The fine structure of the procerebrum of pulmonate molluscs, Helix and Limax

Neuronal perikarya of the procerebrum of Helix and Limax are generally naked and lie side by side. The cell mass contains large numbers of axosomatic and axoaxonic synapses represented by boutons of two types; dense core vesicles (800-1200 A, in diameter) being characteristic of the first type and clusters of electron lucent vesicles (500-800 A) of the second. Endings of the two types occur also in the terminal mass of the neuropile while the internal mass contains peculiar axonal enlargements filled with fine twisted tubuli. Axons containing dense core vesicles seem to correspond to varicose monoaminergic fibres detected by a fluorescent histochemical method.