As, in some worms and zoophytes, there is indeed no appearance of nerves, and certainly none in plants, which yet possess sensibility, all this gradually approaches to the attraction and repulsion of the magnet and electrics, which, like some of these, are divisible almost to infinity, and yet possess their various powers, which, like the sensibility of the superior animals, connected by nerves, are only evidenced when led by conductors. Hence, I conclude, that sensation, understood in this limited sense, as distinct from perception, and differing, _toto coelo_, from soul, is, like extension, an imprescriptible property of all matter: but it may exist in as many forms and as many relations as it; in its separate particles; in larger combinations, as polypes; in still larger ones, as worms and insects, where these extended and sentient particles, connected by nerves, have more extensive relations and more complete dependence on each other; or uniting to constitute perception in whole bodies, as in the more perfect animals, where a sensorium commune exists, and where, in consequence of the most exquisite arrangement, and the finest relations, no particle can be deranged without affecting all the rest. It is indeed, these various degrees in which it appears, that afford a strictly analogical proof of its existence as a primary property of matter. As man then has not only sensation in the separate parts, but perception arising from the whole, the descent is gradual to beings which have merely sensation in distinct parts, but no general perception; and thence equally gradual to beings which have sensation limited to their individual particles. Now, as the perceptions of two of the superior animals cannot unite to form one perception, so the sensations of two parts of a polyp cannot combine in perception; nor is it of course more wonderful, that the sensations of two of the minute particles of matter cannot unite in one common sensation. As we do not expect electricity to be evidenced without conductors, why should we expect sensation, in any great degree, without those nerves which are its conductors? It would be as irrational to deny the former, when conductors are not present, as to deny the latter (understood as I have defined it), when nerves are absent. Neither is it more wonderful that these sensations, thus limited, are not evidenced; because it is scarcely to be expected, that the functions of that should be evident, the absolute structure of which is unknown, and because it is exactly in proportion to the concentration of sensation (and by no means to its division) that it is, at any time, evidenced.