48 



Papers from the Marine Biological Laboratory at Tortugas. 



the sodium, calcium, and potassium ions and an augmentation in the con- 

 centration of the magnesium, as is shown in table ii. 



Table 12 gives the decline in rate of pulsation shown by 2 rings and 

 9 normal medusae of Cassiopea xamachana in sea-water to which increments 

 of 0.4 molecular MgCl2 have been added. 



Table 12. 



1 15.5 hours after being replaced in sea-water this ring pulsated at the normal rate. 



23 hours after being replaced in sea-water this ring pulsated at its normal rate. 



' After being replaced in sea-water this medusa recovered perfectly and pulsated at its normal rate. 



* After being replaced in sea-water they soon recovered and pulsated normally. 



' These medusae recovered completely and pulsated normally after being replaced in sea-water. 



Upon replacing these medusae in sea-water, they pulsated at normal rates. 

 ' A partial record of this ring is given in record, fig. 19. 



8 See record, fig. 11. 



Table 13, which is derived from table 12, shows the average rates of 

 nerve-conduction in two rings of Cassiopea xamachana in sea-water and in 

 sea-water mixed with 0.4 molecular MgCl2. 



> See fig. 9, full-line curve. 



Table 14 shows the average rates of pulsation of 9 medusae of Cassiopea 

 xamachana in sea-water and in sea-water mixed with 0.4 molecular MgCl2. 

 The rates are reduced to a scale of 100 in natural sea-water. 



Tables 12 and 13 show the results of experiments upon two pulsating 

 rings in sea -water at 28 to 31 C. to which had been added increments of 

 0.4 molecular MgCla dissolved in distilled water. The rings or medusae 

 were permitted to pulsate in any new concentration of magnesium for at 

 least I and usually 3 hours before a record of the pulsation-rate was taken, 



