AVES. 409 
great distan*e; 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 @sophagus 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 ue 
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 larve of 
insects, or the soft parts of other animals. These live always in pairs, 
construct their 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 
acertain 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 uscful to 
man as Mammalia, serve important purposes in the general economy of 
nature. Those whose food is chiefly insects, check the excessive reproduo- 
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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