ICHTHYOLOGY. 
745 
after the fecond or third day; fo that, fome days after, 
the difference may be difcerned by the naked eye ; thole 
that "are not fecundated become every day darker and 
thicker; they Jofe their brilliancy, and look like a hitil- 
ftone juft ready to melt. All the phenomena relative to 
the generation of fifties are exhibited in the lower part of 
the annexed Engraving ; of which the following is an 
explanation. 
Fig. 6. An aquatic plant with fecundated eggs at¬ 
tached to it. Fig. 7. A plant with eggs not fecundated. 
Fig. 8. An egg as leen through a inicrofcope : a, the 
yellow, or yolk; b, the white. Fig. 9. The egg on the 
fourth clay, when motion may be perceived in the em¬ 
bryo. Fig. 10. The fame egg magnified, to fhow r that the 
fpine of the back is already formed. Fig. it. Egg on the 
feventh day, wherein the eyes are perceptible. Fig. 12. 
The fame egg magnified. Fig. 13. Egg w'ith the tail of 
the embryo put forth. Fig. 14. a, a bream juft emerged 
from the egg, of the natural lize; b, the fame eight hours 
afterbirth; c, the fame three weeks old. Fig. 15. A 
bream one day old lying on its belly, as feen through a 
microfcope : a, the ftomach. Fig. 16. The fame, two 
days old, lying on its fide, and magnified : a, the ftomach ; 
b, b, the fcales. Fig. 17. a, the heart; b, the arterial bag. 
Fig. 18. Eggs of the trout. Fig. 19. A bream of four 
days old, lying on its fide, as it appeared under the»mi- 
crolcope 1 a, the heart; b, the arterial bag ; c, the aorta ; 
d, d, the anterior artery ; e, e, the pofterior artery ; f f, 
the intercoftal arteries ; g, the vena cava inferior : h, the 
vena cava fuperior; 2, union of thele veins; k, air-blad¬ 
der. Fig. 20. Scales magnified: a, of the head; b, of the 
back ; c, of the fide. Fig. 21. A piece of the ovary of a 
falmon, where the eggs lie in furrows in particular mem¬ 
branes one over the other in folds. Fig. 22. Six eggs of 
the perch attached to each other, forming a fix-fided 
figure, as feen under the microfcope. Fig. 23. Eggs or 
roe of the perch, as call forth by the female. Fig. 24. 
Spermatic animalcules of the carp. 
“ The eggs of fifties are uniformly round ; the yellow 
and the white are perfectly difcernible; between w'hicli 
appears a vacant fpace in the form of a half-moon. The 
yellow, which is ulually furrounded with white, is not in 
the middle, but rather towards one fide, fig. 8, a. AH 
this may likewife be remarked in the eggs which are not 
fecundated; the difference is, that the yellow is not of fo 
deep a colour. The feminal liquor or milt runs along the 
fpine of the back, fometimes inclofed in one membrane, 
fometimes in two. It is white, and in fpawning-time be¬ 
comes as white as milk, and fpirts out at the navel if the 
fifti be fqueezed ever fo little. I took fome of this fubftance 
on the point of a needle, and put it on a bit of glafs, and, 
having diluted it with clear water, I examined it with a 
inicrofcope, and it exhibited a multitude of little filaments, 
of various fliapes and fizes, fig. 25. called by fome authors 
fpermatic animalcules, and by Buffon organic particles. 
Soon after the death of the fifti, all motion ceafed in the 
fperrn or roe.” On the fubjeft fpermatic animalcules, fee 
the article Animalcule, vol. i. p. 727-729. 
“The unfolding of the fifti in the egg is very curious. 
I fhall fipeak of it in few words. I before remarked on 
the Itate of the egg the firft day. On the fecond, that part 
in the form of a half-moon exhibits a fmall fpot which 
moves^ and there is a diminution of the tranfparency be¬ 
fore obferved inithatpart. On the third day a larger’fpot 
is obferved in that place, which is on one fide ftrongly 
attached to the yolk of the egg, and on the other fide is 
free ; fig. 10, 12. at the end of that part which joins the 
yolk is feen the outline of the heart, which increafes in 
motion, and the whole mafs, or embryo, moves from time 
to time at that end where it is free, that is, the tail. On 
the fourth day, the beating of the pulfe increafes, as well 
as the motion of the whole body. On the fifth day, by 
the politions which the fifti takes in its various motions, 
the circulation of the humours in the veffels may be feen. 
