1. The locomotor rhythm of Carcinus maenas was shown to be relatively similar at 10°, 15°, 20° and 25° C., but it was shown to be modified by changes in temperature.
2. A fall of about 5-10° C. just before the onset of activity usually advanced and enhanced the initial peak of activity, whilst a rise of the same magnitude usually delayed and partly suppressed the initial peak, each without affecting the basic rhythm.
3. A fall in temperature of about 10° C. or more between activity peaks usually initiated transient outbursts of activity, again without affecting the normal rhythm.
4. Chilling to 40° C. for more than 6 hr., irrespective of the time of onset of chilling, resulted in a rephasing of the rhythm with the initial outburst occurring immediately on return to room temperature.
5. In Carcinus from non-tidal docks chilling resulted in a change from the normal approximately nocturnal rhythm to an overt tidal rhythm, but in Carcinus from the virtually tideless Mediterranean the character of the normal nocturnal rhythm was unaffected by chilling.
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