is familiar to almost every one, that in a flower the relative position of
the sepals, petals, stamens, and pistils, as well as their intimate
structure, are intelligible on the view that they consist of metamorphosed
leaves, arranged in a spire. In monstrous plants, we often get direct
evidence of the possibility of one organ being transformed into another;
and we can actually see in embryonic crustaceans and in many other animals,
and in flowers, that organs, which when mature become extremely different,
are at an early stage of growth exactly 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
extraordinary 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 {437}
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 vertebrae 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 vertebrae; 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,