The methodology of culturing tissues outside the organism under conditions that permit detailed morphological examination of growth. One of the first applications of tissue culture to neurophysiology in insects was based on attempts to recreate the neuroendocrine control of molting in a culture chamber. In vivo studies in insects have provided detailed information about the patterns of division and the differentiation of neurons within various lineages, but it has been difficult in vivo to dissect out the nature and intrinsic influences that guide the generation and development of neuronal lineages. Ideally, one could explore developmental interactions involving glial cells in the same way one examines neuronal interactions, that is, by isolating particular interactions in the culture environment. While exploration of the role of trophic factors in vertebrate nervous systems has burgeoned and been greatly facilitated by the use of cell-culture methodology.