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. Proportionate richness. 



Wallace. Sclater. 



1. Palaearctic, area 12,500,000, sp. 650 ~ j^ 



2. Ethiopian, area 6,500,000, sp. 1250 g^ ^ 



3. Indian, area 3,100,000, sp. 1500 -^ -i- 



' ' ' 't^ 2050 2600 



4. Australian, area 2,600,000, sp. 1000 -^ -1- 



' > J > f 2600 3000 



5. North American, area 5,500,000, sp. 660 -i- -1- 



6. South American, area 5,600,000, sp. 2250 -i- -L 



^ 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 



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