102 EVENINGS AT THE MICROSCOPE. 



ered 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 Tnucro of 

 the first ventral segment of the abdomen, will appear. 

 In Keaumur's specimens, these bundles of muscles 

 seem to have been cylindrical ; but in one I dissected 

 {Cicada Oapensis) they were tubiform, the end to which 

 the true drum is attached being dilated. These bun- 

 dles consist of a prodigious number of muscular fibres 

 applied to each other, but easily separable. "Whilst 

 Keaumur 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 ob- 

 sei'vable. 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 them- 

 selves 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 semicircular 

 concavo-convex membrane with transverse folds ; this 

 is the drum. Each bundle of muscles, before men- 

 tioned, is terminated by a tendinous plate nearly circu- 

 lar, from which issues 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 



