Since their first appearance in 1963 there have been a number of variant models of the Daleks, a fictional alien race in the BBC science fiction television programme Doctor Who. First seen in the serial The Daleks (1963–64), the outward manifestation is portrayed as a powerful, technically advanced travel machine in which a hideous and malevolent mutant, the Dalek creature, resides. Although the general appearance of the Daleks has remained the same, details of both the casing and the mutant creature have changed over time. Alterations were made to accommodate the requirements of specific plot elements in various serials and episodes or at the request of producers, designers and directors to revitalise the Dalek appearance. On other occasions design changes have been the result of practical considerations when filming the Dalek props on location, or the mixing of components acquired from different sources. The episodes "Asylum of the Daleks" (2012), "The Magician's Apprentice" (2015) and "The Witch's Familiar" (2015) feature appearances by many of the Dalek variants seen in the Doctor Who programme since its inception. Glossary of primary Dalek components The component names listed below are used in this article as an aid to tracking the detail changes made to the basic Dalek design to create variants. From the base up, the major components are: fender: The projecting base of the Dalek prop. skirt: The section with angled faces, to which the hemispheres are attached. hemispheres: Also known as "hemis" and "sense globes", fifty-six of these items (forty-eight on New Paradigm Daleks) are fixed in four rows to the skirt panels. shoulders: The section between the top of the skirt and the neck bin. collars: Two horizontal bands fitted around the shoulders. slats: Vertical rectangular panels fitted around the upper collar. shoulder mesh: Diamond-section mesh fitted between the slats and the upper collar. appendage boxes: Projecting boxes housing the ball joints for the arm and gun stick. gun stick: Usually portrayed as a variable discharge energy weapon. gun rods: Longitudinal rods forming a cage around the gun stick. gun mantles: Octagonal cross-members bracing the gun rods along their length. arm: A telescopic arm, having two or three sections. plunger: Fixed to the end of the arm and depicted as a Dalek's primary manipulating appendage. neck bin: The section between the shoulders and the dome. neck bin mesh: Mesh fitted between the neck bin and the neck rings. neck rings: