TABLE OF CONTENTS xi 



PART IV. GAMETIC REPRODUCTION IN RELATION 



TO THE AGE CYCLE 

 Chapter Page 



XIII. Origin and Morphological and Physiological Condition 



OF THE Gametes in Plants and Animals 315 



The Theoretical Significance of Gametic Origin; The Origin of the 

 Gametes in Plants; The Origin of the Gametes in Animals; The Mor- 

 phological Condition of the Gametes; The Physiological Condition of 

 the Gametes; The Significance of Maturation; Conclusion; Refer- 

 ences. 



XIV. Conditions of Gamete Formation in Plants and Animals 364 



Conditions of Gamete Formation in the Algae and Fungi; Conditions of 

 Gamete Formation in Mosses and Ferns; Conditions of Gamete Forma- 

 tion in the Seed Plants; Conditions of Conjugation in the Protozoa; 

 Conditions of Gamete Formation in the Multicellular Animals; 

 Parthenogenesis and Zygogenesis; Conclusion; References. 



XV. Rejuvenescence in Embryonic and Larval Development . 403 



The Effect of Fertilization; Parthenogenesis; The Experimental Ini- 

 tiation of Development; Oxygen Consumption and Heat Production 

 during Early Stages of Development; Changes in Susceptibility dur- 

 ing Early Stages; The Morphological Changes during Early Develop- 

 ment; Larval Stages and Metamorphosis; Embryonic Development in 

 Plants; The Degree of Rejuvenescence in Gametic and Agamic Repro- 

 duction; Conclusion; References. 



PART V. THEORETICAL AND CRITICAL 



XVI. Some Theories of Senescence and Rejuvenescence . . 433 



Senescence as a Special or Incidental Feature of Life; Senescence as a 

 Result of Organic Constitution; The Conception of Growth as an Auto- 

 catalytic Reaction and the Resulting Theory of Senescence; Refer- 

 ences. 



XVII. Some General Conclusions and Their Significance for 

 Biological Problems 459 



Index 469 



