Swan

Icarius and Periboea, a Naiad nymph, had five sons, Thoas, Damasippus, Imeusimus, Aletes, Perileos, and a daughter Penelope, whom Ulysses married. Tyndareus and Leda had daughters, to wit, Timandra, whom Echemus married, and Clytaemnestra, whom Agamemnon married; also another daughter Phylonoe, whom Artemis made immortal.

But Zeus in the form of a swan consorted with Leda, and on the same night Tyndareus cohabited with her; and she bore Pollux and Helen to Zeus, and Castor and Clytaemnestra to Tyndareus. But some say that Helen was a daughter of Nemesis and Zeus; for that she, flying from the arms of Zeus, changed herself into a goose, but Zeus in his turn took the likeness of a swan and so enjoyed her; and as the fruit of their loves she laid an egg, and a certain shepherd found it in the groves and brought and gave it to Leda; and she put it in a chest and kept it; and when Helen was hatched in due time, Leda brought her up as her own daughter. And when she grew into a lovely woman, Theseus carried her off and brought her to Aphidnae. But when Theseus was in Hades, Pollux and Castor marched against Aphidnae, took the city, got possession of Helen, and led Aethra, the mother of Theseus, away captive.


- Pseudo-Apollodorus, The Library, Book 3, Chapter 10, Sections 6 and 7