148 HAIR, FEATHERS, HORNS. 



remarked as being peculiarly downy, while those of 

 other birds have a more silky appearance. In the 

 penguin the wing feathers are like small scales, and 

 in the cassowary like porcupines' quills, being des- 

 titute of the barbs. In this remarkable appendage 

 of the skin every variety of colour presents itself; 

 this appears for the most part to be permanent ; but 

 it is extraordinary that in some instances, death, 

 change of temperature, or even change of food is 

 thought to produce a variation of colour. It is a 

 curious physiological fact that, in many birds, in 

 which the plumage is a distinction of sex, the old 

 female is frequently known to assume the plumage 

 peculiar to the male. Feathers, like hair, are re- 

 newed periodically, and readily reproduced if de- 

 stroyed by accident. 



Horns have the same origin as hairs and feathers, 

 they may, in fact, be considered as hairs agglutinated 

 and forming a hollow cone, but with this remarkable 

 difference, that their cavity is filled with a bony 

 process of the skull. The fibrous structure of horn 

 may be perceived, in many animals, at the base, 

 where it unites with the skin ; at this part it receives 

 the additions to its growth ; the apex of the cone 

 advancing as the increase takes place at the root and 

 on the inner surface. The transverse ridges fre- 

 quently seen on horns are indications of the different 

 layers of growth, and they sometimes correspond in 

 number with the years of life. Horns are perma- 

 nent in their nature, and when destroyed by accident 

 are not reproduced. In some annuals, as the ox, 

 the horns are round, while in the sheep, they are 

 flat, and form different curvatures according to the 

 kind. Those of the antelopes are generally very 

 long and nearly straight ; those of the ibex, curved 

 backwards. In fact, they are found under the 

 greatest variety of shape and size. The horn of the 

 rhinoceros differs from those of all other animals,- 

 in being situated on the bones of the nose, and in 

 having no bony support within it 



