20 THE BREEDING OF ANIMALS 



duct; (c) vesiculse seminales; (d) prostate glands; (e) 

 Cowper's gland ; (/) urethra, through which the urinary 

 and genital secretions are conveyed; (g) the penis, 

 through which the semen of the male is conveyed to the 

 female genital organs. The secretions of the vesiculse 

 seminales, the prostate, and the Cowper's gland all empty 

 into the urethra, where they mix with the seminal fluid 

 from the testicles. The testicles, vasa deferentia and 

 urethra and penis are often called the essential organs of 

 generation, while the remaining three are referred to as 

 the accessory organs. 



23. The testicles. The essential sexual elements, 

 the spermatozoa, are formed in the testicles. The removal 

 of the testicles, therefore, destroys the ability of a male 

 animal to elaborate the male germ-cells and permanently 

 destroys his fecundity. The structure of the testis is 

 described in some detail by Marshall as follows : 1 " This 

 organ is enclosed within a fibrous capsule, the tunica 

 albuginea, which is very rich in lymphatics. It is cov- 

 ered by a layer of serous epithelium reflected from the 

 tunica vaginalis. Posteriorly the capsule is prolonged 

 into the interior of the testis in the form of a mass of 

 fibrous tissue (the mediastinum testis). Certain other 

 fibrous processes or trabeculse also project inwards from 

 the capsule, and divide the glandular substance into 

 lobules. The efferent ducts of the testis (vasa efferentia) 

 open into a single convoluted tube situated at the pos- 

 terior margin of the organ and attached to the medias- 

 tinum. This is the epididymis. Its lower extremity 

 is prolonged into a thick-walled muscular tube (the vas 

 deferens) which is the passage of exit for the seminal 

 fluid or sperm-containing secretion. The glandular sub- 



1 Marshall, "The Physiology of Reproduction." 



