366 OSCAR RIDDLE. 



Explanation of Plate XIII. 



All figures are direct prints on solio paper, therefore white shows as black, and 

 vice versa. 



Fig. 6. From a young dove which fed normally during the first week after hatch- 

 ing, poorly fed during the second week, and fed still less during the following ten 

 days. 



Fig. 7. Tail covert of an underfed dove. "Abrasions" a occurring at the fault- 

 bars. Those at d produced artificially by pulling on distal end of barbs. 



Fig. 8. Body covert (from nape of a Sudan-fed chick) with wavy band crossing 

 it; before this region expanded it existed as a constriction (fault-bar type 4) of the 

 feather-germ. 



Fig. 9. Series of the same modifications in body covert of Cardinalis. 



Fig. 10. From region of crop of pigeon. A fault-bar occurs at b which sharply 

 bounds a peripheral pigmented and a proximal unpigmented portion. 



Figs. 11-12. From tail of English sparrow. No. II has an incompletely differ- 

 entiated, unexpanded portion b at a point where the feather which grew beside it (Fig. 

 12) shows a typical fault-bar. 



Fig. 13. Primary of chick (ju venal plumage) showing fault-bars produced by 

 feeding Sudan III. 



Fig. 14. Primary of Japanese turtle dove. A fault-bar at b separates a more pig- 

 mented distal from a less pigmented proximal part. The entire feather is narrowed 

 from b to a showing that poor nutritive conditions prevailed throughout this period. 

 This region seems, by the method of photography here employed, to be more heavily 

 pigmented than other parts ; this is due not to actual pigmentation but to an opacity 

 caused by the extreme cornification and lack of separation of the feather-elements. 



Fig. 15. Showing light and dark fundamental bars in body covert of a Japanese 

 turtle dove. 



Fig. 16. Fundamental bars in wing covert of pigeon (these rather faint bars and 

 those of fig. 15 are here practically lost. The method of direct printing here em- 

 ployed is not equally good for the fault-bars and fundamental bars). 



Figs. 17-19. No. 17 — primary, No. 18 — secondary covert, and No. 19 a body 

 covert from crop region of a chick. The difference in distance between successive 

 fault-bars is an index of the rate of growth and bears a definite relation to the ultimate 

 length of the feather (the fault-bars in Fig. 19 are practically lost in the reproduction), 

 though they were very plain in the specimen. 



FlG. 20. Crumpled primary of right wing of dove showing fault-bars at d. 



Fig. 21. Control of above; the corresponding primary of the left wing of the same 

 dove. 



