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 folowing description, I 
shall call the two eighth-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 :— 
Time after operation. | Segment}. | Segment}. | Segment 3 A.| Segment 3 B. 
3 hour 20 25 27 15 
20 25 27 15 
2 hours 29 25 27 16 
39 19 16 27 12 
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 
