464 R. T. YOUNG 



The experiments to be recorded were performed by arranging 

 two backgrounds, one of straw and one of grass, ^ on the floor of 

 the cage, on each of which were placed in as nearly their normal 

 position as possible five dead grasshoppers of each species. Dur- 

 ing the placing of the insects the birds were confined in a small 

 box on the wall of the cage. After being released they seldom 

 flew directly to the floor of the latter, usually ahghting first on 

 a perch placed about midway between the box and the floor. 

 They would then drop to the floor and hop back and forth in 

 search of food. They did not apparentlj^ espy the insects until 

 coming close to them. The insects were occasionally tumbled 

 over by the birds in ahghting, walking, or flying over the back- 

 grounds; thus in some cases bringing the ventral surface upper- 

 most, and in others causing them to drop down between the blades 

 of straw and grass, and changing the conditions of the experiment. 

 I endeavored to obviate this diflficulty by replacing the insects 

 in position after each time that the birds fed from either back- 

 ground. As the birds were hungry, however, they would usually 

 pick up several insects before I could drive them away, so that 

 a certain amount of uncertainty is necessarily here involved. 

 The reasonably consistent results of the experiment, however, 

 render this uncertainty practically neghgible. 



The order of resemblance between the grasshoppers and the 

 background, as it appeared to my eye, was as follows, giving 

 those combinations first in which the resemblance was greatest: 

 Xyphidium — grass, Xyphidium — straw, Melanoplus — -grass, and 

 Melanoplus — straw. The resemblance between Xyphidium and 

 grass was so great as in many cases to cause me great difficulty 

 in finding the grasshoppers on this background a few moments 

 after placing them, and with my eye at a distance of only about 

 30 cm. above it. The fact that the martins did not approach 

 the insects from above, but from the side, the bird's fine of sight 

 striking the body of the insect a httle above the middle of the 

 latter, necessitates the comparison of the lateral, rather than 

 the dorsal color of the insect with that of the background in 



** In Experiment 2 a single background consisting of a white sheet, and in 5 

 and G, backgrounds of mud and sand, instead of grass and straw, were employed. 



