Comparative Ultrastructural Analysis on the Connective Tissue Organization of Neural Sheaths in Mollusca
In invertebrates the connective tissue is frequently associated with organs of the central and peripheral nervous system (Treherne and Moreton, 1970). In insects in particular, the acellu-lar layer (neural lamella) covering the ganglia was the first connective tissue to be studied in detail because of its physiological importance (Ashhurst, 1968). From morphological studies, two different kinds of connective tissue have been identified in the neural lamella of insects: those possessing large, clearly banded collagen fibrils (Ashhurst and Chapman, 1961) and those with very thin, indistinctly banded fibrils (De Biasi and Pilotto, 1976). In molluscs, the nervous system is covered by a thick fibrocellular envelope, the neural sheath, which is more complex than the neural lamella of insects. The neural sheath has been studied in detail in the gastropod Helix aspersa (Fernandez, 1966; Rogers, 1969; Nicolas, 1974), but no comparative analysis, similar to that carried out for insects, has so far been undertaken. Therefore, we thought it interesting to carry out a morphological investigation on the neural sheaths in three classes of molluscs in order to detect possible differences in the structure and organization of the fibrous connective envelopes in animals with different phylogenetic positions and habitats.
KeywordsCollagen Fibril Stellate Ganglion Pedal Ganglion Helix Aspersa Sodium Maleate
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