EFFECT OF VARYING THE LIGHT - DARK RATIO WITHIN A 24-H PHOTOPERIOD ON THE PHASE RELATIONSHIP OF THE CREPUSCULAR ACTIVITY PEAKS IN MELANOIDES-TUBERCULATA

The crepuscular rhythm of Melanoides appears to be controlled by two oscilators and there appears to be no fixed relationship between the two. The time of light on and off activity peaks is determined primarily by the time of the appropriate light stimuli, and in constant relative darkness the activity peaks retain the approximate phase relationship of the entraining regimen. A similar relationship is seen in constant light only for animals entrained to photoperiods with a scotophase of 12 h or more. With shorter periods of darkness, the light on peak occurs about 12 h after the light off. A model for the control mechanism is postulated and discussed. © 1979.