90 EVENINGS AT TIIE MICROSCOPE. 



true drum, the principal organ of sound, and its aper- 

 ture 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 semicircular concavo-convex membrane with 

 transverse folds; this is the drum. 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 aper- 

 ture in the horny piece that supports the drum, and are 

 attached to its under or concave surface. Thus the 

 bundle of muscles, being alternately and briskly relaxed 

 and contracted, will by its 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, 

 striking upon the mirror and other membranes before it 

 escapes from under the operculum, will be modulated and 

 augmented by them. Probably the muscular bundles are 

 extended and contracted by the alternate approach and 

 recession of the trunk and abdomen. 



" And now, my friend," adds the excellent author, 

 " what adorable wisdom, what consummate art and skill 

 are displayed in the admirable contrivance and complex 

 structure of this wonderful, this unparalleled apparatus ! 

 The great Creator has placed in these insects an organ 

 for producing and emitting sounds, which in the intricacy 

 of its construction seems to resemble that which He has 

 given to man and the larger animals for receiving them. 

 Here is a cochlea, a meatus, and, as it should seem, more 

 than one tympanum ! " * 



* " Intr. to Ent." ; Lett. xxiv. 



