274 .IFXLY-FISH, STAR-FISH, AND SEA-URCHINS. 



like arms under the inverted disc, and heaving the 

 whole bod}^ over by the mere muscularit}^ of these 

 organs. The common Star-fish, however, experiences 

 more difficult}', and executes the manoeuvre 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 rmvements of ronimon 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 

 cf the end is applied flat against the floor of the 

 tank (c). The manoeuvre continuing, the semi-turn 



