THE FINE STRUCTURE OF THE NEURONES IN THE MID-DORSAL LOBES OF THE VISCERAL GANGLION OF THE LAMELLIBRANCH MOLLUSC SCROBICULARIA PLANA (DA COSTA)

Yellow-pigmented, concentrically-laminated and small electron-denseglobules are three kinds of globule present in different neuronesof the mid-dorsal lobes of the visceral ganglion of Scrobiculariaplana. The yellow globules originate from vesicles formed byGolgi cisternae and the other kinds are derived from concentricmembranes. Multiglobular bodies consisting of fused yellow globulesoccupy most of the somata of glial cells. The contents of theglobules and the multiglobular bodies are released into extracellularspaces or blood sinuses byexocytosis. Multivesicular organelles resembling modified mitochondria whichform elementary (neurosecretory) granules are found in someperikarya and axons. Glomeruli are present and resemble those of arthropods. Thelarge central axons and their collaterals contain an intricatesystem of neurotubules; numerous lysosomes and various unidentifiedinclusions are present in the central axons. A few myelinated axons are present in the mid-dorsal lobes.These axons have 30–50 layers of electron-dense membranes.Axo-somatic and axo-axonal synapses are present in glomeruli (Received 6 November 1977;