IT is known that the mosquitoes Culex and Anopheles lay their eggs on water and that Aedes lays its eggs on wet surfaces. If a wet surface is absent, Aedes will not lay eggs1,2 nor will Culex2. In Anopheles, however, some laying can be obtained on a dry surface2,3. When gravid females of A. aegypti were placed over a wet surface without being able to come into actual contact with it they laid a number of eggs on an interposed dry screen. An attempt was made to locate the hygroreceptors involved in oviposition.