MUTATION 161 



only so far as that doctrine applies. As even the 

 most extreme neo-Darwinian school recognizes 

 such units with their representatives (determin- 

 ants of Weismann) in the egg, and as in evolu- 

 tion there must be the acquisition or loss of at 

 least some one character, it might be expected 

 that the idea of mutation as defined above would 

 find universal acceptance. But it has not done 

 so. The difference of opinion relates to the gra- 

 dient of the transition by which a new unit char- 

 acter is introduced or an old one disappears. 

 Mutation in De Vries' sense implies the sudden 

 appearance, complete in the first generation, of 

 the new unit character and its germinal repre- 

 sentative, the pangene or determinant. Muta- 

 tion is regarded by many who call themselves 

 Darwinians as an innovation and as opposed to 

 Darwin's fundamental assumptions. For the 

 neo-Darwinian conceives the determinant as 

 gradually changing in evolution and exhibiting 

 in the adult forms of successive generations the 

 same continuous series that an organ shows in its 

 ontogenetic development. The view of neo- 

 Darwinians is well indicated in the following 

 quotation from Weismann ^ : — 



" If I mistake not we may say at least so much that 

 all variations are, in ultimate instances, quantitative, and 

 that they depend on the increase or decrease of the vital 

 particles, or their constituents, the molecules. . . . 

 What appears to us a qualitative variation is, in reality, 

 nothing more than a greater or less, a different mingling 

 of the constituents which make up a higher unit, an 

 ' The Evolution Theory, Vol. II, p. ISl. 



