42 DOCTRINE OF EVOLUTION 



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elements absent. The horse comes last with one large 

 toe and hoof, but on either side of the main bones of 

 this digit are vestiges of what must have been toes in 

 its ancestors. Among the even-toed forms the hippopot- 

 amus has four which reach the ground, with a vestige 

 of a fifth, so this animal has apparently descended from 

 a typical mammal with the full number along a different 

 line from that taken by the odd-toed forms. A pig 

 has a cloven hoof, made up of what we may call the 

 third and fourth members of a series of five digits, but 

 the second and fifth fingers and toes are present, 

 though they are withdrawn from the ground so as to be 

 no longer functional; this animal seems to have pro- 

 ceeded further along the same line taken by the hippo- 

 potamus. A deer, with still smaller rudiments at the 

 sides of its double foot, leads in the comparative series 

 to the camel with a cloven hoof devoid of any such rehcs. 

 We must pass with only brief mention the lower orders 

 of mammalia, like the insect-eating forms to which 

 armadillos and ant-bears belong. Of greater interest 

 are the pouched mammals like the kangaroo and 

 opossums, which Uve almost exclusively in the AustraUan 

 realm. The kangaroo is endowed with a head somewhat 

 like that of a goat, and well-developed hind legs that 

 enable it to make leaps of astonishing length. Some 

 of its relatives, such as the bandicoot, are like rats, or 

 hke bears, as in the case of the wombat. The Tas- 

 manian wolf is another true marsupial, even though 

 divergent adaptation has brought it to resemble the 

 carnivora of the dog tribe in general appearance and in 

 special structures like the teeth. Finally at the very 

 bottom of the mammalian scale are two small forms 



