﻿CHEMISTRY OF INSECT COLOURS. 285 



This being so, there is some consolation to me for the (chemically) 

 negative and disappointing results of so many of my experi- 

 ments, in the reflection that they have at any rate served to 

 confirm the opinions previously put forth on wholly different 

 grounds by various naturalists. But to this point we will return 

 subsequently. 



Now, with a view to classifying lucidly the explanations that 

 I shall have to give of the various colour phenomena under 

 discussion, I wish at this point to propose a subdivision of these 

 physical colours into several classes, although in so doing it is not 

 easy to avoid making somewhat arbitrary distinctions ; but it 

 must be remembered that these subdivisions are proposed with 

 special reference to these experiments. From Wallace's view, as 

 expressed in the statement* that "the colours which we perceive 

 in material substances are produced either by the absorption or 

 by the interference of some of the rays which form white light, 

 Pigmental or Absorption colours," &c, I must dissent ; for this 

 appears to me to be both an incomplete account and also to con- 

 fuse two different classes — or, if you like, sub-classes — under the 

 one term of absorption colours. The subdivision now proposed 

 is as follows : — 



First, Interference colours — whether of films or fine lines 

 (striated surfaces). Inorganic examples are, — of films, soap- 

 bubbles, the colours of molten metals, iridescent glass, stagnant 

 water, and so on: of striations, the colours of mother-of-pearl, f 

 "shot"-silk, &c. 



Secondly, Reflection " colours " — other than interference 

 colours. Of course all interference colours as seen on the icings 

 of birds and insectsl are reflected ; but under this class-heading 

 I am denoting such "colours" as are produced by simple re- 

 flection without the interference colours due to films or striations. 

 Under this subdivision we shall be chiefly concerned with the 

 " colours " of white-winged species, and also apparently of the 

 " metallic " markings displayed by Argynnis, Plusia, &c. It is 

 almost superfluous to instance as inorganic examples such 

 objects as white paper, and the like large category, for the former ; 

 whilst as regards " metallic or quasi-metallic reflection," it has 

 been also pointed out to me that, besides the coloration of polished 

 metals in this manner, another example is afforded by the colours 

 of aniline dyes under certain circumstances, — e.g., when a drop 

 has been spilled on the neck of the bottle, and dried there. 



* ' Tropical Nature,' pp. 182-3. 



t If a mother-of-pearl shell be impressed upon wax, the colours will be found 

 transferred to the wax also ; clearly demonstrating them to be due to a surface 

 structure. 



I Unless we looked through the gauzy wings of Neuroptera, &c, in which case 

 aid see similar (tfurefiected) interference colours in positions complementary 

 to the reflected colours seen from above. 



ENTOM. — SEPT. 1890. Y 



