452 



HOLMES. 



EXPLANATION OF PLATE XVIII. 



Fig. 13. Apical view of an egg in the 49-cell stage. 



Fig. 14. Lower side of same egg, showing the mesoblastic pole cells, yJ/' and 

 M'^, lying partly in the cleavage cavity. 



Figs. 15, 16, and 17. Lateral views of the same egg. 



Fig. 18. Egg of about 54 cells seen from the vegetal pole. The cells of the 

 fourth quartette are seen in process of division. 



Fig. 19. Lateral view of same egg, showing dexiotropic cleavage of 2a'---'. 

 By an error the same figure is repeated in Fig. 20. 



Fig. 21. Apical view of an egg of about 64 cells, showing a division of two 

 of the basal cells of the cross. 



Fig. 22. View of posterior side of the same egg. The portion of the meso- 

 blastic pole cells, ^/' and M'^, exposed at the surface of the egg, has become 

 considerably reduced. 



Fig. 23. Lateral view of an egg of about 80 cells, showing the division of the 

 upper pair of cells of the third quartette in the a quadrant. 



Fig. 24. Vegetal pole of an egg of about the same stage. The mesoblastic 

 pole cells have entirely disappeared from the surface. 



