50 INTRODUCTION. 



CLASS I. PISCES (Fishes). Breathing-organs in the form of gills. Heart 

 usually of two chambers, rarely of three. Blood cold. Limbs, when present, 

 converted into fins. 



Order I. Pharyngobranchii. Ex. Lancelet (Amphioxus). 



Order 2. Marsipobranchii, Ex. Lamprey (Petromyzan), Hag-fish 



(Afyxine). 



Orders. Teleostei (Bony Fishes). Ex. Eels (Munenidae), Her- 

 rings (Clupeidae), Salmon and Trout (Salmonidae), Cod 

 and Haddock (Gadidae), Flat-fishes (Pleuronectidae), 

 Perch (Percidae), Mackerel (Scomberidae). 

 Order 4. Ganoidei. Ex. Bony Pike (Lepidosteus), Paddle-fish 



(Spatularia), Sturgeon (Sturio). 



Order 5. Elasmobranchii. Ex. Sharks (Carcharidse), Dog-fishes 

 (Scylliadse), Saw-fishes (Pristis), Rays and Skates 

 (Raiidse). 



Order 6. Dipnoi. Ex. Mud-fish (Lepidosiren). 



CLASS II. AMPHIBIA (Amphibians). Breathing-organs in the young in 

 the form of gills alone, afterwards lungs, either alone or associated with gills. 

 Skull joined 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 I. Labyrinthodontia (extinct). 

 Order 2. Ophiomorpha.Ex. Caecilia. 



Order 3. Urodela (Tailed Amphibians). Ex. Water - newts 

 (Triton), Salamanders (Salamandra), Axolotl (Sire- 

 don), Mud-eel (Siren). 



Order^ Anoura (Tailless Amphibians). Ex. Frogs (Rana), 

 Tree-frogs (Hyla), Toads (Bufo), Surinam Toads (Pipa.) 

 CLASS III. REPTILIA (Reptiles). Respiratory organs in the form of 

 lungs, never in the form of gills. Heart three-chambered, rarely four-cham- 

 bered, the pulmonary and systemic circulations always connected 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 I. Chelonia. Ex. Turtles (Cheloniidae), Soft Tortoises 

 (Trionycidae), Terrapins (Emydidte), Land Tortoises 

 (Testudinidae). 



Order 2. Ophidia.Ex. Vipers (Viperidae), Rattlesnakes (Crota- 

 lidae), Sea-snakes (Hydrophidae), Boas and Pythons 

 (Boidse). 



Order 3. Lacertilia. Ex. Lizards (Lacerta), Iguanas (Iguanidae), 

 Monitors (Varanidae), Chameleons (Chamaeleontidae). 

 Order 4. Crocodilia. Ex. Crocodiles, Alligators, Gavials. 

 Order 5. Ichthyopterygia (extinct). Ex. Ichthyosaurus. 

 Order 6. Sauropterygiu (extinct). Ex. Plesiosaurus. 

 Order 7. Pttrosauria (extinct). Ex. Pterodactylus. 

 Order 8. Anomodontia (extinct). Ex. Dicynodon. 

 Order 9. Deinosauria (extinct). Ex. Iguanodon. 



CLASS 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 



