iio 



STRUCTURE AND COMPARISON. 



not need to be renewed, and on which, any number of pictures 

 may be taken, one after the other, and carried to the brain to be 

 developed. And the retina, as it is called, takes not only form 

 and light and shade, but color. 



We have not tried to explain how we see, because that would 

 need much study. It is enough for us to know that our eyes 

 have all the parts of a perfect camera, and that they take 

 pictures in just the same way. And not only our eyes, but 

 those of all beasts, birds, fishes, and reptiles are formed on 

 the same plan. The eye of the vertebrate animal is a little 

 camera. 



i We must not conclude that all eyes are alike, only that 

 they all are made on the same plan. They vary in shape and 

 size and in some points of construction, just as cameras do, 

 but the essential parts are the same. These diagrams of the 



FIG. 36. THE EYE OF THE HAWK AND OP THE OWL. 

 CP Ciliary processes. ON Optic nerve. P Pecten. 



eyes of a hawk and an owl show the differences in shape. 

 In structure they are almost precisely like 'our own eyes except 



