CHAPTER XVI. 

 THE ANCESTRY OF MAN. 



I. FROM THE MONERA TO THE GA8TR-EA. 



Rotation 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. 

 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 Natm-e. The Amoeboid Egg-cells. The Egg is Older than 

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

 duced in the Mornla. A Community of Homogeneous Amoeboid Cells. -- 

 Fourth Ancestral Stage : Planaea, Ontogenetically reproduced in the 

 Blastnla or Planula. Fifth Ancestral Stage : Gastrsea, Ontogenetically 

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

 the Gastraea by Inversion (invaginatid) of the Planaea. Haliphysema 

 and Gastrophysema. Extant Gastraeads. 



" Now, Tery 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 



