328 



NOISES OF INSECTS. 



(postpectus) another membrane, folded transversely, fills an 

 oblique, oblong, or semilunar cavity. 1 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, at- 

 tached to a place opposite to the point of the mucro of the 

 first ventral segment of the abdomen, will appear. 2 In Reau- 

 mur'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. 3 These bundles consist of a prodigious num- 

 ber of muscular fibres applied to each other, but easily sepa- 

 rable. Whilst Reaumur was examining one of these, pulling 

 it from its place with a pin, he let it go again, and imme- 

 diately, 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 observ- 

 able. 4 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 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. 5 Each bundle of muscles, before mentioned, 

 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 



1 Reaum. t. xvi. f. 3. n. n. 



3 Ibid. f. 9. //. 



5 Ibid. f. 6. 1 1. f. 9. 



2 Ibid, ubi supr. f. 6. ff. 

 4 Ibid. £ 3. /. 



