EPIDERMIS OF SKIN 

 APICAL ARBORIZATION 



Fig. 271. Diagrams of feather development. (A from F. R. Lillie: Physiol. Zool., 

 13; C and D redrawn from Strong: Bull. Mus. Comp. Zool. at Harvard, '40.) (A) 

 Semidiagrammatic drawing of the pulp (papilla) of a regenerating feather. The axial 

 artery of the feather is shown traversing the pulp to the distal end. The veins of the 

 pulp (not shown) consist of a series of central and peripheral veins which connect with 

 venous sinuses at the base of the pulp and, from thence, communicate with the cutaneous 

 veins. (B) Part of transverse section of a feather follicle, showing the developing 

 barbs and barbules. (C) Transverse section of a feather rudiment of the tern. Sterna 

 hirundo. Pigment cells, within the barb substance, send out processes which distribute 

 melanin to the cells of the developing barbule. (D) Middle portion of wing-feather 

 barbule, showing pigment within individual barbule cells together with the distal barbicels 

 with their booklets; cornification is not complete. 



577 



