The ontogenetic development of two Recent scleractinian corals, Golaxea fascicularis (Linnaeus) and Acrhelia horrescens (Dana), has been studied in serial thin sections. The origin of the septotheca (a collective term including both eutheca and pseudotheca) is reconsidered. The eutheca is found to be a basic skeletal structure of corals and of primary origin, formed directly from the basal plate, not by the thickening of septa. The eutheca prepares the way for the formation of metasepta. The ontogenetic growth of the metasepta is illustrated. The pseudotheca is formed by fusion of neighbouring septa and is entirely of secondary origin. Its development is occasional. The essential mural structure of oculinid corals with pseudothecal walls is euthecal.