74 EMBEYOLOGY OF THE LOWEK VERTEBEATES CH. 



view and having regard further to the fact that Eeptiles are typi- 

 cally covered with a coating of scales, we may safely also accept the 

 view that feathers are to be looked upon as highly specialized and 

 modified scales. 



While the mode of development of the feather fully substantiates 

 this hypothesis, perhaps the most interesting point that emerges 



c.p. 



cp. 



B 



c.s. 



c..s. 





FIG. 43. Illustrating the neonychinm or claw-pad in the developing Bird. 

 (From Agar, 1909.) 



A, median longitudinal section through tin- claw of a chick of 10 days' incubation. B, claw <if a 

 chick taken in tin- act of hatching. The iieonyrhiuin is seen beginning to bivak away fn.in tin- re>t of 

 tin- claw. C, section similar to A, but from a chick 12 hours after hatching. c,p, claw-].; 

 sole Of Haw ; /,, Haw-]>ad (neonychiuin). 



from its study is that the successive sets of feathers the down 

 feathers of the nestling, and the annual or other sets of feathers in 

 the adult are not to be looked on, as has been customary, as suc- 

 cessive series of independent individual feathers. On the contrary 

 the down leather and the definitive feathers, which succeed it in the 

 series of moults, are all simply portions of a single Lrivatly elongated 

 and basally growing structure the first down feather hem- its tip. 

 and the succeeding leathers being successive portions of it. The 

 moult consists not, in the shedding of the whole feather hut merely 

 in t.he hreakimj oil' of its proj,-ri m^ portion. 



Claws, \\hieJi make thrir lust appearance in A niira .\' 



