CHAPTER VIL 
NATURAL RHYTHM, 
Ir will be convenient here to introduce all the 
observations that I have been able to make with 
regard to the natural rhythm of the Meduse. As 
Dr. Eimer has also made some observations in this 
connection, before proceeding with the fresh points 
having relation to this subject, I shall consider 
those to which he alludes. 
In Aurelia aurita, as Dr. Eimer noticed, the rate 
of the rhythm has a tendency to bear an inverse 
proportion to the size of the individual. Size, how- 
ever, is far from being the only factor in determin- 
ing the differences between the rate of the rhythm 
of different specimens, the individual variations in 
this respect being very great even among specimens 
of the same size. What the other factors in question 
may be, however, I am unable to suggest. 
Dr. Eimer also affirms that the duration of the 
natural pauses, which in Aurelia habitually alter- 
nate with bouts of swimming, bears a direct pro- 
portion to the number and strength of the contrac- 
tions that occurred in the previous bout of swim- 
ming. I observed that Sarsiz are much better 
