x CONTENTS. 
PAGE 
between the Number of ‘Possible or Potential, and the Number of 
Real or Actual Individuals.—Complicated Correlations of all Neigh- 
bouring Organisms.—Mode of Action in Natural SelectionHomo- 
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 Characters).—Transition of Varieties into 
Species.—Idea of Species—Hybridism.—Law of Progress or Per- 
fecting (Progressus, Teleosis) ... and oe pie “a wo 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 ... ee oe se x6 sa aa .-- 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.— 
