EXPLANATION OF PLATE L 



Fig. 1. Section through the germinal disc of a ripe ovarian ovum of 

 the Skate. gv. germinal vesicle. 



Fig. 2. Surface-view of a germinal disc with two furrows. 



Figs. 3, 4, 5. Surface-views of three germinal discs in diflferent stages 

 of segmentation. 



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 segmenta- 

 tion furrows. 



Figs. 6 a and 6 &. Two furrows of the same germinal disc more highly 

 magnified. 



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



