364 OSCAR RIDDLE. 



Explanation of Plate XII. 



Fig. 1. Diagrammatic representation of rectrix of dove in longitudinal section. 

 Barbule cells are formed between x andj/; barb cells in the region of 2 ; cornification 

 complete at w ; Fig. 5, PI. XII., from region v. X M* 



Fig. 2. Semi-diagrammatic cross-section of a feather-germ. X 5°- 



Fig. 3. Longitudinal section of feather-germ of Cardinahs ; constrictions a in- 

 vading pulp. Drawn with aid of camera lucida. X 2 °- 



Fig. 4. Modified region of a feather from a "starved chick." Effects of lack of 

 food are seen in the loss of barbules in the fault-bar region a ; in a very peculiar 

 massing and cornification of barbs at m ; and in an almost total absence of pigment 

 in the shaft at c. X 8. 



Fig. 5. Camera lucida drawing of a segment of the cross-section of the rectrix of a 

 dove, taken at the level v in Fig. 1. No attempt was made to indicate the cellular 

 structures of the pulp ; the red blood corpuscles within the capillaries also omitted. 

 Only such capillaries were indicated as contained red blood cells and thus made their 

 nature certain. Undoubtedly still others were present. The line across the four 

 ridges indicates the plane of section of Fig. 25, PI. XV. X 3 DO - 



