That an animal Organism is made up of several distinct organs, and these the more numerous in proportion to the rank of the animal in the scale of beings, is one of those familiar facts which have their significance concealed from us by familiarity. But it is only necessary to express this fact in language slightly altered, and to say that an animal Organism is made up of several distinct _individuals_, and our attention is at once arrested. Doubtless, it has a paradoxical air to say so; but Natural History is full of paradoxes; and you are aware that a paradox is far from being necessarily an absurdity, as some inaccurate writers would lead us to suppose: the word meaning simply, “contrary to what is thought,”—a meaning by no means equivalent to “contrary to what is the fact.” It is paradoxical to call an animal an aggregate of individuals; but it is so because our thoughts are not very precise on the subject of individuality—one of the many abstractions which remain extremely vague. To justify this application of the word individual to every distinct organ would be difficult in ordinary speech, but in philosophy there is ample warrant for it. An organ, in the physiological sense, is an _instrument_ whereby certain functions are performed. In the morphological sense, it arises in a _differentiation_, or setting apart, of a particular portion of the body for the performance of particular functions—a group of cells, instead of being an exact repetition of all the other cells, takes on a difference and becomes distinguished from the rest as an organ.[5]