d by the
more orthodox school. Then came Herbert Spencer, reasserting evolution
in the old broad spirit, not merely in its application to species, but
as the guiding principle of the whole universe from the integrations
of nebulae into systems of suns and planets to the transformations of
chemical bodies. Before his marvellous generalisations had time to
grip biologists, there came Darwin; and Darwin brought two things:
first, a re-statement of the fact of evolution as applied to the
living world, supported by an enormous body of evidence, new and old,
presented with incomparably greater force, clearness, patience, and
knowledge than had ever been seen before; and, second, the exposition
of the principle of natural selection as a mechanism which might have
caused, and probably did cause, evolution.

Huxley, as has been shewn, like many other anatomists, was ready for
the general principle of evolution. In fact, so far as it concerned
the great independent types which he believed to exist among animals,
he was more than prepared for it. Let us take a single definite
example of his position. In his work on the Medusae, he had shewn how a
large number of creatures, at first sight diverse, were really
modifications of a single great type, and he used language which, now
that all zooelogists accept evolution in the fullest way, requires no
change to be understood:

"What has now been advanced will, perhaps, be deemed evidence
sufficient to demonstrate,--first, that the organs of these
various families are traceable back to the same point in the way
of development; or, secondly, when this cannot be done, that they
are connected by natural gradations with organs which are so
traceable; in which case, according to the principles advanced in
57, the various organs are homologous, and the families have a
real affinity to one another and should form one group.... It
appears, then, that these five families are by no means so
distinct as has hitherto been supposed, but that they are members
of one great group, organised upon one simple and uniform plan,
and, even in their most complex and aberrant forms, reducible to
the same type. And I may add, finally, that on this theory it is
by no means difficult to account for the remarkable forms
presented by the Medusae in their young state. The Medusae are the
most perfect, the most individualised animals of