188 The eSttomologis*. 



directions in which such variations might occur ; either one 

 physical colour might replace another, or it might replace a pig- 

 ment colour, or it might be replaced by a pigment colour. As I 

 have already pointed out,* whenever a replacement of pigmental 

 colours by physical colours occurs, we can only say that the 

 pigment- containing scales have been replaced by unpigmental 

 scales, whose structure is such as to produce the given physical 

 colour. Whether the pigmental scales are merely overlaid by the 

 others, or whether there is an actual absence of pigment, is a 

 highly interesting question, but one into which I am — for want of 

 data — unable to enter here. As examples of such replacement of 

 pigment colour by physical colour, I may refer to the cases of 

 true melanism (as distinguished from melanochroism) : in the 

 Doubleday collection are specimens of V. urticce with the hind 

 wings dull black, of C. dominula and A . villica with all the wings 

 entirely black, of T. orhona with hind wings almost entirely dull 

 black. In recent volumes of the 'Entomologist' have been 

 chronicled a black variety of L. Sibylla (Entom. xxii. 256), of 

 A. aglaia (Entom. xxiii. 350), and so on. To these also I may, 

 perhaps, add the variety of an Argynnis noted as having a 

 brilliant gold spot on the upper surface (Entom. xxii. 233). In 

 all such cases as this it seems perfectly clear that the unpigmental 

 scales — normally present on part of the wings — have invaded and 

 covered the whole surface ; but whether such a variation would 

 occur in a species normally destitute of any, e. g., black scales, is 

 another question that I am unable to answer. Has anyone, for 

 instance, ever found a truly nielanic variety of such a species as 

 G. rhamni? "We can only wait for information to settle this 

 crucial point. 



It may be noted here that in another sense also a pigment 

 colour may be replaced by a physical, viz., when the pigment is 

 not developed in the normally pigmented scales, and the wing is 

 consequently — usually, at least — white ; this, however, is a 

 phenomenon of quite another character from the foregoing, and 

 will be appropriately considered later. 



In the second place, we might have physical colours replaced 

 by pigmental ; this might happen either by the pigmental scales 

 normally present on a wing invading the territory of the e. g. 

 black scales ; almost the only example that I have seen noted of 

 this was a specimen of V. maculata, with only three black spots 

 altogether on the wings (Doubleday collection) : or the pigment 

 might be developed in normally unpigmented scales. Such 

 varieties as this latter are of very great interest, since — unless 

 I am mistaken — it is in this manner that all pigmental colours] 

 have originated. Examples of this variation that I have noted] 

 are the following: a specimen of A. grossulariata (in the Double- 



• Entom. xxiii. SltJ. 



