Sterility of the Male Animal 121 



they meet the ovum and, after the fusion of these two cells to 

 constitute fertilization, the female organs must protect, and afford 

 nutrition to, the embryo for a long period of time. 



While there are certain analogies between the causes and nature 

 of sterility in the two sexes, it is desirable to consider them sep- 

 arately. 



A. Sterility of the Male Animal. 



In order_ that a male animal shall be fertile, it is essential that 

 living, virile spermatozoa shall be secreted and that the animal 

 be competent to copulate with the female and give effective emis- 

 sion to the normal semen. 



The testicles constitute the basis of the male genital system, 

 since they produce the male cell or spermatozoon. In mammalia, 

 the testicles are two in number, a right and a left, variably 

 located according to species. In all our common domestic ani- 

 mals they are normally located in adult life outside the abdomen 

 in the scrotum, which is situated, according to species, in the in- 

 guinal or perineal region, the testicles passing through the 

 inguinal ring in order to reach the scrotal sac. In the elephant, 

 the testes are normally retained within the abdomen throughout 

 life. 



The testes vary somewhat in form and, necessarily, in size in 

 the different species and present some marked differences in their 

 relations. Their general form is oblong or spheroidal and, when 

 they come to rest in the scrotum, their long axes may be perpen- 

 dicular to the spinal axis, as in the bull, or parallel, as in the 

 horse. 



In; addition to its peritoneal coverings, the testicle consists of 

 its fibrous framework, the proper or secretory tissue, excretory 

 ducts, and the vessels and nerves. 



The fibrous framework forms externally a very firm, inelastic 

 capsule, the tunica albuginea. This serves to render the func- 

 tioning testicle one of the most dense, incompressible glands in 

 the body, the very firmness of which bears an important relation 

 to fertility, since any disease causing swelling of the gland 

 tends to seriously affect the proper glandular tissue by the severe 

 compression. 



From the tunica albuginea, fibrous septa pass toward the center 

 of the gland and divide the secretory tissue into small lobules. 



