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 MgCU have been added. 



Table 12. 



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



S3 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. 



Table 13. 



1 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 MgCla. 

 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 MgCl^ 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, 



