AN ANIMAL ROLLED INTO A BALL. 209 



become entangled among the spines, and passing it 

 down the sides of the body until it can be dropped 

 into the water. 



The shell of the animal, like a terrestrial globe, 

 is marked with meridians, ten of them extending 

 from pole to pole, or from the top to the bottom of 

 the sea urchin. Each of these meridians consists of 

 double rows of plates, which fit one another closely 

 and firmly. Five of these meridians are called " r.m- 

 bulacral areas," or walking parts, for through holes in 

 the plates extend tubes with suckers at the ends that 

 serve the animal as limbs and feet. Between each 

 two of these walking parts is another and wider 

 meridional space which is called " inter-ambulacral," 

 or between walking parts, which bears spines instead 

 of tube Hmbs. 



As a sea urchin has legs all around his body, it 

 really does not matter whether he walks upright, on 

 his side, or upside down, or turns himself, as he some- 

 times does, like a ball rolling slowly along, over and 

 over as he advances. 



The mouth, situated at the bottom of this strange 

 animal, has no less than five jaws, each provided with 

 a long, projecting, movable tooth. A complicated 

 muscular system works the jaws up and down and 

 across each other, so that a better mill for grinding up 

 the sea urchin's food could not be invented. Nor is 

 this all or the strangest part of it, for these same jaws 

 are able to hollow out homes for the animals in solid 

 rock, in sandstone, and the hardest granite. That 

 they do it no one can doubt ; how they do it no one 



