CHAPTER XVI. 



THE ANCESTRY OF MAN. 



I. FROM THE MONERA TO THE 



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 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. 

 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 

 Blastnla or Planula. Fifth Ancestral Stage : Gastraea, Ontogenetically 

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

 the Gastraea by Inversion (invaginatioi) 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 ; and it is necessary to perform the experiment 



