BUTTERFLY SOUNDS 95 



of the wing as in those which were naturally cov- 

 ered by the opposite wing. But this peculiarity is 

 not found at all in Ageronia. 



If, however, one will examine the surfaces 

 brought into contact between the two wings in the 

 insects known to produce audible sound, he will 

 note that nearly all the scales on the under surface 

 of the front wing and those on the upper surface 

 of the hind wing next the base, that is, in just 

 those portions of the wing which overlap each 

 other, are much S7naUer and more erect than in 

 any other part of the wing, even than those in the 

 immediate vicinity ; and by experiment can show 

 that when these portions of the wing are rubbed 

 together a rustling noise is produced, while in 

 other butterflies, such as Brenthis, not nearly so 

 much contrast appears. In Ageronia these scales 

 have also a more or less conical shape, as if to 

 intensify the sound produced by their rubbing, but 

 of course one could not imitate by clumsy motion 

 of the hand any possible '*• click" from this source. 



Mr. G. F. Hampson, however, by dissection of 

 Ageronia, has probably discovered the precise 

 instrumentation by which the " click " is effected. 

 At the base of the inner margin of the fore wing 

 he finds a pair of curved horny hooks with enlarged 



