THE HORMONES IN HUMAN REPRODUCTION 



interfere; therefore the treatment must be used only in se- 

 lected cases after thorough study. When the hormone fails, 

 surgical methods are usually still available. 



Interstitial cells. In the angular spaces between the tubules 

 the microscope reveals little clumps of relatively large cells 

 not in any way connected with the sperm-forming cells 

 (Plate XXIII, B), Although there are only a few cells at 

 any one point, there are so many clumps that the total mass 

 of the interstitial cells adds up to a significant proportion 

 of the whole testis. Some writers call the totality of these 

 cells "the interstitial gland." There is an ample network of 

 capillary blood vessels among these cell clumps. The ar- 

 rangement is obviously like that seen in the glands of internal 

 secretion; and it is in fact very probable that this is the 

 source of the testicular hormone. We cannot however be 

 sure that the hormone is not made by the cells of the seminif- 

 erous tubules, as will be discussed later. 



The genital duct system. When the sperm cells have reached 

 completion in the testis, they are perfectly formed but in- 

 active. Freed from their parent cells, they are swept passively 

 along the tubules into the larger ducts that drain the tubule 

 system. If the sperm cells were discharged from the body in 

 this nonmotile state they could not fulfill their task of reach- 

 ing and fertilizing the egg cell. They require a further period 

 of ripening and conditioning until they become fully motile 

 and potent. Furthermore the seminal fluid in which they are 

 to be carried must be made and added to them, bringing suit- 

 able substances for their nourishment and stimulation. 



These needs are served by a complex system of ducts and 

 accessory glandular structures. The dozen or more ducts 

 that leave the testis all drain into a single tube about 7 

 meters (21 feet) long, which is tightly coiled, as shown in 

 Fig. 31, into a dense mass, the epididymis, which lies upon 

 the testis. This coiled duct is lined by special secretory cells 

 and is believed to function as a storage place for sperm cells, 



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