672 
MR, a. J. ROMANES ON THE LOCOMOTOR SYSTEM OE MEDUS2E, 
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 important, viz. the 
relative potency of the lithocysts, and the length of time that elapses between performing 
But although, in the case of Sarsia the lesser endurance of the smaller segment than of the larger cannot he 
regarded as a general rule, it may be so regarded, as already stated, in the ease of Aurelia. The following 
experiment exemplifies this particular rule even more prettily than does the one quoted in the text, from the 
fact that the segments survived the operation for a greater number of days. 
An Aurelia, having a regular and well-sustained rhythm of 20 per minute was divided as already described 
in the text. In five minutes’ intervals on successive days the average rates of the four segments were as 
follows : — 
Eour hours aftei 
: the Operation 
Seg. i. 
Seg- i. 
Seg. i A. 
Seg. iB. 
100 
100 
85 
90 
Next 
Day. 
88 
90 
64 
58 
Next 
Day. 
86 
82 
62 
57 
Next 
Day. 
59 
45 
24 
20 
Next 
Day. 
50 
49 
20 
10 
Next 
Day. 
43 
33 
18 
4 
Next 
Day. 
, 39 - 
32 
19 
Dead. 
Next 
; Day. 
33 
7 
Dead. 
0 
N ext Day. 
28 
j 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. 
