—_ ss 
~~ 
‘ 
the developing feather inside is also indented. The indentations are seen 
to have in some way interfered with the proper formation of the feather 
beneath them; and from the appearances it can be understood that as 
the feather matures and comes to unfold a defect will be formed at the 
level represented by each wrinkling. This is well shown in Figs. 5 and 6, 
where the wrinklings on the unopened part of the feather clearly cor- 
respond with the barring above. From long observation every farmer 
knows, even before the plumes unfold, that bars will be present wherever 
the outer sheath is indented, while if the sheath is smooth all the way 
the feathers will be faultless. Jt can be accepted, then, without any question, 
that the bars represent places ut which the feather, while soft and growing, 
has been wrinkled or indented in such a manner as to prevent the parts 
beneath being fully developed. 
Day anp Nicur Growra. 
The important point, however, is to account for the wrinklings which 
produce the bars, and to explain how they are formed. In some of the 
best examples of barring the defects occur at such regular intervals as to 
suggest that they correspond with some structural feature in the forma- 
tion of the feather. And it has recently been shown that such is actually 
the case. tis now known that feathers, even under the best of conditions, 
do not grow im a continuous manner, uninterruptedly from one end to 
the other, but consist of alternations of day and night growths, and that 
these alternations represent a daily wmcrease and decrease in the physiological 
vigour of the bird.* Under ordinary circumstances, however, there is so 
little distinction between the night and day growth that as the feather 
ripens and opens out practically no evidence of it is seen, and the plume 
appears as a continuous formation without any interruptions; but under 
other circumstances the difference between the night and day growths 
becomes conspicuous and traces of it are noticed when the plumes expand, 
while in extreme cases the night growth becomes indicated by the 
wrinklings which result in the bar. 
This new conception of the formation of a feather calls for careful 
consideration by ostrich farmers, and the evidence for it can be easily 
observed by themselves. If the wing be uplifted the alternations of: 
growth can be seen on the unopened part of most growing feathers as a 
succession of narrow and broad rings which represent a difference in the 
feather density. The rings occur even where no bars are being produced. 
They are most pronounced in young blacks and drabs, in the portion of 
the growing feather freshly drawn from the socket and for some distance 
in the unopened part beyond the socket. This is owing to the fact that 
in blacks and drabs the dark unopened plume inside contrasts strongly 
with the translucent feather-sheath, and thus the denser and lighter parts 
are revealed. The soft growing part of a white wing plume is also often 
dark in colour, and in these the rings are easily distinguished where at all 
well formed. The denser broader rings represent the amount of growth 
added to the feather during the day, and the thinner, narrower rings 
the night growth, the alternation becoming evident owing) to the fact that 
one part is denser or stronger than the other. The night growth appears 
as little more than a narrow ring of separation between the successive day 
growths, and it is manifest that the daily rate of growth can be ascertain- 
ed by measuring the distance between successive day rings on _ the 
unexpanded feather. This is usually about a quarter of an inch in the 
wing plumes, but less in the others. 
*This conception of day and night growth in feathers was first elaborated y 
Dr. O. Riddle of the University of Chicago (Biol. Bull., Vol. XIV., May, 1908). 
