120 LETTERS ON ENTOMOLOGY. 
of the abdomen, will appear. These bundles 
consist of a prodigious number of muscular fibres 
applied to each other, but easily separated. 
Whilst Reaumur was examining one of them, 
pulling it from its place with a pin, he let it go 
again, and immediately the usual sound was 
emitted, though the animal had been long dead. 
On each side of the drum-cavities, when the 
opercula are removed, another cavity of a 
roundish shape, opening into the interior of the 
abdomen, is observable : in this is the true drum. 
If, in this last cavity, the lateral part of the first 
dorsal segment of the abdomen is removed, a 
semi-opaque and nearly semicircular concavo- 
convex membrane, with transverse folds, is dis- 
covered. Each bundle of muscles is terminated 
by a tendinous plate nearly circular, from 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 muscles being 
alternately relaxed and contracted, will, by their 
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 recover its convexity ; 
which sound striking upon the mirror and other 
