12 



A BOOK OF BIRDS 



called, because they form the contour or outline of the body. But 

 besides these there are no less than three other distinct kinds of 

 feathers — down feathers, filo-plumes, and powder-down. 



Down feathers in many birds are conspicuous by their absence, 

 and are developed most abundantly in water-birds, such as Ducks, 

 for example, growing not only between the feathers, but over the 

 otherwise bare spaces as well, so as to form a thick undergrowth, 

 answering to the under-fur of seals, for instance. 



Filo-plumes appear to be present in all birds. They are the long, 

 hair-like growths so conspicuous in the common fowl when plucked. 

 In some birds they attain such a length as to extend beyond the con- 

 tour feathers, forming, as in some Cormorants, long, white delicate 

 plumes. 



The powder-down feathers are found only in a few groups, such 

 as the Herons and Bitterns, and some Hawks and Parrots. In the 

 Herons and Bitterns they form large patches, a pair on the breast, 

 and a patch over each thigh. Of a peculiar woolly appearance, they 

 are remarkable for the fact that they break up, when touched, into a 

 fine powder, which, when rubbed between the fingers, gives an in- 

 describably smooth feeling. It is the powder from these remarkable 

 feathers which gives the peculiar bloom to the beak of many parrots, 

 as well as to the plumage. As to the real purpose of the powder, 

 however, we know nothing. 



This brief survey of feathers would not be complete without a 

 few words as to their structural characters. In the typical feather 

 (say, a quill feather), two main parts are to be distinguished — the 

 stem, and the broad flexible blade known as the vane, or vexillum 

 (fig. 5). The stem may further be divided into the quill, or calamus, 

 the hollow part below the vane, and the shaft or rhachis, which is 

 square in section and filled with a white pith. The vane runs along 

 on either side of the rhachis in the form of a series of tapering, flattened 

 rods, the " barbs." They are set so closely together that they must 

 be carefully sought for ; and give to the vane that finely grooved 

 appearance, or, rather, the appearance of a series of fine lines running 

 obliquely outwards from the shaft. If an attempt be made to pull 

 these apart, it will be found that some considerable force must be 

 used, and this is owing to the fact that they are locked together by 



