Vol. xxvnn „ ., ._. 



1911 J Correspondence. 14/ 



Then I introduced into this back-ground some white pebbles, until the 

 spectator began to be able to detect the object by the extent of its eclipse 

 of these pebbles. To restore its complete effacement I then gave its 

 upward surfaces a few white spots that imitated the white pebbles of its 

 back-ground, and instantly all suspicion of its existence was again removed. 

 (All this is, of course, clearly set forth in our book.) Having thus called 

 attention to this optical principle, I proceeded to show a typical example 

 of its working in the vast class of species that are looked at by their prey 

 or enemies against the sky, or foliage with sky-holes through it, and among 

 whom upward-facing white markings are very common. Nature's wide- 

 spread use of these white marks on aerial species is in startling contrast to 

 the apparently total lack of them upon the vast world of species which, 

 living away from water, dwell too low down, close to the ground, often to 

 be looked at against the sky or sky-spotted foliage. My typical example 

 was as follows: I showed a small stuffed deer placed just above the level 

 of the eye and wholly indistinguishable, because, while his counter-shading 

 reduced him to the uniform flat tone of the twiggery before and behind 

 him, two bright white stripes running down his sides from his dorsal ridge, 

 and a white spot on his head, absolutely passed for the sky seen through 

 the flat twig element represented by his counter-shaded body, thus, as in 

 the former case, perfecting the illusion. Not one of the two score or more 

 spectators could detect the slightest difference between these counterfeit 

 sky-holes and the neighboring real ones of the foliage back-ground, and 

 of course not one of them, consequently, detected the deer, although each 

 in turn stood within ten yards of him and was shown exactly where to look. 

 For each spectator in turn I pointed right at the animal. They all agreed 

 that it was the white sky-counterfeits that most completely prevented 

 their detecting the deer. Ultimately I removed these white patterns, 

 and the same spectators then easily distinguished the deer, although it 

 occupied the very same place. 



Upper surface white marks abound on aerial creatures and on such 

 terrestrial ones as stand or leap high enough to have for their back-ground 

 either sky or foliage with sky holes through it, and on all these species they 

 work constantly the same magical effacement. Persons interested in this 

 subject should read our book very carefully, as well as my letter to 'The 

 Auk' of July, 1910, and my article in the 'Popular Science Monthly' for 

 December, 1909. (I shall be delighted to send a copy of this latter article 

 to any applicant.) 



Let me add here a word about the flamingo to show how entirely his 

 coloring belongs to the same class as that of all other sky-matching costumes 

 of which my white striped deer was so convincing an example. (It is at 

 least absurd to assert positively that the large denizens of the water he 

 wades in, anacondas, alligators, etc., are not dangerous to him. C. G. 

 Schillings found a goose in a crocodile's stomach.) 



These birds are largely nocturnal, so that the only sky bright enough to 

 show any color upon them is the more or less rosy and golden one that 



