246 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
the case of all the specimens thus operated upon, 
the result was the same, and corresponded precisely 
with that which I have obtained in the case of 
marine species; that is to say, the operation pro- 
duces immediate, total, and permanent paralysis of 
the nectocalyx, while the severed margin continues 
to pulsate for two or three days. The excitability 
of a nectocalyx thus mutilated persists for a day or 
two, and then gradually dies out, thus also resem- 
bling the case of the marine naked-eyed Medusz. 
More particularly, the excitability resembles that 
of those marine species which sometimes respond to 
a single stimulation with two or three successive 
contractions. 
“A point of specially physiological interest may 
be here noticed. In its unmutilated state the fresh- 
water Medusa exhibits the power of localizing with 
its manubrium a seat of stimulation situated in the 
bell; that is to say, when a part of the bell is 
nipped with the forceps, or otherwise irritated, the 
free end of the manubrium is moved over and 
applied to the part irritated. So far the movement 
of localization is precisely similar to that which I 
have previously described as occurring in Tiaropsis 
indicans (Phil. Trans., vol. elxviu.). But further 
than this, I find a curious difference. For while 
in Tiaropsis indicans these movements of loealiza- 
tion continue unimpaired after the margin of the 
bell has been removed, and will be ineffectually 
attempted even after the bell is almost entirely cut 
away from its connections with the manubrium, in 
the fresh-water Medusa these movements of localiza- 
