INTRODUCTION. 



IN the series of Land-Birds, properly so called, the Or- 

 ders and Families have "been disposed according to a method 

 in some degree corresponding with the nature of their food, 

 those which are carnivorous being placed first, the insecti- 

 vorous next, and lastly the granivorous and graminivorous. 

 In describing the Water-Birds, strictly so called, or such as 

 are web-footed, one might follow a similar order, placing the 

 piscivorous kinds opposite the carnivorous terrestrial species, 

 those which live chiefly on Crustacea opposite the insectivo- 

 rous, and the graminivorous Geese and Ducks opposite the 

 Pheasants and .Grouse. Or the order might be reversed, the 

 gramivorous species being placed first, and the piscivorous 

 last. But, in reality, an arrangement in strict conformity 

 with the nature of the food, would prove very unnatural, in- 

 asmuch as, in many very natural families, species are found 

 which are carnivorous, others insectivorous, and others fru- 

 givorous. Even in the same genus, Corvus, for example, 

 one, the Raven, is carnivorous, another, the Jackdaw, insec- 

 tivorous, and a third, the Rook, insectivorous and occasion- 

 ally frugivorous. Nevertheless, it will be found that, in a 

 certain degree, regimen corresponds with external form and 

 internal organization ; and I have, therefore, in the se- 

 ries of swimming birds, placed the grass-eating birds by 

 themselves, under the name of Cribratrices, although some 

 of them also eat worms and mollusca, or even fishes. The 



