NATURAL HISTORY. 225 



" It was the owl that shriek'd, the fatal bellman, which gives 

 the stern'st good night." SIIAKSPKUE. 



673. Animals that depend chiefly upon the eye, and especially if they be feoders 

 in the night, or in places to which little light can come, invariably have the eyes 

 very large. This is the case with owls, and other nocturnal birds. The same law 

 is observed even in connexion with the inhabitants of the sea. The surface fishet 

 usually have the eyes small; and they get gradually larger, till, when we 

 come to those which inhabit the depths, and yet are active, feeding upon other 

 fishes, their eyes are very large of which we have an example in the star-gazers. 



674. Why are the eyes of nocturnal birds placed nearer to each 

 other than the eyes of birds which fly by day ? 



Because, with nocturnal birds, the design is that they should 

 have the light concentrated in front of them, in order that they may 

 avoid flying against obstacles, which, under a different arrangement, 

 they would inevitably do in the darkness of the night. 



But in birds that fly by day, their range being of greater extent, 

 it is intended to render their vision effective over as great an area 

 as possible, that they may command the expanse around them. 



675. Why has the eye of the owl and other nocturnal birds a 

 shining substance deposited at the bottom of thr, eyeball ? 



Because this substance, by reflecting the ray. of light, endows 

 the eye with power to distinguish objects in th? dark. 



676. IVTiy are owls enabled to turn their heads r^und in almost 

 a complete circle without moving their bodies ? 



The owl has been gifted with this capability in order to 

 compensate for the absence of motion in the eye, the globe of which 

 is immoveably fixed in its socket by a strong Clastic hard 

 cartilaginous case, in form of a truncated cone. 



677. Why is the head of the owl so disproportionately large ? 



This is partly duo to the looseness of the plumage by which it is 

 covered and is further caused by the existence, between t'^e j^re* 

 10* 



