[176] [cap.35] These things, then, it was necessary to give an idea of beforehand; but for what reason this was necessary we must now say. The nature of animals was originally divided into the portion endowed with and into that devoid of reason, the two being at variance with one another. Again the rational division was subdivided into the perishable and imperishable species, the perishable species being the race of mankind, and the imperishable species being the company of incorporeal souls which revolve about the air and heaven.