376 CHARLES H. SWIFT 



the elongated cells protrude out from the general level of coelomic 

 epitheUum like a .small narrow hillock and if looked at from 

 above, the area has the appearance of a light narrow streak or 

 stria on the medial and anterior face of the pink mesonephros. 

 This region of differentiated coelomic epithelium is the germinal 

 streak of Kolliker ('61) and the germinal epithelium of Wal- 

 deyer (70). 



The primordial germ-cells (ureier, keimzellen, gonocytes, 

 ovules males, ovules primordiaux, urgeschlechtszellen, and germ- 

 cells of the various authors) are found among the cells of the 

 germinal epithelium from its very commencement. They are 

 easily recognized, for they are quite different from the surround- 

 ing cylindrical cells. They are large, oval or round, have a 

 large excentric nucleus, which appears vesicular and does not 

 have much chromatin. The cytoplasm also stains faintly. 

 These cells were discerned by Bornhaupt ('67) and were clearly 

 described by Waldeyer ('70), both investigators noticing them 

 in the germinal epithelium of the chick. Since Bornhaupt many 

 investigators in every vertebrate phylum have seen the cells, 

 and yet there is great uncertainty, even at the present time, 

 in regard to their origin and fate. 



The earlier students, as a rule, believed that they arose in 

 situ, in the germinal epithelium from the epithelial cells by a 

 process of differentiation (Waldeyer, 70; Balfour, '78; and 

 Semon, '87). Of late, however, there is an increasing belief 

 that they antedate the germinal epithelium; that they origi- 

 nate in some region of the embryo at a distance from the site 

 of the future gonads, and only migrate into the Wolffian region 

 at about the time of the appearance of the germinal epithelium 

 (Niissbaum, '80; Hoffman, '92; Eigenmann, '92; Beard, '04; 

 Rubaschkin, '07; and Swift, '14). 



Having given these short explanations of terms which will be 

 frequently employed we are now in a position to review the 

 more important papers which relate to the origin of the definite 

 sex-cells in the male. 



Waldeyer ('70), although he described so exactly the germinal 

 epithelium and primordial germ-cells, did not believe that either 



