420 DR. H. GADOW ON THE COLOUR OF FEATHERS. _[ May 2, 
Position B, in which the bird is placed vertically to the eye, a 
position in which objects are usually described. : 
Position C, in which the bird is held in the same level with, but 
between the eye and light. 
Fig. 3. 
rn Oe Sa 
The three positions in which metallic colours should be observed. 
EXPLANATION OF THE PLATES. 
Piate XXVII. 
Fig. 1. Part of a belly-feather of Pitta moluccensis. s, scapus or shaft; 
7, ramus or barb; p, radius or barbule. 
2. The blue part of the ramus at x (fig. 1), as seen under the microscope 
with transmitted light. 
3. The same, but magnified 640 times.  s¢, transparent surface-coating or 
sheath ; c, the layer of cones, with their sheath (s) and with the fine 
ridges (7). 
4. The same of Cereba. 
5. Yellow radius of Pitta. pp, pigment-corpuscles, the shaft of the radius 
showing the longitudinal ridges. 
6a. Part of another yellow radius of Pitta. No pigment present. 
6 6. Transverse section through 6 a at x. 
7. Yellow radius of Picus. 
8. Part of a metallic golden-green to blue feather of Nectarinia famosa. 
s, shaft; p, radius; 7, ramus, 
9a. Distal half of one radius of Nectarinia, showing the transparent 
sheath which surrounds the compartments. 
9b. The sane, but seen from the edge. 
10. End of a metallic radius of a Jacamar. cc, the suppressed cilizx. 
11. Part of a metallic violet barbule of Sturnus vulgaris. 
12. Part of a barbule of a red non-metallic feather of Nectarinia, 
Prate XXVIII. 
. One metallic violet barbule of Zthopyga. 
. One barbule of a green feather of Paleornis. 
. Barbule of a yellow crest-feather of Parus sultaneus. 
. Part of a colourless barbule of Parus sultaneus. 
. One barbule (radius) of a metallic (coppery-red to bluish) feather of 
aJacamar. ¢, one of the compartments separated from the others, and 
showing its highly convex-concaye shape ; 7, barb or radius. 
Fig. 
Ou Coho re 
