1G6 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 



charging. But if a stimulus of any kind were then 

 applied, the rhythmic discharges at once recom- 

 menced. These generally continued for some little 

 time at a slower rate than that which they had 

 manifested before they Avere affected by the paring 

 down of the contractile tissue. 



Ejects of Temperature on the Rhythm. 



The effects of temperature on the rhythm of 

 Medasi3e are very decided. For instance, a specimen 

 of Sarsia which in successive minutes gave the 

 following number of pulsations, 16, 26, 0, 0, 26, 

 gave sixty pulsations during the next minute, while 

 a spirit-lamp was held under the water in which 

 the Medusa was swimminof. If hot water be added 

 to that in which Sarsia are contained until the 

 whole is about milk- warm, their swimming motions 

 become frantic. If the same experiment be per- 

 formed after the margins of the Sarsiae have been 

 removed, the paralyzed bells remain quite passive, 

 while the severed margins exhibit the frantic 

 motions just alluded to. 



In the case of Aurelia aurita, the characteristic 

 effects of temperature on rhythm may be better 

 studied than in that of Sarsia, from the fact that 

 the natural motions ai-e more rhythmical and 

 sustained in the former than in the latter genus. 

 I have, therefore, in this connection made more 

 observations on Aurelia than on Sarsia. The follow- 

 ing may be taken as a typical experiment. 



A small and active specimen of Aurelia contracted 



