THE AMERICAN NATURALIST [Vol. XLII 



structure in feathers. In a former paper 2 the same author 

 showed that a feather is made up of a series of faint "funda- 

 mental bars," due to the manner of deposition of the feather sub- 

 stance. These bars are somewhat analogous to the annual rings 

 of growth in the trunk of a deciduous tree, the tree rings showing 

 the amount of annual increase in the tree trunk, while the bars 

 mark the daily growth in the production of the feather. The 

 demarkation of the fundamental bars is due to the period of 

 reduced blood-pressure during the early morning hours (1-6 

 A.M.) of each day during the growth of the feather, and the 

 defective transverse lines to malnutrition, or to reduced nutri- 

 tion. As shown by Jones, 3 the nestling down or neossoptile is 

 not a distinct and complete feather growth, but merely an apical 

 segment of the first definitive feather, the first down being "the 

 plumulaceous tip of the first definitive feather." The constric- 

 tion between the two parts Riddle considers to be another 

 variety of this same defect, due to insufficient nutrition. At the 

 time of the hatching of the egg the down portion of the down 

 feather is completed, and the shaft portion immediately succeeds, 

 at a time when the whole source of food-supply is changed, and 

 assimilation impaired by the intervention of a new source of 

 alimentation. While this is obvious, experiments have been 

 conducted to show the effects of underfeeding at the critical stage 

 in the bird's life, and it has been found that a bird in the 

 downy condition can thus be made to wear its downy plumage 

 for months after it should have given place to the definitive 

 feathers. "The 'quill' region is a part of the feather which 

 'normally' almost refuses to grow; by reducing the food-supply 

 during and after its formation further growth may be absolutely 

 inhibited or stopped." 



From the experiments here related, the author concludes that 

 the down portion of feathers is due to poor nutritive conditions, 

 and that "The formation of the quill is probably the direct result 

 of a progressive diminution of an already lessened food-supply." 



Apparently all this bears upon the "how" rather than the 

 "why" of feather production and feather structure, and is not 

 to be given a too-sweeping application. In other words, that in 

 the development of a pennaceous feather, the formation of its 

 different parts— the pennaceous, the downy, and the quill por- 

 a A Study of Fundamental Bars in Feathers. Biol. Bull., Vol. XII, 

 February, 1907, pp. 165-174. Noticed in The Auk, January, 1908, p. 98. 



