Let us never forget that Species have no existence. Only individuals exist, and these _all vary_ more or less from each other. When the variations are slight, they have no name; when they are more marked, and are transmitted from one generation to another, they constitute particular Faces, or Varieties; when the differences are still more marked they constitute Sub-species; but, as Mr. Darwin says, “Certainly no clear line of demarcation has yet been drawn between Species and Sub-species; that is, the forms which in the opinion of some naturalists come very near to, but do not quite arrive at the rank of Species; or again, between Sub-species and well-marked Varieties, or between lesser Varieties and individual differences. These differences blend into each other in an insensible series; and a series impresses the mind with the idea of an actual passage.” But the same process of divergence which establishes Varieties out of individual differences, and Species out of Varieties, also serves to establish Genera out of Species, Orders out of Genera, and Classes out of Orders. It is, doubtless, difficult to conceive by what process of modification, two animals of distinct Genera, say a dog and a cat, were produced from a common stock; but organic analogies in abundance render it easy of belief. If we knew as much of zoology as we do of embryology, in respect of the affinities of divergent forms, it would be far less surprising that two different Genera should arise from a common stock, than that all the various parts of the skeleton should arise from a common osseous element. We know that the jaws are identical with arms and legs—both being divergent modifications of a common osseous structure. We know that the arm of a man is identical with the fin of a whale, or the wing of a bird. The differences here in form, size, and function are much greater than the differences which establish orders and classes in the animal series. Unless animal forms were modifications of some common type, it would be difficult to explain their remarkable affinities. As Mr. Darwin says, “It is a truly wonderful fact—the wonder of which we are apt to overlook from familiarity—that all animals and all plants throughout all time and space should be related to each other in group, subordinate to group, in the manner which we everywhere behold, namely, varieties of the same species most closely related together, species of the same genus less closely and unequally related together, forming sections and sub-genera, species of distinct genera much less closely related, and genera related in different degrees, forming sub-families, families, orders, sub-classes, and classes. The several subordinate groups in any class cannot be ranked in a single file, but seem rather to be clustered round points, and these round other points, and so on in almost endless circles. On the view that each species has been independently created, I can see no explanation