THE FLICKER-RESPONSE CONTOUR FOR THE CRAYFISH

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Abstract
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: Fmax. 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.