This book in views and Definitions of Species How Darwin's differs from that of Agassiz, and from the Common View Variation, its Causes unknown. Darwin's Genealogical Tree Darwin and Agassiz agree in the Capital Facts Embryology Physical Connection of Species compatible with Intellectual Connection How to prove Transmutation. Known Extent of Variation Cause of Likeness unknown Artificial Selection. Reversion Interbreeding Natural Selection. Classification tentative. What Darwin assumes. Argument stated. How Natural Selection works. Where the Argument is weakest. Objections Morphology and Teleology harmonized. Theory not atheistical. Conceivable Modes of Relation of God to Nature .