ZOOLOGY. 77 
animals bear to each other, and to those now living, will 
be treated of in the chapter on Geology, while the Devel- 
opment 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 con- 
clusion, 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 con- 
firm 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 inge. the Newton 
of Natural History. 
