MAMMALIA 653 



teriorly as the vagina. In the ventral wall of the vagina, near the 

 aperture, is a small body of erectile tissue, the clitoris, which corre- 

 sponds to the penis of the male. The pair of testes of the male are 

 contained in a pouch of integ'ument called tiie scrotum, which hangs 

 beneath the anus. Each testis is about one and a half centimeters 

 long by one centimeter thick. The epididymis is a mass of coiled 

 tubules coming from the testis and lying at its dorsal side as a part 

 of the testicle. The vas deferens is the canal leading from this 

 cranially through the ahdominal ring and inguiyial canal into the 

 abdominal cavity, where it enters the urethra on its dorsal side near 

 the prostate gland. During copulation the mature spermatozoa pass 

 into the urethra and are discharged into the vagina of the female by 

 the erected penis. The secretions of the prostate glands and of 

 Cowper's glands just posterior to them, provide a considerable part 

 of the seminal fluid. 



The cat will first breed at the age of one year. The female will 

 receive the male at certain periods only. Mature ova rupture through 

 the wall of the follicle of the ovary and are normally received by 

 the ostium of the oviduct which covers it. Occasionally an ovum 

 falls into the body cavity. In the oviduct the ova are moved pos- 

 teriorly where, if copulation has occurred, they will meet spermatozoa 

 and be fertilized. Cleavage, or divisions of each zygote follows, and 

 each resulting multicelled embryonic mass moves down to the uterus 

 where it becomes implanted in the wall. Here a placenta is formed 

 from a union of certain embryonic membranes with the internal 

 lining of the uterus. Parental blood carries nourishment and oxygen 

 to this membrane where it diffuses through to the embryonic blood 

 in other vessels in the membrane. The time between copulation and 

 birth of young (gestation period) in the cat is from fifty-five to 

 sixty-five days. From three to six young are usually born in each 

 litter. They are fed from the four nipples of the mammary gland 

 along each side of the ventral surface of the trunk. 



