Whilst the greatest effort has been made to ensure the quality of this text, due to the historical nature of this content, in some rare cases there may be minor issues with legibility. Different areas of science characteristically enjoy peak periods, during which curiosity and concern about unsolved problems, availability of re search support, and emerging new results and insights combine to yield eras of exceptional productivity. Shark research is enjoying such a peak phase at the present time. This makes it an especially exciting, as well as a useful, time to take stock of what is known (and What is not known) in this area of sensory physiology and animal behavior. People are interested in sharks, skates, and rays for many reasons. At some point in their studies, Virtually all biology students encounter diagrams or preserved specimens of sharks, the anatomical features of which provide a good starting point for understanding the basic body forms of backboned animals, including man. Marine biologists, dealing with living elasmobranchs in the sea, are fascinated by the many and superb adaptations of these animals that account for their long evolutionary success. People Whose work or recreation takes them into the sea are concerned about the possibilities of being attacked by sharks; thus they are interested in the work of sensory physiologists and ethologists who attempt to understand the behavioral patterns, with their underlying mechanisms, in predatory species. Most recently, engineers and technologists have recognized that some sense organs of elasmobranchs far exceed the capacities of our human sensory apparatus and therefore might provide clues or prototypes for better instrumentation to assist human probings of the sea.