IKSECTS : WINGS AJSD THEIR APPENDAGES. 101 



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 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, the object of which, 

 as Eeaumur 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 : next to this, on 

 the inner side, is another large cavity of an irregular 

 shape, the bottom of which is divided into three por- 

 tions ; of these the posterior is lined obliquely with a 

 beautiful membrane, which is very tense — in some 

 species semi-opaqae, and in other transparent — and re- 

 flects all the colours of the rainbow. This mirror is not 

 the real organ of sound, but is supposed to modulate it. 

 The middle portion is occupied by a plate of a horny 

 substance, placed horizontally, and fonning 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 (postpecius) an- 

 other membrane, folded transversely, fills the oblique, 

 oblong, or semilunar 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 is insufficient to produce the sound of these 

 animals ; one still more important and curious yet re- 

 mains to be described. This organ can only be discov- 



