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 Mr. Flourens, missing the substance and grasping at a shadow, should be blind to the admirable 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 chimaera. 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 at the single _individual_ moment at which the conjunction of the male and female elements takes place."