344 APPLIED PHYSIOLOGY 



626. The eye in lower animals. In all fourfooted animals, 

 and in birds, reptiles, and fishes, the eyes are essentially the same as in 

 man. 



Most insects possess large immovable eyes shaped like a dome. Each 

 eye is made up of many smaller eyes like a honeycomb. Each little 

 eye contains a lens which forms an image 

 upon the nerve at the bottom of the cavity. 

 In some lower forms of animals, like the 

 leech, there is a spot of dark coloring matter 

 under the skin in which the nerves of sight 

 end. Such eyes cannot form an image, on 

 account of the absence of the lens, but a 

 bright light or a shadow of a large object 

 can affect the nerve and give the leech 

 The eye of a house fly. some idea of its surrO undings. Some still 

 a eye, made of many small lower forms of an i ma i s seem to be able to 

 eyes. b mouth. . ,. , ^ / , f , , , 



recognize light, for they fold themselves up 



when darkness comes, and yet they have nothing which at all re- 

 sembles an eye. 



Some plants, like the morning glory, are affected by light, for their 

 flowers fold themselves at night and open again when the sun 

 rises. 



SUMMARY 



1. Light is the name given to the vibrations of a very 



rare gas which fills all space. 



2. The eye is like a photographer's camera. 



3. The eye is set deep in a bony socket, called the orbit, 



and is protected in front by the lids, and moistened 

 by tears. 



4. The eye can see distinctly only a small space directly 



in front, but can distinguish the presence of objects 

 in a full half circle. 



5. A sensation of sight is produced instantly, but persists 



for one tenth of a second after the light disappears. 



6. Some eyes cannot see some colors, especially red. 



