214 THE ELEMENTARY NERVOUS SYSTEM 



are probably not of this nature, for in all cases they ap- 

 pear to be modified muscles rather than independently 

 produced structures. The others, however, give every 

 evidence of independent origin and still exist in many 

 animals as structures unassociated with nerves. Cilia 

 proper and nettle cells seem never to have come under 

 nervous domination, but chromatophores, luminous or- 

 gans, and glands have all in one instance or another been 

 appropriated by the nervous system. Through this 

 agency they have been more or less completely removed 

 from the class of organs whose action is called forth by 

 direct stimulation and have been made subservient to the 

 nervous system. Thus the system that arose secondarily 

 around an independent effector muscle, has in the end 

 gained such supremacy as to take to itself a number of 

 independent effectors, any one of which might in the be- 

 ginning have served as the nucleus around which the 

 first nervous tissue could have taken origin. 



