﻿CHEMISTRY OP INSECT COLOURS. 37 1 



progressive colour-changes which go on as many fruits ripen, and 

 in many leaves towards autumn, that the evolution of red from 

 yellow is emphatically the rule. I hardly think that this will be 

 disputed : very well then ; in every experiment, without exception, 

 in which red or pink was changed by my reagents (and red 

 species in every group of Macro-Lepidoptera have been tested), 

 it was invariably changed to orange and yellow, or in one or 

 two cases to the closely allied chestnut. Here, even if we went 

 no further, is a most substantial base from which to argue that 

 such changes as these reagents produce are always retrogressive. 

 But other instances may be quoted. Everyone knows that the 

 orange of Euchloe is a comparatively recent development on an 

 otherwise white species*: very well; then it is clear that, in 

 dissolving out this colour and leaving the wing white, as it 

 originally was, I have effected a retrogressive change. In fact, it 

 appears to me self-evident that in all cases in which a colour has 

 been dissolved out a retrogressive change has been effected ; but 

 I refrain from relying on this as a proof lest possibly some readers 

 may not incline to admit so much. Next we may take such a case 

 as Thecla rubi. It will undoubtedly be admitted that the green 

 on the lower side of the hind wings has been developed as a pro- 

 tective resemblance to the foliage : this green is changed by every 

 reagent to the brown colour displayed by all the rest of the wings ; 

 what better instance of a retrogressive metamorphosis ? Finally, 

 since we must assume that the uncommon and beautiful blue 

 of Lycsenidse has been developed (why we don't know, unless 

 Darwin's theory of Sexual Selection be adopted) from the dull 

 colours of primeval Lycasnidse, it must be admitted that the 

 abolition of this by the reagents is also a retrogressive change.t 

 I hope now to have made it clear that the whole weight of the 

 evidence — where it can be checked by admitted entomological 

 facts— supports my assumption that these changes are in every 

 case retrogressive. For the contrary assumption (if it should be 

 made in any case where we have only the chemical evidence to go 

 upon) there is no direct evidence from Entomology whatever, and 

 such an assumption can only involve the whole issue in confusion 

 and contradiction. Here, then, I quit the subject, leaving the 

 arguments just instanced to be borne out by the general character 

 of the results obtained by arguing upon this assumption. 



In the next place it will be as well, perhaps, if I draw atten- 

 tion here to an important fact that concerns all the colours gene- 

 rally rather than any one group especially ; and will therefore be 



* Cf. Darwin's ' Descent of Man,' chap. 11. 



t I am afraid, however, that the validity of this last argument will be denied 

 by any who hold, with Wallace, that the bright colours of males are the originals, 

 and the dull colours of females the derivatives. But, at any rate, the argument 

 from red and yellow is irrefragable ; and on the strength of this alone it would be 

 legitimate, arguing from analogy, to hold that all the changes were retrogressive,— 

 at least until any could be directly proved otherwise. 



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