After the formal and material elements of life have been separately discussed, there comes an account of the process by which they are first brought into connexion, for this is how Aristotle views generation. With him it is the information of matter by psychic force; and his notions about the part which each parent plays in the production of a new being are vitiated throughout by this mistaken assumption. Nevertheless his treatise on the subject is, for its time, one of the most wonderful works ever written, and, as we are told on good authority,[257] is now less antiquated than the corresponding researches of Harvey. The philosopher’s peculiar genius for observation, analysis, and comparison will partly account for his success; but, if we mistake not, there is another and less obvious reason. Here the fatal separation of form and matter was, except at first starting, precluded by the very idea of generation; and the teleological principle of spontaneous efforts to realise a predetermined end was, as it happened, perfectly in accordance with the facts themselves. And now, looking back on his cosmology, we can see that Aristotle was never so near the truth as when he tried to bridge over the gulf between his two spheres, the one corruptible and the other eternal, by the idea of motion considered as a specific property of all matter, and persisting through all time; as a link between the celestial revolutions and the changes occurring on or near the earth’s surface; and, finally, as the direct cause of heat, the great agent acting in opposition to gravity—which last view may have suggested Bacon’s capital discovery, that heat is itself a mode of motion. Another method by which Aristotle strove to overcome the antithesis between life as a mechanical arrangement and life as a metaphysical conception, was the newly created study of comparative anatomy. The variations in structure and function which accompany variations in the environment, though statically and not dynamically conceived, bring us very near to the truth that biological phenomena are subject to the same general laws of causation as all other phenomena; and it is this truth which, in the science of life, corresponds to the identification of terrestrial with celestial physics in the science of general mechanics. Vitality is not an individualised principle stationed in the heart and serving only to balance opposite forces against one another; but it is diffused through all the tissues, and bestows on them that extraordinary plasticity which responds to the actions of the environment by spontaneous variations capable of being summed up in any direction, and so creating entirely new organic forms without the intervention of any supernatural agency. V.