142 University of California Publications in Zoology. [Vol. 4 



times when a starfish is turned on its back, it is found to have 

 at the beginning a definite set toward turning in a certain way 

 (see p. 132). The unified impulse is present at the beginning: 

 certain rays bend down, twist, take hold of the bottom and pull, 

 while others rise up and go over. There is no hesitation or waver- 

 ing in the role to be played by each part, from start to finish. 

 This is sometimes found to be the case even with a starfish that 

 has not been under experimentation before, so that the direction 

 of the impulse has not been determined in the way described 

 under (13). There are doubtless other ways in which a per- 

 sistent tendency toward a certain direction of turning may be 

 determined before the animal is placed on its back. It is possible 

 that the direction of locomotion just before the starfish is turned 

 may act as such a determining factor. It would not be surprising 

 if it should be found that the starfish tends to turn toward those 

 rays which were moving in advance at the time the animal was 

 inverted. I regret that I did not test this by experimentation; 

 it did not occur to me as a possible factor till I had left the shore. 



(15) Permanent tendency to turn toward a certain pair of 

 rays. — Will repeated experiments on the same starfish show a 

 tendency to turn in any definite way ? This question was studied 

 in a number of specimens. They were allowed to turn at inter- 

 vals of several minutes on a plane surface, in diffused light, so 

 that the external factors were made as nearly uniform as possible. 

 Moreover, the position was varied in different experiments so 

 that the rays of a given starfish had different relations in each 

 case to the surroundings. The results of these experiments 

 are given in the following. Since in most cases a starfish turned 

 by using a certain pair of rays to attach and turn itself, while 

 the other three arms were merely raised and went over, the 

 method of righting can be given by specifying the two rays that 

 were thus employed. Thus, if in a given case the starfish 

 attached itself by the rays a and h (fig. 10), and pulled itself 

 over by their aid, the record simply states that it "turned on 

 a and i," or that "a and h were used." If there were no pre- 

 dilection in favor of certain rays, we should expect each to be 

 used an approximately equal number of times. 



The actual results are as follows : 



