160 JELL^-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 snstained rhytbm of ... 26 

 Immediately after removal of manubrium, rhythm rose to ... 36 

 Rate then gradually fell for a quarter of an hoar, and became 



stationaiy at . . . .. ... ... ... .. ... 20 



Circular incision just inclndiug ovaries caused rhj'thm to 



rise to ... ... ... ... ... ... ... 26 



After gradual fall during quarter of an hour, rhythm became 



stationary at ... ... .,, , ... 17 



