﻿CHEMISTRY OF INSECT COLOURS. 813 



a merest conjecture that may be utterly erroneous — they are found 

 only among the higher groups of the animal kingdom, and not 

 among the lower ; * and in this connection one is tempted to 

 adduce the fact that black flowers are almost, if not entirely, 

 unknown. It would be somewhat interesting, therefore, to know 

 whether or not black pigments are usually products only of a 

 higher organisation than that of insects. 



Then, again, there is another most interesting problem on 

 which any definite chemical results from black might have thrown 

 considerable light, — whereas, as it is, we are none the wiser. I 

 refer to the phenomena of melanism. With regard to true 

 melanism (as distinguished from melanochroism), it has been 

 a great disappointment to me that nothing bearing upon 

 this interesting subject has come from my work. It may 

 be suggested that the phenomenon of melanism — i. e. of a 

 black colour encroaching on and superseding other colours — is 

 hardly to be reconciled with the supposed absence of any black 

 pigment ; whereas melanism were easily explicable if the ordinary 

 pigments became transformed by some easily conceivable chemical 

 change into a black pigment. But with regard to this objection 

 I may point out that the development of melanism (in the 

 absence of any black pigment) is no more difficult to understand 

 (i. e. as a colour change — I do not speak of its ultimate cause) 

 than the occurrence of black on Argynnis brown, on Rumia 

 yellow, on Pieris white, and on Lyccena blue, &c. Neither is 

 it, perhaps, even so great a difficulty as that of the black wing 

 of Vanessa atalanta, which I believe to have been developed from 

 an ancestral form closely similar to (or identical with ?) V. cardui,\ 

 by a replacement of chestnut by black. In all such cases we 

 must suppose that the "absorptive" — the black — scales have 

 encroached upon the pigment-containing scales. Nevertheless, 

 as a final caution, I must add that, since no melanic forms have 

 come into my hands, I cannot positively state that in them also 

 black is a non-chemical colour, and insensible to the action of 

 reagents. I know only the conduct of ordinary normal blacks, 

 and it is just possible that melanic forms may be due to a real 

 pigment. For the determination of this point I must wait my 

 opportunity ; but I confess to having very little hope of finding, 

 even in melanic forms, a black pigment. 



In view of the complete unanimity of behaviour in the various 

 black species experimented on, it seems unnecessary to animad- 

 vert on them individually, or group them according to the minor 

 varieties of appearance or distribution of colour. As I have 



* One must except, however, the sepia of the Cuttle. I have written the above 

 paragraph only with considerable hesitancy, since it is purely conjectural, and may 

 well be altogether erroneous. 



t Further consideration of this topic I must defer until the brief section on the 

 " Biological Aspect," which it is anticipated will conclude these articles. 



ENTOM. — OCT. 1890. 'Z B 



