1 1 



to that process, also appears in the three above-mentioned forms, but in a 

 different degree; strongest in the form Leptis and least advanced in the type: 

 which makes it probable that also the black on the upper-side of the forewings 

 happens to be in a stage of decrease, and for this reason has still the greatest 

 development in the type ; the type would in this case represent the oldest form 

 of colour which still exists. 



Yet it is a fact that the union of the hooked stripe and the black of the 

 terminal margin of the fore-wings has not progressed so far on the under-side 

 as on the upper-side, which, seeing that, as a rule, the former has proceeded 

 less far in the course of colour-evolution than the latter, may lend support to 

 the view that the extension of the black is still in the period of increase. That 

 the original colour is simultaneously in a state of etiolation does not clash with 

 this, seeing that each of the evolutions independently follows its own course. 

 Nor can the fact that the dark colour on the under-side of the hind-wings 

 evidently also contains much black, and that this is also disappearing, at all 

 militate against this, as this special increase of the black may be caused by 

 the secondary operation of some external influence, which has been mentioned 

 on page V of the Introduction. The whole subject however still continues 

 very difficult. An answer to the question whether the black is in a state of 

 increase or decrease, is always very difficult to give, because it is only clearly 

 evident when remains of that colour are present, in which case a decrease 

 must naturally take place. As such f i. loose, spread, black spots, like those 

 on the upper-side of the fore-wings of the European Pieris Brassicae L. are 

 to be recognized, because the increase of the black, as we have seen, follows 

 fixed rules, to which the said spots do not answer, whilst the decline of that 

 colour has not such a regular character. But such remains are far from being 

 always present, and when they are not, from that fact alone it may not, forsooth, 

 be concluded that an increase of the black takes place. Nor are general con- 

 clusions, in this respect, possible, for with the one species it differs from what 

 it is with the other, yet in general it seems acceptable, that among the Pieridae, 

 an old family of the Rhopalocera, the process of colour-evolution will be pretty 

 far advanced and that, therefor, the fact that so many species of them have 

 grown almost white, may be ascribed to this, and that thus, especially with 

 those in which the white is so strongly extended, the black will already have 

 reached the period of decrease. 



This process of getting paler shows itself strongest in the colour of the 

 under-side of the hind- wings. In the type this colour is mostly dark brown, 

 sometimes mixed with more, sometimes with less yellow; this brown, however, 

 gets paler and becomes greyish. This happens particularly in the form 



