172 University of California Puhlications in Zoology. [Vol. 4 



the righting reaction of the Planarian, as described by Pearl 

 (1903) . But the starfish is a much more complex animal than the 

 flatworm, and its righting- reaction is much less simply brought 

 about. Careful examination of the facts show that the above, 

 suggestion does not hold for the starfish. Certain rays or parts 

 of rays are frequently compelled, in order to facilitate the gen- 

 eral result, to move in ways that do not tend to restore their own 

 natural position, or that may indeed have the opposite effect. In 

 the complicated actions by which the righting is brought about 

 there are many that have no direct tendency to restore the part 

 that is acting to the usual position. Thus, when the starfish at- 

 taches itself by four of the rays, as in fig. 16, there is usually a 

 complicated "walking" process before the natural position is re- 

 gained. The two anterior rays (those on the side toward which 

 the animal is turning) begin to walk backward, while the two pos- 

 terior ones begin to walk forward. Soon the two meet, where- 

 upon the posterior rays release a sufficient number of their suck- 

 ers so that they can curve upward while still retaining their hold 

 at the tips; they thus permit the anterior rays to walk beneath 

 them, and they re-attach themselves progressively anew as the 

 action is completed. This remarkable walking in opposite direc- 

 tions by the two sets of rays is necessary for the final regaining 

 of the normal position, but does not tend directly to restore these 

 rays themselves to that position. 



Often, indeed, a given ray that has partly regained its normal 

 position is compelled, in the interest of the reaction as a whole, to 

 undo what it has already accomplished, to replace itself in the ab- 

 normal position after it has gained the normal one. Thus, often 

 certain rays, as h and c, will have twisted and attached themselves 

 so that the ventral surfaces are down (normal position). Now, 

 certain other rays, as a and e, likewise attach themselves, and an 

 impulse to turn toward a — e appears. Thereupon the rays h — c 

 release and untwist, taking anew the abnormal position; then 

 bend over toward a — e, till the normal position is restored in a 

 new way. Again, when the starfish turns on three contiguous 

 attached rays (as a, e, d), the middle one of these rays often at 

 first doubles directly back from the tip (not twisting to right or 

 left) so as to get its ventral side down for a considerable portion 



