Local control of retinomotor activity in the fish retina.

Small circular spots of light were focussed on otherwise unilluminated retinas of paralyzed fish. C~c~~~rnu bi~e~~tu~ The retinas were sub~uently examined histolo~cally, and a small circular region was found within which the cones and pigmented retinal epithelium were photomechanically tight adapted; rods could not be resolved. The same result was obtained with the optic nerve cut. The region was circular and about the same size as the adapting spot. There existed a transition zone between lightand dark-adapted regions within which the photomechanical state was intermediate. These results exclude the hypothesis that light-induced retinomotor phenomena are systemically controlled. and favor local control. An analysis of the transition tone favors the view that photomechanical light adaptation of a given ce11 may be caused by light caught by that cell or its neighbors. Kq Words-retina; retinomotor; photomechanicai; fish. Animal Clnssifcarion-Cichlasoma bioceilarum (Euteleostei. Perciformes, Cichlidae).