l34 tHfi ENtOMOLOGIST. 



any pigment could possibly yield the extraordinary sheen that 

 characterises this and some other blues.* 



Group 3 is even less satisfactory and less interesting than the last. 

 I have already referred to the blue of P. machaon. Anyone who 

 wishes to observe a good example of the behaviour of a physical 

 colour should try the experiment of thoroughly wetting this blue 

 spot on machaon, and watching the blue reappearing as the wing 

 dries. The blue of S. ocellatus is most unsatisfactory, and, I 

 believe, of the same nature as that of machaon. As to C. fraxini, 

 I have, in a former place, expressed my intense disappointment 

 at being able to find no kind of clue or connection between this 

 blue and the scarlet of nupta, and so many other CatocalceA It 

 is however, I think, hardly possible to doubt that in Catocala 

 fraxini we have simply a physical blue in evidence, and that by 

 no means a brilliant one either. 



Before proceeding to group 4, 1 must make a passing reference 

 to Hypolimnas salmacis. My only reason for placing this in a 

 group by itself was not any peculiarity in its behaviour, but 

 simply the fact that its natural colour was a violet, something 

 different, therefore, from any of the other species included in my 

 lists. It is, of course, merely another physical colour. 



Now for group 4 — the Vanessidse. Sadly, indeed, was I dis- 

 appointed in these species. In the early days of my experiments 

 I expected great things from experimenting on these beautiful 

 blues. Knowing that in flowers blue usually appeared on highly 

 differentiated parts, it appeared to me of special interest that in 

 the Vanessce the blue should, in most cases, appear as a row of 

 spots near the edge of the wing; and, also, on V. io in the 

 conspicuous and clearly highly developed ocellus. To the 

 examination of the Vanessa blues, therefore, I devoted myself 

 with special interest and attention in the early stages of my 

 work, and made very numerous, repeated, and careful experiments 

 on them. I had not then learned how heavy were the probabilities 

 against any blue being a pigment colour ; and it seemed scarcely 

 credible to me that so highly differentiated a pigment, as I 

 assumed the blue to be, should offer any resistance to strong 

 reagents. However, after long and careful experimenting, — in 

 the course of which, as will be noted, I examined four species of 

 Vanessa, and in two species separately examined the blue on 

 different parts of the wing, — the hard logic of facts drove me to 

 conclude that in Vanessa the blue is pretty certainly physical. 

 The phenomena throughout are in accord with this, especially so 

 the frequently observed fact that the blue might vanish during treat- 

 ment, but reappear on drying the wing. It will be noted that in 



* There is another brilliant blue species, whose name I do not know, often to be 

 seen in dealers' cases. In one light this is a brilliant blue, like menelaus ; in 

 another, a dull colourless brownish. Of course it is positively certain that such a 

 colour must be physical* 



f Ante, p* 15. 



