The Dioscuri were Castor and Polydeuces (or Pollux), the twin sons of Leda and Zeus and the brothers of Helen of Troy. Because Zeus came to Leda in the form of a swan, they are sometimes presented as having been born from an egg.
Jung’s seminar notes identify Leda as the mortal mother of the Dioscuri, explicitly connecting her myth to the swan-transformation of Zeus and the resulting egg-birth motif central to the numinous intrusion of divinity into human life.
, Dream Interpretation Ancient and Modern: Notes from the Seminar Given in 1936-1941, 2014thesis