Book excerpt: Advances in Comparative Physiology and Biochemistry, Volume 4, presents five papers on the different aspects of comparative physiology. The first two studies deal with movement. The first examines the effects of environmental conditions on the motile behavior of amoebas. The second investigates the mechanisms and coordination of cellular movement. The third study on the endocrine functions of the hypothalamus in the fishes, amphibians, and reptiles provides the comparative endocrinologist with a basis for integrating the state of knowledge on non-mammalian and mammalian function of this organ complex. The fourth study deals with the central and peripheral control of arthropod movements. The final study surveys the comparative physiology of populations of gametes. Aside from providing readers with a comparative vista of reproductive physiology from a unique perspective, it introduces a new hypothesis on the overproduction of gametes commonly found in living organisms — a hypothesis which may have far-reaching consequences for the interpretation of the reproductive process.