NATURAL RHYTHM. 151 



than as liable to frequent exception; for, as already 

 observed, I cannot say that my experiments have 

 tended to confirm it. I am only able to say that 

 there is general tendency for the smaller segments 

 of an Aurelia divided in this way to contract less 

 frequently than the larger segments. 



It would be tedious and unnecessary to quote 

 any observations in this connection; but as these 

 observations brought out very clearly a fact which 

 I had previously suspected, I may detail one ex- 

 periment to illustrate this point. The fact in ques- 

 tion is, that the potency of the, lithocijsts in any 

 given segment of a divided Aurelia has more to do 

 with the frequency of its pulsations than has the 

 size of the segment. As previously mentioned, one 

 or more lithocysts may often be observed to be per- 

 manently prepotent over the others; and I may 

 here observe that the segmentation experiments 

 just described have shown the converse to be true, 

 viz. that one or more lithocysts are often per- 

 manently feebler than the others. Well, if a 

 specimen of Aurelia exhibiting decided prepotency 

 in one or more of its lithocysts be watched for a con- 

 siderable length of time, so as to be sure that the 

 prepotency is not of a merely temporary character, 

 and if the animal be then divided into segments in 

 such a way that the prepotent lithocysts shall 

 occupy the smaller segments, it may be observed, 

 provided time be left for the tissues to recover, that 

 the segments containing the prepotent lithocysts, 

 notwithstanding their smaller size, contract more 

 frequently than do the larger segments. Con- 



