LEPIDOPTERA. 217 



there exists near the base of the costal margin of the hind 

 wings a strong bristle or bunch of bristles named the frenu- 

 lum, or little bridle (Fig. 237,/). As the frenulum projects 

 forward under the fore wing it tends to depress the hind 

 wing when the fore wing is depressed, thus insuring the act- 

 ing together of the two pairs of wings. Usually the frenulum 

 consists of two or more bristles in females and of a single 

 stronger bristle in males. The difference is due to the fact 



o 



that in males the bunch of bristles have grown together into 

 a single strong bristle. There is also another sexual differ- 

 ence. In the males the tip of the frenulum fits into a mem- 

 branous hook borne on the lower surface of the fore wing, 

 thus firmly tying together the two wings (Fig. 237, f.h). 

 This frenulum hook is rarely found in females. In certain 

 moths there is, besides the frenulum hook, a tuft of hairs 

 projecting forwards from just behind the cubitus of the fore 

 wing near its base, which tends also to keep the frenulum in 

 place. 



With some moths and with all skippers and all butterflies 

 the base of the costal portion of the hind wings, the humeral 

 angle as it is termed, is largely developed, so that it projects 

 far under the fore wing (Fig. 241). This overlapping of the 

 two wings at the base to so great an extent insures their act- 

 ing together without the aid of the frenulum ; and, conse- 

 quently, there being no use for a frenulum, this organ has 

 disappeared. In other words, the frenulum has been super- 

 seded by the large development of the humeral angle. But 

 as we believe that these moths, skippers, and butterflies have 

 descended from forms which had a frenulum, we class them 

 with the moths that still possess this organ under the sub- 

 order Frenatse. 



A more easily observed character which serves to distin- 

 guish members of this suborder is a striking difference in 

 the venation of the two pairs of wings, the hind wings hav- 

 ing fewer veins than the fore wings. 



