THE EFFECT OF SEX AND AGE ON THE TEMPERATURE AT WHICH REVERSAL IN REACTION TO LIGHT IN ERISTALIS TENAX OCCURS

¹ Department of Biology, University of Buffalo, Buffalo, N. Y.

1. Over 1,620 observations were made on over 1,000 flies in ascertaining the temperature at which Eristalis tenax becomes negative to light.

2. In a luminous intensity of 700-foot candles Eristalis is highly photopositive within a temperature range between approximately 10° and 30° C. Outside these limits it is highly negative. Reversal of the photopositive reaction can be produced either by increase or decrease of the temperature.

3. In high temperatures the temperature at which Eristalis changes in its reaction to light depends on the sex of the flies. Females cease their positive reaction to light and become negative at a higher temperature than do males.

4. In high temperatures the temperature at which Eristalis changes in its reaction to light depends also on the age of the flies. The younger the fly, the higher the temperature at which it ceases its positive reaction to light and becomes negative.