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Show 288 MISS NEWBIGIN ON T H E [Feb. 18, colour, it may be noticed as a fact for future investigators that, as is indicated in the figures, the laminae in the feather described show more or less distinctly an arrangement of cross-bars (or compartments). This is common in the case of the Humming-birds, but it is also sometimes distinctly visible in the laminae of the barbules of Sun-birds (see PI. X I . fig. 3 and PI. XII. fig. 18), so that its significance is somewhat doubtful. One other fact in connection with the metallic colour may be noted. Contrary to the usual rule, the featherof the Humming-bird mentioned under certain circumstances exhibits metallic tints by transmitted light even under |" objective. W h e n this occurs, it is clearly seen that the colour is confined to the dark infolded part of the barbule, which alone under ordinary circumstances is visible (see PI. X I . fig. 10). This infolded part cannot, however, be itself the cause of the metallic colour, for it is absent from the metallic feathers in some cases (see PI. XII. fig. 19). The ridging of the surface of the feather produced by the way in wiiich the barbules are inserted, though apparently a factor in colour production, cannot be absolutely essential, for it is sometimes absent. Thus, in Calothorax lucifer in the brilliant throat-patch the feathers in the middle line are very distinctly ridged and have the usual plate-like structure, while those at the sides of the throat are quite devoid of ridges but do not show diminished brightness. Similarly, in Cyanolesbia gorgo the brilliant green feathers of the crest are perfectly smooth, and have a certain hard gloss which is absent in the ridged feathers. The fact that in Humming-birds it is the proximal, and in Sun-birds the distal region of the barbules which is metallic has more effect upon the general coloration than might at first sight be supposed. It is, in the first place, n o w obvious that there is nothing in the structure of the metallic feathers of Humming-birds which is likely to affect their efficiency even in quill-feathers. We can thus understand how it is that many of the tail-quills in Humming-birds, and even the wing-quills in Eulampis jugularis, may exhibit metallic colour and yet perform their usual function. But this is not the only effect produced by the difference. In Sun-birds the lamina is rudimentary in the metallic barbules ; now the lamina tends to become rudimentary in the barbules at the bases of the barbs, that is in downy barbules, and in the barbules at the apices of the barbs. Downy barbules never seem to show a tendency to become metallic, and w e thus find that in Sun-birds the metallic barbules occur only at the ends of the barbs. A little reflection will show that the consequence of this is, that the metallic barbules will forin a transverse band on contour-feathers, where the ends of the barbs stand much on the same level, and a longitudinal band on quill-feathers where the rachis is much elongated. The position of the bands of metallic colour on the feathers of Sun-birds is thus a consequence of the kind of modification to which their metallic barbules are subject. (See PI. X I . fig. 1 and PI. XII.fig. 17.) In Humming-birds there is an almost complete reversal of this, state of affairs. In them the metallic barbules have an extremely |