The “original type” which constitutes the foundation of every organic form “as the inner original community” is the _inner constructive force_, which receives the original direction of form-production—that is, the tendency to give rise to a particular form—and is propagated by _Inheritance_. The “uninterruptedly progressive transformation,” on the other hand, which “springs from the necessary relations to the outer world,” acting as an _external formative force_, produces, by _Adaptation_ to the surrounding conditions of life, the “infinite variety of forms” (Gen. Morph. i. 154; ii. 224). The internal formative tendency of _Inheritance_, which retains the unity of the original type, is called by Goethe in another passage the _centripetal force_ of the organism, or its tendency to specification; in contrast with this he calls the external formative tendency of _Adaptation_, which produces the variety of organic forms, the _centrifugal force_ of organisms, or their tendency to variation. The passage in which he clearly indicates the “equilibrium” of these two extremely important organic formative tendencies, runs as follows: “The idea of _metamorphosis_ resembles the vis centrifuga, and would lose itself in the infinite, if a counterpoise were not added to it: I mean the tendency to _specification_, the strong power to preserve what once has come into being, a vis centripeta, which in its deepest foundation cannot be affected by anything external.” Metamorphosis, according to Goethe, consists not merely, as the word is now generally understood, in the changes of form which the organic individual experiences during its individual development, but, in a wider sense, in the transformation of organic forms in general. His idea of metamorphosis is almost synonymous with the theory of development. This is clear, among other things, from the following passage:—“The triumph of physiological metamorphosis manifests itself where the whole separates and transforms itself into families, the families into genera, the genera into species, and then again into other varieties down to the individual. This operation of nature goes on ad infinitum; she cannot rest inactive, but neither can she keep and preserve all that she has produced. From seeds there are always developed varying plants, exhibiting the relations of their parts to one another in an altered manner.”