v COLOURS OF ANIMALS 353 
comparatively rare and not great in amount, whereas among 
birds they are very frequent and very largely developed. So 
among insects, they are abundant in butterflies, while they are 
comparatively uncommon in beetles, wasps, and hemiptera. 
The phenomena of sexual variations of colour, as well as of 
colour generally, are wonderfully similar in the two analogous 
yet totally unrelated groups of birds and butterflies ; and as 
they both offer ample materials, we shall confine our study of 
the subject chiefly to them. The most common case of differ- 
ence of colour between the sexes is for the male to have the 
same general hue as the females, but deeper and more intensi- 
fied—as in many thrushes, finches, and hawks, and among 
butterflies in the majority of our British species. In cases 
where the male is smaller the intensification of colour is 
especially well pronounced—as in many of the hawks and 
falcons, and in most butterflies and moths in which the 
coloration does not materially differ. In another extensive 
series we have spots or patches of vivid colour in the male, 
which are represented in the female by far less brilliant tints 
or are altogether wanting—as exemplified in the gold-crest 
warbler, the green woodpecker, and most of the orange-tip 
butterflies (Anthocharis). Proceeding with our survey, we 
find greater and greater differences of colour in the sexes, till 
we arrive at such extreme cases as some of the pheasants, the 
chatterers, tanagers, and birds-of-paradise, in which the male 
is adorned with the most gorgeous and vivid colours, while 
the female is usually dull brown, or olive green, and often 
shows no approximation whatever to the varied tints of her 
partner. Similar phenomena occur among butterflies ; and in 
both these groups there are also a considerable number of 
cases in which both sexes are highly but differently coloured. 
Thus many woodpeckers have the head in the male red, in 
the female yellow; while some parrots have red spots in the 
male, replaced by blue in the female, as in Psittacula diop- 
thalma. In many South American Papilios, green spots on 
the male are represented by red on the female ; and in several 
species of the genus Epicalia, orange bands in the male are 
replaced by blue in the female, a similar change of colour to 
that in the small parrot above referred to. For fuller details 
of the varieties of sexual coloration we refer our readers to 
2A 2 
