460 



MANUAL OF ZOOLOGY 



SECT. 



Each digit of the foot is terminated by a claw which is also 

 a horny product of the epidermis, and the beaks are of the 

 same nature. The rest of the body, however, is covered by 

 feathers, a unique type of epidermal product found nowhere 

 outside the present class. 



inf.uittb 



FIG. 274. Columba liyia. A, proximal portion of a remex. cal, .calamus; inf. 

 umb, inferior umbilicus; rch, rachis; sup. umb, superior umbilicus. B, fifo- 

 plume. C, nestling-down. (C, from Bronn's Thierreich.) 



A feather (Fig. 274) is an elongated structure consisting 

 of a hollow stalk, the calamus or quill (cat), and an ex- 

 panded distal portion, the vexillum or vane. At the 

 proximal end of the quill is a small aperture, the inferior 

 umbilicus (inf. umb), into which fits, in the entire bird, a 



