ULTRASTRUCTURAL STUDY OF NEURONS OF GANGLIONIC CHAIN OF NEREIS PELAGICA L (ANNELIDA POLYCHAETA)

The electron microscopic study of the ganglionic chain of Nereis pelagica L. shows neurons with numerous elementary granules, essentially localized in the medio-ventral part of the chain. These neurons probably correspond to the A and B cells and to the ≪ordinary≫ neurons previously described with the light microscope. This preliminary survey does not permit a conclusion as to whether A and B cells are of neurosecretory nature. A comparison between neurons of the ventral chain and of the supraoesophageal ganglion shows that the homology between A and I cells remains doubtful and that B and II cells differ from each other. The appearance of the axon terminals observed in the neuropil and on muscle fibres suggests the possible existence of two neurotransmitter substances other than acetylcholine. The relationship between these axons and perikaryons located in the ganglionic chain are established with certainty only for neurons Cb which must be compared with neurons Vb of the brain. © 1969 Springer-Verlag.