4 NUMBER OF SPECIES CHAP, i 



oceanic in origin. The continents and oceans are peopled by 

 rather over three thousand species of Mammalia, a number which 

 is considerably less than that of either birds or reptiles. It 

 seems clear that, so far at any rate as concerns the numbers of 

 families and genera, the mammalian fauna of to-day is less varied 

 than it was during the Mid - tertiary period, the heyday of 

 mammalian life. It is rather remarkable to contrast in this way 

 the mammals and the birds. The two classes of the animal 

 kingdom seem to have come into being at about the same period ; 

 but the birds either have reached their culminating point to-day, 

 or have not yet reached it. The Mammalia, on the other hand, 

 multiplied to an extraordinary extent during the Eocene and the 

 Miocene periods, and have since dwindled. The break is most 

 marked at the close of the Pleistocene, and may be in part due 

 to the direct influence of man. At present man exercises so 

 enormous an effect, both directly and indirectly, that the future 

 history of the Mammalia is probably foreshadowed by the in- 

 stances of the White Rhinoceros and the Quagga. On the other 

 hand, the economic usefulness of the Mammalia is greater than 

 that of any other animals ; and the next most important era 

 in their history will be probably that of domesticity and " pre- 

 servation." 



