] 64 THE CAUSES WHICH PROPAGATE 



stalks, with elytral expanse often exceeding- six inches, approxi- 

 mate the pi-esent leaf-crickets, althoug-h absence of salta- 

 torial leg's leaves the matter still contested. The mirror 

 sexually discriminative, is likewise traceable in Locusta speciosa 

 and L. amada, Hag,, from the Oolitic Solenhofen ; extinct types 

 in which an attempt at restoration I was once kindly per- 

 mitted to undertake at the British Museum, seemed to reveal 

 a complex and oblique elytral venation, like that of the aerial 

 migratory species of locust, Pachi/ti/Ius, Fieb., united with a 

 sabre-shaped locustinal ovipositor in their females; while the 

 thorax and hind legs affiliated them to the genus Dedicus of 

 Serville. This circumstance has led me to surmise that these 

 leaf-crickets in ancient times had much greater powers of dis- 

 semination than now possessed by their family. Lastly, there is a 

 cast of an elytron of a large species of true Becficus, about twice 

 the size of our present Wart-biter, in the national collection, 

 from the Purbeck of Swanage, with about as clear indications 

 of the usual lima as can be drawn from a plaster impress. 



ACRIDIID^ (locusts AND GUASSHOPPERS) . 



The Akrides, or Locusts, " produce their song by the hind legs 

 with which they leap,^^ says Aristotle, writing over 2,000 years 

 ago. And in this group (Plate II., Fig. 3) we find them fashioned 

 so as to answer both the purpose of leaping and that of music. 

 For here, as in other saltatorial insects, they are longer than the 

 two fore pail", with the femoral joint consequently raised and form- 

 ing an acute angle with the tibia. Then the thicker crank-shaped 

 thigh or femur is characteristically large, tough, and powerful, 

 and along its inner and hinder part runs a furrow in which the 

 shin or tibia is placed previous to leaping, and in which it is carried 

 likewise when producing the music. In front of this groove runs 

 the hard keel or ridge that plays the active part in the stridor 

 (Plate II., Fig. 6, I). The passive organ is seen in a certain vein 

 which is raised from the elytral surface at either side (Plate II., 

 fig. 3, y or x) ; or in one singular instance it is transposed to the 

 abdomen. 



The timbre of the notes of the grasshoppers, according to 

 Yersin, is less adaj)ted than that of the cricket to be attained 

 and notated by human musical instruments, having most in 



