FRILLS AND FUNDAMENTAL BARS AS PLUMAGE CHARACTERS. 155 



Thinking it of interest to see the second feathers, I plucked and mounted these 

 juvenal feathers and awaited the growth of others. The bird died when 10 weeks 

 old, but the plucked feathers were already replaced, and here both of the wing-bars 

 are well-developed and complete. 



The peculiar transverse bars which were seen in the first feathers have been lost 

 by the deposition of more pigment, which is also more evenly distributed; only 

 faint traces of the bars are visible in 3 or 4 of the secondaries; traces are seen also 

 in a few of the long coverts. The increase in pigment is very marked, especially in 

 the long coverts. 



In an old owl-pigeon of pale-silver color I find similar, very distinct, transverse 

 bars. From measurements of the bars in the distal ends of the feathers, where the 

 bars are plainest, I learn that the light and dark bars are wider in the longer feathers, 

 and that the bars are of nearly equal width in an individual feather, though they 

 vary a little (pi. 72). 



The feathers of this same bird were re-examined 2 years (1905) and 4 years 

 1907) later. In the feathers of 1905 (pi. 73) the transverse barring is present, but 

 quite obscure. Comparing this set of feathers with the earlier strongly barred ones 

 brings out the interesting fact that the chequers of the wing-bars are larger and 

 darker, and extend upon more feathers in the 1905 series; and, further, that the 

 feathers themselves of this latter series are decidedly larger. 25 



In 1907 some feathers of this bird showed rather plainly the fundamental bar- 

 ring. These bars were more obscure on the lower than on the upper webs. The 

 "defect bars" 26 are also present in these feathers as narrow lines — one on the proxi- 

 mal edge of each dark fundamental bar. 



Very pronounced transverse barring was found in two juvenile Jacobins, from 

 red-and-white parents. The wing of one of these, while in molt, showed the first 

 feathers strongly barred, while the new set of feathers were without barring and 

 decidedly black (pi. 74); the other was at first similarly barred (pi. 75), but showed 

 none of the barring in its adult feathers. 



The editor would here venture a concluding statement: If the author is correct 

 in his conclusions, stated in the first two paragraphs of this section, we are in a 

 position to obtain a close view, in the case of this character, of the basis upon which 

 an hereditary character rests. For, if "from these fundamental bars, or their 

 secondary derivatives, a multitude of specific characters have been evolved by 

 gradual modification," it follows that these specific characters have arisen from a 

 much simplified situation, which can now be described with considerable complete- 

 ness in terms of physiology. My own studies showed conclusively that a daily 

 rhythm of growth accompanies the development of the feathers of birds; that the 

 period of slowest growth, in the several species examined, is during the later hours 

 of the night (1 to 5 a.m.); that the reduced pigmentation characteristic of the 

 "light" fundamental bar coincides with this period of slowest growth; and that 

 the periods of slowest growth and reduced pigmentation further coincide with the 



- b The size differences will doubtless not be apparent after the plates have been reduced in size for reproduction. 

 The editor has therefore measured the two series of long coverts (all drawn to natural size) of plates 72 and 73. The 

 two series were to each other as 61 : 67. 



26 See Riddle, Biol. Bull., vol. 12, Feb. 1907. 



