1887.] OF THE •WINGS OP 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 func- 

 tion 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. 

 There appears to be no trace of remigial structure at all in this 

 wing. 



Origin of JVing 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 ances- 

 tral 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 fbretypes on the dorsal 

 surface. The Penguin's paddle represents, perhaps, a highly modi- 

 fied 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 follow- 

 ing 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 \yere originally on the 

 dorsal surface and have been carried down to the ventral in the for- 

 mation 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 



^ Prof. W. K. Parker's recent paper " On the Morphology of Birds," read at 

 the Royal Society, Jau. 27, 1887. 



