382 CHARLES H. SWIFT 



peritoneal cells, from which these cords arise. This development of 

 undifferentiated peritoneal derivatives to form primitive sex cells is 

 probably homologous with the process by which germinative cells 

 (descendants of the peritoneal cells of the germinal epithelium) of the 

 seminiferous tubules of the testis and the cells of the cords of Pfliiger of 

 the ovary are being transformed into primitive sex-cells. 



And again : 



Clear transition forms are found to connect the primitive sex-cells 

 with the germinative cells of the seminiferous tubules. Transition 

 forms connecting the germinative cells with the sex cells occur in the 

 pig embryos between 2.5 cm. and 13 cm. leng-th; later states show no 

 transition forms. 



As regards the formation of the definitive sexual cells he said : 



It has been shown in the pig and rabbit, however, that these sex 

 cells, appearing in the indifferent stages, do not contribute to the for- 

 mation of functional sex products in the ovary. The same is probably 

 true of the testis, it being at least certain that the great bulk of the 

 spermatogonia are formed from the germinative cells — cells derived 

 originall}' from the peritoneum and maintaining, first, their indifferent 

 character, at least so far as our technique is able to show. 



Dustin ('07, '10) studied the question of germ-cells origin, 

 migration and evolution in Amphibia — Triton and Rana— and 

 in Reptilia^ — Chrysemys. 



In the first paper, dealing with the Amphibia, he reported 

 that the primordial germ-cells were of mesoblastic origin ; from a 

 part of the primitive coelom which he called gonocle. He called 

 the germ cells gonocytes of the first line and found that they 

 reached the sites of the definitive sex glands by active migra- 

 tion. He found that a second line of gonocytes was produced 

 by transformation of small germinative cells, which were in 

 their turn the result of peritoneal epitheliimi proliferation. 

 Both lines of gonocytes were able to produce definitive sexual 

 cells. 



In his second paper relating to Chrysemys, he found that 

 there were also two lines of gonocytes, with this exception, that 

 in the reptile the primarj^ gonocyte came from the entoderm. 



Deux especes de cellules sexuelles se succedent done au cours de 

 I'ontogenese ; Tune privient de I'endoderme; elle est extraordinaire- 



