On the whole, then, before the coming on of the Glacial epoch, we may be pretty sure that plants and animals on the one hand had learned organically and automatically to recognize the existence of the year and to adapt themselves to it; and that men or the progenitors of men on the other hand had also learned to correlate the recurrent seasons of food supply with the movements of the sun, though nothing equivalent to winter and summer as we know them to-day existed as yet on any part of our planet. I say advisedly "on any part of our planet," because even near the pole itself remains of a subtropical vegetation in Tertiary times have been amply indicated. Nevertheless, in all parts of the world then, as in the tropics now, we may gather that plants and animals ran through annual cycles--that the year, as I have put it, was organically recognized. Trees had their time to sprout, to bud, to flower, to fruit, to seed, to shed their leaves (in the evergreen way); birds had their time to nest and hatch out their young; insects had their fixed periods for laying, for larval life, for assuming the chrysalis form, for becoming winged beetles or bees or butterflies. In one word, the year is a terrestrial reality, not merely an astronomical fact, in the tropics now; it was a terrestrial reality over the whole planet in the Tertiary period. But it was hardly more marked, apparently, into distinct seasons than it is marked to-day in the equatorial region. Rainfall and drought must have had more to do in determining the annual cycles than winter and summer. From all this it must result that the conception of the year as an epoch at all (save for advanced astronomy) is almost or entirely due to that tilt of the earth's axis which causes the seasons--dry or wet, cold or hot. Without the seasons, in one form or other, we might have been ages longer in discovering the fact that the earth moved round the sun, and that some three hundred and sixty-five days (I omit those important fractions) were needed for its revolution. Certainly, without the seasons, at least to the extent that they occur in the tropics, plant and animal life could hardly have assumed its fixed annual cycles, nor could early men have caught at the idea of the year at all as a period of time, a unit of measurement.