Thus Oken postulated, as the specific vehicle of life, a primitive substance, in essence at least homogeneous. But he went further, and maintained that his 'Urschleim' assumed _the form of vesicles_, of which the various organisms were composed. 'The organic world has as its basis an infinitude of such vesicles.' Who is not at once reminded of the now dominant _Cell-theory_? And, in fact, thirty years later, when the cell was discovered, Oken did claim priority for himself. In so doing, he obviously confused the formulating of a problem with the solving of it; he had, quite rightly, divined that organisms must be built up of very minute concentrations of the primitive substance, but he had never seen a cell, or proved the necessity for its existence, or even attempted to prove it. His vesicle-theory was a pure divination, a prevision of genius, but one which could not directly deepen knowledge; it did not prompt, or even hasten, the discovery of the cell. Here, as throughout in his natural philosophy, Oken built, not from beneath upwards, by first establishing facts and then drawing conclusions from them, but, inversely, he invented ideas and principles, and out of them reconstructed the world. In this he differs essentially from his predecessors Erasmus Darwin, Treviranus, and Lamarck, who all reasoned inductively, that is, from observed data. Thus the whole evolutionary movement was lost in indefiniteness; because men wanted to find a reason for everything, they missed even what might then have been explained. Moreover, the theory of evolution still lacked a sufficiently broad basis of facts; the 'Naturphilosophie,' by its want of moderation, robbed it of all credit; and it is not to be wondered at that men soon ceased to occupy themselves with the problem of the evolution of the living world. A few indeed held fast to the doctrine of evolution during the first third of the century, but then it disappeared completely from the realm of science.