The first row of the series is formed by the major coverts; these, like the primaries, have their free-edges directed towards the tip of the wing, and hence are said to have a distal overlap. The next row is formed by the median coverts. These, on the forearm, commonly overlap as to the outer half of the row distally, and as to the inner half proximally. On the hand this series is incomplete. Beyond the median are four or five rows of coverts known as the minor coverts. These may have either a proximal or a distal overlap. The remaining rows of small feathers are known as the marginal coverts, and they always have a distal overlap.
The three or four large quill-like feathers borne by the thumb form what is known as the “bastard-wing,” ala spuria.
The coverts of the under follow an arrangement similar to that of the upper surface, but the minor coverts are commonly but feebly developed, leaving a more or less bare space which is covered by the great elongation of the marginal series.
One noteworthy fact about the coverts of the under side of the wing is that all save the major and median coverts have what answers to the dorsal surfaces of the feather turned towards the body, and what answers to the ventral surface of the feather turned towards the under surface of the wing. In the major and median coverts, however, the ventral surfaces of these feathers are turned ventralwards, that is to say, in the extended wing they, like the remiges, have the ventral surfaces turned downwards or towards the body in the closed wing.
But the most remarkable fact in connexion with the pterylosis of the wing is the fact that in all, save the Passerine and Galliform types, and some few other isolated exceptions, the secondary series of remiges appears always to lack the fifth remex, counting from the wrist inwards, inasmuch as, when such wings are examined, there is always found, in the place of the fifth remex, a pair of major coverts only, while throughout the rest of the series each such pair of coverts embraces a quill.
This extraordinary fact was first discovered by the French naturalist Z. Gerbe, and was later rediscovered by R. S. Wray. Neither of these, however, was able to offer any explanation thereof. This, however, has since been attempted, simultaneously, by P. C. Mitchell and W. P. Pycraft. The former has aptly coined the word diastataxic to denote the gap in the series, and eutaxic to denote such wings as have an uninterrupted series of quills. While both authors agree that there is no evidence of any loss in the number of the quills in diastataxic wings, they differ in the interpretation as to which of the two conditions is the more primitive and the means by which the gap has been brought about.
According to Mitchell the diastataxic is the more primitive condition, and he has conclusively shown a way in which diastataxic wings may become eutaxic. Pycraft on the other hand contends that the diastataxic wing has been derived from the eutaxic type, and has produced evidence showing, on the one hand, the method by which this transition is effected, and on the other that by which the diastataxic wing may again recover the eutaxic condition, though in this last particular the evidence adduced by Mitchell is much more complete. The matter is, however, one of considerable difficulty, but is well worth further investigation.
The wings of struthious birds differ from those of the Carinatae, just described, in many ways. All are degenerate and quite useless as organs of flight. In some cases indeed they have become reduced to mere vestiges.
Those of the ostrich and Rhea are the least degraded.
In the ostrich ankylosis has prevented the flexion of the hand at the wrist joint so that the quills—primaries and secondaries—form an unbroken series of about forty in number. Of these sixteen belong to the primary or metacarpo-digital series, a number exceeding that of any other bird. What the significance of this may be with regard to the primitive wing it is impossible to say at present. The coverts, in their disposition, bear a general resemblance to those of Carinate wings; but they differ on account of the great length of the feathers and the absence of any definite overlap.
The wing of the South American Rhea more nearly resembles that of flying birds since the hand can be flexed at the wrist joint, and the primaries are twelve in number, as in grebes, and some storks, for example.
The coverts, as in the African ostrich, are remarkable for their great length, those representing the major series being as long as the remiges, a fact probably due to the shortening of the latter. They are not, however, arranged in quincunx, as is the rule among the Carinatae, but in parallel, transverse rows, in which respect they resemble the owls.
In both ostrich and Rhea, as well as in all the other struthious birds, the under surface of the wing is entirely bare.
The wing of the cassowary, emeu and apteryx has undergone complete degeneration; so much so that only a vestige of the hand remains.
Remiges in the cassowary are represented by a few spine-like shafts—three primaries and two secondaries. These are really hypertrophied calami. This is shown by the fact that in the nestling these remiges have a normal calamus, rhachis and vane; but as development proceeds the rhachis with its vane sloughs off, while the calamus becomes enormously lengthened and solid.
In the emeu the wing is less atrophied than in the cassowary, but is not yet completely degenerate. Altogether seventeen remiges are represented, of which seven correspond to primaries. Since, however, these feathers have each an aftershaft as long as the main shaft—like the rest of the body feathers—it may be that they answer not to remiges, but to major coverts.
The wing of apteryx, like that of the cassowary, has become extremely reduced. The remiges are thirteen in number, four of which answer to primaries. These feathers are specially interesting, inasmuch as they retain throughout life a stage corresponding to that seen in the very young cassowary, the calamus being greatly swollen, and supporting a very degenerate rhachis and vane.
