THE ALIMENTARY SYSTEM. 75 



ter, and a more decided one to the omnivorous, show 

 a little more seasonal change ; and, though race after 

 race is constantly breaking in and destroying the 

 regularity of the gradation, there is an increase of 

 change till we come to those families which may be 

 said to bloom and fade yearly, something after the 

 manner of plants. 



It is these breakings in of one tribe of birds upon 

 the characters of another, which makes the system- 

 atic arrangement of this class of animals so uncer- 

 tain and difficult ; and the more that we study them, 

 nay, the more intimately and accurately that we 

 become acquainted with them, the less hope have 

 we that any future knowledge can remove the diffi- 

 culties. The four systems — the food and the three 

 habitats — air, land, and water, present themselves in 

 such varied combinations and proportions, that the 

 conclusion which we might very fairly draw from one 

 character is barred by an opposite one, which follows 

 as naturally from another ; so that we cannot have a 

 chapter of the inductive results of our observation 

 of birds without an appendix of exceptions of still 

 greater length. 



But, though we must receive it with exceptions and 

 limitations, there is still observable in birds, accord- 

 ing as they depart in their general characters from 

 the rapacious ones, an increase of seasonal change, 

 connected with that energy, which is awakened at 

 the pairing time ; and though the individual charac- 

 ters of this change vary exceedingly, there are two 

 great and not very badly marked divisions of it, the 

 one taking place in those birds which are more vege- 

 table in their feeding, and the other in those that 

 feed more upon insects. In the former, it displays 

 itself in greater brilliancy of plumage, and more 



