c^MisTRY OF Insect colours* l3^ 



Now, the first remark that I have to make about blue is that 

 this is a thoroughly disappointing and unsatisfactory colour. 

 There is almost as little satisfaction (in the way of discovering 

 any pigment) to be got out of blue as out of black and white ; whilst, 

 in addition, there is considerable worry and perplexity attending 

 the study of these blue wings. I may say at once that in this, 

 alone of all the five colours, I have no clear evidence as yet of 

 there being any pigment present ; nay, further, in all the groups, 

 except the Lycasnidse, — concerning which I am still in doubt, — it 

 seems fairly certain that the colour is simply " physical." It is, 

 of course, well known how comparatively rare a colour among 

 flowers is blue ; it seems there to mark some special complexity 

 and specially high differentiation in the parts so coloured. It is, 

 therefore, possible that there is, chemically, some considerable 

 difficulty in the evolution of a blue pigment; and, may be, such 

 has not been evolved among the Insecta ; but, be that as it may, 

 we must certainly admit that the want of pigmental blue in the 

 Lepidoptera has been far more than compensated by the un- 

 surpassable brilliancy of the physical blues in which they rejoice. 

 Unfortunately, these physical blues, though very beautiful from 

 an aesthetic standpoint, possess only the minimum of interest from 

 the chemical. 



After what I have said in the preceding section on "physical" 

 greens and bronzes, &c., my readers will be able to follow 

 the present discussion without further explanation on these 

 points. 



First, of all, as to group 1. In all three of these species there 

 is the same rich purple velvet glow, unmistakably characterising 

 this as a physical colour. Wallace had remarked, some years ago, 

 that the blue of A. iris was probably a physical colour, and my 

 experiments fully confirm this. Directly that A. iris came into 

 my hands in the course of this research, I felt convinced that 

 there was no pigment colour here ; and so it proved. In these 

 three species, the various reagents either are without effect or 

 produce temporary dulling, or permanently injure the surface 

 structure, and consequently the colour. 



No. 2 group is still more unsatisfactory. The colours of the 

 species noted here are clearly closely related to those greens 

 which become bronzed or browned ; it will be noticed that some 

 of these become of a dull " leaf-brown," which seems to point to 

 some temporary injury or alteration of a fine surface structure ; 

 others become of a steel-blue, which is strikingly " physical " in 

 appearance. Concerning this group, also, there can be no doubt 

 as to the physical nature of the colours throughout. I have 

 included in this group, also, M. menelaus, the brilliant blue of 

 which, as I only too truly anticipated, is simply physical. Indeed, 

 it may well be doubted (is there even room for doubt ?) whether 



