xx THE INFLUENCE OF ENVIRONMENT 399 



an over-populated community of weaklings ? Organism, 

 function, and environment must evolve together. 



3. The Transmissibility of Acquired Characters or 

 Somatic Modifications. When animals of the same kind 

 are carefully compared they usually show individual 

 peculiarities, which may be conveniently called ' the 

 observed differences." When we begin to sift out these 

 " observed differences ' we find that some may be due 

 to differences of age and sex, and thcs? can be kept by 



FIG. 124. HALF-LOP RABBIT, AN ABNORMAL VARIATION, WHICH BY 

 ARTIFICIAL SELECTION HAS BECOME CONSTANT IN A BREED. 



(From Darwin.) 



themselves. Others are the direct results of peculiarities 

 in the individual's surroundings, nutrition, and habits, 

 and these are called " modifications," or " somatic modifi- 

 cations," or " acquired characters." They may be 

 defined as structural changes in the body of the organism 

 directly induced in the individual lifetime by peculiarities 

 in function or environment, ichich transcend the limit of 

 organic elasticity and thus persist after the inducing con- 

 ditions have ceased to operate. Now, when we subtract 

 from the total of observed differences between members 



