Two more of the Argonauts were Castor and Pollux, the twin sons of Leda, queen of Sparta.  She had also two daughters, named Helen and Clytemnestra, and Helen was growing into the most beautiful woman in the world.  These children, in the fable, had been hatched from two huge swans’ eggs; Castor and Clytemnestra were in one egg, and Pollux and Helen in the other.  Castor and Pollux were the most loving of brothers, and while Castor was famous for horsemanship, Pollux was the best of boxers.  They, too, had been pupils of Chiron; so was Peleus of Ægina, who had wooed Thetis, one of the fifty Nereids, or sea-nymphs, though she changed herself into all sorts of forms when he caught her first—fire, water, a serpent, and a lioness; but he held her fast through all, and at last she listened to him, and all the gods and goddesses had come to the wedding feast.  They had one son, named Achilles, whom Thetis had tried to make immortal after Ceres’ fashion, by putting him on the fire at night; but, like Triptolemus’ mother, Peleus had cried out and spoilt the spell.  Then she took the boy to the river Styx, and bathed him there, so that he became invulnerable all over, except in the heel by which she held him.  The child was now in Chiron’s cave, being fed with the marrow of lions and bears, to make him strong and brave.