Eggs of Culex pipiensL. are laid in rafts on the surface of still or slow moving water, whereas those of Mansonia africana (Theobold) are deposited beneath tho surface of the water on the undersides of floating leaves (Laurence & Smith 1958; Laurence 1959). The eggs of both species are surrounded by air, those of Culex pipiens are in direct contact with the external atmosphere, whereas those of Mansonia africana are partially surrounded by a bubble of air trapped between them. The anterior onds of the eggs of Mansonia africana project through the bubble of air into the surrounding water. This bubble of air is only found around living eggs and disappears if tho eggs die and shortly before they hatch. Iyengar (1935) has shown that the eggs of Ficalba minima Theo. although often deposited on the same leaf as those of Mansonioides, are laid above the water line and resemble in structure those of Culex and Coquillettidia. The structure of the egg-shell of both Culez pipiens and Mansonia africana is described and discussed.