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Show 1896.] METALLIC COLOURS OF BIRDS. 295 EXPLANATION OF PLATES XI. & XII. Fig. 1. Violet metallic feather of Cinnyris amethystina, showing three zones: a=apical metallic zone; &=brown pigmented zone with closely connected barbules and basal indentation; c=downy basal zone. Fig. 2. Two downy barbules from same : ^rudimentary lamina; f= filamentous region, much elongated and with rudimentary cilias. Objective I", Ocular B. Fig. 3. Proximal radius from region b of same, showing well-developed lamina, slightly pigmented and marked with cross-bars, and filamentous region with well-developed cilia. Ob. %', Oc. B. Fig. 4. Proximal radius of same, showing transition to metallic condition. The lamina is rudimentary, and the filamentous region is pigmented and somewhat expanded. Ob. J", Oc. B. Fig. 5. Metallic radius of same, showing shape, compartments, and peculiar flattening. The last three figures are all of radii taken from different levels on the same barb. Fig. 6. Fragment of metallic barb under low power, to show position of barbules: p = proximal radii; ^=distal. Ob. 1", Oc. B. Fig. 7. Metallic feather from gorget of Basilinna leucotis: a = naked barbs, corresponding to zone a of fig. 1; b= metallic region of feather, corresponding to zone b of fig. 1 ; c=downy region. 7 a is a diagrammatic cross-section of a single barb, to illustrate the formation of the surface-ridges of the feather: ^=distal radius; p=proximal radius; 4=barb. Fig. 8. Proximal radius from the base of one of the metallic barbs of above feather. The lamina is only faintly pigmented. Ob. J", Oc. B. Fig. 9. Distal radius from brilliantly metallic region of same. The lamina is deeply pigmented and has a folded-in edge. The filament is without pigment. Ob. -}'', Oc. B. Fig. 10. Fragment of metallic barb of same with distal barbules only, to illustrate normal position of barbules. Owing to the angle of insertion of the filamentous region, this is not visible in surface view. Ob. \", Oc. B. Fig. 11. Tip of barb of breast-feather of Eustephanus femandensis 2, to illustrate apical modification of barbules. The lower barbules in the figure are metallic. Ob. 1", Oc. B. Fig. 12. Tip of barb of gorget-feather of Basilinna leucotis, with naked barb furnished only with rudiments of apical barbules. Ob. 1", Oc. B. Fig. 13. Barbules from three different levels on a barb of a contour-feather of Phaetkornis eurynome to show details of the modification of the original apical barbules. Note in passing towards the apex of the barb the reduction of the lamina and flattening of filamentous region. The filamentous region is, however, unpiginented. Ob. }", Oc. B. Fig. 14. Fragment of barb of Cinnyris amethystina for comparison, and to show junction of metallic and non-metallic regions. Ob. 1", Oc. B. Fig. 15. Three barbules from the yellow edging to a quill of Mthopyga seherics. Ob. I", Oc. B. Fig. 16. Three barbules from metallic edging of quill of Anthreptes malaccensis. Ob. i", Oc. B. Fig. 17. Tail-quill of Anthreptes malaccensis (?), with metallic edging on right side (m). Fig. 18. Three non-metallic barbules from above. Ob. }", Oc. B. Fig. 19. Three metallic barbules from tail-quill of Eustephanus femandensis, Ob. i", Oc. B. Fig. 20. Three brilliantly metallic barbules from central tail-quill of Mthopyga seheriw. Ob. ]-", Oc. B. Fig. 21. Barbules from same quill, but much nearer rachis ; they show partial transformation, and in their natural position exhibit a faint though distinct metallic sheen. This partial transformation occurs chiefly in the case of distal barbules, and produces a visible effect to the unaided eye. Ob. i", Oc. B. |
