CONTENTS. XI 



PAGE 



Differentiation of the Primitive Intestinal Tnbe into a Respiratory 

 and a Digestive Intestine. — Gill-intestine and Stoinach-intestine of 

 the Amphioxus and Ascidian. — Origin and Significance of the Gill- 

 openings. — Their Disappearance. — The Gill -arches and the Jaw- 

 Skeleton. — Formation of the Teeth. — Development of the Lnngs 

 from the Swim-bladder of Fish. — Differentiation of the Stomach. — 

 Development of the Liver and Pancreas. — Differentiation of the 

 Small and Large Intestines. — Formation of the Cloaca ... ... 311 



CHAPTER XXIV. 



DEVELOPMENT OF THE VASCULAR SYSTEM. 



Application of the Fundamental Law of Biogeny. — The Two Sides. — 

 Heredity of Conservative Organs. — Adaptation of Progressive 

 Organs. — Ontogeny and Comparative Anatomy complementary of 

 each other.— New "Theories of Evolution" of His. — The "En- 

 velope Theory " and the " Waste-rag Theory." — Main Germ and 

 Supplementary Germ. — Formative Yelk and Nutritive Yelk. — Phy- 

 logenetic Origin of the latter from the Primitive Intestine. — Origin 

 of the Vascular System from the Vascular Layer, or Intestinal- 

 fibrous Layer. — Phylogenetic Significance of the Ontogenetic Suc- 

 cession of the Organ-systems and Tissues. — Deviation from the 

 Original Sequence ; Ontogenetic Heterochronism. — Covering Tissue. 

 — Connective Tissue. — Nerve-muscle Tissue. — Vascular Tissue. — 

 Relative Age of the Vascular System. — First Commencement of 

 the Latter ; Coelonia. — Dorsal Vessel and Ventral Vessel of Worms. 

 — Simple Heart of Ascidia. — Atrophy of the Heart in the Am- 

 phioxus. — Two-chambered Heart of the Cyclostoma. — Arterial 

 Arches of the Selachii. — Double Auricle in Dipneusta and Am- 

 phibia. — Double Ventricle in Birds and Mammals. — Arterial Arches 

 in Birds and Mammals. — Germ-history (Ontogeny) of the Human 

 Heart. — Parallelism of the Tribal-history (Phylogeny) ... ... 348 



CHAPTER XXV. 



DEVELOPMENT OF THE URINARY AND SEXUAL ORGANS. 



Importance of Reproduction. — Growth. — Simplest Forms of Asexual 

 Reproduction : Division and the Formation of Buds (Gemmation). — 

 Simplest Forms of Sexual Reproduction : Amalgamation of Two 

 Differentiated Cells ; the Male Sperm-cell and the Female Egg-cell. 

 — Fertilization. — Source of Love. — Original Hermaphroditism ; 



