ORIGIN OF THE NERVOUS SYSTEM 345 



instances their action is independent of nervous control, while in others 

 it is under this control. In my opinion the instances of independent 

 action represent a primitive state; the others a condition brought about 

 through the appropriation of these organs as end-organs by a develop- 

 ing nervous system. 



If what has been stated in this article is correct, we must picture to 

 ourselves as steps in the evolution of the nervous system not only the 

 independent origin of muscle around which the nervous organs subse- 

 quently develop, but also the independent origin of other effectors such 

 as chromatophores, glands and phosphorescent organs and the second- 

 ary appropriation of many of these by a developing nervous system. 

 This principle of appropriation I believe to be as significant in elucida- 

 ting the present condition of the nervous system and its appendages, as 

 the principle of evolutionary sequence of parts, muscle, sense organ, 

 and central nervous organ, as given in the first three articles. 



Refebences 



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VAN RyNBEBK, G. 



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vol. lxxv.— 23. 



