Studies in Diurnal Rhythms

Abstract

Visual experiments on two small British species of millipedes have demonstrated that the diurnal cycle of rhythmic activity as represented by the number of animals on the surface is primarily a response to light and darkness, but is also correlated with the stimulus of falling temperature in the evening. Aktograph experiments on two large West African species of millipedes have demonstrated an endogenous diurnal rhythm independent of fluctuating light and temperature, and persisting (in Ophistreptus) up to 19 days. Locomotory activity is stimulated both by increases and decreases of temperature; and it is probable that temperature fluctuations are of primary importance in the initiation of diurnal rhythms. The effect of light on activity is slight, but constant temperatures over long periods have, a depressing effect.