170 THE PHYSIOLOGY OF REPRODUCTION 



According to Loisel/ the orientation of the sperms in the testis 

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



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 ; a', parts of spermatids which dis- 

 appear when spermatozoa are fully formed ; i, seminal granules. 



' Loisel, "Facteurs de la Forme et de la Fasciculisation des Spermies 

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



