4 8o MANUAL OF ZOOLOGY SECT. 



(Apteryx), the South American Ostriches (Rhed), and the 

 true Ostriches (Struthio) ; and the latter including all the 

 rest. 



One of the most characteristic features of Birds in 

 general is the covering of feathers peculiar epidermal 

 structures which differ widely in shape and arrangement 

 from their equivalents, the horny scales of Reptiles and the 

 hairs of Mammals. The arrangement of the feathers 

 follows closely that briefly described as observable in the 

 Pigeon, with great diversity in detail. The distribution of 

 the contour feathers in feather tracts or pterylse separated 

 from one another by featherless tracts or apteria is almost 

 universal in the Carinatae, but is not distinguishable in the 

 Ratitae except in the young condition. In many Birds 

 each feather has a secondary vane or aftersAaft, as it is 

 termed, springing from the main shaft near the umbilicus, 

 and sometimes (Fig. 275) this may be as large as the main 

 shaft itself. A shedding or " moulting " of the feathers 

 takes place at regular intervals, usually annually a new set 

 of feathers growing from the pulps of the old ones. 



The colours of feathers present great variety. Black, 

 brown, red, orange, and yellow colours are due to the 

 presence of definite pigments, i.e. are absorption-colours. 

 White, and in some cases yellow, is produced by the total 

 reflection of light from the spongy, air-containing substance 

 of the feather, there being, as in nearly all other natural 

 objects, no such thing as a white pigment. Blue, violet, and 

 in some cases green, are produced by the light from a 

 brown pigment becoming broken up as it passes through 

 the superficial layer of the feathers in its passage to the eye ; 

 no blue or violet pigments occur in feathers, and green 

 pigments are very rare. The beautiful metallic tints of 

 many birds are entirely the result of structure, owing their 



