Phyletic Parallelism in Metamorphic Species. 397 



morphological systems are not compatible with 

 the admission of an internal transforming power. 

 That a certain amount of influence is exerted by 

 the environment on the course of the processes of 

 development of the organic world, will however be 

 acceded to by the defenders of the phyletic vital 

 force. It must therefore be demonstrated that 

 deviations from complete congruence occur, which, 

 from their nature or magnitude, are incompatible 

 with the admission of innate powers, and, on the 

 other hand, it must likewise be attempted to show 

 that the departures from this congruence as well 

 as the congruence itself can be explained without 

 admitting a phyletic vital force. 



In the following pages I shall attempt to solve 

 this question for the order Lepidoptera, with the 

 occasional assistance of two other orders of insects. 

 Neither the Echinodermata nor the Hydromedusse 

 are at present adapted to such a critical examin- 

 ation ; the number of species in these groups 

 of which the development has been established 

 with certainty is still too small, and their biological 

 conditions are still to a great extent unknown. 

 In both these respects they are far surpassed by 

 the Lepidoptera. In this group we know a large 

 number of species in the two chief stages of their 

 development and likewise more or less exactly the 

 conditions under which they exist during each of 

 these phases. We are thus able to judge, at least 

 to a certain extent, what changes in the conditions 



