EXCRETORY AND REPRODUCTIVE SYSTEMS 203 



fresh specimen this protuberance may be picked open and the 

 ovum expelled on a slide for examination with the microscope. 

 The ovum is scarcely visible to the unaided eye. The human 

 ovum is still smaller. 



The ova of all mammals, except the duck-bill and spiny 

 ant-eater, are very small. When the ovum becomes mature, 

 the protruding wall of the follicle bursts, permitting its con- 

 tents to be received by the expanded end of the uterine tube, 

 whence it passes to the uterus. If the male element, the sper- 

 matozoon, enters the ovum, the latter is soon enveloped by a 

 growth of mucous membrane and retained in the uterus for 

 development. Ripe ova occur near the close of the first year 

 of the cat's life and new ones probably continue to mature 

 during the next ten years. The discharge of the ova from the 

 ovary is accompanied by a constitutional disturbance, during 

 which an extra amount of blood is sent to the sexual organs, 

 and the sexual appetite becomes very marked. In the human 

 species this disturbance occurs about every twenty-eight days. 

 Mature ova occur in the human ovary between the thirteenth 

 and forty-eighth years. 



The mammary glands of the adult female cat reach their 

 full development when it gives h)irth to young. They may 

 be seen by carefully removing the skin from the ventral aspect 

 of the body, when they will appear somewhat like a thin layer 

 of adipose tissue extending from near the axilla to the pubic 

 symphysis. There are four teats or nipples on each side. In 

 some mammals the nipples are less numerous and confined 

 either to the thoracic or inguinal region. In the elephant, 

 Chiroptera, and Primates there are but two nipples, and they 

 are thoracic. In most Ungulates the nipples are inguinal. 

 THE MALE REPRODUCTIVE SYSTEM 



The organs of generation in the male consist of the testes, 

 the ducts leading from the testes to the urethra, the prostate 

 gland, hulbo-urethral glands (Cowper's gland), and the penis. 



