DIRECTION OF LOCOMOTION OF THE STARFISH 5 



tively small specimens (from 5 cm. to 14.5 cm. in diameter) 

 were chosen; but except for this, no selection was made, further 

 than that care was taken to see that all individuals used w^ere 

 normally active and that all their arms were normally devel- 

 oped, specimens with one or more arms decidedly deficient in 

 size,'* or in any way noticeably abnormal, being rejected. The 

 method of procedure in the trials was as follows. When all 

 was ready the starfish was picked up and held inverted with 

 the aboral disc resting on the operator's finger tips. It was 

 held in this position usually from a half-minute to two minutes, 

 or until the arms of the starfish drooped down aborally. The 

 specimen was then placed oral side do^n in the center of the 

 dish of sea water, care being exercised to handle it, in so far as 

 possible, by the disc alone, in order to avoid the possibility of 

 an unequal stimulus which might result from handling the ani- 

 mal by the raj's. Furthermore, that any possible unilateral 

 stimulating effect of the environment might be eliminated, the 

 specimen was rotated one-fifth of its circumference in each suc- 

 ceeding trial, the arms a, b, c, et cetera, being turned toward the 

 observer successively. Between each successive trial it was 

 removed from the water, being handled in the same way, and 

 held inverted on the fingers for a period as described above. 

 It was felt that if the starfish were simply moved back to the 

 center of the dish each time, this action might not be enough 

 to break up the action of the impulse under which it was crawl- 

 ing in a given direction in the previous trial. In other words, 

 any trial might then be considered merely a continuation of 

 the previous one. Jennings ('07, p. 141) for example, found 

 in studying the righting reactions of Asterias forreri that the 

 animals tended to right themselves in the same way as in the 

 preceding case, that is, the impulse was retained from a previous 

 reaction. To what extent the method employed to break up 

 their impulse was successful in the present experiments will be 

 discussed later (p. 16). 



* In the case of specimen No. 3 it was noted that arm c was slightly shorter, 

 while in No. 5, arm d was noticeably shorter. 



