§ 34. To make yet more manifest the fact that the degree of life varies as the degree of correspondence, let me here point out, that those other distinctions successively noted when contrasting vital changes with non-vital changes, are all implied in this last distinction--their correspondence with external co-existences and sequences; and further, that the increasing fulfilment of those other distinctions which we found to accompany increasing life, is involved in the increasing fulfilment of this last distinction. We saw that living organisms are characterized by successive changes, and that as the life becomes higher, the successive changes become more numerous. Well, the environment is full of successive changes, and the greater the correspondence, the greater must be the number of successive changes in the organism. We saw that life presents simultaneous changes, and that the more elevated it is, the more marked the multiplicity of them. Well, besides countless co-existences in the environment, there are often many changes occurring in it at the same moment; and hence increased correspondence with it implies in the organism an increased display of simultaneous changes. Similarly with the heterogeneity of the changes. In the environment the relations are very varied in their kinds, and hence, as the organic actions come more and more into correspondence with them, they too must become very varied in their kinds. So again is it even with definiteness of combination. As the most important surrounding changes with which each animal has to deal, are the definitely-combined changes exhibited by other animals, whether prey or enemies, it results that definiteness of combination must be a general characteristic of the internal ones which have to correspond with them. So that throughout, the correspondence of the internal relations with the external ones is the essential thing; and all the special characteristics of the internal relations, are but the collateral results of this correspondence. §§ 35, 36. Before closing the chapter, it will be useful to compare the definition of Life here set forth, with the definition of Evolution set forth in _First Principles_. Living bodies being bodies which display in the highest degree the structural changes constituting Evolution; and Life being made up of the functional changes accompanying these structural changes; we ought to find a certain harmony between the definitions of Evolution and of Life. Such a harmony is not wanting.