﻿370 THE ENTOMOLOGIST. 



CONTRIBUTIONS to the CHEMISTRY of INSECT COLOURS. 



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



(Continued from p. 343). 



V. — The Chemical Aspect (continued). 



E. 



Perhaps before entering into details concerning yellow, 

 which is our first pigment colour, I ought to justify an assump- 

 tion that has been made from the outset concerning the changes 

 wrought in all the colours experimented on, — viz., that the trans- 

 formation effected by my reagents is uniformly and invariably 

 retrogressive ; that in no instance has a progressive modification 

 been effected, — for the apparent exception of Melanargia galatea 

 has already been explained, and shown to be no exception at all. 

 The justification of this assumption I feel to be important, since 

 to disprove it were to pretty nearly demolish the entire fabric of 

 theory and explanation that I have built upon my experimental 

 data. And yet to say truth, when I first set myself to give a 

 formal demonstration of this fundamental principle, I felt some- 

 what nonplussed. The evidence for it is so essentially of a 

 cumulative character that it would be far easier simply to call 

 attention to the assumption, and then leave it to be justified by 

 the whole mass of experiments, and its reasonableness shown by 

 the satisfactory results yielded by inferences drawn from it. As 

 a matter of fact, this conception of the character of my experi- 

 mental results has grown up almost irresistibly in my mind during 

 the progress of my experiments, and has seemed to me through- 

 out a matter of course. But it is evidently impossible that my 

 readers, by merely reading of experiments, should evotve the 

 same mental conviction that has gradually grown up in myself: 

 some more formal justification must be offered to them ; and I 

 was really somewhat taken aback when it occurred to me to ask 

 myself how I should justify to others a conviction founded on 

 experience that is naturally incommunicable. At any rate, how- 

 ever, it behoves me to try what account can be rendered. 



I think, then, that I should base my case primarily and 

 especially on the behaviour of reds. It is universally admitted, 

 I suppose, that red is developed through orange from yellow ; 

 the very stages almost may be seen in some species, as Arctia caia 

 and Catocala nupta, in which species the deep red of the wing 

 shades off into a very pale colour where it is overlapped by the 

 fore wing. Moreover, as previously pointed out, A. caia and 

 Vanessa atalanta, when first emerged, are often rather of an 

 orange than a red colour, the colour deepening in a day or two. 

 This evolution of red from yellow and orange is not confined to 

 insects; everyone may easily satisfy himself by observing the 



