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 

 Medusae 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 sevej-ed 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 in 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 



