CHAPTER XVI 



HUMAN REPRODUCTION 



In Part I of this book we dealt with the human body viewed as a self- 

 maintaining individual organism. In that treatment the reproductive 

 system was not included, for the primary functions of that system relate 

 to maintenance not of the individual but of the race. Nevertheless the 

 reproductive system does profoundly affect the development, structure, 

 and functioning of the individual, as will be evident in what follows. 

 Here we shall use man as a concrete example to illustrate some of the 

 reproductive structures and processes described in general terms in the 

 last chapter. 



The reproductive system of the male. The male gametes, known 

 as spermatozoa, are developed in the convoluted seminiferous tubules that 

 make up the bulk of the testis (plural testes). In mammals, including 

 man, the paired testes are suspended below the pubic region in a loose 

 pouch, the scrotum, into which they descend from the abdominal cavity 

 in late embryonic life. 1 



Certain cells of the seminiferous tubules, like the follicle cells of the 

 ovary, nourish the germ cells while the latter are undergoing the changes 

 that transform them into mature spermatozoa. The seminiferous tubules 

 communicate by short ducts with a coiled tube, the epididymis, which 

 lies in the scrotum alongside the testis and, perhaps with the aid of the 

 seminal vesicles, acts as a storehouse for the spermatozoa until they are 

 ejected. From each epididymis a duct, the vas deferens, passes from the 

 scrotum up into the abdomen, over the symphysis pubis or junction 

 of the pubic bones, and around to the lower rear side of the bladder. 

 Here it is joined by the duct of an elongated saclike seminal vesicle, the 

 principal function of which is to contribute a part of the fluid that, with 

 the spermatozoa, makes up the semen. Beyond this point, the vasa 

 deferentia are called the ejacidatory ducts; they open a short distance 

 beyond the neck of the bladder into the common channel for urine and 

 semen, the urethra. The prostate gland surrounds the ejaculatory ducts 



1 Mammalian spermatozoa are injured by the high temperatures prevailing in the 

 abdominal cavity, and when descent of the testis fails to occur (as sometimes happens), 

 spermatozoa are not formed. 



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