CHAPTER XVI. 

 THE ANCESTRY OF MAN. 



I. From the Moneea to the Gaste^a. 



RolfttJOTi of the General Inductive Law of the Theory of Descent to tho 

 Special Deductive Laws of the Hypotheses of Descent.— Incompleteness 

 of the Three Great Records of Creation : Palaeontology, Ontogeny, and 

 Comparative Anatomy. — Unequal Certainty of the Various Special 

 Hypotheses of Descent. — The Ancestral Line of Men in Twenty-two 

 Stages : Eight Invertebrate and Fourteen Vertebrate Ancestors. — Distri- 

 bution of these Twenty-two Parent-forms in the Five Main Divisions of 

 the Organic History of the Earth. — First Ancestral Stage : Monera. — 

 1'he Structureless and Homogeneous Plasson of the Monera. — Differen- 

 tiation of the Plasson into Nucleus, and the Protoplasm of the Cells. — 

 C^'tods and Cells as Two Different Plastid-forms. — Vital Phenomena 

 of Monera. — Organisms without Organs. — Second Ancestral Stage : 

 Amoebae. — One-celled Primitive Aniuials of the Simplest and most Un. 

 differentiated Nature. — The Amoeboid Egg-cells. — The Egg is Older than 

 the Hen. — Third Ancestral Stage: Syn-Ainneba, Ontogenetically repro- 

 duced in the Morula. — A Community of Homogeneous Amoeboid Cells.— - 

 Fourth Ancestral Stage: Planaea, Ontogenetically reproduced in the 

 Rlastula or Planula. — Fifth Ances'ral Stage: Gastrsea, Ontogenetically 

 reproduced in the Gastrula and the Two-layered Germ-disc. — Origir-. of 

 the Gastraea by Inversion (invaginatio') of the Planaea. — Haliphyseina 

 and Gastrophysema. — Extant Gaotraeads. 



*' Now, very probably, if the course of evolution proves to be so very 

 eimple, it will be thought that the whole matter is self-evident, and that 

 research is hardly required to establish it. But the story of Columbus and 

 the egg is daily repeated ; and it is necessary to perform the experiment 



