as its nearest
representative, B,--still less, of course, that such should be a general
rule throughout all the thousands and millions of species which have
ever inhabited the earth. But, equally of course, on the theory of a
natural evolution this is so necessary a consequence, that if no
correlation of such a two-fold kind were observable, the theory would be
negatived. Thus the question whether there be any indication of such a
two-fold correlation may be regarded as a test-question as between the
two theories; for although the vast majority of extinct species have
been lost to science, there are a countless number of existing species
which furnish ample material for answering the question. And the answer
is so unequivocal that Mr. Wallace, who is one of our greatest
authorities on geographical distribution, has laid it down as a general
law, applicable to all the departments of organic nature, that, so far
as observation can extend, "every species has come into existence
coincident both in space and time with a pre-existing and closely allied
species." As it appears to me that the significance of these words
cannot be increased by any comment upon them, I will here bring this
introductory chapter to a close.

CHAPTER II.

CLASSIFICATION.

The first line of direct evidence in favour of organic evolution which I
shall open is that which may be termed the argument from Classification.

It is a matter of observable fact that different forms of plants and
animals present among themselves more or less pronounced resemblances.
From the earliest times, therefore, it has been the aim of philosophical
naturalists to classify plants and animals in accordance with these
resemblances. Of course the earliest attempts at such classification
were extremely crude. The oldest of these attempts with which we are
acquainted--namely, that which is presented in the books of Genesis and
Leviticus--arranges the whole vegetable kingdom in three simple
divisions of Grass, Herbs, and Trees; while the animal kingdom is
arranged with almost equal simplicity with reference, first to habitats
in water, earth, or air, and next as to modes of progression. These, of
course, were what may be termed common-sense classifications, having
reference merely to external appearances and habits of life. But when
Aristotle laboriously investigated the comparative anatomy of animals,
he could not fail to perceive that their entire structures had to