The Connective - Tissue Sheath of the Nervous System of

THE connective-tissue sheath around the nervous system of insects began to attract attention after Hoyle (1953) had shown that it was essential for the normal functioning of the nervous system in Locusta migratoria. The sheath, which consists of two layers, the neural lamella and the sheath cells, controls the passage of ions from the haemolymph into the nervous system. In electron-microscope studies, Hess (1958) and Smith and Wigglesworth (1959) have shown that collagen fibrils are present in the neural lamellae of Periplaneta americana and Rhodnius prolixus respectively. Hess also described the sheath cells which are characterized by the large number of mitochondria in the cytoplasm. It has been suggested from histochemical evidence that the neural lamella of L. migratoria contains collagen fibres embedded in a matrix of neutral mucopolysaccharide (Ashhurst, 1959). It was also shown that the sheath cells form a layer under the neural lamella, and that the cytoplasmic inclusions of these cells are mitochondria and lipochondria. This paper describes an electronmicroscope study of the connective-tissue sheath in the locust. An attempt is made to correlate the evidence of the light-microscope study with the results obtained in the electron microscope. The nomenclature of the layers of the sheath is that used by Ashhurst (1959).