CONTENTS. 



PAGB 



Layer and tlie Skin-fibrous Layer.— The Entoderm or Intestinal 

 Layer gives rise to the Intestinal-fibrous Layer and the Intestinal- 

 glandular Layer 184 



CHAPTER IX. 



THE VERTEBRATE NATURE OF MAN. 



Relation of Comparative Anatomy to Classification. — The Family-rela- 

 tionship of the Types of the Animal Kingdom. — Different Signi- 

 ficance and Unequal Value of the Seven Animal Types. — The 

 Gastrcr^a Theory, and the Phylogenetic Classification of the Animal 

 Kingdom. — Descent of the Gastrsea from the Protozoa. — Descent 

 of Plant-animals and Worms from the Gastraea. — Descent of 

 tlie Four Higher Classes of Animals from Worms. — The Verte- 

 brate Nature of Man. — Essential and Unessential Parts of the 

 Vertebral Organism. — The Amphioxus, or Lancelet, and the Ideal 

 Primitive Vertebrate in Longitudinal and Transverse Sections. —  

 The Notochord.— The Dorsal Half and the Ventral Half.— The 

 Spinal Canal. — The Fleshy Covering of the Body. — The Leather- 

 skin (coriuni), — The Outer-skin (epidermis). — Body-cavity (cceloma). 

 — The Intestinal Tube. — The Gill-openings. — The Lymph-vessels. 

 — The Blood-vessels. — The Primitive Kidneys and Organs of Re- 

 production. — The Products of the Four Secondary Germ-layers ... 244 



CHAPTER X. 



THE CONSTRUCTION OF THE BODY FROM THE GERM- 

 LAYERS. 



The Original (Palingenetic) Development of the Vertebrate Body from 

 the Gastrula. — Relation of this Process to the Later (Kenogenetic) 

 Germination, as it occurs in Mammals. — The most important act in 

 the Formation of the Vertebrate. — The Primary Germ-layers, and 

 also the Secondary Germ-layers, which arise by Fission of the Prima, 

 ries, originally form Closed Tubes. — Contemporaneously with the 

 Completion of the Yelk-sac, the Germ-layers flatten, and only later 

 again assume a Tabular Form. — Origin of the Disc-shaped Mamma- 

 lian Germ-area. — Light Germ-area (area peUticida) and Dark Germ- 

 area (area ojmca). — The Oval Germ-shield, which afterwards 

 assumes the Shape of the Sole of a Shoe, appears in the Centre of 

 the Light Germ-ai-ca (a. pellucida). — The Primitive Streak 



