1899] THE COLOURS AND PIGMENTS OF BUTTERFLIES 141 



is unfortunately not considered. The obvious difficulty that in 

 ontogeny white appears before yellow or red, the author ingeniously 

 removes by pointing out that this early white is probably optical, 

 while the white colour of the adult is due to uric acid acting as a 

 white pigment. 



We cannot here follow our author into his discussion of the 

 bearing of his results on the chief controversies in regard to 

 colour phenomena, but their relation to concrete details may be 

 noticed. 



In the first place, the view that bright scarlet is the most primitive 

 colour in the Pieridae, with the correlated statement that the males 

 in the family are frequently more primitive in regard to their 

 colours than the females, will be found somewhat difficult of 

 acceptance by most. At the same time, when it is recollected 

 that the examples chosen were largely tropical forms, that the 

 red and yellow pigments are chemically nearly related, and that 

 there is some evidence to show that various external conditions, 

 especially heat, are of importance in the production of red varieties 

 from forms normally yellow, it would seem that our author's 

 statements can be reduced to the simpler form that red, yellow, 

 and white are primitive colours in the Pieridae, and, in nature 

 as in the laboratory, are readily converted into one another. When 

 we remember that these three colours in the Pieridae are due 

 to uric acid and its derivatives, there seems nothing improbable 

 in the suggestion that in the course of evolution they tend to 

 disappear as the dark pigments develop, and are replaced by the 

 brilliant optical colours which are apparently associated both with 

 these dark pigments and with the progressive differentiation of 

 the scales. Such a suggestion I have indeed already made in 

 " Colour in Nature." Piepers seems, however, disposed to apply 

 his theory not only to the Pieridae but to butterflies in general, 

 in which pigments certainly allied to uric acid have not yet been 

 demonstrated. We have just seen also that Baer's work tends 

 rather to emphasise than to destroy the distinctions between the 

 pigments of the Pieridae and of other butterflies. On the other 

 hand, the fact that in the case of species of Papilio and Vanessa 

 the Countess Maria von Linden found that black was the last 

 colour to develop in ontogeny ; that the wings of pupae were first 

 yellowish-red ; and that those early colours were later concealed by 

 the development of dark scales on the top of the light ones, certainly 

 suggests a course of evolution similar to that occurring in the 

 Pieridae. The question is not likely to be decided until we know 

 the exact relation of the bright pigments of other butterflies to 

 those of the Pieridae. Nor can we hope to clearly understand 

 the colour phenomena of the Lepidoptera in general, until we also 

 know the relation between the dark and the bright pigments, 



10 NAT. SC. VOL. XIV. NO. 84. 



