DIRECTION OF LOCOMOTION OF THE STARFISH 17 



If.. Rotation of the impulse 



Inspection of table 3 reveals another interesting relation exist- 

 ing in the trial records. This is what may be called a tendency 

 to 'rotation of the impulse.' Not only is there a slight vacilla- 

 tion in the direction of the impulse, but there appears to be a 

 well-marked tendency for the impulse as a whole to shift gradu- 

 ally around one way or the other. This was more pronounced 

 in some individuals than in others. It is especially marked 

 in the records of specimens No. 4, No. 5, No. 7, No. 8 and No. 

 9. With the records spread out flat as they are here the records 

 of successive trials tend to trail out diagonally across the space 

 allotted to the individual, as is indicated by the diagonal dotted 

 lines enclosing them. But to express the proper relationships 

 they should be plotted on a cylinder (for on the animal c and 

 he are adjoining) and the tendency of the impulse to rotate in 

 one direction or the other would then be expressed by the spiral 

 path of the records around the cylinder, to right or left as the 

 case might be. This would bring the figures lying on each side 

 of the flat diagrams together and make the result appear more 

 striking. 



In the case of five of the starfishes (Nos. 1, 3, 6, 9 and 10) 

 the direction of rotation of the impulse around the animal is 

 plainly to the right, or clockwise; in four (Nos. 4, 5, 7 and 8) 

 it is as evidently to the left, or counter clockwise. In only one 

 specimen (No. 2) is there definitely shown a change in the direc- 

 tion of this rotation during the recording of the fifty trials. This 

 individual was apparentl}^ right-handed in this respect at first, 

 and changed to left-handed after about the fifteenth trial. There 

 is nothing recorded in the notes which would appear to furnish 

 an explanation of this change. 



It will be observed that the width of the 'paths' between the 

 dotted lines in the table is in a degree a measure of the 'inten- 

 sity,' if we may so call it, of the impulse; in some cases the im- 

 pulse remained so nearly fixed in a particular region that trial 

 after trial the starfish crawled with the same ray forward. Take 

 for example, specimens Nos. 3, 4, 5, 7 and 8 (after about trial 



THE JOUK^TAl, OF EXPERIMENTAL ZOOLOGY, VOL. 14, NO. 1 



