Abstract
1. In the mutant 'short vein' of Drosophila virilis the effect of high and low temperatures on the manifestation of the character, with special reference to the 'temperature effective period, ' has been studied.
2. The high temperature (30°C) tends to make the grade of disappearance of wingveins higher, while the low temperature (18°C) makes it lower.
3. The effective period of the high temperature extends from the previous day of pupation to the second day after pupation. The period during which the high temperature gives the greatest effect is one day after pupation.
4. The low temperature inhibits the activity of the short vein gene. The effective period extends from the middle larval age to the middle pupal age.
5. Males are more sensitive to both high and low temperatures, and their effective period is about one day longer than that of the females.
