4 PULSATION OF JELIvYFISHES. 



The calcium of the sea-water assists the NaCl to resist the retarding 

 effects of magnesium. Thus Cassiopea will pulsate from half an hour 

 to an hour in a solution containing the amounts and proportions of 

 NaCl, magnesium, and calcium found in sea-water, but usually ceases 

 to pulsate in less than two minutes in a solution containing only the 

 NaCl and magnesium. 



Unlike calcium, potassium does not assist the NaCl to overcome the 

 Stupefying influence of the m,agnesium.* Thus Cassiopea ceases to 

 pulsate almost as quickly in a solution containing NaCl, magnesium, 

 and potassium of sea-water as it does in a solution containing only 

 the NaCl and magnesium-. 



The potassium of sea-water serves, however, to stimulate pulsation 

 in connection with both calcium and NaCl. Thus Cassiopea pulsates 

 only from 20 to 120 minutes and at about a normal rate in NaCl 

 -)- K2SO4, or in NaCl + KCl, whereas it pulsates for more than three 

 hours at fully twice its normal rate in NaCl -V K2SO4 -h CaSOj, or 

 NaCl-hKCl-hCaClj. 



We see, then, that the NaCl, K, and Ca of the sea-water unite in 

 stimulating pulsation and in resisting the stupefying effect of the 

 Mg. All four salts conjointly produce, in sea-water, an indifferent, or 

 balanced, fluid which neither stimulates nor stupefies the disk of Cas- 

 siopea, and permits a recurring internal stimulus to produce rhythmic 

 movement. 



6. Cassiopea does not pulsate when its marginal sense-organs are 

 removed, simply because the sea-water does not stimulate it. If stimu- 

 lated in sea-water, in any manner, it readily pulsates. This is also true 

 of Gonionemus , and Loeb's statement that both the K and Ca of sea- 

 water inhibit pulsation is not supported ; for the center of Gonionemus 

 will pulsate actively, though temporarily, in sea-water whenever it is 

 touched by a crystal of any potassium salt, or otherwise stimulated. t 



On the other hand, the disks oi Aurelia and Dactylometra begin to 

 pulsate in sea-water in a few minutes, as soon as they recover from 

 the shock of the operation resulting in the loss of their marginal sense- 

 organs. Unlike Cassiopea and Gonionemus, both Aurelia and Dactylo- 

 m,etra are weakly stimulated by the sea-water as a whole and pulsate 

 almost immediately after the removal of their margins. 



*The general anesthetic effect of magnesium has been well known since the re- 

 searches of TuUberg, 1892 ; Archiv. Zool. Exper. et Gen., Tome x, p. 11. 



f As a matter of fact, the disk of Gonionemus is often seen to give isolated pulsa- 

 tions, at irregular intervals, in sea-water without apparent external stimulation. (See 

 Yerkes, 1902.) 



