If then the male is a principle and a cause, and the male is such in virtue of a certain capacity and the female is such in virtue of an incapacity, and if the definition of the capacity and of the incapacity is ability or inability to concoct the nourishment in its ultimate stage, this being called blood in the sanguinea and the analogue of blood in the other animals, and if the cause of this capacity is in the first principle and in the part which contains the principle of natural heat therefore a heart must be formed in the sanguinea (and the resulting animal will be either male or female), and in the other kinds which possess the sexes must be formed that which is analogous to the heart.