The Story of the RocJcs 



139 



to her pouch where their mouths become temporarily attached 

 to the mother's teats and where they grow in safety until 

 ready for their second debut in the world. "Well-known ex- 

 amples are our own opossum, and the Australian kangaroo. 

 The distribution of modern marsupials is very peculiar and 

 with other facts has given rise to interesting speculations re- 

 garding the earlier form of Mother Earth. Their repre- 

 sentatives are found today exclusively in Australia and ad- 

 jacent regions, South America and tropical North America, 

 with the exception of the opossum of the United States. In 



THE SPINY ANT-EATER 

 A monotreme, one of the most primitive of. mammals. 



Photo by Elwin R. Sariborn 

 By permission of the New York Zoological Society. 



Mesozoic and Eocene time however the marsupial stock was 

 distributed over North America and Europe and possibly 

 Asia as well. 



The distribution of the ostrich in Africa and its relatives, 

 the rhea in South America, and cassowary and emu in Aus- 

 tralia and the East Indies and the recently extinct moa of 

 New Zealand, is similar to that of the marsupials. These 

 facts and other similar ones have led many biologists and 

 palaeontologists to the belief in a migration of life from the 

 northern hemisphere into the southern at some very early 

 period in the earth's history. They have also suggested the 

 existence of former land connections between South Amer- 



