Malcolm S. Gordon, Professor of Biology at the University of California, Los Angeles, is coauthor of Invasions of the Land: The Transitions of Organisms from Aquatic to Terrestrial Life (1995) and of Animal Physiology: Principles and Adaptations (fourth edition 1982), among other books. Soraya M. Bartol is a Postdoctoral Investigator in the Biology Department of the Woods Hole Oceanographic Institution.