[Illustration: FIG. 14. Great events of the Glacial Epoch. To the left the relation of glacial and interglacial stages in Europe and North America, with the author's theory regarding the divisions of time, the beginning of the Old Stone Age, and the successive appearance in Europe of different branches of the human race. To the right the prolonged warm temperate period in Europe in the non-glaciated regions, followed by the relatively brief cold period during the past 70,000 years. Prepared by Dr. C. A. Reeds, in co-operation with the author.] MAMMALS OF FIVE DISTINCT GEOGRAPHIC REGIONS (Compare Color Map, Pl. II, and Fig. 15) As we have already observed, during the whole history of mammalian life in various parts of the world never did there prevail conditions so unusual and so complex as those which surrounded the men of the Old Stone Age in Europe. The successive races of Palæolithic men in Europe were all flesh eaters, depending upon the chase. The mammals, first pursued only for food, utensils, and clothing, finally became subjects of artistic appreciation and endeavor which resulted in a remarkable æsthetic development. From the beginning to the end of Palæolithic times the various races of man witnessed the assemblage in Europe of animals indigenous to every continent on the globe except South America and Australia and adapted to every climatic life-zone, from the warm and dry plains of southern Asia and northern Africa to the temperate forests and meadows of Eurasia; from the heights of the Alps, Himalayas, Pyrenees, and Altai Mountains to the high, arid, dry steppes of central Asia with their alternating heat of summer and cold of winter; from the tundras or barren grounds of Scandinavia, northern Europe, and Siberia to the mild forests and plains of southern Europe.(71) Members of all these highly varied groups of animals had been evolving in various parts of the northern hemisphere from the Eocene Epoch onward. In Pliocene times they had become thoroughly adapted to their various habitats. Throughout early Pleistocene times, with the increasing cold extending southward from the arctic circle, such mammals as the elephant, rhinoceros, musk-ox, and reindeer had become thoroughly adapted to the climate of the extreme north. There is every reason to believe that when these tundra quadrupeds first arrived in Europe, during early mid-glacial stages, they had already acquired the heavy coat of hair and undercoating of wool, such as now characterizes the musk-ox, one of the living representatives of this northern fauna. MIGRATIONS AND EXTINCTIONS OF MAMMALIAN LIFE DURING THE FOUR GLACIAL, THREE INTERGLACIAL, AND POSTGLACIAL STAGES