STAEFISH 113 



of motion ? Can it swim ? Does it always move 

 with the same ray ahead ? Study the movements 

 of a single ambulacral foot. Are all of the feet 

 used for progression ? Are the rays flexible ? If 

 so, in what directions do they bend? Turn a 

 specimen over on its aboral surface. Through 

 what motions does it go in righting itself ? Does 

 the starfish lose the power of locomotion when 

 removed from the water ? Can it bend its rays 

 under such circumstances? 



B. Nutrition. — Look along the wharves at low tide for 

 clusters of mussels on which starfishes may be 

 found. Examine such a starfish to see if the 

 cardiac portion of the stomach is not protrud- 

 ing and partially enwrapping a mussel. See if 

 you can find that the stomach or disk moves at 

 all. Quickly pick the starfish off the mussel 

 and watch the withdrawal of the stomach into 

 the body. How soon does it take place? In 

 studying the internal anatomy, did you find any 

 structures which could bring about this move- 

 ment of the cardiac pouches ? Do you find any 

 specimens which though not feeding have the 

 stomach protruding? Examine the stomachs of 

 a number of fresh or alcoholic specimens for the 

 shells of small molluscs. Do these shells bear 

 any evidence of having been broken to pieces 

 in the body of the starfish ? Judging from the 

 structure of the mouth-parts and of the stomach, 

 what kind of food is the animal fitted to eat ? 

 Starfishes kept in an aquarium may sometimes 

 be found feeding on other small animals kept 

 in the same tank. 

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