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
Calamus caryotoides Calamus caryotoides Calamus caryotoides (also "Palmijuncus caryotoides"), more commonly known as fishtail lawyer cane is a North-East Queensland tropical forest climbing palm with very thin () flexible trunks; no crownshaft; small spikes; dark green, glossy, fish-tail shaped leaves reaching up to high ( spread); and very thin hooked flagella. It tends to clump and grow up into the shaded understory of Queensland's wet tropical forests, and is a close relative of the more infamous "Calamus radicalis" (aka Wait-a-While). The Cairns Botanical Gardens records local Yidinydji, Yirrganyydji, Djabuganydji, and Gungganydji use "Calamus caryotoides" (also known to Yidinydji as Bugul, pronounced BOOK-KOOL)