The MS. evidence for some of the stories concerning the Tuatha de Danann is as old as that for the oldest heroic cycle (the Ultonian of Conchobar and Cuchulainn). But the Tuatha de Danann legends have retained throughout Irish literature greater plasticity and vitality than those of the Ultonian cycle, and many stories are not older in their present state than the 14th and 15th centuries. This is probably the case with the present story. The oldest known MS. only goes back to 1718, but this and the MS. of 1721, used by O'Curry for his edition, are certainly copied from much older MSS. The interesting question for storiologists is whether the themes of the story--the swan-metamorphosis consequent upon the stepmother's jealousy, and the protecting role assigned to the sister--are of old native or of recent imported nature. In support of the first hypothesis, it may be noted that the theme of stepmotherly jealousy was current in Ireland in the 10th century at the latest, as it is woven into the saga of the Destruction of Daderga's Fort (see my article "_Folk-lore_," ii.). The final episode of the sudden aging of the miraculously long-lived swans is also genuinely Irish, but its true significance is obscured in our story in a way that sufficiently demonstrates the late and secondary character of the text. The idea is that the dwellers in Faery, whether fairy-folk or mortals penetrating thither, enjoy perpetual life, forfeited by the latter the moment they return to this earth. As children of the Tuatha de Danann, Fionngula and her brothers are deathless, and the episode as it stands in our text results from a contamination of the original form of the story in which the swan-metamorphosis was annulled under certain conditions (the removal of the chains), when the original shape was resumed, and the familiar story of the mortal returning from Faery after hundreds of years, which he deems to be but a short space of time, shrinking into dust the moment he touches earth.