136 DEVELOPMENT OF THE FROG'S EGG [Ch. XII 



origin of the differentiation is to be found in the ultimate struct- 

 ure of the cytoplasm of the egg or embryo, although even then 

 we do not know how this mechanism could be started. Whit- 

 man ('95) has stated his conviction that it is erroneous to think 

 of the embryo as only the sum-total of cells interacting upon 

 one another, but that the embryo itself is to be thought of as a 

 whole, which regulates its parts regardless of cell-boundaries. 

 According to this view, each portion of the embryo has its fate 

 sealed, not because the given portion forms a member of the 

 community of cells, but because the whole directs the fate of 

 each special part. Driesch has pointedfout that the egg seems 

 to act like an intelligent being. If so, are the causes of dif- 

 ferentiation and of regeneration the same in kind as physico- 

 chemical causes, or do they belong to the category of intelligent 

 acts, and can these latter be accounted for by the known princi- 

 ples of chemistry and physics ? The plain answer is, we do not 

 know. 



