Fig. 6. Interior view of Periophthalmus modestus egg chamber. (1) Eggs on the mud wall of a laboratory-incubated chamber (scale bar 1 mm). (2–7) Endoscope video frames documenting hatch-induction behaviour (June 19, 2002). Vertical view is down, through the egg chamber (note glistening monolayer of eggs on the mud wall), to the burrow-water surface. The male appears at the surface with its mouth open, and becomes progressively larger as it moves closer to the camera. Removing mouthfuls of air (3,4,6,7) raises the water level, which immerses the eggs, causing them to hatch. (8) Hatched larvae [average total length 2.84 mm (Kobayashi et al., 1972)] swimming in the flooded egg chamber 48 min after frame 7 (see also Movie 1 in supplementary material).