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1919] Brdiin: Wing Structure of Lepid^^a 351 



division, even though an apparently wider gap may exist 

 somewhere between two divisions of a group, due to incomplete 

 preservation of connecting forms or insufficient knowledge on 

 our part. 



In the present paper, the relative value of those factors 

 indicating community of descent and relationship of the insects 

 constituting the Trichoptera and Lepidoptera and those indi- 

 cating divergence is considered in its bearing on the question of 

 classification. 



With regard to the taxonomic problem involved, the question 

 is essentially this: Are certain characteristics possessed by 

 the Micropterygidae in common with the Trichoptera of such 

 taxonomic importance as to necessitate the conclusion that the 

 Micropterygidae are trichopterous insects or are these char- 

 acteristics merely retained as a common inheritance, later to 

 undergo far-reaching modifications which can be traced back 

 to the Micropterygidae. 



Certain characters which are possessed in common by the 

 Micropterygidae and Trichoptera and which seem sharply to 

 separate the Micropterygidae from frenate Lepidoptera, will 

 be shown to undergo far-reaching modification and in this 

 modified form to persist in many of the comparatively primitive 

 groups of the frenate Lepidoptera. The fact that the course 

 of such modification can be traced makes it evident that the 

 gap between the Micropterygidae and the remaining Lepidoptera 

 is not as wide as is sometimes supposed. This fact, and the 

 fact that certain acknowledged lepidopterous characters origi- 

 nate in the Micropterygidae, necessitate the conclusion that the 

 Micropterygidae are lepidopterous insects. 



II. Wing Structure. 



The structure of the wings presents the most obvious and 

 available characters for the study of the phylogeny and taxo- 

 nomy of the Lepidoptera and Trichoptera. The following 

 discussion of the structure of wings of Lepidoptera deals with 

 the modification and disappearance of trichopterous characters 

 and with the origin of some distinctively lepidopterous char- 

 acters. The data are presented under (a) venation, (b) mode 

 of insuring synchronous action of fore and hind wings, (c) 

 distribution of fixed hairs. 



