274 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
like arms under the inverted disc, and heaving the 
whole body over by the mere muscularity of these 
organs. The common Star-fish, however, experiences 
more difficulty, and executes the manceuvre mainly 
by means of its suckers. That is to say, it twists 
round the tip of one or more of its rays (Fig. 47) 
until the ambulacral feet there situated are able to 
Fig. 47.—Natural righting mcvements of common Star-fish. 
get a firm hold of the floor of the tank (a) ; then, by 
a successive and similar action of the ambulacral 
feet further back in the series, the whole ray is 
twisted round (b), so that the ambulacral surface 
of the end is applied flat against the floor of the 
tank (c). The manceuvre continuing, the semi-turn 
