STEREOTROPISM AS A FUNCTION OF NEUROMUSCULAR 



ORGANIZATION. 



By a. R. MOORE. 



{From the Physiological Laboratory of Rutgers College, New Brutisuick, 

 N. J., and the Marine Biological Laboratory, Woods Hole, Mass.) 



(Received for publication, January 15, 1920.) 



When a starfish is put on its back, it rights itself and, though it 

 has been known that this is a case of stereotropism, the details of the 

 reaction have thus far not been accounted for. Thus it has happened 

 that some authors have spoken of this reaction as a case of ''trial and 

 error" on the part of the animal. The experiments described in this 

 paper show that the righting reaction of the starfish is a necessary 

 consequence of the neuromuscular organization of the ray and that 

 no room is left for the assumption of "trial and error." 



It usually has been assumed by writers on the subject that the 

 movements of the starfish, including those of righting, are accom- 

 pHshed entirely by the tube feet.^ The writer has observed, how- 

 ever, that nicotinized individuals, in which all the tube feet except a 

 few at the tip of the ray — the "feelers" — are retracted and inactive, 

 begin righting movements, and in some cases complete the righting 

 in course of half an hour or so. This indicates that the essential 

 movements of righting can be accomphshed by means of the nerves 

 and muscles of the arms themselves without the use of the tube feet 

 as locomotor organs. It therefore follows that the functioning of 

 the Asterias ray in righting is based on principles similar to those 

 which operate in the case of ophiurans. It seems probable that 

 the principal role of the tube feet of Asterias in normal righting lies 

 in their service as delicate sense organs, making possible quick and 

 accurate functioning of the ray musculature. They also act as 

 accessory locomotor organs and contribute to the speed of the 

 somersault. 



^ Belonius, P., De Aquatibus, Paris, 1553. 



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