with as much precision as if man had " had "consciously selected" it by the aid of a sieve. Physical Geology is full of such selections of the picking out of the soft from the hard, of the soluble from the insoluble, of the fusible from the infusible, by natural agencies to which we are certainly not in the habit of ascribing consciousness. But that which wind and sea are to a sandy beach, the sum of influences, which we term the "conditions of existence," is to living organisms. The weak are sifted out from the strong. A frosty night "selects the hardy plants in a plantation from among the tender ones as effectually as if it were the wind, and they, the sand and pebbles, of our illustration; or, on the other hand, as if the intelligence of a gardener had been operative in cutting the weaker organisms down. The thistle, which has spread over the Pampas, to the destruction of native plants, has been more effectually "selected" by the unconscious operation of natural conditions than if a thousand agriculturists had spent their time in sowing it. It is one of Mr. Darwin's many great services to Biological science that he has demonstrated the significance of these facts. He has shown that-given variation and given change of conditions-the inevitable result is the exercise of such an influence upon organisms that one is helped and another is impeded; one tends to predominate, another to disappear; and thus the living world bears within itself, and is surrounded by, impulses towards incessant change. But the truths just stated are as certain as any other physical laws, quite independently of the truth, or falsehood, of the hypothesis which Mr. Darwin has based upon them; and that M. Flourens, missing the substance and grasping at a shadow should be blind to the admi rable exposition of them, which Mr. Darwin has given, and see nothing there but a "dernière erreur du dernier siècle "a personification of Nature-leads us indeed to cry with him: "O lucidité! O solidité de l'esprit Français, que devenez-vous ?" M. Flourens has, in fact, utterly failed to comprehend the first principles of the doctrine which he assails so rudely. His objections to details are of the old sort, so battered and hackneyed on this side of the Channel, that not even a Quarterly Reviewer could be induced to pick them up for the purpose of pelting Mr. Darwin over again. We have Cuvier and the mummies; M. Roulin and the domesticated animals of America; the difficulties presented by hybridism and by Palæontology; Darwinism a rifacciamento of De Maillet and Lamarck; Darwinism a system without a commencement, and its author bound to believe in M. Pouchet, &c. &c. How one knows it all by heart, and with what relief one reads at p. 65 "Je laisse M. Darwin!" But we cannot leave M. Flourens without calling our readers' attention to his wonderful tenth chapter, "De la Préexistence des Germes et de l'Epigénèse," which opens thus: "Spontaneous generation is only a chimera. This point established, two hypotheses remain: that of pre-existence and that of epigenesis. The one of these hypotheses has as little foundation as the other." (P. 163.) "The doctrine of epigenesis is derived from Harvey: following by ocular inspection the development of the new being in the Windsor does, he saw each part appear successively, and taking the moment of appearance for the moment of formation he imagined epigenesis." (P. 165.) On the contrary, says M. Flourens (p. 167), "The new being is formed at a stroke (tout d'un coup), as a whole, instantaneously; it is not formed part by part, and at different times. It is formed at once; it is formed at the single individual moment at which the conjunction of the male and female elements takes place." It will be observed that M. Flourens uses language which cannot be mistaken. For him, the labours of Von Baer, of Rathke, of Coste, and their contemporaries and successors in Germany, France, and England, are nonexistent; and, as Darwin "imagina" natural selection, so Harvey "imagina" that doctrine which gives him an even greater claim to the veneration of posterity than his better known discovery of the circulation of the blood. Language such as that we have quoted is, in fact, so preposterous, so utterly incompatible with anything but absolute ignorance of some of the best established facts, that we should have passed it over in silence had it not appeared to afford some clue to M. Flourens' unhesitating, à priori, repudiation of all forms of the doctrine of the progressive modification of living beings. He whose mind remains uninfluenced by an acquaintance with the phænomena of development, must indeed lack one of the chief motives towards the endeavour to trace a genetic relation between the different existing forms of life. Those who are ignorant of Geology, find no difficulty in believing that the world was made as it is; and the shepherd, untutored in history, sees no reason to regard the green mounds which indicate the site of a Roman camp, as aught but part and parcel of the primeval hill-side. So M. Flourens, who believes that embryos are formed "tout d'un coup," naturally finds no difficulty in conceiving that species came into existence in the same way. ་ XIV. ON DESCARTES' "DISCOURSE TOUCHING THE AND OF SEEKING SCIENTIFIC TRUTH." 1870 IT has been well said that "all the thoughts of men, from the beginning of the world until now, are linked together into one great chain;" but the conception of the intellectual filiation of mankind which is expressed in these words may, perhaps, be more fitly shadowed forth by a different metaphor. The thoughts of men seem rather to be comparable to the leaves, flowers, and fruit upon the innumerable branches of a few great stems, fed by commingled and hidden roots. These stems bear the names of the half-a-dozen men, endowed with intellects of heroic force and clearness, to whom we are led, at whatever point of the world of thought the attempt to trace its history commences; just as certainly as the following up the small twigs of a tree to the branchlets which bear them, and tracing the branchlets to their supporting branches, brings us, sooner or later, to the bole. It seems to me that the thinker who, more than any other, stands in the relation of such a stem towards the philosophy and the science of the modern world is René Descartes. I mean, that if you lay hold of any charac teristic product of modern ways of thinking, either in the region of philosophy, or in that of science, you find the spirit of that thought, if not its form, to have been present in the mind of the great Frenchman. There are some men who are counted great because they represent the actuality of their own age, and mirror it as it is. Such an one was Voltaire, of whom it was epigrammatically said, "he expressed everybody's thoughts better than anybody." But there are other men who attain greatness because they embody the potentiality of their own day, and magically reflect the future. They express the thoughts which will be everybody's two or three centuries after them. Such an one was Descartes. Born, in 1596, nearly three hundred years ago, of a noble family in Touraine, René Descartes grew up into a sickly and diminutive child, whose keen wit soon gained him that title of "the Philosopher," which, in the mouths of his noble kinsmen, was more than half a reproach. The best schoolmasters of the day, the Jesuits, educated him as well as a French boy of the seventeenth century could be educated. And they must have done their work honestly and well, for, before his schoolboy days were over, he had discovered that the most of what he had learned, except in mathematics, was devoid of solid and real value. 66 "Therefore," says he, in that "Discourse "2 which I have taken for my text, as soon as I was old enough to be set free from the government of my teachers, I entirely forsook the study of letters; and determining to seek no other knowledge than that which I could discover within myself, or in the great book of the world, I spent the remainder of my youth in travelling; in seeing courts and armies; in the society of people of different humours and conditions; in gathering 1 I forget who it was said of him: “Il a plus que personne l'esprit que tout le monde a." 2 "Discours de la Méthode pour bien conduire sa Raison et chercher la Vérité dans les Sciences, |