ELECTRICAL RESPONSES TO PHOTIC STIMULATION IN THE EYES AND NERVOUS SYSTEM OF NEREID POLYCHAETES

¹ Department of Biology, Reed College, Portland, Oregon 97202

1. Anterior and posterior pairs of prostomial eyes in Nereis diversicolor and Platynereis dumerilii display similar electroretinograms.

2. Electrical responses recorded from the ventral nerve cord elicited by changes in the level of illumination with and without prostomial eyes are as follows: (a) Prostomial eyes alone may be capable of triggering a giant fiber response at "off." (b) Ablation of prostomial eyes leads to a longer latency in the giant fiber response but does not abolish it. (c) In the absence of prostomial eyes a giant fiber response is elicited at "off" only if the light level change involves the anterior part of the worm. (d) Fine fiber responses at both "off" and "on" occur in the absence of prostomial eyes when the change in illumination occurs at any place on the body of the worm.

3. Localization experiments indicate that dermal photoreceptors are located primarily on the pro- and peristomium and on the parapodia.

4. Attempts to habituate the cord responses indicate that the site of habituation for the giant fiber response is on the sensory side of the pathway.

5. The significance of the different responses to illumination changes (fast head withdrawal, slow tail withdrawal) in relation to the mode of life of the worm and its powers of regeneration are discussed.