INTRODUCTION. 23 
Crass II. AMpHIBIA (Amphibians).—Breathing-organs in the young 
in the form of gills alone, afterward lungs, either alone or associated 
with gills. Skull jointed to the backbone by two articulating surfaces 
(“condyles”). Limbs never converted into fins. Heart in the young 
of two chambers only, in the adult of three chambers. Blood cold. 
Order 1. Ladbyrinthodontia (extinct). 
Order 2. Ophiomorpha.—Lx. Cecilia. 
Order 3. Urodela (Tailed Amphibians), — Zx. Water - newts 
(Triton), Salamanders (Salamandra), Axolotl (Siredon), 
Mud-eel (Siren). 
Order 4. Azoura (Tailless Amphibians). —Zx. Frogs (Rana), 
Tree-frogs (Hyla), Toads (Bufo), Surinam Toads (Pipa). 
Oxass III. RepriiiA (Reptiles).—Respiratory organs in the form 
of lungs, never in the form of gills. Heart three-chambered, rarely 
four-chambered, the pulmonary and systemic circulations always con- 
nected together directly, either in the heart itself or in its immediate 
neighbourhood. Blood cold. Skull jointed to the backbone by a 
single articulating surface or ‘‘ condyle.” Each half of the lower jaw 
composed of several pieces. Appendages of the skin in the form of 
scales or plates. 
Order 1. Chelonia.— Ex. Turtles (Cheloniidz), Soft Tortoises 
(Trionycidze), Terrapins (Emydidze), Land Tortoises 
(Testudinide). 
Order 2. Ofhidia.—Ex. Vipers (Viperidz), Rattlesnakes (Crota- 
lidze), Sea-snakes (Hydrophide), Boas and Pythons 
(Boidee). 
Order 3. Lacertilia.—Ex. Lizards (Lacerta), Iguanas (Iguanide), 
Monitors (Varanidze), Chameleons (Chameleontidz). 
Order 4. Crocodilia.—Ex. Crocodiles, Alligators, Gavials. 
Order 5. /chthyopterygia (extinct).—Zx. Ichthyosaurus. 
| Order 6. Sauropterygia (extinct)—Z. Plesiosaurus. 
Order 7. Prerosauria (extinct).—x. Pterodactylus. 
Order 8. Anomodontia (extinct).—#x. Dicynodon. 
Order 9. Deinosauria (extinct).—£x. Iguanodon. 
Cass IV. Aves (Birds),—Respiratory organs in the form of lungs, 
never in the form of gills. Lungs connected with air-receptacles placed 
in different parts of the body. Heart four-chambered. Blood warm. 
Skull connected with the backbone by a single articulating surface or 
“condyle.” Each half of the lower jaw composed of several pieces. 
Appendages of the skin in the form of feathers. Cavities of the chest 
and abdomen not separated by a complete partition (diaphragm). 
Fore-limbs converted into wings. Animal oviparous. 
Order 1. Matatores (Swimmers). — x. Penguins (Spheniscide), 
Gulls (Laride), Ducks (Anatide), Geese (Anserinz), 
Flamingos (Pheenicopteridz). 
Order 2. Grallatores (Waders). — x. Rails (Rallide), Water- 
hens (Gallinulze), Cranes (Gruidee), Herons (Ardeide), 
