GENESIS OF FAULT-BARS IN FEATHERS. 349 



feather-germ, but that the latter sustains and enjoys these same 

 relations long after its maturity. 



In discussing feather nutrition attention may be called to cer- 

 tain general nutritive relations which the feather bears to the 

 surrounding parts. It has been pointed out by Poulton 1 that 

 the feather follicle itself is merely a mechanism whereby " a better 

 nutrition and support" of the feather is attained. The extreme 

 vascularity of the papilla is another condition favoring a high 

 nutrition. Further, the pulp cavity is widest and the epidermal 

 parts thinnest at the region of most active growth (PI. XII., Fig. i). 



Structural Relations Between the Feather- elements and the 

 Blood. — A word is necessary here concerning the more intimate 

 relations between the blood and the growing feather-elements. 

 From PI. XII., Figs. 4-5, much of these relations can be seen at 

 a glance. It will be noted that (1) the capillaries are extremely 

 numerous along the outer edge of the pulp ; (2) of the epidermal 

 structures the thin cylinder-cell layer lies nearest the capillaries ; 

 (3) the barb-forming region is narrowly separated from the capil- 

 laries by the cylinder»cell layer ; (4) the barbule-forming region 

 is still further removed from the capillaries ; (5) lymph spaces 

 extend presumably from the pulp to the outer sheath ; (6) the 

 large pigment cells occupy positions between the cylinder-cell 

 layer and some barb-forming cells on the one hand and the bar- 

 bule forming cells on the other. 



It is obvious that the cylinder-cell layer occupies the favored 

 position as regards all exchanges with the blood. It is an 

 observed fact that its component cells continue to divide longer, 

 i. e., at a higher level in the feather, than any other part of the 

 germ. Further, the barb-forming region is in a more favored 

 position than the barbule-forming portion, the former being closer 

 to the capillaries, and is also able to profit by adding to itself 

 some of the newly formed cells of the cylinder-cell layer. That 

 the barbules actually suffer more than the barbs under reduced 

 feeding, etc., is proved by the structure of every fault-bar, and by 

 reduced cell-division and growth of this region, as demonstrated 

 by sections. This is also shown by the seven-day starving 

 experiment already cited. 



Poulton, E. B., The Quart. Jour. Micr. Set., Vol. XXXVI., 1894. 



