The larva of Stegomyia fasciata passes through four distinct phases after it emerges from the egg and before it pupates. Under circumstances favourable to growth these phases are passed through very rapidly and the whole larval stage may occupy less than a week. In one experiment ten larvae which had hatched from their eggs on 1st April between 12 noon and 2 p.m. were isolated singly in small glass tubes containing a three-days-old broth medium. All these larvae cast their first pelts on the second day (2nd April), their second pelts on the third day, and their third pelts on the fourth day. The fourth and last larval pelt was not cast simultaneously by all the larvae, perhaps because by this time the nutrient value of the medium in the different tubes had begun to vary to an appreciable degree. Two larvae cast the fourth pelt on the seventh day, one on the eighth day, three on the ninth, one on the tenth, and one on the thirteenth day, and two died in this phase. One pupa died, but all the others hatched on the second day after pupation. In this experiment therefore the larval stage lasted on the average nine days, the shortest time being under seven days, and the longest thirteen days.