Advances in Comparative Physiology and Biochemistry, Volume 7, presents four papers that illustrate a logical progression from evolutionary and genetic aspects of the biochemistry of a family of enzymes to the biochemical. The first study deals with the comparative biochemistry, physiology, and genetics of animal a-amylases. The second study examines the biochemistry of intercellular recognition, which is a component of so many biological phenomena. It covers the evolution of intercellular recognition processes; primitive sex mechanisms as precursors of intercellular recognition; conjugation in single-celled eukaryotes; fertilization in metazoans; cell aggregation as a developmental event in cellular slime molds; aggregation of dissociated sponge cells; and contact cellular interactions during embryonic development. The third paper explores the role of amino acids in neurotransmission. The final paper on the biochemical and biophysical aspects of the complex range of functions of the swimbladder in fishes establishes a link with the higher categories of organismal interaction in the fields of behavior and ecology.