1907] Jennings. — Behavior of the Starfish. 99 



reference to the body), just as is the leg' of a higher animal. That 

 is, the tube foot acts as a lever for swinging or shoving the body 

 forward, not as a rope for hauling it forward. Since the tip is 

 against a solid body and does not slip, the impulse to swing back 

 results really in moving the body forward, just as in ourselves or 

 the horse ; there is no actual swinging back of the distal end of 

 the foot, but a swinging forward of the proximal end with the 

 body attached to it. The tube foot acts as a partly rigid lever, 

 though it becomes curved more or less, and may shorten or 

 lengthen, in the act of walking. The walking of the starfish is 

 therefore mechanically similar in essentials to that of a higher 

 animal, the suckers merely serving for getting a firm foothold. 



As the tube feet after attaching themselves swing the body 

 forward, they do not pull; on the contrary they push backward 

 a certain amount, just as do the feet of a higher animal. This 

 becomes clearly evident when the animal is watched from the side 

 while walking on loose sand. The sand grain to which a tube foot 

 is attached is not lifted up as the body moves forward, though 

 the lightest pull would suffice for this. But often it is pushed 

 back a little, in the case of very loose sand, showing that the 

 action is like that of the leg of a higher animal when a stone on 

 which it has stepped rolls backward as the animal moves forward. 



Fig. 7. — Diagram of the movement of a tube foot in locomotion. The 

 letters a to e show successive positions of the tube foot. The forward move- 

 ment of the starfish is of course not shown in the diagram. 



When the tube foot is first pushed forward, it is long (fig. 7, 

 a). As the body moves forward the stalk of the foot becomes 

 shorter and soiuewhat curved, while the body is raised a little 

 (fig. 7, 6). Next the tube foot becomes longer and straightens as 

 it becomes inclined backward ; it seems to aid in pushing the body 

 ft)rward, for the grain of sand to which it is attached is still not 



