THE OPOSSUM 63 



be compared with other before known mammals and also 

 with it. Moreover, though the American opossum is a 

 marsupial, and possesses all the characters of the didel- 

 phous sub-class, it is none the less the representative of 

 a very distinct family of that sub-class. It has been 

 pointed out how distinct are the apes which inhabited 

 the Old World from all those in America. It is just the 

 same with the marsupials. There is no single species of 

 mai'supial found in Australia or anywhere else out of 

 America which is in the present day also found in 

 America. The American opossums are as much marsu- 

 pials as are any marsupials. Nevertheless, they do not 

 exhibit such great anomalies as do the kangaroos and 

 bandicoots with respect to their feet, or the myrmecobius 

 with respect to the number of its teeth. 



But the geographical limits of the whole order, or sub- 

 class, of marsupials are very interesting, for they are, at 

 the same time, the limits of many other groups of animals 

 and also of plants. We have not only an animal popula- 

 tion (or fauna), but also a set .of plants (or flora) which 

 is characteristic of what is called the Australian region, 

 that is extending not only over Australia and Tasmania, 

 but more or less over New Guinea and the Moluccas, 

 reaching as far north-west as the Island of Lombock, 

 and even to Timor. 



In India, the Malay Peninsula, and the great islands 

 of the Indian Archipelago, we have another and a very 

 different fauna and flora that, namely, at the Indian 

 region ; and Indian forms of life extend downward south- 

 cast as far as the Island of Bali. Now, Bali is separated 

 f lorn Lombock by a strait of about fifteen miles broad. 

 Yet that little channel is the boundary line between 

 these two great regions the Australian and the Indian. 

 The Indian fauna advances to its western margin, while 



