380 CHAELES H. SWIFT 



a process of differentiation, while Niissbaum noticed the pri- 

 mordial germ-cells at a distance from the sexual primordium. 



Hoffman ('92) employed in his researches about a dozen species 

 of birds, mainly taken from the group of waders, and in three of 

 them, Haematopus ostralegus, Sterna paradisea, and Gallinula 

 chloropus, there was sufficient evidence brought out to show that 

 some, if not all the primordial germ-cells, did not arise in the 

 modified coelomic epithelium. In the three species mentioned 

 above, he found at the proper time, numbers of the primordial 

 ova in the germinal epithelium, but, in addition, he found cells, 

 supposedly primordial ova, because of their resemblance to those 

 found later in the germinal epithelium in embryos of 23 somites. 

 An embryo of 23 somites does not possess the so-called germinal 

 epithelium, the coelomic epithelium over the Wolffian body not 

 having been modified at this age, yet in these he found primor- 

 dial germ-cells far removed from the site of the future sex gland, 

 in the splanchnic plate of mesoderm, in the region between 

 splanchnic mesoderm and entoderm and in the entoderm itself. 



To quote Hoffman : 



Maintenant qu'il est evident que les ovules primitifs ne derivent pas 

 des cellules peritoneales previlegiees, mais qu'ils se rencontrent deja 

 dans tres jeunes periodes de developpement, bien que leur premiere 

 ebauche chez les Vertebres, soit encore entierement inconnue il sera 

 necessaire de laisser tomber le mot "epithelium genuinatif." Voila 

 pourquoi j'appellerai desormais, cette partie de I'epithelium perito- 

 neal, qui se transforme en un assise, dont les cellules sont disposees en 

 pousieurs rangees et entre lesquelles sont placees les ovules primitifs, 

 couche des ovules primitifs. 



This ''couche des ovules primitifs" gave origin to the true 

 sexual cords in the male, and the medullary cords and cortical 

 cords in the female. 



The true sexual cords in the male and the medullary cords in 

 the female are homologous — the cords of first proliferation ac- 

 cording to Firket ('14). The cortical cords — cords of second 

 proliferation — occur only in the female and appear later. The 

 true sexual cords in the male produce the sexual elements of the 

 male. The medullary cords in the female — their equivalents — 

 go partly into the formation of ovarian stroma, but in greater 

 part disappear, while the second crop in the female — the cor- 



