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;     

THE CRUCIFORM MUSCLE AND ITS ASSOCIATED SENSE ORGAN IN SCROBICULARIA PLANA (DA COSTA)

Long dendritic processes from neurones of the sense organ ganglionpenetrate the epithelial lining of the narrow and short ductsituated between the intramuscular slit and a large posteriorcavity which opens to the siphonal space through a narrow canalin the sense organ papilla. Motor nerve fibres innervate theanterior ends of the cruciform muscle strands. The latter becomesstretched during opening of animal and contracted during closure.The slit is widened during opening and narrowed during closure.The sense organ responds to foul water suggesting that it isa chemoreceptor for this stimulus. (Received 10 July 1977;