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MR. a. J. ROMANES ON THE LOCOMOTOR SYSTEM OE MEDTJSiE. 
invariably followed by immediate, total, and permanent paralysis of the entire structure. 
I say almost uniformly true , for it will be remembered that in one individual instance 
three distinct centres of spontaneity remained after removal of all the marginal tissue. 
This individual instance occurred in a medusid belonging to the species Staurophora 
laciniata ; and as this is the species which I found best suited for my experiments in 
electrotonus, I have had occasion to remove the marginal tissue from many scores 
of individuals belonging to it, and have never met with any but this one exception to a 
rule shown to be general by hundreds of experiments on the thirteen species named. 
With the covered-eyed Medusae the case is not so definite ; for although centres of 
spontaneity unquestionably occur in the margins of all the members of this group which 
I have examined, these are not always, nor even generally, the only centres present. 
Looking to the order as a whole, so far as my experience extends, it is the exception and 
not the rule to obtain complete and permanent paralysis by excision of the marginal 
tissue of individuals composing this group. Considerable differences, however, are 
manifested by different species in this respect. 
In Sarsia I find that a higher degree of paralyzing effect is produced by cutting out 
the four eye-specks alone than is produced by cutting out the intertentacular tissue 
alone; and I therefore conclude that the eye-specks are the principal seats of sponta- 
neity. But they are far from being the only seats of spontaneity ; for even the smallest 
atom of intertentacular tissue is sufficient, in the case of vigorous specimens, to animate 
the entire nectocalyx. 
In none of the covered-eyed Medusae examined have I found any evidence of the 
marginal tissue between the lithocysts being endowed with spontaneity. On the 
contrary, in the case of Aurelia aurita , which from its flat shape admits of fairer experi- 
mentation in this connexion than do any of the other genera examined, it is quite 
certain that all the spontaneity of the margin, and so, in most cases, of the whole animal, 
is concentrated in the eight lithocysts. 
All Medusae, after being paralyzed by the loss of their marginal centres, respond to 
all kinds of stimulation, and this by performing whatever action they would have 
performed in response to the stimulation employed had they been in their perfect state. 
Different species, however, manifest different degrees of irritability in their behaviour 
towards stimulation, although in all cases the degree of irritability is high. 
Regarding electrical stimulation, both severed margins and the swimming-organs from 
which they have been taken are responsive both to the constant and to the induced 
current ; but while severed margins remain responsive to weak induction-shocks after 
they cease to be affected by make and break of strong constant currents, the reverse 
is true of the mutilated swimming-organs ; for, in the case of Sarsia , these remain 
responsive to make and break of the constant current even after they cease to respond 
to Faradaic electricity with the secondary coil pushed to zero (one cell). 
The presence of excitable tracts has been proved in the case of Sarsia by means of 
electrical stimulation. The results are, that there is a progressive increase of excitability. 
