AUSTEALIAK FArNA. 9 



no other way could we satisfactorily account for the remarkable 

 development of the marsupial types, and the almost total absence 

 of the commoner fonns that are elsewhere so abundant. The 

 oceanic barriers have evidently prevented that diffusion of species 

 which would otherwise have sufficed to render the Australian fauna 

 cosmopolitan in character. That this isolation, further, of the con- 

 tinent has been of very great duration is proved by the long period 

 of time, dating from the Cretaceous epoch, during which the 

 most diverse forms of mammalians have existed, and the high 

 specialisation that its own fauna has acquired. It may appear not 

 a little surprising, in view of what has preceded, that two groups of 

 animals, so widely removed from the rest of the Australian mam- 

 malian fauna as are the mice and bats, should yet constitute a 

 part of this fauna. In the case of the bats it is not difficult to ac- 

 count for their occurrence in the region in question, since their 

 powers of flight have enabled them to overcome such obstacles 

 as to other animals might have proved true barriers to migration. 

 The mice, on the other hand, whose disposition to gnaw into, and 

 conceal themselves among, timber of all kinds, is well known, may 

 have found their way hither from the Asiatic continent or its ad- 

 joining islands through the intermedium of floating masses of vege- 

 tation. Much more inexplicable is the occurrence of the single 

 non- Australian family of marsupials, the opossums, on the American 

 continent, which is removed by a continuous water-way of several 

 thousands of miles, when not a single member of the entire sub-class 

 of implacental mammals is found on any other part of the earth's 

 surface outside the Australian region. The hypothesis that land 

 connection by way of the Antarctic region at one time existed be- 

 tween Australia and South America, and, possibly, also Africa, 

 may or may not be true, but the evidence that has thus far been 

 adduced tending to show that by such connection a transferrence 

 of one section of the Marsupialia has been effected from one con- 

 tinent to the other is certainly very slim. Yet it is by no means 

 impossible that such may have been the case. The Edentata — 

 armadillos, ant-eaters, pangolins — whose home is preeminently the 

 two great continents of the Southern Hemisphere, and which barely 

 trespass north of the Tropic of Cancer, and the struthious birds, 

 like the rhea, ostrich, and cassowary, offer equal perplexities in the 

 way of an explanation of their anomalous distribution with the 

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