LEPIDOPTERA 



597 



great extent. This overlapping of the two wings insures their syn- 

 chronous action ; and the frenulum, being no longer needed for this 

 purpose, is lost. Illustra- 

 tions of different stages in 

 the reduction and loss of 

 the frenulum are given in 

 the discussions of family 

 characters given later. 



As a rule the frenulum 

 of the female, when present, 

 consists of several bristles, 

 while that of the male con- 

 sists of a single strong, 

 spine-like organ. If one of 

 the bristles of the compound 

 frenukmi of a female be ex- 

 amined, it will be found to 

 be a typical seta, containing 

 a single cavity. But if a 

 frenulum of a male be ex- 

 amined, it will be found to 

 contain several parallel cav- 

 ities. Evidently the fren- 

 ulimi of the male is com- 

 posed of several setae, as is 

 that of the female, but 

 these setae are grown together, 



Fig. 723.- 

 hook. 



id A 



-Wings of a moth: f h, frenulum- 



This can be seen by examining a 

 bleached wing that has been mounted in balsam; usually the cavities 

 in the sette contain air, which renders them visible. 



The frenukmi-hook, which is present in the males of certain moths, 

 is a membranous fold on the lower surface of the fore wing for receiv- 

 ing the end of the frenulum, and thus more securely fastening the two 

 wings together (Fig. 723, / A). As a rule the frenulum-hook arises 

 from the membrane of the wing near the base of cell C; but in some 

 moths (Castnia) it seems to have been pulled back so that it arises 

 from the subcostal vein. 



THE GENERALIZED FRENAT^ 



Under this heading are grouped those families of moths that are 

 supposed to retain more nearly than any other Frenatte the form of 

 the primitive Frenatse, those that were "the first to appear on earth. 

 In most of the families included here, the wings approach the typical 

 form, except in the reduction of the nimiber of branches of radius of 

 the hind wings, which is true of all Frenatae ; usually the base of media 

 of one or both pairs of wings is preserved throughout a considerable 

 part, at least, of the discal cell; and the anal veins are well preserved, 

 there being two or three in the fore wing and three in the hind wing. 

 The frenulum is usually well preserved. 



