This volume examines the extent to which the design and function of terrestrial and aquatic animals are determined by the physicochemical properties of the media in which they live. The topic is addressed from the viewpoint of scientists representing a variety of disciplines and approaches. Anatomists, biochemists, biophysicists, physiologists and zoologists each contribute their perspectives. The general topics examined include: respiration; acid base balance; osmoregulation; water and ionic exchanges; nutrient acquisition and absorption; nitrogen and sulfur metabolism; locomotion; sensory information and behaviour; energy metabolism; and temperature and evolution. Four or five papers deal with each of these general topics.