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 ambulacral feet have been 
still more reduced to rudiments, and are of no use 
at all, either 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.—A pedicel of Astropecten Fig. 45.—The same, showing the 
(magnified), showing the absence method of extemporizing a 
of any terminal sucker, 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 flat horizontal surfaces. When it 
desires to move rapidly, it uses two of its opposite 
arms upon the horizontal floor with a motion like 
swimming (Fig. 46); at each stroke the animal 
