CONTENTS. 



PACE 



between the Number of Possible or Potential, and tlie Number of 

 Keal or Actual Individuals. — Complicated Correlations of all Neigh- 

 bouring Organisms. — Mode of Action in NatmTil Selection. — Homo- 

 chromic Selection as the Cause of Sympathetic Colourings. — 

 Sexual Selection as the Cause of the Secondary Sexual Characters. 

 — Law of Separation or Division of Labour (Polymorphism, Differ- 

 entiation, Divergence of Chai-acters) . — Transition of Varieties into 

 Species. — Idea of Species. — Hybridism. — Law of Progress or Per- 

 fecting (Progressus, Teleosis) ... ... ... ... ... ... 252 



CHAPTER XII. 



LAWS OF DEVELOPMENT OF ORGANIC TRIBES AND OF 

 INDIVIDUALS. PHYLOGENY AND ONTOGENY. 



Laws of the Development of Mankind : Differentiation and Perfecting. 

 — Mechanical Cause of these two Fundamental Laws. — Progress 

 without Differentiation, and Differentiation without Progress. — • 

 Origin of Rudimentary Organs by Non-use and Discontinuance of 

 Habit. — Ontogenesis, or Individual Development of Organisms. — 

 Its General Importance. — Ontogeny, or the Individual History of 

 Development of Vertebrate Animals, including Man. — The Fructi- 

 fication of the Egg. — Formation of the Three Germ Layers.— 

 History of the Development of the Central Nervous System, of the 

 Extremities, of the Branchial Arches, and of the Tail of Vertebrate 

 Animals. — Causal Connection and Parallelism of Ontogenesis and 

 Phylogenesis, that is, of the Development of Individuals and Tribes. 

 — Causal Connection of the Parallelism of Phylogenesis and of 

 Systematic Development. — Parallelism of the three Organic Series 

 of Development 280 



CHAPTER XIII. 



THEORY OF THE DEVELOPMENT OF THE UNIVERSE AND OF 

 THE EARTH. SPONTANEOUS GENERATION. THE CARBON 

 THEORY. THE PLASTID THEORY. 



History of the Development of the Earth. — Kant's Theory of the De- 

 velopment of the Universe, or the Cosmological Gas Theory. — 

 Development of Suns, Planets, and Moons. — First Origin of Water. 

 — Comparison of Organisms and Anorgana. — Organic and Inorganic 

 Substances. — Degrees of Density, or Conditions of Aggregation. — - 

 Albuminous Combinations of Carbon. — Organic and Inorganic 

 Forms. — Crystals and Formless Organisms without Organs. — 



