SEX-CORDS AND SPERMATOGONIA IN CHICK 383 



ment precoce et subit line serie de migrations qui liii assurcnt trois 

 localisations succcssives (gl. paires primaries, glande impaire, gl. 

 paires definitives); I'autre est d'origine mesodermique et se developpe 

 in situ, au niveau des glandes definitives. 



Chez Chrysemys marginata, les gonocytes de la premiere espece ne 

 presentent de karyokineses qu'au debut de leur differenciation ; ul- 

 terieurement ils ne se multiplient plus; beaucoup d'entre eux deg^- 

 nerent meme. 



He believed that more of the primary gonocytes functioned, in 

 producing definitive sexual cells, in Amphibia than in Reptilia. 



Rubaschkin ('12), working with the guinea-pig, stated that 

 the definitive sex cells in both testis and ovary are descendants 

 of the primordial germ-cells. Rubaschkin used as his criterion 

 for distinguishing the primordial germ-cells the granular type 

 of mitochondria. He believed that the primitive cells, or blas- 

 tomeres, possessed this type of mitochondria, and that as the 

 somatic tissues were differentiated from them, the cells of the 

 tissues acquired the rod-shaped mitochondria. In this way he 

 was able to recognize the germ-cell at any stage in the young 

 embryo and differentiate it from the ordinary somatic cell. By 

 this means he came to the conclusion that the definitive sex 

 cells were descended from the primordial germ-cells. 



For a more detailed account of the literature on the subject 

 of the origin of the definitive sexual cells, the reader is referred 

 to the ample bibliographies of Bouin ('00), Allen ('04), and 

 Firket ('14). 



MATERIALS AND METHOD OF STUDY 



In the course of this investigation two fixatives were employed- 

 namely, Meves' modification of Flemming's fluid and the acetic, 

 osmic-bichromate mixture. In a previous investigation on the 

 primordial germ-cells of the chick ('14) the osmic acid content 

 of these fluids was found to be a serious disadvantage owing 

 to their staining of the numerous vitellus granules, which, when 

 blackened, obscured the cytological details. However, that 

 drawback was not present in the embryos and young chicks 

 used in this research for the germ-cells had lost their vitellus 



