COORDINATION AND RIGHTING IN THE STARFISH. 363 



in a normal starfish the stimulus produced by the pulling of two or 

 three arms in the same direction has an inhibitory effect on the 

 other arms." Again (p. 65), he explains the movement of a 

 starfish in a^'direction away from a ray which has been stimu- 

 lated by saying that "the feet of this arm are drawn in and the arm 

 becomes inactive," and "therefore, according to the parallelogram 

 of forces, a movement away from the point of stimulation will 

 take place." While stimulation of an arm may cause temporary 

 inactivity of the feet of that arm and this might aid in initiating 

 movement in the opposite direction (Moore, '10), the careful obser- 

 vations of Jennings ('07, p. 97) seem, however, to show that this 

 explanation is only partial. He remarks on this point: " It is pos- 

 sible that in some cases when one ray is stimulated locomotion 

 takes place entirely with the other rays, but such cases are very 

 rare ; though I have watched carefully for this, I have never seen 

 one. As a rule the walking away from the stimulated region is due, 

 like the usual locomotion of the starfish, to the cooperation and co- 

 ordination of the tube feet of all the rays .... The active 

 tube feet of all the rays are pushed forward in thedirection in which 

 the starfish is going; their suckers attach themselves, and by the 

 contraction of the tube feet . . . the starfish is carried forward, 

 the action of all the tube feet aiding in this." My own obser- 

 vations agree in this respect with those of Jennings. It is there- 

 fore evident that in locomotion as in righting an impulse is 

 established, by- which the different parts act in more or less 

 complete harmony toward the accomplishment of a certain 

 result. It is generally assumed, and is undoubtedly true, that 

 this unity of action is made possible by the mediation of the 

 nervous system. 



SECTION OF RADIAL NERVES. 



The question naturally arises, however, whether it is not 

 possible that an impulse toward the accomplishment of a definite 

 end might be 'established without nervous connection between 

 the different parts of the organism, just as an earthworm con- 

 tinues its coordinated locomotor contractions after section of 

 the ventral nerve cord, or indeed if the worm itself be cut entirely 

 through and the halves united by thread (Friedlander, 1888). 



