Evolution and Taxonomy 



87 



This fold, or frenulum hook, is so well known that it is un- 

 necessary to enter upon a detailed discussion of it. I will, 

 therefore, merely record a few observations that I have made 

 upon it. In all families in which I have observed it, it arises 

 trom the membrane of the wing near the base of cell I (Fig. 

 22), except that in 

 Castnia it seems to 

 have been pulled 

 back so that it arises 

 from the subcostal 

 vein. The unifor- 

 mity in the position 

 of the fre n ulum 

 hook indicates that 

 it was developed be- 

 fore those families 

 in which it exists 

 had become separ- 

 ated phylogenetic- 

 ally. For if it had 

 been independently 

 developed in the 

 different families 

 there would proba- 

 bly have been a lack 

 of uniformity in its 

 position. 



Some light is 

 thrown upon the 



probable origin of the frenulum hook by the fact that in many 

 females there is a tuft of curved scales projecting back from 

 the base of cell I, and serving to hold the frenulum in place. 

 In many moths there is also a tuft of scales projecting forward 

 from the base of cell VII, which functions in a similar way. 



In certain families of moths (Saturniina, Lasiocampidse, and 

 Drepanidae) and in all butterflies there is neither a frenu- 

 lum nor a jugum. But in other respects the wing characters 

 of these moths and of butterflies agree quite closely with those 



Fig. 31. — Perophora. 



