_Argument._--A strictly mechanistic hypothesis of evolution compels us to regard the organic world, and the inorganic environment with which it interacts, as a physico-chemical system. All the stages of an evolutionary process must therefore be equally complex: they are simply phases, or rearrangements, of the elements of a transforming system. The physics on which these mechanistic hypotheses were based was that of a discontinuous, granular, Newtonian universe, that is, one consisting of discrete particles, or mass-points, attracting or repelling each other with forces which are functions of the distances between them. It was a spatially extended system of parts. Therefore at all stages in an evolutionary process, or one of individual development, the elements of the system constitute an extensive manifoldness, and the obligation of mechanistic hypotheses of evolution and development to accept this view has shaped modern theories of heredity. Life is an intensive manifoldness, but in individual or racial evolu- tion this intensive manifoldness becomes an extensive manifoldness. Life is a bundle of tendencies which can co-exist, but which cannot all be fully manifested, in the same material constellation, therefore these tendencies become dissociated in the evolutionary process. In this dissociation there is direction and co-ordination, which are the Vital Impetus of Bergson, or the Entelechy of Driesch. Entelechy is an elemental agency in nature which we are compelled to postulate because of the failure of mechanism. It is not spirit, nor a form of energy, but the direction and co-ordination of energies. There is a sign, or direction of inorganic happening which absolutely characterises the processes which are capable of analysis by physico-chemical methods of investigation, and the result of this direction of inorganic happening is material inertia. Yet this direction cannot be universal: it must be evaded somewhere in the universe. It is evaded by the organism. The problem of the nature of life is only a pseudo-problem. APPENDIX MATHEMATICAL AND PHYSICAL NOTIONS 342 Infinity and the notion of the limit. Functionality. Frequency distributions and probability. Matter, force, mass, and inertia. Energy-transformations. Isothermal and adiabetic transformations. The Carnot engine and cycle. Entropy. Inert matter. INDEX 377 THE PHILOSOPHY OF BIOLOGY CHAPTER I THE CONCEPTUAL WORLD