CHAPTER 16 



COORDINATION 



The business of coordination is obviously 

 a fundamental problem from the very be- 

 ginning, because even the tiniest single- 

 celled animals have some method of co- 

 ordinating their separate parts. Amoeba 

 must decide which way it will throw out 

 its pseudopods in order to move in a certain 



like nerve cells are seen in planaria, where 

 there is a well-defined anterior brain with 

 two large lateral nerve cords running poste- 

 riorly. Being a larger animal composed of 

 more cells, and a much more complicated 

 animal, a more elaborate coordinating 

 mechanism is essential. The idea of central- 



direction. Euplotes (Fig. 16-1) shows an ization in the coordinating mechanism is 

 advanced degree of specialization because continued and elaborated through the in- 

 it is able to control the rhythmic beating of vertebrate and vertebrate groups as animals 

 its cilia so that the direction of progression become larger and more complicated. The 

 can be changed suddenly. However, Meta- gro\\i:h and organization of the individual 

 zoa such as hydra have a coordinating may be hkened to the expansion of a tele- 

 mechanism in the form of a simple arrange- phone system as the small monohippic vil- 

 ment of nerve cells, the nerve net. The first lage grows to a great city. As the latter in- 

 steps toward a centralization of these net- . creases in size, the system becomes more 



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