1. Persistent rhythms of primary solar and primary lunar frequencies are described for O2-consumption of two species of fiddler crabs, Uca pugnax and Uca pugilator, and for the salamander, Triturus viridescens. 2. These rhythms appear to be statistical rather than overt ones. The forms of the rhythms become apparent only upon the averaging of several days of data. 3. The form of the daily variation in O2-consumption shows a monthly variation, the form of the rhythm for a two-week period straddling a new moon being different from the form for a two-week period straddling a full moon. 4. The hourly values in the rate of respiration show a significant correlation with the concurrent rate of barometric pressure change. In all three species, the rate of O2-consumption increases in a direct relationship with the concurrent rate of barometric pressure fall and decreases in a direct relationship with the rate of pressure rise. 5. There appears, in some instances, to be a correlation with the absolute concurrent barometric pressure, but this is distinctly less. The correlation was a positive one for the two species of fiddler crabs and a negative one for the salamander. 6. It was demonstrated that O2-consumption in all three species of animals displayed, therefore, imposed daily rhythms and in all probability, also imposed lunar rhythms. 7. The striking similarity of the forms and phase relations of these imposed daily and lunar rhythms of O2-consumption to ones which are being described else-where for three species of plants, the alga, Fucus, and the carrot and potato, is pointed out. The rhythms are also compared with very similar statistical solar and lunar rhythms of opening and closing of the shells recently described for the oyster. 8. There is a brief discussion of the environmental forces which might be involved, and speculation as to possible relationships between these imposed rhythms and the demonstrated endogenous rhythms in producing the temperature-independent overt rhythms observed in many processes in animals.