io INTRODUCTION 



VERTEBRATE ANIMALS 



The Vertebrate animals are usually arranged in five 

 classes : 



I. Mammalia (Latin mamma, a teat). Animals which 

 suckle their young, bringing them into the world alive. 

 Examples : Man, monkey, ox, elephant, and whale. 



II. Aves (Latin, avis, a bird). Birds are oviparous ; they 

 are produced from eggs by the application of heat, usually 

 supplied by the body of the mother bird in close contact 

 with them. The covering of mammals varies very consider- 

 ably, but birds are always clothed with feathers, which are 

 a part of their special construction for flight. Examples : 

 Eagle, swan, ostrich, and lark. 



III. Reptilia (Latin, repo, 'I creep'). Reptiles are cold- 

 blooded animals, protected by scales and not infrequently 

 by hard bony plates. They are mostly oviparous, but 

 developed from the eggs more or less casually by the heat 

 of the sun. They can endure long periods of abstinence, 

 and are so tenacious of life that many of them will survive 

 the severest bodily injuries. ' Reptile' is not an apt name, 

 for there are many members of the class that do not creep. 

 Examples : Crocodile, lizard, tortoise, and snake. 



IV. Batrachia (Greek, batrochos, a frog), or Amphibia 

 (Greek, amphibios, having a double life). In this class 

 were once included the reptiles and certain fishes, and the 

 latter term is still popularly used to denote animals that can 

 exist for a considerable time on dry land or in water. They 

 are oviparous, hatched by the heat of the sun from eggs, 

 covered with a soft glutinous membrane, which the mother 

 has laid in the water. In the early period of their existence 

 they are fishlike in their structure, breathing by means of 

 gills and a two-chambered heart ; in the later stages of 

 their development they acquire lungs and a heart of three 

 chambers. A true amphibian possesses at once both lungs 

 and gills. Examples : Frog, toad, and newt. 



V. Pisces (Latin, piscis, a fish). Fishes are oviparous. 

 Their bodies are covered with scales, which form an 

 important part of their special organisation for life in the 



