MICHIGAN ACADEMY OF SCIENCE. 
215 
the fate of these periblast nuclei is somewhat unsettled it is quite com- 
monly agreed that they do not aid in the formation of any structure 
of the embryo.* The possibility Suggests itself however that these 
periblast nuclei because of their large size, apparently primitive con- 
dition and the possession of yolk globules may really be the undiffer- 
entiated blastomeres, some of which may become the centers of the 
primordial germ cells (the origin of germ cells directly from blastom- 
eres is common among invertebrates). 
Embryos in stages between those shown in Figs. 10 and 11 are being 
studied in an effort to determine the fate of some of these nuclei and 
the earlier history of the germ cells. 
May 1st, 1912/ 
*See H. F. Ziegler’s Lehrbuch der vergleichenden Entwickelungegeschichte der niederen Wirbeltiere. 
Jena, 1902. Verlag von Gustav Fischer. Pages 172-17S. 
