produce a 128-cell blast During the blastula stage, cells no longer cleave of local groups of cells proceeds, divisions gradually decrease remain synchronous, but these regions in size, and eventually the cell cycle lengthens and becomes largely randomized(Dan et al., 1980). The early blastula is an epithelial monolayer enclosing a central, s blastocoel(3.10) whose cells develop septate junctional contacts between one another(Spiegel and Howard, 1983) and begin to produce the basal lamina lining the blastocoel. The exterior, apical ends of the epithelial cells possess numerous microvilli, which are embedded in the hyaline layer, and apical lamina(Hall and Vacquicr, 1982). The cells of the blastula eventually seal off the internal