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Ryder, John A.
On the Development of Osseous Fishes, Including
- Marine and Fresh-water Forms.
Report U.S. Fish Commission, XIII, Washington, 1885.
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XX.-0N THE DEVELOPMENT OF OSSEOUS FISHES, INCLUDING
MARINE AND FRESHWATER FORMS. *
BY JOHN A. RYDER.
I.—GADUS MORRHUA L. (The Cod.)
The main features of the development of this species have been de-
scribed and illustrated in a previous memoir” by the author, so that it
will not be necessary to do more than to add observations made since
the publication of that paper, and otherwise complete the record of the
early life-history of this important food-fish.
The views of Hoffmann” as to the meaning and sequence of the phe-
momena attending the fertilization of fish ova have been disputed since
the above-cited essay was written, and apparently upon the basis of
well-determined data. The most recent contribution to this subject is
by Agassiz and Whitman,” who state, page 19, in reference to the de-
velopment of Ctenolabrus, that “immediately after the penetration of
the spermatozoön a disk-like thickening of the cortical layer appears
at the lower pole of the egg; and at the center of this disk may be
seen, in mounted preparations, the minute male pronucleus. It is a
curious fact, of which the proof will be given in our second memoir, .
that the male pronucleus becomes the center of attraction around which
the discoidal aggregation of protoplasm takes place, and towards which,
after the formation of the second polar globule, the female pronucleus
gravitates.”
In another paper* Agassiz and Whitman have also discussed the
origin of the periblast, as it is called by them, reaching the conclusion
that the “autoplasts” (Lankester), the free nuclei of authors, do not
arise Spontaneously in the layer of protoplasm underlying the germinal
disk, nor from a single nucleus developed at the time of the first cleav-
*A contribution to the embryography of osseous fishes, with special reference to the
development of the cod (Gadus morrhua). Report of the United States Commissioner
of Fish and Fisheries, part x, for 1882, pp. 455–605, pls. xii. Washington, 1884.
* C. K. Hoffmann. Zur Ontogenie der Knochenfische, chapters i-viii, 4to. Amster-
dam, 1881.
*A. Agassiz and C. O. Whitman. The development of osseous fishes. I. The pe-
lagic stages of young fishes. Studies from the Newport laboratory. Mem. Mus. Comp.
Zool.., xiv, No. 1, part 1, 4to, pp. 56, 19 plates. Cambridge, 1885.
* On the development of some pelagic fish eggs, preliminary notice. Proc. Am. Acad.
Arts and Sciences, xx, 8vo, pp. 23–75, 1 pl. 1884.
[1] as
490 REPORT of commissionER of FISH AND FISHERIES. [2]
age, as held by Hoffmann (op. cit.), but are segmented off from the
marginal cells of the segmenting blastodisk as suggested by the Writer
in his first paper on the cod.
With the further growth in diameter of the blastodisk the marginal
cells, which are without well-defined outlines, are finally covered over by
the spreading blastodisk. In this way the nuclei of the periblast (a
layer which is in reality a syncytium) are finally brought into such a
position that they seem to underlie the blastodisk. The nuclei in the
periblast are, however, always most abundant near the edge of the blas-
todisk at an early stage of development. During the later stages the
nuclei of the periblast are most numerous just beneath the embryonic
axis, especially under the head.
The marginal segmentation, which gives rise to the so-called “free nu-
clei” of the periblast, first clearly described by Agassiz and Whitman,
leads to the formation of a wreath of flat cells which form a more Or
less well-marked zone around the blastoderm upon the completion of
the segmentation of the blastodisk. This marginal wreath of cells, “nu-
clear zone” of Kupffer, has been figured by the latter," E. Van Bene.
den,” the writer," Brook,” Cunningham,” and by Agassiz and Whitman.
The essential agrºment of so many observers working upon very dif.
ferent species slit..'s that this nuclear zone must be very generally de
veloped in the eggs of Teleosts, and even amongst the Salmonidae,
where it is not so easily observed in the living egg, but which is shown
in the sections figured by E. Ziegler.”
The development of this “nuclear zone” in the eggs of the cod es-
caped my observation when I studied the development of that species
in 1881, but I have during the past year (1885) observed it, and have,
moreover, satisfied myself that it arises as observed in Ctenolabrus, by
Agassiz and Whitman, and that it is subsequently covered over by the
spreading blastoderm, while the nuclei of the periblast, also subdivide
by the indirect method, and proliferate inwards beneath the blastodisk.
Cunningham's observations are in accord with these.
The synonymy of the term periblast may profitably be considered
here. It obviously corresponds to the “white yelk” of the bird's egg;
* Kupffer. Beobacht. ii. der Entw. der Knochenfische. Arch. f. mikr. Anat., iv, pl.
xvi, fig. 1. 1868.
° E. Van Beneden. A contribution to the embryonic development of the Teleosteams.
Quar. Jour. Mic. Sci., xviii, 1 pl. 1878.
7 J. A. Ryder. Development of the Spanish mackerel. Bull. U. S. Fish Com., i,
1881, pp. 135–172, pl. i., fig. 4.
7"J. A. Ryder. Development of the silver gar. Bull. U. S. Fish Com., i, 1881, pp.
283-301, pl. xix, fig. 3.
* Brook. Preliminary account of the development of the Lesser Weever-fish, Trachi-
nus vipera. Journ. Linn. Soc. Zool.., xviii, 1884, pp. 274–291, pl. iii, figs. 8, 9–9a.
*J. T. Cunningham. On the relations of the yeak to the gastrula in Teleosteans,
and in other vertebrate types. Quar. Jour. Mic. Sci., 1885, pp. 38, plb. iv.
"Die embryonale Entwickelung von Salmo salar. Inaug. Diss., Freiburg i, B.,
1882. Taf, i, figs, 6–10.
[3] DEVELOPMENT OF OSSEOljS FISHES. 491
“Subgerminale Platte” of Kupffer; Dotterhaut and membrana vitellina of
CEllacher; couche intermédiaire of Van Bambeke; intermediary layer of
authors; parablast of His, Waldeyer, Hoffmann, Gasser, Kupffer; yelk-
hypoblast of the writer; couche harmatogéne of Vogt; and the plasmedium
of Rauber.
The annular thickening of the periblast, just under the edge of the
blastodisk, is clearly homologous with the Keimwall of His or the Keim-
wulst of Kölliker, as seen in the ova of Sauropsida. The function of
this periblast is also clearly established throughout the various series
of Vertebrates which develop meroblastic ova; its cells, in fact, in-
corporate yelk particles, by a process which is essentially one approx-
imating that of intracellular digestion. Finally, the periblast may give
rise directly to free cells, which pass into the vascular channels of the
embryo as blood-corpuscles.
This disposition to absorb the underlying quiescent plasma is also
shown by the lower cells of the true hypoblast which immediately over-
lies the periblast. Such hypoblastic cells which are larger than their
neighbors have been called megasphaera by His, arſd have also been
figured by Kölliker in the Avian blastodisk, while they have been en-
countered by the writer in the blastodisks of Teleosts.
In the eggs of the cod, as in most pelagic fish the periblast is
quite thin after the closure of the blastopore, but as the veik diminishes
in quantity with the progress of development this layer becomes de-
cidedly thicker. The entire yelk is, in fact, first converted into the
plasmodial substance of the periblast before it is absorbed by other
parts of the embryo. It therefore results that the last portion of the
yelk to disappear is the periblast.
The periblast is undoubtedly hypoblastic in position, and in many
large-yelked forms is homologous with the splanchnopleure, as in the
case of the embryos of Salmonoids, in which, together with the vascular
network traversing it superficially, it eventually occupies the position
of the splanchnopleural mesoblast in relation to the other layers.
(1) Development of the hypoblast or the gastrulation of the egg.—This
almost threadbare subject I return to reluctantly, because so much
which is erroneous has been written about it. Balfour's account in his
Comparative Embryology, ii, 57, is far from clear, and conveys but
little definite information as to the origin of the hypoblast. That the
latter is developed as a “centripetal ingrowth of cells from the margin .
of the blastodisk” (Agassiz and Whitman) there can no longer be any
doubt, though in my earlier studies on the development of the cod I
opposed that view, because I had not succeeded in witnessing the pro-
cess, which I have observed since in detail, as has also been done by
Cunningham.
I find that the cells at the edge of the blastodisk are inflected around
its entire margin, but that at the point where the future embryo is
formed the ingrowth is most rapid, and soon becomes somewhat wider.
492 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [4]
Later, the hypoblastic layer, which has arisen by the process of inflec-
tion just described, forms a sort of rounded promontory or tongue of
cells, several deep, which is prolonged inwards under the epiblast with
the progress of the development and the growth in length of the two-
layered rudiment of the embryo. The views of Goette,” Haeckel,” Hen-
neguy,” Ziegler, Kingsley and Conn,” Agassiz and Whitman, Brook,
and of Cunningham, on this point, agree pretty closely as to the main
fact of the occurrence of a marginal inflection of the blastodisk.
As observed by a number of investigators, the centripetal inflection
of the margin of the blastodisk of Teleosts does not lead to the for-
mation of a continuous plate of cells underlying the sensory layer of
the epiblast, and of the same area as the latter. A very considerable
area beneath the epiblast, and occupying an excentric position in the
blastodisk, is not invaded by the ingrowing hypoblastic layer. The
space not so invaded and bounded by the epiblastic layer above, the
inflected lips of the hypoblastic layer at the sides, and by the periblast
below, is the depressed or flattened blastocoel of the Teleostean ovum.
It is perfectly homologous with that of Branchiostoma, but is flattened
or depressed by the way in which the growth of the blastula is modified
by the presence of a large yelk, which is itself invested by the peri-
blast or yelk-hypoblast. The blastula becomes, in fact, a hollow disk.
The yelk-periblast or yelk-hypoblast, and the inflected hypoblast are
hypoblastic in their relations, and must accordingly be invested in the
course of development by the epiblast by epibole. The epiblast and
hypoblast are accordingly fused at the margin of the blastodisk. The
entire margin of the blastodisk must consequently be regarded as the
blastopore or archistome of the developing Teleostean ovum, as origi-
nally implied by Haeckel. Such a condition of things would be brought
about by loading or surcharging the cells of the hypoblastic pole of the
blastula of Branchiostoma with yelk substance. The way in which the
discoblastula arose may be very easily understood, if the gastrula stages
of Branchiostoma, Rana, and Gadus are carefully compared.
With the gradual increase in the size of the yelk in the vertebrate
series, it finally happens that the principal morphological features of
the embryo are distinctly developed long before yelk absorption is com-
pleted. As a result of this, the yelk, which occupies a ventral position
in reference to the intestine, is finally excluded from direct connection
with the latter, and the periblast (hypoblastic in origin) is made to as-
sume a new function, viz, that of ministering to the incorporation of
* Goette. Berlin. medicin. Centralblatt, 1869, No. 26, pp. 404–466, and Arch, für mik.
Anat., ix, 1873, p. 679. -
*Haeckel. Die Gastrula und die Eifurchung. Jena. Zeitschr., ix, 1875.
19 Henneguy. Note sur quelques faits relatifs aux premiers phénomènes du dével-
oppement des poissons osseux. Bull. Soc. Philom. de Paris, 10 Apr., 1880, p. 4.
*Kingsley and Conn. Some observations on the embryology of Teleosts. Mem.
Bost. Soc. Nat. Hist., iii, pp. 183—212, ple. xiv-xvi, 1883.
[5] DEVELOPMENT OF OSSEOUS FISHES. 493
the vitelline matter. Kollmann” has lately presented some strong evi-
dence in favor of this view, but is in error in assuming that the lips of
the inflected rim (hypoblastic stratum) of the blastoderm are the lips
of the blastopore. If this view is admitted, we are logically forced to
conclude that the yelk is something extraneous, and is not an integral
part of the ovum, as we know it to be, judging from the way in which
the periblast arises. The manner in which the latter is formed.shows
that the continuity of the blastodisk with the plasmic layer investing
the yelk is perfect, and that the cleavage cavity is exactly homologous
with that developed in a holoblastic ovum. There is, therefore, a blas-
tula stage developed in Teleosts which is most distinctly evident at the
time the “nuclear zone” is formed. The vesicular syncytium formed by
the periblast is, however, so enormously distended with passive yelk
that gastrulation is modified to an extreme degree. Kollmann's argu-
ments against the final closure of the blastopore at the edge of the
blastoderm and at the hinder extremity of the axis of the embryo breaks
down completely, if the processes of gastrulation of Branchiostoma, Rana,
and Gadus are compared, because such a comparison shows: First, that
a gradual loading of the entoblastic pole of the blastula with yelk causes
the latter to be constricted around its equator in the course of develop-
ment, thus leading to the formation of a blastodisk with an inflected
two-layered margin. Secondly, since the foregoing is true, it results
that active development is shifted so entirely towards one pole of the
egg that gastrulation also occurs there, and an attempt is made to re-
produce the state of things seen in the gastrula of Branchiostoma, but
in the effort of the active pole of the blastula to envelop the passive
one by epibole it appears as if the annular entoblastic invagination was
incomplete, leaving the “Urmund” of Kollmann open. This “Urmund”
is homologous with a circular opening which might be produced by a
rupture near the center of the inflected entoblast of the gastrula of
Branchiostoma, and therefore is in no sense homologous with the true
blastopore. The opening in the floor of the discoblastula of Teleosts
and Elasmobranchs, identified by Kollmann with the blastopore, I pro-
pose to call the discopore, in order to permanently distinguish it from
the true blastopore of authors. An equally fatal objection to Koll-
mann's view is that on the basis of his interpretations the blastopore of
Teleosts and Selachians would not open to the exterior.
A view resembling in some respects that of Kollmann was enter-
tained by me in 1881 (see 7a, 8wpra, p. 298), though it way immedi-
ately qualified in paragraph 2 which followed on the same page, and
was subsequently adopted in a modified form in my first paper on Gadus
(Contr. Embryog. Oss. Fishes, p. 569). I had also observed” and
figured the segmentation of the “nuclear zone” or “marginal wreath of
"Kollmann. Gemeinsame Entwickelungsbahnen der Wirbelthiere. Arch. f. Anat.
u. Physiol., 1885. Anat. Abth; pp. 279–306, pl. xii.
* See No. 7, p. 146, fig. 4, pl. 1; and also No. 7a, p. 287, fig. 3, pl. xix.
494 REPORT OF COMMISSIONER OF FISH AND EISHERIES. [6]
cells” from the edge of the blastodisk. And contrary to what some of
the more recent writers on Teleostean development would seem to imply,
I had already suggested that the nuclear zone gave rise to the nuclei of
the periblast, as the following quotation will show : “The free nuclei
of the yelk-hypoblast apparently proliferate as the blastoderm spreads.
They are, at any rate, at first confined to the germinal pole of the
ovum, and are only found at the opposite pole after the yell:-globe has
been included by the blastoderm. The inference, therefore, is that they
spread and multiply with the lateral growth of the blastoderm. It is
these nuclei possibly which are the centers of certain free cells around
the margin of the germinal disk when the latter has attained the morula
stage, as in Cybium and Tylosurus, as shown in fig. 3, pl. xix, of my
essay on the latter form. If such is the case, it is possible that the
germinal wall (Keim wall) at the edge of the blastoderm of the chick is
homologous with the yelk-hypoblast of the fish ovum” (Contr. Embryog.
Oss. Fishes, p. 569). \
The marginal inflection of the blastodisk is figured by Kingsley and
Conn (No. 14) in Ctenolabrus, and by Brook," " as being composed of
larger cells than that of the epiblast. Kingsley and Conn represent
only a single layer in Ctenolabrus, a condition which I have never
found to exist in sections of the disks of any of the species studied by
me. Brook represents several layers of larger cells in the hypoblast.
That the inferior stratum of cells of the inflected hypoblastic layer are
perhaps somewhat larger than those of the epiblast I admit, but that
they are generally very unuch larger or that the inflected hypoblast is
ever formed of a single layer, as held by Kingsley and Conn, I am dis-
posed to question.
Cunningham (On the relation of the yelk to the gastrula in Teleos.
teans, etc.,) has studied the development of three Gadoid forms, and has
been the first English investigator who has declared himself an advo.
cate of the concrescence theory, which, in its various forms, has been
supported by His,” Rauber,” Whitman,” and myself,” and latterly by
Duval” and Kollmann. - -
* Brook. On some points in the development of Motella mustela L. Journ. Linn.
Soc. Zool., xviii, Nov., 1884, pp. 298–307, pls. viii-x.
"Brook. On the origin of the hypoblast in pelagic Teleostean ova. Quar. Journ.
Mic. Sci., Jan., 1885, pl. iii.
1° W. His. Ueber die Bildung der Haifischembryonen. Zeitschr. f. Anat. u.
Entwickelungesch., ii, 1877, pls. vii; also, Untersuch. iib. die Entwick. von Knochen-
fische, etc., in vol. i of same journal, 1 pl.
*Rauber. Primitifstreifen und Neurula ; also, Die Theorien der excessiven Monstra,
Virchow's Archiv. lxxi, 1877, ple. 3.
* Whitman. Embryology of Clepsine. Quar. Jour. Mic. Sci., July, 1878, pp. 101,
ple. xii-xv.
* Ryder. On the formation of the embryonic axis of the Teleostean embryo by the
concrescence of the rim of the blastoderm. Am. Naturalist, 1885, pp. 614–615, 1 fig.
* Mathias Duval. De la formation du blastoderme dans l'oeuf d'oiseau. Ann. Sci.
Naturelles. Zool., 6° sér., tome xviii, pp. 208, ple, 5, 1884. -
. [7] DEVELOPMENT OF OSSEOUS FISHES. 495
The strenuous opposition to the doctrine of concrescence manifested
by Balfour arose apparently from his too constantly interpreting all of
the higher vertebrate types of development upon the basis of his bril-
liant researches on the Elasmobranchs. Later research has only con-
firmed the doctrine and added little except a clearer knowledge of the
details of the process, and I may add that Whitman has recently gone
over the subject of the concrescence of the germ bands in Clepsime, and
will shortly present the most conclusive evidence of the soundness of
the views which he originally published in 1878. The evidence as to its
occurrence in Gadus becomes palpable upon the advent of the initial
steps of the inflection of the blastodermic margin. The inflected layer
soon becomes wider in the region where the embryo" is formed and is
prolonged with the progress of the extension of the blastoderm over the
yelk. The concrescence of the lips of the primitive blastopore in the
middle line of the embryo would also tend to carry a larger number of
periblastic nuclei under the anterior and middle region of the true hypo-
blast. It does not necessarily follow, however, that the floor of the in-
testine is formed by cells derived from the periblast, as occurs in Elas-
mobranchs (teste Balfour), and as held by Cunningham, though there
is no objection to such a view. The principal conclusions reached by
Cunningham as to the homologies of the yelk-blastopore are, however,
not new, as Rauber” and myself” had previously reached the same or
very similar interpretations. g
Rauber considers what I have called the “yelk-blastopore” to repre-
sent the “blastostomion verum ” or true blastopore in types with a large
yelk. The blastopore of the latter types, usually regarded as such by
embryologists, and developed at the anterior part of the primitive streak,
Rauber calls the “blastostomion consecutivum seu intermedium.” Both
openings together are for him simply differentiations of the primitive
“blastostome.” This blastostome, or the blastopore, as it is usually
called, of the Bilateralia, whether round or drawn out into a cleft by a
process of growth in length, or of concrescence, I have elsewhere” dis.
tinguished as the archistome.
(2) Later development.—The more advanced stages of the cod embryo,
though studied by Sars and others, have never been correctly figured
by any one because of the fact that a very large vesicle on the upper
side of the head has been entirely overlooked, probably because of the
extreme transparency of this portion of the young fish. In my first
paper on the development of the cod (Contrib. Embryog. Oss. Fishes,
plg. xi and xii), figs. 45 and 49, which are side views of embryos,
figured ten and seven days after hatching, give the erroneous impres-
sion that the median fin-fold extends quite forward between the nasal
*Rauber. Die Lage der Keimpforte. Zoolog. Anzeiger, ii, 1879, pp. 499–503.
*Ryder. On the position of the yelk-blastopore as determined by the size of the
vitellus. Am. Naturalist, April, 1885, pp. 411–415.
* Ryder. The Archistome Theory. Am. Naturalist, Nov., 1885, pp. 1115–1121.
496 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [8] .
pits. The same would also be inferred from another figure representing
an advanced larval cod, published in a later paper* by the writer.
The true state of the case is as follows, as may be gathered from figs.
1 and 2, plate i : The true median dorsal fin-fold only extends as such
forwards as far as to about or slightly behind a vertical line passing
through the base of the pectoral. The larval integument continuous with
the median dorsal fin-fold and covering the brain and fore part of the
spinal cord is not prolonged forwards as a flat duplicature or fold, but
is distended as an oblong vesicle and filled with a serous fluid, as shown
from the side in fig. 1 and from the front in fig. 2.
Immediately after hatching, this sinus or space between the integu-
ment and the brain is small, as may be observed in fig. 40, plate ix,
of my first paper, but in about one day after hatching it begins to be
obvious that the integument, over the brain and as far back as to the
vertical from the end of the intestine, is being lifted up and becoming
filled with fluid. This proceeds until at the end of a week or ten days
the larval cod, when viewed from the side or front, presents a most sin-
gular resemblance to the conventional dolphins of the ancient sculptors.
The rounded and swollen front and top of the head is in marked con-
trast with the majority of pelagic fish larvae.
That the integument is actually lifted up from the underlying struct-
ures is shown by the fact that the long efferent branches of the vagus
group of nerves which pass outward to button-like thickenings of the
epiblast armed externally with stiff protoplasmic hair-like processes,
may be traced through the wide space between the integument and the
brain when the embryo is examined by transmitted light. Three pairs
of such segmental sense organs or neuromasts (Wright) are found in
the walls of the large integumentary vesicle overlying the head and
body of the young cod. These organs are disposed quite symmetrically
on the fore part of the body, but posteriorly they are not symmetrically
disposed on the sides of the tail, as may be seen by referring to plate
x, fig. 42, Embryog., Oss. Fishes. Agassiz and Whitman, in their last
memoir (Pelagic stages of young fishes), also figure and describe larval
fishes in which there was more or less asymmetry noticeable in the ar-
rangement of the caudal neuromasts.
The great anterior dorsal integumentary vesicle of the larval cod is
gradually developed after hatching, and appears to increase in size as
the yelk sack diminishes and becomes empty. I first noticed and
described what is obviously homologous with this vesicle, which is
so exaggerated in dimensions in the larval cod, in 1881, in the Span-
ish mackerel, as may be learned if the reader will consult plates iii
and iv, figs. 14, 15, 16, and 17, illustrating my paper on the develop.
ment of that species (Bull. U. S. Fish Com., i, 1881, p. 157), where it is
also stated that it is developed after hatching, as is shown by the con-
* Ryder. An outline of a theory of the development of the unpaired fins of fishes.
Am. Naturalist, Jan., 1885, pp. 90–97, fig. 3, r
[9] DEVELOPMENT OF ossEoUs FISHEs. 497
dition of the vesicle in a larva just hatched and figured on plate ii of
the paper cited. At that time I named the space in the supracephalic
vesicle of the Spanish mackerel, the “supracephalic sinus.” Now, while
it is clear that this sinus is the homologue of the much larger one in the
larvae of Gadus, it is also clear that in the latter it extends not alone
over the brain as in Scomberomorus, but even back dorsally beyond the
hinder limits of the body cavity. -
I have good reasons for believing that a sinus of the same character
overlies the brain in a number of the species figured by A. Agassiz and
his associate Whitman as well as in the larvae of Trachinus and Motella
figured by Brook. In fact, I doubt if the structurerepresented in advance
of the first developed dorsal fin-ray on the head of the larva of Lophius
by A. Agassiz” is a fin-fold at all, but merely the integumentary vesicle
or bulla described above, though the contrary is expressly stated on.
page 282 of the memoir last cited. A still more remarkable instance of
the extension apparently backward and laterally of what I have called
the “supracephalic sinus” is represented however by Agassiz and Whit-
man on plate xii, figs. 7 and 8, of their recent memoir (Pelagic stages
of young fishes, part I, 4to, 1885). In this form the sinus has been ex-
tended back for two-thirds of the length of the larva and also over the
sides of the head. The form in question is supposed by its describers
to be near Motella.
It is therefore probable, taking into account the facts recited above,
that the true, median, dorsal fin-fold is never extended as far forward
as the front of the head, as I had assumed in my paper cited above on
the development of the median fins, but that such an apparent anterior
dorsal extension of the fin-fold is due to the illusion produced by the
extreme transparency of the integument of the dorsal vesicle or bulla
just described, the presence of which is not easily made out until the
living embryo is viewed from in front. The true median fin-fold in the
larvae of Gadus is therefore but little longer proportionally than that of
other types of larvae which are without a supracephalic bulla. The
archaic extension of the fin-folds in fishes therefore, it seems, must have
been about the same as that generally prevalent to-day in young larvae,
or an extension of the fin-folds which is most nearly approximated by
such adult forms as the Dipnoi. :
The contents of the bulla or sinus have been but little studied, but it
is probable, judging from certain observations upon the contents of the
fin-folds of larval fishes by Emery,” that this bulla in Gadus contains
coagulable albumen. I have found such a coagulum in the fin-folds of
hardened embryos of Clupea. And in embryos of Scomberomorus I found
loose granular matter in the sinus on the top of the Yead and fin-folds.
* A. Agassiz. On the young stages of osseous fishes. Part iii, Proc. Am. Acad.
Arts and Sci., xvii, 1882, pla. xvi, xvii.
*Emery. Sulla existenza del cosidetto tessuto di secretione nei vertebrati. Atti
R. Acad. Sci., Torino, xviii, 1883.
S. Mis. 70 32
498 REPORT OF COMMISSIONER or FISH AND FISHERIES. [10]
In larvae of Gadus hardened in chromic acid there seems to be such a
coagulum existing in the dorsal bulla already fully described. This
bulla therefore partakes of the nature of a lymph-space.
(3) Changes of position of the cod's egg and embryo during development.—
The germinal disk of the cod’s egg, like that of the ova of most Teleos-
teams, is developed at the time of impregnation. The single spermato-
zoön necessary to effect impregnation and initiate developement enters
the egg through a minute round pore in the egg-membrane or zona
radiata, known as the micropyle. But one such opening is found in the
egg of the cod, and I believe that reliable authorities concur in the be-
lief that there is but one such opening in the inembrane which invests
the ovum of Teleosts.
The male element can therefore enter the ovum at one point only,
and, inasmuch as the superficial cortical layer at the time of impregna-
tion, and from which the blastodisk or germ is developed, lies in imme-
diate contact with the egg-membrane or zona, the point of contact be
tween the egg and spermatozoön is also limited by the area on the ovum
covered by the micropyle. That area is excessively small. The polar
cells in the cod’s egg are also extruded immediately beneath the micro-
pyle and invariably in very close relation to it. Furthermore, the active
plasma of the egg gravitates towards the point where the spermatozoön
entered the egg, and the greater part thus accumulates in the vicinity
of the micropyle, as shown in fig. 3, pl. i., where the polar cells joining
the egg to its membrane are also indicated. I never saw any polar
globules expelled through the micropyle.
As soon as the blastodisk becomes apparent as a thickening or ag-
gregation of the substance of the cortical layer it assumes an inferior
position, because the specific gravity of the plasma of the disk is greater
than the same volume of yelk, the whole of which now occupies the
upper pole of the egg. Later still, when the disk D, fig. 4, is better
defined, the force of gravity, still acting in the direction of the arrow,
which points toward the micropyle, constantly keeps the disk in an in-
ferior position, which is maintained until the blastodisk begins to
spread and the embryo to be formed. When the blastodisk or the
blastoderm, as it may now be more appropriately called, has spread
over one-half of the Vitelline globe, as shown in fig. 5, the embryo is
pretty well defined at one side of the blastoderm, and extends from its
margin to its center. This causes the blastoderm to become heavier
at the side upon which the embryo is formed, and, as a consequence,
the whole egg is slightly rotated upon its own center so that a radius
drawn from the latter to the center of the original site of the blastodisk
of an earlier stage will be inclined to the horizon at an angle of 459.
As development proceeds still further the embryo of course lengthens
as the blastoderm spreads, till finally the embryo embraces an arc of
180° on the yelk-globe. As a result of this the radius passing from
the center of the egg to the original site of the center of the blastodisk
[11] DEVELOPMENT OF OSSEOUS FISHES. 499
is swung round still farther, so that the total rotation of the egg now
amounts to about 90°, as a comparison of fig. 6 with fig. 4 will show, as
indicated by the arrows.
Further changes of the position of embryo in the egg as development
advances are hard to follow, but these are the principal and most strik-
ing ones. When hatching takes place the vitellus is always so much
lighter than the embryo that the latter floats about in the water on its
back. In the course of a day or so the embryo is able to right itself.
The next change in the position of the free embryo, when at rest in
the water, occurs some days after hatching and seems to result from
the development of the great bulla already described and which is grad.
ually developed on the head and over the upper part of the body. When
larvae of a few days old swim they are inclined to move the body for-
ward horizontally in a right line, but as soon as they come to rest the
tail drops down into an inclined position, and forms an angle of about
45° with the horizon. This was so constantly observed to be true of
advanced embryos that I have inferred that the bulla developed on the
head caused the latter to be buoyed up, just as the less advanced
embryo is buoyed by the yelk before its absorption. This seemed all the
more probable from the fact that the very rudimentary air-bladder in
larvae of that age does not as yet appear to contain air.
The function of the integumentary bulla on the head, therefore, seems
to be, in part at least, to serve as an organ aiding in the flotation of the
embryo. This seems all the more probable from the strongly marked
pelagic tendencies manifested by the eggs and larvae of the cod at all
stages in sea-water of normal specific gravity or in water having a
density of 1.025.
(4) The most recent and successful method of hatching cod and other pe-
lagic eggs.-I will here reproduce in part what I have already published
elsewhere.”
For four seasons experiments have been carried on for the purpose of
discovering a practical method of hatching the eggs of the cod—one of
the most fertile and valuable of the food-fishes found off our coast.
IDuring the period mentioned no less than forty forms of apparatus have
been devised and operated, with varying success, by different persons
connected with the work of the U. S. Fish Commission. Up to the
present time no device has fulfilled the required conditions, even ap-
proximately, with Such success as the apparatus just devised by H. C.
Chester, superintendent of the Wood's Holl station of the Commission.
This apparatus is essentially automatic, and needs so little attention
that one man will by its aid readily care for a hundred millions of eggs.
It consists of a trough, 7 feet 6 inches in length, 2 feet in width, and 2
feet 4 inches in depth. At about 1 foot from either end, vertical wooden
partitions, extending to within 4 inches of the bottom of the trough,
* Ryder. Success in hatching the eggs of the cod. Science, vii, 1886, No. 153, pp.
26–28. Also, Hatching codfish eggs. Forest and Stream, xxv, No. 25, Jan. 14, 1886,
p. 488. - *
500 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [12]
are secured. This leaves a space about 5 feet 6inches in length between
the partitions. In this space 6 or 8 large glass jars are supported upon
a frame, with their tops downward. Those used for the purpose at
Wood's Holl are ordinary cylindrical, four-gallon specimen jars, with a
half-inch hole drilled in the bottom. The stoppers of the jars are re-
moved, and a single thickness of coarse cheese-cloth is secured over the
mouth with strong twine. The jar is then inverted and lowered into
trough, so that its bottom is about even with the top of the trough.
Strips nailed across the top of the trough serve to keep the jars upright.
The accompanying figure, showing the device in longitudinal vertical
section, modified and designed on a somewhat smaller scale than the de-
vice now in use and accommodating only four jars (two in a row), will en-
able the reader to get a clear conception of the way in which the appa-
ratus is used. The trough A is filled with unfiltered sea-water through
the faucet i, the water rising to the level of the line a before the capa-
cious outlet siphon s begins to operate. This siphon, through which
the water runs out of the trough faster than it comes in at i, soon brings
the water down to the level of the line b, when the siphon takes in air and
ceases to operate, after which the trough again slowly fills up with water
to the level of the line a. This process is repeated automatically, and
as long as the water is permitted to flow through the device. It requires
ten minutes for the water to rise or fall from the one level to the other;
and, since the jars have only a cloth tied over the mouth below, the
water rises and falls to the same extent in them. This very slow and
gentle rise and fall of the water in the jars and trough has been found
sufficient to aerate the eggs and give them all the movement they need.
All of the good eggs in this contrivance float at the surface; some,
during the latter stages of hatching, will fall below the surface, but if
such ova are washed, they will again rise to the surface, and an exceed-
ingly small percentage of the eggs ever sink and die, as in almost all
of the other forms of apparatus hitherto used. The result is that the
mortality is probably under 5 per cent—a percentage of loss not greater
than that experienced in the most successful treatment of shad ova in
the McDonald jar. - - *
The freshly fertilized ova, treated with an abundance of good milt,
are introduced into the hatching device through the hole in the center



