Decebibee 11, 1896.] 



SCIENCE. 



869 



the ground. They were covered with some 

 sticky material, and dry earth from the 

 road on which they stood was sprinkled 

 over them so that they would be the same 

 color as the background. The two end 

 ones were then painted white on the under, 

 side, and the white color was shaded up 

 and gradually mixed with the brown of the 

 sides. When viewed from a little distance 

 these two end ones, which were white below, 

 disappeared from sight, while the middle 

 one stood out in strong relief and appeared 

 much darker than it really was. Mr. 

 Thayer explained that terrestrial birds and 

 mammals which are protectively colored 

 have the under parts white or very light in 

 color, and that the color of the under parts 

 usually shades gradually into that of the 

 upper parts. This is essential in order to 

 counteract the effect of the shadow, which 

 otherwise, as shown by the middle potato, 

 makes the object abnormally conspicuous 

 and causes it to appear much darker than 

 it really is. In the case of Mr. Thayer's 

 experiment some of the witnesses could 

 hardly believe that the striking difference 

 in the visibility of the three potatoes was 

 entirely due to the coloring of the under 

 side, and Mr. Thayer was asked to color 

 the middle one like the two others in order 

 that the effect might be observed. Mr. 

 Thayer complied with the request, paint- 

 ing the under side of the middle potato 

 white, and shading the white up into the 

 sides as in the case of the others. The 

 effect was almost magical. The middle 

 potato at once disappeared from view. A 

 similar experiment was tried on the 

 lawn. Two potatoes were painted green to 

 resemble the green of the grass above which 

 hey were suspended. One was painted 

 white on the under side and at once be- 

 came invisible when viewed from a little 

 distance, while the other showed plainly 

 and seemed very dark, the shadow, super- 

 added to the green of the under side, mak- 



ing it remarkblj^ conspicuous. The experi- 

 ments were an overwhelming success. In 

 the discussion that followed, Mr. Thayer 

 called attention to the winter dress of the 

 ptarmigan, and stated that inasmuch as the 

 body of the bird is white all over it is 

 clearly impossible for the under parts to be 

 any whiter, and consequently the bird's 

 shadow would tend to make it conspicuous 

 when standing on the snow. To offset the 

 effects of the shadow the under side of the 

 bird would be lightened by the reflected 

 light from the snow. In addition to this, 

 the black of the ptarmigan's tail would 

 have the effect of lessening the apparent 

 depth of the shadow, thus serving to render 

 the bird less conspicuous. Dr. Merriam 

 stated that additional illustrations of the 

 same kind might be mentioned, and cited 

 those of the polar hare and ermine, in 

 which animals the black of the ears and 

 tail would have the same effect as the black 

 tail of the ptarmigan. Dr. Merriam re- 

 marked further that the absence of black 

 from the ears and tail of the polar bear, 

 arctic wolf and arctic fox served to prove 

 the correctness of Mr. Thayer's theory, in- 

 asmuch as these latter animals chase their 

 pre}^, and consequently would be rendered 

 more conspicuous by black markings which, 

 being in motion, would direct attention to 

 them. 



The subject created much discussion. A 

 vote of thanks was given Mr. Thayer. 



Mr. Louis Agassiz Fuertes gave an ex- 

 hibition of some of his own unpublished 

 drawings of birds from life. Examples of 

 the work pf Mr. Ernest E. Thompson were 

 also shown. 



Mr. Edward H. Forbush, Field Director 

 of the Massachusetts Gypsy Moth Commis- 

 sion, asked for information and suggestions 

 regarding the advisability of introducing 

 in the United States foreign birds that feed 

 upon the eggs of the gypsy moth. From 

 the trend of the remarks which followed, it 



