upernatural design. Now, if adaptations were caused by
natural selection, we can very well understand why they should never be
homologous in different lines of descent, even in cases where they have
been brought to be so closely analogous as to have deceived so good a
naturalist as Mr. Mivart. Indeed, as I have already observed, so well
can we understand this, that any single instance to the contrary would
be sufficient to destroy the theory of natural selection _in toto_,
unless the structure be one of a very simple type. But on the other
hand, it is impossible to suggest any rational explanation why, if all
adaptations are due to supernatural design, such scrupulous care should
have been taken never to allow homologous adaptations to occur in
different divisions of the animal or vegetable kingdoms. Why, for
instance, should the eye of a cuttle-fish _not_ have been constructed on
the same ideal pattern as that of vertebrate? Or why, among the
thousands of vertebrated species, should no one of their eyes be
constructed on the ideal pattern that was devised for the cuttle-fish?
Of course it may be answered that perhaps there was some hidden reason
why the design should never have allowed an adaptation which it had
devised for one division of organic nature to appear in another--even in
cases where the new design necessitated the closest possible resemblance
in everything else, save in the matter of anatomical homology.
Undoubtedly such may have been the case--or rather such _must_ have been
the case--if the theory of special design is true. But where the
question is as to the truth of this theory, I think there can be no
doubt that its rival gains an enormous advantage by being able to
_explain_ why the facts are such as they are instead of being obliged to
take refuge in hypothetical possibilities of a confessedly
unsubstantiated and apparently unsubstantial kind.

Therefore, as far as this objection to the theory of natural selection
is concerned--or the allegation that homologous structures occur in
different divisions of organic nature--not only does it fall to the
ground, but positively becomes itself converted into one of the
strongest arguments in favour of the theory. As soon as the allegation
is found to be baseless, the very fact that it cannot be brought to bear
upon any one of all the millions of adaptive structures in organic
nature becomes a fact of vast significance on the opposite side.

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