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BIRD GALLERY. 



Colour. The colour of feathers is due to one of three causes: 

 (]) It may arise from the presence of actual pigment, (2) from pigment 

 overlaid by colourless structures, or (3) from iridescence due to the effect 

 of light falling on the polished, ridged or pitted surfaces of the feather 

 which act as prisms. 



Fig. 4. 



,5. 



Side view of Right Foot of a Purple Gallinule (Porphyno) to show the 

 composition of the horny covering (podotheca). 



1. Hallux or hind toe. 



2. Inner toe. 



3. Middle toe. 



4. Outer toe. 



5. Scales (Scutellce). 



6. Reticulate scales. 



Yellow colour, like black, brown and red, is as a rule due to pigment 

 diffused throughout the substance of the feather. Some yellow feathers, 

 however, contain no pigment whatever, the colour being due to the 



