TABLE OF CONTENTS xi 



PART IV. GAMETIC REPRODUCTION IN RELATION 

 TO THE AGE CYCLE 



Ch.^PTER p^j.g 



XIII. Origin axd jMorphological and Physiological Coxditiox 



OF THE Gametes in Plants and Aniivl\ls 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 ^laturation; Conclusion; Refer- 

 ences. 



XIV. Conditions of Gamete Formation in Plants and Anbuls 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 IMorphological 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 450 



Index 469 



