CONTENTS ix 



CHAPTER PAOB 



XII. REPRODUCTION: SEXUAL AND ASEXUAL METHODS 238 



General Types of Reproduction. Reproduction 

 in Unicellular Organisms. Reproduction in 

 Multicellular Organisms. Division without 

 Cell Union. Multiplication by Cell Union. 

 The Union of the Sex Bodies or Fertilization. 

 The Relation of the Chromatin to Heredity. 

 The Purpose of the Union of the Sexes. 



XIII. DISTRIBUTION OF SEXUAL AND ASEXUAL 



METHODS. ALTERNATION OF GENERATIONS 262 



Summary of the Methods of Reproduction. 

 Origin of Sex Union. Distribution of Asexual 

 Reproduction. Distribution of Sexual Repro- 

 duction. Reproductive Bodies or Reproductive 

 Cells. Cross Fertilization the Rule. Alterna- 

 tion of Sexual with Asexual Methods of Repro- 

 duction. 



XIV. DEVELOPMENT OF THE FERTILIZED EGG . . 280 



Embryology and Metamorphosis. Embryology 

 of the Frog. 



XV. THE SOURCE AND NATURE OF VITAL ENERGY . 292 



Matter and Energy. The Conservation of 

 Energy. The Transformation of Energy. The 

 Living Organism as a Machine. The Life of a 

 Plant. The Life of an Animal. 



XVI. THE MECHANICS OF THE LIVING MACHINE . 303 



Details of the Action of the Machine. Vital 

 Force or Vitality. Summary. What is Life? 



