316 Papers from the Department of Marine Biology. 



as migrating by way of developing blood-channels to the splanchno- 

 pleure and thence, by amoeboid activity, to the primitive gonads. 



In the lizard Lacerta agilis, von Berenberg-Gossler (1914) follows 

 the origin of the so-called "primordial germ-cells" ("entodermal 

 wandering cells"- Danchakoff, 1908) to the entoderm of the open gut; 

 but he denies for them a direct genetic relationship to the definitive 

 germ-cells, and regards the whole process as a late phase of mesoderm 

 derivation from entoderm contributing largely to the formation of the 

 mesonephric (Wolffian) duct. 



Still others (e. g., Felix, 1906, 1911; Dustin, 1910; Firket, 1914) 

 admit the occurrence of primordial germ-cells in the entoderm and 

 their migration in part to the developing genital gland, but attribute 

 to this process only a phylogenetic significance, an ontogenetic remi- 

 niscence of an earlier phylogenetic experience; and they claim that 

 these primitive sexual elements early degenerate and are replaced by 

 secondary sex-cells which are differentiated from the mesothelium 

 of the genital ridge. 



In view of these discordant conclusions it seemed desirable that the 

 scope of these investigations should be extended to include many more 

 vertebrate forms and additional workers. Among the whole group of 

 investigators Swift was the first to describe, or even to suggest, a 

 vascular route of early migration. Von Berenberg-Gossler (1914) 

 confirms this point for chick and for duck. The possibility seemed to 

 remain, however, that these intravascular so-called genital-cells might 

 indeed be only a type of blood-cell progenitor, perhaps a hypertro- 

 phied hemoblast. With this possibility in mind, suggested also by 

 Minot's earlier tentative interpretation (1894) of these cells as ele- 

 ments enlarged in preparation for mitosis, and the later claim of Wini- 

 warter and Sainmont (1909) that they are hypertrophied mesoderm- 

 cells, the work on the loggerhead turtle embryos was planned. 



It may be added also that my previous study of the early history 

 of the female germ-cells of the starfish Asterias forbesii (1908) had led 

 me to the conclusion that in this form the germ-cells most probably 

 arose by differentiation from the peritoneal epithelium, and so inclined 

 me to a belief in the essential accuracy and general applicability of 

 Waldeyer's original theory. But a steadily augmenting body of 

 cytologic and genetic data would seem to demand a continuous "germ- 

 plasm," which demand does not appear to be met by a derivation of 

 germ-cells from already differentiated soma-cells. 



MATERIAL AND METHODS. 



The first essential requisite was a complete series of embryos. The 

 second requisite was a favorable staining technic, such as would clearly 

 differentiate the primordial germ-cells at all stages of their early his- 

 tory; which condition was in turn dependent upon the employment 



