Difficulties of the Subject—General Aspect of the Animal Life of Equatorial Forests—Diurnal Lepidoptera or Butterflies—Peculiar Habits of Tropical Butterflies—Ants, Wasps, and Bees—Ants—Special Relations between Ants and Vegetation—Wasps and Bees—Orthoptera and other Insects—Beetles—Wingless Insects—General Observations on Tropical Insects—Birds—Parrots—Pigeons—Picariæ—Cuckoos—Trogons, Barbets, Toucans and Hornbills—Passeres—Reptiles and Amphibia—Lizards—Snakes—Frogs and Toads—Mammalia—Monkeys—Bats—Summary of the Aspects of Animal Life in the Tropics
IV. Humming-Birds: as Illustrating the 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 Relations and Affinities of Humming-Birds—How to Determine Doubtful Affinities—Resemblances of Swifts and Humming-Birds—Differences between Sun-Birds and Humming-Birds
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 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
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