beginnings and earlier stages of development at least quite indifferent, often directly obstructive to the individual in its struggle for existence, and therefore would have been called into existence and developed by agencies which had an effect directly counteracting natural selection. How high, for instance, stand the vertebrates above the invertebrates! Yet how could the first deviation from the ganglionic system of the nerves of the invertebrates to the cerebro-spinal system of the vertebrates have occurred?-and, especially, how could the first deposit of the vertebral column have procured any benefit to the individual in the struggle for existence? We quote this objection from Karl Planck's "Wahrheit und Flachheit des Darwinismus," ("Truth and Platitude of Darwinism”), Nördlingen, Beck, 1872.

Still more striking is the insufficiency of the selection theory for the explanation of the origin of the organs of motion in the higher classes of vertebrates. A. W. Volkman says of it, in his instructive lecture, “Zur Entwickelung der Organismen," ("Development of the Organisms") Halle, Schmidt, 1875, p. 3 ff: "Without doubt, animals with extremities will come from animals which lacked extremities. Now if the metamorphosis originated in the course of one generation, the animals with extremities would have an advantage over the rest, which ought to show itself in the natural selection; but if the development of an extremity needs 10,000 generations, the individual in which the process of the development begins produces Too of the extremity and the advantage, resulting therefrom is reduced to zero. For an organ can only be of advantage when it performs its functions; and on

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the first of the 10,000 stages of development the extremity can not perform its functions. Just think of the cetacea! Of the hind extremity, only its carrier, the pelvis, has been developed; and even this is only represented by the two hip-bones, hanging in the flesh. As to the python, the hind extremities are more complete, but they lie hidden under the skin, and therefore are of no use for local movement. Such examples show that in the history of the development of an organ thousands of years may pass, and numerous generations may arise and disappear, until it reaches that grade of perfection where it is of use to its owner. How therefore, can we look upon such an organ, when finally it is perfect, as a product of selection in the sense of Darwin?"

We find the scientific objections to the selection theory collected in detail in the before-mentioned works of Wigand, Blanchard, His, von Baer, and especially in Mivart's "Genesis of Species," (London, MacMillan, 1871); and it is a praiseworthy testimony of Darwin's love of truth, that lately he himself, the originator of the selection theory, willingly admits these weak points in his theory,* while Häckel and many of his followers

* Darwin says, on page 146, Eng. Ed., of his "Descent of Man": "In the earlier editions of my 'Origin of Species,' I perhaps attributed too much to the action of natural selection or the survival of the fittest. * * I did not formerly sufficiently consider the existence of structures which, as far as we can at present judge, are neither beneficial nor injurious; and this I believe to be one of the greatest oversights as yet detected in my work. An unexplained residuum of change, perhaps a large one, must be left to the assumed uniform action of those unknown agencies, which occasionally induce strongly-marked and abrupt deviations of structure in our domestic productions.”

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in Germany still stoutly reject every doubt of the autocracy of the selection principle.

In summing up all we have said thus far about the theories of descent, of evolution, and of selection, we still find all three solutions of the scientific problems to be hypotheses, but hypotheses of very different value. The idea of descent has the most scientific ground; it will, as a permanent presupposition, govern all scientific investigations as to the origin of species, even if it does not exclude the idea of an often-repeated primitive generation of organisms-especially of those that stand still lower in development. More uncertain and less comprehensive is the position of the evolution theory; in all likelihood, the idea of an origin through development will have to share the sovereignty with the idea of origin by leaps through metamorphosis of germs. Still more unfavorable is the state of the selection theory. It possesses the merit of having started the whole question as to the origin of species; it may explain subordinary developments; natural selection may have coöperated as a regulator in the whole progress and the whole preservation of organic life. Ed. von Hartmann, in his essay, “Truth and Error of Darwinism," (Berlin, Duncker, 1875), on page 111, compares its functions with those of the bolt and coupling in a machine; but that the driving principle which called new species into existence lay or originated in the organisms, and did not approach them from without, seems to be confirmed more and more decidedly with every new step of exact investigation as well as of reflection.

BOOK II.

THE PHILOSOPHIC SUPPLEMENTS AND CONSEQUENCES OF THE DARWINIAN THEORIES.

THE PHILOSOPHIC PROBLEMS.

Although, in accordance with the requirements of the task before us, we have to restrict ourselves to giving the results of natural science only in their general outlines, still we believe that we have not overlooked any essential result which is of importance to the question of the origin of species and of man. We have now finished our scientific review; and the conclusion to which we see ourselves brought is that natural science, in its investigation of the origin of species, has arrived at nothing but problems which it is not able to solve. There is a very great probability of an origin of species, at least of the higher organized species, through descent ; but whether through descent by means of gradual development or of metamorphosis of germs, or whether with one group of organisms it is in this way, with another in that, is not yet decided. The attempt to explain their entire origin exclusively by the selection theory, must be regarded as a failure; all indications rather show that, supposing the descent principle correct, the deciding agencies which formed new species did not approach the old species out of which the new ones originated from

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without, but that they originated or were already in existence within them. But what these agencies were, natural science is at present unable to state; and not only those scientists who reject every idea of a descent, but also those who are favorable to the ideas of descent and of evolution, rejecting only the selection theory, are at one in silent or open acknowledgment of this limit of our knowledge, be it permanent or temporary.

But now the question arises: does the search after these agencies henceforth remain the exclusive task of natural science, and have we therefore simply to wait and see whether it will succeed in finding them? or have we to look for the answer to these questions, which natural science can no longer give, in another science-namely, philosophy? The first question we will have to answer in the affirmative, the second in the negative. It is certainly understood that metaphysical principles must underlie all physical appearances; and the right to define these principles, so far as they can be known, is willingly conceded to philosophy by the scientists, with the exception of those of materialistic and naturalistic tendencies. This mutual re-approaching of philosophy and natural science is one of the most gratifying, and, to both, most fruitful evidences of the intellectual work of the present generation. But these metaphysical principles themselves become cognizable only when the physical effects, whose cause they are, become accessible to our knowledge; and every attempt to find them a priori, or only to extend them a priori, will always fail through the opposition of empirical facts; or even if this attempt accommodates itself to the existing state of knowledge at a given time, it will always be overcome by the pro