406 NOISES OF INSECTS, 



and reflects all the colours of the rainbow. Tiiis mir- 

 ror 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 

 forming the bottom of the cavity. On its inner side this 

 plate terminates in a carina or elevated ridge, com- 

 mon to both drums'". Between the plate and the after- 

 breast (postpectus) another membrane, folded trans- 

 versely, fills an oblique, oblong, or semi-lunar cavity". 

 In some species I have seen this membrane in tension 

 — ^probably the insect can stretch or relax it at its plea- 

 sure. 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 that side of the back of the abdomen which an- 

 swers to the drums, two bundles of muscles meeting 

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

 site to the point of the mucro of the first ventral seg- 

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

 specimens these bundles of muscles seem to Isave been 

 cylindrical ; but in one I dissected {Tetligonia 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 



* Reaum. iibi supra f. 3. insii. " Ibid, q.q.c. " Ibid. nn. 



" Ibid./. 6. //. ' Ibid./. 9.//. Plate VIH. Fig. 19. bb. 



