SEGMENTATION. 245 



Fig. 6. Section through the germinal disc represented in fig 3. n. nucleus; x. edge 

 of germinal disc. The engraver has not accurately copied my original drawings in 

 respect to the structure of the segmentation furrows. 



Figs. 6 a and 6l>. Two furrows of the same germinal disc more highly magnified. 



Fig. 6c. A nucleus from the same germinal disc highly magnified. 



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

 fig. 4. n. nucleus; nx. modified nucleus; nx'. modified nucleus of the yolk; f. furrow 

 appearing in the yolk around the germinal disc. 



Figs. 7 a, fl>, 7<r. Three segments with modified nuclei from the same germinal 

 disc. 



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

 of yolk. 



Figs. 8 a, 8t>, Sc. Modified nuclei from the yolk from the same germinal 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 shews the larger collection of cells at the embryonic end of the germinal disc than 

 at the non-embryonic, ep. epiblast. 



