THE STAR-FISHES. 153 
used for the purpose of locomotion. When the pressure upon 
the bag of fluid is relieved, the water returns back to its recep- 
tacle, and the cylinder becomes limp, and contracts. In spite of 
the great number of these ambulacral organs, the star-fish does 
UPPER AND UNDER SURFACE OF A STAR-FISH. 
(Astropecten spinulosus.) 
not move any quicker than other inhabitants of salt water which 
possess only one foot or none at all. 
If you turn an asteria over upon its back, at first it remains 
motionless, with its feet contracted; soon, however, it pushes them 
out like so many little worms, spreading them here and there 
as if feeling for the ground; it then inclines them towards the 
bottom of the vase, and fixes them one after the other; when it 
