THE FLICKER-RESPONSE CONTOUR FOR THE CRAYFISH

II. RETINAL PIGMENT AND THE THEORY OF THE ASYMMETRY OF THE CURVE

¹ From the Biological Laboratories, Harvard University, Cambridge

Injection of Cambarus bartoni with extract of eyestalks of this species forces migration of retinal pigments of individuals kept in darkness into positions characteristic of the light-adapted eye. In this condition the receptor elements of each ommatidium are effectively shielded from light passing through their neighbors. The flicker-response contour then differs in four particulars from that found when the retinal pigment is in the "dark" position, for which effective screeing of the ommatidia is not present: F_max. is lowered; the whole curve is moved to higher intensities; the spread of the log I thresholds for the cumulative population of sensory effects is lessened; and the asymmetry of the F — log I curve is markedly reduced. It is pointed out that these results are to be expected if the asymmetry of the curve in normal dark-adaptation is due to the relation between flash-intensity and the curvature of the optic surface and divergence of the ommatidial axes.