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By means of the oxygen consumption, the influence of constant and diurnally alternating temperatures on the metabolism rate of the American cockroachPeriplaneta americana was investigated.By analysing the daily rhythm of the metabolism, the resting and activity phase of the animals could be distinguished.During the activity phase the level of the metabolism was determined only by the acute experimental temperature independent of the temperature pretreatment of the animals.In the resting metabolism, however, an influence of the temperature pretreatment could be shown. In nearly all experimental temperatures the metabolism of animals, pretreated at 25°C, was higher than in animals pretreated at warmer or colder temperatures. This relative high oxygen consuption of the 25°C-animals indicates that the metabolism of the cockroaches is optimally adapted only to a small temperature range of about 25°C. Animals pretreated with extremely low Temperatures (15°C) showed during the light time in warm experimental temperatures a clearly higher metabolism rate than cockroaches pretreated at 25°C, but this increase of oxygen consumption could be explained in the main by an annomal locomotory activity during the light.The mean daily oxygen consumption of nymphs, taken out of alternating temperatures, corresponds to those values which would be expected of animals, taken out of constant temperatures.Considering locomotory activity and feeding behaviour a temperature compensation, as described by Dehnel (1956) in nymphs ofPeriplaneta americana, could not be verified neither in constant nor in diurnally alternating temperatures.