INSECT VARIETY. 



151 



subject both interesting and important, forming as it does a key 

 to the classification of the species and a method of distinguishing 

 the sexes. For in all Orthoptera we are led to recognise three 

 fields or discs in the fore-wing or semi-elytron, parted by constant 

 veins, namely, a marginal, m, an intermediate, i, and 

 an anal, a. (See Figure). Out of these areas. Nature, 

 in an ingenious hinging and folding by a method of 

 parallel veins — indicated in the diagram by plain and 

 dotted lines — forms at once a series of acoustic instru- 

 ^ ments, and an elytron or cover for the delicate 

 hind- wings. From these sutures it is evident we can 

 form an acoustic box in at least three ways. If 

 we bend down the marginal areas and cross the 

 wings, we have the section m of the elytron as we find 

 it in crickets. If we incline the marginal and inter- 

 mediate, we shall have the section a presented by leaf- 

 crickets and grasshoppers. A transition form, M i A, is indi- 

 cated in the exotic genus Grijllacris. We likewise notice when a 

 species of Orthoptera has finished its music, and is desirous to fly 

 or launch on a floating leap, it becomes not only necessary for it to 

 expand the organs of flight, but also to turn these areas on their 

 hinges, so as to restore the normal sustaining surface. 



It appeal's, then, that all the tuneful species 

 of Saltatoria produce their notes by vibration of 

 the elytra, but they may also be observed lowering 

 their prothoi'ax, in order to elevate their wing-covers 

 more or less previous to stridulating. and thereby 

 enclosing a portion of air above the body, which, 

 when these begin to vibrate during the friction 

 of the lima over its clasp, takes up these hori- 

 zontal waves of sonorous vibration, and intensifies 

 them in ratio of its volume, as the sound of the 

 tuning-fork is increased when placed on its stand, 

 or the musical cylinder increases the sound gene- 

 rated by its teeth. It is at least probable that the 

 sonorous pulses are likewise transmitted to the large air-bladders 

 that distend the bodies of these insects, and that the notes thus 

 receive a further increment. We know at least this is a direct 

 sound accumulator, with regard to the males of the South African 



M 



