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 Creek Bridge Calamus Creek Bridge The Calamus Creek Bridge near Maxwell, Iowa is a concrete Luten arch bridge that was built in 1905. At a cost of $900, it was built by N.M. Stark and Company, a firm which built several Luten arch bridges that are listed on the National Register of Historic Places (NRHP). The Calamus Creek Bridge was listed in 1998. It has a single span and a total length of . The NRHP nomination for the bridge asserts:Before the codification of bridge design in the state in 1913, Stark built perhaps hundreds of Luten arches throughout Iowa, in exclusive