460 The American Naturalist. [June, 



I mention these vestiges of some of the first steps in crea- 

 tion to illustrate the extraordinary conservative power of her- 

 edity (which is even more forcibly seen in our embryological 

 development), partly also to show how widely our organs 

 differ in age. Galton has compared the human frame to a new 

 building built up of fragments of old ones ; extend this back 

 into the ages and the comparison is complete. 



Development, Balance, Degeneration. — It is probable that 

 none of our organs are absolutely static and that the apparent 

 halt in the development of some is merely relative, as where 

 a fast train passes a slow one. The numerous cases of arrested 

 evolution in nature are always connected with fixity of envir- 

 onment, an exceptional condition with man, and we have 

 ample evidence that some organs are changing more rapidly 

 than others. 



Adaptation to our changing circumstances is mainly effected 

 by the simultaneous development and degeneration of organs 

 which lie side by side, as in the muscles of the foot or hand ; 

 in terms of physiology, we observe the hypertrophy of adapt- 

 ive organs and atrophy of inadaptive or useless organs. This 

 compensating readjustment, whereby the sum of nutrition to 

 any region remains the same during redistribution to its parts, 

 may be called metatrophism. It is the gerrymander principle 

 in nature. 



In practical investigation it is very difficult in many cases 

 to determine whether an organ is actually developing or degen- 

 erating at the present time ; although its variability or ten- 

 dency to present individual anomalies indicates that some 

 change is in progress. I may instance the highly variable 

 peroneus tertius muscle (Wood). The rise or fall of organs is 

 so constantly associated with their degree of utility that in 

 each case the doubt can be removed by a careful analysis of 

 the greater or less actual service rendered by the part in ques- 

 tion. Apart from the question of causation it is a fixed prin- 

 ciple that a part degenerating by disuse in each individual 

 will also be found degenerating in the race. 



