1907] Jennings.- — Behavior of tJie Starfish. 121 



The righting reaction has been much studied, by Romanes 

 (1885), Preyer (1886), von Uexkiill (1900), Loeb (1900) and 

 others, but a really thorough analysis of the factors on which it 

 depends and of the way in which it occurs has never been made. 

 The work of Romanes, Loeb and von Uexkiill was done mainly 

 with a view to the analysis of the functions of the nervous sys- 

 tem. That of Preyer was done from a broader standpoint, and 

 brings out much that is of great interest, though he did not make 

 a careful analysis. Driesch (1903), with his usual acuteness in 

 detecting essentials, has discussed some of the fundamental prob- 

 lems which underlie behavior of this character, and has noted 

 the need of a thorough study of this and similar reactions (1. c. 

 p. 17, 36). Driesch 's discussion will be spoken of further. The 

 purpose of the following is to give a thorough experimental 

 analysis of the righting reaction. 



A good picture of the general course of the righting reaction 

 is given by Loeb. "If a starfish be laid on its back, the tube feet 

 of all the arms are stretched out at once and are moved hither 

 and thither as if feeling for something, and soon the tips of one 

 or more arms turn over and touch the underlying surface with 

 their ventral side. The tube feet of these arms attach themselves 

 to this surface and tl^e animal is then able to turn a somereault 

 and regain its normal position. For this result it is essential 

 that all five arms do not attempt simultaneously to bring the 

 animal into the ventral position. Should the tips of all five. 

 or even four tug simultaneously, it would be impossible for the 

 animal to turn over. In normal starfish having five arms, not 

 more than three begin the act of turning; the other two remain 

 quiet." (Loeb 1900, pp. 61-62.) 



Is this reaction stereotyped, always occurring in the same 

 way ? On this question we have Preyer 's statement of the results 

 of his extensive experiments: "Neither in one species or the 

 other is the method of turning always the same. I have likewise 

 seen Astcrias glacialis, which was several times in succession 

 turned on its back without change in the outer conditions, right 

 itself sometimes in one manner, sometimes in another. The 

 spirals of the twisted arms do not work each time in correspond- 

 ing directions, but at first the neighboring arms often oppose 



