VI CONTENTS. 



CHAPTER XVI. 



TUB ANCESTRY OF MAN. 



I. FBOM THE MONERA TO THE GASTRJEA. 



MM 



I 'elation of the General Inductive Law of the Theory .of Descent to 

 the Special Deductive Laws of the Hypotheses of Descent. Incom- 

 pleteness of the Three Great Eecorda 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 Verte- 

 brate Ancestors. Distribution 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 Homo- 

 geneous Plasson of the Monera. Differentiation 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, Ontogeneti- 

 cally reproduced in the Mornla. 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 (invagi- 

 natid) of the Planaea. Haliphysema and Gastrophysema. Extant 

 Gastrajads ... ... ... ... ... ... 34 



CHAPTER XVIL 



THE ANCESTRAL SERIES OF MAN. 

 II. FROM THE PRIMITIVE WORM TO THE SKULLED ANIMAL. 



The Four Higher Animal Tribes are descended from the Worm Tribe. 

 The Descendants- of the Gastraa; in one direction the Parent 

 Form of Plant- Animals (Sponges and Sea-Nettles), in the other 

 the Parent Form of Worms. Radiate form of the former, Bilateral 

 form of the latter. The Two Main Divisions of the Worms, 

 Acoelomi and Coelomati: the former without, the latter with, a 

 Body Cavity and Blood-vessel System. Sixth Ancestral Stage : 

 Archelminthes, most nearly allied to Turbellaria. Descent of the 



