332 Papers from the Department of Marine Biology. 



work of King, Allen, Beard, and others who hold to the view of a 

 genetic independence between coslomic epithelium and germ-cells is 

 that they have studied only the earlier periods of the ontogeny. But 

 in the male chick Swift has now (1916) examined also the young post- 

 incubation stages, as late as 10 days, and still finds all the evidence in 

 accord with the segregation view. 



Gatenby describes the tadpole ovary as formed of (1) germ-cells of 

 peritoneal origin; (2) germ-cells of retro-peritoneal origin; (3) germ- 

 cells of endoderm (yolk-sac) origin. He inclines to believe that the 

 germ-cells of the yolk-sac are all laid at the first spawning. He de- 

 scribes and illustrates intermediate stages between peritoneal cells and 

 young germ-cells, but one is forced to the criticism that his figures give 

 no adequate support to his claim of a transformation of mesoderm-cells 

 into germ-cells. 



In the lizard embryo (Lacerta agilis), according to von Berenberg- 

 Gossler, the migration of the " primordial germ-cells" is not so strongly 

 limited to the early developmental stages as described, e. g., for 

 Chrysemys; and the cells ("entodermal wandering cells") are relatively 

 much more numerous; nor do any of them disintegrate; they become 

 converted into mesoderm-cells. ''The migration of cells out of the 

 entoderm in Lacerta has no other significance than a dilatory develop- 

 ment of mesoderm from entoderm" (pp. 247-248). He extends this 

 interpretation to cover the so-called extra-regional genital cells of 

 reptiles and mammals. As mesodermal cells they may possibly 

 metamorphose into cells of the ccelomic epithelium, as earlier main- 

 tained by Hoffman. They wander from the entoderm largely to the 

 location of the future pronephric (Wolffian) duct, to the construction 

 of the caudal portion of which they greatly contribute. Occasional 

 cells are found also in the somatopleure. None of the cells while 

 within the mesoderm were found in process of mitosis. All these cells 

 are believed to become changed into mesoderm-cells; thus they 

 apparently disappear, but from some of those scattered among the 

 cells of the peritoneal epithelium definitive germ-cells arise. This 

 interpretation eases the difficulty of accepting the view of certain 

 investigators (e. g., Firket, Dustin, Gatenby, Felix) that both primary 

 and secondary genital cells are formed, the primary becoming displaced 

 through "degeneration" by the secondary. The whole genital gland 

 would then arise from mesoderm, as maintained by some of the earlier 

 investigators. 



No attempt is made by von Berenberg-Gossler to apply the above 

 interpretation to conditions in the chick, where these cells during 

 early stages have an intravascular distribution. However, he expresses 

 doubt regarding the germ-cell nature of these intravascular " germ- 

 cells," many of which are in process of degeneration. A common 

 interpretation of the phenomena relating to these "entodermal wan- 



