xxii INTRODUCTION. 



with teeth, the food undergoes no preparation in the mouth, 

 but is swallowed in unbruised and untasted morsels. Yet there 

 is reason to believe that the first action of the stomach, or its 

 preparatory ventricultis, affords in some degree the ruminating 

 gratification of taste, as after swallowing food, in some insectiv- 

 orous and carnivorous birds, the motion of the mandibles, ex- 

 actly like that of ordinary tasting, can hardly be conceived to 

 exist without conveying some degree of gratifying sensation. 



The clothing of birds varies with the habits and climates 

 they inhabit. The aquatic tribes, and those which live in 

 northern regions, are provided with an abundance of plumage 

 and fine down, — from which circumstance often we may form a 

 correct judgment of their natal regions. In all climates, aqua- 

 tic birds are almost equally feathered, and are provided with 

 posterior glands containing an oily substance for anointing 

 their feathers, which, aided by their thickness, prevents the 

 admission of moisture to their bodies. These glands are less 

 conspicuous in land birds, — unless, like the fishing Eagles, their 

 habits be to plunge in the water in pursuit of their prey. 



The general structure of feathers seems purposely adapted 

 both for warmth of clothing and security of flight. In the 

 wings of all birds which fly, the webs composing the vanes, or 

 plumy sides of the feather, mutually interlock by means of reg- 

 ular rows of slender, hair-like teeth, so that the feather, except 

 at and towards its base, serves as a complete and close screen 

 from the weather on the one hand, and as an impermeable oar 

 on the other, when situated in the wing, and required to catch 

 and retain the impulse of the air. In the birds which do not 

 fly, and inhabit warm climates, the feathers are few and thin, 

 and their lateral webs are usually separate, as in the Ostrich, 

 Cassowary, Emu, and extinct Dodo. In some cases feathers 

 seem to pass into the hairs, which ordinarily clothe the quadru- 

 peds, as in the Cassowary, and others ; and the base of the 

 bill in many birds is usually surrounded with these capillary 

 plumes. 



The greater number of birds cast their feathers annually, and 

 appear to suffer much more from it than the quadnqieds do 



