1 SEGMENTATION 15 



underlying, unsegmented, yolk (Fig. 9, C) and in surface view the 

 blastoderm assumes the appearance shown in Fig 8, D. 



Up to and including the seventh division mitosis takes place 







#72.. 



•"V«°*i*^''»i'-' ^s^ i \'Si''.'' ,s °* 



Fig. 9. —Vertical sections through Elasmobraneh blastoderms illustrating the process of 

 segmentation. (After Ruckert, 1899.) 



A, C, D, E, Torpedo ; B, Scyllmm ; F, G, Pristiurus. E, F, and G are sagittal sections with posterior 

 edge of blastoderm to the right. 



practically synchronously throughout the blastoderm. In Torpedo 

 Eiickert (1899) found that even in the ninth division the majority 

 of the nuclei still divided synchronously and that in some eggs the 

 same was the case with the tenth division but in any case approxi- 



y 



