26 THE VARIATION AND CORRELATIONS OF 



The organs of the short- winged group are more variable and slightly 

 less correlated than those of the long-winged group. Undoubtedly, 

 short-wingedness is the newer condition and a degeneration. The 

 greater variability and lesser correlation may be connected with this 

 fact, but can not be explained by it. The two groups are, within 

 themselves, built upon much the same structural plan, as shown by the 

 regression lines. 



Wing-length, both with regard to the relative abundance of the 

 dimorphs and the length of the wing of one of them, seems to be influ- 

 enced by climatic differences; but the climatic influences are often 

 weaker than local environmental factors. 



A study of the variation and correlations of the genus as a whole 

 indicates that local populations are selected samples of it, having differ- 

 ent constants but following the same laws of relative variability and 

 correlation of organs. 



"Species" within this genus is a question of fluctuating variability, 

 and only in one organ, conspicuous but relatively unimportant, do we 

 find a clear case of mutation. 



