Movement and Problem Solving in Ophiura 



205 



gentlich audi starker in Aktion treten." Both Preyer('86) and 

 Grave ('00) state that the "posterior" pair is dragged behind, and 

 I have never observed more than insignificant movements in it. 



Type // (Fig. 2), observed by all of the v^^riters mentioned, and 

 called Typus Unpaar hinten by von Uexkiill, may be described as 

 two pairs of arms working synchronously, or alternately, the 

 anterior pair initiating movement at one time, the posterior at 

 another, or the movement may be begun by arms 2 and 4; by / 

 and j; by 2 and /; or by 5 and ^; the only constant factor is the 

 behavior of arm 5 which is invariably dragged behind. 



A third type of movement. Fig. 2, ///, not previously recorded, 

 involves the activity of all the arms in such a manner that the 

 animal is forced forward by three arms on one side and a pair on 

 the other. This type may be thought of as a modification of /, C, 



n 



m 



Fig. 2 



in which arms ^ and 5 have become active, or as //, in which arm 5 

 has becom.e active. Type ///, is really /, C, plus an additional 

 pair, and as in /, C, the course is zigzag if arm 2 alternates regu- 

 larly from side to side, circular if the stroke falls always in the same 

 direction. 



It is not necessary to describe the finer variations to which these 

 types of movements are subject; to point out, as has been done in 

 von Uexkiill's excellent paper ('05), how one may pass over into 

 another, or how the course is aftected by differences either constant 

 or variable in the rate and strength of stroke of particular arms or 

 particular combinations of arms. With the exception of type 



