RHYTHMICAL PULSATION IN SCYPHOMEDUS/E. - -II. 



BY ALFRED GOLDSBOROUGH MAYER. 



The following paper presents the results of a continuation of certain 

 studies, the first report of which appeared in publication No. 47 of the 

 Carnegie Institution of Washington, 1906. The present paper aims to 

 correct certain errors in the previous report, and to announce some new 

 results. 



CONCLUSIONS. 



(1) Sea-water is a balanced fluid neither inhibiting nor stimulating pul- 

 sation in Cassiopea .vantacliaua. This is due to the fact that the sodium 

 chloride of the sea-water is a powerful nervous and muscular stimulant; 

 but the magnesium, calcium, and potassium are inhibitors, and exactly coun- 

 terbalance the effect of the sodium chloride thus producing a neutral fluid. 



The sea- water itself, being indifferent, permits any weak, constantly 

 present, internal stimulus to produce the nervous responses which cause 

 rhythmical pulsation of the muscles. 



(2) The stimulus which causes pulsation is due to the constant formation 

 of sodium oxalate in the terminal entodermal cells of the marginal sense- 

 organs. This sodium oxalate precipitates calcium, as calcium oxalate, thus 

 setting free sodium chloride and sulphate which act as nervous stimulants. 

 Pulsation is thus caused by the constant maintenance at the nervous centers 

 in the sense-organs of a slight excess of sodium over and above that found 

 in the surrounding sea-water. 



(3) If we cut a strip of heart tissue, or of subumbrella tissue of a medusa 

 in such manner as to give it the shape of a ring or of any closed circuit, and 

 then start a contraction-wave moving in any one definite direction through 

 this circuit, the wave will continue to travel at a uniform rate around the 

 circuit. This wave will maintain itself indefinitely, provided the circuit be 

 long enough to permit each and every point in the path of the wave to 

 remain at rest for a certain period of time before the return of the wave 

 through the circuit. No one localized point on the circuit acts as a dominant 

 center for maintaining the wave, but all points on the path of the wave take 

 an equal share in passing the wave onward to points beyond them. In 

 nature the structure of pulsating organs, and their manner of stimulation, 



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