430 JAMES ROLLIN SLONAKER 



MUSCLE AND VISUAL TESTS 



Several tests were made on sparrows to determine how nearly 

 the bird could see directly in front, and, if possible, to determine 

 how much the bird could converge its eyes. The left eyes of 

 two sparrows, a male and a female, were extirpated. Recovery 

 was rapid and inside of a week the wound had healed in a nor- 

 mal way. A third normal sparrow was also tested. All these 

 birds had been kept in captivity in a large cage for a period of 

 about five weeks. 



Twenty-nine days after the operation the following experi- 

 ments were made. The cage in which the sparrows were con- 

 fined during the tests was situated directly in front of a south 

 window. Black oil-cloth was spread over all sides of the cage 

 except the one farthest from the window which was left partially 

 open for observation. The bird was therefore in semidarkness. 



Sunlight was thrown on the head of the bird while it was fac- 

 ing the observer and in other positions. This was accomplished 

 by means of a mirror and consisted of flashes of short duration 

 with intervals of rest of several seconds intervening. The bird 

 remained at a distance of 50 cm. from the mirror during the 

 tests. Each of the sparrows which had but one eye was given 

 fifty tests. The results were tabulated and the angle which 

 was made by the sunbeam and the median plane of the head 

 was computed. 



The results were very consistent and showed no wide varia- 

 tions. The male bird showed a slightly greater range of varia- 

 tion than the female. The angle formed by the sunbeam or 

 line of sight, and the median plane in the male ranged from to 

 6°, in the female from to 5°. The average in each of these 

 cases was 3° and 2|°, respectively. 



One may infer from this that the sparrow can see almost 

 directly in front of it. That this power of sight is not the most 

 acute vision it is capable of is indicated by the behavior of the 

 bird when the light stimulus met the eye from the side. In 

 this case the bird turned its head so that the rays of light entered 

 the eye practically parallel to the axis of vision. That is, so 



