-68- 



It would be obviously impossible for the suckers to attach., yet tha 

 animals (Asterina especially) righted themselves quite as neatly as 

 on a solid substrate. Pilaster, however, would not right easily un- 

 less in active locomotion at the time of inversion* 



A specimen actively crawling in the direction of a e 

 (fig. 16) was quickly inverted on sand. The tube feet, which were 

 retracted because the animal was lifted from the substrate, extended 

 at once toward a e. B and moved up orally and twisted toward a e, 

 bent up and over the disk while a s- twisted toward each other and 

 the tube feet, as soon as they came in contact with the sand, began 

 executing the step reflex. Thus each ray moved so as to set itself 

 more nearly at right angles to its actively extended (Oriented) tuba 

 feat. The stepping activity of the tube feet on a a resulted in their 

 doubling back under themselves, so that the tube feet were striking 



<je 



out toward the disk instead of away from it (see rays A fig. 18, 19, 20). 

 The step reflexes of the tube feet in contact with the sand were very 

 active, the ends of the feet plou^iing back through the sand and scat- 

 tering the grains on all sides to a distance of one or two centimeters. 

 The movements thus initiated continued until the rays a e had walked 

 back under the disk and the other rays had moved up over the disk far 



enough to overbalance the animal and complete the somersault. Loco- 



' ' -* ^^^L^L^L^L^HI 



motion then continued in the direction of a e 



The righting reaction of Asterina on sand is even neata&r 

 than that of Pisastar. This is dua to the very great flexibility of 

 the ray tips and to the strength and size of the large disked tube 

 feet. The animal rights nearly as quickly and easily as on a solid 

 substrata. 



INTJRPRKTATIOH OJ THJ RIGHTING REACTION Aj^ A PHASE 



OF LOCOMOTION 

 3Svide.no a from the mo veme.nt of the tube feet and arms.. 



