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TEXT-BOOK OF ZOOLOGY 



much. (Why do we not meet with birds possessed of an armour-like 

 shell, like, e.g., the tortoises'?) 



(a) The Different Kinds of Feathers. — The feathery covering of a bird 

 is made up of two kinds of feathers, viz. : down- 

 feathers, which form an under-coat ; and larger 

 clothing or contour feathers, forming an upper 

 covering for the body which shuts off from the 

 outside the warm layer of air enclosed by the soft 

 hairy down-feathers. (In what direction are the 

 contour feathers disposed, and why ?) The 

 contour feathers are called after the parts of 

 the body which they cover (neck-, shoulder-, 

 breast-feathers, etc.). The large feathers at the 

 posterior margins of the wings, which convert 

 the fore-limbs into broad, oar-like surfaces, are 

 termed flight-feathers ; those which convert the 

 tail into a rudder the tail-feathers or " rectrices." 

 (/)) Parts of a Feather. — A fully-developed 

 feather consists of the following parts : a firm 

 stem {scapus), which supports the whole structure, 

 and the real blade of the feather, the vane or 

 vexillum. The lower, generally transparent, 

 portion of the stem is known as the quill or 

 ealamus, while its upper portion, which contains 

 a pith-like substance analogous to marrow, is 

 termed the shaft or racl/is. The quill of a per- 

 fect feather contains a fine dry membrane or pith 

 which, while the growth of the feather is still 

 incomplete, is traversed by bloodvessels. The 

 vane consists of a series of horny plates, the 

 barbs, placed obliquely along the shaft, and giving off pointed processes, 

 the barbules, from their anterior and posterior margins. The anterior 

 barbules are generally provided with small hooks which interlock with 

 the posterior barbules of the preceding barb, the vane thus coming to 

 form a connected whole. (This is especially important in the case of the 

 wing-feathers, see Section 11.) 



(c) Moulting of the Plumage. — As a rule, with the beginning of autumn 

 the bird changes its plumage, a process known as ■moulting. It then 

 assumes what is known as the winter dress, which changes its colour, 

 especially in the males, with the approach of spring (spring moult), being 

 now changed into the /redding or breeding dress, from the fact that it is 

 assumed at the pairing and breeding season. The plumage of the young 



Lower Portion of a Quill 

 Feather. 



1C, Scapus; Sp., quill or 

 calamus; F., vane; !->., pith. 



