EXPLANATION OF PLATE IL 



Fig. 7. Section through a germinal disc of the same age as that 

 represented in fig. 4. ?l nucleus; nx. modified nucleus; nx'. modi- 

 fied nucleus of the yolk; /. furrow appearing in the yolk around the 

 germinal disc. 



Figs, la, lb, 7c. Three segments -^Nith modified nuclei from the same 

 germinal disc. 



Fig. 8. Section through a somewhat older germinal disc. ep. epiblast ; 

 71 '. nuclei of the yolk. 



Figs. Sa, 8 b, 8 c. Modified nuclei from the yolk from the same ger- 

 minal disc. 



Fig. 8 d. Segment in the act of division from the same germinal 

 disc. 



Fig. 9. Section through a germinal disc in which the segmentation is 

 completed. It shows the larger collection of cells at the embryonic end of 

 the germinal disc than at the non-embryonic. ep. epiblast. 



