Nor shall I here discuss the various definitions which have been given of the term species.

No one definition has satisfied all naturalists; yet every naturalist knows vaguely what he means when he speaks of a species.

Generally the term includes the unknown element of a distinct act of creation.

The term "variety" is almost equally difficult to define; but here community of descent is almost universally implied, though it can rarely be proved.

We have also what are called monstrosities; but they graduate into varieties.