VARIATION AND HEREDITY 117 



them without analysis is very apt to lead to 

 biological fallacy. Many of the differences 

 may be wrapped up with sex, and these can 

 be readily sifted out from the slumped total. 

 Others may be wrapped up with age, and 

 these can also be analyzed out. Others are 

 due to something unusual in the "nurture" 

 in the wide sense; that is, they are the direct 

 results of peculiarities in surrounding influ- 

 ences and of peculiarities of habit. Such 

 changes in the bodies of plants and animals 

 are extrinsic, not intrinsic, in origin; they are 

 acquired, not inborn. They are technically 

 called "acquired characters," or much more 

 clearly "modifications." They may be de- 

 fined as structural changes in a part of the 

 body, directly induced by peculiarities of use 

 or disuse, or by some change in surroundings 

 and nurture generally, which transcend the 

 limit of organic elasticity and thus persist 

 after the inducing conditions have ceased to 

 operate. No convincing evidence of their 

 transmission has as yet been forthcoming. 



Now the point is that when we subtract 

 from the total of observed differences all 

 that can be regarded as individual modi- 

 fications, we have a very interesting remain- 

 der, which we thus define off as inborn or 

 germinal variations. They are intrinsic, not 

 extrinsic; inborn, not made. We cannot 



