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 (DTP) for its support for automatic kerning even where adjacent characters are set in different fonts or at different sizes. Its high modularity offers features for almost every purpose in desktop publishing. Calamus also was one of the first DTP apps to support real virtual objects and frames, nondestructive vector masks, and editable PS/PDF import. Its (adjustable) measurement base of 1/10,000mm allows accurate positioning of elements. Calamus was ported to Windows by MGI Software and was released as Calamus 95. The current version of Calamus is Calamus SL 2015, also available as SLC 2015 (complete edition with all additional modules) and