152 Our Food Mollusks 



It has also been stated that they break off the edges of the 

 oyster's shell so as to make an opening to the interior. 

 A mere examination of the body of the starfish would 

 show this to be impossible. They have been thought to 

 kill their prey by some poison, and even to dissolve the 

 shell by some acid. 



The whole performance of disposing of the oyster 

 may be witnessed in an aquarium, and appears to be as 

 follows. Slowly creeping on to its victim, the starfish 

 wraps its rays about it, at the same time taking up such 

 a position that its mouth is nearly opposite the shell 

 edges. The oyster responds even to this cautious and 

 gentle caress by contracting its adductor muscle and clos- 

 ing its shell. The contraction of the muscle may be 

 made so powerful that if one should attempt to pry the 

 valves apart, the tough shell might break without caus- 

 ing the muscle to yield. 



The starfish cannot match such a sudden demonstra- 

 tion of muscular strength. It simply camps on the trail 

 in oriental fashion. If it cannot win now, it may later, 

 and it invariably wins. Scores of its feet are attached to 

 each valve of the shell. Apparently they contract so as 

 to exert a gentle pull in opposite directions, and against 

 the oyster's powerful muscle, which in time becomes 

 fatigued. Eventually it yields altogether, incapable of 

 further effort, and the valves of the shell gape open. It 

 is possible that the sucker feet have each in turn en- 

 joyed periods of rest during this siege. At any rate, 

 their gentle insistence conquers in the end. 



The shell valve will not open far, and the digestible 

 part of the mollusk's body is still some distance away 

 but not out of reach. It is a physical impossibility for 

 the captor to get the great mass of food into its 



