PHYSIOLOGY OF SYNAPTULA HYDRIFORMIS 377 



chains of neurones so arranged as to permit only one type of 

 response viz., a total reaction (the swimming movement)- 

 from all possible forms of stimulation, and that in successive 

 later stages this generalized type is gradually replaced by a 

 series of special reflexes involving more diversified movements. 

 . . . . The simple reflex arc . . . . , which is adapted 

 for the execution of a single movement in response to a particu- 

 lar stimulus, is the final stage in the developmental process, 

 whose initial stages are much more complex and diffuse arrange- 

 ments of neurones adapted for total reactions of a more general 

 sort" (Herrick, '15, p. 66). 



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