﻿CHEMISTRY OF INSECT COLOURS. 841 



ever, be most laborious, seeing how imperceptibly one white 

 shades off into another ; and hence it was that I attached so 

 much importance to the evidence that might be obtained by means 

 of reagents. But such evidence is not forthcoming, and my hopes 

 must be abandoned. 



Let me now draw attention to the behaviour of some few 

 species in particular. First, as to Pieris. The statement made 

 some time since in ' The Entomologist,' that the white of Pieris 

 is due to reflection from air-spaces, has already been quoted. I 

 do not know on what evidence this view was originally put 

 forward by Dr. Dimmock, but it appears to me to be supported 

 b}' the reaction with staining reagents. The effect of methyl- 

 aniline green and violet (see Table, p. 220) was to produce an 

 apparent thicPcness of colour, such as I saw in no other instance. 

 The appearance of the stained wing strongly suggested to me 

 the thought that this " thickness " was due to the stain filling up 

 these air-spaces.* 



Next as to Melanargia galatea. I drew special attention, in the 

 Table, to the fact that this species had been stained by methyl- 

 aniline violet a different colour from that produced in any other 

 species. It is of course impossible to convey, by a mere descrip- 

 tion, the difference in appearance between this and other stained 

 species ; but I think that anyone who had seen the experiments 

 would have felt as I did, that in the unique appearance of galatea 

 we had additional illustration of its unique constitution, — its 

 difference from other white species. But with regard to the yellow 

 produced by various reagents in this species, no doubt it will be 

 asked what explanation, if any, can be offered of this exceptional 

 and anomalous behaviour of galatea : why should it react in a 

 manner so contradictory and opposed to all that one might expect, 

 — judging from the other experiments ? Well, after studying the 

 question, I conclude that the anomaly and exception — striking 

 though they seem — are apparent only, and not real ; that if the 

 views laid down in foregoing paragraphs be assented to, there is 

 here no real difficulty at all. Nay, more, the reactions of galatea 

 may be interpreted as lending additional support to my theory ; 

 and, in fact, I am confirmed in my views by the independent 

 support that they derive from this behaviour of galatea, since I 

 was originally led to such conclusions without any reference to 

 the phenomenon now in question. If, however, my views be 

 entirely wrong, — if there be a white pigment which gradually 

 developed into yellow or chestnut, — if the destruction of yellow 

 and chestnut by reagents be due not to a solution of the pigments, 



* In this connection I might add that the white of some species of flowers is 

 certainly due to this cause. If pressure be applied the air-spaces are broken, the 

 white disappears, and a colour appears, due to a pigment present in slight quantity, 

 whose effect was apparently veiled before. 



