two
divisions, namely, first those of largest generality, and next a few of
the most special character that can be found.

As explained in the Preface, the present instalment of the treatise is
concerned with the theory of evolution, from the appearance of the
_Origin of Species_ in 1859, to the death of its author in 1882; while
the second part will be devoted to the sundry post-Darwinian questions
which have arisen in the subsequent decade. To the possible criticism
that a disproportionate amount of space will thus be allotted to a
consideration of these post-Darwinian questions, I may furnish in
advance the following reply.

In the first place, besides the works of Darwin himself, there are a
number of others which have already and very admirably expounded the
evidences, both of organic evolution as a fact, and of natural selection
as a cause. Therefore, in the present treatise it seemed needless to go
beyond the ground which was covered by my original lectures, namely, a
condensed and connected, while at the same time a critical statement of
the main evidences, and the main objections, which have thus far been
published with reference to the distinctively Darwinian theory. Indeed
while re-casting this portion of my lectures for the present
publication, I have felt that criticism might be more justly urged from
the side of impatience at a reiteration of facts and arguments already
so well known. But while endeavouring, as much as possible, to avoid
overlapping the previous expositions, I have not carried this attempt to
the extent of damaging my own, by omitting any of the more important
heads of evidence; and I have sought to invest the latter with some
measure of novelty by making good what appears to me a deficiency which
has hitherto obtained in the matter of pictorial illustration. In
particular, there will be found a tolerably extensive series of
woodcuts, serving to represent the more important products of artificial
selection. These, like all the other original illustrations, have been
drawn either direct from nature or from a comparative study of the best
authorities. Nevertheless, I desire it to be understood that the first
part of this treatise is intended to retain its original character, as a
merely educational exposition of Darwinian teaching--an exposition,
therefore, which, in its present form, may be regarded as a compendium,
or hand-book, adapted to the requirements of a general reader, or
biolog