remains in the Pampean strata side by side with the descendants of the Tertiary animals of Patagonia, are too distinct to be transformations. There is no doubt that they emigrated from North America. The faunas formed on the soil of Patagonia were not influenced by the new arrivals. Rather than become modified many of the species died out, showing to the end the separation of the southern world from the northern world.

Analogous conditions existed in Australia, where the mammals have scarcely passed the stages of our Eocene genera.

Thus, the surface of the earth is divided into two portions, the Northern Hemisphere where the progress has been continuous to our day, and where life is manifested in all its magnificence; and the Antarctic regions where the animal kingdom has suffered an arrest of development. Why? We do not know yet. This is a new problem which confronts students of the evolution of organisms, but it is not necessary that two centers of creation should be recognized, one in the Northern Hemisphere and the other in the Southern Hemisphere.

Gaudry died at the age of 81, after having passed the last years of his life in the study of Antarctic forms. He left a posthumous memoir, a very remarkable one, on Pyrotherium, one of the most curious creatures of the southern world, a work which will soon appear, and will be, as it were, a last homage rendered to his

memory.

In the foregoing pages I have only skimmed over the work of Gaudry, but sufficiently to show its variety and greatness. It is due to him and his contemporaries and his followers, Cope, Marsh, Osborn, Leidy, Scott, and Ameghino in America; Fowler, Seely, Woodward, and Lydekker in England; Neumayr, Zittel, and Rütimeyer in Austria, Germany, and Switzerland; Douvillé, Boule, and Depéret in France, etc., that the evolution of the ancient world has been definitely and solidly established.

But it is necessary to remember that Gaudry was the precursor. By the depth of the problems which he studied, by the influences which he exerted, and by his theoretical conceptions, Albert Gaudry stands with Lamarck. But he is also, in virtue of his remarkable observations, the Darwin of the vanished faunas, and his name should shine side by side with the names of these illustrious scholars.

CHARLES DARWIN.C

By AUGUST WEISMANN.

Forty-one years ago, when I delivered my inaugural address as a professor of this university, I took as my subject "The Justification of the Darwinian Theory." It is a great pleasure to me to be able to lecture again on the same subject on the hundredth anniversary of the birth of Darwin.

This time, however, I need not speak of justifying the theory, for in the interval it has conquered the whole world. Yet there remains much that may be said—much, indeed, that ought to be said at the present time. In my former lecture I compared the theory of descent or evolution to the Copernican Cosmogony in its importance for the progress of human knowledge, and there were many who thought the comparison extravagant. But it needs no apology now that the idea of evolution has been thoroughly elaborated, and has become the basis of the science of life.

You know that Darwin was not the only one, and was not even the first, to whom the idea of evolution occurred; it had arisen in several great minds half a century earlier, and it may therefore be thought an injustice to give, as we now do, almost all the credit of this fruitful discovery to Darwin alone.

But history is a severe and inexorable judge. She awards the palm not to him in whose mind an idea first arises, but to him who so establishes it that it takes a permanent place in scientific thought, for it is only then that it becomes fruitful of, and an instrument for, human progress. The credit for thus establishing the theory of evolution is shared with Charles Darwin only by his contemporary, Alfred Russel Wallace, of whom we shall have to speak later.

Nevertheless, a reflection of the discoverer's glory falls upon those who, about the end of the eighteenth and the beginning of the nineteenth century, were able to attain to the conception of evolution, notwithstanding the incomparably smaller number of facts

• An address delivered at the University of Freiburg on the occasion of the Centenary of Darwin. Reprinted by permission from The Contemporary Review July, 1909.

known to them. As one of these pioneers we must not omit to mention our own poet, Goethe, though he rather threw out premonitory hints of a theory of evolution than actually taught it. "Alle Gestalten sind ähnlich, doch keine gleichet der andere, und so deutet der Chor auf ein geheimes Gesetz."

