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THE WORLD OF ANIMAL LIFE 



ship to fishes, and so they form a kind of eonnecting-link between 

 the fishes and the reptiles. As an example of this, in their younger 

 stages they breathe by means of gills and live entirely in the water; 

 when the adult stage is reached they breathe by means of lungs, 

 although they still live largely in the water, and they are then more 

 closely allied to reptiles. In a few instances gill-like appendages 



Different Stages in the Development of the Frog 



remain with them through life, so that they to some extent respire 

 water as well as ordinary air. 



In former ages giant amphibians existed. The whole group 

 is now, however, made up of small animals. They have a world- 

 wide distribution, if we except the frigid zones and dry deserts, 

 but they are most common in moist tropical and sub-tropical 

 regions. 



A distinction is made in the animals of this great class by its 

 division into separate orders, the frogs and toads forming the order 

 Ecaudata, the newts and salamanders the order Caudata, and a 

 few worm-like amphibians the order Apoda. 



These orders are divided into a good many families, which 

 embrace a great number of species. 



