i62 THE PHYSIOLOGY OF REPRODUCTION 



membrane.! The layer nearest the membrane consists of clear 

 cubical cells, a few of which show evidence of division. These are 

 the spermatogonia. Certain of the epithelial cells between the 

 spermatogonia are enlarged, and project among the more internal 

 cells in association with developing sperms. These are the cells of 



"^^^' 





f: 





Hr*- 5**? S©*" i* ** »V 



iWs^em^-^ . ' i^- <.t^ \.kh 



Fig. 48. — Section through portion of two seininiferC)U.s tubules in testis of rat. 



a, Basement-meiubiane ; h, spei'matogonium ; c, spermatocyte ; d, sper- 

 matozoa in cavity of tubule ; e, interstitial tissue containing vessels. 



Sertoli. On the inside of the spermatogonia are certain larger cells, 

 known as spermatoc3'tes. These are products of division of sper- 

 matogonia, each of which on dividing into two gives rise to a cell 

 like itself, and another cell, which grows larger, passes into the 

 second layer, and becomes a spermatocyte. 



The spermatids, which in some seminiferous tubules lie on the 



' Curtis, "The Morphology of the JNIammalian Seniinifei'ous Tubule," Araer. 

 Jovr. of Anat; vol. xxiv., 1918, 



