470 PHYSIOLOGY. 



Whether the structure and situation of these vibrating bodies be the 

 same in all buzzing insects, I cannot for the present decide. Another 

 work, devoted exclusively to this subject, will impart all the details 

 that I may discover ; but for the present, thus much is determined. 

 Delicate laminae are found at the entrance of the posterior spiracles of 

 the thorax, which are set in vibration by the streaming in and out of 

 air, and which are the cause of the humming noises produced by bees 

 and flies during their flight. In the buzzing-beetles, for instance, the 

 cockchafer, I could not discover such laminae near the aperture of the 

 thoracic spiracles, and in these, therefore, the outward streaming air 

 must be the sole cause of the tone ; physics teach us also that a stream 

 of air made to pass through any aperture with violence will produce a 

 sound. In fact, the tone of the humming-beetles is weaker, pro- 

 portionately, than that of the much smaller Diptera, and we may thence 

 trace the cause of it to the deficiency of the vibratory laminae. 



271. 



The sounds that are produced by peculiar organs solely adapted to the 

 purpose arc found only in two orders, namely, in the Orthoplera and in 

 the Hcmiptera ; in both cases they are in general peculiar to the male 

 sex alone, and the females are then dumb. The male Orlhoplera, in 

 which we observe such organs of sound, bear them always at the base of 

 the superior wings. Among these the genus Acheta and Locnsta 

 possess them. In both it is a round, flat, shining, very thin plate, 

 seated at the base of the wing, immediately behind the large main 

 nervures, which appear to produce the tone. The following is doubt- 

 lessly its mechanism. By means of the violent volatile motions which 

 agitate the whole body, but during which the wings are not expanded, 

 the air is driven out of the spiracles, and especially out of the central 

 ones of the thorax, and thus bounds against the inflected external 

 margin of the superior wing, which is pressed closely to the thorax. 

 It must necessarily, therefore, to find an exit, rise beneath the wing, in 

 order to escape from it beneath the posterior margin. Pursuing this 

 path, it precisely strikes upon the just described elastic field of the 

 superior wing, which vibrates through the pressure of the air, and 

 consequently emits the sound. To corroborate this view 1 have cut off 

 the wings of several locusts, but they never subsequently made any 

 noise. It is here, therefore, the wings or the vibration of the elastic 

 base of the wings^ which produces the sound upon the motion of the 