[13] DEVELOPMENT OF OSSEOUS FISHIES. 501
of the bottom of each jar by means of a glass funnel. Beyond an occa
sional siphoning-off of the sediment on the bottom of the trough and
the cloth covers of the jars, the eggs require no attention until hatched.
Heretofore great mortality has been caused by the use of metal in the
construction of hatching vessels and strainers. Since the adoption of
glass, wood, and cloth as the only materials used in the construction of
the hatching apparatus here described, combined with the very gentle
movement to which the eggs are subjected, complete success has been
attained. The eggs are caused to oscillate up and down through a
space of only 5 inches from the level of a to that of b, and, withal, so
gently that they suffer no hurtful shocks of any kind whatever. Cap-
tain Chester's device will doubtless be used with great advantage in the
propagation of the Spanish mackerel. In twenty-four hours the em-
bryos of the latter would be ready to be set free from the apparatus;
whereas it requires eleven or twelve days to hatch the eggs of the cod,
with the temperature of the water ranging from 45° to 480 Fahr.
Each of the jars J is 17 inches high by 9 inches in diameter, and will
hold from one-half to one million of cod eggs; so that an apparatus of
the style shown above, and occupying not much over a square yard of
space, would accommodate from two to four millions of ova, in four
jars. -
These results and experiments show that violent movement of the
eggs of the cod is of no advantage; that such movement is, on the con-
trary, injurious if not mortal when continuously maintained. The
requisite conditions for the successful hatching of this important food-
fish having been settled, the great station of the Fish Commission at
Wood's Holl affords unlimited opportunities for conducting the work
for at least three months of the year, during which time from five hun-
dred to one thousand millions of eggs might readily be hatched out by
the aid of the Chester apparatus and set free in the adjacent waters.
The proper specific gravity of the sea-water has a great deal to do
with the healthy development of the eggs of the cod. By accident a
broken valve admitted fresh water to the pumps which supplied our
salt-water tanks, causing the specific gravity of the water to fall from
1.0256 to 1.021 or 1,022. In the latter densities the eggs immediately
sank, but rose at once if placed in sea-water of the specific gravity first
mentioned. The break in the valve through which fresh water was
added to that which was pumped from the harbor for use in our hatch-
ing troughs, caused us to lose over two millions of good eggs. After
this unfortunate experience, and also judging from the fact that ever
since the break in the valve has been mended no eggs have sunk or
subsided to the bottom, we have concluded that the cod egg, in order
that it may develop normally, must float at or near the surface. Under
no other conditions does it seem possible to get them to develop regu-
larly and without serious losses. s f
It was also found in the course of subsequent experience that the
constant flow of cold water around the jars immersed in the troughs
502 REPORT of commissionER or FISH AND FISHERIES. [14]
tended to keep the temperature in the latter constant, so that all the
eggs developed at the same rate. In other apparatus devised in imita-
tion of Chester's device, but in which the hatching vessel was not sur-
rounded by a constant supply of fresh, cold sea-water, irregularities of
development were often very pronounced. This seemed to be due to
the unequal temperature of the water at the sides and center of the
vessel, owing to radiation from the atmosphere of the room. In these
other forms of apparatus, development seemed to proceed normally
until within a day or two of hatching, when the eggs would suddenly
sink and die.
(5) The post-larval stages of development of the cod.—I have not seen
any of the more advanced stages; none older in fact than about ten
days after hatching. A. Agassiz” has figured two stages believed to
appertain to the common cod. These show the chin barbel and the
ventral fins developed, neither of which were yet developed in the old-
est stages seen by me. These specimens measured respectively 20
and 28" in length, or from four to five times as long as the oldest speci-
mens I have seen, so that there still remains a large gap to be filled up
in the iconography of the stages of development of this species.
II.-ROCCUs LINEATUs (BLOCH) G.ILL. (The Striped Bass, or Rockfish.)
The artificial fertilization of the eggs of the striped bass was, I be-
lieve, first accomplished by Mr. E. H. Walke, of the United States Fish
Commission, in 1879, and in 1881 Mr. S. G. Worth” reported his suc-
cess of the previous year in the artificial fertilization of the eggs of this
species. The species is very fertile; a single female was estimated by
Mr. Worth to have contained 3,000,000 eggs in her roes. Spawning
and hatching appear to occur in fresh water, and according to Mr.
Worth the eggs are of less specific gravity than those of the shad, ex-
tremely transparent or pellucid when in the water, and measuring nearly
one-seventh of an inch in diameter after impregnation, when the zona
radiata becomes greatly distended and freed from contact with the wi-
tellus. The freshly extended ova were found to be smaller than those
of the shad, and the vitellus was of a decidedly greenish color. From
the foregoing data it may be assumed that there exists in the egg of this
species, as in that of the shad, a very spacious “breathing chamber,”
or water space, developed between the vitellus and zona at the time of
impregnation, in consequence of the distension of the latter with water
taken in through the pore-canals. At a temperature of 660 to 670 Fahr.
hatching began at the end of 48 hours. ,
The foregoing information is derived from the paper by Mr. Worth,
tand, as there can be no doubt of the fact that the eggs taken were those
of the striped bass, we must suppose, if the young fish identified by A.
*A. Agassiz. On the young stages of osseous fishes, part iii. Proc. Am. Acad. Arts
and Sci., xvii, 1882, pl. viii, figs. 4 and 5, p. 296.
* S. G. Worth. The artificial propagation of the striped bass (Roccus lineatus) on
Albemarle Sound. Bull. U. S. Fish. Com.,i, 1881, pp. 174–177.
[15] DEVELOPMENT OF OSSEOUS FISHES. 503
Agassiz really were of the same species, that the development of its ova
occurs in fresh as well as in sea-water. The larvae captured and figured
by Agassiz,” though it is nowhere specifically im-
plied that these young fishes were not taken from
fresh water, were probably captured in salt water,
as were most of the forms figured by him. Speci-
mens in my possession of young striped bass one
day old, hatched from ova fertilized with the milt
of the white perch, Roccus americanus (Gmel.) J.
and G., measure 3.5" in length, or the same as
the youngest stage figured by Agassiz, but the
jaws and mouth are not nearly as well developed
and the intestine is relatively much longer, nor
are the median fin-folds as wide. The intestine
also in this youngest stage extends backward be-
yond the yelk-sack for a distance equal to half
the length of the latter before it reaches the edge
of the ventral fin-fold to terminate at the anus.
These differences lead me to think that the larval
fishes figured by Mr. Agassiz as pertaining to the
species here under consideration, must belong to
another form, as none of his figures can be rec-
onciled with those taken from larvae of the striped I
bass, the parentage of which is undoubted. In
this opinion I am most conclusively confirmed by
a drawing which has fallen into my hands, by the
late Prof. Henry J. Rice, the figure in question
ği.
#
§
§
§:
%º-kº.ºg
ºgºY. ººº
ºàsQss
C
S
§
§
§
º
2.
being drawn from a larval bass in May, 1879, on ſº §
the sixteenth day after hatching, and which had §
g * N §
been reared from a lot of eggs which were artifici- º
ally impregnated. This drawing, which is repro- ū #
duced here, fig. 7, was taken from a young fish j
measuring 5" in length, and disagrees in many
important respects from a young fish of the same
length and represented in fig. 3, plate i, in the
paper by Agassiz already cited. The figure by i.
Rice shows the tail of the young striped bass to §
be distinctly spatulate and rounded, and not º
tapering and rather acutely rounded, as figured #
by Agassiz. In Rice's figure the anus is situated ºjºs,
at a point very nearly midway between the tip of §§§
the snout and the end of the tail; in the figure %\\
of the same stage given by Agassiz the vent opens
at a point on the ventral border far in advance of
a point situated midway between the end of the snout and that of the
*A. Agassiz. On the young stages of osseous fishes. Part iii, Proc. Aum. Acad.
Arts and Sci., xvii, 1882, pp. 274–275, pl. i. &












