186 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 



tween A and B will not respond to tlie discharge 

 of B ; while the tissue included between B and C, 

 not having been just previously in contraction, 

 will respond. And conversely, of course, if the con- 

 traction-wave had been travelling in the opposite 

 direction. 



Seeing that this explanation is the only one 

 possible, and that it moreover follows as a deduc- 

 tive necessity from my experiments on stimulation, 

 I think there is no need to detail any of the further 

 experiments which I made with the view of con- 

 firming it. But the following experiment, devised 

 to confirm this explanation, is of interest in itself, 

 and on this account I shall state it. Having pre- 

 pared a contractile strip with a single remaining 

 lithocyst at one end, I noted the rhythm exhibited 

 by this lithocyst, and then imitated that rhythm 

 by means of single induced shocks thrown in with 

 a key at the other end of the strip. The eftect of 

 these shocks was, of course, to cause the contraction- 

 weaves to pass in the direction opposite to that in 

 which they passed when originated by the litho- 

 cyst. Now I found, as I had expected, that so long 

 as I continued exactly to imitate the rate of gang- 

 lionic rhythm, so long did the waves always pass 

 in the direction B A — A being the lithocyst, and B 

 the other end of the strip. I also found that if I 

 allowed the rate of the artificially caused rhythm 

 to sink slightly below that of the natural rhythm, 

 after every one to six waves (the number depend- 

 ing on the degree in which the rate of succession of 

 my induction shocks approximated to the rate of 



