28 SCIENCE AND PHILOSOPHY OF THE ORGANISM 



cerned in any correlated motion whatever. I should like 

 to parallel his concepts of " tonus," " tonus - reservoir," 

 "blocking," "latching" (" Klinkung "), etc., directly with 

 the elemental concepts of formative stimulus, prospective 

 potency, inner means, etc., in morphogenesis. For, in fact, 

 all the concepts of von Uexkuell are concerned in any 

 co-ordinated movement whatever, though, properly under- 

 stood, none of them, of course, says anything about the 

 specificity of co-ordination as such, 



Now it is of great importance, that the analytical 

 results of von Uexkuell about the elements concerned in 

 co-ordinated motion are in a most perfect state of harmony 

 with what Jennings discovered about simple motor acts. 



Let us mention at least a few of the elemental nervous 

 relations revealed by von Uexkuell's work. The type of 

 any single act of a combined movement may be altered 

 by the intensity of the stimulus, or by its quality, or by 

 the introduction of a second simultaneous stimulus, either 

 at the same spot or elsewhere, or by the occurrence of 

 previous stimulations ; and there may be a change in the 

 behaviour regarding the single constituents in consecutive 

 times of their realisation ; and one reacting constituent 

 may be stopped by any other one whatever. 



There is hardly one feature in this doctrine of the 

 constituents of combined motion that does not appear in 

 the single motor acts as well. Combined motions thus 

 are far from being a grouping of simple typical reflexes 

 exclusively : most of what was believed to be truly reflex 

 has been proved not to be so. 1 



1 It must be understood that von Uexkuell himself (see Zeitschrift f. 

 Biol. 50, 1907, p. 168) adheres to the reflex-theory of movement, and that 



