Fig. I. 



I. Reflex arc with two elements, receptor and effector. 



II. Reflex arc with one receptor and two effectors, illustrating how, through 

 branching in center, one sensory neurone may influence more than one 

 motor neurone. , 



III. Reflex arc consisting of two receptors and one effector, illustrating 

 principle of convergence; axone of motor neurone is referred to as final common 

 path. 



IV. Diagram showing interaction of two separate reflex arcs through associ- 

 ation neurones a. 



In all four figures letters indicate following: r, receptor; s, surface of body; 

 E, effector (skeletal muscle); i, ganglion cell of receptor; 2, axone of effector; 

 c, central nervous system, e.g., center in spinal cord; fcp, final common path; 

 A, association neurone in central nervous system. 



125 il 



