viii CONTENTS. 



CHAPTER VI. 



PAGE 



Theory of Development and Heredity illustrated among 



Protozoa 'o^ 



CHAPTER VII. 



Application of the Theory to Multicellular Organisms, and 



the Relation of the Germ-cells to the Body . .120 



CHAPTER VIII. 



The Inherited Impylse of Development, or Tendency of 



Growth 13s 



CHAPTER IX. 



Illustration of the Method of Growth and Development, 



and of the Origin of Variations 146 



CHAPTER X. 

 Correlation of Growth I7' 



CHAPTER XI. 

 Dimorphism and Polymorphism in Species . . . 183 



CHAPTER XII. 

 Degeneration and Laws of Variation ..... 198 



