w perfectly distinct have descended from a single
parent-form.

In June, 1859, Professor Huxley gave a lecture before the Royal
Institution on the "Persistent Types of Animal Life". Referring to such
cases, he remarks, "It is difficult to comprehend the meaning of such
facts as these, if we suppose that each species of animal and plant, or
each great type of organisation, was formed and placed upon the surface
of the globe at long intervals by a distinct act of creative power; and
it is well to recollect that such an assumption is as unsupported by
tradition or revelation as it is opposed to the general analogy of
nature. If, on the other hand, we view "Persistent Types" in relation to
that hypothesis which supposes the species living at any time to be the
result of the gradual modification of pre-existing species, a hypothesis
which, though unproven, and sadly damaged by some of its supporters,
is yet the only one to which physiology lends any countenance; their
existence would seem to show that the amount of modification which
living beings have undergone during geological time is but very small in
relation to the whole series of changes which they have suffered."

In December, 1859, Dr. Hooker published his "Introduction to the
Australian Flora". In the first part of this great work he admits the
truth of the descent and modification of species, and supports this
doctrine by many original observations.

The first edition of this work was published on November 24, 1859, and
the second edition on January 7, 1860.

CONTENTS.

INTRODUCTION

CHAPTER I.

VARIATION UNDER DOMESTICATION.

Causes of Variability--Effects of Habit and the use or disuse of
Parts--Correlated Variation--Inheritance--Character of Domestic
Varieties--Difficulty of distinguishing between Varieties and
Species--Origin of Domestic Varieties from one or more Species--Domestic
Pigeons, their Differences and Origin--Principles of Selection,
anciently followed, their Effects--Methodical and Unconscious
Selection--Unknown Origin of our Domestic Productions--Circumstances
favourable to Man's power of Selection.

CHAPTER II.

VARIATION UNDER NATURE.

Variability--Individual Differences--Doubtful species--Wide ranging,
much diffused, and common species, vary most--Species of the larger
genera in each country vary more frequently than the species of the
smaller genera--Many of the species of the larger g