168 THE CAUSES WHICH PROPAGATE 



attractive design of this sounds it is as difficult to say whether 

 production be in measure subservient to the will or no, as 

 to specify the emotional principles, if any, it is capable of 

 expressing. 



Locusts, contrary to the general notion, have some diversity 

 of habit ; while the migratory kinds live in flocks, and move over 

 the pasturing grounds, or rising, waft through the breezy air 

 to distances proportionate to their capability of flight, Fischer 

 speaks of one European species {Acridiam tartaricum) , a hermit 

 from its kith and kin, that lives on trees, and has not only 

 a song deceptively like that of a bird, but also a mimicry of 

 habits, for, he mentions, if any one approaches the perch on 

 which it is sitting, it at once flies off to another at a short 

 distance. This large species is not rarely met with in Italy 

 among the mountain gorges. 



The males of our little autumnal grasshoppers sing in the 

 same fashion as the larger kinds ; ascending some elevated perch 

 on a grass-stem, they lower their prothorax, thereby unlocking 

 their wing-covers, which they raise pent-like to uncover the 

 organs of audition at the base of the abdomen, then, doubling 

 up their hind legs, they pass these backwards and forwards, 

 usually simultaneously, over the exterior surfaces of the wing- 

 covers, winnowing them briskly through a small angle, and 

 producing a blithe note, which varies with the speed, pressure, 

 and length of the stroke indulged in (Plate III., Fig. 8). You 

 may convince yourself it is so, according to Fischer, by watching 

 these minstrels in the open air, or otherwise by the experiment 

 of imitating the motion of the femora, in a living or recently- 

 killed insect. But the song of these merry species only re- 

 sembles that of the former as regards mode of production, for 

 by aid of the magnifying-glass and microscope we soon discover 

 the musical organ is transposed to the keel on the hind femora 

 (Plate II., Fig. 6, l), which in the males bear at their lower end, 

 for two-thirds of their length, a row of acorn-shaped, or lanceo- 

 late, tubercles (Fig. 7), as invariably absent in the mute female. 

 These, by the action of the femora, are played over the inner 

 branch of the chief or scapular vein of the el}'tra (Plate II., Fig. 

 3, y), which in Sfenohof/irns, Fiseh., and Gomphocerns, Thumb., 

 is raised on the surface ; in the latter genus these tubercles are 



