THE CLASSIFICATION OF ANIMALS 61 



it is hardly necessary to speak. One has only to remember 

 that our tables are supplied by fish, domestic poultry, and 

 domestic mammalia, and that all other groups of the animal 

 kingdom form an almost negligible source of food-supply com- 

 pared to these. In tropical countries, Reptilia in the form 

 of lizards and snakes are also consumed, and, as everyone 

 knows, the epicures of the City of London consume the flesh 

 of the marine turtle (another Reptile) at their banquets. Even 

 Amphibia do not escape the attention of man ; the limbs of the 

 larger kinds of Frog are esteemed a delicacy in many countries 

 in Canada the large Bull-Frog is hunted almost to extinction. 



In the earliest days of mankind the large carnivorous 

 Mammalia were amongst man's most serious enemies, and even 

 yet in tropical countries, among backward races of men, the 

 lion and the tiger levy a large annual toll of victims. The 

 poisonous snakes were another group of formidable enemies to 

 mankind, and the dread of them is reflected in our mythologies. 

 But where civilised man holds sway such enemies are rapidly 

 overcome and entirely exterminated. The rate of reproduction 

 of the higher Vertebrata is slow, and they are unable to recover 

 from serious and continued losses. Thus hardly a decade 

 passes that some kind of beast or bird does not become extinct ; 

 and however much the scientific zoologist may deplore this 

 process, it is absolutely inevitable and must go on. Just as 

 the Mammalia drove out the large Reptilia which preceded 

 them, and whose colossal remains astonish the geologist, so 

 Man is gradually exterminating all Mammalia and all birds, 

 except those he finds a use for and those which are sufficiently 

 inconspicuous to escape his attention. Only the fish of the sea 

 with their enormous powers of reproduction seem to defy his 

 efforts. 



We have now passed in rapid review the most important 

 divisions of the animal kingdom. Each primary division or 

 phylum includes many different kinds of animals and is sub- 

 divided again and again. Thus phyla are divided into classes, 

 classes into orders, orders into tribes, tribes into families, 

 families into genera, and genera into species. The species is 

 thus the unit of classification. It includes all animals, indis- 

 tinguishable from one another by any constant mark (apart 

 from the differences due to age and sex), which conjugate freely 



