CHAPTER VI. 

 The Classification op Bieds. 



THE great multitude of Birds — of which upwards of eleven 

 thousand kinds at thte least are known to exist — makes it 

 obviously necessary for those who would study them to arrange 

 or classify them in groups. Otherwise the multitude of species 

 would be too great for our powers of imagination and memory. 

 The arrangement in groups, or Classification, of Birds, follows 

 the principles which have been adopted in the classification of 

 Animals generally. That system is one whereby creatures are 

 sorted into a series of groups, successively smaller, and more 

 and more subordinate. 



Animals, like plants, are, as we said at starting ^, considered 

 as members of one great group, which has been fancifully 

 termed a " Kingdom " — the Animal Kingdom containing all 

 animals, as the Vegetable Kingdom contains all plants. The 

 principles adopted by both zoologists and botanists in subdividing 

 these " Kingdoms " are " morphological." By this term it is 

 meant that the characters upon which these classifications re- 

 pose, and by which the various subordinate groups are defined, 

 are characters taken from the shape, number, structure, and 

 mutual relations of the parts of which the various creatures so 

 classified are built up, and not upon what such parts do — the 

 characters refer to " structure " not to " function." 



The kingdom of animals is divided into a variety of suhhing- 

 doms, each of which is, of course, a very large group of animals 

 indeed. Each subkingdom is again divided into subordinate 

 groups termed classes. Each class is again divided into orders, 

 and each order is further subdivided into families ; each family, 

 into genera,a,Tid each genus into species — a zoological species being 

 " a group of living organisms which differ only by inconstant 



' See ante, p. 3. 



