186 By Leafy Ways. 



The eyes of birds when compared with those of 

 other animals present some marked and palpable dif- 

 ferences. They are much more variously coloured ; 

 the iris is of all hues, from white to .black. It may be 

 red or blue, brown or yellow. The eye is large in 

 proportion to the head, especially in the case of late- 

 flying birds who need to make the most of the dim 

 light of evening. 



Among several singular points of internal structure 

 the most remarkable is the presence of a jointed ring 

 of bone, which lies in front of the eyeball, round the 

 iris. It consists of a number of segments or plates 

 firmly united together, but still admitting of some 

 amount of movement at the will of the bird, who by 

 this means is supposed to be able to alter the shape of 

 the crystalline lens, which lies behind the ring, and 

 thus to vary the focus of its eyes. 



Were the eyes of the kestrel constructed like our 

 own, we might well expect that it would lose sight of 

 so' small an object as a mouse in its descent. We 

 find that birds of prey, have large eyes, with these 

 bony rings particularly broad and strong ; and by this 

 arrangement can keep their prey in view. The swift, 

 again, whose keen wings carry it through the air at the 

 rate of some miles in a minute, has a similar provision, 

 both as regards the size of its eyes and the development 

 of its sclerotic plates. 



A curious modification is seen in the owls, whose 

 eyes are encased in rings, or rather tubes, each con- 



