NOISES OF INSECTS. 3S1 



to produce it, seems not to have been clearly ascer- 

 tained : yet, since they fly with force as well as velo- 

 city, the action of tlie air may cause some motion in 

 them, enough to occasion friction. With respect to 

 Diptera, Latreille contends that the noise of flies on 

 the wing cannot be the result of friction, because their 

 wings are then expanded ; but though to us flies seem 

 to sail through the air without moving tliese organs, 

 yet they are doubtless all the while in motion, though 

 too rapid for the eye to perceive it. When the aphi- 

 divorous flies are hovering, the vertical play of their 

 wings, though very rapid, is easily seen ; but when 

 they fly off" it is no longer visible. Repeated experi- 

 ments have been tried to ascertain the cause of soupd 

 in this tribe, but it should seem with different results. 

 De Geer, whose observations were made upon one of 

 the flies just mentioned, appears to have proved that, 

 in the insect he examined, the sounds were produced 

 by the friction of the root or base of the wings against 

 the sides of the cavity in which they are inserted. To 

 be convinced of this, he affirms, the observer has nothing 

 to do but to hold each wing with the finger and thumb, 

 and stretching them out, taking care not to hurt the 

 animal, in opposite directions, thus to prevent their 

 motion, — and immediately all sound will cease. For 

 further satisfaction he made the following experiment. 

 He first cut off the wings of one of these flies very near 

 the l)ase ; but finding that it still continued to buz as 

 before, he thought that the winglets and poisers, which 

 he remarked were in a constant vibration, might oc- 

 casion the sound. Upon this, cutting both off, he ex- 

 amined the mutilated fly with a microscope, and found 



