Scyphozoa have attracted the attention of many types of people. Naturalists watch their graceful locomotion. Fishermen may dread the swarms which can prevent fishing or eat larval fish. Bathers retreat from the water if they are stung. People from some Asiatic countries eat the medusae. Comparative physiologists examine them as possibly simple models for the functioning of various systems. This book integrates data from those and other investigations into a functional biology of scyphozoa. It will emphasize the wide range of adaptive responses possible in these morphologically relatively simple animals. The book will concentrate on the research of the last 35 years, partly because there has been a rapid expansion of knowledge during that period, and partly because much of the previous work was summarized by books published between 1961 and 1970. Bibliographies of papers on scyphozoa were included in Mayer (1910) and Kramp (1961). Taxonomic diagnoses are also included in those monographs, as well as in a monograph on the scyphomedusae of the USSR published by Naumov (Naumov, 1961). Most impor tantly, a genenttion of scyphozoan workers has used as its 'bible' the monograph by F.S.Russell (1970) The Medusae of the British Isles. In spite of its restrictive title, his book reviews most of the information on the biology of scyphozoa up to that date.