| OCR Text |
Show 1886.] CUBITAL COVERTS OF BIRDS. 201 Gypagus, I have been so much impressed with the uniform style of wing-coverts prevailing amongst this group, that it seems to me difficult to believe that their genetic relationship amongst themselves is more remote than Forbes regarded it. I cannot, after many years' observation of the facts referred to in this paper, help regarding this similarity of style of wing-coverts in birds so different, both in outward form and in their mode of life, as presenting us Fig. 34. with a certain amount of evidence of the transmitted survival, in an unmodified form, of a mode of imbrication of epidermic structures that at some remote period in the genetic history of the common Sauropsidan ancestors of these birds played some really important part in the economy of the wearer. During the differentiation of such parts of the creature's organization as were directly affected by the struggle for existence, other parts, not so affected, either changed at a slower rate, or else were transmitted from generation to generation hardly modified at all. Habit, or mode of life, as birds now live, can at the most have played but a minor part in bringing about these diversities of style. W e have but to compare the Swallows with the Swifts, the Sun-birds with the Humming-birds, and many other parallel cases, and we at once perceive that mode of life has had little or nothing to do with the origin of the features in question. The real cause lies deeper than that, and dates back far into the remote history of the Sauropsida. Reverting to the normal Ciconiine style of coverts, we find Platalea, with Ibis and its allied genera, differing but little from each other and from Ciconia. Tantalus, in this respect, stands nearer to the Limicolee. The Cranes, again (fig. 35, p. 202), present another variation little removed from the central Pluvialine type. Somewhere near to the Cranes and the Storks, but connected in some way with the Gallinaceous style of coverts, stands the wing of the Secretary Bird (fig. 36, p. 202); it is quite unlike the true Accipitrine type. PROC. ZOOL. Soc-1886, No. XIV. 14 |
