Abstract
It appears that in scyphomedusæ the nervous stimulus which produces each pulsation is caused by the constant formation of a uric oxalate of sodium in the marginal sense-clubs. This sodium oxalate precipitates the calcium which constantly enters the sense-club from the surrounding sea-water, and forms crystals of calcium oxalate, while sodium chloride is set free. Thus the stimulus which produces pulsation is due to ionic sodium. Pulsation cannot be maintained by the sense organs unless calcium constantly enters them to form the calcium oxalate, and to set free the ionic sodium.
I find that in annelids, barnacles (Lepas), ctenophores, and medusæ, the sodium of the sea-water is a strong neuro-muscular stimulant while the magnesium, calcium and potassium are inhibitors and exactly counterbalance the stimulating effect of the sodium, thus permitting weak internal stimuli to produce movements.
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