20 



The Living Things of the Earth unit i 



Fig. 20 The spiny anteater of Australia and a Fig. 21 The duckbill of Australia. This iinvnnial 

 model of the egg it has laid. (American museum also lays eggs. (American museum of natural 

 OF natural history) history) 



in a pouch for a long time after birth. 

 See Figure 384, page 433. The kanga- 

 roos of Australia and the opossums of 

 our country belong to this group. In 

 one common species, the Virginia opos- 

 sum, the animal when discovered pre- 

 tends it is dead; it "plays 'possum." 

 There are several other kinds of mar- 

 supials in Australia besides kangaroos. 

 The simplest mammals lay eggs. Duck- 

 bills lay eggs and have bills like a duck 

 but since they have mammary glands 

 and hair they are considered to be mam- 

 mals. Spiny anteaters and armadillos are 

 other simple mammals. Now do Exer- 

 cises 2, 3, and 4. If you would like to 

 continue your study of mammals, you 

 will find it useful to refer to some of 

 the interesting books on mammals listed 

 in the bibliography at the end of the 

 book. 



CLASS - BIRDS 



The characteristics of birds. Birds have 

 feathers. There are no exceptions. That 



is the characteristic by which you recoij- 

 nize them. The feathers are usually 

 lacking on the legs, which are covered 

 with scales. There are two other char- 

 acteristics almost as striking as the first: 

 birds have beaks or bills without teeth 

 and the forelimbs have the structure of 

 wings. 



Birds, like mammals, are \\arm- 

 blooded; their temperature, in general, 

 is higher than that of mammals. Some 

 of them, indeed, have a temperature of 

 112°. Like mammals they have four- 

 chambered hearts and they breathe by 

 means of lungs. There is much that \()u 

 can discover for yoursrlf if you will fol- 

 low the directions ir Exercises 5 and 6 

 carefullv\ 



Subdivision of the class. This class is 

 subdivided into many different orders 

 but the differences between the orders 

 are technical and difficult to learn. In 

 this section, we shall use a simple group- 

 ing based mostly on the kind of feet and 

 bill: birds of prey, scratching birds, 



