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Show 290 MISS NEWBIGIN ON T H E [Feb. 18, tion of the ordinary metallic contour-feathers of most Hummingbirds has been accompanied by a reduction of this terminal band in width and in the individual barbules forming it, a large increase of pigment in the laminae of the barbules forming the blackish-grey part of the feather in Phaethornis, and a specialization of the barbules of this region, of which the most obvious result is the shortening of the filamentous portion and its inclination to the lamina. In the feathers of the patches of especial brilliancy these changes have been carried further, and have been accompanied by a shortening of the feather and rounding of its tip, and a change in the angle of insertion of the barbules. The changes in the wing-quills seem to have been of a simpler description, and to have been chiefly accompanied by a specialization of the lamina. As to the meaning to the individual of this progressive change, one suggestion may be hazarded. The Humming-birds are especially characterized by their powder of flight. N o w of the many correlated variations which must occur during the gradual improvement of the power of flight, an increased development of the lamina and of cilia and hooklets is likely to be important. It is therefore perhaps not unreasonable to suppose that the metallic colours of Humming-birds are due to a persistence in the same line of variation which produced their powers of flight. If Kolliker (" Die Entstehung des Pigments," Zeitsch. f. wiss. Zool. vol. xlv.) is right in his belief that the formation of pigment is connected with the blood-system, it is quite comprehensible that an increase in structural specialization should be accompanied by an increase in the amount of pigment. It might be objected that the Swifts, which are probably nearly allied to the Humming-birds, have also great powers of flight and yet do not show metallic colours. In reply to this objection, it m a y be said that it is generally admitted that Humming-birds have few enemies, and that therefore variations might occur in them unchecked which would possibly lead to ehmination in other forms. A more important objection is that the wings do not usually show metallic colour : it seems impossible to suggest a reason for this beyond the simple fact that the wings seem to be slow to vary in colour. It will be noticed that, in the especially brilliant patches, the extreme closeness of the connection between the adjacent barbs is a variation in the direction of the ordinary condition of the feathers of flight. The course of the development of metallic tints in Sun-birds offers many points of contrast to that just described for Humming-birds. If w e take (PI. XII. fig. 22) one of the ordinary contour-feathers of a non-metallic form, such as a female of a species of Cinnyris, probably C.jugularis, it will be found that it presents considerable resemblance to a corresponding feather from a " hermit" Hummingbird. Thus it consists of a basal downy region, a mid-region pigmented with brownish black, and an apical region with disconnected diverging barbs, usually of a dull olive colour. Beginning with such a feather, the development of metallic colour is accompanied by an increasing predominance and pigmentation of |
