DECLINE IN PHOTOPOSITIVE TENDENCIES WITH AGE IN DROSOPHILA-MELANOGASTER (DIPTERA, DROSOPHILIDAE)

Phototaxis was measured in young, middle-aged, and old Drosophila mela nogaster flies of both sexes. The apparatus allowed us to measure the tendency to go toward light, independently of the time needed to do so ; under such conditions, phototaxis is dissociated from locomotor acti vity. The percentage of photopositive flies decreased slightly with ag e (93.96, 80.17, and 78.97%, respectively, in young, middle-aged, and old flies). Results are discussed in connection with previous data for which the tendency to go toward light and the time to do so were not dissociated.