ties--The isolation of varieties by selective
association--The influence of natural selection upon sterility
and fertility--Physiological selection--Summary and concluding
remarks

CHAPTER VIII

THE ORIGIN AND USES OF COLOUR IN ANIMALS

The Darwinian theory threw new light on organic colour--The
problem to be solved--The constancy of animal colour indicates
utility--Colour and environment--Arctic animals
white--Exceptions prove the rule--Desert, forest, nocturnal, and
oceanic animals--General theories of animal colour--Variable
protective colouring--Mr. Poulton's experiments--Special or
local colour adaptations--Imitation of particular objects--How
they have been produced--Special protective colouring of
butterflies--Protective resemblance among marine
animals--Protection by terrifying enemies--Alluring
coloration--The coloration of birds' eggs--Colour as a means of
recognition--Summary of the preceding exposition--Influence of
locality or of climate on colour--Concluding remarks

CHAPTER IX

WARNING COLORATION AND MIMICRY

The skunk as an example of warning coloration--Warning colours
among insects--Butterflies--Caterpillars--Mimicry--How mimicry
has been produced--Heliconidae--Perfection of the
imitation--Other cases of mimicry among Lepidoptera--Mimicry
among protected groups--Its explanation--Extension of the
principle--Mimicry in other orders of insects--Mimicry among the
vertebrata--Snakes--The rattlesnake and the cobra--Mimicry among
birds--Objections to the theory of mimicry--Concluding remarks
on warning colours and mimicry

CHAPTER X

COLOURS AND ORNAMENTS CHARACTERISTIC OF SEX

Sex colours in the mollusca and crustacea--In insects--In
butterflies and moths--Probable causes of these colours--Sexual
selection as a supposed cause--Sexual coloration of birds--Cause
of dull colours of female birds--Relation of sex colour to
nesting habits--Sexual colours of other vertebrates--Sexual
selection by the struggles of males--Sexual characters due to
natural selection--Decorative plumage of males and its effect on
the females--Display of decorative plumage by the males--A
theory of animal coloration--The origin of accessory
plumes--Development of accessory plumes and their display--The
effect of female preference will be neutralised by natural