RHYTHMICAL PULSATION IN SCYPHOMEDUSAZ. — II. 
By ALFrep 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 sonie new 
results. 
CONCLUSIONS. 
(1) Sea-water is a balanced fluid neither inhibiting nor stimulating pul- 
sation in Cassiopea xamachana. 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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