'562 GOUREAU ON THE 



thorax, and the motion of the wings striking the air during 

 this kind of locomotion. The posterior stigmata of the pro- 

 thorax do not appear to me to have any thing to do with the 

 production of this sound : these stigmata are remarkable in 

 presenting, in a still more striking manner than those of the 

 grasshoppers, the appearance of an eye deprived of its ball, 

 the movable eyelids of which open and shut at the will of the 

 insect. Those of the prothorax are accompanied by a protu- 

 berance somewhat resembling a bud, near one extremity. 



Most entomologists are aware of the sub-alary cavity on 

 each side of the first segment of the abdomen, in both the 

 males and females of these insects. Latreille has described it 

 in the Annales da Museum d'Histoire Naturelle (viii). I am 

 only acquainted with the work of this celebrated entomologist 

 through a note in the Regne Animal of Cuvier." I see by this 

 note, he suspects this organ may contribute to stridulation, 

 Linnasus thought so, and a great number of naturalists have 

 agreed with him herein; M. Burmeister, of Berhn, still enter- 

 tains this opinion." In spite of the opinion of these great 

 authorities, an opinion which I have myself endeavoured to 

 support," I must now abandon this view of the subject, the 

 facts I have related compelling me to do so. It may be that I 

 have observed incorrectly ; in this case, I shall return with 

 pleasure to the opinions of these illustrious men, when I know 

 them to be confirmed by facts. If the sub-alary cavities called 

 drums by Latreille, contribute to stridulation, they can only 

 act in the manner of a speaking-trumpet, by strengthening the 

 sound : I do not think they originate it. 



These organs, whatever their functions may be, deserve 

 attention. The form of the cavities, the thin and transparent 

 membrane composing their envelope, the external auricle 

 which partially covers them, the internal small bones to which 

 they are united and which strengthen them, the canal by which 

 they are perforated in their opaque and scaly part, at the 

 lateral origin of the auricle, cause them to seem complicated 

 organs, probably performing an important part in the economy 

 of life ; their functions however are unknown. I have closed 

 these cavities with a thin layer of tallow in the living insect ; 



* Cuvier, Rigne Animal, Vol. V. p. 186'. 



^ Revue Entomologique, Vol. 1. p. 186. _^ 



'■ Ihid. Vol. III. p. 101. 



