EXCRETORY AND REPRODUCTIVE SYSTEMS. 173 
The prostate gland surrounds the urethra dorsally and 
laterally about two or three centimeters from the bladder. 
This gland secretes a milky fluid which is poured into the 
urethra through many ducts, during copulation, and serves 
as a medium for the spermatozoa (Fig. go). 
Cowper’s glands are two in number, about the size of a 
pea, and lie in the angles formed by the urethra and the 
crura of the corpora cavernosa. These glands secrete a 
viscid fluid of unknown function. One duct from each 
gland opens into the urethra. 
REMARKS ON THE MAMMALIAN UROGENITAL SYSTEM. 
The urogenital system is subject to some variations in 
the different orders of Mammalia. In the Ormithodelphia, 
the mammary glands are devoid of teats and the oviducts 
corresponding to the Fallopian tubes and horns of the 
uterus do not unite in the median line to form the body of 
the uterus, but unite with the urethra, forming the uro- 
genital canal. The latter opens into an enlarged terminal 
portion of the rectum, called the cloaca. The ureters also 
open directly into the cloaca, so that there is but one ex- 
ternal opening for the genital and excretory products. In 
the above features the Monotremes resemble the Amphibia 
and reptiles. All mammals are viviparous except the 
Monotremata, which are oviparous, laying eggs as large 
as those of the robin. The Ornithorhynchus incubates its 
eggs in an underground nest, while the Echidna carries her 
single egg in a temporary abdominal pouch. 
The Marsupiaha bring forth their young in a very im- 
mature condition. They are then carried for several 
months in an abdominal integumentary pouch, the mar- 
supium, within which are the nipples. In the Monotremata, 
Cetacea, Sirenia, and elephant the testes do not descend 
into a scrotum, but are retained in the primitive location 
