174 COLOUR IN NATURE 



Variation in Colour 



I. Natural. — With regard to those variations of 

 colour in insects, especially butterflies, which occur 

 in nature there are some interesting observations. 

 Much of their interest is of course due to the 

 fact that butterflies show such a marked tendency 

 to develop into geographical varieties distinguished 

 primarily by their colour. Mr. Bateson, in his 

 Materials for the Study of Variation, pp. 44, 45, 

 describes several cases having especial reference to 

 yellow, orange, and red pigments. Thus Colias hyale, 

 the Pale Clouded Yellow (Pieridae), is usually sulphur- 

 coloured but may occur in white varieties, or may 

 be of a " rich sulphur colour " with apical marginal 

 patches of a red colour. A more interesting case is 

 that of Gonepteryx rhamni, a British Pierid, in which 

 the male is of sulphur-yellow colour, while a South 

 European species, G. cleopatra, is very similar but has 

 more orange on the fore- wings. Not only have 

 forms closely resembling G. cleopatra been found in 

 Britain, but intermediate forms have also been found, 

 and also forms in which the fore-wings were broadly 

 suffused with scarlet instead of orange. These facts 

 are of interest not only on account of the relation 

 which we have already noticed as existing between 

 yellow, orange, and red pigments, but also on 

 account of their importance in regard to questions 

 of mimicry and of the effect of environment on 

 colour. We shall see in the chapter on mimicry 

 that such colour variations often occur simultaneously 

 in very different genera, and so give rise to what are 



