28  JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
of the muscular system, there being no subsequent 
movements or twitchings of a reflex kind to disturb 
the absolute quiescence of the mutilated organism. 
The experiment is particularly beautiful if per- 
formed on Sarsia; for the members of this genus 
being remarkably active, the death-like stillness 
which results from the loss of so minute a portion 
of their substance is rendered by contrast the more 
surprising. 
From this experiment, therefore, I conclude that 
in the margin of all the species of naked-eyed 
Medusze which I have as yet had the opportunity 
of examining, there is situated an intensely localized 
system of centres of spontaneity, having at least for 
one of its functions the origination of impulses, to 
which the contractions of the nectocalyx, under 
ordinary circumstances, are exclusively due. And 
this obvious deduction is confirmed (if it can be 
conceived to require confirmation) by the behaviour 
of the severed margin. This continues its rhyth- 
mical contractions with a vigour and a pertinacity 
not in the least impaired by its severance from the 
main organism, so that the contrast between the 
perfectly motionless swimming-bell and the active 
contractions of the thread-like portion which has 
just been removed from its margin is as striking a 
contrast as it is possible to conceive. Hence it is 
not surprising that if the margin be left im situ, 
while other portions of the swimming-bell are 
mutilated to any extent, the spontaneity of the 
animal is not at all interfered with. For instance, 
if the equator of any individual belonging to the 
