NATURAL RHYTHM. 163 
tracting, how are we to know whether the action 
of the ganglia is truly automatic, or sustained 
from time to time by stimuli proceeding from other 
parts of the organism? In most cases experiments 
cannot be conducted with reference to this question, 
but in the case of the Medusze they may be so, and 
it was with the view of throwing light on this 
question that the experiments just described were 
made. Now in these experiments the fact is 
sufficiently obvious that mutilations of any part of 
the organism modify the rhythm of the marginal 
ganglia most profoundly. That this modification 
does not proceed from shock, would seem to be 
indicated by the facts that the first effect of the 
mutilation is to guicken the rhythm; that there is a 
sort of general proportion to be observed between the 
amount of tissue abstracted and the degree of slowing 
of the rhythm produced; and that the slowing effects 
continue for so long atime. All these facts seem 
to show that we have here something other than 
mere shock to deal with. 
A strong suspicion, therefore, arises that the cause 
of the slowing of the rhythm which results from 
removing the manubrium, or a part of the general 
contractile tissue of the bell, consists in the destruc- 
tion of some influence of an afferent character which 
had previously emanated from the parts of the 
organism which have been removed, and_ that 
the normal rhythm before the operation was partly 
due to a continuous reception, on the part of the 
ganglia, of this afferent or stimulating influence. 
In support of this view are the facts that the first 
