2l8 



Heredity and Environment 



olm'ch. 



Fig. 79. Posterior Half -embryos of Styela, the anterior cells having 

 heen killed in the 4-cell stage. Muscle cells and intestinal cells are present 

 hut no portion of neural plate or chorda. 



bodies, and similarly there are cases in which part of an egg 

 cannot give rise to a whole animal. The evidence available at 

 present favors the view that in cases where one of the cleavage 



