Colouration of Vertebrata. 91 



In P. Wilsoni we have a wonderful example of morphological 

 emphasis. The head is bare of feathers, and coloured blue, except 

 along the sutures of the skull, where lines of tiny black feathers 

 map out the various bones. 



But morphological emphasis exists everywhere in birds. The 

 wing-primaries, which attach to the hand, are frequently differently 

 decorated from the secondaries, which feathers spring from the ulna ; 

 and the spur-feathers of the thumb, or pollux, are different in shape, 

 and often in colour, from the others, as every fly-fisher who has used 

 woodcock spur-feathers knows full well. The wing-coverts and tail- 

 coverts are frequently mapped in colour ; and the brain case is 

 marked by coloured crests. The eye and ear are marked by lines 

 and stripes ; and so we might go on throughout the whole bird. We 

 may remark that these very tracts are most valuable for the 

 description and detection of species, and among ornithologists 

 receive special names. 



Now, this distribution of colour is the more remarkable inasmuch 

 as the feathers which cover the surface — the contour feathers — are 

 not evenly distributed over the body, but are confined to certain 

 limited tracts, as shown by Nitzsch ; and though these tracts have a 

 morphological origin, they are rendered quite subsidiary to the 

 colouration, which affects the whole bird, and not these regions in 

 particular. In fact, the colouration is dependent upon the regions 

 on which the feathers lie, and not upon the area from which they 

 spring. In other words, we seem to have in birds evidence of the 

 direct action of underlying parts upon the surface. 



In more obscurely coloured birds, and those which seem to be 

 evenly spotted, close examination shows that even here the decora- 

 tion is not uniform, but the sizes and axes of the spots change 

 slightly as they occupy different regions ; as may be seen in Wood- 

 peckers and Guinea-fowl. 



Although the same tone of colour may prevail throughout the 

 plumage, as in the Argus Pheasant, great variety is obtained by the 

 fusion of spots into stripes. A symmetrical effect is produced by the 

 grouping of unsymmetrical feathers ; as is so often seen in plants, 

 where irregular branches and leaves produce a regular contour. 



Sometimes, especially on the breast and back, the feathers of one 

 region seem to unite so as to form one tract, so far as colour is 

 concerned. Thus, if in P. Wilsoni the black borders of the dorsal 

 regions were suppressed, all three areas would be of one hue. This 



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