ORIGIN OF NEURON PATTERN 205 



No one is more keenly aware than myself of the 

 hypothetical character of the discussion and of the 

 criticisms which may be brought against it. It is evi- 

 dent, however, that a consideration of the origin and 

 development of the nervous system, such as has been 

 attempted' in this book, cannot stop short before the 

 problem of neuron pattern and refuse to consider it. 

 Neuron pattern is a feature, both of nervous and of organ- 

 ismic pattern. Moreover, the neuron itself develops an 

 axiate pattern, and the resemblance of this to certain 

 types of axiate organism, suggests the possibility of 

 physiological resemblance. I have merely suggested an 

 interpretation of neuron pattern in terms of organismic 

 pattern. 1 



1 Since this and the preceding chapter were written, I have been 

 informed through the kindness of Dr. R. G. Harrison, under whose 

 direction the work was done, that Dr. Ingvar has succeeded in determin- 

 ing the direction of outgrowth of neuroblasts in tissue culture by means 

 of electrical currents. A report of Ingvar's work is now in press and 

 soon to appear in Proceedings of the Society for Experimental Biology 

 and Medicine. This work represents, so far as I know, the first step in 

 experimental determination of polarity in neuroblasts and, so far as it 

 goes, constitutes an experimental basis for a hypothesis of electrical 

 determination, but much further work is of course necessary to deter- 

 mine, whether or how far the particular hypothesis advanced in these 

 chapters will account for the facts. 



