It is the organism, with the brain, its supreme representative, which constitutes the real personality; comprising in itself the remains of all that we have been and the possibilities of all that we shall be. The whole individual character is there inscribed, with its active and passive aptitudes, its sympathies and antipathies, its genius, its talent or its stupidity, its virtues and its vices, its torpor or its activity. The part thereof which emerges into consciousness is little compared with what remains buried, but operative nevertheless. The conscious personality is never more than a small fraction of the psychical personality. The unity of the Ego is not therefore the unity of a single entity diffusing itself among multiple phenomena; it is the co-ordination of a certain number of states perpetually renascent, and having for their sole common basis the vague feeling of our body. This unity does not diffuse itself downwards, but is aggregated by ascent from below; it is not an initial but a terminal point. Does then this perfect unity really exist? In the rigorous, the mathematical sense, assuredly it does _not_. In a relative sense it is met with,--rarely and for a moment. When a good marksman takes aim, or a skilful surgeon operates, his whole body and mind converge towards a single act. But note the result; under those conditions the sentiment of real personality disappears, for the conscious individual is simplified into a single idea, and the personal sentiment is excluded by the complete unification of consciousness. We thus return by another route to the same conclusion; _the Self is a co-ordination_. It oscillates between two extremes at each of which it ceases to exist;--absolute unity and absolute incoherence. The last word of all this is that since the consensus of consciousness is subordinated to the consensus of the organism, the problem of the unity of the Ego is in its ultimate form a problem of Biology. Let Biology explain, if it can, the genesis of organisms and the solidarity of their constituent parts. The psychological explanation must needs follow on the same track.