediately below

the caudal fin.

’

124 LUNG-FISHES

was similar to Dipterus in its skeletal characters. Its elon-
gate diphycercal tail was continuous with the dorsal and
anal (?) elements; in this, and in the retention of marginal
cusp-like teeth, it resembled the Pleuracanthid sharks.

Living Forms

The three forms of living lung-fishes may reasonably be
looked upon as the survivors of the more generalized Palzo-
zoic forms. Ceratodus, the
Australian genus, appears to
have retained most perfectly
the ancestral conditions; it
has probably remained almost
unmodified from the early
Mesozoic times,* and presents
close affinities to the Coal
Measure family, Crenodontide,
and even to the Devonian
Dipterids. Its outward ap-
pearance is shown in Fig.
127, and its skeleton in Fig.
128. The latter is seen to

resemble closely the charac-

Fig. 128A.— Skull of Ceratodus, : : :
Seen from the ventral side. (After ters of Fig. 122; its paired
ATE) fins are archipterygial; the

c. Occipital rib, d. Dental plates.
na. Anterior and posterior nares. P. mouth is lacking in marginal
Palatine. PSph. Paraspenoid. 4. Z .
Pterygoid. Qu. Quadrate. Vo. Vomer, Cutting plates (cf. V, Fig.

122 A). The dental plates
of the palatine and splenial regions (Fig. 128 A) are seen
to correspond clearly with those of Figs. 125, 125 A.

Ceratodus had long been known to the colonists of

*v.p.10. The recent genus, according to Dr. Gill, is to be distinguished
as Neoceratodus.

THE RECENT LUNG-FISHES 125

Queensland as a plentiful food-fish, a “salmon” in size and
taste, although, curiously enough, it remained undescribed
until 1870 (Krefft, and Giinther). After this its develop-
mental history was eagerly awaited, in the hope that it
would reveal the affinities of the Dipnoans to the sharks,
amphibians, and in general to the early chordates. About
ten years ago Caldwell was sent to Queensland by the

Fig. 129. — The South American lung-fish, Lepidosiren paradoxa, Natter. X }.
(From NICHOLSON, after NATTERER.) A front view of the mouth is shown at 2.
Royal Society, and succeeded in securing a set of the
embryonic stages, but his results still remain unpublished.
A second set of embryos was collected in 1891 by Semon,
from whose recent paper a summary is later given (p. 198).
The development of Ceratodus, however, as far as it is at
present known, has proven in many ways unsatisfactory to
the phylogenist ; its abbreviated growth stages cannot be

126 LUNG-FISHES

looked upon as furnishing clearly the ancestral history of

Dipnoans.

The two remaining forms of recent lung-fishes, Lepz-

Fig. 129 A. — The African lung-fish, Protopterus annectans. X 4. (After MIALL.)

dostren and Protopterus,
resemble each other so
closely that Ayers has
contended that they
should be regarded as
distinct only specifically.

Lepidosiren, the South
American form (Fig.
129), was discovered by
its describer, Natterer,
in 1837 in the upper
Amazon, It then, for
many years, succeeded
in eluding the collectors,
and was known as one
of the rarest specimens
of foreign museums. In
1887 it was, however, re-
discovered in Paraguay,
where it appears to have
long been known as a
food-fish. Its structures
are now regarded as en-
titling it unquestionably
to the rank of a distinct
genus,

Protopterus, common
in the White Nile and
Congo (Fig. 129 A), has
long been the “ Lepido-

RELATIONSHIPS OF LUNG-FISHES 127

siren” of dealers, often of museums. It is the best known
of Dipnoans, on account, partly, of the ease with which it
may be transported alive. In the hardened mud cocoons
with which it encases itself during the dry season, it is
readily dug out of the stream bed and packed for exporta-
tion. When placed in tepid water, the cocoon dissolves
and the fish shortly revives.

Relationships

A review of our knowledge of Dipnoans gives but little
satisfactory suggestion as to their relations as a group.
They must certainly be looked upon as an advancing
phylum from which the amphibia may early have diverged.
Their many amphibian characters have been lately em-
phasized by W. N. Parker. On the other hand, the
evidences of the kinship of Dipnoans to the other types
of fishes can only be interpreted as the common con-
vergence of the ancient phyla toward the structures of the
ancestral form of fish. Thus we find that the types of
Devonian lung-fishes can only be distinguished from
those of the contemporary Teleostomes by the pattern
of arrangement of the plates of the head roof,* a condition
which has led Smith Woodward to believe that these
groups had already diverged before the appearance of
dermal bones.

Lung-fishes have unquestionably many structures which
may have been derived from the more generalized condi-
tions of the sharks; and as a group they may not unrea-
sonably be looked upon as descended from the primitive
elasmobranchian stem. Their ties of kinship to the sharks

* The present writer regards this distinction as somewhat provisional;
median head plates are nominally characteristic of Dipnoans (Fig. 124), but,
as in the sturgeons and siluroids, they are also well known among Teleostomes.
Protopterus has, moreover, a symmetrical arrangement of the head plates.

128 — RELATIONSHIPS OF LUNG-FISHES

have now been closened by the proof that their paddle-
shaped fins may be directly deduced from a “ monoserial
archipterygium,” and that their diphycercal caudal, formerly
regarded as most primitive in plan, may have been acquired
secondarily after a condition of heterocercy (W. N. Parker,
Traquair, Dean).

The resemblances of Dipnoans to Elasmobranchs might ©
be summarized in the following structures: — ,

I. VERTEBRAL Axis. Its notochordal condition and
simple metameral, neural, and hemal elements suggest the
conditions of Cladoselache (p. 80); in that ancient form,
however, the vertebral processes had not come into rela-
tion with the unpaired fins.

II. Sxutzt. The chondrocranium is as yet largely re-
tained; as yet no dentigerous membrane bones of the
mouth rim (maxillary and premaxillary) have appeared.

III. Trern. These are clearly of an elasmobranchian
order; the tubercles of the dental plates (Fig. 125) suggest
closely a shagreen pattern; in Phaneropleuron, marginal
cusps have even been retained. The palatine and splenial
plates parallel strikingly some of the forms of Cestraciont
dentition.

IV. Brain. Its structures are of an advancing elasmo-
branchian order, annectent with reptilian (Ceratodus) and
amphibian types (Protopterus).*

V. VISCERAL CHARACTERS. Heart, gills, digestive tract,
vessels, mesenteries. . -

The closely corresponding characters of Phaneropleuron
and Pleuracanthus might be looked upon as independently
acquired; but in view of the many nearnesses of their
phyla, these characters may reasonably be regarded as
proof of genetic kinship.

* Burckhardt,

ARTHRODIRAN LUNG-FISHES 129

The advancing structures of the Dipnoan include, in
addition: —

I. EXOSKELETAL SPECIALIZATIONS. Head-roofing der-
mal bones (cf., however, Pleuracanthid) and cycloidal scales.
In early forms (Dipterus) these appeared at the surface
and were apparently enamelled. In recent forms they
are deeply sunken in the integument (Prototerus). They
suggest closely the structures of Crossopterygian (p. 149).

II. ARTICULATION OF THE MANDIBLE. This is auto-
stylic, somewhat as in Chimeroid (v. p. 256). Its homol-
ogy is obscure.

III. Arr-BLADDER. (v. p. 264).

IV. ABSENCE OF VENTRAL “CLASPERS” (cf., however,
Cladoselache).

V. TRUE POSTERIOR NARES (amphibian).

VI. THE GREAT SIZE OF THE CELLULAR ELEMENTS OF
ALL TISSUES (amphibian); THE GLANDULAR STRUCTURES

OF THE EPIDERMIS (amphibian).

VII. CrrcuLATORY CHARACTERS: the three-chambered
heart ; aortic arches.

VIII. Limes structure. This, however, is not to be
interpreted as in any way directly transitional to cheirop-

terygium.
The Arthrodiran Lung-fishes

The ARTHRODIRA, as Smith Woodward has shown, may
provisionally be regarded as an order of extinct and highly
specialized lung-fishes. They occur geologically among the
earliest fishes, and include a number of (Devonian) forms
whose peculiar characters and gigantic size must have made
them among the most striking members of ancient fauna.
The group might be regarded as standing in the same rela-

tion to the ancient Dipnoans as Acanthodians to the Cla-
K

130 ARTHRODIRAN LUNG-FISHES

doselachian sharks. As recently as 1887 its members were
associated by Traquair with Pterichthys, but the discovery
of jaws, specialized dentition, fin spines, and highly evolved
pelvic fins at once separate this group from the lowly
Ostracoderms. |

American Arthrodirans, described mainly by Newberry
and by Claypole, have proven of especial interest. They
occur from the Silurian to the Coal Measures. The giant
predatory member of this group, Dinichthys (Frontispiece,
and Figs. 133-137), attained a length of ten feet. TZ7Ztan-
ichthys, less formidable in armour and dentition, may well
have been twenty-five feet in length. These forms occur
almost exclusively in the Waverly of Ohio. Their discovery
has here been due to the efforts of Dr. William Clark
of Berea, Rev. William Kepler of New London, and Mr.
Jay Terrell of Linton; and most of the type specimens
have been preserved in the museum of Columbia College,
New York.

The European member of this group is a small, fresh-
water (?) form, Coccosteus, especially abundant in the Old
Red Sandstone of Scotland. It has thus far yielded the
most complete material for study, and its structural char-
acters might accordingly be described, since they are
probably common to all members of the group.

The lateral view of Coccosteus is shown in Fig. 130, the
dorsal aspect of the anterior region in Fig. 131, and the
ventral view of the visceral region in Fig. 132. It will
accordingly be seen that the general shape of the body
of this Arthrodiran was somewhat depressed; that the ©
head, shoulder, and stomach regions were protected by
bony plates; and that the trunk region was lacking in
armouring, and short in relative length. In well-preserved
fossils the space occupied by the notochord, J, is seen to

COCCOSTEUS 131

pass from the region of hinder plates of the body armour
to that of the tip of the tail. This is seen to be bordered
by neural and hzmal processes, V, H, which in size and
character are somewhat comparable with those of Protop-
terus or Pleuracanthus. The dorsal fin presents a meta-
meral series of supporting cartilages (radial and basal, DR,
DB). The basal supports of each pelvic fin have become
compressed into a flattened plate, VB. Pelvic fins were
present, but there have as yet been found no traces of
pectoral appendages. In Dinichthys Newberry believed
that a pectoral fin spine was present, and that this fin was

Fig. 130. — The Devonian Arthrodiran, Coccosteus decipiens, Ag. X 4. Old Red

Sandstone, Scotland. (Side view, restored; slightly modified, after SMITH WoopD-
WARD.)
A, Articulation of head with trunk. D#Z. Cartilaginous basals of dorsal fin.
DR. Cartilaginous radials of dorsal fin. A. Hzemal arch and spine. MC. Mu-
cous canals. NV. Neural arch and spine. U. Median unpaired plate of hinder
ventral region. V2. Basals of ventral fin. V2. Radials of ventral fin,

probably Siluroid-like (p. 171), but this view has not been
_ confirmed.

The head of Coccosteus was clearly flattened, with
orbits and nasal openings near its anterior margin; it
was roofed by a stout buckler of closely fitted dermal
plates (Fig. 131), whose outer surface was tuberculate,
_ enamelled, and furrowed by sensory grooves, WC. The
_ arrangement of the dermal plates of Coccosteus was early
_ (1861) compared by Huxley with that of recent Siluroids,

132 ARTHRODIRAN LUNG-FISHES

an analogy afterward supported by Newberry, Dean, and
recently, on account of the similar characters of the sen-
sory canals, by Pollard. In their conclusions, however,
fundamental characters of structure seem to have been
overlooked in the unlikeness of Arthrodiran to Tele-
ostome. The inner structure of the cranium of Arthro-

FIG. 131

Figs. 131, 132. — Coccosteus decipiens, Dorsal view of dermal armouring, x b=
(After TRAQUAIR.) 132, Ventral plates. (After TRAQUAIR.) ‘
ADL. Antero-dorso-lateral. AZ. Anterolateral. AVM. Autereeseeuiene
Cc. Central. £. Ethmoid. ZO. Epiotic. JZ. Inferior lateral. 4. Marginal,
MC. Mucous canals. MD. Median dorsal. .4/O, Median occipital, A/V. Me- —
dian ventral, O. Opercular. PDL. Postero-dorso-lateral, PZ. Posterior lateral, —
PM. Premaxillary. PN. Pineal. PO. Preorbital ZO. Postorbital PVZ. —
Postero-ventro-lateral. SO. Suborbital. '

dira was evidently entirely cartilaginous; in a Russian —
Coccosteid, according to Smith Woodward, the base of the —
brain case (parachordal cartilages) has been preserved and —
shows a “tubular canal originally occupied by the anterior —

STRUCTURES OF ARTHRODIRAN * ‘933

extremity of the notochord.” Gill arches and opercula are
not definitely known. The mandible was attached directly
to the skull (autostylic). The jaws were shear-like, their
margins usually with pointed teeth, whose bases fuse with
the tissue of the jaw and constitute dental plates. In
all forms, as in Dinichthys (Frontispiece), there appear to
have been three pairs of these “ plates,” those forming the
rim of the mandible below, and those of the vomerine
and palatine regions (“premaxillary” and “maxillary’’)
above.* This arrangement of the dental plates somewhat
resembles the Dipnoan’s. Those of the Arthrodiran, how-
ever, appear to have been movable, and suggest a dental

condition elsewhere unknown among vertebrates.

Fig. 133.— Restoration of Dinichthys intermedius, Newb. X %. Cleveland
Shales, Ohio.

The body armouring of dermal plates is characteristic of
the group. A carapace, cape-like in shape, begins at the
head angle and broadens out backward and dorsally
towards the median line. It consists of a single median
spade-shaped element, which forms the strong ridge of the
back, and a flanking of lateral plates, all compactly joined.
The rigid shield that is thus formed is movably connected
with the head; an elaborate joint, formed on either side
between the anterolateral dorsal plate, Fig. 131, ADZ, and
the “ epiotic,”” HO,— whence the name Arthrodira, — must

* According to Dr. Clark, an additional symphysial pair of dental plates
was present in both upper and lower jaw (Dinichthys).

134 ARTHRODIRAN LUNG-FISHES

have permitted the head to be thrown backward to a
degree which suggests the thoracic joint of an Elater.
On the ventral side of the trunk there occurs a flattened
plastron (Fig. 132): its dermal elements are connected by
overlapping margins; they are lighter, and in some forms
(Fig. 135) lack the tuberculate surface of the dorsal
plates. Dorsal and ventral shields are connected by stout
lateral elements (Fig. 132, /Z), which, passing ventrally,

FIG. 135

Figs. 134-13'7.— Dermal plates of Dinichthys. 134. Associated plates of head
and shoulders. 135. Plates of ventral armouring. (After A.A. WRIGHT). 136.
Pineal plate of Dinichthys intermedius, surface view. 137. Pineal plate of Dinich-
thys terrelli, visceral aspect. 137A. Pineal plate, in sagittal section.

ADL, Antero-dorso-lateral. AVL. Antero-ventro-lateral. AVM. Antero-
ventro-median. £. Ethmoid. £O. Epiotic. MO. Median occipital. PN.
Pineal. PO. Preorbital. P7O. Postorbital APVL. Postero-ventro-lateral. SO,
Suborbital. .X. External aperture, and >, the axis of the pineal funnel.

meet in the median line, and become the anterior support-
ing rim of the plastron. By some writers these have been
homologized as “ clavicles.”

In further detail little is known of the anatomy of

STRUCTURES OF ARTHRODIRAN 135

Arthrodirans. Sensory canals have been described chan-
nelling the surface of the dermal plates of the dorsal side.
In the body region of Coccosteus evidence of a lateral line
occurs (Smith Woodward) in a white calcified band fossilized
in the region of the space of the notochord. In this form,
too, an endoskeletal plate is known, (Fig. 130, UV) occurring
in the median line in the region of the vent, which must
be regarded as “suggesting an internal element of support
occurring in the vertical septum between the right and
left halves of some paired organ (S. W.).” The character
of the dermal investiture of the trunk has apparently
not been described; it may therefore be of interest to
note that the museum of Columbia College has recently
acquired two of the hinder dorsal plates of Dinichthys
which clearly indicate the presence of integument. The
plates are covered by a crinkled epidermis, whose irregular
surface traceries resemble the roughened finish of Turkey
morocco. This leather-like surface is seen to have been
continued over the margin of the plates along the side
of the trunk; traces of scales or tubercles are altogether
lacking, and its appearance suggests that it may have been
degenerate in structure.

Among Arthrodirans there occurs a series of most inter-
estingly evolved forms; and it is found more and more
evident that they, with other lung-fishes, may have repre-
sented the dominant group in the Devonian period, as
were the sharks in the Carboniferous, or as are the
Teleosts in modern times. There were forms which,
like Coccosteus, had eyes,at the notches of the head
buckler; others, as Macropetalichthys, in which orbits
were well centralized; some, like Dinichthys and Titan-
ichthys, with the pineal foramen present; some with
pectoral spines (?); some with elaborately sculptured derm

136 ARTHRODIRAN LUNG-FISHES

plates. Among their forms appear to have been those
whos shape was apparently sub-cylindrical, adapted for
swift swimming; others (JZy/ostoma) whose trunk was
depressed to almost ray-like proportions. In size they
varied between that of a perch and that of a basking
shark. In dentition (Figs. 138-144) they presented the
widest range in variation, from the formidable shear-like
jaws of Dinichthys to the lip-like mandibles of Titan-
ichthys, the tearing teeth of Trachosteus, the wonderfully
forked, tooth-bearing jaw tips of Dzplognathus, to the
Cestraciont type, Mylostoma. The latter form has hitherto
been known only from its dentition, but now proves to be,
as Newberry and Smith Woodward suggested, a typical
Arthrodiran.

The puzzling characters of the Arthrodirans* do not
seem to be lessened with a more definite knowledge of
their different forms. - The tendency, as already noted,
seems to be at present to regard the group provisionally as
a widely modified offshoot of the primitive Dipnoans, bas-
ing this view upon their general structural characters,
dermal plates, dentition, autostylism. But only in the
latter regard could they have differed more widely from
the primitive Elasmobranch or Teleostome, if it be ad-
mitted that in the matter of dermal structures they may
clearly be separated from the Chimeeroid. It certainly
is difficult to believe that the articulation of the head of
Arthrodirans could have been evolved after dermal bones
had come to be formed, or that a Dipnoan could become
so metamorphosed as to lose-not only its body armouring

* The writer believes that the Arthrodirans may as well be referred to the
sharks as to the lung-fishes; as far as existing evidence goes, they certainly —
differed more widely from the lung-fishes than did the lung-fishes from the
ancient sharks. They may, perhaps, be ultimately regarded as worthy of rank
as a class. :

Sp

Roa Od © | ry Ee

Figs. 138-144. — Mandibles_of Arthrodirans: Cleveland Shale, Ohio. 138.

variabilis, Newb., visceral aspect. 139. Tifanichthys clarki, Newb.,

visceral aspect. x }. (140,) Trachosteus, Ne@Mib., outer aspect. X }. 141. Diplo-

, Newb., outer aspect. xX }. 142. Diplognathus, seen from dorsal side.

(AS Ritlagnathes, visceral aspect, 144. Dinichthys intermedius, outer aspect. X 4.
137

138 ARTHRODIRAN LUNG-FISHES

but its pectoral appendages as well. The size of the
pectoral girdle is, of course, little proof that an anterior
pair of fins must have existed, since this may well have _
been evolved in relation to the muscular supports of
plastron, carapace, trunk, and head. The inter-movement
of the dental plates, seen especially in Dinichthys, is a
further difficulty in accepting their direct descent from
the Dipnoans. |

Vil
THE TELEOSTOMES

ALL fishes not to be grouped among Sharks, Chime-
roids or Lung-fishes, have been included in the fourth
sub-class, Teleostomi. In this are to be merged the two
time-honoured groups, Ganoids* and Teleosts, since it is
now found that there are absolutely no structures of the
one group that are not possessed by members of the other.
The terms, therefore, “Ganoid” and “Teleost,” must
be used in a popular and convenient, rather than in an
- accurate sense ; the former to denote the “old-fashioned ”
Teleostome, with its rhombic bony body plates, and carti-
laginous endoskeleton; the latter, the modern “ bony fish,”
with rounded, horn-like scales and its calcified endo-
skeleton.

Teleostomes present so wide a range of variation that
it becomes exceedingly difficult to include in a single
definition their minor structural characters.

As a basis for the comparison of the Teleostomes, the
characteristic structures of a single type, ¢.g. the Perch,
might conveniently be taken. From these conditions,
typical of a modern and highly specialized form, the simple
structures of the ancient, more primitive, and ancestral
Ganoids may afterward be readily understood.

* The term Ganoid, as here used (as far as p. 147), includes the Crossopte-

rygians as well.
139

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140

STRUCTURES OF TELEOST I4I

General Anatomy

In the Teleost (Fig. 145) the shortened and muscular
body appears admirably adapted to the conditions of
aquatic motion. Anteriorly it is broad and deep, its
trunk muscles firmly attached to the bony prongs of the
enlarged base of the skull, DCR, and to the solid, compact,
calcified vertebre, V, and their stout processes. The
fish’s tapering sides are encased in horn-like cycloidal
scales, CS, a light, flexible armour, whose elements over-
lap, defending every point, and whose smooth and slime-
coated surface provides the least possible resistance to
motion. The fins, D, C, A, PF, VF, are light and strong,
erectile and depressible; their rays are thin, narrow, spine-
like, strong; they are entirely dermal, their cartilaginous
supports sinking within the body wall, RB. The caudal
is large and fan-shaped (homocercal), its crowded rays
providing admirably its needed strength; its stout basal
supports, compacted beneath the tip of the notochord, VC,
show that its form is modified heterocercy. The pectoral
fin, PF, has now taken its position high in the side of the
body ; its basi-radial supporting elements are reduced to a
proximal row of a few small irregular plates.

The skeleton is completely calcified. The vertebral axis
has undergone entire segmentation, the notochord persist-
ing only between the cup-shaped faces of the centra; the
vertebral arches and processes have merged with the
centra, and those of the hinder region, WV, H, with prob-
ably the basal fin supports.as well. Ribs, X, usually with
intersupporting processes, strengthen the walls of the
visceral cavity, and represent calcifications of the myocom-
mata, rather than transverse processes of the vertebrz.
The skull is formed of compact bony elements ; its carti-

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142

STRUCTURES OF TELEOST 143

laginous brain case is replaced by many definite osseous
elements. The floor and roof of the skull, the face region,
jaws, gill arches, and their protecting parts, are all encased
by an elaborate series of membrane bones ; these, however,
must be noted as deeply embedded in the body tissue,
DCR, DN, A, 0, PT, SM, BR, O. The membrane bones
of the jaw rim—maxillary, premaxillary, and dentary, JZX,
PMX, DN— bear teeth, and are especially characteristic
of the Teleostomes; those overlapping and protecting the
gill arches (GA), O, JO, PO, SO, usually four in number,
are also characteristic of the group. The skull is hyostylic.

As to the visceral parts. The gill arches, GA, are
reduced in number, usually widely bent backward, and
closely crowded together ; their gill filaments are enlarged
and specialized. The heart lacks the arterial cone with its
transverse series of valves; in its place a stout bulbus, 2,
forms the base of the aorta. The digestive tract is tubular,
long, and coiled ; its intestine, G, lacks a spiral valve, and
terminates at the body surface, AJ, not in a cloaca; its

glands include a series, often great in number, of pyloric

ezca (pancreas). An air-bladder, AB, is present, which
may, or may not, retain its communication with the gullet.
The ovary, with its many small eggs, and the kidney, dorsal
to it, have often a common external opening in a urino-
genital papilla, UG, in either side of which abdominal pores
mayoccur. The nervous system and sense organs (pp. 275,
277) have many peculiarities: the roof of the fore brain is

non-nervous ; the nasal openings appear in the dorsal side

_ of the head, VO, and are separate; the eye has specialized a
vascular, nutritive structure, the processus falciformis, pro-
jecting from the region of the entrance of the optic nerve

_ into the vitreous cavity of the capsule; the optic nerves
__ Cross in passing to the eyes, but their fibres do not fuse.

144 TELEOSTOMES

Such in outline are
the essential structures
ofa Teleost. They may
now be briefly con-
trasted with the more
important characters of
the Ganoids.

In skeletal structures
the Perch (Fig. 146)
may be strikingly con-
trasted with the most
nearly ancestral form
of Ganoid (Fig. 147).
In this, Polypterus (p.
148), the skeleton re-
tains a_ semi-calcified
condition. Its verte-

DSG. Dermal scales
O. Operculum. P. Pelvic

SF. Jugular bones (scales). LZ. Longitu-

HA, Heemal arches.
NA, Neural arch. MS. Neural spine,
R’. Rib (transverse process). AZ. Radial and basal fin supports. S.

B. Basal fin supports. D. Dermal fin supports. DN. Dentary. DS.
SP’. Splenial.

xX}. This figure should be compared with Fig. 146.
DS’. Secondary dermal spines (radials, in part) of dorsal fin.

¢“@s bral centra are practi-
Oo g
g are g cally separate from the
Sp : £q arches; its ribs, X, are
SS 3% oa ,
: ; 3 <f equivalent to the trans-
s< gee & = verse processes ; its ac-
Sau R :
2s yj d r cessory ribs, AR, to
& uo} .
satsiga2 the “ribs” of Teleosts.
SESES A — nn
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Sea", 'S .
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Stu BaS ° '
egue E %@ tained; the membrane, _
3 3 5% £8 or dermal bones, of the |
woe.
Ta2e ae % head roof, as / P, AY
e#22253 PO, O, are clearly
Se GPaty we ;
i ga 32 scale-like, with an
&®*E2224 enamelled surface, sim-
Ass hn

ilar in character to

GANOIDS AND TELEOSTS 145

those of Dipterus. The shoulder girdle includes outer ©

dermal elements, DSG. The external parts of the unpaired
fins are dermal; but their cartilaginous supports are re-
tained, RZ, even in the tail region. The caudal fin may
be regarded as either diphycercal or heterocercal. The
exposed parts of the paired fins, it is especially interesting
to note, are only in part dermal; the two rows of carti-

____laginous supports are retained in a condition very similar

to that of sharks, R B;* two of the basal elements of the
pectoral fin, however, have retained the rod-like form in
strengthening the front and hinder margin of the fin.

In visceral structures the Ganoids exhibit the fol-
lowing noteworthy characters: a greater number of gill
arches ; a spiracle; a short and almost straight digestive
tube, with spiral valved intestine; a shark-like pancreas;
an arterial cone, with many rows of valves; a cellular air-
bladder, like that of a Dipnoan ; primitive conditions in the
urinogenital apparatus ; shark-like characters in the ner-
vous system and sense organs; a chiasma of the optic

nerves, (pp. 260-279).
Relationships and Descent

Johannes Miiller, when separating Ganoids from Tele-

3 osts, recognized clearly even at that early date (1844) that

the majority of the structural differences of these forms
were bridged over in exceptional instances; there were
thus Teleosts with bony body plates, as well as, it was
afterwards found, a Ganoid (Ama, p. 163) with herring-

a _ like cycloidal scales. But he believed that three structural

characters of the Ganoids separated them constantly from
all Teleosts, and warranted the integrity of the groups.

*Contrast Gegenbaur’s view that this fin represents the simplest known
condition of the archipterygium. é/. on p. 248.

+ 146 TELEOSTOMES

These distinguishing characters were : —

I. Acontractile arterial cone, containing rows of valves.

II. An intestinal spiral valve.

III. The interfusion (chiasma) of the optic nerve. »

It was not until these differences were shown to be of
little morphological importance that the two groups were
merged in'that of Teleostomi (Owen, 1866). Thus transi-
tional characters in the arterial cone of Butrinus (p. 258)
were discovered by Boas: the Teleost Chetrocentrus was
found to present ganoidean intestinal characters ; and the
optic chiasma, as Wiedersheim * demonstrated, could no
longer be regarded as of taxonomic or morphological
value.

The descent of the Teleostomes, like that of the other
groups, has long beena matter of speculation. Their affini-
ties with the Dipnoans are generally admitted (Giinther,
Gegenbaur, Haeckel, Smith Woodward). Rabl derives them
directly from a selachian stem, regarding the Dipnoans
as later evolved ganoidean forms. Beard, on the other
hand, even goes so far as to entirely separate the Teleo- nm
stome stem from that of the shark, lung-fish, and amphibian,
deriving it with a close kinship to Petromyzonts, from the
earliest vertebrates. Palaeontology, however, has lately
been giving rich contributions to this disputed problem,
and there can at present be little doubt that the conditions ‘
in fossil fishes have demonstrated that in most ancient .
times Dipnoan and Teleostome were closely approximated,
Although even in the earliest fossils they may be distin-
guished (e.g. by the arrangement of the head-roofing derm
bones, v. p. 127), yet, as Smith Woodward has noted, forms
occur too clearly transitional to indicate anything less

* One form of lizard was shown to possess a chiasma of the optic nerves;
in its neighbouring genus the nerves were found to cross without fusion,

INTERRELATIONSHIPS OF TELEOSTOMES 147

than genetic kinship. The Crossopterygian, whose ancient

structure is well known, may well have been derived from
an ancestor common to the Ctenodont (Dipnoan) and
Holoptychian (Fig. 153) ; so that the gradual nearing of the
Teleostome stem to that more fixed, of the Dipnoan, is a
strong suggestion as to its derivation. The later descent
of the Ganoids from an ancestor closely akin to, if not
identical with the Crossopterygian, is usually conceded.
Teleosts first occurring in Cretaceous are by evidence of
fossils the almost undoubted survivors of an extensive
group of transitional Mesozoic Ganoids (p. 165). But
whether all Teleosts are to be deduced from a single
ganoidean phylum can at present hardly be established.
Thus catfishes, or Siluroids, appear in many structural
regards closely akin to the sturgeon (p. 160); but as their
fossil remains are lacking before the Eocene—when, how-
ever, they appear to have been in every way as highly
evolved as in recent forms —little clue has been given to
their descent.

Teleostomes may, in the present connection, be briefly
characterized under their two principal subdivisions.

I. CrossoPpTERYGIAN, the more archaic group, uniting
characters of shark, lung-fish, and Ganoid, retaining the
ancient cartilaginous fin bases, radials, and basals in their
lobate fins; in some forms (Holoptychius, Fig. 153), the

__ concrescence of the basal parts of unpaired fins passing

through the same evolution as those of paired fins.

_ Represented in the surviving Polypterus (“Bichir” of
_ the White Nile, Fig. 148), and in the slender Polypteroid

Calamoichthys (of Calabar), and in the extinct Hofoptych-

ius, Undina, Diplurus, and Ccelacanthus.

II. AcrinopTeryGiAN, the spine-finned Teleostomes.
Fins supported by dermal rays ; ancient fin support greatly

.

Fig. 148.—The Nile bichir, Polypterus
bichir. X%. White Nile. (Modified after
L. AGASSIZ.)

A. Dorsal aspect. 2. View of throat re-
gion, showing jugular (gular) plates and ven-
tral elements of the derma! shoulder girdle.

TELEOSTOMES

reduced, implanted with-
in body wall. Includes
Chondrosteans (“ Gan-
oids”) and Teleocephalé
(“ Teleosts ”).

I, CROSSOPTERYGIANS

The CROsSSOPTERYG-
IANS, as_ palzontology
has demonstrated, are
the most ancient Tele-
ostomes. In their struct-
ural characters — espe-
cially in the fins, skeleton, —
nervous system —they
are clearly to be sepa-
rated from the neigh-
bouring Ganoids. And
their transitional charac-
ters have not as yet been
clearly demonstrated.

Polypterus (Figs. 148,
A, B, 149) and its kindred
genus, Calamoichthys
(Fig. 150), stand alone
as the survivors of the
Crossopterygian group.
They have diverged but
little from their Devo-
nian kindred, and demon-
strate in the most inter-
esting way the persistent
survival of fishes. From

RECENT CROSSOPTER YGIAN 149

their isolated position, these recent forms become of ex-
treme interest to the morphologist, and from the side of
their development, when this comes to be studied, they are
expected to throw the greatest light on the relations of the
primitive Teleostome to the sharks and Dipnoans, on the
one hand, and to the Ganoids on the other.

Polypterus * presents the exoskeletal characters of the
ancient Crossopterygians, and the typical conditions of
their lobate pectoral fins; the dermal plates of its head
region are tuberculate as in Dipnoans, but, unlike
these, their arrangement, as in all Teleostomes, is dis-

Fig. 149.— Polypterus lapradei, (After STEINDACHNER.) Head region of
well-grown larva showing external gill, ZG.

tinctly paired, ze. “ethmoids,” frontals, parietals, occipi-
tals (Fig. 148 A), including a pair of gular plates in the
throat region, 8.| Among the structures peculiar to the

* Polypterus occurs in the Nile, but is rarely taken below the Cataract. It
was noted, however, from near Cairo in the Description d’Egvpte, and a spec-
imen in the possession of Professor Innes of the College of Medicine, Cairo, was
taken near Bofilak a few years ago. It is known by the Arabs near Assuan,
and is here occasionally taken in the fykes at the beginning of the flooding-
season. The remarkable series of Polypterus in the Vienna collection was
collected in the White Nile, although some of these specimens, Dr. Stein-
dachner has stated personally to the writer, were taken in Middle Egypt. It
_ seems evident to the writer, from the results of his collecting-trip from Cairo
to Assuan, April and May, 1892, that abundant material of Polypterus is not
readily secured below the Second Cataract. Until, therefore, the interior of
Egypt is made more accessible to foreigners, developmental stages can hardly

be hoped for.
t As in some of the fossil lung-fishes.

Fig. 150. — Calamoichthys calabaricus. xX}. Senegambia,

TELEOSTOMES

recent forms may be included the fringing dor-
sal fin, the tubular nasal opening (Fig. 149),
and an external gill in Polypterus (Steindach-
ner), ZG, in the late larval stages.

Calamoichthys is unquestionably a divergent
member of the stem of Polypterus; its form,
becoming elongated, has acquired a general un-
dulatory movement ; the paired fins have accord-
ingly diminished in relative size, the ventral fins
finally disappearing.

Little is known of either the living or breed-
ing habits of Crossopterygians: in these they
might naturally be expected to resemble the —
Ganoids.

Fossil Crossopterygians

A number of the fossil kindred of Polypterus
are shown in the succeeding figures (Figs. 151-
156 A).

Gyroptychius and Osteolepis, Devonian genera
(Figs. 151, 152), are certainly most nearly in
the ancestral line of the recent forms. Like
many sharks and fossil Dipnoans, they present
a heterocercal tail, a single anal fin, and a pair
of dorsals. The pectoral fin of Osteolepis is
becoming a typical archipterygium. :

Holoptychius, another Devonian form (Fig. —
153), approaches even more closely the dipnoan
types: the scales are cycloidal; its paired fins
are distinctly archipterygial; and the caudal
region, reduced in length, is becoming meta-

morphosed into the typical diphycercal form by the ten-
dency of the second dorsal and anal fin to coalesce with

FOSSIL CROSSOPTERYGIANS ISI

the caudal. In these forms a number of paired gular
plates may occur.
In a closely related genus, Lusthenopteron, also of

Fig. 151

is eae
ha ¥s
ity?

Fig. 151.— Gyroptychius. xX}. Old Red Sandstone, Scotland. (After SMITH
WoopwarbD.)

Fig. 152.— Osteolepis. x }. Old Red Sandstone, Scotland. (Restoration
from SMITH WOODWARD, after PANDER.)

Devonian age (Fig. 154, A, #), the structure of the basal
parts of the unpaired fins is exceedingly interesting ; the
radial supports are unfused, while the basals, merged in a

Fig. 153. — Holoptychius andersoni, Old Red Sandstone, Scotland.

single plate, have come into especial relation with the
axial skeleton ; the subsequent stage of their differentia-

“Suz peyquoqns jo sjuawery ‘OQ gs *seuog Uap [eeEd-sog -zg “umnozadoqng ‘gO § “e[P113 Jopnoys [eullap jo
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152

FOSSIL CROSSOPTERYGIANS 153

tion has been noticed in Fig. 43. The condition of the
caudal fin of Eusthenopteron is also worthy of note; the
tip of the notochord is retained although the functional
_ portion of the fin is derived from the more anterior
body region. The vertebral arches are here clearly sug-
gestive of the conditions of the Dipnoan.

Celacanthus, common in the Coal Measures (Fig. 155),
is the most specialized of the Crossopterygians; it has
retained all of the archaic structures of its kindred, yet
has concealed them under the outward appearance of a
recent bony fish; the general contours of its head, trunk,
scales and fins resemble strikingly those of a dace or

Fig. 155.— Celacanthus elegans, Newb. X 3. Coal Measures, Ohio.
A. Position of calcified swim-bladder.

chub; but on closer view the paired fins are found to be
archipterygial, the scales enamelled and sculptured, the
true caudal fin the degenerate stump of the notochord ;
the functional caudal has been formed of the enlarged fin
rays of the dorsal and anal region. Traces of a calcified
air-bladder, A, are often preserved.

Diplurus and a closely related genus, Undina (Figs 156,
156 A), may finally be noted among the highly evolved
-Crossopterygians. They appear in the Mesozoic when the
majority of their kindred have disappeared ; they have as-
sumed peculiar characters and have apparently reached the
point of differentiation when they shortly become extinct.

154 TELEOSTOMES

Diplurus has become excessively shortened in its body
length ; the head is of relatively enormous size; its derm
bones are squamous, and appear to have been deeply
implanted in the integument; teeth have disappeared;

Fig. 156. — Diplurus longicaudatus, Newb. X }. Triassic, Boonton, N.J.
A. Position of calcified swim-bladder. A’’. Second anal fin (now the ventral
portion of the functional caudal). A. Radial and basal fin supports, C. Caudal
fin (degenerate). D. Hindmost dorsal fin (now the dorsal portion of the func-
tional caudal). ¥. Jugular.

scales have become exceedingly thin and are rarely pre-
served. Fin structures are apparently of a degenerate

character ; their cartilaginous bases, when showing, appear

Fig. r56 A.— Undina gulo, Egert. xX}. Lower Lias of Lyme Regis.
(Restoration after SMITH WOODWARD.)
to have become reduced to single plates, as BR; the
caudal is the elongate tip of the vertebral axis; the
functional caudal, now elongate and diphycercal, is formed

GANOIDEAN FORMS 155

by dorsal and anal elements, D, A’’, as in Ccelacanthus.
The boundary line of the calcified air-bladder, A, is often
preserved.

