Differentiation of Neuroblasts 63 
organs. In every specimen that I have examined it is certainly 
possible that the neuroblasts which develop into motor nerves may 
have been influenced by the regenerating muscles which they 
normally innervate, or by other muscles in the immediate neighbor- 
hood, and in no case cited in the literature which has come under 
my observation has this possibility been excluded. I believe, 
therefore, that further evidence is necessary before it can be 
asserted that any neuroblasts are self-differentiating, and until 
such evidence is produced, that it is safe to assume that all are 
alike dependent on stimulation from end organs or the products of 
the activities of end organs, for differentiation. 
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