How we cite our quotes: (line)
Quote #1
the great wings beating still
Above the staggering girl (lines 1-2)
Zeus transforms himself into a swan in order to rape Leda, but he's not any ordinary swan. The "great wings" of the swan represent Zeus's superhuman power. When a mythical person or god changes form to become something else, the term is metamorphosis.
Quote #2
And how can body, laid in that white rush,
But feel the strange heart beating where it lies? (lines 7-8)
Zeus's transformation is so complete that Leda cannot recognize him: his heart feels "strange" or alien.
Quote #3
A shudder in the loins engenders there
The broken wall, the burning roof and tower
And Agamemnon dead. (lines 9-11)
The crucial point of historical transformation occurs when Zeus impregnates Leda with Helen of Troy. Yeats wants us to pay attention not just to the sexual act as a turning point, but literally to the exact moment of conception, represented by a "shudder" in the swan's loins. He traces a direct historical line from that moment to the destruction of the great ancient city of Troy.