The unity of an individual soul is implied in all feeling; or perhaps we should rather say that feeling constitutes the unity of the individual soul. The individual animal is not merely one for us, who contemplate the connexion between the members organic to its life. It is one in itself, as no material atom or material compound is, in virtue of the common feeling through which, if one member suffer, all the members suffer with it. It is not one, as the atom is supposed to be, in the sense of being absolutely simple and excluding everything else from itself. Nor is it one, like the material universe, merely in respect of unity of relation between manifold elements. It is one in the sense that upon certain occurrences in the parts of a peculiarly constituted body there supervenes feeling, which is not any one or number of the occurrences, nor a result of their combination, in the sense of being analysable into them; which does not admit of being analysed into or explained by anything else, and would therefore be unknown but for our immediate experience of it; which, while it is not the attribute of any or all of the elements organic to it, is incommunicably private to a subject experiencing it, affected by the past and affecting the future of that particular subject, his own and not another's. (§ 119 ¶ 1)

The question of the distinction between animals and plants, the question whether all animals feel, whether any plants do, is one of classification with which we are not here concerned. However such a question may be answered, it does not affect the importance of noticing the distinctive nature of the individuality which feeling constitutes. It is only indeed from experienec of ourselves, not from observation of the animals, that we know what this individuality is; but according to all indications we are justified in ascribing it at any rate to all vertebrate animals. To say that they feel as men do, or that they are individual in the same sense as men, is misleading, because it is to ignore the distinctive character given to human feeling and human individuality by a self-consciousness which we have no reason to ascribe to the animals. But the assertion that they feel no less, and are no less individual, than ourselves seems to be within the mark. And if by desire we mean no more than that felt impulse after riddance from pain which pain carries with it to the individual, or that felt want which survives a feeling of pleasure; if by will we mean no more than activity determined by feeling; then we cannot do otherwise than ascribe desire and will to the animals. (§ 119 ¶ 2)