CLASS AVES 



405 



practically continuous surface, the structure is known as a vane. When 

 the barbs are not systematically arranged and form only a confused, 

 fluffy mass, this is known as down. 



A B D 



Fig. 294. — Types of feathers. A, flight feather. B, contour feather. C, down feather. 



D, filoplume. From specimens. X %■ 



Four types of feathers may be distinguished: (1) The typical feather, 

 known as a contour feather, is downy near its base and toward the tip 

 has a vane. The vanes overlap and provide a smooth outer plumage 

 surface, while the down forms a heat-conserving layer under it. (2) 

 Flight feathers differ from contour feathers in that they have practically 

 no down and in that the vanes are greatly lengthened and stiffened. 

 The flight feathers are set along the posterior margins of the forehmbs 



