CONCLUSION. 407 



nyroca pochard, or white-eyed duck, may be taken 

 as a specimen. 



In this volume we have taken a rapid glance at 

 the general structure of birds, and those characters 

 which distinguish them from the other classes of 

 vertebrated animals ; and we have entered rather 

 more minutely into those peculiarities of their three 

 grand structures, the bill, the feet, and the wings, 

 upon which, singly or jointly, the leading differences 

 of their habits in a great measure depend. It would 

 now remain to investigate their relations to the rest 

 of nature in locality and in season ; but as this part 

 of the subject involves the knowledge also of the 

 natural history of localities and of seasons, it is of too 

 general a nature for being made a specific portion of 

 the natural history of birds, though they cannot be 

 known to the full extent without a knowledge of it, 

 neither can it be understood to the full extent without 

 a knowledge of them. Nature is one workmanship 

 of one Author, and he who wishes to know any sin- 

 gle part well, must lay the foundation in some general 

 knowledge of the whole. 



Though every effort has been made to bring into 

 this volume the greatest possible quantity of matter, 

 there still remain many general principles to be in- 

 vestigated before the reader can be fully prepared for 

 entering upon the details of ornithology, in such a 

 manner as to see clearly the place which each species 

 fills in the system of nature, and the oflftce which it 

 performs. Among these may be enumerated the 

 general and the seasonal distribution of birds ; their 

 migrations, and the reasons why some are migratory 

 while others are not ; their changes of plumage, whe- 

 ther in feathers, in colour, or in both, and the causes, 

 whether of a physical or physiological nature, by 



