ifferent than the immensely long spiral proboscis of a
sphinx-moth, the curious folded one of a bee or bug, and the great jaws
of a beetle?--yet all these organs, serving for such different purposes,
are formed by infinitely numerous modifications of an upper lip,
mandibles, and two pairs of maxillae. Analogous laws govern the
construction of the mouths and limbs of crustaceans. So it is with the
flowers of plants.

Nothing can be more hopeless than to attempt to explain this similarity
of pattern in members of the same class, by utility or by the doctrine
of final causes. The hopelessness of the attempt has been expressly
admitted by Owen in his most interesting work on the 'Nature of Limbs.'
On the ordinary view of the independent creation of each being, we can
only say that so it is;--that it has so pleased the Creator to construct
each animal and plant.

The explanation is manifest on the theory of the natural selection of
successive slight modifications,--each modification being profitable
in some way to the modified form, but often affecting by correlation of
growth other parts of the organisation. In changes of this nature, there
will be little or no tendency to modify the original pattern, or to
transpose parts. The bones of a limb might be shortened and widened to
any extent, and become gradually enveloped in thick membrane, so as to
serve as a fin; or a webbed foot might have all its bones, or certain
bones, lengthened to any extent, and the membrane connecting them
increased to any extent, so as to serve as a wing: yet in all this great
amount of modification there will be no tendency to alter the framework
of bones or the relative connexion of the several parts. If we suppose
that the ancient progenitor, the archetype as it may be called, of all
mammals, had its limbs constructed on the existing general pattern,
for whatever purpose they served, we can at once perceive the plain
signification of the homologous construction of the limbs throughout the
whole class. So with the mouths of insects, we have only to suppose that
their common progenitor had an upper lip, mandibles, and two pair
of maxillae, these parts being perhaps very simple in form; and then
natural selection will account for the infinite diversity in structure
and function of the mouths of insects. Nevertheless, it is conceivable
that the general pattern of an organ might become so much obscured as to
be finally lost, by the atrophy and ultima