LXXXIV. Another of their doctrines is that nature is an artificial fire tending by a regular road to production, which is a fiery kind of breath proceeding according to art. Also, that the soul is sensible, and that it is a spirit which is born with us; consequently it is a body and continues to exist after death; that nevertheless it is perishable. But that the soul of the universe is imperishable, and that the souls which exist in animals are only parts of that of the universe. But Zeno, the Cittiæan, and Antipater, in their treatise concerning the Soul, and Posidonius also, all say that the soul is a warm spirit; for that by it we have our breath, and by it we are moved. Cleanthes, accordingly, asserts that all souls continue to exist till they are burnt up; but Chrysippus says that it is only the souls of the wise that endure. And they further teach that there are eight parts of the soul; the five senses, and the generative faculties, and voice, and reason. And we see because of a body of luminous air which extends from the organ of sight to the object in a conical form, as it is asserted by Chrysippus, in the second book of his Natural Philosophy, and also by Apollodorus. And the apex of this cone is close to the eye, and its base is formed by the object which is seen; so that that which is seen is as it were reported to the eye by this continuous cone of air extended towards it like a staff. In the same way, we hear because the air between the speaker and the hearer is struck in a spherical manner; and is then agitated in waves, resembling the circular eddies which one sees in a cistern when a stone is dropped into it. Sleep, they say, is produced by a relaxation of the æsthetic energies with reference to the dominant part of the soul. And the causes of the passions they explain to be the motions and conversions which take place in connection with this spirit or soul. LXXXV. Seed, they define as a thing of a nature capable of producing other things of the same nature as the thing from which it has been separated. And the seed of man, which man emits, is, together with moisture, mixed up with the parts of the soul by that kind of mixture which corresponds to the capacity of the parents. And Chrysippus says, in the second book of his Natural Philosophy, that it is a spirit according to substance; as is manifest from the seeds which are planted in the earth; and which, if they are old, do not germinate, because all their virtue has evaporated. And Sphærus says, that seed proceeds from the entire body, and that that is how it is that it produces all the parts of the body. They also say that the seed of the female is unproductive; for, as Sphærus says, it is devoid of tone, and small in quantity, and watery. LXXXVI. They also say that that is the dominant part of the soul which is its most excellent part; in which the imaginations and the desires are formed, and whence reason proceeds. And this place is in the heart.