56 



THE ENTOMOLOGIST. 



will form beautiful ornamental patterns of different kinds, according to the 

 conditions under which they diffuse. 



The facially io-form aberrations which develop in a saltatory 

 manner in wild pupae of V. urticce when they are climatised in 

 tropical conditions or exposed to contrasts of temperature offer at 

 least sufficient excuse for that thought. This becomes especially 

 clear when it is remembered that V. urticce actually indulges in a 

 slight degree in seasonal variation, the variety of the hot season 

 often showing the io-form tendency. Cold weather brings the facies 

 nearer to the northern local variety polaris, while a hot season 

 will produce specimens very like those found in the hot valleys 

 of Spain, and even approaching var. ichiusa, Bon., of Corsica 

 and Sardinia (a local heat form), and var. chinensis. Leech, of 

 Asia, hoth of which latter varieties are ioform : ichnusa by its 

 ground colour, the absence of the two puncta on the fore wings 

 (and in the hot season even of the inner marginal blotch), 

 chinensis by its large size and all-brown, irrorated under side. 

 Thus it appears that the facial variation of V. urtica, induced by 

 ■seasonal conditions of light and temperature, is in the hot season 

 slightly ioform, and moreover tends to cover the amount of facial 

 variation in local groups* 



By a simple experiment every one can easily prove for himself 

 that the facial variation of urticce is bound up with the seasonal 

 amount of light and temperature, and not with any mere time of 

 the year as such, nor necessarily with any particular generation. 

 Let any two broods of urticcB develop simultaneously, the one in 

 a warm, sunny room, and the other in a cold, sunless (darkened) 

 room open to the night air; then, in the first case, the resulting 

 imagines will be more or less transitory to the ioform var. 

 ichnusa, in the second to var. polaris, \ and very likely there will 

 be one or two beautiful aberrations extra in both groups. 



Now, the degree of regular variation in V. iirticce is slight as 



=^= Local forms tend more or less, besides indulging in facial variation, to 

 become sexually alien from their type ; they are often " species in the 

 making." They are first induced by temperature, according to the local 

 climate, then they are developed and " fixed " gradually by hereditism under 

 the protection of " local isolation " from the type, which would otherwise in- 

 vade the district and swamp the varietal tendency before sexual alienation 

 had time to take 2}l(ice aud prevent this (compare the effects of regular 

 ■migratory habits in butterflies). How necessary a factor tor jdiysiological 

 divergence "local isolation" is, becomes apparent when it is remembered 

 that nowhere on the mainland of Europe does a fairly constant and distinct 

 variety of ur tic ce exist, while on the Isles of Corsica and Sardinia "insular 

 isolation " has triumphantly produced var. ichnusa. 



f " On the Effect of Eearing Larvae of V. urticce in Darkness," Entom, 

 antea, 1909, p. 39, recorded by Col. N. Manders. Twenty-one of fifty-five 

 butterflies were var. j^olaris, trans. An exaggeration in the sense of var. 

 2^olaris would bring the facies near V. milherti of North America. Even 

 V. io sometimes indulges in a black median fascia like that of V. urticce 

 \&r.])olaris, trans. I reared several such specimens last season. 



