36  JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
supply of their locomotor centres scattered through 
the general contractile tissue of their swimming 
organs. But although the locomotor centres of a 
covered-eyed Medusa are thus, generally speaking, 
more diffused than are those of a naked-eyed 
Medusa, if we consider the organism as a whole, 
the locomotor centres in the margin of a covered- 
eyed Medusa are less diffused than are those in the 
margin of a naked-eyed Medusa. In no case does 
the excision of the margin of a swimming organ 
produce any effect upon the movements of the 
manubrium, | 
