I here sum up Romanes’ theory in a few words. The ganglia liberate a constant and comparatively weak stimulus, one perhaps about minimal. This stimulus sets off the contractile tissue; but as the tissue contracts and becomes exhausted the constant stimulus becomes, in relation to it, sub-minimal, and it does not contract again until it has recovered and the stimulus is again strong enough to set it off. The ganglionic theory of rhythmic contraction supposes that the ganglia liberate stimuli to the contractile tissue at successive intervals. Romanes had this theory suggested to him by the rhythmic contractions he succeeded in obtaining by subjecting deganglionated bells to a continuous but weak faradic stimulus, or by placing them into weakly acidulated water, or into 5 per cent. glycerine. Romanes claims that his theory better explains muscular tonus and the contraction of involuntary muscle. He does not, however, hold this theory to the exclusion of the ganglionic theory, since only too often does he speak in terms of the latter. He further brings in his support the fact that the frog’s tongue, in which no ganglia have been demonstrated, can be made to contract rhythmically when subjected to a weak and continuous stimulus. He also calls attention to the rhythmic contractions seen in the Protozoa, the snail’s heart, etc. Finally, physiologists are much inclined to explain the rhythmic contraction of the heart and other involuntary muscles, in part, at least, as due to a property of the contractile tissue. _Margin, Radial Ganglia, Nerve_--Experiments 18, 21-23, 30.--Complete removal of the margin did not stop pulsation; but the removal of the radial ganglia stopped it permanently. While this experiment seems to have been tried only once, yet, taking into consideration the results of other operations, it would seem that the principal centers of spontaneity reside in these ganglia. (It should here be remembered that the interradial ganglia were probably removed at the removing of the margin.) Cutting the nerve in the eight adradii caused the _pedalia_ to bend inwards at right angles to their normal position but did not in the least affect the coördination of the sides. When, however, the sides were cut in the eight adradii to the base of the stomach, coördination for the main part ceased, and each side pulsated in its own rhythm.