1919] Braun: Wing Structure of Lepidopter a 359 



that it can still act by clasping the anterior tuberosity of the 

 hind wing. The course of modification of shape in the posterior 

 lobe of the fore wing in Nepticulidae from a fibula in females of 

 the more generalized genera can be traced through various 

 changes until it becomes merely a narrow lobe whose free margin 

 is continuous with the inner margin of the wing. Thus we find 

 that while in the females of earlier genera the fibula has pre- 

 served its original structure and is apparently functional, 

 in the males of these genera the posterior lobe is rather promi- 

 nent but lacks the characteristic shape of the fibula as found in 

 the Trichoptera and Micropterygidse. In Nepticula the posterior 

 lobe has lost all resemblance to the fibula; it is extremely 

 narrowed and the axillary furrow is so indistinct as scarcely 

 to separate it from the rest of the wing. This process, whose 

 steps can be observed in this lepidopterous family, would seem 

 to indicate the possibility that a similar process might have 

 taken place in families of the Frenatae, or in other words, that 

 the Frenatae have been evolved from ancestral forms in which 

 a well developed fibula was present. There is some evidence 

 to support this view. In Prodoxiis the posterior lobe of the fore 

 wing is more than usually prominent and is separated from the 

 rest of the wing by a very distinct axillary furrow; it shows a 

 strong tendency to fold under, thus seemingly retaining some 

 of the function of the fibula, although it has lost its characteristic 

 shape. In some Tineidae, the posterior lobe of the fore wing 

 bears some resemblance to a fibula, but it is not of a structure 

 to be functional. In others of the Frenatae where it can be 

 distinguished, it is merely a narrow lobe -whose free margin is 

 continuous with the inner margin of the wing. 



In the Hepialidae the jugum, though homologous with the 

 fibula, differs from it in shape and method of functioning. 

 The difficulty in the way of deriving the Hepialidae from 

 ancestors with a fibula disappears if a process similar to that 

 which is known to take place in the Nepticulidae is postulated. 

 The jugum, in accordance with this view, would be considered 

 a development in another direction from the posterior lobe of 

 the fore wing in a more or less reduced condition. 



The fact that a fibula of identical structure, though showing 

 some variation in function, is present in three different groups, 

 two of which, the Micropterygidas and Rhyacophilidae, are 

 primitive and approach one another closely in other char- 



