Jan., 1913 
CONCEALING AND REVEALING COLORATION OF ANIMALS 
13 
patches of sky showing through, but much more often against a solid dark back- 
ground of canyon wall, river bank or solid green foliage. Of course this proves 
nothing, unless it coincides with the observations of others made with this partic- 
ular question in mind. Even in a level, treeless region, during the past season. I 
could not see that the low bounds of a cottontail ever carried its rump high 
enough to bring it to the sky line, from the standpoint of a coyote, except for a 
fraction of a second at a time. Furthermore, the chief enemies of the rabbit, in 
many localities, are not mammals, but large birds of prey, which surely do not 
often see their quarry against white skies. This is also true of the white-tailed 
prairie-dogs of the intermountain region of Colorado. Whatever their purpose, 
that such white posterior markings are obliterative from the standpoint of the 
possessor’s enemies is altogether too doubtful to be accepted without thorough 
testing on many species. Mr. Thayer’s photographs do not show the animals in 
the position in which they would usually be seen by their enemies at the “critical 
moment,” in my judgment. 
Thayer’s theory of countershading seems correct as an optical principle, but 
needs to be studied from many angles before acceptance as a part of the conceal- 
ing coloration theory. Many animals which are rendered quite indistinct in the 
middle of the day, when the light comes from above, are not so indistinct earlier 
and later in the day. Thayer himself admits this, apparently, in the case of the 
jacanas. I have found it true with the cottontails of the western plains during 
the past summer. As many countershaded animals are in hiding during the 
hours when the countershading would be most effective for concealment, and 
moving about when it is least effective and in some instances even disadvantage- 
ous, it is well to look for some other explanation of the phenomenon and not to 
hastily assume that its purpose is concealment. 
Thayer’s ruptive design theory is possibly one of the most important ones he 
has advanced. In certain environments, at any rate, the breaking up of the out- 
lines of animals in the way suggested is a most effective method of obliteration. 
Nearly all the discussion of concealing coloration has assumed that all ani- 
mals have the same powers of vision as man, see things just as man does, and at 
least one prominent author has expressly declared this to be true. Nothing could 
be farther from the probability. All men, even, have not equal visual powers. 
Aside from individual color blindness, there is strong evidence indicating that it 
is a racial character of some primitive peoples {Science, n. s., xxii, 1905, p. 680), 
thus reviving the old theory that in the development of color perception the colors 
at the long-wave end of the spectrum were first perceived, and that only a few 
animals have yet reached the higher colors. Birds probably have color vision, 
though very little is yet known of its extent or universality. Experiments under 
proper control up to the present time indicate that many of the mammals have 
not color vision, but only the power of distinguishing between brightness and 
dullness. Such experiments, to be of any value whatever, are very difficult. 
There are reasons for the belief that amphibians and reptiles have only motion 
vision, which, if true, would nullify the numerous statements about such animals 
being unable to see their enemies on account of concealing coloration. It is quite 
certain that all animals are more apt to see any object in motion than a motion- 
less one. It is also doubtful whether any animal except the primates has binoc- 
ular vision, a matter of very great importance. It is generally believed to repre- 
sent the difference between an ordinary flat photograph and a stereoscopic view, 
which brings the scene out into sharp relief. Anyhow, binocular vision is one of 
the important factors in the perception of solidity, rotundity, etc. Whether the 
