12 PREFACE. 



for if the idea were completely followed out, any num- 

 ber of persons constructing a system separately would 

 come to the same conclusion ; but the consideration of 

 a single organ, the bill for example, would lead to nu- 

 merous inconsistencies with respect to other organs. 



In the following pages I shall dispose the objects ac- 

 cording to their affinities as exhibited by the bill, the 

 intestinal canal, the feet, the plumage, the wings, the 

 tail, and the general form ; but as in the fauna of a dis- 

 trict or country, where materials are not afforded for a 

 general system, the genera must succeed each other, 

 sometimes over wide gaps, it is not so essential to ex- 

 hibit all the relations of species as to associate them ac- 

 cording to their more obvious affinities. 



Finally, species alone exist in nature. Genera, or- 

 ders, classes, and all other sections, by whatever name 

 called, — tribes, subtribes, families, subfamilies, &c. are 

 merely ideal groups of species. Naturalists have not 

 agreed as to what constitutes a genus or an order ; and 

 I have only to explain, that what I here consider a ge- 

 nus is a group of species, shewing an evident affinity 

 to each other in respect to all their more important or- 

 gans. Another person may call such a group a genus, 

 a subgenus, or a subdivision of an order ; but these dis- 

 tinctions are merely arbitrary ; and, provided one has 

 an idea of what he means by the phrase genus or class, 

 whether that genus or that class correspond with those 

 of another arrangement, is not of the least importance. 



