It is extraordinary how an investigator who has accomplished so much, not only as a historian of his special branch and as a critic of ideas, but who is also fully equipped with knowledge of biology, should have paid no heed to the fact that every organic being is indivisible from the first, and is not composed of anything like atoms, monads, &c. The first distinctive mark of the living as opposed to inorganic matter is that the former is always differentiated into dissimilar, mutually dependent parts, and is not homogeneous like a crystal. And so it should have been borne in mind that it was at least possible that individuation, the fact that organic beings are not united, like Siamese twins, would prove to have importance in psychical matters, and the ego, therefore, was more than Mach’s idea of it as a mere waiting-hall of perceptions. It may be that there exists a psychical correlation even amongst animals. Everything that an animal feels and perceives has a different “note” or “colour” in every individual. This individual quality is not only characteristic of the class, genus, species, race, and family, but also is different in every individual of the same family, &c. The idioplasm is the physiological equivalent of this specific individual quality of the sensations and perceptions, and there are reasons analogous with those in favour of the supposition of an idioplasm for the supposition of an individual character amongst animals. The sportsman who has to do with dogs, the trainer with horses, and the keeper with animals will readily admit the existence of this individuality as a constant element. It is clear that we have to do here with something more than a mere rendezvous of perceptions. But even if this psychical analogue of the idioplasm were proved to exist in the case of animals, it could not be ranked with the intelligible character, the existence of which in any living creature except man cannot be maintained. The intelligible character of men, their individuation, has the same relation to empirical character that memory has to the simple power of recognition. And finally we come to identity, by which the structure, form, law, and cosmos persist even through the change of contents. The considerations from which is drawn the proof of the existence in man of such a noumenal, trans-empirical subject must now be stated briefly. They come from logic and ethics.