CRITICAL ILLUMINATION FOR RESPONSE TO FLICKERED LIGHT,WITH DRAGONFLY LARVAE (ANAX), IN RELATION TO AREA OF EYE

Arthropods with large convex eyes provide curves of critical illumination for response as a function of flicker frequency (or of visual acuity) which depart from the probability integral type characteristically found for F – log I with vertebrates. By means of experiments with Anax nymphs in which various parts of the eye have been opaqued it is shown that the special shape of the flicker curve is due to the mechanical disadvantage of the periphery of the eye in the reception of light, which is overcome by higher intensities. It is not due to a fixed spatial pattern of intrinsic individual excitabilities of the ommatidia. Reduction of retinal area decreases F_max., and increases log I for F/F_max. = 50 per cent. The direct proportionality of I_m to P.E._1I is independent of area. Certain relations of these facts to the theory of response to flicker have been discussed.