182 SOCIAL LIFE IN THE INSECT WORLD 



The wing-covers are both formed of a dry, broad 

 membrane, diaphanous and as fine as the white skin on 

 the outside of an onion, which is capable of vibrating 

 over its whole area. Their shape is that of the segment 

 of a circle, cut away at the upper end. This segment is 

 bent at a right angle along a strong longitudinal nervure, 

 and descends on the outer side in a flap which encloses 

 the insect's flank when in the attitude of repose. 



The right wing-cover overlaps the left. Its inner edge 

 carries, on the under side, near the base, a callosity from 

 which five radiating nervures proceed ; two of them 

 upwards and two downwards, while the fifth runs 

 approximately at right angles to these. This last nervure, 

 which is of a slightly reddish hue, is the fundamental 

 element of the musical device ; it is, in short, the bow, 

 the fiddlestick, as is proved by the fine notches which 

 run across it. The rest of the wing-cover shows a few 

 more nervures of less importance, which hold the 

 membrane stretched tight, but do not form part of the 

 friction apparatus. 



The left or lower wing-cover is of similar structure, 

 with the difference that the bow, the callosity, and the 

 nervures occupy the upper face. It will be found that 

 the two bows — that is, the toothed or indented nervures — 

 cross one another obliquely. 



When the note has its full volume, the wing-covers 

 are well raised above the body like a wide gauzy sail, 

 only touching along the internal edges. The two bows, 

 the toothed nervures, engage obliquely one with the 

 other, and their mutual friction causes the sonorous 

 vibration of the two stretched membranes. 



The sound can be modified accordingly as the strokes 



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