Feather These barbules have minute hooks called barbicels for cross-attachment. Down feathers are fluffy because they lack barbicels, so the barbules float free of each other, allowing the down to trap air and provide excellent thermal insulation. At the base of the feather, the rachis expands to form the hollow tubular "calamus" (or quill) which inserts into a follicle in the skin. The basal part of the calamus is without vanes. This part is embedded within the skin follicle and has an opening at the base (proximal umbilicus) and a small opening on the side (distal umbilicus). Hatchling birds of some
Acorus calamus Karpos, of Zephyrus (the West Wind) and Chloris (Spring). When Karpos drowned in a swimming race, Kalamos also drowned and was transformed into a reed, whose rustling in the wind was interpreted as a sigh of lamentation. The plant was a favorite of Henry David Thoreau (who called it "sweet flag"), and also of Walt Whitman, who added a section called the "Calamus" poems, to the third edition of "Leaves of Grass" (1860). In the poems the calamus is used as a symbol of love, lust, and affection. Lewis Carroll uses the plant in "Through the Looking-Glass" as a symbol