INSECTS : WINGS AND THEIR APPENDAGES. 91 



they are produced by the ebiission of air from the breath- 

 ing organs, yet not by means of the mouth. One of the 

 most eminent of continental entomologists, Dr. Burmeister, 

 tells us so. Finding that the buzz of a large fly {Eristalis 

 tenax) still continued after the winglets, the poisers, and 

 even the wings, had been quite cut off except their stumps 

 (only in this last case the sound was somewhat weaker 

 and higher), he conceived that the spiracles, or breathing 

 holes, lying between the meso and meta-ihorax must be the 

 instruments of the sound ; which, accordingly, he found to 

 cease entirely when they were stopped with gum, though 

 while the wings were in vibration. Pursuing his researches, 

 he extracted one of these spiracles, and opening it care- 

 fully, 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 delicate, horny laminae, the central one 

 being the largest, while those on each side become grad- 

 ually smaller and lower ; so it is, he is persuaded, in con- 

 sequence of the air being forcibly driven out of the trachea 

 and touching these laminae that they are made to vibrate 

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

 the larynx. Dr. Burmeister (who remarks that Chabrier, 

 in his Essai sur 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 

 laminas which lie at the aperture of the spiracles), in order 

 to be certain that the laminae in question in the posterior 

 spiracles of the thorax are alone concerned in producing 

 sound, also inspected the anterior ones, but without find- 

 ing in them any trace of these laminae. He explains, the 

 weaker and sharper tones produced when the wings, all 

 but the very roots,, are cut off, 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 



