closer acquaintance with the manner of their origin is not only no disturbance to his ground of belief, but, on the contrary, an addition to his knowledge of the method of God's action. In every man of sound mind, the religious faith is not antagonistic or even indifferent to the scientific impulse toward investigation, but stands upon a most intimate footing with it. Hence the human intellect again and again makes the attempt to find an answer to the problem of the origin of species in a scientific way, and each endeavor of this kind necessarily ends with the dilemma that either the first individuals of a species, no matter whether it be the highest or the lowest, have been evolved out of inorganic matter, or they originated by descent from the most closely related species of their predecessors. The denial of the first part of our dilemma, and the affirmation of the second, is the "Theory of Descent."

But this theory of descent leads us at once into another dilemma. If the species originated by descent from the most closely related lower species, and under certain circumstances also from species of the same rank, and even by degeneration from the next higher, it must have occurred in one of two ways: either by leaps -called by naturalists "metamorphosis of germs or "heterogenetic conception"—or by a succession of imperceptibly small alterations of the individuals from generation to generation. Each of these changes would have been no greater than the differences we observe to-day between the individuals of the very same species, but became in the course of time so massed and strengthened in one direction that new species have been evolved. This hypothesis is called the "Theory of Development,"

or "Evolution." We retain this name, although well aware of the fact that the authors do not agree in their use of the term "evolution." Professor Wigand, who adopts only the theory of a descent from one primordial cell to another, and who positively rejects the idea of a progress from one fully developed species to another, claims among other things that one value of his own theory is that he secures for the idea of evolution its full meaning. The expression still has a meaning for those who reject the real descent of the species or their primordial germs one from another, and acknowledge only the ideal bond of a common plan in their successive manifestations. But as soon as we examine more closely the literal and logical meaning of the word, we shall find it of most weight when we understand by it the beforementioned gradual evolution in opposition to the theory of progress by leaps or new creations. Moreover, it is well known that long before this no other term than evolution was used to designate the growth of a single organic individual from the primordial cell and egg to its fully developed form and vital function. Besides, we find ourselves also in harmony with most of the authors, so far as they have distinct conceptions of the different scientific problems, if we use the term "theory of evolution" for the gradual development of one species from another, in opposition to the hypothesis of a metamorphosis of germs, or even of a genealogy of primordial cells.

But each evolution theory leads again to new theories, as soon as it has to be proved in a scientific way. For it can claim a scientific worth only when sustained by earnest attempts to find and prove the produc

tive power, agencies and laws of such an evolution of species. Those attempts can be made in various ways. As a philosophical question, many attempts at solution have been made, both in ancient and modern times; but being mainly in the realm of metaphysics, they do not come within the limits of our scientific essay. As a question for investigators of natural phenomena, only two attempts of sufficient importance to be mentioned have been made. The first one was made by Lamarck, who, taking the really different ideas of descent and evolution as one, made use of the hypothesis of transmutation; thus becoming the pioneer of Darwinism. The other attempt was made by Darwin in his theory of natural selection, or struggle for existence, and is called the "Theory of Selection.'

In defining our problem, therefore, we find ourselves under the influence of a scientific law of development. The simple problem which we started from has developed into a trinity of problems and attempts at solution. The simple question of the origin of species led us into the dilemma of a generatio æquivoca, or a descent; the hypothesis of a descent led to the dilemma of a heterogenetic conception, or an evolution; and the hypothesis of an evolution rendered necessary the attempt at explaining this evolution, and showed Darwin's method of explaining it by his selection theory. It will be well for the reader to keep distinctly in mind the difference between these problems and theories, in following our investigations, even if we cannot arrange our historical sketch according to the natural principle of division arising from these differences.

For it lies in the nature of the question itself, that

these theories, in their historical progress, did not appear singly, but together. Those who inclined to the theory of a descent of species could claim for it the attention of scientific investigators only after having also made the attempt at conceiving this descent in a concrete way, and according to certain analogies of observation. The only analogy of the kind appeared in the sphere of individual development and individual differences on the one hand, and in that of closely related characters of allied species on the other; and thus led of itself to the evolution theory. As soon as the naturalists thought they had found the causes of such an evolution of the species, they naturally placed these causes in the foreground of their demonstrations, and erected upon them the structure of their entire theory; thus treating descent, evolution and selection as one single and indissolubly connected theory. But this manner of treating the question had also its dangers, which have already caused a great deal of confusion and misunderstanding, as well as much unprofitable controversy. Often friends and enemies of the theories placed that which was in favor of the theory of descent to the credit of the evolution or selection theory; and, on the other hand, that which seemed opposed to the selection theory was often held to be a weakening of the evolution and descent theory; and this was done, not only by amateurs, but often enough by the highest authorities also. In reality, however, it is quite conceivable that the idea of a descent may prove correct, and possibly the idea of an evolution of the species will have to be replaced by that of a heterogenetic generation, or by the theory that certain groups in the organic system are originated

by heterogenetic generation, and others by evolution; and so the evolution theory must share with the theory of heterogenetic generation, or of a metamorphosis of germs. On the other hand, it is conceivable that even where the evolution theory is confirmed, the evolution can be accounted for wholly or partly by other reasons than those derived from the selection theory. And even this result of present investigations is not inconceivable that the reasons for and against the different theories will be found to balance one another to such a degree that they will sooner or later lead science, in answering the question of the origin of species, to the old confession of Socrates-" Ignoramus.

We shall, therefore, have to arrange our historical sketch according to the historical order of the appearance of the theories, and treat the problems more or less as an undivided whole. But we shall keep in mind, during our historical sketch, not only the logical separation of the problems in question, in order not to lose clearness of judgment, but we shall also at the end of our review, if we consider the present condition of the problems, have to examine the same once more in detail, so far as regards the above mentioned separation.