The penguins afford another object-lesson in degeneration of this kind. Here the wing has become transformed into a paddle, clothed on both sides with a covering of small, close-set feathers. A pollex is wanting, as in the cassowary, emeu and apteryx, while it is impossible to say whether remiges are represented or not.
Authorities.—The following authors should be consulted for further details on this subject:—
For General Reference as to Structure, Colour, Development and Pterylosis.—H. Gadow, in Newton’s Dictionary of Birds (1896); W. P. Pycraft, “The Interlocking of the Barbs of Feathers,” Natural Science (1893).
On the Colours of Feathers.—J. L. Bonhote, “On Moult and Colour Change in Birds,” Ibis (1900); A. H. Church, “Researches on Turacin, an Animal Pigment containing Copper,” Phil. Trans. clix. (1870), pt. ii.; H. Gadow, “The Coloration of Feathers as affected by Structure,” Proc. Zool. Soc. (1882); Newbegin, Colour in Nature (1898); R. M. Strong, “The Development of Color in the Definitive Feather,” Bull. Mus. Zool. Harvard College, vol. xl.
On Moulting.—J. Dwight, “The Sequences of Plumage and Moults of the Passerine Birds of New York,” Annals N.Y. Acad. Sci., vol. xiii. (1900); W. E. De Winton, “On the Moulting of the King Penguin,” Proc. Zool. Soc. (1898–1899); W. P. Pycraft, “On some Points in the Anatomy of the Emperor and Adélie Penguins,” Report National Antarctic Expedition, vol. ii. (1907).
On Development of Embryonic, Nestling and Adult Feathers.—T. H. Studer, “Die Entwicklung der Federn,” Inaug.-Diss. (Bern, 1873); “Beiträge zur Entwickl. der Feder,” Zeitsch. f. wiss. Zool., Bd. xxx.; J. T. Cunningham, “Observations and Experiments on Japanese Long-tailed Fowls,” Proc. Zool. Soc. (1903); H. R. Davies, “Beitrag zur Entwicklung der Feder,” Morph. Jahrb. xiv. (1888), xv. (1889); W. P. Pycraft, “A Contribution towards our Knowledge of the Morphology of the Owls,” Trans. Linn. Soc. (1898); W. P. Pycraft, “A Contribution towards our Knowledge of the Pterytography of the Megapodii,” Report Willey’s Zoological Results, pt. iv. (1900); W. P. Pycraft, “Nestling Birds and some of the Problems they Present,” British Birds (1907).
On Pterylosis.—H. Gadow, “Remarks on the Numbers and on the Phylogenetic Development of the Remiges of Birds,” Proc. Zool. Soc. (1888); Z. Gerbe, “Sur les plumes du vol et leur mue,” Bull. Soc. Zool. France, vol. ii. (1877); J. G. Goodchild, “The Cubital Coverts of the Euornithae in relation to Taxonomy,” Proc. Roy. Phys. Edinb. vol. x. (1890–1891); Meijere, “Über die Federn der Vögel,” Morphol. Jahrb. xxiii. (1895); P. C. Mitchell, “On so-called ‘Quintocubitalism’ in the Wing of Birds,” Journ. Linn. Soc. Zool. vol. xxvii. (1899); “On the Anatomy of the Kingfishers, with special reference to the Conditions known as Eutaxy and Diastataxy,” Ibis (1901); C. L. Nitzsch, “Pterytography,” Ray Soc. (1867); W. P. Pycraft, “Some Facts concerning the so-called ‘Aquintocubitalism’ of the Bird’s Wing,” Journ. Linn. Soc. vol. xxvii.; C. J. Sundevall, “On the Wings of Birds,” Ibis (1886); R. S. Wray, “On some Points in the Morphology of the Wings of Birds,” Proc. Zool. Soc. (1887). (W. P. P.)
Commercial Applications of Feathers.—The chief purposes for which feathers become commercially valuable may be comprehended under four divisions:—(1) bed and upholstery feathers; (2) quills for writing; (3) ornamental feathers; and (4) miscellaneous uses of feathers.
Bed and Upholstery Feathers.—The qualities which render feathers available for stuffing beds, cushions, &c., are lightness elasticity, freedom from matting and softness. These are combined in the most satisfactory degree in the feathers of the goose and of several other allied aquatic birds, whose bodies are protected with a warm downy covering. Goose feathers and down, when plucked in spring from the living bird, are most esteemed, being at once more elastic, cleaner and less liable to taint than those obtained from the bodies of killed geese. The down of the eider duck, Anas mollissima, is valued above all other substances for lightness, softness and elasticity; but it has some tendency to mat, and is consequently more used for quilts and in articles of clothing than unmixed for stuffing beds. The feathers of swans, ducks and of the common domestic fowl are also largely employed for beds; but in the case of the latter bird, which is of course non-aquatic, the feathers are harsher
