NOISES OF INSECTS. 



327 



increased in the ratio of his size, could be heard all over the 

 world. So that Stentor himself becomes a mute when com- 

 pared with these insects. 



You feel very curious, doubtless, to know by what means 

 these little animals are enabled to emit such prodigious sounds. 

 I have lately mentioned to you the drum of certain grass- 

 hoppers: this, however, appears to be an organ of a very 

 simple structure ; but since it is essential to the economy of 

 the Cicadse that their males 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 I 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 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. 1 These are the drum-covers or opercula, from be- 

 neath which the sound issues. At the base of the posterior 

 legs, just above each operculum, there is a small pointed tri- 

 angular process (pessellum) 2 , the object of which, as Reaumur 

 supposes, is to prevent them from being too much elevated. 

 When an operculum is removed, 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 3 : 

 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-opaque, 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. 4 The middle portion 

 is occupied by a plate of a horny substance, placed horizon- 

 tally, and forming the bottom of the cavity. On its inner 

 side this plate terminates in a carina or elevated ridge, com- 

 mon to both drums. 5 Between the plate and the after-breast 



1 Reaum. v. t. xvi. f. 5. u u. 2 Reaum. ubi supra, t. xvi. f. 11. b. 



3 Reaum. ibid. f. 3.11. 4 Ibid, ubi supra, f. 3. m m. 



5 Ibid. q. q. c. 



Y 4 



