Exploring what he considers to be the outstanding aspects of fish biology, Mr. Marshall surveys the present knowledge in the field and suggests possibilities for future investigation. He considers the causes of the overwhelming predominance of the teleost fishes, discusses the biology of deep-sea fishes, and studies such aspects of dynamic design as body form, fin pattern, muscular organization, and certain neural features in relation to movement and water. His last chapter, on convergent evolution, deals with convergences among fishes as well as with convergences among fishes and invertebrates, particularly crustaceans and cephalopods. The volume is illustrated with a chart on evolutionary relationships of fishes and over fifty line drawings.