Primitive fishes are a relatively untapped resource in the scientific search for insights into the evolution of physiological systems in fishes and higher vertebrates. Volume 26 in the Fish Physiology series presents what is known about the physiology of these fish in comparison with the two fish groups that dominate today, the modern elasmobranchs and the teleosts. Chapters include reviews on what is known about cardiovascular, nervous and ventilatory systems, gas exchange, ion and nitrogenous waste regulation, muscles and locomotion, endocrine systems, and reproduction. Editors provide a thorough understanding of how these systems have evolved through piscine and vertebrate evolutionary history. Primitive Fishes includes ground-breaking information in the field, including highlighs of the most unusual characteristics amongst the various species, which might have allowed these fishes to persist virtually unchanged through evolutionary time. This volume is essential for all comparative physiologists, fish biologists, and paleontologists. * Provides an analysis of the evolutionary significance of physiological adaptations in "ancient fishes"* Offers insights on the evolution of higher vertebrates* The only single source that presents an in-depth discussion of topics related to the physiology of ancient fishes