150 THE CAUSES WHICH PROPAGATE 



because they are so thin and fragile that they could not resist it ; 

 but there is every reason to think that the very quick movement 

 which the leaf -cricket gives to the veins, rubbing them on one 

 another, produces a kind of fluttering in the membrane, which 

 gives an augmentation to the sound. But De Geer nevertheless 

 was ignorant of the microscopic aspect of the rubbing vein, as 

 was L. Frisehs, who otherwise gives an accurate description of 

 the crepitation of the Verual Field-cricket in his pretentious work 

 on " All the Insects of Germany,^^ published at Berlin in 1766, 

 and in which he goes so far as to state that the shi'illing vein, 

 which he correctly indicates, acts on the principle of a lock-spring, 

 so that the important discovery of the file or lima remained for 

 Goureau, a colonel in the French engineers, being first brought to 

 notice in his paper in the Transactions of the French Entomo- 

 logical Society for 1837. And since then this interesting 

 mechanism, originally found to be present on the shrilling vein 

 of the crickets (Plate II., Fig. 8, /), and leaf-crickets (Fig. 5b, I) 

 and on the ridge at the inner side of the femora of the gi'ass- 

 hoppers (Fig. 6), has come to be recognised as the source of 

 sound in insects of other orders. 



These stridulating organs and their accessories characterise 

 the males, being alone perfect and efficient in male 

 grasshoppers and crickets, although in female leaf-crickets 

 they may be found exceptionally developed. Their masculine 

 music, presenting a twofold stimulus, love and rivalry, fulfils a 

 twofold object, reproduction and dispersion ; and while the 

 variety and modulation in specific music at the pairing season, 

 paralleling or rivalling that of the rostrate cicadae, confers on this 

 group precedence as instrumentalists, the ordinary challenge and 

 answers of the males indicate a phenomenon of rivalry cognate 

 with the dances in other orders, serving to band the species in 

 terrestrial migration with the mute females following attentively 

 in the track of their musical chanticleers. Fear, elsewhere the 

 source of music, in this order is rarely, if ever, expressed by a 

 modulation of the notes. 



The structure of wings in relation to their action as aerial 

 levers we have already discussed. In investigating the music it 

 becomes necessary to consider the design evinced by the fore- wing 

 in a new and strange adaptation to an instrument of sound, a 



