The influence of temperature has been studied simultaneously on the pumping, filtration, and digestion rates of Phallusia mammillata (Cuvier, 1815). Eighteen experiments were made between 7 ~ and 25~ on 5 individuals. The average velocities of the water current varied between 3.37 and 9.65 cm sec-1 (maximum 34.90 cm sec-1). No recognizable rhythm emerged; pumping was continuous except at 7~
where it soon ceased. Above 20~ the curves were irregular and reflected the high sensitivity of the ascidian. The pumping rate was highest at 15Oc (mean = 5,788 ml h -I g-1 dry weight of organs). At I0~ the mean was 3,560; at 20~ 2,629 ml h -I g-1 dry weight of organs. At 20~ the coefficients of variation displayed higher values, indicating a more irregular pumping at this temperature. Although there was no filtration rhythm, the variability of the results was higher at 20~ and above. As for pumping, maximum values were observed at 15~ (mean = 4,286 ml h -I g-1 dry weight of organs) decreasing with lower and higher temperatures, such decreases being more marked at the higher temperatures. Means were 352 ml h-1 g-1 dry weight of organs at 7~
2,935 at IO~ 1,995 at 20~ 973 at 25~
The mean temperature coefficients for the filtration rates were: QIO for 7 ~ to 15~ = 11.86, QIO for 10 ~ to 20~ = 0.66, QIO for 15 ~ to 25~ = 0.22. The filtering efficiency was fairly constant throughout an experiment; the pumping and filtration curves were in fact almost parallel. The filtering efficiency of the branchial sac was high (75 to 85%), with constant values at 10 ~ and 15~ it became smaller (59%) at 20~ with a higher coefficient of variation. The digestion rate also displayed maximum values at 75~ (mean = 5.47 mg of albumin equivalent 24 h -I g-1 dry weight of organs). It was lower at I0~ (mean = 3.60 mg) and reached its minimum at 20~ (mean = 1.71 mg). The higher temperature affected the percentage of food utilization, which showed smaller values at 20~ (59%) than at I0~ (89%) and 15~ (87%).