CHAPTER XVI. 



THE ANCESTRY OF MAN. 



I. Feom the Moneea to the Gaste^ea. 



Relation of the General Inductive Law of the Theory of Descent to the 

 Special Deductive Laws of the Hypotheses of Descent.— Incompleteness 

 of the Three Great Eecords 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. — 

 The Structureless and Homogeneous Plasson of the Monera. — Differen- 

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

 Cytods and Cells as Two Different Plastid-forms. — Vital Phenomena 

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

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

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

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

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

 Fourth Ancestral Stage : Planaea, Ontogenetically reproduced in the 

 Blastula or Planula. — Fifth Ancestral Stage : Gastraea, Ontogenetically 

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

 the Gastraea by Inversion (invaginatio) of the Planaea. — Haliphysema 

 and Gastrophysema. — Extant Gastraeads. 



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

 simple, 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 j and it is necessary to perform the experiment 