Il. ACTINOPTERYGIANS

A. Chondrosteans (Ganoids). Ganoids agree with the
Crossopterygians in their exoskeletal characters, although
usually lacking in gular plates. The most important
differences between these groups have been reduced to
those of fin structures; the Ganoids have no longer the
lobate form of the paired fins’; their basal fin supports
have become greatly reduced and are usually represented
by a single row of a few metamorphosed elements in the

Fig. 15'7.— The short-nosed gar-pike, Lepidosteus platystomus, Raf. X }. Mis-
sissippi basin. (After GOODE in U.S. F. C.)

most proximal region of the fin. The transitional stages
—if they exist—- between the lobate and the monoserial
fins have not as yet been demonstrated.

Fossil Forms

From the middle of the Palzozoic period to the end of
the Mesozoic there seems to have been a culminating time
of forms like the still existing Gar-pike (Fig. 157) ; their
fossils are generally the most numerous, and, on account
partly of their strong body armouring of interlocking
rhombic plates, the most perfectly preserved of fossil
fishes. They usually exhibit the structural characters

156 TELEOSTOMES

which Lepidosteus has retained, while diverging widely on
all sides in matters of shape, size, special dentition, and

Ar .\ YY NY
Si NN AS
ANY PN AON

SN

Fig. 158. 2 pias (Rhabdolepis) macropterus (Giebel), Bronn. xX }.
(After L, AGASSIZ.) Lower Permian, Rhenish Prussia.

features of the body armouring, — characters, apparently,
of minor morphological importance. But a few of the char-
acteristic types of the early Ganoids can be noted in the
present connection. Some of the more important have
been figured in Figs. 158-164.

Fig. 159. — Zurynotus crenatus, Agassiz. x 4. (After TRAQUAIR.) Calcif-
erous Limestone, Scotland.

Thus Elonichthys (Fig. 158) was a form which had
evolved a small size and narrow sculptured body plates ;

FOSSIL GANOIDS 157

Eurynotus (Fig. 159) had attained a great depth of body
and prominent dorsal fin; Chetvodus (Fig. 160) was dis-
tinctly flattened; Semionotus (Fig. 161) was small, with

Fig. 160.— Cheirodus granulosus, Young. X 4. Coal Measures, Scotland.
(After TRAQUAIR.) :

elaborate fin conditions; Aspidorhynchus (Fig. 162) had a
remarkable pointed snout and a reduced number of body

SS ot

xX <2 oJ 28. {/
CE "a

o AL
MELT,

Fig. 161.— Semionotus kapfi, Fraas. X 4%. (From ZITTEL, after FRAAS.)
Keuper, Stuttgart.
plates ; Microdon (Fig. 163), flattened like Cheirodus, had
evolved an admirable series of crushing teeth (-Pycnodont).
And, finally, is to be mentioned Pa/goniscus (Fig. 164),
a form whose abundance, numerous species, and long sur-

158 TELEOSTOMES

vival (Palzeozoic-Mesozoic) have made it the most widely
known of fossil fishes. Of all extinct Ganoids there

mS 4

% -
Sse
EBAY

LVS
ETAT INS
"9 r >» ‘“

>

c= fl eee — <==
> — 3

Fig. 162. — Aspidorhynchus acutirostris, Agassiz. X }. (After ZITTEL.) Jura,
Solenhofen.

appears to attach to Palzeoniscus the greatest morphological
interest; on the one hand, it seems closely akin to the

Lien

LUIS ME

LIL 4

NED:
\ \y
\ \"
NN
LS

NERA (AN)

\ \)

TE AW \
vii

Fig. 163. — Microdon wagneri, Thiollitre. 4}. (From ZITTEL, after THIOL-
LIERE.) Jura, Cerin.

LIVING GANOIDS 159

recent gars, and, on the other, even as evidently to the
sturgeons ; of all fossil kindred of these living forms, it
seems most nearly in the ancestral line.

Fig. 164.— Paleoniscus macropomus, Agassiz. x %. (After restoration of
TRAQUAIR.) Upper Permian.

Ganoids certainly outrank the Crossopterygians in the
number and variety of their ancient forms. Their few
living representatives give but little idea of the importance

of the group, and can suggest but faintly the lines of its
evolution.

Living Types

The recent Ganoids include the Gar-pike, the Sturgeons,
and Amia. The first is of especial interest in connecting
the group most closely with the Crossopterygians, the last
as best illustrating the intermediate stage between the
Ganoids and Teleosts.

The Gar-pike, Lepidosteus (Fig. 157), resembles Polyp-
terus in many characters of skeleton and dermal defences.
It is a form not uncommon in the fresh waters of North
America, and is especially abundant in the Mississippi,
Great Lakes, and rivers of the Southern States. In South
Carolina the writer has known the gar-pikes to occur in
such numbers that they would fill the shad nets, and for
many days render this fishery impracticable. They some-
times attain a length of six feet, and are said to become

160 TELEOSTOMES

as aggressive as sharks. They are remarkably tenacious My
of life, and their complete armouring of dermal plates
renders them practically invulnerable. .

In development Lepidosteus has apparently more prim-
itive features than Acipenser (v., p. 207; also Jour. of
Morph, X1, No. 1).

Of all recent Ganoids, Lepidosteus must certainly be
looked upon as retaining most perfectly the structural
characters of the most abundant and probably the most
generalized Palzozoic and Mesozoic forms. Its genus, it
is true, is not known to occur earlier than the Eocene, but
its structures — scales, fins, labyrinthine teeth and partially
calcified skeleton —are known to have been possessed,

Fig. 165.— The sturgeon, Acipenser sturio,L. X yy. Streams entering North
Atlantic. (After GOODE in U. S. F. C.)

even in their details, by a number of the older genera and
families. >

The Sturgeons, Acipenser, Scaphirhynchus, Psephurus,
Polyodon, must in many ways be looked upon as of a highly
adaptive or even retrogressive character. There is strong
evidence that in their descent a large proportion, and, in
cases, all of their dermal armouring has been lost, and that
their cusp-like ancestral teeth have either disappeared or t3
are retained in a rudimentary condition. |

The interrelationships of the four surviving forms of
sturgeons have not as yet been definitely suggested ; transi-
tional fossil forms have thus far been lacking, and the
relative importance of the different structures in the recent

THE STURGEONS 161

genera cannot, therefore, be determined for purpose of
comparison.

The genus of the common sturgeon, Acipenser, is the
most completely studied of the recent forms. It includes
twenty or more “species,” varying in length from one
(A. brevirostris, of the Eastern United States) to ten yards
(A. huso, of Russia), and is altogether one of the most valu-
able food-fishes of the rivers, lakes, and coasts of the north-
ern hemisphere. It is a sluggish, bottom-feeding fish,
common in muddy streams. Its broad and pointed snout,
sensory barbels, and greatly protractile jaws are the most
striking differences from the Palzoniscoid; its dermal

Fig. 165 A. — Chondrosteus acipenseroides. X 3. From Lias of Lyme Regis.
(Restoration of skeleton after SMITH WOODWARD.)

armouring has become reduced to the five longitudinal
bands of body plates,* but is more perfect in the tail
region ; its skeleton retains an entirely cartilaginous con-
dition. In its larval stage conical teeth are known to be
present, and the entire series of dermal plates are much
larger in relative size.

A figure of Chondrosteus, a Liassic sturgeon, may here

* It is interesting to note that in Palzoniscoids there is sometimes a notice-
able tendency for the five rows of plates, dorsal, and the paired lateral and
ventral, to increase in size, suggesting the first steps in the origin of the derm
plates of Acipenser.

162 TELEOSTOMES

parenthetically (Fig. 165 A) be inserted; it is of especial
interest as suggesting an approximation of the type of the
modern sturgeon to that of the Palzoniscoid ; its snout is
shorter than in Acipenser ; its jaws larger, and apparently
less protrusible; its dermal plates of the head region,
including the branchiostegals, are clearly of the ancient _
pattern, and the fins, fin supports, and vertebral characters,

Fig. 166.— The shovel-nose sturgeon, Scaphirhynchus platyrhynchus (Raf.),
Gill. xX}. Mississippi basin. (After GOODE in U. S. F. C.)

together with the general small size of the fish, suggest
intermediate conditions.

Of the remaining sturgeons, the shovel-nose, Scaphi-
rhynchus (Fig. 166), of the Mississippi and of Central Asia,
seems to possess the closest relations to Acipenser;
although it is apparently a more modified form, on account
of its elongate body shape and flattened snout, it still
retains many interesting and archaic features. Among

Fig. 166 A. —Psephurus gladius,Giin. x 3. Rivers of China, (After GUNTHER.)

=

these it includes the most complete dermal armouring of
recent forms, its hinder body region being entirely encased. — a

Psephurus (Fig. 166 A), of the Chinese rivers, and Poly
odon, or Spatularia (Fig. 165 4), of the Mississippi, are
the other forms of living sturgeons. Their greatly elon-
gate snouts, giving them the popular names of Spoonbills,
Paddle-fish, Spear-fish, are among the most remarkable

STURGEONS AND AMIA 163

sensory appendages of fishes. They have been but little
studied, and their relations to Acipenser have never been
satisfactorily determined. They have certainly many feat-

Fig. 166 B. — The spoon-bill sturgeon or paddle-fish, Polyodon spatula (Walb.),
jJ.and G. xX}. Ventral and side view. Mississippi basin. (After GOODE.)
ures in skeletal parts, fin structures, lateral line organs,
jaws, teeth,-which can only be looked upon as of primitive
character ; on the other hand, their highly specialized ros-
trum, degenerate opercula, and want of dermal amouring
would suggest an early divergence from the main stem of
the sturgeons. To the writer, Psephurus seems the more
generalized of these peculiar forms.

Fig. 167. The bowfin, Amia calva, L. x }.
Central and Eastern United States.

(After GOODE in U. S. F. C.)

Amia calva (Fig. 167) is the last of the recent Ganoids
to be noted. Its distribution corresponds closely with
that of the gar-pike; it is a common form, worthless as

164 TELEOSTOMES

a food-fish, but deemed worthy of a host of local names,
-as: Bowfin, Grindle, Dog-fish, Mud-fish, Sawyer, Joseph

Fig. 168.— Amia. Ventral view of jaw
region. X11. (After ZITTEL).

brs. Branchiostegal rays. 4. Cerato-
hyal. jug. Jugular plate. md. Mandible.

air-bladder is cellular, and of respiratory value (Wilder). —

Fig. 169.— Caturus furcatus. xX}. (From SMITH WOODWARD, after AGAS-
SIZ.) Lithographic stone (Upper White Jura), Solenhofen.

The relations of Amia become of especial interest, in
view of the number and range of its fossil kindred. Its

Grindle, Lawyer-fish. Its
interest, as already sug-
gested, is in its close kin-
ship to the Teleosts on
the one hand, and to the
sturgeons and gars on the
other. Its cycloidalscales,
its fin structure, and cal-
cified skeleton seemed of
so modern a character,
that it was long included
among the members of
the herring group; only
after a closer examination
did its primitive struct-
ures become apparent.
It is one of the few Gan- —
oids which possess a gular
plate (Fig. 168, ug). Like
that of Lepidosteus, its —

TELEOST-LIKE GANOIDS 165

group is known to have attained its prominence at a later
geological time than the other Ganoids; it is doubtless
derived, more or less directly, from the main ganoidean
stem. Three of the more typical Mesozoic forms are
shown in Figs. 169, 170, 171, in Caturus, Leptolepis, and

Fig. 170. —Lepftolepis sprattiformis, x 3. (From SMITH WoopWaRD.) _ Lith-
ographic stone, Solenhofen.

Megalurus. To these amioid forms the ancestry of the
(majority of the) Teleosts is reasonably to be traced.

A general scheme of the phylogeny of the Teleostomes
is suggested on the adjoining page (Fig. 171 A).

B. Teleocephali (Teleosts.) This group, popularly known
as that of the bony fishes, or Teleosts, includes as great
a proportion perhaps as 95 per cent of the kinds of fishes

Fig. r71.— Megalurus elegantissimus, Wagner. X%. (After ZITTEL.) Jura,
Solenhofen,

living at the present time. The immense number of their
genera and species is doubtless suggestive of the form
changes which occurred during the flowering periods of
the sharks, chimzeroids, or lung-fishes.

Teleosts have diverged most widely of all fishes from

166 TELEOSTOMES

what seem to have been their primitive structural condi-
tions. Their skeleton has become highly calcified, its ele-
ments multiplying, fusing, and specializing. The notochord _
has practically disappeared, owing to the complete formation :
of bony vertebra. The derm bones of the head, whichin

ANCESTRAL
_ TELeostome
(TABLE IV)
‘
'
\ \N -- PALAEOZOIC M
CROSSOPTERYGIAN
AS PaLaeozoic
\ PALAEONISCOID
\\ ---- Mesozoic
\ IN GANoID
\ w---= MeESOzZ016
| xe CATURIO
\ XS
\
‘\ \
STURGEON i i.
Leriposteus —SiLUROID Fungnovene LOPHOBRANCH = SN
‘POLYPTERUS Amia ACANTHOPTERYGIAN SYNGNAT

Fig. r71 A. — The Phylogeny of the Teleostomes.

the ancestral Ganoid were at the surface, enamel-coated,* |
are now deep-seated in the head, resembling true cartilage __

* The enamel of Ganoid plates (ganoine) appears to be derived from the r: ‘
underlying bony tissue, not deposited by the overlying epidermis (enamel —
organ). pa

woes tj

EVOLUTION OF TELEOSTS 167

‘

and their character is often squamous. Scales are widely
specialized, thin, horn-like, ornate, overlapping their outer
margins, their inner rims set deeply but loosely in dermal
pockets (Fig. 31). Fins are dermal structures, their ancient
basal supports hardly to be distinguished; the primitive
tail structure is so masked by clustered and fused skeletal
elements that its heterocercy is scarcely apparent. In
short, the most widely modified conditions can be shown
to exist in Teleosts in almost every structural character,
as in gills, teeth, opercula, circulatory and urinogenital
organs, sensory structures, and nervous system. They
have evidently been competing keenly in the struggle for
survival, for in every detail of form or structure the most
varied conditions exist. In addition to these structural
adaptations of Teleosts, changes in coloration have been
rendered possible by the transparency of their scales ; and
in their different families these changes have taken place
often with striking results: adaptive coloration, brilliant,
dull, mottled, inconspicuous, occurs with a range of varia-
tion which is not surpassed even by the colours of birds.

It is not remarkable, therefore, that members of the
different groups of Teleosts should often parallel each
other in structural likenesses, when placed under the same
environmental conditions. Each organ, in fact, may be-
come a centre of variation, and confuse the line of the
descent of the minor groups; for the keenest judgment
cannot select of all these varying structures those which
can definitely be made the standards of general comparison.
Environment, like a mould, has impressed itself upon
forms genetically remote, and in the end has placed them
side by side, apparently closely akin, similar in form and
structure.

A striking instance of changes due to environment is

168 TELEOSTOMES |

well known in the case of Deep-sea Fishes, in their acquir-—
ing a characteristic shape under the conditions of abyssal
life. The head region of these forms becomes greatly
exaggerated in size, and the trunk tapers suddenly away
toward the tip of the pointed tail. The tissues become
extremely modified, soft, porous, delicate, often trans-
parent ; skeletal parts are deficient in lime, and loosely
articulated. Many organs are retained in curiously unde-
veloped or aborted conditions ; the vertebral axis is noto-

—— SS .

— SS

—

Figs. 1'72-1'74. — Deep-sea fishes. (After GUNTHER.) 172. Paraliparis bathy-
bius. 640 fathoms. 173. Bathyonus compressus. 1400 fathoms. 174. Notacanthus
sexspinis. 1800 fathoms, s

chordal ; gill arches, as many as six (?) in number, may open
freely to the surface, never enclosed by opercula; sensory
canals remain as open grooves as in the most generalized
fishes ; paired fins are retained either in an undeveloped
condition or are not produced at all. Absence of light has
been not without its effects ; body colours are usually dark
and meaningless ; while, on the other hand, when eyes still —

DEEP-SEA TELEOSTS AND FIERASFER 169

occur, a widely modified series of integumentary phos-
phorescent organs are often evolved as lures by predatory
forms. It is evident, in the case of deep-sea fishes, that
the simple condition of their structures does not separate
them widely in point of descent from more specially
evolved Teleosts. Intermediate forms, occurring in shal-
lower water, often connect them clearly with different, and
widely distinct, groups of bony fishes. In this way the

oO gas
LEE

Fig. 175.— Fierasfer acus, Kaup. X %. (After EMERY.) Commensal of sea-
cucumber in southern waters,

forms which are shown in Figs. 172, 173, 174 are severally
connected with the cottid, the cod and the salmon, al-
though the striking similarity of their outward structures
would naturally lead one to regard them as far more
intimately related.

Another interesting instance of the modification of a
fish’s form by its living conditions has often been noted in
the case of Fierasfer (Fig. 175). This small Teleost lives

. as acommensal in the branchial chamber of the sea-cucum-

170 TELEOSTOMES

ber, and from its peculiar life habit retains permanently
a number of its embryonic characters; it has thus its
elongated larval form, a functional pronephros, a noto-
chordal skeleton and immature fin conditions (Emery,
Ref. p. 249).

To what degree the structures of fishes may be varied
by artificial selection is an interesting question, but one
that has as yet received little attention even from those
who have made artificialization an especial study. In the
instance of the Go/dfish it is well known how wide a

Fig. 176. — Goldfish, Carassius auratus (‘‘Telescope” variety). x1. (After
GUNTHER.) Japan.

variation has been produced in colour, size, and proportions.
Fin structures are elaborately developed, long, drooping,
lace-like, often to a degree which must render progression
both slow and difficult. Even the eyes have been made
to become large and protruding (Telescope-fish, Fig. 176).
In carp the variation in scale character, due to artificializa-
tion, is also to be mentioned. It is natural, perhaps, that
artificial selection has been most successfully practised

CA TFISHES 171

among these forms which compete most actively for
survival.

To conclude the present chapter, several forms of Tele-
osts may be briefly discussed as especially characteristic
of the group, namely the catfish, Mormyrus, eel, perch,
cod, flounder, porcupine-fish, sea-horse.

The catfish, representing the Sz/urvotds, has, as already
noted, many structural affinities to the sturgeon, and is,
perhaps, a direct descendant of some early type of Mesozoic
Palzoniscoid. It is a representative of a large and wide-
spread family, usually of river fishes. Its habits are slug-

Fig. r77.— The bull-head (catfish), Amiurus melas (Raf.), Jord. and Cope-
land. xX 4. (After GOODE in U.S. F.C.) Eastern North America.
gish and mud-loving. Its trunk is heavy, rounded, and
without Teleostean scales; its broad mouth margin is pro-
vided with barbels ; the fin rays of its dorsal and pectoral
fins fuse into a stout, serrate, erectile spine. In North
American forms armouring derm plates are developed
only on the head roof (Fig. 177). Closely akin to these
are ‘the Asiatic genera, and the single European species,
Silurus glanis, the gigantic We/s of the Danube. The.
Nile is of interest if only for its forms of catfish to
parallel the shapes and structures of the recent Teleosts.

172 TELEOSTOMES

In South America the catfish is a regnant type, and is
remarkable for the variety as well as for the number and
size of its forms. Many, completely armoured (Fig. 178),
are strongly suggestive of Ganoids. Their armouring is

My f | peel

Fig. 178.— South American Siluroid, Cadlichthys armatus. X1. (After

GUNTHER.) Upper Amazon.

metameral and archaic, their sensory canals primitive in

structure and arrangement.
Mormyrus, \ike the catfish, appears to have long been
divergent from the main stem of the Teleosts. Its species

et

sk

Fig. 179. — Mormyrus oxyrhynchus. X%. (After GUNTHER.) Nile.

are restricted to the Nile, one — the long-nosed MW. oxyrhyn-
chus (Fig. 179) — figuring prominently in Egyptian myth.
In many of its structures it is archaic, as in axial skeleton,
fins, dermal characters, sensory canals ; in others, e.g. hear-

ZEL-LIKE FORMS 173

ing organ, it is most highly specialized. Its group is an
interesting one, and has been but little studied.
The £e/ (Fig. 180) might well be taken as one of the

Fig. 180.— The eel, Anguilla vulgaris, Turton. X }. (After GOODE in U.S.
F.C.) Europe, South Asia, North Africa, North America.

fish forms evolved by special environment. Living in soft
river bottoms, a serpent-like movement in progression has
gradually been acquired; its form has, therefore, become

elongated and rounded, and the internal structures corre-
spondingly modified. Fin structures have accordingly been

Pig. 181.— The perch, Perca americana (= fluviatilis ?), Schrank. x 4. (After
GoopE in U. S. F.C.)

metamorphosed, ventral fins lost, tail degenerated, and a
continuous dorsal and ventral secondarily evolved; scales
have become reduced in size, supplanted by mucous layers.

174 TELEOSTOMES

Similarity in eel-like form, e.g. as of Murena, is not in
itself indicative of direct kinship. (Afodes.)

The Perch (Fig. 181) has long been taken as a repre-
sentative Teleost. Perfect in its “lines,” its compact,

wedge-like shape cleaves the water by vigorous thrusts of __

a strong broad caudal; its fins are stout, supported by

spinous rays ; its dermal armouring light, smooth, and flex-

ible; its colour is brilliant under its transparent scales,
So adapted is it to its environment that its organ of static
equilibrium, the air-bladder, has lost its valvular connec-
tion with the gullet. Of existing fishes about one-half are
essentially percoid. (Acanthopterygit.)

Fig. 182. — The sone, Gadus morrhua, L. X%. (After GOODE in U. S.
F.C.) North Atlantic.

The Cod (Fig. 182) is scarcely less important as a repre-
sentative Teleost. Its structural differences may perhaps
represent the result of a competition less active than that
of the perch in the struggle for survival. Heavy in body,
its sluggish form has become blunted and rounded; its
fins are depressed, their rays soft and yielding; its scales —
are reduced in size, colours less vivid; its swim-bladder
loses its connection with the gullet. As many, perhaps,
as one quarter of the existing genera of fishes may be
assigned to this type. (Anacanthini.)

The Flounder (Fig. 183) should be mentioned as a singu-

FLOUNDERS AND PORCUPINE-FISHES 175

lar instance of environmental evolution, its flattened body
adapting itself both in shape and colour to its bottom
living. Its entire side, —not the ventral region, as in the
rays,—is flattened to the bottom. The unpaired fins now
become of especial value ; they increase in size, and their
undulatory movements enable the fish to swim rapidly yet
retain its one-sided position ; ventral fins become useless,
and degenerate. The further. adaptations of the flat fish
include its pigmentation only on the upper or light-exposed
side, and the rotation of the eye from the blind to the upper

Fig. 183.—The winter flounder, Pseudopleuronectes americanus (Walb.), Gill,
xX}. (After GOODE in U.S. F.C.) North Atlantic.
side, — in this giving one of the most remarkable cases of
adaptation known among vertebrates. (Heterosomata.)

The Porcupine-fish (Fig. 184) may be referred to as
another singular result of environmental evolution. Its
globular and inflatable form bespeaks slowness of motion
and helplessness if exposed to changes of temperature
or current. Its fins are reduced and feeble, suited, how-
ever, to its tranquil habitat; its fused jaws, parrot-like,
show in how special a way its food is best secured. It
has evolved a protective casing of enormous needle-like
scales, whose shape parallels that of the derm denticles

176 TELEOSTOMES

of the shark. As a somewhat transition form to the more
usual conditions of the Teleost, the Raddit-fish has been
figured (Fig. 184 A). (Plectognathi.)

Fig. 184.— The porcupine-fish, Chilomycterus geometricus (Schn.), Kaup. x #.
(After GOODE in U.S. F. C. report.) Warmer Atlantic,

Fig. 184 A.— The rabbit-fish, Lagocephalus levigatus (L.), Gill. x %. (After
GOODE in U.S. F.C.) Northeast Atlantic.

A final, perhaps the most bizarre, instance of adapta-
tion among Teleosts is that of the Sea-horse (Fig. 185).
In spite of its many structural oddities, its genetic kin- —
ship with the Sticklebacks (Hemibranchiates) cannot be
doubted. Yet to have attained its present form its evolu-
tion must have been carried along a widely divergent path.
It may, in the first place, have fused the lines of its meta-
meral scales, dividing off the surface of its elongate body

SEA-HORSE AND PIPE-FISH 127.

in sharp-edged rectangles, whose corners became produced
as spines. At this stage of evolution its appearance might
well be represented by (Fig. 185 A) the kindred Pipe-jish,
To secure more perfect.anchorage in its algous feeding-
ground, its body terminal must now have discarded its fin
membranes and become frehensile, — probably the most
remarkable adaptation in the
entire class of fishes, since it
causes metameral organs to
change the plane in which they
function from a horizontal to a
vertical one. As a probable de-
velopment of prehensilism, three
changes may next have been
wrought : the flexure of the neck
region, the thickening of the
trunk, and the metamorphosis
of the fins. The first change
may have been brought about
by the normal position of the
fish’s axis becoming, as is well
known, vertical; the head then
assumes its normal horizontal
_ plane and thus parallels mildly
the cranial flexure of higher ani-
mals. The enlargement of the
ie ; 5 Fig. 185.— The sea-horse, Hif-
trunk region is evidently of static pocampus heptagonus, Raf. x }.
value. The alteration of the po- (After Goope in U.S. F.C.) East
sition, size, and degree of move-
ment of the pectoral fins, the loss of the ventrals and the
changed function, now one of propulsion, of the dorsal,
appear clearly the result of the altered plane of the fish’s

motion. Further structural changes might with interest
N

178 _ TELEOSTOMES

be followed, as in characters of viscera, gills, and endo- “ 4
skeleton. In its life habits mimicry is strongly evinced;

Fig. 185 A. — The pipe-fish, Syngnathus acus 3, L., showing abdominal pouch,
x 1. (AfterGUNTHER.) Coasts of Europe and Africa,

the well-known genus Phyllopteryx, whose entire body
surface develops pigmented appendages, is with difficulty

to be distinguished from a rough-shaped seaweed. (Lopho-
branchit.)

VIII

THE DEVELOPMENT OF FISHES

THE groups of fishes have hitherto been contrasted
_in the structures of their living and fossil forms. They
should next be reviewed in the light of their mode of
development ; for the developmental stages of the Shark,
Lung-fish, or Teleostome might be expected, according
to time-honoured belief, to furnish important evidence
as to their descent and interrelationships. The younger
stages of the various forms of fishes should thus suggest
their ancestral characters: the developing Teleost should
approach the Ganoid; the Lung-fish and the Ganoid
should resemble their supposed elasmobranchian ancestor.
But the embryology of fishes is in this regard very
inconclusive, if at present in any important way sugges-
tive. The majority of the forms, including some of the
most important, are developmentally unknown; yet suffi-
cient is known of the representative members of the
groups to show the most perplexing characters. On the
one hand, the developmental processes of forms which are
regarded by the morphologist as closely akin seem often
_ widely distinct; and, on the other hand, the fishes which
_ should, a priori, exhibit an archaic mode of development
actually present complex processes of early growth which
can only be interpreted as highly specialized. In fact,
there are far greater differences in the developmental plans
179

180 DEVELOPMENT OF FISHES

of the closely related Ganoid and Teleost, than in those of
a Reptile and a Bird; and even among the members of the
single group, Teleosts, there are more striking embryolog-
ical differences than those between Reptiles and Mammals.
Adaptive characters have entered so largely into the plan
of the development of fishes that they obscure many of
the features which might otherwise be made of value for —
comparison. And until the controversies regarding some
of the most fundamental principles in embryology —eg.
the importance of the loss or gain of food yolk — shall be
decided, it seems impracticable to use the plan of develop-
ment as in any strict sense a guide in phylogeny.

It is, accordingly, rather with the view of contrast-
ing the groups of fishes, whose external features have
hitherto been compared, that the present chapter seems ~
of especial importance. They may briefly be reviewed in
their (A) spawning’habits, (B) the mode of fertilization
of their eggs, (C) their embryonic, and (D) larval de-
velopment.

A. EGGS AND BREEDING HABITS

The eggs of typical fishes in Figs. 186-199, illustrate
how wide a range occurs in their shapes and sizes. All —
are of about actual size, except Figs. 189-191, which have
been reduced about two-thirds. From the figures the —
character of the egg membranes may also be contrasted.

Among Cyclostomes, which are usually looked upon —

as of close genetic kinship, there appears a striking dif-
ference in the characters of the eggs. Those of Bdello-

stoma and Myxine (Figs. 186, 187) are large and bluntly —
spindle-shaped, encased in a horn-like capsule; those, on —
the other hand, of Petromyzon are minute, spherical, and —
enclosed in delicate and jelly-like membranes (Fig. 188).

182 DEVELOPMENT OF FISHES

The eggs of Myxinoids are probably deposited at a
single time; at first extruded by pressure of the body
wall; then drawn out string-like, one egg following
another, attached by hooked and thread-like processes
(Figs. 186 A, 187A). Little is known, however, of the
actual breeding habits of Myxinoids, either as to locality,
mode, or season ; individuals of Myxine and Bdellostoma
with ripe spawn have never been taken even in the
most favourable regions. It is supposed that their spawn- —
ing does not occur in the immediate neighbourhood of —
the shore, since detached eggs have been dredged in the
deeper water. Their breeding time is probably in the
early spring, although possibly intermittent spawning
takes place. In Myxine, according to Putnam,* the bulk
of the eggs may be deposited as late as the beginning of
winter.

The spawning habits of Petromyzon, on the other hand,
have been especially favourable for observation. The eggs
are deposited in shallow and clear water and the move-

ments of the fish may readily be followed. In the small
stream at Princeton, for example, the lampreys make their

appearance about the middle of May and remain on the

spawning grounds two or three weeks. Their “nests”
are seen scattered thickly on the gravelly shoals, often but
a few feet apart. Each will be occupied by several males
and a single female, the latter conspicuous on account of
greater size. When spawning, the lampreys press together

and cause a flurry in the water at the moment when the |

eggs and milt are emitted. This portion of eggs will now

* As observed at Grand Menan. Pro. Bost. Soc. Nat. Hist. Feb. 74.

+ Professor McClure and Dr. O. S. Strong have here repeatedly observed
the spawning lampreys; it is to their account that the writer is here indebted.
Compare, also, the excellent account given recently by Professor Gage.
Ref. p. 234.

EGGS OF ELASMOBRANCHS 183

be covered with a thin layer of sand or gravel, —the
spawners always returning to the same nest, —and a sec-
ond, third, and more tiers of eggs will be added. When
the eggs have finally been deposited, the nest is fortified
by a dome-like mass of pebbles and stones, which the lam-
preys carefully drag to the spot. The nest is thus marked
out as well as protected, and is said to be made of partial
use during the following season. The hatching of the
eggs takes place within about a fortnight.

The eggs which Sharks and Rays deposit are usually
enclosed in a stout, horn-like capsule; this is in general of
oblong or rectangular outline, its surface smooth or ridged;
the case of the egg of Scy/lium (Fig. 189), shows thread-
like terminal processes, while these in the ray (Fig. 189 A)
are stout and spine-like. A great variation may exist in
the size of the egg and in the character of its envelopes
among the different groups of Elasmobranchs. The egg
of the Port Jackson shark, Cestracion (Fig. 190), is of enor-
mous size and possesses an extremely thick, spiral-rimmed,
pear-shaped capsule ; that of the Greenland shark, Lemar-
gus, is said to be spherical and relatively small, and to be
deposited unprotected by capsule.

The breeding habits of Elasmobranchs are but imper-
fectly known. With the exception, perhaps, of Lamargus,
the sexes copulate.* The clasping appendages of the male
_ are inserted either singly or together into the cloaca and
oviduct of the female, and the eggs appear to be fertilized
in the uppermost portion of the oviduct. The egg then
becomes surrounded by a glairy albuminous envelope, and
thereafter by the secretion of the oviducal gland, which in
the lower oviduct hardens into the horny capsule. The

* The copulation of sharks has been but rarely observed (¢,. by Bolau in
Hamburg ; cf. Ref. on p. 241).

184 DEVELOPMENT OF FISHES

majority of sharks and rays are viviparous; the eggs are

retained in the lowermost portion of the oviduct (uterus) __

and the embryo establishes a “placental” circulation, the
vascular yolk sac becoming adherent to the walls of the
uterus. Other sharks deposit their eggs, and their mode
of oviposition has been observed. The egg (Fig. 189),
when slightly protruded from the cloaca, is rubbed against
brush-like objects, and when its terminal processes become
finally entangled, the egg is withdrawn. The processes of
the egg case which leave the body last, the longer ones,
are often greatly straightened out when the egg is depos- —
ited; subsequently their elastic character causes them
to curl tightly, and often to secure a firm attachment
to neighbouring objects. The eggs of oviparous skates
(Fig. 189 A) are said to be deposited on sand flats near
the mark of low water. Mr. Vinal N. Edwards of Wood’s
Holl, Massachusetts, believes that they are implanted ver-
tically in the sand, and, from the occurrence of “beds”
of skate eggs, that the fishes are singularly local in their
places of spawning. Eggs of Elasmobranchs* are often
many months in hatching; the young fish finally escapes
through a slit at the end of the egg case.

Nothing is known definitely of the breeding habits of
Chimzroids. The mode of copulation of the sexes is
doubtless similar to that of sharks. Their clasping organs
are highly specialized sperm ducts, and the hook-bearing
organs at the anterior margin of the ventral fin, and on
the forehead of the male, function in all probability in
retaining the female. The forehead spine could certainly
prove of such service if the position of the fishes during
mating was at all similar to that figured for Scyllium by

* In the case of Scy//lium the eggs are deposited about six days after they
have been fertilized ; they then hatch in from 200 to 275 days.

EGGS OF FISHES 185

Bolau.* The egg case of Callorhynchus (Fig. 191) is

essentially shark-like; it is of spindle-shaped outline, and
_ its broad, fringing margin gives it an almost seaweed-like
appearance. .The egg is believed to be deposited in deep
water.

The spawning of but one of the three existing Lung-
fishes has been recorded. Ceratodus, according to Semon,
has a spawning season extending over several months; it
deposits its eggs in shallow water, scattering them broad-
cast. The female fish is attended by several males, and
the emission of eggs and milt appears to be simultaneous.
The egg (Fig. 192) lacks a horny capsule, but is amply
protected by a thick, jelly-like hull. It hatches during the
second week.

Eggs of Ganoids are shown in Figs. 193, 194. They
are encased in a jelly-like envelope, especially viscid in the
case of sturgeon. When deposited, they speedily adhere
_ to whatever they touch, and often remain attached until
the time of hatching. The spawning grounds are in
shallow water; the fish occur in numbers during a few
days of May and June, each female attended by several
males: ova and milt are emitted simultaneously, at short
intervals. The eggs develop rapidly, hatching in about a
week.

The eggs of Teleosts present the utmost variety in
number, form, membranes, and mode of deposition. In
some forms (Embiotocids, Blenniids, Cyprinodonts) they
may even develop within the ovarian tissue, establishing
there a “placental” circulation. They have been fertilized
within the fish, the anal fin spine of the male having in
some cases been metamorphosed into a copulatory organ.
The eggs of Siluroids (Fig. 195) are generally of large size,

*V. Ref. p. 241.

186 DEVELOPMENT OF FISHES

and somewhat adhesive; they are deposited in “nests,” Z.¢,
bowl-like depressions, and are attended by the male fish.*
Other adhesive eggs are those of carp, Christiceps, Batra-
chus. Eggs of Salmonids are deposited loosely in “nests”
on a clean, gravelly bottom; their membranes are thick
and parchment-like. On the other hand, the majority of
pelagic fishes produce eggs which float (Figs. 196, 197) ;
of these the membranes are extremely hygroscopic and
transparent, and an oil globule, located in the yolk region
of the egg, serves to diminish its specific gravity. The
egg membranes of a number of Teleosts, e.g. Blennies
(Fig. 199), appear essentially shark-like; a horn-like cap-
sule is evolved, whose terminal processes afford it a firm
attachment. Aberrant modes of oviposition are not lack-
ing; the South American Siluroid, Aspredo, as is well
known, carries its eggs attached to its ventral surface; the
pipe-fishes and sea-herses, Siphostoma, Solenostoma, Hip-
pocampus, have specialized a pouch-like fold of the abdo-
men and of the ventral fins, which serves to retain the
eggs and larve. It is curious to note that this remark-
able condition occurs only in the made.

The breeding habits of Teleosts are in general like those
of Ganoids; their spawning season is usually during the
spring and summer, but is seldom of very brief duration.
The hatching of the eggs depends largely upon water
temperature, and may vary from a few days to several
months (Salmo). .

B. THE FERTILIZATION PHENOMENA
The processes of the maturation and fertilization of
the egg have as yet shown but minor differences in the

*In several genera they are carried about in the gill chamber of the male,
thus ensuring aération.

EARLY DEVELOPMENT 187

groups of fishes. In the forms which have thus far been
studied * there have been few noteworthy variations from
what appear the normal conditions of vertebrates. The
sperm usually gains admission to the egg through a micro-
pyle in the egg membranes which becomes formed imme-
diately after the extrusion of the polar bodies. A sperm
cell, invariably a single one, participates in the actual
fertilization. This may occur directly by the formation of
a single male pronucleus, as e.g. in Petromyzon, Teleosts ;
while in the sharks, on the other hand, Riickert describes
a multiple fertilization (polyspermy), where many male
pronuclei} are formed, the one nearest in position fusing
subsequently with the female pronucleus. An_ inter-
mediate condition seems to be retained in the sturgeon,
where several (six to nine) micropyles have been noted,
although but a single one occurs in the kindred Ganoid,
Lepidosteus (Mark, Ref. p. 249).

Cc. THE EMBRYONIC DEVELOPMENT

When the egg of a fish is deposited, it contains but the
elements of a single cell. Its size and its enveloping
membranes may vary widely, but its constituents are con-
stant,— cytoplasm and nucleus. The size of the egg in
different fishes varies with the amount of food material,
or yolk, stored away in its cytoplasm; the enormous egg
of the shark differs from the minute egg of the lamprey
strikingly in this regard. But even in the minute lamprey
egg there is a certain amount of yolk material present.

