152 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 



versely, if the larger segments happen to contain 

 feeble lithocysts, their contractions will be but few. 

 I have, indeed, seen cases in which the lithocysts 

 appeared to be quite functionless, so far as the 

 origination of stimuli was concerned. 



The following observations were made on a 

 healthy specimen of Aurelia having all its litho- 

 cysts in good condition but prepotency being well 

 marked in the case of one of them, and also, though 

 in a lesser degree, in the case of another. I divided 

 the animal so as to leave one of these two pre- 

 potent lithocysts in each of the eighth-part seg- 

 ments, and the next most powerful lithocysts in the 

 quadrant segment. In the following description, I 

 shall call the two eiglith-part segments A and B, 

 the former letter designating the segment contain- 

 ing the most powerful lithocyst. The Aurelia be- 

 fore being divided manifested for several hours a 

 very regular and sustained rhythm of thirty-two 

 per minute. After its division, the various segments 

 contracted at the following rates, in one-minute 

 intervals : — 



Next morning, the water which contained the 

 segments was somewhat foul, and this, as is always 

 the case, gave rise to abnormally long pauses. This 

 effect was much more marked in the case of some 



