With regard to artificial rhythm caused by chemical stimuli, by far the most conspicuous instance that I have observed is that of the paralyzed nectocalyx of Sarsia. This consists in a highly peculiar motion of a flurried, shivering character, which is manifested by this organ when its marginal ganglia have been removed and it is exposed to the influence of faintly acidulated water. Now, when read in the light of the foregoing facts, there can be no doubt that the present one falls into its place very satisfactorily: it is an additional and very valuable instance of the display of artificial rhythm under the influence of a constant stimulus of low intensity; for the shivering motions of the mutilated nectocalyx under these circumstances are most unmistakably of a rhythmic nature. Viewed from a little distance, indeed, these motions are not distinguishable from the natural swimming motions of the unmutilated animal, except that, not being of quite such a powerful character, they are not so effective for locomotion. Viewed more closely, however, it may frequently be seen that the whole bell does not contract simultaneously, but that, as it were, clouds of contraction pass now over one part and now over another. Still, whether the contractions are partial or universal, they are more or less rhythmical. As this was the only case that had ever been observed of rhythm as due to a constant chemical stimulus, I studied it with much care, and shall now give a full description of what appears to me an important body of physiological facts.