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THE AMERICAN NATURALIST [Vol. XL VIII 



larger area the number of species is more than double 

 what it is in the smaller area, the increase in genera is 

 only about one third, increasing the index of modification 

 from 2.25 to 3.63. 



Table XII shows practically the same thing in the case 

 of the hawk moths of the family Sphingidae. 



TABLE XII 

 Data from de Bothschild and Jordan (1907) 



West Indies j 76,000 



Mexico and Central America 975,200 



South America 7,000,000 



Mex., Cent. Am., and S. Am 7,975,200 



Mex., Cent. Am., S. Am., and W. I. . . . 8,051,200 



i 965 



228,000 



11,772,000 



Africa and Mad ; 12,000,000 



Africa, Mad., and Bourbon 12.000,965 



In this case two series of tabulations were made, one 

 showing the number of genera and species in various 

 Neotropical areas, and combinations of these areas, the 

 other showing a similar tabulation for various Ethiopian 

 areas, with similar combinations. It will be observed that 

 the speciation in the West Indies is very large for the size 

 of the area involved, but when we consider the abundant 

 opportunity that has been given for isolation to operate, 

 this is not surprising. The index of modification is quite 

 low. Mexico and Central America have a larger specia- 

 tion, compared with South America, than would normally 

 be expected, the reason being that Central America is the 

 American center of distribution. The index of modifica- 

 tion, however, reflects the smaller size of the area, being 

 considerably lower than that for South America. The in- 

 crease in index of modification from 5.62 to 6.39, as areas 

 are successively added to South America, is significant. 

 Looking now at the Ethiopian regions, we find that there 

 is the same disproportionate increase of species over 



