physico­chemical manifesta­tions, but it is true that the essential is not explained thereby; for no fortuitous coming together of physico­chemical phenomena constructs each organism after a plan and a fixed design (which are foreseen in advance) and arouses the admirable subordina­tion and harmonious agreement of the acts of life. . . .

We can only know the material conditions and not the intimate nature of life phenomena. We have therefore only to deal with matter and not with the first causes or the vital force derived therefrom. These causes are inaccessible to us, and if we believe anything else we commit an error and become the dupes of metaphors and take figurative language as real. . . . Determinism can never be but physico­chemical determinism. The vital force and life belong to the metaphysical world.

In other words, Bernard thinks it his task to account for individual life phenomena on a purely physico­chemical basis—but the harmonious character of the organism as a whole is in his opinion not produced by the same forces and he considers it impossible and hopeless to investigate the “design.” This attitude of Bernard would be incomprehensible were it not for the fact that, when he made these statements, the phenomena of specificity, the physi­ology of development and regenera­tion, the Mendelian laws of heredity, the animal tropisms and their bearing on the theory of adapta­tion were unknown.

This explanation of Bernard’s attitude is apparently contradicted by the fact that Driesch2 and v. Uexküll,3 both brilliant biologists, occupy today a standpoint not very different from that of Claude Bernard. Driesch assumes that there is an Aristotelian “entelechy” acting as directing guide in each organism; and v. Uexküll suggests a kind of Platonic “idea” as a peculiar characteristic of life which accounts for the purposeful character of the organism.

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. 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.

It may be of some interest to point out that we do not need to make any definite assump­tion concerning the mechanism of evolu­tion and that we may yet be able to account for the fact that the surviving organisms are to all appearances harmonious. The writer pointed out that of all the 100,000,000 conceivable crosses of teleost fish (many of which are possible) not many more than 10,000, i. e., about one-hundredth of one per cent., are able to live and propagate. Those that live and develop are free from the grosser type of disharmonies, the rest are doomed on account of a gross lack of harmony of the parts. These latter we never see and this gives us the erroneous concep­tion that harmony or “design” is a general character of living matter. If anybody wishes to call the non-viability of 9999/100 per cent. of possible teleosts a process of weeding out by “natural selec­tion” we shall raise no objec­tion, but only wish to point out that our way of explaining the lack of design in living nature would be valid even if there were no theory of evolu­tion or if there had never been any evolu­tion.

3. v. Uexküll is perfectly right in connecting the problem of design in an organism with Mendelian heredity. The work on Mendelian heredity has shown that an extremely large number of independently transmissible Mendelian factors help to shape the individual. It is not yet proven that the organism is nothing but a mosaic of Mendelian factors, but no writer can be blamed for considering such a possibility. If we assume that the organism is nothing but a mosaic of Mendelian characters it is difficult indeed to understand how they can force each other into a harmonious whole6; even if we make ample allowance for the law of chance and the corresponding wastefulness in the world of the living. But it is doubtful whether this idea of the rôle of Mendelian factors is correct. The facts of experi­mental embryology strongly indicate the possibility that the cytoplasm of the egg is the future embryo (in the rough) and that the Mendelian factors only