KOISfcS 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 a . 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 (pessellum) b , the object 

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

 being too much elevated. When an operculum is re- 

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

 hollow cavity, with a mouth somewhat linear, which 

 seems to open into the interior of the abdomen c : 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 obliquely with a 

 beautiful membrane, which is very 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 it d . 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 6 . Between 

 the plate and the after-breast (postpectus) another mem- 

 brane, folded transversely, fills an oblique, oblong, or 

 semi-lunar cavity f . 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 



a PLATE VIII. FIG. 18. c. f. Reaum. v. t. xvi./. 5. u u. 



b PLATE VIII. FIG. 18. q'". Reaum. ubi supra, t. xvi./. 11. b. 

 Reaum. ibid./. 3. / /. d Ibid, ubi supra,/. 3. m m. 



e Ibid. q. q. c. f Ibid. n. n, 



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