DIRECTION OF LOCOMOTION OF THE STARFISH 7 



explanation of the departure from the normal behavior. Cer- 

 tain specimens showed a tendency always to change their course 

 in the same direction, while others swayed a little first to one 

 side and then to the other. 



My observations still further confirm those of Jennings ('07, 

 pp. 97, 115) with regard to the 'unified impulse' in locomotion. 

 When a starfish once establishes progression in a definite direc- 

 tion, the tube feet of all the rays are extended with reference 

 to the movement in that general direction, and not according 

 to their relation to the particular rays. 



As to the position of the rays during locomotion, there is 

 again much variation; two rays may be pushed in advance, 



Fig. 2 Diagram of starfish crawling with two rays in advance and three fol- 

 lowing. Arrow indicates direction of locomotion. 



with three following (fig. 2) or three may be in advance and two 

 behind (fig. 3). Sometimes the arms are all flattened to the 

 surface on which the starfish is crawling; at other times, or in 

 other individuals, they are curled upward at the tips. In cer- 

 tain instances it was noted that flexible specimens were more 

 active than the more rigid ones, and such specimens would go 

 through fifty successive experimental trials often with no appre- 

 ciable slowing in the rate of locomotion. The more sluggish 

 individuals sometimes slowed down towards the end of the series, 

 and in one case (No. 5) it was necessary to fill out the last five 

 trials of the fifty on the succeeding day. 



