ly, we have seen that one of the guiding principles of
classification has been empirically found to consist in setting a high
value on "chains of affinities." That is to say, naturalists not
unfrequently meet with a long series of progressive modifications of
type, which, although it cannot be said that the continuity is anywhere
broken, at last leads to so much divergence of character that, but for
the intermediate links, the members at each end of the chain could not
be suspected of being in any way related. Well, such cases of chains of
affinity obviously tell most strongly in favour of descent with
continuous modification; while it is impossible to suggest why, if all
the links were separately forged by as many acts of special creation,
there should have been this gradual transmutation of characters carried
to the point where the original creative ideal has been so completely
transformed that, but for the accident of the chain being still
complete, no one of nature's interpreters could possibly have discovered
the connexion. For, as we have seen, this is not a case in which any
appeal can be logically made to the argument from ignorance of divine
method, unless some independent evidence could be adduced in favour of
special creation. And that no such independent evidence exists, it will
be the object of future chapters to show.

CHAPTER III.

MORPHOLOGY.

The theory of evolution supposes that hereditary characters admit of
being slowly modified wherever their modification will render an
organism better suited to a change in its conditions of life. Let us,
then, observe the evidence which we have of such adaptive modifications
of structure, in cases where the need of such modification is apparent.
We may begin by again taking the case of the whales and porpoises. The
theory of evolution infers, from the whole structure of these animals,
that their progenitors must have been terrestrial quadrupeds of some
kind, which gradually became more and more aquatic in their habits. Now
the change in the conditions of their life thus brought about would have
rendered desirable great modifications of structure. These changes would
have begun by affecting the least typical--that is, the least strongly
inherited--structures, such as the skin, claws, and teeth. But, as time
went on, the adaptation would have extended to more typical structures,
until the shape of the body would have become affected by the bones and
muscle