so JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 



one cannot here, as with the naked-eyed Medusae, 

 predict with any great confidence what will be the 

 immediate result of any particular experiment. 

 Further, although such mutilation of an umbrella is 

 usually followed by a paralysis as sudden and 

 marked as that which follows such mutilation of a 

 swimming-bell, the paralysis of the former differs 

 from the paralysis of the latter, in that it is very 

 seldom permanent. After periods varying from a 

 few seconds to half an hour or more, occasional 

 weak and unrhythmical contractions begin to mani- 

 fest themselves, or the contractions may even be 

 resumed with but little apparent change in their 

 character and frequency. The condition of the 

 animal before the operation, as to general vigour, 

 etc., appears to be one factor in determining the 

 effect of the operation ; but this is very far from 

 being the only factor. 



Upon the whole, then, although in the species of 

 covered-eyed Medusiie which I have as yet had the 

 opportunity of examining, the effects which result 

 from excising the margins of umbrellas are such as 

 to warrant nie in saying that the main supply of 

 locomotor centres appears to be usually situated in 

 that part of these organs, these effects are neverthe- 

 less such as to compel me at the same time to con- 

 clude that the locomotor centres of the covered-eyed 

 Medusc© are more diffused or seo'rea^ated than are 

 those of the naked-eyed Medusse. Lastly, it should 

 be stated that all the species of covered-eyed 

 MedustB resemble all the species of naked-eyed 

 Medusse, in that their members will endure any 



