xii CONTENTS 



CHAPTER PAGE 



VI. LOCALIZATION AND DIFFERENTIATION OF NERVOUS 

 STRUCTURE IN RELATION TO THE ORGANISMIC 

 PATTERN 107 



The Nervous System as a Product of Physiological 

 Factors. The Localization of Nervous Structure. The 

 Early Differentiation of Nervous Structure. 



VII. THE PHYSIOLOGICAL RELATION OF THE CENTRAL 

 NERVOUS SYSTEM TO OTHER PARTS IN DEVELOP- 

 MENT 118 



Physiological Independence and Dependence in Develop- 

 ment in Relation to the Gradients. The Physiological 

 Independence of the Apical Region and Head in Experi- 

 mental Reproduction. The Relative Independence of 

 the Nervous System in Development. The Significance 

 of the Facts. 



VIII. THE NERVOUS SYSTEM IN RELATION TO SEGMEN- 

 TATION 130 



IX. NERVOUS CENTRALIZATION AND CEPHALIZATION IN 



EVOLUTION 142 



Centralization in Relation to Axiation. Progressive 

 Centralization and Cephalization in Various Groups. 

 The "Stepladder" Type of Nervous System in the 

 Invertebrates. The Position of Peripheral Receptors. 

 Conclusion. 



X. THE PROBLEM OF NEURON PATTERN .... 155 



The Neuron. The General Morphological Character- 

 istics of Neuron Pattern. Neuron Pattern as a Case of 

 Axiate Pattern. The Possible Factors Concerned in the 

 Axiation of the Neuron. Kappers' Theory of the Origin 

 of Neuron Pattern. 



XI. SUGGESTIONS CONCERNING THE ORIGIN AND DEVEL- 

 OPMENT OF NEURON PATTERN 179 



Electrical Polarization as a Localizing and Orienting 

 Factor. Axon Development. Dendrite Development. 

 The Neurons of the Spinal Ganglia. Kappers' "Neu- 

 robiotaxis" of the Cell Body. Certain "Monopolar" 

 Neurons. The Cells of the Nervous Reticulum. Con- 

 clusion. 



