Summary
A study of the anatomy of the larger second-order neurones of the median and lateral ocelli of the locust, leads to a prediction of the types of third or higher order neurones which may be expected to occur in the central nervous system. The validity of these predictions is tested in a study of ocellar ‘off ’ units and considerable agreement is found between the expected units and those which are observed. Three main categories of ocellar ‘off’ unit are found in the locust thoracic cord. These are
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1.
Units which produce ‘off’ spikes at the end of illumination of the ipsilateral and of the median ocellus, but not of the contralateral ocellus.
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2.
Units which produce ‘off’ spikes at the end of illumination of the median ocellus alone.
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3.
Units which produce ‘off’ spikes at the end of illumination of the median and of the contralateral ocellus, but not of the ipsilateral ocellus.
Units which show ocellar ‘off’ spikes and which are also spontaneously active in the dark, show an inhibition of spontaneous activity during illumination of those ocelli which produce ‘off’ spikes at the end of the period of illumination. Illumination of those lateral ocelli which do not generate ‘off’ spikes in the unit may produce an excitation of the spontaneous activity and possible explanations of this effect are discussed.
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This work was supported by a grant to L.G. from the British Science Research Council.
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Patterson, J.A., Goodman, L.J. Relationships between ocellar units in the ventral nerve cord and ocellar pathways in the brain ofSchistocerca gregaria . J. Comp. Physiol. 95, 251–262 (1974). https://doi.org/10.1007/BF00625447
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DOI: https://doi.org/10.1007/BF00625447