CLASSIFICATION OF LIVING THINGS 145 



Class 2. Amphibia. Cold blooded vertebrates with 

 naked scaleless skin. Breathe by lungs in adult 

 life commonly, the larvse breathe by gills. Heart 

 with two auricles and a single ventricle. Frogs, 

 toads, salamanders. 



Class 3. Reptilia. Cold blooded scaly vertebrates. 

 Breathe by lungs; heart with auricles and two 

 imperfectly separated ventricles. Snakes, turtles, 

 alligators, lizards. 



Class 4. Aves. Warm blooded, oviparous, bipedal 

 vertebrates covered with feathers. The chambers 

 of the heart are completely separated. The an- 

 terior appendages have the form of wings. Birds. 



Class 5. Mammalia. Warm blooded, hairy vertebrates. 

 Viviparous; mammary glands with which they 

 suckle the young. Red blood corpuscles non- 

 nucleated. Mammals. 



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