104 EVENINGS AT THE MICEOSCOPE. 



and liiglier) he conceived tliat tlie spiracles lying be- 

 tween tlie ineso- and meta-tliorax must be the instrn- 

 ments of the sonnd ; which, accordingly, he fonnd to 

 cease entirely when they were stopped with gum, 

 thongh while the wings w^ere in vibration. Pursuing 

 his researches, he extracted one of these spiracles, and 

 opening it carefully, found its posterior and inner lip, 

 which is directed towards the commencement of the 

 trachea^ to be expanded into a small, flat, crescent- 

 shaped plate, upon which are nine parallel, very deli- 

 cate, horny laminae, the central one being the largest, 

 while those on each side become gradually smaller and 

 lower ; so it is, he is persuaded, in consequence of the 

 air being forcibly driven out of the trachea and touch- 

 ing these laminae that they are made to vibrate and 

 sound, precisely in the same way with the glottis of the 

 larynx. Dr. Burmeister (who remarks that Chabrier, 

 in his Essai siir le Vol des Insectes., p. 45, &c., has also 

 explained the hum of insects as produced by the air 

 streaming from the thorax during flight, and also speaks 

 of laminae which lie at the aperture of the spiracles), in 

 order to be certain that the laminse in question in the 

 posterior spiracles of the thorax are alone concerned in 

 producing sound, also inspected the anterior ones, but 

 without finding in them any trace of these lamina?. 

 lie explains the weaker and sharper tones ])roduced 

 when the wings, all but the very roots, are cut oft", as 

 resulting from the weaker vibrations of the contracting 

 muscles, and consequently less forcible expulsion of the 

 air when the vibratory organs are removed ; and he 

 thinks with Chabrier that some air may escape through 

 the open tracheae of the wings which are cut off. 



