The principle objective of this work is to add to our knowledge of functional aspects of the vertebrate visual system. I choose two approaches. In the first, the effects of extrinsic electrical currents on the retina of the frog are investigated, with the hope that results from the frog will be generalizable to all vertebrates, and that electrical stimulation will be developed as a tool for vision researchers, both basic and clinical. The second approach is an analysis of the neural retina, in particular the ganglion cells, of aquatic vertebrates. An attempt is made to understand the adaptive significance of many of the features of aquatic retinas which differ from retinas of terrestrial animals. This approach is motivated by the belief that we can better understand how aerial retinas (such as our own) work if we know how they differ from those adapted to aquatic vision.