INNERVATION OF OESOPHAGUS OF SEA-URCHIN HELIOCIDARIS ERYTHROGRAMMA

The fine structure of the oesophagus of the sea-urchin Heliocidaris erythrogramma is described. Two distinct nerve plexuses have been demonstrated in the wall there appears to be no connection between them along the length of the oesophagus. The inner nerve plexus is the more extensive and there are some indications that it may innervate the large secretory cells that line the lumen of the oesophagus. Some of the axons within the outer nerve plexus contain large granular vesicles up to 2,000 Å in diameter, others contain small agranular vesicles up to 500 Å in diameter. These axons form neuromuscular junctions with muscle cells in both the longitudinal and the circular layers. The presence of two vesicle types within separate axons may indicate dual innervation of the muscle cells. Two or three axons in some cases form neuromuscular junctions with the same muscle cell, suggesting polyneuronal innervation. No nexuses or cytoplasmic bridges between the muscle cells were observed after fixation with potassium permanganate. © 1969 Springer-Verlag.