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Show 1887.] OF THE WINGS OF BIRDS. 353 this is all. On the dorsal the first four rows of feathers show a certain amount of differentiation, being somewhat elongated, and showing what might be looked upon as a tendency to form remiges and coverts, which was early lost, the wing taking a different function to those which developed into organs of flight. The embryo of the Penguin shows in its wings no signs of being a degeneration or modification of the specialized flight-wing of other Carinates. Ihere appears to be no trace of remigial structure at all in this wing. Origin of Wing and General Conclusions. The study of the wings of living birds leads to the conclusion that the power of flight was gradually acquired, and also tends to throw some light upon the way wings were originally evolved from a reptilian manus. Recent researches ' seem to show that the ancestral form of the avian manus was probably a webbed form, and inferentially belonged to an aquatic type of animal. From this " webbed paw " was developed the starting-point of the wing, by special modification of the scales or feather foretypes on the dorsal surface. The Penguin's paddle represents, perhaps, a highly modified survival of this starting-point; the Ratite wings are modified conditions of the intermediate stage in the wing-formation. At some future time I hope to bring forward the evidence in favour (or otherwise) of this view more fully worked out; however, the following are some of the points which tend to support that view. In the adult flight-wing of the Carinates there are two rows of feathers situate on the ventral side of the wing, reversed in position, the t. majores and mediae. Sundevall explains this by saying it is an aftershaft developed at the expense of the feather-shaft, and states (S. p. 419) that the aftershaft is entirely deficient; but in a Pheasant I have found it normally developed, though small in these feathers. His explanation is erroneous. The true explanation probably is that these feathers or their antetypes were originally on the dorsal surface and have been carried down to the ventral in the formation of the " ala membrana " by the excessive development of the remiges and tectrices majores. That is, that originally on the dorsal surface of the arm and manus there took place a special modification of the scales or feather foretypes by which rows of these were directed backwards in the "primitive embryonic" position of the limb. Next two or three rows began to be specialized and to become larger and more prominent than the others ; then these, by their unequal growth, carried over a fold of skin and formed the wing-membrane, carrying some of the structures to the ventral side, which are now seen as the reversed feathers (cf. diagrams, Plate XXXII. figs. 1-5). In the embryo bird the feather-rudiments first appear on the dorsal surface, pointing to the fact that the modification here is very ancient and deep-seated ; the remiges and greater coverts (superior) being the earliest to appear; quickly they begin to assume 1 Prof. W. K Parker's recent paper " On the Morphology of Birds," read at the Royal Society, Jan. 27, 1887- |
