RICHARD W. HILL is Professor in the Department of Zoology at Michigan State University, USA and a frequent Guest Investigator at Woods Hole Oceanographic Institution. His research interests include: temperature regulation and energetics in birds and mammals, especially neonates; and marine sulphur physiology, especially in the contexts of biogeochemistry and animal--algal symbioses. GORDON A. WYSE is Professor of Biology and Associate Dean for Academic Affairs, College of Natural Sciences and Mathematics, at the University of Massachusetts, Amherst, USA. His research uses caterpillars and Limulus as model organisms to explore the neural circuits and neurotransmitters underlying feeding behaviour and other behaviour patterns. MARGARET ANDERSON is Professor of Biological Sciences and Director of the Programme in Neuroscience at Smith College, USA. Her research interests include the functional properties of excitable cells.