452 ROBERT W. HEGNER 



into view the chondriosomes. He shows that the chondriosomes 

 of the undifferentiated cells are granular, and that as differentia- 

 tion proceeds, these granules unite to form chains and threads 

 (fig. 23, B). '^Zwischen den somatischen und Urgeschlechts- 

 zellen existiert ein Unterschied in der Structur, welcher sich 

 dadurch offenbart, dass die Urgeschlechtszellen primitive kornige 

 Chordriosomen besitzen, wahrend die somatischen Zellen mit 

 veranderten, d.h. fadenformigen Chondriosomen ausgestattet 

 sind" (p. 428). The germ cells are those which remain in an 

 undifferentiated condition situated in the posterior part of the 

 embryo among the entoderm cells. Tschaschkin ('10) in the 

 same year, came to a similar conclusion from studies made with 

 chick embryos. Rubaschkin ('12) has also extended his investi- 

 gations on guinea-pig embryos. The accompanying diagram 

 (fig. 24) shows the fertilized egg and the early cleavage cells 

 all alike (in black) ; some of their descendants become differen- 

 tiated into the somatic cells of the germ layers (circles), but 

 others (in black) remain in a primitive condition and are recogniz- 

 able as the primordial germ cells (p.g.c); these remain at rest 

 for a considerable period, but finally multiply and become part 

 of the germinal epithelium (g.ep.). 



yon Berenberg-Gossler ('12) considers the 'Netzapparat' in 

 the primitive germ cells of the chick of particular importance 

 (fig. 23, D) comparing it with the 'wurstformige Korper' described 

 by Hasper ('11) in Chironomus (p. 385, fig. 1). The appearance 

 of this structure in the 'Keimbahnzellen' is thought to be due to 

 the long period during which these cells do not divide. 



Certain events take place during the spermatogenesis of 

 mammals which are concerned with the differentiation of germ 

 cells. I refer to the formation of the Sertoli cells of man, as 

 reported by Montgomery ('11), and in part confirmed by von 

 Winiwarter ('12). The Sertoli cells are intimately connected 

 with the germ cells in the mammalian testis and probably per- 

 form three functions: (1) they nourish the spermatocytes; 

 (2) they provide the spermatic fluid; and (3) they exert some 

 chemico-tactic stimulus which serves to orient the spermatozoa 

 into bundles. The origin of the Sertoli cells has been for many 