In every egg there can usually be distinguished at sight

*Lamprey by Kupffer and Béhm, and Calberla ; Sharks by Riickert ; Te-
leostomes by Hoffman, Agassiz and Whitman, Kupffer, Bohm, and others.

+ These appear later to undergo karyokinesis, and are thereafter to be
regarded as supplemental merocytes (p. 195).

188 DEVELOPMENT OF FISHES

an upper and a lower zone: the latter rich orange in colour,
caused by the settling of the heavier yolk material; the
former lighter in colour, containing the nucleus of the egg,
and originating the growth processes.

The less the amount of yolk in the lower, or vegetative,
region, the smaller is naturally the egg, and the more
obscure becomes the limit of the upper zone, or germ, or
animal pole, as it is indifferently called. In the yolk-
filled egg of the shark, on the other hand, the upper zone
becomes reduced to a mere “germ disc”’ on the surface of
the egg (Fig. 216, GD). If but little yolk is present, the
early growth processes, z.e. the splitting of the germ cell,
or egg, into many cells, or blastomeres, to give rise to the |
embryo, affect the entire egg. If, however, much yolk is
present, the cells at first multiply only at the animal pole,
and the yolk-filled region, remaining unsegmented, fur-
nishes the nutriment for the cell growth above.

In the present outline of the development of fishes,
the following types are reviewed : —

I. Petromyzon ; II. Shark ; III. Lung-fish ; IV. Ganoid ;
V. Teleost.

I. The Development of Petromyzon

The egg of Petromyzon is of small size (Fig. 188), and
is poorly provided with yolk material ; in surface view one
can only distinguish the germinal from the yolk region by
its slightly lighter colour. In the side view of the egg of
Fig. 200, the beginning of the first cleavage plane is seen ;
a vertical plane, passing through the egg, completes the
stage of the two blastomeres of Fig. 201. The nuclei were.
at first close to the upper, or animal, pole, but they shortly
take their position somewhat above the plane of the egg’s
equator. A second cleavage plane is again vertical, ap-

qaxvesmeeeeter®

NER

U Z3 . .
Ce ..

A
+ =),
5 _
SEES

WN,

m)
Ne

re
n)

Yi}
Uf}

‘Tas

rs
rs

Figs. 200-215.— Development of lamprey, Petromyzon planeri. Figs. 200-204, 208-212

_ & 18, others x ut 30. 200, 201. First cleavage, beginning and concluded. 202. Third

oe: 203. Fourth cleavage, in section, showing Man nage of segmentation cavity. 204,

2 ly and late blastulz, in section, 206, 207. Early and late gastrule, in section. 208,

_ 210, 212. Early embryos showing growth of head end. 209, 211. Sagittal sections of early

@ wot fab, rentiation of organs. 213, 214. Transverse sections of early embryos.

«25. on of newly hatched larva, Ammocetes. (Figs. 211, 215, after GOETTE, others
after V. KUPFFER.)

BP. Biastopore. C. Coelenteron. CH. Notochord. DZ. Dorsal lip of blastopore. EC.

NV. Entoderm. ZF. Epiphysis. G. Gut. #. Heart. 4. Central nervous
MES. Mesoblast. N. Nasal pit. MC. Neurenteric region. S. Mouth pit, stomo-
SC. Segmentation cavity. 7. Thyroid gland. Y. Yolk and yolk cells.

189

>»

190 DEVELOPMENT OF FISHES

proximately at right angles to the first; the third, which
shortly appears, is horizontal (Fig. 202), giving rise to the
stage of eight blastomeres; this plane, passing slightly
above the equator, causes the upper blastomeres to be
slightly smaller in size than those of the lower hemisphere.
The amount of yolk in the egg, it is accordingly inferred,
although not sufficient to prevent the passage of cleavage
planes, is enough, nevertheless, to retard the nuclear cleav-
ages in the region of the lower, or vegetative, pole. In
Fig. 203, showing a vertical section of the following
stage, another horizontal cleavage has been established in
the upper part of the egg; the segmentation cavity is seen
in the centre of the figure arising as the central space
between the blastomeres. This is seen to have become
greatly enlarged in Fig. 204, a slightly later stage where
in vertical section is seen a greatly increased number of
blastomeres. Repeated cleavage of all blastomeres now
continues regularly, and results in the production of a
blastula, a smooth-surfaced cell mass containing the seg-
mentation cavity, SC (in section, Fig. 205); this is seen
to be located in the region of the animal pole. In the
next developmental stage, gastru/a, seen in section in
Fig. 206, the primitive digestive tract, calenteron, C, is
appearing ; it arises as an indentation of the side of the
blastula. The ccelenteron, soon greatly increasing in depth,
reduces in size and finally obliterates the segmentation cav-
ity, taking the position, C, shown in section in Fig. 207.
Here the segmentation cavity has practically disappeared ;
the surface opening of the ccelenteron is the d/astopore,
BP; the cell layer of the gastrula’s surface is the ecto-

derm, EC; the cell layer lining the ccelenteron is the en-—

toderm, EN: the coelenteron, it will be seen, is closely
apposed to the ectoderm at the left of the figure, — the

ee ee eee

DEVELOPMENT OF LAMPREY Ig!

future dorsal region of the embryo; on this side the
margin of the blastopore is known as the dorsal lip, DL,
while to the right the ventral lip is seen greatly enlarged
by the yolk-bearing cells, Y. A somewhat later stage
(Fig. 208) shows the blastopore as a narrowly constricted
opening, BP, whose dorsal lip is slightly raised at its left-
hand margin. The head of the embryo is to arise near
the opposite pole (as in Fig. 210), and is thence to elon-
gate into neck and trunk (Fig. 212). A sagittal section of
a stage, slightly older than Fig. 208, shows admirably the
structures of the embryo that have thus far been differ-
entiated (Fig. 209). Contrasting with Fig. 207, it will
thus be seen that the ccelenteron, arising at BP, has
become greatly elongated ; at its blind end its lining mem-
brane, entoderm, ZV, is in contact with an indented por-
tion of the ectoderm, at S, where later the opening of the
mouth will be established ; and that ventrally the ccelen-
teron has given off a pouch which passes into the yolk, and
will later be differentiated as the liver. That the entire
dorsal wall of the ccelenteron has become thickened, con-
stitutes the main difference between the sections of Figs.
207 and 209; there have, in other words, arisen between
the entoderm and ectoderm of Fig. 207 the central ner-
vous system, or medullary cord, WY, and the notochord, CH.
The origin of these structures may best be traced in the
cross-section of a slightly earlier stage (Fig. 213); the
ceelenteron, or gut, is at G, the ectoderm at ZC, the yolk
cells intervening at Y; and the notochord and medullary
cord, CH, and M, in the sagittal region immediately be-
tween the gut and the ectoderm. In the medullary region
the ectoderm cells are seen pressed together, growing down-
ward and sidewise, forming altogether a compact cell cord *
* As in Teleosts, but unlike other vertebrates.

192 DEVELOPMENT OF FISHES

passing down the back of the embryo ; the notochord is aris-
ing from the differentiating cells of the roof of the gut. In
the cross-section shown in Fig. 214, the subsequent con-
ditions of these structures may be seen; the medullary
nerve cord, JV, is now in section elliptical, separated dor-
sally from the ectoderm, and its cellular elements are of
more uniform size, arranged with bilateral symmetry, its
central lumen having not as yet appeared; the notochord,
now constricted off from the wall of the gut, takes upon
it its characteristic form and structure. It is, however,
in the differentiation of the walls of the gut that this
section is of especial interest; the gut is seen to have
greatly enlarged, and at the expense of the yolk material ;
its lining membrane, entoderm, ZW, is now directly ap-
posed to the outer germ layer, ectoderm, EC. The middle
germ layer, mesoderm, MES,—out of which cartilage,
muscular and connective tissue, are formed, —is now seen
taking its origin as paired evaginations of the dorsal wall
of the gut. The mesoderm shortly loses its connection
with the entoderm, and by the rapid increase of its cellular
elements rapidly invests the remaining embryonic struct-
ures ; its segmental character may be seen in the surface
view shown in Fig. 210, its dorsal portions appearing as
the primitive segments.

Later developmental stages are shown in the sagittal
sections, Figs. 211, 212. These may best be compared
with Fig. 209. In Fig. 211 the head end of the body has ~
greatly elongated, and with it the gut cavity has dilated ;
entoderm is now composed of very minute cells, whose
nuclei are suggested by dots; the yolk has become more
definitely restricted to the region of the hinder gut; the
blastopore is still seen; at its lips the germ layers are
alone fused.

DEVELOPMENT OF FISHES 193

Il. Zhe’ Development of the Shark

On the side of embryology a shark presents many points
of striking contrast to the lamprey; yet it may in many
regards be looked upon as archaic in its developmental
characters. Its contrasting structures (together with those
of lung-fish, Ganoid, and Teleost) may best be reviewed
in the table, p. 280.

The egg of the shark is of large size, richly provided
with yolk material. When removed from its membranes,
it is seen to be of a bright orange colour; its form is elon-
gated, and the weight of its pasty substance causes it to
assume a flattened ovoid (Fig. 216). At the upper pole of
the egg is a small, light-coloured spot, the germ disc, GD,
which figures prominently in the early stages of develop-
ment. It would represent the lamprey’s entire egg, if one
could imagine a point of the lower pole of the latter hugely
dilated with yolk. It is in the region of this germ disc
alone that every process of development as far as gastrula-
tion occurs.

The segmentation of the germ disc is shown in Figs.
217-220. In the first of these (Fig. 217) the germ is seen
to be sharply marked off from the surrounding yolk by a
circular band ; two cleavages have traversed it in the form
of narrow grooves separating the blastomeres. In Fig.
218 the fifth cleavage has been completed; the furrows
dividing irregularly the surface of the germ disc fade away
at its periphery. Fig. 219 represents a vertical section of
the germ disc at this stage ; the upper, finely dotted layer,
thinning away at either side, is the germ disc ; the coarsely
granular material below is the yolk; the depth of the
cleavage furrows is seen, and it will be noted that up to

this stage of development there have been no horizontal
°

GD

FIG. 216

SINAN AG A
whe

aut

\
OR ddrdtatee

ake
my
9D).
a Ni veer =
Pere’ 4
5 ae

8 es

YA —

Figs. 216-230. — Development of shark, Scy//ium (mainly). (All but 216 after BAL- | .
vouns 216. Egg freed from case showing germ disc GD. 217. Germ discatsecond |
cleavage. 218. Germ disc at fifth (?) cleavage. 219. Vertical section of similar
220. Vertical section of slightly older germ disc. 221. Blastula, 222, Early a
223. Blastoderm showing early growth of embryo. 224-226, Sige later stages
of embryo. 227. Stage showing early embryo and mode in which the blastoderm sur- |
rounds yolk. 228. Early embryo viewed as a transparent object. 229, 230. Transverse -
sections of early embryo.

A. Anal invagination. AU. Auditory vesicle. BP. Dorsal lip of blastopore. GC.
Ceelenteron. CF, Tail folds. CH. Notochord. CP. Cephalic plate. ZC. erm. —
EN. Entoderm. G. Gut. GD. Germ disc. GS. Gill slits. A. Heart. AA. Head —
eminence. MM, Central nervous system. /’, Yolk nuclei, merocytes. M2#S, Mesoblast. —
NC. Neurenteric canal. OP. Optic vesicle. PS. Primitive segments, S$. Mouth pit, —
stomodzeum, SC, Segmentation cavity.

194 ‘

DEVELOPMENT OF SHARK 195

cleavages. A stage in which early horizontal cleavages
are represented is shown in Fig. 220. This may well be
compared with the last figure; the germ disc, while not
increasing in diameter, is now seen to have multiplied its
blastomeres by horizontal cleavages; it is converted into
a plug-shaped mass of cells, sunken into the yolk material.
At J’ are cell nuclei, which have found their way into the
adjacent yolk, and which there acquire a developmental
importance. They become the so-called merocytes, or
yolk nuclei.

The section of the germ shown in Fig. 221 represents
a subsequent stage of development ; the blastomeres, by
continued subdivision, have become greatly reduced in size,
and are clearly to be distinguished from the smooth-sur-
faced, yolk-like material lying beneath. Merocytes, 1/7’,
are apparent in the superficial layer of the yolk; they are
supposed to serve a twofold function, — on the one hand, to
elaborate the yolk’ material and fit it for the embryo’s use ;
on the other, to supply the cells which are being con-
tinually added to the germ’s margin. In the figure a large
cavity is shown to exist between the yolk and the mass of
blastomeres. This cavity has been identified as the seg-
‘mentation cavity, SC, and the developmental stage as the
_ blastula; it is as though the lower hemisphere of the
_ lamprey’s blastula (Fig. 205) had become enormously
enlarged, and all traces of the cells in the floor of its
_ segmentation cavity lost, except in the layer of the

_ metamorphosed cells, the merocytes.

In the next growth process the extent of the germ area
becomes greatly increased; the thick blastula is now
thinned out into a surface layer of regular cells, an en-
larging disc-like d/astoderm, which will eventually grow
_ around and enclose the entire egg. The blastoderm of

196 DEVELOPMENT OF FISHES

Fig. 223 is a pale-coloured circular membrane of about a
half inch in diameter lying on the surface of the egg.
Sectioned at an earlier stage (Fig. 222) the blastoderm is
seen to present the following contrast to the blastula of
Fig. 221 : the floor of the segmentation cavity has flattened, —
and a sharp rim forms the outline of the blastoderm ; at
one side this rim is seen to protrude over the yolk mass,
leaving a narrow, fissure-like cavity between. This stage
is identified as the gastrula; the fissure-like cavity, the
coelenteron ; its marginal blastoderm, the dorsal lip of the
blastopore ; its ventral lip, the entire yolk mass.

The growth of the embryo’s form takes its origin at the
blastopore’s dorsal lip. In Fig. 223 the rim of the blasto-
derm is seen indented near the point CF, and its thicken-
ing at this region becomes more and more marked in
subsequent stages; on the other hand, the anterior por-
tion of the blastoderm, growing continually on all sides,
becomes excessively thin, flattening ifself tightly to the
yolk, and reducing the segmentation cavity to the small
area indicated at SC. The growth of the embryo in the
mid-region of the blastopore’s dorsal lip may next be
followed in the stages, Figs. 224, 225, 226. The inden-
tation of the rim may thus be seen to assume a creese-
like thickening, thrusting forward its blunt end, the head
eminence, HE, over the blastoderm; at the points C/,
the tail eminences, the rim of the blastoderm is thick,
protruding, appearing to be pressing together in the
median line, and causing the body of the embryo to be
actually pushed into form and thrust above the level of
the blastoderm. In Fig. 225 the sides of the embryo are
separated dorsally by a deep groove, the medullary furrow,
the future canal of the central nervous system. In Fig.
226 this is seen at a more advanced stage; its hinder

DEVELOPMENT OF SHARK 197

portion has been roofed over by the coalesced sides, and
the process of enclosing the groove is being continued
anteriorly, although the head end of the embryo is now
flattened out as the prominent cephalic plate.

In the stage figured in 227, the form of the embryo has
‘been acquired; the head in the manner already outlined,
the tail by the coalescence and subsequent outgrowth

s of the tail folds; C# The entire embryo now rises above

the blastoderm, as this continues to enclose the yolk. In
the figure the yolk has thus been more than half enclosed ;
its final appearance is seen in the oval space outlined by a

dotted line behind the embryo.

The origin of the germ layers is not as readily traced
as in the Cyclostome. Ectoderm is the most clearly
marked ; even in the blastula (Fig. 221) it has appeared
‘as an outer single-celled stratum clearly differentiated
from the underlying cells. Entoderm is only to be
seen on the dorsal wall of the ccelenteron: the ventral
entoderm (cf. Fig. 222) is merged with the yolk. Meso-
derm takes its origin from the inner layer on either side
of the median line, but it arises as a solid cell mass
instead of as the pouch-like diverticula in Petromyzon.
Cross-sections of an embryo represented by Fig. 224
have been figured in Figs. 228 and 229; the former is of
the hinder region and illustrates the mode of growth of the
mesoderm, J7ES; the latter across the head region,
shows that in this region the mesoderm is separated
from the inner layer. Both sections show the simple

character of the medullary groove, and the latter section

_ the mode of origin of the notochord, CH, z.e. as an axial
_ thickening of the entoderm.

An embryo of about the stage of Fig. 227 is extremely
delicate and may readily be viewed as a transparent object.

198 DEVELOPMENT OF LUNG-FISH

By this time (Fig. 230) it will be seen that its prominent
organs have already been differentiated. There are thus:
medullary canal, 1, with optic, OP, and auditory, AU,
vesicles; gut with gill slits, GS, neurenteric canal, VC,
and suggestion of mouth, S, and anus, A; notochord,
CH; segmented mesoderm (primitive segments), PS,
and heart, H. The medullary groove was converted into
a canal, as has been already suggested, by the overroofing
and fusion of the summits of the medullary ridges; its
anterior dilatation is the brain; the gut, G, communicates
freely below with the yolk mass; it is a cavity, a portion
of the coelenteron that has been constricted off with the
embryo; its openings, the mouth, anus, and gill slits, are
secondary, acquired after there have been established in
these regions fusions of entoderm and ectoderm; the
neurenteric canal, VC, a communication between medul- -
lary tube and gut, is-a structure acquired in the stage of
Fig. 226, where the hinder medullary groove was roofed
over, allowing, in the region of the tail folds, a communi-
cation to exist between medullary canal and ccelenteron.

The notochord has by this stage been completely sepa- |
rated from the entoderm; it already assumes a supporting |
function.

III. Zhe Development of Ceratodus

The development of a Lung-fish has thus far been de-
scribed (Semon) only from the outward appearance of the _
embryo. The egg of Ceratodus (Fig. 192) is seen without —
its covering membranes, enlarged, in Fig. 231. Its upper
pole is distinguished by its fine covering of pigment. The
first fine planes of cleavage are shown in Figs. 232-236;
and from these it will be seen that the yolk material of the
lower pole is not sufficient to prevent the egg’s total seg-

from

199

200 DEVELOPMENT OF FISHES

mentation. The first plane of cleavage is a vertical one,
passing down the side of the egg (Fig. 233) as a shallow
surface furrow, not appearing to entirely separate the sub-
stance of the blastomeres, although traversing completely
the lower hemisphere (Fig. 232). A second vertical furrow —
at right angles to the first is seen from the upper pole in
Fig. 234; it is essentially similar to that of Fig. 233. The
third cleavage of Fig. 235 is again a vertical one (as in all
other fishes, but unlike Petromyzon), approximately meridi-
onal; its furrows appear less clearly marked than of earlier
cleavages, and seem somewhat irregular in occurrence. The
fourth cleavage is horizontal above the plane of the equator.
Judging from Semon’s figure (Fig. 236), at this stage the
furrows of the lower pole seem to have become fainter, if
not entirely lost. A blastula showing complete segmenta-
tion is seen in Fig. 237; the blastomeres of the upper
hemisphere are the more finely subdivided ; the conditions
of the segmentation cavity may be expected to prove
similar to those of Fig. 205. Two stages of the gastrula
are shown in Figs. 238 and 239, showing a full view of the
blastopore. In the earlier one (Fig. 238) the dorsal lip of
the blastopore is crescent-like; in the later (239) the
blastopore acquires its oblong outline, through which the
yolk material is apparent; its conditions may later be
compared to those of a Ganoid (Figs. 254, 255).

The growth of the embryo is illustrated in the remaining
figures (Figs. 240-248). A side view of an early embryo
is shown in Fig. 240; at the top of the egg to the right is |
the head region, to the left the blastopore and tail. The |
surface view of the head region (Fig. 241), the medullary
folds, MF, may be compared with those of Fig. 225,
although they are low and widely separated; the axial
seam is referred to by Semon as a demonstration of the

DEVELOPMENT OF LUNG-FISH 201

theory of the embryo’s concrescence. In the hinder region
‘of the same embryo (Fig. 242) the blastopore is still
apparent, BP, reduced to a narrow, fissure-like aperture ;
around it is the tail mass, corresponding generally to CF

___ of Fig. 226; and encircling all is the hinder continuation

of the medullary folds.

_ The next change of the embryo is strikingly amphibian-
like ; the medullary folds rise above the egg’s surface, and,
arching over, fuse their edges in the median dorsal line.
In Fig. 243, the tail region of a slightly older embryo, this
process is clearly shown; the medullary folds, I/F, are
seen closely apposed in the median line; hindward, how-
ever, they are still separate, and through this opening the
blastopore, BP, may yet be seen. At this stage primitive
segments are shown at PS; in the brain region in Fig.
244 the medullary folds are still slightly separated (cf. CP,
Fig. 226). .

Two views of an
older embryo are fig-
ured (Figs. 245 and
246), where the fish-
like form may be rec-
ognized. The medul- ‘Fig. 248.— Embryo of Ceratodus, near the time

4 of hatching.
lary folds have com- Gs, Gillslits. 44. Mouth pit. OP. Optic vesi-

: cles. PN. Primitive kidney, pronephros. 7. Tail
pletely fused in the oF ice,

median line, and the

embryo is coming to acquire a ridge-like prominence;
optic vesicles and primitive segments are apparent, and
at BP the blastopore appears to persist as the anus. The
continued growth of the embryo above the yolk mass,
Y, is apparent in Fig. 247; the head end has, however,
grown the more rapidly, showing gill slits, GS, auditory,
optic, and nasal vesicles, AU, OP, and O, at a time when

202 DEVELOPMENT OF GANOID

the tail mass has hardly emerged from the surface. Pro-
nephros has here appeared at PN (cf. with Fig. 247, Fig.
210). It is not until the stage of the late embryo of Fig.
248 that the hinder trunk region and tail come to be
prominent. The embryo’s axis elongates and becomes
straighter; the yolk mass is now much reduced, acquiring
a more and more oblong form, lying in front of the tail, 7;
in the region of the posterior gut (cf. Figs. 211 and 212).
The head, and even the region of the pronephros, PJ,
are clearly separate from the yolk sac; the mouth, JZ is
coming to be formed.

IV. The Development of Ganoids

The development of Ganoids is next to be outlined.
The eggs of the sturgeon and gar-pike are poorly provided
with yolk. They have still, however, a greater amount -
than those of the Jamprey or lung-fish, and in many
regards of development suggest nearnesses to the Elasmo-
branchs.

The egg of the sturgeon shown in Fig. 249 shows
clearly two distinct zones; the upper, blotched with pig-
ment at the animal pole, is pale in colour; the lower, rich
in yolk, is orange-coloured, well speckled with pigment.
The early cleavages appear at first only in the upper pale-
coloured area which corresponds apparently with the germ
disc of the shark’s egg. In Fig. 250 there have been
two cleavages, vertical and at right angles to each other;
these have sharply traversed the germ area, the earlier
one being now produced slightly into the yolk region of
the egg—only, however, as a slight surface furrow. The
third cleavage (Fig. 251) presents a stage closely corre-
sponding with that of Ceratodus of Fig. 235, its plane tend-
ing to pass parallel to the first cleavage: the germ disc

‘yaa

TRIE
ws
$ es se :

+

‘Figs. 249-268. — Development of Ganoids, Acifenser and (last four figures) Lefi-
dosteus. X about 12, 249. immediately before cleavage. 250. Second cleavage.
251. Third cleavage. 252. Blastula, 253. Vertical section of blastula, 254. Early
gastrula, 255. Late OY gee 256. Vertical section of late gastrula. 257. Early
obs 258. Sagi section of same stage. 259, 260. Head and tail regions of
slightly later embryo. 261. Transverse body section of hinder body region of same
—. 262, 263. Head and tail regions of late embryo. 264. Embryo immediately

hatching. 265. idosteus’ blastula. 266. Vertical section of early gastrula.
267. Late gastrula. 268. bryo, showing mode of separation from yolk.

BP. Dorsal lip of blastopore, C. Coelenteron. ZC. Ectoderm, ZN, Entoderm.
¥. Pectoral fin. GS, Gill slits. AY. Heart. HZ. Head eminence. AV. Kupffer's
vesicle, LC. Marginal limit of coelenteron. A/, Mouth pit. A/C. Medullary canal.
MES. Mesoblast. NC. Neurenteric canal. OZ. Olfactory pits. OP. Optic vesicles.
PN. Primitive kidney, pronephros. PS. Primitive segments. SC. Segmentation
cavity. 7. Tail eminence. VZ. Ventral lip of blastopore. Y. Yolk, yolk mass.
YP. Yolk plug.

203

204 DEVELOPMENT OF FISHES

is deeply cut by the furrows; the yolk area, however, only
superficially ; the shallow furrow of the first cleavage on
the yolk hemisphere now passes through the lower pole;
the second cleavage, passing downward, has made a shal-

low groove extending half-way between the rim of the

germ area and the lower pole of the egg. It is the great
amount of-yolk in the lower hemisphere that retards the
cleavage of the blastomeres. In Fig. 252 the entire
germ area has become subdivided into a mass of small
cells, while the large, irregular blastomeres of the yolk
hemisphere are separated only by superficial furrows.
This stage, the blastula, is seen in section in Fig. 253:
the yolk, unsegmented, occupies the lower hemisphere ;
the germ area contains a segmentation cavity, SC, with

a roofing of small cells, and a floor of irregular cells half

engulfed in a deep, underlying zone transitional between
germ and yolk.

An early gastrula is seen in Fig. 254: the more rapid
multiplication of the cells of the germ region has given
rise to a down-reaching cap of cells, whose boundary is
here sharply marked off from the large and imperfect yolk
cells of the lower hemisphere. At A&P, the rim of the cell
cap, or blastoderm, is sharply distinct from the yolk; it is
the dorsal lip of the blastopore; the remaining portion of
the rim is, generally speaking, the remainder of the rim
of the blastopore; more accurately it is the circumcres-
cence margin of Hertwig. The late gastrula of Fig. 255
shows the greatly increased extent of the blastoderm: its
margin is continually reducing the size of the blastopore,
BP; on its dorsal lip at AZ, the outline of the embryo
is appearing. A sagittal section of this stage (Fig. 256)
shows at BP the dorsal, and at VZ the ventral, lip of the
blastopore ; at YP the yolk material appears at the egg’s

DEVELOPMENT OF GANOID 205

surface as a plug-like mass; at SC is the segmentation
cavity. The dorsal lip of the blastopore is seen to be far
longer than the ventral lip; its rim is the more inflected,
at KV occurring a recessus which the writer compares
to the Kupffer’s vesicle of Teleost development; the
cavity, C, coelenteron, between the wall of the blastopore
and the yolk mass is in this region the largest. The
germ layers in this stage, EC, MES, EN, are seen to
be confluent at the blastopore’s rim; at the termina-
tion of the ccelenteron, entoderm and mesoderm are
merged; the ectoderm forms the roof of the segmenta-
tion cavity.

The form of the embryo next becomes more definitely
established. In Fig. 257 the blastopore, much reduced
in size, is seen at BP; its thickened rim is whitish in
colour; the darkened area, whose boundary is LC, is the
cceelenteron, seen faintly through the translucent margin
of the blastopore; the embryo is the opaque area of the
blastopore’s dorsal lip, terminating anteriorly in the dilated
tract, H, the head region. In a sagittal section of a
slightly later stage (Fig. 258), the relations of germ
layers, EC, MES, EN, coelenteron, C, and yolk mass,
Y, may be compared with those of the section (Fig. 256),
wherein the region YP corresponds to that of VC. A
thin ectoderm will now be seen to have enclosed the
entire egg; the segmentation cavity has disappeared ; the
rim of the blastopore, becoming continually constricted,
causes the yolk material to recede from the surface, and
leaves the blastopore disappearing, as the blunt diver-
ticulum of VC. The neurenteric canal, WC, is the last
communication between the surface of the egg and the
ceelenteron ; this has become established before the blas-
topore closes in the stage of Fig. 257 at its dorsal lip;

206 DEVELOPMENT OF FISHES

the medullary furrow of the embryo has here been the
deepest, and has been bridged over by a coalescence of
its margins. At the anterior end of the embryo the
inner, EN, and middle, MES, germ layers become
greatly thinned, in the region where the heart is shortly
to arise.

The next stage of development is represented in Figs,
259, 260, showing front and hinder regions of the same
embryo. The curiously flattened mode of growth char-
acteristic of the sturgeon is here very apparent; the
embryo has surrounded over three-fourths of the .egg’s
circumference, yet has not risen above its surface curva-
ture; the head region is especially flattened; mouth, JZ
heart, H, gill slits, G.S, brain, and optic vesicles are broadly
spread out: the fourth ventricle at J/C, the pronephros
at PN, the primitive segments at PS. In the tail region
the medullary folds appear at J/, the pronephric duct at
PN, the neurenteric canal at VC. A favourable section
through the hinder body region of an early embryo is
shown in Fig. 261; it illustrates the mode of origin of the
following structures : the notochord as an axial thickening
of entoderm, EN, immediately under WC; the medullary
canal, as an infolding of (an under, or formative layer of)
the ectoderm, its sides, folding over dorsally, coming to fuse
in the median line; the mesoderm, J7ES, as in sharks,
arising (partly) from the entoderm on either side of the
notochord.

The later stage, shown in Figs. 262 and 263, may be con-
trasted with Figs. 259 and 260; the head region, though
still greatly flattened out, is now rising above the surface ;
the trunk region is becoming prominent ; the tail is bud-
ding out, and separating from the egg surface; sense
organs are well outlined, and pectoral fins, ¥, elasmobran-

DEVELOPMENT OF TELEOST 207

chian in character, are appearing. An embryo shortly
before hatching is next figured (Fig. 264); the head has
now entirely lost its flattened character; the mouth in-
vagination occurs at J/; the tail, much elongated, is
compressed laterally, and already presents the dermal
embryonic fin; the yolk sac is attached along the an-
terior body region, in a position more nearly that of the
shark than of the lung-fish.

Of the two Ganoids, sturgeon and gar-pike, the latter,
as the writer has pointed out, * has the more shark-like
developmental features. Its segmentation is incomplete,
since the yolk pole of the egg is at no time traversed even
by superficial furrows. The blastoderm, or cell cap, is
“early apparent, and is clearly marked off by a furrow from
the irregular marginal blastomeres (Fig. 265). It resem-
bles closely the segmented germ disc of an Elasmobranch,
and the irregular marginal blastomeres may be compared
to merocytes. The section of a late blastula of Fig. 266
does not differ widely from that of the shark of Fig. 221;
a segmentation cavity is present, whose floor is smooth,
and contains a well-marked zone of merocytes, 7; the
smaller quantity and firmer consistency, perhaps, of the
yolk do not, on the other hand, permit the blastula to
occupy the sunken position of that of the shark. In the
gastrula of the gar, further, a well-marked notch appears
at the dorsal lip (as in this stage, Fig. 223, of the shark),
representing the primitive blastopore. And, finally, the
form of the embryo rises boldly from the surface, and
early presents the well-marked head and tail eminences,
HE and 7, of Fig. 268, comparable with Figs. 225 and
227.

* Am. F. Morph., Vol. X1, No. I.

FIG. 269

]
LAN TY
<

Figs. 269-283. — Development of Teleost, Serranus atrarius, (After H.V. WILSON.)
Fig. 276 X 25. 269. Egg immediately prior to segmentation, showing position of germ
disc and of oil globule. 270, Germ disc after first cleavage. 271. Germ disc after third
cleavage. 272. Vertical section of blastula, 273: Vertical section of blastula, sh
origin of periblast. 274. View of marginal cells of blastula of similar stage. 275. G
of blastoderm around yolk mass. 276. A slightly later stage, showing growth of embryo,
277. Continued growth of embryo and reduction in size of the blastopore. 278. Sagittal _
section of tail region of embryo of last figure. 279, 280, 281. Cross-sections of embryos, __
showing successive stages in the development of notochord, gut, neuron, mesoblast. 282,
Cross-section of young embryo, showing the mode of formation of gill slit, 283. Embryo
shortly before hatching.

A. Anus. AU. Auditory vesicle. BP. Dorsal lip of blastopore. CH. Notochord,
EC. Ectoderm. ZN. Entoderm, G. Gut. GD. Germ disc. G&. Germ ring, GS,
Gill slit. H. Heart. HP, Head process. AV. Kupffer's vesicle. MM. Spinal nervous
system. MZS. Mesoblast. MP. Marginal periblast cells, OG. Oil globule. OL. Ol- —
factory pit. OP. vgs capsule, /. Periblast. PS. Primitive ents, SC. ‘
tation cavity, SCH, Subnotochordal rod. 7M. Tail mass. Y. Yolk. .

208

DEVELOPMENT OF TELEOST 209

-

V. The Development of 7. eleost

The mode of development of bony fishes differs in
many and apparently important’ regards from that of
their nearest kindred, the Ganoids. In their eggs a large
amount of yolk is present, and its relations to the embryo
have become widely specialized.

As a rule, the egg of a Teleost is small, perfectly spheri-
‘eal, and enclosed in delicate but greatly distended mem-
branes (Fig. 269). The germ disc, GD, is especially
small, appearing on the surface as an almost transparent
fleck ; it may occupy the same position as in the other
fishes, or, as in the figure, it may occur at the lowermost
pole. Among the fishes whose eggs float at the surface
during development, as of many pelagic Teleosts, e.g. the
Sea-bass, Serranus atrarius,—to which all the accom-
panying figures refer,—the yolk is lighter in specific
_ gravity than the germ; it is of fluid-like consistency,
almost transparent. In the yolk at the upper pole of
the egg an oil globule, OG, usually occurs; this serves
to lighten the gravity of the entire egg, and from its
position must aid materially in keeping this pole of the
egg uppermost.

The early segmentation of the germ is seen in Figs.
270, 271. In the former, the first cleavage plane is estab-
lished, and the nuclear divisions have taken place for the
second; in the latter, the third cleavage has been com-
pleted. As in other fishes these cleavages are vertical,
the third parallel to the first. A segmentation cavity,
SC, occurs as a central space between the blastomeres,
as it does in the sturgeon and gar-pike.

Stages of late segmentation are seen in section in Figs.

272, 273. In both the segmentation cavity, SC, is greatly
P

210 DEVELOPMENT OF FISHES

flattened, but extends to the marginal cells of the germ
disc; in Fig. 272 its roof consists of two tiers of blasto-
meres, its floor a thin film of the unsegmented substance
of the germ; the marginal blastomeres are continuous
with both roof and floor of the cavity, and are produced
into a thin film which passes downward, around the sides
of the yolk. In Fig. 273 the segmentation cavity is still
further flattened; its roof is now a dome-shaped mass of
blastomeres ; the marginal cells have multiplied, and their
nuclei are seen in the layer of the germ, P, below the
plane of the segmentation cavity. These are seen at WP
in the surface view of the marginal cells of this stage
(Fig. 274); they are separated by cell walls only at the
sides ; below they are continuous in the superficial down-
reaching layer of the germ. The marginal cells, JP,
shortly lose all traces of having been separate; their
nuclei, by continued division, spread into the layer of germ
flooring the segmentation cavity, and into the delicate film
of germ which now surrounds the entire yolk. Thus is
formed the ferzb/ast of teleostean development, which from
this point onward is to separate the embryo from the yolk;
it is clearly the specialized inner part of the germ, which,
becoming fluid-like, loses its cell walls, although retaining
and multiplying its nuclei. It would accordingly corre-
spond to that portion of the germ of the sturgeon in Fig.
253 which lies below the plane of the segmentation cavity,
and which extends downward at the sides of the yolk; in
this case, however, the surface outlines of the cells have
not been lost. It will be seen from later figures (Figs.
278-282) that the periblast, P, comes into intimate rela-
tions with the growing embryo; it lies directly against
it, and appears to receive cell increments from it at various
regions; on the other hand, the nuclei of the periblast,

DEVELOPMENT OF TELEOST 211

from their intimate relations with the yolk, are supposed
to subserve some function in its assimilation.

Aside from the question of periblast, the growth of
the blastoderm appears not unlike that of the sturgeon.
From the blastula stage of Fig. 273 to that of the early
gastrula (Fig. 275), the changes have been but slight ; the
blastoderm has greatly flattened out as its margins grow
downward, leaving the segmentation cavity apparent at
SC. The rim of the blastoderm has become thickened,
as the ‘germ ring;’ and immediately in front of ABP, the
dorsal lip of the blastopore, its thickening, as in Fig. 255,
marks the appearance of the embryo. In Fig. 276 the
germ ring, GR, continues to grow downward, and shows
more prominently the outline of the embryo; this now
terminates at AHP, the head region; while on either side
of this point spreads out tail-ward on either side the indefi-
nite layer of outgrowing mesoderm, JES. In the stage
of Fig. 277 the closure of the blastopore, BP, is rapidly
becoming completed; in front of it stretches the widened
and elongated form of the embryo. A sagittal section
through a late stage of the blastopore appears in Fig. 278;
with it may be compared the corresponding region of the
sturgeon of Fig. 256; the yolk plug, Y/, of the latter is
now replaced by periblast, P, the dorsal lip at BP, by
TM, the tail mass, or more accurately the dorsal section
of- the germ rim; the ccelenteron under the dorsal lip
has here disappeared, on account of the close approxima-
tion of the embryo to the periblast; its last remnant,
the Kupffer’s vesicle, KV, is shortly to disappear. At
TM, the germ layers become confluent as at BP in Fig.
256, but, unlike the sturgeon, the flattening of the dorsal
germ ring, 7, does not permit the formation of a neu-
renteric canal.

212 DEVELOPMENT OF FISHES

The process of the development of the germ layers
in Teleosts appears an abbreviated one, although in many
of its details it is but imperfectly known. In the develop-
ment of the medullary groove, as an example, the follow-
ing peculiarities exist: the medullary region at HP (Fig.
276) is but an insunken mass of cells without a trace of
the groove-like surface indentation of Fig. 261 or 229. |
Its condition is figured at 1/7 in Fig. 282. It is only later,
when becoming separate from the ectoderm, EC, that it
acquires its rounded character (Fig. 279), 17; its cellular
elements then group themselves symmetrically with refer-
ence to a sagittal plane, where later by their disassocia- _
tion (?) the canal of the spinal cord is formed (Fig. 280), JZ.
The growth of the entoderm is another instance of special-
ized development. In the section of the embryo of Fig.
279, the entoderm exists in the axial region, its thickness
tapering away abruptly on either side; its lower surface
is closely apposed to the periblast; its dorsal thickening .
will shortly become separate as the notochord. In a fol-
lowing stage of development (Fig. 280), the entoderm is
seen to arch upward in the median line as a preliminary
stage in the formation of the cavity of the gut. Later,
by the approximation of the entoderm cells in the median
ventral line, the condition of Fig. 281 is reached, where the
completed gut cavity exists at G.

