Comparative.] A N A T 
whole of this lymphatic joins the thoracic dudt of the fame 
fide : but, on the right fide, part of it goes into the infide 
of the jugular vein a little above the angle; whilft ano¬ 
ther joins the thoracic dinft, and with that dutt forms a 
common trunk, which opens into the infide of the jugular 
vein, a little below the angle which that vein makes with 
the fubclavian. This fydem in birds differs mod from 
that of quadrupeds, in the chyle being tranfparent and co- 
lourlefs, and in there being no vilible lymphatic glands, 
neither in the courle of the latteals, nor in that of the 
lymphatics of the abdomen, nor near the thoracic du6ts. 
The kidneys lie in the hollow excavated in the fide of 
the back-bone, from which there is fent out a bluifh-co- 
loured canal running along by the fide of the vas deferens , 
and terminating direftly into the common cloaca. This is 
the meter, which opens by a peculiar aperture of its own, 
and not at the penis. Fowls having no vefica urinaria, lbme 
authors thought that they never paffed any urine, but that 
it went to the nourifliment of the feathers: but this is 
falf'e ; for that whitilh Jubilance covering their greenilh 
faeces, and which turns afterwards chalky, is their urine. 
The teficles are ii mated one on each fide of the back¬ 
bone ; and are proportionally very large in proportion to 
the creature’s bulk. From thefe run out the vaja ftmini- 
ferae ; at full ftraight, but, after they recede farther from 
the body of the tellicle, they acquire an undulated or con¬ 
voluted form, as the epididymis in man. Thefe convolu¬ 
tions partly fupply the want o ivcficulezfeminalcs: they ter¬ 
minate in the penis, of which the cock has tw o, one on 
each fide of the common cloaca, pointing directly out¬ 
wards. They open at a dillance from each other, and are 
very fmall and (hort; whence they have elcaped the no¬ 
tice of anatomifts, who have often denied their exillence. 
In birds there is no proflate gland. This is what is chiefly 
remarkable in the organs of that male. 
Tl'.e racemus vitellorum, being analogous to the ovaria in 
the human fubjedt, are attached by a proper membrane to 
the back-bone. This is very fine and thin, and continued 
dowm to the uterus. Its orifice is averfe with refpedt to 
the ovaria ; yet notwithflanding, by the force of the orgaf- 
inus venereus, it turns round and grafps the vitcllus, which 
in its padage through this dudt called the infundibulum, re¬ 
ceives a thick gelatinous liquor fecreted by certain glands. 
This, with what it receives in the uterus, compoles the 
white of the egg. By this tube then it is carried into the 
uterus. The fliell is lined with a membrane : and in the 
large end there is a bag full of air, from which there is 
no outlet. 
The uterus is a large bag, placed at the end of the in¬ 
fundibulum, full of wrinkles on its infide; here the egg 
is completed, receiving its lafl involucrum, and is at lad 
puffed out at an opening on the fide of the common cloaca. 
From the telles in the male being fo very large in propor¬ 
tion to the body of the animal, there mull necelfarily be 
a great quantity of femen fecerned ; hence the cock is fa- 
lacious, and becomes capable of impregnating many fe¬ 
males. The want of the veficulai feminales is in fome 
meafure fupplied by the convolutions of the vafa deferen- 
tia, and by the fmall difiance between the fecerning and 
excretory organs. The two penes contribute alfo very 
much to their fhort coition: at which time the opening of 
the uterus into the cloaca is very much dilated, that the 
effedt of the femen on the vitelli may be greater. A hen 
will of herfelf indeed lay eggs ; but thefe are not impreg¬ 
nated, and yet they appear entirely complete. 
We come now to confider the nutrition of the foetufes 
of oviparous animals, and fhall give a fhort hiftory of an 
egg, and of the changes brought on by incubation. The 
Ihell ct an egg becomes more brittle by being expofed to 
a dry heat. It is lined every where with a very thin, but 
fomewhat tough, membrane ; which, dividing at or very 
near to the obtufe end of the egg, forms a fmall bag, 
where air only is contained. In a new-laid egg, this folli- 
culus appears very little, but becomes larger when the egg 
is kept. 
