XII CONTENTS. 



tion of the Skull from the Head-plates. — Gill-openings and Gill- 

 arches. — Sense-organs. — Limbs. — The Two Front Limbs and the 

 Two Hind Limbs 328 



CHAPTER XII. 



THE GERM-MEMBR&NES AND THE FIRST CIRCULATION OF 

 THE BLOOD. 



The Mammalian Organization of Man. — Man has the same Bodily 

 Structure as all other Mammals, and his Embryo develops in 

 exactly the same way. — In its Later Stages the Human Embryo is 

 not essentially different from those of the Higher Mammals, and in 

 its Earlier Stages not even from those of all Higher Vertebrates. — 

 The Law of the Ontogenetic Connection of Systematically Related 

 Forms. — Application of this Law to Man. — Form and Size of the 

 Human Embryo in the First Four Weeks. — The Human Embryo in 

 the First Month of its Development is formed exactly like that of 

 any other Mammal. — In the Second Month the First Noticeable 

 Differences appear. — At first, the Human Embryo resembles those 

 of all other Mammals ; later, it resembles only those of the Higher 

 Mammals. — The Appendages and Membranes of the Human 

 Embryo. — The Yelk-sac. — The Allantois and the Placenta. — The 

 Amnion. — The Heart, the First Blood-vessels, and the First Blood, 

 arise from the Intestinal-fibrous Layer. — The Heart separates 

 itself from the Wall of the Anterior Intestine. — The First 

 Circulation of the Blood in the Germ-area (a. germinativa) : Yelk- 

 arteries and Yelk-veins. — Second Embryonic Circulation of the 

 Blood, in the Allantois : Navel-arteries and Navel- veins. — Divisions 

 of Human Germ-history P63 



CHAPTER XIIL 



THE STRUCTURE OF THE BODY OF THE AMPHIOXUS AND 

 OF THE ASC1DIAN. 



Causal Significance of the Fundamental Law of Biogeny. — Influence 

 of Shortened and Vitiated Heredity. — Kenogenetic Modification of 

 Palingenesis. — The Method of Phylogeny based on the Method of 

 Geology. — Hypothetic Completion of the Connected Evolutionary 

 Series by Apposition of the Actual Fragments. — Phylogenetio 

 Hypotheses are Reliable and Justified. — Importance of the Amphi* 



