Mr. Wallace on the Geographical Distribution of Birds. 451 
mean. This gives for the North American region 5,500,000 
square miles. South American region with West Indies 5,600,000 
square miles, making a total which agrees with Balbi. 
Now, taking my corrected areas and your number of species, 
the proportionate richness or square miles to each species is as 
follows :— 
Zoological Regions. 
1. Palsearctic, area 12,500,000, sp. 650 . 
2. ^Ethiopian, area 6,500,000, sp. 1250 . 
3. Indian, area 3,100,000, sp. 1500 . 
4. Australian, area 2,600,000, sp. 1000 . 
5. North American, area 5,500,000, sp. 660 
6. South American, area 5,600,000, sp. 2250 .... 
Proportionate richness. 
Wallace. 
SCLATER. 
i 
1 
19,200 
21,000 
1 
1 
5200 
0600 
1 
1 
2050 
2600 
1 
1 
2600 
3000 
1 
1 
8300 
9000 
1 
1 
2500 
2400 
From the above estimate it results that the Indian region is 
in proportion to its area the richest in species of birds, and, 
when we consider how much less known it is than South Ame¬ 
rica, we may expect that the proportion will increase. In Birmah, 
Cochin China, and China, the ornithology of extensive regions is 
absolutely unknown; while in South America there is scarcely 
a spot which has not been repeatedly and thoroughly explored. 
Though no one is more profoundly impressed than myself with 
the vast and inexhaustible riches of South America in every de¬ 
partment of natural history, and pre-eminently in birds, yet I 
am also convinced that a considerable portion of its great appa¬ 
rent superiority to all other countries is due to the universal 
spread of the Spanish and Portuguese races over every part of its 
vast interior, which is thus absolutely as free as Europe to the 
researches of naturalists, who have not been slow to take advan¬ 
tage of it. No other part of the Tropical world is in this con¬ 
dition. In three-fourths of the African and Indian regions, the 
naturalist only penetrates at the risk of his life ; and, even where 
this is safe, I can speak from personal experience of the great 
difference between these regions and those of South America as 
to the inducements to a traveller to prolong his stay. In these 
countries we have absolutely no community of ideas, feelings, or 
2 t 2 
