90 The Life Story of the Fish 



Having proved this to our own satisfaction, what of it? 

 Just this. Any object to the fish's right, outside the lines 

 AOE'B, is seen by the right eye only, and its image is sent to 

 the left side of the brain. Any object to the fish's left, out- 

 side the lines COE"D, is seen by the left eye only, and its 

 image is sent to the right side of the brain. But any object 

 within the angle AOC is seen by both eyes, and its image is 

 sent to both sides of the brain. The fish's visual sensations are 

 divided into two distinct classes: one occurring in one side of 

 the brain or the other, and one occurring in both sides of the 

 brain simultaneously. 



We are now in a position to ask ourselves a lot of ques- 

 tions many of which we cannot answer. In the first place, do 

 the two classes of sensations make dijfferent final impressions 

 on the fish's consciousness? Is an object on one side of him, 

 producing an image in only one eye and stimulating only 

 one half of his brain, seen less clearly than the same object 

 when it is directly in front, seen by both eyes and stimulat- 

 ing both halves of the brain? We are all familiar with the way 

 in which a fish whirls, when something appears to one side 

 or the other, and brings itself head on. Does not this mean 

 that the single image so produced is inadequate, merely a 

 signal that there is something which needs more thorough 

 examination, and that it is necessary to bring both eyes to 

 bear on it to see it really well? And if this is so, of what use 

 are the large portions of each eye through which come the 

 single images produced by objects to the right and left of 

 the common field? 



You can obtain some of the answers by an experiment 

 performed without getting out of your chair, and with ap- 

 paratus no more complex than your own finger. Close your 

 left eye and hold your finger, at a comfortable distance away 

 and on a level with your eyes, at a point as far to the left as 

 you can see it distinctly. Then without moving the finger. 



