NOISES OF INSECTS. 501 
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 trian- 
gular process (pessel/um) ?, the object of which, as Reaumur supposes, is to 
prevent them from being too much elevated. When an operculum is re- 
moved, 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 ab- 
domen*: 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 allthe colours of therainbow. 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 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 (pos/pectur) 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 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 segment of the abdomen, will appear.?_ In Reaumur’s spe- 
cimens 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 prodi- 
gious 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 true drum, 
the principal organ of sound, and its aperture is to the Cicada what our 
larynx is to us. 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 cayity 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 bya 
tendinous plate nearly circular, trom 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 
1 Reaum, v. t. xvi. f. 5. uu. 2 Reaum. ubi supra, t. xvi. f. 11. db. 
5 Reaum. ibid. f. 3.72 4 bid. ubi supra, f. 8. m m. 
; Pb. 4:4 C. ae Reaum, t. xvi. f. 3. n nm, 
id, ul supra, f, 6. ffi Ibid. £9. ff. 
oibiee e 1 Tid t OE 8 £9, 
KK 3 
