THE WORLD OF LIVING ORGANISMS 149 



Portions of the central network are split off, along with their 

 centres which control special groups of representatives and 

 the muscles belonging to them, and these muscles constitute 

 a definite locomotor apparatus controlling a leg, an arm, 

 a wing, or a fin. 



In cuttle-fishes it can be shown that in this way there 

 arise higher and lower central motor apparatuses, of which 

 the lower are arranged from the point of view of position, the 

 higher from that of function. In insects the activities of the 

 several limbs are completely governed by the centres directly 

 coordinated with them ; and all that is effected by the sen- 

 sory part of the network in the brain is the onset or cessation 

 of the movement. 



The sensory network is gradually moved further forward 

 to where the main receptors lie, which, excited by the stimuli 

 they receive, govern the activity of the animal as a whole. 



Differentiation of the sensory network appears relatively 

 late. In many cases, a division comes about simply by the 

 regions which belong to the various sense-organs separating 

 away from one another. In such animals, the function-circle 

 of the enemy employs other receptors and parts of the sensory 

 network than those used by the function-circle of food. 



As soon as outlines serve the body as indications, differ- 

 entiation of the sensory part of the nervous system speeds 

 off. For now it is useful so to combine quite definite sensory 

 nerves of the eye, that their common or successive excitations 

 are linked up into a whole, which makes its way into the 

 guiding mechanism as a new unity. I have called these 

 nervous unities " anatomical schemata," because they do 

 not give a complete reflection of the outline in the external 

 world, but merely a summary combination of its most import- 

 ant parts, and this with a degree of exactness suitable for the 

 particular animal. 



The appearance of such schemata in the brain is of two- 



