v. Uexküll supposes as did Claude Bernard and as does Driesch that in an organism or an egg the ultimate processes are purely physicochemical. In an egg these processes are guided into definite parts of the future embryo by the Mendelian factors of heredity--the so-called genes. These genes he compares to the foremen for the different types of work to be done in a building. But there must be something that makes of the work of the single genes a harmonious whole, and for this purpose he assumes the existence of “supergenes.”[4] v. Uexküll’s ideas concerning the nature of a Mendelian factor and of the “supergenes” are expressed in metaphorical terms and the assumption of the “supergenes” begs the question. The writer is under the impression that this author was led to his views by the belief that the egg is entirely undifferentiated. But the unfertilized egg is not homogeneous, on the contrary, it has a simple but definite physicochemical structure which suffices to determine the first steps in the differentiation of the organism. Of course, if we suppose as do v. Uexküll and Driesch that the egg has no structure, the development of structure becomes a difficult problem--but this is not the real situation. [2] Driesch, H., _The Science and Philosophy of the Organism_. 2 vols. The Gifford Lectures, 1907 and 1908. [3] v. Uexküll, J., _Bausteine zu einer biologischen Weltanschauung_. München, 1913. [4] v. Uexküll, J., _Bausteine zu einer biologischen Weltanschauung_. München, 1913, p. 216. 2. Claude Bernard does not mention the possibility of explaining the harmony or apparent design in the organism on the basis of the theory of evolution, he simply considers the problem as outside of biology. It was probably clear to him as it must be to everyone with an adequate training in physics that natural selection does not explain the origin of variation. Driesch and v. Uexküll consider the Darwinian theory a failure. We may admit that the theory of a formation of new species by the cumulative effect of aimless fluctuating variations is not tenable because fluctuating variation is not hereditary; but this would only demand a slight change in the theory; namely a replacement of the influence of fluctuating variation by that of equally aimless mutations. With this slight modification which is proposed by de Vries,[5] Darwin’s theory still serves the purpose of explaining how without any pre-established plan only purposeful and harmonious organisms should have survived. It must be said, however, that any theory of life phenomena must be based on our knowledge of the physicochemical constitution of living matter, and neither Darwin nor Lamarck was concerned with this. Moreover, we cannot consider any theory of evolution as proved unless it permits us to transform at desire one species into another, and this has not yet been accomplished. [5] de Vries, H., _Die Mutationstheorie_. Leipzig, 1901.