FACTS AND FACTORS OF DEVELOPMENT 29 

 A 



B f pb 



Fig. 11. Four Stages in the Cleavage of the Egg of the 

 Sheep; pb, polar bodies. (After Assheton.) 



successive generations of cells continually 

 grow smaller (Figs. 6, 11). This process 

 is known as the cleavage of the egg, and 

 by it the egg is not only split up into a con- 

 siderable number of small cells, but a much 



