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 pos- 

 sess 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 be- 

 cause of their agreement, 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 be- 

 lieved by all but a few advanced thinkers that the individu- 

 als 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 distinct 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 compos- 

 ing 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 separ- 