504 REPORT of commissionER OF FISH AND FISHERIES. [16]
tail. Very pronounced hooked teeth are shown in both jaws in Rice's
figure, and the air-bladder is developed relatively farther back than is
shown in the figures given by Agassiz. The earlier stages which I have
seen of undoubted embryos of Roccus lineatus are likewise more slender
than those figured by Agassiz, and this point is also confirmed by the
later stage figured by Rice.
HYREIDIZATION OF THE STRIPED BASS WITH OTHER EISEIES.
It is rather extraordinary that the striped bass should so readily lend
itself to the purpose of cross-fertilization with other closely allied spe-
cies, such as the white and yellow perch, but it is still more astonishing
that it should be possible to cross this species with another belonging
not simply to a different family, but even to a widely different order
and sub-class. That the eggs of the shad (Clupea sapidissima) might
be fertilized with the milt from the male striped bass seems almost in-
credible, yet it seems that the evidence showing that the eggs of a
physostomous form may be fertilized by the milt from a physoclistous
acanthopterygian is incontestable, and that the eggs of the latter type
may even be fertilized with milt taken from the first-mentioned type.
The shad and striped bass therefore appear to be fertile inter se, as the
following evidence seems to prove.
That the shad ovum may be fertilized with the milt of the striped
bass seems to be established by the evidence presented in a paper* by
the writer published in 1883, from which I quote as follows:
A number of young fish which had already lost their yelk-sacks, in
consequence of which it is to be supposed that they were already several
days old, were received from Havre de Grace, Md., at the central
station on the evening of June 13, 1882. They were immediately placed
in an aquarium, but all of them died in a day or two after save about
fifty, which were transferred by the writer to one of the smaller of the
carp ponds in charge of Dr. Rudolph Hessel, where, as Professor Baird
had suggested, they might possibly find some food suited to their wants
and grow large enough for us to learn something of their future history.
The case is an extraordinary one, as the possibility of interbreeding
members of such very distinct families as the Clupeoids and Percoids,
unless the impregnation was performed under the very eyes of the nat-
uralist, might well be doubted by those familiar with the recorded facts
which have generally been considered to prove that fertile interbreed-
ing even between different genera was out of the question. The evi-
dence in favor of the fact in this case is, however, too strong to be
passed over, and until we know more of the later history of this singu-
lar hybrid, the following notes on the differences which were presented
by the embryos in question when compared with those of the true shad
*Ryder. Notice of an extraordinary hybrid between the shad and striped bass.
Bull. U. S. l’ish Com., ii, 1882, p. 187.
[17] DEVELOPMENT OF OSSEOUS FISHES. 505
must suffice. The striped bass was the male and the shad the femal
parent in this case. -
Teeth more numerous and more recurved in the lower jaw; at least
three pairs present; only two pairs in the larvae of the shad of the same
age. Lower jaw longer, with the gape of the mouth much wider; ear
capsule proportionally much larger than in shad larvae of same age,
and pigment and fine radii of fins slightly more developed than in the
latter. Intestine much more slender, that is, its lumen is much less
spacious than in larvae of Cluped. Liver in about the same position as
in larval Clupea, but gall-bladder and eye relatively and perceptibly
larger; Meckel's cartilage a fourth longer. General form that of the
larval shad, but head more prolonged and acuminate anteriorly. The
preponderance of characters appears to be those of the female parent,
and these larvae appear to be undoubted hybrids. The eggs were taken
by some of the crew of the steamer Fish Hawk at Havre de Grace,
and were impregnated with the milt of the striped bass, because no
ripe male shad happened to be at hand.
The head of this singular hybrid, represented by fig. 11, plate ii, inay
be compared with fig. 7, representing an advanced larva of the striped
bass, also with the figures of the larvae of the shad, shown on plate xxii.
Since the foregoing appeared Mr. R. B. Roosevelt has published a
a paper* on hybridism between the striped bass and shad, in which
the former was the female and the latter the male parent. No speci-
mens of these larvae appear to have been preserved so that all the in-
formation I can give in this instance is to quote Mr. Roosevelt's remarks
on the subject as follows:
“A ripe female striped bass or rockfish, Labraw lineatus, being caught
in the nets during the course of operation of the shad hatchery on the
Hudson River, and there being no male bass to be obtained, the eggs
were taken and brought into contact with the milt of the male shad.
Alosa sapidissima. Then these eggs were placed in a box entirely by
themselves, and every precaution was taken to make the experiment
perfect. The eggs hatched; of that there is no question, but whether
the product was the result of that impregnation or whether it was
reached by the chance contact with floating seminal animalcules from
bass, or whether the young lived after they were hatched, may be re-
garded as still open for consideration. As there was no possibility of
keeping the fry in confinement the experiment goes no farther than
opening the field of study and research.”
III.-CLUPEA VERNALIS MITCH. (The Alewife or Branch Herring;
Gaspereau.) -- \
This Clupeoid is anadromous and lays its eggs in adherent masses;
the zona is much thicker than that of the egg of C. sapidissima. The
*R. B. Roosevelt. Fertility in hybridization. Proc. Am. Ass. Adv. Sci., xxxiii,
1885, pp. 510–515.
506 REPORT of commissionER OF FISH AND FISHERIES. [18]
egg of this species is also very much smaller than that of the shad, and
as the zona invests the vitellus or embryo quite closely, there is no
spacious breathing chamber developed at the time of impregnation, as
in the egg of the shad.
Fig. 8, plate ii, represents a larval Clupea vernalis on the second day
after hatching, when it measures very nearly 5" in length. It is ex-
tremely transparent, the only ornamentation with pigment spots is a t
row of small ones on either side of the tail, on a level with the lower
side of the intestine. The yelk is very clear and does not contain any
oil drops. The liver is produced as a nearly solid, elongated outgrowth
from the inferior side of the intestine and behind the yelk sack, in the
same position as in Clupea sapidissima. The liver is represented in the
figure by the long black patch behind the yelk sack. It will also be
noticed that the intestine terminates very far back, as it does in fact
in most Clupeoids.”
IV.—IDUs MELANOTUs. (The Golden Ide.)
The ova of this beautiful cyprinoid are adhesive, and, like those of
the gold-fish, are usually found to adhere singly to the water-plants
amongst which the parent fishes spawn. The zona radiata is rather
thick, and there is but little space between it and the vitellus.
The young golden ide when it leaves the egg measures 6.6" in length.
Its form at that time is shown in fig. 9, plate ii. The Cuvierian ducts
embrace the anterior end of the yelk, which is composed of small
spherical refringent granules. The yelk sack is much prolonged, and
extends from the cardiac region nearly to the vent, tapering slightly
as it is prolonged backwards. As in cyprinoids generally, there is a
complete circulation at the time of hatching, which is not the case with
the embryos of several clupeoids and many forms having pelagic eggs.
The figures given by Von Baer of the embryos of other forms of cypri-
noids also show the yelk-sack to be elongated. (See his Untersuchungen
iiber die Entwickelungsgeschichte der Fische, 4to, Leipzig, 1835.)
V.—CARASSIUs AURATUs. (The Goldfish.)
The ova of the common gold-fish are laid singly upon weeds and other
fixed objects in the water. They measure about 1.5" in diameter, and
develop with comparative rapidity, hatching in 8 or 9 days after fertil-
ization. Three of the earlier stages of the development of this form
are shown in figs. 16, 17, and 18, plate iii. The yelk is quite gran-
ar and similar to that of Idus and Leuciscus (Van Bambeke”), and the
embryonic axis embraces almost the entire circumference of the vitellus,
*Filippo de Filippi. Nouvelles recherches sur l'embryogenie des Poissons, Ann. des
Sci. Nat. 3me Ser. Zool., vii, 1847, pp. 65–72, 1 plate. (Figures the larva of Clupea finta.)
*Van Bambeke. Recherches sur l'embryologie des Poissons Osseux. Mem. Cour.
de l'Acad. ray. de Belgique, XL, 1875, Pl. II.
[19] DEVELOPMENT OF OSSEOUS FISHIES. 5()7
So that the blastopore closes beyond a point opposite the original site
of the blastodisk, as also happens in Leuciscus. The vesicle of Kupffer
is well developed just under the caudal end of the embryo, as may be
seen by referring to figs. 16 and 18.
A more advanced embryo is represented in fig. 10, plate ii, measur-
ing 5.75" in length, at five and a half days old. The ornamentation
of pigment spots is quite elaborate at this stage. The yelk is elongated
and fusiform, and its anterior end is embraced by the Cuvierian ducts.
Just behind the urinary bladder the caudal vein is dilated and forms a
fusiform sinus. It is then continued forward over the yellº, upon the
dorsal surface of which it breaks up into a coarse vascular network.
For many weeks after hatching the young gold-fish does not develop
any red or bluish-black pigment cells in the skin. When these are de-
veloped, which occurs after the fish is an inch or more in length, it is
probable that the fish is approaching adolescence, as it has been found
that this species reproduces when still comparatively small.
VI.-ELACATE CANADA (LINN.) GILL. (The Crab-eater.)
The ova of this species are very well characterized. They are pelagic,
in salt water having a density of 1.020. A large and refringent oil
globule is imbedded in the yelk at a point nearly opposite the site of
the blastodisk and at the upper pole of the egg. The blastodisk is
directed downward, like that of most pelagic fish ova. The egg measures
about 1.25" in diameter and the yelk is broken up into a few very large
irregular masses of deutoplasm, separated by thin films or processes of
the cortical layer of protoplasm, as is indicated by the network of dot-
ted lines in figs. 13 and 14, plate iii. This subdivision of the vitellus
by thin sheets of plasma running into the yelk-substance is apparent
even in the yelk-sack of the young fish after it is hatched.
The changes undergone by the developing blastodisk for the first
four hours are quite complex. The development is quite rapid, and
hatching takes place in about 36 hours after impregnation. A broad
zone of marginal cells are segmented off from the margin of the blasto-
disk, and the margin of the latter is rapidly inflected. The growth of
the blastoderm is quite rapid, the entire vitellus being included and
covered over by the epibolic growth of the blastoderm in about eight
hours. e
As I have already referred to the very remarkable phenomena ob-
served by me just previous to the closure of the blastoderm in this
species, and not being likely soon again to have an opportunity to study
the same form, I will now describe and figure what was then observed
in a number of ova, from which I infer that the peculiarity about to be
described is characteristic of the development of this form.
Fig. 13, plate iii, represents the embryo formed and lying on the
surface of the vitellus, and is shown as if foreshortened; anteriorly the
optic lobes op, on the other side of the vitellus, show through the trans-
508 REPORT of commissionER or FISH AND FISHERIES. [20]
parent surface of the latter. The embryonic axis shows the segments
or somites m, distinctly developed, but it is very remarkable that the
segmentation does not end at the point where the axis of the embryo,
thus far developed, ends. The right and left limbs of the blastodermic
rim, or lips of the blastopore, form a A-shaped mass, together with the
embryonic body anteriorly; but, unlike any other normal Teleostean
embryo, both the diverging limbs of the rim of the blastoderm show
distinct indications of metameric segmentation at m, and behind the
point where concrescence has already taken place.
Just within the yellº and a little in front of the yelk blastopore, which
runs forward into the acute angle formed by the limbs of the blasto-
dermic rim br, lies the large oil-drop o. A lozenge shaped mass of cells
lies in the acute angle of the A-shaped terminal part of the embryo,
which appears to contain or overlie Kupffer's vesicle, kv, and what was
assumed to be the posterior end of the chorda ch at the time the draw-
ing was made; but of the certainty of this determination I am not at
present satisfied. I was enabled to sketch this and a slightly more ad-
vanced stage several times, and, as already stated, I found the same
condition of things present in a number of embryos, which appeared to
be developing normally. Four other sketches show that the blasto-
derm finally closes very much as in other Teleostean embryos, and that
pronounced wrinkles radiate from the crater like opening upon the yelk
where the yelk-blastopore finally closes. •,
The conclusions of His and Rauber, to the effect that the embryonic
axis is formed by the gradual fusion from before backwards of the edges
or lips of the yelk blastopore as it advances over the surface of the vitel-
hine globe, are completely and emphatically confirmed in the case of
this species. It must be admitted, however, that the presence of the
cellular mass between the limbs of the blastodermic rim where they
join the anterior portion of the embryonic body is not a little puzzling.
This species I was enabled to study, through the kind help of Col. M.
McDonald and Mr. W. P. Sauerhoff, at Cherrystone, Va., during the
first week of August, 1881. -
VII.-SIPHOSTOMA FUSCUM (STORER) J. & G. (Common Pipefish.)
The earliest noteworthy observations upon the development of any
species allied to the one here considered, which I have been able to find,
were recorded by Rathke.” The embryos of a species called Syngnathus
argentatus is figured on plate v of Rathke's memoir, and he shows the
gill clefts exposed or uncovered in the young, a condition not observed
by later authors. The next memoir in historical order is by A. de
Quatrefages, and deals with another species, probably another genus, in
which the eggs are not covered by lateral folds extending down from
* H. Rathke. Zur morphologie; Reisbemerkungen aus Taurien. 4to, pp. 192,
plg. 5, Riga and Leipzig, 1837. -
[21] DEVELOPMENT OF OSSEOUS FISHES. 509
the sides of the body. The memoir of de Quatrefages” is, however,
very superficial, for the courses and distribution of the blood-vessels in
the embryo are drawn altogether diagrammatically and with the help
of the imagination of the artist. The next paper* published was by the
writer, in which some of the stages of development of Siphostoma fuscum.
were discussed and described. About two years later Dr. J. P. McMur-
rich took up the study of the development of this species and published
a memoir” which is valuable for the information it affords as to the
ontogeny of the cranial skeleton.
The eggs of Siphostoma are developed under a pair of integumentary
folds placed behind the vent, forming a brood-pouch, which is devel.
oped on the under side of the tail of the female. The ova are small,
measuring only about 0.75” in diameter. They are embedded in a
viscid mucus contained within the pouch alluded to. A blastodisk is
evidently formed in the usual way. The yelk is clear lemon-yellow in
color, and its outer stratum contains small, numerous deeper yellow
oil drops, the distribution of which is shown in fig. 20, plate iv. The
presence of Kupffer's vesicle was not made out at this stage.
The next stage of development, which was observed in the eggs taken
from the brood-pouch of another male, is represented in fig. 19, when the
embryo, after being freed from the egg, measured very nearly 3" in
length. This is a considerably earlier stage than that represented by
fig. 1, pl. xlii, in McMurrich's paper, as the fold indicating the commence-
ment of the formation of the caudal fin is not yet present in fig. 19. The
median aorta and caudal artery extend almost to the end of the tail,
where it is continued into the recurrent cava and the subintestinal vein
which return the blood to the heart. As soon as the subintestinal vein
reaches the posterior pole of the yelk it bends down and traverses its
posterior median and anterior face towards the heart, the venous end of
which rests upon the yelk. The branchial arches are formed, though
there are no branchial filaments yet developed. The pectoral fin-fold is
already present as a low lobular process just behind the auditory capsule.
The dorsal fin is just becoming clearly evident as a low median fold be-
hind the vent. There is as yet no trace of an anal fin-fold visible. The
oil drops have a more general distribution over the yelk than in fig. 20;
the head is much flexed downward, and the brain is very conspicuous.
In passing I would state that in McMurrich's fig. 1 the mid-brain is
identified by mistake with the cerebellum, the cerebellum is confounded
with the pineal gland, while the medulla oblongata is erroneously iden-
tified with the mid-brain and medulla oblongata together.
*A. de Quatrefages. Memoire sur les embryons des Syngnathes (Syngnathus
ophidion, Linn.), Ann. des Sci. Naturelles, xviii, 2d ser., 1842, pp. 193–212, pls. 2.
*Ryder. A contribution to the development and morphology of the Lophobranchi-
ates; (Hippocampus antiquorum, the sea-horse). Bull. U. S. Fish Commission, i,
1881, pp. 191–199, pl. xvii. -
*J. P. McMurrich. On the osteology and development of Syngnathus peckianus
(Storer), Quar. Jour. Mio. Sci., xxiii, a. s., pp. 623–650, pls. 2,
510 REPORT OF COMMISSIONER of FISH AND FISHERIES. [22]
A more advanced stage is shown in fig. 21, plate iv, measuring about
3.5* in length. The pectoral fin at this stage has already partially
rotated on its base. The dorsal fin is more developed, while the tail
begins to show signs of the development of the permanent rays from
the coalescence of the embryonic rays or actinotrichia. The circulation
is more developed and the blood may be seen circulating through the
gill arches, but there are still no filaments formed. A more enlarged
view of the head of this stage is shown in fig. 12, plate iii, where the four
gill arches are more clearly indicated.
I must here take exception to certain of McMurrich's statements in
his paper already cited in reference to the development of the fins. He
says (p. 648): “In the young stages an anal is present, which, how-
ever, does not pass beyond the stage in which fibrillation [development
of actrinotrichia] begins, but aborts and is entirely wanting in the
adult.” This is an error, because a careful inspection of the adults of
both sexes of Siphostoma fuscum, apparently the same species as was
used in his studies, reveals a small but undoubted anal fin just behind
the vent. The erector and depressor muscles are also not attached to
the oval cartilaginous nodules at the bases of the fin-rays, as stated by
McMurrich, but to the bases of the fin-rays themselves. This author's
statement that the tail of Siphostoma is heterocercal at first is not borne
out either by the method of development of the tails of fishes generally,
or by the evidence supplied by figs. 19 and 20 of this species here given;
these two stages just referred to being really much younger than any
figured by McMurrich, and they serve to show that the young of Siphos-
toma pass through what I have called an archicercal stage.
A very curious and interesting morphological fact is revealed by a
study of the development of the Lophobranchii, namely, the manner in
which the neural arches are duplicated several times on each vertebral
centrum. The proximal parts of the parallel cartilaginous bars sup-
porting the rays of the dorsal fin in Hippocampus and Siphostoma afford
the basis for the ossification of about five neural arches to a single cen-
trum in the region of the dorsal fin. And, since the more anterior and
posterior vertebrae also have a number of dorsal arches, it is probable
that the cartilaginous rudiments of such arches are also duplicated in
those regions in an analogous manner, but at a somewhat later stage of
development. This peculiar method of development and duplication of
the neural arches will very probably serve to distinguish the Lopho-
branchiates from other families of fishes.
In plate xvii of my first paper on the Lophobranchiates, cited above,
I fell into an error in the identification of the cranial cartilages of Hip-
pocampus, as pointed out by McMurrich. In the skull, figured on the
plate indicated, the names of several cartilaginous elements must be
changed. The unpaired element sy, given as “symplectic,” must be re-
garded as genio-hyoid, the “element w” is the quadrate and pterygoid,
while a is not “labial,” but pterygo-palatine and not “ethmo-palatine,”
[23] DEVELOPMENT OF OSSEOUS FISHES. 511
as it is identified by McMurrich. The element q, given as “quadrate,”
must be regarded as the symplectic portion of the hyomandibular jar.
VIII.-MONOCANTHUS BROCCUs (MITCH.) DEK. (Fool- or File fish.)
The eggs of this species were obtained by me from adult females capt-
ured in the pound-nets near Cherrystone, Va., about the middle of
July, 1880. The eggs are quite small, and measure not quite .7" in
diameter. They are very adhesive, and adhere again and again to for-
eign objects if detached. They are pale green in color and have a group
of small refringent oil-drops embedded at one side of the vitellus. An
unimpregnated egg of this species is figured on plate iii, fig. 15. The
lot of eggs to which the one figured belongs was not fertilized, as far
as I am aware, yet the blastodisk was very distinctly developed, as the
figure shows. At the end of about two hours no segmentation was ob-
served.
IX.-APELTEs QUADRACUs (MITCH.) BREEVOORT. (The Four-spined
Stickleback.)
For the opportunity to study the development of this interesting
species I am indebted to Mr. W. P. Seal, who supplied me with devel-
oping ova and a pair of spawning adults in April, 1881, and on which
I shortly after published some notes” and observations. I kept one
pair of adults which were about to spawn in an aquarium extemporized
for the purpose; the male very industriously completed the spinning
and weaving of a nest under my observation.
The early stages of development I did not witness, as the first lot of
eggs had the blastoderin already formed and inclosing the vitellus. The
lot of eggs laid by the pair in confinement were unfortunately not fertil-
ized.
The egg-membrane is a true zona radiata, being perforated by numer-
ous pore canals, and is covered by an adhesive material which agglu-
tinates the eggs together into a mass to the number of 15 to 20, the
number deposited at one time by the female. The ova sink to the bot-
tom, and must be taken charge of by the male, as the female, after hav-
ing discharged them, takes no further interest in their fate. The male,
with his mouth, lifts the eggs into the little nest which he has prepared
for their reception.
The egg of the four-spined stickleback measures about a line, or some-
what over 2*, in diameter, and are of a decidedly dark amber color.
I was not able to make out the position of the micropyle. At one pole
of the egg a large number of flat, button-shaped appendages are at.
tached to the surface of the egg-membrane by means of very short pedi-
cels, and it is in the midst of these that the micropyle is found in the
European species, Gasterosteus leiurus, according to Ransom.
* Ryder. Notes on the development, spinning habits, and structure of the four-
spined stickleback, Apeltes quadracus. Bull. U. S. Fish Com., i, 1881, pp. 24–29.
512 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [24]
There is no germinal disk developed when the egg first leaves the
ovary, and the cortical layer of germinal matter is uniformly distributed
at first over the vitellus, which itself incloses a number of very re-
fringent oil spheres, very variable in size. It appears that the blasto-
disk in this species may develop without the influence of impregna-
tion, but no true segmentation occurs under such circumstances.
| }n the fourth or fifth day after impregnation the primary divisions
of the brain are marked off, one of the most striking characters being
the unusual spaciousness of the cerebral vesicles, the walls of the brain
cavity being relatively thin when compared with those of other forms.
The optic cups soon become quite deep, so that a considerable space
(the vitreous humor) exists at an early period between the floor of the
cup and the lens. The origin of the latter from a thickened induplica-
tion of the epiblast may be very readily traced. Some of these and
other features to be described later, are represented in figs. 22, 23, and
24, plate v. Immediately behind the auditory vesicles, and shortly
after their invagination, the rudiments of the breast fins appear as a
pair of low longitudinal folds. In the stickleback the breast or pectoral
fins develop very rapidly and while the young fish is still in the egg.
Pigment is also rapidly developed on the embryo, as is shown in figs.
25 and 26, plate v, representing the young, 6" long, of Apeltes when
it quits the egg. During still earlier stages and while still in the egg
pigment is formed so rapidly over the embryo that it soon becomes im-
possible to see the outlines of the viscera through the mantle of crowded
pigment cells; such is the case with a still older stage represented by
fig. 27, plate vi. About the time of hatching, a second kind of pig-
ment cells, brown in color instead of black, and much larger than the
latter, make their appearance. These brown pigment cells blotch the
embryo symmetrically on the sides and along the median dorsal line,
being confined to sharply circumscribed areas in those regions, as may
be gathered from figs. 25 and 26. The style of pigmentation preva-
lent at the time of hatching foreshadows that of the adult.
The heart appears about the fourth day as a heap of mesoblastic cells
just below the hinder part of the head, and is at first a simple sinus.
It does not begin to pulsate vigorously until the seventh day, when its
pulsations are nearly if not quite 100 per minute. Its venous end rap-
idly elongates until it extends fully the diameter of the body beyond
the right side of the embryo; a large pericardial space is developed be-
low the head at this point for its lodgment; this space dips down deeply
into the amber-colored vitellus. It continues to pulsate from this time
onwards, but there are as yet no blood corpuscles. A wide space now
appears on the right side of the embryo and underneath the latter.
This latter we may consider as a vascular sinus or channel of definite
outline. The floor of this space, as far as I have been able to observe,
seems to consist of the periblast (hypoblast), from which knobbed cells
project upward, and which appear to be budding off portions of them.
[25; DEVELOPMENT OF OSSEOUS FISHES. 513
Selves, which will apparently become blood corpuscles. The sinus, at
any rate, becomes much crowded with what are evidently blood cor-
puscles. Now follow what seem to be amoeboid"contractions of the yelk,
or its periblastic investment, as a result of which this sinus is pushed
out more to the right and over the vitellus. This sinus, as it is further
extended, in a girdle-like manner, over the vitellus, as in figs. 22, 23,
and 24, is seen to be obviously homologous with the edge of the area
wasculosa of Avian embryology or to the sinus terminalis of the mam-
malian embryo. Smaller vessels are soon formed which lead from the
under side of the posterior end of the embryo and join the great mar-
ginal trunk anteriorly which leads to the heart. The asymmetry of the
vessels which spread over the yelk and take up its substance is very
striking during the first few days of development. By the time the
young fish is about to hatch the marginal sinus or trunk has gradually
assumed a median position on the under side of the yelk, and small
vessels pass out on either side of the body on the upper surface of the
yelk in a quite symmetrical manner, as shown in figs. 25 and 26.
When the great vascular sinus or first trace of a vascular system is
developed, it can scarcely be said that there is a circulation; the blood
corpuscles now present are merely swayed back and forth by the pulsa-
tions of the heart. As soon as the aortic channel, underneath the chorda
dorsalis, is forced through, the blood commences to pour through the
sinus from the tail end of the embryo headward over the yelk, as there
is now a complete and open vascular cycle of vessels developed. The
cardinal and caudal veins are formed about the same time. From them
the feeders of the sinus, now the vitelline vessels, are soon developed,
and they are rapidly spread out over the yelk as narrow channels, be-
coming more and more numerous. They at first spread out over the
aboral pole of the yelk, and a great common venous channel, derived
from the sinus first mentioned, begins on the left side of the embryo
and goes round to the right side over the yelk, like a girdle, to feed
the heart. Into this somewhat tortuous, equatorial, vascular girdle
the blood pours.from the small veins traversing the yelk. The main
vessel is symmetrically disposed in reference to the median plane of
the embryo, and is gradually swung round over the yelk in front of the
head as in fig. 24. Eventually the venous end of the heart is also
swung round, and is pushed out under the front of the head instead of
extending outwards over the yell; at one side of the head. The arrange-
ment and changes undergone by the omphalomeseraic vessels of the
embryo stickleback are characteristic, and have not been met with, as
far as I am aware, in the embryos of any other Teleosts.
Rupffer's vesicle was found to be present. The urinary bladder
occupies the usual position; it is large and inclosed by a proper cellular
wall. The course of the intestine, when the embryo is nearly ready to
hatch, is marked by a greenish color. The hind gut, during the earlier
stages of development, is decidedly swollen and has a spacious lumen.
S. Mis. 70—33
514 REPORT of commissionER OF FISH AND FISHERIES. [26]
The blood becomes red in color before the embryo leaves the egg. The
vascular system is better developed in this species at the time of hatch-
ing than in any other, known to me, as well-defined vascular loops
already exist in the dorsal and ventral median fin-folds. The branchial
vessels, arches, and opercula are also in an advanced condition of de-
velopment at this period, unusually so when compared with the embryos
of most other forms at the same stage.
Lateral sensory or segmental sense organs are developed on the
skin at the time of hatching. If the young fish is allowed to assume
its normal position in a live-box, and the microscope applied, looking
down past the sides of the body from above, certain thickenings of the
epiblast or integument will be noticed. These thickenings are sur-
mounted by transparent cells which project freely for a little distance
from the general level of the surface. The outer ends of these cells, ten
or twelve in number, are somewhat separated from one another, and
have blunt truncated tips which are not surmounted with sensory hairs
or filaments. The segmental sense organs of the lateral line in the
young stickleback, therefore, differ very widely from those of the cod.
Fig. 27 represents an older larva in which the lower lobe of the tail is
beginning to develop.
THE SPINNING HABITS OF THE ADULT MALE IDURING THE BREED-
ING SEASON.
It has been known for a long time that the males of the different spe-
cies of sticklebacks build a nest in which they place the eggs laid by the
females. The water is continually forced through the mass of eggs by
the male fish, which moves his fins for the purpose, and also draws or
pumps the water through the clump of eggs with his mouth in execut-
ing the movements of the jaws, gills, and opercula incident to respira-
tion. Just how the nest was built, however, never seems to have been
observed until about 1879 or 1880, when Mr. W. P. Seal noticed that
the nest was built of threads drawn out through an opening near the
vent of the male, and that the latter wound these threads round the clus-
ter of weeds chosen to support the nest in a wonderfully intelligent
manner. Specimens with which this gentleman lºindly supplied me in
1881, upon dissection, showed that there was present, lying on the right
side of the rectum, a large sack filled with a viscid secretion, and that
this was the source of the material of which the threads were formed.
These observations, which were published four years since, have appar-
ently been overlooked by Möbius,” who has recently given an account
of his observations on the spinning organs of Spinachia vulgaris Flem.,
though his observations are far more complete than were my own.'
On the habits of the male Apeltes, I wrote as follows in 1881: “The
male binds the nest together by means of a compound thread which he
* K. Möbius. Ueber die Eigenschaften und den Ursprung der Schleimfäden des See-
stichlingsnestes. Arch. f. mikr. Anat., xxv, 1885, 1 plate. Also, Die Niere des männ-
lichen Seestichlings, eine Spinndriise. Biolog. Centralbl., v., 1886, pp. 647–648.
[27] DEVELOPMENT OF OSSEOUS FISHES. 515
spins from a pore or pores behind the vent, while he uses his bobbin-
shaped body to insinuate himself through the interstices through which
he carries his thread with which he binds a few stalks of Anacharis or
other water-weeds together, bringing in his mouth every now and then
a contribution of some sort in the shape of a bit of a dead plant or other
object, which he binds into the little cradle in which the young are to
be hatched. The thread is spun fitfully, not continuously. He will go
round and round the nest for perhaps a dozen times, when he will rest
awhile and begin again, or turn suddenly round and force his snout
into its top with a vigorous plunging motion, as if to get it into the
proper shape. Its shape is somewhat like an inverted truncated cone;
an opening is left at the top through which it is supposed that he intro-
duces the eggs. The thread is wound round and round the nest in a
horizontal direction in the case we are describing, and if this thread is
placed under the microscope when freshly spun it is found to be com-
posed of very thin transparent fibers to the number of six or eight;
where they are broken off or terminate they have attenuated tapering
ends, as though the material of which they were made had been ex-
hausted when the spinning ceased. Very soon after the thread is spun
particles of dirt adhere to it and render it difficult to interpret its char-
acter. I have seen the thread being drawn out from the abdomen re-
peatedly, but not from the vent; it appeared to me more probable that
it came from the openings of a special spinning gland. Its glass-like
transparency shows that it is not made up of ingested food, the parti-
cles of which would exhibit themselves were that the case. The nest
measures half an inch in height and three-eighths in diameter.
“Upon opening the male I find a large vesicle filled with a clear, ex-
tremely viscid secretion which coagulates into threads upon contact
with water. This vesicle appears to open directly behind” the vent,
separately from the latter. It measures one-fifth inch in length and an
eighth in diameter. As soon as it is ruptured it loses its transparency,
and whatever secretion escapes becomes whitish after being in contact
with water for a short time. This has the same tough, elastic qualities as
when spun by the animal itself, and is also composed of numerous fibers,
as when a portion is taken which has been recently spun upon the nest.
The nature of the opening was not learned with precision, as I possessed
only a single specimen. The vesicle lies to the right side of the intes-
time, and there is very little doubt that it opens behind the anus. The
testes are two ovoid glands, the ducts of which unite into a common
canal, both glands and ducts being covered with black pigment cells;
the testes, during the breeding season, measure somewhat less than an
eighth of an inch in length. As to the origin of the secretion I have
* By mistake it is stated, in this paragraph of my original account, that the sac
opens “in front of the vent.” I make the needed correction here, as I find that the
sketches which I made at the time show that it opened behind the vent, as stated in
the first paragraph.
516 REPORT of commissionER of FISH AND FISHERIES. T28]
no suggestion to make, but there are certain glandular structures lying
close by, the significance of which I am at a loss to understand.”
Since the above was written the inspection of additional material en-
ables me to state that the secretion is present only during the breeding
SO2SOI).
Möbius has investigated the subject much more thoroughly in the
larger European stickleback, Spinachia vulgaris, and he finds that the
sac, found by me in Apeltes to be filled with a viscid secretion, is really
the urinary bladder. And, further, that the sources of the viscid secre-
tion are the kidneys, the secretion being poured out from the epithelial
cells of the uriniferous tubules. The bladder acts simply as a reservoir
in which it accumulates. In Spinachia the threads measure 0.12 to
0.13" in diameter, the male winding them around weeds to form a nest,
in the same manner as the male of Apeltes. The secretion or viscid
spinning material belongs, according to Möbius, to the mucines. Boil-
ing hydrochloric acid stains it a violet color and then dissolves it.
Nitric acid stains it yellow but does not dissolve it. It is insoluble in
acetic acid; soluble in caustic potash solution, and when in solution in
the latter, if acetic acid is added drop by drop, a White precipitate is
formed, which is again dissolved if acetic acid is added in excess. Boil.
ing baryta-Water dissolves it, but boiling lime-water does not.
Möbius traced the secretion to the epithelial cells lining the urinary
tubules of the kidneys or wolfſian bodies. After the breeding season
the volume of the kidneys and urinary bladder diminishes, and they
then contain urine only, while during the breeding season they are
principally filled with the slimy secretion, the thread being spun from
the genito-urinary opening just behind the vent.
X.—Esox RETICULATUS LE SUEUR. (Common Eastern Pickerel; Green
| Pike.)
From material supplied by Mr. W. P. Seal, I am enabled to give fig-
ures of two stages of this type; the youngest 9" long and the most
advanced 11.5" in length. These are represented by figs. 28 and 29.
The young of this species become pigmented rather soon. The gill
arches remain exposed for a considerable time, as is shown in fig. 29,
in which the depressed, produced snout characteristic of the pike
family is also already evident. Caudal metamorphosis is also begin-
ning to manifest itself in this older stage, the tail having become lancet-
shaped, and proportionately narrower than in the younger stage pre-
ceding. There is a well-developed vitelline circulation which has been
figured by Truman” in the embryo of Esoa lucius. The same species
has also been investigated by 'Swirski,” who has worked out the devel.
*E. B. Truman. Observations on the development of the ovum of the pike,
Monthly Mic. Journ., Oct., 1869, pp. 185–203, pls. 27–29 and part of 30.
* Georg 'Swirski. Untersuchungen über die Entwickelung des Schultergiirtels und
des Skelets der Brustflosse des Hechts. Inaug. Diss., Dorpat, 1880, pp. 60, pls. 2.
[29] IDEVELOPMENT OF OSSEOUS FISHES. 517
opment of the skeleton of the shoulder-girdle and pectoral fins of this
type. The most important contribution to our knowledge of the devel-
opment of fishes of this type, however, is a paper by Walther.” e
It is interesting to note that 'Swirski found no less than fifteen carti-
laginous modules at the distal ends of the still cartilaginous actinosts
or basipterygial pieces, of which he finds four, but the distal end of the
fifth and most dorsal in position is bifurcated, showing that it is prob-
ably compound, having doubtless originated by the proximal coales-
cence of two parallel bars. Some of the distal nodules or actinophores
were transitory. The sixteen or seventeen rays of the pectoral devel-
oped as do those of the rays of the median fins, viz, by the proxi-
mal concrescence or blending of horn fibers or actinotrichia. The large
number of pectoral actinophores found at various stages would indi-
cate, even if two rays must be reckoned to a segment, that at least eight
metameres have thrust processes of tissue into the pectoral fold during
its development. These data seem to indicate, in fact, that considerable
reduction has occurred in the number of metameric elements in the
paired fins of Teleosts, since certain of these elements are transitory.
Walther's paper discusses especially the chondrocranium and the re-
lation of the cementum plates, at the bases of the conical enamel-crowns
of the teeth, to the formation of the membrane bones of the jaws and
mouth. -
X.—SI’ECIES NO."l.
This fresh water species, which I cannot identify, has a very adhesive
egg, 1.6mm by 1” in diameter, as shown in fig. 31, plate vii. The blas-
toderm constricts the yell; in a very remarkable Way during its growth
over the yelk globe, as shown in figs. 30 and 31. A very large refrin-
gent oil-drop is embedded in the yelk; the larger oil-drop is also sur-
rounded by a wreatlı of much smaller ones. Kupffer's vesicle is devel-
oped under the tail end of the embryonic axis in the stage represented
by fig. 33. Fig. 32 represents nearly the same stage in profile, and
shows the oil-sphere pushed quite to the ventral and anterior pole of
the yelk, where it remains until absorbed, as shown in fig. 34.
Three days after hatching, the embryo measures about 4” in length,
has a well-marked vitelline circulation developed, and a row of dark
pigment spots are developed along the side of the body, while a very
singular and peculiar arrangement of pigment is found on the yelk-
sack. On the latter, as may be seen in fig. 34, the pigment spots are
confined to the points where the minute vessels join each other.
These eggs were found adherent to a piece of leather in a single layer
at Havre de Grace, Md., in the early part of May, 1881. The adhesive
*Johannes Walther. Die Entwickelung der Deckknochen am Kopfskelett des
Hechtes (Esox lucius). Jenaische Zeitschr., xvi, n. f., ix, 1. und 2. Heft, Jena, 1882,
pp. 59–87, ple. iii-iv.
518 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [30]
agglutinating matter which covered the zona radiata seemed to have
flowed down over the egg and hardened into a kind of flat disk at one
side, as shown in fig. 31. The yelk is quite transparent, but the disk
and blastoderm are rather thick; these characters lead me to think
that it is the egg either of a Cyprinoid or a Centrarchid, most probably
the latter, as the yelk of the Cyprinoids is generally very granular.
XI.-PERCA AMERICANA SCHRANCK. (Yellow Perch; American or
Ringed Perch.)
I have not yet had an opportunity to study the development of this
valuable fresh-water species, which spawns in April and May. Like the
European P. fluviatilis, it lays its eggs in flat bands consisting of a sin-
gle layer, agglutinated together by an adhesive material. These flat
bands of eggs somewhat resemble those of the goose-fish or Lophius,
but they are not as large and do not float on the surface as do the egg-
ribbons of the latter; on the contrary, in this species, they are quite
heavy and sink to the bottom, and are suspended by the female in all
probability upon submerged objects where they are left to hatch out.
The envelopes of the eggs of the yellow perch are, however, so com-
plex in structure that they may be recognized with the greatest readi-
ness. The vitellus measures 1.75” in diameter. It contains a large
oil-sphere which occupies an eccentric position. The oil-sphere is not
represented in fig. 35, plate viii, representing the egg of the Ameri-
can perch, which measures, including the spacious and thick-walled
egg-membrane, 3.5” in total diameter.
The egg-membrane is exceedingly complex, and consists apparently
of an internal layer, 2, which is homologous with the zona radiata of
other types. Immediately overlying the zona there is a very thick,
highly elastic layer, g, which is traversed radially by fibers or canals
which widen perceptibly at the outer surface. A third thin investment,
a, overlies this thick elastic layer, and it consists of the hardened mucine-
like material which agglutinates the eggs together. At one point on
the surface of the egg there is a wider pore canal which leads to the mi-
cropyle m. The outer layer, a, serves to agglutinate the egg to the outer
layer of adjacent eggs, as shown in fig. 35.
XII.—RocCUs AMERICANUs (GMEL.) J. & G. (White Perch.)
The eggs of this species are quite small and measure only about .73"
or one thirty-fourth of an inch in diameter, are very adhesive and stick
together in masses or in thin layers over fixed objects in the water.
The zona radiata is quite thick and is traversed by fine pore-canals.
The micropyle is a minute opening measuring .0075” in diameter.
Externally the zona radiata is at first covered by a thick layer of ad-
hesive matter, which flows toward the points where the eggs come into
[31] DEVELOPMENT OF OSSEOLS FISHES. 519
contact with a foreign body or with each other. At such points disk-
like hardened accumulations of the adhesive investment of the egg are
developed, as shown in figs. 36 and 37, plate viii. The oil-drop in the
vitellus is relatively quite large, as an inspection of the figures named
Will show.
The blastodisk is also quite bulky in comparison with the bulk of the
yelk, as is indicated by the stippled areas, showing the blastodisk in op-
tical section, in figs. 36 and 37. When the blastoderm is developed
and has spead over one-half of the yelk, as shown in fig. 38, it is char-
acterized by its great thickness and its much swollen rim. The yelk is
also more or less constricted at a later stage by the rim of the growing
blastoderm, in the same way as shown in figs. 30 and 31. The embryo,
before the tail begins to grow out, embraces considerably more than half
the circumference of the yelk. Kupffer's vesicle is also developed at
this stage, or by the time the condition shown in fig. 39 is reached.
In six days, with the water at a temperature ranging from 519 to 53°
l'ahr., the young fish leaves the egg. Viewed as a transparent object,
the young White perch at the time of hatching presents the appear-
ance represented in fig. 40, when it measures 2.3" in length. No fin-
folds have as yet appeared and the head seems as if it almost formed
a continuum with the yelk-sack below it. On the first day after hatch-
ing considerable growth is made by the embryo, since it now measures
somewhat over 3” in length. This stage is represented by fig. 41,
plate ix. At the end of three days but little more growth has been
made, as is shown in fig. 42, but after the young fish has been hatched
five or six days, as shown in figs. 43 and 44, the head begins to project
forward. The oil-drop now occupies the forward part of the yelk-Sack
and is covered by cells derived from the periblast. Stellate pigment
cells also begin to make their appearance at this time over the oil-drop,
and a few scattered ones develop on the sides of the tail and back part
of the yelk-sack.
During the later stages the yelk-sack becomes more elongated, and
the liver develops as a bud-like outgrowth from the ventral wall of the
mesenteron. The rudiments of the pectoral fins appear as a pair of low
horizontal folds of the larval integument some distance behind the ear-
capsules. The mouth is barely more than indicated at this stage of
development. The spawning season of this species is in April and
May.
XIII.-STIZOSTEDIUM VITREUM (MITCH.) JoFDAN AND COPELAND.
(Wall-eyed Pike.)
The eggs of this species measure nearly a line in diameter or nearly
2". Shortly after hatching, the embryo measures 5.8" (see fig. 45).
The pectoral fin is already developed and the oil-drop is anterior in po-
sition as in the embryos of the preceding species. The eggs and embryos
520 REPORT of commissionER of FISH AND FISHERIES. [32]
observed by the writer came from Northville, Mich., and were hatched
on the 15th of June, 1885, at the Central Station, Washington.
XIV.-SCOMBEROMORUS MACULATUs (MITCH.) J. & G. (Spanish
Mackerel.)
Figs. 46 to 56, plate x, relate to this species and give a few d tails
of structure which it was not possible to work out by the methods of
study which I was obliged to pursue at the time my first paper was
Written.
Fig. 46 represents a transverse section through the first cerebral
vesicle; the nasal pit is also cut through at ma. Fig. 47 represents a
section through the mid-brain and the origin of the optic nerves. A
segmental sense organ is also cut through just above the front portion
of the eye. Fig. 48 is from a section a little farther back than the pre-
ceding. Fig. 49 is a very much enlarged representation of a section
through one of the Segmental sense organs, showing the columnar
character of the cells of the lower layer of the integument in these struct-
ures. Fig. 50 is a representation of a section cutting transversely
through the hinder region of the mid-brain and shows the course of the
fibers of the optic nerves through the retinal walls. Fig. 51 represents
a cross-section through the fore part of the medulla oblongata ; a Seg-
mental sense organ is also shown in section. Fig. 52 represents a
cross-section cutting through the auditory capsule aw, with a segmental
sense organ, 88, below it; below the pharyngeal region, in the middle
line, the bulbus arteriosus and ventricle is cut through. Eig. 53 repre-
sents a longitudinal Section of a young Spanish mackerel somewhat off
the median line. Above the pericardial cavity po the branchial and
hyomandibular arches are cut across. The heart h opens directly, as in
fig. 56, into the space surrounding the periblast p, as I have elsewhere
described in the embryo of Clupea. The trabeculae cranii trare seen to
be feebly developed at this stage, as shown in both figs. 53 and 56.
Fig. 54 represents a cross-section through the pectoral fin-fold p", the
yellº-sack, and segmental ducts sq. The periblast in this section is seen
to be well developed and contains nuclei. Fig. 55 represents a cross-
Section through the tail of a young Spanish mackerel, a segmental sense
organ having also been cut through. Rig. 56 shows that the oil-drop o,
at the posterior end of the yelk, is mainly enveloped by the periblast.
The intestine i is cut through at several points, and the segmental duct
sd of one side is split lengthwise, the section passing through the urinary

