-36- 



are essentially the same as those which determine the anterior 

 as the impulse is being foriae* and operate through the 

 same mechanism, .vith respect to the sense of the reaction which thy 

 elicit thay can therefore be grouped into (1) the positive and 

 $2) the negative. With respect to the receptors on whicn they 

 perate they can be grouped into (1) those acting a the dermis and 

 directly on the tube feet and(*)those acting on the terminal tube 

 feet of the rays (or eye spot which is a modified tube foot). 

 Such Common factors in the environment of the starfish Contact 

 chemical stimulation and g light have been seen to affect the 

 Unified impulse in the uncoordinated starfish in one or more 

 of the above mentioned ways and it will be seen from the following 



that they affect the coordinated impulse once it is started in 



' 

 the same sense and in the same way* 



Po si tive reaction to r contact 



tOhen. 



$ one of the ray tips of starfish migrating actively 

 under the influence of the "unified impulse" bruslWagainst the 

 side of the aquarium the tube feet at the end of this ray luve 

 been seen *p stretch out actively, those behind them coordinated and 

 soon the direction cf locomotion changed and the animal was 

 walking up the side of the aquarium 



Iterative reaction to_ con tact 



On pinching one of the rays of such a,locomotor starfish, 

 serial retraction or inaotivation of the tube feet will ensue 

 spreading more or less among the tube feet, but last and least 

 effectively to the tube feet of the opposite side of the starfish. 

 The lalle-r y-^-wie <a4\ViTy first and orient mor 



nearly in the direction of the ray on which they are borne i.e. 

 away from the source of stimulation. The tube feet behind these 

 coordinate themselves with them in the same direction so that the 

 coordinated impulse (to ;# away from the stimulus ) spreads 



