The distribution of the neural fat body sheath and the accessibility of the extraneural space in the stick insect, Carausius morosus.

The fluid compartment delimited at the surface of the central nervous system by the closely applied fat body sheath has been shown to be accessible to molecules of horseradish peroxidase and Indian ink particles. Quantitative analysis indicates that leakage via the intercellular spaces between fat body cells would preclude the possibility of a significant involvement of the fat body cells in sodium regulation of the extraneural fluid. This possibility is further precluded by the absence of a fat body sheath from peripheral nerves.