This dictionary is a comprehensive reference work on all aspects of the study of animals. Fully revised for this edition, with over 5000 entries, it provides wide coverage of topics including animal behaviour, ecology, physiology, genetics, cytology, evolution, and Earth history. There is taxonomic coverage of arthropods, other invertebrates, fish, reptiles, amphibians, birds, and mammals. The text has been revised to incorporate the discovery of "extremophiles" - organisms living in environments formerly considered impossibly hostile - and the toxonomic reclassification that this has entailed.