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Show 294 MISS NEWBIG1N ON T H E [Feb. 18, velvety black. The black region extends further up the vane on one side of the rachis than on the other. In mounted specimens the overlapping of the quills occurs in such a manner that the successive feathers cover over the black region of the feathers in front. There seems to be no difference in the amount of pigment present in the two regions. Bemembering the, as yet, unexplained fact that metallic colours occur only on exposed parts of feathers, it seems impossible to doubt that the black region is associated with the overlapping of the feathers. The tail is forked, and in consequence it is hardly probable that the rectrices can be separated and spread out to form the " parachute "-like structure which has been described in other forms ; the black area is thus permanently covered up. In Sappho sparganura the conditions are almost reversed, the exposed parts of the tail-quills are brilliantly metallic, with a band of black at the apex. It seems most probable that in this case, as in Topaza pella, the black colour is produced by an excess of melanin pigment. Summarg.-From the account given above it is seen that in the metallic feathers of Sun-birds the radii are without cilia and their distal regions are more or less completely modified into flattened club-shaped bodies containing a large amount of brownish pigment, and consisting of a series of " overlapping compartments," as described by Gadow. It is also seen, however, that the barbules near the apices of the barbs tend throughout this family to become modified in this way, so that the distinction between male and female, or specialized and unspecialized forms, is less in the structure of the barbules than in the amount of brownish pigment present. From the fact that similar conditions are observed in the Pheasant it seems probable that this occurs not infrequently. In the case of the Humming-birds the metallic colour is confined, like the brownish pigment, to the proximal part of the barbules, and its presence is not associated with any modification of the barbules which affects their efficiency in the feathers of flight. In their case, therefore, metallic colours m a y occur in the quills of the tail or (rarely) wing without interfering with the powers of flight. Further, as the metallic colour is associated with a specialization of the proximal region of the barbule, it cannot in contour-feathers primitively form a terminal band; the apparently terminal position is produced by the gradual suppression of the apical barbules, in which the proximal region is never well-developed. The examination of specimens upon which this paper is based was chiefly carried on in the M u s e u m of Science and Art, Edinburgh, and I have to record m y obligations especially to M r . Eagle Clarke for his kindness in affording m e facilities for doing so, and especially for furnishing m e with several feathers for microscopic investigation. The systematic part of the paper is based on Shelley's 'Monograph of the Sun-birds' (London, 1876-80), and Salvin's Catalogue of Humming-birds (B. M . Catalogue of Birds, vol. xvi. 1892). |