THE EFFECT OF ILLUMINANCE ON THE REVERSAL TEMPERATURE IN THE DRONE FLY, ERISTALIS TENAX

Abstract
Observations were made on 2700 young flies in ascertaining the temp, at which E. tenax be-comes negative to light in the following intensities 250, 600, 800, 1200, and 1600 foot candles. As the illumination increases from 250 to 1600 f. c, the mean temps, at which the male flies reverse decrease to a min. at 800 f. c, and then increase. As the illumination increases from 250 to 1600 f. c, the mean temps, at which the female flies reverse decrease to a min. at 800 f. c. Further increase in light intensity causes no further significant change in the mean reversal temp. In light of 600 and 800 f. c, the temp, at which Eristalis changes in its reaction depends upon the sex of the fly. Females cease their positive reaction to light and become negative at higher temps, than do the males. This difference between the sexes does not exist at the following intensities: 250, 1200, and 1600 f. c.

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