BOOK I.--The work commences with a general review of the animal

kingdom, and several suggestions for a natural arrangement of animals in groups, according to their external form or their mode of life, a comparison of animals among themselves, and a description of some of their habits. Aristotle then introduces the human form, the best known to man, as the standard of comparison to which he refers the rest of the animal kingdom. The concluding chapters of this book are occupied with a description of the several parts of the human body, both internal and external.