1 68 OSCAR RIDDLE. 



away at even distances from the shaft. Duerden l states that this 

 abnormality is also very rarely met with among ostriches. 



The recognition of the defective lines in all feathers throws a 

 new light on abrasion and wear in feathers. That there are birds 

 which "normally " have the barbules broken off at certain fairly 

 definite points in the more distal barbs has been observed by 

 Meves, 2 Chapman, 3 Dwight, 4 Strong 5 and others. Meves and 

 Chapman have noted, too, that the barb itself may be broken 

 near the distal end. I have seen several cases of the breaking of 

 a series of barbs at the point where they were crossed by the 

 same defective line, and I believe that further study will prove 

 that most feather abrasions occur by the space between two de- 

 fective lines breaking away as a single piece. 



The Defects in Feather-germs. I have been able to observe 

 the defects in several formative stages. I shall say only a word 

 concerning them here. The prominent defects in the unexpanded 

 germ are easily recognized by the unaided eye ; sometimes they 

 appear as definite constrictions (Cardinalis virginianus, see Fig. 

 2, .), but very often as points of a different color (rectrices of 

 Turtur risorius). A microscopic examination of a region which 

 would develop a defective area shows a reduction of cell-growth 

 and division particularly in the region of the barbules. 



EXTENT AND DISTRIBUTION ON THE ABNORMALITIES. 



In the Bird Groups. In looking for the cause of the defects 

 one turned naturally to the birds to find whether they were wide- 

 spread or restricted phenomena. I stated that at the time the 

 present work was begun, there was in the literature but a single 

 account of them, and that account had to do with a single speci- 

 men a hybrid pigeon. Recently Professor J. E. Duerden has 



Duerden, "Bars in Ostrich Feathers," Agr. Jour. Cape of Good Hope, May 

 1906. 



2 Meves, W. , " Uber die Farbenveranderung der Vogel," Jour, fur Ornith., 

 Bd. 3, 1855. 



"Chapman, F. M., "On the Changes of Plumage in the Snowflake," Amer. 

 Mus. Nat. Hist., vol. 8. 



1 Dwight, J., Jr., " The Sequence of Plumages and Moults in the Passerine Birds 

 of New York," Ann. N. Y. Acad. Set., vol. 13, No. I. 



"> Strong, R. M., "The Development of Color in the Definitive Feather," Bull. 

 Mus. Comp. Zool., vol. 40, no. 3. 



