a speck in the sky, with a single meteoric dart it seizes a 

 chicken in the farmyard or a sparrow in the field, an object 

 much smaller than itself and wholly invisible to our eyes 

 from that distance. We can scarcely follow the lightning- 

 like darts of the humming bird, yet he comes to rest as 

 lightly as a feather on a tmy twig. We have no means of 

 knowing at what distance he first perceived it, but how- 

 ever far away, the interval to focus the object could be but 

 a fraction of a second. 



The physical construction of the eye differs so little 

 from that of other animals as to scarcely warrant so great 

 a difference in efficiency. A bird may see directly in front as 

 well as at each side. The eye has three eyelids, an upper and 

 lower like the human eye, but the positions are reversed, that 

 is, closing from the bottom instead of from the top, excepting 

 in owls, whippoorwills and other night birds. The third 

 lid, called the "winker," a delicate translucent membrane, 

 starts from the side nearest the bill and operates across the 

 eye at a right angle to the other lids. Menace a bird's eye 

 with the finger and this lid rushes across to protect the 

 eyeball. Owls sit in the daytime with this curtain shading 

 their eyes from the light. When duck-hunting the writer 

 has observed birds swimming under water with this film 

 apparently drawn over their eyes. 



Mention of the respiratory system should be made be- 

 cause it resembles that of no other animals except the 

 reptiles, and more remotely the fishes. As we think of a 

 turnip as being nearly all water, so we might say that a 

 bird is nearly all air, being literally permeated with it. We 

 may divide the system into three parts; the lungs, bones and 

 skin, all of which are connected by an intricate network of 

 air tubes similar to the blood vessels. 



The lungs, enormously developed, are situated in the 

 thoracic cavity, which is not separated from the abdominal 

 cavity. There is a rudimentary diaphragm, but of little if 

 any use. Inspiration and expiration are performed both by 

 the breast muscles and the abdominal muscles. Instead of 

 the usual single bone, a bird's rib consists of two bones 

 joined by a cartilaginous hinge which allows for this breast 

 movement. Each cavity takes its turn in inhaling and ex- 

 haling. 



The bones, particularly those of the legs and wings, are 

 hollow and are filled, not witli marrow, but with air supplied 

 by tubes from the lungs. One eminent authority says that 

 a bird is able to breathe directly through a hole at the end 

 of the humerus. The writer recollects that when a boy he shot 



52 



