1 8 PULSATION OF JKLLYFISHES. 



recovered and pulsated at the rate of 1 1 per minute. The large Medusa, 

 which pulsated only 3 times per minute in 25 per cent sea- water plus 

 75 per cent fresh water, revived quickly and pulsated 18 times per 

 minute in 50 per cent salt plus 50 per cent fresh water. 



If instead of mixing the sea- water with distilled water, we employ 

 a solution of fresh water containing the amounts of potassium and 

 calcium found in the sea- water, the Medusae do not survive as well 

 as they would in ordinary brackish water, and their rates of pul- 

 sation are much slower, as will appear from the following : Three 

 Medusae in pure sea-water had rates of pulsation of about 60 per 

 minute ; the same Medusae in 55 per cent sea-water plus 45 per cent 

 rain-water containing the same amounts of potassium and calcium 

 as sea-water, pulsated 8 to 14 times per minute ; in 45 per cent sea- 

 water plus 55 per cent rain-water containing the same amounts of 

 potassium and calcium as sea- water, they pulsated 2 to 9 times per 

 minute; in 40 per cent sea-water plus 60 per cent rain-water containing 

 the same amounts of potassium and calcium as sea-water, they pul- 

 sated i to 6 times per minute; in 35 per cent sea-water plus 65 per cent 

 rain-water containing the same amounts of potassium and calcium as 

 sea -water, they pulsated o to 2 times per minute; in 25 per cent sea- 

 water plus 75 per cent rain-water containing the same amounts of 

 potassium and calcium as sea- water, two dead, one pulsated about 

 once every 10 minutes. 



Evidently a uniform reduction of the magnesium, sodium, potassium, 

 and calcium is less injurious than a reduction of the sodium chloride 

 and magnesium alone. As Ringer, Loeb, and others have shown, 

 a balance in the proportions of the constituents of the sea-water is more 

 important than the presence of any single salt. 



As might be expected in Medusae living in shallow lagoons, where 

 evaporation is great, Cassiopea will withstand a considerable concen- 

 tration of the salt water ; however, Medusae in 100 cc. sea- water plus 

 i gram NaCl will survive for 12 hours, but their pulsation becomes 

 irregular, although on the average of about normal rate. The mouth- 

 arms, however, are strongly contracted, and the Medusa exhibits 

 alternate periods of rest and activity in its rhythmical movements. 



Cassiopea will pulsate normally in sea- water saturated with CaSO 4 . 



As will be apparent from the above, Cassiopea xamachana is one of 

 the hardiest of Scyphomedusae. It survives for months in aquaria 

 with but ordinary care, and exhibits wonderful recuperative powers 

 from the effects of poisons. If subjected to constant shaking, as in a 

 floating live-car, it does not thrive as well as in stationary aquaria 

 where the water is not so pure. 



