360 GENERAL SCIENCE 



Reptiles. Reptiles are lung-breathing vertebrates 

 having a scaly tough skin. Common reptiles are snakes, 

 turtles, alligators, and crocodiles. In the turtle the scaly 

 covering has developed into a bony shell. Reptiles are 

 related to birds. They reproduce themselves by means 

 of eggs which they lay in the ground. A few snakes are 

 poisonous. In the United States the most dangerous 

 are the rattlesnake, the copperhead, and the water 

 moccasin. 



Birds. - - The principal characteristics of birds are their 

 protective covering of feathers and the presence of wings. 

 The feathers are developed from the skin and show a 

 variety of form and color. The bills of birds also exhibit 

 a variety of forms adapted to the ways in which the dif- 

 ferent birds get their food. Birds of prey have a hooked 

 beak. The woodpecker has a sharp straight bill. Birds 

 breathe much faster than we do and have a very rapid 

 circulation of blood. This causes a high body tempera- 

 ture. The body temperature of birds is often eight or 

 ten degrees Fahrenheit higher than that of man. 



Mammals. --The class of animals known as mammals 

 includes man, a large number of quadrupeds such as the 

 dog, cat, sheep, pig, horse, and cow, and a few animals 

 like the whale and seal. They are called mammals be- 

 cause they nurse their young with milk secreted by glands 

 known as mammary glands. Other characteristics of 

 mammals are their covering of hair, well-developed lungs, 

 and a highly developed nervous system. 



Most of the mammals live on land. Some, like the 

 seal and sea lion, inhabit islands and waters near the land ; 

 a few, like the whale, live in the ocean. These animals 

 are variously adapted to their particular kind of life. 

 Some live in trees ; others burrow in the ground. Some 



