Fig. 2. Time course of changes in the internal osmolality of embryos (homogenised eggs) sampled from ovigerous crabs (A, Hemigrapsus sexdentatus; B, H. crenulatus) reared in dilutions of seawater: red, 100% (osmolality 1000 mmol kg^–1); blue 50% (osmolality 500 mmol kg^–1); green 25% (osmolality 250 mmol kg^–1). The abscissa shows the estimated elapsed time from egg extrusion. The hyposaline exposure was commenced either during cleavage (1 day after extrusion, broken lines and open symbols) or after gastrulation (11 days and 8 days respectively after extrusion, solid lines and closed symbols). The final measurement was made just before hatching (for embryos in 100% seawater and those exposed to 50% seawater as gastrulae) or before abortion (25% seawater and those commenced during cleavage). Horizontal coloured lines show the osmolalities of the corresponding external seawaters. Values are means ± s.e.m., N=5–7 (A) and 3–5 (B).