Confining our attention under this heading to the naked-eyed Medusæ, I find that the following proposition applies to every species of the group which I have as yet had the opportunity of examining: _Excision 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 Medusæ, 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.[6] Indeed, I do not know of any case in the animal kingdom where the removal of a centre of spontaneity causes so sudden and so complete a paralysis 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 performed 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. [6] I 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 sheet of contractile tissue lining the nectocalyx.