94 GOUUEAU ON THE 



and parallel nervures. One of these surfaces is placed on the 

 back of the insect, and may be called the back-cover (couvre- 

 dos) ; the other passes along the side, and may be conveniently 

 termed the side-cover {couvre-flanc). The back-cover is 

 divided into numerous compartments by other (regularly- 

 curved) nervures, forming two principal sets : the first of 

 which is composed of four nervures or cords, and rests on the 

 middle of another nervure, which I have named the bow 

 {Varchet) ; the second is formed of three nervures which take 

 their rise at a remarkable point of the internal border which I 

 call the brush {la hrosse). These two sets are separated by a 

 nervure which touches at its lower extremity an oval space 

 surrounded by another nervure. The ends of the elytra are 

 reticulated. In order to have a good view of the bow, we must 

 look at it with a magnifying glass from below ; we shall then 

 see a large nervure, thicker in the middle than at the ex- 

 tremities, running from the internal border towards the base of 

 the elytron, spreading a little across on its retux'n, and termi- 

 nating towards the origin of the elytron. This nervure pro- 

 jects and is striated, or cut transversely like a file. Below its 

 origin at the internal border the brush is seen, formed of a 

 bundle of short stiff hairs, and above a space which is of a 

 firmer consistence, and more transparent than the rest of the 

 elytron, and somewhat triangular in form : to this I have given 

 the name of treble-string {la chanterelle). Now if we imagine 

 the two elytra crossed and rubbed against each other, we shall 

 perceive that the bow of the upper passes over the treble- 

 string of the lower one, and that the striae rubbing against the 

 border would excite vibrations there, which would be com- 

 municated to the whole of the elytra, and produce sounds. By 

 a reciprocal action the bow vibrates itself, and causes the 

 elytron to which it is attached to vibrate also ; so that stridu- 

 lation is the result of the simultaneous vibration of the two 

 elytra. The use of the nervures that cross the elytra is 

 obvious : they divide their surfaces into a great number of 

 variously-formed compartments, which have each a particular 

 vibration and a separate sound ; the combination of all these 

 little sounds produces the general sound or stridulation. Be- 

 sides this use they strengthen the membrane of the elytron, 

 and prevent its being bent, and thereby contribute to the pre- 

 servation of the instrument. 



