GEOGRAPHICAL DISTRIBUTION OF ANIMALS 301 
is an essential unity of life over this vast area, and the rec- 
ognition of North America as a separate (nearctic) realm, 
which some writers have attempted, seems hardly practi- 
cable. 
The Neotropical or South American realm includes 
South America, the West Indies, the hot coast lands of 
Mexico, and those parts of Florida and Texas where frost 
does not occur. Its boundaries through Mexico are not 
sharply defined, and there is much overlapping of the north 
temperate realm along its northern limit. Its birds espe- 
cially range widely through the United States in the sum- 
mer migrations, and a large part of them find in the North 
their breeding home. Southward, the broad barrier of the 
two oceaus keeps the South American fauna very distinct 
from that of Africa or Australia. The neotropical fauna is 
richest of all in species. The great forests of the Amazon 
are the dreams of the naturalists. Characteristic types 
among the larger animals are the snout or broad-nosed 
(platyrrhine) monkeys, which in many ways are very distinct 
from the monkeys and apes of the Old World. In many of 
them the tip of the tail is highly specialized and is used as 
a hand. The Edentates (armadillos, ant-eaters, etc.) are 
characteristically South American, and there are many 
peculiar types of birds, reptiles, fishes, and insects. 
The Indo-African realm corresponds to the neotropical 
realm in position. It includes the greater part of Africa, 
merging gradually northward into the north temperate 
realm through the transition districts which border the 
Mediterranean. It includes also Arabia, India, and the 
neighboring islands, all that part of Asia south of the limit 
of frost. In monkeys, carnivora, ungulates, and reptiles 
this region is wonderfully rich. In variety of birds, fishes, 
and insects the neotropical realm exceeds it. The monkeys 
of this district are all of the narrow-nosed (catarrhine) 
type, various forms being much more nearly related to 
man than is the case with the peculiar monkeys of South 
