x TABLE OF CONTENTS 



CHAPTER PAGE 



VII. THE ROLE OF NUTRITION IN SENESCENCE AND REJUVENESCENCE 



IN Planaria 155 



Reduction by Starvation in Planaria; Changes in Susceptibility during 

 Starvation in P. dorotocephala and P. velata; The Production 

 of Carbon Dioxide by Starved Animals; The Rate of Decrease 

 in Size during Starvation; The Capacity of Starved Animals for Accli- 

 mation; Partial Starvation in Relation to Senescence; The Character 

 of Nutrition in Relation to the Age Cycle; References. 



VIII. SENESCENCE AND REJUVENESCENCE IN THE LIGHT or THE PRE- 

 CEDING EXPERIMENTS 178 



Review and Analysis of the Experimental Data; The Nature of Senes- 

 cence and Rejuvenescence; Periodicity in Organisms in Relation to 

 the Age Cycle; Senescence and Rejuvenescence in Evolution; 

 References. 



PART III. INDIVIDUATION AND REPRODUCTION IN RELATION TO 



THE AGE CYCLE 



IX. INDIVIDUATION AND REPRODUCTION IN ORGANISMS . . . . 199 



The Problem; The Axial Gradient; Dominance and Subordination of 

 Parts in Relation to the Axial Gradients; The Nature and Limits of 

 Dominance; Degrees of Individuation; Physiological Isolation and 

 Agamic Reproduction; References. 



X. THE AGE CYCLE IN PLANTS AND THE LOWER ANIMALS . . 237 



Individuation and Agamic Reproduction in the Life Cycle of Plants; 

 The Vegetative Life of Plants in Relation to Senescence; The Occur- 

 rence of Dedifferentiation and Rejuvenescence in Plant Cells; The Rela- 

 tion of the Different Forms of Agamic Reproduction in Plants to the 

 Age Cycle; Individuation, Agamic Reproduction, and the Age Cycle 

 in the Lower Animals; Senescence as a Condition of Reproduction and 

 Rejuvenescence; Conclusion; References. 



XI. SENESCENCE IN THE HIGHER ANIMALS AND MAN .... 266 



Individuation and Reproduction in the Higher Forms in Relation to 

 the Age Cycle; The Process of Senescence in the Higher Forms; The 

 Rate of Metabolism; The Rate of Growth; Nutrition, Growth, and 

 Senescence; Changes in Water-Content and Chemical Constitution; 

 The Morphological Changes; Conclusion; References. 



XII. REJUVENESCENCE AND DEATH IN THE HIGHER ANIMALS AND MAN 293 



Rejuvenescence in the Life History; Length of Life and Death from 

 Old Age; Some Theories of Length of Life; Conclusion; References. 



