On the Question of Nervous Syncytia: Lack of Axon Fusion in Two Insect Sensory Nerves

Abstract

Electron micrographs of insect antennal nerves reveal that 98% of the nerve fibres are below 0.5 µ in diameter and are packed in bundles of naked axons without individual glia sheaths (average fibre calibre: 0.3 µ in Bombyx, 0.12 µ in Rhodnius). Re-examination of earlier light-microscopic fibre countings, which led to the hypothesis of axon fusion in insect sensory nerves, is now necessary. In the two nerves studied, each antennal sense cell is individually connected with the brain by its own axon. The results are compared with other cases of proposed axon fusion (e.g. giant fibre systems) and the physiological consequences are discussed.