280 NORMAL HISTOLOGY AND ORGANOGRAPHY. 





" Middle piece. 



Tail. 



produce spermatozoa, it is believed that the secre- 

 tions from the interstitial cells react upon the devel- 

 opment of the body as a whole. While the semi- 

 niferous tubules function in the production of sper- 

 matozoa, it is not clear that the accumulation of 

 semen prompts the sexual act. For instance, the 

 testicles sometimes do not descend into the scrotum 



but remain in the body cav- 

 fry. Frequently such testi- 

 cles are of the infantile type, 

 that is, no semen is devel- 

 oped ; and yet the copulation 

 act in such males is not only 

 possible, but the sexual crav- 

 ings may be actually exagge- 

 rated. The interstitial cells 

 of such testicles are well de- 

 veloped and the male is other- 

 wise normal. Again, the im- 

 potency that sometimes 

 comes with old age is said to 

 be due to impaired functional 

 activity of the interstitial 

 cells rather than to lack of 



spermatozoa. We have no specific medical treat- 

 ment for such cases, extracts from normal testes 

 having been tried without satisfactory results. 



Spermatogenesis and Spermatozoa. The develop- 

 ment of spermatozoa begins in man in early youth 

 and usually continues into old age. This phenom- 

 enon is in marked contrast to ovulation in woman, 

 where there is a cessation or menopause at about the 



End piece. 



Fig. 210. Human sper- 

 matozoa, side and flat view. 



