SEGMENTATION OF FROG'S EGG. 



IQI 



in the number of superficial cells l as well as of those which are 

 wholly within the egg. At the end of the 64-cell stage there 

 are 64 cells present in the egg, a number, about 12, of which do 

 not appear on the surface. Also the series between the 64- and 

 128-cell cleavage stages show an increase in the number of cells 

 coming to the surface, as well as the number of cells of the in- 



II 



terior, so that there is no cleavage stage between which and the 

 following stage delamination takes place. 



Figs, i, 2, 3 and 4 show sections through the middle of eggs 

 of 28, 53, 64 and 105 cells respectively. A number of cells in 



1 In the cleavage of the frog's egg, the division for the next cleavage stage begins 

 in the cells of the dark pole, while the cells of the light pole are completing the di- 

 vision for the preceeding cleavage stage. 



