CHEMISTRY OP INSECT COLOURS. 209 



In accordance with what has been previously stated,* it 

 appears not improbable also that green varieties of pale yellow 

 species, and very occasionally red varieties of some chestnut 

 species, may be found. It is scarcely necessary to point out that 

 while there are definite data for predicting retrogressive varieties 

 for any given coloured species (the genealogy of whose colour is 

 known), there are no such reasons for predicting progressive 

 variation, i. e., an advance to a higher colour, which the history 

 of other species shows to be possible, but cannot show to be 

 inevitable. Enough has, however, now been said to show along 

 what lines we should look for coloric varieties. 



There now remains one further point only for discussion, viz., 

 the genetic relations of white, yellow, and red. I had originally 

 supposed that it would be necessary to argue this at some length, 

 in order to convert those who may have adopted Mr. Cockerell's 

 views ; but I think that by this time the amount of evidence 

 that has been detailed, bearing more or less directly on this 

 discussion, renders any lengthened argument at this stage super- 

 fluous. 



Mr. Cockerell proposed — if I understand him — as a hypo- 

 thetical explanation, that the primeval! colour was yellow, that 

 from this was evolved white, and from (?) this again red. I think, 

 however, that the evidence brought forward in these articles may 

 be considered absolutely to demonstrate the incorrectness of this 

 view, and to show that the order has been white, yellow, red. 

 Both the experimental evidence and the entomological evidence 

 {i.e., of variation, &c.), are dead against Mr. Cockerell's view. 

 Eed and yellow are proved to b.e pigment colours, white is not : 

 are we to suppose that originally there was a yellow (i. e., pig- 

 mental) wing ; that then, by an evolutionary advance, a white 

 (i. e., unpigmented) wing was produced ; and then, finally, a red 

 (i. e., pigmented) ? Again, on such a view it is incomprehensible 

 that yellow varieties of red both occur naturally, and appear as 

 the result of chemical reagents acting on red species ; while 

 white varieties are almost, if not quite, unknown in nature, and 

 very rare in experiment, and then only as subsequent to yellow. 

 Moreover, the one or two instances in which I have obtained 

 white wings from red form the last link in the chain of evidence, 

 and are absolutely convincing against such a view ; for, as has 

 been already stated,! if we take Delias hierte or eucharis, we have 

 side by side red, yellow, and white : acids instantly turn the red 

 to yellow, and then this yellow and the original yellow alike 

 dissolve, leaving a pure white wing.§ Nothing could more plainly 

 demonstrate that the genetic order of the colours is white, 



* Cf. Entom. xxiv. pp. 118, 119, and 138, 139. 



t I do not mean of all species, of course. 



X Entom. xxiv. 13. 



§ Gf., too, G. Cleopatra. 



