150 JELLY-FISH, STAR-FISII, AND SEA-URCHINS. 



Effects of Segmentation on the Rhythm. 



We have next to consider Dr. Eimer's observa- 

 tions concerning the effects on the rhythm of 

 Aurelia which result on cutting the animal into 

 segments ; and here, again, I much regret to say 

 that I cannot wholly agree with this author. He 

 says he found evidence of a very remarkabhj fact, 

 viz. that by first counting the natural rhythm of an 

 unmutilated Aurelia, and then dividing the animal 

 into two halves, one of these halves into two 

 quarters, and one of these quarters into two eighths; 

 the sum of the contractions performed by these four 

 segments in a given time was equal to the number 

 which had previously been performed in a similar 

 time by the unmutilated animal. And not only so, 

 but the number of contractions which each segment 

 contributed to this sum was a number that stood in 

 direct proportion to the size of the segment; so 

 that the half contracted half as many times, the 

 quarter a quarter as many times, and the eighth 

 parts one-eighth part the number of times that the 

 unmutilated Aurelia had previously contracted in a 

 period of equal duration. I am glad to observe 

 that Dr. Eimer does not regard this rule otherwise 



and expenditure of energy of all the rest of the observations, he 

 will find the net result to accord very precisely with the propor- 

 tion he previously obtained. But, as already stated, any such 

 precision as this is certainly the exception rather than the rule. 



It may hei'e be stated that after the sixty seconds of I'est above 

 recorded, the animal began another swimming bout. It was then 

 iniQicdiately bisected, and the subsequent observations are de- 

 tailed in the next footnote. 



