266 TYPES OF ANIMAL LIFE 



allied ; though the resemblance is but an external one, 

 and, so far as it goes, yet further illustrates the doctrine 

 of the independent origin of similar structures. These 

 two animals are the echidna and the native sloth. The 

 echidna has the powerful claws, the long snout, the 

 vermiform tongue, and the copious spittle-glands, fitted 

 for a creature which is by habit an ant-eater. Neverthe- 

 less, in essential structure, it is poles asunder from the 

 true ant-eaters : for as we saw in our article " The 

 Opossum," the echidna and platypus together constitute 

 the most aberrant of all the groups which compose the 

 class of beasts, namely, the group known as " Ornitho- 

 delphous mammals," which form a sub-class by them- 

 selves. 



Similarly, the native sloth, or koala, is a creature 

 which resembles the true sloth, because it also is formed 

 to pass the greater part of its life clinging to the 

 branches of trees. It lives on the tender shoots of trees 

 and on leaves, and has a round head, long claws and 

 short tail, and it is also very tenacious of life, and even 

 when severely wounded will not quit its hold of the 

 branch to which it may be clinging. But however many 

 superficial points of resemblance the koala may have to a 

 sloth, it is a most diflferent kind of animal, for as we 

 have seen, it belongs to the sub-order of pouched-beasts, 

 or Marsupials ; while the sloths are what we ourselves 

 are, namely, Monodelphous mammals. Therefore, what- 

 ever structural resemblance may exist either between 

 the echidna and the ant-eater, or between the koala and 

 the sloth, must be resemblances which have been 

 induced — arisen independently — and have never been 

 inherited from a common ancestor. 



But if the sloth has no affinity to any animals outside 

 the Edentate order, has it any special affinity to any of 



