PERIPHERAL MECHANISM OF NERVOUS ACTIVITY IN LATERAL EYE OF HORSESHOE CRAB

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Abstract
Silver-filled microelectrodes designed for extracellular recordings were inserted within ommatidia exposed by cutting the compound lateral eye of the horseshoe crab. The action potentials which were detectable from a restricted region within the ommatidium consisted of a negative slow potential change and a train of impulses superimposed on it. Each of the impulses was diaphasic, starting with a positive spike potential. The same type of electrode placed on the nerve strand at a point immediately behind an ommatidium also recorded diphasic impulses but with the polarity reversed; they started with a negative spike potential. The electrical excitability as measured at the above two regions showed a similar contradistinction: to the nerve strand, negative pulses were more effective than were positive, whereas positive pulses were more effective when a stimulating microelectrode was within the ommatidium. The above finding led the author to believe that certain cells within ommatidia respond to illumination only with the slow ommatidial action potential which acts upon a proximal locus to initiate the impulse discharge, and that the impulses recorded from within the ommatidium are of passive nature fed back electrotonically from the locus of the impulse initiation.

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