In the writings of Homer we find that the knowledge of the anatomy of the human body had already made considerable progress; and the inspection of the animals offered in sacrifice cannot fail to have added much to the general knowledge of their history. A century later, we have the poems of Hesiod, devoted to the encouragement of agriculture and rural pursuits. Pythagoras, in the seventh century B.C., may perhaps have left no writings, but we know that he was an eminent student and exponent of natural phenomena. His contemporary, Alcmæon of Crotona, is especially mentioned by Aristotle; and he is eminent among natural philosophers as the first who is said to have recommended to his followers the practice of dissection. Empedocles of Agrigentum left a work on the phenomena of nature, of which a few fragments still remain, and there were also others who, if they did not enter into the details of what we now call natural history, treated generally of the nature of things, and opened the field to those who would study the subject in its particular parts. The empire of Persia was still the dominant power, and was carrying the civilization of the East to every part of the known world when Ctesias wrote his great works, of which, unhappily, only a few fragments remain. He described not only the history of his own time, but also the natural history of Persia and of India, and that probably with more accuracy than has been usually attributed to him. India he had not visited personally, so that he could only describe it from the information of others; but this implies that he was not alone in the studies which he devoted to natural objects. With such predecessors and aided by his own acute observations, we need not wonder that Aristotle produced a work which has ever been admired by naturalists, and must continue to rise in their estimation the longer it is in their hands.