COMPARATIVE ANATOMY 
AMPHIBIA. 
Tlie tortoise has a manifest clitoris lying 
in the cloaca. The oviduct and ovarium 
have on the whole much analogy with those 
of birds ; but all these parts are double, 
and have two openings into the cloaca. 
The frogs of this country have a large 
uterus, divided by an internal partition into 
two cavities, from which two long convo- 
luted oviducts arise, and terminate by open 
orifices at the sides of the heart. The ova- 
ria lie under the liver, so that it is difficult 
to conceive how the ova get into the above 
mentioned openings. The uterus opens 
into the cloaca. 
The toads have not the large uterus; 
but their oviducts terminate by a common 
tube in the cloaca. 
The lizards of this country have on the 
whole a similar structure to that of the last 
mentioned animals. Their oviducts are 
larger, but shorter, and the ovaria contain 
fewer ova. 
Female serpents have double external 
openings of the genitals for the reception 
of the double organs of the male. The 
oviducts are long and much convoluted. 
The ovaria resemble rows of beads com- 
posed of yellow vesicles. 
FISHES. 
We shall take the torpedo and the carp 
as examples of the two chief divisions of 
the class, as we did in speaking of the male 
organs. 
In the former fish there are two uteri, 
communicating with the cloaca by means 
of a common vagina. The oviducts form 
one infundihulum, which receives the ova 
as they successively arrive at maturity. 
Tliese are very large in comparison with 
tliose of the bony fishes. The yolk, in its 
passage through the oviduct, acquires its 
albumen, and shell. The latter is of a 
horny consistence, and is known by the 
name of the sea-mouse. It has an elon- 
gated quadrangular figure, and its four 
corners are curved and pointed in the 
skate, while they form horny plaited emi- 
nences in the sharks. The secretion of the 
albumen, and the formation of the shell 
are performed by the papillous internal 
surface of the duct ; and chiefly by two 
glandular swellings which appear towards 
its anterior extremity in the summer months, 
while the eggs are being laid. 
The structure is much more simple in the 
carp, and probably also in the other ovipa- 
rous bony fishes. The two roes occupy 
the same position as the soft roe of the 
male does. They are placed at the side 
of the intestines, liver, and swimming blad- 
der, as far as the anus. They consist of 
a delicate membrane inclosing the ova, 
which are all of one size, and extremely 
numerous (more than 200,000 in the carp) ; 
and terminate by a common opening be- 
hind the anus. 
The immense number of ova contained 
in the ovaria of fishes, accounts to us sa- 
tisfactorily for the astonishing multitudes 
in which some species are formed. In a 
perch weighing one pound two ounces, there 
were 69,216 ova in the ovarium ; in a mac- 
karel of one pound three ounces, 129,200 ; 
in a carp of eighteen inches. Petit found 
342,144 ; and in a sturgeon of one hundred 
and sixty pounds, there was the enormous 
number of 1,467,500. 
EMBRYO OF THE MAMMALIA. 
The mode of connexion of the pregnant 
uterus with the membranes of the ovum, 
and thereby, with the embryo itself, display 
three chief differences in the various mam- 
malia. 
Either the whole external surface of the 
ovum adheres to the cavity of the uterus, 
or the connection is effected by means of a 
simple placenta, or by more numerous small 
placenta; (cotyledons). 
The first kind of structure is observed in 
the sow, and is still more manifest in the 
mare. In the latter case, the external 
membrane of the ovum, the chorion may 
be said to form a bag-like placenta. Nu- 
merous and large branches of the umbilical 
vessels ramify through it, particularly in the 
latter half of the period of pregnancy ; and 
its external surface is covered with innu- 
merable flocculent papillae, which connect 
it to the inside of the uterus. 
In those animals of this class, where the 
embryo is nourished by means of a pla- 
centa, remarkable varieties occur in the 
several species ; sometimes in the form and 
successive changes of the part ; sometimes 
in the structure of the organ as being more 
simple or complicated. 
In most of the digitated mammalia, as 
well as in the quadruniana, the placenta has 
a roundish form ; yet it consists sometimes 
of two halves lying near together ; and in 
the dog, cat, martin, &c. it resembles a 
belt (cingulum or zona). Its form in the 
pole-cat holds the middle between these 
two structures, as there are two round 
