226 



Heredity and Environment 



FIG. 79. POSTERIOR HALF-EMBRYOS OF Styela, the anterior cells having 

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

 but no portion of neural plate or chorda. 



meaning of these results. On the one hand it has been said that 

 the totipotence of any one of the first four cleavage cells proves 

 that all of these cells are alike and that they have not yet begun 



