NATURAL RHYTHM. 165 
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 ganglion. 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 with 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 have entirely ceased dis- 
