H8 EVENINGS AT THE MICROSCOPE. 



pin may be introduced without resistance. When the pel- 

 licle is removed, a large cavity appears. In my opinion 

 this aperture, cavity, and above all the membrane in 

 tension, contribute much to produce and augment the 

 sound emitted by the grasshopper." * 



In this case we may without hesitation conclude that 

 the friction of the thigh-plates and shank-points on the 

 rough-edges of the wing-cases, produces the musical vibra- 

 tion on the tense membrane, as rubbing a wet glass with 

 the finger will yield a loud musical note. 



The most elaborate contrivance for the production of 

 sounds among the Insect races, however, is found among 

 the Cicadas, celebrated in classical poetry as the very im- 

 personations of song and eloquence. I regret I cannot 

 show you this apparatus ; for though we have a British 

 species, — lately discovered in the New Forest, — it is very 

 rare. Should you travel, however, either in the old or new 

 world, you will have abundant opportunities of using your 

 microscope to verify the following description by our 

 prince of entomologists, Mr. Kirby : — 



" If you look at the under side of the body of a male, 

 the first thing that will strike you is a pair of large plates 

 of an irregular form — in some semi-oval, in others triangu^ 

 lar, in others again a segment of a circle of greater or less 

 diameter, covering part of the belly, and fixed to the 

 trunk between the abdomen and the hind legs. These 

 are the drum covers or opercula, from beneath which the 

 sound issues. At the base of the posterior legs, just 

 above each operculum, there is a small pointed triangular 

 process, the object of which, as Reaumur supposes, is to 

 prevent them from being too much elevated. "When an 

 operculum is removed, beneath it you will find on the ex- 

 terior side a hollow cavity, with a mouth somewhat linear, 

 which seems to open into the interior of the abdomen : 

 next to this, on the inner side, is another large cavity 

 * De Geer, iii. 471. 



