ae 
1877.] The Colors of Animals and Plants. 659 
color will most frequently appear. Now, there is little doubt 
that the external changes of animals and plants in adaptation 
to the environment are much more numerous than the internal 
changes, as seen in the varied character of the integuments and 
appendages of animals (hair, horns, scales, feathers, etc.) and in 
plants (the leaves, bark, flowers, and fruit), with their various 
appendages, compared with the comparative uniformity of the 
texture and composition of their internal tissues; and this accords 
with the uniformity of the tints of blood, muscle, nerve, and 
bone, throughout extensive groups, as compared with the great 
diversity of color of their externalorgans. It seems a fair con- 
clusion that color per se may be considered to be normal, and to 
need no special accounting for, while the absence of color (that is, 
either white or black), or the prevalence of certain colors to the 
constant exclusion of others, must be traced, like other modifi- 
cations in the economy of living things, to. the needs of the 
Species. Or, looking at it in another aspect, we may say that 
amid the constant variations of animals and plants color is ever 
tending to vary and to appear where it is absent, and that natu- 
tal selection is constantly eliminating such tints as are injurious 
to the species, or preserving and intensifying such as are useful. 
This view is in accordance with the well-known fact of colors 
which rarely or never appear in the species in a state of nature, 
continually occurring among domesticated animals and cultivated 
plants, showing us that the capacity to develop color is ever 
present, so that almost any required tint can be produced which 
may, under changed conditions, be useful, in however small a 
degree. | 
Let us now see how these principles will enable us to under- 
stand and explain the varied phenomena of color in nature, tak- 
Ing them in the order of our functional classification of colors 
(page 650). 
Theory of Protective Colors—We have seen that obscure or 
Protective tints in their infinitely varied degrees are present in 
_ €very part of the animal kingdom, whole families or genera being 
H kinds of ray 
often thus colored. N ow, the various brown, earthy, ashy, and 
other neutral tints are those which’ would be most readily pro- 
iced, because they are due to an irregular mixture of many 
S; while pure tints require either rays of one kind 
only » or definite mixtures in proper proportions of two or more 
ds of rays. This is well exemplified by the comparative diffi- 
culty of producing definite pure tints by the mixture of two or 
