82 



HORNY SURFACE. 



The horny surface of birds varies in hardness in 

 different species, and ma}', in general, be said to be 

 firm in its texture in proportion as it is dark in colour. 

 The more powerful iDirds of prey have the beak and 

 claws black, with a slight bluish tinge ; but some 

 even of these have them yellow when in the imma- 

 ture state, whatever maybe the colour when they are 

 full grown. This change of colour in horny sub- 

 stances appears to be the effect of atmospheric air and 

 light ; and it is not confined to birds, but takes place 

 in the hoofed mammaha, the young of which, in gene- 

 ral, have the hoofs yellow, though they turn black 

 after a short time. The forms of the bills and the 

 claws of birds, being closely connected with some of 

 their principal habits, will be noticed in another 

 chapter of this volume. 



NAKED SKIX. 



The naked skin of birds has generally a porous or 

 spongy appearance ; and in many species it has a 

 bloom of colour in the living state, which is often very 

 brilliant, and displays an iridescence which is not 

 very easily describable, and which fades the instant 

 that life is extinct. The bills of some birds, such for 

 instance as the toucans, are covered with a membrane, 

 in which there is a similar display of colour, that 

 fades in the same manner ; but in most birds these 

 portions of naked membrane with perishable colours 

 are on other parts of the body. When there is a 

 naked membrane reflected on the upper mandible of 

 the bill at its base, that membrane is called a cere, ^rom 

 its surface having some resemblance to that of wax. 

 When it extends to, or surrounds the eye, it is Cbdied 

 a lore, which means an armature, or covering. Some- 



