NATURAL RHYTHM. 151 
than as liable to frequent exception ; for, as already 
observed, I cannot say that my experiments have 
tended to confirm it. Iam 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 lithocysts 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- 
