2io The Bird 



reflects the black pigmented tissue at the back of the eye- 

 ball. The image passes through this lens and is thrown 

 upon the curtain of jet, and here the brain nerves find it 

 and know it how, we cannot even guess. 



If the eye-camera of the bird has no long bellows to 

 focus out and back, it has something infinitely better 

 the coloured ring or iris which surrounds the pupil. We 



FIG. 151. Head of living Sloth. 



are all familiar with the way the oval iris of a cat nar- 

 rows to a slit in bright sunlight and broadens at night 

 to let in all the light possible. Look closely at the eye 

 of an owl or parrot, even in broad daylight, and the 

 circle of the iris will be seen to contract and enlarge at the 

 will of the bird. We have always been inclined to pity 

 the poor "blind" owl during the daytime, but the truth 

 is that, because of this power of adjustment, almost 



