﻿250 Darwin, and after Darwin. 



constant characters classed as varietal, although it is 

 well known that they are " blastogenetic." Moreover, 

 we can scarcely doubt that many specific characters 

 which are also hereditary characters owe their exist- 

 ence, not to natural selection, but to the direct action 

 of external causes on the hereditary structure of 

 " germ-plasm " ; while, even apart from this con- 

 sideration, there are at least three distinct and highly 

 general principles of specific change, which are ac- 

 cepted by the great majority of Darwinists, and the 

 only common peculiarity of which is that they pro- 

 duce hereditary changes of specific types without any 

 reference to the principle of utility. 



