If we ever wonder why it took so long before the thought of evolution should have fully dawned upon the world, the answer is not far to seek. No student of Natural History in ancient or medieval times had the faintest conception of the enormous number of animals and of plants in the world. The old Greek or Roman student of Natural History gives no evidence of knowing more than a few hundred animals. Men have named to-day, with systematic Latin names, hundreds of animals for every one that Pliny ever knew, and he knew more than any other man of early times of whom record has come to us. In early days men who traveled into foreign countries brought back accounts of what they saw. The whole Natural History of ancient times was filled with the most absurd and ludicrous stories of all sorts of things to be seen in distant lands. Sir John Mandeville tells tales almost as imaginative and quite as amusing as those attributed to Baron Munchausen. Upon the great awakening of the fifteenth century, with its new study and its wide-ranging travel, an entire change came over the human mind. Men who journeyed into far countries brought back with them not only accounts of what they saw, but, so far as might be, the things themselves. Collections of plants and of such parts of animals as could be readily preserved soon began to accumulate in every great center of Europe. It was only a question of time when such acquisitions must be arranged and classified, but as yet there was no system by which this could be done. The great Swedish botanist, Linnaeus, who lived in the eighteenth century, first taught us to give to each animal and plant two Latin names, the first of these to be the name of the group, known as a genus, to which it belongs, the second to be the name of that sort, or species, of animal. The cat, for instance, is _Felis catus_, the lion _Felis leo_, the tiger _Felis tigris_, and so on. Linnaeus then arranged the genera (plural of genus) into families, and these families into orders and so classified the animal and plant world as far as he knew it. In his earlier years Linnaeus thought of each species as being utterly apart and distant from any other. He believed it had been so from the first, each species having sprung in its complete form from the creative hand of God. In later life he came to show some evidence of the belief in development, but his great work is all built on the idea of the entire fixity of species.