EXPERIMENTS ON ECHINODERMS 63 



destroy the nervous connection between the arms, for 

 instance, by making two incisions at a and 6, Fig. 18, 

 this cooperation of the arms ceases. The normal 

 starfish requires but a few minutes to turn over, but 

 the specimen represented in Fig. 18 remained on its 



FIG. 18. THE SAME EXPERIMENT ON A STARFISH WHOSE NERVE-RING 

 HAS BEEN SEVERED IN TWO PLACES (a AND b). 



The right and left arms are consequently no longer connected nervously. If such an ani- 

 mal is laid on its back, the tube-feet of four or even all the arms in most cases tug 

 simultaneously. This prevents the animal from righting itself. 



back the whole afternoon, although the arms were 

 struggling constantly to right it. The experiments 

 seem to indicate that 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. This inhibition ceases when the nervous con- 

 nection between the single arms is broken. Romanes 



