178 JELLr-FlSII, STAR-FISn, AND SEA-URCHINS. 



more pronounced up to a certain point, when it 

 would gradually have begun to pass into more 

 persistent tetanus. But as in this case, instead of 

 streno^thenino^ the current still further, I as^ain 

 weakened it to its original intensity, the rhythm 

 immediately returned to its original rate and regu- 

 larity. 



Such being the facts, the question arises as to 

 their interpretation. At first I was naturally in- 

 clined to suppose that the artificial rhythm was 

 due to a periodic variation in the strength of the 

 stimulus, caused by some slight breach of contact 

 between the terminals and the tissue on each con- 

 traction of the latter. This supposition, of course, 

 would divest the phenomena in question of all 

 physiological meaning, and I therefore took pains 

 in the first instance to exclude it. This I did in 

 two ways : first, by observing that in many cases 

 (and especially in Cyanyea capillata) the rate of the 

 rhythm is so slow that the contractions do not 

 follow one another till a considerable interval of 

 total relaxation has intervened; and second, by 

 placing the terminals close together, so as to include 

 only a small piece of tissue between, and then 

 firmly pinning the tissue all round the electrodes to 

 a piece of wood placed beneath the Medusa. In 

 this way the small portion of tissue which served 

 as the seat of stimulation was itself prevented from 

 moving, and therefore the rhythmic motions which 

 the rest of the Medusa presented cannot have been 

 due to any variations in the quality of the contact 

 between the electrodes and this stationary scat of 

 stimulation. 



