370 OSCAR RIDDLE. 



Explanation of Plate XV. 

 Photomicrographs. 



Fig. 25. Longtudinal section of a fault-bar region soon after fault-bar producing 

 conditions were past. This being a tail feather, from the chick which was given 

 amyl nitrite, taken four hours after the chick was removed from the amyl nitrite 

 atmosphere. 



This "bar" occurs about 1.5 mm. from the extreme proximal tip of the feather and 

 occupies a position which maybe better understood by reference to Fig. 5, PI. XII. 

 It is a region on the border line of barb, barbuleand pigment producing cells. Cell 

 outlines in such a region are usually indistinct ; the nuclei «, however, have not 

 photographed perfectly, so that an idea of the looser, more irregular arrangement of the 

 cells is only imperfectly given. That an actual reduction of growth occurred here, is, 

 however, beautifully shown by the large clefts cl or clear areas of the pulp which have 

 here been left between the several barb-formations (ridges). Killed in Kleinen- 

 berg's picro-sulphuric mixture, and stained in hsematoxylin and eosin. X 3°°- 



Fig. 26. Fault-bar b with reduced pigmentation of all elements of the feather, 

 including the shaft c, in a rectrix of the ring dove. X 4°- 



