NOISES OF INSECTS. 405 



means these little animals are enabled to emit such 

 prodigious sounds. I have lately mentioned to you the 

 drum of certain grasshoppers ; this, however, appears 

 to be an organ of a very simple structure : but since it 

 is essential to the economy of the Cicadae that their 

 inales should so much exceed all other insects in the 

 loudness of their tones, they are furnished with a much 

 more complex, and indeed most wonderful, apparatus, 

 which 1 shall now describe. If you look at the under- 

 side of the body of a male, the first thing that will 

 strike you is a pair of large plates of an irregular form 

 — in some semi-oval, in otliers 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 (pessellutn)^, 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 '^ : next 

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

 irregidar 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 — 



= Plate VIII. Fig. 18. aa. Reaam. v. t. xvi. /. 5. uu. 



" Plate Vlir. Fig. 18. bh. Reaiira. ubi supra t. xvi. /. 11. i. 



' Reaiun. ibid. /. 3. U. 



