This dictionary is a comprehensive and up-to-date reference work on all aspects of the study of animals. Now fully revised for this new edition, with over 5,000 entries, it is ideal for students and will be invaluable to amateur naturalists and all those with an interest in the subject. Key features of this second edition: * Wide coverage including animal behavior, ecology, physiology, genetics, cytology, evolution, Earth history, zoogeography * Full taxonomic coverage of arthropods, other invertebrates, fish, reptiles, amphibians, birds, and mammals * Completely revised to incorporate the recent discovery of \'extremophiles\'--organisms living in environments formerly considered impossibly hostile--and the taxonomic reclassification that this has entailed * New entries on genetics, evolutionary studies, and mammalian physiology