Phylctic Parallelism in Met amor f>hic Species. 509 



final cause of the incongruence lies therefore in this 

 case also in the fact that one stage has suffered 

 stronger changes than the other, so that a deeper 

 division of the group has occurred in the former 

 than in the latter. 



The analogous incongruences in single families 

 of the Lepidoptera may have arisen in a similar 

 manner, as has already been more clearly shown 

 above ; only in these cases we are as yet unable 

 to prove in detail that the larval structure has 

 become more strongly changed through special 

 , external conditions of life than that of the 

 imagines. 



In the smallest systematic group varieties, it 

 has been possible to furnish some proof of this. 

 The one-sided change here depends in part upon 

 the direct action of external influences (seasonal 

 dimorphism, climatic variation), and it can be shown 

 that these influences (temperature) acted only on 

 the one stage, and accordingly induced change in 

 this alone whilst the other stage remained un- 

 altered. 



It has now been shown not indeed in every in- 

 dividual case, but for each of the different kinds of 

 incongruence of form-relationship that there is an 

 exact parallelism corresponding throughout with 

 the incongruence in the conditions of life. 

 Wherever the forms diverge more widely in one 



ment of the Hymenoptera into Terebrantia and Acnleata. See 

 also note 5, p. 488. R.M.] 



