CHAPTER XXXIX 



THE ORDERS OF MAMMALS 



The seventy-five hundred species of living mammals may be 

 grouped into a number of orders. Some orders contain more 

 common or more important species than others and a few are 

 represented only by a few little-known animals. The groups 

 described in the following paragraphs are for the most part illus- 

 trated by species that occur in this country. 



Egg-laying Mammals. — These primitive mammals are con- 

 fined to Australia, New Guinea, and Tasmania. Their most 

 conspicuous peculiar- 

 ity is their egg-laying 

 habit, since they are 

 the only mammals that 

 reproduce in this way- 

 The young before 

 hatching live on the 

 yolk contained in the 

 egg. After hatching 

 they are for a time 

 nourished by milk from 

 the mammary glands. 



The duckbill (Fig. 

 284) is adapted for 

 life in the water. It 

 possesses webbed feet, 

 a thick covering of waterproof fur like that of a beaver, and a 

 duck-like bill with which it probes in the mud under water for 

 worms and insects. During the daytime the duckbill sleeps in 



419 



Fig. 284. 



- The duckbill. (From Shipley and 

 MacBride.) 



