﻿310 THE ENTOMOLOGIST. 



and the remaining colours have totally failed, and the failure has 

 taught us almost nothing, — and in fact left the problem somewhat 

 more perplexed than it originally was ; whereas any success in 

 the attempt to change the black colour by chemical reagents 

 might have taught us a good deal. Nothing observed in the 

 course of my investigations caused me, perhaps, more surprise 

 or disappointment than this immovability of black. As has been 

 shown, in every case it has resisted the action of every reagent, 

 and although I experimented on the most various species, selected 

 from widely different families and groups of Lepidoptera, yet in 

 not a single instance did I effect any change. Under these cir- 

 cumstances, then, I think it is justifiable to conclude that the 

 black of Lepidoptera is simply a physical absorption colour, and 

 in no way due to pigment. It seems to me quite hopeless to 

 farther examine black species of Lepidoptera ; and although, in 

 pursuing this investigation among the exotic species sent to me, 

 I shall continue to experiment on some black species, this will be 

 done merely on principle and as a precaution, but with very slight 

 hope of success. For although, in one sense, it may seem very 

 rash to argue so confidently from the results yielded by a few dozen 

 English species, yet the unbroken uniformity of these results 

 and the representative character of the species are, I think, 

 sufficient justification, — especially, too, when the significance of 

 all the other results is considered. 



Now a caution is requisite here. I most certainly would not 

 assert that, because the colour of a given species cannot be 

 chemically altered, therefore it is a physical colour and not a 

 chemical : it may certainly seem surprising that a pigment should 

 resist the action of powerful chemical reagents, but among the 

 yellows we have pretty conclusive evidence that many do^ If the 

 table of results in yellow be consulted it will be seen tharwhilst 

 some yellows are turned completely white, others are with diffi- 

 culty affected, and some are absolutely immovable. Now I am not 

 at present prepared to assert that all of these immovable yellows 

 are pigment colours, although I shall presently show reasons for 

 suspecting so ; but I do contend for it as indisputable that some 

 are. It is, I think, impossible to deny that the yellows of Arctia 

 villica and Callimorpha hera lutescens are pigment colours, in 

 the face of the close relationship of these species to the red 

 pigmented species ; but these two yellows are absolutely immov- 

 able. And if stronger evidence still be asked, we have it in the 

 fact that whereas in almost all species red is rapidly changed to 

 yellow by the reagents, the change stops here* and although we 

 have clearly a pigment in evidence, that pigment is sensitive to a 



* I stated (Entom. 158) that in no instance had I succeeded in carrying a retro- 

 gressive change further back than one stage. Since that was written I have 

 succeeded, in at least one striking instance, in getting a second retrogression ; details 

 will be given in their due place. 



