584 KARL T. WAUGH 



compared with the size of the eye, is much larger than in man (see 

 fig. 9) ; and, second, the homogeneity of the retina is demonstrated 

 in a later section (IV) of this paper. 



From these considerations we feel justified in concluding that 

 there is in the mouse a portion of the field of view which is shared 

 by the two eyes. 



Concerning the second requirement for binocular vision it is 

 exceedingly difficult to secure data from observation of the ani- 

 mal. The uniform appearance of the surface of the eye makes it 

 almost impossible to detect movements of the eye. The black 

 glistening beadiness of the eye is always the same. 1 Several 

 attempts were made to obtain a point of reference on the eye-ball 

 by using a small square of paraffined Chinese white, but without 

 success. The animal would close the eye immediately and dis- 

 lodge it. Finally on close observation under a very bright light 

 a faint line of the pupil could be distinguished, and when the light 

 struck the eye at a certain angle, its movements could be observed. 



The animal was held on the palm of the hand facing the ob- 

 server and trials were made by moving a finger back and forth on 

 different sides to learn the nature of the eye movements. When 

 the finger was brought slowly above the level of the palm, within 

 the field of vision for one eye, the mouse would turn its head 

 slightly toward the finger. When the finger was moved to and fro, it 

 was not followed by the eyes. Under these conditions the ani- 

 mal always reacted by remaining perfectly still with the eyes in a 

 fixed position. A more rapid movement of the finger would elicit 

 only a slight further turning of the head in the direction of the 

 movement. The finger was then lowered and raised on the other 

 side of the animal's head. These conditions were alternated and 

 repeated about twenty times. The reaction was in all cases the 

 same. 



Fear cannot reasonably be suggested as a cause for the move- 

 ments not being followed with the eyes, for the animal was per- 

 fectly tame. It was used to being handled daily and would run to 



1 It might naturally be supposed that the uniform beady appearance of the eye 

 is of biological value in permitting the animal to make movements of the eye 

 which, while enabling it to see its enemies, would themselves remain undetected. 



