Phototaxis in Limulus Under Natural Conditions: Evidence for Reception of Near-Ultraviolet Light in the Median Dorsal Ocellus

Abstract

1. Phototactic behaviour in Limulus mediated by lateral eye and dorsal ocellus was studied under full-spectrum and restricted-spectrum (near-u.v. and visible light) sunlight on a beach. 2. All eyes (lateral eyes, dorsal ocelli) were occluded excepting one, which mediated the response. 3. It was found that either a lateral eye or a dorsal ocellus alone could mediate positive phototaxis in adult Limulus under full-spectrum sunlight. 4. When the sunlight stimulating the dorsal ocellus was filtered into restricted wavelengths, the near-u.v., but not the visible light, elicited positive phototaxis.