The writer (Judd, 1954) reported upon the results of a survey of mosquitoes conducted at London, Ontario in 1952, during which seventeen species were found to occur. Larvae and pupae were taken from pools in six areas in London and its vicinity and were reared to the adult stage at room temperature in the laboratory. Each larva or pupa to be reared was placed in a separate small jar covered with cheesecloth and containing some of the water from the pool from which the specimen had been taken. As the insect went through its series of moults the exuviae were preserved and a record was kept of the dates on which moults occurred. One hundred and seven larvae, representing ten species, successfully passed through the pupal stage to produce adults. The data accumulated from these rearings thus give information concerning the length of the pupal period of the species represented. This information was not included in the publication referred to above and is presented herewith in Table 1.