Jones — Nestling Feathers. 



PLATE IV. 



Figs. 45 and 46. From a 20-day chick embryo, x 618. Taken in the re- 

 gion marked X, Figure 3, Plate I, at different stages in the development 

 of this region. 



Figs. 47, 48, 49. Cross sections of barb-vane ridges at 47, 48, 49. Figure i, 

 Plate I. X 618. 



Figs. 50 and 51. Entire cross sections at 50 and i, Figure i, Plate I. 

 X 618. 



Fig. 52. A completely cornified down barbule from Larus atricilla. x 330. 



Fig. 53. Distal ^ of a down barb with barbules, from Larus atricilla. 

 X28. 



Fig. 54. A barbule with filaments (fil), one of which is a booklet or ha- 

 mule, at 54, Figure 142. 



Fig. 55. A barbule with filaments (fil) at 55, Figure 142. 



Fig. 139. A down barb dividing into two definitive feather barbs, one de- 

 finitive feather barb having broken away. From a fully fledged Crym- 

 ophilus fulicarius. x 62. 



Fig. 140. Four down barbs passing into definitive feather barbs, showing 

 incomplete separation of the barbs. From a fully fledged Oxyechus 

 vocifera. x 28. 



Fig. 141. A single down barb passing into three definitive feather barbs. 

 From a fully fledged Actitis macularia. x 28. 



Fig. 142. A single down barb dividing into three definitive feather barbs. 

 Barbules are fully developed along the whole course of this feather. 

 From a fully fledged juvenile Larus atricilla. x 39. 



