No. 3-] ACUTE VISION IN VERTEBRATES. 4S9 



smell, but also hearing. Mammals in general do not see a man 

 if he remains quiet, but the crow easily recognizes him, and 

 can distinguish his stick from a gun. The dog looks into your 

 face, but you cannot tell whether he is looking into your eyes 

 or at your mouth. He has an indefinite gaze, and, like most 

 mammals, is not satisfied with the sense of sight alone, but 

 must confirm and improve by the sense of smell and hearing. 



In the present study it is impossible to make a more definite 

 comparison of the powers of vision in the different vertebrates. 

 Many years of careful observation of the visual habits and 

 related histological structure of each animal will be necessary. 

 But so far as experiments have gone, the power of quiet and 

 close discrimination of an object at rest seems to be present 

 only in those animals whose development of the retina has pro- 

 ceeded a stage farther above that of the simple area — to the 

 fovea centralis. 



