HEREDITY. 457 



"The experiments of Driesch, Wilson, and Hert- 

 wig upon the early stages of developing ova show that 

 heteromorphosis begins with the very earliest divisions 

 of the egg. Thus Driesch, working upon echinoderm 

 embryos, was able to flatten out the stage where there 

 was a sphere of sixteen cells into a flat plate where all 

 the cells were in the same plane. In such a plate, the 

 nuclei of the cells occupied relative positions very dif- 

 ferent from the normal conditions. Yet from these 

 Driesch obtained normal plutei larvae. It was, in fact, 

 as if the cells could be pushed about like billiard balls 

 without destroying the future shape and characters of 

 the embryo. Did each cell contain only the determi- 

 nants that would correspond to the structures that 

 would arise from it under normal conditions then 

 change of its normal position would have arrested de- 

 velopment. Each cell must, on the other hand, have 

 contained the determinants for all the animal, and 

 have allowed those to come into operation that were 

 required by the new positions into which the cells were 

 forced. Driesch, by separating the first two and the 

 first four segmentation-spheres of an Echinus ovum, 

 obtained two or four normal plutei, respectively one- 

 half and a quarter of the normal size. Here again 

 each sphere must have contained all the determinants 

 for the whole organism. Heirs-equal division must 

 have occurred. So, also, in the case of Amphioxus, 

 Wilson obtained a normal, but proportionately dimin- 

 ished, embryo with complete nervous system from a 

 separated sphere of a two or four or eight-celled 

 stage. 



"Hertwig himself, some years ago, published the 

 results of experiments he made upon the development 

 of frogs' eggs under abnormal conditions. He showed 



