In History of Animals, Aristotle analyzes differences-in parts, activities, modes of life, and character-across the animal kingdom, in preparation for establishing their causes, which are the concern of his other zoological works. Over 500 species of animals are considered: shellfish, insects, birds, fish, reptiles, amphibians, and mammals-including human beings. In Books I-IV, Aristotle gives a comparative survey of internal and external body parts, including tissues and fluids, and of sense faculties and voice. Books V-VI study reproductive methods, breeding habits, and embryogenesis as well as some secondary sex differences. In Books VII-IX, Aristotle examines differences among animals in feeding; in habitat, hibernation, migration; in enmities and sociability; in disposition (including differences related to gender) and intelligence. Here too he describes the human reproductive system, conception, pregnancy, and obstetrics. Book X establishes the female's contribution to generation. The Loeb Classical Library (R) edition of History of Animals is in three volumes. A full index to all ten books is included in the third (Volume XI of the Aristotle edition).