-21- 



g the stop reflex (Pulling ability) 



Hot only does the ratio of strength of attachment to strength 

 Of pull # vary between different species, but also the pulling ability 



# Soheinmetz (1896) states that a starfish (Aetsrias gluoialis) is 

 able to exert a pull of 1360 g in opening a bivalve, to which pull the 

 bivalve gave way, under experimental conditions in short order* His 

 method of measuring the pull, however, was directed rather to measure 

 the strength of the attaching reflex because he recorded the pull that 

 caused a starfish to let loose its prey and not the puU which would 

 overcome a maximal contraction of the longitudinal musculature of the 

 tube feet* The amount of pull exerted by a tube foot, under conditions 

 of locomotion at least, is aa we have seen from one -half to one-third 

 of the strength of attachment at that moment* Soheinmetz in this 

 interesting paper also lists five ways in which the starfish has been 

 supposed to open Oysters; : (1) by taking the mollusc by surprise, (2) 

 by besetting the oyster 90 long that it would be compelled by hunger 

 and want of air to open. (3) by hypnotizing the molluscs, (4) by boring 

 through their shell, (5) by poisoning them, all of which he shows are 

 fallacious* Beamur (1710) quotes Aristotle and Pliny as attributing 

 to the starfish a body heat, by which it kills its prey, derived no 

 doubt by poetic analogy from the stare of heaven* He himself believed 

 tint the starfish pries open the oyster with its oral spines and sucks 

 out the meat with its laouth* 



considered alone* Tor instance, a small specimen of Pisactar about 



12 cm in diameter was attached one noon to the recording spring and 

 induced to pull against it* During the whole afternoon the tension 

 varied between 40 g and 60 g* The drum was removed and the animal left 

 tugging at the thread all night* The next morning it was pulling in 

 the same direction but had advanced slightly* The tension during that 

 whole day varied from 95 to 190 g* There was much activity of the 

 tube feet when the animal was going forward or being pulled back by the 

 spring* When the animal was holding stationary tube feet were seen to 

 be arrested in the various phases of the step reflex so that only a 

 portion of them were extended forward at such an angle that they could 

 pull the animal forward* Toward evening the pulling increased and 

 somewhere between seven and nine p*m* reached a peak of 



