1 74 
COLOUR IN NATURE 
CHAP. 
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 
