ARRANGEMENT OF BIRDS. 47 



according to the same law, so that we cannot form a 

 classification, even upon the relations which they bear 

 to each other. 



Thus, while birds are remarkably well defined as a 

 class, while they are among the most interesting 

 of all nature's productions, and while in their indi- 

 vidual habits in wild nature, they are more acces- 

 sible to our observation than, perhaps, any other 

 animals, they are perfect puzzles when we attempt 

 to systematise them ; indeed the best that we can 

 do is to go to wild nature, and study them individually 

 in forest, field, or flood. 



Their double motion, that of the feet and that of 

 the wings, which is so modified that it becomes the 

 four motions of walking, flying, swimming, and div- 

 ing, is the chief cause of the perplexity. Some birds, 

 as the common swift, have very little motion, save the 

 aerial one ; others, such as the ostrich, have none 

 but the terrestrial one : some again, as the penguins, 

 have very little more than the aquatic ones ; and 

 some, such as the pochard ducks, have all the four. 

 Those which have the same kinds of motions have the 

 one or the other predominating in an endless variety of 

 degrees ; and the character of the bill, according to the 

 motions which we observe from other species, some- 

 times agrees more with the one system of motion, and 

 sometimes with the other. All these perplexing cir- 

 cumstances increase the interest of the study of 

 birds, at the same time that they increase the difla- 

 culty ; and therefore, though none of the systems are 

 quite consistent — that is, though no single character 

 can be carried through the class — there has been no 

 want of systems, or of ability in the formation of 

 them. We have no desire to add another to the 

 number, as the labour would be but of little value, 



