XI 



process of evolution, although not usually side by side on the surface of the 

 same wing, in such a way as to show as clearly how they have succeeded one 

 another in that process, as for instance with the colours and relic-stripes which 

 appear side by side on the wing surface of certain Hebomoia species, referred 

 to on p. 35 of my monograph on the Pieridae. Moreover the course of this 

 process does not seem to be the same in one family as in another. While in 

 the Pieridae the yellow stage is very common, this colour is only rarely seen 

 in the Lycaenidae. Orange, in this case, apparently often changes so quickly 

 into white that the yellow stage cannot be observed. At the same time we 

 constantly get the impression that the evolution of colour proceeds gradually, 

 not by sudden changes, or so-called mutation. Where these pigmental colours, 

 therefore, in general appear just as in other Rhopalecera, we may undoubtedly 

 assume that the change of colour in the Lycaenidae is also caused bij the 

 ordinary process of colour-evolution, and in consequence the direction in which 

 the change is proceeding, is known. The white colour found in many 

 Lycaenidae must therefore often be the final stage of this evolution ; at the 

 same time it need not necessarily always be so, because, as has been already 

 stated, white may originate in another way. As a special study has not yet been 

 made of this matter, it is often difficult to establish the nature of this colour in 

 Lycaenidae; judging merely by its external appearance, the white does not appear 

 to be of the same kind in all species ; but here we are upon unknown ground. 

 In the case of the Lepidoptera the increase and decrease of the dark 

 pigment plays an important part in the change of colouring; in the Lycaenidae 

 this is also the case. And here it is often difficult to know, whether, when 

 the dark pigment is found upon a surface, it is extending upon it, or 

 diminishing after a former extension. In cases of a strongly marked darkening, 

 an increase of dark pigment is certainly indicated, but where it is only 

 partial or weak it may equally well indicate a partially developed stage in 

 the process of increase, or one in which the completed darkening has again 

 partially disappeared. For the scales which contain the dark pigment, when 

 this is increasing, cover those in which the other pigmental colours are found ; 

 on plate XV fig. 30^- in my monograph on the Satyridae, the way in which 

 this takes place in Cyllo Constantia Cram is represented. On Plate xv fig. 300- 

 is shown a colour form of a nearly related species, when the darkening is 

 greatly decreased, and the sub-lying colour is partially visible again, especially 

 on the under surface. As a rule it is in a much faded condition, as the 

 process of colour- evolution has not stood still with the underlying pigmental 

 colours during the time that they were covered over, which may have been 

 a very long period ; for example in Cyllo Leda L. what was red at the time 



