open country, and moreover this advertising coloration exists in both sexes and throughout the year.  It is a brilliant white, all over, except the long wing-quills and the ends of the tail-feathers, which are black.  The first one I saw, at a very long distance, I thought must be an albino.  It perches on the top of a bush or tree watching for its prey, and it shines in the sun like a silver mirror.  Every hawk, cat, or man must see it; no one can help seeing it.

These common Argentine birds, most of them of the open country, and all of them with a strikingly advertising coloration, are interesting because of their beauty and their habits.  They are also interesting because they offer such illuminating examples of the truth that many of the most common and successful birds not merely lack a concealing coloration, but possess a coloration which is in the highest degree revealing.  The coloration and the habits of most of these birds are such that every hawk or other foe that can see at all must have its attention attracted to them.  Evidently in their cases neither the coloration nor any habit of concealment based on the coloration is a survival factor, and this although they live in a land teeming with bird-eating hawks.  Among the higher vertebrates there are many known factors which have influence, some in one set of cases, some in another set of cases, in the development and preservation of species.  Courage, intelligence, adaptability, prowess, bodily vigor, speed, alertness, ability to hide, ability to build structures which will protect the young while they are helpless, fecundity—­all, and many more like them, have their several places; and behind all these visible causes there are at work other and often more potent causes of which as yet science can say nothing.  Some species owe much to a given attribute which may be wholly lacking in influence on other species; and every one of the attributes above enumerated is a survival factor in some species, while in others it has no survival value whatever, and in yet others, although of benefit, it is not of sufficient benefit to offset the benefit conferred on foes or rivals by totally different attributes.  Intelligence, for instance, is of course a survival factor; but to-day there exist multitudes of animals with very little intelligence which have persisted through immense periods of geologic time either unchanged or else without any change in the direction of increased intelligence; and during their species-life they have witnessed the death of countless other species of far greater intelligence but in other ways less adapted to succeed in the environmental complex.  The same statement can be made of all the many, many other known factors in development, from fecundity to concealing coloration; and behind them lie forces as to which we veil our ignorance by the use of high-sounding nomenclature—­as when we use such a convenient but far from satisfactory term as orthogenesis.