232 OUR NATIVE SONGSTERS. 



not ; but we know that without tliis faculty the 

 bird must either lose its chance of finding food, or, 

 on the other hand, be utterly unfitted to direct its 

 wing over wood, and sea, and mountain, as it now 

 does. The swallow could not skim through the 

 air without instant danger of being dashed against 

 some hard object, could it not discern this from a 

 distance, and be thus enabled to moderate its rapid 

 flight. The carrier-pigeon could not traverse 

 vast extent of countries, did it not discover, from 

 on high, the landmarks which guided its course ; 

 and neither, without great power of vision, could 

 our lark come straight to its home from its sojourn 

 in the clouds. One marked peculiarity in the 

 eye of birds enables us to understand how the 

 lark can endm'c the dazzling light of the sun. 

 Besides the two eyelids, common to most animals, 

 birds have a membrane which serves as a tliird. 

 This thin membrane, when not in use, is folded in 

 the inner angle of the eye ; but can be spread all 

 over the orb at the will of the bird, which is thus 

 enabled to gaze, as through a delicate gauze veil, 

 into a shaded light. This little curtain does not 

 move up or down like our eyelids, but is spread 