The formation of the mesoderm in Teleosts is not defi-
nitely understood. It is usually said to arise asa process
of ‘delamination,’ ze. detaching itself in a mass from the ~
entoderm. Its origin is, however, looked upon generally
as of a specialized and secondary character.

The mode of formation of the gill slit of a Teleost does
not differ from that in other groups; an evagination of
the entoderm, GS (Fig. 282), coming in contact with an

LARVAL FISHES 213

invaginated tract of ectoderm, EC, fuses, and at this point
an opening is later established.

In Fig. 283 has been figured a late embryo. This may
be compared with that of the sturgeon of Fig. 264. The
Teleost, though of rounded form, is the more deeply im-
_ planted in the yolk sac; it is transparent, allowing noto-
chord, primitive segments, heart, and sense organs to be
readily distinguished; at about this stage both anus, A,
and mouth, J/, are making their appearance.

D. THE LARVAL DEVELOPMENT OF FISHES

When the young fish has freed itself from its egg mem-
branes, it gives but little suggestion of its adult form. It
enters upon a larval existence; which continues until matu-
rity. The period of metamorphosis varies widely in the
different groups of fishes—from a few weeks’ to longer
than a year’s duration ; and the extent of the changes that
the larva undergoes are often surprisingly broad, invest-
ing every organ and tissue of the body,—the immature
fish passing through a series of form stages which differ
one from the other in a way strongly contrasting with the
mode of growth of amniotes; since the chick, reptile, or
mammal emerges from its embryonic membranes in nearly
its adult form.

The fish may, in general, be said to begin its existence
as a larva as soon as it emerges from its egg membranes.
In some instances, however, it is difficult to decide at what
point the larval stage is actually initiated: thus in sharks,
the excessive amount of yolk material which has been pro-
vided for the growth of the larva renders unnecessary the
emerging from the egg at an early stage; and the larval
period is accordingly to be traced back to stages that are
still enclosed in the egg membranes. In all cases the

214 DEVELOPMENT OF FISHES

larval life may be said to begin when the following con-
ditions have been fulfilled: the outward form of the larva
must be well defined, separating it from the mass of yolk,
its motions must be active, it must possess a continuous
vertical fin fold passing dorsally from the head region
to the body terminal, and thence ventrally as far as the
yolk region; and the following structures, characteristic
in outward appearance, must also be established, the sense
organs, —eye, ear and nose, — mouth and anus, and one
or more gill clefts. :

Among the different groups of fishes the larval changes
are brought about in widely different ways. These larval
peculiarities appear at first of far-reaching significance,
but may ultimately be attributed, the writer believes,
to changed environmental conditions, wherein one proc-
ess may be lengthened, another shortened. So too the
changes from one stage to another may occur with sur-
prising abruptness. As a rule, it may be said the larval —
stage is of longest duration in (I) the Cyclostomes, and
thence diminished in length in (II) Sharks, (III) Lung-
fishes, (IV) Ganoids, and (V) Teleosts; in the last-named
group, a very much curtailed (z.e. precocious) larval life
‘many often occur.

I. Larval Cyclostomes

The Cyclostome larva is represented in a stage as
early as that of Fig. 212: its form is here retort-shaped ;
the yolk material is concentrated in the ventral region
immediately in front of the blastopore (the anus?), but
is distributed in addition in the cells of other body regions.
In the section of a slightly older larva (Fig. 215), in which
the mouth is all but established, the form outline has
become regular, the bulk of the yolk, Y, restricted to the

LARVAL SHARKS 215

cavity of the intestine, the only instance of this condition
known among fishes (Ceratodus ?), and, with but a single
exception (Ichthyophis),* among all other vertebrates.
The larval lamprey is by this time a quarter of an inch
long, yellowish white in colour; its movements are slug-
gish, rarely more than to cause it to wriggle worm-like
from the bottom. A few weeks later it has acquired its
brownish grey colour, its fin fold is well marked, and its
habit is active; it now feeds on muddy ooze rich in
organic matter. It by this time possesses the essential
characters of the well-grown larva, long looked upon
as a distinct genus, Ammoceites. In its larval stage the
lamprey appears to live a number of years; in Petromyzon
planeri the adult stage is said to be sometimes deferred
until the autumn of the fourth or fifth year. The trans-
formation is then a surprisingly sudden one; the head
attains its enlarged size, the mouth its ring-like and suc-
torial character, losing its more anterior position, and its
lip-like flaps (cf. Fig. 72, C,.D); teeth are developed in place
of the numerous mouth papillz; gills, formerly simpler
in character, opening directly from neck surface to gullet,
now enter the branchial chamber, a ventral diverticulum
of the gullet; eyes become prominent, complete their
development, and attain the head surface; unpaired fin,
formerly of great extent, is now reduced to its adult
position and proportions.

Il. Larval Sharks

The larval history of Sharks has been summarized in
Figs. 284-289: the younger of these stages (Figs. 284,
285, 286) have not as yet escaped from their egg mem-
branes. The hatching, in fact, of the young shark is

* The writer has not confirmed Salensky’s observation upon the sturgeon.

FIG. 284.

Figs. 284-289.— Larval sharks. (Figs. 284-287 after BALFOUR.) 284. Pristiurus
(embryo, X 5) with yolk sac (x 2). 285, 286. Larvae of Scyllium. X 4. 287. Ventral
view of head of larval Scy//ium, slightly younger than that of last figure. 8. 288, Larva
of Acanthias. X 4. 289. Late larva of Acanthias, X }.

G. Gills. GS. Gill slits, PF. Pectoral fin. SP. Spiracle. Y. Yolk sac. YS, Stalk
of yolk sac.

216

LARVAL SHARKS 217

an exceedingly slow one; Pristiurus emerges from the
egg in about nine months, Scyllium in about seven. And
in consequence of the large amount of yolk stored in
the yolk sac, the young shark, as in Fig. 289, has fully
acquired its adult outward characters by the time the yolk
is exhausted and its sac absorbed.

In Fig. 284 is figured a stage in the development of
Pristiurus which may be regarded as either embryonic
or larval; the form of the larva is well established ; gill
clefts, muscle-plates, mouth, and sense organs are present ;
but, on the other hand, unpaired fin and anus are lacking.
There is shown the abrupt constriction, characteristic of
Elasmobranchs, which separates the animal from the yolk
sac, —a construction which in later stages becomes narrow
and tubular. The relatively larger size of the yolk sac
in later stages is, of course, the result of the bulkier elabo-
ration of the yolk material.

The youngest stage (Fig. 284) shows prominently the
great enlargement of the anterior end of the embryo, a
marked cephalic flexure, large optic capsule, and irregular
gill slits of graded sizes; a tubular tail end, bulbous at
the terminal, where the neurenteric canal occurs; as yet
the nasal pits are in close proximity to the mouth. In the
next stage (Fig. 285), the elongated trunk has its unpaired
fin, the neurenteric canal disappearing; the beginnings
of the pectoral fins are noticeable; gill clefts are of more
uniform size; and the anal region is indicated. In the
stage of Fig. 286, further advances are seen in the con-
_ stricting off of the unpaired fins, the appearance of the
ventral and the continued growth of the pectoral fins;
in the reduced foremost gill slit (spiracle); in the jaw
region, and, in fact, in the entire shaping of the head;
in the appearance of the lateral line. In the ventral head

218 LARVAL DEVELOPMENT

region (Fig. 287), is to be noted the prominence of the
mouth cavity, and the enlarged gill arches, showing by
this time the outbudding branchial filaments. In the
stage of Fig. 288, the larva begins to appear shark-like;
the fins are longer and more noticeable, the anus has
appeared, and the branchial filaments by continued growth
protrude at all gill openings. The external gills thus
acquired are seen in a later stage (Fig. 289) to have
disappeared ; they have aided, however, as Beard, Turner,
and others have shown, in absorbing nutriment, and must
be looked upon as an especial organ of the larval life of
the animal. Fig. 289 illustrates a final larval stage: in it
there appear all of the structures of the adult outward form,
e.g. shagreen, fin spines, nictitating membrane, anterior
and posterior nasal openings. This larva has been esti-
mated to be about a year older than that of Fig. 284.

Ill. Larval Lung-fish

The larval history of the lung-fish, Ceratodus, as recently
described by Semon, seems to offer characters of excep-
tional interest, uniting features of Ganoids with those of
Cyclostomes and Amphibians.

The newly hatched Ceratodus (Fig. 290) does not
strikingly resemble the early larva of shark (Fig. 284).
No yolk sac occurs, and the distribution of. the yolk
material in the ventral and especially the hinder ventral
‘region is suggestive rather of lamprey or amphibian; it
is, in fact, as though the quantum of yolk material had
been so reduced that the body form had not been con-
stricted off from it. The caudal tip in this stage appears,
however, to resemble that of the shark, and as far as can
be inferred from surface views a neurenteric canal persists. —
Like the shark there then exists no unpaired fin; the

—

“% & spout cemeh

=
— aU Ore

x Sag

at y

7 = TOLL

LL, il Ld, Yip

Figs. 290-295. — pe hese Silos: Ceratodus. (After SEMON.) X 6. 290.
Embryo at about the time of hatching. 291. Young larva. 292. Larva of two weeks.
293. Larva of four weeks, ventral side. 294. Larva of six weeks. 295. Larva of ten
weeks,

A, Anus. AU. Auditory vesicle. 2G. External vi GS. Gill slits. A. Heart.
M. Central nervous system. J/C. Mucous canals. O. Opercular flap. OZ. Olfac-
_ tory organ. PF. Pectoral fin. PN. Pronephros. PS. Primitive segments. 5S. Mouth
pit, stomodzeum.

219

220 DEVELOPMENT OF FISHES

gill slits, five (?), GS, are well separated, and there is an
abrupt cephalic flexure. In this stage pronephros and
primitive segments, PS, are well marked, and are out-
wardly similar to those structures in Ganoid; the mouth,
S, is on the point of forming its connection with the
digestive cavity; the anus is the persistent blastopore; —
the heart, well established, takes a position, as in Cyclo-

stomes, immediately in front of the yolk material.

In a later stage the unpaired fin has become perfectly
established, the tail increasing in length; the gill slits
have now been almost entirely concealed by a surrounding
dermal outgrowth, the embryonic operculum; a trace of
the pectoral fin, P/, appears ; the lateral line is seen pro-
ceeding down the side of the body; near the anal region
the intestine * becomes narrower and the beginnings of
the spiral valve appear. In a larva of two weeks (Fig. 292),
a number of developmental advances are noticed: the fish
has become opaque, the primitive segments are no longer
seen; the size of the yolk mass is reduced; the anal fin
fold appears; sensory canals are prominent in the head
region; lateral line is completely established ; the rectum
becomes narrowed ; and the cycloidal body scales are already
outlined. Gill filaments may still be seen beyond the rim of
the outgrowing operculum. In the ventral view of a some-
what later larva (Fig. 293), the following structures are to
be noted : the pectoral fins which have now suddenly budded
out,} reminding one in their late appearance of the mode of

* The yolk appears to be contained in the digestive cavity as in Ichthy-
ophis and lamprey. 2

+ The abbreviated mode of development of the fins is most interesting ;
from the earliest stage they assume outwardly the archipterygial form ; the re-
tarded development of the limbs seems curiously amphibian-like ; the pec-
torals do not properly appear until about the third week, the ventrals not until
after the tenth.

LARVAL GANOIDS 221

origin of the anterior extremity of urodele ; the greatly en-
larged size of the opercular flap ; external gills, still promi-
nent ; the internal nares, OL, becoming constricted off into
the mouth cavity by the dermal fold of the anterior lip (as
in some sharks) ; and finally (as in Protopterus and some
batrachian larvze) the one-sided position of the anus.

The larva of six weeks (Fig. 294) suggests the outline
of the mature fish; head and sides show the various open-
ings of the tubules of the insunken sensory canals; and
the ‘archipterygium’ of the pectoral fin is well defined.
The oldest larva figured (Fig. 295) is ten weeks old; its
operculum and pectoral fin show an increased size; the
tubular mucous openings, becoming finely subdivided, are
no longer noticeable ; and although the basal supports of
the remaining fins are coming to be established, there is
as yet little more than a trace of the ventrals.

IV. Larval Ganotds

The larval forms of a Ganoid, Acipenser (Figs. 296-
302), resemble far more closely those of the shark than of
the lung-fish. When newly hatched, the young sturgeon
(Figs. 296, 297) is attached to the well-rounded yolk sac
situated in the throat region, in exactly the position one
would expect the yolk stalk to be situated if the yolk mass
were larger; it resembles the shark larva of Fig. 295 in
its unpaired fin, in gill slits, in olfactory, OL, optic, OP,
and auditory, AU, organs, and in the fact that it possesses
even at this stage a trace of the neurenteric canal; on the
other hand, it suggests the Ceratodus larva of Fig. 291 in
its stout trunk region, prominent muscle segments, pro-
nephros, PJ, and anus, A; at the foremost corner of the
yolk sac are mouth pit (stomodazum, S) and heart. A
larva of the second day resembles in many features the

Fic.296 AU, GS
op

ee

Meseesics ee NEE / :
ee

Figs. 296-302. — Larval sturgeons. (All but Fig. 302 after KUPFFER.) Fig.299, X 18;
296-300, X 10; 301, X 8; 302, X 4. (Enlargement approximate.) 296, 297. Larvae —
shortly after hatching. 298. Larva two days old. 299. Mouth region of larva of third —
day. 300. Larva of fourth day. 301. Larva of twenty-eight days. 302. Sturgeon es
twelve months.

A, Anus. AU, Auditory vesicle. B. Barbel. GS. Gill slit, A. Heart. OZ. or }
factory pit. OP. Optic vesicle. PF, Pectoral fin, PN. Pronephros, 5S. Mouth pit, —
SP. Spiracle.

222

LARVAL TELEOSTS 223

shark larva of Fig. 286: dorsal, caudal, and anal regions are
outlined in the unpaired fin; a pectoral fin of a fin-fold
character, P/, has appeared; the spiracle, SP, is becom-
ing established. The mouth region is more clearly indi-
cated in this stage, S, but may better be seen in ventral
view in a slightly later larva; here (Fig. 299) the posterior
lip is constricted off from the yolk region, and the anterior
lip is budding off near the median line a pair of the tactile
barbels ; the dermal fold (operculum) enclosing the gills
is in a condition very similar to that of Ceratodus in
Fig. 293. A larva of the fourth day (Fig. 300) shows
well-marked advances : the snout is elongated ; the opercle
is enclosing the gills, which are now seen to protrude as
external branchial; the pectoral fin elongates and is tend-
ing to protrude its fin axis; body segments and heart are
encroaching into the region of the now elongate yolk sac;
the lateral line has been formed. In a larva of four weeks
(Fig. 301), the essential outlines of the sturgeon may be
recognized, although the head appears of strikingly larger
proportions: barbels, nares, mouth, operculum, and spiracle
are as in the adult ; fins, of the mature outlines, are want-
ing in all save basal supports ; yolk material has long since
been exhausted. A very late larva (Fig. 302), supposed to
be twelve months old, differs outwardly from the sexually
mature form in but its colouring and dermal plates: those
of the regular rows are of great size, conspicuous in their
abrupt spines and well-roughened borders ; and those of the
remaining trunk integument are remarkably prominent ; the
tail of the larva shows clearly its palzoniscoid character.

V. Larval Teleosts

The metamorphoses of the newly hatched Teleost
must finally be reviewed; they are certainly the most_

FIG. 303

304

a 4y seenettry .
SAE Tar {PALS claaie
ee Re fg
ee ees : Se Ss
a

eS OS — ,

SS: ite,

Figs. 303-309.— Larvze of Teleost, Ctenolabrus. (After A. AGASSIZ.) Fig.
309 X about 7, other figures X about 14. 303. Larva shortly after hatching. 304,
305. Larvee of first few days. 306, 307. Larva of one week. 308. Larva of two
weeks (?). 309. Final larval stage, four (?) weeks.

A. Anus. AU. Auditory vesicle. CH. Notochord. GR. Gill protecting der-

mal rays. H. Heart. MM. Central nervous system. OZ, Olfactory capsule, OP,
' Optic vesicle. PF. Pectoral fin. S. Stomodzeum.

224

LARVAL TELEOSTS 225

varied and striking of all larval fishes, and, singularly
enough, appear to be crowded into the briefest space of
time; the young fish, hatched often as early as on the
fourth day, is then of the most immature character; it
is transparent, delicate, inactive, easily: injured; within
a month, however, it may have assumed almost every
detail of its mature form. A form hatching three mille-
metres in length may acquire the adult form before it
becomes much longer than a centimetre.

The larval life of the common Sea-bream, or Cunner,
Ctenolabrus ceruleus, has been admirably figured by A.
Agassiz. The newly hatched fish (Fig. 303) has the yolk
sac appended at the throat, as a large, transparent, if
slightly tinted, globule; save for its great delicacy and
_ transparency, it may generally be compared to the corre-
sponding larva of Acipenser (Fig. 296). By the third day
(Fig. 304), the yolk sac has become greatly reduced, the
trunk elongated, the fin fold less conspicuous; primitive
segments have appeared’; the pectoral fin has arisen, but
is not of the elasmobranch form of the similar stage (Fig.
298) of sturgeon; it is long, thin, transparent, and its
rapid growth indicates its metamorphosed character. The
mouth, S, is in this stage on the point of formation. In
a slightly older larva (Fig. 305), the yolk has almost dis-
appeared ; its gill slits, GS, and mouth have now been
formed, and with the latter the nasal apertures. In a fol-
lowing stage (Figs. 306, 307), a well-marked opercular fold
makes its appearance; pectoral fins acquire their com-
pleted outline and the fin fold undergoes changes: ante-
riorly it acquires supporting actinotrichia, posteriorly the
dermal supports of the caudal fin appear and at their bases
the coalesced radio-basals; a ganoidean heterocercy is
here apparent, its distal tip the membranous opisthure, O.

Q

bd F eT oh

226 LARVAL TELEOSTS

ance of abundant plement masses (not shown in
figure) in all regions of the trunk; branchion aa
GR, and traces of pelvic fins are noted; the caudal fin
has become separated from the dorsal and anal elements. — :
And finally, in the stage of Fig. 309, the fish, acho Be

of pigmentation and fin proportions.

LIST OF DERIVATIONS OF PROPER NAMES

Acanthodes, dxav@adys, provided with spines.
Acanthopterygii, dxav@a, spine, rrépvé, fin(ned).
Acipenser, dxtryjotos, classic name of sturgeon.
Actinopterygii, dxris, stout ray, rrépvé, fin(ned).
Alopias, dAwzrexias, classic name of the fox shark.
Amia, dia, classic name of tunny(?).
_ Amiurus, dia, Amia, ovpd, tail(ed).
_ Ammoccetes, dypos, sand, xoirn, (a bed) abider.
- Anacanthini, dvd, without, dxav@a, spine.
_ Anguilla, classic name of eel.
Arthrodira, dpOpov, joint, (?)8is, double.
Aspidorhynchus, dows, shield, pvyyos, snout.

Bdellostoma, B3éAAa, leech, ordya, mouth.
Belonorhynchus, feAdvy, classic name of gar-fish, f¥yxos, snout.

Calamoichthys, calamus, a reed, ixOis, fish.

Callichthys, xéAAos, beautiful, ixOvs, fish.

Callorhynchus, xdAAos, beautiful, pvyxos, snout.

Carassius, ydpag, classic name of (sea)fish.

__ _Caturus, xara, on the under side, ovpa, tail.

_ Cephalaspis, xe@ad#, head, domis, shield.

___Ceratodus, xépas, horn, d8ovs, tooth(ed).

__ Cestracion, xéorpa, classic name of (pavement-toothed) sea-fish.

_ Cheirodus, yeép, hand, d8ovs, tooth(ed).

_ Chimeera, xiatpa, fabulous monster, —lion’s head, goat’s body, dragon’s
tail

_ ___-Chlamydoselache, yAapvdds, frilled, ceAdyn, shark.
___Chondrostei, xévépos, cartilage, daréov, bone(d).

__ Cladoselache, for Cladodonto-selache, xAddos, branch, éSovs, tooth(ed),
ss @eAdxn, shark.
_ Climatius, xAiua, a gradation (in allusion, perhaps, to the graded row
s of fin spines).

227

228 FISHES, LIVING AND FOSSIL

Coccosteus, xoxxos, rough like a berry, éaréov, bone.
Ccelacanthus, xotAos, hollow, dxavOa, spine(d).
Crossopterygii, xpooods, fringe or tassel, rrépvé, fin.
Ctenodus, xreis (xrevds), comb, édovs, tooth(ed).
Cyclostomata, xv«Aos, circular, eréua, mouth.

Dinichthys, devds, terrible, ixOus, fish.
Diplognathus, dirAds, double (pointed), yva6os, jaw.
Diplurus, dAds, double, ovpa, tail(ed).

Dipnoi, dépvoos, double breathing.

Dipterus, dis, two, rrépov, fin(ned).

Edestus, éSeorr7s, a devourer.

Elasmobranchii, éAacpés, strap-like, Bpay ua, gill(ed).

Elonichthys, (?)€Ave, to twist, iyOus, fish.

Erythrinus, éptOpds, red-coloured. ree
Eurynotus, edpvs, wide, v@ros, back(ed).
Eusthenopteron, evoGerys, strong, rrepor, fin.

Fierasfer, derivation of Cuvier uncertain, perhaps from proper name.
Gadus, classic name of cod.

Ganoid, ydvos, enamelled.

Gnathostome, yaBos, j jaw, oTopa, mouth.

enamel).

Harriotta, from the proper name Harriott.
Hemitripterus, hemi, half, rpeis, three, wrepdv, fin(ned). b
Heptanchus, érrd, seven, dyxw (referring to the compressed gill —
openings). 4
Hippocampus, classic name, “ sea-horse.” : 7 ;
Holocephali, éAos, whole or complete, xeady, head. at
Holoptychius, 6Aos, entire(ly), mrvytos, folded (referring to the tooth —
enamel). .
Hybodus, ¥ Bos, hump, 8o%s, tooth. oe
Hyperoartia, trrepyia, palate, dpreos, entire.
Hyperotretia, trepwa, palate, rperds, pierced.

Ichthyotomi, ixvs, fish, réuvw, separate (referring perhaps to the a
distinctness of this group). a
Ischyodus, ioxvs, power(ful), d50vs, tooth(ed).

oe

DERIVATION OF NAMES 229

_Leemargus, classic name of a shark.
___Lagocephalus, Aayds, rabbit, xepadrj, head.
____Lamna, Adyva, classic name for a shark.

___ Lepidosiren, Aeris, scale(d), siren, salamander.
____ Lepidosteus, Aemis, scale, daréov, bone.

____ Leptolepis, Aerrds, smooth or delicate, Aemis, scale(d).
~ Lophobranchii, Aéqos, tuft, Bpdyxvor, gill ed).

_ Marsipobranchii, papofmov, pouch, Bpayyxua, gills.
' Megalurus, péyas, large, oipd, tail(ed).
Microdon, pixpos, small, d3ovs, tooth(ed).
Mormyrus, classic name of a (sea) fish (— from poppvpw, I murmur).
Myliobatis, pvAias, pavement (toothed), Baris, skate.
Mylostoma, pvAos, mill(like), oropua, mouth. -
_ Myriacanthus, pvpeds, ten thousand, dxavOa, spine.
* Myxine, pv€ivos, slimy-fish.

‘Onychodus, dvvé, claw; d8ovs, tooth(ed).
Ophidium, é¢éd.ov, a snake.

Osteolepis, daréov, bone, Aeris, scale(d).
Ostracoderm, éorpaxtov, shell, dépya, skin.

Palzaspis, maAatds, ancient, domis, shield.

Palzoniscus, waAatds, ancient, dvicKos, a sea-fish.

Palzospondylus, maXatos, ancient, oxdvdvdos, vertebra.

Parexus,? wapéxw, have as one’s own (referring to the peculiar nature

of the fish?).

_ Perca, classic name of fish.

- Petromyzon, mérpos, stone, pufdw, to suck.

_-Phaneropleuron, avepds, well marked, wAevpd, side (fins) or ribs(?).
Pisces, fishes.
__ Plagiostomi, Adytos, transverse, ordua, mouth.
: ‘Plectognathi, wAexrds, twisted, yvdOos, jaw.

- Pleuropterygii, mhevpd, side, arépvé, fin(ned).
_ Pogonias, rwywvias, bearded.

~ Polyodon, modus, many, ddwv, tooth(ed).
Polypterus, modws, many, arepov, fin(ned).

_ Prionotus, Tpiwy, saw, v@tos, back.

, Pristiophorus, mpioris, a saw, popew, to carry.
__ Pristis, mploris, a saw-fish.

_ Protopterus, zparos, ancient, rrepdy, fin(ned).

230 FISHES, LIVING AND FOSSIL

Psammodus, Wapjos, sand, d8ovs, tooth (ed).

Psephurus, yjdos, a little stone, odd, tail.

Pseudopleuronectes, Weddos, false, rAevpdv, side, vyxtys, swimmer.
Pterichthys, wrépvé, fin or wing, ixOvs, fish,

Raja, classic name of skate.

Rhabdolepis, fades, nail, A€ms, scale(d).
Rhina, pivy, a rasp.

Rhinobatus, fiva, Rhina, Baris, skate.
Rhynchodus, pvyxos, snout, ddovs, tooth(ed).

Scaphirhynchus, oxadiov, shovel, piyxos, snout.
Scomberomorus, oxéuPpos, mackerel, poptov, part.
Scyllium, oxvAvov, classic name of this shark.
Selachii, veAdyn, shark.

Semionotus, oypetov, a standard, v@ros, back.
Silurus, classic name of fish.

Siphostoma, oipwy, tube, ordua, mouth.
Sirenoidei, sven, salamander, otdos, like.
Squaloraja, sgualus, shark, raja, skate.

Squalus, classic name of a shark.

Squatina, a classic name of a sea-fish.

Teleocephali, réAcos, entirely, daréov, bone, kepady, head.
Teleost, réAcos, entirely, doréov, bone.

Teleostomi, réAcos, entirely, daréov, bone, ordya, mouth.
Titanichthys, tan, giant, ix@us, fish.

Torpedo, classic name (from the root of Torpor, stupefy).
Trachosteus, tpaxvs, rough, édoréov, bone.

Trygon, tpvywy, the thorny ray.

Urogymnus, oipa, tail, yiuvos, naked.

Xenacanthus, évos, strange, dxavOa, spine.

BIBLIOGRAPHY

>

IN the following list the writer aims to present the more recent and
more important works relating to the general subject of fishes. Titles
have been classified, and most of the references give more or less com-

plete bibliographies of their special subjects. Of the journals in which
papers occur the principal abbreviations are as follows : —

A . . . Archiv (or Archives).-

AH... Abhandlungen.

Ann. N.H Annals and Magazine
of Natural History.

- Bulletin.

- Contes rendus.

- Denkschriften.

- Journal

JB. . . Jahrbuch

JH. . . Jahreshefte

J.R.M.S . Journal ofthe Royal Mi-
croscopical Society.

- Mittheilungen

Jj as
oe
DS . *

mr

Q.J-M.S Quarterly Journal of
Microscopical Science.

P. . . Proceedings.

R. . . Report.

S. . . Society.

SB . Sitzungsberichte.

Sci . Science, or Scientific.

Tr. . . Transactions.

U.S.F.C United States Fishery
Commission.

VH - Verhandlungen.

Z. . . Zeitschrift.

The Roman numerals denote the number of the volume, the Arabic

numerals the pages.

WORKS ON THE GENERAL SUBJECT, FISHES

- Woopwarp, A. Smitu Catalogue of Fossil Fishes in the British
: Museum. Vols. I, II (and III).

GUNTHER, A.

London, 1889-(95).

Catalogue of the Fishes in the British

Museum. Vols. I-VIII. London, 1859-70.

GUNTHER, A.

An Introduction to the Study of Fishes. 8vo.

pp. 720. Illustrated. Edinburgh, 1880.

GUNTHER, A.

Fishes: Challenger Reports. Vol. I, pt-

VI, Vol. XXXI, pt. LX XVIII.

London, 1880-89.

Fishes: Standard Natural History.

Boston, 1885.

231

232 FISHES, LIVING AND FOSSIL

GoopE, G. Brown. . Fishery Industries of U.S. U.S. F.C.
Washington, 1884.
DumeErRIL, A.. . . . Histoire naturelle des Poissons. Vols.
I-II (Sharks, Chimeroids, Lung-fishes,
Ganoids, Lophobranchs). Paris, 1890.

Acassiz,L. . . . . Recherches sur les Poissons Fossiles. Vols.
I-V, with Atlas volumes. ;
Neuchatel, 1833-43.

ZITTEL, K.v. . . . Handbuch der Palaeontologie. Fische.
Munich, 1887,
ROLLEsTON, G. . . .° Forms of Animal Life. Second edition. -
Oxford, 1888.
Huxtey, T. . . . . Manual of the Comparative Anatomy of

Vertebrated Animals. | New York, 1872.
JORDAN and GUILBERT Manual of the Vertebrates of Eastern N. A.
McClurg. Last edition.

SKELETON. —’86 Baur, G., Squamosum, Anat. Anz. °87 Ribs,
Am. Nat. xxi, 942-945. °86 Corr, E. D., Caudal vertebra, Am.
Phil. Soc. 243. °93 BoULENGER, G. A., Hemapophyses, Ann.
N.H. xii, 60-61. °92 DOLLo, L., Ribs, vertebra, B. Sci. Fr. Belg.
xxiv. ’87 GEGENBAUR, Occipital region, Kolliker Festschr. 1-33.
°79 GOETTE, A., Wirbelsaule, A. mikr. Anat. xvi, 428. °89 HaT-
SCHEK, Rippen, VH. Anat. Gesell. Berl. (Jena). °78 IHERING,
H., Wirbelverdoppelung, Zool. Anz.I, 72-74. '93 JORDAN, D.S.;
Temperature and vertebra, Wilder Quarter Century Book, Ithaca,
13-37- °93 KLAatscH, H. (Vertebre), Morph. JB. xix, 649-
680, and xx, 143-186. °68 KLEIN, Schadel, Wiirt. Nat. JH. 71-
171, and (81) xxxvii, 326-360. °87 Luorr, B. (Chorda and
Sheath), B. S. Mosc. 227-342 (442-482, German). °77 PARKER
and BETTANY, Morph. of the Skull, London, pp.-14-90. ‘89
PoucHET and BEAUREGARD, Traité de Ostéol. Comp. Paris,
398-451. °87 STRECKER, C. (Condyles), A. Anat. Phys. Anat.
Abth. 301-338. ;

INTEGUMENT, TEETH. —/’92 AGassiz, A., Chromatophores, B. —
Mus. Comp. Zool. xxiii, 189-193. '82 BAUME, A., Odont. Forsch.
Leip. 41-52. %77 HERTWIG, O., Hautskelet, Morph. JB. HI,
328-395, and v (79), 1-21. °90 KLAatscu, H., Schuppen, op.
cit., 97-202 and 209-258. °45 OweEN, Odontography, London.
93 RypER, J. A., Mechanical genesis of Scales, Ann. N. H., xi,
243-248. ’82 Tomes, C., Dental Anat. Ed. 2.

BIBLIOGRAPHY: FISHES 233

FINS. —’90 Corr, Homologies, Am. Nat. 401-423. "79 DAvIDOFF,
M., Pelvics, Morph. JB. v, 450-520, vi (’80), 125-128, 433-468.
*87 Emery, C., Homologies, Zool. Anz. x, 185-189. °65 GEGEN-
BAUR, C., Brust Flosse, Leip. 4to, pp. 176. °70 Jen. Z., v, and
(73) Archipterygium, vii. 79 Morph. JB., v, 521-525.
94 Op. cit. xxi, 119-160. °89 HATSCHEK (Paired), VH. Anat.
Gesell. Berl. 82-90. °68 PARKER, W. K., Shoulder girdle, Ray

_ Society, Lond. pp. 237. °83 RAUTENFELD, E. V., Ventrals, Dor-
pat (82), 48 pp. °79 RypeER, J. A., Bilateral symmetry, Am. Nat.
xiii, 41-43. °85 Unpaired fins, op. cit. xix, 90-97. ‘86 Em-
bryol. of fins, R. U. S. F. C., 981-1086. °86 Fin rays and degen-
eration, P. U. S. Nat. Mus. 71-82. °87 Homologies, P. Acad.
Philadel. 344-368. °77 THACHER, J., Homologies, Tr. Conn.
Acad. III. °92 WiIEDERSHEIM, R., Gliedmassenskelet, Jena, 266
pp- °92 Woopwarp, A. S., Evolution, Nat. Sci. 28-35.

VISCERA, GLANDS, CIRCULATORY.—’84 Ayers, H., Pori
abdominales, Morph. JB. x, 344-349. °89 Carotids, B. Mus.
Comp. Zool. xvii. °82 BALFour, F. M., Head kidney, Q.J. M.S.
Xxx, 12-16. °’87 Boas, J. E. V., Arterienbogen, Morph. JB. xiii,
115-118. °79 BripGE, T., Pori abdominales, J. Anat. Phys. xiv,
81-102. *85 CLELAND, J., Spiracle, R. Br. Ass. 1069. °87
EBERTH, C. J., Blutplattchen, Kolliker Festschrift, 37-48. ’66
GEGENBAUR, Bulbus, Jen. Z. ii, 365-375. °84 Abdominal poren,
Morph. JB. x, 462-464. °91 Conus, op. cit. xvii, 596,610. °85
GROSGLIK, S., Kopfniere, Zool. Anz. viii, 605-611. ’90 HowEs,
G. B., Intestinal canal and blood supply, J. Linn. S. xxiii, 381-410.
64 HyrtTt, J. (Hepatic and portal), SB. Acad. Wiss. Wien,
167-175. ‘85 Puisavrx, C., Rate, Paris, 8vo. ‘90 ROsE,C.,
Herz, Morph. JB. xvi, 27-96. °82 SoLGER, B., Niere, A. H. Gesell.
Halle, xv, 405-444. °84 WELDON, W. F. R., Suprarenals, P.
Roy. S. xxxvii, 422-425.

SWIM-BLADDER.—’86 ALBRECHT, P., Non-homologie des
poumons, Paris and Brux, 44 pp. °80 Day, F., Zool. 97-104.
66 GourieT, E., Ann. Sci. Nat. vi, 369-382. 73 Hasse, C.,
Anat. Studien, I, Heft 4. °90 LrieBReEIcH, O., A. Anat. Phys.
Phys. Suppt. 142-161, 360-363. °85 Morris, C., P. Acad. Nat.
Sci. Philadel. 124-135, Anat. Anz. (°85) xxvi, 975-986.

NERVOUS SYSTEM AND END ORGANS. —’83 BavupE Lot, E.,
fol. Paris, 178 pp. °88 BATESON, Sense organs, J. Mar. Biol.
Ass. 1, No.2. °85 BEARD, J., Branchial sense organs, Q. J. M.S.
xxvi. °82 BERGER, E. (Eye), Morph. JB. viii, 97-168. °’84
BLAvE, J. (Nasal membrane), A. Anat. Phys. 331-362. ‘83

234 FISHES, LIVING AND FOSSIL

CANESTRINI, Otoliths, Atti. Soc. Pad. viii, 280-339. °86 Hearing
organ, op. cit. ix, 256-282. ’91 CHEVREL, R., Sympathetic,
Thése faculté des sciences, Paris. °79 DeRcuM, F., Lateral line,
P. Acad. Phil. 152-154. 70 F&xE, F., Systéme lateral, Mem. S.
Sci. Nat. Strasb. vi, 129-201. °73 HAssE, C., Gehérorgan, Anat.
Stud. I, Heft 3. ’88 JuLIN, C., Epiphysis, B. Sci. Nord. x, 55-65.
90? KoOKEN, E., Otoliths, Z. geol. Gesell. xliii, 154. ‘91
OwsJANNIKOW, P. (Pineal eye), Rev. S. Nat. St. Petersb.
100-111. ’81 Retzius, G., Gehérorgan, Stockholm, fol. 222 pp.
°71 ScuuLtTzE, F. E., Seitenlinie, A. mikr. Anat. vi, 62. 70
StTIEDA, L., Centralnervensystem, Z. wiss. Zool. xxi, 273-456.

EMBRYOLOGY.—’85 HAACKE, W., Uterinaler Brutpflege, Zool.
Anz. viii, 488-490. HALBERTSMA, H. J., Normal en abnormal
Hermaphroditismus, Tijd. Nied. Dier. Ver. Amst. °87 Hocn-
STETTER, F., Venensystem, Morph. JB. xiii, 119-172. °86 Horr-
MAN, C. K., Urogenital, Z. wiss. Zool. xliv, 570-643. *91 KUPFFER,
C. v., Kopfniere, VH. Anat. Gesell. 22-55. ’90 LAGUESSE, E.,
Rate, J. de VTAnat. Phys. xxvi, 345-406 and 425-495. 77?
LANKESTER, E. Ray. Germ layers, Q. J. M.S. xvii. "93 Lworr, B.,
Keimblatterbildung, Biol. Centralb. xiii, 40-50, 76-81. "79 MAR-
TENS, E. V., Hermaphroditische Fische, Naturf. 116. ’80 Nuss.
BAUM, M., Differenzirung d. Geschlechts, A. mikr. Anat. xviii,
1-121. °89 ScHWARZ, D., Schwanzende, Z. wiss. Zool. xlix,
IgI-223. °92 VircHOw, H., Dotterorgan, Z. wiss. Zool. liii,
Suppl. 161-206.

THE CYCLOSTOMES

GENERAL. —’93 Ayers, H., Bdellostoma, Woods Holl Lectures,
125-161. °92 BEARD, J., Lampreys and Hags, Anat. Anz. viii,
59-60. ’91 Buyor, P., La metamorphose de l’'Ammoccetes, Rev.
Biol. du Nord de la France, iii, pp. 97. °93 GAGE, Lake and
Brook Lampreys, Wilder Quarter Century Book, Ithaca, 421-493.
*91 Howes, G. B., Lamprey’s affinities and relationships, P.
Tr. Liverpool Biol. Soc. vi, 122-147. ’89 JuLIN, C., Morphologie
de ’Ammoceete, B. Sci. France et Belge, 281-282. "90 KAENSCHE,
C. C., Metamorphose des Ammoceetes, Schneider's Zool. Beitrage,
II, 219-250.

