The Biology of Euglena, Volume III: Physiology covers areas of investigation on Euglena, focusing in particular on its physiology. The book demonstrates the wide utilization and research on the members of the genus, especially Euglena gracilis. The book discusses, in particular, the essential features of organelle distribution and structure in Euglena, and euglenoid surfaces. It presents circadian rhythms reported for Euglena, as well as the organism's movement and locomotion. It also explains the various aspects of sensory responses of Euglena gracilis to photic, chemical, and mechanical stimuli. In addition, the book addresses the stimulation and inhibition of the metabolism and growth of Euglena gracilis. Lastly, the Euglena chloroplast membrane, including its structure, function, and photocontrol of its development are described.