INTRODUCTION 21 



scopic vision, he has, by extended and more rapid movements 

 of both eyes and head, increased the range of his field of 

 fixation. 



The different visual requirements thus outlined for dif- 

 ferent forms of environments have involved considerable 

 alterations in the structural architecture of the visual organs. 

 It is with these structural alterations that I now proceed 

 to deal, dividing them up for descriptive purposes under 

 the following headings: I. The Field of Vision; II. Light- 

 sense; III. Form-sense; IV. Accommodation and Con- 

 vergence; V. Color-sense; VI. The Protective Mechanisms 

 of the Eyeball. 



