Another reason which has led me to publish this volume at the present
time is, that there are some important points on which I differ from Mr.
Darwin, and I wish to put my opinions on record in an easily accessible
form, before the publication of his new work, (already announced,) in
which I believe most of these disputed questions will be fully
discussed.

I will now give the date and mode of publication of each of the essays
in this volume, as well as the amount of alteration they have undergone.

I.--ON THE LAW WHICH HAS REGULATED THE INTRODUCTION OF NEW SPECIES.

First published in the "Annals and Magazine of Natural History,"
September, 1855. Reprinted without alteration of the text.

II.--ON THE TENDENCY OF VARIETIES TO DEPART INDEFINITELY FROM THE
ORIGINAL TYPE.

First published in the "Journal of the Proceedings of the Linnaean
Society," August, 1858. Reprinted without alteration of the text, except
one or two grammatical emendations.

III.--MIMICRY AND OTHER PROTECTIVE RESEMBLANCES AMONG ANIMALS.

First published in the "Westminster Review," July, 1867. Reprinted with
a few corrections and some important additions, among which I may
especially mention Mr. Jenner Weir's observations and experiments on the
colours of the caterpillars eaten or rejected by birds.

IV.--THE MALAYAN PAPILIONIDAE, OR SWALLOW-TAILED BUTTERFLIES, AS
ILLUSTRATIVE OF THE THEORY OF NATURAL SELECTION.

First published in the "Transactions of the Linnaean Society," Vol. XXV.
(read March, 1864), under the title, "On the Phenomena of Variation and
Geographical Distribution, as illustrated by the Papilionidae of the
Malayan Region."

The introductory part of this essay is now reprinted, omitting tables,
references to plates, &c., with some additions, and several corrections.
Owing to the publication of Dr. Felder's "Voyage of the Novara"
(Lepidoptera) in the interval between the reading of my paper and its
publication, several of my new species must have their names changed for
those given to them by Dr. Felder, and this will explain the want of
agreement in some cases between the names used in this volume and those
of the original paper.

V.--ON INSTINCT IN MAN AND ANIMALS.

Not previously published.

VI.--THE PHILOSOPHY OF BIRDS' NESTS.

First published in the "Intellectual Observer," July, 1867. Reprinted
with considerable emendations and additions.

VII.--A THEORY OF BIRDS' NESTS; SHOWING THE RELATION OF CERT