﻿CHEMISTRY OF INSECT COLOURS. 339 



greys, et id omne genus, are really pigment colours ; but so far as 

 I can at present interpret them, my experiments do not seem to 

 countenance this view. And if black be admitted as a physical 

 and not a pigment colour, then my view derives much support 

 from the colour phenomenon, so abundantly displayed in the 

 Noctuse, where black shades off by the most imperceptible 

 degrees into greys, duns, and browns. 



D. 



Since it is evidently best that we should dispose of all the 

 disappointing and uninteresting colours in the first place, before 

 passing on to those which have yielded some results other than 

 nil to the experimenter, we will now consider the case of white. 

 As already explained, I had originally anticipated (as doubtless 

 most would have done) that white would prove a very interesting 

 colour. Its manifest connection with yellow, as seen in so many 

 of the Pieridse, e. g., naturally suggested that it might be possible, 

 by means of reagents, to promote in the partly or wholly white 

 species colour changes (to orange and yellow), that nature had 

 already brought about in neighbouring species ; or, in part only, 

 in an otherwise white species. But my readers fully understand 

 by this time how fallacious were all such hopes ; and after the 

 arguments that I have already adduced to support the view that 

 black is no pigment colour, but merely a physical absorption 

 effect, it is hardly necessary here to do much more than propose 

 the view that white is equally a physical colour, but due to 

 reflection. As with black, so again here, I can instance the com- 

 plete unanimity (always excepting galatea and the fringes of 

 Lyccena, &c.) among experiments made on the most widely- 

 sundered species, — an unanimity the more striking since there 

 are manifest differences in appearance between the various whites. 

 The whites of Pieris, Vanessa, Hepialus, Larentia, and Liparidte, 

 for instance, are by no means identical in appearance. 



An argument against this view (of the non-pigmental cha- 

 racter of white) might be found in the fact that many yellows — 

 as I have myself shown — are turned white by most of the re- 

 agents employed ; and from this fact it might be argued that if 

 yellow — an acknowledged pigment colour — is convertible chemic- 

 ally into white, therefore conversely white must be a pigment 

 colour, and convertible by some other reagents (if one only knew 

 what "some"), or at any rate by Nature, into yellow. But this 

 argument, if advanced, were altogether futile, and for this simple 

 reason: — the yellows, e.g., of Colias and Euchloe are not changed 

 into white at all, in the sense that a yellow pigment becomes 

 wliite ; but the yellow pigment is dissolved out of the wing, 

 having this of the same pure white that the primeval Colias and 

 Euchloe, no doubt, displayed thousands of years ago. Therefore, 



