CONTENTS xiii 



CHAPTER PAGE 



XII. CERTAIN FEATURES OF TRANSMISSION AND CON- 

 DUCTION IN RELATION TO THE PHYSIOLOGICAL 

 GRADIENTS 206 



The Development of Excitation and Conduction. Trans- 

 mission in Certain Non-nervous or Neuroid Paths. 

 Transmission in the Row of Swimming Plates of the 

 Ctenophore. Certain Axiate Organs as Physiological 

 Gradients. The " All-or-None " Principle in Nervous 

 Conduction. Conduction in the Neuron and the Prob- 

 lem of the Synapse. 



XIII. THE REFLEX ARC IN RELATION TO THE GRADIENT 233 



The Physiological Characteristics of Reflex Arc and 

 Excitation Gradient. Historical and Critical. The 

 Functional Direction in the Nerve Net. Functional 

 Direction in Certain Bilateral Invertebrates. Func- 

 tional Direction in the Higher Animals. The Problem of 

 the Origin and Development of the Cerebral Cortex. 



XIV. GENERAL CONCLUSIONS 268 



REFERENCES 273 



INDEX 289 



