7_> EMBRYOLOGY OF THE LOWER VERTEBRATES CH. 



inent the unincised basal portion forming the quill of the feather. 

 The horny sheath becomes strongly cornitied and then breaks open 

 and the longitudinal thickenings of the epidermis, now also strongly 

 cornified, break away from the sparse cornified dermal tissue of the 

 axis and form the fluffy barbs of the down feather. 



In the basal quill portion of the feather the epidermis immedi- 



Ki.;. -12. Illustrating the development of feathers. (After Da vies, 1889.) 



A, H, (', longitudinal sections ; I), E, F, transverse SIT! ions (I). K, down leather ; F, tli^ht feather) : 

 <i, longitudinal <! ion through h:irl> rudiment showing developing barlmles : H. Ion-it n<lin:ii 



ther. I; barb; bb, bar-bill*-; <-, horny septa ; c.r, layt-r of cylindrical epithelium ; 

 r rndinn-nt ; ./. u"-i ininal region ; p, ]>\\\]> ', '/, quill ; /, lachis ; sii. sheath. 



ately covering the outer end of the axial dermal tissue m- pulp terms 

 a thin Strongly cnniiiied superficial LiyiM* \\liicli st'paralt-s nil' as a 

 septum cutting across the cavity of the quill. This pnrv>s being 

 repeated |MTio<lir ; ,Hy gives rise- to a scries <!' horny e;ips lilting on%f 

 the ^ther, in the interior of the quill (Fig i' ll.c). 



Th- ilal leathers, found as contour leathers arranged in jatehe> 

 over the genej-.il smiace and as l;rmi : j(;s and Ke-irices in ihe wings 



