116 THE WANDERINGS OF ANIMALS [CH. 



* ant-eater ' Myfmecobius of West Australia and the 

 small ' marsupial mole,' Notoryctes typhlops, a blind 

 digger in the barren centre. II. Diprotodonta, with 

 only one pair of lower incisors, usually enlarged, e.g. 

 the numerous kangaroos, Macropodidae, one genus 

 of which, Dendrolagus, contains the tree-kangaroos. 

 The phalangers are a very diversified family ; all 

 are climbers ; some, e.g. Petaurus, look exactly like 

 flying squirrels, others like mice. The tiny Tarsipes 

 lives in Western, the koala or l native bear,' Phascol- 

 arctos, in East Australia. Two phalangers are 

 restricted to Celebes. Phascolomys, the wombat, 

 has assumed rodent-like characters. Lastly, two 

 small species of Caenolestes in Ecuador and Co- 

 lombia are also diprotodont and possibly more 

 nearly related to the Australian phalangers than to 

 the strictly American opossums. 



A time-honoured explanation of the present dis- 

 tribution of marsupials is that they had an almost 

 world-wide range when Australia was still accessible 

 from the north. When, after the separation, the 

 Placental mammals had been evolved in Arctogaea, 

 the marsupials could no longer hold their own, except 

 those which were safely shut up in the Australian 

 region, and except the few opossums in America 

 which saved themselves by early adopting an arboreal 

 life. In principle this story is right, but wrong in 

 detail. It is also awkward for this hypothesis that 



