XXXIII. The Stoics divide reason according to philosophy, into three parts; and say that one part relates to natural philosophy, one to ethics, and one to logic. And Zeno, the Cittiæan, was the first who made this division, in his treatise on Reason; and he was followed in it by Chrysippus, in the first book of his treatise on Reason, and in the first book of his treatise on Natural Philosophy; and also by Apollodorus; and by Syllus, in the first book of his Introduction to the Doctrines of the Stoics; and by Eudromus, in his Ethical Elements; and by Diogenes, the Babylonian; and Posidonius. Now these divisions are called _topics_ by Apollodorus, _species_ by Chrysippus and Eudromus, and _genera_ by all the rest. And they compare philosophy to an animal, likening logic to the bones and sinews, natural philosophy to the fleshy parts, and ethical philosophy to the soul. Again, they compare it to an egg; calling logic the shell, and ethics the white, and natural philosophy the yolk. Also to a fertile field; in which logic is the fence which goes round it, ethics are the fruit, and natural philosophy the soil, or the fruit-trees. Again, they compare it to a city fortified by walls, and regulated by reason; and then, as some of them say, no one part is preferred to another, but they are all combined and united inseparably; and so they treat of them all in combination. But others class logic first, natural philosophy second, and ethics third; as Zeno does in his treatise on Reason, and in this he is followed by Chrysippus, and Archedemus, and Eudromus. For Diogenes of Ptolemais begins with ethics; but Apollodorus places ethics second; and Panætius and Posidonius begin with natural philosophy, as Phanias, the friend of Posidonius asserts, in the first book of his treatise on the School of Posidonius. But Cleanthes says, that there are six divisions of reason according to philosophy: dialectics, rhetoric, ethics, politics, physics, and theology; but others assert that these are not divisions of reason, but of philosophy itself; and this is the opinion advanced by Zeno, of Tarsus, among others.