Electrical coupling and dye transfer between axon segments in the medium giant axon of the earthworm.

Electrical coupling between axon segments has been studied in the medium giant axon, which had been partially isolated from the ventral nerve cord of the earthworm. Evidence has been obtained that in addition to the coupling structures in the septum there are diffusion- and current-pathways through the pseudo-myelin which seem to be more permeable to fluorescein than the channels in the septum. These findings offer an explanation for the discrepancy of the experimentally determined specific resistance of the septum and the expected values based on nexus density and channel size in the septum.