. Electro-physiology . single fibres which constitute FIG. 149.—Section of a nerve from the proboscis of Amphiporus marmoratus with paired cells. (Methylene-blue preparation from O. Burger.) the bundle are tolerably uni- form, we elsewhere find marked differences. In insects and crus- tacea, ,broad band-shaped axis-cylinders frequently run alongside very small and fibril-like filaments in the same sheath, and this not merely in the coarser nerve-trunks, but in the finest terminal branches also, where the calibre would justify us in reckoning them individually as nerve-fibres. But it is in
. Electro-physiology . single fibres which constitute FIG. 149.—Section of a nerve from the proboscis of Amphiporus marmoratus with paired cells. (Methylene-blue preparation from O. Burger.) the bundle are tolerably uni- form, we elsewhere find marked differences. In insects and crus- tacea, ,broad band-shaped axis-cylinders frequently run alongside very small and fibril-like filaments in the same sheath, and this not merely in the coarser nerve-trunks, but in the finest terminal branches also, where the calibre would justify us in reckoning them individually as nerve-fibres. But it is in these muscular nerves of Arthropoda with their copious ramifications ( in the familiar instance of the crayfish), that it is most easy to show that no essential difference in structure exists between the coarser and finer branches of the nerve, apart from the number of axis-cylinders contained within one sheath of connective tissue. Neither the one nor the other must be designated as nerve-fibres, but must be treated simply as bundles. Notwithstanding therefore that, even in the minutest ramifications, and actual terminal branches, there may be several axis-cylinders in a common sheath, the morphological definition of a nerve-fibre must be strictly con- fined to one such axis-cylinder. It follows that the richly developed connective-tissue sheath of the finest nerve-branches in invertebrates must not be regarded as analogous to the
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Keywords: ., bo, bookcentury1800, bookdecade1890, bookpublisherlondonmacmillan
