XXXIV INTRODUCTION. 



present age is to accumulate facts, ami not to generalize ; 

 but we have now a sufficiency of fjicts, and want our Lyell 

 to explain them. 



By the consent of most naturalists, all objects of nature 

 are divided into kingdoms, sub-kingdoms, classes, orders, 

 families, and genera, and, in some cases, where the families 

 are numerous, tribes, sub-families, and sub-genera are 

 added. Birds are a class of the sub-kingdom Yer- 

 tebrata, of the Animal kingdom. The Orders of birds 

 are founded chiefly on the form of the bill, and more 

 especially of the feet. Families are characterized by more 

 minute distinctions of the bill and feet, together with 

 characters drawn from the wings, tail, and certain habits, 

 more or less common to all. A Genus comprises one or 

 many species closely resembling one another in the 

 structure of bill, feet, wings, and tail, and in habits, 

 yet differing, it may be, in color, size, or some minute 

 differences of structure. To give a familiar example, the 

 European Kite and the common Kite of India are species 

 of the same sjenus, Milvus ; and the Enf-lish Kino-fifcher 

 and the little Indian Kingfisher, are separate species of 

 the same irenus Alcedo, each of these o'enera containinet 

 several other species. Of late years genera have been 

 greatly divided and multiplied, some of them being classed 

 as sub-genera ; but, in practice, and till the whole realm of 

 Ornithology is presided over by a master hand, no distinc- 

 tion can be satisfactorily pointed out, or acted on. When 

 the families of any order are very numerous, they are 

 classed in tribes ; and when the genera of any ftxmily 

 are numerous, or comprise several distinct forms, they are 

 grouped into snb-fjimilies. 



In every natural assemblage of forms, whether it be 

 genus, family, or order, there is some one form which pre- 



