330 



THE WINGS OF LEPIDOPTERA 



merely a cubito-anal fold. The second anal vein is apparently simple; 

 but in an adult wing before me it contains two tracheae, one of which 

 extends into the cross-vein between this vein and vein Cu + ist A. This 

 may indicate that the second anal vein was formerly forked and that the 

 cross- vein is a portion of one of the forks. The third anal vein is forked; 

 the second branch of it supports the jugum, as already described. 



The posterior tuberosity of the fore wing is divided by the second anal 

 vein; the elevated portions of this tuberosity are between veins; this is an 

 unusual condition. 



The venation of the hind wings (Fig. 334) resembles very closely that of 

 the fore wings except for some differences at the base of the wing. The 

 vein which appears to be homologous with the posterior arculus but which 

 may be the base of vein M., extends transversely, instead of longitudinally as 

 it does in the fore wing; veins Cu and ist A do not coalesce at the base; 

 the third anal vein is forked as in the fore wing, but as there is no axillary 

 excision the second branch of this vein is not in a detached portion of the 

 wing. 



(/) THE WINGS OF THE FRENAT^ 



In the Frenatae the two wings of each side are united by an organ, which 



is termed the frenulum., or by a substitute for this organ, the greatly 



expanded humeral angle of the 

 hind wing ; the fore and hind wings 

 differ greatly in venation, due to a 

 reduction of the radius of the hind 

 wings ; the media of both fore and 

 hind wings is reduced to a three- 

 branched condition; and the base 

 of the first anal vein does not coal- 

 esce with the cubitus. 



The frenulum and the frenulum 

 hook. — The frciiulitni (Fig. ^,^8, f) 

 is a strong spine-like organ or a 

 bunch of bristles borne by the hind 

 wing at the humeral angle, and 

 which projects beneath the fore 

 wing. In the males of certain 

 moths, where the frenulum is highly 

 developed, there is a membranous 

 fold on the fore wings for receiving 



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



together; this is the frenulum-hook (Fig. 338, / h). 



Except in the Microlepidoptera the frenultun of the male consists of a 



single strong spine-like organ ; and that of the female, of two or more bristles. 



Fig. 338.— Wings of Thyridopteryx; f, 

 frenulum; f h, frenulum hook. 



