In 'De Partibus Animalium I' Aristotle sets out his philosophy of biology, discussing cause, necessity, soul, genus and species, definition by logical division, and general methodology. In 'De Generatione Animalium I' he applies his hylomorphic philosophy to the problem of animal reproduction. This volume also includes passages from 'De Generatione Animalium ll' which completes Aristotle's theory of reproduction. The translation is close, in order to serve the needs of readers of Aristotle without a knowledge of Greek, the notes interpret Aristotle's arguments and discuss his views on major issues such as natural teleology. This edition is brought up to date by the inclusion of a wide - ranging report on recent work and a large additional bibliography.