INSECTS : WINGS AND THEIR APPENDAGES. 89 



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 modu- 

 late it. The middle portion is occupied by a plate of 

 a horny substance, 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 (post- 

 ])ectus) another membrane, folded transversely, fills an 

 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 remains 

 to be described. This organ can only be discovered by 

 dissection. A portion of the first and second segments 

 being removed from the side of the back of the abdomen 

 which answers to the drums, two bundles of muscles meet- 

 ing each other in an acute angle, attached to a place oppo- 

 site to the point of the macro of the first ventral segment 

 of the abdomen will appear. In Reaumur's specimens, 

 these bundles of muscles seem to have been cylindrical ; 

 but in one I dissected {Cicada Capensis) they were 

 tubiform, the end to which the true drum is attached 

 being dilated. These bundles consist of a prodigious 

 number of muscular fibres applied to each other, but 

 easily separable. Whilst Reaumur was examining one of 

 these, pulling it from its place with a pin, he let it go 

 again, and immediately, though the animal had been 

 long dead, the usual sound was emitted. On each side 

 of the drum-cavities, when the opercula are removed, 

 another cavity of a lunulate shape, opening into the 

 interior of the abdomen, is observable. In this is the 



