166 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 were affected by the paring 
down of the contractile tissue. 
Iifects of Temperature on the Rhythm. 
The effects of temperature on the rhythm of 
Medusz 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 swimming. 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 Sarsiz 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 are 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 
