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. 



Tig. 3. 



The three positions in which metallic colours should be observed. 



EXPLANATION OF THE PLATES. 



s, seapus or shaft ; 



Plate XXVII. 



Fig. 1. Part of a belly-feather of Pitta moluccensis. 

 r, ramus or barb; p, radius or barbule. 



2. The blue part of the ramus at * (fig. 1), as seen under the microscope 



with transmitted light. 



3. The same, but magnified 640 times, st, transparent surface-coating or 



sheath ; c, the layer of cones, with their sheath (a) and with the fine 

 ridges (r). 



4. The same of Careha. 



5. Yellow radius of Fitta. pp, pigment-corpuscles, the shaft of the radius 



showing the longitudinal ridges. 

 6 a. Part of another yellow radius of Pitta. No pigment present. 

 6 /;. Transverse section through 6 a at ». 



7. Yellow radius of Picus. 



8. Part of a metallic golden-green to blue feather of Nectarinia famosa. 



s, shaft ; p, radius ; r, ramus. 

 9«. Distal half of one radius of Nectarinia, showing the transparent 



sheath which surrounds the compartments. 

 9 h. The same, but seen from the edge. 

 1(1. End of a metallic radius of a Jacamar. cc, the suppressed ciliae. 



11. Part of a metallic -violet barbule of Stvrnus vulgaris. 



12. Part of a barbule of a red non-metallic feather of Nectarinia, 



Plate XXVIII. 



Fig. 1. One metallic violet barbule oi Mthopyga. 



2. One barbule of a green feather of Palceornis. 



3. Barbule of a yellow crest-feather of Partis sultaiieus. 



4. Part of a colourless barbule of Parus aultancus. 



5. One barbule (radius) of a metallic (coppery-red to bluish) feather of 



a Jacamar. c, one of the comjjartments separated from the others, and 

 showing its highly convex-concave shape ; r, barb or radius. 



