548 The American Naturalist. [June, 
some of the present highly colored genera were evolved produced 
normally two pigments, unless some distributing force were brought to 
bear upon them, they would naturally be combined at first. It is only 
after long selection that the component colors become apparent. The 
examples cited are, as might be expected, among the most highly 
specialized genera. The woodpeckers are colored black, white and 
scarlet. The combination would produce brown, which is still the 
body color of some species. _In the genus Tyrannus the original color 
was probably olive green, the special colors are black and yellow: 
In the blue jays that are blue in the adult together with black and white, | 
the mixture of these colors gives the grays of the young, and of the less 
specialized forms, as Perisoreus and Picicorvus. Besides black and 
white, most North American genera appear to contain but two fanda- 
mental colors, but in the tropics three frequently occur in a single 
genus. 
In discussing protective coloring, repetitive marks, and recognition 
marks, the most recent literature upon this subject is cited and illus- 
trated with numerous facts of the author’s own observation. 
Having considered the factors that influence the evolution of colors 
of North American birds, Mr. Keeler gives a brief account of the 
families and genera with an application of the principles discussed. 
Mr. Keeler’s review of the factors of organic evolution is comprehen- 
sive and intelligent. He appreciates the fundamental difference 
between the origin of characters and the selection of characters, though 
occasionally he slips into the customary confusion on this point by 
ascribing the origin of some color marks to natural selection. T 
reviewer takes this opportunity to refer to one misunderstanding into 
which hein common with many others has fallen, in his reference to 
effort as prior to use in developing structure. He says (p. 75) “All 
that can be said to the above [the theory of effort] is that`it may be 
true but that it has not yet been demonstrated. -There is indeed a b 
difference between the assumption that use can modify a part which a 
already exists, and the assumption that desire or effort can originate 
something which does not exist. Moreover, evem if effort be a vañd 
factor in creation, it cannot it seems to me have the general applica- a 
tion ascribed to it by Professor Cope. For example, it could appa 
ently have no influence on the origination of new colors. Does — 
bird desire to be protectively colored? If so it must decide what cok 
ors would be most in harmony with its surroundings, and then make - 
an effort of will to have these colors developed ; all of which is on the 
face of it inconceivable. Or by what imaginable sort of effort cm” 
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