258 W. J. Cbozier, 



the other. Then, beginning always at the anterior end, the body 

 becomes slowly twisted in such a way as to bring the pedate sur- 

 face to the bottom; the body muscles are more important in this 

 proceedure than the tube feet. This type of righting behavior is 

 very like that practised by Planarians, slugs, earthworms, etc. A 

 modification of this method of righting was used in a few instances : 

 the anterior and posterior ends would for a moment bend ventrad 

 rather quickly, and the animal thus was enabled to roll over 

 suddenly with sufficient momentum to regain its normal orientation 

 without the use of longitudinal twisting. 



Holothurians with the anterior end (nerve ring, stone ring, etc.) 

 amputated did not right themselves until several hours after the 

 operation. This was probably due to the inability to develope 

 internal water pressure in the usual way; but sooner or later the 

 "headless" pieces became righted after the manner above described 

 for the normal animals. With animals cut cross wise into two 

 equal parts, the righting movements of the posterior half began at 

 the tail end — showing a condition somewhat comparable to the 

 non-use of injured arms (starfish — Mooee, 1910) or injured regions 

 (sea urchin — Eomanes, 1885) in other echinoderms. Cole (1913b) 

 concluded that a starfish could not coordinate its righting move- 

 ments in the absence of a complete nerve-ring; it is probable that 

 the simpler structure of Holothuria makes possible a better coordi- 

 nation through the mutual pull of the body parts than is the case 

 in Asierias. Some tests were made with holothurians suspended in 

 the water by a thread through the dorsal integument. Two types 

 of behavior were seen in such animals; some individuals squirmed 

 about incessantly, while others assumed a contracted form and kept 

 it as long as the experiment was continued (3—4 hours), in one 

 case autotomizing the viscera. Detached tube-feet, and the tube- 

 feet of holothurians held resting on their dorsal surface, readily 

 became attached to the surface of bits of stone etc., but not so 

 frequently to glass rods. Direct contact with a rough surface is 

 the stimulus which provoques their attachment. H. surinamensis 

 was sometimes collected from the under side of slabs of rock, and 

 this fact, taken in conjunction with those already described, argues 

 for the conclusion that the normal righting reaction depends on 

 the positive stereotropisra of the tube feet. When the pedicels are 

 detached the animal assumes such a form as best to make possible 



