OCEAN ANIMALS: SPONGES, SEA-ANEMONES, ETC. 137 



Starfishes hatch from ecjgs, and in their early stages 

 are very different in appearance from the adults, being 

 more or less ellipsoidal in shape, and having many cilia 

 on the outer surface. They swim freely about in the sea, 

 feeding on microscopic organisms. In size starfishes vary 

 from a fraction of an inch in diameter to three feet. They 

 are yellow or red, or brown or purple, and the number of 

 rays varies from five to thirty or more in different kinds 

 (fig. 97). Some have the spaces between the rays filled 

 out nearly to the tips of the arms, making the animal 



Fig. 98. — A sea-urchin, SirongylocentrotJis franciscamts. (One-half natural 

 size; from specimen from Bay of Monterey, Calif.) 



simply a pentagonal disk. Starfishes are able to re- 

 generate a lost ray — that is, if one or more rays are bitten 

 off by enemies, new ones grow out in their places. I 

 once found a starfish in Samoa which was regenerating 

 four new rays and the central disk from a single old ray! 

 The sea-urchins (fig. 98), of which more than three hun- 

 dred species are known, while without arms or rays yet show 

 their radiate structure in having the tube-feet arranged in 

 five rows radiating from the center. This can be seen in a 

 "shell " or body-wall, from which the spines have been 



