Rhythmical Pulsation in Scyphomedusa. 131 



It is well known that Romanes, I885, 1 demonstrated that the stimulus of 

 a weak faradaic current of electricity applied to the subumbrella would 

 cause Scyphomedusse deprived of sense-organs to resume rhythmical 

 pulsations. 



The nervous stimulus which causes pulsation can not be produced at the 

 extreme outer end of the sense-club where the calcic oxalate crystals are 

 forming, for the calcium in solution must be relatively reduced at this place, 

 and this would permit the magnesium to repress the stimulating effect of 

 any slight excess of sodium. The free sodium salts must pass backward 

 by osmosis to the nervous center near the base of the sense-club where the 

 calcium is normal in concentration. We may prove this experimentally, for 

 if we cut off the tip of the sense-club, removing the entire otolith mass, we 

 may still stimulate the stump of the club into activity by a solution of one 

 part by weight of sodium chloride in 1000 parts by weight of sea-water. 



We are now in a position to state that the nervous stimulus which pro- 

 duces pulsation is caused by a slight excess of soluble sodium at the gang- 

 lionic center, but the chemistry of the change that takes place in the nerve 

 itself while the pulsation-stimulus is passing through it remains undiscovered. 



International Scientific Series, vol. 49, New York. Also: Philosophical Trans- 

 actions Royal Soc., London, vols. 166, 167, 171. 



