NERVOUS ORGANIZATION 



155 



for a jointed animal to function with any degree of suc- 

 cess all of the segments must work in harmony. Hence 

 the machinery of nervous correlation in these must be so 

 organized as to extend from joint to joint. As Fig. 43 

 shows, the arrangement is to connect each ganglion with 

 its neighbors on either side by nerve-cells which extend 

 directly from ganglion to ganglion. Since these are 

 neither sensory cells nor motor cells but connections, we 

 give them the name of connecting cells. The presence 



Fig. 43. — Diagram illustrating the nervous system in a jointed 

 animal. In addition to the structures shown in figure 42 the con- 

 necting nerve cells (c) and (c') are shown, by which nervous dis- 

 turbances can pass from joint to joint. For the sake of simplicity 

 part of the possible nerve connections in the second ganglion are 

 omitted. 



of these connecting cells opens up additional possibilities 

 of complexity in the movements of nerve impulses, for 

 now a disturbance originating in any receptor and passing 

 from it to the ganglion is not confined in its outward path 

 to the motor nerves leading directly from that ganglion 

 to the effector, but may pass over the connecting nerve- 

 cells to an adjoining ganglion and so to an effector in the 



