The organization of the central nervous connectives in Anodonta cygnea (Linnaeus) (Mollusca : Eulamellibranchia).

The cerebro-visceral connective of Anodonta cygnea comprises a non-cellular neural lamella, a few randomly distributed glial elements, and axons, together with an extensive extracellular system. The axons are relatively small, the majority being less than 2.0 micro in diameter. The neural lamella is underlaid by a thin layer of peripheral glial processes. The membranes of the proximate glial processes do not reveal any junctional complexes at this level. In addition to glycogen and fat deposits, the glial cytoplasm contains abundant 'glial granules' which in histochemical tests react like mucoproteins. The extracellular space appears to be freely accessible, for apart from the neural lamella no other visible structures are interposed between it and the fluid surrounding the connective. These structural findings are discussed in relation to the available evidence concerning the ability of axons to function in preparations bathed in low-sodium media.