Vll 



PACE 



Ccelomati from tlie Acoelomi. Mantled Animals (Tunicata) and 

 Chorda- Animals (Chordonia) . Seventh Stage: Sof t -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- 

 donia) . 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 (Crania to) .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- 

 noioke and Petromyzonidce) ... ... ... ... ... 71 



CHAPTER XVIII. 



THE PEDIGREE OP MAST. 

 III. FBOM 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 Batrachiana 

 (Salamanders and Mud-fish). Frog Batrachiana (Frogs and 

 Toads). Chief Group of the A.mnion Animals, or Amniota (Reptiles, 

 Birds, and Mair.mi>,ls). Descent of all the Amniota from a Common 



