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Show 286 MISS N E W B I G I N O N T H E [Feb. 18, then metallic quill-feathers must be useless for purposes of flight. Owing to the absence of cilia, the barbules are wholly unconnected, and so can offer little resistance to the air. The unconnected nature of the barbules may frequently be observed in metallic feathers by the unaided eye, e. g., in the feathers of the Peacock. In confirmation of the belief that such metallic feathers must be useless for purposes of flight, w e find that the long metallic feathers of the Peacock or Quezal are not the tail-quills, but merely the tail-coverts, and that the wing-quills in both cases are non-metallic. While endeavouring to continue this chain of reasoning, however, the writer was struck by the fact that in Humming-birds, where the power of flight is so marked, not only are the rectrices frequently metallic, but they displayed a closeness of texture which seemed incompatible with Gadow's statement that ciliae are always absent from the radii of metallic feathers. The metallic feathers of Sun-birds, on the other hand, show always a certain looseness of texture as compared with the non-metallic. On examining the respective feathers of Sun-birds and Humming-birds microscopically, it was found that marked differences exist between them. W e will first describe a purple metallic feather of the Sun-bird Cinnyris amethystina. W h e n examined by the unaided eye (PI. XI. fig. 1), this feather is seen to be divided into three regions. There is a distinct terminal band of metallic colour, distinguishable by its deep pigmentation and pecuhar structure. Next w e have a band of close texture and brown colour, which has an indentation at its lower end. Finally, the base of the feather is of an ashy colour and downy structure. The basal indentation of the brown band possesses some interest, because Darwin (' Descent of Man,' 2nd edition, p. 430 et seq.) regarded a similar indentation in the centre of the ocellus of the Peacock as evidence of its origin from two confluent ocelli. It is possible to obtain from the feather described a single barb which bears barbides belonging to each of the three regions: in this way transition forms can be very readily seen. The basal barbules exhibit the usual structure of downy barbules, that is to say the distal portion, which from its (apparent) shape may be called the lamina, is more or less rudimentary, while the distal or filamentous region is greatly elongated and very slender, has only rudimentary ciliae, and consists of a series of joints slightly overlapping one another (PI. X I . fig. 2). The barbules of the middle region possess a well-developed lamina and a long filamentous region furnished with cilia and, in the case of the distal barbules, with distinct hamuli (PI. XI. fig. 3). The barbules of the metallic region are metamorphosed into short, wide, club-shaped bodies, supported on broad stalks (PI. XI. fig. 4). These clubs are deeply pigmented with brown, and show very distinctly transverse bars-the compartments of Gadow. Although to the unaided eye the transition between the metalhc and the non-metallic barbules is abrupt, yet microscopically it is sufficiently |