|33] DEVELOPMENT OF OSSEOUS FISHEs. 521
bladder al and the pronephric funnel pn anteriorly. The chorda ch is
cut through at Several points, and the floor of the pericardial cavity pe
is shown to be very thin and continuous with the venous end of the
heart h. The latter, therefore, opens directly into the body cavity be.
hind it, the body cavity itself being directly continuous with the
cleavage cavity of an earlier stage, the latter becoming the former in the
course of development. These sections were prepared from Spanish
mackerel embryos which had left the egg only about twenty-four hours,
and measured about 3” in length.
XV.—CHAETODIPTERUS FABER (BROUss.) J. & G. (Angel-Fish;
Porgee, or Moonfish.)
The ova of this species are pelagic or floating in habit, in sea-water
having a specific gravity of 1.014. They hatch out in twenty-four hours
when the temperature of the water is 800 IFahr. This species spawns in
the Chesapeake during the latter part of June and the early part of
July. It is prodigiously fertile, the female probably discharging a
million ova during a single season.
The egg measures somewhat over a millimeter in diameter. The
blastodisk will develop independently of fertilization, as shown in fig.
57. Cleavage is very rapid and it requires only about one hour to pass
from the condition shown in fig. 58 to the morula condition shown in
fig. 60. Pig. 59 shows the form assumed by the cells of the morula
stage, and traces are also present of the subquadrate form assumed by
the blastodisk at the time of the completion of the second cleavage.
After the blastodisk begins to spread, the development of the mar-
ginal cells at its edge becomes very well marked, as shown in fig. 61.
The oil-drop, shown in figs. 58, 60, and 61, remains for a time almost
cxactly opposite the center of the blastodisk, and later, when the em-
bryo is formed, it occupies a median ventral position in the yelk-sack,
as shown in figs. 62 and 63, and is not finally shoved to the posterior
end of the latter, as in the embryo Spanish mackerel.
In thirteen hours the embryo fish is fairly outlined, as shown in fig.
62, and the oil-drop becomes covered by the periblast in which nuclei
seem to be differentiated. At this stage faintly-colored pigment cells,
mostly of a rounded form, become developed on the body of the embryo.
At the under side of the tail Kupffer's vesicle is also distinctly developed.
All over the blastoderm, enveloping the yellº at this stage, faintly-colored
pigment cells are discernible. -
At the end of twenty-four hours the young fish leave the egg, measur-
ing about 2.5mm in length. Sixteen hours later, as shown in fig. 63,
the embryo has grown about half a millimeter in length, and the
greater part of the yelk has been absorbed, so that an immense se-
rous space is left in front of the yelk, between the periblast envelop-
ing the latter and the outer somatopleural sack. This wide space has
522 REPORT of commissionER OF FISH AND FISHERIES. [34]
been derived directly from the cleavage cavity. By this time the pig-
ment cells on the body and tail have begun to aggregate in definite
groups, as shown in fig. 63, and the majority have also become dis-
tinctly stellate.
Fig. 64 represents the recently-hatched moonfish. The body cavity
8c, formerly the cleavage cavity, is already very spacious, as the yelk is
being absorbed more rapidly than the outer somatopleural envelope of
the yelk is collapsing. This outer somatopleural covering of the yelk
in this species, as in all young fishes, even Elasmobranchs, is quite free
and is not fused with the periblast-splanchnopleure beneath it. The
oil-drop, it will also be noticed, is now invested by distinct cells of peri-
blastic origin, which have well-defined borders, and are more or less
stellate. It also bulges outward, more or less distinctly, but it is easy
to see that it is still invested by the yelk. The pectoral fin-fold appears
far behind the auditory involution in the stage represented by fig. 64;
it is somewhat more developed in the more advanced stage represented
by fig. 63. The ventral fins appear quite late, as they were absent in
the oldest stages observed by me. -
Twenty-eight hours after hatching, the young moonfish measures
3.5* in length, and presents the appearance shown in fig. 65. Em-
bryonic fin-rays have by this time made their appearance at the end
of the tail; the pectoral fin is well developed, and the intestine is
longer and the urinary bladder is larger. The yelk has also diminished
greatly in size, and the mouth will soon be open. There is still no com-
plete circulation, though all the principal subdivisions of the heart are
developed and that organ is pulsating vigorously. By this time traces
of a reddish pigment begin to appear on the upper and lateral portions
of the abdomen. O -
Rifty-three hours after hatching the young moonfish has grown
mainly in height of the body, as shown in fig. 66. The snout is very
blunt and declivous and foreshadows the form of the blunt, rounded
profile of the parent fish. The yelk is nearly absorbed and over the
abdominal walls there is now developed a strongly-marked group of
stellate red pigment cells. A flexure of the intestine is also developed
and the urinary bladder is very large and distinct. The pectoral is
strongly developed and a complete circulation is apparent, though the
aorta bends upon itself and is continued forward against the caudal
vein at a point less than half the distance between the vertical from the
vent and the end of the tail. The pigment cells have also by this time
been more definitely aggregated into a definite band on the tail and on
the integument above the pectoral. The young fish by this time meas-
ures nearly 4” in length. s
I have seen some of the post-larval stages of the young of this species
in Chesapeake Bay measuring from one-half to one inch and a quarter
in length. In these the transverse dusky bands seen in the adult are
intensely bluish-black in color. It is, therefore, obvious that the color-
[35] DEVELOPMENT OF OSSEOUS FISHES. 523
ation diminishes greatly in brilliancy with age. I have very strong
reasons to suspect that the larvae of this species are phosphorescent at
night.
XVI.—GADUs ToMCod WALB. (Tom-cod; Frost-fish.)
The eggs of this species of Gadoid are somewhat larger than those
of the common codfish. The egg-membrane is rather thick and tough
and is covered externally by an adhesive coating of a mucine-like Sub-
stance which agglutinates the eggs together in masses, the latter being
very frequently, if not usually, attached to sea-weeds and stones at the
bottom of the littoral zone. The eggs are not pelagic, like those of the
cod, though there is a very conspicuous oil-drop in the vitellus; as de-
velopment progresses this oil-drop is pushed forward to the anterior
pole of the yelk-sack.
When hatched the gape of the mouth is very much greater than that
of the larva of the common cod. The intestine terminates at the margin
of the ventral fin-fold, instead of some distance from it, as in the larval
cod, as may be seen by comparing figs. 1 and 67. There is no integu-
mentary vesicle or bulla developed over the head as in the young cod,
so that the larval stages of this species differ very widely from its con-
gener, though both spawn in winter or during the colder months of the
year. The larvae of the tom-cod are also more robust in build than
those of the cod, and measure at the time of hatching very nearly, if
not quite, 5* in length.
XVII.-CLUPEA SAPIDISSIM.A WILSON. (The Common Shad.)
The interest attaching to the development of this species is two-fold,
namely, that which appeals to the economist and that which appeals
to the biologist. While the description of the morphological changes
which this species undergoes during development will be of immediate
interest only to the latter, the former, if he be a fish-culturist, and not
otherwise interested in the life-history of the type under consideration,
may still perhaps derive useful information from what is to follow re-
specting the manner in which the perpetuation and development of this
valuable food-fish is accomplished. With the invention of greatly im-
proved appliances, the hatching of this form from artificially fertilized
eggs is now accomplished to the number of perhaps fifty to seventy
millions annually along the Atlantic slope, reckoning in this total the
combined efforts of the United States and the different State fish com-
missions of the coastwise States. The species is anadromous and quite
fertile, a single female yielding during the season, if unmolested, about
200,000 ova. These ova are probably discharged in shoal water and
mainly after night-fall. Spawning occurs during the spring months of
April and May, and as late as June and July in the latitude of Wash-
ington and Baltimore.
524 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [36]
The freshly-extruded egg of the shad is of a very pale amber color,
and is invested by a very much wrinkled zona radiata, as shown in fig.
68. At this time, if the egg is allowed to lie on a plane surface, its
form is considerably flattened, and its outline from above is subquad-
rate and irregular. The freshly-laid egg, if examined with a low power
of the microscope, is found to be very closely invested by the zona
radiata 2, fig. 69; immediately below the zona lies the cortical layer
cl, in which numerous minute roundédbodies or corpuscles are imbedded.
This cortical layer of plasma also sends down into the yelk thin laminar
prolongations of itself which envelop the large yelk masses y into which
the body of the vitellus is subdivided. Immediately after the ova are
brought into contact with the sperm or milt of the male shad a great
change in their appearance occurs. This change consists mainly of the
distension of the wrinkled zona with water, as a result of which the egg
becomes spherical, its bulk at the same time becoming about seven times
greater than in the unimpregnated state. This change may occur in
the presence of water without the agency of impregnation, but it is then
not apt to affect all of the ova in this way. As a result of the disten-
sion of the zona radiata or egg-membrane, the latter is lifted up from
contact with the surface of the vitellus so that it lies quite free in its
spherical envelope with a wide space all around it, as shown in fig. 70,
in which the vitellus is shown as an oval black dot and the contour of
the egg-membrane as a simple circle. This figure represents the egg of
the shad of the natural size with the vitellus lying in the lower half of
its envelope. With the further progress of development no additional
distension of the egg-membrane occurs, but during the whole of the
time the space surrounding the egg or embryo remains the same, as may
be seen by reference to fig. 101, plate xvi; figs. 126 and 127, plate
xviii; and fig. 136, plate xix.
Upon the impregnation of the egg, which is effected by the entrance
of a spermatozoön through the single minute pore or micropyle, which
admits of the passage of the male element to the vitellus from the out-
side through the zona, a germinal thickening of the cortical layer or a
blastodisk is rapidly developed. In its natural position in the zona,
the vitellus of the shad, surrounded by its envelope of germinal matter,
assumes the form of an oblate spheroid or that of a somewhat flattened
sphere, when viewed in optic section, as shown in figs. 71, 72, and 73.
At first there is no blastodisk present, but a few minutes after impreg-
nation the cortical layer at one side of the ovum becomes perceptibly
thicker over one pole of the vitellus by the concentration or aggregation
of its substance at that point, as shown in profile in fig. 71, and from
above in fig. 75. The substance of the cortical layer becomes slowly
heaped up after impregnation into a depressed conical mass at one pole
of the vitellus, as shown in figs. 71, 72, 73, 74, and 76. Normally, the
blastodisk is lateral in position when the egg is at rest. From its in-
ferior side strands of protoplasmic matter pass down between the large
[37] DEVELOPMENT OF OSSEOtjS FISHES. 525
Vitelline masses into which the yellº is subdivided. These strands of
plasma radiate from the under side of the blastodisk into the yelk some-
what in the same way as the roots of a plant radiate from the base of
its principal stem into the surrounding soil, as is slown in figs. 71 to
78, inclusive, plate xiv.
In the course of about fifteen minutes after fertilization, I have sev-
eral times witnessed the expulsion of the polar cells from the develop-
ing blastodisk of the ovum of the shad. A distinct prominence is first
developed near the center of the thickening of the cortical layer, as
shown in fig. 74. At intervals of a minute or so apart, the changes
which that prominence undergoes I have represented in fig. 79, a, b, c,
d, e, f. The two polar cells at first lie close to the surface of the in-
cipient disk; later, they remain adherent only by a slender filament
of protoplasm, as shown at c. Finally, they are detached from the
filament, as shown at d, and at last the filament itself is slowly with.
drawn into the cortical layer, disappearing entirely at a stage a little
more advanced than that shown at f. The polar cells in this species
are finally detached, and seem to disintegrate in the large water space
surrounded by the zona, and in which the egg lies. Such a detachment
of the polar cells is not without precedent, for Bischoff represents them
as detached in the segmenting ovum of Mammalia, and I have myself
observed their detachment from the segmenting ova of Nudibranchiate
mollusks, and saw them drop into the perivitelline space just as seems
to be the case in Clupea. -
At the end of about half an hour, with the water at a temperature of
750, the blastodisk is formed, and at the end of one hour and twenty
minutes the first cleavage furrow has been formed. This ſurrow di-
vides the blastodisk into two equal conical masses, as shown in figs.
77, 78, and 80. These figures represent the cleavage in its most active
phase, when the plasma of the disk is heaped up into two remarkably
prominent blunt cones. The disk becomes much elongated as a re-
sult of the development of the first cleavage, nor does it lose its elon-
gated squarish form for a considerable time after the second cleavage
furrow is developed, as shown in fig. 81, from above, and in figs. 82 and
85 in profile. Certain irregularities of cleavage are sometimes appar-
ent, such as the development of five cells in the disk at this stage, in-
stead of four, or the normal number. An abnormal disk of this kind
is represented in fig. 83. The second furrow is developed about two
hours aſter fertilization.
Upon the advent of the third set of furrows, which divide the four
cells of the last stage transversely, the blastodisk is subdivided into
eight cells lying in two parallel rows of four each, as shown in figs. 86,
87, and 88. The third set of furrows appears about half an hour after
the second cleavage has been completed. In the course of the next
forty minutes the thirty-two celled stage of segmentation has been
passed over, as represented in figs. 84, 89, and 90. The morula condi-
526 REPORT of commissionER OF FISH AND FISHERIES. [38]
tion is now entered upon, but its development is not completed until
about four to five hours after fertilization. Consequently, the next
change which the blastodisk undergoes is the further subdivision of its
component cells. Just after the stage represented in fig. 90, the blas-
todisk becomes divided into two layers of cells, as shown in fig. 91.
At about this time the nuclei of the periblast become sundered from the
nuclei of the cells at the edge of the blastodisk. The morula stage is
finally completed when the segmented blastodisk assumes in section
the lenticular form represented in figs. 92, 93, and 95; nuclei are already
apparent in the periblast of the latter.
Immediately succeeding the morula stage comes the blastula condi-
tion, when, for the first time, the blastodisk becomes markedly lifted up
at its center from the underlying periblast. As a result of this lifting
up of the middle of the blastodisk, which at the same time becomes
thinner in the center, a space appears under its central part, known as
the cleavage cavity, as shown in figs. 137 and 138, plate xix. The
duration of this phase, of the blastula is brief and is almost immediately
followed by the gastrula stage.
The advent of the gastrula stage is characterized by the inflection of
the margin of the blastoderm. This becomes greatly thickened at one
point at its margin, or where the future embryo will be formed, as
shown in optic longitudinal section, in fig. 137, at 8, as a swelling.
Other views of this stage are also given in figs. 138 and 139. At this
time the cleavage cavity has a kidney-shaped outline as viewed from
above, but it soon becomes somewhat crescent-shaped, as in fig. 140,
for the swelling 8 of the previous stages is extending inwards to form
the embryonic shield e. In Sagittal, optic section this same stage is rep-
resented in fig. 141, with the egg in another position. Both these last
figures were carefully drawn from micro-photographs.
The gradual advance of the blastoderm over the vitellus is repre-
sented by figs. 140 and 141, plate xix; fig. 96, plate xv; figs. 118, 119,
and 120, plate xvii; and in figs. 98, 101, and 102, when the yellº-blas-
topore or protostoma of the egg of the shad may be said to have closed,
the margin of the spreading blastoderm being considered the margin
of the gastrula mouth and the whole yelk as hypoblast, together with
the formative hypoblast h, as shown in figs. 96 and 118. Such an ar.
rangement causes the gastrula mouth from 0 to o to be greatly expanded
or widened in order that it may embrace the greatly hypertrophied
hypoblast with its inclusions of passive deutoplasm. s
Before the blastoderm of Clupea begins to spread a well defined thin
cuticle or epidermis is developed over its whole surface, composed of a
single layer of squamous cells, as shown in fig. 95. This is the first
differentiation of tissue layers which occurs in the blastodisk of the
ovum, aside from the formation of the periblast. As a result of the
inflection of the margin of the blastoderm, the hypoblast and epiblast
are developed, the former from the inflected stratum of cells, h, and the
[39] DEVELOPMENT OF osseous FISHEs. 527.
latter, e, from the epithelial and immediately underlying cells of the
disk. From these two primitive organs all those of the young shad
are evolved by further differentiation, folding, expansion, invagination,
&c. }
The central nervous system is developed wholly from the epiblast.
This will be rendered the more obvious from a glance at figs. 106 to 108,
representing transverse sections through the embryonic axis of an em-
bryo shad represented in fig. 101, plate xvi. The spinal cord N in
these is shown to arise as a thickening of the layer e, and extends the
entire length of the body at this stage, and is here characterized by its
solidity, as in the embryos of all Osseous fishes and the Lampreys.
During a later stage the cord N becomes separated from the layer e, as
is shown in cross-sections (figs. 109 to 112) of a much later stage, viz,
that shown in fig. 126, though the sundering of the embryonic spinal
cord from the epiblast in reality occurs considerably earlier, or by the
time the stage represented in fig. 103 is reached. *
As the blastoderm spreads, the portion e, fig. 140, lengthens to form
the embryo, the component layers of the latter, fig. 96, e and h, be-
coming much thickened in the vicinity of the median longitudinal
plane. From the inferior thickened part of the inflected band of tissue
h, the chorda ch, figs. 106, 107, and 108, is formed, together with the myo-
blasts or myotomes on either side of the chorda, as dorsal outgrowths,
fig. 97, M M M, of the primitive hypoblast h. These rudiments of the
musculature of the body in the embryo shad are not hollow, as in Bran-
chiostoma, or composed of two layers forming the inner and outer walls
of the series of myoblastic segments, as in Elasmobranchii. They are
therefore not clearly defined paired archenteric diverticula or gut
pouches, but their solid condition is probably due to an abbreviation of
development like that which has affected and retarded the appearance
of the cavity of the spinal cord and brain and that of the intestine.
The inferior part of the layer h, in fig. 96, gives rise in the middle line to
the intestine i, as shown in figs. 106 and 107. The lumen of the intes-
tinal canal appears very slowly, and at first is a mere pore in cross-
sections, as shown in figs. 109 to 112 at i. During the early stages the
hypoblastic band which gives rise to the intestine is thickest at the
posterior end of the embryo, and gradually thins out and widens as it
extends toward the head. This is rendered obvious upon comparing a
section near the tail end of the embryo, fig. 111, with a more anterior
one, fig. 109, from the region of the back part of the medulla oblongata.
The lumen of the intestine in this anterior region is also no longer pore-
like, but flattened, cleft-like, and transverse.
At a slightly earlier stage than is shown by the sections represented
in figs. 106 and 107, the chorda ch is found to be united inferiorly with
the layer i, which gives rise to the intestine. The chorda, myotomes,
and the intestine are therefore to be regarded as differentiations of the
layer h in figs. 96 and 118.
528 REPORT OF COMMISSIONER of FISH AND FISHERIES. [40]
The myotomes gradually increase in number, and at the time the blas-
topore closes but three or four are visible, as shown in fig. 120. Some-
what later more are added behind those already formed, as shown in
figs. 98, 101, 102, 103, 123, 126, 127, until the full complement is devel-
oped, as shown in fig. 151.
Of the sense organs, the optic lobes, from which the eyes are formed,
are the first to become developed. These appear as a pair of lateral
elongated thickenings of the epiblast at the front end of the embryonic
axis. Four stages of the differentiation of the optic lobes are shown,
as viewed from the above, in figs. 114 to 117. These phases of the de-
velopment of the eyes and head may be readily connected with the more
advanced ones represented in figs. 113 and 128.
The gradual extension of the cleavage cavity Sc under the growing
blastodisk may be traced by reference to figs. 137,138,139,140,141,118,
119, 120, 121, 98, 102,103,122, 126, and 127. After the entire yelk is cov-
ered by the blastoderm the only cellular membranous covering invest-
ing it externally is the extremely thin epiblastic membrane e, shown
in section, fig. 121, and between this and the periblast p of the same
figure the cleavage cavity sc is included; this again being directly con-
tinuous with the body cavity be on either side of the intestine i. This
relation of the surrounding parts to the cleavage cavity demonstrates
very conclusively that the membrane e, in fig. 121, must be the Soma-
topleure, while the periblast p must undoubtedly be homologized with
the splanchnopleure. The vascular network developed over the peri-
blast and in intimate connection with it, in the ova of many species of
fishes, is also splanchnopleural and homologous with the area vasculosa
or omphalomeseraic meshwork developed over the yelk of higher forms.
Of the correctness of this homology I think there can scarcely be any
doubt whatever.
The yelk of Clupea, and of Teleost embryos generally, it may therefore
be said, is intra-abdominal; it is excluded from direct connection with
the intestine, but remains adherent to it for a considerable time by its
inferior face, through the intermediation of the periblast immediately
underlying the intestine. The yelk is almost naked were it not for the
thin syncytium, known as the periblast, and which, on the lower and
lateral portions of the yelk, can hardly be considered to rank as a true
membrane, on account of the widely-scattered or diffused nuclei it con-
tains. The splanchnopleure (= periblast) of osseous fishes is therefore
rudimentary or very feebly developed over the vitellus, so that the lat-
ter may be considered to be intra-abdominal, not only because there
is no umbilical stalk developed, but also because it is very imperfectly
inclosed by the splanchnopleure.
The chorda is unusually well developed in Clupea and forms a mas-
sive axial rod at the time of hatching, as shown in cross-section at
ch, fig. 121, and for its whole length in fig. 148. Derived as already
Stated from the median dorsal part of the hypoblast, it retains its con-
[41] DEVELOPMENT OF OSSEOUS FISHES. 529
nection with the last-named layer longest at its posterior extremity, as
shown in fig. 98. After the tail begins to bud out, however, its inti-
mate connection with the hypoblastic layer is broken, and it then termi-
nates after becoming somewhat enlarged in the cellular terminal mass
in which the lateral myoblastic m, neural N, and post-anal section of the
gut i terminate, as shown in cross-section in fig. 104, and in vertical and
transverse optic section in figs. 103 and 113. The histological differentia-
tion of the chorda has already been described by Kupffer, Kowalevsky,
and others, so that there is no occasion for me to redescribe it, as it takes
place in very nearly the same way in the embryos of all Chordata. The
cells of the chorda of Clupea are, however, unusually large and contain
very spacious cavities, in which no coagulable albumen is present.
The later stages of the development of Clupea involve mainly the
completion of structures, the rudiments of which were laid down during
the evolution of the stages already described.
The renal apparatus of the larval shad is extremely simple, and con-
sists, at the time the tail begins to bud out, of a pair of parallel tubes
differentiated from before backwards from the outer portions of the
mesoblast at the time it splits into somatopleure and splanchnopleure.
The segmental ducts sal finally lie just above the somatopleural peri-
toneum and extend from a little way behind the pectoral plate pp, fig.
113, or the pectoral fins, fig. 148, to a point just behind the vent where
they debouch into a common cavity, the urinary bladder which opens
outward behind the vent. At their anterior extremities the segmental
ducts terminate in a single nephridial funnel which opens into the body
cavity, the mouths of the pair of funnels being directed backward and
inward, so that the anterior extremities of the ducts are bent upon
themselves in the form of a shepherd's crook. -
The development of the cranium is not precocious, and its primary
cartilaginous elements are not very apparent until after hatching. The
most obvious portions are the trabeculae Tr, figs. 142, 143, and 144,
'the branchial bars i, ii, iii, iv, and v, and the hyomandibular arch, com-
posed of the hyomandibular Hm, interhyal Ih, quadrate Q, Symplectic
Sy, Meckel's cartilage Mk, and the cerato- and glosso-hyal elements Ch
and Gh. The auditory vesicles Au are quite large, but are not entirely
invested by cartilage; only the outer and inferior aspects being closed in
by chondrified tissue, as shown in cross-section in fig. 147, which was
prepared from a larva about six days old. Fig. 144 represents a very
nearly mesial longitudinal section through the head of a just-hatched
larva, in which the positions of the cranial cartilages crossing the
middle line are indicated. Fig. 143 represents the cranial cartilages
of a slightly older larva constructed from a series of sections. Fig.
142 represents the cranial cartilages of a still more advanced larva, in
which the antorbital process Ao and trabecular rostrum R are more
strongly developed. The branchial and hyomandibular arches have
also reached a considerably greater development than in the preceding
S. Mis, 70—34
530 REPORT OF COMMISSIONER of FISH AND FISHERIES. [42]
stage, while the anterior end of the notochord has become more com-
pletely covered by the parachordal cartilages. This inclosure of the
anterior extremity of the chorda by the parachordal elements pa is more
distinctly displayed in figs. 146 and 147, plate xxi, drawn from cross-
sections of the same stage as that represented by fig. 142. The teg-
men cranii Tc, fig. 142, is not developed during the earlier stages, shown
in figs. 143 and 144. The palatopterygoid is not present until the stage
represented by fig. 142 is attained, or perhaps even later. An element
which I identify as palatopterygoid is present in the cross-section rep-
resented in fig. 145, and has been cut through just belów the eye at pt.
This element, at any rate, seems to be developed quite independently
of any connection with the hyomandibular.
The heart at the time of hatching opens directly into the cleavage
cavity (=body cavity), as represented in fig. 144, and it is not until
some days after hatching that connection is established between its
venous end and the jugular and portal veins jj', and po, as shown in
fig. 152. The yelk seems to be absorbed by the heart and portal ves-
sels, which pass above it, and its anterior end is finally drawn out into
a pointed process, which is directed toward the heart, as shown in fig.
152. I have witnessed the budding of free cells from the periblast p
in the stage represented in fig. 144, and have, also, seen such cells pass
directly into the cavity of the heart, though there was, as yet, no com-
plete circulation.
The other visceral organs are differentiated as appendages of the
alimentary canal. The first and most conspicuously developed is the
liver L, figs. 133, 148, 150, and 152, it being formed as an outgrowth
of the ventral wall of the intestine. Just a little distance behind the
posterior extremity of the liver, the alimentary canal is constricted at
py; this marks the point just behind which the pyloric appendages will
grow out. Just in advance of the pyloric constriction, and on the dor-
sal side of the Oesophageal portion of the alimentary canal, the air-blad-
der grows out as a saccular diverticulum of the intestinal wall at ab, fig.
133. The first traces of the air-bladder do not appear until some days
after hatching, and the same may be said of the gall-bladder Gb, fig.
133, which is formed at the anterior end of the liver. In the course of
about three weeks the metamorphosis of the visceral organs is nearly
completed, as may be gathered from fig. 131, as this figure represents
the pneumatic duct pm, posterior end of the Oesophagus oe, the rudi-
mentary stomach st, and the pylorus py of a young shad nearly an inch
long and three weeks old, reared in confinement. There are still no
pyloric capca, but the permanent form of the alimentary tract of the
Clupeoids is already very clearly apparent.
We may now review the principal and most striking changes in ex-
ternal form which the young shad undergoes within the egg. Starting
with the pliase represented in figs. 137, 138, 139, 140, and 141, when
the first trace of the embryo becomes obvious at one side of the blasto-
[43] DEVELOPMENT OF OSSEOUS FISHES. 531
ë
derm the embryo is finally quite distinctly outlined when the stage
represented in figs. 101 and 102 is reached. A little later the tail be-
gins to bud out as shown in fig. 103. Tater still, and usually by the
end of the second day, the young fish has reached the condition repre-
sented in fig. 126. Somewhat later the stage represented in fig. 127
is attained. The yelk is still quite large at this time and the peritoneal
or segmentation cavity sc is obvious. At this time the horizontal folds
which give rise to the pectorals appear, as shown in fig. 128 from above
and in diagrammatic section in figs. 129 and 130. A more advanced
stage of the development of the pectoral fin is represented in fig. 134,
at which time it begins to be rotated on its own base. As a result of
this rotation, its posterior or metapterygial border becomes directed
downward, while its anterior or propterygial border is directed upwards
or dorsally. Shortly after the stage represented in fig. 136 is reached
the young fish leaves the egg. By the time this stage is reached the
nouth is open, but there is no open or free passage through the Oesopha-
gus. The gill and hyomandibular arches are obvious, though the bran-
chial clefts are still very narrow. After hatching, as shown in fig. 149,
the tail of the larva is perfectly lophocercal and shows no well-marked
signs of heterocercality until some time after the absorption of the yelk.
The larva now measures 10” in length. Fig. 148 represents a stage
about two days older than that shown in fig. 149, and in which the
gill-arches and jaws are more fully developed, so that the mouth is
opened and closed voluntarily by the young fish. A feeble branchial
respiration is established about this time. The auditory vesicles are
now fully differentiated and the semi-circular canals, otoliths, and audi-
tory end-organs of the seventh nerve are developed as shown in fig.
132. Two pairs of recurved teeth have also been developed in the
lower jaw at this stage. -
At the end of about the fifth day the yelk has been almost entirely
absorbed; only a small fusiform mass of vitelline matter, Y, fig. 151,
remains and causes the ventral wall of the abdomen to bulge down-
wards behind the pectoral fins. By this time the mesoblast begins to
proliferate into the median dorsal fin-fold to form the foundation of
the permanent dorsal, as indicated at the base of the widest portion of
the dorsal fold in fig. 151. On the thirteenth day a decided notch at the
posterior end of the future dorsal, as shown in fig. 133, marks the point
in advance of which that fin will be formed. In the course of twenty-
one to twenty-eight days the young shad has about completed its meta-
morphosis, when it is still much slenderer than the adult, though it has
all of the fins developed, even the ventrals, which grow out quite late
and about midway between a vertical passing through the pectorals
and another passing through the anus. In six months the larvae of the
shad, if kept where they can find an abundance of small crustacea, in-
sects, &c., will grow to a length of 43 inches. By the time they reach
that size they are readily recognizable by their external characters as
appertaining to this species. -
U.
532 REPORT OF COMMISSIONER of FISH AND FISHERIES. [44]
The gill-clefts remain uncovered for a long time, as shown in figs.
150, 151, and 153, but by the twenty-first to the twenty-eighth day the
opercular folds have grown to such an extent that the clefts and gills
are quite concealed from observation externally. When the fish reaches
that stage of development it measures 22mm in length, or not far from
an inch, and has a heterocercal tail in which the permanent rays are
well developed, as they are in all of the fins except the ventrals. The
first obvious intimation of heterocercality in the larval shad appears on
the seventeenth day, as shown in fig. 150, representing a rather stunted
larva measuring 14 nm in length. The food during the later larval stages
does not accumulate in the stomach, but accumulates in the intestine I,
just behind the pylorus, as shown in fig. 150. It is only after the young
fish acquires mobility of its jaws that it begins to feed, and after the
small teeth already mentioned have appeared; indeed, the larvae about
this time occasionally become so ravenous that they have been known
to attempt to eat each other, and finally strangle in their efforts at con-
summating cannibalism.
The temperature at which the ova of the shad develop normally ranges
from about 550, or perhaps slightly less, up to about 800 Fahr. Experi-
ments made to determine the lowest temperature at which normal de-
velopment would take place gave some very interesting results. It was ,
found that at a little below 520 Fahr. abnormalities of various kinds were
sure to appear. Some of these I have figured from micro-photographs
on plate xviii. Pigs. 122 and 123 show how the development of the
tail and notochord was impaired when the embryos were subjected to a
temperature ranging from 45° to 480 Fahr. Fig. 124 shows how the
development of the blastodisk became impaired when subjected to the
same low temperature. - *
A great variation in the period of hatching of this species is caused
by variations in the temperature of the water during the hatching sea-
son; for example, at 740 Fahr. hatching occurs in about seventy hours;
at 64.50 Fahr. in one hundred and nine hours; at 57.2° Fahr. in one hun-
dred and forty-eight hours or over six days. I have known it to require
seventeen days for the ova of the shad to hatch when the average tem-
perature of the water was 53.750 Fahr. In ordinary pleasant spring
weather the eggs usually hatch during the third or fourth day after
fertilization.
The first paper of note on the development of the shad was published
by the late Prof. H. J. Rice” in 1878. Since then the writer has pub.
lished additional observations” on the development and the retardation
of the development of the eggs and on the feeding” of this species.
*H. J. Rice. Notes upon the development of the shad (Alosa sapidissima 2). Re-
port of a Commissioner of Fisheries of Maryland, January, 1878, pp. 95–106, pl. vi.
*7.J. A. Ryder. On the retardation of the development of the ova of the shad.
Bull. U. S. Fish Com., i, 1881, pp. 177-190 and 422–424. &
*J. A. Ryder. Observations on the absorption of the yelk, the food, feeding, and
development of embryo fishes. Bull. U. S. Fish Com., ii, 1882, pp. 179—205. One fig-
ure in text.
J.
©
[45] DEVELOPMENT OF OSSEOUS FISHES. - 533
The illustrations accompanying the present note on the development
of Clupea sapidissima have been drawn in part with the camera lucida at
various times during the last five years; a number are redrawn from a
series of very successful micro-photographs made by Mr. T. W. Smillie,
under the direction of the author.
XVIII.—ICTALURUs ALBIDUs (LE SUEUR) J. & G. (White Catfish;
Channel Cat of the Potomac.)
I have already given a short account of the development of this
species elsewhere,” but as the many remarkable phases presented by
its larval growth cannot be understood without illustrations, I will now
give a fuller and more detailed description, with such figures as are
ready for publication.
A number of individuals of this Siluroid were brought from the Poto-
mac River to the Armory Building in the spring of 1883, and deposited
in the large aquaria in that institution at about the close of the shad-
hatching season of that year. One pair of these fishes afterward
spawned while in confinement, and thus afforded the writer the oppor-
tunity of observing and describing some of the more interesting phases
of development of this singular family of fishes. There has hitherto
been little attention paid to the development of this type, probably
from the lack of opportunity; and these notes may therefore prove of
interest to naturalists. The literature of the subject is scanty; and,
besides a paper by Jeffries Wyman * on the development of Aspredo
larvis and Bagrus, I know of no separate essays on the development of
this group, except some remarks in Günther's Introduction to the Study
of Fishes, and in his article Ichthyology, ninth edition of the Encyclopae-
dia Britannica, on the development of Arius. An egg of this genus is
there figured in an advanced state of development, from which it ap-
pears that this form is very similar in its embryological features to
AElurichthys, some ova of which are in my possession, measuring three-
fourths of an inch in their longest and five-eighths of an inch in their
shortest diameter. Arius and Ælurichthys are marine forms, and the
males have the habit of carrying the ova in the linder part of the
oral cavity or branchial region until the young are hatched. These
marine species, however, have only a few very large ova. So concealed
in the mouth of the male at one time. They are probably far less pro-
lific than the species the development of which is about to be described.
The adults were kindly identified for me by Professor Gill. Its habits
of spawning and care of the young are probably characteristic of all of
the species of the genus, of which there are said to be eight found within
the limits of North America. -
*J. A. Ryder. Preliminary notice of the development and breeding habits of the
Potomac cat-fish, Amiurus albidus (Le Sueur) Gill. Bull. U. S. Fish. Com., iii, 1883,
pp. 225–230.
* J. Wyman. On some unusual modes of gestation. Am. Journ. Arts and Sciences,
xxvii, 1859, pp. 5–13.
534 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [46]
On the morning of the 13th of July, a little after 10 o'clock, we noticed a
mass of whitish eggs in one of our aquaria inhabited by three adult speci-
mens of Ictalurus albidus, two of which were unmistakably the parents of
the brood, for thereason that they did not permitthe third one to approach
near the mass of eggs which one of them was watching vigilantly. One of
the individuals remained constantly over the eggs, agitating the water
over them with its anal, ventral, and pectoral fins. This one subsequently
proved to be the male and not the female, as was at first supposed. The
female, after the eggs were laid, seemed to take no further interest in
them, the whole duty of renewing and forcing the water through the
mass of adherent ova devolving upon the male, who was most assidu-
ous in this duty until the young had escaped from the egg-membranes.
During all of this time, or for a period of about a week, the male was never
seen to abandon his post, nor did it seem that he much cared even after.
wards to leave the scene where he had so faithfully labored to bring
forth from the eggs the brood left in his charge by his apparently care-
less spouse. The male measured 15 inches in length, the female a fourth
of an inch more. º
On the 30th of June, or when the young were seventeen days old, it
was determined to make an examination of the internal organs of both
parents, which was done in the presence of Professor Gill, to learn which
one of the parent fishes it was that had acted as nurse. Fortunately
there was considerable difference between the two in color; the female
had also lost a part of one maxillary barbel, so that it was easy to dis-
tinguish the two fishes apart. The darker specimen, with the broader
head, we found was the male, which, as already stated, had acted as
the nurse. Upon cutting him open and removing a portion of the milt
or testes they were found as a lobulated pair of organs, lying one on
either side of the mesentery and depending from the dorsal wall of the
abdominal cavity. The lobes of the testes were digitate. Upon com-
pressing fragments of the testes under the microscope, active Sperma-
tozoa were passed out. The spent roe or ovary of the female was a
paired organ, the right and left sacs of which were joined together pos-
teriorly. The ovarian lobes or leaflets were disposed transversely in
the Sacs. l
The mass of ova deposited by the female on the 13th of July in one
corner and at one end of the slate bottom of the aquarium measured
about 8 inches in length and nearly 4 inches in width, and was nowhere
much over one-half to three-fourths of an inch in thickness. There were
probably 2,000 ova in the whole mass, as nearly as could be estimated.
The single ova measured about one-sixth of an inch in diameter a short
time after oviposition. -
The ova were covered with an adhesive but not gelatinous envelope,
so that they were adherent to the bottom of the aquarium and to each
other where their spherical surfaces came in contact, and consequently
had intervening spaces for the free passage of water, such as would be
[47] DEVELOPMENT OF OSSEOUS FISHES. 535
found in a submerged pile of shot or other spherical bodies which had
been piled in a heap. It was evident that the male was forcing fresh
water through the interstices in this mass of eggs by hovering over it
and vibrating the anal, ventral, and pectoral fins rapidly.
All of the ova left in the care of the male hatched, while about one-
half of the mass which he had detached from the bottom of the aqua-
rium on the third day, during some of his vigorous efforts at changing
the water, were transferred to another aquarium, supplied with run-
ning water, and left to themselves. Those which were hatched by the
artificial means just described did not come out as well as those left to
hatch under natural conditions. Nearly one-half of the former failed
to hatch, apparently because they were not agitated so as to force fresh
water through them and kept clean by the assiduous attentions of the
male parent. - -
The eggs measure about one-sixth of an inch after the large water
space is formed, which is normally developed in this, as in the ova of
other fishes, after fertilization, the zona radiata being lifted up, some.
what from the vitellus. The vitellus measures one-eighth of an inch in
diameter. The egg-membrane is double, that is, there is a thin inner
membrane representing the zona radiata, external to the latter and
supported on columnar processes of itself which rest upon the inner
membrane; there is a second one composed entirely of a highly elastic
adhesive substance. The columns supporting the outer elastic layer
rest on the zona and cause the outer layer to be separated very dis-
tinctly from the inner one. It is these elastic columns and the elastic
outer adhesive membrane which permits the adult fish to shake and
move the mass of ova so violently without injury to the embryos in
process of development within. This peculiar double egg-membrane,
with a well defined space between its inner and outer layers, is highly
characteristic, and bears no resemblance to the thick, simple zona in-
vesting the egg of Ælurichthys, nor has anything resembling it ever
been described, as far as I am aware, in the ova of any other Teleos-
tean. -
The germinal disk was formed at the upper pole of the vitellus im:
mediately after oviposition and gradually spread in the usual manner
over the lower pole of the opaque, whitish, granular, vitelline globe.
In the early part of the second day the body of the young fish was dis-
tinctly outlined and the tail had grown out to a considerable length,
and before the body of the embryo had encircled much more than one-
fourth of the circumference of the. vitellus, as shown in figs. 154 and
155—the first figure being drawn from a hardened embryo of the
second day, viewed as an opaque object and the second from a living
embryo of the same age, viewed as a transparent object. On the third
day, the tail of the embryo had acquired considerable length, as shown
in fig. 159, and its free extremity was moved from side to side grace-
536 REPORT OF COMMISSIONER of FISH AND FISHERIES. [48]
fully and rhythmically through the contents of the water space sur-
rounded by the zona.
The water space from the first was filled with an immense number of
free refringent but very minute corpuscles, which made it difficult to
make out the form of the embryo during the early stages, unless the
zona was first removed. These corpuscles were not of the nature of
blood cells, and seemed to become less abundant toward the close of
the period of development within the egg. So abundant were these
corpuscles at first, coupled with the opacity of the vitellus and the
peculiar whiteness of the germinal matter, that even an experienced
observer would be led to suppose at first that all of the eggs were
bad, having the “rice-grain” appearance of blasted shad ova. The
corpuscles mentioned are visible in sections of the entire egg of Ic-
talurus, and are very abundant in the water space forming adherent
masses. In life the movements of the tail of the embryo cat-fish whirl
these corpuscles about in the water space in clouds, so that it seems as
if a whitish sediment was being constantly stirred up within the egg-
membrane. The presence of vast numbers of such bodies of plasmic
origin within the egg-membranes of Teleosts it seems had not been ob.
served in any other form up to the time that the writer had published
his observations on the development of the cat-fish. Recently, however,
it has been found by Solger” that they are present in the water space
of the ova of other species, especially of Leuciscus rutilus. These
corpuscles becoming less abundant toward the close of the hatching
period is very probably to be accounted for on the supposition that
they are taken up and appropriated by the epiblastic tissues of the em-
bryo by a process of intracellular digestion.
On the third day the vascular system begins to be evident, and the
heart h, figs. 156 and 157, is extended forward beneath and in advance
of the head over the anterior end of the yelk. A pair of vascular arches
(Cuvierian ducts) are soon formed just in advance of the rudiments of
the pectorals. These vessels grow outward and split up into vitelline
capillaries and eventually join a median ventral vitelline vessel which
empties into the venous end of the heart, as shown in figs. 163 and 164.
The mouth is not yet open on the second day, fig. 155, but at this
stage if the embryo be removed from its envelope and viewed as an
opaque object, the rudimentary branchial arches and clefts, fig. 154,
b, are visible. The first traces of the pectoral thickenings or outgrowths
p, in advance of the lateral extensions of the muscular somites of the
body, are evident at this stage. . The eyes e, fig. 154, are unusually
small for young fishes at this stage, and remind one of the compara-
tively small eyes of embryo sturgeons, bony gars, and amphibians. The
choroid fissure is prolonged obliquely downward and forward on the
second day, as shown in fig. 155.
* B. Solger. Dottertropfen in der intracapsulāren Flüssigkeit von Fischeiern.
Arch, f, mik. Anat, xxvi, 1885 pp. 321–334,
[49] IDEVELOPMENT OF OSSEOUS FISHES. 537
On the third day the mouth is wide open, figs. 156 and 157, and the
branchial clefts b, fig. 158, are developed with a free circulation through
the arches. The opercular folds op, fig. 159, which lead to the forma-
tion of the opercles of the adults, are also beginning to be quite obvious.
The caudal part of the aorta and caudal vein are also developed at this
stage, and the intersegmental vessels are formed a little later, from
which loops run out into the mesoblast of the median fin-folds.
The pectoral fin is formed as a lateral outgrowth p, figs. 158 and
159, just in advance of the inferior and lateral extension of the muscu-
lar segments m m, which eventually form the muscular portions of the
lateral body-walls. In this early condition the pectoral is a mere flat,
immobile lobe, into which muscular and other mesoblast has prolifer-
ated; it also begins to show evidences of a slight rotation or torsion on
its own base. At its base and a little way toward the middle line.of
the embryo there is a patch of thickened epiblastic tissue composed of
very large cells. This is the rudiment of a peculiar integumentary or-
gan, situated in the adult above the base of the pectoral and behind
or upon the shoulder girdle, and is composed of a series of vesicular
cavities which contain particles of calcareous matter.
The development of the median fins is very similar in character to
that usually observed in other forms. On the second day the median
natatory fold began to grow out on the dorsal and ventral sides of the
embryo and over the end of the tail. By the end of the third day the
median fin-fold was well developed, and the tail had not yet exhibited
any inclination to become heterocercal.
The remarkably developed barbels of the embryos of this species make
their appearance very early, especially the maxillary pair; these appear
on the second day as a pair of bosses or thickenings of the epiblast at
points near where the future angles of the mouth will be situated. On
the third day this pair of barbels is developed as flat prominent lobes
bl at the angles of the mouth, as shown in figs. 156, 157, and 158. The
barbels on the lower jaw do not appear till the fourth day of develop-
ment is completed, as shown in fig. 152. The last of all to be devel-
oped is the nasal pair, which grow out at the anterior side of the pos-
terior nareal openings, as shown in fig. 164; this pair does not appear
until the Seventh day. The development of a cartilaginous axis in the
barbels takes place as early as the formation of the other portions of
the chondro-skeleton, but the fuller description of these supports of the
barbels will be postponed until I come to the account of the cartilagi-
nous cranium, with which the cartilages found in the barbels are in in-
timate relation.
The nasal pits, or the first traces of the olfactory organs of Ictalurus,
appear on the second day as a pair of thickenings of the epiblast, just
in advance of the eyes. On the third day they are visible as a pair of
much antero-posteriorly elongated depressions or pits, in the same lo-
cation, as shown in fig. 160. On the fourth day the edges of the elon.
538 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [50]
gated olfactory depressions begin to grow toward each other in the
middle, and by the fifth day a bridge is formed across the nasal sack,
so that an anterior and posterior opening is left, corresponding to the
anterior and posterior nostril of the adult. *
Hatching occurs on the sixth day, at which time the embryo presents
the appearance shown in fig. 163, when viewed as a transparent object.
... It now measures 9” in length, or somewhat over a third of an inch.
. The heart is now prolonged downward over the anterior pole of the yelk.
. The branchial arches are quite hidden by the downward and backward
extension of the opercular folds. The tail has also become decidedly
heterocercal, and distinct indications of the future permanent caudal
rays are developed. The anterior dorsal fin is also becoming evident,
just behind the head, where mesoblast has begun to proliferate into the
median dorsal fin-fold.
On the seventh day, as shown in fig. 164, the fins have undergone
still further development. The pectoral has completed its rotation,
and the anterior dorsal and the anal fins are outlined. The caudal lobe
is wider and its rays more evident. The entire set of four pairs of bar-
bels is also now evident, and a more intricate meshwork of vessels
traverses the surface of the yelk. º
On the eighth day, as shown in fig. 165, the yelk has diminshed
somewhat in size. The anterior dorsal is now also sharply defined, and
some distance behind it the dorsal fin-fold is widening at the point
where the second or soft dorsal will be formed. The ventral fins have
also appeared as a low horizontal fold at the ventral side, between the
vent and the yelk-sack. The rudiments of permanent rays are also evi.
dent in the pectoral.
On the ninth day, as shown in fig. 166, the ventral is a more pro-.
nounced lobe than on the preceding day, but no rays have yet made
their appearance. The upper or first ray of the pectoral is also now
developed as a spine, and the position of the soft dorsalis indicated by
a decided notch at its posterior extremity. . . . 2"
On the tenth day the permanent rays of the dorsal become clearly
defined, as shown in fig. 167, and the ventral has become somewhat
more prominent. The yelk is now rapidly disappearing, and by the
eleventh day comparatively little is left to distend the abdomen, as
may be noted in fig. 168, representing a young Ictalurus of that age.
At this stage the rays of the ventral begin to be apparent, while those
of the pectoral, dorsal, anal, and caudal are clearly differentiated; acces-
sory caudal rays are also beginning to be formed, and the nasal bar-
bel is conspicuous. - - *
On the fifteenth day all of the fins are well developed and permanently
outlined, but the lower lobe of the caudal is still shortest, as shown in
fig. 169. Five days later the lower lobe of the caudal is somewhat
longer, as shown in fig. 170. The anterior spinous ray of the first dor-
sal and of the pectoral is now developed, and the latter has assumed a
[51] DEVELOPMENT OF OSSEOUS FISHES. 539
nearly horizontal position. The young Ictalurus is now twenty days
old and would be readily recognized as possibly belonging to one of
several American genera, though at this stage it resembles most nearly
the adult of the genus Noturus, indicating that the latter is a less
... specialized type than the one here under consideration. *
When the young Ictalurus is eighty-eight days old, as shown in figs.
171 and 172, from the side and from above, its external generic fea-
tures become distinctly apparent. The anterior dorsal spine and the
pectoral spines, armed posteriorly with recurved hooks, are now devel-
oped. The post-scapular process is evident beneath the skin and the
air bladder forms a strongly marked rounded prominence just behind
the shoulder-girdle, where it presses the body-wall outwards. The soft
dorsal is now quite free and sharply defined posteriorly, and the pig-
mentation, which has gradually increased in depth since the time of
hatching, is now very nearly that of the adult. At this stage of devel-
opment the young fish measures 19.5” in length. At the end of one
hundred and twelve days the young of Ictalurus, measures 25” in length,
or about 1 inch. When one hundred and seventy days old the young
fish measures 35* in length. These two stages I have not figured, since
the resemblance to the adults is sufficiently obvious in fig. 171, repre-
senting a much younger individual. The young of Ictalurus therefore
more than double their length in eighty-two days, and nearly quadruple
it in one hundred and sixty-four days after hatching, as the foregoing
data demonstrate.
On the fifteenth day after oviposition it was found that the young fishes
would feed. While discussing with the writer what should be provided
for them Mr. J. E. Brown threw some pieces of fresh liver into the
aquarium, which they devoured with avidity. It was now evident that
they were provided with teeth, as they would pull and tug at the frag-
ments of liver with the most dogged perseverance and apparent feroc-
ity. This experiment showed that the right kind of food had been sup-
plied, and as they were then fed, up to August 1, with nothing else with-
out our losing a single one of the brood, nothing more in the way of
food seemed to be required.
It is worthy of note that when pieces of liver were thrown into the
aquarium the parent fish would apparently often swallow them, with
numbers of his offspring eating at and hanging to such fragments. I
was soon agreeably surprised to find that the parent fish swallowed
only the meat, and that he invariably ejected the young fish from the
mouth uninjured, as he seemed to be able to discriminate, instinctively
and before deglutition occurred, between what was his proper food and
what were his own young. As soon as the young began to feed they
commenced to disperse through the water and to all parts of the aqua-
rium, and to manifest less desire to congregate in schools near the male,
who also abated his habit of fanning the young with his fins, as was his.
wont during the early phases of development. •
540 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [52]
The air-bladder became perceptible through the semi-transparent
bodies of the young on the tenth day, as a dorsal outgrowth of the back
part of the Gesophagus, and is placed far forward, a little above and
behind the level of the insertion of the pectoral fins, and as it grew more
capacious the young fish commenced to Swim higher in the aquarium.
When first hatched, and for some days afterwards, the young fish ex-
hibited a great tendency to gather together in a dense school.
Of the development of the viscera I shall have but little to say at
present. The intestine is not prolonged backwards very far beyond
the posterior end of the yelk-sack. On the thirteenth day the greenish
secretion of the liver can be seen in its cavity.
The liver is developed on the ventral side of the intestine and very
Soon displaces, more or less extensively, the coarsely granular yelk
below it. It is crowded into the anterior end of the yelk-sack close to
the heart, at first growing downward and outward on the left side as a
rather elongated structure lying between a vertical traversing the hinder
part of the opercles anteriorly and a vertical cutting through the
shoulder girdle posteriorly. A capillary network of vessels traverse
the liver and pour their contents directly into the Vitelline or portal
system of vessels which convey the blood back to the heart.
Behind the vent a distinct urinary duct could be seen by the sixth
day, and by the tenth day the urinary bladder was developed in the
usual position in the extreme hinder portion of the body cavity and
just behind the posterior section of the gut. The renal apparatus was
present and had reached an advanced stage of development on the
tenth day, urinary tubules and glomeruli being found in advance of the
air-bladder, and also behind it.
In the upper posterior part of the gill-cavity of either side a large
glandular organ is found on the tenth day, which is undoubtedly the
thymus gland; it is embedded only in the posterior part of the upper
wall of the gill-chamber.
The air-bladder is formed as an outgrowth of the dorsal wall of the
fore-gut. The saccular diverticulum, from which this organ is formed,
acquires a lumen about the fifth day after the commencement of devel-
opment, and on the tenth day the organ presents the form of a depressed
oval sack. By the twentieth day the hinder end of the air-bladder be-
comes emarginate and shows traces of the bilobed character which it
presents in the adult. By this time also the muscle plates overlying its
exterior right and left aspects have aborted more or less completely, so
that its walls come into close juxtaposition with the integument just
behind the shoulder girdle. -
The cranium of Ictalurus albidus when ten days old I have figured on
plate xxx. At this time its principal elements are represented by car-
tilage, though the membranous representatives of parostoses are rap-
idly developing external to the chondrified parts. None of these have
been represented in fig. 173. This drawing was made from a series of
[53] DEVELOPMENT OF OSSEOUS FISHES. 541
superimposed outlines of the cartilages of the skull, as cut at successive
levels in a series of sections of uniform thickness, extending from the
outer side of the head to the middle line. Stereograms of this character
may be readily constructed with the aid of the camera lucida from a se-
ries of sections, if a uniform amplification is employed and patience and
care is exercised in drawing the outlines.
It will at once be noticed that, as compared with the chondrocranium
of Salmo, as figured by Parker,” or of Gambusia, as figured by my-
self,” the cartilaginous cranium of Ictalurus presents some very impor-
tant modifications. These involve mainly the structure of the palatop-
terygoid arch Pl Pt, which is composed in Ictalurus of two pieces in-
stead of one. The narrow bar T Cr, representing the tegmen cranii
in Ictalurus, is much wider in both the other types named, and the build
of the skull in the type here described is complicated by the presence of
no less than three pairs of cartilaginous appendages for the support of
the barbels, representing chondrified elements which are probably not
found in the skulls of young fishes of any other type. The skulls of
the Nematognathi are therefore distinguishable from those of other or-
dinal groups of fishes at a very early period of development.
The chondrocranium of the young Ictalurus, as a whole, is depressed,
but relatively far less so than in the adult. The auditory apparatus is
quite completely covered in laterally and inferiorly by a cartilaginous
investment in the region marked Aw. Below and mesially, the para-
chordal elements Pa C are found, although now quite completely fused
with the auditory capsules laterally and the trabecular bars Tranteriorly.
The cartilaginous brain box is perforated laterally on either side in the
exoccipital region to give passage to the ninth and tentlı pairs of nerves
at IX and X. In advance of the articulation of the hyomandibular bar,
Hm, there is a large lateral fenestra in the cranial box through which
the second or optic, the fifth or trigeminal, and the seventh or facial
nerves pass at II, V, and VII. Just in front of this is the orbit O, and
forming its lower inner walls is seen the chondrified plate Ps destined
to form the presphenoid. In front of the orbit there is a high ect-
ethmoidal ridge, EE, in advance of which lies the olfactory fossa Ol.
Anteriorly the skull terminates in the trabecular rostrum R. There is
a wide fontanelle behind the tegmen cranii or frontal bridge, and a
smaller one in front of it. These fontanelles persist in the median line
as narrow clefts, partly separating the frontals in the ossified cranium
of the adult. At the posterior end of the cranial box and in the median
line, the supraoccipital, 80, is developed as a separate block of cartilage.
The extent to which the chorda is prolonged into the base of the skull
is indicated by the dotted line below the auditory capsule Aw.
* W. K. Parker and G. T. Bettany. Morphology of the skull, London, 1877, p. 59,
fig. 17.
**J. A. Ryder. Development of Viviparous Oss. Fishes. Proc. U. S. Nat. Mus., 1885,
pl. x, pp. 150–151.
542 REPORT of commissionER of FISH AND FISHERIES. [54]
The appendicular skeleton of the cranium, or the cranial visceral
arches possessing endoskeletal supports, are apposed to the infero-lateral
parts of the skull at the anterior part of the auditory region.
The most important of these arches is the compound hyoid and man-
dibular, supported by a common hyomandibular element, Hm, which
abuts with its upper end upon the anterior wall of the auditory capsule.
Inferiorly the hyomandibular gives support (1) to the mandible, now
entirely constituted of Meckel's cartilage, Mk, but around which articu-
lar, angular, and dentary parostoses are subsequently laid down in
membrane; and (2) to the hyoid arch, through the intermediation of a
short cylindrical element, the interhyal I Hy, which in its turn sup-
ports a series of elements consisting of the ceratohyal C Hy, hypohyal
H Hy, and urohyal G Hy. …
The changes which the hyomandibular has undergone in the course
of further development are quite complex. The principal portion of
the upper half becomes the ossified hyomandibular element of the
adult, an articular knob being formed on its posterior border, which
supports the operculum. Its inferior half represents the quadrate of
authors. Between the quadrate and hyomandibular portion the carti-
lage representing the symplectic does not seem to be well distinguished.
The inner, upper, anterior part of the hyomandibular bar takes part in
the formation of the hinder part of the pterygoid, i. e., the metaptery-
goid of the adult. The ecto- and entopterygoid are apparently differen-
tiations of the posterior separate element of the palatopterygoid arch
Pl Pt. - - g
The branchial arches are five in number; the posterior is imperfectly
developed above. At the inner ends of the posterior branchial bars
are placed a pair of epipharyngeal plates, Phb, bearing teeth even at
this early stage. The branchial bars are not yet definitely segmented
into their lateral elements. Cartilaginous copulac or basibranchials, B
B, are present in the floor of the branchial region, as shown in section
in fig. 174. } -
A very remarkable series of cephalic appendages now remains to be
described. These are the maxillary, nasal, and mental barbels. Of
these the nasal pair only is not represented in cartilage at the stage of
development here under consideration, but even this one develops a
chondrified axial support at a later stage.
Whether the endoskeletal part of the upper end of the so-called max-
illary barbel in reality represents the maxillary bone of other fishes
seems somewhat open to doubt, as the proximal ossification of the car-
tilaginous support of this barbel would give this element in the cat-
fishes a cartilaginous origin, which is at variance with what is known
of the development of its homologue in all other forms of Teleosts, in
which it arises as a membrane bone. True, it ossifies on the surface of
the cartilaginous support of the barbel, even in Ictalurus, yet it is barely
[55] DEVELOPMENT OF OSSEoUs FISHEs. 543
possible that the so-called adnasal of McMurrich,” may, if not actually
a part of the suborbital chain, as he surmises, in reality represent the
maxillary of other fishes, since this adnasal element is clearly a mem-
brane bone, while it is not altogether certain that the so-called “max-
illary” of the Nematognathi can be considered such. While the ossifica-
tion of the upper end of the cartilaginous bar Ma'b is superficial, old
specimens of Ictalurus show that the cartilage is invaded and replaced
by the process, so that its terminal portion only remains cartilaginous.
The other barbels, viz, the nasal and the mental, are also occasionally
ossified at the base, especially in old specimens. Both the internal
pair of mental barbels Ib and the external pair Eb are at first laid down
in cartilage in the embryo. The strongest argument in favor of regard-
ing the ossified basal parts of the lateral barbels as maxillary elements
is derived from a study of the distribution of the branches of the fifth
group of nerves as worked out by Wright,” though it must not be for-
gotten that these organs in Siluroids are specialized as tactile organs,
and that they may therefore be richly supplied with nerves, in corre-
spondence with their high degree of specialization.
A longitudinal, median, vertical section through the head of Ictalurus
is represented in fig. 174, prepared from an embryo of the same age
as that used in working out the cranium represented in the preceding
figure. The brain is shown in mesial section and illustrates the rela-
tions of the cerebrum Cer anteriorly to the pineal body Pn just behind
it. The narrow midbrain mb is also shown, and upon which the re-
markably voluminous cerebellum Cb encroaches from behind. . At an
earlier stage the great antero-posterior width of the cerebellum is far
less obvious, so that it is quite clear that the excessive anterior exten-
sion of the cerebellum in the Siluroids is a result of the exaggerated
development or specialization of this portion of the brain of the ordi-
nary Teleostean type. The medulla oblongata mo is massive. The in-
fundibulum Inf departs but little in its form from that usually met with
in the embryos of osseous fishes. The cranial nerves and brain of
Amiurus has been so carefully described by Wright (op. cit.) that no
further discussion of this part of the subject will be entered upon here,
except to call attention to the disposition of the sacculus vasculosus S
and the hypophysis Hy.
A mesial section of the heart is also displayed in fig. 174. The thin-
walled sinus venosus SW, the muscular ventricle Ve, and the bulbus aortae
18a, have been cut through. The tip of the liver L, crowded into a cav-
ity in the coarsely granular yelk Y, is also shown, together with the more
homogeneous periblast P, which invests the mass of granular deuto-
plasm. The granules of deutoplasm in the yelk-sack are characteris-
*J. P. McMurrich. Osteology of Amiurus, Proc. Canadian Inst. Toronto. N. S., ii,
No. 3, p. 278, pl. ii, fig. 1, An.
*R. R. Wright. On the nervous system and sense organs of Amiurus. Proc. Cana-
dian Inst. Toronto. N. S., ii, No. 3, pp. 366–368, pl. iv.
544 REPORT OF COMMISSIONER of FISH AND FISHERIES. [56]
tically firm in character, but globular instead of flattened and oval or
elongated, as in the ova of Ganoids, Amphibians, and Elasmobranchs.
The muscular bundles M. M., cut through at several points, actuate or
belong to the pharyngeal, branchial, submaxillary, and hyoid regions
of the head. The intestine I, Oesophagus Oe, and air-bladder Ab, are
cut through in the middle line in the section here represented. The
anterior part of the chorda Ch has also been divided in the middle line, .
and the rudiments of the three anterior centra aſ a: a are seen to be
shorter than those which follow. Two of these centra eventually coa-
lesce with each other, and with the fourth and fifth form the co-ossified
anterior segment composed of four vertebral bodies in the spinal col-
umn of the adult. Some of the lateral processes and parts of the neural
arches of these co-ossified vertebrae, especially the first, second, and third,
give rise, according to McMurrich, to the series of ossicles by which the
air-bladder and auditory apparatus are brought into intimate physiolog-
ical relations with each other.
The development of the shoulder girdle is remarkable from the cir-
cumstance that the coracoid portion originally laid down in cartilage is
excessively developed, extending downward as a great flat cartilagin-
ous blade, Cor, from the base of the pectoral fin, as shown in fig. 173.
In front of the coracoid the membranous basis of a parostosis is already
formed; this is clearly the rudiment of the element termed the clavicle
by Huxley and Parker in other osseous fishes. The scapular portion Sc
of this cartilage is small, and is prolonged anteriorly into two cornua,
between which there is a well-marked glenal fossa in which the basal
ends of the pectoral rays are lodged; two nodules of cartilage, 1, 2, rep-
resent with some doubt the actinosts. The metapterygial actinost, if
it be such, is the larger of the two and the most anterior, forming, in
fact, the basal part of the first pectoral ray which eventually becomes
developed as a strong spine. This relation of these nodules to the rays
would indicate that they were actinophores and that therefore true ac-
tinosts are not developed in Ictalurus.
The nomenclature followed above in naming the chondriſied parts of
the shoulder girdle is that used by Huxley. Dr. Gill, however, regards
the whole cartilaginous plate Sc and Cor as scapula, but there is no sub-
division of this plate into hypercoracoid and hypocoracoid elements, but
it forms a solid piece, the upper part of which alone gives support to
the pectoral and the reduced actinosts, or perhaps rather actinophores,
already described."
546 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [58]
EXPLANATION OF PLATE I.
GADUs MoRREIUA. (The Cod.)
FIG. 1. Young cod 5mm long showing the large supracephalic integumentary sinus ss
over the head and body; i, intestine; y, yelk. Viewed from the side. x 32.
FIG. 2. Same, viewed obliquely from in front to show the size of the sinus 88.
FIG. 3. Position of cod's egg in the water shortly after impregnation, showing the
polar cells, germinal plasma, and micropyle at inferior pole.
FIG. 4. Illustrating the inferior position of the blastodisk when the egg of the cod is
at rest at the surface of the water.
FIG. 5. Illustrating the slight rotation of the egg as the embryo is gradually length-
ened.
FIG. 6. Illustrating the quarter-rotation of the egg when the blastopore is about to
close, bringing the embryo into an inferior position.
Report U. S. F. C. 1885.-Ryder.
Osseous fishes.
PLATE I.

