172 THE ELEMENTARY NERVOUS SYSTEM 



ferences of opinion are really as pronounced as they 

 sometimes appear on paper, but it is perfectly evident 

 that the two general views represent real differences on 

 a subject about which the truth can not at present be 

 easily stated. 



More or less of this difference is doubtless due to the 

 various methods of attack which different investigators 

 have used in this field of work. Since the external stimuli 

 are more easily measured and otherwise controlled than 

 the internal states, these were naturally first studied, 

 with the result that the work of Loeb, Nagel, and others 

 led to a general conception of an actinian as a delicately 

 adjusted mechanism whose activities were made up of a 

 combination of simple responses to immediate stimula- 

 tion. This view has been criticized by Jennings (1905) 

 as giving an unnaturally sharp, clear-cut and simple pic- 

 ture of actinian behavior. Jennings, moreover, has drawn 

 attention to the physiological state of the animal, includ- 

 ing the effects of previous stimulation, of its metabolism 

 and so forth, in fact of its general past history, as an in- 

 ternal element of no small importance in interpreting its 

 reactions. But this view is not without its serious lim- 

 itations. As von Uexkull (1909) and Baglioni (1913) 

 have recently pointed out, it too often tempts the worker 

 to be satisfied with the statement of inferred internal 

 states as explanations of conditions which upon careful 

 scrutinizing prove to be dependent upon quite different 

 factors, and the consequent vagueness and uncertainty 

 with which it often surrounds the subject obscures the 

 real questions for investigation. 



Keeping in mind these two tendencies, what can be 

 said about the psychology of actinians? First of all, it 

 seems fairly certain that their behavior is chiefly deter- 



