COLUMBA 119 



The vane is made up of a large number of barbs on each side 

 of the central stalk or rachis, and each barb carries a number 

 of barbules on either side. The barbules bear hooks and 

 notches, by means of which the barbules of one barb are 

 attached to the barbules of adjacent barbs. In this way a stiff, 

 air-resisting plane is formed, which is especially well developed 

 in the flight-feathers. The flight-feathers on the wings are 

 called remiges, those on the tail rectrices. The remiges which 

 are carried on the " forearm " (radius and ulna) are the 

 " secondaries," those on the " hand " (carpals, metacarpals, 

 and phalanges) are called the " primaries." Contour feathers 

 cover the body and give it a smooth surface which presents 

 little resistance to the air during flight. They are smaller 

 than flight-feathers, and the hooks or hamuli on the barbules 

 are not so well developed. Contour feathers usually possess 

 an aftershaft, which is like a duplicate vane arising from the 

 base of the rachis. As a rule it is small, but in the cassowary 

 the aftershaft may be as long as the main shaft. The base 

 of the quill beneath the vane is a hollow cylinder, opening 

 below by the inferior umbilicus, and above at the base of the 

 vane by the superior umbilicus. The superior umbilicus is 

 between the main shaft and the aftershaft, which relations 

 become obvious from a study of the development of the 

 feather (see p. 224). 



In addition to the pennae there are in most birds down 

 feathers or plumulae. In these the barbules and hamuli are 

 very degenerate so that there is no stiff vane at all. The down 

 feathers form a dense layer which prevents the movement of 

 the air in it, and therefore functions as a non-conductor of 

 heat. This is important because birds are warm-blooded, 

 and without this protection they would lose their heat rapidly 

 by radiation from the skin to the surrounding air. 



Some feathers consist only of a slender stalk with scarcely 

 any barbs ; they resemble hairs and are known as filo- 

 plumes. 



The kinds of feathers described above are characteristic 

 of adult birds, and may collectively be called teleop tiles. In 

 the young birds they are preceded by nestling- feathers, or 



