EXCRETORY AND REPRODUCTIVE SYSTEMS. ^73 



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.' 90). 



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 Ornithodelphia, 

 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 Marsupialia bring forth their young in a very im- 

 mature condition. They are then carried for several 

 months in an abdominal integumentary pouch, the mar- 

 supiuni, 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 



