Vi CONTENTS. 



CHAPTER XVI. 



THE ANCESTRY OF MAN. ' . 



I. From the Monera to the Gastr^a. 



rA3t 



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

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

 pleteness 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 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 Pi'otoplasm 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 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 (^invagi- 

 natio) of the Plansea. — Haliphysema and Gastrophysema. — Extant 

 GastruDada <•• ... .c ... ... ... 34 



CHAPTER XVII. 



THE ANCESTRAL SERIES OF MAN. 



II. From the Primitive Worm to the Skulled Animal. 



The Four Hiffher Animal Tribes are descended from the Womi Tribe. 

 — The Descendants of the Gastraea; 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 : 

 Ai'chelminthes, most nearly allied to Turbcllaria. — Descent of the 



