1. Eggs of the British woodland mosquito, Aedes puncror (Kirby), were subjected to a variety of media in an attempt to determine the hatching stimulus.2. It was found that continuous immersion in distilled water evoked almost no hatching (0.2%); intermittent removal from the water gave low hatching (8.9%).3 . Slow deoxygenation of the medium by either bacterial growth or the introduction of nitrogen produced the highest level of hatching (26.0-90.0%). Eggs of A.punctor were shown to hatch within a 4 h period of the oxygen concentration in the medium reaching zero.

1 . Eggs of the mosquito Aedes punctor Kirby were found t o be aggregated in a horizontal band within woodland depressions.2. The height of the peak o f egg density above the lowest point in the depression varied from 24 to 39 cm in six transect studies.3. One depression, 2 m in diameter, was analysed in detail and found t o contain a total of 923 1 eggs with a maximum density of 944 eggs in a 250 cmz area.