338 COMPARATIVE MORPHOLOGY OF VERTEBRATES. 
fold continues down the genital ducts forming the ligament of the 
ovary or testis. In the male broad ligament and ligamentum testis 
together form the gubernaculum. Unequal growth of body and 
these ligaments draws the gonads (except in the monotremes) farther 
back into the pelvic region. 
There is some variation in the ovaries. In the monotremes the left is larger 
(cf. birds) and it is interesting to note that eggs have been found only in the left 
oviduct. There is also some variation in shape in the marsupials. Elsewhere 
the ovaries are relatively small (sometimes increasing in size at the breeding season), 
rounded or oval and with the surface smooth or furrowed. 
In male whales, elephants, some edentates, etc., the testes remain 
permanently in the abdominal cavity. In all others a descent of the 
testes occurs. By the same relative difference of growth of body 
and gubernaculum the testes are drawn out of the abdomen into a 
pouch (scrotum)—really a part of the body wall into which a part 
of the ccelom (bursa inguinalis) extends. The wall of this is formed 
in part from the genital folds (see copulatory organs) which surround 
the genital prominence. This scrotum is in front of the penis in the 
marsupials, behind it in all placentals. When the canal connecting 
the cavity of the bursa with the rest of the ccelom remains open (mar- 
supials, insectivores, rodents, bats, etc.) the descent is temporary, the 
testes being withdrawn into the ccelom at the close of the breeding 
season by a ‘cremaster muscle.’ In other mammals the descent 
is permanent, though in some species it does not occur until the time 
of sexual maturity. 
In the oviducts (Miillerian ducts) two regions can be recognized 
in monotremes (figs. 338, 339, A), three in all other forms. The two 
are the Fallopian tube, which opens into the body cavity by a broad, 
fringed ostium tube, and second the uterus, in which the egg is retained 
for a part of its development. In the other mammals Fallopian tube 
and uterus are retained, the latter being specialized for the longer 
development of the young, and the third region is added—the vagina, 
which receives the copulatory organ of the male. The vagina opens 
into the urogenital sinus (fig. 339, B), but in the monotremes the 
vagina is lacking and the uterus and the sinus are directly connected. 
In the marsupials a vagina is developed for each Miillerian duct, and 
in some there is a peculiar fusion of the ducts distal to the vagine so 
that a cecal pocket results, and in a few this pocket also connects with 
the urogenital sinus, thus forming a third vagina (fig. 339, B). 
