alike.
How inexplicable are these facts on the ordinary view of creation! Why
should the brain be enclosed in a box composed of such numerous and
such extraordinarily shaped pieces of bone? As Owen has remarked, the
benefit derived from the yielding of the separate pieces in the act of
parturition of mammals, will by no means explain the same construction
in the skulls of birds. Why should similar bones have been created in
the formation of the wing and leg of a bat, used as they are for such
totally different purposes? Why should one crustacean, which has an
extremely complex mouth formed of many parts, consequently always have
fewer legs; or conversely, those with many legs have simpler mouths?
Why should the sepals, petals, stamens, and pistils in any individual
flower, though fitted for such widely different purposes, be all
constructed on the same pattern?
On the theory of natural selection, we can satisfactorily answer these
questions. In the vertebrata, we see a series of internal vertebr
bearing certain processes and appendages; in the articulata, we see the
body divided into a series of segments, bearing external appendages;
and in flowering plants, we see a series of successive spiral whorls of
leaves. An indefinite repetition of the same part or organ is the
common characteristic (as Owen has observed) of all low or
little-modified forms; therefore we may readily believe that the
unknown progenitor of the vertebrata possessed many vertebr ; the
unknown progenitor of the articulata, many segments; and the unknown
progenitor of flowering plants, many spiral whorls of leaves. We have
formerly seen that parts many times repeated are eminently liable to
vary in number and structure; consequently it is quite probable that
natural selection, during a long-continued course of modification,
should have seized on a certain number of the primordially similar
elements, many times repeated, and have adapted them to the most
diverse purposes. And as the whole amount of modification will have
been effected by slight successive steps, we need not wonder at
discovering in such parts or organs, a certain degree of fundamental
resemblance, retained by the strong principle of inheritance.
In the great class of molluscs, though we can homologise the parts of
one species with those of another and distinct species, we can indicate
but few serial homologies; that is, we are seldom enabled to say that
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