C0NTENT8. 



Coelomati from the Acoelomi. — Mantled Animals (Twnxcata) and 

 Chorda- Animals (Chordoma) .—Seventh Stage : Soft- Worms (Scole. 

 cida). — A Side Branch of the latter : the Acorn-Worm (Balano- 

 glossus). — Differentiation of the Intestinal Tnbe into Gill-intes- 

 tine and Stomach-intestine. — Eighth Stage : Chorda-Animals (Chor- 

 doma). — Ascidian Larva exhibits the Outline of a Chorda-Animal. — 

 Construction of the Notochord. — Mantled Animals and Verte- 

 brates as Diverging Branches of Chorda-Animals. — Separation of 

 Vertebrates from the other Higher Animal Tribes (Articulated 

 Animals, Star-Animals, Soft-bodied Animals). — Significance of the 

 Metameric Formation. — Skull-less Animals (Acrania) and Skulled 

 Animals (Craniota) . — Ninth Ancestral Stage : Skull-less Animals. 

 — Amphioxus and Primitive Vertebrate. — Development of Skulled 

 Animals (Construction of the Head, Skull, and Brain). — Tenth 

 Ancestral Stage : Skulled Animals, allied to the Cyclostomi (Myxi- 

 noida and Petromyzonidce) ... ... ... ... ... 71 



CHAPTER XVIII. 



THE PEDIGREE OF MAN. 



III. From the Primitive Fish to the Amniotic Animal. 



Comparative Anatomy of the Vertebrates. — The Characteristic Qualities 

 of the Double-nostrilled and Jaw-mouthed : the Double-Nostrils, 

 the Gill-arch Apparatus, with the Jaw-arches, the Swimming- 

 bladder, the Two Pairs of Limbs. — Relationship of the Three 

 Groups of Fishes : the Primitive Fishes (Selachii), the Ganoids 

 (Ganoides), the Osseous Fishes (Teleostei). — Dawn of Terrestrial 

 Life on the Earth.— Modification of the Swimming-bladder into 

 the Lungs. — Intermediate Position of the Dipneusta between the 

 Primitive Fishes and Amphibia. — The Three Extant Dipneusta 

 (Protopterus, Lepidosiren, Ceratodus). — Modification of the Many- 

 toed Fin of the Fish into the Five-toed Foot. — Causes and Effects 

 of the latter. — Descent of all Higher Vertebrates from a Five-toed 

 Amphibian. — Intermediate Position of the Amphibians between the 

 Lower and Higher Vertebrates. — Modification or Metamorphosis of 

 Frogs. — Different Stages in Amphibian Metamorphosis. — The 

 Gilled Batrachians (Proteus and Axolotl). — The Tailed Batrachians 

 (Salamanders and Mud-fish). — Frog Batrachians (Frogs and 

 Toads). — Chief Group of the Amnion Animals, or Amniota (Reptiles, 

 Birds, and Mammals). — Descent of all the Amniota from a Common 



