DIFFERENTIATION AND PROTEIN SYNTHESIS 



103 



Fig. 46. Diagrams of cross-sections of a feather to show the dorsal fusion 

 of barbs to form the rhachis (A-F) ; the fusion of barbs ventrally to form 

 the hyporhachis (D-F); the lateral fusion of rhachis and hyporhachis 

 to form the calamus (F) ; the structure of the calamus (G) and the tip of 

 the new feather forming within the base of the calamus of its predecessor 

 (H); ba, barb of aftershaft; bs, barb of shaft ; ca, calamus; h, hypo- 

 rhachis; i, intermediate cells (i.e. collar); p, pulp; ri, ridge; s', sheath 

 of old feather; s", sheath of new feather. (Redrawn from Hosker (1936).) 



