86 THE ENTOMOLOGiSt. 



Lyc.ena astrarche. — Does not exhibit any material difference 

 .from European examples. 



The Heterocera will be considered in a future paper. 



CONTRIBUTIONS to the CHEMISTRY of INSECT COLOURS. 



By F. H. Perry Coste, F.C.S., F.L.S. 



(Continued from p. 60.) 



V. — The Chemical Aspect (continued). 

 G. 



In this subsection we have to consider the case of chestnut, a 

 colour sufficiently interesting,* but one which need not detain us 

 for an unduly long time. 



My readers are already familiar with the broad facts as to this 

 colour, viz., that it is a close analogue of yellow, and, like it, has 

 been developed on or in, but not from, white wings, and also in 

 one or two cases in wings of another " colour " than white ; that 

 it also, like yellow, belongs to the class of soluble, as distinguislied 

 from alterable, pigments ; and that in exceptional cases it may also 

 — as yellow so frequently does — develop into a red. Furthermore, 

 we are able to distinguish with chestnut, as with yellow, pro- 

 gressive stages in stability (insolubility) ; and, as apparently a 

 yet closer analogy, we find it possible that the chestnut pigment 

 may advance to a very high stage of brilliancy, while yet remain- 

 ing in the primeval stage as to solubility. This fact is exemplified 

 by V. urticce, and Polyommatus phloeas and virgaurea — instances 

 that may, perhaps, be compared with E. cardamines among the 

 yellows. And, in saying this, I should like to take the opportu- 

 nity of clearing up a passage that 1 fear is reprehensibly ambiguous, 

 and very liable to misinterpretation, in the foregoing subsection. 

 In classifying the yellows (Entom. xxiv. p. 9), I divided them into 

 three classes, according to their solubility or otherwise, and I placed 

 E. cardamines in the fiist class, as possessing a very soluble pig- 

 ment. So far, this is all right ; but I fear that my subsequent 

 remarks may very well be interpreted as implying that E. carda- 

 mines represented the initial stage of colouring — a stage beyond 

 which the yellow species in classes 2 and 3 have considerably 

 advanced. Now, seeing that cardamines is far more brilliantly 

 coloured than many of the species in these two later classes, such 

 a statement must seem very incongruous. But I ought to have 

 more strongly emphasised the fact that while in so many yellow 

 species an advance in depth of colour seems to go pari passu 

 with a decreasing solubilit}^ — this being the contention that my 



* And the more so since — to quote Wallace — " reddish or yellowish brown is, 

 jDerhaps, the commonest colour among butterflies " (' Tropical Nature,' p. 190). 



