ment. The habits of the animal 

 determine the character of the eye. 

 Birds of rapid flight and those which 

 scan the earth minutely from lofty 

 courses are able to adjust their vision 

 quickly to long and short range. The 

 eye of the Owl is subject to his will as 

 he swings noiselessly down upon the 

 Mouse in the grass. The nearer the 

 object the more the eye is protruded 

 and the deeper its form from front 

 to rear. 



The human eye adjusts its power 

 well for small objects within a few 

 inches and readily reaches out for those 

 several miles away. A curious feature 

 is that we are able to adjust the eye 

 for something at long range in less 

 time than for something close at hand. 

 If we are reading and someone calls 

 our attention to an object on the 

 distant hillside, the eye adjusts itself 

 to the distance in less than a second, 

 but when we return our vision to the 

 printed page several seconds are 

 consumed in the re-adjustment. 



The Condor of the Andes has great 

 powers of sight. He wheels in beauti- 

 ful curves high in the air scrutinizing^ 

 the ground most carefully and all the 

 time apparently keeping track of all 

 the other Condors within a range of 

 several miles. No sooner does one of 

 his kind descend to the earth than those 

 near him shoot for the same spot hop- 

 ing the find may be large enough for a 

 dinner party. Others soaring at greater 

 distances note their departure and fol- 

 low in great numbers so that when the 

 carcass discovered by one Condor 

 proves to be a large one, hundreds of 

 these huge birds congregate to enjoy 

 the feast. The Condor's eyes have 

 been well compared to opera glasses, 

 their extension and contraction are 

 so great. 



The Eagle soars towards the sun 

 with fixed gaze and apparent fullness 

 of enjoyment. This would ruin his 

 sight were it not for the fact that he 

 and all other birds are provided with 



an extra inner eyelid called the nicti- 

 tating membrane which may be drawn 

 at will over the eye to protect it from 

 too strong a light. Cuvier made the 

 discovery that the eye of the Eagle, 

 which had up to his time been supposed 

 of peculiarly great strength to enable 

 it to feast upon the sun's rays, is closed 

 during its great flights just as the eye 

 of the barnyard fowl is occasionally 

 rested by the use of this delicate semi- 

 transparent membrane. Several of 

 the mammals, among them being the 

 horse, are equipped with such an inner 

 eyelid. 



One of my most striking experi- 

 ences on the ocean was had when I 

 pulled in my first Flounder and found 

 both of his eyes on the same side of 

 his head. All Flat-fish are similarly 

 equipped. On the side which glides 

 over the bottom of the sea, the Hali- 

 but, Turbot, Plaice, and Sole are 

 almost white, the upper side being 

 dark enough to be scarcely distinguish- 

 able from the ground. On the upper 

 side are the two eyes, while the lower 

 side is blind. 



When first born the fish swims up- 

 right with a slight tendency to favor 

 one side ; its eyes are on opposite sides 

 of the head, as in most vertebrates 

 and the head itself is regular. With 

 age and experience in exploring the 

 bottom on one side, the under eye 

 refuses to remain away from the light 

 and gradually turns upward, bringing 

 with it the bones of the skull to such 

 an extent that the adult Flatfish 

 becomes the apparently deformed 

 creature that appears in our markets 

 as a regular product of the deep. 



The eyeless inhabitant of the 

 streams in Mammoth Cave presents a 

 curious instance of the total loss of a 

 sense which remains unused. These 

 little fishes are not only without sight 

 but are also almost destitute of color 

 and markings, the general appearance 

 being much like that of a fish with 

 the skin taken off for the frying pan. 



ii8 



