the soul. They consider that the passions are caused by the variations of the vital breath. Semen is by them denned as that which is capable of generating offspring like the parent. And the human semen which is emitted by a human parent in a moist vehicle is mingled with parts of the soul, blended in the same ratio in which they are present in the parent. Chrysippus in the second book of his Physics declares it to be in substance identical with vital breath or spirit. This, he thinks, can be seen from the seeds cast into the earth, which, if kept till they are old, do not germinate, plainly because their fertility has evaporated. Sphaerus and his followers also maintain that semen derives its origin from the whole of the body ; at all events every part of the body can be reproduced from it. That of the female is according to them sterile, being, as Sphaerus says, without tension, scanty, and watery. By ruling part of the soul is meant that which is most truly soul proper, in which arise presentations and impulses and from which issues rational speech. And it has its seat in the heart. Such is the summary of their Physics which I have deemed adequate, my aim being to preserve a due proportion in my work. But the points on which certain of the Stoics differed from the rest are the following. Chapter 2. ARISTOX (c. 320-250 B.C.) Ariston the Bald, of Chios, who was also called the Siren, declared the end of action to be a life of perfect indifference to everything which is neither virtue nor vice ; recognizing no distinction whatever