CHAPTER XVIII. 

 THE PEDIGREE OF ]VIAN. 



III. Feom the Primitive Fish to the Amniotic Animal. 



Comparative Anatomy of the Vertebrates. — The Characteristic Qualities of 

 the Donble-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 Pri- 

 mitive Fishes (^Selachii), the Ganoids {Ganoides), the Osseous Fishes 

 (Teleostei). — Dawn of Terrestial 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, LepidosireUy Ceratodua). — 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 (Salaman. 

 ders and Mud-fish). — Frog Batrachians (Frogs and Toads). — Chief 

 Ghroup of the Amnion Animals, or Amniota (Reptiles, Birds, and 

 Mammals). — Descent of all the Amniota from a Common Lizard.like 

 Parent-form (Protamnion) . — First Formation of the Allantois and of the 

 Amnion. — Branching of the Amnion Animals in Two Lines : on the one 

 side, Reptiles (and Birds), on the other side. Mammals. 



** The imagination is an indispensable faculty ; for it ifl that which, by 

 forming new combinations, occasions important discoveries. The naturalist 

 needs both the discriminating power of abstract reason, and the generalizing 

 power q{ tb0 imagination, and that the two should be harmoniously inter. 



