The effects of low temperature pulses in rephasing the endogenous activity rhythm ofCorophium volutator(Pallas)

The endogenous rhythm of swimming activity shown by Corophium is reset by pulses of sub-zero temperature, the activity maxima being rephased to the time of rewarming at the end of the cold period. Chilling is not equally effective at all stages of the tide, pulses applied during the flood tide causing a phase delay, while those applied during the ebb advance the rhythm. Chilling at the time of low water induces arrhythmic swimming and it is suggested that the rhythm enters a state of equivocation at this time when an advance and a delay in phase are both equally probable. This results in the loss of synchronization between individuals and the disappearance of the overt rhythm from the sample population.