4-02 NOISES OF INSECTS. 



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 dis- 

 section. A portion gf the first and second segments 

 being removed from that side of the back of the abdo- 

 men 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 a . 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 at- 

 tached being dilated b . These bundles consist of a pro- 

 digious 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 re- 

 moved, 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 cavity last described, 

 if you remove the lateral part of the first dorsal seg- 

 ment of the abdomen, you will discover a semi-opaque 

 and nearly semicircular concavo-convex membrane with 

 transverse folds this is the drum d . Each bundle of 



a Reaum. ubi supr.f. 6.//. b Ibid./ 9.//. PLATE VIII. 



FIG. 19. C". c Reaum./. 3. / . d Ibid./. 6. t t.f. 9. 



