General Phenomena of Colour--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--Typical Colours--The Nature of Colour--How Animal Colours are Produced--Colour a Normal Product of Organization--Theory of Protective Colours--Theory of Warning Colours--Imitative Warning Colours--The Theory of Mimicry--Theory of Sexual Colours--Colour as a Means of Recognition--Colour proportionate to Integumentary Development--Selection 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 the Display of Ornaments by Males--Natural Selection as neutralizing Sexual Selection--Greater Brilliancy of some Female Birds--Colour-development as illustrated by Humming-Birds--Theory of Typical Colours--Local Causes of Colour-development--Summary on Colour-development in Animals--Concluding Remarks on Causes of Bright Colour in the Tropics _pages 158-220_ VI. The Colours of Plants and the Origin of the Colour-Sense. Source of Colouring-matter in Plants--Protective Coloration and Mimicry in Plants--Attractive Colours of Fruits--Protective Colours of Fruits--Seeds how Protected--Attractive Colours of Flowers--Attractive Odours in Flowers--Attractive Grouping in Flowers--Why Alpine Flowers are so Beautiful--Why Allied Species of Flowers differ in Size and Beauty--Absence of Colours in Wind-fertilized Flowers--The same Theory of Colour applicable to Animals and Plants--Relation of the Colours of Flowers and their Geographical Distribution--Recent Views as to the Direct Action of Light on the Colours of Flowers and Fruits--Concluding Remarks on the Importance of Colour in the Organic World--The Origin of the Colour-sense.--Supposed Increase of Colour-perception within the Historical Period--Concluding Remarks on the Colour-sense _pages 221-248_ VII. BY-PATHS IN THE DOMAIN OF BIOLOGY. BEING AN ADDRESS DELIVERED TO THE BIOLOGICAL SECTION OF THE BRITISH ASSOCIATION (GLASGOW, SEPTEMBER 6TH, 1876) AS PRESIDENT OF THE SECTION. Introductory Remarks--ON SOME RELATIONS OF LIVING THINGS TO THEIR ENVIRONMENT.--The Influence of Locality on Colour in Butterflies and Birds--Sense-perception influenced by Colour of the Integuments--Relations of Insular Plants and Insects--RISE AND PROGRESS OF MODERN VIEWS AS TO THE ANTIQUITY AND ORIGIN OF MAN--Indications of Man’s Extreme Antiquity--Antiquity of Intellectual Man--Sculptures on Easter-Island--North American Earthworks--The Great Pyramid--Conclusion _pages 249-303_ VIII. The Distribution of Animals as Indicating Geographical Changes.