THE INFLUENCES OF NURTURE 95 



butterflies ; others are able to adjust their coloration 

 or that of their pupae to the brown, green, or gold colour 

 of the box in which they are kept. 



Definition. — Such, then, are the changes which are 

 called " bodily modifications " or " individually ac- 

 quired characters." It is advisable to drop the tech- 

 nical term " acquired characters " altogether, for it 

 always gives rise to misunderstanding. It is not open 

 to the argumentative to re-define " acquired characters " 

 or " somatic modifications " to suit their convenience 

 or convictions. The term has been historically defined 

 in the course of prolonged discussion. 



Modifications may be defined as structural changes 

 in the body of the organism, directly induced in the 

 individual lifetime by peculiarities in function, nutri- 

 tion, or environment, which transcend the limits of 

 organic elasticity and thus persist after the inducing 

 conditions have ceased to operate. More briefly, modi- 

 fications are persistent, individually acquired, direct 

 results of peculiarities of nurture. Modifications, being 

 wrought upon the creature from without, are to be con- 

 trasted with variations or mutations which arise from 

 within ; they are impressions in contrast to expressions ; 

 they are exogenous or extrinsic. In a word, they are 

 dints, not outcomes. 



It may be convenient, though too much should not 

 be made of it, to distinguish among modifications (a) 

 those due to peculiarities of use and disuse, (6) those due 

 to peculiarities of food, and (c) those due to peculiarities 

 in surroundings. Thus there are {a) functional, (6) 