548 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [60]
EXPLANATION OF PLATE II.
FIG. 8. Embryo Clupca vernalis on the second day after hatching. x 32.
Fig. 9. Embryo golden ide, Idus melanotus, just hatched. 6.6mm long. x 20.
FIG. 10. Embryo gold-fish, Carassius auratus. Five and one-half days after hatching.
x 21. *
Fig.11. Head of a larval fish; a hybrid between the shad and rock-fish, the former
being the female and the latter the male parent. x 32.
Report U. S. F. C. 1885.-Ryder. Osseous fishes.
PLATE II.
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550 REPORT of commissionER OF FISH AND FISHERIES. [62]
EXPLANATION OF PLATE III.
Fig. 12. Head of young Siphostoma fuscum.
FIG. 13. Developing egg of Elacate canada, showing the spacious cleavage cavity as,
Kupffer's vesicle kv, the chorda ch, the segments m 'm of the embryo, and the limbs
br of the concrescing blastopore, the oil-drop o, and the optic vesicles op.
Fig. 14. An earlier phase of the development of an egg of the same species.
FIG. 15. The unimpregnated ovum of the file-fish, Monacanthus broccus, showing the
position of the oil-drops and the form of the blastodisk.
FIG. 16. The developing ovum of the gold-fish Carassius auratus, showing the extent
to which the embryo embraces the circumference of the vitellus. x 32.
FIGS. 17 and 18. Other views of a similar stage of the same species.
PLATE III.

