146 



Heredity and Environment 



owing probably to the peculiarities of the cytoplasm of these cells. 

 These nuclear differentiations are caused by differential divisions 

 of the cytoplasm and not of the nucleus. But while the chromo- 

 somes invariably divide equally, other portions of the nucleus 



A« 



Fig. 47. Cleavage of the Egg of Styela, showing distribution of the 

 yellow protoplasm (stippled) and of the clear and gray protoplasm to 

 the various cells, each of which bears a definite letter and number. 



