baser passion, and the various sections came together to form bodies. The combinations, unfortunately, were entirely accidental, and did not always result in satisfactory creatures. One body, for example, might possess several heads and no legs; another might have an abundance of arms and legs, but be without a head. These monstrosities were unable to keep themselves alive, and so perished, leaving the world to the bodies that had come together in proper combinations. Thus Empedocles, more than two thousand years before the first zoologist framed and taught a theory of organic evolution that seemed to offer anything worth while, conceived one of the most important of evolutionary principles—that of natural selection.
But by far the most striking figure among the early Greek philosophers who gave their attention to natural history was Aristotle, (384–322). He lived more than three hundred years before the Christian era, and was a pupil of Plato and a teacher of Alexander the Great. He wrote upon a wide variety of subjects—politics, rhetoric, metaphysics, psychology, philosophy, and natural history—and published several hundred works, most of which have been lost. It is true that Aristotle's books are full of errors, and if the philosopher were to be judged by the standards of twentieth century science he would not appear very important. But it must be remembered that he was a pioneer who, by the force of his own ability created the serious study of natural history. The workers who had preceded him had dis-
