CHAPTER VII. 



NATURAL RHYTHM. 



It will be convenient here to introduce all the 

 observations that I have been able to make with 

 regard to the natural rhythm of the Medusae. 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 diiferences 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 Sarsiye are much better 



