A naturalist who to his own satisfaction has traced the pedigree of the human intellect, conscience, and religion, to Ascidian skin-bags sticking to the sea-side rocks, is not likely to arrest the genealogy there, at a stage so little fitted to serve as a starting-point of derivative being. Or, if his own retreat should go no further, others will take up the regressive race, and, soon passing the near and easy line into the vegetable kingdom, will work through its provinces to its lichen-spotted edge: and, after perhaps one shrinking look, will dare the leap into the dead realm beyond, and bring home the parentage of all to the primitive elements of "matter and force." To give effect to this extension over the universe at large of the theory of Evolution, the scientific imagination of our day has long been meditating its projected book of Genesis, and has already thrown out its special chapters here and there; and though the scenes of the drama as a whole are not yet arranged, the general plan is clear: that the Lucretian method is the true one; that nothing arises for a purpose, but only from a power; that no Divine Actor therefore is required, but only atoms extended, resisting, shaped, with spheres of mutual attraction and repulsion; that, with these _minima_ to begin with, a growth will follow of itself by which the _maxima_ will be reached; and that thus far the chief and latest thing it has done is the apparition of Mind in the human race and civilization in human society, conferring upon man the melancholy privilege of being, so far as he knows, at the summit of the universe. The main support of this doctrine is found in two arguments, supplied respectively by physical science and by natural history; each of which we will pass under review.