1CHTH 
tion of the fpine of the back, fig. 19, e. I 'obferved alfo 
another artery in front, which paffed along the belly to 
the tail, fig. 19, d, d. which began near the head, and took 
‘its origin from aorta. From the firft branches off, in a 
right angle, at each vertebra, an artery, fig. 19, ff. which 
takes its- direftion along the fide. The blood’of the ar¬ 
teries, which are extremely delicate, is partly collected in 
the afcending vena cava, fig. 19, g. partly in the defcend- 
ing, fig. 19, h. Thefe two veins form an obtul'e angle, 
fig. 19, i. behind the air-bladder, and drive the new blood 
towards the heart. In new-born fifties, the head is Irnall 
in comparifon to other animals, and the air-bladder is 
large; this keeps the animal balanced when in an upright 
pofition. 
“ Means fhould be taken to keep off water-flies, if pof- 
fible, when you would hatch the eggs of fifh, becaufe they 
devour young fry. I had thirty little fifh in a tub, with 
fome plants whereon were worms and other aquatic infects; 
but at the end of a few days the filh dilappeared entirely, 
not the lealt veltige of their bodies remaining. Having 
afterwards found a little fnail in the throat of one of thofe 
infefts called p/iryganea grandis by Linnaeus, I concluded 
that this in fieri: had eaten my fifli. 
“ From thefie few experiments I draw the following, I 
hope ufieful, conclufions on the fubjeri: of economy and 
phyfiology. 
1. That lakes and ponds may be flocked with fifli at a 
very cheap rate, by obfierving the exaft time of fpawning 
in each fipecies ; and, as fifli even of the fame fipecies do 
not all fipawn at once, but at three different periods ac¬ 
cording to their fize, and as there is a diffance of nine 
days between each, and as the eggs remain eight or nine 
days more before they Open, there is plenty of time to 
provide the plants whereon the eggs are depofited. 
2. That by thefie experiments a queftion long agitated 
is decided with certainty, though the philofophers of our 
own days are yet divided upon it, namely, Whether the 
mixture of the male and female fiemen be necelfiary for 
generation ? For it is certain that this does not take 
place within the bodies of fiffies at leaft. 
3. It appears that the female furnifties the germ or fiub- 
ftance of the animal, and that the male gives it life/and 
motion ; for the tranfiparent part or embryo appears in the 
unfecundated egg, but it is the femen of the male-vvhich 
communicates motion to the heart. I fliall leave it to 
others to examine, whether that feminal vapour, ( aura fe~ 
minalis,) which dilbovers itfelf in moft animals by a difi- 
agreeable fmell, paffes from the milt into the egg, to give 
motion to the heart; or whether the fpermatic animalcules 
penetrate there, and give it life by their rapid movements. 
The daft opinion fieems to me moft reafionable, as I never 
obferved the leaft odour in the milt of filhes. The vola¬ 
tile particles which caufie that finiell fieem more proper to 
other animals who propagate their fipecies in the ufiuai 
way. Neither have I remarked any odour in the feed of 
birds ; but, as the roes of fillies fmell and caufie a difia- 
greeable fienfiation at the approach of fpawning-time, fib 
do the tefticles of birds fiwell at a certain period, fib that, 
from being lcarcely vifible, they become full as big as a 
hazel-nut. 
4. It is hereby eafily underftood why there appears not 
among male fifties the lealt jealoufiy in their amours ; for 
many males together rnay be feen following the females. 
And, among the females, there appears not the leaft fign 
by which they excite the male to fulfil-the work of fecun¬ 
dation or generation. 
5. That the motion of the'heart dilates the blood-vefi- 
fels, and thereby infufes life into the fetus. 
6. That the fiemen and embryo arifing from it are en- 
clofied in a common membrane with the yolk of the egg ; 
and they are fio clofiely united by means of the vificera of 
the filh and .the veflels of the yolk, that they are not fie- 
parated even when the filh is half-way out of the egg. 
