THE INFLUENCE OF THE INTENSITY OF LIGHT ON THE RATE OF GROWTH AND DURATION OF LIFE OF DROSOPHILA.

The duration of the larval and imago periods of Drosophila cultures which had been previously grown in the dark for 200 generations has been determined at various light intensities. 1. The duration of the larval period is shortened slightly at intensities around 2,500 meter candles, but becomes increasingly longer at higher intensities. The larvae are killed by continuous exposure to light of 7,000 to 10,000 meter candles. 2. The pupae are killed at intensities greater than 5,000 meter candles. 3. Above 1,000 meter candles the duration of the imago period is rapidly shortened. 4. The duration of life of the imago at different intensities of illumination can be quite accurately predicted by assuming that the light produces an independent "rate of aging" which is proportional to the intensity of the light. 5. The result of short exposure of the imago shows that light does not merely accelerate the normal "rate of aging," and also that the effect is only partially reversible. Diffuse daylight does not affect the upper temperature limit of growth.