O M Y. 66 -i 
The albumen, or white of an egg, is contained in con- 
centrical membranes, but is not all of the fame confidence; 
for the exterior part of it is thin, and diffufes itfelf almoft 
like water when the membranes are broken ; whereas its 
anterior part is more vifeous. The white of an egg can 
make its way through the fliell, as appears from its waft¬ 
ing by keeping, efpecially if expofed to gentle heat. 
The globular viteilus, or yolk, would feern to be no 
other than a liquor inclofed in a membrane ; becaufe, 
whenever the membrane is broke, it runs all out; and is 
fpecifically heavier than the white. The chalazae are two 
white fpongy bodies, rifing very fmall from the oppofite 
tides of the membrane of the yolk, bqt gradually become 
larger as they are flretched out from it in an oblique di¬ 
rection with regard to the two ends of the egg. If we 
compare the chalazce to the extremities of an axis palling 
through the fpherical viteilus, this fphere will be com- 
pofed of two unequal portions, its axis not palling through 
its centre; confequently, fince it is heavier than the white, 
its fmaller portion mult always be uppermoft in all pofi- 
tions of the egg. 
The yellowifh-white round fpot, called cicatricula, is 
placed in the middle of the fmaller portion of the yolk ; 
and therefore always appears on the fuperior part of the 
viteilus. The cicatricula feems to be compofed of feve- 
ral circles of different colours ; and, in a fecundated egg, 
contains the embryo or chick. Eggs, whofe obtufe ends 
are all rubbed over with linfeed-oil, or fucli other fubftan- 
ces as block up fmall pores, are as fit for bringing forth 
chickens, wdien incubated by a hen, as other eggs are. 
After incubation, the folliculis atris is gradually extended; 
till, near the time of the exclufion of the chick, it occu¬ 
pies more than a third of the cavity of the fliell. The ex¬ 
tended folliculus does not collapfe, upon being expofed 
to the preffure of the atmofphere, after incubated eggs are 
opened. By incubation the albumen becomes thinner and 
more turbid, efpecially on its upper part near the air-bag, 
where it is alfo firft confumed: and it is afterwards dimi- 
niihed towards the fliarp end of the egg, till at laft nothing 
of it is left except a white cretaceous fubftance at the 
lower part of the fhell. 
As the part of the white neared to the cicatricula is 
wafted, its membrane and the cicatricula dill approach 
nearer, till they become contiguous. This membrane of 
the albumen is what is commonly called the chorion. Some 
time before the albumen is quite confumed, what remains 
of it is placed at the lower part of the egg ; and therefore 
the yolk is interpofed between it and the membrane which 
immediately contains the foetus. The white of a fecun¬ 
dated egg is as fweet and free from corruption, during all 
the time of incubation, as it is in a new-laid egg. I taded, 
fmelled, and fwallowed, fays Dr. Monro, the whites of 
eggs during all the dates of incubation, both when they 
were raw and boiled, and condantly found them fweet ; 
and therefore cannot imagine how Bellini could affirm it 
to have a heavy abominably ungrateful tade, a dinking 
fmell, and not only to occafion, when fwallowed, a trou- 
blefome fenfation in the domach and guts, but to prove 
purgative. He mud unluckily have examined none but 
fubventaneous eggs : which is further confirmed by his 
defeription of the fmall particles in the colliquated albu¬ 
men, that refledt light fo firongly as the eye cannot bear 
it. Very foon after incubation, the volume of the yolk 
appears increafed ; and, by its rifing then nearer to the 
upper part of the egg, we may conclude that its fpecific 
weight decreafes. The yolk becomes pale and more fluid 
for fome time, efpecially on the fide next to the chick, 
where its bulk alfo fopned increafes ; but afterwards the 
membranes of the yolk turn firmer and dronger, and the 
liquor in them is lefs in quantity, and becomes more vif¬ 
eous. As the chick increafes, the yolk is deprefled in the 
middle ; and is foon brought into, a form fomething like 
to a horfe-flioe, in the middle of which the chick is lodged. 
The yolk remains frefh and uncorrupted all the time ol 
incubation, and is always coagulable. 
Not 