ANATOMY, GENERAL.—’86 CuNNINGHAM, J. T., Critique of
Dohrn’s views of Cyclostome morphology, Q. J. M. S. xxvii, 265—
284. ’88 JuLtn, C., Anatomie de l’Ammoceetes, B. Sci. du Nord
de la France, x, 265-295. "75 LANGERHANS, P., Untersuchungen
ii. Petromyzon, VH. d. n. Gesell. Friburg, XI, Heft 3. 37

BIBLIOGRAPHY: CYCLOSTOMES 235

MULLER, J., Vergleich. Anat. d. Myxinoiden, AH. K. Akad. Wiss.
Berlin, 65-340, 9 pls. °79 SCHNEIDER, A., Beitrage zur vergleich.
Anat. 4to, pp. 164, Berlin.

SKELETON.—’92 Burne, R., Branchial Basket in Myxine, P. Zool.
S. 706-708. °69 GEGENBAUR, C., Sketelgewebe, Jen. Z. V. ’93
Hasse, C., Wirbel. Z. wiss. Zool. 290-305. °76 HUXLEy, T.
H., Craniofacial Apparatus, J. Anat. Phys. x, 412-429. (’84)
PARKER, W. K., Monograph of Skeleton of Petrom. and
Myxine, P. Roy. S., °82, 439-443 and Phil. Tr. Roy. S., 83, 373-
457. °78 PEREPELKINE, K., Structure de la Notochorde, B. Mosc.
liii, 107-108. °92 Retzius, G., Caudalskelet der Myxine, Biol.
Foren. iii, 81-84.

MUSCULATURE.—’75 FURBRINGER, P., Muskulatur des Kopf-
skelets, Jen. Z. ix, N. F. I]. °67 GRENACHER, H., Muskulatur, Z.
wiss. Zool. xvii. °59 KEFERSTEIN (Histological), Du Bois R’s. A.
f. Anat. 548. °82 SCHNEIDER, A., ii. d. Rectus, Zool. Anz. N. 107,
p- 164. ‘'52 Stannius, H. (Heart fibres), Z. wiss. Zool. iv, 252.
52 (Histology), L’Institut, xx, 132-134, and Géottin. Nachricht.
"51, 225-235. °82 STEINDACHNER, A., ii. d. Rectus. Zool. Anz. v,
660.

FINS.—’85 CLELAND, J., Tail of Myxine, R. Br. Ass. Adv. Sci. 1069.

INTEGUMENT, TEETH.—’88 Bearp, J., Teeth of Myxinoids,
Nature, xxxvii, 499, and Anat. Anz. iii, 169-172. "91 BEHRENS,
Hornzahne v. Myxine, Zool. Anz. xiv, 83-87. °82 BLOMFIELD,
S. E., Thread. cells of Epidermis of Myx. Q. J. M. S. xxii, 355-361.
'76 FOETTINGER, A., Structure de l’Epiderme, B. Acad. roy. d.
Belge. ix, No. 3. °94 Jacosy, M., Hornzihne, A. mikr. Anat.
117-148. °60 KOLLIKER, Inhalt d. Schleimsicke d. Epidermis,
Wiirzb. naturwiss. Zeitschr. i, I-10. °64 MULLER, H., Epidermis,
Wiirzb. naturwiss. Zeitschr. v, 43-53. °89 PoGojEFF, L., Haut,
A. mikr. Anat. xxxiv, 106-122. °61 ScHULTZE, M., Kolben-
formig Gebilde, A. Anat. u. Phys.

VISCERA, GLANDS, CIRCULATORY.—’46 Duvernoy, G. L.,
Sinus veineux génital, C. R. xxii, 662. "76 Ewart, T. C., Abdom.
pores, J. Anat. and Phys. x. °78 Vascular peribranchial spaces,
J. Anat. and Phys. xii, 232-236. ’89 GaGeE, S. H., Blood, P. Am.
S. Micros. x, 77-83, and J. R. M. S. 494. °17 Home (Gills), Isis,
25-35. °93 Howes, G. B., Abnormal gill clefts in Pet. and Myx. P.
Zool. S. 730-733. °87 JULIN, Cu. (Two anterior gill slits), B. Acad.
Roy. Sci. Brux. xiii, 275-293. °88 Appareil vasculaire, Zool. Anz.
xi, 567-568. °94 KERKALDy, J. W., Head-kidney of Myx. Q. J.

236

FISHES, LIVING AND FOSSIL

M. S. 353-359. °90 KLINCKOwsTRGM, A., Darm-u. Lebervenen.
b. Myx. Biol. Féren. 62-67. °93 KuprFeEr, C. v., Pankreas, SB.
Morph. Gesell. Miin. ix, 37-59. °82 LeGouts, P. S., Pancreas,
C. R. xcv, 305-308, and Ann. S. Sci. Brux. viii, 187-304. °32_
MaAyER, C., milz. Gror. Nat. xxxiv, 165-166. "76 MEYER, F.,
Nieren, Centr. f. d. medicin. Wiss. No. 2. °89 MULLER, J,
Gefasse : Wundernetze, Monatsheft, Berlin, 184-186, and 272-292.
39 Lymphgefasse, AH. d. Berl. Akad. ‘73 MULLER, W.,
Urniere b. Myx. Jen. Z. vii. °75 Urogenital system, AH. d.
Ak. d. Wiss. Berl. ix. °21 OKEN, J. (Gills), Isis, 271-272, and
29 VH. Gesell. Natur. Berl. I, 133-141. °46 Rosy, C., Systéme
veineux, L’Inst. xiv, 120-123. °87 THompson, D’A. W., Blood,
Ann. N. H. xx, 231-233, and Anat. Anz. ii, 630-632. °84 WELDON,
W. F., Head-kidney of Bdell. Q. J. M. S. xxiv, 171-182. —

NERVOUS SYSTEM, END ORGANS.—’82 AHLBORN, F., Gétt-

ing. Nachr. 677-682. °83 Z. wiss. Zool. xxxix, 191-294. "84
Hirnnerven, Z. wiss. Zool. xl, 286-308. °88-’89 Brarp, J.,
Parietal eye, Nature, xxxvi, 246-298, and 340-341, also Q. J. M. S.
xxix, 55-73. 77 FREuD, S., Nervenwurzeln im Riickenmark,
SB. Ak. Wien, lxxv. °78 Spinalganglien, SB. Ak. Wien, Lxxviii.
°78 GOETTE, A., Spjinalganglien, A. mikr. Anat. xv, 332-338.
°72 HAssE, Auditory organ, Anat. Studien, I, Heft 3, and Ketel,
ibid. 489-541. °79 JELENEF, A. (Cerebellum), B. Pétersb. xxv,
333-345. °86 JuLIN, C. (Sympathetic), A. Zool. exper. vi, and
Anat. Anz. °87, 192-201. °87 Nerfs latéral, B. Acad. R. Brux.
xiii, 300-309. °92 KonL, C., D. Auge v. Pet. u. Myx. Leip.
Reudnitz. br. °37 MULLER, J., Gehdrorgan, Abh. Berl. Acad.
°38 Nervensystem d. Myx. Berl. Monatsber, 16-20. °85 NANSEN,
F., Aarsber. Berg. Mus. 55-78 (trans. in Ann. N. H. xviii,
209-226. °64 OWSJANNIKOW, P., Gehér. Mém. Acad. St. Pétersb.
viii. °83 (Sympathetic), Arb. Naturf. Gesell. xiv, and °84 B.
Acad. St. Pétersb. xxviii, 439-448. °88 (Pineal eye), Mém.
Acad. St. Pétersb. xxxvi. °86 RANSOM, W.and THOMPSON, D’A.,
Spinal and visceral nerves, Zool. Anz. ix, 421. °80 RETZzIvs,
G., Riechepithel. A. f. Anat. u. Phys. °90 (Myxine: caudal
heart, nerve and sub-cutaneous ganglion cells), Biol. Untersuch.
Neue Folge, Stockholm, Fol. °92 Nervenendungen in der Haut,
des Pet., op. cit. (2) III, 37-40, and (tail structures), op. cit. iv,
36-41. °93 Gehirn-Auge v., Myx. op. cit. v, 27-30. And
Geschmacksknospen bei Pet. op. cit., 69-70. °82 ROHON, J. V.,
Ursprung d. acusticus. SB. Ak. Wien, lxxxv, 245-267. °84 Sac-
CHI, T. (Neuroglia of retina), Arch. Ital. Biol. vi, 76-96.

BIBLIOGRAPHY: CYCLOSTOMES 237

80 SCHNEIDER, A., Nerven, Zool. Anz. 330. "71 SCHULTZE, M.,
Retina, SB. nieder-rhein Gesell. 6 Nov. "79 SELENEFF, A. (Cere-
bellum), B. Acad. St. Pétersb. xxv, 333-343, and 80 Mélanges
Biol. St. Pétersb. x, 307-325. °88 WuHITWELL, J. R., Epiphysis,
J. Anat. Phys. xxii, 502-504. "79 WIEDERSHEIM (Brain and
nerves), Zool. Anz. 589-592 and ‘80 in Jen. Z. xiv, 1-24.

EMBRYOLOGY.
I. General. °88 GOETTE, A., Zool. Anz. xi, 160-163 and "90 in AH.

3, Entwicklungesch. d. Thiere, 5 Heft. ‘88 KuprFER, C. v., SB.
bayer. Akad. I, 70-79, and ’90 in A. mikr. Anat. xxxv, 469-558.
°90 NESTLER, Zool. Anz. xiii. ‘81 NuEL, J. B., A. d. Biol. i, and
82 ii, 403-454; also J. R. M. S. ii, 26-27. "70 OWsJANNIKOW, B.
Acad. St. Pétersb. xiv, 325 and °89, xxxii, 83-95, and °91 Mél.
Biol. xiii, 55-67 and B. Acad. St. Pétersb. 13-55, and ‘93 Ann.
N. H. xi, 30-43. °81 Scott, W. B., Q. J. M.S. xxi, 146-153, Zool.
Anz. (80) 422, and Morph. JB. vii. Also 82, A. Zool. expér.
ix, and (pituitary body and teeth) Science, ii, 184-186, 731-732.
Also ’88 J. of Morph. i, 253-310. °87 SurpLey, A. E.,Q.J.M.S.
xxvii, 325-370, and A. Zool. expér. i. Also Stud. Morph. Lab.
Camb. iii.

Il. Ovary, Sperm, Fertilization. °93 BEARD, J., Testes with ova,

Ill.

Anat. Anz. viii, 59-60. °87 Boum, A. A., Befruchtung, SB. bayer.
Akad. 8 Feb., and A. mikr. Anat. xxxii. °77 CALBERLA, E.,
Befruchtungsvorgang. Z. wiss. Zool. xxx, 437-486. °87 CUNNING-
HAM, T., Ova of Bdell. Tr. Roy. S. Edinb. xxx, 247-250, (Myxine)
Zool. Anz. 390-392, and Q. J. M. S. xxvii, 49-76. °91 Sper-
matogenesis of Myx. Q. J. M. S. xxxiii, 169-186, and Zool. Anz.
xiv, 22-27. °83 FERRY, L. (Internal fecundation), CR. Ixxxxvi,
721-722, and Ann. N. H. xi, 388. °75 GuLLIVER, Spermatozoa,
P. Zool. S. 336. °78 KupFFER, C. v., u. BENECKE, Befruchtung.
Festschr. Th. Schwann K6nigsberg. °86 NANSEN (Protandric),
Myxine, Zool. Anz. 676, °87 in Bergens Mus. Aarsber, pp. 34, and
89 (Q. J. M.S. 188-189) Zool. Anz. 261. °80 NussBAuM, M.
(Eggs and spawning), A. mikr. Anat. xviii, 1-121. °89 RETzIvs,
Entwick. d. Myx. Biol. For. i, 22-28, Anhang. 50-51 (Dec. ’88).
63 STEENSTRUP, J. (Egg of Myxine), Oversigt. o. d. K. danske
Videnskabernes Selskabs Forh. 233-239. °87 WEBER, M.
(Reply to Cunningham), Zool. Anz. 318-321. Geslachtsorganen v.
Myx. Ned. Dierkd. Vereen, 4 pp. D. I. Afi. 3-4.

Organogeny. °77 CALBERLA, E., Medullarrohr, Morph. JB. iii.
82 Dourn, Hypophysis, Zool. Anz. 587-588, 83 in MT. z. Stat.
Neapel, iv, 172-189. °84 Visceralbogen, op. cit. v, 152-189.

238 FISHES, LIVING AND FOSSIL

86 Thyreoidea, op. cit. vi. °87 (Thyroid, Spiracle, Pseudo-
branch), op. cit. vii, 301-337. °88 Nerven u. Gefisse, op. cit. viii,
233. ‘92 Harta, S., Germinal Layers, J. Coll. Sci. Japan, v,
129-147. 84 HERMS, E., Nervus acusticus, SB. math. nat. Acad.
Miinch. 333-354. "93 McC.ure, Early stages, Zool. Anz. xvi,
429. °85 SuipLey, A. C., Mesoblast and blastopore, P. Roy. S.
Lond. xxxix, 244-248. °86 Nervous system, P. Camb. Phil. S.
Vv, 374. °79 WIEDERSHEIM, Brain and spinal nerves, Zool. Anz.

ii, 589-592.

THE OSTRACODERMS AND PALASOSPONDYLUS

(Cf. SmirH Woopwarp’s Cat. Foss. Fishes.)

85 Corr, E. D., Position of Pterichthys, Am. Nat. xix, 289-291.
*92 CLAYPOLE, E. W., Pteraspidian family, Q. J. Geol. S. xlviii,
542-562. °90 PATTEN, W., Q. J. M. S. xxxi, 359-365. ‘94
Limulus and Pteraspis, Anat. Anz. °94 ROoHON, J. V. (Meta-
merism of Cephalaspids), Zool. Anz. 51. °88 TRAQUAIR, R. H.,.
Asterolepids, Ann. N. H. ii, 485-504, and (’89) P. Phys. Soc.
Edinb. 23-46. °90 Paleospondylus, Ann. N. H. vi, 485, and
93 in P. Roy. Phys.-Soc. Edinb. xii, 87-94, and °94 op. cit. xii,.
312-321. °92 SmiITH WoopwarbD, Forerunners of Backboned
Animals, Nat. Sci. i, 596-602.

THE SHARKS

GENERAL. —’65 DumErIL, A, Hist. nat. d. poissons, Tome I
(Sharks, Skates, and Chimera), pp. 720, Paris. "79-80 MIKLOUHO--
MACLAY, Plagiostomes of the Pacific, i, ii, iii (Anat. notes:
Dentition of young Cestracionts), P. Linn. S. N. S. Wales, iii,
306-326. 41 MULLER, u. HENLE, Syst. Beschr. d. Plagiost.
folio, 60 pls. Berlin. :

ANATOMY, GENERAL. —’85 Garman, Chlamydoselache, B. Mus.
Comp. Zool. (cf. Giinther in Challenger report). °90 JAEKEL,.
O., Kiemenstellung u. System. d. Sel. (?) Berlin. °91 Pristi-.
ophorus, A. f. Naturges, 15-48. LruckarT, R., Bildung d.
Korpergestalt b. Rochen. Z. wiss. Zool. ii, 258. °93 MAREY
(Swimming movements of Ray), C. R., exvi, 77-81. °92 MarR-
SHALL and Hurst, Practical Zodlogy (Dog-fish), Putnam, N. Y.
84 PARKER, T. J., Zodtomy (Skate), Macmillan. °84 WILs,.
H. B., Squatina. Lugd. Bat.

SKELETON. —’85 Donen (Visceral arches of Skate), MT. z. Stat.

BIBLIOGRAPHY : SHARKS 239

Neapel, vi. "72 GEGENBAUR, Kopfskelet, 4to, Leip. °78 HAssE,
C. (Vertebra, Morph. JB. iv, 214-268, and op. cit. Supplt. 43-58,
and Berl. Verh. Naturw. 173-174 (Zool. Anz. i, 144-148 and 167-
171). Also 85, 4to, 27 pp. Leip. °84 HASWELL, W. A., P. Linn.
S. N. S. Wales, ix, 71-117. °78 HuBRECHT, Bronn’s Klassen u.
Ordnungen. °64 KOLLIKER, Wirbel, Senkenb. Naturf. Gesell. v,
51-99. Also 4to. Frankfurt. ‘90 PARKER, T. J., Sternum in
Notidanus, Nature, xliii, 142. °78 PARKER, W. K., Skull (with
develop.) of shark and skate, Tr. Zool. S. x, 184-234. °84 ROSEN-
BERG, E., Occiput, Festschr. Dorpat. 4to, 20 pp. And °87 in SB.
Gesell. Dorp. viii, 31-34. °73 STEENsTRUP, J. (Gill rakers of
Selache), Overs. Dan. Selsk. No.1. °90 WHITE, P. J., Skull and
visc. skelet. of Lemargus, Anat. Anz. v, 259-261.

FINS AND GIRDLES.—’81 Ba.rour, Skates, P. Zool. S. °70
GEGENBAUR, Skel. of, Jen. Z. v, 397-447, also (claspers) 448-458.
90 Howes, Batoid and Squaloraja, P. Zool. S. 675-688. °85
MAYER, P., Unpaaren Flos. MT. z. Stat. Neap. vi, 217-285. °79
METSCHNIKOFF, O. (Morph. of girdles), Z. wiss. Zool. xxviii, 423-
438. °79 Mivart, St. G., T. Zool. S. x, 439-484. °92 MOLLIER,
S. (Entwickelung), Vorl. MT. Anat. Anz. vii, 351-365, also "77
THACHER, J., Tr. Connec. Acad. iii.

INTEGUMENT AND TEETH. W— 44 Aaassiz, L., Dents et rayons,
4to, Neuchatel. *68 HANNovER, A., Ecailles. (?). HARLESS, E.,
Zahnbau v. Myliobates, 4to (?). 74 HERTWIG, O. (also develop-
ment), Jen. Z. viii. °72 RANVIER, L., Etranglements annulaire
(Rays), C. R. 1129-1132.

VISCERA, VESSELS, GLANDS. —’92 Antipa, G., Thymus, Anat.
Anz. vii, 690-692. °88 Ayres, H., Carotids (Chlamydosel.), B.
Mus. Comp. Zool. xvii, 191-224. *78 BLANCHARD, R., Superanal
gland, J. de l’Anat. Phys. xiv, 442-450, and B. S. Zool. Fr. vii,
399-401. °79 BRIDGE, Pori abdominales, J. Anat. Phys. °82
Droéscuer, W. (Histol. of gills), A. f. Nat. xlviii, 120-177. °90
Ewart, J. C., Spiracle of Lamna, J. Anat. Phys. xxiv, 227-229.
°78 FURBRINGER, Excretory system, Morph. JB, 49-56. ‘91
GEGENBAUR, Cécalanhinge v. Mitteldarm, Jen. Z. (?), 180-184.
*90 Howes, Kidney of Raja, J. Anat. Phys. xxiv, 407-422. °90
Visceral anat. of Hypnos, P. Zool. S. 669-675. °72 HyRrTL, J.,
Kopfarterien, DS. Ak. Wiss. Wien, xxxii, 263-275. °85 List,
J. H., Cloakenepithel, SB. Akad. Wien (?), and Anat. Anz. vii,
545-546. "80 ParKeER, T. J., Spiral valve of Ray, T. Zool. S. xi,
49-61, and Venous system, Tr. N. Zeal. Ins. xiii, 413-418. °86
On the vessels of Mustelus, and (’87) on Carcharodon, P. Zool.

240 FISHES, LIVING AND FOSSIL

S.(?). °90 Pitutet, A. (Histol. of liver), C. R. Soc. Biol. ii,
690-694. °82 PouCcHET, G., Termin. vascul. d. la Rate, J. de
P’Anat. Phys. xviii, 498-502. °88 RUCKERT, J., Excretions-organe,
A. Anat. Phys. (Anat.), 205-278. °77 SToHR (Valves in arterial
conus), Morph. JB. ii, 197-228. °79 Trois, E. F. (Carotids of
Oxyrhina), Atti del Inst. Ven. and °83 (Of Alopecias), op. cit.
°73 TURNER, W., Visceral Anat. of Lamargus, J. Anat. Phys.
233. 75 Spiny Shark, op. cit. °79 Pori abdominales, op. cit.
xiv, 101-102. "81 Teeth and gill-rakers of Selache, op. cit. xiv,
273-286. °93 VircHOw, H., Spritzlochkieme, SB. Gesell. n.
Freunde, Berl. 177-182; Augengefasse (90) A. Anat. Phys.
(Phys.), 169-173. °67 MIKLUCHO-MACLAay, Schwimmblasenrudi-
ment, Jen. Z. iii, 448-453.

NERVOUS SYSTEM AND END ORGANS. —’92 Braus, H.,
Rami ventrales d. vord. Spinalnerven. Inaug. Diss. 35 pp. Jena.
83 CaTTIE, J. F., Epiphysis, Z. wiss. Zol. xxxix, 720-722, and
A. Biol. iii, 101-196. °90 CHEVREL, R., Sympathetic, A. Zool.
expér. v, 196 pp. °91 Coael, A., Vésicules de Savi (Torpedo),
A. Ital. Biol. xvi, 216-224. °92 EDINGER, L., Zwischenhirn, AH.
Senck. Gesell. xviii, 55 pp. (and Anat. Anz. vii, 472-476). °78
EHLers, E., Gehirn u. Epiphyse, Z. wiss. Zool. xxx, Suppl. 607.
90 Ewart, J. C., Cran. nerves of Torpedo, P. Roy. S. xlvii,
240-291. °92 Electric organ of Skate, Phil. Trans. clxxxiii,
389-420 (Abs. in P. Roy. S. 474-476). °92 Sensory canals of
Lemargus, and Skate, Tr. Roy. S. Edinb. Nos. 5-6 (Abs. in
Zool. Anz. xv), 116-120. °88 FRITSCH, G., Bedeuting d. Kanalsyst. —
SB. Ak. Berl. 273-306. °88~’89 GARMAN, Lateral line (figures
many forms), B. Mus. Comp. Zool. xvii, No. 2. °71 GEGENBAUR,
Kopfnerven v. Hexanchus, Jen. Z. 497-560. °75 JACKSON, W. H.,
and CLARKE, Brain and nerves, J. Anat. Phys. x, 75-197. "87
L&éGER, M., Cervelet d’un Alopias, B. S. Philom. xi, 160-163.
*81 MARSHALL, A. M., Head cavities and nerves, Q. J. M. S. xxi,
72, and (with SPENCER) 469-499. °80 MERKEL, Sens. nerven in
d. Haut. Rostock. *70 MikLucHO-MACLAY, Gehirn, 4to, 74 pp.
Leip. °78 Retzius, G., Memb. Gehorlabyr. A. Anat. Phys.
(Anat.), 83-105. °91 Rex, H. (Morph. of cran. nerves), Morph.
JB. xvii, 417-466. °78 Rouon, J. (Brain), DS. Ak. Wien, xxxviii,
43-108. °86 SANDERS, A., Phil. Trans. clxxvii, 733-764, and P.
R. S. xl. °89 SHoRE, T. W., Vagus, J. Anat. Phys. ili, 428-451.
*80 SOLGER (Organs of lateral line), A. mikr. Anat. xvii. °73
STIEDA, L., Riickenmark, Z. wiss. Zool. xxiii, 435-442. °73
Toparo, F. (Gustatory buds and branch. membr.), Récherche

BIBLIOGRAPHY: SHARKS 241

lab. univers. Roma. (Abs. in A. Zool. expér.) 534-558. ‘91
VALENTI, G., Histogenesis, A. Ital. Biol. xvi, 247-252. °76
ViauLt, F., Histology, A. Zool. expér. v, 441-528. °83 VIGNAL,
Sys. ganglionaire (Ray), op. cit. i, xvii.

EMBRYOLOGY, GENERAL. —’76 Ba.rour, G. M., in Q. J. M.S.
xiv, and Camb. J. Anat. Phys. xi, pt. I. Also "78 Monograph,
Macmillan, London. °90 BEARD, J., Skate, R. Fish. Board, Edin.
*89 EIGENMANN, C. H. and R. S., Young stages, West Am.
Nat. vi, 150-151. °85 HASWELL, W. A., Young Pristiophorus, P.
Linn. S. N. S. Wales, ix, 680-681. °77 His, W., Ueb. d. Bildung
v. Haifishembryonen, Z. wiss. Zool. ii, 108-124. °81 HOFFMANN,
C. K. (?), Harlem. °88 KAsTSCHENKO, N., Anat. Anz. iii, 445-
467. °70 KowALewsky, A. (Russian), Trans. Kiew. Soc. of
Nat. i. °52 LeypiG, F., Mikr. Rochen u. Haie, Leip. Englemann,
iv, 127 pp. "76 MALM, A. W., Kongl. vet. akad. forhand. Stock-
holm. °42 MULLER, J. (Emb. differences of Shark and Ray),
fol. Berlin. °86 PERENYI, J., Torpedo, Zool. Anz. ix, No. 227,
433-436. °77 ScHuLTz, A., A. mikr. Anat. °92 SEDGWICK, A.,
Q. J. M. S. xxxiii, 559-586. °64, WyMAN, Raja, Mem. Am. Acad.
Arts and Sciences, ix.

I. Breeding, Gestation. —°73 AGassiz, A., P. Bost. Soc. xiv,
339. °90 Atcock, A., J. A. Soc. Bombay, lix, 51-56. (Of
Rays) 92 Ann. N. H. ix, 417-427, and x, 1-8. °79 BoLau, H.
(Of Scyllium), VH. Ver. Hamb. iii, 122-130 and (’81) Z. wiss.
Zool. xxxv. °67 Coste (Of Scyllium), C. R. 99-100, and Ann.
M. N. H. xix, 227. *70 Home, E., Ovoviviparous Sharks. ——
*68 MACDONALD, J. D., and BARRON, CH., Heptanchus, P. Zool. S.
371-373. °85 MATTHEWS, J. D., Oviduct of Skate, J. Anat. Phys.
xix, 144-149. "90 MEHRDORF, C. (Gestation), Rostock, 51 pp.
°72 MEYER (Scyllium), Zool. Gart. 371. ’85 OERLEy, L.
(Gestation), Term. fiizetek. ix, 293-309. ‘90 PARKER, T. J.,
Mustelus, Tr. N. Zeal. Inst. xxii, 331-333. °77 PETRI, K. R.,
Copulationsorgane, Z. wiss. Zool. xxx, 288-385. °75 SCHENK,
S. L., Kiemenfader, SB. Akad. Wien, 12 pp. *79 SCHMIDTLEIN, R.,
MT. z. Stat. Neap. 1, 61. °91 Woop-MAson and ALCcock, Gesta-
tion of Pteroplatea, P. Roy. S. xlix, 359-367, and 1, 202-209.
67 Trois, E. F. (Acanthias’ gestation), Atti. Inst. Ven. 171-176.
77 (Gestation of Myliobatis and Centrina), op. cit. ii, 429.
°77 TURNER, W., Lemargus’ oviducts, J. Anat. Phys. xii, 604-

. 607, and (85) op. cit. xix, 221-222.

Il. Zgg, Gastrulation.—’92 DOouRN, Schwann’schen Kerne, Anat.

Anz. vii, 348-351. °72 GEeRBE, Z., Segmentation, J. de l’Anat.
R

242

III.

IV.

FISHES, LIVING AND FOSSIL

Phys. °81 HERRMANN, G., Spermatogenése, C. R. xciii, 858-860,
and °83 J. l’Anat. Phys. xviii, 373-432. °83 HeERtTwiG, O.
(Middle germ layer), Jen. Z. xvi, 287-290. °83 Horrmann,C. K.
(Middle germ layer), Arch. Neerland. xviii, 241. °92 Endothelial
Anlage d. Herzens, Anat. Anz. vii, 270-273, and 93 in Morph.
JB. xix, 592-648. °88 KASTSCHENKO, Dotterkerne, Anat. Anz.
*90 (Early develop. and muscles), Zool. Beitr. ii, 251-266. °86
KOLLMANN, Fiirchung (C. R. 84), Congr. pér. internat. d. se.
méd. Copenhague, i, Sect. d’Anat. 50-52, and VH. d. Natur.
Gesell. Basle, Th. viii, Heft 1. "78 LA VALLETTE, St. GEORGE, A.,
Spermatosomatum, Bonn, 4to, 9 pp. °79 LUTKEN, Lemargus’
eggs, oviduct, Vid. Medd. (’80) 56-61. °84 PERRAVEX, M. E,
(Egg case), C. R. xcix, 1080-1082. *89 OsTRouMoFF, A., Blasto-
porus u. Schwanzdarm, Zool. Anz. xii, 364-366. °85 RUCKERT, J.,
Keimblattbildung, SB. Gesell. Morph. Miinchen, i, 48-104, and
*89 in Anat. Anz. iv, 353-374. 7°86 Gastrulation (and middle
germ layer), Anat. Anz. 286-287, and ’87 op. cit. 97-112 and
151-174. °91 Befruchtung, Anat. Anz. vi, 308-322. ‘92 Ova-
rialei, vii, 107-158, Chromosomen, viii, 44-52. ‘86 RYDER,
Segmentation, Am. Nat. xx, 470-473, and B. U. S. F C, 8-10.
*82 SABATIER, A., Spermatogenése, C. R. xciv, 1097-1099. "75
ScuuLtz, A. (Ovogenesis), A. mikr. Anat. xi, 569-582. °73
ScHENK, S. L. (Egg and oviduct), SB. Akad. Wien, Lxxiii.
74 Dotterstrang, op. cit. Ixix, 301-308. °90 SCHNEIDER, A.
(Gastrula-muscles), Zool. Beitr. ii, 251-266. °85 SWAEN, A.
(Germ layers and blood), B. Acad. roy. Belgique, ix, and °86 in
A. de Biol. vii, 537-585. °83 Trois, E. F., Spermatozoi, Atti. Inst.
Ven. and J. Microgr. vii, 193-196. °84 VAILLANT, L., Orientation
des ceufs dans l’utérus, B. Soc. Philom. viii, 178-179. °88 ZIEGLER
(Mesenchyme), A. mikr. Anat. xxxii. °92 ZIEGLER, H. E. and F.
(Early development), A. mikr. Anat. xxxix, 56-102.

Integument, Skeleton. —’81 BENDA, C., Dentinbildung, A. mikr.
Anat. xx, 246-270. °79 HassE, C., Knorpel, Zool. Anz. ii,
325-329, 351-355, and 371-374. °82 Wirbelsdule, Jena (°79),
4to. °92 Wirbelsaule, Z. wiss. Zool. lv, 519-531. "60 KOLLIKER,
A., Chorda u. Wirbel. Wiirz. °87 PERENyI, J., Chorda, peri-
chordal. Math. u. Naturwiss. Ber. a. Ungarn, iv, 214-217, and
(89) in 218-241. °93 PLATT, JULIA B., Ectodermic cartilage,
Anat. Anz. 506. "78 REICHERT, Vordere Ende d. Chorda, AH.
Ak. Berl. 49-113. 84 ROSENBERG, E., Occipitalregion, Festschrift,
Dorpat, 26 pp. 4to.

Viscera. —’87 BEARD, J., Segmental duct, Anat. Anz. ii, 646-652.

BIBLIOGRAPHY: SHARKS 243

85 BEMMELEN, J. F. v. (Rudimentary gill slits), MT. z. Stat.
Neap. vi, 165-184. °79 BLANCHARD, R., Fingerformigen Driise,
MT. Emb. Inst. Schenk, iii, 179-192, and (°77) J. de l’Anat. xlv,
442-450. °84 Dourn, Kiemenbogen, Flossen, MT. z. Stat. Neap.
v, 102-189. 87 Mayer, P. (Circulatory), op. cit. vii, 338-370,
and (°88) viii, 307-373. Also Anat. Anz. ix, 185-192. °77
Mayer, F., Urogenitalsys. SB. Gesell. Leip. (76), 38-44. °92
RaBL, C., Venensys. Leuckart Festschr. 228-235. °92 Rar-
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ROcKeErRT, J., Endothel. Anlagen d. Herzens, Biol. Centralbl.
viii. *89 Excretionssys. Zool. Anz. xii, 15-22. °75 SEMPER, C.,
Urogenitalsys. Arb. a. d. Zool. Zoot. Inst. Wiirz. ii. ‘88 WHJHE,
J. W. v., Excretionsorgane, Zool. Anz. xi, 539-540, and Anat.
Anz. iii, 74-76, and 89 in A. mikr. Anat. xxxiii, 461-516.

V. Nervous System and End Organs. —’85 BEARD, J., Cranial
ganglia, Zool. Anz. viii, 220-223, Anat. Anz. iii, 874-905, and
op. cit. "92, I91-206. ‘91 KILLIAN, Metamerie, VH. Anat.
Gesell. 85-107. °88 DOHRN (Motor fibres), MT. z. Stat. Neap.
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Froriep, Kopfnerven, VH. Anat. Gesell. 55-65. °92 LENHOSSEK,
M. v. (Spinal ganglia and cord), Anat. Anz. vii, 519-539. "85
Onoptl, A. (Nerve roots), Ber. Math. Nat. Ungarn, ii, 310-336.
*89 Ostroumorr, A., Froriep’schen Ganglien, Zool. Anz. xii,
363-364. °90 PLaTT, J. B., Anterior head cavities, Zool. Anz. xiii,
239, and °91 J. of Morph. v, 79-106, and Anat. Anz. vi, 251-265.
*96 Punts, G. C., Pineal eye, P. Phys. Soc. Edinb. 62-67. °92
RaBL, C., Metamerie, VH. Anat. Gesell. 104-135. °80 RABL-
RUCKHARDT (Metamerism), Morph. JB. vi, 535-570. °93 Lobus
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VH. Akad. Wiss. Amsterdam. °76 WILDER, B. G., Anterior
brain mass, Am. J. Sci. xii, 103-106.

MORPHOLOGY OF FOSSIL SHARKS.—V. ref. in S. Wood-
ward’s Catalogue, also in present writer's article on Cladoselache,
°94 J. of Morph. ix, 112. In addition, 88 BROGNIART ET SAUVAGE,
Etudes sur le Terrain Houiller de Commentry, Liv. iii, B. de la
S. d. l'Indus. minér. ii, 1-39. °93 CLAYPOLE, E. W., Cladodonts,
Am. Geol. 325-331, and (’95) op. cit. Jan. °93 CopEr, Clado-
donts, Am. Nat. Sept. Also 94 J. Am. N. S. Phila. ix, 427-441.
92-94 Davis, J. W., Pleuracanths, Acanthodians, Tr. Dub. Roy.
S. °94 Dean, B., Cladodont, Tr. N. Y. Acad. Sci. 115-119. °92
JAEKEL, O. (Eocene sharks), SB. Gesell. Nat. Fr. Berlin, p. 61,

244 FISHES, LIVING AND FOSSIL

and Cladodus, l.c. 156-158. °95 SmirH Woopwarp, Primeval
sharks, Nat. Sci. vi, 38-44. :

THE CHIMAROIDS
(Cf. esp. DuMERIL, Ref. p. 238.)

°94 BEAN, T. H., Harriotta, P. U. S. Nat. Mus. xvii, 471-473. 52
Costa (Anatomy), Faun. regno Napoli. °51 Leypia, F., Anat.
and Hist. Miil. A. f. Anat. Phys. xviii, 241-271. 76 HUBRECHT,
A., Kopfskelet, Nied. A. Zool. iii, 255-276, and °77 in Morph, JB.
iii, 280-282. °86 PaRKER, T. J., Claspers of Callorhynchus, Nat.
xxxix, 635. "75 SOLGER, B. (Visceral skeleton), Morph. JB. I,
H.I. °37 Duvernoy, G. Z. (Heart and vessels), Ann. d. Se.
Nat. 1-16. °78 LANKESTER, E. R., Heart, P. Zool. S. 634, and
79 in Tr. Zool. S. x, 493-506. °42 MULLER, J. (Nerves and
heart, critique of Valentin), A. f. Anat. (’43) ccliii. ‘89 GARMAN,
S., Lateral line, Mus. Comp. Zool. xvii. "70 MIKLUCHO-MACLAY
(Brain), Jen. Z. v, 132. °79 SoLGER, B. (Lateral line), A. mikr.
Anat. xvii, 95-113. 42 VALENTIN (Brain and Nebenherzen), A.
mikr. Anat. 25-45. °77 WILDER, Brain, P. Philadel. Acad. Sci.
219-250. °90 ALCOCK, Egg capsule of Callorhynchus, Ann. N. H.
viii, 22. 71 CUNNINGHAM, Callorhynchus’ egg, Notes on the
N. H. of the Straits of Magellan, 340. °89 GUNTHER, Chimera’s
egg, A. N. H. iv, 275-280.

For literature of Fossil Chimzroids v. SMITH WOODWARD'S
Catalogue.

THE LUNG-FISHES

GENERAL (NATURAL HISTORY).—’94 Bouts, Fang u. Lebens- i

weise v. Lepidosiren. Nachr. Gesell. Gottingen, 80-83. °76 Cas-
TLENAU, F., Ceratodus, C. R. lxxxiii, 1034. °92 Dusors, R., —
Respiration, “hibernation,” Ann. S. Linn. Lyon, xxxix, 65-72. —
66 DumeriL, A. M. C., C. R. 97-100, and Ann. N. H. xvii, 160. —

°70 (Swim-bladder, etc.), Angers? °94 EHLERS, E., Lepid,n.s.

