94 MAN AND THE LOWER ANIMALS n 



Every year tends to bring about a greater 

 uniformity of opinion throughout the zoological 

 world as to the limits and characters of these 

 groups, great and small. At present, for example, 

 no one has the least doubt regarding the characters 

 of the classes Mammalia, Aves, or Reptilia ; nor 

 does the question arise whether any thoroughly 

 well-known animal should be placed in one class 

 or the other. Again, there is a very general 

 agreement respecting the characters and limits of 

 the orders of Mammals, and as to the animals 

 which are structurally necessitated to take a place 

 in one or another order. 



No one doubts, for example, that the Sloth and 

 the Ant-eater, the Kangaroo and the Opossum, 

 the Tiger and the Badger, the Tapir and the 

 Rhinoceros, are respectively members of the same 

 orders. These successive pairs of animals may, 

 and some do, differ from one another immensely, 

 in such matters as the proportions and structure 

 of their limbs ; the number of their dorsal and 

 lumbar vertebra ; the adaptation of their frames 

 to climbing, leaping, or running ; the number and 

 form of their teeth ; and the characters of their 

 skulls and of the contained brain. But, with all 

 these differences, they are so closely connected in 

 all the more important and fundamental characters 

 of their organization, and so distinctly separated 

 by these same characters from other animals, that 

 zoologists find it necessary to group them together 