The "secret law" was the law of descent, and the first to define this idea and to formulate it clearly as a theory was, as is well known, also a Darwin, Charles Darwin's grandfather, Erasmus, who set it forth in his book, "Zoonomia," in 1796. A few years later Treviranus, a botanist of Bremen, published a book of similar purport, and he was followed in 1809 by the Frenchman, Lamarck, and the German, Lorenz Oken.

All these disputed the venerable Mosaic mythos of creation, which had till then been accepted as a scientific document, and all of them sought to show that the constancy of species throughout the ages was only an appearance due, as Lamarck in particular pointed out, to the shortness of human life.

But Cuvier, the greatest zoologist of that time, a pupil of the Stuttgart Karlsschule, would have none of this idea, and held fast to the conception of species created once for all, seeing in it the only possible explanation of the enormous diversity of animal and plant forms.

And there was much to be said for this attitude at that time, when the knowledge of facts was not nearly comprehensive enough to afford a secure and scientific basis for the theory of descent. Lamarck alone had attempted to indicate the forces from which, in his opinion, the transmutation of species could have resulted.

It was not, however, solely because the basis of fact was insufficient that the theory of the evolution of organic nature did not gain ground at that time; it was even more because such foundation as there was for it was not adhered to. All sorts of vague speculations were indulged in, and these contributed less and less to the support of the theory the more far-reaching they became. Many champions of the "Naturphilosophie" of the time, especially Oken and Schelling, promulgated mere hypotheses as truths; forsaking the realm of fact almost entirely, they attempted to construct the whole world with a free hand, so to speak, and lost themselves more and more in worthless phantasy.

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This naturally brought the theory of evolution, and with it Naturphilosophie," into disrepute, especially with the true naturalists, those who patiently observe and collect new facts. The theory lost all credence, and sank so low in the general estimation that it came to be regarded as hardly fitting for a naturalist to occupy himself with philosophical conceptions.

This was the state of matters onward from 1830, the year in which the final battle between the theory of evolution and the old theory

of creation was fought out by Geoffroy St. Hilaire and Cuvier in the Paris Academy. Cuvier triumphed, and thus it came about that an idea so important as that of evolution sank into oblivion again after its emergence, and was expunged from the pages of science so completely that it seemed as if it were for ever buried beyond hope of resurrection.

Scientific men now turned with eagerness toward special problems in all the domains of life, and the following period may well be characterized as that of purely detailed investigation.

Great progress was made during this period; entirely new branches of science were founded, and a wealth of unexpected facts was discovered. The development of individual organisms, of which little had previously been known, began to be revealed in all its marvelous diversity; first, the development of the chick in the egg; then of the frog; then of insects and worms; then of spiders, crustaceans, starfishes, and all the classes and orders of mollusks, as well as of backboned animals from the lowest fish up to man himself. Within this period of purely detailed investigation there falls also the discovery, in animals and plants, of that smallest microscopically visible building stone of the living body, the cell, and this discovery paved the way for the full development of the newly founded science of tissues, histology.

In botany the chief progress in this period was in regard to the reproduction and development of the lower plants, or cryptogams, and the discovery of alternation of generations, a mode of reproduction that had previously been known in several groups of the animal kingdom, in polyps and medusæ, in various worms, and later in insects and crustaceans.

At the same time it was found that the proposition, which had hitherto been accepted as a matter of course, that an egg can only develop after it has been fertilized, is not universally valid, for there is a development without previous fertilization-parthenogenesis, or virgin birth.

Thus, in the period between the Napoleonic wars and 1859, an ever increasing mass of new facts was accumulated, and among these there were so many of an unexpected nature that further effort was constantly being put forth to elucidate detailed processes in every domain. This was desirable and important-was, indeed, indispensable to a deeper knowledge of organic nature. But in the endeavor to investigate details naturalists forgot to inquire into the deeper causes and correlations, which might have enabled them to build up out of the wealth of details a more general conception of life. So great was the reaction from the unfortunate speculations of the so-called "Naturphilosophie," that there was a tendency to shrink even from taking a comprehensive survey of isolated facts, which might lead to the induction of general principles.