THE HORMONES IN HUMAN REPRODUCTION 



They wage a varied battle for existence and are swayed by 

 many circumstances. Perpetuation of the race amid such dis- 

 tractions requires especially active maintenance of sexual 

 vigor and the urge to mate. This too becomes a function of 

 the testis as an organ of generation. 



THE MALE REPRODUCTIVE ORGANS 



The testis. To follow the story in detail we must first review 

 the anatomy of the testis and the associated male organs of 

 reproduction. The diagram (Fig. 30) will serve to orient us. 

 The two testes lie in their pouch of skin (scrotum) . They are 

 objects of ovoid shape, about the size of walnuts, that is to 

 say 4.5 x 3 centimeters (2x1% inches) in diameter. Within 

 these small rounded bodies the business of sperm cell produc- 

 tion is carried on inside an extraordinary system of tubular 

 canals. The testis, in fact, consists essentially of many hun- 

 dred small tubules, called seminiferous tubules, each about 30 

 to 70 centimeters (1 to 2 feet) in length and about as large 

 in diameter as a strand of sewing silk. These tubules are coiled 

 very tightly in the small space available, and thus when we 

 look through the microscope at a section of the testis, we see 

 countless sections of the individual tubules, cut in every pos- 

 sible direction (Plate XXIII, A). How they actually run, 

 and how they are connected, was for a long time one of the 

 most difficult problems of microscopic anatomy. We should 

 get a similar picture if we took a thoroughly tangled ball of 

 twine and cut a section through it with a sharp knife. Nobody 

 could possibly tell from such a cut whether the ball of twine 

 contained one long piece of twine, or several shorter ones, or 

 how they were joined together. Likewise a section of the testis 

 cannot tell us anything about the course of the seminiferous 

 tubules. For a century microscopists applied their various 

 technical tricks to this problem, including the making of mag- 

 nified models from serial sections, but with only imperfect suc- 

 cess, owing to the difficulty and laboriousness of following 



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