478 DISTRIBUTION OF LAND ANIMALS 



In ancient times a land bridge united Alaska and Asia, 

 and apparently there was a similar connection with 

 Europe by way of Greenland, so that animals in both 

 hemispheres were free to mingle. This accounts for the 

 fact that both the Old and the New World are the 

 home of wildcats, foxes, weasels, bears, elk, deer, wild 

 oxen, beavers, squirrels, and hares. Among the animals 

 characteristic of this realm in the Western Hemisphere 

 are the musk ox, prong-horn, antelope, raccoon, musk 

 rat, and prairie dog, while the Eastern Hemisphere is the 

 home of the two-humped camel, musk deer, chamois, and 

 yak. The differences between these two sub-realms are, 

 however, no greater than those separating Alaska and 

 California; and they are far less than those distinguishing 

 the Holarctic from any other realm. 



The Neotropical Realm. — The Neotropical or South 

 American realm includes South America, Central America, 

 and the West Indies. Like the Holarctic, it is an enor- 

 mous tract, characterized by mountain chains, vast ex- 

 panses of grassy plains, and fully half of its area is covered 

 by dense and luxuriant forests. No other realm is so rich 

 in species, and over half of the known families of animals 

 are represented within its borders. Among the char- 

 acteristic mammals are the distinct group of broad-nosed 

 monkeys, the vampire bats, the guinea-pig and several re- 

 lated species, sloths, armadillos, the tapir, and several wild 

 dogs and tiger cats. The birds are represented by over 

 four hundred species of humming birds, many parrots, 

 toucans, tanagers, the ostrich-like rheas, and numerous 

 other species. In Mexico the boundaries of this realm are 

 not perfectly distinct, since several Holarctic species, 

 such as the hare, the ground squirrel, certain mice, the 

 puma, deer, and skunk, are distributed as far south as the 

 Isthmus of Panama and even farther. On the other hand, 

 certain species of monkeys, the jaguar, armadillo, tapir, 

 peccary (a pig-like creature), and several other animals 

 extend from the south into Mexico or beyond. Broadly 



