A cotemporary of Chrysippus, but probably somewhat his senior, was Teles, from whose writings a few extracts [53] have been preserved by Stobæus, [54] in the shape of popular moral considerations written from a Cynic or Stoical point of view. The same age also produced the Cyrenaic Eratosthenes, [55] a man distinguished in every branch of knowledge, but particularly celebrated for his mathematical attainments, who was gained for Stoicism by Aristo. [56] Another cotemporary of Chrysippus, and perhaps his fellow-student, [57] who in many respects approximated to the teaching of the Peripatetics, [58] was the Stoic Boëthus. The proper scholars of Chrysippus were without doubt numerous; [59] but few of their names are known to us. [60] The most important among them appear to have been Zeno of Tarsus, [61] and Diogenes of Seleucia, [62] who succeeded Chrysippus in the presidency of the School. [63] The pupil and successor of Diogenes, in his turn, was Antipater of Tarsus, [64] in connection with whom Archedemus his countryman is frequently mentioned. [65] Under Panætius, Antipater’s scholar, Stoicism entered the Roman world, and there underwent internal changes, to which attention will be drawn in the sequel. [66] CHAPTER IV. AUTHORITIES FOR THE STOIC PHILOSOPHY: ITS PROBLEM AND DIVISIONS. [A. Authorities for the Stoic philosophy.] [(1) Review of authorities.] To give a faithful exposition of the Stoic philosophy is a work of more than ordinary difficulty, owing to the circumstance that all the writings of the earlier Stoics, with the exception of a few fragments, have been lost. [67] Those Stoics whose complete works are still extant—Seneca, Epictetus, Marcus Aurelius, Heraclitus, Cornutus—lived under the Roman Empire, and therefore belong to a time in which all Schools alike exposed to foreign influences had surrendered or lost sight of many of their original peculiarities, and had substituted new elements in their place. The same remark applies to writers like Cicero, Plutarch, Diogenes, Sextus Empiricus, and the commentators on Aristotle, who may be considered as authorities at second hand for the teaching of the Stoics; but it is more than doubtful whether everything which they mention as Stoic teaching really belongs to the older members of that School. That teaching can, however, be ascertained with sufficient certainty on most of the more important points, partly by comparing accounts when they vary, partly by looking to definite statements on which authorities agree for the teaching and points of difference between individual philosophers, such as Zeno, Cleanthes, Chrysippus; partly too by consulting such fragments of their writings as are still extant. Yet, when the chief points have been settled in this way, many difficulties still remain. In the first place, it will be found that only isolated points of their teaching, with at most a few arguments on which to base them, are recorded; but the real