NATURAL RHYTHM. 105 



find if this view as to the essentially reflex character 

 of the natural rhythm is the true one. 



If this view is the true one, the question next 

 arises as to the nature of the process which goes on 

 in the excitable tissues, and which afterwards acts 

 as a stimulus on the ganglionic tissues. This 

 question, however, I am quite unable to answer. 

 Whether the process is one of oxygenation, of 

 chemical changes exerted by the sea-water, or a 

 process of any other kind, further experiments may 

 be able to show ; but meanwhile I have no sugges- 

 tion to offer. 



Effects of lessening the Amount of Tissue adhering 

 to a Single Ganglion. 



The above experiments led me to try the effects 

 of cutting out a single lithocyst of Aurelia, and, 

 after the rhythm of the detached segment had 

 become regular, progressively paring down the 

 contractile tissues around the ffanolion. I found that 

 this process had no very marked effect on the 

 rhythm, until the paring reached within an inch or 

 two of the ganglion: then, however, the effect 

 began to show itself, and wi^h every successive 

 paring it became more marked. This effect con- 

 sisted in slowing the rate of the rhythm, but more 

 especially in giving rise to prolonged pauses: indeed, 

 if only a very little contractile tissue was left 

 adhering to the ganglion, the pauses often became 

 immensely prolonged, so that one might almost 

 suppose the ganglion to liave entirely ceased dis- 



12 



