We have seen that though the laws of nature are constant, yet some of the conditions which determine specific change may be exceptionally absent at the present epoch of the world's history; also that it is not only possible, but highly probable, that an internal power or tendency is an important if not the main agent in evoking the manifestation of new species on the scene of realized existence, and that in any case, from the facts of homology, innate internal powers to the full as mysterious must anyhow be accepted, whether they act in specific origination or not.

Besides all this, we have seen that it is probable that the action of this innate power is stimulated, evoked, and determined by external conditions, and also that the same external conditions, in the shape of "Natural Selection," play an important part in the evolutionary process: and finally, it has been affirmed that the view here advocated, while it is supported by the facts on which Darwinism rests, is not open to the objections and difficulties which oppose themselves to the reception of "Natural Selection," as the exclusive or even as the main agent in the successive and orderly evolution of organic forms in the _genesis of species_.

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