238 BEHAVIOR OF THE LOWER ORGANISMS 



2. Reaction by Varied Movements, with Selection from the 



Resulting Conditions 



In the foregoing section we have dealt with the fact that stimulation 

 often causes the performance of actions that are of a definite, typical 

 character, such as are often called reflexes. But this by no means ex- 

 hausts the problem of behavior, as our account of the matter in unicel- 

 lular animals and in Ccelenterata has shown us. Indeed, we find it not 

 to be the rule that an animal when stimulated performs a single definite 

 movement, then returns to its original state. On the contrary, stimula- 

 tion is usually followed by varied movements, and the animal may con- 

 tinue active long after the external agent has ceased to impinge upon it. 

 The continued varied movements subject the organism successively to 

 many different conditions, external and internal. In one of these con- 

 ditions the animal remains through a cessation of the changes in activ- 

 ity. It may thus be said to select certain conditions through the pro- 

 duction under stimulation of varied movements. We have seen many 

 examples of this type of behavior in the groups thus far considered. 



Behavior of this character is very general in lower animals. We 

 shall in the present section give a number of examples, taken from 

 diverse classes of invertebrates. 



As we have seen, the echinoderms furnish perhaps the best examples 

 of organisms in which the behavior is made up largely of more or less 

 independent "reflexes." Yet in the same group we find that much of 

 the behavior is of the type now under consideration. There is, of course, 

 no opposition between the two, the different "reflexes" forming the 

 variables out of which behavior of the present sort is made up. The 

 pedicellarke of the sea urchin have, as we have seen, a number of these 

 definite reflexes. When the entire animal is suddenly and strongly 

 stimulated, by mechanical shock, by a chemical, or by light, the pedi- 

 cellariae respond, not by a single definite reflex, but by beginning to 

 move about in all directions (v. Uexkiill). They seem to feel and 

 scrape the entire surface of the body, seizing anything with which they 

 come in contact, and this behavior may continue for an hour or more 

 after stimulation has ceased. Similar effects are often produced in the 

 spines by a general stimulus. They wave about, their tips describing 

 circles, and this may continue for a long time. Such reactions are seen 

 also in the tube feet. When the sea urchin or starfish is suspended in 

 the water or is placed on its back, the tube feet extend and wave back 

 and forth, as if searching for something to which they might attach 

 themselves. 



On a more extensive scale, the "righting" reaction of the starfish is 



