28 THE BIOLOGY OF BIRDS 



New Feathers. — Except in the case of the first feathers - 

 after the down, a new feather arises indirectly rather than 

 directly from its predecessor. According to Frieda Born- 

 stein (i9ii),a new germ arises, while the old feather is still 

 growing, at one side of the base of the feather follicle. 

 The new feather-germ forms a process which grows into the 

 deeper layers of the cutis, and from this process the new 

 papilla is formed. The old papilla atrophies after the old 

 feather falls off. 



Studies of feather replacement in fowls by Raymond 

 Pearl and Alice M. Boring (19 14) brought out the following 

 points : (i) In the general body plumage a feather is not 

 usually regenerated more than three times. Wing primaries 

 have the maximum regenerative capacity. (2) If a feather 

 follicle has been brought into a quiescent state by the 

 successive removal of feathers and has remained absolutely 

 inactive for a long period, e.g. six months, before the natural 

 autumn moult, it nevertheless forms in connection with 

 the moult a new feather, in the same manner as does any 

 other follicle in the body. The process of moulting re- 

 activates the follicle. (3) The precise pattern of the 

 feather is usually reproduced each time with extreme 

 fidelity of detail. But if the feather is removed from the 

 follicle as soon as it is fully formed, thus forcing continuous 

 regenerative activity, the patterns tend gradually to break 

 up. It may be that the hereditary factor material in the 

 feather follicle becomes exhausted if repeatedly called upon 

 without due intervals. (4) The secondary sexual feathers 

 of the male only appear as adult plumage. The follicles 

 that produce them previously produced, as juvenile plumage, 

 ordinary undifferentiated feathers. But if the juvenile 

 feather be removed apart from the normal moult, the next 

 feather will be a secondary sexual feather, and after that 

 all the regenerations will be of the secondary sexual type. 



The embryological evidence seems to suggest that a 

 feather is something superadded to the scale-primordium — 

 an extra-differentiation. Joseph Schleidt (1913) notes 

 that the primordia of the scales on the chick's feet are very 



