88 GENERAL ORNITHOLOGY. 



but are always covered by contour-feathers. As implied in the name, the alleged distinctions 

 of semipluraes are equivocal, and not easy to verify in all cases. Better marked are — 4. Filo- 

 plumes, filopliimcB, or thread-feathers, which have au extremely slender, almost invisible stem, 

 not well distinguished into calamus and rhachis, and usually no vane, unless a terminal tuft 

 of barbs be held for such. Long as they are, they are usually hiddeu by contour-feathers, close 

 to which they stand as accessories, one or more seeming to issue out of the very sacs in which 

 larger feathers are implanted. Sometimes they come to the surface, as the hairs on the neck 

 of birds of the genus Criniger, so named from this fact ; and some think the thready white 

 plumes on the neck and flanks of Cormorants in nuptial plumage are filoplumaceous. Typical 

 filophmies are the nearest approach to hairs that birds have ; they are very well shown on 

 domestic poultry, being what a good cook finds it necessary to siuge ofi" after plucking a fowl 

 for the table. 5. Certain down-feathers are remarkable for continuing to grow indefinitely, 

 and with this unlimited growth is associated a continual breaking down of the ends of the 

 barbs. Such plumulae, from being always dusted over with dry, scurfy exfoliation, are called 

 powder-down ; they may be entitled to rank as a fifth kind of teleoptiles, which I have named 

 pulviplumes. They occur in the Hawk, Parrot, and Gallinaceous tribes ; also in certain Pica- 

 rian birds (Leptosomus and Podargus) ; and especially in Herons and their allies. They are 

 always present in the latter, where they may be readily seen as at least two large patches of 

 greasy or dusty, whitish feathers, matted over the hips and on the breast. Pulviplumes are 

 said to be luminous at times with a sort of phosphorescence ; but what good it does a bird to 

 wear such fungus-like puff-balls is unknown. 



Colors of Feathers, in almost endless diversity of shade, hue, or tint, are reducible to 

 three categories (see Newton's Diet., p. 95). 1. Chemical, absorptive, or pigmentarij colors, 

 due to the deposition in the caratine or substance of the feather of certain pigments, either in 

 the form of fixed granules, or diffuse solution. Such colors are unvarying in any light in which 

 they may be viewed. Some kinds of pigment have been distinguished by name as follows : 

 Zoomelanin, or black ; zoonerythrin, or red ; and sooxanthin, or yellow ; the names being de- 

 rived from Greek words meaning "animal," and "black," "red," "yellow." To these add 

 turacin, the particular red pigment of birds of the genus Turacus, family Musophagidce ; and 

 turacoverdin, the green pigment of the same birds; the red color is due to copper and the green 

 to iron. Browns are due to varying mixtures of red and black pigments. AVhite is no color, but 

 results from the molecular structure of the feather, in the absence of pigment. Gloss, of what- 

 ever color, is due to smooth polish of the surface of a feather. 2. "What have been called 

 objective structural colors result from surface-conditions of the feather in connection with under- 

 lying pigments. All blues, most greens, and some yellows belong in this category, as no blue 

 pigment is known, and under the microscope these colors are always seen to depend upon the 

 structure that overlies pigment of a different color. For example, the color basis of a blue 

 feather may be a brownish or blackish pigment, and the blue only show as a condition of the 

 surface of the barbs and barbules. 3. Subjective structural, prismatic or so called metallic col- 

 ors constitute iridescence, or the glittering scintillation of those feathers which change rainbow- 

 like according to the position in which they are viewed by the eye with regard to light, i. e., to 

 angle of incidence of light-rays. Iridescence is thus wholly due to superficial texture of a 

 feather, without regard to the subjacent dark or black pigment. Prismatic hues are mostly 

 confined to exposed surfaces of feathers, and to barbules which lack barbiccls, and also have a 

 particular disposition. Iridescence is to be distinguished from mere sheen, gloss, or " bloom " 

 of a feather; it is carried to its pitch of perfection in Humming-birds, though many other 

 groups of birds also exhibit this optical phenomenon. 



Whatever be the coloration normal to any bird, that is its chrosis (Gr. xp^i^fts, chrosis, 

 coloring). But any bird may exhibit abnormal color or lack of color, either as a pathological 



