364 Annals Entomological Society of America [Vol. XII, 



of the Trichoptera, the Micropterygidse and certain other of 

 the more primitive famihes of the Lepidoptera, Nepticuhdae, 

 Hepialidas, Incurvariidae, etc., where they are distributed over 

 the entire wing surface, but even in these most plentiful on 

 the underside of the fore wing near the dorsal margin. In many 

 Lyonetiidse, e. g., Hieroxestis, Oinophila, Coptodisca, besides 

 the fixed hairs on the underside near the inner margin, there 

 is a patch in the middle of the fore wing near the base; in 

 Tischeria and Opostega, there are additional scattered fixed hairs 

 on the wing surface. In other groups the fixed hairs are confined 

 to the under side of the fore wing near the base of the dorsal 

 margin, with the rare presence of such hairs on other parts of 

 the wing, e. g., in Tineola. The very fact that the fixed hairs 

 are most numerous in the most primitive groups, tending to 

 become scattered and later confined to definite areas of the 

 wing, and finally persisting only in a limited area on the 

 underside of the fore wing, where they may function to a 

 slight degree in holding the wings together in flight, shows 

 that while taken in connection with other characters, their 

 presence may indicate a comparatively primitive condition of 

 the forms possessing them, the character is not one upon which 

 a taxonomic division can be made. 



III. Summary and Conclusions. 



The discussion of wing structure in Lepidoptera has dealt 

 chiefly with those characters which have been handed down 

 from the common ancestor of both Lepidoptera and Trichoptera, 

 and which have been preserved without modification in the 

 most primitive Lepidoptera, but which have undergone more 

 or less far-reaching modification in all other groups of Lep- 

 idoptera. In m.any instances the steps in the process of modifi- 

 cation have been traced, and it has been possible to identify 

 these characters in their modified form in many of the more 

 primitive groups of frenate Lepidoptera. These changes in 

 structure have sometimes been correlated with changes in 

 function of certain parts of the wing or with the taking over of a 

 particular function by a different organ. 



The conclusion reached from a study of certain features of 

 venation is that the Micropterygidas are not as sharply separated 

 from the rest of the Lepidoptera as might be inferred from a 