Nachr. Gesell. Gottingen. Frirscu, A. (Living and Fossil Lung- —

fishes and their affinities), Prag. 4to. °87 GIGLIOLI (Rediscovery

of Lepidosiren), Nat. xxxv, 343, and °88, Nat. xxxvili, 112.
56 Gray, J. E., “ Lepidosiren,” P. Zool. S. Lon. 342. °88 HOWES, —
Rediscovery of Lep. Nat. xxxviii, 126. "41 JARDINE, W., Ann. —
N. H. vii, 24. °64 Krauss, F., Protopterus, Wiirt. n’t’rwiss.
Jahresber. 126-133. "70 KReEFFT, Ceratodus, P. Zool. S. 221- —

WZ

BIBLIOGRAPHY: LUNG-FISHES 245

224, and Ann. N. H. 221-224, and (’71) P. Roy. S. 377.
*91 LACHMAN, H., Protop. Zool. Gart. xxxii, 129. "73 MARNO,
E., Protop. Zool. Gart. 44. °58-’59 MCDONNELL, R., Protop. Z.
wiss. Zool. x. "37 NATTERER, J., Lepid. Ann. Wien. Mus. II.
*94 NATURAL SCIENCE, Lepid. 324-325. ‘39-41 Owen, Lepi-
dosiren annectans, Tr. Linn. S. xviii. ‘45 PETERS, W., Protop.
Mill. A. °76 Ramsey, E. P., Cerat. P. Zool. S. 698. SCHMELTz,
Cerat. J. Mus. Godeffr. viii, 138. °66 SCLATER and BATEs, Lepid.
P. Zool. S. 34. "92 SPENCER, W. B., Cerat. Vict. Natural. Melb.
‘June to, and P. Roy. S. Vict. iv, 81-84. °89 STUHLMAN, F.,
Cerat. SB. Akad. Wiss. Berl. 32. °87 WIEDERSHEIM, Protop.
Anat. Anz. ii, 707-713, and R. Br. Ass. 738-740.

ANATOMY, GENERAL. —’85 Ayers, H., Jen. Z. Naturwiss. xviii,
479-527. °87 Baur, G., Lepid. Zool. JB. ii, 575. °40 BiscHorr,
T., Lepid. Leip. "71 GUNTHER, Ceratodus, Ann. N. H. vii, 227
and Phil. Trans. (°72) clxi, 511-571, and P. Roy. S. 377-379,
Nat. Nos. 99, 100, 102. °76 HuxLrEy, Ceratodus, P. Zool. S.
24-58. °64 KLEIN, Protop. Wiirt. n’t’rwiss. Jahresber. 134-144.
°78 MIALL, L., Cerat. and Protop. Palzont. S. xxxii, 1-32. °88
PARKER, W. N., Ber. d. Naturforsch. Gesell. Friburg, VB. iv, H.
3, Nat. xxxix, 9-21, and Tr. Cardiff Nat. S. xx. ‘91 Protop.
P. Roy. S. xlix, 549-554. °92 Protop. (Large memoir), Tr. R.
Irish Acad. xxx, 115-227. °66. PETERS, Monatsber. Ak. Wiss.
Berl. 12-13.

SKELETON. —’93 K.aatscu, H., Wirbel, VH. Anat. Gesell, 130-
132. °91 TELLER, F., Skull of Ceratodus, AH. Geol. Reichanst.
xv, H. 3.

MUSCLES. — °72 Humpurey, G. M., Ceratodus and Protop. J. Anat.
and Phys. vi.

FINS AND GIRDLES. —’86 ALBRECHT, P., Protop. Fin forked, SB.
Ak. Berl. 545-546. °91 BoULENGER, Protop. Renewed pectoral.
83 Daviporr, M., Cerat. Pelvic fin. ‘84 GriLL, T., Shoulder
girdle, Ann. N. H. xi, 173-178. °83 HASWELL, W. A., Cerat.
Paired fins, P. Linn. S. N. S. Wales, vii, 2-11. °91 HopLey, C.,
Protop. Renewed pectoral, Am. Nat. xxv, 487. °87 Howes, G.
B., Cerat. Paired fins compared with sharks’, P. Zool. S. 3.
94 LANKESTER, E. Ray, Lepid. Villous processes of hind limbs,
Nat. Apr. 12. °86 SCHNEIDER, A., Zool. Anz. ix, 521-524, and
(87) Zool. Beitr. ii, 97-105. *71 TRaguatr, R. H., Protop. Tail
restored, Br. Ass. R. °90 VANHOFFEN, Cerat. VH. Gesell. D.
Naturf. ii, 134.

246 FISHES, LIVING AND FOSSIL

INTEGUMENT AND TEETH.—’87 Béck Len, H., Cerat. Denti-
tion, JH. Ver. Wiirt. xliii, 76-81. °60-'61 KOLLIKER, A., Protop.
Histol. of Skin, Z. Naturwiss. Wiirzb. i. °65 PAULSON, M.,
Protop. Histol. of epidermis, B. Acad. Sci. St. Pétersb. viii,
141-145. °92 Rose, C., Zahnbau u. Zahnwechsel, Anat. Anz. vii,
821-839. °89 WALTHER, G., Prot. Skin, Z. f. Phys. Chem. xiii,
H. 5. °80 WIEDERSHEIM, R., Scales, A. mikr. Anat. xviii.

VISCERA, VESSELS, GLANDS. —’80 Boas, E. V. (Heart and
arteries), Morph. JB. vii, 321-354. °78 FURBRINGER (Excretory),
Morph. JB. iv, 60. °76 HuxLey, Anterior nares, P. Zool. S.
180. 45 HyrtTL, J., Lepid. AH. d. béhm Gesell. Prag. °78
LANKESTER, E. R., Heart, P. Zool. S. 634, and ("79) Tr. Zool. S.
x, 493-506. °89 PARKER, W. N., Veins (L. cardinal), P. Zool. S.
145-151. '94SPENCER, W. B., Cerat. Vessels (complete memoir),
Macleay Mem. Vol. Linn. S. N. S. Wales, 2-32.

NERVOUS SYSTEM, END ORGANS.—’82 BEAUREGARD, H.
(Cranial), J. de Anat. Phys. xvii, 230-242. °91 BURCKHARDT,
R., Zirbel. Anat. Anz. vi, 348-349. °92 Cent. nerv. sys. Berlin,
64 pp. Also Zool. Gesell. ii, 92-95, and SB. Nat. Fr. Berl.
23-25. °94 (Zwischenhirndach), Anat. Anz. 152. °86 FuL-
LIQUET, G. (Brain), A. Sci. Naturelles, xv, 94-96, and Rec.
Zool. Suisse, iii, 1-130. °94 Prnkus, F. (Undescribed nerve),
Anat. Anz. ix, 562-566, and (Cranial nerves of Protop.) Morph.
Arb. (Schwalbe), 275-346. °89 SANDERS, A., Cent. nerv. sys.
Cerat. Ann. N. H. iii, 157-188. °80 WIEDERSHEIM, Skel. and
cent. nerv. sys. Jen. Z. xiv, and Morph. Stud. Heft 1, Jena. °82
WIjHE, J. W. van, Visceralskel. u. d. Nerven. Cerat. Nied. A.
Zool. v, 207-320. °87 WILDER, B., Brain, Am. Nat. xxi, 544-548. >

EMBRYOLOGY. —’86 BEDDARD, F. E., Ovarian ovum, P. Zool. S.
272-292, and Zool. Anz. ix, 635-637. °8& CALDWELL, W. H.,
(Preliminary), J. and P. Roy. S. N.S. W. xviii, and (’87) in Phil.
Trans. clxxviii. ’93 HassE, C., Wirbelsdule, Z. wiss. Zool. lv, _
533-542. °93 Semon, R. (Habits and development—surface
views of eggs and larve), DS. d. Med. Nat. Gesell. Z. Jena, pp. 50. —

THE GANOIDS

GENERAL (NATURAL HISTORY).—’70 DumErIL, Aug. Tome
ii, pp. 625, Roret, Paris. °35 HECKEL, J., Scaphirhynchus, SB.
Akad. Wien. °71 LUTKEN (Classification), Transl. in Ann. N. H.
329-339. "85 Orr, H. (Phylogeny) Inaug. Dissert. Jena, 37 pp.
65-66 SmitH, J. A., Calamoichthys, P. Roy. S. Edinb. v, 654-

BIBLIOGRAPHY: GANOIDS 247

659, and (°66) 457-479. ‘69 STEINDACHNER, F., Polypterus, SB.
Wien. Akad. lx.

GENERAL ANATOMY.—’87 Twanzow, N., Scaphirhynchus, B.
S. Mosc. 1-41. °54 LeypiG (Histology of Polypterus), Z. wiss.
Zool. v. °50 Lirrany, M., Acipenser, B. S. Mosc. xxiii, 389-445.
44 MULLER, J., Bau u. Grenzen, A. f. Anat. and (46) AH. d.
Berl. Akad. d. Wi Sy *92 POLLARD, H. B., Polypterus, Anat. and
phylogeny, Rick vehgh V, 387-428, and preliminary in (’91)
Anat. Anz. vi, 338-343. ‘48 WaAGNER, A., de Spatulariarum
Anat. Inaug. Diss. Berol. "75 WILDER, B., Notes on Am. Gan,

I. Respir. of Lepid. and Amia. II. Tail formation of Lepid.

Ill. Pect. fin formation of Lepid. IV. Brains of Amia, Lepid.,
Acip., and Polyod. P. Am. Ass. Adv. Sci. xxiv, 151-193.
°76 +Brains, Philadel. Acad. P. xxxviii, 51-53. °78 Amia and
Lepid. rudimentary spiracle, P. Am. Ass. (unpub’d), and Am. Nat.
xix, 192. And in the respiration of Amia, P. Am. Ass. 306-
313. °85 WriGutT, R. R., Notes on anat. of fishes: A. Cutan-
sense organs. B. Spiracular cleft of Amia and Lepid. C. Aud.
organ of Hypophthalmus, Am. Nat. xix, 187-190 and 513. D.
Hyomand. clefts and pseudobranchs of Amia and Lepid. and
Amia, J. Anat. Phys. xix, 477-497. E. Amia’s serrated append-
ages, Sci. iv, 511. ‘87 ZoGRAFF, N., Monograph (Russians) on
Sturgeon, Tr. S. Nat. Mosc. lii, pp. 72. °87 Affinities of ganoids,
Nat. xxxvii, 70.

SKELETON.—’77 BripGE, T., Cranium Amia J. Anat. Phys. xi,
605-622. 78 Polyodon, Phil. Trans. clxix, 683-734. ‘89
Cranial anat. Polypterus, P. Birmingham, Phil. S. vi, 118-130.
B83 CAFAUEK, F. (Prag.). “47 FRANQUE, H., Amia, Folio,
Berolini. “78 GoretrTe, A., Wirbelsdule, A. mikr. Anat. x, 442-
641. °93 Hasse, C., Wirbelsadule, Z. Wiss. Zool. 76-g0. °60
KOLLIKER, Ende d. Wirbelsdule, Leip. °20 Kuyt u. HASSELT
Ost. of Sturgeon, Kuhl’s Beitr. Zool. in Vergl. Anat. 2 Abth.
188-202. °51 MOLIN, R., Scheletro dell. Acipenser, SB. Acad.
Wien, vii, 357-378. *82 PARKER, W. K:, Skull (and develop.) of
Acip. P. Roy. S. 142-145, of Lepidos. 443-491. °83 SAGEMEHL,
M. (Skull of Amia), Morph. JB. ix, 177-227. °92 Scumrpt, L.
(Vertebre of Amia), Z. wiss. Zool. liv, 748-764. °85 SHUFELDT,
R. W., Amia, R. U. S. F. C. (°83) 747-834. °70 Tragualr, R.
H., Calamoichthys, J. Dub. Geol. Soc. June 8. °70 Skull of
Polypterus, J. Anat. Phys. v, 166-183. ‘82 WijHE, J. W. VAN,
Visceralskelet (u. Nerven) — includes Ceratotlus, — Nied. A. Zool.
Vv, 207-320,

248 FISHES, LIVING AND FOSSIL

MUSCLES.—’85 McMurricu, J. P., Head of Amia, Stud. Biol. Lab.
J. Hop. Univ. iii, 121-153. °82 SCHNEIDER, H., Augenmuskeln,
Jen. Z. xv, 215-242.

INTEGUMENT, TEETH.—’78 Barkas, W., Teeth of Lepid. Tr.
Roy. S. N. S. Wales, xi, 203-207. °77 MACKINTOSH, H. W.,
Scale of Amia. (?). °80 PAwLow, H., Teeth of Sturgeon, Arb.
St. Pétersb. Nat. Gesell. No. 9, 494-508. °59 REISSNER, Schup-
pen v. Polyp. and Lepid. A. f. Anat. °87 ZoGRAFF, N., Zahne d,
Knorp. gan. Biol. Centralb. vii, 178-183 and 224.

VISCERA. —’86 CaTTANEO, G., Glandula gastriche nell’ Acip. Rend.
Inst. Lomb. xix, 676-682. "78 FURBRINGER, Excretory sys. Morph.
JB. iv, 56-60. °72 HERTWIG, R., Lymph. Driisen d. Stérherzens,
A. mikr. Anat. ix, 62-79. HOEVEN, J. v. D. (Air-bladder of
Lepid.) 4to. (?). °91 Hopkins, G. S., Structure of stomach
of Amia, P. Am. Micr. S. xxii, 165-169. °92 Diges. tracts of
N. A. Gan. P. Am. Ass. xli, 197. °69 HyRTL, J., Blutgefisse
d. aus. Kiemendeckel-Kieme v. Polyp. SB. Ak. Wien, lx, 109-113.
*86 MACALLuM, A. B., Diges. tract and pancreas of Acip., Amia,
Lepid. J. Anat. Phys. xx, 604-636. °91 SEMON, R., Zusammen-
hang d. Harn- und Geschlechtsorgane, Morph. JB. xvii, 623-635.
°77 STOHR (Valves in conus—compares sharks’), Morph. JB. ii,
197-228. °90 VircHOW, H., Spritzlochkieme v. Acip. A. Anat.
Phys. (Phys. Abt.) 586-588. °86 WILDER, Serrated a
of Amia, P. Am. Ass. xxxiv, 313-315.

FINS. —’94 GEGENBAUR, Flossenskelet d. Crossopterygier, Morph. ;
JB. xxi, 119-160. °82 RAUTENFELD, E. V., Skel. hint. Glied-
massem Inaug. Diss. Dorpat, 47 pp. °77 THACHER, J, Ventral
fins, Tr. Connec. Acad. iv, 233-242. °80 Daviporr, M. V.,
Skel. d. hint. Gliedmassen, Morph. JB. vi, 126-128 and 433-468.
°66 HUXLEY, Illus. of struc. of Crossopt. 4to, Lon.

NERVOUS SYSTEM, END ORGANS. —’89 ALLIs, Lateral line
of Amia, J. of Morph. °83 CartrTiE, J. T., Epiphysis, Z. wiss.
Zool. xxxix, 720-722, and A. de Biol. iii, 101-196. °94 CoL- —
LINGE, W. E., Sensory canals, of Polypterus, P. Birmingh. S.
viii, 255-262; of Lepid. op. cit. 263-272; of Polyodon Q. J. M.S.
xxxvi, 499-437. °83 DOGIEL, A., Retina, A. mikr. Anat. xxii, 419-
472, and ’84 Naturf. Ges. Kasan, xi, 124 pp. °86 Geruchsorgan, Tr.
Kasan. Univ. xvi, 82 pp. °88 Retina, Anat. Anz. iii, 133-143.
°79 Gisow, A., Gehérorgan, Bonn. °81 Gisow, A., Gehérorgan,
A. mikr. Anat. xviii, 484-519. °88 GoronowitTscH, N., Gehirn
u. Cranialnerven v. Acip. Morph. JB. xiii, 427-514. °70

BIBLIOGRAPHY: TELEOSTS 249

MIKLUCHO-MACLAY, N. v., Mittelhirn, Leip. 4to, pp. 74. ‘81
Retzius, Gehérorgan,v. Polyp. Stockh. °81 SCHNEIDER, H.,
Augenmuskelnerven, Jen. Z. viii, 215-242. °87 WALDSCHMIDT,
J., Centr. nerv. u. Geruchsorg. v. Polyp. Anat. Anz. ii, 308-322.

DEVELOPMENT. —’°78 AGassiz, A. (Larve of Lepid.), P. Am.
Acad. A. and Sc. xiii, 65-76. °89 AtLtis, E. P., Lateral line,
Amia, J. of Morph. °81 BALFour and PARKER, Str. and devel. of
Lepid. P. Roy. S. xxiii, 112-119, and *82 in Phil. Trans. (large
memoir). °89 BEARD, J., Early devel. of Lepid. P. R. S. xlvi,
108-118. °95 DEAN, B., Early devel. gar and sturgeon, J.
Morph. xi, No. I, 1-62. °82 DunsBar, G., Breeding of Lepid.
Am. Nat. May. °94 FULLEBORN, F. (Breed. habits Amia and
Leipd.), SB. Akad. Wiss. Berl. xl, 1-14. °67 GEGENBAUR, Wir-
belsdule d. Lepid. Jen. Z. iii, 359-414. °93 JUNGERSEN, H. F. E.,
Embryonalniere d. Stérs, Zool. Anz. 464, and (94), Amia, op. cit.
No. 451. “70 KOWALEWSKY, OWSJANNIKOW, U. WAGNER, Stor,
B. Acad. St. Pétersb. xiv, 287-325, and Mél. Biol. du B. Acad.
St. Pétersb. vii, 171-183. °91 KuprFER, K. v., Kopf. v. Acip.
SB. Gesell. Morph. Miinchen, 107-123, and (93) memoir, Leh-
man, Miinchen. *90 Mark, E. L., B. Mus. Comp. Zool. xix,
1-127. °82 PARKER, W. K., Skull of Lepid. and Acip. P. Roy.
S. °87 PeLTsaAM, E. D., Segmentaticn (Russian), MT. Gesell.
Mosc. Univ. I, Heft 1, and Protocolle d. SB. Zool. Sect.
Mosc. (86) I, Heft 1, 206. °89 Ryper, J. A., Sturgeon, Am.
Nat. xxii, 659-660, and (90) B. U.S. F. C. viii, 231-281. °78
SALENSKY, W., Sturgeon, SB. Gesell. Nat. Kasan (77), 34
(Russian). Also Post-Emb. Entwickel op. cit. (°78) 21 (Rus-
sian). (Segmentation) Zool. Anz. (’78) 243-245, and (Skeleton)
266-269, 288-291. (General) Mém. S. Nat. Univ. Kasan, vii
1-226 (Russian). 80 Pt. II, Post-Emb. and Organogeny, op.
cit. x, 227-545. Abstract in HOFMAN and SCHWALBE’s JB. vii.
213, 217-225. ‘81 (French), A. de Biol. ii, 233-278.

THE TELEOSTS
(Literature greatly summarized.)

GENERAL ANATOMY.—’93 ParkeER, T. J., Zodtomy (Cod).
*88 ROLLESTON, Forms of animal life, 83-102, and 95 VoctT and
JunG, Anatomie comparée, Vol. II. °80 Emery, C., Fierasfer,
Fauna u. Flora d. Golfes v. Neapel, ii.

SKELETON. —’83 Brooks, H. S., Haddock, P. Roy. S. Dub. iv,
166-196. °90 GiLL, T., Skeleton. notes, P. U. S. Nat. Mus. xiii,

250 FISHES, LIVING AND FOSSIL

157-170, 231-242, 377-380. 79 GogrTTE, A., Wirbelsdule u.
Anhange, A. mikr. Anat. xvi, 117-142. "84 Gio}, E. A. (Derm
bones of Catfish, Balistes, Acipenser), Jen. Z. xvii, 401-447. °82
KosTLER, M., Knochenverdickungen, Z. wiss. Zool. xxxvii, 429-
456. °73 VRoLix, A., Verknickerung, Nied. Arch. Zool. 219-314.

TEETH, INTEGUMENT.—’78 Boas, J. E. V. (Scarid dentition), Z.
wiss. Zool. xxxii, 189-215. °78 CARLET, M., Ecailles, Ann. Sci.
Naturelle, viii, Art. 8. °86 ScHAFF, E., Lophobranchier, Inaug.
Diss. Kiel.

VISCERA, GLANDS, CIRCULATORY.—’80 Boas, J. E. V.,,
Conus, Morph. JB. vi, 527-533. °87 Brock, J., Urogenital, Z.
wiss. Zool. xlv, 532-541. °91 CALDERWOOD, W. L., Head kidney,
J. Mar. Biol. Ass. ii, 43-46. ’82 Emery, C. (Kidney), A. Ital.
Biol. ii, 135-144, Atti. Acc. Rom. xiii, 43-49, (’85) Zool. Anz.
viii, 742-744. °77 FURBRINGER (Excretory), Morph. JB. iv, 43-
49. °83 MAURER, F., Pseudobranchien, op. cit. ix,229-251. ’86
Thymus, op. cit. xi, 129-172. ’86 WEBER, M., Abdominalporen
(Geschlechtsorgane), op. cit. xii, 366-406.

SWIM-BLADDER.—’90 BripGE, T. W., P. Birm. Phil. S. vii, 144-
187. ’89 BRIDGE and Happon, A. C., Siluroids, P. Roy. S. xlvi,
309-328, Phil. Trans. (’93) clxxxiv, 65-333. °88 CORNING,
H. K., Wundernetz, Morph. JB. xiv, 1-53.

NERVOUS SYSTEM, END ORGANS. — ’82 Carttir, J. T., Epiph-
ysis, A. Biol. iii, 101-196. °88 CHEVREL, R., Sympathetic,
C. R. cvii, 530-531. ’91 GuUITEL, F., Ligne latérale, A. Zool.
expér. ix, 125-190, 671-697. °92 HERRICK, C. L., Fore-brain,
Am. Nat. xxvi, 112-120, and Anat. Anz. vii, 422-431. ’87 LEN-
DENFELD, R. v., Phosphorescent organs, Challenger, xxii, 277-
329. °81 MayseEr, P., Gehirn, Z. wiss. Zool. xxxvi, 259-364. "84
SEDE DE LIEoux, P. DE, Ligne latérale, Paris, 115 pp.

EMBRYOLOGY, GENERAL. —’91 Whitson, H. V., Sea-bass,
U.S. F.C. B. ix, 209-277 (with references). ’81-’91 RYDER, J.
A., U.S.F.C. R.and B. Larval Teleosts:’77 AGAssiz, A., P. Am.
Acad. v, 117-126, (’78) xiv, pp. 25, (°82) 271-303, and Mem.
Mus. Comp. Zool. xiv, 1-56. ’87 CUNNINGHAM, J. T., Tr. Roy. S.
Edinb. xxxiii, 97-136, (91) J. Mar. Biol. Ass. ii. °83 HILGEN-
DoRF, SB. Nat. Fr. 43-45. °90 Hott, E. W. L., Sci. Tr. R. Dub.
S. 432-474. °80 LUTKEN, C., Dan. Selsk. xii, 413-613. ’91
McIntosh, W. C., R. Fish. Scot. ix, 317-342. ’90 McINTOSH and
PRINCE, Edinburgh, 4to. °87 RAFFAELE, F., MT. z. Stat. Neap.
viii, 1-84, (90) ix, 305-329.

BIBLIOGRAPHY: TELEOSTS At ono ee

APHRODITISM. —’91 Howes, G. B., J. Linn. S. xxiii, 539-

558. 67 JACKEL, H., AH. Nat. Gesell. Niirn. iii, 245. °76'MALM,
A.W.,CE. v. Ak. Forh. Stockholm. '67 Sarru, J. A., P. Roy. S.
_ Edinb. ’64 '65, 300-302, (’70) J. Anat. Phys. iv, 256-258. ’91
a ‘Smirn, W. R., R. Fish. Scot. ix, 352. °84 WEBER, M., Ned.
"Tijdschr. Amst. 21-43, (°87) 128-134.

-AROUS DEVELOPMENT. —’85 Ryper, P. U. S. Nat. Mus.
4 viii, 128-156 (with references).

252

FISHES, LIVING AND FOSSIL —

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253

SKELETON OF FISHES

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Figs. 310-315. — Skulls of fishes, to illustrate the mode of articulation of jaws and
branchial arches, 310. Skull of Scy/lium. (After MARSHALL and sett gir. He
tanchus (Notidanus). (After HUXLEY.) 312. Chimera. 2 313. Ceratodus. (Slightly m
fied after HUXLEY.) 314. Polypterus. 315. Salmon. (After PARKER.)

A. Articular. AG. Angular. BR. Branchiostegal rays. CHY., Ceratohyal. D. —
Dentary. EAHY. Epihyal. LPH, LG. Epihyal ligament. PO, Epiotic. / Frontal.
GHY, Glossohyal HHY. Hypohyal. AWM. Hyomandibular. /O. Interoperculum,
F. Jugal. LC. Labial cartilages. MCK. Meckel’s cartilage. MP7. Metapterygoid,
MSPT,. Mesopterygoid. MX. Maxillary. NM. Nasal. NC, Nasal capsule. O.
lum. OC. Opercular cartilage. Of. Suborbital ring. /. Parietal. PAZ. e,
PMX, Premaxillary. PO, Preoperculum. PTZ7O, Pterotic. P7Q. Palatoquadrate.
PTY. Palatopterygoid. @Q. Quadrate. SQC. Supraoccipital. SZ. Supra-ethmoid. SA
Symplectic. SO. Supraorbital. SP. Splenial UAC. Upper median (not
frontal spine of male),

Figs. 310, 314, 95 are regarded by HUXLEY as “hyostylic” (7.e. the hyoid element,
HM, attached by ligaments to the jaw hinge, ens! an important part in su
of the jaw; 311, a modified hyostylic condition; the hinder upper margin of Nad m-
ing greatly enlarged, and attached by ligaments to the skull, is spoken of as “amphistylic";
312-313, were “autostylic,” ze. the upper jaw element fused with the skull.

254

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FISHES, LIVING AND FOSSIL —

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Figs. 316-325. — Heart and arterial cone of fishes, 316, Heart of shark; 317, Heart
of catfish, Si/urus glanis ; 318, Heart of shark, shown opened at the side. 319. Conus
arteriosus (inner view) of Chimera. 320. Conus of Ceratodus. 321. Conus of Protopte-
rus. 322. Conus of Lepidosteus. 323. Conus of Amia. 324. Conus and bulbus of the
Teleost, Autrinus. 325. Conus and bulbus of the Teleost, Clupea. (Figs. 316-318
after WIEDERSHEIM, 320-325 after BOAS.)

A. Aorta, AU, Auricle. &. Bulbus. C. Conus. V. Valves. VEN. Ventricle.

258

NEES

MN
|

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SS;

_

——_ LI

Figs. 9-12. — ement of gills of Bdellostoma (9), Myxine (10), Shark (11), and
Teleost (12). In each figure the surface of the head region is shown at the left.
B. Barbels. BD. Outer duct from gill chamber, BS. BO. Common opening of outer
ducts from gill chambers. 4.5. Branchial sac, or gill chamber. 4.5’, Branchial sac, sec-
med so as to show the folds of its lining membrane. G. Lining membrane of gullet.
GB. Gill bar, seppenting vessels and filaments of gills. GC. Outer opening of gill cleft.
GF, Gill filament. GA. Gill rakers. GV. Vessels of gill. ¥, ¥'. Upper and lower jaw.
4M. Mouth opening. N, NV’. Anterior and posterior opening of nasal chamber. OP, Oper-
culum. SP. Spiracle. $7, Tendinous septum between anterior and posterior gill filaments.
* Denotes the inner branchial opening; -+, the direction of the water current,

259

FISHES, LIVING AND FOSSIL

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261

GILLS AND GILL DEFENCES

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Figs. 326-331. — Digestive tracts of fishes. 326. Cyclostome, Pefromyszon. 327. Shark. —
328. Chimzeroid, Callorhynchus. 329. Lung-fish, Protopterus. (After W. N. PARKER.) —
330. Ganoid, Acipenser sturio, 331. Perch. (After WIEDERSHEIM.)

A. Anus. AC, Branchial chamber. BZ. Bursa entiana (duodenum), CL. Cloaca, —
GC. Gill openings. /. Intestine. J. Mouth, MM/. Mid-gut. NN’. Anterior and poste-
rior nares. OZ, Gullet. PC. Pyloric coeca (pancreas). PY. Pyloric end of stomach, —
Fe Rectum. #G, Rectal gland, S, Stomach. SP. Spiracle. SP. V. Spiral intestinal —
valve,
262

263

DIGESTIVE TRACT

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FIG, 13

ap. STURGEON

AND MANY
TELEOSTS

LEPIDOSTEUS
AND AMIA

ERYTHRINUS

CERATODUS

POLYPTERUS
AND

LEPIDOSIREN
AND
PROTOPTERUS

Figs. 13-19. — Air-bladder of fishes, shown from the front and sides. Cf. p.
264. A, Air-or swim-bladder. AD. Air duct. D. Digestive tube. (After WILDER.)
13. Sturgeon and many Teleosts. 14. Amia and Lepidosteus. 15. Erythrinus, a
Cyprinoid Teleost. 16. Ceratodus. 17. Polypterus and Calamoichthys, 18, Lepi-
dosiren and Protopterus. 19. Reptiles, birds, and mammals. The diagrams illus-
trate the paired or impaired character of the organ, its varied mode of attachment
to the digestive tube, and the smooth or convoluted condition of its lining mem-

265

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“ln, fw et
A AP

Figs. .— Urinogenital ducts and their external openings. 332. Cyclostome,
Petromyzon, (After W. K. PARKER.) 333. Shark, 9. oo Chimeeroid, juv. 2. 335.
Ceratodus. 336. Ganoid, 2. 337. Teleost (Salmonoid), 2. (After BOAs.)

A, Anus. AP. Abdominal pore. CZ. Cloaca. G. Genital opening. MD, MD’.
Left and right Miillerian ducts. OVD, OVD’. Left and right oviducts (not Miillerian
ducts). #. Rectum. U, U’. Left and right ureters. UG. Urinogenital opening. UG’,
UG". Left and right urinogenital ducts. UG/P. Urinogenital papilla, showing distal
opening. UGS. Urinogenital sinus. UP. Urinary papilla,

267

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FISHES, LIVING AND FOSSIL

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*(snuls jeytuesouLn jo JO) vovojO Jo uLsreu uIYIIM ysnf ‘yUdA JO Opts JayjIO UO ‘parE *sourojs0[9A9

SHuUXOd “IVNINOCGAV “AIX

*SO]OIUUTY Ul U1I9} 9Y} JO 9SUdS 94} UT SOIydouLjoUr ay OU ATquqoIg »

*pur[Z oy Jo souvysqns
ay} Ul SoUMeEUIOS st Id}0r
*uinjoa1 0} sassed SZuruado
Lisa gaan awos bat “Bur
-uado ensn
&xeuuip) “uaa putysq Sutuado
ee a ee a an

beste oO eur sjan ’ *“yuonguos AN

yew woody ajyeredas aq ion 10 pm mi (‘A9;sesa1

: paun 10 ojeredes oq Avu ‘aSre] Ar9a oq Aeur | ur suonoung

(syonp [ewuauZos =) s19}019) ae | hae ”» ae saayey :suonouny ”» oo” *s}S00T9L

“ut ovat Ajoyes

-edas uado siajoin | juasaid

(Qonp an JO t1M0133N0

Paqoiig & =) sappeyq Areuts
” ” ” ” ” ” ” ” ” i ” ” ” ” “vary
” ” ” ” ” ” ” ” ” ct ”» ” ” ” “sna}soprdaT

EXCRETORY SYSTEM: ABDOMINAL PORES

FIG, 339

Figs. 339-344. — The brain of fishes. The dorsal view of each brain is shown in the —
upper figure, the ventral view immediately below. 339. Bdellostoma. (After JOH,
MULLER.) 340. Petromyzon (Ammocates stage). (After ZIEGLER’S model.) 34%.
Shark (angel-fish, Sguatina), (After DUMERIL.) 342. Chimera, (After WILDER.)
343. Lung-fish, Protopterus. (After BURCKHARDT.) 344. Perch, Perca, (After T. J.
PARKER.) an
. AQS, Aqueduct of Sylvius. DSZ, Diverticula of saccus endolymphaticus. 2, —

272 :

e

Epiphysis. £P. Epencephalon. JN. Infundibulum. ZH. Lobus hippocampi. Z/. Lobi
inferiores. 7. Lamina terminalis. 47. Mesencephalon (optic lobes). M/Z. Myelen-
cephalon (spinal cord). 4/7. Metencephalon (medulla). 4/7". Anterolateral lobes of
metencephalon. /. Prosencephalon (cerebral hemispheres). 7: Pituitary body. 2.
Olfactory lobes. SV. Saccus vasculosus. 7. Thalamencephalon. V4. Fourth ven-
tricle. Numbers /—X. Cranial nerves. ,s. First spinal nerve.

Z 273

FISHES, LIVING AND FOSSIL

274

[e1aye] OUT POPIAIP ssa] 10 BOUL,oPENUAA WIM uopvyderuasoad Sqing LILO MOIJOY ¥ OU! soB¥[Ua Udy) pUR ‘pros |
JO Mo[JoY ‘snyovs, & OpuY AjLoPLa}UB SoNUUOD qo] A1OjoRJ[O-sod payieUl-ljam v :payeredas [Jom sed sy !oyeTuoja ureig “youLsqowsETY
“sousty

’

*s19Xv] peons0o ou | Ajje1oued poseyeos aie s[jao DAJOU dy} BOULISqNS UTeIq By} UT “siNd90 SaAiou ONdo ay} Jo vUIsETYD
¥ ‘pqnop wayss snoyyedwidg 9 “ayrun you op jnq ‘sayouviq [ejUaA puv [esIOp OU! BPIAIP YIOq ‘sjO01 JOLaysod pue
JOLAjUY oywUIAY" SaAioU S}t ‘gq UL Se peuayey proyo eulds ‘woyvydaruszau ayy Ut (st[eploquioys snuts) Suruedo proiq
B WE sy puryeq { [ews uogvydsruega : Suyuado [ejuad yusurWOId puL saqo] [esIOp YIM wozpygaruasaue ‘ Sa10LIAZUT IQO]
pue wnyjnqipuryur poyivur-jjam ev !snxaid sojayur Suryou| ‘suxajd prosoyo ajduus v ‘(¢) wmjaa ou ! (¢ afa peourd) ueB0
pus yr yyeys persXydida Suoj w ‘yuau;woid pue pastes wovy¢s 7PYF JO SAGO] ‘sntLO,O¥gO}sod 10 1duredoddry 1qo]

ou ‘ajoorydurerwoy ‘saousurmoid ayeredas yum wevsg-240f ajqeysinsuysip Ajrpear a1ow syred sy !g ul uey) Je#uo] uremg

*sinooo Ajqeqoid saasou ondo ay} jo vuseIyo YW ‘sn3ea oy} Jo youvlq [euNsayut
Suoj oy Aq poywuasoidas se popreSa1 oq 31 ssajun uasaid wiayshs onayyeduids ON’ 1990} asNy s}OOI 1OLI9}Ue jo Ited
qos Woy paaLiop seyouviq [esiop ynq ‘ayrun AjUO sjOOI [eUDA dy} ASA} JO 13001 AOLIa}sOd I 0} JOLI|}Ue z Ajpe19UaT
WIA saaiou st ‘Ajpenuaa-osiop pousyey poo jeurdg ‘sainssy [esjUIA pue [esIOp asioasuey ydniqe Aq ureiq oy) Woy
payeredas ‘Suuode; Ajdreys pue api (wozvydaruazaue) eyynpowt ‘ MoLINy [esiop uvIpaw YIM (wozvyge2uags) wINI[aqaia9
pue (woypyge2uasam) saqo, ondo ‘juaurmoid ‘iaaamoy ‘sisXydida tpaonpar Avoid Ajuaredde uozvyga2uauvzvy; ayy

JO uolZer oy) ‘ poyervdas Ayjred (wopvyga2uasozg) saqo, yeiqaiad : payetedas saqoy A1ojowjo ‘ (¢) pros oeduroo ‘jews ureig

soysy jo sdnoi3 ay} ury}IM saouarlayIp yurzodurt aout oy} Jo Arwwiuins y

(PrE-6EE “sB1q JD)

SHHSIH AO WHLSAS SNOAYHN IVALNAD AHL “AX

‘uozAwo.nag

*BUlO}sO][Epg
*soumozsopoAg

275

*s[]90 [BONIOD OY} JO UOHRNUAIAYIP JO S9OVI} YIM JO ‘SNOAIOU-UOU SI UTCIq-9105
ayy Jo soos at ! payenuosayrp A[ySi1y st urerq oy) Jo douLJsqns oY], “SplouND sUIOS puv sxIvYs Uy sv ‘sn3va ay) WIM
you ‘(sayerqaziaa JOySIY Ul sv) PATO [eLULIO PITY) 94) YIM Aj1OLI9jUeB S}OoUUOD wiajsks onayyeduits oy, “INd90 jou svOp
euiserqo ondo uy ‘a[oLnuaA YyyINoy ay} Jo uoISa1 ayy Aj1OL1a}sod Suyjesoucs puv Suiddejioao ‘yuourwoid uozvydgaruaga
t posred Apounsip ‘azts yeo18 yo saqoy (Ondo) |esiop s,mozpydgaruasoue ayy £kpoq Areyinqid yuourwoid v puv saloLiajut 1qo}
paSigjua Ayvord yt ‘sin900 wnynqipungur Suo] & apis [e1jUBA By} UO ‘ Paploy Apysys ‘ajduits snxajd proroyo oy} pue
‘Krgjuounpni st sisXydide sy ! Mata pesiop ur uses oq 0} ATprey yng ‘api uopvygaruauivyoys : (¢ yureooddiy snqo[) paqot
Ayounsip uorgar yesiop sy ‘paonpar Ajpjeoid saqoy ArojovyzO sy ‘[peus uopoygaruasoag ayy ‘poyipow Ajapia siajov1eyo
jeorSojoysty st pu ‘ySus] ur paonpar Award uyeiq ay], “SUONIPUS ULIYOULIGOWISE|I 0} a[QuIJor a1B SaINjONLYS
Si YOIYM YSnosyj ‘sprouedy oy} Jo yey} JO UOHVoyIpow suUloyXe Uv SU pepive1 aq Avur sysoajay, jo wiayss snoasou oy], *yS029]9,L,

*s19XhR] [LONIOO OM} OY] OJUT PUB VoUYSqnS
AaiZ yexyuao & O}UT poyeNUaroyIp useq aavY S{[90 uoysued pue !oyeuys Ajoanruntd st wnyenjs sndioo ay} ‘ payenuasayip
Ayurey ynq axe uresq ayy jo sijeo oarou ayy, *(104Ied “N “M ¢) Supuem wajsks onewmajsks y “exT-yLeYs JeI9UET
ut pioo yeurdg 9 ‘payeorput Ajurey saarou ondo ay} jo vulseryo oy ‘snoneydusjopus snooes ay} JO BINOIM@AIp UPI
JOAO P2JOOI St IOLIUIA YANO ayy Ajsolsa}sod | yeYs JO soy} 0} AVIPWIIS Soqo] [w19};e[-ONUL Suoppygaauaaut Sejapoiyy
pue Asidwe, jo suonrpuoo ay} SunseSsns ‘payenuosayip you (¢ snpoyesaD ut) uoppygaouaga ‘Ssoayey OjUL paprlAIp
Ajpreajno jou ‘ureiq-a10j oy) uLY} JoyeUIs svy wozvyderuasau ‘ Kpoq Areymytd yuauyword pur ‘sozopayur tqoy snonards

-uooUut YIM Mofaq ‘snxajd proroyo poproy puv sisXydida yuourwosd ym ‘Buc, puv Mo1eU uopvygoquaunyoy, *yauasaid (*sn.10}d0}014)
iduresoddiy 1qoj !seqol A10joRO payeyip uy Ajrorsayue oyeurutts) Yyorys ‘soayey OUT poyeredas ureiq-o10j ! ayeSuoja ureig *ysy-dun’'y]
‘syreys Ut

se Ajqeqoid wiaysXs onoyyeduiss pur ‘saarou ‘pioo yeuldg ‘saasou ondo jo vuseryo YW “Se1OLJUt [qo] adie] = ‘apu}
-u9A ypNos oy} jred yeorS url JaA0 Suygoos ‘pauopim Apwasd savy suuts [euLSivur sy ‘paynjoauoo Ayeoid are uozpygoruajaue
ayy JO Soqol eae, JOO;UE oy) / wopvyde2uasem ayy SuyeaduD ‘syed UTeIq Surureuias oy} aaoqe ysty peyenyts
pur ‘aSre; woppydesuade ayy ! poyeSuoja Avoid uopvydorusunypys oy) ! IOS aIQUAIwUIaL ¥ JO Inq ‘OyL Ys [e19UES Uy UTI, — “PyoraeatyyD

*SurdnosZ pwoys00 uly) B Jo seoRT) jNq IPIM ‘opuULUT aINUe OY} NOYSNOIY) Po19}ywOS Iv S]]99 uoysues | payenuasaytp
apy mq ore uorBar ureiq oy Jo sjjeo ay, ‘sIM990 vUseIyD oNdO UY ‘sNBva ayy YIM poyouUoS yuasoid st wioyshs
oneyeduks y “saysy somo ur sv Ajjenuassa saasou yeurds puv pros jeurdg ‘uado Ajapim pue ‘Moyfeys “Su st 9[o|UDA
nos op / uopvydaquage pasivs-[jom & MO[Oq AjoyeIPoUIUIT SyPMOISINO [CIOye] JOPLaJUY YIM Mozy soruazeue { uopoy ga?

