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HOW DO STARFISHES OPEN OYSTERS? 



margin, and less laminated than those at Naples, such places as those 

 just described, made by breaking away portions of the shell, will 

 naturally not be found. On them, therefore, it will not be possible 

 to ascertain the spot where the starfish has taken hold. 



Thus, I have come to the conclusion that the starfish opens the shell 

 of his victim by force, and I must now bring forward proof that the 

 animal does actually possess sufficient strength for the purpose. To 

 do this, the strength of a moderate-sized starfish must first of all be 

 measured. As may be seen from Figs. 3, 4, and 5, the starfish does 

 not use all its tube-feet in opening a bivalve, but, at most, only those 

 on the central halves of the arms. In measuring the strength exerted. 



Fig. 8 



the other tube-feet, therefore, must be left out. I succeeded in doing 

 this in the following way : — 



A hole was cut in a board of a size corresponding approximately to 

 that of the portion of the starfish which comes into play in opening 

 molluscs. One side of the board was covered with a glass plate (in 

 which was a corresponding hole), giving the starfish the opportunity 

 of attaching itself firmly with the remainder of its tube-feet. An 

 Asterias was now enticed with a bivalve on to the board, and the 

 mollusc offered to him through the hole in the board. The bivalve 

 itself was bound round with a string, which was passed, by means of a 

 pulley, over the edge of the dish, and carried at its end a board upon 

 which weights could be placed. After the starfish had taken the 

 mollusc, weights were put on until it let it go. This happened with 

 a weight of 1350 grams. This figure does not, however, represent 



