Movement and Problem Solving in Ophiura 215 



righting time they neither increase nor decrease — the apparent 

 increase being due to the failure to respond, for had this failure 

 occurred sooner, some of the last measurements would have been 

 smaller than the first. Fatigue played no part in the result, as the 

 figures are too uneven. 



The objection might be advanced that these cases w^hich I have 

 called "problems," were not such; that there was no reason why 

 the animals should modify their behavior, and that what they did 

 under the conditions of the experiment was nothing that they 

 would not have done under normal conditions. This objection is 

 met satisfactorily I believe by the following experiments. 



A given arm was stimulated by encumbering it with a rubber 

 tube, or by painting it with strong or dilute formalin or hydro- 

 chloric acid of different strengths. These trials, of which I made 

 a great many, yielded very definite results. In only one case did 

 an animal progress in the direction of the stimulated arm; in a few 

 cases at an angle to it, using it as one of the propellers, whereas in 

 the vast majority of cases it moved in the direction diametrically 

 opposite the stimulated arm. If the stimulus was strong, the 

 movements were very violent, but no difference in direction was 

 noted in the case of weak and strong stimuli. Under ordinary 

 circumstances it is impossible to predict the direction in which an 

 ophiuran, all of whose arms are of the same size, will move, but if 

 one of the arms be encumbered the prediction that the animal will 

 move away from the stimulus will be verified in the vast majority 

 of cases. I think it is justifiable to assert that the direction of pro- 

 gression has been determined in these cases, and if this is true 

 there is a determining cause — a problem. 



My second line of inquiry — whether encumbered animals 

 showed a noticeable increase in the number of movements best 

 adapted to solve the particular problem given, was begun by find- 

 ing the percentage of crosses and contacts in the same animals 

 under the two conditions stated. The results are summarized in 

 Table V. 



As contacts and crosses usually result from wavings I counted 

 these in animal // unencumbered and with one arm encumbered. 

 The results are summarized in Table VI 