NERVOUS SYSTEM OF FISHES

— ia ss
E a

FISHES, LIVING AND FOSSIL

276

Hil eget Aaa wien cagae

~noaorwas € oy ! payequasaytpun ynq
‘poisons ase snssoo01 pue snjnsows
S9OBPINS 9} WIM uUoNOaUUOD uUdado
(4jrensn) Suruyeyaz ynq ‘aSejyseo poy
oy Ut peppaquia ‘ajduls ajnqnsa,,

‘dy snoqing & yi ‘ty 3u9]
ul paonpar st (prourxAyy) snoneydurd|
“opus snjonp ayy, ‘in990 syj}mo13
NO IVjNILyN pue sensovs ajduurs pue
ayndwe aye ay) ut ! uozAwoNag UI
(1eon194) & pure ‘sprourx<yy ur euro

_avmoujorwias ‘ynojys ‘asus ev peppy

SI SIY} 0} Sa0RpINs oY} YIM payoouu0D
Ja3u0j ou ynq ‘ey!D WLM pour] anqusoa
JO sjstsuoo ! padojaaapun pur |[eug

"uvd4Q Kaojipny

‘spuvj3 oN ‘quasaad Ajyensn (spjoy
[euliap) pryjefo pue auviquiow Sur
yeyoru Sasvlyswo yA pousysuays
onossjos ‘ajduis ‘adr, ojnsdep

*yuasoid st wnjade} oN
*eauIOO Se Sutuonouny urys Suidj1aa0
ay} ‘aJooowWULY Ul Suryouy osje are
asay} ‘sual ‘SLT ‘oMOraIOs ‘sajosnu aka
SOV] splourxAy ur ! uozhwoeg yNnpe
ay} Ul s}usUIa[9 [eNSN oY} suTEJUOD

"ah

ss pucseoaea Sioa Ine 20 tose sda yee
ay, “Wwaoe[pe sjasopo ‘qing Az0}9eyI0 snowoUD
ue WO peatiap st (SUI ][e Ul Se ‘payeT[NpoUT
-uou) Ajddns: aarou sy |! umryamyide Arosuas
ay} Supvaq vides Sunerpes ynojs yum ‘padeys
-dno ‘adiey Ajaayejer ajnsdva A10;oRo yory

~ “paired st ajns
-deo A1ojoRjo oy} Jo Ajddns saiou ayy, ‘yoo!
you oy} ysnoi1y} Suruado yeyuaa ueipau
e (sprourx4jy ul) pue oor pray oy} ur 10
uorgal ynous 94} ur Suruedo pairedun uv ‘ ureiq
ay} JO jUOY ut Ajayerpowurw pray oy} ur payuyjd
-ut Ajdaap ajnsdeo ay) ‘porredun Aquoreddy

“uDSAQ) MSDN

SNVOYO ASNHS AHL ‘IAX

277

THE SENSE ORGANS

“Te snourse]
-yIeo IO snouviquiow Aq ureiq Woy

poyeredas uesiQ ‘“payipow Ajapim
‘adie, suo} «= *vuase, yuoururoid
uayo oyeSuoja qIM yo pajonjsuoo
]]@M snnooes ‘juourwoid snssao01
Saovpjins oy} ye uado Jasuo] ou joNp
tsainjonys pozieroeds Auvw wt

*A[UO [BAK
snouviquoam Aq uteiq woy pojer
~edes uvSiQ) ‘euaSy, ayy-qingq WIM
snjnooevs ‘pedojaasp ait smssaoo1
+ S¥IBYS Ul SB JONp sy puv anqnsap,

*Atuo [prem
snouviquiaw Aq ureiq woy poyeredas
UBBIQ *paajoaa Apoayiod a10u svadde
aeyndwe pue ‘snssacar ‘snnooes aq)
+yaeqs Ul se jONp sy pu anqnso~

*yuasaid st umjody} oN
*eayuasie puv PlOlOYO UIaMJoq BAIDU
oydo svau simooo Ayjensn pues pro1
-oyo Y ‘“uoNepourwooor ur Ajqeqoid
peuis0U0d st Wt !suay ay} Jo IOyenbo
ays GWA (LayeET ejnuvdures oy} Aq)
Ajpeystp paiauuos st pue ‘qinq oy}
JO youq oy} je sastie (1e[NoOsnur ‘snoa
-I9u ‘re[nosvaA ‘pajuow sid) ssaooid
wWuosloyyy B !yuaseid vajuesie | Kuoq
uayo ajnsdeo ‘pazteroads A[yS1y aAqy

*eauasiv ON ‘soposnur
Axerpio ut “aaamMoy ‘Suryovy ‘vaur0o ay}
Suiyono} ysourye ‘yeorayds ‘asrey sual
faanyenosnur a1qooj YIM ‘|peus aAqT

“SYIBYS JO-9SOY} O} AV[LWITS
SI9}OVIVYO S$} ‘azZISs yeaid yo ajnsdea

‘ayl-eqn} psonpoid usyo suits peyoo I9y} ‘[pews
‘ayeredas ore sSuruado [eseu oy} ! prey oy} jo
OPIS [esiop-o019}e, oy} UO Ajrensn st uOHIsOd sy
‘Sqinq jeseu psonpal Ajyyeal3 yuaoe[pe oy) Woy
st A4iddns oasou st ‘vjdes A1osuas ynoyM 10
UUM ‘Tews ‘paus}ey ‘Moyjeys ojnsdevo yeseN

‘sdey [eulop ou ore osoy) | ayeid ,, autiowioa,,
ay} JO UISIeUI JOUUT ay} ye YINOW oy) UIYIM
Jaye] dy} “nous ay} JO ul oY) UIQ sreodde
Jawio0y oy} ‘ajnsdeo se(nqny ay} jo ssurusdo
ay} ore sareu Jolajsod pue 10Lajue 94} {azIs
ul paonpar Apeord st aasou st! vjdas (Sunerper
Ayysys) ssioasuey yy ‘saps oy} ye pouayey
‘re[nqn} yeyMoulos ‘ayeSuoja ‘ajnsdeo jeseNy

*saqeid yejuap ,, oULIOWIOA ,, pue oun
-eyed jo anjounf oy) ye uLsiew dy oy yyeouaq
SI slivu Jor19}sod oy} ‘dy ynous ay) Japun Mojay
aytsoddo s}t 0} asojo Aj1o1sayue Suruado ‘renqny
JEYMOUIOS SI SLIVU JOLIOjUv AY], "sase[Nsvo peseu
-orqu, pezyerads ayy Aq payeordwos fjawan
-xa aulodeq ssurusdo yeseu ay} ‘azts poonpas
Apvosd yo qing Arojvyjo uv woy paatap st
Aiddns oarou sy !syrvys uy sv aynsdeo jesey

“S9UI0}S09T0,,,

FISHES, LIVING AND FOSSIL

278

; sroXv] snoarou (4q)Py)
‘anss) daANIOUUOD-qns ¥ UI a[qQeyIeWa1 ov ynq ‘somnjonays
asoyy ur Suryou, are sprourxdyy “peay ayy uo sour peordAy
9914} UL pus ‘ouT] [eloye] Jomo] puv soddn uv ut pesuvue oe
‘sud ur uayuns spnq pua aaieu uozkwoyog uy ‘panquy
“sip Ajjesauad ‘sossaooid ayerj!o yam ‘sjja9 por paqovjaq

*sunSigy haosuay pousaq

*sorod ouy WIM paosoid st Japsoq rejNONNo sy
{UIMNLIOD ay} YIM pajyoouUOD ore sassa00id asoy ‘sij90 reynuRAT
adv] puv ‘(jsinq pue sovyins ay) 0} astT YoryM) sijeo padeys
-qnjo poyesuoja ‘s][ao ya[qo8 yeioysodns sureyuoo stuapide ay}
uozAwonag ul ‘UONeIOas snoonuI dy} UTe}a1 0} YOU at}
Surmioy ‘sajsuvj pvoiyy se ‘syuoju0d say} aSieyosip pue
DOBJINS JY} 0} DUIOD YOIYA ‘s[[9d Iv[NUBIT VS1e] Joy}O are asay}
UWA JayJes0} ‘{s[jad ya1qo3 jo A[qujou pasoduioo are siakv|
1199 19]NO daIy} Oy SplourxXAW UT ‘UOH!PUOD payeT|IO vO} a]qu
~Jajar (weysiapat) A[qeqoid st Japsoq sejnoyN ayenys AJouy
ay} taepnpurls A[ySty 1ajno oy) ‘paysreur Ajsvajo siakel ULyS

*s}UDWIITO Ie[NOSNUL Ul Suryory st ynq ‘s]j9o anssy
aanoauUOD posuvsie Ajasoo] jo siafvy Aueul jo sjsisuoo vauczp ayy
+ (s[[99 JO}aI ‘s[[a9 39[GOS) spuyjs se[N]Je0ouoW Oyu! payenuaroy
FIP uayo ‘syuawala svjNy[99 ayuysp pue asie] jo pasodwoo st
studapiga ayy, “poradel-omy Ayreajo | yoru) Ajoaneias [er9uesd uy

mes,

“seuro}s0joAQ

SNVOUO ASNAS AYVINANNSDALNI GNV LNAWNDALNI AO SYALOVUVHD ‘IIAX

279

INTEGUMENT AND SENSE ORGANS

*s}SOa]o,J, Ul snor9uINU AT[RIO
-adsa (spnq jaws ‘spnq sjoysepy ‘suedi0 j1d) suvS10 A10s
“uas polayVog = *(adur[oD ‘snurwosry jo ‘sdeysod ‘uonippe
oy} WIA) uvoudiq ur se payearlouUT sueS10 !sysoajay, Ut
Sa[BOS ayI][-u10Y 0} po}depe puv ‘sprouvy ut (sarod 39}snI9)
poplaipqns Ajoynurut sSuruedo yeusajxa |! uetsA1a}dossor9
ur Ajeroodsa uowesuvize ul ox-yreYys sjeuvo A1osuag

“‘spnq 9suas poioyjvos ou ! (2) sueS10 Areyjndure ou
! (2) uonvarouUl puv juomasuvrie Ul oUT|-yxAVYsS OUT] [e19}e]

*suolse1 Yun.) pu poy ur yjoq sno1swMNuU
Ai9A av SYDO][IY pue spnq osuas uoNIppe uy ‘snasudreyd
-OSS0|3-05vA jo 3001 pe1oads Aq yun Jo ‘ferovy Jo s}oo1 AIOy
-Ipne-aid jerods Aq uorga1 proy jo uonvAlouUuy “yun. oy)
Ur Saywos OF poziperseds ! pvay oy) UL UONIPUOD oyT]-2A0013 YW
“SYIVYS O} JVYMOWIOS ILIIWIS S[euLd Poy PUL OUT] [e1O}e"]

*spnq asuds paloyeos ON
*sndva puv yer Aq uonvalouuy ‘uo1se1 proy oy} Ul IN900
(turzusi07y) sjeuvo Areyndure poaziperedg ‘sovjins ay} 0}
sjonp avynqn) ojduns ‘sulsoy pazyersued ut oyI]-0A0013 ynq
Jejnqn; pue uayuns Ajjensn sjeuvo peay puy our [esoje]

*SOTVOS DYI[-U1OY 10 uvoprloury
‘s19fe] snoiqy payenuolsyip AjapIm jo vuneaq ‘pojyuou did
-uou puv pajuowsid ‘jnynuad sjjoo poyouvsq !oovpins oy} ye
WOHIIIS 194} IF1VYyOsIP Yoty ‘s[jao snoonur yorqos jnynuald
sure}u0d !eUep Wo’ MOjaq Yo poxreur Ajdievys ‘1eps0q rel
“OND poywLys YIM ‘sjjao yeuosAjod poyseur-][am Jo stumepidy

*sayeid [eulop puv usaiseys
‘spuyjs Areyuoumnsajur yereds ynoyywa foyy-yreys ulys

*so]eos [eprojoAo pue uveploury “elWJOp oY} O}UT
umop Surddrp ‘spurs repnyjoonnu ‘erqrydwy ut se ‘pue ‘juasaid
aie spurs jajqos ‘aeynpuyjs A[ysiy pue payoeduioo Ajasoo,
‘azIs years jo A[ANVIOI div s}USWII[a S}I !vULIop Woy MOlaq
yo poyrvur Ajdaeys tsepi0oq avjnoyno ayenys yytas stuuepidy

‘uga1seyS *porod peasy] ay} Surmmp poys Apsed st puv ‘umnaus09
winjeys & SxOR] yt {s]j9o snoonut podeys-ysey ynoyIM ‘repNosea
Ajperouss ‘azis jyews jo Ajaanejer ou sjuswiaya sy !evuep ayy
qa Arepunoq poyseur Ajdieys & yuasaid jou sop stuuepidy

"Seml0}S00]0,

“Sploremyy)

“suvoudiq

“sqIVys

280

FISHES, LIVING AND FOSSIL

i pe . Se i i i
Se ok ya ere ee

xs “ta .

SHHSIA AO LNAWNdOTHAAC ATAVA AHL TWIAX

io, = _ Ty bo a ve, a prs me “act : ft aes 4h ee vale _ é “f a x. ty
— b —- a : ; 45 “5! 4 ; D pe Deer papdun ae * re * sa 4 ‘
‘s 19 a 2: 243 e Cosas 0: ‘ , | yon '* ices -omy i ys 1 )
; *G@esuadiny) pro) = -Aiquqoad “$9 woes :
} [UR_QaYWYMIUIOS /SAIP-AIVYS | -ey “Bas at -——
ery JO pue snoisop > f Silks
"On| -1do] Jo soBeis Arvo} —“suonerrea Ayiea “m} *(2)
“Seiqoiow Apuenxg | onseiqojoy Ayjens~) [yA onsEqo[OH, | “ONSEIqoIO_ | -Se{qosour Ajouronxy | “onseIqojOH{ | ONsE[qorsPy | “uoneUEWZag
“Suryorey ut
“stjuow £-sAep $ *SYOM T-T *syaom z-1 | *(3) syUOy, _— “‘syyuour S1~g syoom z-1 | *(3) syyuoyy =| ou jo
*payisodap “‘uoseas Sut
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282

XIX. THE SUPPOSED DESCEN

Interrelationships and lines of descent as suggested by a number o
noted on each scheme. * Denotes that the diagram is the present writ

FISHES, LIVING AND FOSSIL

hee a
s Bite
4 re

x

yy
Br

Towes (’91)*
(On Urino Genital System)

-

Maeckel ('98)*
(On Anatomy)

W.N. Parker (’92)*
(On General Anatomy)

Ancestral Stem
of Amphibians
and Fishes

Burckhardt (’92)
(On Central Nervous System)
ae —— Petromyzon

Teleost

Smith Woodward ('92)*
(On Palaeontology)

Retzius (°98)
(Nervous System and End Organs)

SUPPOSED DESCENT OF GROUPS 283

OF THE GROUPS OF FISHES

observers ; their views have been based on the different lines of investigation
interpretation of the text of the author cited.

Balfour ('80) ui
Gunther (’80)*
(Ou Babryelogy and Anatomy), og) (On Anatomy)
Ancestral Elasinobranch (On Circulatory System) Includes Lancelet and Cyclostomes
/ as 2 Sub classes of Fishes
Protoganoid a Palaeichthys
of \ Bony Ganoids \ ae
e Ganoids
Dipnoan anoid Amphibia (With Dipnoans)
Fyeloplares Chondrosteans
Ceratodus (Sharks and Chimaeroids)
Teleost
Gill (95)
(On Structural Characters)
Davidoff (80)
-------Pleuracanthid (On Extremities and Girdles)
2 * Primitive Gnathosteme
Dipnoan ! !
Chimaeroid Elasmobranch Scaphyrhynchus
Selachian -
Bridge (78) Acipenser -———
(On of Ganoids) | Shark Rays(!)
Heptanchus —Acanthias
Apneumato-—} |
)
Es emer aad Polypterus
Elasmobranch
| l I
= |
Dipnoi Physostome
Selachoidei
Teleosteoidei
Rabl (’89)
(On Embryology)
Cyclostomes Amphioxus Pollard (’91)
(On Anatomy of Head)
Mears co’) | Pad
(On Embryology and Brain) Selachians Crossopterygian
/ | UN ed
Selachodichthyidae Ganoids wen) =
\ | phi
Teleosts Amphibia Ceratodus
and Protamuia (Trias)
Ischyodus poe
(ura)
Selachians
Protopterus
Holocephall
Dipnoans and
Amphibia

INDEX

Abdominal pores, 271.
Acanthias, \arva of, 216 (Figs. 288,
289).
waonnnedes, gill shields, 20; a fossil
- shark of the Coal Measures, 79;
‘structure of, 80, 81; A. wardii, 81
(Fig. 87); shagreen and denticle of
_ A. gracilis, 81 (Fig. 88); affinities
of, 95; diagram of affinities, 98
(Fig. 103); gill arches, 114.
hckethinlinns, antiquity of, 9; fin
spine and pectoral fin, 28, 29 (Fig.
32); pectoral fin of Parexus, 42
(Fig. 51), 44-
ri ay ae wardii, teeth of, 82
(Fig. 88 A).
Mcaibbopleryelen, 166 (Fig. 171 “).
ACANTHOPTERYGI, in classification, 9;
as a subdivision of Teleocephali, 174.
Acipenser, in classification, 8; antiquity
of, 9, 166 (Fig. 171 4); swim-blad-
der of, 22 (Fig. 13); description of,
159-161; A. sturio, 160 (Fig. 165);
eggs and breeding habits, 181 (Fig.
194), 185; fertilization, 187; devel-
opment of eggs, 203 (Figs. 249-
264), 207; larval development of,
221-223 (Figs. 296-302); heart,
~ conus and bulbus arteriosus, tables,
260; gills, spiracle, gill rakers and
opercula, tables, 261; digestive tract,
tables, 262 (Figs. 326-331); swim-
bladder, tables, 264, 265 (Fig. 13);
- genital system, tables, 266; urino-
- genital ducts and external openings,
tables, 267 (Figs. 332-337); excre-
tory system and urinogenital ducts,
tables, 271.

285

ACTINOPTERYGII, in classification, 8,
147; description of, 155-178 (Figs.
157-185 4A); Chondrosteans (Gan-
oids), 155; fossil forms, 155-159
(Figs. 158-164); living types, 159-
178 (Figs. 165-185 4).

Actinotrichia, 31, 33 (Fig. 39).

Atheolepis, ganoid plates of, 24 (Fig.
25), 25- s

Agassiz, L., 37, 66, 107, 111.

Agassiz, A., 224.

Air-bladder, v. Swim-bladder.

Allis, E. P., 50, 51.

Alopias, 89; A. vulpes (thrasher shark),
89 (Fig. 95).

Alosa, eggs and breeding habits, 181
(Fig. 197), 186.

American Arthrodirans, 130.

American Geologist, 80.

Amia, in classification, 8; antiquity
of, 9, 166 (Fig. 171 4); swim-blad-
der of, 21, 22 (Fig. 14);_ sensory
tracts in head dermal plates, and
scales of, 50-52 (Figs. 64-68); 4
calva, 51 note; a Ganoid with her-
ring-like scales, 145; description of,
163-165 (Figs. 167, 168); Mesozoic
forms, 164, 165 (Figs. 169-171);
heart, conus and bulbus arteriosus,
tables, 260; gills, spiracle, gill rakers,
and opercula, tables, 261; digestive
tract, tables, 263; swim-bladder,
tables, 264, 265 (Fig. 14); genital
system, tables, 266;. excretory sys-
tem and urinogenital ducts, tables,
271.

Amiurus, barbels of, 46, 47 (Fig. 58).

Ammocetes, head of, 61 (Fig. 72 C),

286 INDEX

62; development of egg, 189 (Fig.
215).

Peat / fas affinities of the shark, 98
(Fig. 103).

AMPHIOXUS, in classification, 7; gills
of, 16.

ANACANTHINI, 174.

Anal fins, v. Fins.

Anatomy, v. Shark, Cladoselache, Acan-
thodes, Climatius, Pleuracanthus,
Chondrenchelys, Chimera, Dipnoan,
etc.

Angel-fish, v. Rhine.

Anguilla, v. Eel.

APODES, 173.

Aquatic breathing, 16-23; modes of, 20.

Archipterygium, 39.

Arius, eggs and breeding habits, 181
(Fig. 195), 185, 186.

Armour plates, 23; evolution of, 25.

ARTHRODIRA, in classification, 8; de-
scribed, 129-138 (Figs. 130-144);
geological position of, 9, 129; asso-
ciated with Prerichthys by Traquair,
130; American, described by New-
berry and by Claypole, 130; Din-
ichthys, 130 (Frontispiece and Figs.

133-137); varying size of, 136; den- |:

tition, jaws, and mandibles, 136, 137
(Figs. 138-144) ; affinities, 136-138;
differing from lung-fishes and from
sharks, 136 note.

Aspidorhynchus, 157; A. acutirostris,
158 (Fig. 162).

Aspredo, eggs and breeding habits, 186.

Authors, comparison of phylogenetic
tables of, 282, 283; v. Bibliogra-
phy.

Ayers, H., 57, 60, 181.

Balfour, F. M., 40, 193, 216; phylo-
genetic table of, compared, 283.

Barbels, 46-48 (Figs. 55-60).

Basking shark, v. Cetorhinus.

Bass, striped, numerical lines of, 5
(Fig. 8).

Bathyonus compressus, 168 (Fig. 172).

Batrachus, eggs of, 186.

Bdellostoma, gills of, 17 (Fig. 9); "9
anatomy and general description of __
B. dombeyi, 57, 58 (Fig. 69 A), 59,
60 (Fig. 70), 61 (Fig. 72 4); eggs
of, 180, 181 (Fig. 186); genital sys-
tem, tables, 266; excretory system
and urinogenital ducts, tables, 270;
brain of, tables, 272 (Fig. 339); cen-
tral nervous system, tables, 274.

Bean, T. H., 103, 108, 110.

Beard, J., 57, 61, 146, 217; phylo-
genetic table of, compared, 283.

Berycids, antiquity of, 9.

Bibliography, 231-251.

Blenniids, eggs of, 185 (Figs. 198-
199), 186.

Blenny, v. Blenniids.

Blood-vessels, v. Fishes, circulation in,
Heart, Chimee.oids, etc.

Boas, J. E. V., phylogenetic table of,
compared, 283. é

Boéhm, A. A., 187.

Bolau, H., 185.

Bony fishes, v. Teleosts.

Bow-fin, v. Amia calva.

Brain, of Chimzroids and shinies 114;
resemblances between lung-fishes
and Elasmobranchs, 128; compari-
son tables of, 272 (Figs. 339-341),
273 (Figs. 342-344), 274-275.

Branchial arches, table of relations of, —
254 (Figs. 310-315), 256-257.

Breathing, aquatic, 16-23. ;

Breeding habits, 180-186; table of the
early development of fishes, 280-281.

Brevoortia (menhaden), gills of, 20.

Bridge, T., phylogenetic tables of,
compared, 283. y

Bulbus arteriosus, comparative tables
of, 258 (Figs. 316-325), 260. «a

Bull-head, v. Catfish. _—

Burkhardt, R., 128; phylogenetic
table of, compared, 282. z

Butrinus, heart, conus and bulbus ane
teriosus, 258 (Fig. 323); —_—
son tables of, 260.

Calamoichthys, swim-bladder of, 22 .

INDEX

(Fig. 17); median fins of, 31; an-
tiquity of, 148; described, 150;
C. calabaricus, 147, 150 (Fig. 150).

Callichthys, respiration of, 20; ganoid
plates of, 24 (Fig. 26), 26; origin
of dermal cusps, 30; C. armatus,
172 (Fig. 178); eggs and breeding
habits, 186.

Callorhynchus, \ateral line lost, 49;
description of, 104, 109; mandibu-
lar, 106 (Fig. 110); bottle-nosed
Chimera, 109 (Fig. 118); eggs
and breeding habits of, 181 (Fig.
191), 185.

Canals, v. Lateral line.

Carassius auratus, 170 (Fig. 176).

Carp, scales of, 26 (Fig. 31 4); eggs
of, 187.

Catfish, barbels of, 46, 47 (Fig. 58);
description of, 171, 172; Amiurus
melas, 171 (Fig. 177).

Cattie, J. T., 54.

Caturus, 164-165; C. furcatus, 164
(Fig. 169); Mesozoic caturid, 166
(Fig. 171 4).

Caudal fins, 35; evolution of, 35-39
(Figs. 44-48).

Central nervous system, v. Nervous
system. ’

Cephalaspis, antiquity of, 9; described,
67; C. lyelli, 66 (Figs. 78, 79).

Cephaloptera, v. Dicerobatis.

Ceratodus, antiquity of, 9, 10; swim-
bladder of, 22 (Fig. 16); archip-
terygial pectoral fin of, 39, 40, 42
(Fig. 54), 44, 45; description of,
123 (Fig. 127), 124; skeleton of,
123 (Fig. 128); skull of, 124 (Fig.
128 A); embryonic stages, 125;
eggs and breeding habits, 181 (Fig.
192), 185; development of egg,
198-202 (Figs. 231-248); larva of,
218-221 (Figs. 290-295); skeleton
of, tables, 253; jaws and branchial
arches, tables, 254 (Fig. 313), 257;
heart, conus and bulbus arteriosus,

287

tables, 258 (Fig. 320); comparison
tables of heart, etc., 260; gills,
spiracle, gill rakers, and opercula,
tables, 261; digestive tract, tables,
263; swim-bladder, tables, 264, 265
(Fig. 16); genital system, tables,
266; urinogenital ducts and external

» openings, tables, 267 (Fig. 335);
excretory system and urinogenital
ducts, tables, 270; abdominal pores,
tables, 271.

Cestracion, antiquity of, 10; jaw of,
24 (Fig. 27); caudal.fin, 36, 37
(Fig. 45), 38; anatomy of, 85 (Fig.
91), 86; Port Jackson shark, 181
(Fig. 190), 183.

Cestraciont, antiquity of, 9, 10; gills
of, 16 note; anatomy of, 85, 86;
dentition of, 86; affinities of, 95,
96; dental evolution, 112.

Cetacean, fish-like form of, 5 (Fig.
7), 6.

*Cetorhinus, 90 (Fig. 96 A).

Challenger report, quoted, 87, 103.

Characteristic structure of fishes, 14.

Cheirodus, 157; C. granulosus, 157
(Fig. 160).

Cheiropterygium, 39.

Chilomycterus geometricus, 175, 176
(Fig. 184).

Chimera, sensory canals of the head,
30; lateral line of, 49, 51 note;
affinities to shark, 98 (Fig. 103);
anatomy of, gg-1o1 (Fig. 104);
skeleton of, 101-103; skeleton of
C. monstrosa, 102(Fig. 105); genus,
104; mandibular, 106 (Fig. 109);
palatine plate, 106 (Fig. 109 A);
clasping spine of forehead, 107 (Fig.
113); ventral fin and clasping organ,
107 (Figs. 116, 117); bottle-nosed
Chimera, 109 (Fig. 118); general
description, 110 (Fig. 119), III
(Fig. 120) ; dermal plates, 113 (Fig.
104); comparison tables of skeleton
of, 253; jaws and branchial arches,
tables, 254 (Fig. 312), 256; urino-
genital ducts and external openings,

288 INDEX

tables, 267 (Figs. 332-337); ab-| Chondrosteus, 161, 162; C. — -
dominal pores, tables, 271; brain] roides, 161 (Fig. 165 A). Be >
of, 273 (Fig. 342). ° Chordates, ancestors of, 16 note; d
CHIMROIDS, in classification, 7, 8; | scription of, 63-65. teat ‘ >
antiquity of, 9, 10; gill shields, 20; | Chrésticeps, eggs of, 186. —
affinities to shark, 96; general de- | Circulatory characters in Dipnoans,
scription of, 99-115 (Figs. 104-| 129.
120); anatomy of, 99-101 (Fig. | Cladodus, teeth of, 80 (Fig. 86 B).
104); skeleton of, 101-103 (Fig. | Cladoselache, in classification, 8; an-
105); embryology and larval his-| tiquity of, 9; gill slits, 16; ae ~
tory of, 103; fossil Chimzroids,} shields, 20; dorsal fins of, 33 (Fig. __
103, 104 (Fig. 105 4); living Chi-} 41); caudal fin of, 36, 37 (Fig. 46),
meroids, description of, 104-111} 38; pectoral and ventral fins of, 42
(Figs. 117-120); spines and clasp-| (Figs. 49, 50), 43-46; a primitive
ing organs, 107 (Figs. 113-116); | form of, 78; description of, 79;
affinities, 111-115; dental plates,| anatomy of, 79 (Figs. 86 and 864
111 (Fig. 111); history of fossil| and 86 8); dentition of, 86; affini- _
forms, 112; dental evolution, 112;| ties of, 95, 98 (Fig. 103); gilts
structural affinities to shark, 112-| arches, 114. ¢. an
115; divergences from elasmo- | Clark, W., 1 30, 133 note, Frontispiece.
branchian structure, 113; skull and | Clasping spine of Chimeroids, 114;
mandible of, 113; fins and fin spines, | absence of, in Dipnoans, 129.
113; skin defences and teeth, 1135 | Claypole, E. W., 66, 67, 71, 80, 130. —
gill arches, 114; brain of, 114; lat- | C/imatius, anatomy of, 82 (Fig. 89):
eral line, 114; clasping spine, 114; | Clupeoid, antiquity of,9; heart,conus
descent of, 115; diphycercal tail} and bulbus arteriosus, 258 (Fig. = 4
compared with that of sharks, 115; | 320); heart, etc., con tables
separated from Arthrodirans, 136;| of, 260. - ae
eggs and breeding habits, 181 (Fig. | Coccosteus, in classification, 8; locale a
191), 184, 185; list of authors and} _ ties, 130; anatomy of C. decipiens,
works on the Chimeroids, 244;| 131-133 (Figs. 130-132); dermal
gills, spiracle, gill rakers, and oper-| and ventral plates of, 132 (Figs.
cula, tables, 271; genital system,| 131,132); lateral line in, 135; eyes —
tables, 266; circulation in, tables,| of, 135.
269; central nervous system, | Cochliodonts, 86; dental evolution of
tables, 275; sense organs of,| I12.
tables, 277; integument and in-| Cod, barbels of, 46, 47 (Fig. 55)»
tegumentary sense organs, 279; 171; description of eu morrhua, —
early development of, tables, 280-| 174 (Fig. 182); circulation in
281. tables of, 269. y
Chlamydoselache, antiquity of, 10; gill | Ce/acanthus, in classification, 8; dor: 5
shields, 20; lateral line, 49, 50 (Fig. | sal fin of, 33, 34 (Fig. 43), 433 de-
61); C. anguineus, 87 (Fig. 92);| scription of, 87 (Fig. 92), 153; as —
affinities to shark, etc., 96; gill] a Crossopterygian, 147; C. elegans, :
arches, 114. 153 (Fig. 155). :
Chondrenchelys, 78; anatomy of, 85. | Columbia College Museum, 130, 1357 =
CHONDROSTEI, in classification, 8, Frontispiece. e
161, 162. Conte arteriosus, comparison tables of,

INDEX

258 (Figs. 316-325), 260; v. Sharks,
etc.

Cope, E. D., 8, 10; phylogenetic
table of, compared, 282.

Cricotus, 54; parietal foramen of, 54.

Crossoprerycil, in classification, 8;
antiquity of, 9; unpaired fins of, 33
(Fig. 43); affinities to shark, 96;
included in the term Ganoid, 139;
ancestry of, 147; a group of Teleo-
stomes, 147; description of, 148-
155 (Figs. 148-156 4); habits of
living and breeding, 150; fossil
forms, 150-155 (Figs. 151-156 4);
paleeozic, 166 (Fig. 171 4).

Ctenodus, in classification, 8; median
foramen of, 55; affinity to Cerato-
dus, 122, 124; ancestry of, 147.

Ctenolabrus ceruleus, larval develop-
ment of, 224 (Figs. 303-309), 225.

Curves of fishes, 5, 6.

Cusk, barbels of, 46, 47 (Fig. 55).

Cusps, v. Derm cusps.

CyYcLosToMEs, in classification, 7, 8;
antiquity of, 9; metamerism in, 14-
16; gills of, 18; lampreys, 57-63;
their affinities, 63-65; palzichthyic
affinities, 70; eggs-and breeding
habits of, 180, 181 (Figs. 186, 187);
fertilization of eggs, 187 note; larval
development, 214, 215 (Figs. 212,
215, p. 189, and 72, p. 60); names of
authors and works, list of, 234-238;
skeleton of, tables, 252; heart, conus,
and bulbus arteriosus, tables, 260;
gills, spiracles, gill rakers, and oper-
cula, tables, 260; digestive tract,
tables, 262 (Fig. 326), 263; swim-
bladder, tables, 264; genital system,
tables, 266; urinogenital ducts and
external openings, tables, 266, 267
(Fig. 332); abdominal pores, tables,
271, 272 (Fig. 340); central ner-
vous system, tables, 274; sense or-
gans, tables, 276; integument and
integumentary sense organs, tables,

278.
Cyprinodonts, eggs of, 185.
U

289

Davidoff, M., phylogenetic table of,
compared, 283.

Davis, J. W., 84.

Dean, B., 8, 78, 128, 132.

Deep-sea fishes, lateral line in, 49.

Defences, v. Dermal and Teeth.

Dental plate, of Sandalodus, 24 (Fig.
28), 28; of sting-ray, 24 (Fig. 29);
of eagle-ray, 24 (Fig. 30), 27; of
Arthrodirans, 136, 137 (Figs. 138-
144); of Dinichthys, 136-138.

Denticle, v. Dermal defences.

Dentine, v. Shark, skin of.

Derm cusps, origin of, 30.

Dermal defences of fishes, 23-30; of
shark, 23, 24 (Figs. 30, 31); evolu-
tion of, 24 (Figs. 24-26), 25; of
Chimeeroids, 113; of Coccosteus de-
cipiens, 132 (Fig. 131); v. Fin
spines.

Dermal sense organs, v. Sensory or-
gans, integumentary.

Development, v. Fishes, Eggs, larval,
etc.; comparison table of early, 280,
281.

Devil ray or mantis, v. Dicerobatis.

Dicerobatis, 95, 96 (Fig. 102 A).

Digestive tract, comparison tables of,
263 (Figs. 326-331).

Dinichthys, Frontispiece; pineal fun-
nel, 55; general description, 130-
138; type specimens in Columbia
College Museum, 130 (Frontispiece
and Figs. 133-137); fin and fin
spine, 131; D. intermedius, resto-
ration of by Newberry, 133 (Fig.
133 and Frontispiece); elater-joint
of, 134; dermal, ventral, and pineal
plates of, 133 note; dorsal plates in
Columbia College Museum, 135;
jaws of, 136, 137 (Figs. 138-144); in-
ter movement of dental plates of, 138.

Diphycercal-shaped fin, 35, 37 (Fig.
47).

Diplognathus, jaw of, 136, 137 (Figs.
141-143).

Diplurus, 147, 153,154; D. longicau-
datus, 154 (Fig. 156).

