ORTHOPTBRA. 283 



against the rounded hind-corner of the opposite wing, the edge 

 of which is thickened, colored brown, and very sharp. In the 

 right wing, hut not in the left, there is a little plate, as transpar- 

 ent as talc, surrounded by nervures, and called the speculum. In 

 Ephippiger vitium, a member of the same family, we have a 

 curious subordinate modification; for the wing-covers are great- 

 ly reduced in size, but "the posterior part of the pro-thorax is 

 "elevated into a kind of dome over the wing-covers, and which 

 "has probably the effect of increasing the sound.""' 



We thus see that the musical apparatus is more differentiated 

 or specialized in the Locustidse (which include, I believe, the 

 most powerful performers in the Order), than in the Achetidae, in 

 which both wing-covers have the same structure and the same 

 function."* Landois, however, detected in one of the Locustidse, 

 namely in Decticus, a short and narrow row of small teeth, mere 

 rudiments, on the inferior surface of the right wing-cover, which 

 underlies the other and is never used as the how. I observed the 

 same rudimentary structure on the under side of the right wing- 

 cover in Phasgonura viridissima. Hence we may infer with con- 

 fidence that the LocustidsB are descended from a form, in which, 

 as in the existing Achetidae, both wing-covers had serrated ner- 

 vures on the under surface, and could be indifferently used as the 

 bow; but that in the Locustidse the two wing-covers gradually 

 became differentiated and perfected, on the principle of the divis- 

 ion of labor, the one to act exclusively as the bow, and the other 

 as the fiddle. Dr. Gruber takes the same view, and has shown 

 that rudimentary teeth are commonly found on the inferior surface 

 of the right wing. By what steps the more simple apparatus in 

 the Achetidse originated, we do not know, but it is probable that 

 the basal portions of the wing-covers originally overlapped each 

 other as they do at present; and that the friction of the nervures 

 produced a grating sound, as is now the case witU the wing- 

 covers of the females.™ A grating sound thus occasionally and 

 accidentally made by the males, if it served them ever so little as 

 a love-call to the females, might readily have been intensified 

 through sexual selection, by variations in the roughness of the 

 nervures having been continually preserved. 



In the last and third Family, namely the Acridiidse or grass- 

 hoppers, the stridulation is produced in a very different manner, 

 and according to Dr. Scudder, is not so shrill as in the preceding 

 Families. The inner surface ot the Femur (fig. 14, r) is fur- 

 nished with a longitudinal row of minute, elegant, lancet-shaped, 



" Westwood, 'Modern Class, of Insects,' vol. i. p. 453. 



=8 Landois, 'Zeitsch. f. wiss. Zoolog.' B. xvii. 1S67, s. 121, 122. 



" Mr. Walsh also informs me that he has noticed that the female 

 of the Piatyphyllum concavum, "when captured makes a feeble grat- 

 "Ing noise by shufBing her wing-covers togetheSj'' 



