CONTRIBUTIONS to the CHEMISTRY of INSECT COLOURS. 

 By F. H. Perry Coste, F.C.S. 

 (Continued from vol. xxiii. p. 374.) 

 V. — The Chemical Aspect (continued). 

 Let us then endeavour, as a first step towards understanding 

 yellow, to analyse the results tabulated on p. 248, and group 

 them into subclasses. Without postulating too rigid a separation, 

 or regarding such subdivisions as other than convenient artifi- 

 cialities, we seem able to distinguish three main classes of yellow 

 species. Firstly, those that are utterly unaffected by any reagent ; 

 secondly, there is the least exact division, consisting of those 

 species that a7'e affected, but slowly and indefinitely, yielding an 

 unsatisfactory sickly whitish, or faded yellowish; thirdly, we have 

 the highly interesting and satisfactory class of yellows that 

 rapidly dissolve and leave a pure white wing ; a pigment being 

 indubitably in evidence here. This difference will be more 

 clearly brought out if we tabulate the species in three columns 

 thus (and I take the opportunity of adding, by way of further 

 illustration, the names of a few among the tropical species sent 

 me) : — 



UNAFFECTED. 



All metamorphosed reds. 

 Callimorpha hera lutescens. 

 Arctia villica. 

 Papilio thoas. 

 Triphaena pronuba. 

 Heliaca tenebrata. 

 Catocala palseogama. 

 Angerona prunaria. 

 Xanthia silago, 

 (The last two or perhaps 



three not being quite so 



absolutely unaffected as 



the others). 



UNSATISFACTORILY AFFECTED. 



Papilio machaon. 



Vanessa antiopa. 



Gonopteryx rhamni. 



Lyceena alexis. 



Hepialus humuli. 



Bunaia cratsegata. 



Venilia macularia. 



Camptogramma bilineata. 



Catocala cerogama. 



Abraxas grossulariata. 



(This last species would 

 perhaps be almost more 

 justly placed in the third 

 class). 



EAPIDLY DISSOLVED. 



Euchloe cardamines. 



Colias edusa. 



Euremia hecabe senegal- 



iensis. 



Tsenias nise. 

 T. vabella(?). 

 Delias hierte and eucharis, 

 and one metamorpJwsed red, 



viz.,D. hierte (eucharis). 



It thus appears that although I have throughout insisted on 

 yellow being emphatically a pigment colour,* yet the species in 



* There is another and somewhat different view as to the nature of these various 

 yellows that ought, perhaps, to be pointed out at any rate. In the earlier stages of 

 my experiments it so happened that I had no specimens of edusa or cardamines to 

 hand. For a long time, therefore, my knowledge of yellow was derived entirely 

 from those species that are either entirely obdurate, such as T. pronuba, or very 

 unsatisfactorily affected, as G. rhamni, &c. Add to this the fact that in every red 

 species examined the change stopped at yellow, — which could be in no case further 

 affected, — and it will create no surprise that I was very near concluding yellow to be 

 always an immovable colour ; a result as disappointing as unexpected. The first 

 species that opened my eyes was A. grosaulariata : in this case I found the yellow 

 slowly but completely disappear. This result was so contrary to my previous 

 experience that I carefully repeated the experiments, but with the same result. I 

 thus had forced upon my notice the fact that some yellow ivas sensitive to reagents 

 (a result so strikingly and abundantly confirmed when I came to examine edusa, 

 cardamines, &c.). Now, if such species a'^/)?-o?()//w and rhamni, on the one hand, be 



