Functioning of the Insect Ocellar Nerve

Abstract

1. The median ocellar nerve preparation of the locust Locusta migratoria has been re-investigated. 2. The nerve contains six nerve fibres of which the two largest are 8µ in diameter. 3. The nerve fibres transmit propagated nerve impulses when the ocellus is illuminated or darkened. This disposes of the claim (Parry, 1947) that the ocellar nerve exerts an effect on the brain as the result of electrotonic spread from a depolarized region in the ocellus. 4. The retinal potentials consist of a reduction of potential at the back of the ocellus on illumination and vice versa on darkening. This is the converse of the situation implicit in Parry's exposition. 5. Three kinds of nervous response are obtained from the ocellar nerve: an ‘on’-discharge, an ‘off’-discharge and a continuous dark-discharge. 6. Corresponding discharges of nerve impulses are obtained from the circumoesophageal commissure. 7. The ocellus must function principally as an indicator of changes in light intensity.