way through countless ages of geologic time, but it must not be supposed that any and every conceivable form and variety has been produced. There are only two great diverging lines of descent from original living matter—only the animals and the plants. And in each of these there are and have been only a limited number of branches to the pedigree—some coming off at a lower level, others at higher points when more elaborate structure has been attained. It is easy to imagine groups of both plants and animals with characters and structures which have never existed and never will exist. The limitation of the whole process in spite of its enormous duration in time, its gigantic output and variety, is a striking and important fact. Linnaeus said, 'There are just as many species as in the beginning the Infinite Being created'; and the modern naturalist can go no further than the paraphrase of this, and must say, 'There are and have been just so many and just so few varieties of animal and vegetable structure on this earth as it was possible for the physical and chemical contents of the still molten globe to form up to the hour now reached.'
8. The Emergence of Man.
As to how and when man emerged from the terrestrial animal population so strictly controlled and moulded by natural selection is a matter upon which we gain further information year by year. There must be many here who remember, as I do, the astounding and almost sudden discovery some forty-five years ago of abundant and overwhelming evidence that man had existed in Western Europe as a contemporary of the mammoth and rhinoceros, the hyaena and the lion. The dispute
