solution from which it was formed. But the constituent parts of organic bodies can severally maintain their existing states, only while remaining in connexion. Even in the lowest living forms, mutilation cannot be carried beyond a certain point without decomposition ensuing. As we advance through the higher up to the highest forms, we see a gradual narrowing of the limits within which the mutilation does not cause destruction: a progressive increase of mutual dependence or integration which is, at the same time, the condition to greater functional perfection. In societies this truth is equally manifest. That the component units slowly segregate into groups of different ranks and occupations, is a fact scarcely more conspicuous than is the fact that these groups are necessary to each other’s existence. And we cannot contemplate the still-progressing division of labour, without seeing that the interdependence becomes ever greater as the evolution becomes higher. It remains only to point out definitely, what has been already implied, that these several forms of change which have been successively described as making up the process of Evolution, are not in reality separate forms of change, but different aspects of the same change. Intrinsically the transformation is one and indivisible. The establishment of differences that become gradually more decided, is evidently but the beginning of an action which cannot be pushed to its extreme without producing definite divisions between the parts, and reducing each part to a separate mass. But with our limited faculties, it is not possible to take in the entire process at one view; nor have we any single terms by which the process can be described. Hence we are obliged to contemplate each of its aspects separately, and to find a separate expression for its characteristic. Having done this, we are now in a position to frame a true idea of Evolution. Combining these partial definitions we get a complete definition, which may be most conveniently expressed thus—_Evolution is a change from an indefinite, incoherent homogeneity, to a definite, coherent heterogeneity; through continuous differentiations and integrations._ It may perhaps be remarked that the last of these clauses is superfluous; since the differentiation and integration are implied in the first clause. This is true: the transition which the first clause specifies, is impossible save through the process specified in the second. Nevertheless, a mere statement of the two extreme stages with which Evolution begins and ends, omitting all reference to changes connecting them, leaves the mind with but an incomplete idea. The idea becomes much more concrete when these changes are described. Hence, though not logically necessary, the second clause of the definition is practically desirable.