32 THE THEORY OF EVOLUTION 



knowledge permits, the degrees of relationship be- 

 tween them. In this elaborate scheme, which was 

 developed by Linnaeus about the middle of the 

 eighteenth century, the unit, so to speak, is the 

 species, the storm-centre of many controversies. Lin- 

 naeus believed that species were real, objective en- 

 tities, which it was the business of the naturalist to 

 distinguish, describe and name, and for a very long 

 time the principal occupation of zoologists and botan- 

 ists was the discrimination of species, furnishing them 

 with names and arranging them in genera, families, 

 orders and other groups of higher rank. This pro- 

 cedure may best be explained by an example. The 

 European wolf is a species, lupus, which, with other 

 typical wolves, is included in the genus Canis and is 

 therefore designated as Canis lupus, for the name of 

 a species requires that of its genus to identify it and 

 hence the Linnaean scheme of nomenclature is said 

 to be binomial. The true wolves, jackals, foxes, 

 (genus Vulpes) and many other genera of differing 

 dog-like forms are grouped together in the family 

 CanidcB, which, associated with all the other ter- 

 restrial beasts of prey, cats, bears, raccoons, weasels, 

 otters, etc., etc., are included in the sub-order Fis- 

 sipedia. The latter are joined with the marine forms, 

 seals, sea-lions, walruses, etc., to constitute the order 

 Carnivora. Omitting certain intermediate groups, 

 we find that the order Carnivora belongs in the class 

 Mammalia, or warm-blooded quadrupeds, which, in 

 turn, is a member of the phylum Vertebrata, or 



