Vv 
THE COLOURS OF ANIMALS AND SEXUAL SELECTION ! 
General Phenomena of Colour in the Organic World—Theory of Heat and 
Light as producing Colour—Changes of Colour in Animals produced 
by Coloured Light—Classification of Organic Colours—Protective 
Colours—Warning Colours—Sexual Colours—Normal Colours—The 
Nature of Colour—How Animal Colours are produced—Colour a 
normal product of Organisation—Theory of Protective Colours— 
Theory of Warning Colours—Imitative Warning Colours—The Theory 
of Mimicry—Theory of Sexual Colours—Colour as a means of Recog- 
nition—Colour proportionate to Integumentary Development—Selec- 
tion by Females not a cause of Colour—Probable use of the Horns 
of Beetles—Cause of the greater Brilliancy of some Female Insects— 
Origin of the Ornamental Plumage of Male Birds—Theory of Display 
of Ornaments by Males—Natural Selection as neutralising Sexual 
Selection—Greater Brilliancy of some Female Birds—Colour-develop- 
ment as illustrated by Humming-Birds—Theory of Normal Colours— 
Local causes of Colour-development—The influence of Locality on 
Colour in Butterflies and Birds—Sense-perception influenced by Colour 
of the Integuments—Summary on Colour-development in Animals, 
General Phenomena of Colour in the Organic World 
THERE is probably no one quality of natural objects from 
which we derive so much. pure and intellectual enjoyment as 
from their colours. The heavenly blue of the firmament, the 
glowing tints of sunset, the exquisite purity of the snowy 
mountains, and the endless shades of green presented by the 
verdure-clad surface of the earth, are a never-failing source of 
pleasure to all who enjoy the inestimable gift of sight. Yet 
these constitute, as it were, but the frame and background of 
1 A first sketch of this essay appeared in Macmillan’s Magazine of Sep- 
tember 1877. 
