FUNCTIONAL DIVISIONS OF THE NERVOUS SYSTEM. 95 



CHAPTER V. 



THE FUNCTIONAL DIVISIONS OF THE NERVOUS 



SYSTEM. 



The nervous system can be understood only by studying it 

 from the standpoint of the work which it does. It must be insisted j 

 that a knowledge of mere structure is of little value and may be 1 1 

 misleading without a knowledge of function. For this reason 

 in speaking of the nervous system the term mechanism is preferable 

 to architecture; for mechanism implies work as well as structure. 

 It implies structure in action. The work of the nervous system is 

 to adapt the activities of the animal to the conditions of its life 

 and of the perpetuation of the species. As the necessary adap- 

 tations and correlations are successfully carried out the organ- 

 ization of the nervous system is perfected through experience. In 

 all vertebrates the same general plan of organization is seen; 

 the degree of organization is a measure of adaptation and is 

 correlated with the survival of the best adapted. The higher 

 animals are adapted to more complex and changing conditions 

 of life and have more highly organized nervous systems. 



We may distinguish two main groups of activities in the verte- 

 brate organism which have determined the general plan of organ- 

 ization of the nervous system: actions in relation to the external 

 world, and internal activities having to do with the processes of 

 nutrition and reproduction. The actions toward the external 

 world consist of the finding and capturing of food, fighting 

 with other animals, preparing nests or homes for protection 

 against the physical elements, and many minor reactions to 

 changes in heat, light, moisture, etc. The internal activities include 

 all the processes related to metabolism, the distribution of nutritive 

 material to various parts of the organism, and the various pro- 

 cesses connected with the formation of the reproductive elements 

 and the nutrition of the embrvo. 



