50 



Of active locomotion, the rays that were anterior will crawl 

 on into the tubes while the ray that were posterior will 

 start to crawl out of them* Usually before one of these rays 

 f leaves go its hold on the float, or at any rate soon afterward, 

 the impulse in thia ray is reversed and it la aeen to be 

 active in its migration toward its own tip, regardless of the 

 direction in which the other rays are crawling. If now the 

 tubes are removed from their floats and set on the bottom of the 

 aquarium, -vith the tip of a ray in each, the coordimt i impulse 

 is quickly re -established and the animal migrates back ad forth 

 within the confines set up by the ends of the tubes* After 

 extensive experimentation with the reactions of Pisaster in 

 these floats, I have very seldom seen the unified impulse appear 

 when the floats were free to move separately, and having 

 appeared it seldom lasts more than a minute or two* It appears 

 quite promptly and lasts for a long time ( an hour or more) 

 if the tubes are not separately moveable but are resting on the 

 bottom of the aquarium* 



Supplementary experiments were carried on with flat free 

 swinging substrates* One, two or three of the rays were put on 

 the substrate and the others allowed to han^ over the iide on 

 the floor of the aquarium half a cm* below* The part, on one 

 substrate was often seen to migrate while that on the other 

 remained stationary, and they were not infrequently seen to 

 migrate in different directions. Of course this would not be 

 likely to happen if the substrates were not separately moveable, 



From the above experiments it would seem that a factor in 

 the unity of the coordinated impulse is the unity of the 

 substrate or rather of the animals relation to the 



