118 THE CAUSES WHICH PROPAGATE 



them were some fine Swallow-tails, quivering- tlieir wings as 

 they drank, and lovely blue Hair Streaks. The latter, when they 

 alight, rub their wings together, moving their curious tail-like 

 appendages up and down/' 



Here we have corroborative evidence o£ the alternate motion 

 that certain of these little-tailed butterflies, when reposing, 

 impart to their hind wings, which forcibly recalls the stridula- 

 tory action in the genus Vanessa, differing in this respect, that, 

 whereas the hind wing is rubbed by the fore one in the one case, 

 it is the fore-wing that is rubbed by the hind one in the other. 

 Having become impressed with this analogy, I, one May, gave 

 my attention to the habits of the indigenous Green Hair Streak 

 Butterfly, to see if anything similar was observable in its 

 economy. Nor was I disappointed in this, for on two occa- 

 sions when it was reposing sedately on a bramble leaf with shut 

 wings I was rewarded by seeing it alternately lift the hinder 

 wings, and in a leisurely fashion rub them backwards and 

 forwards over the fore ones, although I could catch no audible 

 sound. The movement may be also observed in numerous 

 species of the genus of " Blues " {Polyommatm) that flit over 

 our Palaearctic meadows. Regarding the presence or absence of a 

 stridulating organ in connection with this rhythmical action, it 

 will be found that beneath, on the overlap of the fore-wing in 

 various species of Thecla, or Hair Streak, the scales are sup- 

 planted by a patch of hair, and just above, the anal vein is bare 

 and raised. This bare raised portion in the Green Hair Streak, 

 submitted to a microscopical scrutiny, appears crossed at uniform 

 distances by pronounced strise, which indicate internal dia- 

 phragms, and constrict the tube into a series of bead-like forma- 

 tions. T. JEtolus, one of the butterflies noticed by Mr. 

 Wallace performing, the overlapping fore-wing has its anal vein 

 decidedly denuded beneath, indicating friction, and, at the base, 

 it is also blackened, indurated, and striate. We thus see in 

 Rhopalocera or club-antennaed Butterflies the alar limije intimate 

 vein induration, with abnormal protrusion or constriction of 

 their tracheal helix, while their music may express love, 

 rivalry, fear, or anger — certainly the latter. 



Moths distinguished from butterflies by the absence of the 

 button terminating the antennae have many of their groups 



