When seen from an outsider's vantage point, the development of knowledge in the sensory sciences must appear massive and the result of some carefully followed master plan. In reality, it is the result of numerous relatively independent human endeavors shaped by application of the scientific method. The comprehensive construction of quantitative theories of sense organ function has occurred only recently -but at an explosive rate prefaced by centuries of expansion in the physical sciences. Predicated on this growth, the twentieth century may become known as the age of the biological sciences....