DARWIN, NAEGELI AND DE VRIES 133 



nates as "mutations" and upon which he bases his 

 new theory. They result not merely from a quantita- 

 tive but from a qualitative modification of the pan- 

 genes. It may happen that at a certain time a pan- 

 gene is divided up into two slightly dissimilar halves or 

 dissimilar daughter-pangenes which, when multiply- 

 ing, will determine a new character. 



We could raise against De Vries' theory the very 

 objection raised against the theories which preceded 

 his and ask what determines the attraction certain cells 

 exert on the Darwinian gemmules, what excites Nae- 

 geli's micellar strands, what drives De Vries' pan- 

 genes out of the nuclei? Thus far the question has 

 not been satisfactorily answered. 



