138 University of California Pnblications in Zoology. [Vol. 4 



on its back, and a small object, as a pebble, was placed on the 

 ventral surface of a ray. This was seized by the tube feet. In 

 a certain starfish this determined five times in succession the 

 direction of the turning, — the tube feet of all the rays at once 

 inclining toward the object, so that the starfish turned in that 

 direction. The pebble was placed in a different position in each 

 case. In many other specimens such an object had no effect in 

 determining the direction of turning. 



(7) Bays that first become attached by their tube feet. — In 

 many cases several or all of the rays come in contact by their 

 dorsal surfaces with the bottom at about the same time. The 

 tube feet of these rays then feel about, and some of them finally 

 become attached. Up to this time the different rays have acted 

 independently, each seeking for a hold. But as soon as the suck- 

 ers of one or two rays are attached, one often sees all the other 

 tube feet cease their irregular movements ; they all incline toward 

 the attached rays. The direction of the impulse has been de- 

 termined, and the starfish now rights itself by turning toward 

 the attached rays. 



The action of this factor is often prevented or overcome by 

 that of others. One frequently sees two rays become attached in 

 a manner that would be most convenient for turning. Neverthe- 

 less, the other rays continue their searching, take hold, and may 

 finally determine the turning, — the rays first attached being 

 released. We shall later see certain reasons for this. 



The rays that first come in contact with the bottom are of 

 course likely, other things being equal, to be the first that be- 

 come attached, so that factors (4) and (7) work together. But 

 this is by no means always the case. Sometimes the rays that 

 first come in contact do not find the bottom with their tube feet 

 until after the later rays have done so. The result depends on 

 the more or less independent activity of the rays and of the tube 

 feet ; both are variable. 



(8) Number of opposed rays that become attached. — Some- 

 times on one side of the disk a single ray may be attached, on 

 the opposite side two are attached, tending to turn the animal in 

 the opposite direction from the first ray. In such cases, other 

 things being equal, the side having fewer rays attached yields. 



