30 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
one cannot here, as with the naked-eyed Medusa, 
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 Medusze 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 me 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 
Medusze are more diffused or segregated than are 
those of the naked-eyed Medusz. Lastly, it should 
be stated that all the species of covered-eyed 
Meduse resemble all the species of naked-eyed 
Meduse, in that their members will endure any 
