It is in the receptors of the vertebrate retina that the characteristic visual process - the transduction of radiational energy into physiological activtty of a different kind - takes place. The way these receptors modify or redistribute the incident radiation and thereby control the light ab sorption by the visual pigments they contain, is the central theme of this book. As far back as 1843 Brucke put forward a well-reasoned model for the optics of a receptor, assuming simple ray optics, and it is already some forty-seven years since the dependence of receptor sensitivity on retinal angle of...