410 ORIGINATIVE FACTORS IN EVOLUTION: 



due to peculiarities in environment, nutrition, and function, 

 which transcend the limits of organic elasticity and persist 

 after the inducing causes have ceased to operate. As there 

 is not at present any convincing proof of the transmissibility 

 of these somatic modifications, either as such, or in any 

 representative degree, they must be left out, in the first 

 instance, in our inquiry into the origin of the distinctively 

 new. They may be of great import for the individual, a 

 life-saving veneer, but if they are not transmitted they can- 

 not be of more than indirect importance to the race. 

 It does not follow, however, that a changeful environment 

 may not be an originative factor in evolution. 



When we subtract from the total of observed differences 

 those that can be shown to be modifications, when we also 

 eliminate the peculiarities associated with differences of age 

 and sex, the remainder are for the most part (in proportion 

 to the success of our subtraction) what are called variations 

 inborn not acquired, intrinsic not extrinsic, blastogenic 

 not somatogenic, endogenous not exogenous, arising from the 

 constitution of the germ-cell not impressed from without, 

 expressions not indents. Some of them at least aro very 

 transmissible, and it may be said that these constitute the 

 raw materials of evolution. 



3. Discontinuous Variations (or Mutations} and 

 Continuous Variations (or Fluctuations}. 



The next step is to inquire whether all the inborn varia- 

 tions are on the same platform, and here we may go back 

 to Darwin's distinction between (a) " single variations " 

 and (b) " individual variations ", though the terms are not 

 felicitous. (a) By " single variations " Darwin meant 

 sports, abrupt changes, sometimes of notable amount, such 



