MELANISM AND MELANOCHROISM. 171 



very clear (although showing seasonal variation within certain 

 limits), white on the upper, and yellow or greenish grey on the 

 under surface. In many Scotch and Irish localities it is nor- 

 mally much darker and more suffused, and on the Alps the 

 spring form — var. bryonicB — is very dark. But in the South of 

 England, Pieris napi settles on leaves, where its yellow or 

 greenish underside protects it to a great extent ; while in the 

 Alps, the extreme form frequently settles on the bare ground, 

 or on vegetation more or less blackened by cold and exposure, 

 where its darker coloration is now particularly protective. The 

 undersides of Vanessid(S bear great resemblance to dead leaves, 

 the yellow and greenish undersides of Pieridce to green leaves ; 

 the speckled undersides of Lycenidcs to the inflorescence of 

 grasses, and, indeed, it could easily be proved that every parti- 

 cular species has its undersides particularly developed to suit 

 its surroundings, e.g., Euchloe cardauiines, HipparcJiia seinele, and 

 Thecla riibi, are striking examples. I think I have shown that 

 all our butterflies (for purposes of variation) should be studied 

 from their undersides, and have cited enough examples to show 

 that white or other coloured butterflies will continue to exist 

 side by side with dark moths, and that such facts are not at 

 variance with the theory advanced. Geometers which rest in 

 the same position as butterflies will also have to be studied from 

 the same standpoint. The genus Selenia occurs to me at the 

 present moment. 



Again, a thoughtful lepidopterist says : — " If your theory be 

 true, then the same effect ought to produce the same result. 

 Take for example Folia chi ! Why in Durham are the dark 

 specimens of c/ii always inclined to var. olivacca, while the dark 

 var. in Yorkshire is so different ? " The reason is not far to 

 seek, but our lepidopterists must bear in mind that we have 

 two^ strong causes at work: — (i). The exciting cause in the 



^ I would ask all my readers who pay attention to this subject, not to form hasty 

 opinions where their observations do not appear to coincide with my conclusions, but 

 to take into account all the surrounding circumstances, and above all to have plenty 

 of material for comparison. It is useless to form an opinion on the difference be- 

 tween a few (say less than a score or so) specimens from different localities, and 

 equally useless to compare specimens from comparatively adjacent districts, e.g., 

 Lancashire and North Wales, and expect a striking difference. Often there will be, 

 but more often there will not. Apkcta uebitlosa from Glasgow is occasionally of a 

 beautiful white colour, altogether different from our South of England specimens. 

 Following out my theoi-y the Glasgow specimens should be darker,"but some outside 

 force undoubtedly modihes the species in this district, with the result that it differs 

 in the way I have pointed out. I do not doubt that if I saw this insect in naturd 

 at Glasgow, I could easily explain this apparent opposition to my theory, but I 

 know nothing about its environment there. — J.W.T. 



