Evening star. [volume] (Washington, D.C.) 1854-1972, 1883-05-16

Efom the Observations Of j. 4. Ryder,
q the United states Fish Cosnmis-
sion.

0100s
In connection with the artificial Matching and
distribution of the young of some OF our most
important food fishes Investigations have been
carried on with view TO the know ledge Of all
Their phases OF development and of the effects
upon them of surrounding conditions These
Investigations have great interest to the natur-
allsf, as, on account of the links of union that
bind together all forms of Ijfe particularly
among creatures possessed of a backbone they
tend to throw light upon the most obscure part
OF lifes history. L. q, its commencement from q
germ consisting Ot s.,sl-rr cell.
such invest cations have also great practical
value from a strictly food and cash point of view
since the facts dscoyesed are or viii ultimately
be utilized in the interest OF food-prOduction.
The egg of the sayory shad. s0p5diSn.a or
most sapid, as the natura!ists name this clupeod
beloved of gUurnIud-. Is. when first eXtruded
from the parent fish. about one fOurteenth of ON
inch In diameter. and Of q somewhat tiattencd
and irregularly rounded form. covered by an
egg-membrane that IL much wrinkled and lies r
Close contact with the yitellus or interior sub
stance that Will be eventually converted into
nsh. After impregnation by the Inilt OF the
male, an operation which, i'm most fishes
takes place In the open water. the wrnk led outer
covering becomes tense. and the egg is appar-
entity much larger as much as the One-eighth or
even One-seventh of an inch in diameter. This
Increase in bulk Is due entirely to the entrance
Of water through the substance of the MEM
brane, so "a to fill the space between if and tine
viteilus, which has not gained In size aud lies
upon the lowest part of the egg membrane " hen
the Oyum is at rest.
In all eggs of true fishes the greater part of
the substance Is yeIk or nutritive matter, while
the germinal portion, or embryo. commences at
spot known az the gerinlnal disk. The
gefE1inal part undergOes augmentation: that is
u breaks up into numerous celiules and these
gradually form the rudments of a head anteri-
Orly, while they arch over the yelk-mass as o
developing body and inclOse it with thin COW
ering. The eggs of birds develop In some
what similar way: that is, the embryo proper
forms only small part of the Ovum, tine larger
part OF which is a yeik-Gass destined to serve
As nutriment for the young ANIMAL into the
substance of which it is finally absorbed. The
eggs of the amphiba frogs. salamanders.
etc. differ In that the whole OF their substance
seginents, and is directly formed into the en-
bryo, and the same is the case with all the
maniinala. quadrupeds, whales, bats, monkeys
and man.
IL shad as I'm other fishes the gcrmnal disk
Is first formed by the coming together of tine
gerninal prOtOplasm then commences to break
up CT segment, and Increase in size. The rudi-
meDts of the axis, longitudinal line of the
embryo fish becomes apparent along the In
creasing germinal disk. which Is separated from
the yelh-mass by a shallow watcfl-glass shaped
cavity that grows laterally as the disk grows.
This space is filled with film of fluid enabling
the growing disk to spread without friction over
the yelk, and remains even when the disk, or
baIs'OderDl, has finally closed over the en-
tire yeik. Eighteen to twenty SODsites.
or embryonic segments. become apparent in
the line of the axis of the embryo. each one
q rudiment of the paired muscular plates
that occupy the opposite sides of the body of
the adult Thus the egg of the shad recognize
able at its first eXtrusiOn as such by its size and
by the absence OF the Ol-glObules which are
present i'm the Oya of many fishes and later by
the tendency of the germinal disk to occupy a
lateral position when the Ovum is ut rest. be-
comes still more marked out as on the way to
be shad and nothing else. by the early ap-
peaTance OF tOleTably fixed and small number
OF muscular plates. The embryo ear-fish has
seventy-five of these sOmtes. Thus it is evident
that Ova are not. a. some have said all alike i'm
Their first stage, but present differences of such
nature that it is probable. as Mr. Ryder re-
MARKS. that with more know ledge of the subject
We may distinguish species apart by the eggs
alone, as botanlsts distinguish plants by their
seeds
The germnai disk as has been said, grows
gradually around the yelk till it embraces it,
but the principal part OF the embryo lies arched
over the yelk. Prominent among the structures
developed while the animal is still in the eng is
the siOtoci7ft. or cartiiaCinOuS rod. which is the
primitive backbone. and which persists i'm some
or the lowest yertebrateS, while IN the majority
ever OF iiSiit.. it disappears yerebr:p are de-
velOred around If. rs growth proceeds the ru-
0mentS al the eye and ear become visible. the
tail IL ndrSrd out, and around it a membrane is
formed which II the primitive organ from which
al the impaired fins are ultimately developed
The line OF the axis Of the embryo was ut first
marked by shallow groove. but this is ere lon.
closed over. and canal is formed called the
meCuilary canal. At the anterior extremity of
this the brain Is developed. and the rest forms
the spinal cord. The division OF the brain into
hind brain. md-brain and cereorum or fore
brain. Is clearly marked when the embryo s
katched Before Matching the heart also Origi-
mates from some cells beneath the head and the
rudments OF the breast or pectOral fins bud out
"a a pair of delicate rounded lobeS.
Immediate ely after Matching our Young shad is
still but a larya. in many respects unlike the
adult. Much of its bulk consists of the yelk,
which. although some part has probably already
been absorbed by change into blOod-cels. yet
forms the larger portion OF the larval fish, whose
Read projects in trent, while the tail, with its
continuous hn-membrare. prOtrudeS pOsteriOrly.
At this stage the mouth is but rudiment con-
tanning rudimentary tongue that can be seen
Through the transparent walls of the cheeks; the
nasal capsules are evident at the tip of the
A0Out: behind them are the larger partly deyel-
eyed eyes; behind and above these the Begin
Aings of the ears (Which in fishes represent only
part OF the ear of mammais). and back of
these the breast-ins. The notOchOrd lies along
the dorsal line of the embryo. aterminat-
ing In front slightly behind the eye:
shove 1t runs the incpent spinal cord and
below its anterior end are the beginnings of the
gill arches. The intestine OF rather intestinal
canal, for the greater part OF. it, is eventually
longitudinal depression along the back of the
yeik-maSs. but below the nOtochord In the
space between the yek-mass and the mouth Is
the pulsating heart. now become the prime
mover in the process of the absorption of the
yelk, which becomes converted into blood
cells. and thus nOurishes the embryo until 1t is
sufficiently developed to feed. The heart COM
municateS freely with the cavity filed with
nuid that has already been mentioned. In
closed In this Is the yelk, which, through the
microscope, is seen to consist of comparatively
coarse masses OF clear protoplasm surrounded
by layer of amber-cOlored cellues. On the
surface of this layer minute spherical promi-
nences form at the end next TO the heart, and
these tiny bodies finally drop freely into the fluid
OF the surrounding SPACE and are drawn into the
circulation These bodies are quite cOlOrless,
and resemble the white bood-cells of human
blood The red coloring matter of the blood is
later development. As the work of conversion
OF the yelk into the substance of the embryo
continues the diminished yek-mass becomes
pointed in front. but is still covered by the
amber-colOred layer, which is thickest ante
rfOrly, and persists until the whole Of its con-
tents have disappeared. when 1t also fades
away, leaving no trace behind. 1t appears that
the entire central portion of the yelk is bit by
p.aIx-1 t..tf rI% tx.S