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 CERTAIN DIFFERENCES OF COLOUR IN BIRDS TO THEIR MODE OF NIDIFICATION. First published in the "Journal of Travel and Natural History" (No. 2), 1868. Now reprinted with considerable emendations and additions, by which I have endeavoured more clearly to express, and more fully to illustrate, my meaning in those parts which have been misunderstood by my critics. VIII.--CREATION BY LAW. First published in the "Quarterly Journal of Science," October, 1867. Now reprinted with a few alterations and additions. IX.--THE DEVELOPMENT OF HUMAN RACES UNDER THE LAW OF NATURAL SELECTION. First published in the "Anthropological Review," May, 1864. Now reprinted with a few important alterations and additions. I had intended to have considerably extended this essay, but on attempting it I found that I should probably weaken the effect without adding much to the argument. I have therefore preferred to leave it as it was first written, with the exception of a few ill-considered passages which never fully expressed my meaning. As it now stands, I believe it contains the enunciation of an important truth. X.--THE LIMITS OF NATURAL SELECTION AS APPLIED TO MAN. This is the further development of a few sentences at the end of an article on "Geological Time and the Origin of Species," which appeared in the "Quarterly Review," for April, 1869. I have here ventured to touch on a class of problems which are usually considered to be beyond the boundaries of science, but which, I believe, will one day be brought within her domain. * * * * * For the convenience of those who are acquainted with any of my essays in their original form, I subjoin references to the more important additions and alterations now made to them. _ADDITIONS AND CORRECTIONS TO THE ESSAYS AS ORIGINALLY PUBLISHED_. Essays I. and II. are unaltered, but short notes are added at pp. 19, 24, 29, and 40.