MODIFICATIONS AiYD INBORN VARIATIONS 73 



term " accommodations " for the frequently occurring indi- 

 vidual adjustments which many organisms are able to make 

 to new conditions. 



5. Modifications. — Besides being plastic, organisms are 

 modifiable : that is to say, in the course of their individual life 

 they are liable to be so impressed by changes in surrounding 

 influences and by consequent changes in function that, as a 

 direct result, modifications of bodily structure or habit are 

 acquired. Modifiability is the capacity of registering the 

 direct results of changed function or of changed environment. 

 " Modifications " may be defined as structural changes in the 

 body of an individual organism, directly induced by changes 

 in function or in environment, which transcend the limit of 

 organic elasticity and persist after the inducing conditions 

 have ceased to operate. They are often inconveniently called 

 " acquired characters." They are not proved to be trans- 

 missible as such or in any representative degree, but they are 

 often adaptive and individually very valuable. They are dis- 

 tinguishable from temporary adjustments or accommoda- . 

 tions on the one hand, and from inborn variations on the 

 other. 



6. Inborn Variations. — Finally, when we subtract from a 

 total of " observed differences " between members of the same 

 species all that can be described as accommodations and modi- 

 fications, we find a large remainder which we must sharply 

 define off as variations. We cannot causally relate them to 

 peculiarities in habit or in surroundings ; they are often distinct 

 at birth or hinted at before birth; and they are rarely alike 

 even among forms whose conditions of life seem absolutely 

 uniform. They may be large or small in amount, fluctuations 

 or freaks, progressive or retrogressive — that is a matter for 

 further analysis — but they agree in having a germinal origin. 

 They are endogenous, not exogenous ; they are born, not made ; 

 and they are more or less transmissible, though they are not 



