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AVES. 409 



great distance ; but this, from recent observation, seems doubtful. The 

 tongue in birds, is supported by a production of the hyoid bone. 



The taste is not very delicate. Digestion in birds is in proportion to the 

 activity of their life, and the quantity of their respiration. The stomach is 

 composed first of the crop, which is a dilatation of the oesophagus at the 

 base of the neck. The food remains in this duct for some time, and there 

 imbibes a fluid analogous to the saliva, which is secreted from the inside 

 of the canal. When softened by the action of heat and moisture, it passes 

 little by little into a muscular bag, called the gizzard, where the food is 

 triturated the more easily, that many species swallow little stones to in- 

 crease the effect. The gizzard, it has been remarked, is strongest in the 

 birds which have slender bills, and which are of course unable to break 

 down their food ; in those which feed on fish or flesh, the muscles are much 

 weaker, and the stomach is almost membranous. By the outlet of this 

 stomach, the food, reduced to a species of chyme, flows through the remain- 

 der of the intestinal canal, where the nutritious parts are absorbed, and the ''^ 

 remainder expelled by a cloaca, an orifice common to the urinary and genital 

 organs. Birds, such as the partridge and common fowl, whose young are 

 able to walk and feed themselves on their departure from the egg, do not 

 generally live in pairs. One male serves many females, and the young are 

 entirely trusted to the maternal care. The greater part of birds, however, 

 are blind and helpless at their birth, and their parents are therefore under 

 the necessity of providing for their subsistence. Pigeons disgorge half 

 digested grains, to feed their young ; and linnets bring them larvee of 

 insects, or the soft parts of other animals. These live always in pairs, 

 construct tlieir nest with great care, and constantly in the same manner ; 

 and each species appropriates for this purpose certain materials. All possess 

 a kind of instinct which leads them to choose the most convenient places 

 for their nests, such as best afford concealment, or which render them 

 inaccessible to their enemies. In birds the ova exist already formed in the 

 mother before fecundation ; and it is not a rare occurrence to see eggs laid 

 without impregnation, similar in every respect to those which produce 

 young. Fecundation, in most of the species, is accomplished by mere juxta- 

 position. The eggs of birds differ much in the color of their calcareous 

 covering. They have generally the form of an elongated ball, and one 

 of their extremities is thicker than the other. The fecundated eggs require 

 a certain heat, to be hatched ; and the observation of this fact has led to 

 the practice in Egypt, and elsewhere, of hatching large broods of chickens 

 by artificial heat. The class of birds, though not apparently so useful to 

 man as Mammalia, serve important purposes in the general economy of 

 nature. Those whose food is chiefly insects, check the excessive reproduc- 

 tion of insect races, and for this purpose migrate at certain seasons to places 

 where their food abounds. The indiscriminate destruction of crows and 

 sparrows, in some districts, has accordingly been found to give rise to an 

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