552 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [64]
EXPLANATION OF PLATE IV.
SIPHOSTOMA FUSCUM. (The Pipe-fish.)
FIG. 19. A young embryo, in which the tail is still archicercal and the dorsal and pec-
toral fins are just developing.
Fig. 20. A still younger stage, in which the tail is just beginning to grow out.
FIG. 21. An older stage, in which the caudal fin is beginning to be formed.
Report U. S. F. C. 1885.-Ryder,
Osseous fishes.
PLATE IV.
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554 REPORT of commissionER OF FISH AND FISHERIES. [66]
EXPLANATION OF PLATE V.
APELTES QUADRACU.S. (Four-spined Stickleback.)
FIG. 22. Embryo in the egg, showing the asymmetrically disposed vitelline vessels.
FIGS.23 and 24. Other views of the same stage, showing the lateral position of the
heart.
Fig. 25. Dorsal view of a recently hatched embryo, showing the distribution of the
brown pigment blotches on the median line and the symmetry in the distribution
of the vascular channels on the dorsal side of the yelk.
FIG.26. Side view of the same stage, showing the pigmentation and vascular loops in
the dorsal fin-fold.
Report U. S. F. C. 1885.-Ryder. Osseous fishes. - PLATE V.
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556 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [68]
EXPLANATION OF PLATE WI.
Fig. 27. Young Apeltes one week old, with the lower lobe of the caudal developing
and becoming heterocercal.
Fig.28. Recently hatched embryo of Esox reticulatus, showing the wide median fin-
folds, the distribution of vitelline vessels, and the course of the caudal and subin-
testinal veins. *
FIG.29. A much older stage of Esox reticulatus, in which the flat snout is becoming ap-
parent and the rudiments of the caudal, anal, and dorsal fins are becoming evi-
dent.
Report U. S. F. C. 1885.-Ryder.
Osseous fishes.
PLATE VI.
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558 . REPORT OF COMMISSIONER OF FISH AND FISHERIES. [70]
EXPLANATION OF PLATE VII.
(Species No. 1.)
FIG. 30. Showing developing egg removed from its membrane. The spreading blas-
toderm has greatly constricted the yelk.
FIG. 31. A somewhat earlier stage of the same in its membrane, over a part of which
the adhesive covering of the latter has collected and formed a disk-like mass, by
which it adhered to a piece of leather.
FIG. 32. A more advanced stage of the same.
FIG. 33. A still more advanced stage, in which the distribution of the oil-drops is evi-
dent and Kupffer's vesicle is developed under the posterior end of the embryo.
FIG.34. A larva which was developed from this same lot of eggs, three days after
hatching, showing the distribution of the pigment on the body, tail, and at the
junctions of the vessels of the yelk-sack.
Report U. S. F. C. 1885.-Ryder. Osseous fishes.
PLATE VII.
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560 REPORT of commissionER OF FISH AND FISHERIES. [72]
EXPLANATION OF PLATE VIII.
FIG. 35. Magnified view of an egg of the common yellow perch, showing the micro-
pyle m, the thin zona radiata 2, the thick, elastic, canaliculated or fibrillated
layer g, and the outer adhesive layera.
FIGS. 36 and 37. Views of ova of the white perch, in which the large blastodisk is
formed; also showing the way in which the adhesive covering of the egg forms
disk-like accumulations where they come in contact with each other or with flat
surfaces. s e
FIG. 38. A more advanced stage of the development of the same species, showing the
very thick blastoderm in optic section.
FIG. 39. A still more advanced stage of the same species.
Report U. S. F. C. 1885.-Ryder. Osseous fishes. PLATE VIII.
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562 REPORT OF COMMISSIONER OF FISH AND FISHERIES. T74]
EXPLANATION OF PLATE IX.
Roccus AMERICANUs. (The White Perck.)
FIG. 40. The just hatched embryo. x 32.
FIG. 41. The young white perch one day old. x 32.
FIG. 42. The same, three days old. x 32.
FIG. 43. The same, five days old. x 35.
FIG. 44. The same, six days old. x 32.
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564 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [76]
EXPLANATION OF PLATE X.
ScomberOMORUS MACULATUS. (Spanish Mackerel.)
FIG. 46. Cross-section through nasal region of young embryo; na, nasal pit. x 65.
FIG. 47. Cross-section through region of the optic crus. x 65.
FIG. 48. Cross-section through mid-brain, trabeculae cranii tr, and eyes. x 65.
FIG. 49. Section through a segmental sense-organ of the lateral line. x 250.
FIG. 50. Cross-section through back part of mid-brain, infundibulum, eyes, and optic
nerves. x 65.
FIG. 51. Cross-section through fore part of medulla oblongata. x 65.
FIG. 52. Cross-section through the auditory vesicle au, a segmental sense-organ ss,
front end of chorda, heart, and branchial region. x 65. }
FIG. 53. Longitudinal vertical section through the head of an embryo near the me-
dian line; h, heart; p, periblast; pc, pericardiac cavity; tr, cranial trabecula;
o, space of oil-drop. x 65.
FIG. 54. Cross-section through the pectoral region; 8d, segmental duct; p, periblast;
p', pectoral fin. x 65.
FIG. 55. Cross-section through the tail. A segmental sense-organ has been cut
through at one side. x 65.
FIG. 56. Longitudinal nearly median vertical section through the head, trunk, and
yelk-sack of an embryo; ch, chorda; m, myotomes; sd, segmental duct ; al, uri-
nary bladder; pn, pronephric funnel; i, intestine; p, periblast; 0, space oc-
cupied by oil-drop; h, heart; pc, pericardiac cavity; tr, cranial trabecula. x 65.
Report U. S. F. C. 1885.—Ryder. Osseous fishes.
PLATE X.

