The Sea - Urohin. 35 



sea-urchia walk oa the sackers, while the spines reach oat 

 so far beyond them ? To understand this and to know 

 how beautiful the little creature really is, we ought to 

 have a living one in a glass dish or jar of sea water, and 

 watch it press out its tube-feet till they are waving on 

 every side, far beyond the spines, like threads of spun 



' - ■*■■-■ %. ■ ' j._". *» "■''. •' -■■'■►1 



■w - -- ■ ,tj^ • -, 





Fig 2. Fig. 3. 



glass. It stretches them out to their fullest extent, fast- 

 ens the suckers, then pulls the body up to them. We 

 touch it, and instantly every one is drawn safely in be- 

 hind the barrier of sentinel spines. 



Since the tube-feet of the sea-urchin are forced out in 

 the same way as those of the star-fish, we see the need of 

 a sieve to filter the water that does this work. We find 

 it, a five-sided, spongy body (Fig. 3, a), at one side of 

 the little disk in the center of the back. 



