FUNDAMENTAL EXPERIMENTS. 27 
walls of the bell are drawn together ; the capacity 
of the bell being thus diminished, water is ejected 
from the open mouth of the bell backwards, and the 
consequent reaction propels the animal forwards. 
In these swimming movements, systole and diastole 
follow one another with as perfect a rhythm as 
they do in the beating of a heart. 
Effects of excising the entire Margins of Nectocalyces. 
Confining our attention under this heading to 
the naked-eyed Medusz, I find that the following 
proposition applies to every species of the group 
which I have as yet had the opportunity of ex- 
amining: Hzcision of the extreme margin of a 
nectocalyx causes immediate, total, and permanent 
paralysis of the entire organ. Nothing can possibly 
be more definite than in this highly remarkable 
effect. I have made hundreds of observations upon 
various species of the naked-eyed Medusz, of all 
ages and conditions of freshness, vigour, etc.; and I 
have constantly found that if the experiment be 
made with ordinary care, so as to avoid certain 
sources of error presently to be named, the result is 
as striking and decided as it is possible to desire.* 
Indeed, I do not know of any case in the animal 
kingdom where the removal of a centre of spon- 
taneity causes so sudden and so complete a paralysis 
* T have only met with one individual exception. This occurred 
in a specimen of Staurophora laciniata, where, after removal of 
the entire margin, three centres of spontaneity were found to 
remain in the shcet of contractile tissue lining the nectocalyx, 
