descent. And this difficulty would, indeed, be almost
fatal to the theory of evolution by natural selection, if the apparent
similarity were a real one. Unfortunately for the objection, however,
Mr. Darwin clearly showed, in his reply, that in no one anatomical
feature of typical importance do the two structures resemble one
another; so that in point of fact the two organs do not resemble one
another in any particular further than it is necessary that they should,
if both are to serve as organs of sight. But now, suppose that this had
not been the case, and that the two structures, besides presenting the
necessary superficial resemblance, had also presented an anatomical
resemblance; with what tremendous force might it have then been
urged,--"Your hypothesis of hereditary descent with progressive
modification being here excluded, by the fact that the animals compared
belong to two widely different branches of the tree of life, how are we
to explain the identity of type manifested by these two complicated
organs of vision? The only hypothesis open to us is intelligent
adherence to an ideal type." But as this cannot now be urged in any one
case throughout the whole organic world, we may, on the other hand,
present it as a most significant fact, that, while within the limits of
the same large branch of the tree of life we constantly find the same
typical structures modified so as to perform very different functions,
we never find any vestige of these particular types of structure in
other large divisions of that tree. In other words, we never find
typical structures appearing except in cases where their presence may be
explained by the hypothesis of hereditary descent; while in thousands of
such cases we find these structures undergoing every conceivable variety
of adaptive modification.

Consequently, special creationists must fall back upon another position
and say,--"Well, but it may have pleased the Deity to form a certain
number of ideal types, and never to allow the structures occurring in the
one type to appear in any of the others." I answer, undoubtedly it may
have done so; but if it did, it is a most unfortunate thing for your
theory; for the fact implies that the Deity has planned His types in
such a way as to suggest the counter-theory of descent. For instance, it
would seem to me a most capricious thing in the Deity to make the eyes
of an innumerable number of fish on exactly the same ideal type, and
then to m