160 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
immediately become accelerated. This acceleration, 
however, only lasts for a few minutes, when it 
gradually begins to decline, the rate of the rhythm 
becoming slower and slower, until finally it comes 
to rest at a rate considerably less than was pre- 
viously manifested by the unmutilated animal. If 
a circular piece be now cut out from the centre of 
the umbrella, the rhythm of the latter again be- 
comes temporarily quickened; but, as before, gradual 
slowing next supervenes. This slowing, however, 
proceeds further than in the last case, so that the 
rate at which the rhythm next becomes stationary 
is even less than before. If, now, another circular 
ring be cut from the central part of the umbrella— 
i.e. if the previously open ring into which this 
organ had been reduced by the former operation be 
somewhat narrowed from within—the same effects 
on the rhythm are again observable; and so on 
with every repetition of the operation, the rate of 
the rhythm always being quickened in the first 
instance, but then gradually slowing down to a 
point somewhat below the rate it manifested before 
the previous operation. It will here suffice to quote 
one experiment among many I have made in this 
connection -— 
An Aurelia manifested a regular and sustained rhythm of ... 26 
Immediately after removal of manubrium, rhythm rose to ... 36 
Rate then gradually fell fora Na of an hour, and became 
stationary at. bs 20 
Circular incision a4 scainciner ovaries ened digas a 
rise to eis 26 
After gradual fall aise Gees of an eer vay thier teen 
stationary ut . ove nee eve ove eee one ee 
