324 'Journal of Comparative Neurology and Psychology. 



from the pliysiological analysis based on their other movements (19, 

 p. 105) ; if they did the sea urchin would not regain its normal 

 position. In the starfish the method of action may he changed by 

 the formation of habits, and this is doubtless true also for the sea 

 urchin. Thus any formulation that is complete must provide also 

 for the laws of change of behavior; for its regulatory features. 

 Possibly no complete formulation can ever be reached, but the most 

 direct way to approach it is by such analysis as v. irexkilll gives. 



Later Investigations. 

 We have given this account of the spines as a type of v. UexkiilFs 

 methods of analysis ; by following carefully such a concrete case 

 the reader will get a better idea of the nature and justification of 

 his work than by any systematic survey of the concepts to which 

 he finally comes. Let us now follow further the development of 

 these concepts. As we have seen, the central concept is that of tonus, 

 and the laws of the changes of tonus are the chief object of research. 

 To research on this matter, to studying the properties of tonus in 

 various organisms, and to devising schemata which shall help us 

 to understand how it acts, and hence how behavior takes place, have 

 lieen devoted the later researches of v. Uexkiill. He has thus far 

 analyzed from this point of view, besides the sea urchin, the worm 

 Sipunculus (25), the brittle-star (27), the leech (28), the heart- 

 shaped sea urchin (30), and the dragon fly (31). In the latest 

 contrilmtion, on the dragon fly, v. Uexkiill attempts to make provi- 

 sion for a modification of the machinery of behavior through the 

 experiences of the organisms. It would manifestly l)e impossible to 

 resume here these researches, filled as they are with minute and 

 technical detail. 



V. IlEXKiTLT/s Syste:\i of Concepts. 

 A view of V. Uexkiill's system of concepts can be gotten most 

 directly from his '''Guide to Experimental Biology" (20). But 

 here one does not see the development of the ideas ; the actual grounds 

 that have given origin one after another to the jjccnliar concepts, so 

 that they are likely to seem on first introduction Inzarre and artificial, 

 having little similarity to anything dealt with in orthodox physiology. 



