BY R. J. TILLYARD. 



635 



turns, and has become far more abundant in families, genera and 

 species. But it is essential that we should see clearly that 

 neither the Lepidoptera nor the Planipennia are of aquatic origin, 

 and neither can possibly be derived from its closely related 

 aquatic Order. The close similarity between the archetypic vena- 

 tions of the Trichoptera and Lepidoptera will be sufficiently 

 obvious from a perusal of the characters already set down, and 

 the archetypic diagrams (Text-figs. 71, 75) . Their differences 

 are perhaps not so obvious; but they are of very great import- 

 ance for the right understanding of the phylogenetic problem, 

 and are set down in the accompanying Table ( Table ii . ) 



TABLE II. 



Table of Differences in the Wing-characters of the Archetypes 

 of the Trichoptera and Lepidoptera. 



With respect to these six differences, the Trichoptera are the 

 more archaic in (4) and (6), and in (2) as regards the forewing 

 only; the Lepidoptera are the more archaic in (1), (3) and (5), 

 and in (2) as regards the hindwing only. Thus the specialisa- 

 tions are fairly equally divided between the two Orders; and 

 it is evident, on more than one count, that neither can be an- 

 cestral to the other. They must have arisen as a dichotomy from 

 a common stem, which combined the archaic characters of both 

 Orders . 



We must now consider a little more fully the venation of the 

 Lepidoptera, in order to show quite clearly how the archetypic 

 characters have been determined . 



