596 GEOGRAPHICAL DISTRIBUTION 



line called Wallace s line dividing the two realms passes 

 northwards between Bali and Lombok, between Borneo and 

 Celebes and eastwards of the Philippines. Celebes has, 

 however, some claims to be regarded as belonging to 

 Arctogoea. 



We may naturally ask — What is the meaning of this 

 faunistic character of the realm Notogoea? How has this 

 realm come to be a sort of '^ preserve " for the two archaic 

 sub-classes to the almost entire exclusion of the third and 

 more highly organised sub-class ? The past history of 

 Notogoea does not help us much, for its geological strata 

 have not been sufficiently investigated. Remains of the 

 modern Monotremes are found in the Pleistocene of 

 Australia. The same is true of the Metatheria, including 

 the large extinct forms of Diprotodon and Thylacoleo. 

 Further back than the Pleistocene, or at least the Pliocene, 

 we know nothing of the fossils of Notogoea. On the other 

 hand, w^e find that remains of Metatheria occur in Europe 

 and North America from the Triassic through Jurassic 

 to Cretaceous. Indeed, Europe and North America, 

 and possibly Asia by inference, were largely peopled by 

 Metatheria during the secondary period ; but, we have as 

 yet no evidence of Eutherian mammals during this 

 period. Hence in these important respects the fauna of 

 Notogoea at the present day resembles that of Eurasia in 

 the secondary period. The inference is that at that period 

 Notogoea (Australia and New Guinea) was connected by 

 Jand with the Eurasian continent, and further, that this land 

 connection was broken at the dawn of the Tertiary epoch 

 before the Eutherian mammals were evolved. The connec- 

 tion having never since been restored, the Metatheria in 

 Notogoea have been free to become modified and adapted 

 into their numerous types now existing. The few Eutheria 

 now existing in Notogoea have on this assumption effected a 

 crossing either in canoes (man and probably the native 

 dingo), or timber (the Muridce), or by flight (the bats). Man 

 has more lately introduced the Eutherian rabbit and sheep, 

 besides other types, and the rabbit at least appears to be 

 making up rapidly for the time lost since the early Tertiary, 

 during w^hich it has been excluded from the district. If 

 we may regard the Allotheria as true Prototheria^ we may 



