STRONG : DEVELOPMENT OF COLOR IN DEFINITIVE FEATHER. 159 



Schwann ('39), who gave a very good general description of them. 

 Since then they have been considered by various writers on the struc- 

 ture of the feather. I have nothing to add to the more recent accounts, 

 except to call attention to the venti-al ridge (crs'.) of the cortex of the 

 barb, which is shown in transverse section for several birds (Plate 1, 

 Figs. 7, 8, 9 ; Plate 5, Fig. 24), and also to the structure of the 

 dorsal thickened portion of the cortex (Plate 5, Fig. 23, ctx. d. ; Fig. 24, 

 ctx?). I find the ventral ridge, or keel, a frequent and important feature 

 of the ventral cortex. It furnishes a convenient "ear niarlc"for the 

 orientation of barb sections ; its apex in transverse sections alwaj's 

 points towai'ds the shaft. During the process of cornification, it be- 

 comes much reduced fi'om the conspicuous size which it has in stages 

 corresponding with that shown in Figure 23, but it still retains the same 

 characteristic want of symmetry (Fig. 24, c?V.). 



The dorsal portion of the cortex is made up of cells which fuse at a 

 comparatively late date in the feathers I have studied. 



Haecker ('90) described thick-walled medullary cells which he found 

 in the barbs of certain birds, designating them by the term " Schirm- 

 zellen." I have examined sections of the barbs from two of the species 

 of birds which he studied (Cotinga cayana and Pitta nioluccensis), and 

 also from Pitta sordida, and have identified his so-called " Schirmzellen" 

 (Plate 2, Figs. 10 and 11, d. med.)} I regret not having been able to 

 get material for the study of their development ; but there seems little 

 reason to doubt that they are modified medullary cells, as Haecker him- 

 self leaves one to infer. 



They were observed and figured by Krukenberg ('82) in Irene puella; 

 he called them thickened medullary cells (" Markzellen "). Gadow 

 ('82) saw them in Pitta nioluccensis, but his figures and descriptions 

 are incorrect. He described them as prismatic columns with minute 

 parallel ridges on their surfaces; but neither Haecker nor I have found 

 any ridges. Gadow seems to have depended solely on observations from 

 the exterior, having apparently worked without the aid of sections. 



The " Schirmzellen," as described by Haecker, occur mostly on the 

 dorsal side of the barb immediately underneath the cortex ; but they 

 are also represented by two or three typical thick-walled cells on the 

 ventral side in Pitta moluccensis. 



1 As this paper goes to press and since the printing of the plates, an article ap- 

 pears by Haecker und Georg Meyer ( : 01) in which the Schirmzellen are recog- 

 nized as modified medullary cells and are re-named " Kastchenzellen," a much more 

 appropriate term. 



