1919] Braitn: Wing Structure of Lepidoptera 361 



these costal spines are functional in females, but in the male, 

 where there is a single spined frenulum, they are rarely preserved 

 with the same structure and function. In Nepticulidas when 

 functional, they are larger and stronger than in any other 

 Lepidoptera (except perhaps Opostega) ; they are decidedly 

 stronger than in the Micropterygidae. The spines are present 

 in several of the more primitive frenate lepidopterous groups, 

 often in combination with other primitive characters, and some- 

 times persist in more specialized groups. In the females of 

 many groups of Lepidoptera this is the only method of insuring 

 the united action of the fore and hind wings. These spines 

 are present in females in Prodoxidse, Adelidae and Incurvariidae, 

 together with a few weak and useless short spines in the position 

 of the frenulum. Homologous structures much modified and 

 without function of holding may be distinguished in the males 

 in these families, together with a well developed single-spined 

 frenulum. In many genera of Lyonetiidce they persist par- 

 ticularly in the female where there is also a functional frenulum, 

 and they may also be distinguished as definite structures in the 

 male, different from the rest of the scale covering of the wing. 

 It is questionable whether they are functional except in rare 

 instances in this family. 



The possession of the row of costal spines by many of the 

 Trichoptera and by more primitive Lepidoptera indicates that 

 it is a persistent primitive character, and as such indicates 

 common descent of the two groups. The preservation of these 

 spines in many frenate Lepidoptera is one of the few connecting 

 links between them and the Micropterygidae. 



The series of costal hooks — the hamuli — which have 

 developed in the more specialized families of Trichoptera as a 

 means of locking the fore and hind wing together, is a specializa- 

 tion not found in the Lepidoptera. 



The true frenulum spines are situated on the costal sclerite 

 of the hind wing. Although structures homologous with a 

 frenulum, consisting of several stiff spines on the costal sclerite 

 of the hind wing are found in some of the more specialized 

 Trichoptera, the frenulum in its specialized form, culminating 

 in the single-spined frenulum with the well developed frenulum 

 hook of the male, is a distinctly lepidopterous development. 

 In most Trichoptera, in Micropterygidae, in females of Nepti- 

 culidae, in females of Prodoxus, Adela, etc. (Figs. 1, 2, 5, 4a, 8), 



