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



manner, by constricting the tube on one side after 

 it has brought this side into opposition with the 

 solid surface (Fig. 45). 



In the Brittle-stars the ambulacra! feet have been 

 still more reduced to rudiments, and are of no use 

 at all, cither as suckers or for assisting in locomotion. 

 These Star-fish have, therefore, adopted another 

 method of locomotion, and one which is a great 



Fig. 44. — .\ pedicel of Astropecten 

 (magnified), showing the absence 

 of any terminal sucker. 



Fig. 45.— The same, showing the 

 method of extemporizing a 

 sucker. 



improvement upon the slow crawling of other 

 members of the Star-fish group. The rays of the 

 Brittle-stars are very long, flexible, and muscular, 

 and by their combined action the animal is able 

 to shuffle along fiat horizontal surfaces. When it 

 desires to move rapidly, it uses two of its opposite 

 arms upon the horizontal floor with a motion like 

 46) ; at each stroke the animal 



swimming (Fi 



