THE YOUNG NATURALIST. 



91 



VARIATION 

 IN LEPIDOPTERA. 



By John E. Robson. 

 REVERSION. (Second Paper.) 



Last month I endeavoured to show that 

 those instances of variation among the 

 Geometrce where the band across the centre 

 of the wing showed more developement 

 than in the normal form of the insect, were 

 owing to that tendency in all animals to go 

 back at times to the markings of some older 

 form, from which theirancestors had sprung, 

 which has well been called Reversion. I 

 now propose to give an additional instance 

 or two of the same principle, that Young 

 Naturalists may not imagine it is at all 

 restricted in its application. As far as 

 possible I will confine myself to British 

 species, and where this cannot be done, I 

 will endeavour to take my illustrations 

 from species that are easily obtained. 



The Clouded Yellow (Colias edusa) is a 

 very well known butterfly. Both sexes are 

 rich orange yellow, with black borders to 

 all the wings. The females are distinguished 

 by having the black borders spotted with 

 yellow, while the males have the veins 

 yellow through the borders. A well known 

 variety of this butterfly is called Helic:. It 

 occurs in the female only, and resembles the 

 ordinary form in every respect but one, 

 instead of being of a rich orange yellow 

 colour, it is very pale greenish yellow in 

 hue, almost the same shade as the female 

 of Gonepteryx rhamni. If this variety stood 

 alone it would probably be considered an 

 example of what Mr. Jenner Weir calls 

 Xanthism, where the specimen appears of a 

 much paler shade of the normal colour, 

 yet not pale enough to be classed among 

 the albinos, or white varieties. The Pale- 

 Clouded Yellow (Colias Hyale) is much rarer 

 in this country than Edusa. It is pale 



bright yellow in colour, with a black border 

 on the forewings only. The females are 

 similar to the males, but as in Edusa, a form 

 of the female is found, like the ordinary 

 female in all respects but one, instead of 

 being a bright pale yellow, it is very pale 

 greenish yellow, so like the Helice form of 

 Edusa, that were their markings similar it 

 would not be easy to distinguish them. If 

 the case were stopped here, it would be 

 quite legitimate to assume that these pale 

 forms of the females of our two Clouded 

 Yellows, are not examples of Xanthism, 

 but of Reversion ; that the original form 

 from which they sprung, was an insect 

 with a dark male and pale female. The 

 case however can be carried very much 

 further. Most, perhaps all of the Continental 

 and Exotic species of the genus Colias. have 

 these pale females, and the noticeable fact 

 is this, that while the species differ greatly 

 in the various shades of yellow, the pale 

 varieties are all of the same very pale 

 greenish hue. But by referring to one or 

 two of other Continental Butterflies the 

 case would have been made still stronger 

 and clearer, by the evidences of species still 

 in a state of transition. In some instances 

 the female still retains the pale hue that 

 I suppose the original form to have poss- 

 essed. Phicomone, a butterfly occurring in 

 the Alps, Pyrenees, and perhaps in northern 

 Europe also, is an appropiate illustration. 

 The female is always of the pale greenish 

 shade of our own Helice, and I am not aware 

 that it ever occurs of the yellower hue of 

 the male. Paloeno, another mountain species, 

 occurring not only in Europe, but also in 

 northern Asia, and in the Dominion of 

 Canada has also a pale female, but this spe- 

 cies may be considered to be rather more 

 advanced than Phicomone for a rare form of 

 the female is found of the brighter yellow of 

 the male. In this instance the pale female 

 is assumed to be the type, and the rare 

 yellow one is known as var. Werandi, H, S. 



