and only slowly disentangle themselves from the lower forms which constitute their matrix. Thus the image little by little lifts itself butterfly-like out of its chrysalis, the percept. Similarly, what we call thinking, with its conscious comparing and relating of the products of sense-perception, emerges in the most gradual way out of lower forms of psychosis.
But this is not all, or the main thing. While the higher and lower forms of intellection undoubtedly exhibit qualitative differences, it may be possible to transcend these differences by going deeper, and detecting the veritable elements of the intellective process. This deeper analysis is emphatically the work of modern psychology, and, as every reader of Mr. Herbert Spencer knows, is of vast assistance to the evolutionist in following the psychical process from its rudest conceivable form in the lower grades of animal life up to the highest achievements of human thought. The luminous idea that all intelligence is at bottom a combination of two elementary processes, differentiation and integration, seems to lift one at once high above the perplexities with which our author so laboriously deals. It enables us to say that animal intelligence, just because it is intelligence, must be identical in substance with our own. The qualitative differences between perception and conception, or, to take Dr. Romanes's example, "the logic of recepts" and the logic of concepts, which obstinately persist so long as we look at the process ab extra, now appear as mere results of different degrees of complexity, of unlike modes of combination of the ultimate elements; just as to the physiologist the manifold variety of color resolves itself into different modes of combination of two or three elementary sentient processes.
When once this fundamental identity of all intellective processes is clearly apprehended, the question where exactly in the evolutionist's tree the twig of thought proper, or better, perhaps, of conscious generalization, branches off, sinks to its proper place as a question of quite secondary importance. At the same time we may agree with Dr. Romanes that the point has its real historical or genealogical interest, and that he has not done amiss to devote a volume to its discussion.
The question turns mainly on the point how much the animal can do by means of pure imagining and the aid of association. Our author clearly recognizes that this will carry animals some way, and may give to their mental operations the appearance of a true generalizing process. But he has not fixed the limits of this pictorial or suggestive inference with the precision one looks for, partly, no doubt, because his whole view of the generic image as somehow involving a generalizing process tended to obscure from him the real point. One might safely, perhaps, hazard the assertion that the diving-bird can get on very well without any-
