8 MANUAL OF ZOOLOGY 



find a natural as opposed to an artificial classification of 

 animals. Good instances of artificial classification are the 

 grouping of bats with birds on the ground that both possess 

 wings, and of whales with fishes on the ground that they both 

 possess fins and live in the water. An equally good example 

 of a natural classification is the grouping of both bats and 

 whales under the head of Mammalia because of their agree- 

 ment, in all essential points of anatomy, histology, and 

 embryology, with the hairy quadrupeds which form the bulk 

 of that class. 



With the older zoologists the difficulty was to find some 

 general principle to guide them in their arrangement of 

 animals some true criterion of classification. It was 

 believed by all but a few advanced thinkers that the in- 

 dividuals of each species of animal were descended from 

 a common ancestor, but that the original progenitor of each 

 species was totally unconnected with that of every other, 

 having, as Buffon puts it, "participated in the grace of a dis- 

 tinct act of creation." To take an instance : all wolves were 

 allowed to be descended from a pair of ancestral wolves, and 

 all jackals from a pair of ancestral jackals, but the original 

 pair in each case was supposed to have come into being by 

 a supernatural process of which no explanation could or 

 ought to be offered. Nevertheless it was obvious that a 

 jackal was far more like a wolf than either of them was like 

 a tiger, and that in a natural system of classification this fact 

 should be expressed by placing the wolf and jackal in one 

 family, the tiger in another. 



All through the animal kingdom the same thing occurs : 

 no matter what group we take, we find the species com- 

 posing it resemble one another in varying degrees, or, as it 

 is sometimes expressed, have varying degrees of relationship 

 to one another. On the view that each species was sepa- 



