340 TROPICAL NATURE, AND OTHER ESSAYS. 



entire country been isolated from tlie northern continent 

 during middle and late Tertiary times, would long since 

 liave become extinct. 



The A ustralian Region. — There only remains for us 

 now to consider the relation of the island-continent 

 of Australia to Asia and South America, with both 

 which countries it has a certain amount of zoological 

 connection. 



Australia, including New Guinea (which has in recent 

 times been united with it), differs from all the other 

 continents by the extreme uniformity and lowly organ- 

 isation of its mammalia which almost all beloDo: to one 

 of the lowest orders — the marsupials. Monkeys, carni- 

 vora, insectivora, and the great and almost ubiquitous 

 class of hoofed-animals, are all alike wanting ; the only 

 mammals besides marsupials being a few species of a 

 still lower type — the monotremes, and a few of the very 

 smallest forms of rodents — the mice. The marsupials, 

 however, are very numerous and varied, constituting 

 G families and 33 genera^ of which there are about 120 

 known species. None of these families is represented 

 in any other continent ; and this fact alone is sufficient 

 to prove that Australia must have remained almost or 

 quite isolated during the whole of the Tertiary period. 



In birds there is, as we might expect, less complete 

 isolation ; yet there are a number of very peculiar types. 

 About 15 families are confined to the Australian region, 

 among which are the paradise-birds, the honey-suckers, 

 the lyre-birds, the brush-tongued lories, the mound- 

 makers, and the cassowaries. 



Our knowledge of the former mammalian inhabitants 



1 



