2 34 SECTION D. ARTHROPODA. 



island of Celebes, Papilio ascalapJms Bsd., that when the case 

 presents itself of an unequal advance in evolution between the sexes 

 of the same species, only a certain number of times, as in the case 

 of P. ineinno7t L., some of the intermediate forms in which this is 

 the clearest to be seen, have been preserved, most times, however, 

 only the extreme forms. This explains the fact of there being 

 sometimes a small, sometimes a great difference in colour — 

 occasionally also in form — in the sexes of the same species of 

 Lepidoptera, in consequence of the change of colour only having 

 begun in one of the sexes, while the other was in a state of 

 genepistasy and remained unaltered. 



Such an evolution in the imagines of the Lepidoptera is certainly 

 very common ; most probably it is as general a rule as is the case 

 with the caterpillars of the Sphingidae. 



In order to obtain more certainty on this subject I have 

 thoroughly investigated about a thousand species of the family of 

 the Pieridae, particularly iit for this object by its peculiar colours, 

 in an article entitled " Die Farbencvolution {Phylogejiie) bei den 

 Pieriden,'' in the " Tijdschrift der NederlandscJic dierkundige vereeni- 

 ging," sen 2, vol. 5. As the result my opinion has been completely 

 confirmed. I found in truth that just as the caterpillars in the 

 family of the Sphingidae, so all the imagines of the Pieridae were 

 subject to an evolution of colour which must have begun in the 

 original form, living in the tertiaries, and which, although constantly 

 following the same direction, changes in a very unequal manner — 

 not only with reference to the species but also to the sex ; and 

 besides that the region in which they live or the season in which 

 they appear cause divergences ; the evolution being moreover again 

 and again retarded by genepistasy. According to my investiga- 

 tions the present colour of all the Pieridae must have proceeded 

 from a general red colour, subsequently passing into white, be 

 it directly through orange and yellow or green, or replaced by 

 brown or black before or partly at the same time, which is, however, 

 later on again driven away by white, and thus all become uniformly 

 white ; perhaps even the colour contained in the wing-scales will in 

 time get quite exhausted and be lost. The difference in colour 

 between the various species of this family is thus the result of the 

 way in which this process makes its appearance on the different 

 parts of the wings ; all kinds of remnants of these different shades 

 of colour are to be seen there, now in a greater, then in a lesser 

 degree, now in one place, then in another, except in those species 

 which are so far advanced in the evolution as to have become 

 nearly completely white — the well-known " white ones." 



But this investigation procured me still more results. It was 

 made evident to me that this very phenomenon of " evolution of 

 co/o?ir" must be in general the cause of the great difference in 

 colour of the Lepidoptera, which characterises so highly this order 

 of animals. But the succession of colours in this evolution seems 



