NATURAL RHYTHM. 159 
of the rhythm manifested by the smaller than by 
the larger segments in the stale water, and the 
fact is presumably to be accounted for by the con- 
sideration that the ganglia in the smaller segments 
were more potent than those in the larger. 
With regard, therefore, to the original point 
under consideration, I conclude that, although the 
size of the segments is doubtless one factor in 
determining the relative frequency of contraction, 
there are at least two other factors quite as impor- 
tant, viz. the relative potency of the lithocysts, and 
the length of time that elapses between performing 
the operation and observing the rhythm. Hence it 
is that in my experience I have found but very few 
examples of Dr. Eimer’s rule. 
Effects of Other Forms of Mutilation on the Rhythm. 
The next point I have to dwell upon is one of 
some interest. Ifthe manubrium of Aurelia, or of 
any other covered-eyed Medusa, be suddenly cut off 
at its base, the swimming motions of the umbrella 
Next day. 
Seg. 3. | Seg. 1. | Seg. }. | Seg. 3 A. 
33 | 7 | Dead. | 0 
Next day. 
28 | Dead. | 0 | 0 
Next day, the temperature unfortunately rose sufficiently to 
cause the death of the single surviving segment, which otherwise 
would probably have lived for one or two days longer. 
