452 THE GENERAL PRINCIPLES OF ZOOLOGY 



of the Dromaeognathae are terrestrial, and some of the Euor 

 nithes as well. The Impennes, or penguins, are really aquatic, 

 belonging to the littoral marine fauna. Nearly all of the Mam- 

 malia are terrestrial. As we ascend to higher and higher points 

 in a mountainous country, the facies of the fauna changes nota- 

 bly. The greater the elevation the fewer the animals we meet 

 with, and in the higher regions they are so characteristically dif- 

 ferent from animals at lower levels that they may be said to 

 constitute an alpine fauna. The chamois and mountain goats 

 are familiar examples of alpine mammals, while many insects 

 and birds are confined to these great altitudes. 



In the aerial fauna are included such animals as are capable 

 of sustaining themselves for long periods in the air, although 

 fundamentally terrestrial ; these are notably many insects, many 

 birds, and the bats. 



The study of the geographical distribution of animals dis- 

 closes a number of interesting facts for the explanation of which 

 we must turn to a considerable extent to geology and palaeon- 

 tology. It is a matter of common knowledge that certain ani- 

 mals are restricted to certain localities. Thus the hippopotamus 

 is confined to Africa, the opossum to South America and a por- 

 tion of North America, the reindeer to the Arctic regions. But 

 in considering the natural distribution of animals, we must be 

 careful to eliminate such as have become inhabitants in any 

 country through the agency of man. Thus the gypsy moth, the 

 English sparrow, the horse, and the camel are living to-day in 

 the United States, where none of them would now be found if 

 it had not been brought from the Old World by man. 



Scientists have divided the land into a number of zoogeographi- 

 cal regions as they are called, the basis for this division being 

 the avian and mammalian faunae, but the areas are so sharply 

 marked off from one another that they hold good for the great 

 majority of other land animals as well. Six zoogeographical 

 regions are commonlv recognized. 



The Palasarctic region is the largest and comprises all Europe, 

 Asia north of the Himalayas, including Japan, as well as Arabia 

 and Africa north of the tropic of Cancer, and in addition Iceland 

 and the islands in the eastern portion of the North Atlantic. It 

 is a matter of some surprise that the fauna of Africa north of 



