'34 



PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



come nearer to the two objects, A and B, L being shut 

 and R looking across at A. The image of A falls all 

 the time on the fovea, a. The image of B falls on the 

 inner or nasal side of the fovea at b, but not far enough 

 to reach the entrance of the 

 optic nerve, o (R t ) (i). But as 

 the face comes nearer the eye R 

 turns more and more, the image 

 of B falls first near the place 

 (2), then on the place (3) of the 

 entrance of the optic nerve. 

 As R approaches still nearer 

 (4), the image of B has crossed 

 and appeared on the other or 

 nasal side of the optic entrance 

 and reappears. 



Spatial Representative of 

 the Blind Spot.— Every part 

 of the retina has its representa- 

 tive in the field of view. There- 

 fore the blind spot has also. 

 Why, then, do we not see it ? 

 When both eyes are open, of 

 course we do not see it, because 

 we see with the one eye the spot 

 which represents the blind spot 

 of the other eye. There is no 

 place that represents the blind 

 spot of both eyes. But even 

 with one eye shut we see noth- 

 ing. In fact, the expectation of seeing such a repre- 

 sentative shows a misconception. The only true rep- 

 resentative of a blind spot must be an invisible spot. 

 It can not be differentiated from the rest of the field. 

 Nevertheless the place of the representative of the 



Fig. 88. 



