This book is about the major groups of animals, their structure, physiology and ways of life. Each chapter, except the first, deals with a taxonomic group of animals, usually a phylum or class. Brief descriptions of a few examples are followed by more detailed discussion of selected topics. Some of the topics are peculiarities of the groups (for example, the shells of molluscs and the flight of insects). Others are more widespread features or properties of animals which can be illustrated particularly well by reference to the group. Many experiments are described, on the grounds that it is as important and interesting to know how information is obtained, as to know the information itself. The text demonstrates the extraordinary diversity of animals, without becoming encumbered with excessive morphological and taxonomic information.