Extracellular crystalline material in intercellular spaces of cockroach peripheral glia

Campaniform sensilla on legs of the cockroach, Blaberus discoidalis, are mechanoreceptors; each sensillum functions via a single bipolar neuron. The cell bodies of the bipolar neurons are tunicated; that is, they are spirally wrapped by one or more glial cells. An elaborate extracellular channel is defined by the plasma membranes of adjacent glial cell folds surrounding a given neuron. The electron microscope reveals that this extracellular space often contains conspicuous crystalline material whose lattice planes, oriented at right angles to the long crystal axis, are manifest as parallel electron-dense lines separated by an intercentre distance of 150 A. The chemical nature of these crystals has not been determined in the present study. Like most biological crystals, however, this precisely ordered crystalline material is probably proteinaceous.