Temperature Relations of an Endogenous Daily Rhythmicity in the Fiddler Crab, Uca

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Abstract
The diurnally rhythmic color change observed in Uca was shown to persist for as long as 30 days under constant conditions of darkness, temp., and humidity. It was established that the white chromatophores of Uca exhibit a diurnal rhythm to the same extent and in the same direction as do the black chromatophores. The frequency of the rhythm of both black and white chromatophores was shown to be unaffected by temps. of 6 26 C. Evidence is presented which indicates that when all metabolic processes are greatly reduced in rate by temps. approaching 0 C , the diurnal rhythm is delayed by an interval approx. that of the time of exposure to the low temp. A rhythm which has been delayed for approximately 6 hrs. appears to continue in constant darkness as a 24-hr. rhythm, 6 hrs. out of phase. This has been observed to continue unmodified for at least 6 days. It is concluded from the foregoing that the frequency of the rhythm must, at least in part, be metabolically determined.

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