OF WASHINGTON, VOLUME XVI, 1914 49 



The classification of these masters has been adopted and further 

 developed by all modern students, and the one paramount char- 

 acter used in this classification is the wing venation. This does 

 not mean that it is the only character used. Every structural 

 difference, especially of the palpi, antennae and legs, is considered, 

 as are the early stages and the biology, but all of these are given 

 less weight than the venation and are now never used except in 

 connection with the venation. 



That this is a sound scientific view is easily understood when it 

 is considered that all of the external characters more or less di- 

 rectly serve some purpose useful to the insect and therefore tend 

 to become modified in response to the requirements of changed 

 conditions in the environment. 



On the other hand, the venation is not influenced in such a 

 direct way and undergoes changes but slowly through long periods 

 of evolution. It might be supposed that the mechanical func- 

 tion of the veins as a support to the wing surface would invite 

 modification of the veins, and such is truly the case to some ex- 

 tent, the tendency in the evolution being a strengthening of the 

 costal area at the expense of the dorsal. But the mechanical 

 support would not be especially benefited by such minute changes 

 in the structure as we find; the entire outline of the wing may be 

 greatly changed without any radical change in the venation. 



At the same time, the venation is so plastic as to mirror in 

 minute modifications any and every step in the evolution of the 

 genera. Given merely the denuded wings of a Microlepidopteron 

 it is possible with certainty to place the species generically. 



It has long been realized that the origin of all Lepidoptera is to 

 be found in the Micropterygidse. These possess several addi- 

 tional veins, which cannot be explained in any other way than as 

 primitive characters, according to the fundamental law that no 

 new organ can be developed except as a modification of an exist- 

 ing character. The survival of a few species of this ancestral 

 group is exceedingly fortunate. Without these we should be with- 

 out the key to the relationship of the entire order, because the 

 higher Lepidoptera are so different from any other group of insects 

 that their relationship hardly could have been established without 

 the connecting link of the Micropterygidse. 



The Micropterygidse are in turn generally conceded to have 

 developed from the caddis-flies; certain of the Trichoptera (the 

 genus Rhyacophila) agree very closely in neuration as well as in 

 other characters with the more generalized Micropterygidse, 

 while no other insect of any order approaches this type. This is 

 correctly taken as conclusive evidence that the Micropterygidu' 

 are derived from, or are at least correlated with the Trichoptera, 



