102 EVENINGS AT THE MICROSCOPE 



are produced by the emission of air from the lungs vari- 

 ously modified by the organs of the mouth. But no insect 

 breathes through its mouth; no air is expelled thence in a 

 single species; it is a biting, or piercing, or sucking organ; 

 an" organ for the taking of food, or an organ for offence or 

 defence; but never an organ of sound. 



The wings are in most cases the immediate causes of 

 insect sounds. On this subject you will read with pleas- 

 ure some very interesting remarks by the learned Mr. 

 Kir by, inquiring, "by what means these sounds are pro- 

 duced." 



"Ordinarily, except perhaps in the case of the gnat, 

 they seem perfectly independent of the will of the animal; 

 and, in almost every instance, the sole instruments that 

 cause the noise of flying insects are their wings, or some 

 parts near to them, which, by their friction against the 

 trunk, occasion a vibration as the fingers upon the strings 

 of a guitar yielding a sound more or less acute in propor- 

 tion to the rapidity of their flight, the action of the air 

 perhaps upon these organs giving it some modifications. 

 Whether, in the beetles that fly with noise, the elytra [or 

 wing sheaths] contribute more or less to produce it, seems 

 not to have been clearly ascertained; yet since they fly 

 with force as well as velocity, the action of the 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, be- 

 cause their wings are then expanded; but though to us 

 flies seem to sail through the air without moving these 

 organs, yet they are doubtless all the while in motion, 

 though too rapid for the eye to perceive it. When the 

 aphidivorous flies are hovering, the vertical play of their 



