When goldfish are placed in a rotating annular chamber of which the outer wall is glass, they can be induced to swim steadily at a rate which varies with the temperature when the water is aerated. When the subjects have been in each case previously acclimated to the experimental temperature the best performance is attained at temperatures from 20 to 30 °C., the highest temperature to which goldfish can be acclimated being 41 °C. Subjects acclimated to a variety of experimental temperatures gave curves of performance in relation to temperature which were unique for each level of acclimation.