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THE INTERNAL ENVIRONMENT OF THE BODY 



Part III 



Sertoli cell 



Undifferentiated 

 germ cell 



Spermatogonium 



Sperma 

 tozoon 



Primary Spermatocyte 



_„^„ Secondary Spermatocyte 



Spermatid 



Primary Spermatocyte 



Fig. 18.7. Photograph of the seminiferous tubule (x 550) in which spermato- 

 zoa develop. The outermost dark band is the wall of the tubule, mainly connec- 

 tive tissue. All of the other cells are developing sperms and cells (Sertoli) which 

 nourish the sperms. The nearly mature spermatozoa are nearest the fluid filled cen- 

 ter of the tubule. Their dark, oval heads are crowded together and their exces- 

 sively slender tails (flagella) extend into the fluid. Between them and the wall of 

 the tubule are sperms in successive stages of development beginning near the wall. 

 They multiply; their nuclei divide by mitosis and each sperm has 48 chromosomes. 

 Nearer the center others that are further developed divide by meiosis and each 

 mature sperm has 24 chromosomes. (Courtesy, Ham: Histology, ed. 2. Philadel- 

 phia. J. B. Lippincott Co., 1953.) 



orchid. Rarely, as in armadillos, elephants, and whales, the testes remain 

 permanently in the body cavity and yet are not injured by the body tempera- 

 ture. Under some strain of the abdominal muscles a loop of the small intestine 

 may be forced into the passage through which the testis slips; this is called 

 inguinal hernia. 



The seminiferous tubules of each testis unite to form a dozen larger ducts 

 which in turn open into the epididymis, a single tortuously coiled duct about 

 21 feet long. This duct is lined by secretory cells which contribute to the semi- 

 nal fluid in which the sperm cells slowly mature and develop part of their 

 motility (Fig. 18.6). From the epididymis they move into the sperm duct 

 (vas deferens). These sperm ducts, one from each testis, pass upward into 



