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it takes the same course aa a starfish. This ease is oited since the 

 spines of the sea urchin do not attach and their behavior in this con- 

 nection indio.itss a rathar striking similarity between the physiology 

 of the spine and that of the tube foot* 



The value of the "deviation push* of this specimen, was found 

 to average 15 g. This was increased to 17 g when a load (about 40 g) 

 was placed on the dorsal side of the animal. The "pulling ability" was 

 found to be (average of 6 trials) 10 g unloaded and 15 g loaded. Allow- 

 ing for a certain amount of fatigue in the later trials the "pulling 

 ability" was found to be approximately equal to the "deviation push". 



The same relationship seams to nold with Pyonopodia. As 

 seen above the pulling ability averages 47 g. the deviation reaction 

 (average of four trials 60 g 45 g 60 g 30 g) is 48g. These are in- 

 creased to V2 and 105 g respectively by loaning the animal with 80 g. 

 of glass-flare* If the animal is placed on sand the values are similarly 

 related to each otli.sr but are reduced as follows* Pulling 15 fim, pull- 

 loaaed -with 80 gnu 32 gm, deviation 29 gm, deviation loaded 35 cm. 



Due to the fact that Pisa a tor and Asterjna are able to pull 

 very much harder in proportion to their size than are the sea urchin 

 or Pyonopodia and since this pull is due to the constant increase of the 

 attaching tendency correlated with the pull, we find that the deviation 

 push correlates more closely with the pulling ability on sand, taking 

 into account of course its lesser frictional coefficient, than with the 

 pulling reaction on a solid substrate* The average deviation push of 

 Pisaster (about 15 cm in diameter) is 20 g. on a solid substrate and 6 g 

 on sanJ. Agtarina (8 cm) on a solid substrate exerts a deviation push of 

 4 g t but with 4 g. weight on ita back this is increased to 6 g. This is 

 ~*ith the pulling ability of a larger specimen on sand of 7.5g. 



