hosts of ancestral horses, all bring the North American [fauna] much nearer
to the Old World than it is now. Even the horse, represented in all South
America by Equus only, was probably a temporary immigrant from the north.

As to extending too far the principle (yours) of the necessity of
comparatively large areas for the development of varied faunas, I may have
done so, but I think not. There is, I think, every probability that most
islands, etc., where a varied fauna now exists, have been once more
extensive--eg., New Zealand, Madagascar: where there is no such evidence
(e.g., Galapagos), the fauna is very restricted.

Lastly, as to want of references: I confess the justice of your criticism;
but I am dreadfully unsystematic. It is my first large work involving much
of the labour of others. I began with the intention of writing a
comparatively short sketch, enlarged it, and added to it bit by bit;
remodelled the tables, the headings, and almost everything else, more than
once, and got my materials in such confusion that it is a wonder it has not
turned out far more crooked and confused than it is. I, no doubt, ought to
have given references; but in many cases I found the information so small
and scattered, and so much had to be combined and condensed from
conflicting authorities, that I hardly knew how to refer to them or where
to leave off. Had I referred to all authors consulted for every fact, I
should have greatly increased the bulk of the book, while a large portion
of the references would be valueless in a few years, owing to later and
better authorities. My experience of referring to references has generally
been most unsatisfactory. One finds, nine times out of ten, the fact is
stated, and nothing more; or a reference to some third work not at hand!

I wish I could get into the habit of giving chapter and verse for every
fact and extract; but I am too lazy, and generally in a hurry, having to