as was absolutely necessary to give precision to the descriptions and to enable us to deduce from them some conclusions of importance.

The remaining chapters have all a more or less direct connection with the leading subject. The family of humming-birds is taken as an illustration of the luxuriant development of allied forms in the tropics, and as showing the special mode in which natural selection has acted to bring about considerable changes in a limited period. The discussion on the nature and origin of the colours of animals and plants, is intended to show how far and in what way these are dependent on the climate and physical conditions of the tropics. The chapter entitled "By-paths in the Domain of Biology" contains an account of certain curious relations of colour to locality, which are almost exclusively manifested within the tropical zones; while the essay on "Distribution of Animals and Geographical Changes," elucidates the relations of the several continents in past time, and the probable origin of many of the groups now characteristic of tropical or of temperate regions.

While discussing the general laws and phenomena of colour in the organic world, and its special developments among certain groups of animals, I have been led. to a theory of the diverse colours of the sexes and of the special ornaments and brilliant hues which dis

tinguish certain male birds and insects, which is directly opposed to the view held by Mr. Darwin and so well explained and illustrated in his great work on "The Descent of Man and on Selection in Relation to Sex." Being strongly impressed with the importance and fundamental truth of this theory, I published my first sketch of the subject in Macmillan's Magazine in order that it might have the benefit of criticism before making it public in a more permanent form. Taking advantage of some suggestions from Mr. Darwin and from a few other correspondents, I have made considerable additions to the original essay and have rearranged, and I trust strengthened the argument, which I now hope may attract the attention of all who are interested in the subject. I may be allowed here to remark, that my theory cannot be properly understood without reading the whole chapter on "The Colours of Animals;" because the view set forth and illustrated in the first part of that chapter-that colour in nature is normal, and that its presence hardly requires to be accounted for so much as its absence-is an essential part of the theory.

CROYDON, April, 1878.

CONTENTS.

I. THE CLIMATE AND PHYSICAL ASPECTS OF THE EQUATORIAL ZONE.

The three Climatal Zones of the Earth-Temperature of the Equatorial

Zone-Causes of the Uniform High Temperature near the Equator-

Influence of the Heat of the Soil-Influence of the Aqueous Vapour of

the Atmosphere-Influence of Winds on the Temperature of the Equator

-Heat due to the Condensation of Atmospheric Vapour-General

Features of the Equatorial Climate-Uniformity of the Equatorial Cli-

mate in all Parts of the Globe-Effects of Vegetation on Climate-Short

Twilight of the Equatorial Zone-The Aspect of the Equatorial Heavens

-Intensity of Meteorological Phenomena at the Equator-Concluding

Remarks.

pages 1-26

II. EQUATORIAL VEGETATION.

The Equatorial Forest-belt and its Causes-General Features of the Equa-

torial Forests-Low-growth Forest-trees-Flowery Trunks and their

Probable Cause-Uses of Equatorial Forest-trees--The Climbing Plants

of the Equatorial Forests-Palms-Uses of Palm-trees and their Pro-

ducts-Ferns-Ginger-worts and Wild Bananas--Arums-Screw-Pines-

Orchids-Bamboos-Uses of the Bamboo-Mangroves-Sensitive-plants

-Comparative Scarcity of Flowers-Concluding Remarks on Tropical

Vegetation.

pages 27-68

III. ANIMAL LIFE IN THE TROPICAL FORESTS.

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-Picarie-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.

pages 69-123

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

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

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-Indica-

tions 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.

Old Opinions on Continental Changes-Theory of Oceanic Islands-Present

and Past Distribution of Land and Sea-Zoological Regions-The Palæ-

arctic Region-The Ethiopian Region-The Oriental Region-Past changes

of the Great Eastern Continent-Regions of the New World-Past His-

tory of the American Continents-The Australian Region-Summary

and Conclusion

pages 301-347