HEARING IN INSECTS. 91 



Wasp fly (Chrysotoxum fasciolatum). 



was continued when we held the insect by the feet ; 

 but, on placing a slip of card loosely over the wings, 

 it became so muffled as to be almost imperceptible, 

 and, on laying hold of the wings, it ceased altogether. 

 From all we could observe respecting this sound, it 

 appeared that it could not be referred simply to any 

 muscular movement, but must have arisen either from 

 air playing on the membranous edges of the wings 

 at their origin, as in the case of an Eolian harp-string, 

 or by the stroke or friction of some internal organ 

 upon the roots of the nervures*. 



Latreille seems to have overlooked the vibrating 

 tremor to which we have alluded, when he contends 

 that the noise of flies on the wing cannot be the result 

 of friction, because the wings are then expanded f. 

 But, even if the tremor were invisible to the eye, we 

 should not be authorized to conclude that it was not 

 produced ; for the ingenious experiments devised 

 by Dr. Chladni, of Berlin, and recently extended by 

 M. Savart, distinctly exhibit the existence of vibra- 

 tions in metallic plates when their edges are played 

 upon by a violin bow, in the curious forms into which 

 sand spread on the plates arranges itself; though 

 otherwise these vibrations are for the most part im- 

 perceptible. We may also refer to Dr. Wollaston's 

 * J. R. f Hist, Gener, des Insectes. 



