animals bear to each other, and to those now living, will be treated of in the chapter on Geology, while the Development or Embryology of the groups will be more detailed in the chapter on that subject. Though Geology and Embryology confirm the view of the gradual production of a tree of life, it seems to us that the structure of animals, without any other evidence, suggests such a conclusion, though we were never able to show the cause of it. Few astronomers after the time of Kepler doubted that the orbits of planets were ellipses: it remained for Newton to show that the attraction of gravitation was the cause of the ellipse; Lamarck and others have been to Biology what Kepler was to Astronomy; if future biologists confirm Darwin's views as to the cause of the evolution of life, as Laplace, Lagrange, D'Alembert, and Euler placed the Newtonian theory on a more secure foundation, then Darwin will be, as he has been already called, the Newton of Natural History.
