THE RISE OF THE MAMMALIA 123 



the breeding season. Here, after a very short incu- 

 bation, the young Echidna hatches out in a very 

 undeveloped and helpless state, and it proceeds to 

 suck the milk of the mother which is secreted by 

 mammary glands, the openings of which are scattered 

 over the surface of the breast in the region of the 

 pouch. In this situation the young Echidna continues 

 to develop, until it is ready to go out and seek its 

 insect food for itself. At no time of its life does the 

 Echidna develop any teeth, though the palate and 

 tongue are covered with horny spines for masticating 

 the bodies of the ants on which it feeds. 



The Platypus, which is really very closely related 

 to the Echidna, follows a very different mode of life, 

 being amphibious in its habits and frequenting rivers 

 and mountain lakes where it feeds upon fresh- water 

 molluscs and the fry of fish. Instead of being covered 

 with quills, it is clothed with a very rich and smooth 

 fur, something like an otter's ; its toes are webbed 

 and it possesses a flat horny bill very much like a 

 duck's, with which it catches the shell-fish. The jaws 

 are furnished with horny plates in place of teeth for 

 grinding the hard shells, but this animal during 

 development exhibits the rudiments of true tuber- 

 culated teeth in its jaws which are never cut to the 

 surface, thus proving that these animals possessed in 

 the past the Mammalian type of teeth. The Duck- 

 billed Platypus excavates a burrow in the bank of 