566 REPORT of comMISSIONER of FISH AND FISHERIES. [78] .
\
EXPLANATION OF PLATE XI.
CHAEToDIPTERUs FABER. (The Moonfish.)
FIG. 57. Blastodisk of an unimpregnated egg, viewed from the side.
FIG. 58. Mature egg, showing the position of the oil-drop, and with the blastodisk
formed. -
Fig. 59. Blastodisk, with about 32 cells, viewed from above, and showing the subquad-
rate form usually assumed at this stage.
FIG. 60. Entire egg, with the blastodisk developed to about the condition represented
in the preceding figure.
FIG. 61. The blastodisk of Chaotodipterus more advanced in development, with the large
marginal, flattened cells very apparent.
FIG. 62. An egg in which the embryo is apparent, the oil-drop covered by periblast
cells, pigment cells developed, and Kupffer's vesicle formed. &
Fig. 63. An embryo sixteen hours after hatching, showing the increased capacity of
the cleavage space so, due to the rapid absorption of the yelk; the pigment cells
aggregated at definite points. -
Report U. S. F. C. 1885.-Ryder.
Osseous fishes.
-
PLATE XI
º
ºvar
ºrrº
tº
º





568 REPORT OF COMMISSIONER of FISH AND FISHERIES. [80]
EXPLANATION OF PLATE XII.
CHAETODIPTERUS FABER. (The Moonfish.)
FIG. 64. Young fish just hatched, with the oil-drop lying at the inferior side of the
yelk, partly invested by cells derived from the periblast.
FIG. 65. Young fish twenty-eight hours after hatching, showing the yelk nearly ab-
snºrbed.
Report U. S. F. C. 1885.—Ryder. Osseous fishes.
PLATE XII.