290 INDEX

Drpnoans, in classification, 7, 8; an-
tiquity of, 9, 10, 147; swim-bladder
of, 21; affinities to shark, 96, 98
(Fig. 103); general description of,
116-129 (Figs. 121-129); structural
characters and general anatomy of,
116-120 (Fig. 121); skeleton of,
118 (Fig. 122), 119; fossil forms,
120-124 (Figs. 123-126); living
forms, 123-127 (Figs. 127-129 4);
relationships, 127-129; amphibian
characters of, 127, 129; kinship to
sharks, 127; the advancing struc-
tures of, 129; the Arthrodiran lung-
fishes, 129-138 (Figs. 130-144);
arthrodiran affinities, 136; eggs and
breeding habits, 181 (Fig. 192),
185; larval development of, 218-
221 (Figs. 290-295); names of
authors and works on, list of, 244-
246; comparison tables of skeleton,
253; skeleton of Protopterus annec-
tans, 119 (Fig. 122); skull and
branchial arches, table of relations
of, 257; heart, conus and bulbus
arteriosus, tables of, 258 (Figs. 320,
321); comparison tables of heart, etc.,
260; digestive tract, 262 (Fig. 329) ;
comparison tables of digestive tract,
263; genital system, tables, 266;
urinogenital ducts and _ external
openings, tables, 267 (Figs. 332-
337); circulation in, tables, 269;
brain, 272 (Fig. 343); central ner-
vous system, tables, 275; sense or-
gans, tables, 277; integument and
integumentary sense organs, tables,
279; early development of, compari-
son tables, 280-281.

Dipterus, in classification, 8; antiquity
of, 9; description of, 121 (Figs.
123-125), 122.

Dohrn, A., 40, 63.

Dolphin, fish-like form of, 6.

Dorsal fin, v. Fins.

Drum-fish, barbels of, 46, 47 (Fig.
56).

Dugong, fish-like form of, 6.

Eagle-ray (Myliobatis), dental plates —
of, 24 (Fig. 30), 27. : os

Early development, v. Development. eo

Edestus heinrichsti, fin spine of, 28-300
(Figs. 35-38).

Edinburgh Society, Transactions of, —
quoted, 70.

Edwards, V. N., 184.

Eel, movement of, 2 (Fig. 2); gills of,
18; median fins of, 31; description
of Anguilla vulgaris, 171, 173 (Fig.
180).

Eggs of fishes, 180-186 (Figs. 186-
199), v. Comparison tables of the
early development of fishes, 280,

ELASMOBRANCHII, in classification, 8,
9; antiquity of, 9; description of, —
72-97 (Figs. 83-102); affinities of,
95; resemblances to lung-fishes, 128,
129; to Athrodirans, 136, v. Shark;
eggs and breeding habits of, 183,
184 (Figs. 189, 189 4); circulation
in, 268 (Fig. 338), 269; central ner-
vous system, tables of, 274, 275. _

Elonichthys, 156; E. (Rhabdolepis)
macropterus, 156 (Fig. 158).

Embiotocids, eggs of, 185.

Emery, C., 169, 170.

Enamel of shark skin, 23, 24 (Fig.
20); enamel organ of shark, 23, 24
(Fig. 20). . a

Entering angle of fishes, 5, 6. a

Environment, changes due to, 167 ;
169 (Figs. 172-174).

Erythrinus, swim-bladder of, 22 (Fig.
15).

Eurynotus, 157; £. crenatus, 156
(Fig. 159).

Eusthenopteron, 151-153; £. igs
152 (Fig. 154).

Evolution, of fishes, slowness of, ert) by
of fins, 30-46; of unpaired fins, 31-
39 (Figs. 39-43); of paired fins, 39- .
46 (Figs. 49-54). =

Excretory system, tables of, 270, 7
(Figs. 332-337, p- 267).

Exoskeletal specializations of Dip-
noans, 129.

INDEX

Eye, v. Pineal eye.

Feeling, sense of, 46-48.

Fertilization phenomena, 186, 187, v.
comparison tables of the early devel-
opment of fishes, 280.

Fierasfer, 169,170; F. acus, 169 (Fig.
175).

Fins, location of, 3, 4; evolution of,
30-46 (Figs. 39-54); unpaired, 31-
39 (Figs. 39-43); dorsal and anal,
31-35 (Figs. 39-43); caudal, 35-
39 (Figs. 44-48); paired, 39-46
(Figs. 49-54); pectoral, 41-43 (Figs.
49, 51-54); ventral, 41-43 (Fig.
50); of Chimeroids, 113; primitive
dermal, 31; of Cladoselache, 33 (Fig.
41); of Celacanthus, 34 (Fig. 43);
of Crossopterygian (/Yoloptychius),
33 (Fig. 43).

Fin spines, 23; description of, 28-30
(Figs. 32-38); of Acanthodian, 29
(Fig. 32); of Hybodus, 29 (Fig.
33); of sting-ray, 28, 29 (Fig. 34);
of Edestus heinrichsii, 28, 29 (Figs.
35-38); of Chimeroids, 113.

Fishes, defined, 1; movement of, 1, 2
(Figs. 1, 2); type of swift swim-
ming fish, 3,4 (Fig. 3); balanced
in water, I, 4; symmetry of, 4; nu-
merical lines of, 5,6 (Figs. 5-8);
effect of environment of, 7; classifi-
cation of, 7, 8; geological distribu-
tion of, 9; importance of group, 10;
permanence of, 10; evolution of, 11;
generalized, 12; characteristic struc-
ture of, 14-56 (Figs. 9-60); meta-
merism, 14-16; aquatic breathing,
gills, etc., 16-23 (Figs. 9-19); der-
mal defences of, 23-30 (Figs. 20-
38); teeth in highly modified fishes,
28; development of, 179-225 (Figs.
186-309); embryology of, 179; eggs
and breeding habits of, 180-1386
(Figs. 186-199); fertilization of
eggs of, 186, 187; development of
eggs of, 187-214 (Figs. 200-283) ;
larval development of, 213-225

291

(Figs. 284-309); names of authors
and works, on the general subject,
231-234; skeletons, table of, 252,
253 (Figs. 69, 84, 105, 122, 146,
147, and 310-315); skull, jaw, and
branchial arches, tables, 254 (Figs.
310-315); heart of, 258 (Figs.
316-325), 260; comparison tables
of heart of, 260; gills, spiracles,
gill rakers, and opercula, tables,
259 (Figs. 9-12), 260, 261; di-
gestive tract, tables, 262 (Figs. 326-
331), 263; swim-bladder, tables,
264, 265 (Figs. 13-19); genital
system, tables, 266, 267 (Figs. 332-
337); circulation in, tables, 268
(Fig. 338), 269; excretory system
and urinogenital ducts, 270, 271
(Figs. 332-337, p- 267); abdominal
pores, 271; brain of, 272 (Figs. 339-
341), 273 (Figs. 342-344); central
nervous system, tables, 274, 275;
sense organs, tables of, 276, 277;
characters of integument and in-
tegumentary sense organs, 278,
279; early development, compari-
son tables of, 280, 281.

Flounder, 171; description of, 174,
175; Pseudopleuronectes america-
nus, 172 (Fig. 183).

Fossil forms, v. Sharks, Chimeroids, etc.

Fraas, 157.

Fric, 102, 119.

Frilled shark, v. Chlamydoselache, etc.

Fritsch, A., 42, 83.

Gadoid, 9.

Gadus, v. Cod.

Gage, S., 182.

Ganoid plates, in theolepis, 24 (Fig.
25); in Lepidosteus, 24 (Fig. 24);
in Callichthys, 24 (Fig. 26).

GANOIDS, in classification, 8, 148; an-
tiquity of, 9; dermal plates, 24 (Fig.
25), 25; Ganoid includes the Cros-
sopterygians, 139 note; the term
“Ganoid ” used in the popular sense
to denote the Teleostomes, 139; con-

a
292 INDEX ‘s
trasted with Teleost, 144 (Fig. 147); | Goode, G. B., 3, 47, 89, 90, 92, 94, 95,

air-bladder like that of a Dipnoan,
145; J. Miiller as to structural differ-
ences between Ganoids and Tele-
osts, 145; recent Ganoids, 159;
Mesozoic, 166 (Fig. 171 4); eggs
and breeding habits, 181 (Figs. 193,
194); fertilization of eggs of, 187;
development of eggs of, 202-207
(Figs. 249-268) ; larval development,
211-223 (Figs. 296-302); names of
authors and works on, 246-249;
skeleton, tables of, 253; skeleton of
Polypterus bichir, 144 (Fig. 147);
digestive tract, tables, 262 (Figs.
326-331); urinogenital ducts and
external openings, tables, 266, 267
(Figs. 332-337); abdominal pores,
tables, 271; tables of early devel-
opment, 280, 281.

Ganoine, 166 note.

Garman, 87, 93, 109, II.

Gar-pike, v. Lepidosteus.

Gegenbaur, C., 39, 40, 42, 146.

Generalized fishes, defined, 112.

Genital system, comparison tables of,
266 (Figs. 332-337), 270, 271.

Geological distribution of fishes, 9.

Geologist, American, quoted, 80.

Gill, T., 110; phylogenetic table of,
compared, 283.

Gill rakers, 20; comparison tables of,
260.

Gill shields, 20; v. Sharks, Chimzeroids,
etc.

Gills, 16-23; evolution of, 18; of
Amphioxus, 16; of Bdellostoma, 17
(Fig. 9); of Myxine, 17 (Fig..10);
of shark, 17 (Fig. 11); of Teleost,
17 (Fig. 12); of Cyclostomes, 18;
of Heptanchus, 16, 19; of mullet,
20; of Brevoortia (menhaden), 20;
of Selache, 20; number of gill slits,
16, note; table of comparison of,
260, 261 (Figs. 9-12, p. 259).

Goette, A., 189.

Goldfish, 170; Carassius auratus, 170
(Fig. 176).

103, 108, 155, 160, 162, “ir 7h
173-177-

Graf, A., 75, 102, 119. :

Greenland shark, v. Lemargus, .

Guitel, F., 181.

Gunn, M.,, 70.

Giinther, A., 60, 90, 96, 103, 123, 125, r
146, 162, ‘168, 170, 172, 178, 1815 ic
phylogenetic table of, compared, —
283.

Gurnard, v. Prionotus. ;

Gyroptychius, 150, 151 (Fig. 151).

Haeckel, 146; phylogenetic table, —
compared, 282. a

Hagfish, in classification, 8; v. Afyxine. E

Harriotta, 103, 104, 108 (Fig. 117) iS
clasping spine of, 115. iN - 4

Heart, v. Sharks, etc. a

HEMIBRANCHIATES, 176, ‘ee

Hemitripterus, barbels of, 46, 47
(Fig. 57).

Heptabranchias, v. Notidanus, —

Heptanchus, v. Notidanus.

Hertwig, O., 54, 204.

Heterocercal caudal fin, 35, 37 (Figs.
455 46).

HETEROSOMATA, 175.

Hippocampus, 176; H. heptagonus,
177 (Fig. 185); eggs and breeding —
habits, 186.

Hofer, B., 24. ‘

Hoffman, 187 note. ee

HOLOcEPHALI, v. Chimeroids; heart,
conus and bulbus arteriosus, tables, —
260; digestive tract, tables, 2635
swim-bladder, tables, 264. “4

Holoptychius, in classification, 8; un-
paired fins of, 33 (Fig. 33); ances-
try of, 147; description of, 150; H. a:
andersont, 151 (Fig. 153).

Homocercal caudal fin, 35, 37 (Fig. 48).

Howes, G. B., 42; phylogenetic fable
of, compared, 282.

Huxley, 131, 257.

Hybodus, number of gill slits, 16 nota f
fin spines of, 28, 29 (Fig. 33).

INDEX

Hydrolagus colliei, general anatomy
of, 100 (Fig. 104), 110.
HYPERORARTIA, 62.

IcHTHYOMI, in classification, 8.

Innes, W., 149.

Integument, v. Shark, sense organs,
etc. .

Intestine, v. Digestive tract.
Ischyodus, 103 (Fig. 106); mandibular
of, 106 (Figs. 111, 112), 112.

Jaekel, O., 92, 113.

Janassa, 86.

Jaws of fishes, 24, 27; of Port Jackson
shark, 24 (Fig. 27), 27; table of
relations of, 254 (Figs. 310-315),
256, 257.

Journal of Morphology, quoted, 51
note, 160.

Kepler, W., 130.

Klaatsch, phylogenetic table of, com-
pared, 282.

Kner, 82.

Kreft, 125.

Kupffer, K. v., 187 note, 189, 222.

Labrax lineatus, v. Bass.

_ Lemargus, shagreen denticle of, 24
(Fig. 21), 25; described, 90 (Fig.
96 B); breeding habits of, 183 and

Lagocephalus, description of ZL. levi-
gatus, 176 (184 A).

Lamna, 89, 90 (Fig. 96).

Lamprey, classified, 8; metamerism
in, 14-16; gills of, 17; v. Petromy-
zon, Cyclostomes, etc.

Lampreys, v. Cyclostomes, etc.; com-
parison table of the early develop-
ment of, 280, 281.

Lankester, E. R., 66.

Larva, v. Fishes, larval development
of.

Lateral line, 48-53 (Figs. 61-68); of
Chimzroids and shark, 114; in Coc-
costeus, 135.

293

Lepidosiren, in classification, 8; swim-
bladder of, 22 (Fig. 18); account
of, 125 (Fig. 129), 126; swim-
bladder, tables of, 264, 265 (Fi ig.
18).

Lepidosteus, in classification, 8; an-
tiquity of, 9, 166 (Fig. 171 A);
swim-bladder of, 21, 22 (Fig. 14);
ganoid dermal plates of, 24, 25 (Fig.
24); especial interest of gar-pike in
connecting the Ganoids with the
Crossopterygians, 159; gar-pike, Z.
platystomus, described,159-160 ( Fig.
157); eggs and breeding habits of,
181 (Fig. 193), 185; fertilization
of, 187; development of egg of, 203
(Figs. 265-268), 207; heart, conus
and bulbus arteriosus, 258 (Fig.
322); comparison tables of heart,
etc., 260; gills, spiracle, gill rakers,
and opercula, tables, 261; digestive
tract, tables, 263; swim-bladder,
tables, 264, 265 (Fig. 14); genital
system, tables, 266; excretory sys-
tem and urinogenital ducts, 271.

Leptolepis, 165; L. sprattiformis, 165
(Fig. 170).

Leydig, F.%51 note.

Limb structure in Dipnoans, 129.

List of names of authors and of their
works, 231-251.

List of the derivations of proper
names, 227-230.

LoPHOBRANCHH, 166 (Fig. 171 A),
178.

Lung-fishes, v. Dipnoans.

Lungs, v. Swim-bladder.

Mackerel shark, v. Zamna.

Mackerel, Spanish, movement and fins
of, 2, 3 (Fig. 3); front view of, 4
(Fig. 4); lines of, 5 (Fig. 6).

Macropetalichthys, eyes of, 135.

Manatee, fish-like form of, 6.

Mandibles of Chimzeroids, 113; articu-
lation of in Dipnoans, 129.

Mantis, or devil-ray, v. Dicerodatis.

Marey, 2.

294

MARSIPOBRANCHS, vy. Cyclostomes ;
tables of the early development of,
280, 281.

McClure, 182.

Mechanical adaptation of the fish’s
form, 5, 6.

Median fins, v. Fins.

Megalurus, 165; M. elegantissimus,
165 (Fig. 171).

Megaptera, v. Whale; MM. longimana,
numerical lines of, 5 (Fig. 7), 61.

Menaspis, skin defences of, 113.

Menhaden, v. Brevootia.

Metamerism, vertebrate, of fishes, 14-
16; of lampreys, 15; of sharks, 16,

Miall, L., 126.

Microdon, 357; M. wagneri, 158
(Fig. 163).

Mivart, St. G., 40

Modern fishes, v. Teleostomes.

Mollier, S., 39.

Monk-fish, v. Rina.

Mormyrus, 171,172; M. oxyrhynchus,
172 (Fig. 179).

Morphology, Journal of, quoted, 51
note.

Mouth of fishes, v. Jaws, Teeth, etc. ;
of catfish (a Teleostoma), 64 note.

Movement in water, I, 2 (Figs. 1 and
2%.

Mucous canal system, v. Lateral line.

Miiller, Johannes, 145.

Mullet, gills of, 20.

Murena, 173.

Myliobatis, v. Eagle-ray.

Mylostomids, in classification, 8; trunk
of, 136; jaws of MZylostoma varia-
bilis, 136, 137 (Fig. 138).

Myriacanthus, in classification, 8 ;
restoration of, 104; head region of,
105 (Fig. 106); dermal plates of
head and snout, 105 (Figs. 106,
A and B), 113; mandibular, 106
(Fig. 107); dorsal spine, 107 (Fig.
114); dental evolution, 112; sha-
green tubercles and dermal bones
and plates, 105 (Fig. 106), 107
(Fig. 114), 113.

INDEX

Myxine, classification, 8; gills of, 17_

(Fig. 10), 18; general description, ;
of M. glutinosa, 59, 60 (Fig. 71),

61 (Fig. 72 B); eggs of, 180-182.
(Fig. 187); genital system, tables
of, 266; excretory system and urino-
genital ducts, 270.

Myxinoid, Californian, gills of, 18;
teeth of, 57; eggs of, 182 (Figs. 186
_A and 187 A); comparison tables
of the early development, 280, 281.

Names, list of authors and their
works, 231-251.

Names, list of derivations of, 227-230.

Nares, in Dipnoans, 129.

Natterer, J., 125.

Necturus, swim-bladder of, 21.
Nervous system, central, 272 (Figs.
339-341), 273 (Figs. 342-344)

274, 275. tie
Newberry, J. W., 78, 106, 120, 130,
131, 132, 136.
Newton, 106.
Nicholson, H. A., 125.
Notacanthus sexspinis, 168 (Fig. 194).
Notidanus, antiquity of, 9; gill slits,
16, 19; pectoral fin, 40-42 (Fig.
52), 44, 45; described, 87-89 (Fig.
93);5 affinities, 96; skull, jaws, and

branchial arches of, 254 (Fig. oa

311).
Numerical lines of fishes, 5, 6 (Figs.
5-8).

Onychodus, in classification, 8.

Operculum of Teleosts, 19; comparison
tables of, 260.

Ophidium, barbels of, 46, 47 (Fig.

55):
Opisthure, 111.

Osteolepis, in classification, 8; descrip-

tion of, 150, 151 (Fig. 152).
OsTRACODERMS, classified, 8; antiquity
of, 9; description of, 65-71; types
of, 67; affinities of, 66 (Fig. 77),
70; list of authors and works on —
Ostracoderms, 238.

INDEX

Paddle-fish, v. Polyodon.

Palaaspis americana, 67 (Fig. 75);
paired fins or spines, 71 note.

Paledaphus, median foramen, 55.

Pal@oniscus, in classification, 157, 158
(Fig. 164); Palozic, 166 (Fig.
171 A).

Palaospondylus, in classification, 8;
antiquity of, 9, 71; P. gunni, 65
(Fig. 73), 70; palzichthyic affini-
ties, 70; list of authors and their
works on Palaospondylus, 238.

Pander, 121, 151.

Paraliparis bathybius, 168 (Fig. 172).

Parexus, pectoral fin of, 42 (Fig. 51),

. 44

Parker, W. N., 7, 117, 127, 128.

—, T. J., 41, 58.

Parsons, 5, 6.

Perca, v. Perch.

Perch, antiquity of, 9; scales of, 25
(Fig. 31 A), 26, 171; described,
174; Perca americana (= flyvia-
talis ?), 173 (Fig. 181); digestive
tract, tables of, 262 (Figs. 326-331).

Petalodonts, 86.

Petromyzon, 61; P. marinus, 60 (Fig.
72), 61 (Fig. D), 62; skeleton of,
58 (Fig. 69); eggs of, 180-183;
eggs of P. marinus, 181 (Fig.
188); fertilization of eggs, 187;
development of, 188-192; develop-
ment of P. planeri, 189 (Figs. 200-
214); digestive tract, tables of, 262
(Fig. 326); genital system, tables
of, 266; urinogenital ducts and ex-
ternal openings, 267 (Fig. 332);
excretory system and urinogenital
ducts, 270; brain of, 272 (Fig.
340); central nervous system, 274.

Phaneropleuron, in classification, 8;
description of, 122 (Fig. 126).

Phocena lineata, v. Porpoise.

Phylogeny, tables of, 98 (Fig. 103),
166 (Fig. 171 A); comparison of
the phylogenetic tables of the differ-
ent authors, 282, 283.

Phyllopteryx, 178.

295

PHYSOSTOME, 166 (171 A).

Pineal eye, 53-56.

Pipe-fish, v. Syngnathus.

Pisces, v. Fishes.

PLECTOGNATHI, 176.

Pleuracanthus, in classification, 8;
gill slits, 16; a fossil shark, 78;
anatomy and skeleton of, 83 (Fig.
go); dermal bones of head roof,
84 (Fig. 90 A); teeth of, 84 (Fig.
go £); affinities of, 95, 98 (Fig.
103); anterior spine of dorsal fin,
114; tail of, 115; Coccosteus com-
pared with, 131.

PLEUROPTERYGII, in classification, 8.

Pogonias, v. Drum-fish.

Pollard, H. B., 64, 113, 132.

Polyodon, barbels of, 46, 47 (Fig. 59),
48; described, 160-163; P. spatula,
162 (Fig. 166 8); gills, spiracle,
gill rakers, and opercula, tables of,
261.

Polypterus, swim-bladder of, 21, 22
(Fig. 17); origin of derm cusps, 30;
caudal fin of, 36, 37 (Fig. 47); tail
of, 115; skeleton of P. dichir, 144,
147 (Fig. 147); contrasted with
Teleosts, 144; P. dichir described,
148 (Fig. 148), 149 note; P. lap- .
radet, 149 (Fig. 149); in table of
phylogeny, 166 (Fig. 171 4); skull
and branchial arches, 254 (Fig.
314); table of relations of skull and
branchial arches, 257; comparison
tables of gills, spiracle, gill rakers,
and opercula, 261; digestive tract,
tables, 263; swim-bladder, tables,
264, 265 (Fig.17); excretory system
and urinogenital ducts, tables, 270.

Porcupine-fish, v. Chilomycterus.

Porpoise, striped, lines of, 5 (Fig. 5).

Port Jackson shark, v. Cestracion.

Powrie, 82.

Prionotus, barbels of, 46, 47 (Fig. 60),
48.

Pristiophorus, antiquity of, 9; descrip-
tion of, 92 (Fig. 99); affinities of,
96-98 (Fig. 103).

296

Pristis, antiquity of, 9; description of,
gt (Figs. 98 and 984A); affinities
of, 96-98 (Fig. 103).

Pristiurus, \arval development of, 215,
216 (Fig. 284).

Protocercy, 35.

Protopterus, swim-bladder of, 22 (Fig.
18); anatomy of, 116 (Fig. 121);
paired fin structure, 118 (Fig. 122),
119; jaws and skull, 119 (Fig.
122 A); account of, 126 (Fig.
129 A); Coccosteus compared with,
131; heart, conus and bulbus arte-
riosus, 285 (Fig. 325); comparison
tables of heart, etc., 260; gills,
spiracle, gill rakers, and opercula,
tables, 261; digestive tract, tables,
262 (Fig. 329), 263; swim-bladder,
tables, 264, 265 (Fig. 18); circula-
tion in, tables, 269; excretory sys-
tem and urinogenital ducts, 270;
abdominal pores, 271; brain of, 273
(Fig. 343); central nervous system
tables, 275.

Psammodus, dentition, 86. ,

Psephurus, 160-163; P. gladius, 162
(Fig. 166.4),

Pseudopleuronectes, vy. Flounder.
Pteraspis, antiquity of, 9; described,
67 (Figs. 74, 76, 77).

Pterichthys, antiquity of, 9; described,
69 (Figs. 80-82); Arthrodira associ-
ated with by Traquair, 130.

Putnam, 182.

Pycnodont, 157, 158. :

Rabbit-fish, v. Lagocephalus.

Rabl, C., 146; phylogenetic table of,
compared, 283.

Raja, v. Ray.

Rat-fish, v. Chimera.

Ray, in classification, 8; antiquity of,
9; shagreen of, 24 (Fig. 23); de-
scription of, 93-95 (Figs. 100-102) ;
barn-door skate (2. devis), 94 (Fig.
101); affinities, 95, 96, 98 (Fig.
103); eggs and breeding habits, 181
(Fig. 189 4), 183, 184.

INDEX

Recent sharks, v. Sharks.

Relationships, v. Affinities, under the *%

family and species.

Respiration, vy. Aquatic breathing.

Retzius, G., phylogenetic table of, com-
pared, 282.

Rhina, 91 (Fig. 97); affinities to
shark, 96, 98 (Fig. 103); brain of,
tables of, 272 (Fig. 341).

Rhinobatus, antiquity of, 9; descrip-

tion of, 93 (Fig. 100); affinities to
shark, 98 (Fig. 103).

Rhyncodus, mandibular of, 106 (Fig.
III), 111.

Riickert, J., 187,

Ryder, J. A., 31, 37, 115.

Salensky, W., 214 note.

Salmonid, antiquity of, 9; eggs and
breeding habits, 186; skull and
branchial arches, table of, 254 (Fig.
315), 257:

Sandalodus, dental plates of, 24 (Fig.
28), 28.

Scales, 23; of Teleost, 24 (Fig. (31)5
degeneration of, 26.

Scaphaspis, 66 (Fig. 77), 67.

Scaphirhynchus, 160; S. platyrhyncus,
162 (Fig. 166). ,

Scomberomorus maculatus, 2, 3 (Fig.
3); front view of, 4 (Fig. 4); lines
of, 5 (Fig. 6).

Sculpin, barbels of, 46, 47 (Fig. 57).

Scyllium, shagreen of, 24 (Fig. 22),
25, 90; eggs of, 181 (Fig. 189),
183, 184 and note; development of
egg of, 193 (Figs. 216-230); larvae
of, 215, 216 (Figs. 285-287); skull,

jaw, and branchial arches of, 254

(Fig. 310), 256.
Sea-bass, v. Serranus.
Sea-cat, v. Chimera and Callorhyn=
chus.
Sea-horse, v. Hippocampus.
Sea-raven, v. Hemitripterus.
Sea-robin, v. Prionotus.
Seal, fish-like form of, 6.
Selache, gills of, 20.

a

INDEX

SELACHII, in classification, 8.

a” 157; S. Aapfi, 157 (Fig.
161).

Semon, R., 125, 181, 199, 200, 219.

Sense organs, characters of, 46-56;
tables of, 276-277; integument and
integumentary sense organs, tables
of, 278, 279.

Sense of feeling, 46-48.

Sensory canals in head of Chimera,

30.
Sensory tubules, v. Lateral line.
Serranus, eggs of, 181 (Fig. 196), 186;

development of egg of S. atrarius,

208 (Figs. 269-283).

Shad, v. Alosa.

Shagreen denticle of - shark, 23-25
(Figs. 20-22) ; of sting-ray, 24 (Fig.
23), 25-

SHARKS, movement of, 2; in classifi-
cation, 7, 8; antiquity of, 9, 10, 72;
gills of, 17 (Fig. 11), 19; spiracle
of, 19; gill shields of, 20; skin,
enamel, and dermal denticle of, 23-
26 (Figs. 20-22) ; shagreen denticle
of the Greenland shark (Lemargus),
24 (Fig. 21); jaw of Port Jackson
shark (Cestracion), 24 (Fig. 27),
27; evolution of the dermal armour-
ing, 25, 26 (Figs. 25, 26); unpaired
fins of, 33, 34 (Figs. 39-43); caudal
fin of, 36-39 (Figs. 45-47); lateral
line of, 49, 50 (Figs. 61, 62), 51, 76;
description of, 72-98 (Figs. 83-103) ;
position of, 72; general anatomy of,
73 (Fig. 83); skeleton of, 74-76
(Fig. 84); sub-notochordal rod in
skeleton, 76 (Fig. 85); integument
of, 76; brain of, 76; nasal organ,
eye, and ear, 76; renal and repro-
ductive system of, 76; digestive
tube, viscera, 77; heart, 77; clasp-
ers, 77; fossil sharks described, 77-
86 (Figs. 86-91); teeth of fossil, 86;
recent sharks, 87—95 (Figs. 92-101) ;

- affinities of, 95-98 (Fig. 103); eggs

and breeding habits, 181 (Figs. 189-

190), 183, 184; fertilization of eggs,

297

187 note; development of egg of,
194-198 (Figs. 216-230); larval de-
velopment of, 215-218 (Figs. 284-
289); list of authors and their works
on sharks, 238-244; comparison
tables of the skeleton of, 252; skel-
eton of Cestracion galeatus, 75 (Fig.
84), 255; skull, jaws, and branchial
arches, tables, 256; heart, tables,
258 (Fig. 317), 260; gills, spiracle,
gill rakers, and opercula, tables, 262

(Fig. 11, p. 259); swim-bladder,

tables, 264; genital system, tables,

266; urinogenital ducts and exter-

nal openings, 267 (Fig. 333), and

tables, 270; plan of circulation in,
tables, 268 (Fig. 338), 269; ab-
dominal pores, tables, 271; brain of,

272 (Fig. 341); sense organs of,

tables, 276; integument and integ-

umentary sense organs, tables, 279;

comparison tables of the early devel-

opment of, 280, 281.

Siluroid, antiquity of, 9; affinity and
phylogeny of, 147, 166 (171 A),
171; South American Siluroid (Ca/-
lichthys armatus), 172 (Fig. 178);
eggs and breeding habits of, 181
(Fig. 195), 185, 186 and note;
heart, conus and bulbus arteriosus,
tables of, 258 (Fig. 318).

Siphostoma, eggs and breeding habits
of, 186.

SIRENOIDEI, in classification, 8.

Skates, description of, 93-95 (Figs.
100-102) v. Ray.

Skeleton, v. Shark, Pleuracanthus, Chi-
mzroid, Dipnoan, Ceratodus, etc.

Skin defences, v. Dermal and Teeth.

Skull of fishes, dermal bones of head
root of Pleuracanthus, 84 (Fig. 90
A); of Chimeroids, 113; resem-
blances of skull of lung-fishes to
Elasmobranchs, 128; of Dinichthys
intermedius, 133 (Fig. 133 and Fron-
tispiece) ; table of relations of skull,
jaws, and branchial arches of, 254

(Figs. 310-315), 256.

298

Smithsonian Institution, Heplanchus,
88 (Fig. 93).

Solenostoma, eggs and breeding habits,
186.

South American lung-fish, v. Lepido-
siren.

South American Siluroid, v. Cad/ichthys.

Spatularia, v. Polyodon.

Specialized fishes, defined, 12.

Spines, 23; v. Fin spines, Clasping
spines.

Spiracle of shark, 18;
tables of, 260.

Spook-fish, v. Chimzra and Chimz-
roids.

Spoon-bill sturgeon, v. Polyodon.

Squaloraja, in classification, 8; affini-
ties of, 98 (Fig. 103); restoration of,
104, 105 (Fig. 106 4); mandibular
of, 106 (Fig. 108); frontal spine of,
107 (Fig. 115); dental evolution of,
112; skin defences of, 113.

Squalus, 89 (Fig- 94).

Squatina, v. Rhina.

Steindachner, F., 149, 150. ”

Sticklebacks, v. Hemibranchiates.

Sting-ray, shagreen of, 24 (Fig. 23);
dental plates of jaw, 24 (Fig. 29),
25; fin spine of, 28, 29 (Fig. 34).

Stomach, v. Digestive tract.

Strong, O. S., 112.

Structure, characteristic, of fishes, 14.

Sturgeon, v. Acipenser; spoon-bill
sturgeon, v. Polyodon and Psephu-
rus; shovel-nose sturgeon, v. Sca-
phirhyncus ; a Liassic sturgeon,
v. Chondrosteus.

Swim-bladder, hydrostatic, 1, 21, 22
(Figs. 13-19); of Amia, 21, 22
(Fig. 14); of gar-pike, 21, 22 (Fig.
14); of Dipnoans, 21; of Polypterus
and Calamoichthys, 21, 22 (Fig. 17);
of NMecturus, 21; of sturgeon, 22
(Fig. 13); of Teleosts, 22 (Fig. 13);
of Lrythrinus, 22 (Fig. 15); of
Ceratodus, 22 (Fig. 16); of Lepido-
siren, 22 (Fig. 18); of Protopterus,
22 (Fig. 18); of Dipnoans, 129;

comparison

INDEX

compared with reptiles, birds, and
' mammals, 20 (Fig. 19); comparison

tables, 264, 265 (Figs. 13-19).
Swimming: eel, shark, mackerel, 2.

Symmetry of fishes, 4. 1

Synechodus, dentition of, 86,

Syngnathus, 166 (Fig. 171 A); de-
scription of, 177, 178; S. acus, 178
(Fig. 185 4); eggs and breeding
habits of, 186,

Tail, v. Caudal fins.

Teeth, general, 23, 24 (Figs. 27-30);
description and evolution of, 27, 28;
of Port Jackson shark, 24 (Fig. 27),
27, 86; of highly modified fishes,
28; of Myxinoids, 57; of Cladodus,
80 (Fig. 86 B); of Acanthodopsis,

_ 82 (Fig. 88 4); of Pleuracanthus,
84 (Fig. 90 B); of fossil sharks, 86;
of Chimeroids, 113; resemblances
of lung-fishes to Elasmobranchs as
to teeth, 128.

TELEOCEPHALI, included in Actinop-
terygians, 8, 148; description and
phylogeny of, 165, 166 (Fig. 171 4).

TELEOST, antiquity of, 9, 147; gills of,

17 (Fig. 12), 19; operculum of, 19;

gill rakers of, 20; swim-bladder of,
22 (Fig. 13); swim-bladder of Zry-
thrinus, 22 (Fig. 15); scales of, 24

(Fig. 31); caudal fin of, 36, 37

(Fig. 48); the term “ Teleost” used
in the popular sense to denote the
modern “ bony fish,” 139; the perch
a convenient type, 139; general
anatomy of, 141-145 (Figs. 145,
146); skeleton of Perca fluviatilis,
142 (Fig. 146); relationship and
descent, 145-147; description and

phylogeny of, 165,166 (Fig.1714);
modified conditions of, 167-171; —

eggs and breeding habits, 181 (Figs.
196-199), 185, 186; fertilization of,
187 and note; development of egg,
207-212 (Figs. 269-283); larval

development, 223-225 (Figs. 303-
list of authors and their

309) ;

INDEX

_ works, 249-251; comparison tables
of the skeleton of, 253; heart, conus
and bulbus arteriosus, tables, 258
(Figs. 324, 325), 260; digestive tract,
tables, 262 (Fig. 331), 263; urino-
genital ducts and external openings,
267 (Fig. 337), and tables, 271;
circulation in, tables, 269; abdomi-
nal pores, tables, 271; brain of, 273
(Fig. 344); central nervous system,
tables, 275; comparison table of the
early development of, 280, 281.

TELEOSTOMES, in classification, 7, 8;
antiquity of, 9, 10; mouth of, 64
note; opercular apparatus of, 114;
tail of, 115; affinities to Arthrodirans,
136; general description of, 139-
178 (Figs. 145-185 A); skeleton
of, 141-143 (Fig. 146); visceral
parts of, 143; contrasted with
Ganoids, 144 ( Fig. 147); Teleosts
and Ganoids merged into one group
by Prof. Owen, 146; descent of,
146; affinities with the Dipnoans
generally admitted, 146; Rabl de-
tives them from a selachian stem,
146; Beard and Woodward as to
their descent, 146; two principal
subdivisions of, 147; phylogeny,
scheme of, 165, 166 (Fig. 171 A);

_ comparison tables of skeleton of,
253; table of relation of skull, jaws,
and branchial arches, 257; heart,
conus and bulbus arteriosus, tables,
260; gills, spiracle, gill rakers, and

tables, 261; digestive
tract, tables, 263; swim-bladder,
tables, 264, 265 (Fig. 13); genital
system, tables, 266; sense organs,
tables, 277; integument and integu-
mentary sense organs, tables, 279.

Telescope-fish, v. Carassius.

Terrell, J., 130.

Thacher, J., 40.

Thiolliére, 58.

Thrasher shark, v. A/opias.

Tissues, cellular elements of, in Dip-
noans, 129. . oes

299

Titanichthys, pineal foramen of, 55,
56, 135; size and localities of, 130;
lip-like mandibles of, 136; mandi-
bles of 7. clarki, 136, 137 (Fig.
139).

Torpedo, 95 (Fig. 102).

Trachosteus, jaws of, 136, 137 (Fig.
140).

Transactions of Edinburgh Society,
quoted, 70.

Traquair, R. H., 65, 68, 70, 71, 78,
128, 130, 132, 156, 157, 159.

Trygon, dental plates of jaw of, 24
(Fig. 29); fin spine of, 28, 29 (Fig.

Turner, W., 217.

Undina, 147, U. gulo, 154
(Fig. 156 4).

United States Fish Commission Re-
ports, quoted, 3, 89, 90, 92, 94, 95,
155, 160, 162, 163, 171, 173-177.

United States National Museum, Pro-
ceedings of, quoted, 103.

Urinogenital system, comparison tables
of, 266, 267 (Figs. 332-337), 270,
271.

Urogymnus, shagreen of, 24 (Fig. 23).

153;

Ventral plates of Coccosteus decipiens,
132 (Fig. 132).

Vertebral axis of lung-fishes, resem-
blance to Elasmobranchs, 128.

Vienna collection, 149 note.

Visceral characters, resemblance be-
tween lung-fishes and Elasmo-
branchs, 128; of Teleost, 143; of
Ganoids, 145.

Walcott, 65.

Ward, H. A., 75.

Whale, fish-like form of, 6.

Whale, humpback, numerical lines of,
5 (Fig. 7).

Whiteaves, 152.

Whitman, C. O., 187 note.

Wiedersheim, R., 40, 113.

Willey, A., 16.

Wilson, H. V., 208. _

Woodward, A. S., 8, 10, 24, 25, 33,
42, 66, 68-71, 80, 81, 106, 107,
112, 321, 127, 129, 131, 132, 135,
136, 146, 151, 154, 161, 164, 165;
phylogenetic table, compared, 282.

Works on the general subject, fishes,
231-234; on the Cyclostomes, 234-
238; on the Ostracoderms and
Paleospondylus, 238; on the sharks,
238-244; on the Chimzroids, 244;
on the lung-fishes, 244-246; on the

INDEX

Ganoids, 246-2495 on
249-251.

Xenacanthus, pectoral 4
om 53)» 455 pai :

ee:

Zittel, K. v., table of geol
tribution of fishes, 9;
82, 104, 124, 157, 158)

Zodlogical Society, :
257 note.

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