The Nutrition of the Central Nervous System in the Cockroach Periplaneta Americana L. the Role of Perineurium and Glial Cells in the Mobilization of Reserves

The organs and tissues of insects are mostly composed of single layers of cells separated from the circulating blood by thin connective tissue membranes (Wigglesworth, 1956a; Pipa & Cook, 1958). The supply of nutrients to such organs presents no problem. But the central nervous system is an exception. The ganglia are the only solid organs in the insect body. They consist of densely packed peripheral cells surrounding a central neuropile, the whole ganglion being covered by a tough fibrous sheath or neural lamella continuous with the connective tissue membranes elsewhere. The total thickness of the ganglion may be 1 mm. or more. The need for oxygen is met by the tracheae and tracheoles which pass through the neural lamella and ramify inside. But there is no circulation of haemolymph within the ganglion. All nutrient substances must diffuse through the neural lamella and be passed on to the deeper layers. One would, therefore, expect to find some special provision for the transport and storage of such nutrients. After passing through the neural lamella the nutrient substances must be taken up by the perineurium cells, transferred to the glial cells, and conveyed by these to the neurones. In an earlier paper (Wigglesworth, 19596), the probable importance of both perineurium and glial cells in the nutrition of the neurones was emphasized. The present paper, which deals with histology and histochemistry, is part of a general study of the nutrition of the nervous system in the cockroach. The biochemical observations are published separately by Treherne (i960).