GREEK BIOLOGY AND MEDICINE reproduction of their own particular species, and the sphere of action with certain animals is similarly limited. The faculty of reproduc- tion, then, is common to all alike. If sensibility be superadded, then their lives will differ from one another in respect to sexual intercourse through the varying amount of pleasure de- rived therefrom, and also in regard to modes of parturition and the ways of rearing their young. Some animals, like plants, simply procreate their own species at different seasons; other animals busy themselves also in pro- curing food for their young, and after they are reared quit them and have no further dealings with them; other animals are more intelligent and endowed with memory, and they live with their offspring for a longer period and on a more social footing. "The life of animals, then, may be divided into two acts, — procreation and feeding; for on these two acts all their interests and life concentrate. Their food depends chiefly on the substance of which they are severally con- stituted; for the source of their growth in all cases will be this substance. And whatever is in conformity with nature is pleasant, and all animals pursue pleasure in keeping with their nature." ^^
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