208 CLARKE. 



EXPLANATION OF PLATE X. 



(All the figures are mine ) 



FlG. 12. Blastoderm of an egg taken out of an alligator from the dorsal surface. 



FlG. 13. View of another embryo, at the same stage, from the ventral surface. 



Fig. 14. A slightly older embryo, in dorsal view. 



FlG. 15. A ventral view of the embryo shown in Fig. 14. 



FlG. 16. A dorsal view, somewhat more advanced than Fig. 15. It shows the 

 peculiar fold in the head, by which the cephalic end of the neural folds is made. 



FlG. 17. A ventral view of the head end of the embryo shown in the last figure. 



Fig. 18. An embryo from the dorsal side in nearly the same stage as the last 

 embryo, a little older. 



FlG. 19. The same embryo as in Fig. 18, from the ventral surface. 



FlG. 20. This is a dorsal view after the secondary median fuld at the anterior end 

 is broken through. Compare Figs. 16 and 18 with this. 



