246 JELLY-FISH, STAR-FISH, AND SEA-URCHIXS. 



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 MedusiB. 

 More particularly, the excitability resembles that 

 of those marine species which sometimes respond to 

 a sinoie 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. clxvii.). But further 

 than this, I find a curious difference. For while 

 in Tiaropsis indicans these movements of localiza- 

 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- 



