38 PULSATION OF JEHYFISHES. 



other salt this was made isotonic with the NaCl of sea-water. The 

 potassium was so introduced as always to give the same amount of the 

 element (K) as is found in sea- water. 



Table 3. — Hotv calcium revives rhythmical pulsation in Cassio^ea after all 

 ■movem,ent has ceased in solutions contaiuing Na or Li, isotonic ivith the NaCl 

 of sea--water, and fotassium. in the sam,e amount as is found in sea-water. 



Table 3 shows that Cassiopea pulsates longer and more rapidly in 

 a solution of NaCl + KCl than in any other solution named in the 

 above table. Also, sodium and potassium nitrates are more injurious 

 than a solution in which the sodium is replaced by an isotonic amount 

 of lithium. Evidently the anions as well as the cations of the salts 

 have a decided influence upon the rhythmical movement. This is 

 also shown by the fact that Medusae pulsate longer and with greater 

 regularity of movement in NaCl -1- K2SO4 + CaSO^ + CaCOa than 

 they do if we omit the CaCOg and replace it by an equivalent amount 

 of CaSOi. It will be recalled that Rogers (1905, p. 249) found that 

 the addition of small amounts of NajCOs or NaOH to solutions 

 have a beneficial effect in maintaining the rhythm of the crab's heart, 

 and he attributes this effect to the neutralization of small amounts 

 of free acid in the solutions. Ammonia, KOH, or NaOH in small 

 amounts have, however, little effect upon the rhythm of Cassiopea, 

 but if the sea-water be rendered almost neutral by HCl (it is nor- 

 mally decidedly alkaline at Tortugas) the pulsations of the Medusae 

 lose energy, and finally the rate declines, and movements, although 

 regular, are feeble and slow. Thus the rates of three Medusae declined 

 in six hours from 37-50 to 13-17 per minute, due to the effect of a 

 minute quantity of HCl in the sea-water, causing it to become almost 

 neutral, but still alkaline to litmus test. It seems improbable, how- 



