330 



A. W. BELLAMY. 



Cleavage begins first and proceeds more rapidly in the pig- 

 mented hemisphere than in the vegetative hemisphere, establish- 

 ing early in development an inequality in the size of the cells in 

 the two hemispheres. In an early cleavage stage, the size rela- 



FIG. 9. Diagram to illustrate the gastrular angle, g.a 



tion of the cells in the two regions is in the proportion of 4/10 

 to 5/10, a ratio that decreases in value up to about the time of 

 gastrulation, when the ratio may be represented by 2.5/10 to 

 3.5/10. During mid-cleavage stages the cell size ratio is approxi- 

 mately 3.5/10 to 4/10. This does not take into account those 



FIG. 10. A, control egg with a cleavage ratio of approximately 3.5/10-4/10. 

 B, egg from the same batch as the one in Fig. 10, A, in which the cleavage ratio 

 approximates 10/10. Same treatment as egg illustrated in Fig. 7. (Experiment 

 KNC B 3.) 



pigmented cells on the grey crescent side of the egg, which are 

 slightly smaller from the beginning of cleavage than the other 

 pigmented cells (Morgan and Boring, 1903). Immediately pre- 

 ceding the appearance of the blastopore, those cells in the dorsal 

 lip region are smaller than any of the other surface cells. 



