EYE OF THE ENGLISH SPARROW 431 



that the fovea was involved. This was quickly followed by 

 turning so as to almost face the stimulus as above described. It 

 would fix its gaze apparently on the stimulating object and 

 remain quiet. If the stimulus of sunlight were continued the 

 bird would sit facing it until a copious secretion of lacrimal fluid 

 would cause sneezing, swallowing, and shaking of the head. 



When the strength of the stimulus was greatly reduced very 

 different results were obtained. A small piece of white card- 

 board was suddenly brought into view of the bird by raising it 

 quickly above the floor of the cage. The results were tabulated 

 and the angles formed by the median plane and the rays of 

 light from the card computed. This was found to be 24° in the 

 male and 26° in the female. This is approximately the angle 

 formed by the optic axis and the median plane. 



In experimenting with the noniial bird very different results 

 were obtained. When strong sunlight was reflected onto the 

 head, in no case could it be made to face the illuminating mirror. 

 It continually turned, first one side, then the other, toward the 

 stimulus in rapid succession. No fixation of vision, so easily 

 and constantly gotten in the experiments on the birds with one 

 eye, could be obtained from the normal bird. Neither could the 

 copious reflex secretion of tears be elicited. 



The movements of the normal bird were too quick for ac- 

 curate observation, but as nearly as could be determined the 

 stimulating rays of light met the median plane at an angle close 

 to 25°. This coincides closely with the results gotten with the 

 cardboard on the birds with one eye and indicates that the 

 fovea is involved in this act of vision. 



In explanation of these results three questions may be raised: 

 1. Is the bird able to rotate its eye in the socket sufficiently to 

 bring the optic axes parallel? 2. Is the temporal portion of the 

 retina capable of perceiving objects directly in front of the 

 bird? 3. May not both of the above factors operate in bring- 

 ing about binocular vision in the sparrow? 



The fact that only a slight movement of the eyeball has been 

 observed would conclusively prove that the optic axes cannot be 

 so converged as to become parallel in the sparrow. Binocular 



