stinct object in view, and
do not look to some unknown plan of creation, we may hope to make sure but
slow progress.

_Morphology._--We have seen that the members of the same class,
independently of their habits of life, resemble each other in the general
plan of their organisation. This resemblance is often expressed by the term
"unity of type;" or by saying that the several parts and organs in the
different species of the class are homologous. The whole subject is
included under {434} the general name of Morphology. This is the most
interesting department of natural history, and may be said to be its very
soul. What can be more curious than that the hand of a man, formed for
grasping, that of a mole for digging, the leg of the horse, the paddle of
the porpoise, and the wing of the bat, should all be constructed on the
same pattern, and should include similar bones, in the same relative
positions? Geoffroy St. Hilaire has insisted strongly on the high
importance of relative connexion in homologous organs: the parts may change
to almost any extent in form and size, and yet they always remain connected
together in the same order. We never find, for instance, the bones of the
arm and forearm, or of the thigh and leg, transposed. Hence the same names
can be given to the homologous bones in widely different animals. We see
the same great law in the construction of the mouths of insects: what can
be more different 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 {435} natural selection of
successive slight modifications,--each modification being profitable in
some way to th