536 NOISES OF INSECTS. 



rior legs, just above each operculum, there is a small pointed triangular 

 process (^pessellumy, the object of which, as Reaumur supposes, is to prevent 

 them from being too much elevated. When an operculum is removed, 

 beneath it you v/ill 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 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 colors 

 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 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 (postjjecius) 

 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 appa- 

 ratus 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 answers 

 to the drums, two bundles of muscles meeting each other in an acute angle, 

 attached to a place opposite 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 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 theopercula 

 are removed, another cavity of a lunulate shape, opening into the interior 

 of the abdomen, is observable.^ In this is the true drum, the principal 

 organ of sound, and its aperture is to the Cicada what our larynx is tons. 

 If these creatures are unable themselves to modulate their sounds, here are 

 parts enough to do it for them : for the mirrors, the membranes, and the 

 central portions, with their cavities, all assist in it. In the cavity last 

 described, if you remove the lateral part of the first dorsal segment of the 

 abdomen, you will discover a semi-opaque and nearly semi-circular concavo- 

 convex membrane with transverse folds : this is the drum.^ Each bundle 

 of muscles, before mentioned, is terminated by a tendinous plate nearly 

 circular, Jfrom which issue several little tendons that, forming a thread, pass 

 through an aperture in the horny piece that supports the drum, and are 

 attached to its under or concave surface. Thus the bundle of muscles being 

 alternately and briskly relaxed and contracted, will by its play draw in and 

 let out the drum : so that its convex surface being thus rendered concave 

 when pulled in, when let out a sound will be produced by the effort to 



1 Reaum. ubi supra, t. xvi. f. 11. b. ' Reantn. ibid. f. 3. II. 



^ Ibid, ubi supra, f. 3. m m. •* Ibid. q. q. c. ^ Reaum. t. xvi. f. 3. n. n. 



« Ibid, ubi supr. f. 6. //. ' Ibid. f. 9. / /. » jbid. f. 3. /. » Ibid. f. 6. t t. f. 9. 



