170 THE PHYSIOLOGY OF REPRODUCTION 



According to Loisel, 1 the orientation of the sperms in the testis 

 is due to a secretion from the cells of Sertoli, together with 



U' 



"N-/ 



FIG. 43. A cell of Sertoli with which the spermatids (three of which are 

 shown) are beginning to be connected human. (After Bramman, from 

 Schafer.) The cell contains globules of nutritive substance and similar 

 smaller globules are seen in the spermatids. 



FIG. 44. Diagram illustrating the cycle of phases in spermatogenesis. 

 (From Schafer.) 



a, spermatogonia (seen dividing at 6) ; a', a", Sertoli cells ; b, spermatocytes 

 (seen dividing at 5) ; c, spermatids ; ', parts of spermatids which dis- 

 appear when spermatozoa are fully formed ; , seminal granules. 



1 Loisel, " Facteurs de la Forme et de la Fascicnlisation des Spermies 

 dans les Testicules," Jour, de I'Anat. et de la Phys., vol. xlii., 1906. 



