MR. G-. J. ROMANES ON THE LOCOMOTOR SYSTEM OE MEDUSAE. 
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. 
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 severed margin. 
This continues its rhythmical 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 genus 
Sarsia (fig. 1, p. 27 6) be cut completely through, so that the swimming-bell instead of being- 
closed at the top is converted into an open tube, this open tube continues its rhythmical 
contractions for an indefinitely long time, notwithstanding the organism so mutilated is, 
of course, unable to progress. Thus it is a matter of no consequence how small or how 
large a portion of contractile tissue is left adhering to the severed margin of the swim- 
ming-bell ; for whether this portion be large or small, the locomotor centres contained in 
the margin are alike sufficient to supply the stimulus to contraction. Indeed if only 
the tiniest piece of contractile tissue be left adhering to a single eye-speck cut out 
of the bell of Sarsia , this tiny piece of tissue in this isolated state will continue its 
contractions for hours or even for days. 
This observation, then, on the effect of removing the extreme periphery of necto- 
calyces, as it undoubtedly demonstrates the presence of an intensely localized system of 
locomotor centres in at least some of the Medusae, and as it thus opens the way for a 
great amount of further experimental research — this observation I shall afterwards speak 
of as the fundamental observation. I very much regret to say, however, that, in conse- 
quence of my having been this year engaged in another line of experimental research 
which necessitated my constant residence in one locality, I have hitherto been able to make 
this fundamental observation only in the case of six genera of the naked-eyed Medusae. 
As yet, therefore, it would be premature to predict with much confidence that subse- 
quent experiments will prove the locomotor centres to be equally localized in the case 
of all the naked-eyed Medusae. Nevertheless, as the genera which I have already sub- 
mitted to the simple operation just described are genera which happen to present the 
most extreme differences as to form, size, and structure that occur among the true 
Medusae, I think my results afford very good analogical grounds for expecting that 
future researches will prove the exclusive localization of spontaneity in the marginal 
