﻿CHEMISTRY OF INSECT COLOURS. 311 



certain extent only, and after that is absolutely unassailable. I 

 must, however, defer the full discussion of this interesting phe- 

 nomenon until we are dealing with the yellows; my object in 

 anticipating so far here being simply to show that apparently 

 indubitable pigment colours may resist the action of all the 

 reagents, and that therefore it is not legitimate to assume any 

 given one or two colours to be physical, and not pigment, colours, 

 because they are chemically unaffected. Nevertheless I do think 

 the assumption fairly legitimate in the case of black, owing to 

 the unbroken uniformity of the results and the absence of any 

 single contravening result. 



It should be remembered how very various are the species 

 that have been examined, and how very different the relations ot 

 black in them to the other colours. It is not as though all these 

 species were uniformly black, or as though in all of them black 

 were found associated with the same second colour, or occupied 

 the same position on the wings. If that were the case it might 

 justly be said that the only legitimate inference would be that one 

 black of wide occurrence was immovable, and not a pigment 

 colour ; whilst other blacks might exist that were pigment colours. 

 But the case is not so. Consider how different in character are 

 these blacks. In Pieris black occurs with tvhite, as spot and tips ; 

 in Melanargia galatea and Arctia caia equally distributed with 

 white ; in Spilosoma menthastri as small dots on white, and simi- 

 larly in A mphidasys betularia ; and as larger spots on white in 

 Abraxas grossidariata. Then, in combination with yelloiv, we 

 find it as broad tips in Colias and Triphcena, and small spots on 

 Venilia macularia. With the closely allied chestnut, too, it 

 occurs as prominent tips, blotches, or ocelli, on Argynnis, Melitcea, 

 Vanessa cardui, Pararge megcera, Epinephele tithonus, Coenonympha 

 pamphilus, Polyommatas pldceas. Combined with red we find it 

 in Vanessa atalanta as apparent base or ground colour, and very 

 glossy ; as almost tarry blotches on the hind wings of Arctia, 

 and as groundwork again in Catocala. Combined with green it 

 occurs in Agriopis aprilina and Moma orion, and with grey in 

 Acronycta psi. So that here we have found it in various 

 positions combined with all the chief colours (except blue) ; and, 

 lastly, we have it alone as occupying the whole wing in Tanagra 

 atrata, Lyccena astrarche v. artaxerxes, and Epinephele hyperantlies. 

 But it is very remarkable that, however and wherever it occurs, 

 it is always the same immovable black. 



Now when we find any two or more pigment colours on the 

 same species, the conclusion is almost irresistible that a genetic 

 relationship must exist between them, if we can only discover it. 

 If any one given colour be found in different species, combined 

 in turn with all the other colours, a very especial interest 

 attaches to it, since one naturally hopes to find in it a common 

 basis by which to connect genetically all the other colours ; 



