144 THE ORIGIN OF THE NERVOUS SYSTEM 



already present in the developing organism before the 

 nervous system as a specialized organ appears, and 

 that the physiological gradients as the earliest distin- 

 guishable features of organismic pattern are fundamental 

 factors in the process which determines the localization 

 and development of a nervous system. 



From this viewpoint the nervous system appears as 

 a morphological and physiological expression of the 

 gradients in the developing organism, and both its 

 early differentiation and its function as an organ of 

 excitation and transmission indicate its intimate relation 

 to these fundamental factors of organismic pattern. If 

 we accept this view, we can expect to find an uncen- 

 tralized nervous system only in animals which are 

 completely anaxiate and which possess only a surface- 

 interior pattern, and it is difficult to conceive how such 

 a system could contribute in any way to organismic 

 integration. All receptors of such a system would be 

 equally susceptible to excitation, conduction would be 

 diffuse and equal in all directions, and the resulting 

 integration would be temporary, and probably in many 

 cases only partial as in Amoeba, and would soon give 

 place to another integration with another receptor as 

 the dominant region. As a matter of fact, some degree 

 of organismic and even of axiate pattern and integration 

 already exists before the nervous system appears (p. 242) 

 and the development of the nervous system merely con- 

 tinues the process. If strictly an axiate animals exist 

 they do not give rise to nervous systems. All animals 

 in which any visible differentiation of nervous structure 

 appears are to some extent axiate before nervous differ- 

 entiation occurs, though in the sessile coelenterates, 



