FUNCTION OF IDENTIFIED NERVES IN ORIENTATION TO WATER-FLOW IN TRITONIA-DIOMEDEA

We determined which sensory and motor nerves mediate orientation to fl ow in the marine slug Tritonia diomedea, and tested the hypothesis tha t the slug orients to water flow by comparing the intensities of water flow stimulation on each side of its body. Lesion experiments reveale d which nerves carried information necessary for flow orientation. The lateral branches of Cerebral Nerve # 2 were the only cerebral nerves necessary for flow orientation, Cutting all cerebral nerves except the lateral branches of Cerebral Nerve # 2 did not eliminate flow orienta tion. Thus, the lateral branches of Cerebral Nerve # 2 were both neces sary and sufficient (among the cerebral nerves) for flow orientation. Denervation of one side of the head by cutting Cerebral Nerves # 1-4 o n one side did not eliminate normal flow orientation. We have revised our model of how Tritonia diomedea orients to flow to allow for this u nilateral determination of flow direction. Unilaterally cutting Pedal Nerve # 3, which contains many pedal motor axons, reduced turning towa rd that side, but did not affect final orientation to flow. The abilit y to detect flow direction was not compromised by the inability to ini tially turn towards flow.