xii 



CONTENTS. 



iv. humming-blrds : as illustrating ths luxuriance of 

 Tropical Nature. 



Structure — Colours and Ornaments — Descriptive Names — The Motions and 

 Habits of Humming-Birds — ^Display of Ornaments by the Male — Food 

 —Geographical Distribution and Variation — Humming-Birds of Juan 

 Fernandez as illustrating Variation and Natural Selection — The Kelations 

 and Affinities of Humming-Birds — How to Determine Doubtful Affinities 

 — Kesemblances of Swifts and Humming-Birds — Differences between 

 Sun-Birds and Humming-Birds pages 124 — 157 



V. The Colours of Animals and Sexual Selection. 



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 

 Deve^-^pment— 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 2^«i/'^'^ 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—218 



