XII 



ACRIDIIDAE 



287 



the Wengern Alp with a friend/' he says, " the grass on each side 

 of the path swarmed with Insects which to me rent the air with 

 their shrill chirruping. My friend heard nothing of this, the 

 Insect world lying beyond his limit of audition." If human 

 ears are so different in their capacities for perceiving vibrations, it 

 of course becomes more probable that auditory organs so differently 

 constituted as are those of Insects from our own may hear sounds 

 when the best human ear can detect nothing audible. On the 

 whole, therefore, it would appear most probable that the Orthoptera 

 provided with acoustic organs, and which we consider dumb, are 

 not really so, but produce sounds we cannot hear, and do so in 

 some manner unknown to us. If this be the case it is probable 

 that these ears are special organs for hearing particular sounds. 



Scudder, who has given considerable attention to the subject 

 of Orthopteran music, says that in 1^. America " the uniformity 

 with which each species of Stenohothrus plays its ow^n song is 

 quite remarkable. One kind, Stenohothrus curtipennis, produces 

 about six notes per second, and continues them from one and a 

 half to two and a half seconds ; another, S. melanopleurus, makes 

 from nine to twelve notes in about three seconds. In both 

 cases the notes follow each other uniformly, and are slower in the 

 shade than in the sun." 



Some of the species of Acridiidae, it should be noticed, produce 

 a noise during their flights through the air, due to the friction 

 of the wings ; whether this has a definite importance, or whether 

 it may be entirely incidental, has scarcely yet been considered. 



Information of a satisfactory kind as to the pot-embryonic 

 development of the Acridiidae is but scanty. "We have repre- 

 sented in Fig. 84, A, the condition in which a migratory locust, 

 Sclhistocerca percgrina, leaves the egg, and we will here complete 

 the account of its growth ; following Brongniart,^ whose statement 

 is confirmed by Lestage and other naturalists. Immediately 

 on leaving the egg the young locust casts its skin, and is then 

 of a clear green colour, but it rapidly becomes brown, and in 

 twelve hours is black. At this early age the gregarious in- 

 stinct, possessed by this and some other species of Acridiidae, 

 becomes evident. In six days the individual undergoes a second 

 moult, after which it is black, spotted and banded with white, and 

 with a rose-coloured streak on each side of the hind body. The 

 1 Bull. Soc. Philomath. (8) v. 1893, p. 5. 



