le toe furnished with two claws. Notwithstanding this
similarity of pattern, it is obvious that the hind feet of these several
animals are used for as widely different purposes as it is possible to
conceive. The case is rendered all the more striking by the American
opossums, which follow nearly the same habits of life as some of their
Australian relatives, having feet constructed on the ordinary plan.
Professor Flower, from whom these statements are taken, remarks in
conclusion: "We may call this conformity to type, without getting much
nearer to an explanation of the phenomenon;" and he then adds "but is
it not powerfully suggestive of true relationship, of inheritance from a
common ancestor?"

Geoffroy St. Hilaire has strongly insisted on the high importance of
relative position or connexion in homologous parts; they may differ to
almost any extent in form and size, and yet remain connected together in
the same invariable 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 widely different
purposes, are formed by infinitely numerous modifications of an upper
lip, mandibles, and two pairs of maxillae. The same law governs 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 pleased the Creator to construct all
the animals and plants in each great class on a uniform plan; but this
is not a scientific explanation.

The explanation is to a large extent simple, on the theory of the
selection of successive slight modifications, each being profitable in
some way to the modified form, but often affecting by correlation other
parts of the organisation. In changes of this nature, there will be
lit