6. All these causes are equally unknown to us as regards their nature and mode of action. We know them merely by phenomena. We can, therefore, make no conjecture as to the relations, more or less close, which may exist between them. 7. We nevertheless give names to these causes for the sake of convenience, and of facilitating the discussion of the facts. VIII. We can now return to the problem which gave rise to these expansions, and ask the question: Whether Man should take his place in the animal kingdom? a question which evidently leads to another: Is man distinguished from animals by important and characteristic phenomena, absolutely unknown in the latter? For more than forty years I have answered this question in the affirmative, and my convictions, tested by many controversies, are now stronger than ever. But it is neither in the material disposition, nor in the action of his physical organism, that we must look for these phenomena. From this point of view, man is neither more nor less than an animal. From an anatomical point of view, there is less difference between man and the superior order of apes, than between the latter and the inferior orders. The microscope reveals equally striking resemblances between the elements of the human organism and those of the animal organism; and chemical analysis leads to the same result. It was easy to foresee that the action of elements and organs would be exactly the same in man and beast, and such was found to be the case. Passions, sentiments, and characters, establish between animals and ourselves equally close relations. The animal loves and hates; we recognise in it irritability and jealousy; unwearying patience, and immutable confidence. In our domestic species, these differences are more apparent, or perhaps we only notice them more closely. Who has not known dogs which have been playful or snappish, affectionate or savage, cowardly or courageous, friendly with everybody, or exclusive in their affections. Again, man has true instincts, were it only that of sociability. Faculties, however, of this order, which are so fully developed in certain animals, in man are evidently very much reduced in comparison with the intelligence. The relative development of the latter certainly establishes an enormous difference between man and animal. It is not, however, the _intensity_ of a phenomenon which gives value to it from our present point of view, but simply its _nature_. The question is whether human intelligence and animal intelligence can be considered as of the same order.