Focusing on how animals function, this book examines the physiological mechanisms of processes such as internal communication, respiration, reproduction, digestion and excretion. The regulation and control of the various systems is considered throughout, along with the physiological basis for the adaptation of animals to a range of different environments. The author has worked on a number of Open University courses, including Animal Physiology and the Biological Basis of Behaviour, and he has written over 60 papers and reviews. The text is part of a series designed mainly for undergraduates, but it is also suitable for S Level students of biology.