THE ALLIES OF THE SQUIRREL: MAMMALIA 409 



that they lay eggs inclosed in a white, flexible shell, remind- 

 ing one of the egg of a reptile. The duckbill gets its name 

 from its peculiar duck-like beak, which is toothless when the 

 animal is full grown, the teeth being shed after they have 

 been used for a while. The male has a hollow spur on the 

 heel, which is connected with a poison-gland in the thigh. 

 The duckbill is semiaquatic, and lives in burrows in the 



FIG. 215. Duckbill 

 (From Lydekker's Geographical History of Mammals) 



banks of ponds and streams. Its food consists of mollusks, 

 small insects, worms, and crustaceans. Spiny ant-eaters are 

 inhabitants of elevated rocky districts and feed on ants. 

 They are protected by a covering of spines intermixed with 

 the hairs. 



Kangaroos, Opossums, and Allies. The order Marsupia'lia 

 (Lat. marsupium, a pouch) contains a large number of spe- 

 cies, almost all of which are confined to Australia and the 



