Now, I think that the strictly rhythmic action of the paralyzed swimming-bell of Aurelia in answer to constant stimulation is a fact of the highest significance; for here we have a tissue wholly, or almost wholly, deprived of its centres of spontaneity, yet pulsating as rhythmically in answer to artificial stimulation as it previously did in answer to ganglionic stimulation.[25] Does not this tend to show that for the production of the natural rhythm the presence of the ganglionic element is non-essential; that if we merely suppose the function of this element to be that of supplying a constant stimulus of a low intensity, without in addition supposing the presence of any special resistance-mechanism to regulate the discharges, the periodic sequence of systole and diastole would assuredly result; and, therefore, that the rhythmical character of the natural swimming motions is dependent, not on the peculiar relations of the ganglionic, but on the primary qualities of the contractile tissue? Or, if we do not go so far as this (and, as I may parenthetically observe, I am not myself inclined to go so far), must we not at least conclude that the natural rhythm of these tissues is not _exclusively_ due to any mechanism whereby the discharges of the ganglia are interrupted at regular intervals; but that whether these discharges are supposed to be interrupted or continuous, the natural rhythm is probably in a large measure due to the same cause as the artificial rhythm, viz. in accordance with our previous hypothesis, to the alternate exhaustion and recovery of the excitable tissues? This much, at least, must be allowed even by the most cautious of critics, viz. that if, as current views respecting the theory of rhythm would suppose, it is exclusively the ganglionic element which in the unmutilated Aurelia causes the rhythm of the swimming motions by intermittent stimulation, surely it becomes a most unexpected and unaccountable fact, that after the removal of this element the contractile tissues should still persist in their display of rhythm under the influence of constant stimulation. At any rate no one, I think, will dispute that the facts which I have adduced justify us in reconsidering the whole theory of rhythm as due to ganglia. [25] It will not be forgotten that there are a multitude of ganglion-cells distributed throughout the contractile tissues of the Medusæ; but forasmuch as these are comparatively rarely instrumental in originating stimulation, I think it is probable that artificial stimulation acts directly on the contractile tissues, and not through the medium of these scattered cells.