198 FOOT-NOTES TO EVOLUTION. 
life, though gradual, to be more rapid. The barrier of 
frost which keeps the fauna of the tropics from en- 
croaching on the northern regions once crossed, we 
come to the multitude of animals whose life depends on 
sunshine, the characteristic forms of the neotropical 
realm. 
The neotropical realm includes South America, the 
West Indies, and the hot coast lands of Mexico and 
Central America. To the northward this 
realm overlaps the holarctic in the tran- 
sition regions of Sonora, Arizona, Texas, 
and Florida; but to the southward the barrier of the 
broad ocean keeps it practically distinct from all others. 
The richness of this fauna in forms and species makes 
the great forests of the Amazon the dream of the 
naturalist. Joaquin Miller gives a vivid picture of the 
life of tropical America: 
Neotropical 
realm. 
“ Birds hung and swung, green-robed and red, 
Or drooped in curved lines dreamily, 
Rainbows reversed from tree to tree; 
Or sang, low hanging overhead, 
Sang soft as if they sang and slept, 
Sang low like some far waterfall, 
And took no note of us at all.” 
Corresponding to the neotropical realm in position, 
but with a less rich and varied fauna, is the Ethiopian 
realm. This includes the greater part 
of Africa, merging gradually on the 
north into the holarctic realm, through the transition 
regions of Barbary, Italy, and Spain. In monkeys, her- 
bivorous animals, and reptiles, this region is wonderfully 
rich. In variety of birds and fishes the neotropical 
region far surpasses it. 
The Indian realm comprises southern Asia and the 
neighbouring islands. Its rich fauna has much in com- 
‘Ethiopian realm. 
