H. Keffer Hartline has conducted research on vision and the retina. His researches have extended into many and diverse branches of the field, and he has studied the retinas of various representatives of each of the three major phyla having well-developed eyes--the arthropods, the vertebrates, and the mollusks. This is a collection of papers from his laboratory, papers assembled for publication as a collection to honor Professor Hartline on the occasion of his seventieth birthday, 22 December 1973.