On the fixth day the lpine of the back, and the ribs 
wfcich fpring from it, may be diftinguiftied. On the le* 
•3 
venth you may fee with the naked eye two black fpot?, 
fig. n, 12, which are the eyes; and now the whole fliape 
of the fifti is perceptible; and the vertebrae and ribs are 
fo diftimft, that they may ealily be counted by the help 
of a common magnifier. Though the yolk of the egg di- 
minifties in proportion to the growth of the embryo, the 
young fifti as yet has not room enough to lie ftraight, but 
the tail is bent upwards, as feen at fag. 12. The motion* 
are now fo quick, that, as it turns from fide to fide, the 
yolk moves with it; and thefe motions increafe as the 
birth approaches, which happens between the feventh and 
ninth clay. The continued llrokes of the tail againft the 
egg-ftiell render it lb thin, that it breaks at laft, and the 
fifti comes out tail foremoft, as ftiown at fig. 13, ltrug- 
gling to difengage its head, which is attached to the yolk. 
It foon after feems to enjoy its new exiftence, and moves 
very quickly about in the water. As fifties are hatched 
by the heat of the fun, and as the rays are not always 
equally ltrong, the appearances we have mentioned may 
happen a day fooner or later, according to eircum- 
llances. 
“Befides the fifties above-mentioned,! havealfohatched 
the eggs of others, and have made the fame obfervations. 
It is a curious remark, that even in. the egg the difference 
is perceptible between the bream and the bley, becaufe in 
the latter.the yellow iris may be actually, difcerned in the 
egg. It is a pleafing fpeftacle to fee fo many little ani¬ 
mals of this kind moving in the water with great celerity, 
as ftiown in fig. 14, a. 
“.Though the fifti grows but flowly, yet in eight hours 
lie is fenfibly bigger ; within that time he luddenly at¬ 
tains the fize marked fig. 14, b. But after this his growth- 
is fo imperceptible, that at the end of three weeks lie is 
no bigger than appears in fig. 14, c. On the ninth day, 
befides the two black fpots, a third may be feen by the 
help of the microfcope, which is the ftomach and the food a. 
it contains, fig. 15, a. On the fame day the pulfe may 
be difcerned to beat fixty ftrokes in a minute; whereas the 
heart of the embryo made but thirty articulations in the 
fame fpace of time. The little globules are red while in 
the heart; but in the other veffels they affume a white 
colour. On the fecond day thofe of the heart are redder, 
and thofe of the veffels yellow. On the third day they 
are entirely of a clear red; in the veins they are of a pale 
red, and then form the liquid called blood. Befides this, 
the peftoral fins may be difcerned on the firft day; but 
the other fins are invifible, as well as the inteftines ; be¬ 
caufe, being extremely delicate, they fuffer the rays of light 
to pafs through them. On the third day the fin of the 
tail is perceptible, which as yet is ftraight, fig. 17, b. The 
dorfal fin appears on the fifth day ; the ventral and oval 
fins may be feen with a microfcope on the eighth. About 
this time a good microfcope will ftiow on the body fome 
black fpots, fig. 16, b, b. lome round, others lengthened, 
as they appear fig. 20, a, b, c, being the firft outline of the 
fcales. Thofe upon the head are the fmalleft, thofe of the 
back the largeft, and thofe on the fides are of a fize be¬ 
tween the two. The tail foon begins to take a curved 
form, as ftiown at fig. 16, c. It now becomes curious to 
obferve the circulation of the blood, and other humours. 
In one place are fountains of a red colour, corapofed of 
the moft delicate little globules. Near the head the heart 
is placed, conlifting of a membranous bag, fig. 19, a. 
which drives the blood through an artery of the fame-form, 
called faccus arteriafus, fig. 17, b. fig. 19, b. which artery 
comp relies itfelf to drive it into the aorta, fig. 19, c. While 
the artery is conrtrifted, the voiia cava carries the blood to 
the heart, which was till then at reft, fig. 19, 2!. and now 
the heart drives it into the veins, which till then alfo 
were at reft. v 
“ As fifties have a very ftiort breaft, and no neck, they 
have no carotid arteries, but the aorta paftes immediately 
to the gills, which are very near; and thence into the 
other parts of the body. As in young fifties the gills are 
not yet vifible, I have feen the arteries-go dire&ly to the 
head, return behind the eye, and then follow the direc- 
tiau. 
