1902 Feathers: Their Structure and Uses 173 



ing. The papilla becomes enclosed and sunk in a sac, — 

 the feather -follicle, — from which it later on protrudes as 

 the feather- germ. The horny layer {stratum corneum) of 

 the epidermis forms a sheath, which is, however, only 

 temporary, and which is thrown off as the feather grows 

 and expands. As the feather-germ grows the cells of the 

 Malpighian layer begin to proliferate and give rise to a 

 series of vertical folds, which are arranged along a central 

 axis, and which extend inwards to the pulp. These folds, 

 which are surrounded by the horny sheath, become cor- 

 nified and separated, and by drying of the pulp gradually 

 give rise to a tuft of horny barbs. 



The majority of birds are hatched with the feathers in 

 this state, which look uncommonly like hairs. The sur- 

 rounding horny sheath splits and the barbs become free, 

 and if they are all like one another a down -feather has 

 been formed. 



The lower part of the feather- germ remains embedded 

 in the skin and forms the quill. The down -feathers may 

 remain as such throughout life, or may be replaced by 

 regular feathers. A second follicle, or sac, is gradually 

 developed below that of the down-feather with which it is 

 connected. The papilla which develops inside this new 

 lower follicle quickly grows and pushes the down -feather 

 out of its follicle, or pocket, and comes to the top. Each 

 feather at first resembles a down-feather in structure, but 

 in course of growth one of the barbs becomes thickened 

 and forms the shaft, or rachis, to which barbs are attached. 



The ordinary feathers which cover the body are called 

 contour feathers, because they indicate the form or shape 

 of the body. They have generally soft barbs at their base. 

 Many birds have a more or less quantity of down, which 

 is made up of very soft feathers, sometimes having an after- 

 shaft, and sometimes having not even a shaft at all ; in this 

 case the soft barbs diverge from the top of the quill. ^ 



^ A number of birds, when young, pass through no downy stage at all ; such 

 are the whole orders of Woodpeckers, Cuckoos, and their allies, and the Pigeons. 

 The majority of the large order of Perching Birds (Passeres), of which the sparrow 

 is a type, pass through no downy stage — an exception being the lyre-bird of 

 Australia, the young of which are hatched thickly covered with down. Young 

 birds which are always covered with down are the Game Birds, of which the 

 domestic fowl is a conspicuous example, 



