The lobster optic lamina. IV. Glial cells.

There are 3 distinct types of glial cells in the optic lamina of the lobster: dark, light, and sheet cells, all distinguished from the neurons by being multipolar and not having dictyosomes. Dark cells are surrounded by intercellular material and together with light cells constitute a structural support for the groups of nerve cells. Light cells are also sheath cells for the neuron somata. The sheet cells have numerous flat processes which together form the 2 glial layers in which the synaptic region is sandwiched. An extensive system of extracellular cisterns between the sheet processes may serve for fluid transport towards the fibres and synapses, and the numerous vesicles in the sheet cells may represent an extension of the extracellular transport system.