570 REPORT of commissionER of FISH AND FISHERIES. [82] .
EXPLANATION OF PLATE XIII.
FIG. 66. Young Chaetodipterus faber, sixty-three hours after hatching.
FIG. 67. Young tom-cod, Gadus tomcod, just after hatching, drawn from a dead
specimen, the mouth being thrown wide open. x 24.
Ireport U.S. F. C. 1885.-Ryder.
Osseous fishes.
PLATE XIII.
ſă
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№ĚŇŘŠŤŠĶĒRĶĒŽĢģ,
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572 REPORT of commissionER of FISH AND FISHERIES. [84]
EXPLANATION OF PHLATE XIV.
CLUPEA SAPIDISSIM.A. (The Common Shad.)
FIG.68. The freshly extruded egg enlarged, showing its envelope much wrinkled and
its surface covered with small round vesicles.
FIG.69. An optic section of the periphery of the preceding more enlarged, showing
the zona 2, the cortical layer cl, with its embedded vesicles, and the large yelk-
spheres y surrounded by their films of protoplasm. g
FIG. 70. A shad's egg, showing the vitellus and distended egg-membrane, natural
S126), ſº
FIGS. 71,72, and 73. Represent three stages in the development of the blastodisk of the
shad's egg at the lateral pole of the vitellus.
FIG.74. Shows the gradual accumulation of the germinal matter at one pole of the
egg, the polar prominence externally, and the presence of plasmic processes ex-
tending down through the vitellus.
FIG. 75. Shad ovum with the blastodisk just forming, viewed from above.
FIG. 76. Shad ovum with the blastodisk formed and with protoplasmic processes pass-
ing from its under surface down into the vitellus. g
Figs. 77 and 78. Views in optic section of shad ova at the time the first cleavage
- furrow is developed.
FIG. 79, a, b, c, d, e,f. The changes which the polar prominence shown in fig. 74, under-
went at short intervals of time, during half an hour, till the polar cells were de-
tached. te
FIG. 80. Surface view from above of the blastodisk of the shad, at the time of the first
cleavage.
FIG. 81. A similar view of an older blastodisk at the time of the completion of the
second cleavage. g
FIG. 82. Side view of a similar stage.
FIG.83. Side view of blastodisk which has abnormally segmented into five cells.
FIG. 84. Blastodisk actively segmenting, and rapidly approaching the sixteen-celled
stage. The irregularities in the form of the cells is due to the unequal contrac-
tractions of their plasma.
FIG.85. Blastodisk composed of four cells at the time of the second cleavage; side
V10 W.
FIGS. 86 and 87. Oblique views of two different blastodisks at the end of the third
cleavage after eight cells have been developed.
FIG.88. Side view of a blastodisk at the same stage as the preced
FIG.89. Side view of a blastodisk during the active stage of the fourth cleavage.
FIG.90. Surface view of a blastodisk which has advanced somewhat beyond the fifth
cleavage, or thirty-two celled stage.
FIG.91. Optic section through a still more advanced stage of the development of the
blastodisk, when the latter is composed of three to four layers of cells.
FIG.92. Blastodisk at the time it has assumed the lenticular form, and is composed of
very small cells, just before it begins to spread over the yelk. Optic section.
-- - - -
- - - - -
- - - - - -
- * -
- - - - -
- - -
- - º
- -
-
- Report U. S. F. C. 1885.-Ryder. Osseous fishes.

574 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [86]
EXPLANATION OF PLATE XV.
CLUPEA SAPIDISSIM.A. (The Common Shad.)
FIG. 93. Section through the blastodisk of an egg at a stage intermediate between
those represented in figs. 91 and 92.
FIG. 94. A section of the germinal pole, same egg, near the edge of the blastodisk,
showing the thick layer of periblast just under its margin.
FIG. 95. Section through a blastodisk somewhat older than that shown in fig. 92,
showing the epidermal layer differentiated and with large nuclei at one side
embedded in the periblast. -
Fig. 96. Sagittal section through a more advanced stage, showing the cleavage cavity
sc beneath the central portion of the epiblast e, and the inflected hypoblastic
layer hjust within the lips oo of the blastopore.
FIG. 97. Portion of a longitudinal vertical section of the side of the body of an embryo
at the stage represented in fig. 98, to show that the solid myotomes M M M are
more intimately united to the hypoblast h than to the epiblast e. Very much en-
larged.
FIG. 98. Semidiagrammatic longitudinal median section through an embryo after
the blastopore has closed, to show the position of the first myotomes and the con-
tinuity of the chorda ch posteriorly with the lower or hypoblastic layer; so, cleav-
age cavity. -
FIG. 99. Median longitudinal section through the head of a more advanced embryo,
through the nasal pit, eye, gill-arches, brain, and chorda, and showing the rela-
tions of the periblast p. -
FIG. 100. A similar section of the same stage somewhat off of the median line. The
auditory capsule au is cut through, also the gill-arches, the heart h, and the oral
cavity b above the latter.
Report U. S. F. C. 1885.-Ryder. Osseous fishes. PLATE XV.

576 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [88]
* EXPLANATION OF PLATE XVI.
CLUPEA SAPIDISSIM.A. (The Common Shad.)
FIG. 101. An embryo shad, somewhat older than the stage represented in section in
fig. 98, in its natural position in its spacious enveloping membrane. From a
photograph.
FIG. 102. An embryo of the same age drawn without details, and showing the position
of Kupffer's vesicle at kv, and the heart h.
FIG. 103. A still more advanced embryo, showing the hind gut hg just under the out-
growing tail.
FIG. 104. Cross-section through the budding tail of an embryo of the preceding stage,
showing the relations of the muscle plates m 'm to the nervous cord N, the chordach,
and the post-anal section of the intestine i. The median fin-folds are still quite
rudimentary, and are developed as very slight, ridge-like folds of the skin above
and below in the median line. e
FIG. 105. A similar cross-section of an embryo of the same age, somewhat farther for-
ward.
FIGS. 106 and 107. Cross-sections through the body of an embryo somewhat younger
than that represented in fig. 102. The hypoblastic layer has not yet been differ-
entiated into the intestine at i. The nervous cord N is still continuous with the
epiblast e of the embryo. The chorda ch and muscle plates have been differen-
tiated.
Fig. 108. A similar cross-section through the anterior part of the trunk of an embryo
of the same age as that from which the preceding sections were prepared.
FIGs. 109, 110, 111, and 112. Four cross-sections through different regions of the body
cavity of a much more advanced embryo, the first being the most anterior. The
nervous cord N is detached from the skin, the segmental ducts are well defined,
and the intestine i has a narrow lumen.
FIG. 113. Diagrammatic representation of an embryo of about the age of the one rep-
resented in fig. 103, but unrolled from the vitellus, to show the course of the
segmental ducts 8d and the extension outward of the pectoral plates pp, which
are intimately concerned in the development of the pectoral fins.
Report U. S. F. C. 1885.-Ryder.
Osseous fishes.
PLATE XVI.
-

578 REPORT of commissionER OF FISH AND FISHERIES. [90]
EXPLANATION OF PLATE XVII.
CLUPEA SAPIDISSIM.A. (The Common Shad.)
FIGS. 114, 115, 116, and 117. Four views of successive stages of the development of
the head and optic lobes of the embryo shad, commencing with the stage when
the front end of the head of the embryo is visibly differentiated when viewed as
a transparent object with transmitted light.
Fig. 118. Section through the spreading blastoderm of the shad at a somewhat earlier
stage than that shown in fig. 96; h, hypoblast; e, epiblast; so, segmentation cav-
ity; oo, lips of the blastopore.
FIG. 119. Diagrammatic sagittal section through the embryonic axis e of a shad egg,
the blastoderm of which has enveloped one-half of the vitellus. The jagged line
represents the lateral limit of the cleavage cavity go.
Fig. 120. Egg of the shad in which the blastopore has just closed. Only four myo-
tomes have been developed in the mid-region of the embryonic axis.
Fig. 121. Cross-section through the body and yelk-sack of a young shad in about the
condition of development represented in fig. 127; ch, the thick chorda; i, intes-
tine; bo, body cavity; p, periblast or splanchnopleure investing the yelky; so,
cleavage cavity; e, thin outer epiblastic investment of the yelk.
S. Mis. 70—37
Report U. S. F. C. 1885.-Ryder. Osseous fishes. PLATE XVII.

580 REPORT OF COMMISSIONER of FISH AND FISHERIES. [92]
EXPLANATION OF PLATE XVIII.
CLUPEA SAPIDISSIM.A. (The Common Shad.)
FIGs. 122 and 123. Two views of unhatched embryos of nearly the same age, which
developed in a temperature of 45° F., producing distortions of the tail and noto-
chord. From photographs.
FIG. 124. Egg which was impregnated at a normal temperature and which developed
the blastodisk in a normal way, but subsequently, exposed to a temperature of
45° F., the blastodisk was distorted as here shown. From a photograph.
FIG. 125. Transparent view from below of front end of an embryo at about the time
the mouth is formed.
FIG. 126. An egg-envelope with its contained embryo, forty-four hours after impreg-
nation, viewed as a transparent object.
Fig. 127. An egg-envelope with its contained embryo at the beginning of the third
day of development. From a photograph.
FIG. 128. Dorsal view of the front part of an embryo at the time the pectoral fins
are beginning to appear as lateral folds.
Fig. 129. Diagrammatic cross-section through the pectoral fin of an embryo, to illus-
trate the way in which the mesoblast is proliferated into the integumentary fin-
fold. ‘
Fig. 130. Transverse profile view of the dorsal pectoral region of an embryo in the
stage represented in fig. 128.
Report U. S. F. C. 1885.-Ryder. Osseous fishes. PLATE XVIII.
º tº -
& S$- -> .
~
- - ~
ººls:
*t . . ."

582 REPORT of comMISSIONER of FISH AND FISHERIES. [94]
EXPLANATION OF PLATE XIX.
CLUPEA SAFIDISSIM.A. (The Common Shad.)
FIG. 131. Pneumatic duct pm, rudimentary stomach 8t, pylorus py, and swollen an-
terior part of hind gut I, and back part of oesophagus oe, of a young shad 22mm
long, which had acquired ventral fins. From a specimen three weeks old reared
in confinement. -
FIG. 132. View from above of the head of a young shad fourteen days old, showing
the relations of the auditory capsules, brain, and eyes. -
FIG. 133. Side view of a young shad thirteen days old, viewed as a transparent object.
ab rudimentary air-bladder, L liver, Gb gall-bladder.
FIGS. 134 and 135. Two views of the heads of embryos nearly ready to hatch, show-
ing the rudimentary gill-arches and pectoral fin, nasal pits, wide oral fossa, and
short lower jaw. Drawn from opaque specimens hardened in chromic acid.
FIG. 136. An embryo in its envelope, on the third day of development, nearly ready
to hatch.
FIGS. 137, 138, and 139. A lateral, a posterior, and a view from above of the blasto-
derm of the shad, just at the time the cleavage cavity, so, is beginning to be evi-
dent, the tail swelling, 8, formed, and the hypoblast developed by inflection of
the edge of the blastoderm.
FIGS. 140 and 141. Two views of an egg after the blastoderm has spread considerably
and the embryonic area e is well defined. From photographs.
Report U. S. F. C. 1885.-Ryder. Osseous fishes.
PLATE XIX.
;
|\

584 REPORT OF COMMISSIONER of FISH AND FISHERIES. [96]
EXPLANATION OF PLATE XX.
CLUPEA SAPIDISSIM.A. (The Common Shad.)
Fig. 142. Cartilaginous cranium of the larval shad on the sixth day after hatching.
Aw auditory capsule, Hm hyomandibular, Ch' ceratohyal, Gh glossohyal, Mk
Meckel's cartilage, Ih interhyal, Tr cranial trabecula, Ao antorbital process, Rros-
trum, i, ii, iii, iv, v, branchial arches; To tegmen cranii, Sy symplectic, Bp basip-
terygial plate from which the actinosts are developed, So coraco-scapular plate
perforated by a foramen.
FIG. 143. Cartilaginous cranium of a young shad shortly after hatching. Lettering
as before, except Ch, which in this figure indicates the chorda; Q the quadrate, a
continuation of the hyomandibular.
FIG. 144. Mesial section through the head of a young shad shortly after hatching.
mo medulla oblongata, Cb cerebellum, mb mid-brain, Pn pineal body, Cer cer-
ebrum, Infinfundibulum, Hy hypophysis, bb basibranchial, Ch' basihyal, Gh glos-
sohyal, Tranterior prolongation of the trabeculae as the rostral plate, Mk Meckel's
cartilage, i, ii, iii, iv, v, the open lumina of the branchial clefts, M M M an-
terior myotomes, ba bulbus aortae, ve ventricle, sv sinus venosus, po pericardia
cavity, Yyelk, p periblast, so cleavage cavity.
Report U. S. F. C. 1885.-Ryder. Osseous fishes. PLATE XX.
ºf:::::A;
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º:
|
º
º










586 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [98]
EXPLANATION OF PLATE XXI.
CLUPEA SAPIDISSIM.A. (The Common Shad.)
FIG. 145. Cross-section through the region of the eyes of an embryo ten days old;
bb basibranchial, ch ceratohyal, MK Meckel's cartilage,pt palatine, Tr trabeculae
cranii, E eye, Mb mid-brain, Cer cerebrum.
FIG. 146. Cross-section through the anterior part of the auditory region of the same
embryo; aw auditory vesicle with acoustic macula or end organ in its lower
wall, Mo medulla oblongata, Ch chorda, Hm upper end of hyomandibular, i, ii, iii,
and iv branchial arches, pa parachordal cartilages.
FIG. 147. Cross-section through the posterior part of the auditory region of the same;
lettering the same, except that the basibranchial barbb is cut through, as well
as the whole five branchial arches, also the auditory canals and vestibule of the
membranous labyrinth.
Beport U. S. F. C. 1885.—Ryder.
PLATE XXI.
Osseous fishes.
º
&I.
ºs-
~



588 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [100]
EXPLANATIONS OF PLATE XXII.
CLUPEA SAPIDISSIM.A. (The Common Shad.)
FIG. 148. Young fish on the third day after hatching, viewed as a transparent object
to show the extension of the segmental duct forward; the chorda ch, and liver L.
Fig. 149. Young fish immediately after hatching, viewed as an opaque object and
somewhat obliquely from one side, so as to display the relations of branchial and
hyomandibular arches, and the position of the pectoral fin.
FIG. 150. Young fish seventeen days after hatching, viewed partly as an opaque and
partly as a transparent object; py pylorus and rudimentary air-bladder above it;
I intestine, filled with the remains of ingested food. The opercula are already
so far developed as partly to conceal the branchiae.
FIG. 151. Young fish five days after hatching, very much enlarged, and viewed as an
opaque object. Only a slight remnant of the yelk-sack Y remains.
FIG. 152. Anterior portion of a young fish on the fourth day. To show the relations
of the liver L to the yelk Y, over which the portal vessel po passes forward to
empty into the venous sinus, in common with the anterior and posterior jugu-
lars j' and j, ba bulbus aortae, ve ventricle. -
FIG. 153. View of the fore part of a young fish seventeen days old, from the ventral
side.
Report U. S. F. C. 1885–Ryder. Osseous fishes. PLATE XXII.
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590 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [102)
EXPLANATION OF PLATE XXIII.
ICTALURUs ALBIDUs. (White Cat-fish.)
FIG. 154. Embryo of the second day removed from its envelope; brudimentary branch-
ial arches and clefts, e eye, mm myotomes, p pectoral plate or thickening. Drawn
from a hardened specimen. x 24.
FIG. 155. Living embryo of the second day freed from its envelope, and viewed as a
transparent object. x 16. tº
Fig. 156. Head of embryo on the third day, viewed from in front and somewhat
obliquely; h heart, bl maxillary barbel. x 16.
FIG. 157. Head of embryo on the third, from in front, viewed as an opaque object; bl
maxillary barbels, h heart, n nasal grooves. x 24. -
FIG. 158. Head of embryo on the third day, from the side, viewed as an opaque object;
b branchiae, bl barbels, m myotomes, p pectoral. x 24.
FIG. 159. Embryo of third day freed from its envelope, and viewed from above, as an
opaque object; op opercular fold, p pectoral, m n myotomes. x,24.
Report U. S. F. C. 1885.—Ryder. Osseous fishes. PLATE XXIII.


592 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [104]
EXPLANATION OF PLATE XXIV.
IcTALURUs ALBIDUs. (White Catfish.)
FIG. 160. Embryo on the fourth day, viewed as an opaque object from the front. x 24.
FIG. 161. The same, viewed from the side. x 24.
FIG. 162. Head and yelk-sack of embryo on the fifth day, viewed from in front. x24.
Report U. S. F. C. 1885–Ryder. Osseous fishes. PLATE XXIV.
-
-
-
-
- - -
-




594 REPORT of commissionER of Fish AND FISHERIES. [106]
A
1EXPLANATION OF PEATE XXV.
IctalURUs ALBIDUs. (White Cat-fish.)
Fig. 163. Young cat-fish of the sixth day, just hatched, viewed as a transparent ob
ject. x 16.
Fig. 164. Young cat-fish of the seventh day, viewed as a transparent object. x 16.
Report U. S. F. C. 1885.-Ryder.
Osseous fishes.
PLATE XXV.
ſſſ
%：
§§YŃ




596 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [108]
EXPLANATION OF PLATE XXVI.
ICTALURUS ALBIDU.S. (White Cat-fish.)
"FIG. 165. Young cat-fish, eight days old, viewed as an opaque object. x 16.
FIG. 166. Young cat-fish, nine days old, viewed as an opaque object. x 16.
Report U. S. F. C. 1885–Ryder. Osseous fishes.
PLATE XXVI.


598 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [1 10]
EXPLANATION OF PLATE XXVII.
ICTALURUs ALBIDUs. (White Cat-fish.)
!
FIG. 167. Young cat-fish, ten days old, viewed as an opaque object. x 16.
FIG. 168. Young cat-fish, eleven days old, viewed as an opaque object.. x 10.
Report U. S. F. C. 1885.-Ryder. Osseous fishes.
PLATE XXVII.
I-7

600 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [112]
EXPLANATION OF PLATE XXVIII.
ICTALURUS ALBIDUs. (White Cat-fish.)
Fig. 169. Young cat-fish, twelve days old, viewed as an opaque object. x 10.
Fig. 170. Young cat-fish, twenty days old, viewed as an opaque object. x 10.
Report U. S. F. C. 1885.-Ryder. Osseous fishes.
PLATE XXVIII.
-
-




602 REPORT OF COMMISSIONER of FISH AND FISHERIES. [114]
EXPLANATION OF PLATE XXIX.
Ictalurus albidus. (White Cat-fish.)
FIG. 171. Young cat-fish, eighty-eight days old, viewed as an opaque object. x 8.
Fig. 172. The same, viewed from above. x 8.
Report U. S. F. C. 1885.-Ryder. Osseous fishes. PLATE XXIX.



604 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [116]
EXPLANATION OF PLATE XXX.
ICTALURUs ALBIDUs. (White Cat-fish.)
FIG. 173. Cartilaginous cranium of young fish, ten days old, constructed from a series
of longitudinal vertical sections. x 35.
Au, auditory vesicle; CHy, ceratohyal; Cor, coracoid; EE, ectethmoid ridge; Eb, car-
tilage of external chin barbel; Fo, fontanelle; GHy, urohyal; Ib, cartilage of
internal chin barbel ; IHy, interhyal ; Hm, hyomandibular; HBy; hypohyal; Mk,
Meckel's cartilage; Mab, cartilage of maxillary barbel; 0, orbit; Ol, olfactory
fossa; Pa C, parachordal region ; Phb, pharyngobranchials; Ps, presphenoid la-
mina; Pl Pt, palatopterygoid elements; R, rostrum; Sc, scapular portion of
shoulder-girdle; so, supraoccipital ; TCr, tegmen cranii; Tr; trabecula; II, V,
VII, IX, X, foramina for cranial nerves.
FIG. 174. Median longitudinal vertical section of the head of a young fish, ten days old.
x 35.
Ab, air-bladder; BB, basibranchials; Ba, bulbus aortae; Cb, cerebellum; Cer, cere-
brum; Ch, chorda; ES, erector spinae; Hy, hypophysis; I, intestine; Inf, infun-
dibulum; L, liver; M, pharyngeal and Oesophageal muscles; mb, mid-brain; MK,
Meckel's cartilage; mo, medulla oblongata; Oe, oesophagus; Ot, optic tract ; P,
periblast; Pc, pericardiac cavity; Pn, pineal body; R, rostrum; S, sacculus
vasculosus; SV, sinus venosus; Tr, trabecula; Ve, ventricle; a. a z, rudiments
of anterior co-ossified vertebrae; Y, yelk.
Report U. S. F. C. 1885–Ryder. Osseous fishes.
PLATE XXX.
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