INSECT VAItlETY. 123 



greater in the male sex, the orgaus by which it is produced having 

 in it the greatest development. Many species possess a high 

 degree of susceptibility, and pertinaciously sham death in the net ; 

 while the pervading brightness o£ their colour seems at first sight 

 to extend the law pertaining to the butterflies and negative that 

 pertaining to the leaping grasshoppers, where, as a rule, a dulness 

 of hue indicates an increase in the capacity for music in a species. 

 The organism by means of which these moths produce, or pro- 

 bably produce, a stridor, consists in a little triangular bladder 

 (Fig. 11, Plate IV.), external, and formed, it would appear, by a 

 vesicular dilatation of the integument of the episternum of the 

 metathorax, over the surface of which runs a lenticular crumpling 

 representing a lima (/) placed vertically, and lying invariably in 

 the depression on its tense membranous superficies, that receives 

 the inwardly bowed hind femur (*), the inner superficies of 

 which is so directed as to suggest its effecting a stridor by 

 friction. The complete apparatus invites comparison with that 

 of the male Pneiunora. 



This vesicular bladder was first discovered by Sober in a Tiger 

 Moth [Chelonia jpudica) common on the Riviera, and advanced 

 by him in explanation of a sound this insect was heard to 

 produce on the wing. It was noticed to bear stria; on its anterior 

 margin, both by Sober and Laboulbene, about sixteen to twenty 

 in the male, and eight to ten in the female, some six of which 

 are more elevated than the remainder (see Fig. 11, Plate IV.). 

 The latter author, who ascribes the sound to the friction of the 

 hind femora over the striaj, also mentions the vesicle as present 

 and well developed in two other Continental kinds, Chelonia 

 matronula and (Ertzeni, the former of which was observed by 

 Czerny to produce stridulous notes, and in C. jlaria he found the 

 episternum, though denuded, not dilated. The bladder and striae 

 are perceptible in the indigenous Ruby Tiger; they are also present 

 in the common red Rag-weed Moth, as also in Callimorpha Hera, 

 a richly tulip-coloured kind, found as far north as the Channel 

 Islands, though but rarely occurring in England.* 



But this crumpled bladder only needs searching for to 



* If a fresh specimen of C. Hera be taken, and, seizing the extremity of a 

 hind tarsus, the femur be moved over the stria^, a distinct sand-papery sound like 

 the stridor of the Vanessce is heard. 



