204 THE ORIGIN OF THE NERVOUS SYSTEM 



polarity may arise in the cells of these simple forms in 

 relation to the surface-interior pattern and in some 

 cases in relation to the axiate pattern. There can be 

 little doubt that in these forms the surface-interior 

 pattern is more definite and constant than the axiate pat- 

 tern and that the physiological factors concerned in it 

 are therefore more effective in determining, at least 

 locally, a polarity and pattern in individual cells, than 

 the general axiate pattern of the animal. If electrical 

 polarization is concerned in determining such pattern, 

 it is evidently of the first type, since there is tissue- 

 continuity, and the basal outgrowths of such cells 

 correspond physiologically, as regards origin and direc- 

 tion of growth, to the axons of the more highly special- 

 ized neurons. 



CONCLUSION 



This and the preceding chapter constitute merely a 

 brief consideration of some of the more important aspects 

 of neuron development. The present chapter is nothing 

 more than a tentative development of a conception of 

 neuron polarity and external morphology on the basis of 

 physiological factors concerned in organismic pattern. 

 The factors themselves exist, and I have attempted to 

 show that they afford a basis for interpretation of many 

 facts of neuron development in relatively simple terms. 

 That neuron pattern is and must be related physio- 

 logically to organismic pattern is, I think, beyond the 

 possibility of doubt, and if the conception of organismic 

 pattern developed in earlier chapters has any foundation 

 in fact, it must afford a basis for attack on the neuron 

 problem. This chapter is concerned with showing that 

 it does afford such a basis. 



