REPRODUCTIVE ORGANS IN ANIMALS 19 



distance to the scrotum ; thus the testes may reach the groin 

 without passing through the inguinal canals, and in this position 

 they may give rise to much discomfort or pain. The condition 

 of retention of the testicles is known as cryptorchism and is 

 usually accompanied by sterility, but in some individuals there 

 may be a period of temporary fertility lasting for only a few years 

 from the time of puberty and followed by permanent cessation 

 of sperm production. This fact is of great importance to 

 crypt orchid persons who desire to have children. 



Each testis is surrounded by a serous membrane (the tunica 

 vaginalis) and within this is a fibrous capsule (the tunica 

 albuginea). The latter is prolonged posteriorly into the interior 

 of the organ to form the mediastinum testis. The testicle proper, 

 as seen in thin sections through a microscope, is composed of a 

 large number of convoluted tubules supported by a connective 

 tissue stroma containing blood vessels and epithelioid interstitial 

 cells. The tubules are the essential organs which produce the 

 spermatozoa. On the outside of each tubule is a basement 

 membrane supporting several layers of epithelial cells (that is, 

 of cells bounding a free surface or cavity). Inside the basement 

 membrane certain of the epithelial cells are enlarged and form 

 the cells of Sertoli which are supposed to have a nourishing and 

 supporting function. Between these are the spermatogonia, 

 which give rise by division to the spermatocytes on the inside 

 of them. The spermatocytes divide to form the spermatids, 

 and these become elongated out and converted into sperma- 

 tozoa. (See p. 36.) 



A fully developed spermatozoon is formed of an egg-shaped 

 head, which consists almost entirely of the nucleus of the cell, 

 a short cylindrical middle piece, and long vibratile tail. It is 

 by the motion of the tail from side to side that the spermatozoon 

 is propelled forward. The spermatozoa are budded off in the 

 tubules, and thus can move freely in the fluid which is secreted 

 by certain of the epithelial cells. 



The vasa efferentia (or efferent ducts of the testis) are about 

 twelve in number and open into the epididy?ms. This is a single 

 long, convoluted tube situated at the posterior end of the testis. 

 It is lined internally by a ciliated epithelium which is believed 

 to exercise a slight secretory function. Its walls contain smooth 

 muscle fibres, which contract when the contents of the epididymis 



