574 Gideon S. Dodds. 



In embryos a little older, the germ-cells are more clearly 

 marked, owing chiefly to changes in the surrounding tissues. In 

 embryo ' 7 H, ' the mesoblast plates are considerably thickened 

 and the cells have become more densely packed and so more 

 angular, but there is as yet, no separation into myotome and 

 lateral plate. In this embryo there were recognized fourteen germ- 

 cells, all in the mesoblast and all in that part of it which will 

 become myotome when the separation takes place (fig. 3, cf. 

 figs. 2 and 4). 



In embryo '7 F, ' the myotome is very definitely separated 

 from the lateral plate. There were counted fourteen germ- 

 cells, of which twelve were in the myotome and two in the lateral 

 plate (fig. 4). Embr^'-o '7 Fr' was sectioned in a frontal plane 

 and the myotome was. seen to be also clearly separated from the 

 lateral plate but not distinctly segmented. In this embryo nine- 

 teen germ-cells were recognized, all but one of which were in the 

 myotome (fig. 13). In each of these embryos, nearly all of the 

 germ-cells occupied the dorso lateral part of the myotome. 



In embryos of stage 8, several myotome segments are clearly 

 formed (fig. 14). By this time, the germ-cells have almost all 

 migrated from the myotome into the lateral plate (figs. 5 and 14). 

 A careful study of embryo '8 E' showed a total of thirth-nine 

 germ-cells, all but one of which were in the lateral plate, near its 

 inner margin. In embryo '8 D,' with thirty-six germ-cells, two 

 yet remained in the myotome. From a study of embryos it 

 appears that the migration from myotome to lateral plate must 

 be a rapid one and accomplished by the active migration of the 

 cells themselves. 



Embryos of stage 9 show the gut pretty definitely formed, and 

 the beginnings of the coelomic cavity within the lateral plate. When 

 the separation of the lateral plate into somatic and splanchnic 

 layers takes place, the germ-cells are left in the splanchnic layer, 

 or close to the median margin of the lateral plate where no sepa- 

 ration has taken place. In no embryo of this stage did I observe 

 one in the somatic layer (fig. C). In this and the foUowing stages 

 the number of germ-cells is about the same as in stage 8. The 

 actual numbers will be given in a later part of the account. 