7. Filhes do not come into the world head-foremolt like 
Other animals,, but by the tail. 
OOLOGY. 74 7 
8. The period neceffary for the Formation and birth of 
fifties is not fixed, as in other animals, but may be acce¬ 
lerated or retarded by greater or lefs degree of beat. 
9. The yolk of the egg, which diminiflies as the em¬ 
bryo increafes in bulk, is deftined for the nouriflnnent 'of 
that embryo ; the white, on the other hand, has free mo¬ 
tion like the liquor contained in the matrices of vivipa¬ 
rous animals. 
10. It is evident that the germ, or embryo, pre-exiftsin 
the egg ; and all the liypothel'es againft this pre-exiftence 
fall to the ground. • 
11. The animalcules in the femen of fifties are'different 
from thofe in the feed of other animals. 
12. It requires no longer time to hatch the eggs of largs 
fillies than of the fniall ones ; for thofe of the bream and 
of the bleak hatched on the fame day ; whereas among 
birds and quadrupeds the time of geftation is in propor¬ 
tion to the fize of the animal. 
13. In proportion as the developement of the embryo 
in the egg is quick, lb is its growth after the birth flow. 
In two days after fecundation I have feen the heart move, 
and the body has been alfo in motion on the third , yet 
this filh, at two years old, was not more than four or five 
inches long. 
14,. The peftoral fins, which are the principal inftru- 
menfs for fwimming, are the firft formed 5 therefore all 
filhes muft have them. 
15. The circulation of the blood is flower in the fetus 
than in the filh after birth. 
.16. The circulation of the blood is flower in fillies than 
in the young of other animals. 
17. The heart does not throw the blood direridy into 
the arteries; they receive it by a comprelTed motion of the 
arterial bladder; and there is between thefe two an alter¬ 
nate and reciprocal motion of compreflion and dilatation. 
18. The globules of the blood appearing of a red co¬ 
lour on the third day in the heart, and of a white colour 
in the other veflels, proves that this colour in the blood 
arifes from the compreflion of the heart, which, being now 
completely formed, has of courfe more tenfion. From this 
remark fome ufeful hints may be drawn relative to medi¬ 
cine. When, on bleeding, the blood is of a clear full 
red, it is a fign of too great tenlion of the lolids, and the 
prefcription Ihould then be emollients, as a repetition of 
bleeding, diluting drinks, bathing, &c. When, on the 
other hand, the blood is wliitiih, it fliows that the folids 
are relaxed, and a contrary method mult then be purified. 
Hence appears alfo the connection between natural hiftory 
and medicine.” 
Fifties are fubjeri: to fome difeafes. Numbers of them 
are tormented by infefts and worms in the intertines, or 
which faiten on their gills. Bad food diforders them. The 
water is fometimes too cold for them, arifing from a ra¬ 
pid melting of lnow, or from the ftrearn running oft’ hnu r 
being renewed too quickly. When the water is frozen 
over, the parts where they lie may become charged with 
putrid miafmata ; and thus bring on difeafes, fometimes 
mortal, which appear in pultules or excrefcences. Ulcers 
are occafionally found on the liver and other interior parts 
and laftly old age is itfelf an incurable diforder. But ftill 
their longevity is far fuperior to that of other animals. 
We have already feen what ample provilion is made for 
l'upplying them with food, by multiplying the inhabitants 
of the fea : they are, therefore, in little danger of periih- 
ing from want; and, fince filhes refide in an..element but 
little fubjeri: tq change, theirs is an. uniform exilfence ; 
their movements are without effort, and their life without 
Ikbour. Their bones alio, which are united by cartilages, 
admit of indefinite extenfion ; and the different lizes of 
animals of the fame kind among filhes is very various. 
They ftill keep growing; their bodies, instead of ffiffering- 
the rigidity of age, which is the caule of natural decay 
in land-animals, ftill continue increafing with frefli Ifip- 
plies ; and, as thebody grows, the conduits of life furnifh- 
their ftores in greater abundance,. How long a fifh, that. 
Teems, 
