86 



John Henry Corns iock 



to contain several parallel cavities. Evidently the frenulum 

 of the male is composed of several bristles as is that of the 

 female, but these bristles are grown together, forming a single 

 strong spine. This can be easily seen by examining a 

 bleached wing that has been mounted in balsam. Usually 

 the cavities in the bristles contain air which renders them 

 easily visible. 



It is obvious, therefore, that the frenulum of the female ex- 

 hibits a more generalized condition than does that of the male. 



In some females the frenulum 

 is so slightly developed that the 

 bristles composing it are little 

 more than hairs. This fact sug- 

 gests that the primitive frenu- 

 lum was developed from a bunch 

 of hairs, clothing the base of the 

 wing. Such a tuft of hairs pro- 

 jecting under the fore wing 

 would tend in a slight degree 

 to insure the synchronous ac- 

 tion of the two wings ; and as 

 soon as these hairs had assumed 

 this function the tendency of 

 natural selection would be to 

 strengthen them. In the fe- 

 male of Prionoxyshis the frenu- 

 lum consists of a series of bris- 

 tles which vary in size from a 

 short hair to a comparatively 

 This throws much light on the de- 



FiG. 30. 



long spine (Fig. 12, f). 

 velopment of this organ. 



The extent to which the specialization of the frenulum has 

 been carried is remarkable. In the males of some of the Psy- 

 chidae it is a strong spine nearly half as long as the hind wing 

 (Fig. 22). In the Cymatophoridae it is furnished with a knob 

 at the tip. But the most remarkable feature of this speciali- 

 zation is the development of a membranous fold on the fore 

 wings of males for receiving the end of the frenulum, and thus 

 more securely fastening the two wings together. 



