GENESIS OF FAULT-BARS IN FEATHERS. 33 I 



detailed account is, moreover, made imperative because of the 

 basis which it supplies for a later consideration of the origin of 

 color characters. A short description has already been pub- 

 lished by the writer 1 in a preliminary statement of the results 

 which are here given in full. 



The Adult Feather. — The first type of these defects is to be 

 found in the large and rapidly grown feathers of birds. The de- 

 fect consists in the total or partial absence of barbs from definite 

 transverse areas extending across the feather-vane, these areas 

 making with the shaft or rachis an angle always the same — ap- 

 proximately, but not exactly, a right angle. A cross-section of the 

 feather at this point would show only shaft and barbs. One such 

 area in the entire length of the feather was one of the types de- 

 scribed by Strong. I find, however, an abundance of cases where 

 such areas occur at regular intervals, practically throughout the 

 length of the feather. This regularity of the spaces separating the 

 defects furnished, indeed, the clue to the nature of the latter. Fig. 

 i shows a feather from a poorly nourished chick, in which a 

 number of pronounced defects of this type occur. As stated 

 above and as shown in the figure, defects of this type occur more 

 frequently in rapidly grown feathers, and principally in the dis- 

 tal parts of these. Many of these defects may be seen in Pis. 

 XIII. and XIV. 



The second type represents the greatest extreme to be met 

 with among these abnormalities. The feather in the abnormal 

 region has been reduced to shaft only ; both barbules and barbs 

 are gone. The second of the defects described by Strong evidently 

 belongs to this type, though he states that there was no shaft 

 present in his material and that its place was taken by a small 

 cylinder of fused barbs. I have not seen just such a structure as 

 he describes. 



Fig. 2, however, represents something which is, I think, en- 

 tirely comparable. At a is seen a region in which shaft only is 

 present. This part of the shaft is without pigment, although the 

 distal and proximal parts of the shaft are heavily pigmented. 

 We may regard such defects as a sort of record of the very sev- 



1 Riddle, Oscar, "A Study of Fundamental Bars in Feathers," Biol. Bull., Vol. 

 XII., February, 1 907. 



