OCR Text |
Show 1886.] CUBITAL COVERTS OF BHIDS. 185 comparison of the features presented by a large series of living birds, in good health, or of freshly-killed wild birds, leads to a different conclusion. These show that a particular mode of arrangement, or a particular order of overlap, of the median cubital coverts is practically constant for all the individuals of the same species. More extended observations show that the same general mode of disposition is as a rule characteristic of all the species of a genus, and may even be found throughout all the members of groups larger than that. A reference to the wing of the Golden Plover, a central type, and one that in itself represents all the leading modifications (see fig. 1, p. 186), may help to make the nomenclature herein used more intelligible. [In drawing up this scheme I have availed myself of several suggestions made to me by Prof. Flower, and by my colleague Mr. E. T. Newton, after the paper was read before the Society.] The terms used refer mainly to the relations of various parts of the wing to each other and to the body axis, when the wing is extended and is viewed from the dorsal or upper surface. The wing-surface is primarily divided into the manual (primary) region and the cubital (secondary) region, this last embracing all the feathers that originate from any part of the forearm or cubitus. Of the manual region I have nothing that need now be discussed. In the cubital region the Remiges, and the Greater Coverts that come on next above them, are uniform in disposition in all Carinate birds. In these feathers the overlap is uniformly distal ; that is to say, the several feathers are disposed in such a manner that the outer free edges of those nearer the vertebral axis overlap the inner edges of those originating nearer the distal extremity of the wing. The same observation applies also (but with some minor modifications of detail that will not now be taken into consideration) to the Lesser Coverts, or those feathers that mainly originate in the Patagium, and that extend along the anterior border of the wing from the humeral fold to the carpal joint. The remaining feathers, which are generally comprehended under tbe term Median Coverts, vary considerably in both their direction of imbrication and in the number of rows that run parallel to the greater coverts in each case. The present paper is devoted to a consideration of the nature and the extent of the variation referred to, without regard to morphological details of any other kind soever. Many of the facts have either not been noticed, or else, if they have been noticed, their significance appears to have been missed. For convenience of description the tract occupied by the Median Coverts may be divided into three areas by lines parallel to the main direction of the cubital quills. The area nearest the vertebral axis will be referred to as the Proximal area, the next the Middle area, and the remaining third, up to the distal border next the manual region, the Distal area. The rows of feathers composing the median coverts range, in a general way, parallel with the greater coverts. The number of rows varies from one to six, or even more, in different forms of birds; and the row nearest the greater coverts is the one most subject to variation in the disposition of the feathers composing it. PROC. ZOOL. Soc-1886, No. XIII. 13 |