An osmotic hatching mechanism is proposed for the Anostracan Branchiopod Chirocephalus diaphanus, Prevost. In this mechanism, glycerol is thought to accumulate in the egg as a result of the metabolism of the embryo. The osmotic pressure exerted by the egg, largely due to this glycerol accumulation, causes water to enter from the environment. Eventually the hydrostatic pressure thus generated is sufficient to cause rupture of the eggshell. It is recognised that hatching in this Anostracan is a two-staged phenomenon, a process of breaking, in which glycerol is involved, preceding true hatching, in which glycerol is not involved. The egg is described and the physiology and ecological significance of the proposed hatching mechanism are discussed.