That long five years' cruise around the world, the journal of which Darwin has left us in the 'Voyage of the "Beagle,"' proved a marvellous epoch in the great naturalist's quiet career. It left its abiding mark deeply imprinted on all his subsequent life and thinking. Lamarck and Erasmus Darwin were cabinet biologists, who had never beheld with their own eyes the great round world and all that therein is; Charles Darwin had the inestimable privilege of seeing for himself, at first hand, a large part of the entire globe and of the creatures that inhabit it. Even to have caught one passing glimpse of the teeming life of the tropics is in itself an education; to the naturalist it is more, it is a revelation. Our starved little northern fauna and flora, the mere leavings of the vast ice sheets that spread across our zone in the glacial epoch, show us a world depopulated of all its largest, strangest, and fiercest creatures; a world dwarfed in all its component elements, and immensely differing in ten thousand ways from that rich, luxuriant, over-stocked hot-house in which the first great problems of evolution were practically worked out by survival of the fittest. But the tropics preserve for us still in all their jungles something of the tangled, thickly-peopled aspect which our planet must have presented for countless ages in all latitudes before the advent of primæval man. We now know that throughout the greater part of geological time, essentially tropical conditions existed unbroken over the whole surface of the entire earth, from the Antarctic continent to the shores of Greenland; so that some immediate acquaintance at least with the equatorial world is of immense value to the philosophical naturalist for the sake of the analogies it inevitably suggests; and it is a significant fact that almost all those great and fruitful thinkers who in our own time have done good work in the wider combination of biological facts have themselves passed a considerable number of years in investigating the conditions of tropical nature. Europe and England are at the ends of the earth; the tropics are biological head-quarters. The equatorial zone is therefore the true school for the historian of life in its more universal and lasting aspects.