THE ECHINODERMS 357 



with the result that the currents of water ( 338) are stopped 

 and the animal within the shell is killed by suffocation. The 

 shell then gapes open, the starfish's stomach pours in its 

 digestive secretion, the tissues of the oyster are dissolved 

 (digested) while in its own shell, then the digested substances 

 are absorbed by the starfish. Finally, the starfish withdraws 

 its stomach into its own body and leaves the empty shell of 

 the oyster. 



Against such a remarkable enemy an oyster or clam is 

 completely helpless, for the hard shell which protects against 

 enemies which feed like ordinary animals, is of little avail 

 against an animal peculiarly adapted for suffocating the 

 oyster and then digesting its tissues before taking them as 

 food. It is only among the starfishes that there are animals 

 able to evert their stomachs for the purpose of surrounding 

 and digesting food which is too large to be taken into the 

 mouth. 



Owners of oyster-beds now make systematic efforts to 

 destroy starfishes. Formerly, the oyster fishermen used to 

 break the arms from starfishes and throw them back into the 

 sea; but the discovery that starfishes have the ability to 

 regrow or regenerate, and that each of many pieces may 

 soon form a perfect starfish, showed that breaking them into 

 pieces simply multiplied them. Now when starfishes are 

 caught by oyster-dredges, they are killed instantly by boiling 

 water, or they are left on dry land where they die quickly. 



Classes of Echinoderms 



Crinoidea sea-lilies or crinoids. 

 Asteroidea starfishes. 

 Ophiuroidea brittle stars. 

 Echinoidea sea-urchins. 

 Holothurioidea sea-cucumbers. 



