64 TYPES OF ANIMAL LIFE 



the Australian fauna stops short at its eastern margin. 

 The zoological line of demarcation which thus passes 

 through these straits is called "Wallace's line," because its 

 discovery is due to the labours of that eminent naturalist 

 and most persevering explorer. He showed that not only 

 as regards beasts, but also ai regards birds, these regions 

 are thus sharply limited. Australia, he pointed out, has 

 no woodpeckers and no pheasants, those widely spread 

 Indian birds. Instead of these it has mound-making 

 turkeys, honey-suckers, cockatoos, and brush-tongued 

 lories, all of which are found nowhere else in the world. 

 By becoming acquainted with all the various facts here 

 detailed, it is possible to answer the question, " What is 

 an opossum ? " 



We may say that an opossum is a form of marsupial 

 life found only in America, and that it is a member of 

 an order so peculiar as to constitute by itself a sub-class 

 of the great class of beasts or mammalia. It is also a 

 member of a sub-class intermediate between that to 

 which the overwhelming majority of beasts belong, and 

 the very restricted ornithodelphous sub-class which leads 

 us down toward birds and reptiles. We may further say 

 that the opossum is one important link in the evidence 

 which, in some zoological respects, connects the South 

 American continent with Australia, while at the same 

 time it adds one more ground to the many which 

 already exist for believing in the close zoological rela- 

 tionship between North America and the Europe of 

 tertiary times. But the opossum has also another note- 

 worthy distinction in that it exists in isolation in the 

 midst of a vast continent which teams with non-marsupial 

 foi-rns of mammalian life. All the other marsupials live 

 together in one mass, in all but complete isolation from 

 non-marsupial beasts, the only exception being a few 



