142 THE ANIMALS AND MAN 



animal. The starfish cannot see with this "eye;" it can 

 only distinguish between light and darkness. On the under 

 side the mouth is in the center, and from it along each ray 

 runs a groove. In each groove may be seen two double 

 rows of soft, tubular processes with sucker-like tips called 

 the tube-feet. These are the organs of locomotion. If 

 live starfishes can be watched the slow locomotion by means 

 of the tube-feet may be seen, and perhaps also the peculiar 

 mode of taking food. Starfishes are carnivorous, feeding 

 on crabs, snails, and the like. If the live prey is too large 

 to be taken into the mouth it is surrounded by the stomach, 

 which is pushed outward for this purpose. It secrets fluids 

 which kill the prey, after which the soft parts are digested. 



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. 57). Some have the spaces between 

 the rays filled out nearly to the tips of the arms, making 

 the animal simply a pentagonal disk. Starfishes are able 

 to regenerate 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! 



Starfishes hatch from eggs, 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. 



The sea-urchins, of which more than three hundred 

 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 

 removed. Around the mouth, which is at the center of the 

 under side, are five strong teeth. Like the starfishes, the 



