Thus while it may be doubted if, for some years, any one is likely to be
competent to pronounce judgment on all the issues raised by Mr. Darwin,
there is assuredly abundant room for him, who, assuming the humbler,
though perhaps as useful, office of an interpreter between the 'Origin
of Species' and the public, contents himself with endeavouring to point
out the nature of the problems which it discusses; to distinguish
between the ascertained facts and the theoretical views which it
contains; and finally, to show the extent to which the explanation it
offers satisfies the requirements of scientific logic. At any rate, it
is this office which we purpose to undertake in the following pages.

It may be safely assumed that our readers have a general conception of
the nature of the objects to which the word "species" is applied; but
it has, perhaps, occurred to a few, even to those who are naturalists
'ex professo', to reflect, that, as commonly employed, the term has a
double sense and denotes two very different orders of relations. When
we call a group of animals, or of plants, a species, we may imply
thereby, either that all these animals or plants have some common
peculiarity of form or structure; or, we may mean that they possess
some common functional character. That part of biological science
which deals with form and structure is called Morphology--that which
concerns itself with function, Physiology--so that we may conveniently
speak of these two senses, or aspects, of "species"--the one as
morphological, the other as physiological. Regarded from the former
point of view, a species is nothing more than a kind of animal or
plant, which is distinctly definable from all others, by certain
constant, and not merely sexual, morphological peculiarities. Thus
horses form a species, because the group of animals to which that name
is applied is distinguished from all others in the world by the
following constantly associated characters. They have--1, A vertebral