Glen pipes (plurale tantum)
Bagpipe, mouth-blown: 2 stocks (a: single chanter / b: 2 drones in 1 stock)
Named after Robert Glen, who described the instrument in his article »The ancient musical insruments of Scotland« (1879); NB (plurale tantum): The term is also used when referring to 1 instrument only.
The described instrument has 2 small drones, set in a Y-shaped stock (i.e. a forked branch of a tree).
Collinson, Francis: The bagpipe: the history of a musical instrument. London, 1975, p.134, 209, 237 [➺ ref. 8 to Chapter 3].