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2 O O L 
traded portions into a number of pouches corresponding to 
that of the young; and where those horns are straight in the 
unimpregnated state, as in the bitch, they become convo¬ 
luted. 
The uterus anfractuosus of the marsupial animals under¬ 
goes the least change from its usual appearance in the im¬ 
pregnated state. For these strange animals bring their young 
into the world so disproportionately small, that they appear 
like early abortions. 
The Fallopian tubes are convoluted upon each other in a 
kind of knob in some instances, as the simia sylvanus, and 
still more remarkably in the opossum. The fimbriee are 
sometimes shaped like a funnel, as in the rabbit. 
The ovaria are generally of an oval form, and have the 
ovula Graafiana buried in their parenchyma. These vesicles, 
however, project externally in some cases, as in the pig. In 
the hedgehog they are quite loose and separate, so that the 
ovary resembles a bunch of grapes. 
We shall now proceed to examine the evolution of the 
two kinds of germs: first of the ova; and, secondly, of 
the foetus. The ovum has only been properly examined in 
the birds and amphibia. 
The egg is covered, within the shell, by a white and firm 
membrane, (membrana albuminis) which contains no blood¬ 
vessels. The two layers of this membrane, which in other 
parts adhere closely to each other, leave at the large end a 
space which is filled with atmospheric air. 
This membrane includes the two whites of the egg, each 
of which is surrounded by a delicate membrane. The ex¬ 
ternal of these is the most fluid and transparent, the inner 
one thicker and more opaque ; they may be separated in 
eggs which are boiled hard. 
The internal white surrounds the yolk, which is contained 
in a peculiar membrane, called the yolk-hag. From each 
end of this proceeds a white knotty body, which terminates 
in a flocculent extremity in the albumen. These are called 
the chalazce, or grandines. Leveille distinguishes a third 
■white, and considers the chalazse as absorbing vessels float¬ 
ing in it, and destined to absorb it as well as the inner al¬ 
bumen, and mix them with the yolk during incubation. 
A small, round, milk-white spot, called the tread of the 
cock, (cicatricula or macula) is formed on the surface of the 
yolk-bag. It is surrounded by one, or more, whitish con¬ 
centric circles (halones or circuli). 
A small shining spot of an elongated form, with rounded 
extremities, but narrowest in the middle, is perceived at the 
end of the first day, not in nor upon the cicatricula, but 
very near that part on the yolk-bag (nidus pulli, colliqua- 
mentum, areola pellucida). This may be said to appear 
before-hand, as the abode of the chick which is to follow. 
No trace of the latter can be discerned before the begin¬ 
ning of the second day, and then it has an incurvated form, 
resembling a gelatinous filament, with large extremities, very 
closely surrounded by the amnion, which, at first, can scarcely 
be distinguished from it. 
About this time the halones enlarge their circles, but they 
soon after disappear entirely, as well as the cicatricula. 
The first appearance of red blood is discerned on the sur¬ 
face of the yolk-bag, towards the end of the second day. A 
series of points is observed, which form grooves, and these, 
closing, constitute vessels, the trunks of which become con¬ 
nected to the chick. The vascular surface itself is called 
figura venosa, or area vasculosa; and the vessel by which 
its margin is defined, vena terminalis. The trunk of all 
the veins joins the vena portae, while the arteries, which 
ramify on the yolk-bag, arise from the mesenteric artery of 
the chick. 
On the commencement of the third day, the newly-formed 
heart is discerned by means of its triple pulsation, and con¬ 
stitutes a threefold punctum saliens. Some parts of the in¬ 
cubated chicken are destined to undergo successive alter¬ 
ations in their form; and this holds good of the heart in 
particular. In its first formation it resembles a tortuous 
canal, and consists of three dilatations lying close together, 
0 G Y, 
and arranged in a triangle. One of these, which is properly 
the right, is then the common auricle; the other is the only 
ventricle, but afterwards the left; and the third is the dilated 
part of the aorta (bulbus aortee). 
About the same time, the spine, which was originally ex¬ 
tended in a straight line, becomes incurvated; and the dis¬ 
tinction of the vertebrae is very plain. The eyes may be 
distinguished by their black pigment, and comparatively 
immense size. 
From the fourth day, when the chicken has attained the 
length of four lines, and its most important abdominal 
viscera, as the stomach, intestines, and liver, are visible, 
(the gall-bladder, however, does not appear till the sixth 
day,) a vascular membrane (chorion, or membrana umbili- 
calis) begins to form about the navel; and increases in the 
following days with such rapidity, that it covers nearly the 
whole inner surface of the shell within the membrana albu¬ 
minis during the latter half of incubation. This seems to 
supply the place of the lungs, and to carry on the respiratory 
process instead of those organs. The lungs themselves begin 
indeed to be formed on the fifth day; but, as in the foetus of 
the mammalia, they must be quite incapable of performing 
their functions while the chick is contained in the amnion. 
Voluntary motion is first observed on the sixth day, when 
the chick is about seven lines in length. 
Ossification commences on the ninth day, when the ossific 
juice is first secreted, and hardened into bony points (puncta 
ossificationis). 
At the same period, the marks of the elegant yellow ves¬ 
sels (vasa vitelli lutea) on the yolk-bag, begin to be visible. 
On the fourteenth day the feathers appear; and the ani¬ 
mal is now able to open its mouth for air, if taken out of the 
egg- 
On the nineteenth day it is able to utter sounds; and on 
the twenty-first to break through its shell. 
We shall conclude with one or two remarks on those very 
singular membranes, the yolk-bag and chorion, which are so 
essential to the life and preservation of the animal. 
The chorion, that most simple yet most perfect temporary 
substitute for the lungs, if examined in the latter half of in¬ 
cubation in an egg very cautiously opened, presents a surface 
covered with numberless ramifications of arterial and venous 
vessels. The latter are of the bright scarlet colour, as they 
carry oxygenated blood to the chick; the arteries, on the 
contrary, are of the deep or livid red, and bring the carbo¬ 
nated blood from the body of the animal. Hence, as is well 
known, the incubated bird perishes if the shell be varnished 
over, as the respiratory process is thereby suspended. The 
trunks of the arteries are connected with the iliac vessels; 
and on account of the thinness of their coats, they afford 
the best microscopical object for demonstrating the circula¬ 
tion in a warm-blooded animal. 
The other membrane, the membrana vitelli, is also con¬ 
nected to the body of the chick; but by a two-fold union, 
and in a very different manner from the former. It is joined 
to the small intestine, by means of the ductus vitello-iniesti- 
nalis (pedunculus, apophysis,) and also by the blood-vessels, 
with the mesenteric artery and vena portae. This is regarded 
by Leveille merely as a ligament. It is well known that no 
true yolk is discoverable in the intestine of the incubated 
chick. Yet sometimes (not indeed always, but under certain 
circumstances not yet sufficiently understood) air will pass 
from the intestine through this part into the yolk-bag. 
The analogous umbilical bag of the fcetal-shark (which is 
found also in several other fishes, and some reptiles,) is con¬ 
nected to the small intestine; at least to the bursa entiana, 
which is a peculiar dilatation of the posterior end of the in¬ 
testine. 
In the course of the incubation the yolk becomes con¬ 
stantly thinner and paler, by the admixture of the inner 
white. At the same time innumerable fringe-like vessels, 
with flocculent extremities, of a most singular and unex-» 
ampled structure, form on the inner surface of the yolk-bag, 
opposite to the yellow ramified marks above mentioned, and 
