INTRODUCTION 



Every one knows what a bird is ! Whether it be an 

 Ostrich, a Canary, or a Barn-yard Fowl, we immediately 

 distinguish it as a bird by its covering of feathers, if by 

 nothing else. Birds form a separate "class" of the Verte- 

 brate Sub-kingdom of animals, and agree with the mammals 

 in possessing a four-chambered heart and hot blood. In 

 addition to their covering of feathers they are characterised 

 by the fact that they produce their young from eggs laid by 

 the female (a point that is however shared by most reptiles, 

 and by several of the lower mammals), and that the fore- 

 limbs, in the shape of wings, are usually adapted for flight. 

 Their bones are moreover usually rendered lighter by being 

 partly hollow and filled with air ; in addition they have a 

 number of "air-sacs" within their bodies which are also of 

 assistance in flight. Lastly, all modern birds are toothless, 

 at least as far as actual or true teeth are concerned. 



The majority of the members of the avian world are 

 notable for their graceful form, and their power of being able 

 to transport themselves through space with ease and rapidity, 

 a fact which enables them to travel enormous distances. 



Birds are, comparatively speaking, perhaps better known 

 and have attracted more notice than any other group of 

 animals, the beauty of the plumage of many of them, the 

 gift of sweet song with which others are endowed, their 

 economic value which is only now meeting with anything like 

 the recognition it deserves, have all tended to bring this about. 



Birds form the great division or " class " of animals 

 termed "Aves," which class is divided into "families," 

 these again into "genera," and the last into "species." 



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