The Reproductive System 255 



THE MALE REPRODUCTIVE SYSTEM 



Except for the protozoans, all animals have special structures which 

 produce the sperm. These are known as the testes (sing, testis.) In 

 the lower forms (the sponges and coelenterates), the testes are located in 

 the body wall and the sperm are shed directly into the surrounding water. 

 Most of the animal groups above these have special ducts for conducting 

 the sperm outside the body. Many also have special glands and other 

 accessory structures for ensuring the safe transfer of the sperm to the 

 female. 



The Testes. — The testis of the adult mammal is an oval gland 

 surrounded by a thick white capsule formed of fibrous connective tissue. 

 At the posterior edge, this capsule is thicker and projects into the gland 

 as thin partitions which divide the organ into approximately 250 indi- 

 vidual compartments. These compartments are conical in shape with 

 their apices toward the thickened edge of the capsule. 



Within each lobule or compartment are the terminal portions of 

 one to three seminiferous tubules (Fig. 76,A). Occasionally the much- 

 convoluted tubules of one lobule are joined to those of a neighboring one 

 by loops. 



Lining the seminiferous tubules are two types of epithelial cells. A 

 smaller number act as nutritive and supporting cells, while the vast ma- 

 jority are the sex cells. These latter, by a complex series of divisions 

 and changes, become the sperm (Fig. 76,B). Scattered in the angular 

 spaces between the tubules are the interstitial cells which, it is believed, 

 produce the important male hormone, testosterone, 



Embryologically, the testes are formed in the dorsal portion of the 

 body cavity. In many mammals, including human beings, the testes de- 

 scend shortly before birth into the scrotum through the inguinal canals. 

 This descent of the testes is apparently activated by the anterior pituitary 

 with a special structure, the gubernaculum, possibly playing an important 

 role. The gubernaculum is a ligament which extends from the lower 

 portion of each testis through the inguinal canal and into the scrotum. 

 Supposedly either by its failure to grow after the seventh fetal month (in 

 human beings) or by actual shortening, the gubernaculum pulls the testis 

 through the inguinal canal down into the scrotum. This latter structure 

 is simply a special pouch of the skin into which an extension of the body 

 wall accompanies the sac of peritoneum which is carried along with the 

 descending testis and its accompanying blood vessels and ducts. The 

 inguinal canal is the passageway from the body cavity into the scrotum. 



