This phantastic picture of creation seems to us mad enough, but there slumbers in it, all unsuspected though it may have been by the author, the true idea of selection, the idea that much that is unfit certainly arises, but that only the fit endures. The mechanical coming-to-be of the fit is the sound kernel in this wondersome doctrine. The natural science of the ancients, in regard to life and its forms, reached its climax in Aristotle (died 322 B. C.). A true polyhistorian, his writings comprehended all the knowledge of his time, but he also added much to it from his own observation. In his writings we find many good observations on the structure and habits of a number of organisms, and he also had the merit of being the first to attempt a systematic grouping of animals. With true insight, he grouped all the vertebrates together as Enaimata or animals with blood, and classed all the rest together as Anaimata or bloodless animals. That he denied to the latter group the possession of blood is not to be wondered at, when we take into account the extremely imperfect means of investigation available in his time, nor is it surprising that he should have ranked this motley company, in antithesis to the blood-possessing animals, as a unified and equivalent group. Two thousand years later, Lamarck did exactly the same thing, when he divided the animals into backboned and backboneless, and we reckon this nowadays as a merit only in so far that he was the first, after Aristotle, to re-express the solidarity of the classes of animals which we now call vertebrates. Aristotle was, however, not a systematic zoologist in our sense of the term, as indeed was hardly possible, considering the very small number of animal forms that were known in his time. In our day we have before us descriptions of nearly 300,000 named species wherefrom to construct our classification, while Aristotle knew hardly more than 200. Of the whole world of microscopic animals he could, of course, have no idea, any more than of the remains of prehistoric animals, of which we now know about 40,000 named and adequately described species. One would have thought that it would have occurred to a quick-witted people like the Greeks to pause and ponder when they found mussel-shells and marine snail-shells on the hills far above the sea; but they explained these by the great flood in the time of Deucalion and Pyrrha, and they did not observe that the fossil molluscs were of different species from the similar animals living in the sea in their own day.