NOISES OF INSECTS. 401 



plates of an irregular form — in some semi-oval, in others 

 triangular, in others again a segment of a circle of greater 

 or less diameter — covering the anterior part of the belly, 

 and fixed to the trunk between the abdomen and the 

 hind legs ^. These are the drum-covers or opercula, 

 from beneath which the sound issues. At the base of 

 the posterior legs, just above each operculum, there is a 

 small pointed triangular process {i^essellum) ^, the object 

 of which, as Reaumur supposes, is to prevent them from 

 being too much elevated. When an operculum is re- 

 moved, beneath it yon will find on the exterior side a 

 hollow cavity, with a mouth somewhat linear, which 

 seems to open into the interior of the abdomen ^ : next 

 to this, on the inner side, is another large cavity of an 

 irregular shape, the bottom of which is divided into three 

 portions; of these the posterior is lined obHquely with a 

 beautiful membrane, wiiich is ver}' tense — in some species 

 semi-opake, and in others transparent — and reflects all 

 the colours of the rainbow. This mirror is not the real 

 organ of sound, but is supposed to modulate if^. The 

 middle portion is occupied by a plate of a horny sub- 

 stance, placed horizontally and forming the bottom of the 

 cavity. On its inner side this plate terminates in a carina 

 or elevated ridge, common to both drums ^. Between 

 the plate and the after-breast [i^oslpectus) another mem- 

 brane, folded transversely, fills an obli(]ue, oblong, or 

 semi-lunar cavity '^. In some species I have seen this 

 membrane in tension — probably the insect can stretch 

 or relax it at its pleasure. But even all this apparatus 



* Plate VIII. Fig. 18. c. f . Rcaum. v. I. xvi./. 5. u u. 



*> Plate VIII, Fig. 18. q'". Reaum. uhi supra, t. xvi./. 11. i. 

 " Reaum. ibid./. 3. / /. '' Ibid, nbi svpi-n,f. 3. m in. 



* Ibid. q. q. c. ' Ibid. 7i. n, 



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