The idea of Evolution or Development, thus introduced by Schelling into philosophy as a governing principle in the study of matter and of mind, is not to be confused either with the older use of these terms or with their current applications to-day[6]. By evolution (or development) and involution (or envelopment) the earlier speculation on biology had denoted the view that the organic germ contained _in parvo_ all that the matured organism showed in large. As the mature bulb of the healthy hyacinth shows, when cut open, to the naked eye, the stem and flowers that will issue from it next spring; so in general the seed can be treated as a miniature organism needing only an increase of bulk to make it fully visible in details. Growth is thus not accretion, but explication and enlargement of a microscopic organism subsisting in the germ. Evolution, in the present time, and especially since Darwin, means something more than this. It implies a theory of descent of the variety of existing organisms from other organisms of a previous age, less individualised in forms and functions. From comparatively simple and homogeneous creatures there have issued in the course of ages creatures of more complex, more highly differentiated structure; and this process of gradual differentiation may be conceived as going on through an all but infinite period. At one end we may conceive matter, just endowed with the faculties of life and organisation, but in a minimal degree; at the other end of the developmental process, creatures which have organised within themselves powers, maximal both in range and variety. The result (so far as we at present go) is a genealogy of organism which, to quote Darwin, pictures before us a 'great tree of life which fills with its dead and broken branches the crust of the earth and covers the surface with its ever branching and beautiful ramifications.'