In the fresh light which these considerations throw upon the problem of man's origin, we can now see more clearly than ever how great a revolution was inaugurated when natural selection began to confine its operations to the surface of the cerebrum. Among the older incidents in the evolution of organic life, the changes were very wonderful which out of the pectoral fin of a fish developed the jointed fore-limb of the mammal with its five-toed paw, and thence through much slighter variation brought forth the human arm with its delicate and crafty hand. More wondrous still were the phases of change through which the rudimentary pigment-spot of the worm, by the development and differentiation of successive layers, gave place to the variously constructed eyes of insects, mollusks, and vertebrates. The day for creative work of this sort has probably gone by, as the day for the evolution of annulose segments and vertebrate skeletons has gone by, — on our planet, at least. In the line of our own development, all work of this kind stopped long ago, to be replaced by different methods. As an optical instrument, the eye had well-nigh reached extreme perfection in many a bird and mammal ages before man's beginnings; and the essential features of the human hand existed already in the hands of Miocene apes. But different methods came in when human intelligence appeared upon the scene.