Thus then is that increase of heterogeneity which constitutes Evolution, distinguished from that increase of heterogeneity which does not do so. Though in disease and death, individual or social, the earliest modifications may be construed as additions to the heterogeneity previously existing; yet they cannot be construed as additions to the definiteness previously existing. They begin from the very outset to destroy this definiteness; and so, gradually produce a heterogeneity that is indeterminate instead of determinate. Just in the same way that a city, already multiform in its variously arranged structures of various architecture, may be made more multiform by an earthquake, which leaves part of it standing and overthrows other parts in different ways and degrees, and yet is at the same time reduced from definite arrangement to indefinite arrangement; so may organized bodies be made for a time more multiform by changes which are nevertheless disorganizing changes. And in the one case as in the other, it is the absence of definiteness which distinguishes the multiformity of regression from the multiformity of progression. If the advance from the indefinite to the definite is an essential characteristic of Evolution, we shall of course find it everywhere displayed; as in the last Chapter we found the advance from the homogeneous to the heterogeneous. With a view of showing that it is so, let us now briefly reconsider the same several classes of facts. * * * * *