304 PTILOTA : INTERNAL ANATOMY. 



amongst naturalists as to the organ of this sense. Without 

 presuming to offer any opinion of my own upon a point on 

 which so many learned physiologists are at variance, I 

 shall [simply notice the production of sounds caused by 

 insects, which has invariably been employed as an argu- 

 ment in favour of the possession of the sense of hearing 

 by these animals, and then allude to the opinions which 

 have been entertained as to its seat. 



Unlike the higher animals, insects possess no distinct vocal 

 apparatus terminating in the mouth. The noises made by 

 insects may be divided into three kinds, according to the 

 mode in which they are produced. In the first, the sound is 

 produced by the mere friction of one part of the external 

 integument against another, whereby, when an insect is dis- 

 turbed, it forcibly rubs one portion of its body against 

 another in its endeavours to escape. In this manner, by 

 the friction of the prothorax against the base of the meso- 

 thorax, or the abdomen against the elytra in beetles, a con- 

 tinuous and rather loud sound is produced. The second 

 kind of sound is produced by numerous flying insects, and 

 which our bard of the Seasons has alluded to in his lines, — 



" Yet not unpleasant is the ceaseless hum. 

 To him who wanders in the woods at noon." 



The mode in which this sound is produced has been endea- 

 voured to be explained in a variety of ways. I have 

 already alluded to these opinions in my account of the 

 Halteres, and shall only add, that the experiments of Bur- 

 meister and others, together with the fact that bees produce 

 as loud a sound as dipterous insects, although unprovided, 

 like the latter, with winglets or halteres, seem satisfactorily 

 to prove that it is owing to the rushing of the air through 

 the thoracic spiracles that the buzzing is produced. The 

 third kind of sound is produced by a distinct modification of 



