ME. a. J. EOMANES ON THE LOCOMOTOE SYSTEM OE MEDUSAE. 
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species, the action, however, in any given case always precisely resembling that which 
the unmutilated nectocalyx would have performed if irritated in the same way. Now 
Sarsia , in common with all the covered-eyed genera examined, when in the unmutilated 
state always endeavours to swim away from a source of irritation or alarm, and never 
performs any other motions ; so that all the cases conform to this one simple rule : — Every 
Medusa, when its centres of spontaneity have been removed, responds to a single stimu- 
lation by once performing that action which it would have performed in response to that 
stimulation had its centres of spontaneity still been intact. 
Different species of Medusae exhibit different degrees of irritability in responding to 
stimuli ; but in all the cases I have met with the degree of irritability is remarkably 
high. Thus Aurelia aurita is perhaps, of all the species I have experimented upon, 
the least sensitive to stimulation ; yet if a narrow strip of tissue without any centres of 
spontaneity be taken from this animal and made to support in the air the weight of 
another strip which is spontaneously contracting, the slight amount of friction caused 
by the one gelatinous surface passing over the other upon each contraction of the 
uppermost strip is sufficient to determine a responsive contraction in the undermost 
strip. In some of the other species of covered-eyed Medusae I have seen responsive 
contractions of the whole gonocalyx follow upon the exceedingly slight stimulus caused 
by a single drop of sea-water let fall upon the irritable surface from the height of one 
inch. 
§ 2. Electrical Stimulation (A). — All parts of all the Medusae I have examined are 
highly sensitive to electrical stimulation, both of the constant and of the induced 
currents. There is thus a large field for experimental research here opened up, and 
one upon which I have bestowed a considerable amount of labour. In now giving an 
abstract of some of the results hitherto yielded, it is only right that I should take the 
opportunity thus afforded of expressing my obligations and sincere thanks to my 
learned and highly esteemed friend Prof. Burdox-Saxdersox, but for whose prompt 
kindness in sending me all the electrical and various other apparatus in immediate 
answer to my numerous requests, it would have been impossible for me this year to 
have conducted, with any kind of completeness, the investigation which I undertook. 
As just stated, both the severed margin, or system of locomotor centres, and the 
swimming-organ from which these have been removed respond to stimulation both of 
the direct and of the induced currents. There is an important difference, however, 
between the behaviour of the severed margin and of the mutilated nectocalyx with 
reference to these two kinds of stimulation ; for while the former shows itself more 
sensitive to the induced shock than to the direct current, the reverse is true of the 
latter. That is to say, while the severed margin continues responsive even to weak 
induction-shocks after it has ceased to be affected either by make or break of the direct 
current, the mutilated nectocalyx continues responsive to make and break of the direct 
current after it has ceased to respond to the strongest induced shock, or even to 
Paradaic electricity with the secondary coil pushed to zero (one Daniell’s cell in all 
