DIGESTION OF BIRDS. 



25 



" As soon," he adds, " as the pigeons discover a sufficiency of food to entice them to 

 a light, they fly around in circles Tevie^ving• the country below. During their evolutions 

 on such occasions, the dense mass which they form exhibits a beautiful appearance as it 

 changes its direction, now displaying a glittering sheet of azure, when the backs of the 

 birds come simultaneously into view ; and anon suddenly presenting a mass of rich deep 

 purple. Tlicy then pass lower over the woods, and are for a moment lost among the 

 foliage ; but again emerge, and are seen gKding aloft." 



"We find, therefore, in all such instances, a preparation for the extremes of long and 

 short-sighted vision. Thus the bird of prey, at a greater elevation in the air, sees on the 

 surface of the earth the mouse on which it determines to pomice. With the speed of an 



FIG. 20.— BRAIN OF A BIRD , 



FIG. 19.— DIGESTIVE APPARATUS OF THE CHICKEN. 



arrow it descends ; and now it perceives its prey as distinctly as it did when so far remote. 

 For as we draw out or press in the tube of a telescope, according to the distance or 

 proximity of the object on which we are looking, so is there on the part of the bii-d an 

 instinctive adjustment of the organ of vision. It contains, for this express purpose, what 

 has been aptly called " a livuig sponge," filling and separating the parts between which 

 it is placed when this is desirable ; and allowing them to approach when their so 

 doing is required. 



It would have been a puzzling problem for a skilful mechanic, had he been asked to 

 design a mouth for a bird, which should assist in its flight, act as a hand to seize its 

 food, and even tear it in pieces, and on occasion, serve as a weapon of defence. How 



