CHAPTER I. 



DISTINCTIONS OF BIRDS FROM OTHER VERTEBRATED 

 ANIMALS. 



BIRD (Avis, literally " that which files," or in 

 the plural aves, birds). A class of warm-blooded 

 animals, and the second into which the vertebrated. 

 animals are arranged by most of the systematic natu- 

 ralists. 



Birds are a well-marked, and easily distinguished 

 class, even by their external characters ; so that, 

 though they differ much from each other in their 

 appearances and habits, there is not the least dan- 

 ger of confounding them with any of the other classes. 

 They are all produced from eggs, which are very 

 generally, but not universally, hatched by the heat of 

 the parent, which incubates, or sits upon them, warm- 

 ing them with the heat of the breast, which appears 

 to increase for the purpose, and becomes one of the 

 natural inducements for the bird to sit ; and in many 

 cases the breast of the female becomes denuded of 

 great part of its usual covering, by which means the 

 heat is more freely and immediately communicated to 

 the eggs, the natural covering being a bad conductor 

 of heat. 



