Movement and Problem Solving in Ophiura 209 



the disc between them, movements occur whose effect is to bend 

 the ventral surface in the direction indicated by the arrows. When 

 this process, by which a small portion of the ventral surface is 

 brought into the normal position (Fig. 3, A), has proceeded far 



enough, the animal is righted 

 suddenly by its own weight, 

 since while the process de- 

 scribed has been going on, 

 arms j, ^ and 5 have so ele- 

 vated the dorsal surface of the 

 disc that this falls into the 

 normal position. 



In the second type of right- 

 ing movement, Fig. 4, arm 2 

 '"■ ^ curves near its base, and bends 



under the disc which, as in the previous case, is elevated by the 

 other arms, particularly by 4. opposite 2. The disc thus rotates on 

 the base of 2 as a pivot, and after it has been sufficiently elevated, 

 the animal falls into the righted position of its own weight. 



The length of time required to execute the righting reaction was 

 measured on eight individuals. I have summarized these results 

 in Table II, in which are given the average time for each individual, 

 as well as the maximum and mini- 

 mum consumed. (See Table II.) 



These averages of course do not 

 show the differences between the suc- 

 cessive individual rightings of any of 

 the animals used. These differences 

 were in some instances very large, and 

 have had a great effect on the averages. 

 (See Table III.) 



These measurements show that the 

 variations from the mean maybe very 

 great; that because an individual has 

 righted itself very quickly a number 



of times is no reason for believing that it will continue to do so. 

 in spite of those cases in which righting took place slowly, the 



Fig. 4 



