A Study of Photoperiodic Time Measurement of Samples from a Michigan Population of Orconectes Immuni (Hagen)

Experiments were conducted to determine if an hourglass model is the mechanism whereby photoperiodic time is measured by the crayfish, Orconectes immunis. Two experiments were conducted in which there were three series of treatments. Series I and II were T experiments in which T was the total length of the light-dark cycle. In Series I the light phase of the cycle was held at 16 hours with varied lengths of darkness (LD 16:2, T 18; LD 16:8, T 24; LD 16:20, T 36; LD 16:32, T 48). In Series II the dark phase was 8 hours in length and the hours of light were varied (LD 2:8, T 10; LD 16:8, T 24; LD 28:8, T 36; LD 40:8, T 48). Series III contained an experiment designed to determine the response of animals to a light pulse. There were two photoperiod treatments, one in which a light pulse lasted for 5 minutes per day and a 24 hour total darkness treatment. No significant differences were found in the molting responses of the crayfish to the photoperiods in these three series of experiments. These data would then indicate that an hourglass mechanism is not utilized to measure photoperiod under the conditions tested