CHARACTERISTICS OF THE RETINAL ELECTRIC RESPONSE OF THE OCELLI OF LIMULUS

¹ Department of Physiology, University of Illinois, Urbana, Illinois

1. The electrical responses to illumination were obtained from isolated median ocelli of Limulus polyphemus mounted in a capillary tube filled with sea water. These preparations, maintained in a state of dark adaptation, were periodically illuminated at different intensities for different durations.

2. For the most part, the reported data are in accord with similar data obtained from the lateral compound eye of Limulus and the compound eyes of grasshoppers. It was observed that the latent period of the responses elicited by light flashes of different durations at any one intensity is constant; the only factor seemingly affecting the latent period is the intensity.

3. The increase in electrical response magnitude produced either by increasing the intensity and/or the duration of illumination, which is typical of many photoreceptors, is accounted for on the basis of graded responses on the part of sense cells. The possibility exists that recruitment of sense cells is a contributing factor at low intensities of illumination.

4. Comparison of data obtained from the median ocellus of Limulus with data obtained from single optic nerve fibers of the lateral eye of Limulus indicates a parallelism which is in accord with the hypothesis that the retinal action potential sets up local action currents which initiate impulses in the optic nerve.