n of species from
species by any natural law of descent. He did his work so well that
"descent with modification" is now universally accepted as the order of
nature in the organic world; and the rising generation of naturalists
can hardly realise the novelty of this idea, or that their fathers
considered it a scientific heresy to be condemned rather than seriously
discussed.

The objections now made to Darwin's theory apply, solely, to the
particular means by which the change of species has been brought about,
not to the fact of that change. The objectors seek to minimise the
agency of natural selection and to subordinate it to laws of variation,
of use and disuse, of intelligence, and of heredity. These views and
objections are urged with much force and more confidence, and for the
most part by the modern school of laboratory naturalists, to whom the
peculiarities and distinctions of species, as such, their distribution
and their affinities, have little interest as compared with the problems
of histology and embryology, of physiology and morphology. Their work in
these departments is of the greatest interest and of the highest
importance, but it is not the kind of work which, by itself, enables one
to form a sound judgment on the questions involved in the action of the
law of natural selection. These rest mainly on the external and vital
relations of species to species in a state of nature--on what has been
well termed by Semper the "physiology of organisms," rather than on the
anatomy or physiology of organs.

* * * * *

It has always been considered a weakness in Darwin's work that he based
his theory, primarily, on the evidence of variation in domesticated
animals and cultivated plants. I have endeavoured to secure a firm
foundation for the theory in the variations of organisms in a state of
nature; and as the exact amount and precise character of these
variations is of paramount importance in the numerous problems that
arise when we apply the theory to explain the facts of nature, I have
endeavoured, by means of a series of diagrams, to exhibit to the eye the
actual variations as they are found to exist in a sufficient number of
species. By doing this, not only does the reader obtain a better and
more precise idea of variation than can be given by any number of
tabular statements or cases of extreme individual variation, but we
obtain a basis of fact by which to test the statements